human physiology: digestion

Human Physiology:Human Physiology:DigestionDigestionTopic 6.1, 11.3Topic 6.1, 11.3

Option H2, H3, H4Option H2, H3, H4

3 Dietary Categories3 Dietary Categories

HerbivoresHerbivores– Cattle, gorillas, snails, and sea urchins,Cattle, gorillas, snails, and sea urchins,– eat autotrophs (plants and algae)eat autotrophs (plants and algae)

CarnivoresCarnivores– Lions, hawks, spiders, and snakesLions, hawks, spiders, and snakes– Ingest other animalsIngest other animals

OmnivoresOmnivores– Crows, cockroaches, raccoons, and Crows, cockroaches, raccoons, and

humanshumans– Ingest both plants and animalsIngest both plants and animals

How do animals obtain and ingest How do animals obtain and ingest their food?their food? Suspension feedersSuspension feeders

– Extract food particles suspended in the Extract food particles suspended in the surrounding watersurrounding water

– Ex. Clams and oystersEx. Clams and oysters Substrate feedersSubstrate feeders

– Live on or in their food source and eat their way Live on or in their food source and eat their way through it.through it. Ex. Caterpillars and earthwormsEx. Caterpillars and earthworms

Fluid feedersFluid feeders– Obtain food by sucking nutrient nutrient-rich Obtain food by sucking nutrient nutrient-rich

fluids from a living host, either a plant or an fluids from a living host, either a plant or an animal.animal. Ex. Mosquitoes and ticksEx. Mosquitoes and ticks

Bulk feedersBulk feeders– Ingest relatively large pieces of foodIngest relatively large pieces of food– Ex. most animalsEx. most animals

Overview: Food processingOverview: Food processing Four stagesFour stages1.1. IngestionIngestion

The act of eatingThe act of eating2.2. DigestionDigestion

The breaking down of food into molecules small enough for the The breaking down of food into molecules small enough for the body to absorb. body to absorb.

Two phases: Two phases: 1. Breaking food down mechanically (teeth1. Breaking food down mechanically (teethchewing) into chewing) into smaller piecessmaller pieces2. hydrolysis, chemical breakdown, catalyzed by enzymes2. hydrolysis, chemical breakdown, catalyzed by enzymes

3.3. AbsorptionAbsorption Cells lining the digestive tract take up (absorb) the products of Cells lining the digestive tract take up (absorb) the products of

digestion—small molecules such as amino acids and simple digestion—small molecules such as amino acids and simple sugarssugars

Nutrients travel through blood to cells, where they are made Nutrients travel through blood to cells, where they are made into macromolecules or further broken down for energyinto macromolecules or further broken down for energy

4.4. EliminationElimination undigested material passes out of the digestive tractundigested material passes out of the digestive tract

General compartments for General compartments for digestiondigestion

Food vacuoles are the simplest Food vacuoles are the simplest digestive compartments.digestive compartments.– Phagocytosis: cell engulfs food particle, Phagocytosis: cell engulfs food particle,

which then fuses with a lysosome. which then fuses with a lysosome.

Most animals have an Most animals have an alimentary canalalimentary canal, , a digestive tube with two openings, a a digestive tube with two openings, a mouth and an anus. mouth and an anus.

– Allows food to move in one direction, Allows food to move in one direction, with specialized regions in the digestive with specialized regions in the digestive tube that carry out digestion and tube that carry out digestion and absorption of nutrients in sequenceabsorption of nutrients in sequence

General compartments for General compartments for digestiondigestion

Food entering the mouth usually Food entering the mouth usually passes into:passes into:– A A pharynxpharynx, or throat, or throat– Then passes into the Then passes into the esophagusesophagus– Passed to Passed to stomachstomach, muscular and , muscular and

churns and grinds foodchurns and grinds food– Chemical digestion and nutrient Chemical digestion and nutrient

absorption occur mainly in the absorption occur mainly in the intestineintestine– Undigested materials are expelled Undigested materials are expelled

though the though the anusanus. .

Human Digestive TractHuman Digestive Tract

Main parts of human alimentary canal:Main parts of human alimentary canal:– Mouth, oral cavity, tongue, pharynx, Mouth, oral cavity, tongue, pharynx,

esophagus, stomach, small intestine, esophagus, stomach, small intestine, large intestine, rectum, and anus. large intestine, rectum, and anus.

Main digestive glandsMain digestive glands– Salivary glands, pancreas, and liverSalivary glands, pancreas, and liver– Secrete digestive juices that enter the Secrete digestive juices that enter the

alimentary canal through ducts.alimentary canal through ducts.– Secretions from liver are stored in Secretions from liver are stored in

gallbladder before they are released into gallbladder before they are released into the intestine.the intestine.

Human Digestive TractHuman Digestive Tract PeristalsisPeristalsis

– Rhythmic waves of contractions of smooth Rhythmic waves of contractions of smooth muscles in the walls of the digestive tractmuscles in the walls of the digestive tract

– Once food is swallowed, peristalsis propels it Once food is swallowed, peristalsis propels it through the alimentary canal. through the alimentary canal.

– In only 5-10 seconds, food passes from the In only 5-10 seconds, food passes from the pharynx down the esophagus and into the pharynx down the esophagus and into the stomach.stomach.

– Pyloric sphincterPyloric sphincter, a muscular ringlike valve, , a muscular ringlike valve, keeps food in the stomach by regulating the keeps food in the stomach by regulating the pass of food into the small intestive.pass of food into the small intestive. Works like a drawstring, closing off the tube and Works like a drawstring, closing off the tube and

keeping food in the stomach long enough for stomach keeping food in the stomach long enough for stomach acids and enzymes to begin digestion. acids and enzymes to begin digestion.

http://nutrition.jbpub.com/resources/animations.cfm?http://nutrition.jbpub.com/resources/animations.cfm?id=1&debug=0id=1&debug=0

Human Digestive TractHuman Digestive Tract

Final steps of digestion and nutrient Final steps of digestion and nutrient absorption occur in the small absorption occur in the small intestine over a period of 5-6 hours. intestine over a period of 5-6 hours.

Undigested material moves slowly Undigested material moves slowly through the large intestine (taking through the large intestine (taking 12-24 hours), and feces are expelled 12-24 hours), and feces are expelled through the anus. through the anus.

Digestion Begins in the Oral Digestion Begins in the Oral CavityCavity

Saliva is produced by the salivary Saliva is produced by the salivary glands through ducts to the oral glands through ducts to the oral cavity even before you eat; it’s a cavity even before you eat; it’s a response to presence of foodresponse to presence of food

Sight or smell of food causes nerve Sight or smell of food causes nerve stimulation stimulation

In a typical day, salivary glands In a typical day, salivary glands secrete more than a liter of salivasecrete more than a liter of saliva


Saliva contains several substances Saliva contains several substances necessary for food processingnecessary for food processing– Slippery glycoproteinsSlippery glycoproteins

Protects the soft lining of the mouth and lubricates food Protects the soft lining of the mouth and lubricates food for easier swallowingfor easier swallowing

– BuffersBuffers Neutralize food acids, helping prevent tooth decay.Neutralize food acids, helping prevent tooth decay.

– Antibacterial agentsAntibacterial agents Kill many of the bacteria that enter the mouth with Kill many of the bacteria that enter the mouth with

food.food.

– Salivary amylaseSalivary amylase Digestive enzyme that begins hydrolyzing foodDigestive enzyme that begins hydrolyzing food


Oral CavityOral Cavity– Mechanical and chemical digestion begins in Mechanical and chemical digestion begins in

the oral cavity.the oral cavity.– Chewing cuts, smashes, and grinds food, Chewing cuts, smashes, and grinds food,

making it easier to swallow and exposing more making it easier to swallow and exposing more food surface to digestive enzymesfood surface to digestive enzymes

– Teeth and tongue are prominentTeeth and tongue are prominent Teeth grind and crush foodTeeth grind and crush food Tongue, muscular organ with taste buds, allows you Tongue, muscular organ with taste buds, allows you

to taste your meal and manipulates food and helps to taste your meal and manipulates food and helps shape it into a ball called a bolus.shape it into a ball called a bolus.

– In swallowing, it pushed the bolus to the back of the In swallowing, it pushed the bolus to the back of the oral cavity and into the pharynx.oral cavity and into the pharynx.

Pharynx- SwallowingPharynx- Swallowing Pharynx has openings for both the esophagus and Pharynx has openings for both the esophagus and

the trachea (wind-pipe)the trachea (wind-pipe) Most of the time, esophageal opening is closed Most of the time, esophageal opening is closed

and air enters the trachea and proceeds to the and air enters the trachea and proceeds to the lungs. lungs.

When you eatWhen you eat::– a bolus of food enters the pharynx, triggering the swallowing a bolus of food enters the pharynx, triggering the swallowing

reflex reflex – The esophageal sphincter relaxes and allows the bolus to enter The esophageal sphincter relaxes and allows the bolus to enter

the esophagusthe esophagus– Larynx (voice box) moves upwards and tips the epliglottis over Larynx (voice box) moves upwards and tips the epliglottis over

the tracheal opening.the tracheal opening.– Epiglottis prevents food from passing into the trachea.Epiglottis prevents food from passing into the trachea.– After the bolus enters the esophagus, the larynx moves After the bolus enters the esophagus, the larynx moves

downward, the epiglottis moves up again, and breathing downward, the epiglottis moves up again, and breathing passage reopens passage reopens

– Esphogas sphincter contracts above the bolus. Esphogas sphincter contracts above the bolus.

Esophagus: PeristalsisEsophagus: Peristalsis Esophagus is a muscular tube that Esophagus is a muscular tube that

conveys food boluses from the conveys food boluses from the pharynx to the stomach.pharynx to the stomach.

Muscles at the very top of esophagus Muscles at the very top of esophagus are under voluntary control; thus, the are under voluntary control; thus, the act of swallowing begins voluntarily.act of swallowing begins voluntarily.

Then, Involuntary waves of Then, Involuntary waves of contraction by smooth muscles in the contraction by smooth muscles in the rest of the esophagus take over.rest of the esophagus take over.

Esophagus: PeristalsisEsophagus: Peristalsis As food is swallowed, muscles above the As food is swallowed, muscles above the

bolus contract, pushing the bolus bolus contract, pushing the bolus downwarddownward

Simultaneously, muscles around the Simultaneously, muscles around the bolus relax, allowing the passageway to bolus relax, allowing the passageway to open.open.

Muscle contractions continue in waves Muscle contractions continue in waves until the bolus enters the stomach.until the bolus enters the stomach.

Waves of smooth muscle contraction Waves of smooth muscle contraction also move materials through small and also move materials through small and large intestinelarge intestine

Stomach: stores and breaks Stomach: stores and breaks down fooddown food

Stomachs are the main reason we do not have to Stomachs are the main reason we do not have to eat constantlyeat constantly

Highly elastic and can stretch to accommodate Highly elastic and can stretch to accommodate about 2 Liters of food and drink, usually enough to about 2 Liters of food and drink, usually enough to satisfy our body’s needs for many hours. satisfy our body’s needs for many hours.

Some digestion occurs in the stomach.Some digestion occurs in the stomach. The stomach secrete The stomach secrete gastric juice:gastric juice:

– made up of mucus, enzymes, and strong acid.made up of mucus, enzymes, and strong acid.– Functions to break apart the cells in foodFunctions to break apart the cells in food– Also kills most bacteria and other microbes that are Also kills most bacteria and other microbes that are

swallowed with food.swallowed with food.


Stomach wall is highly folded, and has Stomach wall is highly folded, and has pits that lead to tubular gastric glands.pits that lead to tubular gastric glands.

Three types of cells that secrete Three types of cells that secrete different components of the gastric different components of the gastric juice:juice:– Mucous cellsMucous cells: secrete mucous, which : secrete mucous, which

lubricates and protects the cells lining the lubricates and protects the cells lining the stomachstomach

– Parietal cellsParietal cells: secrete HCl acid: secrete HCl acid– Chief cellsChief cells: secrete pepsinogen, an : secrete pepsinogen, an

inactive form of the enzyme pepsininactive form of the enzyme pepsin


Pepsinogen, HCl, and pepsin:Pepsinogen, HCl, and pepsin:– 1. Pepsinogen and HCl are secreted into 1. Pepsinogen and HCl are secreted into

the lumen (cavity) of the stomach.the lumen (cavity) of the stomach.– 2. HCl converts pepsinogen to pepsin.2. HCl converts pepsinogen to pepsin.– 3.Pepsin then activates more 3.Pepsin then activates more

pepsinogen, starting a chain reaction. pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of Pepsin begins the chemical digestion of proteins. Proteins will be further proteins. Proteins will be further digested in small intestine.digested in small intestine.


Prevention of gastric juice from Prevention of gastric juice from digesting away stomach lining:digesting away stomach lining:– Secreting pepsin in the inactive form of Secreting pepsin in the inactive form of

pepsinogen helps protect the cells of the pepsinogen helps protect the cells of the gastric glandsgastric glands

– mucus helps protect the stomach lining mucus helps protect the stomach lining from both pepsin and acid.from both pepsin and acid.

– Still, epithelium is constantly eroded; Still, epithelium is constantly eroded; enough new cells are generated by enough new cells are generated by mitosis to replace the stomach lining mitosis to replace the stomach lining completely about every three days. completely about every three days.


Gastric glands are regulated by a Gastric glands are regulated by a combination of nerve signals and hormones:combination of nerve signals and hormones:– When you see, smell, or taste food, a signal from your When you see, smell, or taste food, a signal from your

brain to your stomach stimulates your gastric glands to brain to your stomach stimulates your gastric glands to secrete gastric juice.secrete gastric juice.

– Once food is in your stomach, substances in the food Once food is in your stomach, substances in the food stimulate cells in the stomach wall to release the hormone stimulate cells in the stomach wall to release the hormone gastringastrin in the circulatory system. in the circulatory system.

– Gastrin circulates in the blood stream, returning to the Gastrin circulates in the blood stream, returning to the stomach wall, stimulating further secretion of gastric juice. stomach wall, stimulating further secretion of gastric juice.

– As much as 3L of gastric juice may be secreted a day.As much as 3L of gastric juice may be secreted a day.– A negative-feedback mechanism inhibits secretion of A negative-feedback mechanism inhibits secretion of

gastric juice when the stomach contents become too gastric juice when the stomach contents become too acidic. acidic.

Acid inhibits the release of gastrin, and with less gastrin in the blood, Acid inhibits the release of gastrin, and with less gastrin in the blood, the gastric glands secrete less gastric juice.the gastric glands secrete less gastric juice.


About every 20 seconds, the stomach contents About every 20 seconds, the stomach contents are mixed by the churning action of muscle in the are mixed by the churning action of muscle in the stomach wall and result in stomach wall and result in acid chyme.acid chyme.

Opening between the esophagus and the Opening between the esophagus and the stomach is usually closed until a bolus arrives. stomach is usually closed until a bolus arrives.

Backflow of acid chyme causes heartburn (which Backflow of acid chyme causes heartburn (which should be called esophagus-burn) should be called esophagus-burn) – Can also cause acid-reflux (gastroesophageal Can also cause acid-reflux (gastroesophageal

reflux disease; GERD)reflux disease; GERD)


Pyloric sphincter helps regulate the passage of acid Pyloric sphincter helps regulate the passage of acid chyme from the stomach into the small intestine. chyme from the stomach into the small intestine.

The stomach takes about 2-6 hours to empty after a The stomach takes about 2-6 hours to empty after a meal; acid chyme leaves stomach only a squirt at a meal; acid chyme leaves stomach only a squirt at a time.time.

Acid chyme rich in fats stimulates the small intestine Acid chyme rich in fats stimulates the small intestine to release a hormone that slows the emptying of the to release a hormone that slows the emptying of the stomach, providing more time for digestion.stomach, providing more time for digestion.

Other hormones secreted by the small intestine Other hormones secreted by the small intestine influence the release of digestive juices from the influence the release of digestive juices from the pancreas and gall bladder.pancreas and gall bladder.

Gastric UlcersGastric Ulcers Gastric Ulcers:Gastric Ulcers:– Open sores that form when mucus, which normally Open sores that form when mucus, which normally

protects the stomach wall from the corrosive effect of protects the stomach wall from the corrosive effect of digestive juice, fails to protect it.digestive juice, fails to protect it. Small intestine and esophagus are also susceptible to ulcersSmall intestine and esophagus are also susceptible to ulcers

– Symptoms are usually gnawing pain in the upper Symptoms are usually gnawing pain in the upper abdomen, which may occur a few hours after eating.abdomen, which may occur a few hours after eating.

– Were formerly thought to result from the production Were formerly thought to result from the production of too much pepsin/and or acid or too little mucus:of too much pepsin/and or acid or too little mucus: For years, the blame was put on factors that cause For years, the blame was put on factors that cause

these effects, such as aspirin, ibuprofen, smoking, these effects, such as aspirin, ibuprofen, smoking, alcohol, coffee, and stressalcohol, coffee, and stress

However, strong evidence now points to…However, strong evidence now points to…

Gastric UlcersGastric Ulcers H. pyloriH. pylori– A spiral-shaped bacteria A spiral-shaped bacteria – Low pH of the stomach kills most microbes, but not this one!Low pH of the stomach kills most microbes, but not this one!– Burrows beneath mucus and releases harmful chemicalsBurrows beneath mucus and releases harmful chemicals– Growth seems to result in a localized loss of protective Growth seems to result in a localized loss of protective

mucus and damage to the cells lining the stomachmucus and damage to the cells lining the stomach– WBC fight infection, causing mild inflammation of the WBC fight infection, causing mild inflammation of the

stomach, called gastritis.stomach, called gastritis.– Gastric ulcers form when pepsin and HCl destroy cells faster Gastric ulcers form when pepsin and HCl destroy cells faster

than the cell can regenerate from the H. pylori attack.than the cell can regenerate from the H. pylori attack.– Eventually, stomach will erode to the pint where it actually Eventually, stomach will erode to the pint where it actually

has a hole in it, which can lead to a life threatening infection has a hole in it, which can lead to a life threatening infection in abdomen or internal bleeding.in abdomen or internal bleeding.

– 70-90% of ulcer and gastritis sufferers have this bacterial 70-90% of ulcer and gastritis sufferers have this bacterial infectioninfection

– Also found in 30% of healthy people.Also found in 30% of healthy people. linked to certain linked to certain kinds of stomach cancerkinds of stomach cancer

Gastric UlcersGastric Ulcers

TreatmentTreatment– Usually respond to a combination of Usually respond to a combination of

anti-biotics and bismuth (the active anti-biotics and bismuth (the active ingredients of Pepto-Bismol) which ingredients of Pepto-Bismol) which eliminates bacteria and promotes eliminates bacteria and promotes healing.healing.

– Drugs that reduce stomach acidity may Drugs that reduce stomach acidity may also help, and researchers are working also help, and researchers are working on preventitive treatment for H.Pylori.on preventitive treatment for H.Pylori.

Small Intestine Once at the S.I., food has been mechanically

reduced to smaller pieces and mixed with juices; it now resembles a thick soup.

Starch digestion began in the mouth, and protein breakdown began in the stomach.

All other chemical digestion occurs in the s.i. Nutrients are also absorbed into the blood from

the s.i. Length of over 6m, making it the longest organ of

the alimentary canal. Diameter is only about 2cm, which is why it’s called the “small” intestine.

Small Intestine

Contributing to digestion in s.i. are two large glandular organs: pancreas and liver.

Pancreas:– Produces pancreatic juice

a mixture of digestive enzymes and an alkaline solution rich in bicarbonate

Alkaline solution neutralizes acid chyme as it enters the small intestine

Small Intestine

Liver– Performs a wide variety of functions,

including the production of bile: Contains bile salts that emulsify fats, making

them more susceptible to attack by digestive enzymes.

Gall bladder stores bile until it is needed in the small intestine.

Small Intestine

First 25 cm or so of the s.i. is called the duodenum. – Where acid chyme squirted from the

stomach mixes with bile from the gall bladder, pancreatic juice from the pancreas, and digestive enzymes from gland cells in the in the intestinal wall.

Small Intestine

All four types of macromolecules (carbohydrates, proteins, nucleic acids, and fats) are digested.

Refer to table 21.11 on pg. 438

Small Intestine

Carbohydrate digestion:– Begins in the oral cavity and is completed

in the s.i.– Pancreatic amylase hydrolyzes starch

(a polysaccharide) into the disaccharide maltose

– Maltose is then hydrolyzed into glucose via maltase.

– Sucrase hydrolyzes table sugar and lactase digests milk sugar (lactose)

Small Intestine Protein digestion:

– S.i. completes protein digestion from the stomach– Pancreas and duodenum secrete hydrolytic

enzymes that completely dismantle polypeptides into amino acids. dipeptidase

– Hydrolyzes fragments only two or three amino acids long. trypsin and chymotripsin

– Break polypeptides into smaller polypeptides– Trypsinogen (in pancreas) is converted into trypsin by the Trypsinogen (in pancreas) is converted into trypsin by the

action of enteropeptidase (the enzyme that is bound to the action of enteropeptidase (the enzyme that is bound to the membranes of the small intestine).membranes of the small intestine).

aminopeptidase and carboxypeptidase– Split off one amino acid at a time, working from both ends

of a polypeptide.

Small Intestine

Nucleic acid digestion:– Nucleases hydrolyzes the nucleic acids

in food. From the pancreas Split DNA and RNA (which are present in the

cells of food items) into their component nucleotides, which are then broken down into nitrogenous bases, sugars, and phosphates by other enzymes produced by the duodenal cells.

Small Intestine Fat digestion:

– Most fat remains undigested until it reaches the duodenum.

– Hydrolysis of fats is problematic due to fats insolubility in water. Emulsification= Problem Solved!!! Bile salts in bile cause fat globules to be physically

broken up into smaller fat droplets, a process called emulsification.

Many small droplets allows for a larger surface area of fat exposed to lipase, an enzyme that breaks fat molecules down into fatty acids and glycerol.

Small IntestineSmall Intestine

Problems with lipid digestion in a Problems with lipid digestion in a hydrophillic medium:hydrophillic medium:– Lipids tend to coalesce (lump together) and are only accessible to Lipids tend to coalesce (lump together) and are only accessible to

lipase at the lipid-water interface.lipase at the lipid-water interface.– Bile molecules have a hydrophobic end and a hydrophilic end which Bile molecules have a hydrophobic end and a hydrophilic end which

emulsifies (prevents from coalescing) the lipidsemulsifies (prevents from coalescing) the lipids– Lipase must be water-soluble and has a hydrophobic active site (for its Lipase must be water-soluble and has a hydrophobic active site (for its

substrate, lipids)substrate, lipids)– The increased surface area allows lipase greater access to its substrateThe increased surface area allows lipase greater access to its substrate

Small Intestine

By the time persistalsis has moved the mixture of chyme and digestive juices through the duodenum, chemical digestion of your meal is just about complete.

Main function of the rest of the small intestine is the absorption of nutrients and water.

Small Intestine

Structurally, great for nutrient absorption. – Lining has a huge surface area– roughly 300

m2, about the size of a tennis court– Extensive surface area results from several

kinds of folds and projections. Villi: large circular folds with numerous, small

fingerlike projections around the inner wall of the s.i. Microvilli: many tiny surface projections found on

epithelial cells lining a villus.– extend into the lumen of the intestine and greatly

increase the surface area across which nutrients are absorbed.

Small Intestine Some nutrients are absorbed via simple

diffusion; other nutrients are pumped against concentration gradients into the epithelial cells

The core of each villus is penetrated by a small lymph vessel and a network of capillaries.– After fatty acids and glycerol are absorbed by an

epithelial cell, these building blocks are recombined into fats and are transported into the lymph vessel.

– Amino acids and sugars pass out of the intestinal epithelium and then across the thin walls of the capillaries into the blood.

Small Intestine Capillaries that drain nutrients away from

the villi converge into larger veins and eventually into a main vessel, the hepatic portal vein, that leads directly to the liver:– Liver gets first access to nutrients absorbed

from a meal– Converts many nutrients into new substances

that the body needs.– One of its main functions is to remove excess

glucose from the blood and convert it to glycogen, which is stored in liver cells.

– From the liver, blood travels to the heart, which pumps the blood and the nutrients it contains to all parts of the body.

Small IntestineSmall Intestine Structural features of an epithelial cell of a villus:Structural features of an epithelial cell of a villus: Villi – provide a huge surface area for absorptionVilli – provide a huge surface area for absorption Epithelium cells – single layer of small cells, packed with mitochondria – the source of Epithelium cells – single layer of small cells, packed with mitochondria – the source of

ATP (metabolic energy) for active uptake across the plasma membraneATP (metabolic energy) for active uptake across the plasma membrane Pump proteins in the plasma membrane of epithelium cells – actively transport Pump proteins in the plasma membrane of epithelium cells – actively transport

nutrients across the plasma membrane into the villinutrients across the plasma membrane into the villi Network of capillaries – large surface area for uptake of amino acids, Network of capillaries – large surface area for uptake of amino acids,

monosaccharides, and fatty acids and glycerol into blood circulationmonosaccharides, and fatty acids and glycerol into blood circulation Lacteal – branch of the lymphatic system into which triglycerides (combined with Lacteal – branch of the lymphatic system into which triglycerides (combined with

protein) pass for transport to body cellsprotein) pass for transport to body cells Mucus from goblet cells in epithelium – lubricates movement of digested food among Mucus from goblet cells in epithelium – lubricates movement of digested food among

the villi and protects plasma membrane of epithelial cellsthe villi and protects plasma membrane of epithelial cells Microvilli – these tiny, finger-like infoldings of the cell surface facing the lumen of the Microvilli – these tiny, finger-like infoldings of the cell surface facing the lumen of the

gut greatly increase the surface area in contact with material to be absorbed.gut greatly increase the surface area in contact with material to be absorbed. Mitochondria – these organelles are present in large numbers, suggesting a significant Mitochondria – these organelles are present in large numbers, suggesting a significant

demand for ATP in these cells.demand for ATP in these cells. Pinocytotic vesicles – these are the site of pinocytosis by which fluid is taken up or Pinocytotic vesicles – these are the site of pinocytosis by which fluid is taken up or

released in tiny vesicles, across the plasma membrane of a cell.released in tiny vesicles, across the plasma membrane of a cell. Tight junctions – these bind together the individual epithelial cells, so that the only Tight junctions – these bind together the individual epithelial cells, so that the only

way into the tissues of the body is through the epithelium.way into the tissues of the body is through the epithelium.


Mechanisms used by Ileum to absorb Mechanisms used by Ileum to absorb and transport food:and transport food:

Facilitated diffusionFacilitated diffusion. Some substances need a little . Some substances need a little assistance to enter and exit cells. The transmembrane assistance to enter and exit cells. The transmembrane protein helps out by changing shape.protein helps out by changing shape.

Active transportActive transport. Some substances need a lot of assistance . Some substances need a lot of assistance to enter cells. Similar to swimming upstream, energy is to enter cells. Similar to swimming upstream, energy is needed for the substance to penetrate against an needed for the substance to penetrate against an unfavorable concentration gradient.unfavorable concentration gradient.

EndocytosisEndocytosis. Cells can use their cell membranes to engulf a . Cells can use their cell membranes to engulf a particle and bring it inside the cell. The engulfing portion of particle and bring it inside the cell. The engulfing portion of the membrane separates from the cell wall and encases the the membrane separates from the cell wall and encases the particle in a vesicle.particle in a vesicle.


Material not absorbed and are Material not absorbed and are egested:egested:– cellulose and lignin from plant mattercellulose and lignin from plant matter– the remains of intestinal epithelial cells the remains of intestinal epithelial cells – bile pigments bile pigments – bacteriabacteria

Small IntestineSmall Intestine Absorption vs. Assimilation:Absorption vs. Assimilation:

– Absorption involves the passage of digested nutrients into the blood Absorption involves the passage of digested nutrients into the blood from the gastro-intestinal tract, glucose, fructose and amino acids go from the gastro-intestinal tract, glucose, fructose and amino acids go straight to the blood capillaries, whereas fatty acids and straight to the blood capillaries, whereas fatty acids and monoglycerides so first into the lymphatic system and then the blood monoglycerides so first into the lymphatic system and then the blood system. system.

Assimilation involves the integration of these absorbed molecules into Assimilation involves the integration of these absorbed molecules into the living processes of the organism that ingested them, using them to the living processes of the organism that ingested them, using them to build new molecules that are necessary for its normal functioning and build new molecules that are necessary for its normal functioning and survival. Or using them to produce energysurvival. Or using them to produce energy

Large IntestineLarge Intestine Also known as the colonAlso known as the colon 1.5 m long and 5 cm in diameter1.5 m long and 5 cm in diameter It joins the small intestine at a T-It joins the small intestine at a T-

shaped junction, where a sphincter shaped junction, where a sphincter controls the passage of unabsorbed controls the passage of unabsorbed food material out of the small food material out of the small intestine.intestine.– One arm of the T is a blind pouch called One arm of the T is a blind pouch called

the cecum.the cecum. A small, fingerlike extension of the cecum is A small, fingerlike extension of the cecum is

the the appendix: appendix: contains a mass of w.b.c’s contains a mass of w.b.c’s that make a minor contribution to immunity.that make a minor contribution to immunity.

Large IntestineLarge Intestine Main function is to absorb water from Main function is to absorb water from

the alimentary canal.the alimentary canal. About 7L of fluid enters the lumen of About 7L of fluid enters the lumen of

the digestive tract each day as the the digestive tract each day as the solvent of the various digestive solvent of the various digestive juices. juices.

About 90% of this water is absorbed About 90% of this water is absorbed back into the blood and tissue fluids, back into the blood and tissue fluids, with the small intestine reclaiming with the small intestine reclaiming most of it and the colon finishing the most of it and the colon finishing the job.job.

Large IntestineLarge Intestine

As water gets absorbed, remains of As water gets absorbed, remains of the digested food become more solid the digested food become more solid as they are moved along the colon as they are moved along the colon via peristalsis.via peristalsis.

Remains make feces, the waste Remains make feces, the waste products of digestion, which consist products of digestion, which consist mainly of indigestible plant fibersmainly of indigestible plant fibers

Large IntestineLarge Intestine

Surprise, surprise!Surprise, surprise!– Bacteria, such as E.coli, live in your Bacteria, such as E.coli, live in your

colon!colon!– Produce important vitamins (biotin, folic Produce important vitamins (biotin, folic

acid, B vitamins, and Vitamin K) that are acid, B vitamins, and Vitamin K) that are absorbed into the bloodstream through absorbed into the bloodstream through the colonthe colon

Large IntestineLarge Intestine RectumRectum: terminal portion of the : terminal portion of the

colon where feces are stored until colon where feces are stored until they can be eliminated. they can be eliminated.

Strong contractions of the colon Strong contractions of the colon create the urge to defecate.create the urge to defecate.

Two rectal sphincters, one voluntary Two rectal sphincters, one voluntary and one involuntary, regulate the and one involuntary, regulate the opening of the anus. opening of the anus.

Large IntestineLarge Intestine DiarrheaDiarrhea

– If the lining of the colon is irritated by a If the lining of the colon is irritated by a viral or bacterial infection, the colon is viral or bacterial infection, the colon is less effective in reclaiming waterless effective in reclaiming water

ConstipationConstipation– Peristalsis moves the feces along too Peristalsis moves the feces along too

slowly; the colon reabsorbs too much slowly; the colon reabsorbs too much water, and the feces become too water, and the feces become too compacted.compacted.

– Usually caused by a diet with not Usually caused by a diet with not enough fiber or from a lack of exercise.enough fiber or from a lack of exercise.

Digestion AnimationDigestion Animation

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Digestion Exocrine Gland Digestion Exocrine Gland CellsCells

Exocrine glands are responsible for the Exocrine glands are responsible for the release of digestive fluids. release of digestive fluids.

Exocrine glands secrete into ducts. Exocrine glands secrete into ducts. Exocrine gland has a duct portion and Exocrine gland has a duct portion and a glandular portion. a glandular portion. – At the end of each branch is an acinus At the end of each branch is an acinus

formed at secretory cells of two types: formed at secretory cells of two types: serous cells (which secrete proteins such serous cells (which secrete proteins such as enzymes), and mucous cells (which as enzymes), and mucous cells (which secrete mucus).secrete mucus).

LiverLiver

Liver performs more functions than any Liver performs more functions than any other organ in the body.other organ in the body.

After breaking down a.a. for energy or After breaking down a.a. for energy or for recycling into other molecules, the for recycling into other molecules, the liver prepares nitrogenous wastes liver prepares nitrogenous wastes (ammonia) for disposal synthesizing (ammonia) for disposal synthesizing urea. urea.

It also converts toxins such as alcohol It also converts toxins such as alcohol and other drugs into inactive products and other drugs into inactive products that can be excreted in urine. that can be excreted in urine.

LiverLiver Liver can synthesize bile for Liver can synthesize bile for

digestion of fats, as well as proteins digestion of fats, as well as proteins essential to many of the body’s essential to many of the body’s functionsfunctions– Proteins made in the liver include Proteins made in the liver include

plasma proteins important in blood plasma proteins important in blood clotting and in maintaining osmotic clotting and in maintaining osmotic balance of the blood, as well as balance of the blood, as well as lipoproteins that transport fats and lipoproteins that transport fats and cholesterol to body tissues.cholesterol to body tissues.

LiverLiver

Regulates the amount of glucose in Regulates the amount of glucose in blood.blood.– Converts glucose into glycogen, which it Converts glucose into glycogen, which it

stores for later use.stores for later use.– Plays a key role in body metabolism Plays a key role in body metabolism

LiverLiver Strategically located between the Strategically located between the

intestines and the heartintestines and the heart Capillaries from the si and li converge Capillaries from the si and li converge

into vessels that lead into the into vessels that lead into the hepatic portal veinhepatic portal vein..– Transports nutrients absorbed by the Transports nutrients absorbed by the

intestines directly to the liver.intestines directly to the liver.– Gives the liver the opportunity to modify Gives the liver the opportunity to modify

and detoxify substances absorbed by the and detoxify substances absorbed by the digestive tract before the heart (and digestive tract before the heart (and then the rest of the body)then the rest of the body)

LiverLiver

LiverLiver Alcohol consumptionAlcohol consumption

– Under heavy, frequent exposure to alcohol, Under heavy, frequent exposure to alcohol, damage may become so severe that damage may become so severe that abnormal scar tissue forms in the liver called abnormal scar tissue forms in the liver called cirrhosiscirrhosis Distorts the liver’s internal structure Distorts the liver’s internal structure Scar tissue slowly replaces functioning liver tissue, Scar tissue slowly replaces functioning liver tissue,

gradually diminishing blood flow through the liver.gradually diminishing blood flow through the liver. Usually causes a build-up of toxins in blood, Usually causes a build-up of toxins in blood,

excessive bruising or bleeding, diabetes, and excessive bruising or bleeding, diabetes, and cancer.cancer.

About 25,000 Americans die each year from About 25,000 Americans die each year from alcohol-related cirrhosis.alcohol-related cirrhosis.

LiverLiver

Cirrhosis treatmentCirrhosis treatment– Stop drinking!Stop drinking!– Liver transplantLiver transplant– To prevent cirrhosis, U.S. guidelines To prevent cirrhosis, U.S. guidelines

advise not more than two alcoholic advise not more than two alcoholic drinks for men and 2 drink for women drinks for men and 2 drink for women per day. per day.

KidneyKidney Main processing centers of our Main processing centers of our

excretory system are the two kidneys.excretory system are the two kidneys. Each is a compact organ, about the size Each is a compact organ, about the size

of your fist, nearly filled with about 80 of your fist, nearly filled with about 80 km of fine tubes (tubules) and an km of fine tubes (tubules) and an intricate network of blood capillaries intricate network of blood capillaries

Body contains about 5L of blood, which Body contains about 5L of blood, which circulates repeatedly, allowing for about circulates repeatedly, allowing for about 1,100-2,000 L to pass though the 1,100-2,000 L to pass though the capillaries in our kidneys every day.capillaries in our kidneys every day.

KidneyKidney From this enormous (1,100-2000 L) From this enormous (1,100-2000 L)

traffic of blood, our kidneys extract traffic of blood, our kidneys extract daily about 180L of daily about 180L of filtratefiltrate..– Filtrate is made of water, urea, and a Filtrate is made of water, urea, and a

number of valuable solutes including number of valuable solutes including glucose, amino acids, ions, and vitamins. glucose, amino acids, ions, and vitamins.

– If we excreted all the filtrate as urine, we If we excreted all the filtrate as urine, we would lose vital nutrients and dehydrate would lose vital nutrients and dehydrate rapidly. rapidly.

– But our kidneys refine the filtrate, But our kidneys refine the filtrate, concentrating the urea and returning most concentrating the urea and returning most of the water and solutes to the blood.of the water and solutes to the blood.

KidneysKidneys

KidneysKidneys In a typical day, we excrete only In a typical day, we excrete only

about 1.5 L of urine.about 1.5 L of urine. ““Plumbing” plan of kidneys:Plumbing” plan of kidneys:

– 1. Blood to be filtered enters each kidney via a 1. Blood to be filtered enters each kidney via a renal artery renal artery

– 2. Blood that has been filtered leaves the 2. Blood that has been filtered leaves the kidney in the renal veinkidney in the renal vein

– 3. urine leaves each kidney via a duct called a 3. urine leaves each kidney via a duct called a ureterureter and passes into the and passes into the urinaryurinary bladder. bladder.

– 4. periodically, the bladder empties during 4. periodically, the bladder empties during urination via a tube called the urination via a tube called the urethraurethra, which , which empties near the female vagina or through the empties near the female vagina or through the male penismale penis

KidneyKidney

Has two main regions: Has two main regions: – Renal cortex Renal cortex (outer layer) (outer layer) – Renal medulla Renal medulla (inner region)(inner region)– Urine flows into a chamber called the Urine flows into a chamber called the

renal pelvisrenal pelvis, and from there into the , and from there into the ureterureter..

KidneyKidney

KidneyKidney NephronNephron

– Tiny functional units of the kidneyTiny functional units of the kidney– About a millionAbout a million– Consists of a nephron tubule and its Consists of a nephron tubule and its

associated blood vessels.associated blood vessels.– Extracts a tiny amount of filtrate from Extracts a tiny amount of filtrate from

the blood and then refines the filtrate the blood and then refines the filtrate into a much smaller quantity of urine. into a much smaller quantity of urine.

– Each nephron starts and ends in the Each nephron starts and ends in the kidney’s cortex; some extend into the kidney’s cortex; some extend into the medullamedulla

KidneyKidney Nephron (continued):Nephron (continued):

– Receiving end of the nephron is a cup-shaped Receiving end of the nephron is a cup-shaped swelling called the swelling called the Bowman’s capsule.Bowman’s capsule.

– At the other end of the nephron is the At the other end of the nephron is the collecting collecting ductduct, which carries urine to the renal pelvis., which carries urine to the renal pelvis.

– Bowman’s capsule Bowman’s capsule envelops a ball of envelops a ball of capillaries called the capillaries called the glomerulus glomerulus which together which together make up the blood-filtering unit of the nephron.make up the blood-filtering unit of the nephron. 1. Here, blood pressure forces water and solutes from 1. Here, blood pressure forces water and solutes from

the blood in the glomerular capillaries across the wall of the blood in the glomerular capillaries across the wall of Bowman’s capsule and into the nephron tubule.Bowman’s capsule and into the nephron tubule.

2. This process creates filtrate, leaving blood cells and 2. This process creates filtrate, leaving blood cells and large molecules such as plasma proteins behind in the large molecules such as plasma proteins behind in the capillaries.capillaries.

Kidney Kidney Nephron (continued)Nephron (continued)– Rest of the nephron refines the filtrate. Rest of the nephron refines the filtrate.

The tubule has three sections:The tubule has three sections: 1. proximal tubule 1. proximal tubule

– in the cortexin the cortex

2. Loop of Henle2. Loop of Henle– A hairpin loop carrying filtrate toward –in some A hairpin loop carrying filtrate toward –in some

cases, into—the medula and then back toward the cases, into—the medula and then back toward the cortexcortex

3. Distal tubule3. Distal tubule– A. Called distal because it is the most distant from A. Called distal because it is the most distant from

Bowman’s capsuleBowman’s capsule– B. Drains into a B. Drains into a collecting ductcollecting duct, which receives , which receives

filtrate from many nephronsfiltrate from many nephrons– C. in the kidney’s many collecting ducts, the C. in the kidney’s many collecting ducts, the

processed filtrate, urine, passes into the renal pelvis processed filtrate, urine, passes into the renal pelvis and then into the ureter.and then into the ureter.

NephronNephron

Kidney animationKidney animation

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KidneyKidney Nephron (continued):Nephron (continued):

– The intricate association between blood The intricate association between blood vessels and tubules is key to nephron vessels and tubules is key to nephron functionfunction

– Two key networks of capillariesTwo key networks of capillaries 1.Glomerulus 1.Glomerulus

– A finely divided portion of an arteriole that branches from the A finely divided portion of an arteriole that branches from the renal artery.renal artery.

– Leaving the Glomerulus, the arteriole carries blood to:Leaving the Glomerulus, the arteriole carries blood to:

2.Proximal and distal tubules2.Proximal and distal tubules– This second network functions with the tubules in refining the This second network functions with the tubules in refining the

filtrate; some of the vessels parallel the loop of Henle, with filtrate; some of the vessels parallel the loop of Henle, with blood flowing down in one vessel and back up through blood flowing down in one vessel and back up through another.another.

Leaving the nephron, the capillaries converge to Leaving the nephron, the capillaries converge to form a venule leading toward the renal vein.form a venule leading toward the renal vein.

KidneyKidney

KidneyKidney

Excretory system produces and Excretory system produces and disposes of urine in four major disposes of urine in four major processes:processes:– FiltrationFiltration

Occurs when water and virtually all other Occurs when water and virtually all other molecules small enough to be forced through molecules small enough to be forced through the capillary wall enter the nephron tubule from the capillary wall enter the nephron tubule from the glomerulus.the glomerulus.

– ReabsorptionReabsorption Refines filtrate; water and valuable solutes, Refines filtrate; water and valuable solutes,

including glucose, salt, other ions, and amino including glucose, salt, other ions, and amino acids are returned to the blood from the filtrate.acids are returned to the blood from the filtrate.

KidneyKidney– SecretionSecretion Also refines the filtrate; substances in the blood are Also refines the filtrate; substances in the blood are

transported into the filtrate. transported into the filtrate. – For example, when there is an excess of H+ in the For example, when there is an excess of H+ in the

blood, these ions are secreted into the filtrate, thus blood, these ions are secreted into the filtrate, thus keeping the blood from becoming acidickeeping the blood from becoming acidic

Eliminates certain drugs and other toxic substances from Eliminates certain drugs and other toxic substances from the bloodthe blood

***both reabsorption and secretion, water and solutes move ***both reabsorption and secretion, water and solutes move between the tubule and capillaries by passing through the between the tubule and capillaries by passing through the interstitial fluid.interstitial fluid.

– ExcretionExcretion Urine, the product of filtration, reabsorption, and secretion, Urine, the product of filtration, reabsorption, and secretion,

passes through the kidneys to the outside via the ureters, passes through the kidneys to the outside via the ureters, urinary bladder, and urethra.urinary bladder, and urethra.

KidneyKidney Reabsorption and Secretion in a Reabsorption and Secretion in a

nephron Figure 25.11: nephron Figure 25.11: – pink arrows show reabsorption , which pink arrows show reabsorption , which

may occur via active transport, passive may occur via active transport, passive diffusion, or osmosis.diffusion, or osmosis.

– Blue arrows show secretion Blue arrows show secretion – Colored area shows the interstitial fluid, Colored area shows the interstitial fluid,

through which solutes and water move through which solutes and water move between the tubules and capillariesbetween the tubules and capillaries Intensity of color reflects solute conc.; cortex has Intensity of color reflects solute conc.; cortex has

lowest conc. and medulla has highest conc.lowest conc. and medulla has highest conc. Solute conc. of the interstitial fluid exceeds that of the Solute conc. of the interstitial fluid exceeds that of the

filtratefiltrate water moves by osmosis out of filtrate into water moves by osmosis out of filtrate into interstitial fluidinterstitial fluid


nephron Figure 25.11 (continued): nephron Figure 25.11 (continued): – Proximal and distal tubule function:Proximal and distal tubule function:

Proximal tubule actively transports nutrients such as Proximal tubule actively transports nutrients such as glucose and amino acids from the filtrate into the glucose and amino acids from the filtrate into the interstitial fluid, to be reabsorbed into the capillaries.interstitial fluid, to be reabsorbed into the capillaries.

NaCl is reabsorbed from both proximal and distal, and NaCl is reabsorbed from both proximal and distal, and water follows by osmosis.water follows by osmosis.

Secretion of H+ and reabsorption of HCO3- also occur Secretion of H+ and reabsorption of HCO3- also occur in both proximal and distal, helping to regulate the in both proximal and distal, helping to regulate the blood’s pH. blood’s pH.

Potassium conc. in blood is regulated by secretion of Potassium conc. in blood is regulated by secretion of excess K+ into the distal tubule.excess K+ into the distal tubule.

Drugs and poisons processed in the liver are secreted Drugs and poisons processed in the liver are secreted into the proximal tubule.into the proximal tubule.


nephron Figure 25.11 (continued): nephron Figure 25.11 (continued): – Loop of Henle and collecting duct Loop of Henle and collecting duct

function:function: Major function is water reabsorptionMajor function is water reabsorption Long loop of Henle carries filtrate deep into the Long loop of Henle carries filtrate deep into the

medulla and then back to the cortexmedulla and then back to the cortex Presence of NaCl and some urea in interstitial fluid in Presence of NaCl and some urea in interstitial fluid in

the medulla maintains the high conc. gradient that the medulla maintains the high conc. gradient that increases water reabsorption by osmosis. increases water reabsorption by osmosis.

As soon as water passes into interstitial fluid, it moves As soon as water passes into interstitial fluid, it moves into nearby blood capillaries and is carried away. This into nearby blood capillaries and is carried away. This prompt removal is essential to avoid diluting the prompt removal is essential to avoid diluting the interstitial fluid and destroying the conc. Gradient interstitial fluid and destroying the conc. Gradient necessary for water reabsorption. necessary for water reabsorption.



function:function: water reabsorption stops at hairpin because water reabsorption stops at hairpin because

the tubule there is impermeable to water.the tubule there is impermeable to water. As filtrate moves back toward the cortex, As filtrate moves back toward the cortex,

NaCl leaves the filtrate, first passively and NaCl leaves the filtrate, first passively and then actively as the cells of the tubule pump then actively as the cells of the tubule pump NaCl into the interstitial fluid. NaCl into the interstitial fluid.

– it is primarily this movement of salt that creates it is primarily this movement of salt that creates the solute gradient in the interstitial fluid of the the solute gradient in the interstitial fluid of the medulla.medulla.



function:function: Final refining of the filtrate occurs in the collecting Final refining of the filtrate occurs in the collecting

duct. duct. By actively reabsorbing NaCl, the collecting duct is By actively reabsorbing NaCl, the collecting duct is

important in determining how much salt is excreted in important in determining how much salt is excreted in the urine. the urine.

In the inner medulla, the collecting duct becomes In the inner medulla, the collecting duct becomes permeable to urea and some leaks out, adding to the permeable to urea and some leaks out, adding to the high conc. gradient in the interstitial fluid.high conc. gradient in the interstitial fluid.

As filtrate moves through medulla, more water is As filtrate moves through medulla, more water is reabsorbed before the urine passes into the renal reabsorbed before the urine passes into the renal pelvis. pelvis.

KidneyKidney

Reabsorption and Secretion in a Reabsorption and Secretion in a nephron Figure 25.11 (continued): nephron Figure 25.11 (continued): – In sum, the nephron returns much of the In sum, the nephron returns much of the

water that filters into it from the blood.water that filters into it from the blood.– Water conservation is one of the major Water conservation is one of the major

functions of the kidneyfunctions of the kidney– Maintain a precise and essential balance Maintain a precise and essential balance

btw water and solutes in our body fluids. btw water and solutes in our body fluids.

KidneyKidney– Antidiuretic hormone (ADH)Antidiuretic hormone (ADH)

Increased in the blood by a control center in Increased in the blood by a control center in the brain when the solute concentration rises the brain when the solute concentration rises above a set point. above a set point.

Signals nephrons to step up water Signals nephrons to step up water reabsorption. reabsorption.

When the solute conc. Is diluted below the set When the solute conc. Is diluted below the set point, as when we drink a lot of water, blood point, as when we drink a lot of water, blood levels of ADH drop and water reabsorption is levels of ADH drop and water reabsorption is reduced, resulting in an increased discharge of reduced, resulting in an increased discharge of dilute urine. dilute urine.

Alcohol inhibits the release of ADH and can Alcohol inhibits the release of ADH and can cause excessive urinary water loss and cause excessive urinary water loss and dehydration, which may account for the dehydration, which may account for the symptoms of a hangover. symptoms of a hangover.

KidneyKidney

DialysisDialysis– A person can survive with only one A person can survive with only one

functioning kidney, but if both kidneys functioning kidney, but if both kidneys fail, the build up of toxic wastes and the fail, the build up of toxic wastes and the lack of regulation of blood pressure, pH, lack of regulation of blood pressure, pH, and ion concentrations will lead to and ion concentrations will lead to certain death if untreated.certain death if untreated.

– Over 60% of kidney disease cases are Over 60% of kidney disease cases are caused by hypertension and diabetes, caused by hypertension and diabetes, but prolonged use of pain relievers, but prolonged use of pain relievers, alcohol, and other drugs are also alcohol, and other drugs are also possible causespossible causes

KidneyKidney Dialysis– How it worksDialysis– How it works

– Dialysis means “separation” in GreekDialysis means “separation” in Greek– Like the nephron, the machine sorts small molecules of Like the nephron, the machine sorts small molecules of

blood, keeping some and discarding others.blood, keeping some and discarding others.– Patient’s blood is pumped from an artery through a series Patient’s blood is pumped from an artery through a series

of tubes made of a selectively permeable membrane.of tubes made of a selectively permeable membrane.– The tubes are immersed in a dialyzing solution much like The tubes are immersed in a dialyzing solution much like

the interstitial fluid that bathes the nephrons. the interstitial fluid that bathes the nephrons. – As the blood circulates through the tubing, urea and As the blood circulates through the tubing, urea and

excess ions diffuse out.excess ions diffuse out.– Needed substances, such as biocarbonate ions, diffuse Needed substances, such as biocarbonate ions, diffuse

from the dialyzing solution into the bloodfrom the dialyzing solution into the blood– Machine continually discards the used dialyzing solution Machine continually discards the used dialyzing solution

as wastes build up.as wastes build up.

KidneyKidney

DialysisDialysis– Although life sustaining, it’s costly and Although life sustaining, it’s costly and

time consuming (three times a week for time consuming (three times a week for 4-6 hours at a time)4-6 hours at a time)

– Also requires severe dietary and lifestyle Also requires severe dietary and lifestyle restrictionsrestrictions

– Waiting list for kidney transplants , Waiting list for kidney transplants , unfortunately, is quite long.unfortunately, is quite long.

human physiology: digestion

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food passes

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breaking food

pass of food

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digestive tube

liversecrete digestive

small intestine