Body water

Question 1

How many litres of water are in a 70kg human?

Answer 1

42L but is dependent on adiposity

Question 2

What is the breakdown of the daily loss of water?

Answer 2

1.5L Kidneys
0.3L Lungs
0.6L Skin
0.1L Digestion

Question 3

How much water is found both intracellularly and extracellularly?

Answer 3

Intracellular - 28L
Extracellular - 14L

Question 4

How does H20 cross epithelia and enter the body?

Answer 4

Absorbed in the gut
Reabsorbed in the kidney

Question 5

How does H20 cross epithelia and leave the body?

Answer 5

Secretion and evaporation via lungs and skin
Secretion/lack of absorption in GI (diarrhoea)
Secretion/filtration/lack of reabsorption in kidney

Question 6

What are the functions of the plasma membrane?

Answer 6

Transport of molecules in/out of cell
Cell recognition via cell surface antigens
Cell communication
Cell junctions and cell adhesion molecules
Enzymatic activity
Determination of cell shape

Question 7

What are receptors coupled to?

Answer 7

Heterotrimeric G proteins

Question 8

What are non-antibiotic drugs targeting 50% of the time?

Answer 8

G-protein coupled receptors

Question 9

How does water get in and out of body?

Answer 9

Water can cross epithelia
Filtration of blood in kidneys
(Re)absorption/secretion

Question 10

When is AQP-2 inserted into the apical membrane of collecting duct cells?

Answer 10

When ADH is present

Question 11

How are aquaporins inserted into the plasma membrane?

Answer 11

AQP-2 vesicle is in cytoplasm while ADH is absent
When ADH is present, the exocytotic vesicle fuses with the membrane and plasma membrane ends up with aquaporin channels
When ADH is absent, an endocytic vesicle forms containing the aquaporins retaining them in the cytoplasm

Question 12

What disorder is caused by AQP-2 not being inserted into the apical membrane in the presence of ADH?

Answer 12

Diabetes Insipidus

Question 13

What is osmolarity?

Answer 13

Concentration of osmotically active ions and molecules in plasma

Question 14

What is plasma homeostasis maintained by?

Answer 14

ADH

Question 15

What is the normal range of blood osmolarity?

Answer 15

280-295 mOsm

Question 16

What part of the brain senses the osmolarity of plasma?

Answer 16

hypothalamus

Question 17

How do we calculate osmolarity?

Answer 17

Amount of osmotically active substance/volume

Question 18

What does alcohol do?

Answer 18

Blocks vasopressin release

Question 19

What is the most important factor of hoemostasis?

Answer 19

Feedback control - negative feedback

Question 20

Where is there an example of positive feedback in the human body?

Answer 20

Blood clot formation

Question 21

How do we calculate total body water?

Answer 21

The dilution principle

Question 22

What is the dilution principle?

Answer 22

Inject a known amount of solute into patient
Allow to equilibrate
Correct for water loss 10mg in urine 6mg in faeces
Measure blood concentration (2mg/l)
Calculate the concentration

Question 23

What are the assumptions of the dilution principle?

Answer 23

Solute injected is not broken down
Equilibration is complete within 24h
No water intake in the period
Correction for water loss is accurate