GIT (Anatomy and Phys)

Mouth

• Mechanical digestion

• Chemical digestion

Mechanical Digestion in Mouth

mixing of food, chewing, mastication

Chemical Digestion in Mouth

partial digestion of CHO due to salavary amylase present in mouth

Esophagus

• upper esophageal sphincter

• lower esophageal sphincter

Upper Esophageal Sphincter

promotes entrance of food from pharynx to esophagus

Lower Esophageal Sphincter

opens to allow entrance of food from esophagus to the stomach

Important: LES

once the food enters the stomach, it must close competently (if it does not, Barrett’s Esophagus may occur)

Barrett’s Esophagus

condition in which the pink lining of the esophagus thickens and becomes red due to acid reflux

Stomach Divisions

• cardia (upper part)

• fundus (body)

• pylorus (lower part)

Stomach Layers (Superficial to Deep)

• Mucosa

• Muscularis

• Submucosa (blood vessels)

• Muscle Layer

• Subserosa

• Serosa

What does seeing blood in feces indicate?

There is bleeding due to erosion or ulceration in the deeper layers of the stomach (until the subserosa)

Stomach Main Function

Food Storage (up to 2-3L)

Other Stomach Functions

• Mechanical digestion

• Chemical digestion

• Intrinsic Factor

Mechanical Digestion of Stomach

further breakdown of food

Chemical Digestion in Stomach

• secretion of gastric juices (HCl)

• secretion of pepsinogen (breakdown CHON)

• has lipase (breaks down fats)

• contains bicarbonate-rich mucous (alkaline) that prevents self-digestion

Intrinsic Factor

aids in absorbing B12 (lack may lead to pernicious anemia)

Small Intestine Parts

• duodenum

• jejunum

• ileum

Small Intestine Function

site of final digestion and nutrient absorption

Digestion in Small Intestine

secretion of intestinal juices (assisted by bile production - bile and intestinal juices emulsify fats)

Enterohepatic Circulation

Liver - Common hepatic duct - cystic duct - gallbladder - common bile duct - sphincter of Odi - Small intestine

Pancreas Function

release of pancreatic enzymes into the small intestine (duodenum)

Pancreatic Enzymes of the Pancreas

• amylase

• lipase

• trypsin

Small Intestine Characteristic

Absorbs nutrients via villi and microvilli into the liver via the hepatic portal vein (second half of enterohepatic circulation)

Large Intestine Parts

• cecum

• ascending colon

• transverse colon

• descending colon

• sigmoid colon

• rectum

Large Intestine Function:

water and electrolyte absorption, elimination of stool/feces

Why does the large intestine have more mucous than the small?

necessary for feces elimination

Stool Characteristics depending on location in Large Intestine

• watery (cecum-ascending)

• semi-solid, mushy, loose (transverse)

• formed stool (descending)

Liver Characteristics

• largest internal organ

• weighs 1,200-1,500g

Functional Unit of Liver: lobule

Blood vessels of the Liver

• Hepatic Portal Vein (nutrient-rich blood from small intestine)

• Hepatic Artery (oxygenated blood)

• Hepatic Vein (deoxygenated blood)

Functions of the Liver

1. Glucose metabolism

2. protein (CHON) metabolism

3. fat metabolism

4. Storage

5. detoxification

6. converting ammonia into urea

7. phagocytosis

8. blood reservoir

9. bilirubin excretion

Glucose Metabolism

• glycogenesis

• lipogenesis

• glycogenolysis

Glycogenesis

breakdown of glucose into glycogen (stored form of glucose)

Lipogenesis

production of fats from carbohydrates (CHO)

Glycogenolysis

breakdown of glycogen into glucose (for hypoglycemia)

Protein (CHON) Metabolism

Synthesis of:

1. plasma CHON

2. clotting factors

3. gluconeogenesis

Plasma CHON Synthesis

• albumin (for osmotic pressure)

• alpha and beta globulins (antibodies)

Clotting Factor Synthesis

• fibrinogen

• prothrombin

Gluconeogenesis

the conversion of CHON (protein) into glucose

Fat Metabolism

• metabolism of triglycerides into fatty acids

• bile synthesis

Bile Synthesis

600 - 1,200mL, yellow-green in color

Function of Bile

• excretion of bilirubin

• emulsification of fats, cholesterol, and fat-soluble vitamins

Bile Composition

water and electrolytes (Na, K, Ca, Chloride, bicarbonate), lecithin, bilirubin, cholesterol, fatty acids, bile salts

Function of Liver: Storage

• CHO, CHON, fats, and fat-soluble vitamins (ADEK)

• water-soluble vitamins

• minerals (iron, copper, magnesium)

Function of Liver: Detoxification

• drugs

• steroid hormones

Function of Liver: converting ammonia to urea

ammonia produced by breakdown of amino acids (proteins)

Function of Liver: Phagocytosis

Kupffer Cells

Kupffer Cells

line the sinusoids of the liver and break down red blood cells

Function of Liver: blood reservoir

can hold 200-400 mL of blood

Pancreas endocrine function

releases hormones directly into the bloodstream

Pancreas exocrine function

enzymes (stimulated by food)

Gallbladder Function

storage and concentration of bile

What happens if bile is kept too long in the gallbladder?

bile becomes concentrated until it turns to stones

When is bile released?

when food is eaten

Process of Ingestion

the process of taking in food through the mouth

Process of Digestion

mechanical and chemical break down of food into small organic fragments

Process of Elimination

elimination of undigested food content and waste products