Consequences of fluid loss from GI tract Flashcards
Give possible sites for water loss.
Skin
-sweating
Respiratory Passageways
-ventilation
GIT
- vomiting
- diarrhoea
- defection
Urinary Tract
- urination
- menstruation
Give Causes of diarrhoea.
- lack of water absorption
- increased water secretion
- both
What is decreased water absorption caused by?
Osmotic diarrhoea
Deranged motility diarrhoea
Secretory diarrhoea
What is Osmotic Diarrhoea?
Inadequate fluid reabsorption due to increase in osmotic particles in intestines leading to retained fluid (lactose, bile salts, saline laxatives, polyethylene glycol)
What is Deranged motility diarrhoea?
Increased rate of flow of intestinal contents, meaning reduced time for reabsorption, causing decreased absorption
What is Secretory Diarrhoea?
Ach, substance P, 5-HT and neurotensin act via increased calcium ion concentration to increase rate of intestinal secretion, causing uncontrolled water secretion
Laxatives can cause secretory diarrhoea.
Cholera bacteria also causes secretory diarrhoea by stimulating adenylate cyclase and leading to Na+, Cl- and H20 loss.
Enterotoxin E.coli bacteria also causes secretory diarrhoea.
What is traveller’s diarrhoea caused by?
E.coli
Give Parasytic causes of diarrhoea.
Entamoeba histolytica
- asymptomatic or amoebic dysentery (painful, bloody, low volume)
- treatment: metronidazole
Giardia lamblia
- steatorrhoea and abdominal pain
- treatment: metronidazole or tinidazole
Give Causes of bloody diarrhoea.
chronic disease
ulcerative colitis
neoplasm (abnormal growth of tissue, characteristic of cancer)
Give Major consequences of severe diarrhoea.
hypovolaemia
hyponatraemia
metabolic acidosis
What is vomiting?
Retrograde giant contraction and oral expulsion of gastric contents and bile
What does vomiting cause?
- Increases salivation
- Increase heart rate
- Increases sweating
- Causes pallor (pale appearance)
- Causes nausea
Where is the vomiting Centre?
In the medulla oblongata and receives neuronal inputs from chemoreceptor trigger zone
Give Inputs that initiate vomiting.
Distension of stomach or small intestine
Action of some substances on chemoreceptors in brain or intestine
Increased pressure in skull
Rotating movements of head (motion sickness)
Intense pain
Stimuli to the back of the throat (gag reflex)
Sight, smell, emotional circumstances
What is responsible for transmitting vomiting signals?
Serotonin (5-HT3)
How does serotonin induce vomiting?
Binds to receptors on nerves in the stomach and brain, which transport impulses to the vomiting centre
Why does chemotherapy and radiotherapy cause vomiting?
Cells lining the intestine are damaged, releasing the serotonin stored in them
Serotonin binds to nerves that transmit vomit-inducing impulse from the intestines to the brain.
Vomiting centre is stimulated, resulting in vomiting.
Give Drugs in treating chemotherapy or radiotherapy induced nausea and vomiting.
5-HT serotonin receptor antagonists
What are the Consequences of Excessive Vomting?
Increased salt and water loss
Severe dehydration
Circulatory problems (hypovolaemia)
Metabolic Alkalosis (due to loss of gastric acid HCl)
Death
Give Consequences of Fluid Loss from GI tract.
Hypovolaemia (hence reduced blood pressure)
Polycythaemia (due to dehydration, therefore increased RBC production and increased blood viscosity, decreasing blood flow)
Dehydration
Ionic imbalance
Malnutrition and increased mortality
What are the Effect of hypovolaemia on metabolism?
Hypovolaemia decreases venous return, causing myocardial dysfunction due to increased myocardial oxygen demand but reduced tissue perfusion.
Therefore, anaerobic metabolism takes place, leading to acidosis.
Acidosis and myocardial dysfunction result in multi-organ failure.
Give Renal Adaptations on Hypovolaemia Caused by Diarrhoea
- Increased Na+ and H2O loss due to diarrhoea
- Decreased plasma volume
- Decreased venous pressure
- Leads to increased activity of renal sympathetic nerves
- Increased constriction of renal arterioles
- Decreased net glomerular filtration pressure
- Decreased glomerular filtration rate
- Decreased Na+ and H2O secretion
The decrease in net glomerular filtration pressure allows more time for reabsorption to occur.
Give some Cardiovascular Adaptations to Hypovolaemia Caused by Diarrhoea
The decreased venous pressure has cardiovascular effects
- Decreased venous pressure causes decreased venous return
- Decreases atrial pressure
- Decreases EDV
- Decreases stroke volume
- Decreases cardiac output
- Decreases arterial blood pressure
Decreased arterial blood pressure then stimulates increased activity of renal sympathetic nerves, also stimulating the renal adaptations to hypovolaemia further.
Give some Physiological Adaptations to Water Loss by Sweating.
- Severe sweating causes loss of hypo-osmotic salt solution
- Decreases plasma volume and increases plasma osmolarity
- Decrease in plasma volume causes a decrease in glomerular filtration rate and an increase in plasma aldosterone.
- Increase in plasma osmolarity causes an increase in plasma vasopressin.
- The decrease in GFR and increase in plasma aldosterone decreases Na+ excretion
- The increase in plasma vasopressin decreases H2O excretion
Explain the RAAS system.
Renin is produced by the kidneys in response to impaired blood flow & tissue perfusion, and converts angiotensinogen in the blood to angiotensin I; ACE converts angiotensin I to angiotensin II in the lungs. Angiotensin II then vasoconstricts and stimulates the release of aldosterone. Aldosterone then promotes Na and water retention as well as K excretion.
Explain the effect of Increased plasma K+.
Can also trigger the RAAS cascade. The increased plasma potassium increases aldosterone secretion, increasing plasma aldosterone concentration and causing increased potassium excretion as well as increased sodium reabsorption (decreased sodium excretion) and increased water retention.
Describe ADH in hypovolaemia.
Decreased plasma volume causes:
•Decreased venous, atrial and arterial pressure
•Reflex is initiated by cardiovascular baroreceptors
•Causes increased vasopressin secretion by posterior pituitary
•Increased plasma vasopressin
•Increased tubular permeability to H2O
•Increased H2O reabsorption
•Decreased H2O excretion
Describe the ADH mechanism of action
Vasopressin binds to V2 receptors on membrane of renal tubule cells
insertion of aquaporin -2 channels in collecting ducts of kidney
increases permeability of collecting ducts to H2O and results in concentrated urine production
Give some Factors that regulate ADH release.
Decrease in blood plasma (detected by baroreceptors)
Severe dehydration (GFR decreases causing less H2O in urine)
Hyperventilation (results in increased fluid loss through exhalation)
Vomiting/Diarrhoea (cause increase fluid loss from GIT)
Fever, heavy sweating and burns cause large H2O loss
Describe what happems to a patient with hypovolaemia becomes thirsty.
Baroreceptors detect decrease in plasma volume.
Osmoreceptors detect increase in plasma osmolarity.
Baroreceptors detect the decreased plasma volume and increase release of angiotensin II, which also stimulates thirst.
The osmoreceptor input and the baroreceptor input also stimulate vasopressin release, which increases water retention and decreases sodium excretion.
Metering of water intake occurs to avoid over-hydration as once a thirsty individual is given access to water, they stop drinking after replacing the lost water as the stimulatory osmoreceptor and baroreceptor inputs are eliminated, decreasing thirst.
What does hypocalacaemia increase the risk of?
kidney stones
kidney failure
dementia
arrhythmia
Give some Symptoms of hypercalcaemia.
• Nausea • Vomiting • Loss of appetite • Constipation • Abdominal pain • Excessive thirst • Fatigue • Lethargy • Muscle weakness • Joint pain • Confusion If hypercalcaemia is mild however, it could be asymptomatic.
