Consequences of loss of fluid from GI Flashcards
What are the sites of water loss?
→Skin →Respiratory passageways →GIT →Urinary tract →Trauma →Menstrual flow
What is the daily NaCl intake?
→ 10.5g in food
What 2 things cause water to be gained?
→ Drinking
→metabolism
What is diarrhoea and what is the criteria for it?
→Increased frequency with increased volume and fluidity of feces
→>3 unformed stools per 24 hrs
Why does diarrhoea occur?
→Failure of water absorption
→Increased secretion of both
What are the causes of decreased absorption?
→Increased number of osmotic particles
→Increase in rate of flow of intestinal contents (deranged motility diarrhoea)
→Abnormal increase in secretions of GIT (secretory diarrhoea)
What is the cause of osmotic diarrhoea?
→decreased absorption of electrolytes and nutrients
→Disaccharidase deficiency
→drug induced
→malabsorption of galactose
What increases the rate of secretion in secretory diarrhoea?
→ACh, substance P, 5-HT and neurotension act via an increase in Ca2+
What causes secretory diarrhoea?
→Excessive laxative use, defects in digestion and absorption (infections eg. Cholera)
→Enterotoxin stimulates adenylate cyclase increases cAMP causes Na+ and Cl- and water loss.
What causes traveller’s diarrhoea?
→ Bacteria
What causes chronic exudative diarrhoea?
→ Inflammatory bowel disease
What causes deranged motility diarrhoea?
→ lack of absorption
→some agents promotes secretion as well as motility
Why can GI stasis promote diarrhoea?
→stimulating bacterial growth
What are the two parasites that cause diarrhoea?
→Entamoeba histolytica
→Giardia lamblia
What condition does entamoeba cause and what is the treatment for it?
→asymptomatic dysentery
→ Metronidazole
What does giardia cause?
→Steatorrhea and abdominal pain
→Maldigestion and malabsorption of lipids, CHOs, vitamin A, vitamin B12, folic acid
What does dysentery cause?
→painful
→ bloody
→low volume diarrhoea
What are the consequences of severe diarrhoea?
→loss of water, nutrients, Na+, K+ and HCO3-
→Decreased blood volume (hypovolaemia)
→Metabolic acidosis - due to loss of HCO3-
What are the consequences of excessive vomiting?
→Increased salt and water loss →Severe dehydration →Circulatory problems →Metabolic alkalosis - due to loss of gastric acid HCl →Death
What is lost in vomit?
→food → mucus →Na+ → K+ → Cl- → HCO3- → gastric acid →upper intestinal contents (bile) → blood
What are the consequences of fluid loss in the GI tract?
→Hypovolaemia
→Haemoconcentration/polycythaemia (dehydration) →Increased RBC
→Dehydration
→Ionic imbalances : poor perfusion of tissues
→Malnutrition and increase in mortality
What are the consequences of hypovolaemia?
→Decreased venous return
→Arterial hypotension
→Myocardial dysfunction due to increased myocardial oxygen demand but tissue perfusion is reduced
→Increased anaerobic metabolism → to acidosis
→Acidosis and myocardial dysfunction → multi organ failure
What are the consequences of dehydration?
→Nausea →headache → irrationality →cramps →increased temperature →dizziness
What is the bodys response to water loss?
→Cardiovascular adaptation
→Renal adaptation
→Behavioral and this stimulates fluid intake when possible
What does the renal system do in response to hypervolaemia?
→Increased sodium and water loss due to diarrhoea
→Plasma volume decreases
→Venous volume decreases
→Increased activity of the renal sympathetic nervous system
→Increased constriction of renal arterioles
→GFR decreases
→Allows more time for reabsorption to occur if there is water present
→Decreased Na+ and water secretion
→Blood volume increases
What are the cardiovascular effects of hypervolaemia?
→The decreased venous return
→Decreases atrial pressure
→Decreased ventricular end diastolic volume
→Stroke volume reduces
→Cardiac output reduces
→Arterial blood pressure reduces
→These effects stimulate the sympathetic nervous renal system
What happens during severe sweating?
→Severe sweating decreases the osmotic salt solution
→Plasma volume decreases
→GFR decreases and plasma osmolarity increases
→This stimulates osmoreceptors in the hypothalamus
Increase the plasma vasopressin concentration (ADH)
→Plasma aldosterone levels increase due to RAAS system
→ADH inserts water channels within the collecting duct of the tubules and decreased water secretion occurs as it takes up more water
Describe how decreased blood volume can cause the RAAS cascade?
→Decreased plasma volume
→Decreased GFR and decreased flow to Macula Densa
→Decreases the arterial pressure
→This has a direct effect on the stretch receptors
→Stimulates an increase in renin secretion
→Increased plasma renin generates angiotensin II
→Plasma aldosterone secretions increase from adrenal cortex
→Sodium reabsorption increases
→Water reabsorption increases
→Plasma volume increases
What is the response to increased K+ concentration?
→A decrease in plasma volume
→Increase plasma angiotensin II
→Increased aldosterone from the renal cortex
→Sodium reabsorption increases so sodium excretion decreases
→Water is retained
→Increased K+ excretion
What can the RAAS cascade be triggered by?
→The RAAS cascade can be triggered by increased K+ concentration and decreased plasma volume.
How does increased water reabsorption occur?
→Decreased plasma volume
→Decreased venous, atrial and arterial blood pressure
→These reflexes are mediated by cardiovascular baroreceptors
→The osmolarity increases
→Osmoreceptors are stimulated
→Hypothalamus causes the secretion of vasopressin
→Plasma levels increase
→Vasopressin stimulates its receptors on the collecting tubules and insert channels ‘aquaporin 2’
→Increased water reabsorption and decreased excretion
How is thirst stimulated?
→Hyperosmolarity occurs →Decreases plasma volume →Baroreceptors are stimulated →Increases angiotensin II levels →This stimulates thirst →And stimulates ADH/vasopressin release
What does dehydration lead to?
→imbalance of electrolytes in the bloodstream (decreased NaCl and K+ but also increase in Ca2+)
What does an increase in Ca2+ cause?
→ Hypercalcaemia
What does hypercalcaemia cause?
→increased risk of kidney stone
→ kidney failure
→ dementia
→arrhythmia
What are the symptoms of hypercalcaemia?
→Nausea →Vomiting →Loss of appetite →Constipation →Abdominal pain →Excessive thirst →Fatigue,lethargy, muscle weakness →Joint pain and confusion
What does ADH stimulate?
→Vasopressin (ADH) - stimulates thirst mechanism
What leads to ADH release?
→Increased osmolarity of body fluids leads to ADH release
How does ADH work?
→ADH activates the V2 receptors on the renal collecting ducts
→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 does the intake of plain H2O do?
→Intake of plain H2O leads to a decrease in osmolarity of the blood and interstitial fluid
→This decreases the ADH secretion and the removal of water channels
What happens if there are no water channels?
→decreased permeability of collecting ducts to water and increased water loss
What are the 5 factors that regulate ADH release?
→Large decrease in blood volume (detected by baroreceptors)
→2.Severe dehydration: under this condition, GFR decreases causing less H2O in urine
→3.Hyperventilation: results in increased fluid loss (exhalation)
→4.Vomiting/diarrhoea: causes increased fluid loss from GIT
→5.Fever, heavy sweating, and burns cause large H2O loss
What does the thirst center in the hypothalamus do?
→ Stimulate the desire to drink
What does angiotensin II do?
→ Stimulate the release of aldosterone 2
What does aldosterone do?
→ Promotes reabsorption of Na+, Cl- and H2O
