The Digestive System of 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

Mouth There 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 Peristalsis: It is a mucus muscular membrane lined tube. There occurs a process known as Peristalsis. Peristalsis: It is an involuntary process of muscular contraction forcing the bolus (food) down to the stomach.

Stomach It 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.

Duodenum It 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.

Ileum Its walls secretes intestinal juices which contain enzymes 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.

Liver Roles: 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

Pancreas It is an endocrine gland because it secretes Insulin hormone - converts excess glucose 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.

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

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.

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.