Consequences of Fluid Loss from the GIT

Question 1

How is water gained and lost?

Answer 1

Gained in liquids, foods, metabolism and is lost in sweat, urine, faeces, menstruation, vomiting

Question 2

What is Diarrhoea?

What can cause bloody diarrhoea?

Answer 2

• • Increased frequency and volume of water faeces
  • Occurs as a result of failure of water reabsorption/increased secretion, due to:
  o ↑Osmolality of stool
  o ↑Gut motility - Deranged motility diarrhoea
  o Abnormal increase in secretions of GIT - Secretory diarrhoea
• Due to Chronic disease, Ulcerative colitis, Neoplasm

Question 3

Compare Osmotic, Secretory, Deranged Diarrhoea

Answer 3

Osmotic Diarrhoea:
Decreased absorption of electrolytes and nutrients
• Drug-induced
• Malabsorption
• Disaccharide deficiency

Secretory Diarrhoea:
Abnormal increase in secretions
• Excessive laxative use
• Infections

Deranged Diarrhoea:
Lack of absorption, may be an increase in motility/secretion
• GI stasis stimulating bacterial overgrowth

Question 4

What are the peristaltic causes of diarrhoea?

What are the consequences of diarrhoea?

Answer 4

• • Entamoeba histolytica - Gradual onset, treat with Metronidazole
  • Giardia - Steatorrhoea, abdominal pain, treat with Metronidazole/Tinidazole
• • Excessive loss of water, nutrients, electrolytes = Hypovolemia, Hypokalaemia, Hyponatraemia
  • Metabolic Acidosis - due to loss of HCO3-

Question 5

What is Vomiting? What does it do?

What are the physiological effects of vomiting?

Answer 5

• • Retrograde contraction of GIT, causing oral expulsion of gastric contents and bile
  • Occurs in pregnancy, metabolic disorders, illness, alcohol dependency
  • Allows for the removal of ingested toxic substances
• Physiological effects include:
  o ↑Salivation, HR, Sweating
  o Pallor, Nausea (avoid ingesting toxic substances again)

Question 6

What is the mechanism of Vomiting?

What are the inputs that initiate vomiting?

Answer 6

• Neuronal inputs from body to Vomiting Centre in the Medulla:

1. Deep inspiration = ↑abdominal pressure - retrograde contraction
2. Breath held, chest fixes to ↓Oesophageal pressure = relaxation of sphincters
3. Retching and forceful expulsion

• Distension of stomach/small bowel, ↑Intracranial pressure, Motion Sickness, Intense pain, Gag reflex, Smell/sight/emotion

Question 7

What are consequences of Vomiting?

Answer 7

• Excessive salt, water, nutrient loss
• Dehydration
• Metabolic Alkalosis - loss of gastric acid
• Hypovolaemia, Hypokalaemia, Hyponatraemia

Question 8

What are the consequences of fluid loss from the GIT?

Answer 8

• Hypovolemia
o ↓Venous return = ↓SV/CO = Hypotension = Myocardial dysfunction due to ↓tissue perfusion. As a result, there is ↑Anaerobic metabolism = Acidosis - Acidosis and Myocardial dysfunction = Multi-organ failure

• Polycythaemia (↑RBC%) - due to reduced plasma volume
• Dehydration and Malnourishment
• Ionic imbalances - poor tissue perfusion

Question 9

What are the responses to water loss?

Answer 9

• Cardiovascular adaptations - Vasoconstriction, RAAS activation
• Renal adaptation - ADH secretion, RAAS activation = ↓Urine production
• Behavioural adaptation - osmoreceptors = ↑Thirst

Question 10

What is Hypercalcaemia a consequence of?

What are its symptoms?

Answer 10

• Dehydration - due to ionic imbalance
• Nausea, Vomiting, Loss of appetite, excessive thirst, Constipation, abdominal and joint pain, Fatigue, lethargy, muscle weakness

Question 11

What are the 4 mechanisms used in the maintenance of water balance?

Answer 11

1. ADH: ↑Permeability of CD = ↑H2O reabsorption
2. Thirst reflex: ↑Desire to drink
3. ANP: Stimulates Natriuresis: ↑Na+, Cl-, H2O excretion
4. RAAS: Aldosterone - ↑Na+/H2O reabsorption

Question 12

How does ADH work in water balance?

Answer 12

• Stimulates the thirst reflex
• ↑Water reabsorption in CD
• Intake of water ↓plasma osmolality, which then ↓ADH secretion