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Digestive System Module > Lecture 12 > Flashcards

Lecture 12 Flashcards

1
Q

Small Intestine

A

Majority of SI is suspended by mesentery
Plyci Circularis: Prominant permanent Circularly arranged rings = Increase SA =contain villi as well for further SA increase

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2
Q

Plicae Circularis

A

contain villi

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3
Q

Villi

A

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

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4
Q

Small Intestine Villi in elderly

A

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

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5
Q

Where is the smooth muscle of villi’s located?

A

Muscularis mucosae

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6
Q

Microvilli

A

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

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7
Q

Glycocalyx

A

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)

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8
Q

Enterocyte Atrophy/Disfunction

A

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

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9
Q

Goblet cells

A

Interspersed between Columnar Absorptive cells/Enterocytes

  • No microvilli on apical surface
  • secrete mucous for lubrication
  • mucous cells contribute to glycocalyx layer?
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10
Q

Enteroendorcrine cells

A

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
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11
Q

Undifferentiated stem cells/Germenative cells

A

Near Gland region
Interspersed
Migrate upwards or downwards to replace cells

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12
Q

Paneth cells

A

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)
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13
Q

Secretin

A

Secreted by enteroendocrine cells of SI

  1. Stimulates pancreatic Ductal cells to increase Bicarbonate (HCO3-) secretion
  2. Inhibits stomach acid production
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14
Q

Cholecystokinin

A

Secreted by enteroendocrine cells of SI

  1. Stimulates gallbladder to contract –> release of bile into Duodenum
  2. Stimulate pancreas to increase Digestive enzyme secretion
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15
Q

Serotonin

A

Secreted by enteroendocrine cells of SI

  1. Increases peristalsis
  2. increase Intestinal secretions (by goblet and Paneth cells etc)
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16
Q

Somatostatin

A

Secreted by enteroendocrine cells of SI

  1. Reduce Gastrin
  2. Facilitates Smooth muscle contraction
  3. Enhances absorption
17
Q

Villi 2x cellular contents

A

Villi=Epithelium

  1. -simple columnar enterocytes/absorptive cells
  2. -goblet cells
18
Q

Crypts 5x cellular contents

A

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
Q

Gastric/Duodenal Junction histology

A

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
Q

Summary of stomach’s chyme output

A 
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
Q

Duodenum summary

A

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
Q

Jejunum summary

A 
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
Q

Ileum Summary

A

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
Q

Caecum

A

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

25
Q

Large Intestine

A

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

26
Q

Colon Mucosa

A

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
Q

What is the function of the colons Columnar Absorptive cells?

A

Absorb Water + Electrolytes

Absorb Vitamins produced by Bacteria (B + K)

28
Q

Colon Muscularis Mucosa

A 
2x layers (ICOL)
OL --> 3x distinct strips/thickenings
=TENI COLI = Thickening of Outer Longitudinal =contracts to form pocket shaped foldings
29
Q

Rectum and Anus of LI

A
  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
Q

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

A

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

31
Q

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

A

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
Q

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

A

Location: Lower 1/2 of glands/Crypts of Lieberkuhn
Surface/Superficial: Days
-eneterocytes/absoprtive cells
Deeper: Months
-protected, specialised and expensive paneth cells

33
Q

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

A

Location: Lower 1/3 of glands/Crypts of Lieberkuhn

Surface cells: Days

34
Q

Overall Pattern of renewal and Differnetiation

A

Not all epithelial cells are replaced at the same rate

35
Q

Chemotherapy

A

-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

Digestive System Module (38 decks)

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