Digestion PDF - BIO10004 Week 10.1

Digestion Dr Greg Davis Martini Chapter 24 Copyright notice  Objectives 1. Identify the organs of the digestive system and list their major functions 2. Describe the anatomy of the abdominal regions 3. Describe the anatomy of the stomach and its blood supply rol...

Digestion Dr Greg Davis Martini Chapter 24 Copyright notice  Objectives 1. Identify the organs of the digestive system and list their major functions 2. Describe the anatomy of the abdominal regions 3. Describe the anatomy of the stomach and its blood supply role in digestion and absorption 4. Describe the anatomy of the small intestine and its blood supply and the accessory digestive organs  Six functions of the digestive system 1. Ingestion 2. Mechanical processing: crushing and shearing 3. Chemical breakdown of food (or digestion) 4. Secretion of water, acids, enzymes, buffers, and salts 5. Absorption of organic substrates, electrolytes, vitamins & water 6. Excretion: removal of waste products Components Structure Peristalsis Views of oral cavity  Swallowing Also called deglutition Can be initiated voluntarily Proceeds automatically Is divided in 3 phases: – buccal phase – pharyngeal phase – esophageal phase Swallowing  Sections Oral cavity Pharynx Oesophagus (esophagus) Stomach The stomach  The stomach This is an important organ First stage of processing and breakdown of food Also stores food The food in the stomach is known as chyme Folded structure that can expand Allows greater surface area Contains acid secreting cells Structure of stomach wall Cephalic phase Gastric phase Intestinal phase Small intestine  The Small Intestine 90% of nutrient absorption occurs in the small intestine Duodenum – 26 cm long: mixes chyme from stomach with digestive secretions from pancreas and liver (uptake of iron) Jejunum – 2.5 meters long: site of most chemical digestion & nutrient absorption Ileum – 3.5 meters long: uptake of vitamin B12 & bile salts  The pancreas has several roles Digestion: When food enters the stomach and duodenum they release hormones (gastrin, cholecystokinin and secretin), this stimulates secretion of pancreatic exocrine secretions (in pancreatic juices) – bicarbonate ions which neutralize HCl – digestive enzymes (from Basophilic cells) very important for digesting fats & proteins. Glucose homeostasis The pancreas is also an important endocrine organ e.g: insulin, glucagon, and somatostatin The pancreas  Roles of the liver Metabolic regulation – Carbohydrate, lipid, amino acid, waste removal, – vitamin, mineral storage, drug inactivation Haematological regulation – Remove old rbc, synthesise plasma proteins, remove circulating hormones, antibodies, toxins – Synthesis and secretion of bile – Function of bile Emulsification, promote absorption by intestinal epithelia The liver  The Large intestine Approximately 1.5 m long and 7.5 cm wide – Cecum: the pouch-like first portion (& appendix) – Colon: the largest portion – Rectum: the last 15 cm – Anus Figure 24–23 Large intestine  Functions of the large intestine Supports bacteria which further digest food Absorption of: – bacteria & their products (includes vitamins) – organic wastes – bile salts (return via blood to liver) – water Compaction/ drying the contents (to make faeces) Storage of faecal material prior to defecation Chemical processes of digestion Water movement in digestive system  Summary 1. Identify the organs of the digestive system and list their major functions 2. Describe the anatomy of the abdominal regions 3. Describe the anatomy of the stomach and its blood supply role in digestion and absorption 4. Describe the anatomy of the small intestine and its blood supply and the accessory digestive organs