BP Control

Question 1

SHORT TERM BP CONTROL
Baroreceptors

Chemoreceptors

Answer 1

– pressure sensors in the carotid artery and aorta walls
/ Stretch receptors generate a chemical response when BP is too high, decrease CO & HR and the PNS releases acetylcholine which also reduces HR. Vasodilation, decreased TPR. So BP falls.
/ Inhibited when BP too low, the SNS releases noradrenaline, higher HR and more contractions, also vasoconstriction so higher TPR. BP increases.

/ Peripheral = in carotid body. Detect high CO2 or low pH/low oxygen. Stimulate
cardioacceleration, so decreased parasympathetic vagus nerve signals cause higher HR and CO as well as vasoconstriction.
/ Central = in medulla oblongata. Detect high oxygen or low pH. Higher blood flow to the brain and vasoconstriction of peripheral vessels and vasodilation of cerebral vessels.

Question 2

LONG TERM BP CONTROL
Endocrine extrinsic events

Net hydrostatic pressure

Answer 2

If BP too low, antidiuretic hormone and aldosterone (steroid) released by the adrenal gland (above the kidneys) causes Na+ and water reabsorption = increased blood volume = increased CO = BP rises.

If BP too high, atrial natriuretic peptide (hormone secreted by heart muscle cells) causes Na+ and water loss (urine) so decreased blood volume = decreased CO = BP falls

• force on capillary walls, ‘pushes’ water and solutes out into interstitial fluid. (35mmHg at arteriole end, 18mmHg at venous end)

Question 3

CAPILLARY HOMEOSTASIS
Decreased BP =

Increased BP =

Answer 3

Short term – sympathetic activation, ^CO and vasoconstriction
Long term – renin (enzyme released by kidneys) released, promotes angiotensin II
(hormone) activation, causes vasoconstriction. Also antidiuretic hormone, aldosterone and
increased thirst increase blood volume = ^BP.

Natriuretic peptides released by the heart, causes Na+ and water loss and decreased thirst = reduced blood volume. Also vasodilation and noradrenalin decrease BP.

Question 4

Hypertension

Idiopathic hypertension

Secondary hypertension

Answer 4

systolic BP >140mmHg and diastolic BP >90mmHg. Can cause atherosclerosis, strokes, heart failure and aneurysms

no known cause, linked to genetic predisposition, obesity and alcohol

kidney/endocrine disorders causing difficulties in regulating BP

Question 5

Treatment;
Alpha –blockers

Beta-blockers

Thiazide diuretics

ACE inhibitors

Answer 5

• inhibit noradrenaline
• less SNS activity centrally, reduce CO
• inhibit aldosterone