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BS - Gastrointestinal System pt.1 > Gastrointestinal Physiology > Flashcards

Gastrointestinal Physiology Flashcards

1
Q

Where does the GI tract extend from and to?

A

It extends from the oral cavity to the anus

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2
Q

What is the length of the entire GI tract and its components?

A

It is heavily folded and is 8-9 m long

The pharynx, oesophagus and stomach are 1m

The small bowel is 6m

The large bowel is 1.5m

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3
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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4
Q

What is involved in the ingestion phase?

A

Material enters the digestive tract via the mouth

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5
Q

What is involved in mechanical processing?

A

Crushing and shearing, wetting and softening, mainly achieved through chewing

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6
Q

What is the purpose of the mechanical processing stage?

A

It makes material easier to propel along the GI tract by mechanically breaking them down into smaller molecules

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7
Q

Why is it important that food is softened during mechanical processing?

A

It helps to prevent blockages in the GI tract

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8
Q

What does digestion require?

A

A large surface area for the enzymes to work efficiently

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9
Q

What is involved in the digestion stage?

A

The chemical breakdown of food into small organic fragments (e.g. glucose, amino acids) for absorption by digestive epithelium

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10
Q

What is involved in the secretion stage?

A

The release of water, enzymes, acids, buffers and salts into the GI tract

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11
Q

What structures are involved in the secretion stage?

A

Glandular organs and the epithelium of the digestive tract

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12
Q

What is involved in the absorption stage?

A

The movement of organic substrates, electrolytes vitamins and water

They move across the digestive epithelium into the interstitial fluid of the digestive tract

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13
Q

What is involved in the excretion stage?

A

The removal of indigestible material and waste products from body fluids

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14
Q

What is the layout of the digestive tract from the mouth to the stomach?

A

the oral cavity leads into the pharynx

the pharynx leads into the oesophagus, which passes through the diaphragm and into the stomach

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15
Q

What must food pass through to enter the small bowel?

A

The pyloric sphincter

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16
Q

What are the 3 parts of the small bowel?

A
  1. duodenum
  2. jejunum
  3. ileum
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17
Q

What are the components of the large bowel?

A
  1. ascending colon
  2. transverse colon
  3. descending colon
  4. sigmoid colon
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18
Q

What is the peritoneum?

A

Layers of membrane which cover the inside of the abdominal cavity, and the organs themselves

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19
Q

What are the 2 types of peritoneum and the differences between them?

A

The parietal peritoneum lines the abdominal cavity

The visceral peritoneum covers the organs

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20
Q

Which organs of the GI tract are retroperitoneal?

What does this mean?

A

Kidney, pancreas and part of the duodenum

They are not surrounded by the peritoneum

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21
Q

How are retroperitoneal organs suspended?

A

They are plastered against the posterior abdominal wall by the peritoneum

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22
Q

What structures does the peritoneum form?

What are the functions of these structures?

A

Mesenteries

They are double layers of peritoneum which suspend the organs, support them and keep them from tangling

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23
Q

What other structures run in the mesenteries?

A

Blood vessels, lymphatics and nerves

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24
Q

What does the peritoneum secrete?

What is the purpose of this?

A

Peritoneal fluid

This provides lubrication that allows the organs to move against each other without friction

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25
Q

What would happen if there was friction between 2 organs?

A

It would cause inflammation and lead to scarring

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26
Q

What is the purpose of the fat pads in the mesenteries?

Where are they particularly common?

A

They help to cushion and protect organs

Common in the greater omentum

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27
Q

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

A

3 branches of the abdominal aorta:

  1. coeliac trunk
  2. superior mesenteric artery
  3. inferior mesenteric artery
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28
Q

Which structures are supplied by the coeliac trunk?

A

Foregut structures

  1. stomach
  2. gall bladder
  3. spleen (part of immune system)
  4. pancreas
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29
Q

What is the branch of the coeliac trunk and what does it supply?

A

The hepatic artery which supplies the liver with oxygenated blood

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30
Q

What structures are supplied by the superior mesenteric artery?

A

Midgut structures

  1. pancreas
  2. all of the small intestine
  3. the first part of the large intestine
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31
Q

What structures are supplied by the inferior mesenteric artery?

A

Hindgut structures

  1. the lower half of the colon and the rectum
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32
Q

What is the main blood supply of the anus?

A

It is mostly supplied by the blood supply of the skin

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33
Q

Where does the majority of blood from the GI tract drain into?

Where does this vessel go?

A

Hepatic portal vein

This goes to the liver for processing

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34
Q

What happens during processing in the liver, as blood enters from the hepatic portal vein?

A

Nutrients from the GI tract are converted into forms that can be used by the body

It also acts as a buffer to prevent glucose surges or levels falling too low

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35
Q

How does the liver receive oxygenated blood?

A

Via the hepatic artery, which branches from the coeliac artery

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36
Q

To what extent do the blood supplies of the GI tract cross over?

A

There is a small degree of cross-over between the blood supplies

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37
Q

What happens in an aneurysm and how does it affect blood supply to the GI tract?

A

Blood forces itself into the wall of the aorta, meaning it is not flowing in the correct pathway

This can lead to ischaemia in the GI tract if parts of the bowel are not receiving blood

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38
Q

How can an alternative blood supply be developed in an aneurysm?

A

Through the anastomoses of the inferior and superior mesenteric arteries

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39
Q

What condition is caused after an aneurysm, if there is inadequate blood supply to the large intestine?

A

Ischaemic colitis

This is inflammation and injury of the large intestine as a result of an inadequate blood supply

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40
Q

What are the 4 layers of the digestive tract, from innermost to outermost?

A
  1. mucosa
  2. submucosa
  3. muscularis externa
  4. serosa
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41
Q

What is the mucosa?

A

The innermost lining of the GI tract, consisting of an epithelial layer and supporting structures

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42
Q

What is the submucosa?

A

This is mainly connective tissue and a supply network

The supply network consists of blood vessels and lymphatics

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43
Q

What is the muscularis externa?

A

A muscular layer that is responsible for gut movement, such as peristalsis

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44
Q

What is the serosa?

A

This consists of the peritoneal layer and more connective tissue

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45
Q

How is the mucosal layer arranged and why?

A

It is thrown up into folds to increase the surface area

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46
Q

What are the two layers of the mucosa?

A
  1. lamina propria

2. mucosal epithelium

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47
Q

What is the role of the lamina propria and mucosal epithelium?

A

The epithelium forms villi to increase the surface area

The lamina propria is connective tissue that supports the epithelium

48
Q

Where is the muscularis mucosae found?

What is its role?

A

Found between the mucosa and submucosa

It helps to maintain the shape of the epithelium

49
Q

What structures are found within the submucosa?

A

Larger arteries, veins and nerve plexi (submucosal plexus)

It projects into the villi to allow lymphatic drainage close to the epithelium

50
Q

What happens when the circular muscle layer contracts?

A

The gut tube becomes narrower

51
Q

What happens when the longitudinal muscle layer contracts?

A

It runs along the length of the gut tube and contracts to make the gut tube shorter

52
Q

Where is the myenteric plexus found?

A

Between the circular and longitudinal muscle layers

53
Q

What are the two layers of the muscularis exerna?

A

Circular and longitudinal muscle layers

54
Q

What structure is important in a sheet of epithelial cells forming an epithelial tube?

A

The adhesion belt with associated actin filaments

55
Q

What is the first stage in forming an epithelial tube?

What is is caused by?

A

Invagination of the epithelial sheet

This is caused by an organised tightening of adhesion belts in selected regions of the cell sheet

56
Q

What is the second stage in forming an epithelial tube?

A

The epithelial tube pinches off from the overlying sheet of cells

57
Q

What determines how epithelial cells are orientated towards the different spaces which they line?

A

The basolateral and apical surfaces of the epithelial cells are different

This means that epithelial cells are polarised

58
Q

What is the role of tight junctions in epithelial cells?

A

They join cells together and separate the basal and apical surfaces

59
Q

What is significant about the formation of epithelial tubes?

A

This process leads to the formation of glands

60
Q

How are glands structured?

A

They have an inside space where things are secreted from

They have an outside space where things are delivered from the bloodstream

61
Q

What is significant about a polarised cell?

A

A polarised cell can target proteins to discrete cell domains

62
Q

How would protein be distributed in polarised and non-polarised cells?

A

Non-polarised: the protein is distributed around the cell and its plasma membrane randomly

Polarised: the protein is targeted to one area of the cell, and the rest of the cell is free from protein

63
Q

What are the types of junctions between epithelial cells, from apical to basal surface?

A
  1. tight junction
  2. adherens junction
  3. desmosome
  4. gap junction
64
Q

What is the function of the tight junctions?

A

They define the apical and basolateral domains

They seal the gap between epithelial cells

65
Q

What type of junction is a tight junction?

A

An occluding junction

66
Q

What is the role of the adherens junction?

A

It is anchored to the actin cytoskeleton, and will connect the actin filament bundle in one cell with that in the next

67
Q

What is the role of the desmosome?

A

It connects the intermediate filaments in one cell to those in the next cell

68
Q

What type of junctions are adherens junctions and desmosomes?

A

cell-cell anchoring junctions

69
Q

What is the role of gap junctions?

channel-forming junctions

A

They allow the passage of small water-soluble molecules between cells

They act as communication channels for electrical coupling

70
Q

What is the role of hemidesmosomes?

A

They anchor intermediate filaments in a cell to the extracellular matrix (basement membrane)

71
Q

What is the role of actin-linked cell-matrix adhesion molecules?

A

They anchor the actin filaments in a cell to the extracellular matrix

72
Q

How are epithelia related to a blood supply?

A

Epithelia are closely associated with a capillary network

This supplies O2 and nutrients, and removes CO2 and waste

73
Q

What are the basolateral and apical membranes of the epithelial cells in contact with?

A

The apical membrane is in contact with the luminal/mucosal fluid

The basolateral membrane is in contact with the interstitial fluid surrounding capillaries

74
Q

What is the role of tight junctions?

A

They prevent diffusion of plasma membrane proteins between apical and basolateral domains

75
Q

Why is the separation of cells into functionally discrete domains important?

A

It is crucial to the process of vectorial (directed) movement of solutes and water

76
Q

What is meant by transepithelial movement of solutes and water?

A

Solutes and water can travel in 2 directions across epithelia:

absorption and secretion

77
Q

What is involved in movement during absorption?

A

Movement from the external compartment (gut lumen) to the internal compartment (blood and lymph)

78
Q

What is involved in movement during secretion?

A

Movement from the internal compartment (blood) into the external compartment (gut lumen)

79
Q

What is meant by a ‘flux’?

What are the 2 types of flux?

A

A ‘flux’ describes the uni-directional movement of solutes and water

This can be an absorptive flux or a secretory flux

80
Q

What is the net flux?

How is it calculated?

A

It is determined by the difference between the secretory and absorptive flux

J(net) = J(abs) - J(sec)

81
Q

What drives a flux?

A

The prevailing electrochemical gradients

82
Q

By which means can absorption take place?

A

This is movement from the lumen to the blood

It can occur via the transcellular or paracellular route

83
Q

By which means can secretion take place?

A

This is movement from the blood into the lumen

It can occur via the transcellular or paracellular route

84
Q

What is involved in the transcellular route?

A

This involves crossing both the apical and basolateral membranes of the epithelial cell

85
Q

What is involved in the paracellular route?

A

This involves passing between the epithelial cells

86
Q

What type of process is paracellular movement?

How does this affect the flux?

A

Paracellular movement is a passive process

There is no way of controlling or driving the flux

87
Q

What type of process is transcellular movement?

How does this affect the flux?

A

Transcellular movement is driven through active transport

This ensures all molecules travel in one direction and none are wasted

88
Q

What is meant by passive transport being ‘not coupled’?

Where may it occur?

A

The solute moves down its electrochemical gradient

It occurs through cells or through tight junctions

89
Q

What molecules are involved in passive transport?

A

Ions and water travel via pores or channels

Transporters will facilitate the diffusion of small non-electrolytes

90
Q

What route must be taken by primary or secondary active transport?

A

Active processes MUST use the transcellular route

91
Q

What is involved in primary active transport?

A

Energy is used directly from ATP to drive transport

ATP forces changes in a protein, which transports a substrate against its electrochemical gradient

92
Q

What is involved in secondary active transport?

A

Energy is used from something flowing down an electrochemical gradient, to drive another process

93
Q

How are primary and secondary active transport linked?

A

An electrochemical gradient from substrate A is set up by primary AT

Substrate B moves against its electrochemical gradient

94
Q

What is the role of the sodium-potassium pump in sugar transport?

What type of active transport is this?

A

Secondary active transport

The Na+/K+ pump will move Na+ ions out of the cell by primary active transport

95
Q

How is glucose moved into the cell, after a low intracellular Na+ is achieved?

A

Na+ in the lumen moves down an electrochemical gradient into the cell

It can only do this when glucose is present

Glucose moves against its electrochemical gradient and accumulates in the cell

96
Q

How is glucose released from the cell into the bloodstream?

A

Through a passive transporter such as GLUC-2

97
Q

Where does water flow to?

By which means can it move?

A

It flows from areas of low osmotic pressure to high osmotic pressure

It can pass through the paracellular or transcellular pathway

98
Q

What is meant by the net solute movement tending to drive the net fluid movement?

A

If there is an accumulation of osmotically active solutes in a compartment, water will move to equalise the osmotic gradient between the compartments

99
Q

How does water cross plasma membranes?

A

Diffusing through the lipid or through aquaporins

Active transport of solute is followed by passive transport of water

100
Q

Where does the main sensory and motor control of the GI tract come from?

A

Parasympathetic nerves

101
Q

Which parasympathetic nerves control which parts of the GI tract?

A

The vagus nerve controls the foregut and midgut derivatives

The pelvic splanchnic nerves supply the hindgut derivatives

102
Q

How does the parasympathetic and sympathetic nervous system affect the activity of the gut?

A

The parasympathetic NS increases the activity of the gut

The sympathetic nervous system inhibits activity of the gut

This allows blood to be diverted to other areas of the body where it is needed more

103
Q

What does the enteric nervous system consist of?

A

The autonomic nervous system acts via the enteric NS

It consists of myenteric and submucosal plexi

104
Q

What is the enteric nervous system and what is its role?

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 layers and underneath the submucosa

105
Q

What is the main function of the enteric nervous system?

A

It controls much of the normal gut motility

106
Q

From which vertebral levels to the sympathetic ganglia supplying the GI tract originate from?

A

Supplying the stomach - T5

Supplying the large intestine - L1

107
Q

From which vertebral levels do the pelvic splanchnic nerves originate from?

A

S2 and S4

sacral region

108
Q

Which components of the GI tract are controlled by the myenteric and submucosal plexi?

A

The myenteric plexus controls the smooth muscle and secretory cells

The submucosal plexus controls the blood vessels and the endocrine cells

109
Q

What are ‘slow waves’?

A

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

This makes it easier for a small signal to initiate contraction and/or action potential

110
Q

What type of signals will initiate activity only during a slow wave?

A

Neural and hormonal signals

111
Q

What is the role of interstitial cells of Cajal in slow waves?

A

They act as ‘pacemakers’ to give a steady rhythm of depolarisation and repolarisation

112
Q

How many times per minute do slow waves occur?

A

3 - 12 times per minute

113
Q

What determines whether the threshold is reached in a slow wave?

What is the result of a threshold being reached?

A

It depends on the other signals received by the interstitial cells of Cajal

If the threshold is reached, the signal is amplified to increase activity

114
Q

What do the interstitial cells of Cajal form connections with?

A

With each other and with smooth muscle cells

115
Q

Why do interstitial cells of Cajal form connections with smooth muscle cells?

A

They drive processes such as peristalsis through action on smooth muscle cells

BS - Gastrointestinal System pt.1 (22 decks)

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