Digestive System - Alimentary Tract 2

Question 1

List the layers of the gut wall.

Answer 1

Mucosa
Submucosa
Muscularis externa
Serosa

Question 2

Describe the structure of the mucosa.

Answer 2

Epithelium - secretion, absorption and protection
Lamina propria - loose CT, blood vessels, gut glands
Muscularis mucosa - 2 thin layers of smooth muscle, independent movement of mucosa

Question 3

Describe the structure of the submucosa.

Answer 3

Collagenous and elastic CT
Plethora of nerves - Meissner’s plexus
May contain glands in duodenum and oesophagus
Highly vascular.

Question 4

Describe the structure of the muscularis external.

Answer 4

2 layers of smooth muscle
Required for peristalsis
Inner layer may be modified to form sphincters
Innervated by myenteric nerve plexus - Auerbach’s plexus.

Question 5

Describe the structure and function of the serosa.

Answer 5

Innermost layer of the serosa consists of a single layer of simple squamous epithelial cells called mesothelial cells
Beneath the mesothelium lies a layer of connective tissue, which provides support and anchorage for the mesothelial cells
Protection - protect the underlying organs from friction and abrasion as they move within the body cavities
Secretion of serous fluid - acts as a lubricant

Question 6

Describe the oral cavity.

Answer 6

Simple squamous keratinising epithelium in dorsal of tongue, hard palate and attached gingiva
Simple squamous non-keratinising epithelium everywhere else
Salivary glands and taste buds present .

Question 7

Describe the oesophagus.

Answer 7

Made of mucosa, submucosa, muscularis and adventita.
Primary function of the esophagus is to transport food, liquids, and saliva from the mouth to the stomach
Muscularis externa - inner circular and outer longitudinal layers
Upper = skeletal muscle
Middle = mixed
Lower = smooth muscle
Simple squamous non-keratinising epithelium
Mucous glands present.

Question 8

Describe the stomach.

Answer 8

Functions - mixes food, preliminary digestion via secretion of digestive enzymes
Rugae - folds of mucosa to increase surface area
Simple columnar epithelium
Regions of stomach;
Cardia - shallow pits and coiled glands, parietal cells + mucous cells
Fundus and body - branched straight tubular glands, chief cells.
Pylorus - long, deep pits and short coiled glands, mucous + entero-endocrine glands.

Question 9

Describe the small intestine.

Answer 9

Function - digestion and absorption
Duodenum - Brunner’s glands, goblet cells
Jejunum - no Brunner’s glands or lymphoid follicles, plicae circulares
Ileum - numerous lymphoid follicles in submucosa
Plicae circulares - folds projecting into the gut lumen
Villi - fingerlike projections from plicae circulares
Microvilli - fingerlike projections on apical surface of absorptive epithelial cells, form a brush border.

Question 10

Describe the
Crypts of Lieberkühn.

Answer 10

Located in the mucosa layer of the small intestine
Each crypt of Lieberkühn is a simple tubular gland composed of several cell types - Enterocytes, Goblet cells, Paneth cells and Enteroendocrine cells
Functions;
Goblet cells within the crypts secrete mucus, which lubricates the intestinal lining
Enterocytes lining the surface of the small intestine absorb nutrients
Enteroendocrine cells release hormones such as serotonin, cholecystokinin (CCK), and secretin, which regulate various aspects of digestion
Stem cells located at the base of the crypts continuously divide to produce new cells
Paneth cells play a critical role in innate immunity by secreting antimicrobial peptides

Question 11

Describe the large intestine.

Answer 11

Structure;
Cecum - pouch-like structure located in the lower right abdomen
Colon - consits of ascending, descending, transverse and sigmoid sections
Rectum - stores faaeces before excretion
Receives its blood supply from branches of the superior and inferior mesenteric arteries
Muscular layer - consists of longitudinal and circular smooth muscle fibres
Mucosal layer - contains goblet cells
Functions;
Supplies mucus to facilitate passage of faeces
Extracts water and electrolytes
Colonic crypts and glands of Lieberkühn

Question 12

Describe the strucutre and function of the rectum.

Answer 12

Extends from the sigmoid colon to the anal canal
Consists of three folds called rectal valves (or Houston’s valves) that help prevent the backflow of feces.
Main function of the rectum is to serve as a temporary storage site for feces before they are expelled from the body during defecation
Absorb water and electrolytes from fecal material