BIO 213 Exam 3: Digestive, Urinary, and Nutrition/Metabolism

main functions of digestive sys

take in food, break down into nutrient molecules, absorb molecules into blood stream and synthesize compounds, rid body of indigestible remains

Mechanical digestion define

physical process of breaking down food

chemical digestion define

utilize enzymes to break down chemical bonds

two parts of digestive system?

alimentary canal/GI tract - trace pathway of digestion

accessory organs - help alimentary canal

organs/parts in alimentary canal

mouth, esophagus, pharynx, stomach, spleen, small intestine, large intestine, an*s

organs/parts accessory organs of digestive sys

tongue & teeth, salivary glands, pancreas, gallbladder, and liver

6 steps of digestion/processing food

1. ingestion (oral cavity) begins chemical breakdown

2. propulsion (esophagus, stomach, SI/LI) includes both swallowing and peristalsis

3. mechanical breakdown (SI) physical process: chewing and segmentation

4. digestion (SI/LI)

5. Absorption (SI/LI)

6. defecation (rectum/anus)

peristalses define

movement via propulsion with smooth muscle

main propulsive force

segmentation define

move/mixing back and forth in the SI

propulsion define

move forward

Peritoneum of digestive sys

visceral peritoneum - external surface

parietal peritoneum - lines body wall

mesentery - double layer of peritoneum

intraperitoneal vs retroperitoneal organs

intraperitoneal - within peritoneal

retroperitoneal - found outside peritoneal (some organs can be both)

4 tunics of alimentary canal and their function

mucosa: deepest secretes, absorbs, and protects via mucus lubrication

submucosa: blood and lymphatic vessels (supply blood nerves and lymphatic vasculature)

muscularis externa: muscles that runs in diff planes to help w/ contraction

serosa: ct tissue how we anchor alimentary canal

splanchnic circulation define

blood supply to digestive organs

arteries branch off aorta to serve GI tract

venous side: Heptatic portal sys send blood to liver for detox

arterial side major branches off descending aorta, serves alimentary canal

enteric nervous sys

‘gut brain’ GI tract’s nervous sys

2 main interconnecting plexi: submucosal and myenteric nerve plexus

both plexi respond to short and long reflex arcs

submucosal nerve plexus function

regulates glands and smooth muscle in mucosa

myenteric nerve plexus function

controls GI tract motility

what structures make up the oral cavity

tongue, teeth, salivary glands, and mouth

how does saliva aid in digestion (3 things)

filter microorganisms from many things going into mouth daily

keep mouth moist

many types of stimuli that can trigger/inhibit salivation

how does deglutition work

deglutition = swallowing

2 phases: buccal and pharyngeal-esophageal phase

buccal: volunary movement of tongue pressed against hard palate

pharyngeal-esophageal involuntary nervous sys take over food pushed down esophagus

structural components of the stomach that aid in digestion

rugae of mucosa: folds of stomach when empty, secretes lots of alkaline mucus

additional muscular layer oblique muscular layer: helps stomach grind and smash food

what tunics of the stomach are modified

muscularis has an extra layer for mechanical digestion: oblique layer

mucosa: mucosal barrier of gastric pits

chyme define

stomach converts bolus of food to paste-like substance called chyme

gastric pits and gastric glands

gastric pits lead to gastric glands: how we accomplish chemical digestion

gastric pits and glands found in walls of stomach

in gastric pits what cells exist

surface mucosal cells secrete mucus

mucous neck cell secrete mucus

parietal cell secrete HCl and intrinsic factor which activates B12 and aids in RBC prod

chief cell secrete pepsinogen (helps digest proteins) and gastric lipase (helps breakdown lipids)

G cell secrete hormone gastrin the hunger home

enteroendocrine cells produce D+G cells which produce gastrin

mucosal barrier created by what

(1) thick layer of mucosal cells (2) tight junctions between epitheal cells (prevent ‘leakage’/juice seeping under tissue (3) high turnover epithealial cells replaced every 3-6 days

how is gastric secretion regulated

regulated by both neural and hormonal secretion

neural (stimulus) vagus nerve stimulation inc secretion (inhibition) sympathetic stimulation dec secretion

hormonal (stimulus) gastrin stiumulates enzyme & HCl secretion by parietal cells (inhibition) gastrin antagonists or G cells secreted by SI

phases of gastric secretion

cephalic phase triggered by aroma, taste, sight, or thought and its a long reflex arc

gastric phase stimulated by stretch receptors or chemicals lasts 3-4 hrs provides 2/3 of released gastric juices

intestinal phase begins when chyme enters small intestine

how is HCl formed in the stomach

formed via parietal cells using bicarbonate system and chloride ions

how is stomach filling and emptying regulated? what processes are involved?

stomach can stretch and accommodate large amts of food consumed emptying stomach

emptying stomach: gastric contractile activity: peristalic waves move toward pyloris 3x a minute chyme is delievered to SI in small increments (~3mL spurts) everything else gets retropulsed and 1 min later another 3 mL spurt released

what does gastric contractile activity include

gastric contractile activty involves grinding propulsion and retropulsion

purpose of liver

produces bile

purpose of gall bladder

stores bile

purpose of pancreas

digestive enzymes and bicarbonate

supplies most enzymes needed to digest chyme as well as HCO-3 to neutralize stomach acid

what is bile

yellow green alkaline solution containing electrolytes phospholipids bile salts bilirubin cholesterol, and triglycerides

function of bile

like ‘soap’ emulsify/break down lipids (like dawn dish soap)

what is pancreatic juice

combines with bile at heptapoetic sphincter

function of pancreatic juice

neutralize chyme and digest proteins activated in duodenum

how are bile and pancreatic juice secreted into the SI

Exocrine: acinar cells secrete pancreatic juices whereas duct cells secrete HCO3 (bicarb)

bile and pancreatic juices empty into the duodenum via hepatopancreatic ampulla and major duodenal papilla

divisions of SI (in order)

duodenum shortest section where majority of digestion happens

jejunum

ileum joins LI at ileocecal valve

structural modifications to increase surface area in SI

circular folds, villi, microvilli (on surface of villi and form brush border)

brunners/duodenal glands secrete HCO3 (bicarb) beneath villi

goblet cells secrete mucus between/on/within villi

why are the structural mods of SI important

increase surface area of small intestine to maximize nutrient and water absorption

how is food digested in SI

when chyme arrives to SI partially digested carbs and fats but also undigested fats

to breakdown fats need bile salts from gallbladder which gets secreted to SI

chyme mixed with bile and pancreatic juices and pH is increased to make it more basic

brush border/microvilli do final digestion and break it down into monomers

how does food move into the large intestine

ileocecal valve/sphincter regulates chyme moving into LI

valve prevents regurgitation/back flow to ileum

structural mods to LI

teniae coli 3 bands longitudinal smooth muscle in muscularis externa

haustra pocket like sacs caused by tone of teniae coli

epiploic appendages fat filled pouches of visceral peritoneum

divisions of LI

ascending colon

transverse colon

descending colon ‘storage tank’

sigmoid colon to the rectum

bacterial flora

tons of bacteria in colon and bacterial breakdown the only breakdown of food stuffs that occurs in LI

function of bacteria flora

thousands of bacteria which aid in fermentation and vitamin synthesis

carbs: how are they digested (1) what enzymes are involved (2) where does this digestion/absorption occur (3)

digested by 4 step process

1. pancreatic amylase breaks down starch and glycogen into smaller carbs

2. brush border break down starch and glycogen into smaller carbs

3. small carbs cotransported across absorptive epithealial membrane

4. monosacc exit across basolateral membrane and enter capillary

enzymes: salivary amylase, pancreatic amylase, and brush border

location in order of enzymes: mouth, SI, SI

proteins: how are they digested (1) what enzymes are involved (2) where does this digestion/absorption occur (3)

digestion: breakdown in similar process to carbs and amino acids move out cells of SI to blood vessels

enzymes: pepsin (in presence of HCl) pancreatic enzymes and brush border enzymes

location in order of enzymes: stomach, SI, SI

lipids: how are they digested (1) what enzymes are involved (2) where does this digestion/absorption occur (3)

digestion:

1. large fats emulsified in SI to smaller fat droplets

2. pancreatic lipases hydrolyze trigly into monoglycerides

3. micelles (consist of fatty acids, monogly, and bile salts) ferry their contents to epithealial cells

4. fatty acids and monogly diffuse from micelle into epithelial cells

5. chylomicron formed

6. chylomicrons extrude from epithelial cells by exocytosis

enzymes: lingual lipase, gastric lipase, emulsification by detergent action of bile salts from pancreatic lipases

location in order of enzymes: mouth stomach SI SI