Mammalian Digestive System

Overview

• The mammalian digestive system is essential for nutrient absorption and acquiring energy, vital for maintaining homeostasis and proper bodily function.

Structure and Function

• Mouth: Initiates digestion by chewing and mixing food with saliva.
• Oesophagus: Moves food to the stomach through peristalsis.
• Stomach: Breaks down food both mechanically and chemically into chyme.
• Small Intestine: Primary location for nutrient absorption via villi.
• Large Intestine: Reabsorbs water and compacts waste material.
• Anus: Eliminates waste from the body.

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Physical Digestion

Introduction

• Physical digestion involves breaking food into smaller pieces to increase surface area, thus facilitating enzyme access.

Mastication and Teeth Roles

• Mastication: The process of chewing, essential for preparing food for swallowing and digestion. Teeth are adapted for cutting, tearing, and grinding.

Type	Function
Incisors	Cutting
Canines	Tearing
Premolars	Grinding
Molars	Crushing

Oesophageal and Intestinal Peristalsis

• Oesophagus: Utilises involuntary muscle contractions to guide food to the stomach.

• Stomach Churning: Combines food with gastric juices, beginning the digestion process.

• Intestinal Peristalsis: Facilitates nutrient and water absorption within the intestines.

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Chemical Digestion

Overview

• Chemical digestion entails the enzymatic breakdown of food into molecules that can be absorbed as nutrients.

Key Enzymes

• Salivary Amylase: Initiates the breakdown of starch in the mouth.

• Pepsin: Converts proteins into peptides in the stomach under acidic conditions.

• Pancreatic Enzymes: Include trypsin, chymotrypsin, lipase, and amylase, which digest proteins, fats, and carbohydrates in the small intestine.

Conditions Affecting Enzyme Function

• pH Levels: Optimal enzyme function varies, being neutral in the mouth, acidic in the stomach, and alkaline in the intestine.

• Temperature: Most efficient at 37°C; deviations can impair enzyme activity.

Gastric and Pancreatic Juices

• Gastric Juice: Comprises HCl and pepsinogen, creating an acidic environment for digestion.

• Pancreatic Juice: Neutralises chyme and comprises enzymes released via secretin.

Role of Bile

• Bile: Breaks down fats to improve efficient lipase action.

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Absorption

Small Intestine

• Villi and Microvilli: 30-fold increase in surface area, enhancing nutrient absorption.

Mechanisms

• Diffusion: Nutrients move from areas of higher to lower concentration.
• Active Transport: Uses ATP to transport nutrients against concentration gradients.
• Facilitated Diffusion: Facilitates passage of larger molecules through protein channels.

Structural Adaptations

• Villi Damage: Conditions such as coeliac disease impair absorption, necessitating dietary modifications.

Nutrient Transport

• Circulatory and Lymphatic Systems: Distribute absorbed nutrients, ensuring equilibrium in the body.

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Elimination of Solid Waste

Large Intestine

• Role: Reabsorbs water to form and eliminate faeces from the body.

Components and Processes

• Components of Faeces: Include water, bacteria, fibre, and additional waste products.

• Gut Flora: Contributes to vitamin synthesis and aids in digestion.

• Peristalsis: Efficiently moves waste through the digestive tract.

• Defecation Reflex: Initiated by neural signals, coordinating muscle contractions to expel waste.

Lifestyle Influences

• Diet, Hydration, Exercise: Significantly affect stool consistency and digestive wellness.