The Digestive Systemof Man

The Digestive System

It is also known as the Alimentary Canal.

Food undergoes four major processes:• Digestion• Absorption • Metabolism• Assimilation

The Lower Part of the Digestive System

MouthThere two major processes which take place:

• Mastication (Chewing): - Breaks down large food molecules. - Increases surface area of food particles. • Secretion of Saliva: - Contains salivary amylase (ptyalin) that digests starch to maltose. - Provides an alkaline medium. - Lubricants and moistens food.

Esophagus• It is a mucus muscular membrane lined tube.• There occurs a process known as Peristalsis.

Peristalsis:It is an involuntary processof muscular contractionforcing the bolus (food) down to the stomach.

StomachIt secretes two substances:• Gastric juice: It contains 2 enzymes namely; - Pepsin for digestion of proteins to peptides. - Rennin for solidifying milk protein in young.

• Hydrochloric acid: - Kills bacteria in food. - Provides an acidic media - Stimulates stomach walls to secrete more gastric juice.

DuodenumIt receives:• Bile: It’s a non-enzymatic green fluid - Breaks down fats into tiny droplets. - Provide alkaline media.

• Pancreatic juice: - Pancreatic amylase for digestion of starch. - Lipase for digestion of fats. - Trypsin for digestion of proteins.

Its walls secretes intestinal juices which containenzymes to complete digestion:• Sucrase for digestion of sucrose to glucose and fructose.• Lactase for digestion of lactose to glucose and galactose.• Maltase for digestion of maltose to glucose molecules.• Erepsin for digestion of peptides & polypeptides to amino acids.• Lipase for digestion of lipids to fatty acids & glycerol.

Ileum

Liver• It is the largest organ in the mammalian body.• It secretes bile which is stored in the gall bladder. Bile breaks down fats into tiny droplets through emulsification.

Roles:• Regulates sugar/glucose.• Breaks down excess RBC.• Storage of blood.• Detoxification.• Generation of heat

• It is an endocrine gland because it secretes Insulinhormone - converts excessglucose into glycogen for storage.

• It is also an exocrine gland because it secretes pancreatic juice in the duodenum - pancreatic juice contains lipase, trypsin and pancreatic amylase for digestion of lipids, proteins and starch.

Pancreas

Absorption

• It occurs within the ileum in finger-like projection known as Villi.

• Amino acids and simple sugars like glucose, fructose diffuse through thin Epithelial cells into the blood capillaries.

• Fatty acids and glycerol enter the Lacteal into the lymphatic system then finally into the blood system through the Innominate vein.

Villi

Adaptations of Ileum• It is very long and wound to increase surface area.• It has millions of villi for food absorption.• Numerous blood capillaries for carrying of amino acids and simple sugars.• Lacteal for fatty acids and glycerol absorption.• Thin epithelial cells through which soluble foods easily diffuse.• Goblet cells secrete mucus which prevents enzymes from digesting ileum walls.