Control of Blood pressure Flashcards
What is cardiovascular homeostasis?
- Controls blood pressure using baroreceptors
- Controlled by medulla
- Effectors are heart rate, stroke volume, caridiac output and vascular tone
What is the difference between systolic and diastolic blood pressure?
- Systolic has a higher number than diastolic
- Systolic force heart pumps whereas diastolic cause resistance of blood vessels.
What are the different ranges of blood pressure to highlight different conditions?
- Normal range: 90/60-120/80mmHg
- Hypotension: 90/60mmHg or lower
- Hypertension: 140/90mmHg or higher
What is cardiac output?
- Amount of blood pumped per ventricle/min.
- CO = HR (heart rate) * SV (stroke volume).
- To increase CO, you need to increase HR, SV or both.
What factors affect heart rate?
- Intrinsic (reflexes, pacemaker rhythm) or extrinsic factors
- Positive chronotropic factors (increase HR) e.g. caffeine, exercise, Ca2+, sympathetic stimuli
- Negative chronotropic factors (decrease HR) e.g. sedative, beta blockers, parasympathetic stimuli, increasing K+ and Na+
How does the brain regulate heart rate?
- Sympathetic division of ANS increases HR and contractility
- Parasympathetic - vagus nerve decreases HR
What makes up the sympathetic division of the ANS that regulates heart rate?
- Sinoatrial and atrioventricular nodes
- Cardiac muscle.
What are the features of the baroreceptor reflex?
- Blood pressure either hypertension (+) or haemorrhage (-)
- Baroreceptors present in aortic arch and carotid sinus.
How does baroreflex work?
- Low BP detected by baroreceptors
- Cardiac output and vasoconstriction increased by medulla sending increased signals to SAN
- BP increased (quick response)
What are the features of the chemoreceptor reflex?
- Peripheral chemoreceptors in aortic arch and carotid body, central receptors in brain.
- Chemoreceptors respond to decreased pO2, increased pCO2 and decreased pH.
Outline the chemoreceptor reflex
- pO2 and pH increase, pCO2
- Vasomotor center stimulated, increasing CO, HR and vasoconstriction
- BP increases.
What are the features of the bainbridge atrial reflex?
- Stretch receptors in both atria
- Prevents damming of blood in atria and veins.
Outline the bainbridge atrial reflex
- Due to high blood return from veins, mechano receptors stretch in myocardium of heart in atria.
- Aferrent fibres in vagus nerve send info to cardiovascular centre medulla oblongata.
- As a result of this, parasympathetic system shuts down, reduction in release of acetylcholine at the sinoatrial node.
- Simultaneously sympathetic system increased, norepipherine released at SA node leading to increase in heart rate.
- Positive chronotrophic result.
What is the equation for stroke volume?
- SV = end diastolic volume (EDV) - end systolic volume (ESV).
What factors affect stroke volume?
- Preload (amount ventricles are stretched by blood)
- Contractility (cardiac cell contractile force)
- Afterload (force exerted on ventricle wall during ejection)
Outline Frank-Starling law
- Volume ejected in ventricular distole depends on volume in ventricle (EDV) - more volume = stronger contraction
- Venous return increases (exercise) or decreases (blood loss) stroke volume
Where do sympathetic nerve fibres innervate?
- Sympathetic nerve fibres from vasomotor centre innervate smooth muscle for blood vessels except capillaries
How does the diameter of arterioles affect blood pressure?
- Diameter of arterioles changes vascular resistance - smaller diameter increases resistance, increasing blood pressure
What is the role of the endothelium in vascular tone regulation?
- Synthesises vasoconstrictions (endothelin-1, thromboxane A2) and vasodilators (nitrous oxide, prostacyclin).
Outline the renin-angiotensin-aldosterone system (RAAS)
- Controls blood volume using hormones
- Renin stimulates angiotensinogen in liver, activating angiotensin 1
- Angiotensin 1 converted into angiotensin 2 in lungs, increasing vasoconstriction and increasing BP
- Angiotensin 2 turned into aldosterone in adrenal glands, reducing water reabsorption, increasing blood volume and pressure
When is ADH released?
- Released from pituitary gland because of reduced blood volume, increased osmolarity of plasma or increased angiotensin 2 levels
What is the role of ADH in blood pressure control?
- Increases water resorption in kidney by increasing Na+ diffusion, more osmosis of water from kidneys to blood
- more blood volume = higher BP
- Acts as a vasoconstrictor, increasing vascular resistance, increasing BP
How does blood volume correlate with blood pressure?
- Hypovolemic shock occurs when blood volume decreases by 20% from blood loss or dehydration
- Body compensates by increasing HR by decreasing preload, stimulating vasoconstriction and RAAS.
How does posture relate to blood pressure?
- When supine, blood evenly distributed in veins
- Increased SV, EDV and central venous pressure
What causes fainting?
- Temporary reduction in blood flow to brain
- Triggered by vasovagal syncope (decreased HR and BP), cardiac syncope (heart problems) or decreased BP from standing up (orthostatic hypotension).
Outline the commonly used antihypertensive drugs (RAAS).
- Angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARB) reduce amount of angiotensin 2
- Vasodilating and reduced water retention lower BP.
Outline commonly used antihypertensive drugs (beta-blockers)
- Heart beats more slowly and with less force
- Blocks epinephrine action
- Used for high BP, heart failure and angina
Outline commonly used antihypertensive drugs (Ca2+ channel blockers)
- Effect blood vessel smooth muscle contraction, electrical conduction of heart and caridac output
- Doesn’t effect sympathetic stimuli
Outline commonly used antihypertensive drugs (diuretics)
- Increase urine production to excrete more water
- Reduces oedema, blood volume and pressure
- Different types target different parts of kidney, inhibiting sodium reabsorption - water follows sodium into urine
What are the different types of blood pressure?
- Normal range: 90/60-120/80mmHg
- Hypotension: 90/60mmHg or lower
- Hypertension: 140/90mmHg or higher
