Digestive System

Digestive TractAlso called alimentary canalHollow tube roughly 8 meters in

length

Structure of the WallLumen - hollow center of tubeMucosa - epithelial layer with

mucous-secreting cellsSubmucosa - connective tissue

layer rich with blood vessels, lymphatic vessels, and nerves

Muscular layer - smooth muscle layerCircular- adjust lumen diameterLongitudinal- adjust tract length

Serosa - outermost layer; secretes serous fluid

Movements of the Tube

Types of DigestionMechanical

Physical breakdown of food into smaller pieces

ChemicalBreakdown of food molecules

into more simple molecules by enzymes

MouthReceives foodPushes into the remaining digestive

tractIncludes: lips, teeth, cheeks,

tongue, and palateTwo cavities:

1) Oral cavity Space between palate and tongue

2) Vestibule Cavity between teeth and lips and cheeks

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Exit Slip

Cheek and LipsCheeks

Contain muscles used during chewing Stratified squamous epithelial tissue

insideLips

Highly mobile skeletal muscles rich in sensory receptors

Aid in sensing temperature and texture of food

TongueFunctions:

Keeps food underneath teeth Mixes food with saliva Moves bolus to the back of the

mouth during swallowingMuscular structure covered with

mucous membraneRoot is attached to hyoid boneAttached to floor of mouth by

frenulumPapillae provide surface friction

and contain taste buds

PalateForms roof of oral cavityHard palate

Anterior portionSoft palate

Posterior portion; includes uvula Soft palate raises during

swallowing to close off nasal cavity

Tonsils Masses of lymphatic tissue Lingual

On the tongue Pharyngeal

Posterior wall of pharynx; also called adenoids

Palatine Back of mouth on either

side of tongue; associated with palate

TeethTwo sets:

1) Primary - 20 teeth Lost/shed, nonpermanent

2) Secondary - 32 teeth Permanent, come in after primary teeth are

lost/shed

Function: Begin mechanical digestion of food

Anatomy of ToothCrown - section above gingiva (gum)Root -section below gingivaEnamel - outer covering on crownDentin - bone-like substance that fills

most of the toothPulp cavity - connective tissue that

contains blood vessels and nervesRoot canal - tubular extension that

brings blood vessel and nerve to the pulp cavity

Cementum and periodontal ligament - hold tooth in alveolar process of jaw bone

Salivary GlandsFunctions:

Moistens food Binds food together Dissolves food (so it can be tasted) Cleanses mouth and teeth Begins digestion of carbohydrates

Two types of cells 1) Serous cells

Secretes serous fluid with enzyme amylase 2) Mucous cells

Secretes mucous

Salivary Glands (cont)3 Types:

1) Parotid glands:Largest glands; anterior and inferior to

ear; secrete watery saliva rich in amylase2) Submandibular:

Located in floor of mouth just inside lower jaw

3) Sublingual:Smallest glands; inferior to tongue;

secrete saliva in mucous concentration

PharynxCavity located posterior to oral cavityProvides connection to larynx and

esophagusThree parts:

1) Nasopharynx - upper potion connecting to nasal cavity

2) Oropharynx - middle section posterior to palate

3) Laryngopharynx - lower portion posterior to larynx opening; leads to esophagus

Squid

Swallowing Action1. Bolus stimulates sensory receptors in

pharyngeal opening2. Soft palate raises- closes nasal cavity3. Larynx elevates; epiglottis closes off

larynx4. Tongue presses against palate5. Longitudinal muscle pull pharynx

towards food6. Muscles relax near esophagus to

open the tube7. Peristalsis moves food into

esophagus

Swallowing

Esophagus Hollow collapsible tube Move food from pharynx to stomach Passes through diaphragm in opening called

esophageal hiatus When food reaches opening of stomach, lower

esophageal sphincter opens

Neck

StomachJ-shaped pouch in

abdomen Holds about 1 liter of food

Functions: Mix food with gastric juices Begin protein digestion Responsible for limited

absorption Moves food into small

intestineSquid Continues

Stomach (cont)Rugae

Thick folds of mucosa and submucosa allow for expansion of stomach wall

Regions of the stomachCardiac - portion near esophagusFundic - portion lateral to cardiac where

stomach ballonsBody - main portion of stomach between

cardiac and pyloric Pyloric - portion near opening to

duodenum Pyloric Sphincter - thick muscle band

controlling entrance into duodenum

Stomach

Gastric SecretionsMucosa is studded with gastric pitsGastric pits are the opening to gastric glands

Gastric glands have three types of secreting cells:1) Mucous cells - secrete mucous;

helps prevent stomach from digesting itself

2) Chief cells - secrete pepsinogen3) Parietal cells - secrete HCl and

intrinsic factor

Gastric secretions (cont) As food enters stomach, mixing actions

occur to breakdown food into chyme Gastric juices are added

HCl creates acidic environment Shortens (activates) pepsinogen and makes

it pepsin Helps with vitamin B12 absorption

Gastric secretions (cont) Limited absorption of the following

occur: Water Salts Alcohol Lipid-soluble drugs

Chyme is moved to pyloric sphincter and pushed through

Control of Gastric Secretions Digestion is controlled by medulla

oblongata Parasympathetic NS:

Increases gastric secretions Sympathetic NS:

Decreases gastric secretions Hormones:

Gastrin - stimulates production of gastric juices Cholecystokinin - released when small intestine

fills with food; decreases gastric motility

Review QuizMouth->Stomach 1. Contains rugae (folds)?2. Contains lower sphincter and opens to stomach?3. Mixes food with gastric juices? 4. Provides connection to larynx and esophagus? 5. Begins mechanical digestion of food?

2. Stomach 3. Esophagus 4. Stomach 5. Pharynx 6. Teeth

PancreasHas endocrine and exocrine function

(Ch 11!)Nestled in C-shaped curve of duodenumPancreatic acinar cells

Secrete pancreatic juicesClustered around tubes that eventually

empty into pancreatic ductPancreatic duct run the length of the

pancreas Empties the juice into the duodenum

Hepatopancreatic sphincter Controls emptying

Pancreatic EnzymesCarbohydrates:

Pancreatic amylase Breaks polysaccharides into

dissaccharidesLipids:

Pancreatic lipase Breaks fats into glycerol and fatty acids

Nucleic Acids: Nucleases

Breaks nucleic acids into nucleotides

Pancreatic Enzymes (cont)Protein:

3 enzymes (break them down into amino acids) Trypsin Chymotrypsin Carboxypeptidase

Stored in zymogen granules in inactive forms Ex: Trypsin’s inactive form is trypsinogen and is

activated by enterokinase which is secreted by mucosa of duodenum

Control of Pancreatic Juices and Enzymes Parasympathetic NS control:

Stimulate release of pancreatic juices Acidic chyme:

Stimulates release of secretin into the bloodstream Stimulates release of pancreatic juice high in

bicarbonate ions Chyme high in protein and fat

Stimulates release of cholecystokinin into bloodstream

Stimulates release of pancreatic juice high in digestive enzymes

LiverFunctions:

Controlling carbohydrate metabolismLipid metabolismProtein metabolismStorageBlood filtering DetoxificationSecretion of bile

Liver Structure Connective tissue divides liver into larger right

lobe and smaller left lobe Liver is further divided into lobules Hepatic cells radiate around a central vein Spaces between the hepatic cells are called

hepatic sinusoids

Liver Structure (cont) Blood from digestive track enters sinusoids from

hepatic portal vein Kupffer cells

Large macrophages (filter out pathogens from sinusoids) Hepatic cells

Take out excess nutrients Blood enters central vein and continues on its path

back to the heart

What is Bile? Yellowish-green liquid secreted by liver

cells Includes:

Bile salts, bile pigments, cholesterol, and electrolytes

What does bile do? Emulsification

Breaks fats globules into smaller droplets Smaller droplets are easier for lipases to

digest Enhances absorption of fatty acids,

cholesterol, and fat-soluble vitamins A, D, E, and K

Bile (cont)Sequence of travel:

Hepatic cells → Bile canaliculi → Bile Ductules → Bile duct → Hepatic duct → Common hepatic duct → Hepatopancreatic sphincter → Duodenum

Gallbladder Between meals, bile up in common hepatic

duct and into the cystic duct that attaches to it Bile is backed up into gallbladder that is

attached to the cystic duct

Gallbladder also absorbs excess water in bile therefore concentrating it

Control of Bile Release Chyme high in protein and fat

Stimulates release of cholecystokinin into bloodstream which stimulates release of bile

Where peristalsis reaches hepatopancreatic sphincter, it relaxes and bile squirts into duodenum

Small Intestine StructureThree parts:

1) DuodenumFirst part after stomach; forms a C-

shape 2) Jejunum

More active than ileum 3) Ileum

Leads to large intestine

Small Intestine Structure (cont)

Mesentary Holds loops of intestine to posterior abdominal wall Supports blood vessels, lymphatic vessels, and

nerves associated with intestine Greater omentum

Double fold of membrane covering intestines Helps wall off infected area Prevent spread throughout cavity

Structure of Intestinal Wall

Wall has many projections called villi Increase digestive surface areaMost numerous in duodenum and first part of

jejunumCovered with simple columnar epithelium Have a connective tissue coreContains blood vessels, a lymphatic vessel

called a lacteal, and nervesAt the base are pockets called intestinal

glands

Small Intestine SecretionsMucosa

Goblet cells secrete mucosMucous

Secreting cell in submucosa - secrete alkaline mucous

Intestinal gland Secrete watery substance

Epithelial cells of mucosa (all release enzymes) Peptidase Sucrase, maltase, and lactase Intestinal lipase

Control of Small Intestine Secretions Parasympathetic NS:

Triggers release when intestine wall is expanded

Other glands are stimulated by chyme (both mechanically and chemically)

Sm. Intes. Absorption

Small intestines = 95% of absorption of nutrients Absorption follows release of chemicals:

Chemicals mix with chyme to help digestion and absorption Bile Pancreatic juices Intestinal enzymes (maltase, lactase, sucrase, trypsin

and chymotrypsin)

Absorption (cont)Carbohydrates:

Simple sugars are moved into the blood stream by diffusion or active transport

Proteins: Amino acids are actively transported into the blood

stream

Lipids Fatty acids and glycerol diffuse into cell of villi Fatty acids with short chains diffuse into blood

stream Other are synthesized into fats and packed with

protein (chylomicron) by the ER These enter the lacteal and are carried to the blood

Movements of Sm Intes

Mixing movements Contractions move chyme from side to

side to mix it Peristalsis

Movement toward large intestine; very slow

Peristaltic rush Forceful contraction if intestine if irritated

or over distended; pushes chyme to large intestine without much absorption’ leads to diarrhea

Ileocecal sphincter Controls movement between ileum and

cecum; normally closed; open after a meal

Structure of Large Intestine Large diameter lumen Composed of:

Cecum Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anal Canal

Structure of Large Intestine Wall

Longitudinal muscle occurs in three bands called teniae coli

Tension in teniae coli creates pouches called haustra in intestine

Functions of Large Intestine Mucous secretion

Protects walls Bind fecal matter Controls pH

Absorption Absorb water and electrolytes in proximal portion

Habitat for bacteria Bacteria digest parts of fecal matter that is

indigestible to us; Synthesize vitamins that are then absorbed

Movements of Large Intestine

Mixing movements Same as small intestine

Peristalsis Waves occur only a few time a day; usually

after mealsDefecation reflex

Feces are forced into rectum; internal anal sphincter is relaxed

Pressure is increased in abdomen which squeezes the rectum

External anal sphincter is relaxed

Composition of Feces Water Undigested material Electrolytes Mucous Intestinal Cells Bacteria

The Science of Farting

Thumbs up, Thumbs Down 1. The large intestines houses bacteria such as E coli? Thumbs up! 2. The liver can absorb excess water in bile. Thumbs down! Gallbladder 3. The small intestines contains mesentery which helps bind and support. Thumbs up! 4. The large intestines helps perform peristalsis and peristaltic rush. Thumbs down! Small intestines 5. The liver metabolizes proteins and lipids and filters blood. Thumbs up!!

Review of Digestive Tract

Digestive Nutrients Macronutrients

Carbohydrates Protein Lipids

Micronutrients Vitamins Minerals

Essential Nutrients Nutrients that body cannot produce itself

Carbohydrates

Process of Digestion: Complex carbohydrate (Polysaccharide) →

Disaccharide → Monosaccharide Indigestible carbohydrates:

Ex: Cellulose - provides roughage (or fiber) to diet

Carbohydrates (cont) Fructose and galactose are converted to glucose

by the liver Excess glucose

Liver converts glucose to glycogen or to fats Deficiency of Glucose

Liver converts glycogen, fats, or proteins to glucose Requirements for carbohydrates varies depending

upon energy expenditures More energy = more carbohydrate requirement Ex: Athletes will consume pasta before event for

more energy

Lipids Process of Digestion:

Fat → Glycerol + Fatty Acids Use of Lipid Products:

Used to synthesize glucose Converted to acetyl CoA and enters

Krebs/Citric acid cycle (of cellular respiration) Stored in adipose tissue (insulation) Used in building cellular structures (cell and

organelle membranes) Used to synthesize some hormones (steroid) Animation

Protein Process of Digestion:

Polypeptide → Amino Acids Uses of Amino Acids:

Used to create enzymes Used to create structural proteins (muscle, etc) Various other uses Deaminated (removal of amine group from amino

acid) by liver Converted into products used in citric acid cycle

(cellular respiration)

Proteins (cont) Nonessential amino acids

Can be synthesized by body; do not need to be in diet Essential amino acids

Cannot be synthesized by body; do need to be in diet Complete proteins

Dietary proteins that contain enough of the essential amino acids

Incomplete proteins Dietary proteins that don’t contain enough of the essential

amino acids Partially complete proteins

Contain enough essential proteins to sustain life but not enough to promote growth

Vitamins Organic compounds requires in small

amounts for normal metabolism Fat-soluble: A, D, E, and K

Accumulate in tissues and can lead to overdoses

Water-soluble: B and C Excess is often excreted

Minerals Elements other than carbon needed for

human metabolism Concentrated in bones and teeth; parts

of structural components and enzymes; free-floating ions

Major Minerals: Ca, P, K, S, Na, Cl, and Mg

Trace Elements: Fe, Mn, Cu, I, Co, Zn, F, Cr

Diseases and disordersHepatitis:

Inflammation of liverCaused by class of viruses

(usually) Names of hepatitis (A-G) come from virus

Symptoms: Lack of appetite Nausea and vomiting Low fever and mild headache Stiff joints and rash Upper right quadrant pain in

abdomen Dark/foamy urine Yellowish skin/sclera of eye

Diseases and disorders Lactose Intolerance:

Lactose sugar unable to be broken down Caused by lack of production of lactase (enzyme

which breaks down lactose) Symptoms:

Bloating Intestinal cramps Diarrhea

Avoidance: Avoid lactose sugar (drink soy/almond milk) Take lactase pills before eating lactose