BIOL 472 GI System

Alimentary Canal

Main GI tube that runs through the body

Mouth

Where food enters the body and is broken down via mastication

Pharynx

Located in the throat and connects the mouth to the esophagus

Esophagus

1. Connects the pharynx to the stomach

2. Moves food via peristaltic wave

3. Located in the chest behind the wind pipe

Stomach

1. Chemically digests food with acid and enzymes

2. Absorbs water, alcohol and acid

3. Located in the upper left abdomen

4. Empties into Small Intestine

Small Intestine

1. Longest portion of the canal

2. Digests chemically with enzymes from pancreas

3. Emulsifies fats with bile from liver

4. Produces hormones

5. Absorbs nutrients

Large Intestine

1. Absorbs water and electrolytes

2. Produce vitamin K and B

3. Moves fecal matter to the rectum

Rectum

1. Temporary storage for feces

2. Triggers urge for bowel movements

Tunica Mucosa

1. Innermost layer

2. Three sub layers

Epithelium Lining

1. Absorption, protection, secretion in the alimentary canal

2. Mucous production

Lamina Propria

1. Connective tissue

2. Connects epithelium to muscularis

3. Contains capillaries and lymphatics

4. Immune protection

Muscularis Mucosa

1. Two layers of smooth muscle

2. Local GI movement

Tunica Submucosa

1. Second innermost layer of the alimentary canal

2. Dense connective tissue

3. Lots of blood vessels

Tunica Muscularis

1. Third layer of the alimentary canal

2. Smooth muscle except in esophagus

3. Two layers. Three in stomach

4. Mechanical digestion

5. Propulsion

Tunica Serosa

1. Outermost layer of the Alimentary Canal

2. Produces fluid to allow for smooth movement

Histological characteristics of the esophagus

1. Contains both smooth and skeletal muscle cells

2. Mucosa cells lubricate pathway

3. Built for propulsion of the bolus

Histological characteristics of the stomach

1. Contains many pits and glands to secrete acids and enzymes

2. Has an extra layer of the tunica muscularis

3. Built for chemical and mechanical digestion

Histological characteristics of the small intestine

1. Contains many glands for secretion of enzymes

2. Contains villi which increase surface area

3. Build for absorption and digestion

Histological characteristics of the large intestine

1. Many goblet cells

2. Built for fecal transport and water intake

Locations of fluid secretion

1. Saliva (1500)

2. Stomach (2000)

3. Bile (500)

4. Pancreas (1500)

5. SI (1500)

Locations of fluid reabsorption

SI (8500)

LI (350)

Amount of fluid excreted

150 mL

Minimum excretion amount

600 mosmol/day

Maximum urine concentration

1200 mosmol/L

Why is it bad to drink salt water?

Salt water has a concentration of 2400 mosmol/L. However the maximum urine concentration is 1200 mosmol/L. This means that for every liter of salt water you drink. You urinate twice as much out.

Functions of the Liver

1. Stores glycogen, releases glucose

2. Manufacturing of cholesterol

3. Synthesis of proteins such as albumins, fibrinogens, and prothrombin

4. Breakdown of old RBC hemoglobin into bilirubin by macrophages

5. Emulsification of fats

6. Chemically alters alcohol and drugs into excretable compounds

Hepatic Portal system

Deoxygenated, nutrient rich blood from the spleen, stomach, pancreas, and the intestines are all routed through the liver for processing and detoxification. From the liver, the blood travels down the hepatic vein to the inferior vena cava.

Cholesterol Homeostasis

1. Bile from the liver emulsifies fats and cholesterol

2. Fat broken down into FFA and monoglcerides

3. Converted to chylomicons in mucosal cells

4. Transported through lymphatic system and stored as fat

Low Density Lipoprotein

1. Bad cholesterol

2. Remains in circulation and causes blockages

3. Ideally <130mg/dL

4. At risk = >160 mg/dL

High density lipoprotein

1. Good cholesterol

2. Promotes fat storage

3. Ideally >45 mg/dL

4. At risk= <35 mg/dL

High Cholesterol Treatment

1. Low Fat Diet

2. Cholestyramine to excrete bile-fat complexes

3. Statins are very effective cholesterol medications

4. Ezetimibe Increases absorption of LDLs

Carbohydrate breakdown

1. Broken down by amylase from the pancreas

2. Absorbed into capillaries either with insulin or with Na+

3. Transported to liver by hepatic portal system

Protein breakdown

1. Broken down by stomach acid and pepsin in the stomach and trypsin from the pancreas

2. Absorbed into capillaries with Na+

3. Transported to liver by hepatic portal system

Fat breakdown

1. Emulsified by bile from the liver

2. Broken into FFAs and monoglycerides from the pancreas

3. Connected with apoproteins in mucosa cells to make Chylomicrons

4. Released into the lymphatic system to be stored as peripheral fat

Exocrine function of pancreas

1. Secretion of alkaline juice to neutralize stomach acid

2. Secretion of enzymes to digest nutrients

Endocrine function of pancreas

Regulation of blood sugar with the release of insulin and glucagon hormones

Short reflex innervation

1. Reflexes entirely within GI system

2. Chemical, hormonal, and tensional stimuli

3. Activates exocrine glands and smooth muscle

Short reflex example

Distension in the small intestine signals slower emptying of the stomach

Long reflex innervation

1. Connection between the CNS and GI system

2. Stimulated by Vagus nerve and serotonin

3. Inhibited by the splanchnic nerves

Long reflex innervation example

1. Filling of the stomach triggers bowel movements

Gastric pits

Exocrine glands in the stomach that contain specialized cells

Mucous Neck Cells

Mucous production in the stomach

Parietal Cells

1. Produces stomach acid (HCl)

2. Reverse chloride shift

   1. H2CO3 + Cl- → HCO3- + HCl

Chief Cells

1. Creates pepsinogen

2. Mixes with acid to form pepsin

3. Protein digestion

G Cells or APUD

1. Produces gastric

2. Increase acid secretion

3. Increase GI motility

Enterochromaffin Cells

1. Histamine production

2. Acid stimulant

D cells

1. Somatostatin production

2. Acid secretion inhibitor

Stomach Acid production

1. cAMP → protein kinase → HCO3- + Cl- exchange

2. Stimulated by histamines and ACH

3. Inhibited by PGE2

4. Proteins buffer acid stimulating stomach action

Acid production control

1. ACH antagoists (atropine)

2. Antihistamines (Zantac)

3. Omeprazole (H+ transfer block)

GIP

1. Opposite of gastrin

2. Decrease GI motility

3. Decrease acid production

CCK-PZ

1. Similar action to GIP

2. Also contraction gall bladder

3. Enzyme and bile secretion

Secretin

1. Releases bicarbonate from pancreas

2. Neutralizes stomach acid in intestines

Motilin

1. Peristaltic wave creator in esophagus

2. Empties stomach

VIP

1. Decreases smooth acid movement