34) Consequences of fluid loss from the GI tract Flashcards

1
Q

What is hypovolaemia?

A
  • Loss of blood volume
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2
Q

What is total body water balance?

A
  • Water taken in = water excreted/lost
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3
Q

What are the sites of water loss?

A
  • Skin
  • Respiratory passage
  • GI tract
  • Urinary tract
  • Menstrual flow
  • Trauma
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4
Q

How is there a total balance of sodium chloride?

A
  • The amount taken in is the same as the amount lost/excreted
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5
Q

How is NaCl taken in?

A
  • In food
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6
Q

How is NaCl lost?

A
  • Sweat
  • Faeces
  • Urine
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7
Q

How is water and NaCl excretion altered?

A
  • Kidneys alter excretion to match gain with loss
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8
Q

How is water lost from the body?

A
  • Defecatuion/ diarrhoea
  • Vomiting
  • Urination
  • Ventilation
  • Sweating
  • Mensturation
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9
Q

How is water gained in the body?

A
  • Drinking

- Metabolism

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10
Q

What is diarrhoea?

A
  • Increased frequency of faeces where there is an increase in volume and fluidity
  • There is a change in bowel movement
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11
Q

Why does diarrhoea occur?

A
  • Failure of water absorption

- Increased secretion of water

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12
Q

What causes decreased absorption in the body?

A
  • There is an increased number of osmotic particles leading to osmotic diarrhoea
  • There is an increased rate of flow of intestinal contents (deranged motility diarrhoea)
  • Abnormal increase in secretion of GI tract (secretory diarrhoea)
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13
Q

What is osmotic diarrhoea?

A
  • Can be caused by decreased absorption of electrolytes and nutrients
  • Can also be caused by disaccharidase deficiency or disaccharide malabsorption leading to the person feeling bloated, nausea and watery diarrhoea
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14
Q

What is secretory diarrhoea?

A
  • ACh and other substances can act via increased concentration of Ca2+ to increase the rate of intestinal secretions
  • Excessive use of laxatives and some infections can also cause secretory diarrhoea as they work through secondary systems where they increase cAMP causing increased Na+, Cl- and water loss
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15
Q

How to treat bacteria?

A
  • Use water, electrolytes and glucose
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16
Q

What is travellers diarrhoea?

A
  • When tourists who are not used to the place they visit may eat street food and other foods which may not be clean
  • It is through these methods that they ingest bacteria and experience diarrhoea
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17
Q

What is inflammatory bowel disease?

A
  • When there is a lot of movement leading chronic exudative diarrhoea (getting diarrhoea every few hours)
18
Q

What is deranged motility diarrhoea?

A
  • GI stasis may stimulate the overgrowth of some bacteria which may promote diarrhoea
  • There is a lack of absorption as some agents promote secretion as well as motility
19
Q

What are parasitic causes of diarrhoea?

A
  • Parasites that are able to survive in anaerobic conditions and cause diarrhoea when ingested
  • Treated by using metronidazole
20
Q

What is dysentry?

A
  • Painful, bloody, low volume diarrhoea
21
Q

What are the causes of blood diarrhoea?

A
  • Chronic disease
  • Ulcerative colitis (inflammation of the bowel)
  • Cancer
22
Q

What are the major consequences of severe diarrhoea?

A
  • We get hypovolaemia (blood volume drops)

- Metabolic acidosis as there is a loss of HCO3

23
Q

What are the consequences of excessive vomiting?

A
  • Increased salt and water loss
  • Severe dehydration
  • Circulatory problems
  • Metabolic alkalosis due to loss of gastric acid (HCl)
  • Death
24
Q

What is lost in the vomit?

A
  • Food
  • Mucus with Na+, K+, Cl- and HCO3-
  • Gastric acid
  • Upper intestinal contents and bile
  • Blood
25
What are the consequences of fluid loss from the GI tract?
- Hypovolaemia - Haemoconcentration (increased production of RBCs) due to dehydration - Dehydration - Ionic imbalances - Tissues become poorly perfused - Malnutrition - Increased mortality
25
What are the consequences of fluid loss from the GI tract?
- Hypovolaemia - Haemoconcentration (increased production of RBCs) due to dehydration - Dehydration - Ionic imbalances - Tissues become poorly perfused - Malnutrition - Increased mortality
26
What are the consequences of hypovolaemia?
- Less venous return - Arterial hypotension - Myocardial dysfunction due to increased myocardial oxygen demand however perfusion is reduced - Increased anaerobic respiration leading to acidosis - Acidosis and myocardial dysfunction leads to multi-organ failure
27
How does the body respond to water loss?
- Cardiovascular adaptations - Renal adaptations - Behavioural response which stimulates fluid intake where possible
28
What is the renal adaptation to diarrhoea?
- When Na+ and water is lost due to diarrhoea there will be a decrease in plasma volume and venous pressure - These changes stimulate renal sympathetic nerves which will affect the kidneys - In the kidneys the renal arterioles are constricted and so there is a decrease in glomerular filtration pressure leading to a lower glomerular filtration rate - Therefore there is a decrease in Na+ and water secretion
29
What is the cardiovascular adaptation to diarrhoea?
- When Na+ and water is lost due to diarrhoea there will be a decrease in plasma volume and venous pressure - This results in a decrease in venous return and hence there is a fall in arterial pressure - Furthermore ventricular end-diastolic volume decreases which means stroke volume and cardiac output decreases - Finally there is an ever bigger fall in arterial blood pressure - Both decreases in arterial blood pressure stimulates the renal sympathetic nerves leading to the renal adaptation - The decrease in arterial blood pressure will also cause net glomerular filtration pressure to decrease causing GFR to decrease and decrease Na+ and water secretion
30
How are renal sympathetic nerves stimulated?
- They are stimulated by a fall in venous and arterial blood pressure - These fall in pressure are detected by baroreceptors
31
What is the physiological adaptations to sweating?
- When severe sweating occurs there is a loss of hypoosmotic salt solution which decreases plasma volume (hypovolaemia) - This means that glomerular filtration rate decreases and also plasma aldosterone increases - These changes cause decreased sodium excretion so water excretion also decreases - Furthermore a loss of hypoosmotic salt solution also causes plasma osmolarity to increase as water concentration decreases - Plasma vasopressin increases (ADH) is released when there is an increased plasma osmolarity or when there is a decreased plasma volume - An increase in ADH means there is less water excretion
32
What is plasma aldosterone?
- A steroid hormone which increases blood volume
33
How does the RAAS cascade respond to hypovolaemia?
- A decrease in blood volume (hypovolaemia) will increase the activity of the renal sympathetic nerves - They stimulate juxtaglomerular cells which secrete renin - Hypovolaemia also causes glomerular filtration rate to decrease causing flow to the macula densa to decrease as well - As a result there is a decrease in NaCl concentration in the macula densa which also stimulates juxtaglomerular cells causing more renin to be secreted - When renin secretion is increased there is an increase in plasma renin and so a signalling cascade is activated which causes plasma angiotensin II to increase - Angiotensin II stimulates the adrenal cortex causing increased aldosterone secretion which increases plasma aldosterone - This causes an increase in Na+ reabsorption which leads to a decreased Na+ excretion
34
What does the macula densa do?
- They senses the concentration of NaCl in the blood - When they detect a low concentration of NaCl in the blood there is an increase in renin circulation and a decrease in the resistance to blood flow in afferent arterioles through vasodilation - This returns GFR to normal
35
What is the physiological response to diarrhoea with increased potassium concentration?
- When sweating (as sodium concentration decrease) K+ plasma concentration increases - This increases aldosterone which causes concentration of aldosterone in the plasma to also increase - As a result there is an increase in Na+ absorption and so there is decreased Na+ excretion - We also experience increased potassium secretion due to the aldosterone which causes potassium excretion to also increase
36
How does the body use vasopressin to counter hypovolaemia?
- A decrease in plasma volume causes venous, arterial and arterial pressure to decrease - As a result there is an increase in vasopressin secretion - Therefore the tubular permeability to H20 increases allowing for more H20 reabsorption and so a decreased water excretion
37
How does the body use thirst to combat hypovolaemia?
- A decrease in plasma volume stimulates baroreceptors which stimulates the increased secretion of angiotensin II which stimulates thirst. - The stimulated baroreceptor can also directly stimulate thirst - An increase in plasma osmolarity stimulates osmoreceptors which stimulates thirst - Dry mouth and throat also stimulates thirst - There is a metering system for water intake in the GI tract which inhibits thirst and prevents over-rehydration
38
What regulates water loss?
- Vasopressin (ADH) as it stimulates the thirst mechanism - Increased osmolarity of bodily fluids causes ADH release - ADH activates V2 receptors on the renal collecting ducts - They insert water channels in the collecting ducts of kidneys which increases their permeability to H20 - As a result concentrated urine is produced as more water is taken in - Intake of water decreases osmolarity of blood and intestinal fluid whihc decreases ADH release - The decrease in ADH causes water channels to be removed which in turn decreases permeability of collecting ducts leading to increased water loss
39
What factors regulate ADH release?
- Large decrease in blood volume (detected by baroreceptors) - Severe dehydration (GFR decreases so less H2O in urine) - Hyperventilation (as fluid is lost in exhalation) - Vomiting/ diarrhoea (as there is increased fluid loss from the GI) - Fever, heavy sweating and burns can cause large H20 loss - These factors lead to the generation of hyperosmolar renal medulla so releases ADH for conservation of water
40
What happens when there is a large intake of water?
- There will be high blood pressure which causes increased glomerular filtration rate and increased H2O in urine