the digestive system

digestion process

(I Make Purple Cake After Dinner)

1. ingestion

2. mechanical digestion

3. propulsion

4. chemical digestion

5. absorption

6. defecation (excretion)

ingestion

mastication

mechanical digestion

mastication, churning, segmatation

mastication definition

chewing

churning

mixing

segmentation

churning while pushing forward

propulsion

via peristalsis: contraction and relaxation of muscled in the organ wall

chemical digestion

involves endocrine, exocrine, paracrine, autocrine

endocrine

enters the bloodstream

exocrine

release into ducts

paracrine

hormone effects nearby cells

autocrine

effect on cell itself

absorption

nutrients from GI tract goes into bloodstream

defecation (excretion)

elimination of solid waste

peritoneum

serous membrane of abdominal cavity, acts as lubrication allowing organs to glide across one another easily

splanchnic circulation

bloodflow to small and large intestines

hepatic portal circulation

collects nutrient rich blood and delivers it to the liver

GI tract layers

4 tunics:

1. mucosa

2. submucosa

3. muscularis

4. serosa

mucosa

protects organs from acids/digestive enzymes; contain hormone and enzyme secreting cells

submucosa

pick up nutrients

muscularis

responsible for peristalsis and segmentation

serosa

outermost protective layer

extrensic regulation

parasympathetic: stim. vagus nerves → stim. lower large intestine

sympathetic: inhibits peristalsis, secretion, and stimulate contraction of sphincters

intrensic regulation

enteric NS

GI Hormones secreted from stomach

gastrin: maintain structure of gastric mucosa

GI hormone secreted by ileum and colon

GLP-1: secrete insulin from pancreatic islets

Guanylin: Secrete Cl-

saliva

contain amylase to start digestion of startch and proteins - mucin, lysozyme, defensin, IgA

autonomous NS

control salivary glands

parasympathetic stimulation

produces watery saliva

sympathetic stimulation

produce viscous saliva

deglutition

oral, pharyngeal, esophogeal

oral deglutition

voluntary

pharyngeal deglutition

involuntary; uvula and epiglottis

esophageal deglutition

autonomic

upper esphogus

lined with skeletal muscle; innervated by somatic motor neurons

lower esophagus

lined with smooth muscle; controled by autonomic NS

esophageal

stays closed to prevents regurgitation, and opens for food

stomach functions

begins protein digestion, kills bacteria (HCL), chyme

stomach structure

(Many People Can Eat Good Dinners)

mucus neck cells, parietal cells, cheif cells, estrochromaffin cells (ECL), G cells, D cells

Mucus neck cells

mucus

parietal cells

Gastric acid (HCL) + intrinsic factor

cheif cells

pepsinogen - digests proteins

ECL cells

histamine, serotonin

G cells

gastrin

D cells

somatostatin

stomach lining

thick bicarbonate rich mucus on stomach wall

HCl secretion

stimulated via second messenger by Ach, histamines, gastrin; drops pH to 2 - optimal for pepsin; salivary amylase not active at pH 2

HCl

primarly active transport of H+ via H+/K+ATPase pumps

small intestine

from pyloric sphincter to ileocecal valve

subdivisions of small intestine

duodenum: 1st 10in

jejunum: middle 2/5

ileum: last 3/5

hepatopancreatic ampulla

where the bile and main pancreatic ducts join

increases surface area

villi, microvilli, Plicae circulation

small intestine digests

carbohydrates from mouth and proteins from stomach, and fats

absorption of nutrients in small intestin

very rapid due to villi and microvilli

brush boarder enzymes

intestinal enzymes: disacchorides, peptidase, phosphase; breakdown disacchorides

disacchorides

sucrase, maltase, lactase

peptidase

aminopeptidase, enterokinase

phosphatase

Ca2+, Mg2+-ATPase, Alkaline phosphatase

pepsin

produces short chain polypeptides

final produts of absorption

amino acids, dipeptides, tripeptides, free amino acids

endopeptides

pepsin in stomach, trypsin, chymotrypsin in small intestine

exopeptides

digests terminal peptide bonds releasing amino acids

monosacchorides absorbed across epithelium by….

scondary active transport with sodium and diffusion through GLUT/SGLT

regions of large intestins

ileum, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, renal, anal canal, anus

function of large intestin

move fecal matter towards anus: produce vit-k and vit-B

microflora

intestinal microbiota

commensal

bacteria benefit human doesnt not harm

mutualistic

both human and bacteria benefit

benefits of microbes

healthy epithelial barrier, limit inflamation, repair damaged epithelium

cellulolytic bacteria

bacillus, pseudomonas, Streptomyces, clostridium

fluid absortion

~200ml left/day to be excreted with feces

total hepatic blood flow

~25% cardiac output to maintain hepatic clearance

enterohepatic circulation

bile absorbed again in small intestin and returned to liver

compounds excreted by liver into bile

detoxication of blood, carbohydrate metabolism, lipid metabolism, protein synthesis, secretion of bile

cholesteral derivatives of bile salt

emulsify and facilitate fat, and cholesterol absorption

bile release

regulated by fatty chyme causing CCK release

bile salt and secretion in blood

stimulates liver to produce bile

gallbladder

sac-like organ attached to interior surface of liver; stores and concentrates bile from liver

Cholecystokinin

causes gallbladder to contract and hepatopacreatic sphincter to relax; suppress hunger

digestion of fats

lipids break down into fatty acids and glycerol

phospholipase A from pancrease

digest phospholipids into fatty acids

transport of lipids into blood

lymphatic system drops chylomicrons into blood stream

ApoE

allows chylomicros to bind to receptors

digested lipoprotein

release free fatty acids

chylomicrons

from intestins that goes to many organs

bilirubin

byproduct of hemoglobin catabolism; not water soluble

bilirubin conjugated with glucuronic acids

makes it water soluble into bilirubin glucuronide

detoxifaction of blood

ammonia into urea

porphyrins into bilirubin

purins into uric acid

pancreatic juice that cleaves internal peptide bands

trysin, chymotrypsin, elastase

pancreatic juice that cleaves amino acids

carboxypeptidas

ghrelin

secreted by stomach when empty; stimulates hunger

polypeptide YY

reduce appetite

eptin

reduce hunger by inhibiting neuropeptide