The

1
The Digestive System of Man
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The Digestive System

• It is also known as the Alimentary Canal.
• Food undergoes four major processes
• Digestion
• Absorption
• Metabolism
• Assimilation

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The Lower Part of the Digestive System
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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.

5
Esophagus

• 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.
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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.

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Duodenum

• It receives
• Bile
• Its 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.

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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.

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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

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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.

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Absorption

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

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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.

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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.