Blood pressure and its regulation Flashcards
Define arterial blood pressure
Pressure exerted by blood flow on blood vessel walls
Arterial BP = CO x TPR
What value is considered to be normal blood pressure?
120mmHg/ 80mmHg - This is the value considered sufficient for enough perfusion and O2 transport to tissues and organs
What do the top and bottom values of blood pressure show respectively?
- Top = systolic pressure - Blood pressure in brachial artery during ejection of blood via left ventricle
- Bottom = diastolic pressure - Blood pressure in brachial artery during relaxation and filling of left ventricle
What can blood pressure tell us about?
- Heart rate
- Stroke volume
- Whether vessels constricted or dilated
- Blood flow to tissues
Due to Arterial BP = CO x TPR
CO = SV x HR
Therefore, BP = SV x HR x TPR
What values are considered high and low for blood pressure?
High - >140/90
Low - systolic <80, diastolic <60
What are causes of hypertension?
- Excessive vasoconstriction - exercise induced
- Excessive blood volume overload
- High LDL cholesterol - plaque formation, decreases diameter of blood vessels
What are causes of hypotension?
- Hypovolemia - fluid loss
- Excessive vasodilation
What are possible consequences of hypertension?
- Myocardial infarction
- Heart failure
- Blood vessel damage
What are possible consequences of hypotension?
- Poor O2 transport and blood flow (poor organ perfusion)
- Ischemia (loss of oxygen)
What component of the autonomic nervous system involved in regulation of BP?
Sympathetic nervous system - responds to decrease in BP
What are the mechanisms that respond to or increase low BP?
- Sympathetic nervous system
- RAAS (renin-angitensin-aldosterone system)
- Anti-diueretic hormone (ADH or called Vasopressin)
What is the mechanism that responds to and reduces raised BP?
Cardiac Natriuretic Peptides
How does the sympathetic nervous system raise BP?
A drop in blood pressure due to decrease in HR< SV or TPR, stimulates baroreceptor reflex, which then stimulates sympathetic nervous system
Can also be stimulated when fear-fight-flight response activated or during exercise :
- Innervates into adrenal gland, releases adrenaline, which can then bind to B1 adrenoceptors on heart, increasing cardiac muscle contraction rate and stroke volume
- Can act via noradrenaline, can increase heart rate via beta 1 binding, but can also bind to alpha 1 receptors on blood vessels to increase vasoconstriction, therefore increasing TPR
- Innervates RAAS (renin-angiotensin,aldosterone system)
How does RAAS raise blood pressure?
Sympathetic nervous system recognises drop in blood pressure/ blood flow to kidneys:
- Kidneys release renin
- Renin converts angiotensinogen (released from the liver) into angiotensin I
- When angiotensin I travels through the blood and lungs, it is converted into angiotensin II. This is mediated by the enzyme Angiotensin-I-converting enzyme (ACE)
- Angiotensin II activates AT1 receptor (angiotensin 1), found on blood vessels and adrenal glands
- On blood vessels, AgII binds to AT1 receptor, causes vasoconstriction, increases TPR
- On adrenal gland, AgII binds to AT1 receptor, causes release of aldosterone, causes decrease H2O release via excretion, which increases blood volume, therefore SV, and therefore CO increases
How does ADH raise blood pressure?
- ADH produced by neurones in hypothalamus, released from terminals into posterior lobe of pituitary gland, excreted into bloodstream
- Secretion of ADH stimulated by:
- Decrease in blood volume due to decrease in blood pressure
- Decrease sensed by cardiac pressure receptors in LA, sends signals to hypothalamus
- ADH causes vasoconstriction, therefore increase in TPR
- ADH binds to receptors in nephron collecting duct, forms water channel increasing reabsorption of water, increasing blood volume, therefore increasing stroke volume, therefore increasing cardiac output.
