Histology of GI tract

Question 1

What are the two points on the GI tract?

Answer 1

• Long muscular tube lined by mucous membrane

- Concerned with the intake, digestion and absorption of climatic waste

Question 2

What is the organisation of the GI tract?

4 layers

Answer 2

• Mucosa
  Epithelium
  Lamina propria
  Muscularis mucosae
• Submucosa
• Muscularis externa
  Inner circular layer
  Outer longitudinal layer
• Adventia/serosa

Question 3

What are the three types of epithelium as you go down the GI tract?

Answer 3

protective
secretory
absorptive

Question 4

Oesophagus:
What is the type of epithelium?
What glands does it have and why?
What is the muscle present?

Answer 4

Stratified squamous epithelium
Submucosal glands for lubrication of food
Voluntary top 1/3, voluntary and smooth middle 1/3 and last 1/3 is smooth.

Question 5

What change of epithelium occurs at the gastro-oesophageal junction?

Answer 5

Stratified squamous epithelium becomes simple epithelium.

Question 6

What are the 3 layers of the stomach and their function?

Answer 6

Fundus - turn the material that arrives in the stomach into an acidic form. Saliva enzymes is alkaline so the first thing tot stomach needs to do is neutralise and acidify this to function.
Body - production of stomach enzymes
Pylorus - food being prepared to enter small intestine. Many cells here are mucus producing cells.

Question 7

What are the 3 layers of smooth muscles in the stomach called?

Answer 7

Oblique, circular and longitudinal.

Question 8

What are the internal large folds in the muscle called?

Answer 8

Rugae which catch material and move them around to create a more efficient mix.

Question 9

What are the secretory parts of the stomach?

Answer 9

Gastric pits and glands

Mucus 
Pepsin
HCl
Intrinsic factor (Vit B12)
Gastrin

Question 10

How do we stop the GI tract from producing enzymes constantly?

Answer 10

Endocrine cells secrete hormones that signal to the next region that food is on its way.

Question 11

What are the layers of the gastric glands?

Answer 11

1) Surface mucous cells
2) Isthmus (Parietal cells)
3) Neck (neck mucous and stem cells)
4) Base of gland

2-4 is gastric gland and 1 is gastric pit.

Question 12

What do parietal cells produce?

Answer 12

Produce HCl

Question 13

Where are all the mucous secreting cells in the gastric glands?

Answer 13

Nearly all mucous secreting cells.

Question 14

Why does the stomach not digest itself?

Answer 14

Surface epithelial cells secrete bicarbonate ions to establish a neutral pH in the mucus layer adjacent to the cells.

Below pH4, low viscosity HCL penetrates the mucus layer like a finger, without mixing.

Above pH4, HCl can’t penetrate mucus at all.

Question 15

Give some anatomical features of the duodenum in the small intestine

Answer 15

Where digestion and absorption occurs.

Brunner’s glands: large glands that project out. Produce alkaline mucus (HCO3-) to neutralise the acidic contents of stomach.
Villi

Question 16

What are the 4 adaptations for the small intestine for absorption?

Answer 16

1. Pilcae circulares (begins in duodenum, most prominent in jejunum and become further apart in ileum
2. Villi (richly vascularised to take food away, has lacteals which are lymphatics which take away fats in chylomicrons which Jonis the lymphatic system)
3. Microvilli (brush-border)
4. Peyer’s patches (lots of typhoid tissue grouped together, found in ileum - mainly formed of B&T lymphocytes)

Question 17

What are the 4 cells of the small intestine epithelium?

Answer 17

1. Enterocytes (absorption)
2. Goblet cells (mucus)
3. Crypts (stem cells)
4. Paneth cells (lysosome)

Question 18

What is the colon function and explain the features of this?

Answer 18

Function = water recovery

No villi, just glands.
Glands actively pump water across and produce mucus.
They form a bolus which is expelled from the body.
Mucus producing cells lubricate the passage of thus.

Very thick muscularis extend, 3 bands of smooth muscles which spiral to wring food out.

Cell types in epithelium:
Enterocytes with microvilli and goblet cells.

Question 19

What is the change in epithelium at the ano-rectal junction?

Answer 19

Transition from glandular structure of colon to a stratified squamous epithelium.

Begins as non keratinising cells and become keratinising.

Question 20

What are the 3 main salivary glands in the face and what is the job of saliva?

Answer 20

1. Parotid
2. Submandibular
3. Sublingual

Lubricates, moistens, begins digestion, antiseptic

Question 21

Is the submandibular or the sublingual gland closer to the oral cavity?

Answer 21

Sublingual (under the cavity)

Question 22

Why is a salivary gland merocrine and what type of structure does it have

Answer 22

A cell is classified as merocrine if the secretions of that cell are excreted via exocytosis from secretory cells into an epithelial-walled duct or ducts and then onto a bodily surface or into the lumen.

Branched acinar structure.

Question 23

What are the two types of salivary secretion?

What does each salivary gland in the face secrete?

Answer 23

1) Serous (thin, watery)
2) Mucous (thick, viscous)

Parotid gland = serous
Submandibular = mixed
Sublingual = mucous

Thicker ones have less distance to travel .

Question 24

When a acinus has both the secretory cell types in the gland, how are they arranged?

Answer 24

As a serous demilune.

Question 25

Explain the concept of the myoepithelial cells in the acinus

Answer 25

Very similar to a fibroblast with some features of a muscle cell.

Question 26

What three tubes does the secretion travel through before it enters the body cavity?

Answer 26

Intercalated duct and then into striated duct (decreases tonicity) and then into the large excretory duct.

Question 27

What is the purpose of the name striated duct?

What happens at this site?

Answer 27

They have infoldings of the basal plasma membrane with vertically aligned mitochondria.

This is the site of the Na+ pumps which reabsorb Na+ and Cl-, replace then with K+ and HCO3-, so the saliva become hypotonic.

Question 28

Functions of the tongue (a muscular organ covered by oral mucosa)

Answer 28

• Manipulation of food
• General sensory reception (heat and pain)
• Special sensory reception (taste)
• Speech

Question 29

Why does the body of the tongue have bundles of skeletal muscles in all orientations?

Answer 29

Permits movement in all directions.

has minor salivary glands

Question 30

Give the anatomical features of the anterior 2/3 of the tongue

Answer 30

Dorsal surface covered with papillae.

• Filiform (keratinised spikes)
• Fungiform (scattered, ricchi vascularised, taste buds)
• Circumvallate (along sulcus terminals, taste buds)

Question 31

Where are the filiform and fungiform papillae found?

Which way around do they sit?

Answer 31

Most anterior part of tongue. They give the roughness of the tongue.

Fungiform ones sit behind the filiform.

Question 32

Give the two things found in the circumvallate papillae

Answer 32

• Taste buds

- Salivary glands (Glands of Von Edner)

Question 33

Give the anatomical features found in the posterior third of the tongue

Answer 33

Relatively smooth oral epithelium overlying abundant lymphoid tissue.