6. Histology of the GIT

Question 1

• What type of gland are salivary glands?
• What are the 2 cell types of salivary glands?

Answer 1

Salivary Glands

• Compound glands
• Two cell types, secrete – Mucin (mucus)
  
  • Pale
  • Called mucous glands
• Enzyme proteins
  
  • Darker
  • Called serous glands

Question 2

What does the GIT consist of?

Answer 2

Gastro-Intestinal Tract (GIT)

• Oesophagus
• Stomach
  
  • Small Intestine
    
    • Duodenum
    • Jejunum
    • Ileum
• Vermiform Appendix
• Colon

Accessory Organs

• Liver
• Pancreas

Question 3

What is the general histological structure of the GIT?

(5 layers)

Answer 3

• *General Structure -** My
• Lovely Poppie Loves Nana, Mickey Mouse Superman & ME*

1. Mucosa
   
   • Epithelial type and glands
   • Lamina propria
   • Lymphoid nodules
   • Muscularis mucosae
2. Submucosa
3. Muscularis externa (2 or more layers)
4. Serosa
5. Enteric autonomic nerve plexus

Mucosa = Important for determining malignant change

Question 3

What is the general histological structure of the GIT?

(5 layers)

Answer 3

• *General Structure -** My
• Lovely Poppie Loves Nana, Mickey Mouse Superman & ME*

1. Mucosa
   
   • Epithelial type and glands
   • Lamina propria
   • Lymphoid nodules
   • Muscularis mucosae
2. Submucosa
3. Muscularis externa (2 or more layers)
4. Serosa
5. Enteric autonomic nerve plexus

Mucosa = Important for determining malignant change

Question 4

What 4 things is the GIT mucosa formed of?

Answer 4

Mucosa - Composed of

1. Epithelium
2. Lamina propria
3. Lymphoid nodules
4. Muscularis mucosae

Question 5

What type of epithelium typically lines the GIT?

• Exception?
• 3 types of specialised cell products?
• Supported by what?

Answer 5

Epithelium of the Mucosa

• Usually columnar epithelium
  
  • Exception is the oesophagus = Stratified squamous
• Various types of specialized cells
  
  1. Mucus producing
  2. Enzyme secreting
  3. Hormone producing
• Supported by the lamina propria (ECM)

Question 6

What are the Lymphoid Nodules of the Mucosa known as?

Answer 6

Lymphoid Nodules of the Mucosa

• Varying number throughout
• Known as Gut Associated Lymphoid Tissue - GALT
• Present in all systems which open to the outside (e.g. Respiratory [Mucosa Associate Lymphoid Tissue – MALT] & Urinogenital)
• Sites of immune surveillance

Question 7

Label this Lymphnoid Nodule of the GIT.

Answer 7

Question 8

What is the structure of the muscularis mucosa of the GIT mucosa?

Answer 8

Muscularis Mucosa of the Mucosa

• Two fine bands of smooth muscle
• Junction between the mucosa and submucosa
• Continuous layer down whole length of the GIT

Question 9

What is the Submucosa of the GIT?

• Function?
• What is located here?
• Mostly made of what?
• What is in the submucosa of the intestines?

Answer 9

Submucosa of GIT

• Anchors mucosa to muscle (muscularis externa)
• Location of neurovascular bundles
  
  • Blood and lymphatic vessels and nerve bundles
• Mostly collagen
• In intestines also place of peripheral nerve ganglia
  
  • (Meissner plexus location of ganglion cells)
    
    • Also Known As (AKA) plexus submucosus

Question 10

What is the structure of the muscularis externa?

• Layers?
• Which plexus is located here?
• What is the exception to this?

Answer 10

Muscularis Externa

• Smooth muscle
• Usually TWO layers
  
  1. Inner circular
  2. Outer longitudinal
• Location of Auerbach plexus (AKA plexus my**entericus ) between the two muscle layers

EXCEPTION: Stomach has THREE* layers

1. Inner oblique
2. Middle circular
3. Outer longitudinal

Question 11

What is the GIT Serosa also known as? (2)

• What is it covered by?
• Which plexus is here?
• Function?
• Which immune cells reside here?

Answer 11

GIT Serosa

• Also called:
  
  1. Adventitia (by definition is different see next slide) or
  2. Fibrosa (connective tissue capsule)
• Covered by mesothelium (visceral)
• Where mesenteric blood & nerve supply enters the GIT (subserous plexus)
• Gathers and anchors the GIT
• Location for mast cells

Question 12

What is the difference between Serosa and Adventitia?

• Which cells form the serosa? What do they secrete?
• What do the serous membrane line?
• What type of tissue forms the adventitia? Function?
• What are peritoneal organs covered in?
• What are retroperitoneal organs covered in?

Answer 12

GIT Serosa compared to Adventitia

Serosa = Smooth membrane of a thin layer of mesothelial cells which excrete serous fluid which reduces friction from muscle movement. Serous membranes line and enclose body cavities (serous cavities).

Adventitia = connective tissue layer binds together or attaches structures to abdominal wall

Question 13

Answer 13

Question 14

What are the histological variations of the esophagus?

Which features are distinct to this organ?

Answer 14

GIT Histology - Variations*

Oesophagus

• Mucosa = Stratified squamous epithelium*
• Muscularis external
  
  • First (upper) 1/3 = skeletal muscle*
  • Middle 1/3 = skeletal mixed with smooth muscle
  • Last (nearest stomach) 1/3 = all smooth muscle
• Submucosa = Tubulo/alveolar mucous glands (upper & lower ends)

* Distinct features of this organ

Question 15

What are the histological variations of the stomach?

Which features are distinct to this organ?

• 3 specialised epithelial cells of the stomach?
• How many layers of muscularis externa is in the stomach?
• Which specialised cells are in the:
  
  • Cardia? (1)
  • Fundus? (2)
  • Antrum? (2)
• What does specialised cells secrete?

Answer 15

Histology of the Stomach

• Folded surface (rugae)
• Mucosal surface deep
  
  • Mucus secreting cells (surface & neck)
  • 3 layers of specialized epithelial cells*
    
    1. Parietal
    2. Chief
    3. Enteroendocrine
• Muscularis externa 3 layers*
  
  1. Inner oblique
  2. Middle circular
  3. Outer longitudinal

* Distinct features of this organ (mnemonic ‘3 & 3’)

Question 16

Answer 16

Question 17

Which specialised epithelial cells are found in the pit, isthmus and base of the stomach folds?

Answer 17

3 rule

Question 18

Label 1, 2 and 3.

Answer 18

1 = Surface mucosal cells - pit

2 = Parietal cells - isthmus

3 = Chief cells - base

Question 19

What are the histological variations of the small intestine?

• Which features are distinct to this organ?
• Which cells does the epithelium contain (black arrow)? What do they secrete?
• In which crypts are Digestive and absorptive cells found?

Answer 19

Histology of Small Intestine

• Villi (plicae circulares)*
  
  • Microvilli*
• Epithelium contains Paneth cells (red granules) which secrete defensins against bacteria & parasites
• Digestive and absorptive cells in crypts of Lieberkühn at base of microvilli

* Distinct features of this organ

Question 20

Label this histological slide of the small intestine.

Answer 20

Question 21

What are the histological variations of the duodenum?

• Which cells are characteristic of the duodenum?
  
  • What do they make?
  • Where are they found?

Answer 21

Histology of the Duodenum

• Brünner glands characteristic*, identifying feature
  
  • Make an alkaline mucus which neutralized the acidic chyme from the stomach
  • Found above & below muscularis mucosae

* Distinct features of this organ

Question 22

What are the histological variations of the Jejunum?

• How do the villi in the jejunum compare to those in the duodenum?
• What are the folds known as? 2 names.
• Function?

Answer 22

Histology of the Jejunum

• Fewer and shorter villi* compared to duodenum
  
  • Finger-like projections of the folds
• Folds known as plicae (plicae circulares)
  
  • AKA (also known as) valves of Kerckring
• Sites of absorption

Question 23

What is a distinctive feature of the ileum?

Answer 23

Histology of the Ileum

• Peyer patches* are large lymphoid nodule aggregates
  
  • Common to this part of the small intestine and make it easily identifiable

* Distinct features of this organ

Question 24

What are the histological variations of the veriform appendix? * What is the veriform appendix? * Where is it found? * Distinctive feature? What does it resemble? * Are crypts of Lieberkühn present in the veriform appendix?

Answer 24

**Histology of the Vermiform Appendix** * Blind out-pocketing of caecum * Near ileo-caecal junction * More lymphoid nodules\* * Resemble tonsil * Still has crypts of Lieberkühn *\** *Distinct features of this organ*

Question 25

Answer 25

Question 26

What are the histological variations of the Large Intestine/Colon? * Are villi present in the large intestine? * Which cells are the large intestine mostly comprised of? * Are Crypts of Lieberkühn present in the large intestine? * Which layer is unusually thick?

Answer 26

**Histology of the Large Intestine (Colon)** * Folded surface * Mucosa without villi * MOSTLY mucus producing goblet\* cells * Crypts of Lieberkühn remain * Thick muscularis externa\* * Proportional to mucosa *\** *Distinct features of this organ*

Question 27

Answer 27

Question 28

What are the 3 sphincters present in the GIT? What are they composed of?

Answer 28

**Sphincters of GIT** * Muscularis externa thickened to prevent back-flow * Sphincter types 1. ***Oesophageal*** = Between oesophagus and stomach 2. ***Pyloric*** = Between stomach and small intestine 3. ***Anal*** = Between rectum and external environment * Other places like oesophagus no such thickening just has increased muscle tone.

Question 29

Answer 29

Question 30

Describe the blood flow to the liver? * How does blood flow between cords of hepatocytes? * What are the portal tracts supported by? * Describe the dual blood supply of the liver?

Answer 30

**Liver - Blood Flow** * Sinusoids# percolate blood between cords of hepatocytes * Portal tracts supported by collagen * **Dual** blood supply: 1. Oxygenated blood from hepatic arteries 2. Nutrients supplied by portal vein from alimentary canal & spleen * Flow from portal tracts through sinusoids to central vein * Lymphatic vessels present * Fine connective tissue (reticulin) support of sinusoids (ECM) #*Fenestrated (windowed) large calibre capillaries*

Question 31

How is bile produced in the liver? * Which molecule is recycled to make bile? * What is bile secreted into in the liver? * What does the bile duct epithelium secrete?

Answer 31

_Liver - Bile Production_ * Exocrine component * Production of bile * Recycled haemoglobin (porphyrin from spleen) * Secreted into canaliculi between hepatocytes * Shunted by bile ducts in portal tracts * Then into gallbladder where it’s concentrated * Duct epithelium secretes a bicarbonate rich fluid, which is added to the bile

Question 32

What is the Histology of the Pancreas? * What is the exocrine component composed of? * Which granules are present? * What is the distinct staining pattern of the pancreas? * Which enzymes are synthesised in the pancreas? * Which proenzymes are synthesised in the pancreas?

Answer 32

_Pancreas (adjacent to the duodenum)_ * Exocrine component - **glands** * Intracellular zymogen granules * Distinctly **two-tone pink/blue** (with H&E staining) * High RER content indicative of manufacture (blue) * **Enzymes** (pink secretions): 1. Amylase, lipase, elastase 2. Ribonuclease, DNase * **Proenzymes**: 1. Trypsinogen 2. Procarboxypeptidase 3. Chymotrypsinogen

Question 33

Answer 33

Question 34

What forms the endocrine component of the Pancreas? *

Answer 34

_Endocrine component - islets of Langerhans\*_ * **beta cells (≅70%)** → Insulin & Amylin (ratio of 100:1) * **alpha** **cells (20%)** → Glucagon * **G** **cells** → Gastrin (small amounts) * **D or d cells** (\<10%) → Somatostatin * **PP, g or F cells (\<5%)** → Pancreatic peptide * **e cells (\<1%)** → Ghrelin (small amounts)

Question 35

Answer 35

Question 36

Which cells stain red in islet of Langerhans in the pancreas?

Answer 36

**Hormone glucagon containing alpha cells in islet of Langerhans\* stained RED**

Question 37

**Differentiation of Different GIT Segments (including the Gallbladder)**

Answer 37