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Physiology 1 Semester 2 > Consequences of Fluid Loss from the GI System > Flashcards

Consequences of Fluid Loss from the GI System Flashcards

1
Q

State the sources of water intake and output in the body and average values for them (ml)

A
  • Intake of water -
  • Liquids - 1200ml
  • Food - 1000ml
  • Metabolically produced - 350 ml
    Total - 2550ml
  • Output of water -
  • Insensible water loss (lungs and skin - 900ml)
  • Sweat - 50ml
  • Faeces - 100ml
  • Urine - 1500ml
    Total - 2550ml
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2
Q

State the sites of water loss in the body

A

Skin - sweating
Respiratory passageways - ventilation
GI tract - vomiting/defecation
Urinary tract - urination
Menstrual flow
Trauma

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3
Q

When is excretion of Na+ and Cl- high?

A

In diarrhoea, sweating, vomiting and haemorrhage - loss of water and salts

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4
Q

State the sources of NaCl intake and output daily including average values (g)

A

Daily NaCl intake -
- Food - 10.5g

NaCl output -
- Sweat - 0.25g
- Faeces - 0.25g
- Urine - 10g - varies a lot
Total output - 10.5g

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5
Q

What is diarrhoea?

A
  • Increased frequency with increased volume and fluidity of faeces
  • More than 3 unformed stools per 24hrs
  • Change in bowel movement
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6
Q

What does diarrhoea result from?

A
  • Failure of water absorption
  • Increased secretion of water
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7
Q

State the causes of decreased absorption

A
  • Increased number of osmotic particles
  • Increased rate of flow of intestinal contents
  • Abnormal increase in secretions of GI tract
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8
Q

Describe the different types of diarrhoea

A
  • Osmotic diarrhoea -
  • Decreased absorption of electrolytes and nutrients
  • Disaccharidase deficiency (disaccharide deficiency/malabsorption)
  • Drug induced
  • Malabsorption of galactose
  • Bloating, nausea, watery diarrhoea
  • Secretory diarrhoea -
  • Acetylcholine, substance P, 5-HT and neurotensin act via increasing the [Ca2+] to increase the rate of intestinal secretion
  • Excessive laxative use, defects in digestion and absorption and infections like cholera
  • Cholera survives the acidic conditions of the gut and the enterotoxins stimulates adenylate cyclase which increases cAMP which then causes Na+, Cl- and water loss
  • The water, electrolytes and glucose can be replaced as a treatment
  • Deranged motility diarrhoea -
  • Lack of absorption, some agents may promote secretion and motility
  • GI stasis may promote diarrhoea by stimulating bacterial overgrowth
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9
Q

Describe the parasitic causes of diarrhoea

A
  • Parasitic causes of diarrhoea -
  • Entamoeba histolytica and giardia lamblia
  • Entamoeba histolytica -
  • Asymptomatic or amoebic dysentery (painful blood low volume diarrhoea) - gradual onset with systemic symptoms like anorexia and headaches
  • Treated with metronidazole
  • Giardia -
  • Steatorrhoea and abdominal pain - maldigestion and malabsorption of lipids, CHO, vit A, vit B12 and folic acid
  • Treated with metronidazole or tinidazole
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10
Q

State the causes of bloody diarrhoea

A
  • Chronic disease
  • Ulcerative colitis
  • Neoplasm
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11
Q

What are the major consequences of severe diarrhoea

A
  • Loss of water, nutrients, Na+, K+ and HCO3-
  • Decreased blood volume (hypovolaemia)
  • Metabolic acidosis - due to loss of HCO3- e.g. in diarrhoea
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12
Q

What are the consequences of excessive vomiting

A
  • Increased salt and water loss
  • Severe dehydration
  • Circulatory problems
  • Metabolic alkalosis - due to a loss of gastric acid
  • Death
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13
Q

What is lost in vomit?

A
  • Food
  • Mucus containing Na+, K+, Cl- and HCO3-
  • Gastric acid
  • Upper intestinal contents including bile
  • Blood
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14
Q

State the consequences of fluid loss from the GI tract

A
  • Hypovolaemia
  • Haemoconcentration/polycythaemia (dehydration) - increases [RBC]
  • Dehydration
  • Ionic imbalances - poor perfusion of tissues
  • Malnutrition and increased mortality
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15
Q

State the consequences of hypovolaemia

A
  • Decreased venous return
  • Arterial hypotension
  • Myocardial dysfunction due to increased myocardial oxygen demand , tissue perfusion is reduced
  • Increased anabolic metabolism leads to acidosis
  • Acidosis and myocardial dysfunction causes multi organ failure
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16
Q

In what ways does the body respond to water loss?

A
  • CVS adaptation
  • Renal adaptation
  • Behavioural
17
Q

Describe the renal and cardiovascular responses to water loss

A
  • There is increased Na+ and H2O is lost due to diarrhoea
  • This then decreases the plasma volume and venous pressure of the blood
  • Renal -
  • This then increases the activity of the renal sympathetic nerves
  • In the kidneys there is increased constriction of the renal arterioles, which decreases the net glomerular filtration pressure and glomerular filtration rate
  • This leads to decreased Na+ and water secretion and more reabsorption
  • CVS -
  • The decreased venous pressure means there is decreased venous return
  • Hence atrial pressure decreases and the ventricular end diastolic volume decreases
  • Stroke volume also decreases which reduces cardiac output
  • The decreased arterial blood pressure then causes increased activity of renal sympathetic nerves and decreases net glomerular filtration pressure
18
Q

Describe how water loss by sweating is responded to

A
  • Severe sweating leads to a loss of hypoosmotic salt solution
  • This decreases the plasma volume which then causes decreased glomerular filtration rate and increased plasma aldosterone which decrease sodium excretion as well as increase plasma vasopressin which reduced water excretion
  • It also decreases plasma osmolarity as the water concentration has decreased which increases plasma vasopressin which then reduces water excretion
19
Q

Describe how the body responds to hypovolaemia with the RAAS cascade

A
  • Decreased plasma volume leads to increased activity of renal sympathetic nerves, decreased arterial pressure and decreased glomerular filtration rate (reduced flow to macula densa
  • The increased activity of renal sympathetic nerves which occurs due to stimulation of intrarenal baroreceptors increases renin secretion from renal juxtaglomerular cells
  • The decreased glomerular filtration rate has decreased flow to macula densa which then decreases the NaCl concentration in macula densa - the macula densa sense [NaCl] passing through it - decreased NaCl causes increased renin release and decreased resistance to blood flow in the afferent arterioles via vasodilation - this increases renin secretion from renal juxtaglomerular cells
  • The reduced arterial pressure has a direct effect as there is less stretch so renin secretion from renal juxtaglomerular cells increases
  • This increases the plasma renin which increases plasma angiotensin II
  • This then increases aldosterone secretion from the adrenal cortex which increases plasma aldosterone
  • This then leads to increased Na+ reabsorption from cortical collecting ducts which decreases Na+ excretion
20
Q

Describe how hypovolaemia is responded to in terms of potassium concentration

A
  • There is a decreased plasma volume which leads to increased plasma angiotensin II
  • There is also increased plasma potassium, both of which lead to an increase in aldosterone secretion from the adrenal cortex
  • This increases the plasma aldosterone which leads to increased sodium and potassium reabsorption from the cortical collecting ducts
  • This decreases sodium excretion and increases potassium excretion
21
Q

How does the body respond to the consequences of hypovolaemia

A
  • Decreased plasma volume leads to reduced venous, atrial and arterial pressure
  • There is then a reflex mediated by cardiovascular baroreceptors which leads to increased vasopressin secretion from the posterior pituitary
  • There is an increased plasma vasopressin which leads to increased tubular permeability to H2O and increased H2O reabsorption in the collecting ducts
  • This leads to reduced H2O in the urine
22
Q

Describe what causes thirst

A
  • There is decreased plasma volume which stimulates baroreceptors and increases angiotensin II which leads to thirst
  • There is also increased plasma osmolarity which stimulates osmoreceptors which causes thirst
  • Dry mouth, throat and metering of water intake by GI tract both cause thirst
23
Q

State what regulates water loss and how it works

A
  • Vasopressin (antidiuretic hormone) - ADH stimulates thirst and ADH release is caused by increased osmolarity of body fluids

How does ADH work?
- ADH activates the V2 receptor on the renal collecting ducts
Inserts water channels (aquaporins 2) in the collecting duct of the kidney
- This increases the permeability of the collecting ducts to water and results in concentrated urine production
- Intake of water causes a decrease in osmolarity of the blood and interstitial fluid which decreases ADH secretion and the removal of water channels
- If there are no water channels this causes decreased permeability of collecting ducts to water and increased water loss in the urine

24
Q

State the factors that regulate ADH release

A
  1. Large decrease in blood volume (detected by baroreceptors)
  2. Severe dehydration - GFR decreases causing less water in urine
  3. Hyperventilation results in increased fluid loss
  4. Vomiting/diarrhoea - causes increase fluid loss of GI tract
  5. Fever, heavy sweating and burns cause large water loss
  • These lead to the generation of hyperosmolar renal medulla
  • ADH secretion in all these cases leads to conservation of body water
  • An intake of copious amounts of water results in high blood pressure which causes increased GFR and increased H2O in urine
25
Q

State the consequences of dehydration

A
  • Water controls your temperature so dehydration can lead to heat shock, headache, fainting and death
  • The heart has to work harder - there is higher blood viscosity, higher blood pressure and blood clotting
  • Brain has priority - takes water from the rest of the body
  • Kidneys get overloaded - toxins accumulate, cannot be flushed away and so kidneys are damaged
  • Digestive problems - constipation, acid reflux, indigestion, toxins accumulate, reduced nutrient absorption
26
Q

How does dehydration lead to hypercalcaemia

A
  • Dehydration causes an imbalance of electrolytes in the bloodstream as NaCl and K+ decrease and Ca2+ increase
  • Increased Ca2+ is hypercalcaemia which causes an increased risk of kidney stones, kidney failure and arrhythmia
27
Q

State the symptoms of hypercalcaemia

A
  • Nausea
  • Vomiting
  • Loss of appetite
  • Constipation
  • Abdominal pain
  • Excessive thirst
  • Fatigue, lethargy, muscle weakness
  • Joint pain, confusion

Physiology 1 Semester 2 (50 decks)

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