34) Consequences of fluid loss from the GI tract Flashcards
1
Q
What is hypovolaemia?
A
- Loss of blood volume
2
Q
What is total body water balance?
A
- Water taken in = water excreted/lost
3
Q
What are the sites of water loss?
A
- Skin
- Respiratory passage
- GI tract
- Urinary tract
- Menstrual flow
- Trauma
4
Q
How is there a total balance of sodium chloride?
A
- The amount taken in is the same as the amount lost/excreted
5
Q
How is NaCl taken in?
A
- In food
6
Q
How is NaCl lost?
A
- Sweat
- Faeces
- Urine
7
Q
How is water and NaCl excretion altered?
A
- Kidneys alter excretion to match gain with loss
8
Q
How is water lost from the body?
A
- Defecatuion/ diarrhoea
- Vomiting
- Urination
- Ventilation
- Sweating
- Mensturation
9
Q
How is water gained in the body?
A
- Drinking
- Metabolism
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
11
Q
Why does diarrhoea occur?
A
- Failure of water absorption
- Increased secretion of water
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)
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
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
15
Q
How to treat bacteria?
A
- Use water, electrolytes and glucose
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
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
