Physiology of HTN Flashcards
Define HTN?
- consistently high BP of at least 140/90
What is primary HTN?
- idiopathic, no recognizable cause (just haven’t figured it out yet - genetic?)
Causes of Secondary HTN?
- OSA
- kidney problems
- adrenal gland tumors - pheochromocytoma
- thyroid problems
- certain defects in blood vessels you’re born with - aortic coarction
- certain meds, such as OCPs, cold remedies, decongestants, OTC pain relievers, and some Rx drugs
- illegal drugs: cocaine (severe coronary artery vasoconstriction) and amphetamines
- alcohol abuse or chronic alcohol use
What are the physiological mechanisms involved in development of primary HTN?
- ANS
- CO
- peripheral resistance
- RAAS
- other factors:
ANP, bradykinin, endothelian, and EDRF (endothelial derived relaxing factor) or nitric oxide
Main factors in HTN?
- Increased CO (increased preload and increased contractability)
- increased peripheral resistance (functional constriction amd structural hypertrophy)
increased COxincreased peripheral resistance = HTN
What is systolic BP?
- force that blood exerts on artery walls as the heart contracts to pump out the blood
- high systolic pressure known to be greater risk factor than diastolic for heart, kidney, and circulatory complications and for death, particulary in middle aged and elderly adults. Wider the spread b/t systolic and diastolic, the greater the danger
Diastolic BP?
- measurement of force as heart relaxes to allow blood to flow into heart, high diastolic is strong indicator of heart attack and stroke in young adults
What is the mean arterial pressure?
- as blood is pumped out of LV into arteries, pressure is generated. The mean arterial pressure (MAP) is determined by the CO, systemic vascular resistance and central venous pressure according to the following relastionshop which is based upon relationship between flow, pressure and resistance
MAP = (COxSVR) - CVP
What is the arterial pulse pressure?
- difference b/t systolic and diastolic readings during ejection
- it appears to be an indicator of stiffness and inflammation in the blood vessel walls
- the greater the difference the stiffer and more injured the vessels are thought to be
- may be a strong predictor of heart problems, particularly in older adults
What is peripheral vascular resistance?
- resistance to flow that must be overcome to push blood through the circulatory system
- resistance offered by the peripheral circulation is called the systemic vascular resistance
What are the neural mechanisms that affect BP?
ANS: intrinsic circulatory reflexes, and higher neural control
Intrinsic: baroceptors and chemoreceptors
extrinsic: pain, cold, isometric exercises
CNS: change in mood or emotion
Neural control of BP?
- sympathetic and parasympathetic divisions of ANS
- contributes through control of CV function through modulation of cardiac and vascular function
- located in medulla oblongata
- three distinct pools that lead to sympathetic innervation of the heart and blood vessels
- vasomotor center and cardioinhibitory center (primarily paraympathetic: vagus nerve)
What are arterial baroceptors and where are they located?
- most impt arterial baroreceptors are located on carotid sinus (at bifurcation of external and internal carotids) and in aortic arch
- respond to stretching of the arterial wall
- as arterial pressure suddenly rises, the walls of these vessels passively expand, which stimulated the firing of these receptors
- inhibits central sympathetic d/c
- the carotid sinus is most impt for regulating arterial pressure
- aortic arch receptors have higher threshold pressure and are less sensitive than the carotid sinus receptors
What are the arterial baroceptors responsible for?What happens when there is a chronic change in BP?
- postural baroreflex: rapid moment to moment adjustmens in BP: change in position
- with chronic changes, the baroreceptors tend to reset to adjust to the increasing CO or arterial pressure and are not as good at regulating the mechanisms to cause a decrease in sympathetic activity
What are the chemoreceptors?
- sensitive to O2, CO2, H+ concentration in the blood
- located in carotid bodies which lie in the bifurcation of the 2 common carotids and aortic bodies of the aorta
- communicate with vasomotor center and can induce widespread vasoconstriction
What controls autonomic regulation of cardiac function?
- parasympathetic: vagus nerve
- sympathetic: SA and AV nodes
Stimulation of autonomic regulation?
- sympathetic stimulation can cause both arteriolar constriction and arteriolar dilation, the ANS has impt role in maintaining a normal blood pressure
- parasympathetic nervous system contributes to the regulation of the heart function, but has little control over the blood vessels
Autonomic neurotransmitters involved in BP control?
- Acetylcholine is postganglionic neurotransmitter for parasympathetic neurons (cholinergic receptors)
- NE is main neurotransmitter for postganglionic sympathetic neurons (adrenergic receptors)
- 2 types of adrenergic receptors: alpha and beta
in vascular smooth muscle, stimulation of alpha receptors produces vasoconstriction and stimulation of b receptors causes vasodilation