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
Ingestion: Food intake
Propulsion: Moving food through the digestive system
Mechanical Digestion:
Mixing in the mouth
Churning in stomach
Segmentation in small intestine
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Continued Processes of Digestion
Chemical Digestion: Enzymes break down food
Carbohydrates to simple sugars (Amylase)
Proteins to amino acids (proteases)
Fats to fatty acids and glycerols (lipases)
Absorption: End products absorbed into the blood
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.