Anatomy and Function of the GIT

Anatomical Consideration of GIT

• The gastrointestinal tract (GIT) is composed of Upper and Lower GIT organs, and accessory organs.
• Upper GIT organs include the esophagus, stomach and part of the duodenum.
• Lower GIT organs include the small intestine (duodenum, jejunum, ileum), large intestine (cecum, colon, rectum), and anus.
• Accessory organs include salivary glands, gallbladder, pancreas, and spleen.

Digestion in the Mouth

• Saliva is an isotonic fluid secreted by parotid, submandibular, and sublingual salivary glands.
• Daily saliva volume is approximately 1.5 liters.
• Saliva's pH is neutral to slightly alkaline (due to bicarbonate).
• Saliva's composition includes water, electrolytes, amylase, mucus, and antibodies.
• Saliva initiates carbohydrate digestion (by amylase).
• Saliva aids in swallowing and speech.
• Saliva provides defense against microbes.
• Saliva neutralizes acids produced by bacteria.

Stomach Function

• The stomach stores food for up to 4 hours and controls its release into the duodenum.
• It digests proteins and lipids using pepsin and gastric lipase enzymes respectively.
• It protects against bacteria by producing hydrochloric acid (HCl).
• It produces the intrinsic factor (IF) for vitamin B12 absorption.
• It plays a role in iron absorption by maintaining iron in the ferrous state.
• It absorbs small amounts of water, ions, alcohol, and certain drugs.
• It produces hormones such as gastrin, glucagon, and somatostatin.

Small Intestine Function

• The small intestine is responsible for digestion and absorption of nutrients from food.
• It absorbs about 80% of water, vitamins, minerals, carbohydrates, proteins, and lipids.
• It secretes digestive enzymes.
• Nutrients are absorbed into the bloodstream.

Role of Respiratory System in Acid-Base Balance

• The respiratory system participates in acid-base balance within seconds.
• It responds to changes in blood pH through chemoreceptors.
• Peripheral chemoreceptors are stimulated by low oxygen (Po2), high carbon dioxide (Pco2), and low pH.
• Central chemoreceptors are stimulated by high Pco2 and low pH.
• Stimulation of chemoreceptors leads to hyperventilation, removing excessive CO2, thus correcting low pH.
• Conversely, high pH decreases stimulation, leading to hypoventilation, raising CO2, and correcting high pH.

Functions of the Gastrointestinal Tract

• Ingestion of food and water
• Digestion of food to absorbable nutrients
• Absorption of nutrients, vitamins, minerals, water and electrolytes into the blood to supply the tissues
• Elimination of undigested materials in waste products.

Small Intestine Fluid Intake

• Approximately 9 liters of fluid enter the small intestine per day.
• This fluid comes from saliva (1.5L), stomach (2.5L), pancreas (1.5L), bile (0.5L), and intestinal secretions (1L).
• Almost all (99%) of this fluid is reabsorbed.

Digestion and Absorption

• Digestion breaks down complex proteins, fats, and carbohydrates.
• Absorption is the process whereby digested products, vitamins, minerals, and water cross the mucosa to enter the lymph or blood.

Liver and Biliary System

• The liver and biliary system play a vital role in secretion, metabolism, and detoxification processes.

Functions of the Liver

• Formation and secretion of bile.
• Metabolism processes like glycolysis and glycogenolysis.
• Protein synthesis like albumin.
• Storage of iron, glucose as glycogen, and vitamins.
• Detoxification of drugs, alcohol, and toxins.
• Removal of bacteria by macrophages.

Bile Composition and Formation

• Bile is alkaline and approximately 1.5 liters are produced per day
• Bile color arises from bile pigments from heme catabolism
• Bile components include water, electrolytes, bile salts, cholesterol, phospholipids, and phosphatase enzymes.

Pancreatic Enzymes

• Pancreatic enzymes include amylase for carbohydrate digestion, lipase and co-lipase for fat digestion, and proteolytic enzymes for protein digestion.

Colon and Defecation

• The colon is responsible for water absorption and feces formation.
• Defecation is the elimination of bowel contents as feces.
• Defecation involves a reflex involving stretching receptors in the rectum triggering the defecation reflex.
• Voluntary control is also possible.

Explore the anatomical structure and functions of the gastrointestinal tract, including the roles of upper and lower GIT organs as well as accessory organs. Also, learn about the digestion process in the mouth and the stomach's function in food storage and breakdown.