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Flashcards in Lecture 12 Deck (35):
1

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

2

Plicae Circularis

contain villi

3

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

4

Small Intestine Villi in elderly

decreased Blood supply and circulation functions (to gut)
Decreased supply/circulation =
decreased absorption
=severe cases = mal absorption/mal nutrition

5

Where is the smooth muscle of villi's located?

Muscularis mucosae

6

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

7

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)

8

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

9

Goblet cells

Interspersed between Columnar Absorptive cells/Enterocytes
- No microvilli on apical surface
-secrete mucous for lubrication
- mucous cells contribute to glycocalyx layer?

10

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

11

Undifferentiated stem cells/Germenative cells

Near Gland region
Interspersed
Migrate upwards or downwards to replace cells

12

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)

13

Secretin

Secreted by enteroendocrine cells of SI
1. Stimulates pancreatic Ductal cells to increase Bicarbonate (HCO3-) secretion
2. Inhibits stomach acid production

14

Cholecystokinin

Secreted by enteroendocrine cells of SI
1. Stimulates gallbladder to contract --> release of bile into Duodenum
2. Stimulate pancreas to increase Digestive enzyme secretion

15

Serotonin

Secreted by enteroendocrine cells of SI
1. Increases peristalsis
2. increase Intestinal secretions (by goblet and Paneth cells etc)

16

Somatostatin

Secreted by enteroendocrine cells of SI
1. Reduce Gastrin
2. Facilitates Smooth muscle contraction
3. Enhances absorption

17

Villi 2x cellular contents

Villi=Epithelium
1. -simple columnar enterocytes/absorptive cells
2. -goblet cells

18

Crypts 5x cellular contents

Crypt=Lamina Propria
1. BVs
2. Lacteal
3. Smooth muscle SM
4. Lymphocytes
5. Fibroblasts (collagen)
-Paneth cells in bottom dark staining with granules of secretion

19

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)

20

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)

21

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

22

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

23

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)

24

Caecum

First part of Large intestine
Distending pouch
Contents controlled by Illio-caecal valve
Ending = appendix (blind ending sac, veriform/worm like in humans)

25

Large Intestine

I-C valve
caecum (ended with veriform/ human wormlike appendix
Ascending, Transverse and Descending colon
Rectum

26

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

27

What is the function of the colons Columnar Absorptive cells?

Absorb Water + Electrolytes
Absorb Vitamins produced by Bacteria (B + K)

28

Colon Muscularis Mucosa

2x layers (ICOL)
OL --> 3x distinct strips/thickenings
=TENI COLI = Thickening of Outer Longitudinal =contracts to form pocket shaped foldings

29

Rectum and Anus of LI

1. Transition of Columnar absorptive + goblet ----> Stratified squamous (for sheering forces of expelled faecal matter/friction out (or protection of things going in)
2. Anal sphincter: Inner Smooth muscle Involuntary control. EXTERNAL SKELETAL muscle- degree of control holding shit together

30

Location and replacement rate of germinative stem cells in the Oesophagus?

Location: Basal part of Epithelium
Surface cells: Days (3ish)
-alot of sheering

31

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

32

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

33

Location and replacement rate of germinative stem cells in the Large Intestine?

Location: Lower 1/3 of glands/Crypts of Lieberkuhn
Surface cells: Days

34

Overall Pattern of renewal and Differnetiation

Not all epithelial cells are replaced at the same rate

35

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