Week 3: The GI tract Flashcards
Name the regions of the stomach
The fundus, cardia, body (secrets acid and pepsin), pylorus, pyloric sphincter
Name the rough layers of the stomach
Mucosa, submucosa, muscularis externa, serosa
What is the mucosa in the stomach comprised of?
Surface epithelium, lamina propria (contains immune cells), muscularis mucosae
What does the submucosa of the stomach contain
Connective tissue and major blood + lymph vessels
How many layers of smooth muscle is the muscularis externa in the stomach made of?
3 Layers
What is the function of the ileum?
Absorbs vitamin B12, bile salts and anything not absorbed by the jejunum
What unique structure is found in the small intestines?
Peyer’s patches- these are immune follicles present in the submucosa of the ileum
What is the function of Peyer’s patches?
They are responsible for sensing any immunoreactive material in the lumen (bacteria). Produces an immune response which goes into the mesentery LN
What is the inner most layer of the large intestines and what does it contain?
The epithelium - crypts, controlled by a large nerve supply)
Name the different Gastric gland cell types
Stem cells, parietal/oxyntic acid secreting cells, mucous neck cells, chief cells, neuroendocrine cells
Name and draw the layers of the fundus and body of the stomach
Gastric pit/faveolus (surface mucous cells)
Isthmus (parietal cells)
Neck (stem cells +parietal cells)
Base of the gland (chief cells)
Where are stem cells found in the stomach layer?
In the isthmus and neck of the fundus and body
Some migrate upwards towards the mucous cells, some downwards towards the parietal cells and the chief cells
Where are parietal cells found in the stomach and what is its function?
In the upper half of the gastric gland, secrete HCL
How can you characterise a parietal cell?
Numerous mitochondria and intracellular canaliculi (fried egg shape)
Where are chief cells found?
In the lower part of tubular glands
What is the function of chief cells and how are they characterised?
To secrete pepsinogen (converted to pepsin) and lipase.
Characterized by many RER
Where do neuroendocrine cells secrete their hormones in the stomach
In the neck of the stomach of the fundus and body
Name the two gastric hormones
Gastrin and somatostatin
What is the function of gastrin and how is it controlled?
Activate parietal cells to secrete acid
Controlled by parasympathetic, as soon as food is detected. Secreted by G cells
What is the function of somatostatin in the context of Gastrin
Secreted by D cells, inhibits the release of gastrin. Stimulated by HCL
What is the histological difference between the fundus and the body of the stomach?
The pylorus has larger foveola to produced enough protective mucin – few parietal cells or chief but mucous secreting cells are present at the base.
Because due to gravity all the acid falls down to the bottom of the stomach, so there are larger foveoli to protect the stomach lining
Draw a diagram of the intestinal crypt
Should include: stem cells just above the bottom cells, paneth cells at the bottom and goblet cells along the sides
What is the proliferative index?
How rapidly cell division occurs
What do Goblet cells secrete?
Mucins (MUC2)
What is characteristic about Goblet cells?
The nuclei are fixed at the basal membrane
What is characteristic about Goblet cells?
The nuclei are fixed at the basal membrane
What is the function of a Paneth cell?
To produce a sterile environment by secreting chemicals in lysozymes
What are APUD cells?
A collective term for a diffuse range of endocrine cell types scattered throughout the body.
APUD cells constitute a component of a universal diffuse neuroendocrine system.
How are APUD cells histologically identified?
these cells can be identified by their staining behaviour as they produce chromogranin A – increases secretory behaviour of cells around them
What is the function of Brunner’s gland
To secrete sodium bicarbonate to neutralise the stomach acid entering the duodenum
What is the shape of a Brunner gland?
compound, tubular, mucous glands
Where are Brunner’s glands located?
In the submucosa of the duodenum
What are the differences between the duodenum and the rest of the GI tract?
- Duodenum contains the Brunner’s gland
- Villi are longer in the duodenum than in the ileum
-Lymphoid tissue more prominent in ileum
-Proportion of Goblet cells increases distally (as you go down)
Where are Plicae circulares most prominent?
Plicae circulares most prominent in jejunum and proximal ileum. Absent in proximal duodenum and distal ileum
What is the function of the cecum?
Cecum - where complex carbohydrates are broken down (e.g. cellulose from grass- so cows have a large cecum)
What is the noticeable difference when the small intestines becomes the large intestines
Transition from villous mucosal surface of ileum (left) to flat mucosa of large intestine (right) at the ileocaecal junction.
What is the main mass of tissue in the appendix?
Lymphoid tissue in the submucosa . The glands are much more spaced out
What is the function of the colon?
Recovery of water, peristalsis of faecal material
What is the predominant structure in the colon?
Crypts are the predominant structure in the colon. (all crypts to absorb water) Single cylinders that rarely branch
What is the notable thing about the histology of the colon?
It lacks villi
What is the transition between the rectum to the anus
Recto-anal junction: abrupt transition from columnar to stratified squamous epithelium (for protective)
What is the histological thing about the colon?
It contains not villi
Where are Meissner’s plexus located?
In the submucosa of the small and large intestines, they are comprised of a network of unmyelinated nerve fibres (generally inconspicuous) and associated ganglia
What is the function of Auerbach’s plexus
To regulate the peristaltic contractions by nerve fibres located between circular and longitudinal layers of muscle
What cells can act as stem cells
Isthmus cells
