Lecture 12 Flashcards
Small Intestine
Majority of SI is suspended by mesentery
Plyci Circularis: Prominant permanent Circularly arranged rings = Increase SA =contain villi as well for further SA increase
Plicae Circularis
contain villi
Villi
Evagination: villus
Depression/invagination: Intestinal Glands/Crypts of Lieberkuhn
-both increase SA for digestion and absorption
Core: support structures
1. 2. -BV - capillaries carrying O2 rich blood towards SI (for metabolic activities) –> become venous, carrying nutrients to liver (joining hepatic portal vein) for processing and re-distribution
3. Lacteal - lymphatic vessel. Core, embedded in CT support.
4. Smooth muscle fibres embedded in core of villus
-a) contraction produces rhythmic villi beating enhancing digestion (form homogenous mixed chyme/maximising exposure of luminal contents with epithelial cells)
-b) lacteals/lymphatic vessels dont have SM in their vessel walls, therefore lamina propria smooth muscle fibres help to squeeze/”milk” lymphatic contents along
Small Intestine Villi in elderly
decreased Blood supply and circulation functions (to gut)
Decreased supply/circulation =
decreased absorption
=severe cases = mal absorption/mal nutrition
Where is the smooth muscle of villi’s located?
Muscularis mucosae
Microvilli
membrane projections filled with cytoplasm
-into luminal surface
on top/apical surface of columnar absorptive cells/enterocytes
Increase SA for absorption and digestion
core contains Actin= connected to cytoskeletal network of cell
- SM in lamina propria contract = BM moves = physically moves cells on BM = mechanical movement moved to cytoskeleton = all transferred to embedded actin filaments
(mechanically connected) = microwhisks –> localised mixing movement of contents
- avoids lumps, and results in homogenous spread and mixing of contents for digestion
-Digestive enzymes in lipid bilayer membrane of microvilli (Glycosidase –> digest CHO carbs) (catalytically active enzymes for digestion)
-Glycocalyx ontop
Glycocalyx
Slippery film located ontop of the membranous microvilli of the columnar absorptive cells (Enterocytes) of SI
-lots of Glyco proteins
-lots of acidic polysaccharides
Selective gatekeeper:
-Attracts desired molecules
-Barrier/blocks to unwanted molecules
-goblet cell’s secretion of mucous cells contribute to glycocalyx layer? (how it is formed)
Enterocyte Atrophy/Disfunction
Columnar Absorptive cells/Enterocytes of SI
-important in digestion
-caused by infections, tumours, inflammation, drugs, surgery, celiac disease
-can cause
-Diarrhea (inadequate absorption)
-stetrohea (in adequate fat absorption = fatty poo)
-abdominal pain and discomfort
-weight loss
- nutritional deficiency
Outcomes all due to the absorptive and digestive role of enterocytes that have been effected
Goblet cells
Interspersed between Columnar Absorptive cells/Enterocytes
- No microvilli on apical surface
- secrete mucous for lubrication
- mucous cells contribute to glycocalyx layer?
Enteroendorcrine cells
Found deep in crypts of lerburkuhn/Intestinal Glands
- Spread out (not defined to specific location)
1. Acidic chyme (Fatty acids and Amino Acids) triggers hormone release into basolateral membrane - Secretin
- Cholecytsokinin
- Serotonin
- Somatostatin
Undifferentiated stem cells/Germenative cells
Near Gland region
Interspersed
Migrate upwards or downwards to replace cells
Paneth cells
Bottom of Crypts of Luberkuhn /coldersac region
- where glands turn around
- Antimicrobial/antiviral function
1. Lysozyme (bacteriocidal - destroys bacterial membranes)
2. TNF-a (inflammatory mediator in response to pathogens)
3. Defensins (increases cell membrane ion channels of the invading organism - increasing their permeability. Complement process)
Secretin
Secreted by enteroendocrine cells of SI
- Stimulates pancreatic Ductal cells to increase Bicarbonate (HCO3-) secretion
- Inhibits stomach acid production
Cholecystokinin
Secreted by enteroendocrine cells of SI
- Stimulates gallbladder to contract –> release of bile into Duodenum
- Stimulate pancreas to increase Digestive enzyme secretion
Serotonin
Secreted by enteroendocrine cells of SI
- Increases peristalsis
- increase Intestinal secretions (by goblet and Paneth cells etc)
Somatostatin
Secreted by enteroendocrine cells of SI
- Reduce Gastrin
- Facilitates Smooth muscle contraction
- Enhances absorption
Villi 2x cellular contents
Villi=Epithelium
- -simple columnar enterocytes/absorptive cells
- -goblet cells
Crypts 5x cellular contents
Crypt=Lamina Propria
- BVs
- Lacteal
- Smooth muscle SM
- Lymphocytes
- Fibroblasts (collagen)
- Paneth cells in bottom dark staining with granules of secretion
Gastric/Duodenal Junction histology
Transition between region= Epithleium changes
Stomach/Gastric: enrichment of Smooth muscle in outer layer (pyloric sphincter) + gastric pits and glands
—>
Small Intestine: Intestinal villi and crypts(no plicae yet) + sub mucosal structures (Lymphatic nodes and Brunner’s glands)
Summary of stomach’s chyme output
Acidic (chyme) Amino acid chains Fatty acids -come through pyloric sphincter (control amount and time (volume and frequency)) -3x combination stimulate SI enteroendocrines to signal pancreas and gallbladder -which both contribute to: 1. Digestive enzymes 2. Bicarbonate 3. Bile -into Duodenum (SI)
Duodenum summary
pH lumen 1-2 —-> 7-8 (pH become neutral as progress down duodenum, due to pancreatic HCO3- and submucosal BRUNNERS glands (in submucosa) which produce alkaline mucous secretion)(neutralise entering acidic chyme) (high amount of B glands –> Decreasing amount)
25cm-short
c-shaped - strong curvature
Jejunum summary
2 + 1/2 metres - long -wound/heavily trwisted to fit into cofined space Mesentery suspended (macroscopic defining feature) -circular profile=sectioning artifact/circular cut through crypt -lots of pronounce plicae and villi
Ileum Summary
3 + 1/2 metres - long
(stop before lots of bacteria of LI)
Enriched in defence (in preparation of bacterial LI)
-less pronounced plicae
-Lots of lymphocytes in gut circulating to patrol local bacteria population
Peyers Patches-Enriched with massive lymphatic aggregates - macroscopically visible (seen with naked eye) (red dots in lumenal surface)
-core of B lymphocytes + Rim of M cells
Mcells (antigen presenting and sensing cells/ antigen sampling cells)
Caecum
First part of Large intestine
Distending pouch
Contents controlled by Illio-caecal valve
Ending = appendix (blind ending sac, veriform/worm like in humans)
Large Intestine
I-C valve
caecum (ended with veriform/ human wormlike appendix
Ascending, Transverse and Descending colon
Rectum
Colon Mucosa
Smooth-no Plicae/Vili
Only increase of SA via Crypts of Lieberkuhn (interchangeable for INTESTINAL glands)
-Columnar absorptive cells - superficial (absorb water + electrolytes + vitamins B + K(produced by bacteria)
-Goblet cells(mucous lubrication)
-Watery contents at start of colon –> absorption –> firmer/viscous/harder/dehydrated contents
- (little —-> alot of mucous) -increasing lubrication
Enteroendocrine yes- but not routinely visible
Undifferentiated Cells present - Lots of Sheer forces occurring in colon, therefore move upwards to replace superficial cells
What is the function of the colons Columnar Absorptive cells?
Absorb Water + Electrolytes
Absorb Vitamins produced by Bacteria (B + K)
Colon Muscularis Mucosa
2x layers (ICOL) OL --> 3x distinct strips/thickenings =TENI COLI = Thickening of Outer Longitudinal =contracts to form pocket shaped foldings
Rectum and Anus of LI
- Transition of Columnar absorptive + goblet —-> Stratified squamous (for sheering forces of expelled faecal matter/friction out (or protection of things going in)
- Anal sphincter: Inner Smooth muscle Involuntary control. EXTERNAL SKELETAL muscle- degree of control holding shit together
Location and replacement rate of germinative stem cells in the Oesophagus?
Location: Basal part of Epithelium
Surface cells: Days (3ish)
-alot of sheering
Location and replacement rate of germinative stem cells in the Stomach?
Location: Near neck of Gastric glands (middle ish)
Surface/Superficial: Days
-to replace mucous secreting cells as important protective layer
Deeper: Months
-chief and parietal highly specialised cells. Alot of energy and metabolic substrate to replace + enetroendocrine cells
-deeper so more sheltered from acidic environment/physcial contact with chym
Location and replacement rate of germinative stem cells in the Small Intestine?
Location: Lower 1/2 of glands/Crypts of Lieberkuhn
Surface/Superficial: Days
-eneterocytes/absoprtive cells
Deeper: Months
-protected, specialised and expensive paneth cells
Location and replacement rate of germinative stem cells in the Large Intestine?
Location: Lower 1/3 of glands/Crypts of Lieberkuhn
Surface cells: Days
Overall Pattern of renewal and Differnetiation
Not all epithelial cells are replaced at the same rate
Chemotherapy
-common Diarrhea and Nausea
-closely tied to mitotically targeting anticancer drugs on highly-replaced cels
Cancer=Net cell growth (more cell growth and death). Disease of cell replication
Chemotherapy- non-distinctly targets all rapidly mitotically dividing cells. Impacts on normal replacement of superficial cells (by germinative stem cells)
-Therefore early chemo drugs have such a large impact on digestive system, as normally their is a high baseline level of mitotic activity
-new drugs more specific/targeted/different mechanism of action
