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Yr 2 - GI & Metabolism > Intro to GI Physiology > Flashcards

Intro to GI Physiology Flashcards

1
Q

What is the GI tract also called?

A

Alimentary canal

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2
Q

What is the GI tract? What is it lined by?

A

It is a muscular tube, lined by an epithelium

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3
Q

Where does the GI tract extend from and to?

A

From the oral cavity to anus (passes through pharynx, oesophagus, stomach, and small and large intestines)

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4
Q

How long is the GI tract?

A

About 8 or 9 metres

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5
Q

How long is the small/large bowel?

A

Small - 6m Large - 1.5m

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6
Q

What are the 6 main functions of the GI tract?

A
  1. Ingestion 2. Mechanical processing 3. Digestion 4. Secretion 5. Absorption 6. Excretion
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7
Q

What is ingestion?

A

Materials enter digestive tract via the mouth

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8
Q

What is mechanical processing?

A

Crushing and shearing, wetting and softening

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9
Q

What is purpose of mechanical processing?

A

Makes materials easier to propel along digestive tract

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10
Q

What is digestion?

A

The chemical breakdown of food into small organic fragments for absorption by digestive epithelium

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11
Q

What is secretion?

A

Is the release of water, acids, enzymes, buffers, and salts by epithelium of digestive tract or by glandular organs

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12
Q

What is absorption?

A

Movement of organic substrates, electrolytes, vitamins, and water across digestive epithelium into interstitial fluid of digestive tract

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13
Q

What is excretion?

A

Removal of indigestible material and waste products from body fluids

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14
Q

What is the peritoneum?

A

Serous membrane forming the lining of the abdominal cavity (parietal peritoneum) Covers organ (visceral peritoneum)

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15
Q

What does the peritoneum form?

A

Mesenteries

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16
Q

What are mesenteries?

A

An organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. Suspend the organs and keep them from tangling

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17
Q

What does the peritoneum secrete?

A

Peritoneal fluid

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18
Q

What is function of peritoneal fluid?

A

Provides lubrication and permits organs to move against each other without friction

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19
Q

What is function of mesenteries?

A

Helps in storing fat (fat protects organs) and carries blood vessels, lymphatics, and nerves to supply the intestines

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20
Q

Where does the blood supply to the GI tract in the abdomen come from?

A

3 branches of the (abdominal) aorta: - Coeliac artery - Superior mesenteric artery (SMA) - Inferior mesenteric artery (IMA)

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21
Q

What does the coeliac artery then supply?

A

Stomach Spleen Gall bladder Pancreas

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22
Q

What does the coeliac artery also branch off to form?

A

Hepatic artery which supplies the liver

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23
Q

What does the SMA supply?

A

Pancreas, small intestine, large intestine

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24
Q

What does the IMA supply?

A

Large intestine, rectum

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25
Q

Where does deoxygenated blood from the GI largely drain into?

A

Hepatic portal vein

26
Q

What carries absorbed nutrients to the liver for processing?

A

Hepatic portal vein

27
Q

What are the 4 main layers of the GI tract? Innermost to outermost?

A
  1. Mucosa (innermost) 2. Submucosa 3. Muscularis externa 4. Serosa (outermost)
28
Q

What is purpose of villi?

A

Increases surface area for absorption

29
Q

What conditions does flattening of villi cause?

A

Coeliac

30
Q

What are epithelia?

A

Layers of cells covering internal or external surfaces

31
Q

How can sheet of epithelial cells form an epithelial tube/gland?

A

Invagination of epithelial sheet by organised tightening of adhesion belts in selected regions of cell sheet Epithelial tube pinches off from overlying sheet of cells

32
Q

What are glands?

A

Structures that produce secretions

33
Q

What are the 4 types of junctions between cells (moving from apical to basal)?

A
  1. Occluding junction 2. Cell-cell anchoring junctions 3. Channel-forming junctions 4. Cell-matrix anchoring junctions
34
Q

What is other name for occluding junctions? What is their function?

A

Tight junctions seals gap between epithelial cells –> prevent leakage of transported solutes and water

35
Q

What is function of cell-cell anchoring junctions / adherens junction?

A

Anchoring junctions are protein complexes that mediate the adhesion of cells to other cells or to the extracellular matrix

  • Stabilise the cells position, provide stability and rigidity, and support tissue integrity by holding cell sheets together.
  • Connect actin filament bundle in one cell with that in the next cell
36
Q

What are channel-forming junctions?

A

Gap junction allows the passage of small water-soluble molecules from cell to cell

37
Q

What are cell-matrix anchoring junctions?

A

Actin linked cell-matrix adhesion anchors actin filaments in cell to extracellular matrix

38
Q

What junctions are of particular significance for epithelial cells?

A

The tight junctions near the apical surface: it is these which define the apical and basolateral domain, and stop proteins from these domains mixing

39
Q

Describe epithelial organisation in organ such as gut/kidney

A

Epithelia are usually closely associated with a capillary network, which supplies O2 and nutrients and removes CO2 and metabolites. The interstitial fluid surrounding the capillaries is in contact with the basolateral (serosal) membrane of epithelial cells. The domain of the plasma membane in contact with the external compartment is called the apical membrane. This segration of the cell into functionally discrete domains is crucial to the process of vectorial (directed) movement of solutes and water.

40
Q

What is function of tight junctions?

A

Prevents diffusion of plasma membrane proteins (e.g. receptors, channels and transporters) between apical and basolateral domains

41
Q

Solutes and water can travel in 2 directions across epithelia (absorption and secretion). Describe direction of absorption

A

From external compartment (gut lumen) to internal compartment (blood and lymph) E.g. glucose absorption in gut and renal tube

42
Q

Describe direction of secretion

A

From internal compartment to external compartment Good examples of this are protons (H+) and potassium in the renal tubule and HCO3- which is secreted by the pancreas.

43
Q

What is equation for net flux?

A

Net flux (Jnet) = Jabs - Jsec

44
Q

Where can absorption take place?

A

From lumen to blood: - via the cells (transcellular route) in which case, two barriers (apical and basolateral membranes) must be traversed - in between the cells (paracellular route)

45
Q

How can secretion take place?

A
  1. Transcellular secretion 2. Paracellular secretion
46
Q

What route must active transport take?

A

Transcellular route

47
Q

What routes can passive transport take?

A

Paracellular or transcellular

48
Q

What is 1ary active transport?

A
  • Energy to drive transport comes directly from ATP - Substrate moves against an electrochemical gradient
49
Q

What is 2ary active transport?

A
  • Energy to drive active transport comes from electrochemical gradient for one substrate (set up by primary active transport) - Second substrate moves against its electrochemical gradient
50
Q

GI tract blood supply

A
51
Q

Sugar absorption

A
52
Q

What is active transport of solute usually followed by?

A

Passive transport of water (osmosis)

Therefore, if there is an accumulation of osmotically active solutes in a compartment, water will tend to move so as to equalise the osmotic gradient between those compartments.

53
Q

What is effect of parasympathetic impulses on GI?

A

‘Rest and digest’ –> promote digestive processes

The vagus controls foregut and midgut derivatives, while pelvic splanchnic nerves supply hindgut components.

54
Q

What is effect of sympatehtic impulses on GI?

A

Depress digestive acitvity

55
Q

What is the ‘enteric nervous system’?

A
  • Much of the activity of the muscle in the gut wall is locally regulated and controlled, by a complex set of nerves lying between the muscle laters, and underneath the submucosa.
  • Controls much of the normal gut motility essentially autonomously
  • Parasympathetic and sympathetic nerves allow some degree of central control
  • Communication withina and between plexi (myenteric and submucosal plexi)
56
Q

Extrinsic nerve supply

A
57
Q

What are interstitial cells of Cajal? Where are they located?

A

Located within the muscle layers of the alimentary tract that mediate communication between the autonomic nervous system and smooth muscle –> mediators of slow waves

58
Q

What are slow waves?

A

Periodic shifts (depolarisations) in the resting membrane potential of the cells

59
Q

What is purpose of slow waves?

A

This makes it easier for a small signal to initiate a contraction and/or an action potential. In practice, what this means is that neural and hormonal signals will initiate activity only during a slow wave: thus the slow waves give an underlying structure to the activity of the smooth muscle.

60
Q

Are epithelial cells polarised?

A

Yes - Polarized cells can target proteins to discrete cell domains (allowing vectorial transport in or out)

Yr 2 - GI & Metabolism (51 decks)

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