ECF fluid regulation 1

Question 1

Two major ECF osmoles

Answer 1

Na+ and Cl-

Question 2

Major ICF osmoles

Answer 2

K+ salts

Question 3

Regulation of ECF volume = ?

Answer 3

Regulation of body Na+

Question 4

How many litres of water is in the body

Answer 4

42l

Question 5

Distribution of body water

Answer 5

ECF = 1/3 (14l)
ICF = 2/3 (28l)

Question 6

Distribution of ECF

Answer 6

Interstitial Fluid ~4/5

Plasma ~1/5

Question 7

What can cause hypovolaemia (low ECF)

Answer 7

Vomiting
Diarrhoea
Excess sweating
Severe bleeding

Question 8

Response to low ECF (hypovolaemia)

Answer 8

Reduced Pulse Volume => reduced venous P => reduced Venous Return => reduced Atrial P => reduced end diastolic volume => reduced systolic volume => reduced cardiac output => reduced BP => reduced carotid sinus baroreceptor inhibition of sympathetic discharge.

Question 9

Effect of sympathetic discharge

Answer 9

increased Sympathetic discharge => increased Vaso Constriction => increased Total Peripheral Resistance => increases BP towards normal

Question 10

Effect of sympathetic discharge on kidney

Answer 10

Increased arterial constriction

Increased renin

Question 11

Effect of increased renin

Answer 11

Increased angiotensin II => increased NaCl and water reabsorption at PROXIMAL TUBULE
Increased angiotensin II => increased Aldosterone => increased reabsorption of NaCl at DISTAL TUBULE

Question 12

What are the changes in proximal tubule Na+ reabsorption due to

Answer 12

changes in the rate of uptake by the peritubular capillaries (greater reabsorpitive forces)

Question 13

What does angiotensin II do to the hydrostatic and oncotic pressure of the peritubular capillaries

Answer 13

Increases oncotic pressure

Decreases hydrostatic pressure

Question 14

What regulates reabsorption of Na+ at the distal tubule

Answer 14

The cortical steroid hormone Aldosterone

Question 15

The smooth muscle of the media, just before it enters the glomerulus, contains what specialised cells

Answer 15

Juxtaglomerular cells aka JG cells (Large epithelial with plentiful granules)

Question 16

What’s the name of the histologically specialized loop of the distal tubule

Answer 16

The Macula Densa

Question 17

What makes up the juxtaglomerular apparatus

Answer 17

Juxtaglomerular cells and the Macula Densa

Question 18

What kind of enzyme is Renin and what does it do

Answer 18

Proteolytic enzyme

Cleaves the alpha2-globulin part off angiotensinogen => angiotensin I

Question 19

How does angiotensin I become angiotensin II and where does most of this conversion occur

Answer 19

Angiotensin I + ACE enzyme

As the blood passes through the pulmonary circut

Question 20

What 3 things increase renin release

Answer 20

Decrease in pressure in afferent arterioles of glomeruli
Increased Sympathetic nerves activity via beta-1 effect
Decreased NaCl delivery at the Macula Densa

Question 21

What 2 things decrease renin release

Answer 21

ADH

Angiotensin II negative feedback

Question 22

4 reasons angiotensin II is important in the body’s response to hypovolaemia

Answer 22

Stimulates aldosterone release => increases NaCl and water retention
Very potent vasoconstrictor
Acts on hypothalamus to secrete ADH => increases water absorption in collecting duct
Stimulates thirst and salt appetite (in hypothalamus)

Question 23

Main determinant of [ADH] in normality and severe hypovolaemia

Answer 23

Normality = Osmolarity 
Severe hypovolaemia  (risk to brain perfusion) = plasma volume 
Will tolerate disturbed osmolarity to perfuse brain