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Y1 LSS Alimentary System > Small bowel and large intestine > Flashcards

Small bowel and large intestine Flashcards

Small intestine anatomy; Digestive epithelium; Large intestine anatomy; Large intestine function; Intestinal microbiome

1
Q

What are the 3 main divisions of the small intestine and what are their approximate lengths?

A

Duodenum - 0.25m
Jejunum - 2.5m
ileum - 3.75m

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2
Q

What are 3 noteworthy features of the small intestine?

A

Villi that increase the internal sfa
Mucosa arranged in folds
Invaginations called cypts of Lieberkühn

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3
Q

How is the small intestine functionally separated?

A

Pyloric sphincter at proximal end

Ileocaecal valve at distal end

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4
Q

What are the 4 sections of the duodenum?

A

1) Duodenal cap - superior
2) Major duodenal papilla - descending
3) Crosses IVC - inferior
4) Duodenojejunal flexure -ascending

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5
Q

What is secreted in the duodenum and why?

A

Bicarbonate rich alkaline solution is secreted to:

  • neutralise acid chyme
  • Protect lining
  • provide optimum pH
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6
Q

What differentiates the jejunum from the ileum?

A

Perfusion
jejunum has longer vasa recta and less prominent arterial arcades
ileum has prominent arterial arcades and shorter vasa recta

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7
Q

What are features of the jejunum?

A

plicae circularis - large submucosal folds like frills
found in upper left quadrant
long vasa recta
less prominant arterial arcades

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8
Q

What are features of the ileum?

A

Up to 100 Peyer’s patches - GALT that contain M cells that have no microvilli (initiate leukocyte and immunoglobulin responses to gut borne pathogens)
found in lower right quadrant
Shorter vasa recta
prominent arterial arcades

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9
Q

What are the roles associated with each section of the small intestine?

A

Duodenum - digestion and gut regulation
Jejunum - absorption
Ileum - absorption

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10
Q

Where do bile and pancreatic juice enter the small intestine?

A

Ampulla of Vater→Sphincter of Oddi→Major duodenal papilla

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11
Q

Where are digestive secretions in the small intestine derived from?

A

Liver
Pancreas
Small intestine wall

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12
Q

What are the two sites where enzymes are effective in the small intestine?

A

Gut lumen - enzymes that cleave big nutrients to small nutrients
Brush border of enterocytes - enzymes that cleave dimeric nutrients into monomers

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13
Q

What are the 3 main functions of intestinal motility?

A

mix ingested food with digestive secretions and enzymes
facilitate contact between contents and mucosal surface
propel contents along small intestine

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14
Q

What are the 3 main mechanisms of motility in the small intestine?

A

Segmentation
Peristalsis
Migrating motor complex

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15
Q

Describe the main features and effects of segmentation

A

Alternate contraction and relaxation of non-adjacent segments of circular muscle in the gut wall
Food pushed forwards then backwards
Major effect is mixing and mechanical breakdown
Minor effect is some propulsion

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16
Q

Describe the main features and effects of peristalsis

A

Sequential contraction of adjacent segments of circular muscle in the gut wall, combined with contractions of longitudinal muscle
Food propelled distally along GI tract
Major effect is propulsion
Minor effect is some mixing

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17
Q

Describe the main features and effects of the migrating motor complex

A

Periodic contractions from stomach to distal ileum during fasted state
Restart once complete
Present in fed state but less ordered
Effects are to prevent colonic flora travelling backwards and to help cleanse small intestine of residual fluid

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18
Q

What are the 5 main cell types in the small intestinal mucosa?

A 
Goblet cells
Enterocytes
Enteroendocrine cells
Paneth cells
Stem cells
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19
Q

What are the main features and responsibilities of enterocytes in the small intestine?

A

Most abundant in gut
Microvilli on apical surface
Connected to each other by tight junctions
Lifespan 1-6 days
Rich network of carbohydrates called the glycocalyx
Responsible for absorption

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20
Q

What is the purpose of the glycocalyx?

A

Traps H20, mucous (and enzymes in small intestine) on cell surface
Protects cell from luminal contents
Regulates digestion and absorption

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21
Q

What are the main features and responsibilities of goblet cells in the small intestine?

A

2nd most abundant cell in gut
Apical cytosol packed with mucin granules
(distorts cell shape giving it goblet shape)
Secretes mucous
Number increases along length of small intestine

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22
Q

What is mucous?

A

Water and glycoproteins

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23
Q

What is the purpose of mucous in the small intestine?

A

Lubricate intestine to facilitate gut passage

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24
Q

What are the main features and responsibilities of enteroendocrine cells in the small intestine?

A

Hormone secreting cells
Located at the bottom of crypts
Sensory apparatus in apical portion
Secretory granules are stored and kept ready for secretion into blood supply
Can be closed- not exposed to the gut lumen

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25
What are common examples of enteroendocrine cells and what do they secrete?
G cells - gastrin I cells - cholecystokinin S cells -secretin D cells - somatostatin
26
What are the main features and responsibilities of paneth cells in the small intestine?
Immunological cells Located at bottom of crypts Contain high number of acidophilic granules Located near stem cells Priority to help protect progenitor cells Engulf bateria Regulate intestinal flora
27
What do acidophilic granules in paneth cells contain and what is their purpose?
Lysozyme - antibacterial enzyme Glycoproteins - protect local cells from enzymes Zinc - common co-factor for lysozymes
28
What are the main features and responsibilities of stem cells?
Continually replace enterocytes and goblet cells Located at bottom of crypts Proliferate in crypts them move up sides of villus Reach top, become sentient and naturally slough off and are broken down and reabsorbed Process extremely energy intensive Essential to normal gut operation
29
What two things does the process of replacing enterocytes and goblet cells allow?
Effects of gut borne toxins/drugs to eventually run their course Leisons are short lived and can be repaired quickly
30
How does radiation affect GI function?
Impairs stem cell activity | Usually results in severe GI dysfunction
31
What is the process of carbohydrate digestion?
Amylase in mouth and pancreatic amylase in duodenum break down chains into dimers of sucrose/maltose/lactose Dimers broken down by brush border enzymes sucrase/maltase/lactase to glucose + fructose/glucose/galactose
32
How are the products of carbohydrate digestion absorbed?
Glucose + Galactose absorbed by 2° active transport via Sodium Glucose Linked Transporter 1 SGLT1 Fructose abosorbed by facilitated diffusion through Glucose transporter 5 channels GLUT5 All 3 diffuse down conc gradient through basolateral membrane via GLUT2 channels
33
What is the process of protein digestion?
Pepsin in stomach breaks long peptides into smaller peptides Proteases (e.g trypsin, chymotrypsin, carboxypeptidase) in pancreatic juice continues breaking down long peptides into tripeptides and dipeptides Final stage of digestion occurs in brush border by enzymes secreted from epithelial cells - tripeptidases and dipeptidases (endopeptidase, dipeptidase, aminopolypeptidase and carboxypeptidase)
34
How are the products of protein digestion absorbed?
Single amino acids absorbed into enterocytes by 2° active transport via AA/Na+ symporters Di/tripeptides absorbed via 2° active transport by AA/H+ symporters and are broken down to amino acids by cytoplasmic peptidase enzymes Amino acids move into blood via facilitated diffusion
35
What is the process of lipid digestion?
Lingual lipase from mouth hydrolyses triglycerides Gastric lipase in stomach cleaves single fatty acid chains from free triglycerides Mechanical churning of stomach slightly emulsifies fats to increase their sfa Bile in duodenum provides chemical emulsification to increase sfa even more Pancreatic juice cleaves 2 fatty acid chains from triglycerides to form monoglycerides and free fatty acids (pancreatic lipase and colipase) As digestion products reach brush border, combine with bile salts to form micelles that can cross aqueous unstirred layer
36
How are the products of lipid digestion absorbed?
Lipolytic products diffuse through apical membrane (bile salts remain in lumen) Monoglycerides and free fatty acids are resynthesised into triglycerides via 2 separate pathways: -Monoglyceride acylation pathway -Phosphatidic pathway Triglycerides then packaged with proteins, phospholipisds and cholesterols = lipoprotein chylomicrons Chylomicrons exocytosed and enter lymphatic system
37
What are the divisions of the large intestine?
Caecum appendix Ascending/transverse/descending/sigmoid colon rectum
38
How is the large intestine innervated?
PNS-vagus nerve innervates ascending and transverse colon, pelvic nerves innervate distal colon SNS-lower thoracic and upper lumbar spinal cord
39
How is the large intestine perfused?
Middle colic artery - ascending and 2/3 transverse colon | Inferior mesenteric artery - last 1/3 of transverse, descending, sigmoid and rectum
40
What are the dimensions of the large intestine?
150 cm long | 6cm wide
41
What are the 3 main functions of the colon?
Reabsorption of water and electrolytes Elimination of waste Microenvironment for gut bacteria
42
What is the purpose of the ileocaecal valve?
Separate ileum from caecum Tonically active and only relaxes to allow passage of fluid chyme Prevents microbiota from migrating into ileum
43
What is the right hand bend of the large intestine called?
Hepatic flexure
44
What is the left hand bend of the large intestine called?
Splenic flexure
45
What is the purpose of the rectum?
Store faeces on 'shelves' formed by transverse folds in rectal submucosa
46
What are the main differences between the structure of the rectum and the rest of the colon?
No taeniae colis | transverse rectal folds in submucosa
47
What is the role and main features of the anal canal?
Controls movement of things out of the GI tract Surrounded by 2 anal sphincters External sphincter under voluntary control by pudendal nerves
48
What are 4 unique features of the large intestine?
``` Appendices epiploicae -Fatty tags that arise from serosa Longitudinal muscle (taenia coli) -3 bands of longitudinal muscle -shorter than the intestine∴causes colon to form pouches called hastra Circular muscle -segmentally thickened -held together by taenia coli Nodules of lymphoid tissue ```
49
How does the large intestine reabsorb ions and water?
Na+ and Cl- absorbed by exchange mechanisms Water absorbed by osmosis Potassium moves passively into lumen via gap junctions
50
How much can the large intestine absorb and how much does it usually absorb per day?
can absorb 4500mL per day usually absorbs 1500mL per day if water volume in colon >4500 = diarrhoea
51
What are the main cells found in the colon?
Abundant enterocytes Abundant goblet cells Stem cells @bottom of colonic crypts few enteroendocrine cells
52
What is the purpose of enterocytes in the large intestine?
Re-absorption of salt creates osmotic gradient | Glycocalyx present but no brush border enzymes present
53
What is the purpose of goblet cells in the large intestine?
Secrete mucous to facilitate passage of luminal contents Cover bacteria and particulates to protect from infection/abraision Abundance increases along length Stimulated by ACh
54
What is the main difference between the large intestine and the small intestine?
No villi ∴ much smaller sfa due to no glucose or amino acid absorption in colon
55
Why are paneth cells not needed in the large intestine?
The presence of commensal bacteria
56
What are basic colonic contractions?
Kneading process Provides minimal propulsion to allow chyme to stay in colon for longer time to promote absorption Short propulsive movements every 30 mins
57
What are anti-propulsive contractions?
Impede propulsion in proximal colon to keep food in that region for longer
58
What are haustral contractions?
In transverse and descending colon | Shuffle contents backwards and forwards
59
What is a mass movement?
1-3 times a day | Co-ordinated contractions propel contents uip to 3/4 of the length of the large intestine in a few seconds
60
What kind of food promotes mass movements?
high fibre food
61
What is defecation?
expulsion of faeces
62
What are the steps of defecation?
Folowing mass movement, afferent sensation of needing to defecate Rectal wall distension detected by pressure receptors Signals sent via the myenteric plexus to initiate peristaltic waves in the descending&sigmoid colon and the rectum Internal anal sphincter relaxes Person makes conscious decision to relax external sphincter
63
What is faeces?
Indigestible waste of chyme
64
How can an individual perceive whether to let things pass or not?
Last centimetres of the rectum can distinguish solids, liquids and gases
65
How much faeces does a healthy adult produce per day?
150 g
66
What gives faeces its brown colour?
Bile pigments
67
What is the most prevalent species of bacteria in the gut?
Bacteriodetes gram -ve anaerobic non spore forming
68
What are the physiological roles of the intestinal microbiome?
Synthesise and excrete vitamin K Prevent pathogen colonisation by acting as competition Antagonise other bacteria (inhibit and kill non indigenous species) stimulate cross-reactive body production stimulate tissue development Fibre can be broken down Links to lipid metabolism, insulin resistance, bile acid metabolism, drug metabolism and obesity
69
What are the possible pathophysiological roles of the intestinal microbiome?
Gut bacteria populations help maintain and prime the immunological system Inappropriate population or loss of commensal bacteria can predispose to infection and illness throughout body Faecal transplant to re-instate bacteria

Y1 LSS Alimentary System (7 decks)

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