Histology Of The GI And Urinary Tract

Question 1

Globally what are the layer of the GI tract ?

Answer 1

The mucosa, submucosa, Muscularis propria and adventitia

Question 2

What is the mucosa ? What layer is it formed of ?

Answer 2

The mucosa protect the GI tract against mechanical damage by food, secrete digestive enzyme, reabsorb digestive product. It possess entero-endocrine cells (secrete hormones to the blood) and paracrine cells (secrete product with immediate effect to its surrounding.

It is divided into :
- epithelial layer
- lamina propria : thin connective tissue that possess lymphoid nodules
- Muscularis mucosa : thin layer of smooth muscle

Question 3

What is the submucosa ? What is it composed of ?

Answer 3

Possess vessels, glands and autonomic nervous plexus which is responsible for regulating the secretion and blood flow of the tissues.

Question 4

What is the Muscularis propria of the GI tract normally composed of ?

Answer 4

2 layer of smooth muscle :
- inner circumferential
- outer longitudinal

Question 5

What is the adventitia or serosa ?

Answer 5

The serosa is the outer layer of the GI tract when the organ is in the peritoneal cavity thus covered by mesothelium.
The adventitia is the outside layer of the GI tract when the organ isn’t covered by the peritoneal cavity, thus without mesothelium but a connective tissue.

Question 6

What changes at the GE junction ?

Answer 6

The epithelial cells change from stratified squamous to simple columnar cells.

Question 7

What are the characteristics of the cardia ?

Answer 7

It is next to the GE junction. It possess short pits and short glands.

Question 8

What are the characteristics of the fundus ?

Answer 8

It is the upper part of the stomach.
It possess short pits and long glands.

Question 9

Function of stomach parietal cells ?

Answer 9

Maintaining acidic environnement. Present in the body and fundus of the stomach.

Question 10

Function of stomach chief cells ?

Answer 10

Secrete pepsinogen that can form pepsin in the acidic environment.

Question 11

What are the characteristics of the pylorus ?

Answer 11

It’s next to the duodenum.
It has long pits and short glands.

Question 12

What are the characteristics of the body of the stomach ?

Answer 12

It has short pits and long glands.

Question 13

How many layer of muscle does the stomach has ?

Answer 13

3 : transverse, horizontal (circumferential), vertical (longitudinal).
To better mix he substances inside.

Question 14

What is the composition of the vili of the small intestine ?

Answer 14

The vili (protrusion) are found on the large ridge called plicae of the small intestine. The microvili are formed of mucosa epithelial cells called enterocytes.

Question 15

What are the characteristics of the mucosa and submucosa of the small intestine ?

Answer 15

All have the same mucosa.
Duodenal submucosa : thick with Brunner’s glands (produce alkaline substance to neutralise acid)
Ileum submucosa : possess Peyer’s patches (contains M-cells sampling antigen to present them to the receptors of the intestinal wall).

Question 16

General histology of the large intestine ?

Answer 16

Mucosa : columnar and goblet cells (to lubricate the stool)
Submucosa : connective tissue, autonomic nerve, vessels
Muscularis propria : possess the Auerbach plexus between the 2 layer

Question 17

What is an hexagonal hepatic lobule ?

Answer 17

Formed of hepatic cells arranged in a cord like manner from a radial structure (central vein opening into the hepatic vein) to a peripheral direction (portal area / hepatic triad)

Question 18

What is present inside the hepatic triad ?

Answer 18

It’s the fusion of interlobular connective tissue. There are an interlobular vein (bring nutritious blood), a branch of the proper hepatic artery (bring oxygen) and bile duct (export bile).

Question 19

How does the blood flow through the hepatic lobule ?

Answer 19

Through the sinusoids towards the central vein opening into the inferior vena cava. There are the exchange between blood and hepatocytes.

Question 20

What are Kupffer cells ?

Answer 20

Present along the sinusoid they have a phagocytic function.

Question 21

What do the hepatocyte do ? Where does it go ?

Answer 21

They produce gall / bile that is then drained by the bile canaliculi present between them.

Question 22

What is the space of Disse ?

Answer 22

Present hepatocytes and the sinusoids endothelial cells. There are present the Ito cells that store fat.

Question 23

How are the wall of the gallbladder ?

Answer 23

Mucosa is folded with simple columnar epithelium.
The Muscularis propria is thin. It’s contraction is induced by the cholecystokinin secreted by enterocytes-endocrine cells in the mucosa of the intestine as a reaction to fat tissue presence.
The serosa is composed of connective and adipose tissue.

Question 24

What are the gland present in the mucosa of the mouth ?

Answer 24

The parotid gland (front of the ear) : watery mucus gland
Submandibular (lower jaw) : watery mucus gland
Sublingual (below the tongue) : more mucus gland

Question 25

What are the function of the gland in the mouth ?

Answer 25

They soften and smoothen the food and the mouth cavity

Question 26

What are the salivary gland composed of ?

Answer 26

Serous acini : darker stain in a round central nucleus
Mucous cell : flat basal nucleus
Myoepithelial cells : surround the acini and form a lobule together

Question 27

What are the exocrine gland of the pancreas made of ?

Answer 27

Rarified gland with acini. Acini composed of acinar cells synthesising enzymes. There are interlobular duct starting in the acinus and emptying into the pancreatic duct.

Question 28

What do the endocrine gland of the pancreas made of ?

Answer 28

Pancreatic islet = number of endocrine cells secreting hormones

Question 29

What does the Bowman’ s capsule consist of ?

Answer 29

An outer parietal layer and an inner visceral layer around the capillaries.

Between the layer is the urinary space.

The inner layer is made of : podocytes that encloses the capillaries with pedicels to allow for narrow filtration => the blood is pressed through opening between epithelial cells : ultrafiltration. The mesengial cells between the capillaries regulate their diameter.

Question 30

What is the urothelium ?

Answer 30

Also called transitional epithelium it lies in the wall of the calyces of the kidney, the ureters, the bladder and the proximal urethra. It protect the underlying tissue from urine because it is impermeable to salt and water.

Question 31

What is the difference in the epithelium of the proximal and distal tubules ?

Answer 31

Less nuclei in the proximal and presence of brush border to reabsorb the nutrients.