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Chapter 14
The Digestive System and Body Metabolism
20 Cool Things You Don’t Know
About the Digestive System
Overview Of
Digestion
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Pill Cam
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Digestive System
Takes in food, breaks it down into nutrient molecules and absorbs them into the bloodstream, then rids the body of indigestible remains
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Anatomy of Digestive SystemAlimentary canal –
digests food and absorbs digested fragments through its lining into the blood
GI, tract - continuous hollow tube: mouth, pharynx, esophagus, stomach, small and large intestine
Accessory digestive organs - assist: teeth, tongue, glands
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Mouth (Oral Cavity)
Food entersMucus membrane-lined cavitylips, cheeks, hard palate (anterior roof), soft
palate (posterior roof)uvula - fingerlike projection of soft palate
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Mouth Tongue - attached to hyoid bone and styloid
processes of skullpapillae containing taste buds on surface
Frenulum - secures tongue and limits its posterior movements
As food enters, it is mixed w/ saliva by tongue and chewed and swallowed
Taste
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Salivary Glands - 3 pair
Parotid glands - anterior to ears mumps is inflammation of parotid
glands Submandibular and sublingual glands -
empty secretions into mouth through ducts
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SalivaProduct of salivary glands, mixture of
mucus and serous fluidsmucus moistens and binds food
together into a mass (bolus)serous part contains salivary amylase
(enzyme for starch digestion)
Polls Everywhere
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Teeth Masticate (chew) Deciduous (baby or milk) teeth - first set; formed
from 6 months to 2 years Permanent teeth - cause baby teeth to fall out b/t 6
and 12 32 permanent teeth 3rd molars (wisdom teeth) form b/t 17 and 25;
sometimes absent or impacted in jawbone and must be surgically removed
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Teeth by shape/function
Incisors - chisel-shaped, cutting Canines - fanglike, tearing/piercing Premolars (bicuspids) Molars - broad crowns w/ rounded tips, grinding
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Pharynx Nasopharynx (respiratory),
oropharynx (potesterior to oral cavity), and laryngopharynx (continuous w/ esophagus)
Peristalsis: Alternating contraction of muscles propel food into esophagus
Peristalsis
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Esophagus
Conducts food from pharynx through diaphragm to stomach
25 cm long
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Walls of Alimentary Canal Mucosa - innermost layer; moist membrane Submucosa - blood vessels, nerve endings,
lymph Muscularis externa - inner circular, outer
longitudinal smooth muscle Serosa - outermost layer
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Stomach C-shaped, left side, nearly hidden by liver and
diaphragm cardioesophageal sphincter - food enters from
esophagus fundus - expanded part body – midportion 3rd oblique layer in muscularis externa to move,
churn, mix, and pummel foodchemically breakdown proteins
Peristalsis
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Stomach Pylorus - funnel-shaped, terminal Pyloric sphincter - goes to small intestine 25 cm long when full, holds 4 liters of food empty - collapses into folds (rugae)
Rugae on Dog Stomach
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Stomach Mucosa has gastric pits which lead into gastric
glands that secrete gastric juice chief cells - produce protein-digesting
enzymes (pepsionogen) parietal cells - produce HCl Chyme is produced
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Stomach - Food Breakdown Secretion of gastric juice by sight, smell, and
taste of food presence of food and falling pH stimulate
release of hormone gastrin that makes stomach produce enzymes, mucus, & HCl
2-3 liters gastric juice per day
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Stomach: Food Propulsion
Peristalsis in lower half, and contractions squirt 3 ml of chyme into small intestine
takes 4 hrs for stomach to empty Irritation (food poisoning) may activate vomiting
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Small Intestine Major digestive organ Muscular tube extending from pyloric
sphincter to ileocecal valve average length: 2 m (6 feet) Hangs from coils suspended by mesentery Large intestine encircles and frames it
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Small Intestine - 3 subdivisions Duodenum - curves around head of
pancreas Jejunum - extends from duodenum to ileum ileum - terminal part that joins large intestine
at ileocecal valve
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Small Intestine Chemical digestion begins Small amount of food processed at a time -
controlled by pyloric sphincter Pancreatic enzymes from pancreatic duct
and bile from bile duct enter duodenum
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Small Intestine - 3 structures that increase absorption Microvilli - tiny projections that give fuzzy
look (brush border) Villi - fingerlike projections that give velvety
appearance Circular folds - deep folds of both mucosa
and submucosa
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Small Intestine: Food Breakdown and Absorption
Takes 3-6 hours By end, digestion is complete and most
absorption has occurred Microvilli have brush border enzymes to break
down sugars and complete protein digestion
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Food Breakdown and Absorption
Pancreatic juice digests starch, proteins, fats, and nucleic acids; contains bicarbonate to neutralize chyme
When chyme enters, it stimulates hormones secretin and cholecystokinin to release bile
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Food Breakdown and Absorption
Bile is necessary for absorption of fats and fat-soluble vitamins K,D,A
At end, all that remains is water, indigestible food and bacteria which enters large intestine
Food propulsion - peristalsis
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Large Intestine Larger in diameter, shorter
in length (1.5 m) Extends from ileocecal
valve to anus Dries out indigestible food
by absorbing water, eliminates residue as feces
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Large Intestine Subdivisions Cecum - saclike, first part Appendix - wormlike structure
hanging from cecum; ideal bacteria location - appendicitis
Colon - ascending, transverse, descending, and sigmoid
Rectum Anal canal - ends in anus which
opens to exterior; has external voluntary sphincter and internal involuntary sphincter
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Large Intestine
Lots of goblet cells to produce mucus to act as lubricant to ease passage of feces
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Large Intestine: Food Breakdown and Absorption Residue is there 12-24 hours Bacteria metabolize nutrients and release
gases (methane, hydrogen sulfide) 500 ml of gas produced each day
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Food Breakdown and Absorption
Absorption limited to vitamins, some ions, and most of remaining water
Feces - solid product delivered to rectum; undigested food residue, mucus, bacteria, and some water
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Large Intestine: Propulsion and Defecation
Peristalsis and mass movements (long, slow-moving, powerful contractile waves that move over colon 3-4 times daily to push contents toward rectum)occur after eating; fiber increases strength of
contraction
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Propulsion and Defecation When feces in rectum, defecation reflex causes
rectum to contract and anal sphincters to relax Diarrhea - food rushes through before water is
absorbed, can result in dehydration and electrolyte imbalance
How fast food Travels thorough.
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Propulsion and Defecation
Constipation - food residue remains too long and too much water is absorbed; due to lack of fiber, poor bowel habits, or laxative abuse
A constipated body
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Other Accessory Digestive Organs – Pancreas
Soft, pink, triangular gland extending from spleen to duodenum
produces enzymes that break down food and neutralize acidic chyme from stomach, produces hormones insulin, glucagon
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Liver Liver - largest gland in body; under
diaphragm on right4 lobesproduces bile which leaves liver
through common hepatic duct
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Gallbladder Small, thin-walled green sac in the inferior surface of liver When digestion is not occurring, bile is stored and
concentrated by removal of waterbile stored too long, it crystallizes forming gallstonesYellow-green, watery solution of bile salts, bile pigments
(bilirubin), cholesterol, phospholipids, and electrolytesbile salts emulsify fats to provide more surface area
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Disease: Jaundice Bile pigments enter bloodstream Can result from hepatitis (inflammation of
liver from viral infection of contaminated water or blood transfusion) or cirrhosis (severe damage from drinking excess alcoholic beverages)
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Nutrition and Metabolism
Most foods used as metabolic fuels (transformed into ATP); some nutrients build cellular molecules
Energy value measured in kilocalories (kcal) or Calories (C)
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Nutrition
Nutrient - substance in food used to promote normal growth, maintenance and repair
Carbohydrates, lipids, proteins - bulk of food; vitamins, and minerals in minute amounts
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.
Water - 60% of volume of foodMost foods are combination of
nutrients from 5 food groups (grains, fruits, vegetables, meats, and milk products)
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Obesity Rates in the US.
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Dietary Sources of Major Nutrients - CarbohydratesFrom plants except lactose and
glycogen in meatssugar - fruit, sugar cane, milkstarch - grains, legumes, root
vegetablescellulose - most vegetables
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Lipids
Neutral fats: saturated in animal products, unsaturated in seeds, nuts, vegetable oils
Cholesterol - egg yolk, meats, and milk
Phospholipids
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Proteins
Animal products, eggs, milkAmino acid polymerslegumes, nuts, and cereals are
low in one or more essential amino acids
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Vitamins
Organic nutrients, small amountsNo one food contains all required
vitamins, need balanced dietMost function as coenzymes: act
w/ enzymes for task
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Minerals
Requires adequate supplies of 7: Ca, P, K, S, Na, Cl, and Mg; trace amounts of others
Fats/sugars have none, cereals and grains poor sources
In veggies, legumes, milk, meats
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MetabolismAll chemical reactions necessary to
maintain lifeCatabolism - substances broken down,
energy released and captured to make ATP
Anabolism - larger molecules built from smaller ones
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Metabolism
Carbohydrates (glucose) - broken down to make ATP
Fats - build cell membranes, myelin sheaths, insulate, ATP
Proteins - structural materials hoarded by body cells
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Carbohydrate MetabolismCarbs - preferred fuel to produce ATP
from glucose (blood sugar): energy from bonds broken binds phosphate to ADP to make ATP
Carbon atoms leave as CO2 and hydrogen combines w/ oxygen to make water
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Carbohydrate Metabolism - Homeostasis of blood glucoseHyperglycemia - high levels;
excess stored as glycogen and converted to fats
Hypoglycemia - low levels; liver breaks down stored glycogen and releases glucose to blood
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Fat MetabolismLiver - make ATP, synthesize
lipoproteins, clotting protein and cholesterol for membranes or steroid hormones
Form myelin sheaths and fatty cushions around organs
Most concentrated form of enegy
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Fat MetabolismTo be used for ATP synthesis, it must
be broken down into acetic acid; when not enough glucose, acetone accumulates in blood making it acidic (acidosis/ketosis)no carb diets, diabetes, and starvation
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Protein MetabolismProteins - bulk of cell structures;
broken down into amino acids for enzymes, membranes
Cells use ATP to actively transport amino acids (8 of the 20 are not made by cells - essential amino acids)
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Protein Metabolism
Amino acids make ATP when protein is in excess or no fats or carbsamine groups are removed as ammonia which is toxic so it combines w/ CO2 to form urea
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Central Role of LiverManufactures bile, detoxifies drugs
and alcohol, degrades hormones, makes substances vital to body, metabolism
We have more liver tissue than needed, so if damaged, it regenerates rapidly and easily
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General Metabolic Functions
Liver maintains blood glucose levels
After high carb meal, glucose is removed from blood and converted to glycogen (glycogenesis) and stored in liver
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General Metabolic Functions
As body cells remove glucose from blood, liver breaks down stored glycogen (glycogenolysis)
gluconeogenesis - make glucose from fat and protein
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General Metabolic FunctionsHormones insulin, thyroxin, and
glucagon control blood sugarFats are oxidized for energy, broken
down into acetic acid or stored as fat reserves
Makes cholesterol and secretes its breakdown products as bile
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General Metabolic FunctionAlbumin - most abundant protein;
holds fluids in bloodstreaminsufficient albumin causes fluid to go from blood to tissues (edema)
Synthesize amino acids and detoxify ammonia
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Cholesterol Metabolism and Transport
Cholesterol - structural base for steroid hormones and vitamin D; major building block of plasma membranes
15% from diet, 85% made by liverBroken down and secreted in bile
salts, which leave as feces
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Cholesterol MetabolismInsoluble in water, so transported bound
to lipid-protein complexes - lipoproteinsLow-density lipoproteins (LDLs) -
transport cholesterol/lipids to body cells; if too much deposited on arteries - “bad lipoproteins”
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Cholesterol MetabolismHigh-density lipoproteins (HDLs) -
transport cholesterol from tissue cells to liver for disposal in bile; high levels are good
Both types necessary; ratio determines whether cholesterol will go to arterial walls
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Body Energy Balance
When fuel is burned, it consumes O2 and generates heat
Energy intake = total energy output (heat + work + energy storage)
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Body Energy Balance
Energy intake - liberated during food oxidation
Energy output - lost as heat (60%) + used to do work (driven by ATP) + stored as fat or glycogen
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Regulation of Food IntakeWhen energy intake and energy outflow
are balanced, body weight is stableFood intake controlled by rising or
falling blood levels of nutrients, hormones, body temp. and psychological factors
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Basal Metabolic RateCarbs & proteins yield 4 kcal/g, fats
yield 9 kcal/gBasal metabolic rate (BMR) - amount of
heat produced by body per unit time at rest; energy supply for breathing, heartbeat, and kidney function
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Basal Metabolic RateAvg. adult has BMR of 60-72 kcal/hr;
influenced by surface area, gender, age, and thyroxin production (more thyroxin produced by thyroid gland, higher O2 consumption and ATP use and metabolic rate)
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Basal Metabolic RateHyperthyroidism - excessive rate,
lose weight despite increased hunger and food intake, bones and muscles weaken
Hypothyroidism - slow rate, obesity, diminished thought process
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Total Metabolic Rate
When active, more glucose must be oxidized to provide more energy for activities
Total Metabolic Rate (TMR) - total amount of kcal body must consume to fuel all activities
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Total Metabolic RateWhen total calories = TMR, weight is
constantIf eat more, excess calories appear as
fat depositsIf active w/o enough food, break down
fat reserves and even tissues to satisfy TMR
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Body Temp RegulationHeat warms tissues and blood
keeping them at homeostatic temps
Reflects balance b/t heat production and heat loss, controlled by hypothalamus, regulated b/t 96-100ºF
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Heat-Promoting MechanismsWhen cold, heat is conserved by
vasoconstriction of blood vessels and shivering makes blood route to vital body organs causing temp of skin to dropif extended, skin cells w/o O2 die leading to frostbite
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Heat-Promoting Mechanisms
Hypothermia - extremely low body temp from prolonged exposure to cold; vital signs decrease, person becomes drowsy and can progress to coma and death as metabolic rate stops
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Heat Loss MechanismsMost loss occurs through skin by
radiation (when body temp increases, blood vessels dilate and heat radiates off surface) or evaporation (too hot - perspiration off skin’s surface; effective unless humid)
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Heat Loss Mechanisms
Hyperthermia (elevated body temp) depresses hypothalamus and positive-feedback cycle occurs: soaring body temp increases metabolic rate, which increases heat production
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Heat Loss MechanismsHeat stroke - skin hot and dry - fatal unless
immersed in cool water and given fluidsHeat exhaustion - collapse during vigorous
activity due to excessive loss of fluids (dehydration), causing low blood pressure, fast heart rate and cool, clammy skin
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Heat Loss MechanismsFever - controlled hyperthermia - results
from infection, cancer, or allergies; pyrogens are released to hypothalamus that set thermostat at higher levelchills - reset lower - sweattoo high - protein denatures
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Developmental Aspects5th week - alimentary canal formscleft palate/lip - child unable to suck
properlytracheoesophageal fistula - connection
b/t esophagus and trachea - causes drool, cyanosis during feedings
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Development AspectCystic fibrosis - blockage of pancreatic
ducts so that fats and fat-soluble vitamins are not digested or absorbed
PKU - inability of tissue cells to use phenylalanine (amino acid) causes brain damage
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Developmental AspectsNewborn: rooting & sucking reflexAppetite decreases in elementary
age and increases in adolescenceGastroenteritis - inflammation of GI
tract due to contaminated foodAppendicitis - common in teens
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Developmental AspectsMiddle age - metabolic rate
decreases 5-8% every 10 yrsulcers & gallbladder problems
Old age - activity of GI tract declines, taste and smell decreasecancer of stomach and colon