Consequences of Fluid Loss from GI Tract Flashcards
What is total body water balance?
average water gain and loss in adults
What is the normal fluid intake in the body?
Liquids: 1200 ml
Food: 1000 ml
Metabolically produced: 300 ml
Total: 2550 ml
What is the normal fluid output?
Insensible water loss: 900 ml
Sweat: 50 ml
Faeces: 100 ml
Urine: 1500 ml
Total 2550 ml
What is meant by insensible water loss?
water loss by transepidermal diffusion (water evaporating through skin & respiratory tract
What are the sites of water loss in the body?
skin respiratory passageways trauma urinary tract GI tract Menstrual flow
Describe the excretion of Na and Cl
Excretion is usually small, but large in: - diarrhoea - sweating - vomiting - haemorrhage → loss of water and salts
What is the daily intake of NaCl?
Food: 10.5g
What is the daily output of NaCl?
Sweat: 0.25g
Faeces: 0.25g
Urine: 10.00g – varies considerably
Total output: 10.5g
Kidneys can alter excretion to match gain with loss
How is fluid lost from the body?
Defecation; diarrhoea Vomiting; food, electrolytes, water Urination Ventilation Sweating
Menstruation
What is lost with fluid during fluid loss?
Water, food, electrolytes, bile, gastric acid etc. is lost in the above
How is water gained in the body?
Drinking
Metabolic
Outline clinical features of diarrhoea
Frequency increases, with ↑ volume and fluidity of faeces
> 3 unformed stools per 24 hrs
Change in bowel movement
Why does diarrhoea occur?
Failure of water absorption
↑ secretion of nutrients (carbs, sugars increase osmotic content in gut and more water absorbed) / bacteria build up decongestion of bile acids/salts to cause osmotic & secretory diarrhoea) or both
What are the causes of decreased water absorption in the gut?
↑ number of osmotic particles (osmotic diarrhoea)
↑ rate of flow of intestinal contents (deranged motility diarrhoea)
Abnormal increase in secretions of GIT (secretory diarrhoea)
What is osmotic diarrhoea?
Decreased absorption of electrolytes and absorbed nutrients Disaccharidase deficiency (disaccharide deficiency/malabsorption), drug-induced, malabsorption of galactose)
en does osmotic diarrhoea occur?
when too much water is drawn into the bowels. If a person drinks solutions with excessive sugar or excessive salt, these can draw water from the body into the bowel and cause osmotic diarrhoea
What is secretory diarrhoea?
ACh, substance P, 5-HT and neurotensin act via ↑[Ca2+] to increase rate of intestinal secretion
What causes secretory diarrhoea?
Excessive laxative use, defects in digestion and absorption; infections [e.g. cholera (Vibrio cholerae)]
Survives acidic conditions of gut
Enterotoxin stimulates adenylate cyclase → ↑ cAMP → Na+, Cl- and water loss
Replace water, electrolytes and glucose
What causes travellers diarrhoea?
Bacteria
Explain how inflammatory bowel disease can cause diarrhoea
Inflammatory bowel disease → chronic exudative diarrhoea
What is deranged motility diarrhoea?
lack of absorption; some agents may promote secretion as well as motility
GI stasis may promote diarrhoea by stimulating bacterial overgrowth
What parasites can cause diarrhoea?
Entamoeba histolytica and Giardia lamblia
Outline the features of diarrhoea caused by Entamoeba histolytica
Entamoeba histolytica → asymptomatic or amoebic dysentery
Gradual in onset → systemic symptoms (anorexia, headache)
Treatment: Metronidazole
Outline the clinical features of Giardia diarrhoea
Giardia → steatorrhoea and abdominal pain; maldigestion & malabsorption of lipids, CHOs, vit A, vit B12, folic acid due to damage of mucosal lining
Treatment: Metronidazole or tinidazole
What are the causes of bloody diarrhoea?
Chronic disease
Ulcerative colitis
Neoplasm
What are the major consequences of severe diarrhoea?
Consequences of excessive loss of water, nutrients, Na+, K+ and HCO3- :
↓ blood volume (hypovolaemia)
Metabolic acidosis – due to loss of HCO3- e.g., in diarrhoea
Volume depletion can lead to alkalosis / acidosis
What are the consequences of excessive vomiting?
↑ salt and water loss Severe dehydration Circulatory problems Metabolic alkalosis – due to loss of gastric acid (HCl) Death
What substances are lost in vomit?
Food Mucus with Na+, K+, Cl-, HCO3- Gastric acid Upper intestinal contents (incl. bile) Blood
What are the consequences of fluid loss from the GI tract?
Hypovolaemia (↓ BV)
Haemoconcentration (reduced BV) / polycythaemia (dehydration) =↑[RBC]
Dehydration
Ionic imbalances; poor perfusion of tissues
Malnutrition and ↑ mortality
What is polycythaemia?
Polycythaemia, or erythrocytosis, means having a high concentration of red blood cells in your blood => thicker blood (less able to flow through vessels)
What are the consequences of hypovolemia?
- ↓ venous return
- Arterial hypotension
- Myocardial dysfunction due to ↑ myocardial oxygen
demand and ↓ tissue perfusion due to ↑[RBC] - ↑ anaerobic metabolism → lactic acid causing acidosis
What is the effect of acidosis?
Acidosis and myocardial dysfunction → multi-organ failure
What are the symptoms of dehydration?
Nausea, headache, irrationality, cramps, ↑temperature, dizziness
How does the body respond to water loss?
Cardiovascular adaptation
Renal adaptation
Behavioural and this stimulates fluid intake when possible to do so
What is EDV?
end diastolic volume - volume of blood in the right and/or left ventricle at (diastole) or the amount of blood in the ventricle
What is the significance of the renal arteries?
Renal arteries carry blood from the heart → kidneys
They branch directly from aorta on either side + extend to each kidney, taking large volume of blood to kidneys to be filtered just before systole
How does the body respond to hypovolemia?
Decreased Na+ secretion due to RAAS causes water minimised water excretion to correct decreased plasma volume
What is physiological response to hypovolemia with increased K+?
RAAS - angiotensin II increases aldosterone secretion
- ↑ Na reabsorption
- ↑ K excretion
How does hypovolemia affect osmolarity?
Osmolarity increases to stimulate osmoreceptors in hypothalamus to cause ADH secretion in posterior hypothalamus = increase Plasma levels
How does ADH reverse hypovolemia?
ADH will stimulate receptors in collecting tubules in kidneys, and insert water channels aquaporin 2
=> increased water absorption and decreased excretion
Why do we feel thirsty?
Feeling thirst is stimulated by lower extracellular volume and higher plasma osmolarity
Angiotensin levels increase to stimulate thirst
How does the body respond to thirst?
The osmoreceptors+ baroreceptors controlling ADH release are samee for thirst.
The brain centres receiving input from receptors and mediating thirst are located in the hypothalamus, close to area producing ADH
What is dehydration?
imbalance of electrolytes in your bloodstream (↓ NaCl and K+), but it also ↑[Ca2+]
What is hypercalcaemia?
↑[Ca2+]
What are the symptoms of hypercalcaemia?
If mild = asymptomatic Nausea, Vomiting Loss of appetite Constipation Abdominal pain Excessive thirst
Fatigue, lethargy, muscle weakness, joint pain, confusion
Explain the mechanism of action of ADH
Inserts water channels (aquaporin-2) in collecting duct of kidney
This increases the permeability of the collecting ducts to H2O and results in concentrated urine production
What causes a decrease in ADH
Intake of plain H2O causes a ↓ in osmolarity of blood and interstitial fluid
This decreases ADH secretion and the removal of the water channels
No water channels causes decreased permeability of collecting ducts to water and increased water loss
What factors regulate ADH release?
Large decrease in blood volume (detected by baroreceptors)*
Severe dehydration: under this condition, GFR decreases causing less H2O in urine*
Intake of copious amounts of water: results in high BP which causes increased GFR and increased H2O in urine
Hyperventilation: results in increased fluid loss (exhalation)*
Vomiting/diarrhoea: causes increased fluid loss from GIT*
Fever, heavy sweating, and burns cause large water loss*
*ADH secretion in all these cases leads to conservation of body water
