Consequences of fluid loss from the GI Tract

Question 1

How much liquid, food and metabolically produced liquid do we consume and contain (ml)?

Answer 1

• Liquids: 1200ml
• Food: 1000ml
• Metabolically produced: 350ml
• Total: 2550ml

Question 2

How much liquid do we excrete (insensible water loss, sweat, faeces and urine)

Answer 2

• “Insensible water loss” (skin and lungs): 900ml
• Sweat: 50ml
• Faeces: 100
• Urine: 1500

Question 3

Excretion is usually small, however when can this increase?

Answer 3

Excretion is usually small, but large in diarrhoea, sweating, vomiting, haemorrhage → loss of water and salts

Question 4

What is our intake and output of NaCl?

Answer 4

Intake (grams):
• Food: 10.5g

Output (grams):
•	Sweat: 0.25g
•	Faeces: 0.25g
•	Urine: 10.00g – varies considerably
•	Total output: 10.5g

Question 5

List ways in which fluid is lost and gained

Answer 5

• Defecation; diarrhoea
• Vomiting: what is lost?
• Urination
• Ventilation
• Sweating
• Menstruation

Water gain:
• Drinking
• Metabolic

Question 6

What causes diarrhoea?

Answer 6

Occurs as a result of:
• Failure of water absorption
• ↑ secretion or both

Question 7

What causes decreased absorption?

Answer 7

Causes of decreased absorption:
• ↑ number of osmotic particles (osmotic diarrhoea)
• ↑ rate of flow of intestinal contents (deranged motility diarrhoea)
• Abnormal increase in secretions of GIT (secretory diarrhoea)

Question 8

Define Osmotic diarrhoea

What causes it?

Answer 8

Decreased absorption of electrolytes and nutrients

Disaccharidase deficiency (disaccharide deficiency/malabsorption), drug-induced, malabsorption of galactose)

Question 9

Define Secretory diarrhoea

What causes it?

Answer 9

ACh, substance P, 5-HT and neurotensin act via ↑[Ca2+] to increase rate of intestinal secretion

• Excessive laxative use, defects in digestion and absorption; infections [e.g. cholera (Vibrio cholerae)]

- Survives acidic conditions of the gut
- Enterotoxin stimulates adenylate cyclase → ↑ cAMP → Na+, Cl- and water loss
- Replace water, electrolytes and glucose (treatment)

Question 10

What causes traveller’s diarrhoea?

Answer 10

Bacteria

Question 11

What is inflammatory bowel disease?

Answer 11

Exudative diarrhea occurs with the presence of blood and pus in the stool. This occurs with inflammatory bowel diseases,

Question 12

What is deranged motility diarrhoea?

What promotes it?

Answer 12

Deranged motility diarrhoea: lack of absorption; some agents may promote secretion as well as motility

GI stasis may promote diarrhoea by stimulating bacterial overgrowth

Question 13

What 2 bacteria cause Parasitic diarrhoea?

Answer 13

Entamoeba histolytica and Giardia lamblia

Question 14

What symptoms does Entamoeba histolytica cause?

Answer 14

• Entamoeba histolytica → asymptomatic or amoebic dysentery
• Gradual in onset → systemic symptoms (anorexia, headache)
• Metronidazole

Question 15

What symptoms does Giardia cause?

Answer 15

• Giardia → steatorrhoea and abdominal pain; maldigestion & malabsorption of lipids, CHOs, vit A, vit B12, folic acid
• Metronidazole or tinidazole

Question 16

What is dysentery?

What does it cause?

Answer 16

Dysentery is an intestinal inflammation, primarily of the colon.

Painful, bloody, low volume diarrhoea

Question 17

What are the major consequences of diarrhoea?

Answer 17

Consequences of excessive loss of water, nutrients, Na+, K+ and HCO3- :

• ↓ blood volume (hypovolaemia)
• Metabolic acidosis – due to loss of HCO3- e.g., in diarrhoea

Question 18

Describe the physiological response to diarrhoea

Answer 18

On image - LEARN IS IMPORTANT

Question 19

Describe the physiological response to sweating

Answer 19

On image

Question 20

Describe the response of the body to the consequences hypovolaemia: RAAS cascade

Answer 20

On image

Question 21

Describe physiologic response to the consequences of hypovolaemia

Answer 21

On image

Question 22

Describe the physiologic response to the consequences of hypovolaemia - THIRST

Answer 22

On image

Question 23

Describe the effects of dehydration on calcium

Answer 23

• Dehydration →imbalance of electrolytes in the bloodstream (↓ NaCl and K+), but it also ↑[Ca2+]
• ↑ [Ca2+] → hypercalcaemia
• Hypercalcaemia → ↑ risk of kidney stones, kidney failure, dementia and arrhythmia.

Question 24

What are the symptoms of hypercalcaemia?

Answer 24

If mild= asymptomatic
•	Nausea
•	Vomiting
•	Loss of appetite
•	Constipation
•	Abdominal pain 
•	Excessive thirst
•	Fatigue, lethargy, muscle weakness
Joint pain, confusion

Question 25

What regulates water loss?

Answer 25

Vasopressin (antidiuretic hormone, ADH)
• ADH stimulates thirst mechanism
• Increased osmolarity of body fluids → ADH release

Question 26

How does ADH work?

Answer 26

• 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
• Intake of plain H2O → a ↓ in osmolarity of blood and interstitial fluid
o This decreases ADH secretion and the removal of the water channels
• If there are no water channels, this causes decreased permeability of collecting ducts to water and increased water loss

Question 27

Describe the factors that regulate ADH release

Answer 27

1. 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*

*ADH secretion in all these cases leads to conservation of body H2O
• This is through the sequence of events we just talked
• Intake of copious amounts of water: results in high BP which causes increased GFR and increased H2O in urine

Question 28

Summary of factors that maintain body water balance

Answer 28

On table