Hypertension and RAAS

Question 1

Baroreflex

Answer 1

Peripheral receptors in the aortic arch and the carotid sinus, send afferent information mainly to nucleus tractus solitarus. Brain signalling, eg through nucleus ambiguous. Efferent response is via parasympathetic and sympathetic output to heart, vasculature and kidneys.

Question 2

Blood pressure equation

Answer 2

Blood pressure = cardiac output x total peripheral resistance.
Or really: arterial BP - venous BP = cardiac output x total peripheral resistance

Question 3

Posture and blood pressure

Answer 3

Changing posture activates arterial baroreflex and cardio-pulmonary reflex. Venous return stimulated means normally supine to upright has little effect despite considerable pooling of blood to feet. Standing up fast after a hot bath when fairly vasodilated = prone to syncope. And standing guards eventual orthostatic loss of control.

Question 4

Consequences of high blood pressure

Answer 4

Increased risk of mortality due to coronary heart disease and stroke - in 10th decile of systolic blood pressure, have 6.5x relative risk increase. Over perfusion of tissues leads to tendency to accumulate plaques. Plaques may break off and travel elsewhere -> blocked vessels causing MI and stroke. Left ventricular hypertrophy due to increased resistance and so work on the heart, leading to failure and also MI.
Potential arterial aneurysm, hypertensive retinopathy, and increased incidence of renal failure and dementia.

Question 5

Essential/primary hypertension

Answer 5

No specific cause can be found, normally due to overall increase in resistance to flow of blood through arterioles, firstly narrowing of proximal resistance arterioles due to increase in vascular tone (which can be reversed with dilators) and then later due to structural change with increase in ratio of wall thickness to internal radius. Very close correlative/causative relationship with atherosclerosis.

Question 6

Causation of primary hypertension experiment

Answer 6

Korner et al. in 1993 performed an experiment on rats where they removed the sympathoadrenal influences, and then found that this prevented the onset of hypertension - hence potential causative link.

Question 7

Secondary hypertension

Answer 7

Hypertension has a specific cause which should be treated primarily. Eg renal artery constriction, Cushing’s disease, pre-eclampsia and primary aldosteronism.

Question 8

Pre-eclamptic toxaemia

Answer 8

In 3rd trimester of about 5% of pregnancies, there is a degree of placental ischaemia and release of toxins into the mother’s circulation due to failure of proper development of the spiral arteries. Impaired NO and prostacyclin production lead to raised circulating endothelin and peripheral vasoconstriction, reduced renal excretion and so hypertension. May then progress to cerebral oedema and fits (=eclampsia).