GI 2

where does food spend the most time in the GI tract

large intestine and rectum

stimuli initiating digestion (4)

thought of food

smell of food

chewing

swallowing

response to digestion stimuli

increase parasympathetic output

physical digestion in the mouth

mastication (chewing)

digestion in the mouth is regulated by what nervous system branches?

somatic + autonomic

muscles of mastication

masseter m

temporalis muscle

autonomic NS response in mouth digestion

involuntary chewing reflex

functions of saliva

digestion

lubrication

protection

enzymes in saliva

alpha amylase

lingual lipase

alpha amylase function

splits starch and glyocgen into disaccharides

lingual lipase function

cleaves a FA residue from glycerol (digest fat)

how is saliva involved in protection (4)

secretes HCO3 to buffer acidic food

dilutes concentrations of things entering GI tract

lubrication for mechanical protection

cleanses mouth by destroying bacteria

salivary glands in the mouth

sublingual

submandibular

parotid

sublingual salivary gland cell type

mucous

submandibular gland cell type

serous and mucous

parotid salivary gland cell type

serous cells

what do salivary serous cells secrete

enzymes

water

electrolytes

what do salivary ductal cells do

modify initial ionic secretion (reabsorb and secrete electrolytes)

parts of the salivary gland

acinus

intercalated duct

striated duct

first phase of salivary secretion

acini release primary secretion of enzymes and/or mucus in a solution of water and ions that has a concentration ~ ECF

2nd phase of salivary secretion

primary secretion flows through salivary ducts

ionic composition is modified

reabsorption/secretion of ions

how is salivary secertion controlled

autonomic nervous system reflexes (primarily parasympathetic)

parasympathetic effect on salivary secretion

salivary flow rate

synthesis and secretion of enzymes/mucus

blood flow to salivary glands

transport activity of ducts

metabolic activity of ducts

salivary secretion is always a _ mediated by the medulla

involuntary neural reflex

factors that inhibit salivary secretion (4)

sleep

fatigue

dehydration

fear

phases of swallowing (voluntary or involuntary?)

oral phase (v)

pharyngeal phase (i)

esophageal phase (i)

the esophagus contain _ to aid in digestion process

mucous glands

where along the esophagus is there a large density of mucous glands

gastric end

description of phase 1 of deglutition

-voluntary

-chewed food rolled into a mass by tongue

-tongue forces bolus into pharynx

pharyngeal phase of swallowing invovles which neural inputs

medulla + lower pons

vagus nerve

enteric nervous system

steps of pharyngeal phase of swallowing

1. soft palate is raised

2. larynx is elevated

3. epiglottis and glottis close off trachea

4. tongue pressed against soft palate to seal oral cavity

5. longitudinal muscles of pharynx contract to pull pharynx up

6. UES relaxes

7. peristaltic wave in the pharyngeal muscles

8. respiration is inhibited for 1-2 s

what prevents food from entering the nasal cavity

soft palate

what prevents food from entering the trachea

glottis and epiglottis

what seals the oral cavity from the pharynx in swallowing

tongue

esophageal phase of swallowing

food is conducted from UES to LES and into the stomach via esophageal peristalsis

primary esophageal peristalsis is coordinated by _

brainstem centers via the vagus nerve

secondary peristalsis of esophagus is coordinated by _

enteric nervous system

afferent fibers in the esophageal wall respond to _

stretch activating enteric reflexes

in peristalsis, circular smooth muscle contracts _ the bolus

behind

in peristalsis, circular smooth muscle relaxes _ the bolus

in front of

where does longitudinal muscle contract in peristalsis

in front of the bolus

stomach functions (6)

stores food

secretes gastric juice

initiates digestion of proteins

kills bacteria via gastric juice

moves bolut into small intestine

absorption of alcohol and aspirin

primary function of the stomach

digestion of proteins

what does the stomach absorb

alcohol and aspirin

folds of the stomach

rugae

gastric pits

where do gastric pits lie

folds within the rugae between gastric glands

cells of the stomach

mucous cells

parietal cells

chief cells

stomach mucus (goblet) cells function

secrete mucus and HCO3 to protect the stomach from acidic environment

where are stomach goblet cells found

throughout gastric mucosa

parietal cells of stomach function

secrete HCl and intrinsic factor

location of stomach parietal cells

fundus and body regions

chief cells of stomach function

secrete pepsinogen

where are stomach chief cells found

fundus and body of stomach

what secretes intrinsic factor

parietal cells of the stomach

where does absorption of vitamin B12 occur

terminal ileum

what is intrinsic factor needed for

absorption of vit B12

what is vit B12 needed for

maturation of RBCs in bone marrow

loss of intrinsic factor can lead to _

pernicious anemia

gastric glandular cells

G cells

D cells

enetrochromaffin-like cells

function of stomach G cells

secrete gastrin

what stimulates stomach G cells

vagal stimulation

presence of HCl

location of stomach G cells

pylorus and antrum

gastrin function

increase HCl secertion (parietal cells)

increase pepsinogen secretion (chief cells)

increase motility

stimulate pancreas for enzyme secretions and insulin

D cells of the stomach secrete _

somatostatin

location of D cells of the stomach

antrum

somatostatin function

inhibits secretion in GI tract

decreases motility

inhibits pancreatic endocrine secretions

enterochromaffin-like cells secrete _

histamine and serotonin

histamine and serotonin act as _ agents within the stomach

paracrine

function of histamine in the stomach

stimulates gastric secretions

function of serotonin in the stomach

stimulates smooth muscle contractions

functions of acidity of stomach

denatures proteins

allows pepsinogen enzymes to breakdown to pepsin

allows pepsin to operate maximally

steps of acid secretion by parietal cells

-h2o proken down to H+ and OH-

H+ pumped into lumen via H/K ATPase

CO2 enters cell

CO2 hydrated to form carbonic acid

carbonic acid dissociates to bicarb and H+

bicarp pumped out of the cell into blood

Cl- actively transported into the cell and diffuses into stomach lumen

water passively diffuses into lumen

HCl formed in lumen

saliva digests _

carbohydrates and fat

direction of secretion via parietal cells

secrete HCl into stomach lumen

secrete bicarb into blood

major regulators of H+ secretion by parietal cells

acetylcholine

gastrin

histamine

G cells contain _ receptor

gastrin releasing peptide (GRP)

parietal cells possess receptors for _

acetylcholine

gastrin

histamine (H2)

phases of stomach acid secretion

interdigestive

emotogenic

cephalic

gastric

intestinal

interdigestive acid secretion

slow continous secretion of acid during periods when stomach is empty

emotogenic acid secretion

increased acid production indued by emotional state

the cephalic phase of acid secretion is entirely _

neurogenic (mediated by CNS)

what initiates the cephalic phase of acid secretion

thought, smell, sight, taste of food

how does the CNS mediate cephalic phase of gastric acid

vagus nerve activates neural plexuses in walls of stomach to increase secretion of gastric glandular cells

what initiates the gastric phase of acid secretion

stretch receptors detect entry of food into stomach

chemical receptors detect changes in stomach acidity

what mediates the gastric phase of acid

neural and hormonal signals

presence of amino acids and peptides (most potent)

what happens as pH falls in the stomach

HCl secretion is inhibited by somatostatin

gastrin secretion inhibited

presence of _ in the duodenum stimulates the release of hormones

H+ and fatty acids

hormones released by small intestine

GIP and CCK

gastric inhibitory peptide effect on stomach

inhibits gastric secretions

decreases motility

CCK inhibits _

gastric motility

components of gastric motility

receptive (stretch) relaxation

peristalsis

receptive relaxation of the stomach

food entry activates stretch receptors -> inhibitory signals mediate relaxation of smooth muscle -> stomach enlargens without changing pressure

effect of gastric receptive relaxation

stomach can accomodate volume without changing pressure

gastric peristalsis is intiated near _

fundus

where do stomach contractions become more intesnse

antrum

what sphincter is maximally constricted during gastric peristalsis

pyloric sphincter

when does chyme exit the stomach

when it is broken down enough to fit through pyloric sphincter

what signals regulate gastric emptying

neural + hormonal

hormonal signal that promotes gastric emptying

gastrin

neural signals that inhibit gastric emptying

norepinephrine (sympathetics)

activation of duodenal mechanoreceptors/chemoreceptors

enterogastric reflex