Digestive Lab Discussion pt. 2

what is gastoenterology?

the study of the GI tract and related diagnoses/ treatments

what is digestion?

processing food and extracting the nutrient content for use in the body

what are the 5 stages of digestion?

ingestion, digestion, absorption, compaction, defecation

how many incisors are there?

8 "biting"

how many canines are there?

4 "puncture/ shred"

how many premolars are there?

8 "grinders"

how many molars are there?

12 "grinders"

how many teeth are in adults?

16 top/ 16 bottom (32)

how many teeth are in children?

10 top/ 10 bottom (20)

what is ingestion?

voluntarily placing food into the oral cavity

what is propulsion?

voluntary phase of swallowing initiated by the tongue, propels food into pharynx

what is mechanical breakdown in the oral cavity?

mastification by teeth and mixing movements by tongue

what is the term for swallowing?

deglutition

what is the function of saliva in the oral cavity?

moistens and cleanses mouth, inhibits bacteria, dissolves molecules, and makes swallowing easier

is saliva hypotonic or hypertonic?

hypotonic (ph= 6.8/7)

what does saliva contain?

mucus, electrolytes, lysozyme, IgA, salivary amylase, and lingual lipase

when is lingual lipase most active?

in acidic environments (stomach)

what does amylase break down?

starches/ carbs

what does lipase break down?

lipids

what are the 3 phases of swallowing?

oral, pharyngeal, and esophageal

what is the oral phase of swallowing?

tongue forms food bolus

what is the pharyngeal phase of swallowing?

airways are blocked while food is pushed into esophagus

what is the esophageal phase of swallowing?

peristalsis drives food down esophagus and LES relaxes to allow for bolus to enter stomach

what epithelium in in the stomach?

simple columnar epithelium

what are stomach cells filled with?

mucin

what is mucin?

protein that when in contact with water forms mucus

what are the cells of the stomach?

mucous cells, stem cells, parietal cells, chief cells, enteroendocrine cells

what do parietal cells secrete?

HCl, intrinsic factor, and ghrelin

what do chief cells secrete?

gastric lipase and pepsinogen

what is the most abundant stomach cell?

chief cells

what do enteroendocrine cells secrete?

hormones and paracrine messengers to regulate digestion

what is the pH of HCl?

0.8 (more acidic than car battery acid)

what activates pepsin?

HCl removes AAs from pepsinogen to activate it

what is the desired pH of pepsin?

1-3

what is intrinsic factor essential for?

vitamin B12 absorption

what is needed after gastric atrophy or removal?

injections of B12 or B12 + IF orally

what is vomitting?

forceful ejection of stomach and intestinal contents (chyme)

what controls vomitting?

emetic center in medulla

what is vomiting commonly induced by?

overstretching of the stomach/ duodenum, chemical irritants visceral trauma, intense pain, psychological/ sensory trauma or memory

what are chemical irritants that can cause vomitting?

alcohol and bacteria

what area primarily leads to vomiting when witnessing trauma?

pelvic organs

what psychological/ sensory trauma things lead to vomiting?

sights, smells, thoughts

what are the 3 mechanisms of regulation in the GI tract?

nervous, hormonal, and paracrine

what are myenteric reflexes?

short reflexes (peristalsis)

what are vagovagal reflexes?

long using ANS fibers (parasympathetic part of CN X)

how much bile is produced a day?

500-1000 mL/ day

how much does the gallbladder concentrate bile?

5-20x

what percent of bile acids are reabsorbed in the ileum and returned to the liver?

80% via enterohepatic circulation

how many times are bile acids reused during the digestion of a meal?

2+ times

what happens to the remaining 20% of bile acids?

excreted in feces

how does the liver form new bile acids?

derived from cholesterol (way of recycling/ disposing cholesterol)

what substances make up the pancreatic juice?

alkaline mixture of eater, enzymes, zygomens, bicarbonate, and other electrolytes

what zymogens does the pancreas release?

trypsinogen, chymotrypsinogen, procarboxypeptidase (protein digestion)

what other enzymes does the pancreas secrete?

pancreatic amylase, pancreatic lipase, ribonuclease, deoxyribonuclease

what are 3 important pancreatic juice stimuli?

acetylcholine, CCK, secretin

how does Ach stimulate the pancreas?

from vagus nerve and enteric neurons to make pancreatic acini secrete enzymes before food is even swallowed

how does CCK stimulate the pancreas?

secreted in response to fats in small intestine and stimulates release of bile from gallbladder

how does secretin stimulate the pancreas?

secreted by the small intestine in response to acidic chyme, stimulates liver and pancreatic ducts to release sodium bicarbonate to neutralize acid

what forms the fuzzy brush border on the enterocyte surface?

microvilli

what does the brush border contain?

enzymes that carry out final stages of chemical digestion

what do paneth cells do?

secrete lysozyme, phospholipase, and defenses (immune-modulating)

what is the typical pH of intestinal juice?

7.4-7.8

what causes peristaltic contractions in the small intestine?

stretching

why is the movement of chyme in the small intestine slow?

for greater absorption of nutrients (takes 3-5 hr for food to pas through small intestine)

what hormones increase peristaltic activity?

gastrin, CCK, insulin, motilin, and serotonin

what hormones inhibit intestinal motility?

secretin and glucagon

where does carbohydrate digestion begin?

mouth (takes up to 2 hrs for carbs in food bolus to digest in stomach)

what are the products of maltose?

glucose + glucose

what are the products of sucrose?

glucose + fructose

what are the products of lactose?

glucose + galactose

where does protein digestion begin?

in the stomach

how are amino acids absorbed and taken into portal circulation to be recylced?

facilitated diffusion

how are proteins taken in in infants?

taken in by pinocytosis and release into blood by exocytosis (how IgA gives passive immunity)

what substance is hydrophobic?

lipids

how picks up the partially digested fats during digestion?

micelles from liver bile

if micelles were not use in lipid absorption how much would be be able to absorb?

only 40-50% of dietary fats and almost no cholesterol

what are contents from the micelles synthesized into within the enterocytes?

triglycerides to by packaged into chylomicrons to diffuse to lacteals for processing before being returned to the blood

what are fat soluble vitamins?

A, D, E, and K

if fat soluble vitamins are ingested without fat-containing food what happens?

they are eliminated in the feces

what are water soluble vitamins?

B complexes and C

what B vitamin is not water soluble?

B12 (cause it is too large)

what liver hormone closely regulated iron absorption and mobilization?

hepcidin (iron overload is very toxic and commonly leads to death in young children)

how is iron released in feces?

binds to ferritin in enterocyte before cell is shed and excreted

how much calcium is absorbed in the small intestine?

40%

what vitamin supports calcium absorption?

vitamin D

how much water does the digestive system receive a day?

~9 L (GI tract only excretes .2)

when does diarrhea occur?

when the large intestine does not absorb enough water due to bacterial irritation or high levels of solute

when does constipation occur?

when fecal movement is too slow due to lack of fiber, lack of exercise, emotional stress, or long term laxative abuse

what is an appendectomy?

removal of inflammed appendix

what is a cholecystectomy?

removal of incompetent bladder

what does atrophy mean?

shrinkage

what is indigestion?

discomfort or pain in upper abdomen

what is lactose intolerance?

Inability to break down lactose after the age of ~3

what are dental carries?

cavities (breakdown decay of tooth enamel)

what is gingivitis?

early-stage gum disease

what is periodontitis?

late-stage gum disease

what is SIBO?

small intestinal bacterial overgrowth

what is GERD?

gastric secretion moving back into the esophagus (heartburn)

what is barretts esophagus?

persistent GERD and causes tissue change in lower esophagus due to acid damage

what is a gastric bypass?

pouch creation to bypass the bulk of the stomach