Long Term Control of Blood Pressure

Question 1

What ions are present in the extracellular fluid

Answer 1

Sodium (most concentrated),
Cloride,
Bicarbonate.
Protein,
Magnesium

Question 2

Describe how ECF volume and extracellular osmolality are maintained

Answer 2

Volume - By adjusting total body content of NaCl. This maintains blood pressure.
Osmolality - Adjusting total body H2O content. This maintains cell volume.

Question 3

Why is sodium so important?

Answer 3

It is the main osmotic constituent of the ECF, where Na moves H2O follows. Therefore the whole-body Na content (which the kidneys control) is the major determinant of the ECF volume.

Question 4

Briefly describe the control of ECF volume

Answer 4

The effective circulating volume is sensed by carotid sinus, aortic arch, renal afferent arteriole and atria. The hormonal transducers (RAAS, SNS, ANP and AVP (ADH) in he short term effect heart, BVs which controls BP. In the long term effects the kidneys to effect Na excretion

Question 5

What acts as the signal for Na homeostasis?

Answer 5

The volume of ECF. This creates the critical parameter for regulating Na excretion which is called the effective circulating volume. If ECV is low then it increases Na retention

Question 6

Describe where the majority of Na transport takes place

Answer 6

• Proximal tubule via sodium hydrogen exchanger 3,
• Thick ascending limb of loop of henle via sodium potassium chloride co-transporter
• Distal tubule via sodium chloride co exchanger,
• Collecting ducts via epithelial sodium channel

Question 7

What is angiotensinogen and what is it cleaved by?

Answer 7

Precursor for angiotensin 1 which is produced by the liver. It is cleaved by renin which is released by juxtaglomerular apparatus of the kidney.

Question 8

What is angiotensin 1 and what occurs to it

Answer 8

It appears to have no biological function except to act as the precursor to angiotensin 2. It is converted via angiotensin converting enzyme

Question 9

Where are ACEs found?

Answer 9

Vascular endothelium in the lungs and the renal afferent and efferent arterioles

Question 10

Describe the functions of angiotensin 2

Answer 10

• Vasoconstriction by acting on vascular smooth muscle (Increases TPR)
• Acts on the hypothalamus to increase released of ADH which increases reabsorption of H2O which increases ECV,
• Zona glomerulosa of adrenal glands which increases secretion of aldosterone, which increases Na reabsorption

Question 11

Described the effects of the renal sympathetic nerve activity

Answer 11

It increases cascular resistance and increases Na reabsorption. It also enhances renin release

Question 12

Describe the function of the Arginine vasopressin hormone

Answer 12

Also known as ADH, it is releases from the posterior pituitary gland in response to increase in extracellular osmolality. This promotes water reabsorption in the distal nephron. Or in response to large reductions in ECV. Secondary functions include vasoconstriction and increasing renal Na retention

Question 13

Describe features of the atrial natriuretic peptide

Answer 13

• Atrial myocytes release ANP in response to stretch whereas a reduced ECV inhibits ANP release. It has many effects that promote natriuresis and diuresis;
• Increases GFR and renal BF,
• Inhibits Na transport (IMCD),
• Decreases renin release,
• Inhibits aldosterone release from adrenals,
• Decreases release of AVP

Question 14

Describe features of osmotic diuretics

Answer 14

Eg, Mannitol. Has main effects upon portions permeable to water (PCT and DL of Henle). Therefore main effect is to increase H2O excretion, small secondary increase in Na excretion. Used in treatment of acute renal failure

Question 15

Describe features of loop diuretics

Answer 15

Eg, Furosemide and bumetanide. They are the most powerful diuretics which inhibit NKCC in the TAL. Resulting in reduction in the reabsorption of Na, K and Cl.

Question 16

When are loop diuretics used?

Answer 16

In the treatment of hypertension WHEN renal function is impaired. Otherwise thiazide diuretics are preferred when renal function is preserved.

Question 17

Describe features of thiazide diuretics

Answer 17

Less powerful than loops. Eg, Bendroflumethiazide and hydrochlorothiazide. They inhibit the NCC resulting in a reduction in Na and Cl reabsorption. Also cause vasofilation.

Question 18

What is significant about potassium sparing diuretics

Answer 18

Limited diuretic action alone so need combined. They also reduce the driving forces for potassium secretion which would cause hyperkalaemia but when combined with loop diuretics, this balanced the plasma potassium

Question 19

Name and describe mechanism of aldosterone antagonists

Answer 19

Spironolactone and eplerenone. They competitively inhibit the mineralcorticoid receptor

Question 20

Name and describe mechanism of ENaC inhibitors

Answer 20

Amiloride/triamterene. Block the epithelial sodium channel