Digestive System

functions of digestive system

bring nutrients in to body, secretions, mechanical and chemical processing, absorption, excretion

gross anatomy of digestive system

mouth, esophagus, stomach, intestines, rectum

accessory organs

salivary glands, liver, pancreas, gallbladder

what separates the parts of the GI tract

sphincters

layers of the peritoneum

parietal peritoneum, peritoneal fluid, visceral peritoneum

parietal peritoneum

lines the walls of the abdominal cavity

visceral peritoneum

covers surfaces of organs

what happens to the visceral peritoneum

folds on itself

greater amentum

covers most of the ventral surface storing adipose tissue

what differentiate absorption and secretion

specializations of epithelia in mucosa

what is the apical surface

surface touching lumen

what is the basolateral surface

touches the blood

what direction does secretion go

into the lumen

what direction does absorption go

from the lumen across cell and into blood

what are the 4 cell layers of the GI tract

serous, muscularis externa, submucosa, mucosa

muscularis externa

longitudinal layer of smooth muscle, circular layer of smooth muscle, and layer of nervous tissue

longitudinal layer of muscularis externa changes what

length

circular layer of muscularis externa changes what

radius

what is the layer of nervous tissue in muscularis externa

myenteric plexus

myenteric plexus

major sensory and motor info from parasympathetic nervous system

what is the submucosa made of

connective tissue

what are the 3 layers of mucosa

muscularis mucosae, lamina propria, epithelium

muscularis mucosae

smooth muscle that shapes mucosa layer

lamina propria

connective tissue that supports small vessels and lymph nodes

epithelia type in mucosa layer

simple/stratified columnar

what cells are found in the mucosa layer of epithelium

enterocytes, enteroendocrine, and mucin-producing cells

peristalsis

forward movement based on pressure gradients

where is peristalsis found

esophagus, stomach, intestines

what side contracts and what side relaxes in peristalsis

proximal contraction distal relaxation

segmentation

back and forth movement for mixing

where is segmentation found

small intestine

what side contracts and what side relaxes in segmentation

there is proximal contraction and distal relaxation at the same time

phasic contraction

quick contraction

where is phasic contraction in GI tract

throughout GI tract

is peristalsis phasic or tonic

phasic

is segmentation phasic or tonic

phasic

is sphincters phasic or tonic

tonic

tonic contraction

long contraction

where are tonic contractions found in GI tract

sphincter muscles

what are important molecules for smooth muscle contractions

calcium, calmodulin, cyclic nucleotides, protein kinases, myosin light chain kinase, myosin light chain phosphate

step of general digestion

1. large complicated (starches, polypeptides, triglycerides)

2. mechanical digestion breaks large food into smaller pieces

3. small, complicated (starches, polypeptides, triglycerides)

4. chemical digestion breaks small pieces down more

5. small simple (simple sugars, amino acids, free fatty acids, monoglycerids)

what type of carbohydrates can be absorbed

simple carbohydrates

what is thr major site of carb digestion

small intestine

where do complex carbs start digestion

the mouth, amylase in saliva begins digestion

what are complex carbs broken into by amylase

disaccharides

what breaks down disaccharides

brush border enzymes/disaccharidases

what are disaccharides broken down into

simple sugars

3 simple sugars

glucose, fructose, galactose

what channels are involved in carbohydrate absorption on the apical side

SGLT 1 and GLUT 5

SGLT 1

symporter that transports glucose and galactose with Na+

GLUT 5

facilitated diffusion of fructose

what channels are involved in carbohydrate absorption on the basolateral side

GLUT 2

GLUT 2

transports all simple sugars into blood

where are fats digested

small intestine

what does mechanical digestion and emulsification of fats

bile produced in the liver makes lipids amplific so the outside of the fat molecules are soluble

what does chemical digestion of fats

lipases produced by pancreas

lipase

converts triglycerides into monoglycerids and free fatty acids

are monoglycerids and free fatty acids polar or non polar

non polar

micelle

simple clumps of monoglycerids and free fatty acids

how are fats absorbed

diffusion of chylomicrons

chylomicron

packs of fats, proteins, and cholesterol that cross basolateral membrane by exocytosis

where do chylomicrons go after exocytosis

go to lymphatic system through lacteals (lymph vessels) then into systemic circulation

why do chylomicrons go into lacteals and not capillaries

they are to big to pass through capillaries, so fats go to heart faster than other molecules.

what is the preferred way to absorb proteins

simple proteins but other forms can b e absorbed

where does protein digestion start

in the stomach

endopeptidases

break peptides in the center of the chain

types of endopeptidases

pepsin, trypsin, small intestine peptidases

where is pepsin secreted

stomach

where is trypsin secreted

pancreas

exopeptidases

cut peptides at the ends of chains releasing single amino acids

type of exopeptidase

carboxypeptidase

where is carboxypeptidase found

pancreas

what channels are involved in protein absorption on the apical side

Na+ symporter, H+ symporter

Na+ symporters

move amino acids using Na+

H+ symporters

move di/tripeptides using H+

transcytosis

large unbroken proteins are engulfed and brought into the cell

hepatic portal steps

1. venous blood from gut

2. goes through portal vein

3. liver metabolism of carbs, amino acids, lipids

4. detoxification

5. hepatic vein

alcohol dehydrogenase

converts EtOH to acetyladehyde

acetyladehyde

toxin that causes headaches, vomiting, and carcinogenic

acetyladehyde dehydrogenase and glutathilone

breaks down acetyladehyde

does peristalsis or segmentation need a pressure gradient

peristalsis

phosphomyosin

increases muscle contraction after adding phosphate to myosin

what phosphorylates phosphomysin

myosin light chain kinases

how does Ca+ increase smooth muscle contraction

Ca+ is brought into the cell by LTCC or by G-PCR Q which produces Ca+. Then Ca+ in the cell activate calmodulin. Calmodulin activates MLCK which phosphorylate myosin to increase contractions

How can smooth muscle be relaxed

myosin light chain phosphatase

myosin light chain phosphatase

removes phosphate to decrease contraction

how does cAMP decrease contractions

GCPR S produces cAMP, cAMP inhibits MLCK so myosin is not phosphorlated and muscle relax

How do GCPR i increase contractions

inhibits cAMP so then cAMP can not inhibit MLCK and the myosin is phosphorylated and contractions increase

how do phosphodiesterases increase muscle contractions

PDE inhibits cAMP so cAMP can not inhibit MLCK and myosin can be phosphorylated increasing contractions