chapter 24: Digestive system

digestive tract

gastrointestinal tract

muscular tube with different parts

accessory organs of the digestive system

teeth, tongue, salivary glands, liver, gallbladder, pancreas, gastrinal and intestinal glands

digestive system function

ingestion, mechanical processing, digestion, secretion, absorption, excretion

ingestion

put food into digestive system

mechanical processing

chewing and swallowing food

digestion

chemical breakdown of food

secretion

cells release h2o, salts, enzymes

absorption

bring stuff from inside tube into blood

nutrients, vitamins, ions

excretion

removes wastes

oral cavity

mouth; contains teeth and tongue

pharynx

throat; passageway for food to the esophagus and air to the larynx

esophagus

A muscular tube that connects the mouth to the stomach.

stomach

large muscular sac that continues the mechanical and chemical digestion of food

small intestine

Digestive organ where most chemical digestion and absorption of food takes place

duodenum, jejunum, ileum

large intestine

Absorbs water and forms feces

cecum, appendix, colons

cecum

the cavity in which the large intestine begins and into which the ileum opens

appendix

A small, fingerlike extension of the vertebrate cecum; contains a mass of white blood cells that contribute to immunity.

transverse colon

passes horizontally from right to left toward the spleen

decending colon

part of colon that progresses downward (caudally)

sigmoid colon

an S-shaped structure that continues from the descending colon above and joins with the rectum below

ascending colon

travels upward from the cecum to the undersurface of the liver

serosa

outermost layer of GI tract

muscularis externa

responsible for segmentation and peristalsis

layers of muscularis externa

inner circular layer and outer longitudinal layer

submucosa

larger CT area

larger blood vessels and nerves

mucosa

epithelium, lamina propria, muscularis mucosae

myentric nerve plexus

controls GI tract motility

segmentation

constricting the tube and dividing its contents

mixing

moving material back and forth slowly

further mixing

maximises nutrient absorbtion

mixing steps

1. segmentation

2. mixing

3. further mixing

peristalsis

coordinated wave of muscular contraction that propels material through the tube

oral cavity functions

sensory analysis, mechanical processing, lubrication, chemical digestion

buccal phase of swallowing

voluntary

tongue moves up, pushes food back, soft palate lifts up, materials enter oropharynx

pharyngeal phase of swallowing

involuntary

cranial nerves cause muscles of pharynx to contract

larynx elevates

epiglottis closes, blocks trachea

esophageal phase of swallowing

esophageal sphincter opens to allow bolus to enter stomach

bolus enters stomach

chemical digestion of food continues

esophigal sphincter

last part of esophagus before stomach

cardia

area around the opening of the esophagus

produces mucous to protect

fundus of stomach

The upper left portion of the stomach, which has a curved, dome-shaped appearance.

storage

body of stomach

mixing chamber

pylorus

controls food moving into the duodenum

stomach function

storage

mechanical/chemical breakdown

intrinsic factor (absorbs b12)

layers of muscularis externa of stomach

outer longitudinal, middle circular, inner oblique

stomach motility

moving material from stomach into duodenum

distention increasing motility

stretch of stomach

activate sensory receptors that activate parasympathetic

hormone increasing motility

gastrin (stomach/duodenum)

gastric secretors and contractions of muscularis externa

distention decreasing motility

enterogastric reflex

stomach slows down

hormones decreasing motility

secretin

gastroinhibitory peptide (GIP)

choleocytoskin (CCK)

from duodenum

gastrocentric reflex

controls movement of materials from stomach into small intestine

gastroileal reflex

controls movement of material from small to large intestine

haustrum

small pouches caused by sacculation, which give the colon its segmented appearance

haustral churning

mixing of material

produces feces

mass movements

large intestine into rectum

defecation

wastes leave the body and eliminates feces from the body

defacation reflex

stimulus: feces in rectum

response: perastalis in rectum

consequences of defection reflex

contractions (descending, sigmoid, rectum)

internal anal sphincters relax

external anal sphincters close

socially acceptable to defacate

anal sphincter relax

socially unnaceptable to defacate

reflex dies down until acceptable

chemical digestion proteins

proteins --> short polypeptides --> single amino acids

chemical digestion carbohydrates

carbs --> di/trisaccharides --> monosaccharides

chemical digestion fats

fats --> triglycerides --> glycerol/fatty acids

saliva

produces 1-2 L a day

h2o, SCH's, mucus, enzymes

lysosome

attacks bacteria

lingual lipase

digest fat

salivary amylase

digest carbs

digestion by saliva

- starch is broken down by salivary amylase into di and tri saccharides

regulation of salivary secretion

cranial nerves --> medulla oblognata --> parasympathetic

gastric juice

highly acidic (ph=2)

secretions from gastric glands

mucous cells

secrete mucus

located in gastric pits

parietal cells

cells of gastric gland

secrete HCL, intrinsic factor (B-12 absorption)

HCl dentures proteins

chief cells

cells of gastric gland

secrete pepsinogen (inactive)

g cells

pylorus

enterodnocrine cells

secretes gastrin

cephalic secretion

increases parasympathetic and digestive function

gastric secretions

neural, hormonal, local

food enters stomach

neural gastric secretion

stretch and chemoreceptors

hormonal gastric secretion

secretes gastrin

local gastric phase

lamina propria release histamine

intestinal secretions

food enters small intestine

neural, hormonal

neural intestinal phase

estrogastric reflex

hormonal intestinal phase

CCK

GIP

Secretin

hepatocytes

produce bile in the liver

bile

emulsifies fats

h2o, ions, bilirubin, bile salts

release of bile

goes through ducts to gall bladder

gall bladder to duodenum

gall bladder

stores and concentrates bile

chyme

acidic soupy mixture from stomach

gall bladder regulation

chyme stimulates cck (concentration of bile)

opens hepadipancreatic sphincter

pancreas

Regulates the level of sugar in the blood

exocrine and endocrine

endocrine pancreas

regulates blood glucose

exocrine pancreas

secretes digestive enzymes

pancreatic juice

water, bicarbonate/phosphate buffers, enzymes

pancreatic alpha-amylase

breaks down starches to di and trisaccharides

pancreatic lipase

breaks down triglycerides to fatty acids and glycerols

nucleases

break down nucleic acids

proleolytic enzymes

break down proteins

inactive proenzymes

proteolytic enzymes secreted

Trypsinogen active enyme

trypsin

What converts trypsinogen to trypsin?

enteropeptidase

trypsin function

activate other enzymes

Chymotrypsinogen active form

chymotrypsin