Lecture Exam: Digestive System Flashcards
Digestive system
the system that processes food and extracts nutrients from it and eliminates residue. Most nutrient we ingest can’t be used in existing form and broken down to smaller components. Once broken down can be used what has been eaten. Disassembly line breaking down nutrients and distributing it to other tissues
Digestion occurs in two ways
: mechanical and chemical
Mechanical-
physical breakdown of food into smaller particles achieved by cutting and grinding of teeth and churning of stomach, which exposes more food surface area to action of digestive enzymes
Chemical digestion-
hydrolysis reactions break dietary macromolecules into monomers: polysaccharides into monosaccharides, proteins into amino acids, fats into monoglycerides and fatty acids, and nucleic acids into nucleotides. Salivary glands, pancreas, and small intestine
five stages of digestion
ingestion digestion absorption compaction defecation
Ingestion:
selective intake of food
Digestion:
mechanical and chemical breakdown of food into a form usable by the body
Absorption:
uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph
Compaction:
absorbing water and consolidating the indigestible residue into feces
Defecation
:elimination of feces
Enteric nervous system and its two networks of neurons
—nervous network in esophagus, stomach, and intestines that regulates digestive tract motility, secretion, and blood flow
Thought to have over 100 million neurons
Can function independently of central nervous system
But CNS usually exerts influence on its action
Often considered part of autonomic nervous system
submucosal
myenteric plexuses
Submucosal(Meissner) plexus-
in the submucosa controlling glandular secretion of mucosa and movement of muscularis mucosa
Myenteric(Auerbach) plexus-
parasympathetic nerve ganglia located between muscularis externa layers controlling peristalsis, and other contractions of muscularis externa
Regulation of the Digestive tract
Motility and secretion of the digestive tract are controlled by neural, hormonal, and paracrine mechanisms. Telling digestive tract what to do in regards to motility and secretion of mucous layers all based on neural hormonal and paracrine secretion.
chyme
acid, soupy, or pasty mixture of digested food
microscopic anatomy of the stomach
stomach wall is covered in simple columnar glandular epithelium in mucosa w/ apical region filled w/ mucin that once secreted swells w/ contact w/ water becoming mucus. Mucosa and submucosa smooth when full, when empty contain longitudinal wrinkles gastric rugae. Muscularis externa has three layers- outer longitudinal, middle circular, and inner oblique. Gastric pits are depressions w/ same cells, w/ 2-3 tubular glands opening in the bottom of each called: cardial, pyloric, and gastric for secretion.
gastric secretions:
hydrochloric acid pepsin-zymogens lipase intrinsic factor chemical factors
hydrochloric acid
activating pepsin and lingual lipase, liquefy and form chyme, converts iron to be absorbed, contributes to innate immunity by breaking down cell wall and destroying ingested pathogens.
pepsin
enzymes as inactive proteins converted to active by HCl, which cuts off amino acids. from chief cells digesting dietary protein to shorter peptide chains auto-catalytic effect once one activated activates more
lipase
chief cells and lingual lipase digests 10-15% of dietary fat digested in stomach w/ most in small intestine
intrinsic factor
by parietal cells is a glycoprotein used to absorb Vitamin B, which is needed to synthesize hemoglobin *only indispensable function of stomach.
chemical messengers
produce and release hormones into blood helping to stimulate distant cells paracrine and peptides in digestive and CNS for communication
gastric motility
food stimulates mechanoreceptors in pharynx transmitting to medulla oblongata and returned by vagus nerve relaxing stomach to accommodate more resist stretcher briefly then relaxes, then peristaltic contraction rhythm by pacemaker cells in longitudinal layers of muscularis externa tight constriction around middle and down getting stronger churning, mixing. Antrum waves and Pylorus end breaks up semi digested food w/ strongest pump to pyloric valve closing downward propulsion. Only small amount of chyme put through duodenum in time to stops the acid if overfilled inhibits gastric motility so not hurting small intestine and doesn’t digest food as well. four hours to empty from stomach less if more liquid higher for more fat meals.
vomiting
Forceful ejection of contents from stomach and small intestine. Emetic center of medulla oblongata- caused by overstretching of stomach and duodenum, chemical irritants (alcohol, bacterial toxins), visceral trauma, intense pain, psychological and sensory stimuli. Preceded by nausea and retching. Abdominal contraction and rising thoracic pressure force upper esophageal sphincter open, esophagus and body of stomach relax, and chyme is driven out of stomach and mouth by strong abdominal contraction w/ reverse peristalsis of gastric antrum and duodenum. When it becomes chronic there are fluid, electrolyte, and acid-base imbalances damaging parts of mouth or teeth, esophagus, and parts of respiratory system
retching
thoracic expansion and abdominal contraction creating pressure difference dilating esophagus. Lower esophageal sphincter relax while stomach and duodenum contract spasmodically, w/ chyme entering esophagus and dropping back into stomach doesnt get past upper esophageal sphincter. Accompanied by Tachycardia, profuse salivation, and sweating
projectile vomiting
sudden vomiting w/ no prior nausea or vomiting, neurological lesions or found in infants.
Absorption-
Absorb aspirin and lipid soluble drugs, alcohol absorbed by small intestine depending upon how empty.
Protection of the Stomach-Stomach is protected in three ways from the harsh acidic and enzymatic environment it creates.
Mucous coat thick layer highly alkaline mucus resists breakdown.
Tight junctions prevent gastric juice from beneath
Epithelial cell replacement live 3-6 days slough off into chyme and digested w/ food, replaced by mitosis in gastric pits w/ new cell layers replacing old
Breakdown causing inflammation ulcer or breakdown of wall
peptic ulcer
Caused by bacteria can damage cells in layers of protection, stress related
Most ulcers are caused by acid-resistant bacteria Helicobacter pylori, that can be treated with antibiotics and Pepto-Bismol. Risk factors- smoking, aspirin NSAIDS
gastritis
inflammation of the stomach, can lead to a peptic ulcer as pepsin and hydrochloric acid erode the stomach wall.
Regulation of Gastric Function- Gastric activity three stages:
By nervous and endocrine system.
cephalic
gastric
intestinal phases
cephalic phase
controlled by brain responding to sight smell taste or thought of food sensory and mental input to medulla oblongata, via vagus nerve, stimulating secretion of gastrin 40% of acid secreted
gastric phase
stomach takes over controlling itself food and semi digested proteins stretches stomach and activates myenteric and vagovagal reflexes stimulating gastric secretion. ½ acid, ⅓ total secretions. Raising pH of contents. Stretch activates short reflex myenteric and long vagal reflex. Gastric secretion stimulated by acetylcholine (parasympathetic of both reflexes) histamine (paracrine), gastrin (in pyloric glands) to secrete HCl and intrinsic factor pepsinogen in response to gastrin. Positive-feedback but below pH of 2 stomach inhibits parietal.
intestinal phase
chyme arrives into duodenum controlling rate of gastric emptying. Duodenum enhances gastric secretions stretching stimulate stomach releasing gastrin furthering stimulating stomach, secretin, cck, and then enterogastric reflex caused by fats and acids when too full inhibiting it while duodenum processes chyme sympathetic suppress gastric, vagal parasympathetic stimulation of stomach inhibited. Chyme stimulates duodenal enteroendocrine cells to release secretin and cholecystokinin stimulate pancreas and gallbladder suppressing gastric secretion and motility. Sphincter tightens decreasing admission. Gastric-inhibitory peptide preps Insulin- secreted to prepare for processing of nutrients absorbed by small intestine more absorbed overlap and occur at same time.
describe the microscopic anatomy of the liver
interior of liver houses hepatic lobules. Consists of central vein (hepatic portal vein from stomach, intestines, pancreas, release glycogen spleen) passing down core surrounded by radiating plates of cuboidal cells (hepatocytes) w/ several cells thick, sinusoids are blood channels filling spaces.
describe microscopic functions of liver
Cells absorb from glucose, amino acids, iron, vitamins, and other nutrients from blood for metabolism or storage. Remove and degrade hormones, toxins, bile pigments, and drugs. Secrete albumin, lipoproteins, clotting factors, angiotensinogen. Blood collected central vein flows into right and left hepatic vein into inferior vena cava.
galbladder
pear-shaped sac on underside of liver store and concentrate bile, simple columnar epithelium, fundus projects beyond inferior portion of liver, neck leads into cystic duct into bile duct. Function is to receive, store, and concentrate bile by concentrating water and electrolytes.
Bile-
yellow-green Made of minerals, cholesterol, neural fats, phospholipids, bile pigments, bile acids, and lipid-transport vesicles (micelles).
billirubin
principal bile pigment formed from decomposition of hemoglobin bacteria in large intestine. Intestine metabolize bilirubin to urobilinogen (colorless) half reabsorbed in small intestine and excreted by kidneys converted to urobilin (yellow), when remain in small intestine converted to stercobilin (brown). Absence of bile, feces are gray white w/ streaks of undigested fat.
bile acids
steroids synthesized from cholesterol aid in fat digestion and absorption. 80% reabsorbed and sent to liver 20% secreted in feces
gallstone
all other components of bile wastes can become concentrated forming gallstones from fatty meals can cause blockages filling bile duct and overflowing into galbladder.
pancreas
structure and ducts
flattened, spongy, retroperitoneal gland posterior to greater curvature of stomach. Globose head encircled by duodenum, body, and blunt tapered tail. endocrine (pancreatic islets concentrated in tail) and exocrine portion (pancreatic juice). Acini have branched duct converting into pancreatic duct lengthwise through middle of gland joining bile duct at hepatopancreatic ampulla w/ sphincter controlling release of both bile and juice. Additional Accessory duct open indepently into duodenum to be released into duodenum w/out bile.
Pancreatic juice-
Alkaline mixture of water, enzymes, zymogens, sodium bicarbonate (buffer Hcl) and other electrolytes. Secreting many protein enzymes, amylase, lipase, ribonuclease, and deoxyribonuclease.
Activation of Pancreatic Enzymes in the Small Intestine
Acetylcholine- vagus and enteric nerves stimulate acini to secrete during cephalic phase. Cholecystokinin (CCK)- mucosa of duodenum in response to fats in small intestine and allowing bile to be released into duodenum. Secretin- small intestine stimulates duct of liver and pancreas to secrete solution flushing enzyme buffering in response to chyme
duodenum
retroperitoneal Begins at pyloric valves of stomach, arcs around head of pancreas ending at duodenojejunal flexure. w/ major and minor duodenal papilla wrinkles receiving pancreatic duct and its accessory. Receives stomach contents, pancreatic juices, and bile. Stomach acid is neutralized Fats are physically broken up by emulsification by bile acids. Pepsin inactivated by high pH, pancreatic enzymes protect from stomach acid do chemical digestion.
jejunum
first 40% of small intestine beyond duodenum, large tall closely spaced folds begins in upper left quadrant of abdomen w/in umbilical region w/ thick muscular walls, rich blood supply, w/ most digestion and absorption occurring here.
Illium-
forms 60% post-duodenal, hypogastric region and pelvic cavity. thinner less muscle and vasculature, w/ prominent lymphatic nodules Pyers patches along mesenteric attachment points. Ileocecal junction end of illium meet w/ cecum of large intestine. Muscularis is thickened forming Ileocecal valve regulating passage of food residue prevents backup
Circulation of small intestine
all supplied by superior mesenteric artery, branches to arteries to villi where it picks up absorbed nutrients to superior mesenteric vein to splenic vein into hepatic portal system.
intestinal villi
w/in small intestine have villi tiny projections largest in duodenum smaller in distal parts containing lacteal in the middle for fat absorption helping w/ secretions and movement of stuff throughout intestine. And microvilli increase surface area absorption of nutrients, contact digestion, and push stuff along. Lower half have dividing stem cells pushing cells up crypt to be sloughed off and digested aiding in immune function as well.
circular folds
largest of internal folds transverse spiral ridges mucosa and submucosa slow progress of chyme flowing on spiral path increasing contact more thorough mixing and absorption begin in duodenum, tallest in jejunum, end in ileum. help push and mix nutrients w/in further exposing them to greater surface area
intestinal motility
purpose of segmentation is to mix, churn bringing it into contact for digestion and absorption, move things along. Segmentation- stationary ring like constriction along intestine contract and then knead and churn slow different cells form rhythm of segmentation. When most absorbed and not a lot left, segmentation declines and just peristalsis begins or waves of contractions pushing towards colon starting in duodenum and food in stomach form gastroileal reflex enhance segmentation in ileum relaxing valve. As cecum fills pressure pinches valve shut prevents reflux of cecal contents into ileum
carbohydrates
about 50% of dietary starch is digested before it reaches the small intestine. Pancreatic amylase resumes starch digestion in intestine. Starches- most digestible dietary carbohydrate first to be. Cellulose- indigestible. Beginning in mouth amylase digests it, it is then denatured by stomach acid and broken down by pepsin before it even reaches small intestine. Small intestine releases pancreatic amylase and further broken down. Absorbed by sodium-glucose transporter 80% of sugar absorbed as glucose carrying by solvent drag out.
lactose intolerance
In people without lactase, lactose passes undigested into large intestine. Still consume yogurt and cheese because bacteria breaks it down and not stomach.
Increases osmolarity of intestinal contents
Causes water retention in the colon and diarrhea
Gas production by bacterial fermentation of the lactose
protein digestion and absorption
pancreatic enzymes take over protein digestion in small intestine by hydrolyzing polypeptides using pepsin turning them into shorter oligopeptides doing most of it. Amino acids absorbed by small intestine come from 3 different sources: dietary proteins, digestive enzymes digested by each other, sloughed epithelial digested. Endogenous and exogenous amino acids (essential and nonessential). Proteases digests any protein or enzyme including itself. Pancreatic enzymes trypsin etc. take over further hydrolyzing then peptidases occuring at brush border enzymes.
Brush border enzymes finish task, producing free amino acids that are absorbed into intestinal epithelial cells
Lipids: Fat Digestion and Absorption-
Hydrophobic digestion and absorption complicate matters using lipases released lingual by intrinsic salivary of tongue, and stomach (gastric) handful lipids before duodenum most there on. Stomach digestion occurs from contraction turning chyme breaking into emulsification droplets. exposing more surface area so easier. Mix w/ pancreatic juices further digesting fat. liver release certain bile acids. bile phospholipid and cholesterol diffuse into center of bile acids and are absorb fat solulble lipids, cholesterol, and monosaccharides, transport lipids to surface of small intestine. Bile acids also bind to droplets in duodenum breaking them up to be further digested. Absorption depends on micelles, bile acid components that allow the transport of broken down lipids into the center to facilitate transport to enterocytes. Some pass through plasma membrane of cells, and some fats are used or continued on to be digested later or excreted. transported through blood by chylomicron
Minerals (iron)
absorbed along entire length of small intestine. Iron taken up by transferrin into blood where it goes to bone marrow for hemoglobin synthesis, muscular tissue for myoglobin synthesis, and liver for storage. Excess is bound to ferritin and passed. Liver hormone- Hepcidin inhibits intestinal absorption and mobilization of iron. excess binds to ferritin until passed.
calcium absorption
only 40% absorbed by transcellular route in calcium channels sodium-calcium pumpin duodenum, the rest passed. Parathyroid hormone secreted in response to drop in calcium, stimulates kidneys to synthesize vitamin D increases calcium channels in apical membrane of duodenum, increases amount of albindin in cytoplasm, and number of calcium-ATPase pumps in basal membrane most actually absorbed in jejunum and ileum but by paracellular where diffusion through epithelial cells and not controlled. Most absorbed from meat and dairy w/ fat retarding.
water absorption controlled by
Water absorbed thorugh salts and dietary minerals. Diarrhea occurs when large intestine absorbs too little water if it is irritated by bacteria and passes too quickly w/ not enough water absorbed. Feces hard- constipation goes too slow too much reabsorbed.
timing of excretion
36-48 hours to reduce meal to feces spending 24 hours in transverse colon reabsorbing water and electrolytes. Feces: 75% water 25% solids (30% bacteria, 30% undigested fiber, 10-20% fat from bacteria), bacteria smaller proteins, sloughed epithelial cells, salts, mucus.
Haustral contractions and mass movements
30 minutes distention of haustrum w/ feces stimulates it to contract, churning and mixing residue promoting water and salt absorption and passing residue distally. Mass movements 1-3 times a day w/ filling of stomach stimulating motility of colon.
Neural Control of Defecation-
Urge to defecate soon after a meal, intrinsic defecation reflex weak responses starts stretch signals to muscular layer contract and internal anal sphincter to relax. Parasympathetic reflex- stretch signals to Spinal cord rectum and spinal cord, pelvic nerves return w/ increase perstaltisand relax internal sphincter. Only occur if both sphincters and rectal muscles that must be relaxed. . Rectalis muscles must be realxed as well. Valsalva Maneuver increase contractions for defecation.
- Filling of the rectum
- Reflex contraction of rectum and relaxation of internal anal sphincter
- Voluntary relaxation of external sphincte
metabolism and nutrition
provides matter needed for cell division, growth, and development
nutrition
starting point and the basis for all human form and function
metabolism
chemical change that lies at the foundation of form and function
weight
determined by the body’s energy balance, if energy intake and output are equal stabilizes gaining if intake exceeds output and vice versa stable over years w/ homeostatic set point for each personfrom hereditary (30-50%) and environmental influences (exercise and sleep)
gut-brain peptides
chemical signals form gastrointestinal tract to brain several hormones that control weight.
short and long term
ghrelin
secreted by parietal cells in gastric fundus, when stomach is empty producing sensation of hunger and stimulates hypothalamus to secrete GHRH priming body to take advantage of nutrients to be absorbed ceasing hour after eating.
