radi 660 gateway 4: GI

do you NEED any part of the GI tract?

not really, mainly acts as a food chute and improves quality of life; don’t NEED esophagus, stomach, small or large intense, DO NEED pancreas and liver

salivary glands produce _ which does what?

amylase; starts carbohydrate digestive process

do we NEED the accessary organs (salivary glands, liver, gallbladder, pancreas)?

YES liver and pancreas, NO salivary glands and gallbladder

functions of the GI tract include:

preparing nutrients for utilization by the cells via ingestion, mechanical digestion, chemical digestion, mixing and propelling movement, absorption, and elimination of wastes

where does mechanical digestion take place?

teeth and stomach

where does chemical digestion take place?

starts in mouth with amylase, continues into stomach and small intestine

how does food get mixed in the GI tract?

segmentation in the proximal small bowel

how does food get propelled in the GI tract?

peristalsis in the stomach, small and large bowels

where does majority of nutrient and water absorption take place?

small intestine

where does elimination of waste take place?

the colon

what are the layers of the GI tract?

(innermost) mucosa, submucosa, muscularis, serosa (adventitia) (outermost)

why do nerves lie in the submucosa and muscularis but NOT in the mucosa?

you don’t want to feel your food moving all the time; downside is you could have a mucosal disease and not know it

muscularis usually has a longitudinal and circular layer except the stomach has a third one called ?

oblique, for churning

epithelium including mucus-producing cells

mucosa

connective tissue - including blood vessels, nerves, lymphatics, secretory glands

submucosa

two layers of muscularis in gut wall are ?

circular and longitudinal smooth muscle layer

visceral peritoneum in the gut wall is called ?

serosa

upper GI tract: what happens in the oral cavity?

initial phase of mechanical breakdown of food, mastication by teeth; initial chemical digestion via salivary amylase which starts the chemical breakdown of carbohydrates; formation of bolus (once food is mixed with saliva it becomes bolus)

upper GI tract: what happens in the pharynx?

swallowing (deglutition)

upper GI tract: what happens in the esophagus?

closed except during swallowing; skeletal muscle at superior end, followed by smooth muscle

what to know about the tongue

contains skeletal muscle, taste buds, and sensory receptors; manipulation of food and speech

what do the teeth do

biting, grasping, tearing, grinding

what to know about the pharynx

transports food to esophagus, swallowing

what to know about the esophagus

posterior to the trachea and anterior to the vertebral column; cardiac sphincter controls passage to stomach; contains skeletal and smooth muscle

protein digestion begins where?

in the stomach

parts of the stomach

fundus, body, pylorus, greater and lesser curvature

mucosal lining of the stomach has folds called _

rugae; also found in gallbladder (bile storage), bladder (urine storage), helps the stomach collapse and fill up with stuff, allows for expansion

3 muscle layers of the stomach

outer longitudinal, middle circular, inner oblique

secrete hydrochloric acid and intrinsic factor; pH regulation

parietal cells

secrete pepsinogen

chief cells

secrete gastrin

endocrine cells

expansible muscular sac that acts as a reservoir for food and fluid

stomach

initial digestion of proteins happens via _ which is formed by combining _ and _

pepsin; pepsinogen and hydrochloric acid

production of intrinsic factor is essential for the absorption of ?

vitamin B12 in the ileum

formation of chyme occurs in the ?

stomach, once the bolus has been partially digested and broken down by stomach acid

absorption of small and lipid-soluble molecules happens in the ?

stomach

3 phases of gastric secretions:

cephalic (thoughts and smells), gastric (presence of food in stomach), intestinal (acid chyme in small intestine)

cell layers of the small intestine:

plicae circulares, villi, microvilli all increase absorptive surface area; each villus contains blood and lymph capillaries (lacteal)

3 sections of the small intestine:

duodenum, jejunum, ileum

small intestine cells produce ?

peptidase (for proteins), maltase, sucrase, lactase (for sugars), lipase (for fats)

small intestine hormones are ?

secretin (stimulates pancreas) and cholecystokinin/CCK (stimulates gallbladder)

large intestine (colon) mucosa

goblet cells

in the large intestine, longitudinal muscle layer has bands (taenia coli) that form ?

a haustra pattern

segments of the large intestine (colon)

cecum, appendix, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon, rectum

absorption of water and electrolytes, elimination of feces

large intestine (colon)

why is muscle contraction more forceful in the large intestine compared to the small intestine

the large intestine moves more solid material (feces) because the small intestine absorbs the water

what does resident normal flora do in the large intestine? (lower gastrointestinal tract)

breakdown of certain food materials, vitamin K synthesis by bacteria (important in clotting process)

which glands secrete saliva?

parotid, submandibular, sublingual glands (salivary glands)

saliva contains…

amylase, water, mucus

cleanses, moistens, dissolves substances for taste, begins digestion of carbohydrates

saliva

function of salivary glands/saliva

chemical digestion

name the 4 lobes of the liver

left, right, caudate, quadrate

the liver receives blood from both the _ and the _

hepatic artery, portal vein

functions of the liver

synthesis of bile salts, synthesis of plasma proteins, storage, detoxification, excretion, carbohydrate metabolism and lipid metabolism, protein metabolism, blood filtering

function of liver

chemical digestion

attached to the surface of the liver by the cystic duct

gallbladder

cystic duct + hepatic duct = ?

common bile duct

_ empties into the duodenum at the ampulla of vater and sphincter of oddi

common bile duct

functions of gallbladder

store and concentrate bile

what is bile composed of? what’s its purpose?

water, bile salts, bile pigments (bilirubin), and cholesterol; emulsify fats

function of gallbladder

chemical digestion

retroperitoneal extends from the duodenum to the spleen; has exocrine and endocrine functions

pancreas

pancreas exocrine digestive enzymes:

amylase (starch), trypsin (proteins), peptidases (peptides), lipases (fats)

pancreas endocrine cells:

islets of langerhans - insulin and glucagon

why do we often get ulcers at the duodenum?

acid from the stomach comes in

stimulates pancreas to secrete a bicarbonate rich fluid, which helps balance pH

secretin

stimulates production of pancreatic enzymes

CCK

function of pancreas

chemical digestion

secreted by mucosal cells (in the stomach) in response to distention of stomach or partially digested substances

gastrin

increases gastric motility, relax pyloric and ileocecal sphincters, promotes stomach emptying

gastrin

increased secretion of hydrochloric acid

histamine

decreases gastric secretions

secretin

inhibits gastric emptying, stimulates contraction of gallbladder

cholecystokinin (CCK)

digestion starts in the mouth; followed by digestion in the small intestine

carbohydrates

digestion starts in stomach; continues in small intestine

proteins

emulsified by bile prior to chemical breakdown; action of enzymes forms monoglycerides and free fatty acids; formation of chylomicrons

lipids

vitamins A, D, E, and K; absorbed with fats

fat-soluble vitamins

vitamins B and C; diffuse into blood

water-soluble vitamins

absorbed by active transport or diffusion

electrolytes

drugs are primarily absorbed in the _

intestine; via various transport mechanisms; some like aspirin may be absorbed in the stomach

water is primarily absorbed in the _ via osmosis

small intestine

3 most common manifestations of digestive system disorders:

nausea, vomiting, diarrhea

may be signs of digestive disorders or other conditions elsewhere in the body:

systemic infection, uremia, emotional responses, motion sickness, pressure in the brain, overindulgence of food or drugs, pain

can cause serious complications like dehydration, acidosis, malnutrition

anorexia and vomiting

often precedes nausea and vomiting

anorexia (lack of appetite/eating)

unpleasant subjective feeling stimulated by distention, irritation, inflammation of digestive tract; also stimulated by smells, visual images, pain, and chemical toxins and/or drugs

nausea

briefly explain the vomiting (emesis) reflex FROM SLIDE

vomiting center is located in the medulla and coordinates activities involved in vomiting, protects airway during vomiting, forceful expulsion of chyme from stomach that sometimes includes bile from the intestine

explain the vomiting reflex DIAGRAM

stimulus to vomiting center, vomiting center coordinates reflex thru CN 5,7,9,10, 12, hypersalivation, pallor, sweat, tachycardia, glottis closes, soft palate rises to close off the airway, deep inspiration, diaphragm contracts, GE sphincter and fundus of stomach relax, abdominal muscles contract forcefully, antiperistalsis waves, increased pressure forces chyme upward from stomach out of mouth

explain vomiting center activation

distention or irritation in digestive tract, stimuli from various parts of the brain in response to unpleasant sights or smells or ischemia, pain or stress, vestibular apparatus of inner ear (motion), increased intracranial pressure can cause sudden projectile vomiting without previous nausea, stimulation of chemoreceptor trigger zone (in the medulla) by drugs, toxins, chemicals

explain vomiting reflex activities

deep inspiration, closing glottis and raising soft palate to protect airway, ceasing respiration to minimize the risk of aspiration of vomitus into lungs, relaxing the GE sphincter, contracting abdominal muscles to force gastric contents upward, reverse peristalsis waves to promote expulsion of stomach contents

presence of blood in vomitus

hematemesis

“coffee grounds” or brown granular material in vomitus indicates what?

action of hydrochloric acid on hemoglobin (digested blood)

active hemorrhage sign relating to vomitus

bright red blood may be in vomitus

yellow or green stained vomitus indicates ?

bile from the duodenum, burns mouth

deeper brown color in vomitus may indicate ?

content from lower intestine/feces

recurrent vomiting of undigested food may indicate ?

problem with gastric emptying or infection

excessive frequency of stools, usually of loose or watery consistency; may be acute or chronic; frequently with nausea and vomiting when infection or inflammation develops; may be accompanied by cramping pain

diarrhea

prolonged diarrhea may lead to ?

dehydration, electrolyte imbalance, acidosis, malnutrition

watery stool resulting from increased secretions into intestine from the plasma; often related to infection

large-volume diarrhea (secretory or osmotic); SUDDEN

often due to inflammatory bowel disease; stool may contain blood, mucus, or pus; may be accompanied by abdominal cramps

small-volume diarrhea; FREQUENT