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Physiology 1 > 34) Consequences of fluid loss from the GI tract > Flashcards

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
Q

What are the consequences of fluid loss from the GI tract?

A
  • Hypovolaemia
  • Haemoconcentration (increased production of RBCs) due to dehydration
  • Dehydration
  • Ionic imbalances
  • Tissues become poorly perfused
  • Malnutrition
  • Increased mortality
25
Q

What are the consequences of fluid loss from the GI tract?

A
  • Hypovolaemia
  • Haemoconcentration (increased production of RBCs) due to dehydration
  • Dehydration
  • Ionic imbalances
  • Tissues become poorly perfused
  • Malnutrition
  • Increased mortality
26
Q

What are the consequences of hypovolaemia?

A
  • 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
Q

How does the body respond to water loss?

A
  • Cardiovascular adaptations
  • Renal adaptations
  • Behavioural response which stimulates fluid intake where possible
28
Q

What is the renal adaptation to diarrhoea?

A
  • 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
Q

What is the cardiovascular adaptation to diarrhoea?

A
  • 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
Q

How are renal sympathetic nerves stimulated?

A
  • They are stimulated by a fall in venous and arterial blood pressure
  • These fall in pressure are detected by baroreceptors
31
Q

What is the physiological adaptations to sweating?

A
  • 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
Q

What is plasma aldosterone?

A
  • A steroid hormone which increases blood volume
33
Q

How does the RAAS cascade respond to hypovolaemia?

A
  • 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
Q

What does the macula densa do?

A
  • 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
Q

What is the physiological response to diarrhoea with increased potassium concentration?

A
  • 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
Q

How does the body use vasopressin to counter hypovolaemia?

A
  • 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
Q

How does the body use thirst to combat hypovolaemia?

A
  • 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
Q

What regulates water loss?

A
  • 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
Q

What factors regulate ADH release?

A
  • 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
Q

What happens when there is a large intake of water?

A
  • There will be high blood pressure which causes increased glomerular filtration rate and increased H2O in urine

Physiology 1 (64 decks)

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