Digestive System By Hassan Imran

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Title

• حوالله الرحمن الرحيم

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Course Information

• Course Name: Physiology

• Course Code:

• Teacher Introduction:

  • Name: Hassan Imran

  • Qualification: M.Phil. Pharmacology

  • Position: Lecturer, UIMLT

  • Faculty: Faculty of Allied Health Sciences (FAHS)

  • Institution: The University of Lahore

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Digestive System Overview

• Learning Objectives:

  • Process of digestion

  • Organs of the digestive system

  • Functions of each organ in digestion

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Parts of the Digestive System

• Mouth

• Esophagus

• Stomach

• Small Intestine

• Pancreas

• Liver

• Gallbladder

• Large Intestine

• Rectum

• Anus

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Digestion Definition

• Process involves mechanical and chemical breakdown of large food molecules into simpler monomers for absorption and transport to cells.

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Mechanical Digestion

• No chemical change; food is broken into smaller pieces and mixed with digestive juices

• Types of digestion:

  • Mastication (chewing)

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Chemical Digestion

• Chemical change; polymers broken into monomers via hydrolysis reactions by enzymes in digestive juices.

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Six Processes of Digestion

1. Ingestion: Food intake

2. Propulsion: Moving food through the digestive system

3. Mechanical Digestion:

   • Mixing in the mouth

   • Churning in stomach

   • Segmentation in small intestine

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Continued Processes of Digestion

4. Chemical Digestion: Enzymes break down food

   • Carbohydrates to simple sugars (Amylase)

   • Proteins to amino acids (proteases)

   • Fats to fatty acids and glycerols (lipases)

5. Absorption: End products absorbed into the blood

6. Defecation: Elimination as feces

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Mouth

• First portion of the alimentary canal; receives food and secretes saliva.

• Formed by cheeks, lips, tongue, teeth, and palate.

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Oral Cavity Functions

• Ingestion

• Mastication

• Mixing food with saliva

• Initiation of swallowing

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Bolus Formation

• Chewed food mixed with saliva called bolus.

• Saliva: aids chemical reduction and lubricates for swallowing.

• Transitions to chyme in the stomach.

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Saliva Production

• Triggered by brain messages; pH of saliva: 7.4 (neutral).

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Composition of Saliva

• Contains:

  • Enzymes: Amylase (starch) and Lipase (fats)

  • Mucus (lubrication)

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Major Salivary Glands

• Parotid Glands

• Submandibular Glands

• Sublingual Glands

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Esophagus

• Connects throat to stomach; muscular tube lined with mucous membrane.

• Receives food via peristalsis.

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Esophagus Functions

• Located behind trachea, uses waves of contraction to move food.

• Gastro-esophageal junction: end of esophagus connected to stomach.

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Peristalsis

• Involuntary reflex action propelling contents along the esophagus.

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Peristalsis Mechanics

• Circular muscles contract to push food bolus down.

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Stomach Anatomy

• Pear-shaped organ linking esophagus to small intestine; major digestion area.

• 4-5 hours transit time; pH: 2-6.

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Stomach Functions

• Temporary food storage, mixing with gastric secretions to form chyme, digestion, and controlled entry to duodenum.

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Gastric Secretions Overview

• Stimulated by hormones and food presence.

• Mucus for protection.

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Parietal Cells and Gastrin

• Produce hydrochloric acid; gastrin stimulates acid and enzyme release.

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Mechanism of Gastric Acid Secretion

• Stimulators include Acetylcholine, Histamine, and Gastrin.

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Digestive Enzymes in Stomach

• Pepsin for proteins, gastric amylase for carbohydrates, gastric lipase for lipids.

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Absorption in Stomach

• Limited to water, alcohol, and some drugs.

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Cells in Gastric Glands

• Mucus neck, chief, parietal, and G-cells with specific secretory functions.

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Small Intestine

• Major site for nutrient absorption; sections include duodenum, jejunum, ileum.

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Duodenum Function

• Neutralizes gastric contents; further digestion initiation.

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Villi in Small Intestine

• Increase surface area for nutrient absorption; over 95% absorption for carbs/proteins.

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Pancreas Function

• Exocrine (digestive juices) and endocrine (insulin, glucagon) roles.

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Digestive Enzymes from Pancreas

• Enzymes for protein (Trypsin, Chymotrypsin), carbohydrates (Pancreatic amylase), fats (Pancreatic lipase).

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Liver Functions

• Processes nutrients, detoxifies chemicals, and metabolizes drugs.

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Bile Production

• Produced by hepatocytes, secreted into bile ducts for fat digestion.

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Gallbladder Role

• Stores and concentrates bile for digestion.

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Large Intestine Overview

• Absorbs water and vitamins; converts digested food into feces.

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Absorption Processes in Large Intestine

• Removes water; semi-solid feces passed to rectum.

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Bacterial Fermentation in Large Intestine

• Converts chyme to feces and produces vitamins K, B1, B2, B6, B12.

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Rectum and Anus

• Rectum stores feces, expelling through the anus.

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Defecation Process

• Stool moves through colon to rectum; sphincter muscles facilitate passage.

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References

• Guyton and Hall Textbook of Medical Physiology 13th edition

• Basic and Clinical Pharmacology 12th Edition

• Essentials of Medical Pharmacology 6th edition

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Closing

• Thank you.