10 - Controlling Hypertension Flashcards
What is hypertension defined as?
What are the two types of hypertension?
- Primary (essential) hypertension: unknown
- Secondary hypertension: causes can be defined, e.g renovascular, Cushing’s, hyperaldosteronism
Why is it important to treat hypertension?
- Asymptomatic but can lead to heart failure, renal failure, MI, stroke
Which type of hypertension causes the biggest problems?
Systolic hypertension
How does hypertension lead to MI, heart failure, aneurysm etc?
What should you do when a patient presents with hypertension?
What is an effective decrease in blood pressure?
10mmHg
What are longer term controls of blood pressure? (short term being baroreceptor reflex)
- Neurohumoral response
- Works by controlling the plasma volume by controlling sodium balance
What are the four pathways of the neurohumoral response?
ALL OCCUR SIMULATENOUSLY
1. Renin-angiotensin-aldosterone system
2. Sympathetic nervous system
3. Antidiuretic hormone (ADH)
4. Atrial Natriuretic Peptide (ANP)
(ANP only one that lowers b.p)
How is the renin-angiotensin-aldosterone system get stimulated?
- Reduced NaCl delivery to distal tubule
- Reduced perfusion pressue detected by baroreceptors in afferent arteriole
- Sympathetic stimulation to JGA
RENIN RELEASED FROM GRANULAR CELLS OF JUXTAGLOMERULAR APPARATUS
How does the renin-angiotensin-aldosterone system increase blood pressure?
What actions do the angiotensin II receptors have at different sites?
Main actions via AT1 receptor
What is the action of aldosterone?
- Acts on cells of collecting ducts
- Activates ENaC, K+ channel and Na/K ATPase so increased Na absorption and low K+ levels
What other molecules does ACE cleave, apart from angiotensin I?
Breaks bradykinin down into peptide fragment so it cannot have a vasodilation effect
What is one of the main side effects of taking ACE inhibitors and why does this occur?
Dry cough as there is a build up of bradykinin in the lungs
Why do you go into hypotensive shock when bitten by the brazillian viper?
- Contains bradykinin potentiation factors blocking the conversin of angiotensin I to angiotesin II by ACE
- Can cause pulmonary oedema, disseminated intravascular coagulation, activation of hypotensive substances, blood loss so hypovolemia
What is disseminated intravascular coagulation?
- Small blood clots develop throughout the bloodstream blocking small blood vessels
- The extra clotting depletes platelets and clotting factors leading to excessive bleeding
What are some examples of ACE inhibitors?
- Ramipril, Captopril, Lisinopril, Perindopril
How does the sympathetic nervous sytem cause an increase in blood pressure?
- High levels of sympathetic stimulatuon reduce renal blood flow, so decreased GFR and decreased Na excretion.
- Stimulates renin release from JG cells
How does ADH increase blood pressure?
- ADH release is stimulated by increase in plasma osmolarity or severe hypovolaemia
- Increases water reabsorption in distal nephron (AQP2), stimulates Na reabsorption in thick ascending limb (Na/K/Cl) and causes vasoconstriction
How do atrial natriuretic peptides decrease blood pressure?
- Stored in atrial myocytes and are released in response to stretch
- Causes vasodilation of the afferent arteriole and increased blood flow increases GFR
- Inhibits Na reabsorption along nephron
- If circulating volume is low ANP release is inhibited
What are some local vasodilators?
- Prostagladin: reduce Na reabsorption and enhance glomerular filtration. Act as buffer to excess vasoconstriction by SNS and RAA. Important when Ang II high
- Dopamine: Formed in kidney and causes vasodilation and increased renal blood flow. Reduces reabsorption of NaCl
How can renal artery stenosis cause hypertension?
- Fall in perfusion pressure due to artery occlusion
- Renin production so activation of RAA
- Need to repurfuse kidney to treat, e.g via a stent
How can renal parenchymal disease lead to secondary hypertension?
- Early stage may be due to loss of vasodilator substances
- Later stage Na and water rentention due to inadequate glomerular filtration
