6. Histology of the GIT Flashcards
- What type of gland are salivary glands?
- What are the 2 cell types of salivary glands?
Salivary Glands
- Compound glands
- Two cell types, secrete – Mucin (mucus)
- Pale
- Called mucous glands
- Enzyme proteins
- Darker
- Called serous glands
What does the GIT consist of?
Gastro-Intestinal Tract (GIT)
- Oesophagus
- Stomach
- Small Intestine
- Duodenum
- Jejunum
- Ileum
- Small Intestine
- Vermiform Appendix
- Colon
Accessory Organs
- Liver
- Pancreas
What is the general histological structure of the GIT?
(5 layers)
- *General Structure -** My
- Lovely Poppie Loves Nana, Mickey Mouse Superman & ME*
- Mucosa
- Epithelial type and glands
- Lamina propria
- Lymphoid nodules
- Muscularis mucosae
- Submucosa
- Muscularis externa (2 or more layers)
- Serosa
- Enteric autonomic nerve plexus
Mucosa = Important for determining malignant change
What is the general histological structure of the GIT?
(5 layers)
- *General Structure -** My
- Lovely Poppie Loves Nana, Mickey Mouse Superman & ME*
- Mucosa
- Epithelial type and glands
- Lamina propria
- Lymphoid nodules
- Muscularis mucosae
- Submucosa
- Muscularis externa (2 or more layers)
- Serosa
- Enteric autonomic nerve plexus
Mucosa = Important for determining malignant change
What 4 things is the GIT mucosa formed of?
Mucosa - Composed of
- Epithelium
- Lamina propria
- Lymphoid nodules
- Muscularis mucosae
What type of epithelium typically lines the GIT?
- Exception?
- 3 types of specialised cell products?
- Supported by what?
Epithelium of the Mucosa
- Usually columnar epithelium
- Exception is the oesophagus = Stratified squamous
- Various types of specialized cells
- Mucus producing
- Enzyme secreting
- Hormone producing
- Supported by the lamina propria (ECM)
What are the Lymphoid Nodules of the Mucosa known as?
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
Label this Lymphnoid Nodule of the GIT.
What is the structure of the muscularis mucosa of the GIT mucosa?
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
What is the Submucosa of the GIT?
- Function?
- What is located here?
- Mostly made of what?
- What is in the submucosa of the intestines?
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
- (Meissner plexus location of ganglion cells)
What is the structure of the muscularis externa?
- Layers?
- Which plexus is located here?
- What is the exception to this?
Muscularis Externa
- Smooth muscle
- Usually TWO layers
- Inner circular
- Outer longitudinal
- Location of Auerbach plexus (AKA plexus my**entericus ) between the two muscle layers
EXCEPTION: Stomach has THREE* layers
- Inner oblique
- Middle circular
- Outer longitudinal
What is the GIT Serosa also known as? (2)
- What is it covered by?
- Which plexus is here?
- Function?
- Which immune cells reside here?
GIT Serosa
- Also called:
- Adventitia (by definition is different see next slide) or
- 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
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?
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
What are the histological variations of the esophagus?
Which features are distinct to this organ?
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
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?
Histology of the Stomach
- Folded surface (rugae)
- Mucosal surface deep
- Mucus secreting cells (surface & neck)
- 3 layers of specialized epithelial cells*
- Parietal
- Chief
- Enteroendocrine
- Muscularis externa 3 layers*
- Inner oblique
- Middle circular
- Outer longitudinal
* Distinct features of this organ (mnemonic ‘3 & 3’)
Which specialised epithelial cells are found in the pit, isthmus and base of the stomach folds?
3 rule
Label 1, 2 and 3.
1 = Surface mucosal cells - pit
2 = Parietal cells - isthmus
3 = Chief cells - base
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?
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
Label this histological slide of the small intestine.
What are the histological variations of the duodenum?
- Which cells are characteristic of the duodenum?
- What do they make?
- Where are they found?
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
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?
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
What is a distinctive feature of the ileum?
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
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?
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
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?
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
What are the 3 sphincters present in the GIT?
What are they composed of?
Sphincters of GIT
- Muscularis externa thickened to prevent back-flow
- Sphincter types
- Oesophageal = Between oesophagus and stomach
- Pyloric = Between stomach and small intestine
- Anal = Between rectum and external environment
- Other places like oesophagus no such thickening just has increased muscle tone.
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?
Fenestrated (windowed) large calibre capillaries
Liver - Blood Flow
- Sinusoids# percolate blood between cords of hepatocytes
- Portal tracts supported by collagen
-
Dual blood supply:
- Oxygenated blood from hepatic arteries
- 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)
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?
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
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?
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):
- Amylase, lipase, elastase
- Ribonuclease, DNase
-
Proenzymes:
- Trypsinogen
- Procarboxypeptidase
- Chymotrypsinogen
What forms the endocrine component of the Pancreas?
*
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)
Which cells stain red in islet of Langerhans in the pancreas?
Hormone glucagon containing alpha cells in islet of Langerhans* stained RED
Differentiation of Different GIT Segments (including the Gallbladder)
