Phys - Exam 4 - Ch 18 Digestive System

function

transfer of nutrients, water, electrolytes from ingested food into body's internal environment

digestive system processes

motility

secretion

digestion

absorption

mechanical digestion

Physical breakdown of large pieces of food into smaller pieces

locations of mechanical digestion

mouth, stomach, small intestine

locations of chemical digestion

mouth, stomach, small intestine

motility

movement

hepatic portal vein

the vein that collects blood from the GI tract and conducts it to the liver

gut --> liver

hepatic vein

blood from liver ---> heart

mucosa

secretes mucus

innermost layer

submucosa

Layer containing blood vessels and nerves.

vascularized

muscular externa

smooth muscle layer

contributes to motility

adventia

outer layer of CT

sphincter function

ensures food passes uni-directionally

cells lining GI tract replaced every

3-5 days

digestive tract

comes into contact with food

digestive tract components

mouth, pharynx, esophagus, stomach, small intestine, large intestine

accessory organs functions

secrete into digestive tract

don't come into contact with food

accessory organs

salivary glands

exocrine pancreas

bilary system (liver, gallbladder)

bilary system

liver

gallbladder

macronutrients absorbed by digestive system

lipids

proteins

carbs

teeth

mechanical breakdown of food initiated

mixes food with saliva

tongue

movement aids in chewing, swallowing

speech

taste buds

saliva glands

3 pairs

produce saliva

saliva

contains salivary amylase - begins breakdown of carbs

mucus provides lubicration

antibacterial action

solvent for molecules that stimulate taste buds

keeps mouth/teeth clean

saliva stimulation

dual, help each other

Symp - constrict vessels promote mucus

Para - stim release of saliva

esophagus

swallowing - starts w/ bolus forced to back of mouth

swallowing

voluntary, yet can't be stopped when begun

upper esophageal sphincter

prevents backflow of food from esophagus back into mouth

lower esophageal sphincter

a muscular ring that controls the flow between the esophagus and stomach

aka cardiac sphincter

peristaltic waves

push food through GI tract

stomach empties into....

proximal region of small intestine (duodenum)

stomach function

stores, mixes, prepares bolus for digestion

stomach secretions

HCl

mucus

pepsin

stomach chemical digestion

only proteins (with pepsin)

stomach mechanical digestion

everything (b/c of peristalsis)

is there any carb/lipid chemical breakdown in the stomach?

NO

are macronutrients absorbed in the stomach?

NOOO

pepsin is secreted by

chief cells

pepsinogen is converted into

pepsin, using HCl

HCl in stomach comes from

parietal cells of stomach

chief cells and parietal cells are stimulated by

gastrin

gastrin comes from

G cells of stomach

pyloric sphincter

controlled release of chyme into small intestine

gastric

stomach

factors in stomach that impact gastric emptying

amount of chyme, main influence of strength of contractions

factors in small intestine that impact gastric emptying

fat - delays

acid - inhibits emptying of acidic gastric contents until neutralization accomplished

hypertonicity - gastric emptying inhibited when osmolarity of duodenal contents start to rise

distension - slows when too high

retrograde

GERD

small intestine

site where most digestion, absorption takes place

small intestine components

duodenum - prox to stomach

jejunum

ileum - distal to stomach

in the small intestine, carbs and proteins are absorbed....

directly into bloodstream

small intestine absorption

carbs

proteins

lipids

in the small intestine, lipids are absorbed...

into the lacteal ducts

--->

drains into lymphatic system (lymph)

motility of small intestine

peristalsis

segmentation

segmentation

pinching off to mix chyme --> max SA --> max abs

SA of small intestine

fold of intestine

villi

microvilli

microvilli

brush border (contains enyzmes that aid in breakdown)

brush border

Surface of a cell covered with microvilli. increases surface area of a cell for absorption

small intestine chemical digestion through:

pancreatic enzymes

brush border enzymes

pancreatic enzymes

secreted into small intestin by exocrine pancreas

lipase

amylase

protease

lipase

breaks down lipids

pancreatic enz

amylase

breaks down carbs

pancreatic enz

protease

breaks down proteins

pancreatic enz

brush border enzymes

Enzymes secreted by the mucosal cells lining the intestine

complete digestion of carbs, proteins

peptidases

disaccharidases

peptidases

brush border enz

breaks down proteins

disaccharidases

brush border enz

breaks down CHO

does the large intestine absorb any macronutrients?

NOOOO

What is the only location where macronutrients are absorbed?

only in small intestine

large intestine functions

-absorption of water

-electrolyte absorption

-vitamin synthesis

-formation and storage of fecal material

need healthy _______________ for overall health and functioning

gut microbiome

large intestine components

colon

cecum

appendix

rectum

appendix

contains a mass of white blood cells that contribute to immunity

important piece of lymphoid tissue

ileocecal sphincter

regulates movement into LI

enters cecal/cecum region of LI

large intestine differs from small intestine:

no digestive enzymes - no abs of macros

no villi/microvilli - doesn't need much SA

no hormones

not tightly coiled - can store

intestinal microflora - gut microbiome; bacteria feeds on fiber; releases gases ---> fermentation ---> allows synthesis of vitamins

movement through GI tract

substances don't move unidirectionally

materials don't exit same order they enter

fats slow gastric emptying

total emptying dependent heavily on diet

pancreas functions

exocrine - secretes pancreatic juice, bicarbonate

endocrine - secretes insulin, glucagon

pancreatic juice

consists of amylase, lips, protease

directly into duodenum

bicarbonate

secreted into duodenum

neutralizes acidic chyme from stomach

what organ also stores fat

liver

liver

largest, most important metabolic organ

first organ to receive absorbed nutrients from hepatic portal vein

produces plasma proteins

removes bilirubin

manufactures bile salts

alc metabolism

stores nutrients

removes, degrades toxins

bile

made by liver, stored concentrated in gallbladder

enter duodenum after meal

bile salts

made from cholesterol

manufactured in liver

fat emulsifier - mixing

reabsorbed into blood

hepatic artery

Supplies oxygenated blood to the liver

digestive motility, secretion regulated by

intraluminal content

autonomous smooth muscle function

intrinsic nerve plexuses

extrinsic nerves

GI hormones

intraluminal content

inside GI tract

autonomous smooth muscle function

A factor for regulating digestive motility: cells display rhythmic, spontaneous variations in membrane potentials. Inherent rate of several digestive processess (e.g., peristalsis and segmentation) depend on these pacesetter cells in tract with this characteristic.

intrinsic nerve plexuses

local sense receptors ---> detect stretch ---> stimulate response

extrinsic nerves

CNS (PNS - rest, digest)

regulation of secretion in GI tract

luminal stimuli

1. mechanoreceptors

2. osmoreceptors

3. chemoreceptors

4. chyme concentration of digestive products

mechanoreceptors

distension of wall - determines contraction

osmoreceptors

osmolarity of chyme

chemoreceptors

acidity of chyme - reg of movement

chyme concentrations of digestive products

what u ate

enteric nervous system

refers to stomach/gut

short, long reflexes

short reflexes

locally

stretch of GI wall, pH change, etc --> stim

long reflexes

all of gut

PNS stim all

(ex. chewing ---> ---> pre-emptive secretion)

(ex. smell ---> stomach growling)

gastrin

secreted by G cells

aid in digestion of proteins

CCK

secreted by small intestine

aid in digestion of a lot

gastric inhibitory peptide (GIP)

secreted by gut

stimulates release of insulin ---> lower blood glucose

secretin

stimulates the pancreas to release bicarbonate to neutralize acid in duodenum

secreted by small intestine

aids in bile production, release

phases of gastric secretion

cephalic phase

gastric phase

intestinal phase