Biology Chapter on Absorption in the Ileum

Hepatic Portal Vein and Nutrient Absorption

• Hepatic portal vein transports absorbed nutrients from the digestive tract to the liver.
• Fatty acids, glycerol, cholesterol, and fat-soluble vitamins enter lacteals and are carried through the lymphatic system, eventually reaching the circulatory system via the subclavian vein.

Adaptations of the Ileum for Absorption

• The ileum is a long tube featuring numerous villi and microvilli, maximizing the surface area for nutrient absorption.
• The thin walls of villi facilitate rapid movement of substances.
• A rich network of blood capillaries in the villi transports soluble nutrients directly to the liver.
• Lymphatic capillaries in villi are responsible for removing fat.

Main Sections of the Large Intestine

• Caecum: Involved in absorbing water and salts.
• Appendix: Serves as a reservoir for beneficial bacteria.
• Colon: Absorbs additional water, salts, and some nutrients; prepares waste (stool) for elimination.
• Rectum: Stores faeces before elimination through peristalsis.
• Anus: Contains a sphincter muscle that controls fecal retention and expulsion.

Role of Symbiotic Bacteria

• Produce vitamins B and K, which are absorbed through the large intestine.
• Outcompete pathogenic bacteria, preventing their establishment in the intestine.

Importance of Dietary Fibre

• Fibre is indigestible material, mainly from plants; it can be soluble or insoluble.
• A high-fibre diet helps prevent constipation by retaining water, making faeces soft and easy to pass.

Functions of Saliva

• Moistens food and dissolves soluble components.
• Softens food to reduce injury risk to the oesophagus and stomach during swallowing.
• Acts as a lubricant for easier passage of the food bolus through the oesophagus.
• Contains amylase, initiating carbohydrate digestion.

Structure and Function of the Oesophagus

• Composed of smooth muscle, it transports food from the mouth to the stomach.
• Food movement is facilitated by peristalsis, a series of muscular contractions.

Anatomy and Functions of the Stomach

• The cardiac sphincter opens to allow food entry, then seals to keep food inside.
• Gastric pits secrete hydrochloric acid, which kills bacteria and activates pepsinogen to pepsin for protein digestion.
• Mucus produced in the stomach wall protects it from acid and enzymes, preventing ulcers.
• The pyloric sphincter regulates the entry of chyme into the duodenum.

Structure and Role of the Small Intestine

• Composed of three sections: duodenum, jejunum, and ileum; approximately six metres long.
• Folded structure increases surface area; exocrine glands secrete bile into the duodenum for fat emulsification.

Digestive Enzymes Overview

• Amylase: Breaks down starch into maltose in the mouth and small intestine, functions optimally at pH 7-10.
• Protease: Degrades proteins into polypeptides in the stomach and small intestine, active at pH 1-10.
• Bile Salts: Emulsify fats in the duodenum, with an optimal pH of 10.
• Lipase: Breaks down fats into fatty acids and glycerol in the small intestine, optimal at pH 10.

Absorption in the Ileum

• Primary site for the absorption of glucose, amino acids, water-soluble vitamins, and minerals.
• Nutrients absorbed via diffusion and active transport into blood capillaries.