L17 Cardiovascular Regulation Flashcards
Define ‘end-diastolic volume’
Amount of blood in each ventricle at the end of ventricular diastole (maximum content of ventricle)
Define ‘end-systolic volume’
Amount of blood remaining in each ventricle at the end of ventricular systole (minimum content of ventricle)
Define ‘stroke volume’
Amount of blood pump out of each ventricle during a single heartbeat.
How can you calculate stroke volume?
SV = EDV - ESV
Define ‘ejection fraction’
Percentage of blood ejected from a ventricle of the heart with each heartbeat. It is a measure of the pumping efficiency of the heart.
How can you calculate ejection fraction?
EF = (SV / EDV) x 100
True or false: A doctor can measure the efficiency of the heart at pumping blood into the pulmonary circulation by calculating the left ventricular ejection fraction.
False.
Left ventricular ejection fraction is a measure of the efficiency of pumping into the systemic circulation, whereas right ventricular ejection fraction is a measure of the efficiency of pumping into the pulmonary circulation.
Define ‘preload’
Degree of stretching in ventricle muscle cells during ventricular diastole. It is proportional to EDV – the greater the preload, the larger the EDV (volume of blood in ventricles at the end of diastole).
Define ‘afterload’
the amount of tension that the contracting ventricle must produce to force open the semilunar valve and eject blood.
True or false: Aortic stenosis will increase the afterload
True.
Increasing the aortic pressure will mean the ventricles must produce greater tension (afterload) to force open the semilunar valve and eject blood.
What is Starling’s law?
“More in, more out”
Stroke volume of the heart increases in response to an increase in end diastolic volume, when all other factors remain constant.
What factors control end diastolic volume (EDV)?
1) Duration of ventricular diastole (filling time)
2) Volume of venous return
True or false: Increasing the EDV also increases SV
True
What factors affect end-systolic volume (ESV)?
1) Preload
2) Contractility of the ventricle
3) Afterload
What affects afterload?
Vasodilation or vasodilation
What factors affect contractility?
1) Autonomic innervation
2) Hormones
Changing which of the following can affect stroke volume?
A) Preload B) Contractility C) Afterload D) A and C only E) All of the above
E) All of the above
What is contractility? It is regulated by which systems?
Amount of force produced during a contraction at a given preload.
Contractility is regulated by autonomic innervation and circulating hormones.
What factors have a positive inotropic effect on the heart (i.e. increase contractility)?
Sympathetic nervous system (e.g. noradrenaline)
Beta-adrenergic agonists (mimic adrenaline and noradrenaline)
What factors have a negative inotropic effect on the heart (i.e. decrease contractility)?
Parasympathetic nervous system (e.g. acetylcholine)
Calcium channel blockers (verapamil)
Muscarinic agonists
Sympathetic antagonists
Increased serum potassium
Anoxia
Acidosis
Would increased serum potassium have a positive or negative inotropic effect on the heart?
Negative
In a normal rhythm, when would you detect the first heart sound?
Immediately following ventricular contraction (End of QRS wave)
In a normal rhythm, when would you detect the second heart sound?
Immediately following repolarisation of the ventricles (end of T wave)
In the cardiac cycle are two periods named isovolumetric contraction and isovolumetric relaxation. What happens in these periods?
Isovolumetric = ‘same volume’
So during these short periods, there is no change in volume, even though the muscle is relaxing or contracting.
These periods are when the valves are closed.
What systolic pressure is required to open the pulmonary valve?
20 mmHg from the right ventricle
What systolic pressure is required to open the aortic valve?
80 mmHg form the left ventricle
If the afterload increases while the preload remains constant, what happens to the stroke volume?
Stroke volume will decrease
True or false: Hypertension causes an increased afterload
True
True or false: Stenosis of arteries causes a decreased afterload
False
Stenosis of arteries increases systemic blood pressure, and this means the ventricles need to overcome a greater pressure to open the semilunar valves. This results in an increased afterload.
Which higher brain centres affect heart rate?
Cerebral cortex, limbic system, hypothalamus
What sympathetic nerves control heart rate?
Cardiac accelerator nerves
What parasympathetic nerves control heart rate?
Vagus nerves (cranial nerve X)
From where do the cardiac accelerator nerves originate?
Thoracic region of spinal cord
Where is the cardiovascular centre located?
Medulla oblongata
The cardiovascular centre (in medulla oblongata) monitors changes in:
A) Blood pressure
B) PO2
C) PH
D) All of the above
D) All of the above
True or false: Autonomic regulation of heart rate is governed by the cardiovascular centre
True
CVC is located in the medulla oblongata
What mechanism allows the parasympathetic NS to slow a person’s heart rate?
Vagus nerves release Ach which opens K+ channels in the plasma membrane. This allows K+ entry, therefore causes hyperpolarisation during repolarisation and slows the rate of spontaneous depolarisation.
True or false: Sympathetic stimulation of the heart reduces repolarisation and allows more rapid depolarisation
True
What is the atrial reflex?
Increased venous return is stimulates stretch receptors. These receptors trigger sympathetic stimulation of the heart: increases heart rate and cardiac output.
Also known as the Bainbridge reflex
Which is/are local vasodilators:
A) Increased O2 B) Lactic acid C) Nitric oxide D) Increased potassium E) Histamine F) A, C, and E G) B, C, D, E H) All of the above
G) B, C, D, E
Local vasodilators include:
- Decreased O2; increased CO2
- Lactic acid
- Nitric oxide
- Decreased pH
- Increased potassium
- Proinflammatory agents (e.g. histamine)
- Elevated local temperature
True or false: local vasodilators work by relaxing smooth muscle cells of precapillary sphincters
True
True or false: Thromboxanes cause localised contraction of precapillary sphincters
True
Thromboxanes are released by platelets in a wound site.
What are endothelins?
Chemicals released by damaged endothelial cells that cause local vasoconstriction
In regulation of blood flow, which system(s) is/are activated first?
A) Endocrine B) Autoregulation C) Neural D) A and C only D) All are activated together
B) Autoregulation
Autoregulation takes place locally.
If autoregulation of BF fails to normalise conditions, neural and endocrine factors are activated.
What three components make up the cardiovascular centre?
- Cardioacceleratory centre
- Cardioinhibitory centre
- Vasomotor centre
Which neural centre controls vasoconstriction and vasodilation?
Vasomotor region of cardiovascular centre.
True or false: The vasomotor centre consists of two populations of sympathetic motor neurons
True
Which of the following are associated with control of vasoconstriction?
- Adrenergic synapses
- Cholinergic synapses
- a1 adrenoceptors
- Nitric oxide
A) 1 and 3
B) 1, 3 and 4
C) 2 and 4
D) 2 only
A) 1 and 3
Neurons innervating peripheral blood vessels in most tissues (internal organs, coronary, skin) are adrenergic. They release NA (sympathetic system) which stimulates a1 adrenoreceptors located in the plasma membrane of smooth muscle cells of blood vessels.
Which of the following are associated with control of vasodilation?
- Cholinergic synapses
- Nitroxidergic synapses
- Nitric oxide
- Acetylcholine
A) 1 and 4
B) 1, 3 and 4
C) 2 and 3
D) All of the above
D) All of the above
Neurons innervating blood vessels in skeletal muscle and in the brain. Stimulation of these neurons relaxes SMCs in the arterioles producing vasodilation. The most common synapses are cholinergic (ACh).
Other synapses are nitroxidergic. Both types stimulate the release of nitric oxide.
If baroreceptors detect a decrease in blood pressure, what happens to excitation of the cardiovascular centre?
If baroreceptors are inhibited due to decreased blood pressure:
- Vasomotor centre is STIMULATED (vasoconstriction)
- Cardioacceleratory centre is STIMULATED (increase cardiac output)
- Cardioinhibitory centre is INHIBITED (increase cardiac output)
If baroreceptors detect a increase in blood pressure, what happens to excitation of the cardiovascular centre?
If baroreceptors are stimulated due to increased blood pressure:
- Vasomotor centre is INHIBITED (vasodilation)
- Cardioacceleratory centre is INHIBITED (decrease cardiac output)
- Cardioinhibitory centre is STIMULATED (decrease cardiac output)
What is the role of atrial baroreceptors? What is the Bainbridge (or atrial) reflex?
Monitor stretch in the right atrium.
If systemic blood pressure increases, more blood will return to the right atria. This activates the atrial baroreceptors, which in turn send a regulatory feedback signal to the cardiovascular centre increasing the sympathetic stimulation of the heart (increasing heart rate)
Low oxygen and low pH in the blood will lead to:
A) Vasoconstriction
B) Vasodilation
A) Vasoconstriction
Chemoreceptors in the carotids, aorta, and medulla oblongata are sensitive to changes in blood O2 and pH.
True or false: ADH is released from the neurohypophysis in response to a decrease in blood pressure.
True
ADH increases blood pressure by:
A) Increasing peripheral constriction
B) Conserving water in the kidneys
C) Both A and B
D) Neither A nor B
C) Both A and B
What stimulus triggers the release of renin from juxtaglomerular cells?
Decrease in blood pressure in the kidneys
What is the role of renin?
Converts angiotensinogen into angiotensin I
Where is angiotensin I converted to angiotensin II? What agent facilitates this conversion?
Lung capillaries
Angiotensin-converting enzyme (ACE)
What are the four important functions of angiotensin II?
1) Stimulate secretion of aldosterone (promotes Na retention and K loss)
2) Stimulates secretion of ADH (water reabsorption, vasoconstriction)
3) Stimulates thirst (increase blood volume by fluid consumption)
4) Stimulates cardiac output
True or false: Ace-inhibitors reduce blood pressure
True
Angiotensin-converting enzyme produces angiotensin II, which acts to increase blood pressure. ACE inhibitors prevent this conversion.
True or false: The effects of angiotensin II on BP is up to 8 times greater than the effect of noradrenaline
True
What stimulus results in the release of erythropoietin?
Decrease in blood pressure and oxygen saturation both lead to release of EPO from the kidneys
How does erythropoietin affect blood pressure?
1) Causes vasoconstriction in blood vessels (smaller lumen = higher pressure)
2) Stimulates production of RBCs (increased volume = increased BP)
What is the effect of natriuretic peptides on blood pressure?
Reduce blood pressure
Natriuresis = excretion of sodium in urine, opposite effect of aldosterone
ANP and BNP released in response to increase atrial (ANP) and ventricular (BNP) stretching - a sign of increased blood pressure.
Since water follows sodium, increased sodium excretion means more water is also excreted. Less blood volume = lower BP.
