Fluid Loss from GI Tract Flashcards
List some ways in which water is lost in the body.
- defecation, diarrhoea
- vomiting
- urination
- ventilation
- sweating
- menstruation
List some different types of diarrhoea.
- OSMOTIC DIARRHOEA
- SECRETORY DIARRHOEA
- TRAVELLER’S DIARRHOEA
- CHRONIC EXUDATIVE DIARRHOEA
- DERANGED MOTILITY DIARRHOEA
- PARASITIC CAUSE OF DIARRHOEA
What is osmotic diarrhoea caused by?
Decreased absorption of electrolytes and nutrients
→Disaccharidase deficiency
→drug induced
What is secretory diarrhoea caused by?
- Increased secretion of ions from crypt cells
- Electrolyte absorption is impaired
→Excessive laxative use, defects in digestion and absorption (infections eg. Cholera)
→Enterotoxin stimulates adenylate cyclase, increases cAMP and causes Na+ and Cl- and water loss.
What is traveller’s diarrhoea caused by?
Bacteria
What is chronic exudative diarrhoea caused by?
Inflammatory bowel disease
What is deranged motility diarrhoea caused by?
- Motility of the SI increases
- Less time for absorption
What is parasitic diarrhoea caused by?
Parasites such as Entamoeba histolytica and Giardia lamblia
What is dysentery?
Painful, bloody, low volume diarrhoea
Bloody diarrhoea is a cause for concern.
What are some of the causes?
- chronic disease
- ulcerative colitis
- neoplasm ( SERIOUS - characteristic of cancer)
What are the consequences of excessive vomiting?
- hyponatremia
- hypovolemia
- metabolic alkalosis (due to H+ loss)
- death
What are the symptoms of excessive vomiting caused by?
Loss of water and nutrients
What is lost in vomit?
- food
- mucus with Na+, K+, Cl-, HCO3-
- gastric acid
- in extreme cases, blood
What can trigger damage to intestinal cells in cancer patients?
Chemotherapy and radiotherapy
How does serotonin induce vomiting?
- Trigger causes the release of serotonin
- Serotonin transmits the vomit signal via nerves from the intestines to the brain
- Stimulates the vomiting centre and induces vomiting.
How can vomiting be averted?
Blocking site of action of 5-HT receptors ∴ blocks action of serotonin
What are the consequences of hypovolemia?
- decreased venous return
- arterial hypotension
- myocardial dysfunction due to increased myocardial oxygen demand and decreased tissue perfusion
What physiological process causes hypovolemic patients to have acidosis?
Anaerobic metabolism
What can acidosis and myocardial dysfunction cause in hypovolemic patients if left untreated?
Multiple organ failure
What is the body’s response to water loss?
- aldosterone is released (decreasing sodium excretion)
- vasopressin is released (decreasing water excretion)
- cardiovascular and renal adaptations
What effect does dehydration have on calcium levels in the body?
Increases calcium levels
What are some symptoms of hypercalcaemia? PART 1
- nausea
- vomiting
- loss of appetite
- constipation
What are some symptoms of hypercalcaemia? PART 2
- abdominal pain
- excessive thirst
- fatigue, muscle weakness
- confusion
What hormone regulates water loss?
ADH
What stimuli causes ADH release?
Increased osmolarity of body fluids
How does ADH work?
- Inserts water channels (aquaporin-2) in collecting ducts of kidney tubules.
- Increases the permeability of the collecting ducts to H2O
- Concentrated urine production.
What occurs when a patient takes in plain water?
- Decreased blood osmolarity
- Reduced ADH secretion
- Removal of water channels
What is the consequence of having no water channels in the collecting ducts?
- Decreased permeability of the collecting ducts to water
- Increased water loss.
List some factors that regulate ADH release. With each factor, give a brief reason why. PART 1
- large decrease in blood volume (detected by baroreceptors)
- severe dehydration - GFR decreases. Reduced water in urine
- greater water intake: results in high BP which causes increased GFR and increased H2O in urine
List some factors that regulate ADH release. With each factor, give a brief reason why. PART 1
- hyperventilation: results in an increased fluid loss (exhalation)
- vomiting/diarrhoea: causes increased fluid loss from GIT
- fever, heavy sweating and burns cause large H2O loss
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
What are the causes of decreased absorption?
→Increased number of osmotic particles
→Increase in rate of flow of intestinal contents
→Abnormal increase in secretions of GIT
What increases the rate of secretion in secretory diarrhoea?
ACh, substance P, 5-HT and neurotension act via an increase in Ca2+
Why can GI stasis promote diarrhoea?
→stimulating bacterial growth
What condition does entamoeba cause and what is the treatment for it?
→asymptomatic dysentery
→ Metronidazole
What are the consequences of fluid loss in the GI tract?
→Hypovolemia
→Polycythaemia
→Ionic imbalances : poor perfusion of tissues
What are the consequences of dehydration?
→Nausea
→headache
→cramps
→dizziness
What does the renal system do in response to hypervolaemia? PART 1
→Increased sodium and water loss due to diarrhoea
→Plasma and venous volume decreases
→Increased activity of the renal sympathetic nervous system
→Increased constriction of renal arterioles
What does the renal system do in response to hypervolaemia? PART 2
→GFR decreases
→Decreased Na+ and water secretion
→Blood volume increases
What are the cardiovascular effects of hypervolaemia? PART 1
→Decreased venous return
→Decreases atrial pressure
→Decreased ventricular EDV
→Stroke volume reduces
What are the cardiovascular effects of hypervolaemia? PART 2
→Cardiac output reduces
→Arterial blood pressure reduces
→These effects stimulate the sympathetic nervous renal system
What happens during severe sweating? PART 1
→Severe sweating decreases the osmotic salt solution
→Plasma volume decreases
→GFR decreases and plasma osmolarity increases
→This stimulates osmoreceptors in the hypothalamus
What happens during severe sweating? PART 2
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. PART 1
→Decreased plasma volume
→Decreased GFR
→Decreases the arterial pressure
→This has a direct effect on the stretch receptors
→Stimulates an increase in renin secretion
Describe how decreased blood volume can cause the RAAS cascade. PART 2
→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?
Increased K+ concentration and decreased plasma volume.
How does increased water reabsorption occur? PART 1
→Decreased plasma volume
→Decreased venous, atrial and arterial blood pressure
→The osmolarity increases
→Osmoreceptors are stimulated
→Hypothalamus causes the secretion of vasopressin
How does increased water reabsorption occur? PART 2
→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
What does angiotensin II do?
→ Stimulate the release of aldosterone
What does aldosterone do?
→ Promotes reabsorption of Na+, Cl- and H2O
