Anatomy and Histology

Question 1

Describe the basic anatomy of the oesophagus?

Answer 1

Cricoid cartilage -> Through diaphragm at T10 -> Stomach at T11.
Inner circular and outer longitudinal muscle layer.
External layer is voluntary striated (1/3), mixed (2/3) and involuntary smooth (3/3).
Upper sphincter is formed by the cricopharengeus muscle.
Lower sphincter is physiological by the angle of His entering the stomach.
Lined by Stratified Squamous Epithelium.

Question 2

Describe basic anatomy of the stomach?

Answer 2

Lies in the epigastric and umbilical regions.
Pyloric sphincter (SM) controls exit of chyme.
Has rugae to increase surface ares.
Has a greater and lesser omentum - folded layers of peritoneum.
Greater has lymph nodes and anchors stomach to the abdominal wall.
Lesser attaches the stomach and duodenum to the liver.
Supplied by left (hepatic) and right gastric (coeliac trunk) arteries, right and left gastro-omental arteries (splenic), and short gastric arteries (splenic).
Parasympathetic innervation is from posterior vagal trunks - contract smooth muscle and have secretomotor function.
Sympathetic is from the coeliac plexus and is for sphincter contraction.
Lined by Simple Columnar Epithelium.

Question 3

Describe basic anatomy of the duodenum?

Answer 3

4 parts - superior, descending, inferior, ascending.
Descending contraits major duodenual papilla, where bile and pancreatic secretions enter via the ampulla of vater.
Villi and microvilli to increase surface area.
Brunners glands which secrete alkaline fluid to protect the lining.
Lined by Simple Columnar Epithelium.

Question 4

Describe histology of the stomach and which layer differs across regions?

Answer 4

1. Mucosa: Simple columnar. 
                  Lamina Propria (areolar CT, glands, lymph, vessels).
             Muscularis Mucosae (SM which folds the mucous membrane). 

2. Submucosa: Areolar CT which binds mucosa to muscularis.
3. Submucosal Plexus

4. Muscularis: Innermost oblique (ONLY IN BODY)
                       Inner circular (Causes constriction and has gap junctions to spread excitation and act as single unit).

5. Myenteric Plexus
6. Outer Longitudinal: No gap junctions so acts as multi unit. Causes shortening.
7. Serosa: Simple squamous and areolar CT. Extends from curvatures as greater/lesser omentum.

Question 5

Name cells of the gastric pits and their secretions?

Answer 5

Mucous cells
Parietal cells: HCl to denature proteins, convert pepsinogen to pepsin, and solubilise calcium and iron.
Also produces intrinsic factor to form an absorbable complex with Vitamin B12.
Chief Cells: Pepsinogen and Gastric Lipase.
G Cells: Gastrin (mainly antrum) - causes parietal cells to secrete more HCl.
D cells: Somatostatin to stop parietal cells producing HCl.
Enterochromffin-like (ECL) cells: Histamine causing parietal cells to produce HCl.