W3 - Lower GI Tract Flashcards
Why is there not much muscle in the SI compared to the stomach and why do the plicae folds of the SI not have any HM stretching signals like the stomach?
Not much muscle - food already broken down so less need, No HM stretching signals - SI primary function is absorption not secretion
What are Peyer’s patches and where are most/least found?
Aggregations of lymphoid follicles that bulge into the lumen, least in duodenum, most in ileum
Epithelium overlies the domes formed by Peyer’s patches, what are these specialised for?
Antigen uptake
What cells in the small intestine have microvilli (increase SA), which produce mucin and which are present at the base of crypts?
Enterocytes, goblets cells, paneth AND stem cells
What is the primary function of the duodenum?
Neutralises stomach acid
What is a crypt the equivalent of in the intestine?
A gland
What 3 things are absorbed along the microvilli on the apical surface of the enterocytes?
Ions, sugars and amino acids
Under the epithelial cells on the are the lamina propria cells, what cell type are these primarily?
Immune cells
The glycocalyx contains enzymes secreted by absorptive cells for final stages of sugar and protein digestion, what else do they do in terms of microvilli?
Increase SA by bedding microvilli and protect the microvilli
Acid mucopolysaccharides and what make up the glycocalyx?
Glycoproteins
The SC are found near the bottom of the crypt in the SI, what cells help them by keeping the crypt sterile?
Paneth cells
What is the region called where the SCs are consistently undergoing mitosis in the crypt of the SI?
Transit-amplifying cells
How long does it take to overturn the the entire amount of epithelial cells in the bowel?
4-7 days
How many times does a crypt divide within a person’s entire lifetime?
3
All cells in SI crypts (goblet, paneth, enterocyte, neuroendo) are derived from a single SC, what do you call these lineages?
Clonal
Goblet cells secrete muc2, what stimulates this secretion?
Neuronal input
PAS-diastase staining reveals the mucous in a goblet cell, what does H+e show?
An unstained vacuole
What do paneth cells produce to help keep the crypts sterile?
Lysozyme and antimicrobial peptides
What particular name is there for all of the neuroendocrine cells present in the body?
APUD cells - Amine and Precursor Uptake and Decarboxylation
Histologically, what HM is produced by APUD cells to increase the secretory behaviour of the cells around them?
Chromogranin A
What glands are specific to the duodenum to secrete alkaline mucus to neutralise stomach acid and where do they sit?
Brunner’s glands, under epithelium
Where are villi longest - shortest?
Longest in duodenum, shortest in ileum
Where are the plicae circulares most and not prominent?
Jejunum and proximal ileum, not in duodenum or distal ileum
What happens to the lymphoid tissues and goblet cells as you go more distal along the SI?
They both increase
What is the difference between surface of small intestine and large intestine?
Large intestine is much smoother, only has crypts and no villi
What does the appendix have lots of in the submucosa and what is the primary function?
Lymphoid tissues for immune surveillance
What does the large amount of immune cells in the appendix mean for the positioning of the glands compared to in the SI?
They are forced to be much more spread out
What are the 2 functions of the colon?
Recovery of water and peristalsis of faecal material
What is the most frequent cell in the colon crypt and why?
Goblet cells, lubricate solid matter
Why is it unnecessary to have microvilli on the enterocytes to absorb water?
The colon is big enough to absorb water as it is
Rectum has no secretory/absorptive but has more goblet cells than LI, what happens to the epithelium at the recto-anal junction and then after the anus what does this transition to?
Goes from simple columnar stratified squamous to columnar which then transitions to skin
What makes up the anal sphincter?
Skeletal muscle
Why does the epithelium transition at the recto-anal junction?
Protection and due to presence of anal sphincter
