Intestinal microanatomy Flashcards
Things that increase SA of the small intestine?
Plicae, villi, crypts of lieberkuhn and microvilli
Purpose of blood vessels to the small intestines?
They carry Oxygen-rich blood to the SI, allowing metabolic activity
Purpose of the venous system of the SI
Carries away nutrient-rich blood to the liver for processing and redistribution (Hepatic Portal Vein)
Purpose of lacteal lymphatic vessels and the SI
transport lipids
What is in the core of a villus
Blood vessels and lacteals, embedded in CT support. muscle fibres extend in from muscularis mucosae
What is the purpose of the smooth muscle fibres in the lamina propria?
Help milk and squeeze the lacteals
Another name for intestinal glands? What is their purpose?
Crypts of Lieberkuhn. To increase SA
What is an issue that can happen to the elderly around blood supply.
Sometimes, especially in elderly, blood supply and circulation can decrease.
> less absorption taking blood away from gut > malabsorption and malnutrition
What is studded in the lipid bilayers?
1000’s of digestive enzymes eg) glycosidase breaks down carbs
What are the cells of the SI
columnar absorptive cells (enterocytes) Goblet cells Enteroendocrine cells undifferentiated cells Paneth cells
Microvilli are
projections of membrane filled with cytoplasm. Have a core of actin filaments. Found at the apical surface of columnar absorptive cells. (enterocytes)
Why do microvilli have a core of actin filaments
Bc the actin filaments are connected to the cytoskeleton network
SM in LP contract > BM of epi. cells move > Cells atop BM move > Microvilli atop epi cells move
This creates localised, homogenous mixing of contents, via ‘microwhisks’.
What is the glycocalyx?
a slippery biological film made of glycoproteins and acidic mucopolysaccharides. Sits atop and coats microvilli
Function of the glycocalyx?
Selective gate keeper, attracts desirable contents and blocks unwanted.
Goblet cells
- no microvilli on apical surface
- secrete mucus for lubrication
- theories that mucus contributes to glycocalyx
Undifferentiated cells are?
Stem cells that can divide and migrate to replace epithelium.
What stimulates enteroendocrine cells, and what do they release?
Stimulus: acidic chyme, FA, amino acids
Release: Cholecystokinin, serotonin, secretin and somatostatin.
Purpose of Cholecystokinin
1) + gall bladder to contract (bile released into duodenum)
2) + pancreas to increase enzyme production and secretion
Purpose of secretin
1) + pancreas to produce bicarbonate (from ductule cells)
2) - acid production by stomach
Purpose of serotonin
1) + peristalsis
2) + intestinal secretion (goblet, paneth etc)
Purpose of somatostatin
1) Reduce gastrin
2) Facilitates SM contraction
3) enhances absorption
Paneth cells around found? what are they for? What do they produce
Found at bottom of crypts
important for antimicrobial and antibacterial purposes
produce TNF-alpa, lysozymes, defensins
acidic chyme, amino acids and FAs from the stomach stimulate?
pancreas and gallbladder > release digestive enzymes, HCO3- and bile into the duodenum
How does the pH of the duodenum change and how does this occur?
from acidic pH 1-2 to eventual 7-8 (neutral).
This is due to submucosal ‘Brunners glands’ (as well as bile)
that secrete an alkaline mucus that counteracts the acidic chyme.
(lots initially, less distally)
Length of the Duodenum, jejunum and ileum
D: 25cm
J: 2.5m
I: 3.5m
Purpose of the pyloric sphincter
To control the volume and frequency of chyme into the duodenum
Features of the jejunum?
Heavily twisted
suspended with mesentery
increased plicae
Identifying feature of the ileum? What is this for?
Macroscopically visible lymphatic aggregates “Peyers Patches”
These have a B cell core, and a M cell outer (antigen presenting/sensing cells for sampling)
This is for defence against the large amount of bacteria in the LI
What is in the lamina propria
BVs, lacteals, SM, lymphocytes, fibroblasts
Muscle type of the anal sphincters
Internal sphincter = smooth muscle
external sphincter = skeletal muscle
The rectum and anal canal has different types of epithelium. What are these?
Rectum: Simple columnar enterocytes + goblet cells
Superior half: simple columnar epithelium
Inferior half: Stratified squamous epithelium
Purpose of the SS epithelium in the anal canal?
protects against the friction of faecal matter leaving
How does the frequency of goblet cells change throughout the colon and why?
Start of colon: Watery substances, few goblet cells
Water is absorbed
End of colon: viscous, dry, dehydrated, many goblet cells
Features of the colon mucosa?
smooth with no plicae or villi
Numerous crypts of lieberkuhn
Main two cells:
1) Columnar absorptive cells (absorb, water, electrolytes and vitamins B&K)
2) Goblet cells (secrete mucus for lubrication)
also have enteroendocrine cells (not visible by light microscope)
undifferentiated cells: at base of glands (migrate upwards
Features of the colons lamina propria
Lots of lymphatics
dense layer of collagen immediately beneath the surface epithelium
Features of the colons muscularis externa.
Still has inner circular and outer longitundinal muscle layers
But outer longitudinal forms three strips ‘teniae coli’ that run along the colon
- this allows segments of the colon to contract independently
- contraction pulls colon into sac like pockets ‘haustraccoli’
is the colon covered in serosa or adventitia?
Posterior surface = adventitia
elsewhere = serosa
Describe the purpose of the rectum/ anus
temporary storage of faecal material (movement of material into leads to the urge to defecate
What are the sections of the rectum/anus
final portion = anal canal (mucosa has anal columns)
distal margin = pectinate line (transverse folds)
anal sphincters = internal and external
end of anal canal = anus
What is the general trend around cell replacement rates
surface/ SF cells: high replacement rate (days)
Deeper cells: replaced every few months
Deeper cells are more specialised, require more energy to replace.
What are some common GI effects of chemo
diarrhoea, nausea.
This is due to the mitotically targeting anticancer drugs affecting the highly replaced surface cells
