Micro-anatomy Flashcards
What are the different layers of epithelium?
Simple squamous, simple cuboidal, simple columnar, stratified squamous, stratified cuboidal and stratified columnar
What are the thickness of the subtypes of epithelium?
Simple = 1
Stratified = more than 1
Pseudo stratified = 1 layer than pretends to be 2
Squamous = flat cell
Columnar = column like cells
What is the entire digestive tract?
It is a Continuous tube with some wide and some narrower bits
What are the 4 layers that the tube consists of?
Mucosa, sub mucosa, muscularis externa and serosa
What are the 3 component layers of the mucosa?
Epithelium, laminate propria and muscularis mucosa
Describe the epithelium in the mucosa?
A thin layer that lines the lumen of the tube, can be simple or stratified, squamous or columnar.
It forms a selective barrier that digested molecules must cross
It may contain mucous secreting goblet cells and endocrine cells secreting digestive hormones
Describe the laminate propria
Loose connective tissue
It has a good blood supply and it often contains lymphatics and numerous white blood cells, it is the first immunological barrier to pathogens in the GI system
Describe the muscularis mucosa
It is a thin layer of smooth muscle cells causing localised contractions in the mucosa
What is the sub mucosa?
It is a layer of dense connective tissue that contains the submucosal plexus
Secretion and blood flow are controlled by the submucosal plexus. It relays information from the gut epithelium and stretch receptors in the wall
It is part of the enteric nervous system
What is the enteric nervous system?
It is a branch of the autonomic nervous system, it is NOT part of the sympathetic or parasympathetic.
It can operate independently of the CNS
What does the enteric nervous system consists of?
It consists of mostly two major plexi within the GI wall - the myenteric and submucosal plexi
Describe the muscularis externa
It consists of two layers of smooth muscle - inner circulation and outer longitudinal.
The myenteric plexus, the second plexus of the enteric nervous system lies between the layers of smooth muscle and it is mainly involved with the control of GI motility
What happens when the inner circular and outer longitudinal layers go through a wave of contraction and relaxation?
Food is forced along these layers along the digestive tract - called peristalsis
What is the serosa?
It is a layer of epithelium that forms part of the peritoneum
Describe the microanatomy of the oesophagus
The muscularis externa of the upper third of the oesophagus consists of a skeletal muscle.
Mucus secreting glands are present in the laminate propria and the sub mucosa
Describe the microanatomy of the stomach
Gastric puts contains the secretory cells of the gastric epithelium
Describe the microanatomy of the small intestine
Villi are finer-like projections that are present, the recessions between the villi are known as crypts.
The epithelial surface of the villi is simple columnar
Describe the villi network in the small intestine
There are numerous microvilli on the surface of the cells that form a ‘brush border’
Each villus contains a capillary network that transports adsorbed amino acids and monosaccharides plus a blind-ended lymph vessel that transports absorbed fat. The capillary network drains into the portal vein
what is the villus considered to be?
The functional unit of absorption
What are the four specialised cells that are present within the epithelium of the villi?
Absorptive cells, goblet cells, granular cells and APUD cells
Where do the four specialised cells arise from?
The undifferentiated cells at the base of the crypts
What are absorptive cells?
They secrete digestive enzyme and absorb nutrients
What are goblet cells?
They produce mucus that lubricates and protects the epithelium from mechanical damage
What are granular cells?
They secrete enzymes and protect epithelium from bacteria
What are APUD cells?
They produce endocrine secretions that regulate secretions and motility of the GI tract
What do absorptive and goblet cells do?
They ascend the villi from the base of crypts
When is the epithelium renewed?
Every 3-6 days, the mature cells are usually located at the tip of the villus until they shed
Where do granular and APUD cells remain?
At the base of the crypts
Describe the microanatomy of the large intestine
The epithelium of the large intestine is not villus, it is simple columnar and contains crypts.
What cells are present in the large intestine?
Goblet cells and absorptive cells, APUD cells are present but they are sparse
What cells is found in larger number in the large intestine than the small?
Goblet cells which means there is more mucus
What is found to be similar in the large and small intestines?
The laminate propria, muscularis and submucosa
What surrounds the large intestine?
The outer longitudinal layer of smooth muscle, except it doesn’t cover the rectum
What is the is the longitudinal layer of smooth muscle called?
Taeniae coli, it is split into 3 separate bands than run the length of the colon
What does the Taeniae coli aid?
It aids peristalsis
What is the Taeniae coli not present on?
It is not present on the rectum, anal canal or the vermiform appendix
