Lower GIT

Question 1

What is the lower GIT composed of? What are the associated organs?

Answer 1

Composed of:
- most of SI
- LI
- Rectum
- Anal canal
Associated organs:
- Pancreas
- Spleen
Liver and Gallbladder

Question 2

How is the Foregut, midgut and hindgut supplied with blood?

Answer 2

Foregut - Celiac trunk
Midgut - Superior mesenteric artery
Hindgut - Inferior mesenteric artery

Question 3

How is the GIT drained?

Answer 3

Lower GIT drained by superior mesenteric vein and respective tributaries. These drain into the Hepatic Portal Vein so the nutrients absorbed from digestion can be processed before the blood is returned to systemic circulation. This is known as a portal venous system.

Question 4

Explain the structure and function of the small intestine.

Answer 4

Structure:
- longest and most convoluted part of GIT
- Narrowest in diameter
- Composed of 3 continuous subdivisions; duodenum, jejunum, ileum.

Function:
- Absorption; has specialisations to increase SA. These are folds created by plicae circularis, as well as vili/microvilli.

Question 5

Structure of jejunum.

Answer 5

• begins at duodenal flexure
• intraperitoneal
• branches of SMA form loops, these loops form arterial arcades, these form long straight arteries known as vasa recta
• large, tall and closely packed plicae circularis.

Question 6

Structure of ileum

Answer 6

• continuation of sa from jejunum
• primary function is to absorb nutrients not absorbed by jejunum
• fewer plicae circularis
• short vasa recta and many short loops

Question 7

What are the 3 parts of the large intestine? What are its functions?

Answer 7

Composed of:
- caecum
- colon
- rectum and anal canal
Function:
- reabsorption of water
- absorption of vitamins
- compaction of intestinal contents into faeces and its storage

Question 8

What distinguishes LA from SA?

Answer 8

Taenia coli
Haustra
Epiloic appendages

Question 9

Role of caecum

Answer 9

Move food into colon

Question 10

Structure of appendix

Answer 10

Begins at ileocecal valve.
Wormlike.

Question 11

What are the 4 portions of the colon?

Answer 11

Ascending
- caecum to hepatic flexure
Transverse
- hepatic flexure to splenic flexure
- most mobile portion of GIT
Descending
- splenic flexure to sigmoid colon
Sigmoid colon
- inferiorly continues as rectum

Question 12

What are the roles of the rectum and anal canal?

Answer 12

Rectum
- retains faeces
Anal canal
- 2 sphincter to release faeces; external - voluntary, internal - involuntary

Question 13

What is the role of the pancreas?

Answer 13

An exocrine (pancreatic juice into ducts) and endocrine (glucagon/insulin into blood) gland.

Lies in curve of duodenum and extends towards hilum of the spleen.
Joins with common bile duct.

Question 14

Role of the spleen.

Answer 14

Filters blood as is a secondary lymphoid organ.

Question 15

Role of liver.

Answer 15

metabolism
storage
synthesis
filters blood
excretion of bilirubin
heat production

directly inferior to diaphragm, closely associated with gall bladder

has 4 lobes ( right, left, caudate, quadrete) and 3 ligaments (triangular, falciform, coronary)

Question 16

What is the porta hepatis?

Answer 16

Transverse fissure in middle visceral surface of liver, allowing neurovascular and lymphatic structures to enter and exit. It gives passage to the portal triad:
- HPV
- HA
- bile duct

Question 17

What is the role of the HPV?

Answer 17

• 75% of blood supply to liver
• drains abdominal viscera
• receives partially deoxygenated blood
• ensures nutrients from GIT are processes in liver

Question 18

Role of gallbladder.

Answer 18

• stores and concentrates bile
• bile emulsifies fat so it can be absorbed in distal intestine

Question 19

What is the enteric NS?

Answer 19

Forms 2 interconnected networks within wall of GIT.
- myenteric controls peristalsis
- submucosal controls secretory activity
Mostly independent of CNS but can receive signals to modify activity.