Blood Pressure and Hypertension Flashcards
What is blood flow
The movement of blood through the vessels from the arteries to the capillaries and then into the veins
How does velocity of blood flow vary
It varies inversely with the (total) cross sectional area of the vessel through which it is flowing. As the total cross-sectional area of the vessel increases, the velocity of flow increases
Where is blood flow slowest and why
It is slowest in the capillaries to allow time for exchange of nutrients and gases
What is vascular resistance
The resistance offered by blood vessels to the flow of blood. Resistance occurs where the blood vessels away from the heart oppose the flow of blood
Which 3 factors accumulate resulting in resistance
Vessel radius, blood viscosity and blood vessel length
What is blood pressure a measure of
The force that blood exerts against the vessel walls as it moves the blood through the vessels
What does vascular tone mean
Smooth muscle walls have a degree of resting tension
What is arterial blood pressure determined by
Total peripheral resistance and cardiac output
What does cardiac output equal
CO = SV x HR
What is a sphygomomanometer and how does it work
It is a device used to measure blood pressure. It is composed of an inflatable cuff to restrict blood flow and a mercury/ mechanical manometer to measure the pressure
Where is blood pressure measured
In the brachial artery
What is normal arterial blood pressure in a healthy adult
120/80
How is blood pressure written
Systolic pressure over diastolic pressure
What is systolic BP
Systole occurs during the contraction and emptying of the heart
What is diastolic BP
Diastole occurs during the relaxation and filling of the heart
What is the difference in systolic and diastolic BP called
Pulse pressure
What happens to normal arterial blood pressure
It falls at night due to patterns in the circadian rhythm
What happens to normal arterial blood pressure with age
Systolic BP increases due to a reduction in the elasticity of the arteries
What happens to normal arterial blood pressure during pain, fear, anger and sexual arousal
Short term increases in arterial BP
What happens to normal arterial blood pressure when you stand up
BP in all vessels below the heart is increased and BP in all above the heart is reduced
What is transient postural hypotension
When you change from lying position to standing about 700ml of blood is lost from the thorax resutling in a decreasing in systolic and diastolic pressures
What happens during vasoconstriction
Vascular resistance increases
What happens during vasodilation
Vascular resistance decreases
What is intrinsic control of blood pressure
Autoregulation which is stretch, temperature and locally released factors
What is extrinsic control of BP
autonomic nervous system or hormones
Which receptors detect pressure during circulatin
Baroreceptors
Where are baroreceptors located
In the walls of the aorta (aortic arch) and carotid arteries (carotid sinus)
What happens when increased BP is detected
Increased BP detected by the baroreceptors info relayed cardiovascular control centre. Results in increased parasympathetic input and decreased sympathetic output which leads to decreased cardiac output. Decreased sympathetic input also leads to decreased peripheral resistance
Where is the cardiovascular control
Located within the medulla oblongata
What do sympathetic cardiac nerves do
Stimulates cardiac output by increasing heart rate and contractility (and so BP)
What do parasympathetic cardiac nerves do
Inhibits cardiac output by decreasing HR
What does the vasomotor centre regulate
Blood vessel diameter
What do vasomotor nerves innervate
Smooth muscles in the arterioles throughout the body to maintain vasomotor tone
What does hormonal control of blood pressure involve
The long term control of blood pressure involves the control of blood volume/ sodium balance by the kidneys
What 5 hormones are involved in the hormonal control of BP
- Adrenaline 2. Angiotensin 3. Aldosterone 4. Antidiuretic hormone (ADH) 5. Atrial natriuretic peptide/ hormone
What does the renin-angiotensin-aldosterone system regulate
Blood volume
What does the renin-angiotensin-aldosterone system do in response to falling BP
Juxtaglomerular cells in kidneys secrete renin into blood. Renin converts angiotension to angiotensin I which is in turn converted to angiotensin II by enzymes from the lungs. Angiotensin II activates 2 mechanisms that raise BP
What are the two mechanisms activated by angiotensin II which raise BP
Vasoconstriction and stimulation of the adrenal cortex to secrete aldosterone
How does vasoconstriction raise BP
Constricted blood vessels reduce the amount of blood delivered to the kidneys, which decreases they kidneys’ potential to excrete water (raising BP by increasing blood volume)
How does stimulation of the adrenal cortex to secrete aldosterone increase BP
Aldosterone reduces urine output by increasing the retention of water and Na+ by the kidneys (raising BP by increasing blood volume)
How do adrenaline and noradrenaline affect BP
They are secreted by the adrenal medulla and raise BP by increasing HR and causing vasocontriction (fight-or-flight response)
How does antidiuretic hormone affect BP
It is produced by the hypothalamus and released by the posterior pituitary gland. Raises BP by stimulating kidneys to retain water (raising BP by increasing blood volume)
How does atrial natriuretic peptide affect BP
Secreted by the atria of the heart, lowers BP by causing vasodilation and by stimulating the kidneys to secrete more water and Na+ (lowering BP by reducing blood volume)
Which hormones raise BP
Adrenaline, Aldosterone, Angiotensin, Antidiuretic hormone
Which hormone lowers BP
Atrial natriuretic peptide
Which part of the kidney does aldosterone affect
DCT
Which part of the kidney does ADH affect
Collecting duct
What is hypertension
High blood pressure
What does hypertension lead to
Stroke, CHD and chronic renal failure
What are risk factors of hypertension
Advancing age, sedentary lifestyle, obesity (BMI greater than 25), salt sensitivity, alcohol, smoking and family history
What is normal BP
What is pre-hypertention BP
120-139/ 80-89
What is hypertension stage 1 BP
140-159/ 90-99
What is hypertension stage 2 BP
>160/ >100
What is secondary hypertension
When high blood pressure occurs as a result of another condition
What percentage of people with high blood pressure have secondary hypertension
20%
What conditions result in secondary hypertension
Pregnancy, Endocrine disorders, Renal disease, atherosclerosis
How does pregnancy result in secondary hypertension
Pregnancy results in elevated hormone levels which may result in increased responsiveness to Angiotensin II
What is an example of an endocrine disease that leads to secondary hypertension and how does it cause high BP
Conn’s and Cushing’s syndrome results in hyperaldosteronism and cortisol increases resulting in a vasoconstrictive effect
What does high BP result in
Increased ‘wear and tear’ on the heart, vessels and organs
What cardiac changes does high BP result in
Heart must work harder with arterial blood pressure increases. Heart muscle hypertrophies to compensate. Diffusion of oxygen from capillaries to enlarged heart becomes less efficient. Left ventricular failure will eventually occur
Compare normal heart and heart of someone with high BP
See diagram
Describe the vascular effects high BP has
- Narrowing of small arteries and arterioles
- Myogenic response due to increase in stretch
- Hypertrophy
- Response to sympathetic stimulation increased
- Arterioclerosis- reduction in elasticity/ hardening
- Rarefaction: reduction of vessels in tissues
- Rarefaction observed in retina and intestines of hypertensive patients
What are the complications of hypertension
Atherosclerosis, kidney damage, heart attack, stroke, enlarged heart- heart failure, blindness
What is the aim of treating hypertension
To lower cardiac output or to lower peripheral BP
What two drugs are used to treat hypertension
Diuretics and vasodilators
Give an example of a diuretic and explain how diuretics work
Thiazides. Diuretics reduce blood volume, they work by inhibiting sodium reabsorption at the beginning of the distal convoluted tubule. Water is lost as a result of more sodium reaching the collecting ducts
Give an example of a vasodilator and explain how they work
ACE inhibitors. Vasodilators decrease vasodilation and inhibit some renal function activities. ACE block the action of the enzymes from the lungs that convert angiotensin I to angiotensin II
