Body Water

Question 1

How much water is in the human body?

Answer 1

42L - 55-60%

Question 2

What volume is found intracellularly?

Answer 2

28L - 67%

Question 3

How much water do we lose a day?

Answer 3

2.5L - 1.5L urine, 0.6L sweat, 0.3L lungs, 0.1L faeces
Increased by exercise, alcohol, coffee, salt

Question 4

Where does water cross epithelia?

Answer 4

IN: absorbed in gut, reabsorbed in kidney
OUT: secretion & evaporation in lungs & skin, lack of absorption in gut (diarrhoea), filtration in kidneys

Question 5

Briefly explain filtration?

Answer 5

Water exits blood via gaps between cells of glomerulus - reabsorbed via pores in membranes in tubular component of nephrons - basement membrane of glomerulus block proteins being filtered out

Question 6

What regulate water transport in cells?

Answer 6

Anti-diuretic hormone & aquaporins

Question 7

Where is AQP-1 found?

Answer 7

In basolateral membrane

Question 8

Where is AQP-2 found?

Answer 8

Retained in secretory vessels in cytoplasm of epithelium of collecting ducts - inserted into apical membrane when ADH is present

Question 9

What happens to the aquaporins in collecting ducts after ADH is secreted?

Answer 9

AQP-2 inserted into apical membrane - water transported across epithelium and exit via AQP-1 in apical membrane - into interstitial space

Question 10

What disease is caused by defective AQP-2?

Answer 10

Diabetes insipidus

Question 11

What monitors plasma osmolarity?

Answer 11

Hypothalamus - (280-295 mOsmol)
Increased osmolarity - solute increased & water volume decreased)
Decreased osmolarity - solute decreased & water volume increased

Question 12

What causes dehydration?

Answer 12

Increased osmolarity - Thirst sensation, ADH secreted, AQP-2 inserted

Question 13

What is homeostasis?

Answer 13

Constant internal environment - body temp., blood pressure, heart rate, respiration rate

Question 14

Explain feedback sensors?

Answer 14

Detect change & sends signal to integrating centre stimulates effectors to produce a negative or reverse direction

Question 15

What is the definition of illness?

Answer 15

Disruption in negative feedback pathways

Question 16

Examples showing negative feedback pathways & disease?

Answer 16

Cancer - dysregulation of cell division
Cholera - dysregulation of water balance
Fever - dysregulation of body temp.
CF - dysregualtion of airway surface liquid composition

Question 17

Is there positive feedback?

Answer 17

Blood clot formation - sequential activation of clotting factors - stops bledding(-ve feedback)