Consequences of Fluid Loss Flashcards
What is average water intake and output in an adult individual?
Total intake (volumes): 2550ml
Liquids: 1200ml
Food: 1000ml
Metabolically produced: 350ml
Total output (volumes): 2550ml
“Insensible water loss” (skin and lungs): 900ml
Sweat: 50ml
Faeces: 100
Urine: 1500
Insensible water loss= water loss by transepidermal diffusion, so evaporates via skin and resp tract
Describe the total balance for sodium and chloride
Daily NaCl intake and loss
Intake (grams): Food: 10.5g
Output (grams):10.5g
Sweat: 0.25g
Faeces: 0.25g
Urine: 10.00g – varies considerably
Kidneys can alter excretion to match gain with loss
What is diarrhoea?
↑ frequency, with ↑ volume and fluidity of faeces
3 unformed stools per 24hrs
Change in bowel movement
Occurs as a result of:
Failure of water absorption, ↑ secretion of water
What is osmotic diarrhoea?
Osmotic diarrhoea: Decreased absorption of electrolytes and nutrients
Due to disaccharidase deficiency/malabsorption
Causes bloating, nausea, watery diarrhoea
What is secretory diarrhoea?
ACh, and substance P act via ↑[Ca2+] to increase intestinal secretion rate
Causes: excessive laxative use, defects in digestion and absorption, infections e.g. cholera
Enterotoxin stimulates AC → ↑ cAMP → Na+, Cl- and water loss
What is deranged motility diarrhoea ?
Deranged motility diarrhoea: lack of absorption of nutrients; some agents may promote secretion as well as motility
GI stasis may promote diarrhoea by stimulating bacterial overgrowth
Describe some parasitic causes of diarrhoea
Entamoeba histolytica:
Gradual onset → systemic symptoms (anorexia, headache)
Metronidazole is used to treat this
Giardia → steatorrhoea, abdominal pain; malabsorption of lipids, Carbs, vit A, B12, folic acid. Steatorrhoea also caused by obstruction, damage to GI tract, bacterial overgrowth.
What are the major consequences of severe diarrhoea and vomiting?
↓ blood volume (hypovolaemia)
Metabolic acidosis due to loss of HCO3- in diarrhoea
Metabolic alkalosis – due to loss of gastric acid (HCl) in vomiting
↑ salt and water loss
Severe dehydration
Circulatory problems
Diarrhoea and vomiting can cause hypovolaemia. What are some consequences of this?
↓ venous return which leads to arterial hypotension
Myocardial dysfunction because tissue perfusion is reduced
↑ anaerobic metabolism → lactic acid buildup which leads to acidosis
Acidosis and myocardial dysfunction → multi-organ failure
Describe the renal response to hypovolaemia due to Diarrhoea
Na and H20 loss decreases plasma volume and therefore venous Pa. This triggers a baroreceptor reflex to increase renal symp nerve activity :
Renal arterioles constrict, decreasing net glomerular filtration pressure, which ↓GFR
↓GFR leads to decreased Na and water secretion
Describe the cardiac response to hypovolaemia due to Diarrhoea
Na and H20 loss decreases plasma volume and therefore venous Pa.
↓ venous pa means ↓ atrial pa, ↓ SV and CO. This decreases arterial BP.
Decreased arterial BP decreases net glomerular filtration pa and GFR, which decreases Na and water secretion and allows more reabsorption.
Also, ↓ atrial pa triggers a baroreceptor reflex to increase activity of renal symp nerves.
How does the RAAS respond to hypovolaemia?
What is the physiologic response to hypovolaemia with increased potassium concentration?
How does ADH control fluid balance?
Increased osmolarity of body fluids → ADH release
ADH activates the V2 receptor on the renal collecting ducts
Inserts aquaporin-2 in collecting duct of kidney
This increases permeability of the CDs to H2O and results in conc urine
What is dehydration and its effects?
Dehydration →imbalance of electrolytes in the bloodstream (↓ NaCl and K+), but it also ↑[Ca2+]
↑ [Ca2+] → hypercalcaemia (risk of kidney stones, kidney failure, and arrhythmia)
These cause symptoms such as nausea, vomiting, appetite loss, constipation and abdominal pain.
