Structure and Function of the Alimentary System Flashcards
Describe the general histological organisation of the GI tract
Mucosa: Epithelium, basement membrane, lamina propia. Site of absorption. Contains enteroendocrine glands. Lymphoid tissue is seen in the lamina propia.
Muscularis mucosa
Submucosa: Contains lymphatics, vessels and nerves (sub-mucosal plexus). Some mucus secreting cells present.
Muscularis externa: Circular and longitudinal layers of muscle. Myenteric plexus is seen in between the muscle layers
Adventitia/Serosa: Outer layer of thick connective tissue. Contains blood vessels, lymphatics and nerves
Describe the structural variations of the tube of the GI tract
Changes in epithelium:
Oesophagus - stratified squamous
Stomach - simple columnar
Small intestine - Villi and crypts formed from enterocytes with microvilli
Large intestine - Columnar ciliated epithelium form crypts but no villi
Duodenum: Has Brunner’s glands for the secretion of HCO3-
Ileum: Has Payer’s patches (in the lamina propia), aggregates of lymphoid tissue
The enteroendocrine cells present within the different regions secrete different gastric hormones
Describe the main functions in the different areas of the GI tract
Oesophagus - transport of food
Stomach - To break down and churn food, generating chyme
Small intestine - Absorption of nutrients
Large intestine - Absorption of water
Rectum - Temporary storage of faeces
Anal canal - Defecation
Describe how the structure and function are related in the GI tract
Oesophagus: Squamous cells due to the passage of food, causing sloughing
Stomach: Has rugae to increase surface area, has cells specialised for its function (e.g. HCl secreting cells),
Small intestine: Duodenum has Brunner’s glands to neutralise the acidic chyme; prominent plicae in the jejunum; villi increase surface area to allow for maximal absorption of nutrients
Large intestine: Villi increase surface area to allow maximal absorption of water.
