GI System: L22 - Introduction to GI system

Question 1

What is the overall primary function of the gastrointestinal system?

Answer 1

To bring nutrients from the external environment to be made available to the cells of the body. To do this, it must be able to remove the necessary nutrients from the things we eat and drink to meet energy needs of the body and provide it with the material for growth.
It must also be able to excrete the waste products of the process.

Question 2

Briefly describe motility.

Answer 2

Involves patterns of contraction and relaxation of the layers of smooth muscle lining the gastrointestinal tract.
The role of motility within the GI tract is movement: the GI tract extends over a long distance so a mechanism is required to move contents along.
Motility also contributes to digestion by mechanically breaking down food, and to absorption by exposing digested food to absorptive surfaces.

Question 3

Briefly describe secretion.

Answer 3

The transfer of material from the blood into the intestinal lumen.
This generally involves:
Secretion of fluid and electrolytes (water+salts) into tract.
Secretion of products (e.g saliva, digestive enzymes) into GI tract when appropriate after they have been synthesised by cells.
Secretion occurs throughout the entire length of the GI tract
It is carried out by the GI tract itself as well as organs such as liver, pancreas and salivary glands.

Question 4

Briefly describe digestion.

Answer 4

Food material is broken down to allow absorption.
Mechanical digestion - where food is physically broken down through motility.
Chemical digestion - carried out by fluids and enzymes.

Question 5

Briefly describe absorption.

Answer 5

Transport of material from intestinal lumen into the body. Absorption occurs in the more distal regions of the GI tract since digestion must occur first (in more proximal regions). Takes place in the:
Small intestine: nutrients, most salt + water.
Large intestine: small amounts of water + salt.

Question 6

Identify the segments of the GI tract from mouth to the anus.

Answer 6

Mouth - where food is ingested + swallowed.
Oropharynx - lies behind oral cavity.
Laryngopharynx - continuous with oropharynx.
Oesophagus - propels food to stomach.
Stomach - food mixed with fluids, becomes chyme.
Small intestine - duodenum, jejunum, ileum.
Large intestine - caecum, colons.
Rectum - faeces are stored.
Anal canal - where faeces are expelled from.

Question 7

What cell layer is the GI tract lined with?

Answer 7

Epithelial layer

Question 8

What cavity are the organs of the GI system packed together in?

Answer 8

Abdominal cavity

Question 9

The anterior portion of the GI tract is covered by a large fold of what?

Answer 9

A large fold of ‘peritoneum’, the serous membrane that forms the lining of the abdominal cavity, called ‘greater omentum’.

Question 10

Accessory organs are associated with the GI tract but not part of the tube itself. They synthesize and deliver material to the lumen of the GI tract via a duct system. Name these organs.

Answer 10

3 pairs of salivary glands: parotid glands, submandibular glands and sublingual glands.
Pancreas
Liver
Gall bladder - storage and concentration system for liver secretions.
Appendix.

Question 11

Where are the 2 serous membranes of peritoneum and why are they serous?

Answer 11

Parietal peritoneum is the outer layer and lines most of the abdominal wall.
Visceral peritoneum is the inner layer and wraps around most of the organs in the abdominal cavity.
The cavity between the 2 layers is a potential space called peritoneal cavity.
The peritoneal cavity contains serous fluid which enables the closely packed organs to slide over each other.

Question 12

What are the mesenteries?

Answer 12

Formed where visceral peritoneum encloses or suspends organs within the peritoneal cavity. Composed of 2 layers of visceral peritoneum, attach organs loosely to posterior abdominal wall to anchor organs without restricting their movement.

Question 13

What is omenta?

Answer 13

Formed where visceral peritoneum encloses or suspends organs within the peritoneal cavity.
Two kinds:
Lesser omentum composed of 2 layers visceral peritoneum.
Greater omentum is folded back on itself so that it is composed of 4 visceral peritoneum layers.

Question 14

What are suspended organs described as being? Why is this not technically well-named?

Answer 14

‘Intraperitoneal organs’, but in reality they are not truely suspended in peritoneal cavity because they are covered with visceral peritoneum.

Question 15

What is the outer layer of these intraperitoneal organs called rather than adventitia?

Answer 15

Serosa.

Question 16

What is the outer layer of retroperitoneal (lie behind peritoneum) called?

Answer 16

Adventitia.

Question 17

In terms of arterial blood supply originating from the abdominal aorta, the branch: celiac trunk supplies what regions/organs?

Answer 17

The celiac trunk supplies organs derived from the foregut. It supplies the gastric artery (stomach), splenic artery (spleen) and the common hepatic artery (liver). Pancreas and duodenum are supplied by both celiac trunk and superior mesenteric arteries.

Question 18

In terms of arterial blood supply originating from the abdominal aorta, the branch: superior mesenteric artery supplies what regions/organs?

Answer 18

Superior mesenteric artery supplies organs derived from the midgut. It divides into the ‘right and middle colic’ arteries (supplies ascending and transverse colons), the ‘intestinal arteries’ (the jejunal arteries and ileal arteries), and the ‘ileocolic artery’ (ileum, caecum, and appendix).
Pancreas and duodenum are supplied by both celiac trunk and superior mesenteric arteries.

Question 19

In terms of arterial blood supply originating from the abdominal aorta, the branch: inferior mesenteric artery supplies what regions/organs?

Answer 19

The inferior mesenteric supplies organs derived from the hindgut. It divides into the left colic artery (supplies descending colon), the sigmoid arteries (sigmoid colon), and the superior rectal artery (rectum).

Question 20

Explain the portal venous system.

Answer 20

The veins draining the blood leaving the GI tract does not go directly to the heart, instead the veins go to the portal venous drainage system which carries it to the liver sinusoids for processing and detoxification. After this, blood will enter hepatic veins, which carry it to the inferior vena cava.