Consequences Of Fluid Loss From The GI Tract

Question 1

List some ways in which water is lost in the body.

Answer 1

• defecation, diarrhoea
• vomiting
• urination
• ventilation
• sweating
• menstruation

Question 2

List some different types of diarrhoea.

Answer 2

• OSMOTIC DIARRHOEA: decreased absorption of electrolytes and nutrients
• SECRETORY DIARRHOEA: increased secretion of ions from crypt cells, so electrolyte absorption is impaired (a common result of cholera)
• TRAVELLER’S DIARRHOEA: due to bacteria
• CHRONIC EXUDATIVE DIARRHOEA: inflammatory bowel disease
• DERANGED MOTILITY DIARRHOEA: motility of the SI increases, meaning there is less time for absorption
• PARASITIC CAUSE OF DIARRHOEA: caused by Entamoeba histolytica and Giardia lamblia

[dysentry: painful, bloody, low volume diarrhoea]

Question 3

Bloody diarrhoea is a cause for concern.

What are some of the causes?

Answer 3

• chronic disease
• ulcerative colitis
• neoplasm (a new growth in the body, characteristic of cancer)

Question 4

What are the consequences of excessive diarrhoea?

Answer 4

There is a loss of water and nutrients (Na+, K+ and HCO3-) so:

• hyponatremia
• lowered blood volume (hypovolemia)
• metabolic acidosis - due to loss of HCO3-

Question 5

What are the consequences of excessive vomiting?

Answer 5

There is a loss of water and nutrients, so:

• esophagitis (ulcerations of the oesophagus)
• hyponatremia
• hypovolemia
• metabolic alkalosis (due to H+ loss)
• death

Question 6

5-HT-blocking drugs can help avert vomiting.

How do they work?

Answer 6

The release of serotonin can induce vomiting.

Either by chemotherapy or radiotherapy (or another trigger), there is damage to the cells in the intestine. This causes the release of serotonin, which transmits the vomit signal via nerves from the intestines to the brain, thus stimulating the vomiting centre and inducing vomiting.

Blocking the site of action of 5-HT3 receptors will block the actions of serotonin, stopping the vomit signal.

Question 7

What is lost in vomit?

Answer 7

• food
• mucus with Na+, K+, Cl-, HCO3-
• gastric acid
• upper intestinal contents (including bile)
• in extreme cases, blood

Question 8

What are the consequences of hypovolemia?

Answer 8

• decreased venous return
• arterial hypotension
• myocardial dysfunction due to increased myocardial oxygen demand and decreased tissue perfusion

The increased anaerobic metabolism leads to acidosis.
The acidosis and myocardial dysfunctions combined can cause multi-organ failure.

Question 9

What is the body’s response to water loss?

Answer 9

• cardiovascular adaptation
• renal adaptation
• behavioural adaptation (this stimulates fluid intake when possible to do so, remember that sometimes access to food and water is not easy)
• aldosterone is released (decreasing sodium excretion)
• vasopressin is released (decreasing water excretion)

Question 10

What effect does dehydration have on calcium levels in the body?

Answer 10

Dehydration causes an imbalance in electrolytes in your bloodstream (decreased NaCl and K+, but it increases your [Ca2+].

Question 11

What are some symptoms of hypercalcaemia?

Answer 11

[if mild, it could be asymptomatic]

• nausea
• vomiting
• loss of appetite
• constipation
• abdominal pain
• excessive thirst
• fatigue, lethargy, muscle weakness
• joint pain, confusion

Question 12

What hormone regulates water loss?

Answer 12

ADH stimulates the thirst mechanism.

With the increased osmolarity of body fluids, we have ADH release.

Question 13

How does ADH work?

Answer 13

It inserts water channels (aquaporin-2) in collecting ducts of kidney tubules.
This increases the permeability of the collecting ducts to H2O and results in concentrated urine production.

With the intake of plain H2O, there’s a decrease in osmolarity of blood and interstitial fluid. This decreases ADH secretion and the removal of water channels.
If there are no water channels, this causes decreased permeability of the collecting ducts to water and increased water loss.

Question 14

List some factors that regulate ADH release.

Answer 14

• 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 an increased fluid loss (exhalation)
• vomiting/diarrhoea: causes increased fluid loss from GIT
• fever, heavy sweating and burns cause large H2O loss