Digestive System

• Mouth:Function:•Ingestion or intake of food occurs in the mouth

  •Begin digestion

  1. Mechanical Digestion

  -Teeth

  -Tongue

  2. Chemical Digestion

  -Salivary glands

  Structure:

  -Cavity in the centre of the face

  -Contains teeth

  -Tongue
• Teeth:Function:

  Mastication

  When food is crushed and mixed with saliva to form a bolus for swallowing

  Adults have 32 teeth. Each jaw has:

  -Four incisors for biting or cutting

  -Two canines for tearing

  -Four premolars for crushing and grinding

  --Six molars for crushing and grinding
• Salivary Glands:•Salivation is an overt reflex prompted by taste and mastication

  •The salivary glands (the parotid gland- largest, submandibular gland and sublingual gland)

  -This moistens food

  -Also releases salivary amylase to begin the breakdown of carbohydrates

  •Chemical digestion
• Swallowing:-After chewing, food is formed into a ball called a bolus.

  -The tongue pushes bolus into the back of the mouth, the pharynx

  -This triggers an involuntary response to swallow
• The Alimentary Canal:A continuous tube from mouth to anus comprising organs for digestion and absorption.
• Peristalsis:To move food, successive bands of circular muscle contract. This constriction creates a wave like movement and pushes food in front of it
• •SPHINCTER:Muscles that control the movement of digesting food from one organ to another
• Esophagus:connects pharynx to stomach

  -Structure: double layer of muscle -circular and longitudingal

  -Mucus secreting cells: assist passage of food

  -Food moves because of gravity and peristalsis
• Stomach Structure:Function:

  •The cardiac sphincter controls the entry of food from the oesophagus into the stomach

  -food storage,

  -digestion

  mechanical through churning

  • chemical through enzymes (protease - proteins)

  -regulation of delivery to the small intestine

  Structure:

  Stomach has three layers of muscles which allows contraction in a variety of ways to churn the food which allows mechanical digestion and mixing of the food with the stomach juices
• Stomach Wall Structure:-the lining of the stomach, the mucosa is specialized for secretion of gastric juice

  -gastric juice is secreted by gastric glands which are found in narrow tube-like structures called gastric pits
• Mucous/Goblet cells:secrete mucus which is thick and has bicarbonate rich that protects stomach lining from acid
• Parietal cells:secrete hydrochloric acid (HCl): produces a pH of about 2 that activates gastric protease (pepsinogen) and also kills many bacteria
• Chief cells:-secrete pepsinogen (or gastric protease). Inactive form of enzyme