Digestive Exam

4 tunics of the GI tract

1. mucosa

2. submucosa

3. muscularis externa

4. serosa

mucosa

innermost layer

protects against acid, enzymes, bacteria, friction

secretion and absorption

submucosa

contains blood vessels, lymp0h vessel, nerves

supplies surrounding tissues

muscularis externa

responsible for movement

creates segmentation and peristalsis

serosa

outermsot covering

protects organs and reduces friction

2 types of control of digestion

1. intrinsic \

2. extrinsic

intrinsic control

enteric nervous system controls digestive activity locally

contains submucosal and myenteric nerve plexuses

extrinsic control

brain and autonomic nervous system influence digestion thru vagus nerve

can the enteric nervous system function without external control

yes

gut brain

what helps trigger digestive activity

mechanical stimuli (strecthing)

chemical stimuli (food chemicals)

gastrin effect

increases stomach acid secretion

acetylcholine (ACh) effect

stimulates gastric secretion

histamine effect

helps stimulate HCl secretion

CCK effect

stimulates gallbladder contraction and pancreatic enzyme release

secretin effect

stimulates pancreatic bicarbonate release

bloodflow thru digestive organs

digestive organs

hepatic portal vein

liver

hepatic veins

inferior vena cava

heart

esophagus difference from other organs

mucosa protects against friction

stomach difference from other organs

has 3 muscle layers

extra oblque layer for churning

small intestine difference from other organs

villi and microvilli increase absorption

large intestine different from other organs

many goblet cells produce mucus

no villi

mucous neck cells

produce mucus

parietal cells

produce HCl and intrinsic factor

chief cells

produce pepsinogen

G cell

produce gastrin

mucosal barrier

mucus protects stomach lining from acid and enzymes

stomach lining must protect itself from HCl and pepsin it produces

important structures of SI

villi

muicrovilli

lacteals

intestinal crypts

peyers patches

duodenum

recieves chyme, bile, and pancreatic secetions

acid is neutralized

jejunum

most active area for digestion and nutrient absorption

ileum

absorbs B12 and contains peyers patches

functions of large intestine

1. absorbs H2O and electrolyes

2. absorbs vit B/K

3. forms and stores feces

4. moves feces to rectum

internal anal sphincter

smooth muscle

involuntary

external anal sphincter

skeletal muscle

voluntary

liver

produces bile

processes nutrients

stores fat soluable vitamins

detoxifies blood

gallbladder

stores/concentrates bile

release bile into duodenum

pancreas

produces digestive enzymes/bicarbonate

acinar cells, ,duct cells, pancreatic islets

functions of digestive system

1. breaks down food

2. absorbs nutrients and water

3. provides nutrients for energy and cell funcction

4. eliminates waste

digestive processes

1. ingestion

2. mechanical breakdown

3. propulsion

4. digestion

5. absorption

6. defecation

ingestion

taking food into the mouth

mechanical breakdown

physically breaking food apart

propulsion

moving food thru the tract

digestion

chemically breaking food down

absorption

moving nutrientrs into blood or lymph

defecation

eliminating waste

why is the GI tract lumen considered external to body

• food inside GI tract does not enter internal body

• nutrients must pass thru digestivce lining to enter body or lymph

• GI tract is not sterile and contains bacteria

• one continuous tube from mouth to anus

  • mucosa protects body from bacteria, acid, enzymes, and machanical stress h

how is digestion controlled

nervous system via intrinsic and extrinsic

intrinsic control

controlled by enteric nervous sytem

gut brain

contains submucosal and myenteric nerve plesuses

can function without external control

extrinsic control

controlled by brain and autonomic nervous system

includes vagus nerve

stimulate or inhibit digestion

digestive process for mouth to esophagus

saliva

enzymes

swallowing

saliva

• 1.5 L produced daily

• mostly H2O, slightly acidic

• contains enzymes, mucus, antibacterial substances

• cleans mouth

• dissolves chemicals for taste

• BEGINS CHEMICAL DIGESTION

enzymes in mouth

salivary amylase - begins starch digestion

small amount of lipase - begins fat digestion

phases of swallowing

buccal phase : voluntary

pharyngeal phase: inviluntary

esophageal phase: involuntary, peristalsis moves food toward the stomach

digestive processes of the stomach

1. gastric gland cells

2. protein digestion

3. HCl production and alkaline tide

gastric gland cells - digestive proceses of stomach

• mucus neck cells

• parietal cells

• cheif cells

• G cells

protein digestion - digestive processes of stomach

pepsinogen converted to pepsin

pepsin breaks proteins into smalled polypepties

infants produce renin which helps digest milk proteins

HCl production and alkaline tide - digestive processes of stomacj

pariteal cells produce HCl

1. H+ ions pumped into stomach

2. Cl- ions enter stomawch

3. H+ and Cl- combine

4. bicarbonate enters bloodstream

5. bicarb causes alkaline tide

why is the alkaline tide important

stomach releases acid into GI tract

pancreas releases bicarb into duodenum

bicarb neutralizes acidic chyme

protects SI and allows pancreatic enzymes to work

phases of gastric secretion

1. cephalic

2. gastric

3. intestinal

cephalic phase

trigger/what happens

seeing, smelling, or thinking of food

vagus nerve stimulates gastic secretions

gastric phase

trigger/what happens

food enters stomach

most gastric juice is produced

intestinal phase

trigger/what happens

chyme enters SI

stomach activity slows down

enterogastric reflex

protective reflex when acdic, fatty chyme enters duodenum

1. SI detects chyme

2. reflex is activated

3. stomach contractions decrease

4. pyloric sphincter tightens

5. less chyme enters SI

purpose of enterogastric reflex

gives SI time to dilute and neurtralize chyme before more enters

SI role in digestion

motility - segmentation/peristalsis

segmentation

• mixes chyme

• mixes digestive enzymes into food

• increases contact w intestinal wall

• helps digestion and absorption

peristalsis

moves chyme thru digestive tract

pushes material from one area to another

liver and gallbladder role in digestion

bile

hormonal regulation

bile role in digestion

• produced by liver

• stored/concentrated in gallbladder

• released into duodenum

• emulsifies fats by breaking large fat globules into smaller droplets

• increases SA for pancreatic lipase

bile composition

1. bile salts

2. cholesterol

3. phospholipids

4. billirubin

hormonal regulation of digestion

CCK

• causes gallbladder contraction and stimulates pancreatic enzyme secretion

secretin

• stimulates bicarb release and bile production

liver dieases

hepatitis

cirrhosis

non alcoholic fatty liver diease

hepatitis

inflammation of liver

types of hepatitis

A/E - transmitted enterically

B/C/D - transmitted thru blood

cirrohosis

progessive liver damage and scarring

non alcoholic fatty liver disease

fat accumulation in liver

associated with obesity and insulin resistance

blood flow through liver

1. hepatic portal vein - brings nutrient rich blood from digestive organs

2. hepatic artery - brings O2 rich blood

3. hepatic veins - carry blood away from liver to inferior vena cava

hepatic portal circulation

1. SI

2. hepatic portal vein

3. liver

4. hepatic veins

5. inferior vena cava

6. heart

main purpose of hepatic portal circulation

nurteients absorbed from digestive tract go to liver first so they can be processed before entering circualting

filters and cleans blood of bad things