Histology Flashcards
What are the 5 functions of the GIT
Digestion Absorption Secretion Movement Protection
Name the 4 layers of the stereotypical GIT walls
Mucosa Submucosa Muscularis externa Serosa * Plus glands in the wall and external glands
What 3 sub layers does the the mucosa consist of?
- Epithelium
- Lamina propria
- Muscularis mucosa
What are the functions of each of the sub layers of the mucosa?
1. Epithelium • Simple columnar or stratified squamous • Can include endocrine cells, • Renewed every 5-6 days 2. Lamina propria • Loose CT containing: -> nerves, small blood vessels and immune cells. 3. Muscularis mucosa • Thin layer of SM • Forming boundary of mucosa + • Facilitates mixing
What are the two types of epithelium found in the GIT?
Where are each of them found?
Simple columnar and stratified squamous
- Stratified squamous is found in the oesophagus and the rectum the rest is simple columnar
Where are blood vessels found in the mucosa?
The lamina propria - they are small (mainly capillaries and lymphatics)
Where is the submucosa located and what is it made up of?
Adjacent to mucosa
It consists of dense, irregular connective tissue
Blood vessels and nerves also present
sometimes contains immune cells/glands (oesophagus + rectum - the Brunner’s gland of the duodenum is submucosal)
What is the role of the submucosa?
strength/elasticity
What are the two layers of the muscularis externa?
- inner circular layer → squeeze gut
2. Outer longitudinal layer → shorten & lengthen gut
What is the primary function of the muscularis externa?
Responsible for gut movement: mixing, propulsion, evacuation (through peristalsis)
Esp important in the stomach stomach where it mixes the chyme together with the acids and enzymes
What is the role of the serosa?
it provides a non stick surface of gut and allows organ movement
What is the serosa composed of?
fluid-secreting simple squamous epithelium (mesothelium)
What is a potential complication arising from surgery that results from the serosa?
Formation of adhesions restricting movement (tissue must be kept moist in surgery to prevent organs sticking!)
Where is serosa found?
Surrounding intraperitoneal organs
What is the enteric nervous system?
It is the 3rd component of the ANS (along with the SNS and the PNS) which supplies the gut
Can the gut function without central nervous system input?
ENS has autonomic motor neurons and autonomic sensory neurons in gut wall
It Doesn’t need CNS to function
How do the number of neurons in the gut compare to those in the spinal cord?
As many in the gut wall as the spinal cord
What are the roles of the ENS?
it is responsible for mixing, peristalsis and secretion
Where are the ENS nerve plexus and what inputs do they provide?
Myenteric ganglia/plexus
Located between the inner circular and outer longitudinal muscles
It provides motor innervation to both layers of the muscular layer, having both parasympathetic and sympathetic input,
Submucosal ganglia/plexus
Located in the submucosa and only parasympathetic fibers and provides secretomotor innervation to the mucosa nearest the lumen of the gut.
What is the epithelium of the oesophagus made of and why?
Non-keratinized squamous epithelium
It is tough, replaceable, resistant to mechanical abrasions by food
Why could the oesophagus not absorb nutrients even if it wanted to?
It has an extremely thick mucosa which provides protection
What is the breakdown of the muscles of the oesophagus?
Upper 1/3 skeletal (voluntary)
Middle 1/3 mixed
Lower 2/3 smooth muscle (involuntary)
What can happen to the epithelium of the oesophagus if exposed to prolonged GERD?
Squamous epithelium converts to columnar mucous form -> Barrett’s oesophagus (metaplasia.) -> cancerous
What is the primary role of submucosal glands in the oesophagus?
Aid in lubrication
What happens to the mucosa as it transitions from oesophagus to the stomach?
Goes from squamous epithelium → highly glandular mucosa (in stomach)
What controls the release of material (acidic chyme) into the intestine?
Pyloric sphincter -
What are the 4 regions of the stomach?
Cardiac region, fundus, body and antrum
What are the functions of the stomach?
Initiatedigestion (mainly of proteins)
Produce chyme (a thick liquid) by mechanical and chemical breakdown
Regulate release of chyme into the intestine
Only minimal absorption
What is the structure of the stomach?
- Simple columnar secretory epithelium
- Prominent muscularis mucosae
- Thick submucosa
- Thick muscularis externa (third, oblique layer in parts)
What is the role of the pyloric sphincter?
important to control as it allows only small amounts of acidic chyme into the small intestine
What are the folds of the stomach called?
rugae
What is found within the gastric pits?
Gastric glands
How many glands per gastric pit?
3-5
What is the arrangement of the glands?
Simple tubular glands - penetrate into the lamina propria
What are the different cells of the gastric glands?
Surface cells Neck cells Regenerative stem cells Parietal cells Chief cells Enteroendocrine cells
What do surface and neck cells do?
They secrete mucous which provides lubrication and protection (not goblet cells)