Ch. 3 Digestion, Absorption, and Transport Flashcards
GI tract
23-foot-long muscular tube, makes up organs of the digestive tract
5 organs of GI tract
- mouth
- esophagus
- stomach
- small intestine
- large intestine
Sphincters
allow food to pass from one organ to the next
4 accessory organs
- liver
- pancreas
- gallbladder
- salivary glands
Bolus (formation and where it enters)
- tongue rolls chewed and moistened food into this
- enters pharynx to be swallowed
Esophagus function
transports food and fluids from mouth to stomach
Two sphincters in esophagus
- Upper esophageal sphincter
- Lower esophageal sphincter (LES)
Upper esophageal sphincter function
allows bolus to enter the esophagus
Lower esophageal sphincter (LES) function (3)
allows bolus to enter the stomach
- loosens after swallowing
- shrinks to prevent stomach contents from returning to esophagus
Epiglottis up…
trachea open
Epiglottis down…
trachea closed
Stomach function (chemical and mechanical)
- mixes food with gastric juices to chemically break it down into smaller pieces
- mechanical digestion: muscles of stomach mix, churn, and push content with gastric juices
How much does the stomach hold?
empty: holds 1 cup
expanded: up to 1 gallon
Chyme
semiliquid, partially digested food mass that leaves stomach and enters small intestine
How much chyme leaves the stomach?
1 tsp of chyme leaves the stomach and enters small intestine every 30 seconds
Pyloric sphincter
allows chyme to enter small intestine from the stomach
Goblet cells (location and function)
cells in GI tract produce mucus
Parietal cells (3)
- secrete HCl
- intrinsic factor
- digestion and absorption of vitamin B12
Innermost layers of stomach contain (2)
- goblet cells
- gastric pits
Gastric pits function
contain gastric glands that produce gastric juices
Chief cells
produce pepsinogen, an enzyme that breaks down proteins
Small intestine (3)
- long chamber (three chambers)
- important in finishing process of food digestion and nutrient absorption
- food is in here for 3 to 10 hours
Segments of small intestine (length) (3)
- duodenum (10 inches)
- jejunum (8 feet)
- ileum (12 feet)
Mechanical and chemical digestion in small intestine
- muscular contractions push chyme forward
- digestive secretions break down nutrients
Villi (2)
small projections that line interior of small intestine
- maximize absorption
Lumen
hollow interior of small intestine; contains circular folds
Enterocytes
absorptive epithelial cells that line the walls (villi) of the small intestine
Microvilli (2)
tiny projections on the villi in small intestine
- maximize nutrient absorption
Crypts (2)
- glands that secrete intestinal juice
- contain stem cells that produce younger cells
How does chyme enter large intestine?
ileocecal valve (leaving ileum, part of cecum)
Large intestine size
5 feet long, 2.5 inches diameter
3 segments of large intestine
- cecum: beginning
- colon: large part
- rectum: final 8-inch portion
Large intestine function
site of water, sodium, potassium, and chloride absorption (indigestible food)
Cecum function
receives waste from small intestine
Ileocecal valve
sphincter that separates small intestine from large intestine
Bacteria produce what vitamins in colon? (5)
vitamin K, thiamin, riboflavin, biotin, and vitamin B12
- only biotin and vitamin K absorbed
Ferment in colon (3)
- undigested and unabsorbed carbs fermented into simpler compounds: methane gas, carbon dioxide, and hydrogen
- intestinal gases produced
- fermented fiber produces short-chain fatty acids
Large intestine fluid/fecal ratio
1 liter of fluid material reduced to 200 grams feces
Time spent in large intestine
12 to 70 hours depending on person’s health, age, diet, and fiber intake
Stool
propelled from large intestine to rectum
Anus (2)
opening of rectum/end of GI tract
- feces voluntary released here
Final stage of defecation (2)
voluntary release of stool
- influenced by age, diet, medications, health, and abdominal muscle tone
Salivary glands (3)
- dissolve small food particles to make swallowing food easier
- body produces 1 quart of saliva daily
- saliva contains water, mucus, electrolytes, and enzymes
Liver size and functions (6)
- largest internal organ (weights 3 pounds)
- helps with digestion, absorption, and transport of nutrients
- makes proteins
- makes bile used to digest fats
- carbohydrate metabolism
- site of alcohol metabolism; removes and degrades toxins and excess hormones
Gallbladder (3)
- receives bile from liver through hepatic duct
- concentrates and stores bile
- releases bile into small intestine through common bile duct
Pancreas (3)
produces enzymes and hormones
- Endocrine function: releases hormones insulin and glucagon to maintain blood glucose levels
- Exocrine function: secretes digestive enzymes into small intestine
How is food propelled through GI tract?
muscular contractions
Peristalsis (3)
- occurs in esophagus, stomach and small intestine
- squeezes food forward through GI tract
- mechanical digestion
Segmentation (3)
- occurs in small and large intestines
- shifts food back and forth along GI tract in the intestines
- allows contact with surface of small and large intestines and increases absorption
Chemical digestion (3)
carried out by digestive enzymes
- regulated by hormones
- finished by the time food reaches large intestine
Enzymes (2)
proteins that drive digestion
- catalyze hydrolysis
Hydrolysis (2)
chemical reaction that uses water to split chemical bonds of digestible nutrients
- hydroxyl group (OH) joins one molecule, hydrogen ions (H) joins the other molecule
3 conditions for enzymes to work
- Compatible enzyme and nutrient must be present
- enzymes compatible with specific substrate
- ex. sucrase (enzyme) hydrolyzes sucrose (substrate) - pH of environment
- enzymes work best in certain acidity and alkalinity - Temperature of environment
- low temperature: slow activity
- high temperature: activity halted
Enzyme in action (3)
- substrate binds to active site
- hydrolysis: bond is broken between two molecules
- products released, process repeated
Enzyme in saliva (2)
salivary amylase
- begins digestion of starch/carbohydrates
Enzyme in stomach (protein)
pepsinogen with substrate pepsin
- beings hydrolysis of polypeptides
Enzyme in stomach (lipids)
gastric lipase
- begins digestion of lipids
Enzyme in pancreas (carbs)
pancreatic amylase
- digests starch
Where does most absorption take place?
small intestine
Passive diffusion (4)
nutrients move from high to low concentration
- NO energy required
- nutrients pass through cell membrane
- simplest diffusion
Facilitated diffusion (2)
nutrients move from high to low concentration with help of carrier protein
- NO energy required
Active transport
nutrients move from low to high concentration with the help of a carrier protein
- energy required
Endocytosis
cell forms a vesicle to surround and engulf nutrient
- whole molecules engulfed by cell membrane
Where are water and salt absorbed?
large intestine
How is water absorbed by cell membrane?
passive diffusion
How is salt absorbed by cell membrane?
active transport
Endocrine and nervous systems function
coordinate digestion, absorption, and excretion of waste
Enteric nervous system
nerve fibers that supply the nerves of the GI tract, pancreas, and gallbladder
Enteric nerves function
monitor stomach contractions after eating and secretions of the cells in GI tract
Hormones functions (3)
- release gastric and pancreatic secretions
- peristalsis
- enzyme activity
Enterogastrones (2)
produced and secreted by cells lining the stomach and small intestine
- influence GI motility, stomach emptying, gallbladder contraction, intestinal absorption, and hunger
Types of hormones (4)
- Gastrin
- Secretin
- Cholecystokinin (CCK)
- Gastric inhibitory peptide (GIP)
Gastrin
stimulates HCl production and release of gastric enzymes
Secretin
stimulates pancreas to release bicarbonate to small intestine; pH is raised
Cholecystokinin (CCK) (3)
- stimulates pancreas to release lipase
- stimulates gallbladder to release bile
- slows down gastric motility
Gastric inhibitory peptide (GIP)
inhibits gastric motility and stomach secretions
Nervous system function in digestion
tells you when to eat and drink, and when to stop
Extrinsic nerves (function and locations)
- communicate changes in GI tract and stimulate motility
- brain and spinal cord
Intrinsic nerves (function and locations)
- receive message from extrinsic nerves and respond by stimulating release of digestive juices
- found in linings of esophagus, stomach, and small and large intestines
Ghrelin
signals when you’re hungry
Peptide YY (PYY)
keeps you feeling full
Nutrient transportation in body
absorbed through bloodstream or lymphatic system
Water-soluble nutrients transport (3)
- absorbed into cardiovascular system (GI tract capillaries)
- through hepatic portal vein (portal vein)
- to the liver
Hepatic vein
substances leave intestine through here
Fat-soluble nutrients transport (3)
absorbed into lymphatic system (fat-soluble vitamins, long-chain fatty acids, and proteins too large to be transported through capillaries)
- Lymph capillaries
- Lymphatic vessels
- Thoracic duct
Excretory system (2)
waste products that remain after nutrient absorption removed here
- kidneys filter blood, waste products excreted through urine
Gastroesophageal Reflux Disease (GERD)
- indigestion or acid reflux
- LES doesn’t close properly, HCl from stomach enters esophagus
Esophageal cancer (3)
- cancer of digestive tract
- males over 50, urban areas, smoke and drink heavily
- treatment: surgery, radiation, and chemotherapy
Belching (2)
- caused by swallowing air
- eating too fast, drinking carbonated beverages, anxiety, chewing gum, and smoking
Stomach flu (2)
- symptoms: nausea, vomiting, diarrhea, and abdominal cramping
- treatment: rest, rehydration, and eating soft foods
Foodborne illness (2)
- consuming food contaminated with E. coli, salmonella, or campylobacter
- treatment: rest and rehydration
Ulcers (5)
- sore or erosion lining lower region of stomach or upper part of duodenum
- cause: Helicobacter pylori (bacteria)
- symptoms: vomiting, fatigue, bleeding, weakness, and burning pain
- treatment: drugs, dietary changes, surgery
- untreated: can cause peritonitis, scar tissue that blocks food and causes vomiting and weight loss
Gallbladder disease (3)
- women and older Americans
- obesity and rapid weight loss
- unhealthy gallbladder = gallstones
Gallstones (3)
- form from cholesterol in gallbladder or bile duct
- treatment: surgery for gallbladder removal, medication, shock-wave therapy
- body adapts to removal of gallbladder by secreting bile into duodenum
Celiac disease (4)
- genetic autoimmune disease
- damages small intestine when foods with gluten are eaten
- causes villi in small intestine to flatten out, causing nutrient malabsorption
- abnormal reaction to protein gluten found in rye, wheat, and barley
Celiac disease symptoms (7)
- abdominal bloating
- cramping/gas
- diarrhea
- foul-smelling stool
- weight loss
- anemia
- bone or join pain
Celiac disease risk, diagnosis and treatment
- increase risk: osteoporosis, diminished growth, and seizures
- diagnosis: blood test and tissue biopsy of small intestine
- treatment: gluten-free diet
Flatulence (3)
- results from formation of intestinal gas
- released 10 to 20 times a day
- causes: foods high in fiber and starch, eating fast, soda, not exercising, smoking
Diarrhea (cause and treatment included) (4)
- releasing watery, loose stools more than 3 times a day
- cause: bacterial, viral, or parasitic infections that cause food/fluids to pass through colon too quickly
- can lead to dehydration and death (children and elderly)
- treatment: fluid and electrolyte replacement
Constipation (cause and treatment included)
- dry, hardened stool
- cause: not enough fiber or water intake, stress, inactivity, smoking, and various illnesses
- treatment: exercise, normal eating patterns, rest, laxatives
- avoid colon cleansing (enema) as treatment
Hemorrhoids
swelling of veins in rectum and anus
- can lead to bleeding, itching, pain
- causes: straining to poop, pregnancy, constipation, diarrhea, aging
- treatment: increase fiber and fluid intake
Irritable bowel syndrome (IBS)
changes in colon rhythm
- overresponse to colon stimuli, changes patterns of diarrhea, constipation, and abdominal pain
- treatment: increase dietary fiber, stress management, and drugs
Ulcerative colitis (4)
- chronic inflammation of large intestine, causing ulcers in lining of the colon
- runs in families
- men and women ages 15 to 30
- treatment: drug therapy, surgery
Crohn’s disease
similar to ulcerative colitis, but ulcers occur in GI tract
- treatment: drug therapy, surgery
- change diet/lifestyle
Colon cancer (4)
- third leading cause of cancer, most curable if detected early
- begins with small polyps in lining of colon, can be surgically removed (can turn into cancerous tumors)
- treatment: radiation, chemotherapy, surgery
- survival rates: depend on age, treatment response, and stage cancer
Mechanical digestion
breaking down food through chewing, grinding, squeezing and moving food through GI tract by peristalsis and segmentation
Chemical digestion
breaking down food through enzymatic reactions
Saliva (3)
- dissolves small food particles
- contains enzyme amylase, which begins breakdown of carbs
- in adults, no other chemical digestion occurs in mouth
