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100 Cards in this Set

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mechanoreceptors

respond to stretch or pressure in the digestive tract

osmoreceptors

respond to changes in osmolarity in the digestive tract

chemoreceptors

respond to pH, substrates, and end products of digestion in the digestive tract

long reflexes

extrinsic control that involves integration from the medulla and output sent via autonomic nerves to GI tract to alter muscle and gland activity, level of hormone secretions, modify intrinsic activity, and coordinate different parts of the GI tract (ex. chewing food causes ↑ secretions in stomach)

short reflexes

intrinsic control that involves the enteric nervous system which are the myenteric and submucosal plexus with the digestive tract wall, and coordinates local activity; can work independently of the CNS or be influenced by extrinsic nerves because it is linked to long autonomic reflex arcs

GI peptides

can act as digestion hormones and paracrine signals, are released into the blood or ECF by cells of the digestive tract, can act on digestive organs and accessory organs to excite or inhibit motility or secretions, and can also act on the brain to trigger hunger or satiety

amylase

salivary enzyme secreted in the mouth that begins the chemical digestion of breaking down carbohydrates (polysaccharides→maltose)

saliva

secreted from serous and mucous cells in the glands of the mouth that consists of mostly water as well as amylase, mucus, lysozyme, and IgA

mucus

moistens food and holds bolus together

lysozyme and IgA

chemicals that provide antibacterial action in the mouth

simple and acquired reflexes

two reflexes that enhance salivary secretion

simple reflex

occur when ingested food stimulates chemoreceptors and pressoreceptors, the cortex trigger the salivary center in the medulla

acquired reflex

occur at the thought of food, the cortex triggers the salivary center in the medulla

parasympathetic nervous system

controls larger volume of saliva, more water, rich with amylase

sympathetic nervous system

controls smaller volume of saliva, more mucus, result in dry mouth

deglutition

another name for swallowing that involves the buccal and pharyngeal-esophageal phases that coordinate activity of the tongue, soft palate, pharynx, and esophagus

buccal phase

involve the bolus voluntarily being forced into the oropharynx

pharyngeal-esophageal phase

involve the involuntary controls from the medulla and lower pons

paristalsis

movement of food through the pharynx and the esophagus

gastroesophageal sphincter

where food enters the stomach from the esophagus

intrinsic factor

stomach secretes this which is required for absorption of vitamin B₁₂

gastric filling


storage


mixing


emptying

phases of gastric motility

muscular antrum

where gastric mixing occur

mucous cells

exocrine cells that produce mucus to protect stomach wall from harsh acids

parietal cells

exocrine cells that produce HCl and intrinsic factor

Chief cells

exocrine cells that produce pepsinogen

pepsinogen

an inactive form of the protein digesting enzyme pepsin

HCl

converts pepsinogen into pepsin

pepsin

enzyme released in the stomach that breaks down proteins into peptide fragments (proteins→peptides)

G cells

endocrine cells that produce gastrin

gastrin

hormone produced by G cells that stimulates parietal cells to produce HCl

enterochromaffin (ECL) cells

coffee stimulates gastrin secretion that stimulates this paracrine cell to secrete histamine; histamine stimulates parietal cells

D cells

low pH triggers this paracrine cell to secrete somatostatin that inhibits secretion of parietal, ECL, and G cells

neural and hormonal mechanisms

they regulate the release of gastric juices

cephalic phase

this reflex phase occur prior to food entry

gastric phase

this phase occur once food enters the stomach

intestinal phase

this phase occur as partially digested food enters the duodenum

ACh

hormone that stimulates parietal, G cells, and ECL cells

excitatory events of cephalic phase

events include:


sight or thought of food


stimulation of taste, smell, chewing


vagal stimulation releases ACh

inhibitory events of cephalic phase

events include:


loss of appetite or depression


decrease in stimulation of the parasympathetic division

excitatory events of gastric phase

events include:


stomach distention activates stretch receptors by neural activation


peptides, caffeine, and alkaline pH activate chemoreceptors

inhibitory events of gastric phase

events include:


acidic pH lower than 2 triggers somatostatin release

intestinal phase

phase in the regulation of gastric secretion that is mostly inhibitory

inhibitory events of intestinal phase

events include:


distention of duodenum, presence of fatty, acidic, or hypertonic chyme in the duodenum

local reflexes


vagal nuclei

inhibitory factors that closes the pyloric sphincter

hormones cholecystokinin (CCK) and secretin


neural enterogastric reflex

these factors regulate gastric emptying

neural enterogastric reflex

occurs when the duodenum fills, stretch receptors are stimulated and the pyloric sphincter closes

cholecystokinin (CCK)

fatty chyme entering the duodenum causes the duodenal wall enteroendocrine cells to release this hormone into the bloodstream and stimulate:


1. gallbladder to contract


2. hepatopancreatic sphincter to relax/release bile


3. pancreas to secrete digestive enzymes

secretin

acidic chyme entering the duodenum causes the duodenal wall enteroendocrine cells to release this hormone into the bloodstream and stimulate:


1. liver to produce bile more rapidly


2. pancreas to secrete bicarbonate-rich juices

vagal stimulation

1. together with secretin, causes weak contractions of the gallbladder to regulate bile release




2. causes release of pancreatic juice

bile salt

this is reabsorbed back into the blood in the ileum and returned by the hepatic portal system; about 5% escapes in feces

gastric inhibitory peptides (GIP)

hormone that inhibits gastric acid secretion, and promotes pancreas to release insulin

gastric and duodenal factors

factors that control the rate of gastric emptying

amount of chyme


fluidity of chyme


extrinsic control of vagus nerve


gastrin

gastric factors that increase gastric emptying

fatty chyme: slower to digest/absorb


acidic chyme: need to be neutralized


hypertonicity: need time to absorb nutrients


distention: needs to cope w/ volume before receiving more

duodenal factors that decreases gastric emptying

duodenum

region of the small intestines that function as chemical digestion and absorption

jejunum
ileum

region of the small intestine that function to absorb nutrients

bile and digestive enzymes

substances that are released into the duodenum to be mixed with the chyme

produce bile to aid in digesting fats


store excess nutrients for later use


detoxify drugs and metabolites


produce plasma proteins

functions of the liver

hepatocytes

cells in the liver that produce and secrete bile into ducts that empty into the common hepatic duct

hepatopancreatic sphincter (sphincter of Oddi)

this muscle at the base of the common bile duct prevents bile from entering the duodenum between meals

gallbladder

where bile backs up and is stored in concentrated form

bile salts


cholesterol


lecithin


bilirubin



composition of bile, an alkaline solution

emulsify fats to increase surface area for lipase action

function of bile

acini cells

cells of the pancreas that secrete digestive enzymes

duct cells

cells of the pancreas that secrete NaHCO₃⁻

sodium bicarbonate (NaHCO₃⁻)

aqueous solution that neutralizes acidic chyme

proteolytic enzymes

enzymes of the pancreas that are released in an inactive form and are activated in the duodenum, that function to break different peptide bonds into short peptides and amino acids

trypsinogen


chymotrypsinogen


procarboxypeptidase

types of inactive proteolytic enzymes

enterokinase

membrane-bound enzyme that activates trypsinogen into trypsin

trypsin

active proteolytic enzyme that activates chymotrypsinogen and procarboxypeptidase into chymotrypsin and carboxypeptidase, respectively.

duodenum

where proteolytic enzyme activation occurs

amylase

pancreatic enzyme that hydrolyzes polysaccharides into disaccharides

nuclease

pancreatic enzyme that hydrolyzes nucleic acids into nucleotides

lipase

pancreatic enzyme that hydrolyzes triglyceride (emulsified fat) into monoglyceride and fatty acid

maltase


sucrase


lactase


aminopeptidase

types of brush border enzymes

plasma membrane of the small intestine's mucosal cells

where brush border enzymes are found and involved in carrying out final chemical digestion

vitamins, nutrients, and electrolytes

complete absorption of these occur in the small intestines

A, D, E, and K absorbed with lipids

fat soluble vitamins

C and B passively absorbed with water

water soluble vitamins

Vitamin B₁₂

this vitamin is combined with intrinsic factors and absorbed by receptor-mediated endocytosis in the ileum

Ca²⁺ and iron

minerals that are absorbed on an as needed basis by active transport

depends on blood Ca²⁺ level


regulated by vitamin D and PTH

when and how Ca²⁺ absorption occur

ferritin

absorbed iron is stored in the epithelial cells as this until needed

transferrin

if blood iron levels are low then it is released into the blood and carried by this to the bone marrow to be used for RBC production

Cl⁻, H₂O, glucose, and amino acids

absorption of these electrolytes depends on active transport of Na⁺ into interstitial fluid

anions passively follow electrical gradient established by Na⁺

what movement of anions depends upon

cotransporter

Na⁺ re-entry through this can drive solutes against the concentration gradient

facilitated diffusion via cotransport with Na⁺

how sugars and amino acids are absorbed

hepatic portal vein

how sugars and amino acids are transported to the liver

synthesizes into triglycerides in the SER


combines with protein in the golgi apparatus


released by exocytosis


enters lacteals


transported systemically via lymph

occur when micelle (sphere of lipid) gets close to the absorptive surface and diffuses into the intestinal cells

chylomicrons

combination of triglyceride and protein

segmentation

most common motion of the small intestine that is initiated by intrinsic pacemaker cells and function to mix chyme with digestive juices and exposes it to the absorptive surface of the small intestines before contents are moved steadily toward the ileocecal valve

distention


gastrin


extrinsic nerves (PNS)

factors that enhances the intensity of segmentation contractions

migrating motility complex

after nutrients have been absorbed, a series of peristaltic waves called this begins with each wave starting distal to the previous and sweeps remnants of the previous meal, bacteria, mucosal cells, and debris into the large intestine

motilin

this hormone regulates motility in the small intestine during the postabsorptive state

mucosa endocrine cell

cell that releases motilin

gastroileal reflex

this reflex is triggered by food entering the stomach, gastrin, and increased motility of the small intestines, thereby allowing chyme to pass into the large intestine by relaxing the ileocecal sphincter

absorb remaining water, electrolytes, vitamin K


excrete indigestible food from the body

function of large intestines

gastrocolic reflex

this reflex is triggered by gastrin and extrinsic nerves when food enters the stomach, causing contraction of the ascending and transverse colon that results in mass movement of content forward into the rectum