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Cardiac Regulation II: Blood Pressure
Terms in this set (31)
There is not enough power to pump blood to the tissues - known as circulatory shock a possible cause is haemorrhage. Tissues will not receive enough oxygen, become hypoxic meaning they are unable to metabolise probably thus become necrotic.
What is the effect of a low perfusion pressure?
A high perfusion pressure can damage delicate capillaries, endothelial injury, thus causing more fluid to leak out into surrounding tissues (fluid exudation), thus tissue function will be impaired. Huge consequences if this occurs at the lungs, as it will have a knock on effect on the whole system.
What is the effect of a high perfusion pressure?
Pressure to high - damage to capillaries lead to fluid exudation
Pressure to low - tissues will become hypoxic, lead to necrosis.
Why is it vital that perfusion pressure is regulated?
System Arterial Pressure (mean)
What are the major determinants of perfusion pressure in tissues?
Lower blood pressure than normal for that animal.
What is hypotension?
Higher blood pressure than normal for that animal.
What is hypertension?
What are the possible effects if perfusion pressure is too low?
State the short term mechanisms which regulate arterial pressure.
Primarily kidneys, controlling fluid volume by vasopressin, renin-angiotensin-aldosterone system
State the long-term mechanisms which regulate arterial pressure.
Total Peripheral Resistance (total resistance in all of the vessels in circulation)
What is TPR?
MAP = CO X TPR
What is the equation for calculating Mean Atrial Pressure?
high resistance, decrease in blood flow.
If arterioles are constricted what is the effect on resistance and blood flow?
Low resistance, increase in blood flow
If arterioles are relaxed what is the effect on resistance and blood flow?
Factors influencing the flow of fluid in a tube.
Resistance increases as the length increase, radius decreases and viscosity increases. Thus the time it takes to for blood to in circulation will depend on dimensions of vessel and viscosity of the blood.
What does poisueille law describe? What does the law tell us?
Flow will increase as pressure increases and decrease as resistance increase.
Describe the relationship between flow, resistance and pressure.
Sensors - ability to monitor pressure
Integrating system - Assess correctness of pressure ie brain
Effectors - mechanisms to return pressure to required level.
What is required for effect regulation of MAP?
The peak pressure in the arteries when the LV is ejecting blood during ventricular systole
What is systolic arterial pressure?
The residual pressure in the arteries when the LV is filling during ventricular diastole.
What is diastolic arterial pressure?
Sensors- need to detect/ monitor the change in pressure, baroreceptors
Integrating system - assess correctness of pressure, the brain (medulla oblongata).
Effectors- Mechanisms to return pressure to required level.
What is required for effective regulation of MAP? think SIE.
Sensitive to stretch, detect distension.
Found in Aortic arch and carotid sinus.
What are baroreceptors sensitive to and where are they found?
Non-encapsulated (free nerve endings) are less specific, but very sensitive stimuli such as pain. E.g. merkels discs (texture), baroreceptors
Encapsulated nerve endings - dendrite is encapsulated with connective tissue, highly specific, but not very sensitive. Meissners corpuscles (touch) and Ruffini corpuscles (located in the skin detects pressure)
What is the difference between encapsulated and non-encapsulated nerve endings? and give examples of each.
In baroreceptors where does the central axon terminate?
Increase BP- increases Stretch in vessels - stimulate baroreceptors (increase firing rate)- impulse sent to the medulla oblongata where response is coordinated.
If there was an increase in BP how would baroreceptors respond?
Upon standing up blood pools lower extremities thus BP falls in upper body. Reduction in firing rate of baroreceptors located in aortic arch and carotid sinus. Impulse sent to medulla Oblongata - need to increase BP thus stimulation of sympathetic NS control.
Veins arteries- vasoconstrict - increase TPR - thus increase in MAP (MAP= CO x TPR)
Cardiac stimulator - SA node, release of noradrenaline by sympathetic nerves bind to beta-adrenergic receptors on cardiac muscle cells, have more leaky Na channels increase rate of depolarisation.
Cardiac inhibitor - parasympathetic stimulation reduced through vagus nerve.
Heart muscle - Myocardial contractility - under sympathetic NS release noradrenaline, binds to Beta adrenergic receptors increase contractility.
thus increase in CO since HR x SV= CO
therefore BP increases since MAP = CO x TPR
Outline the coordinated reflex response in the cardiovascular system to, standing up too quickly.
TPR - resistance in aorta
Myocardial Contractility - controlled sympathetic
Venous return - EDV, increase - increases stretch in muscle thus increase contractility
What are the three variables that affect SV?
Baroreceptors detect increase in distension in aortic arch and carotid sinus.
impulse sent to brainstem - medulla oblongata coordinates response
Increased vagal output - parasympathetic nerves release Acetylcholine this binds to muscarinic choline receptors on SA node decrease number Na+ leaky channels opening, thus slower depolarisation threshold reached much later = ↓ HR
Myocardial contractility- Atrial myocytes - respond to release in ACh ↓contractility. little effect on ventricular myocytes, indirectly mediate via pre-synaptic inhibition of noradrenaline by releasing of ACh binds to muscarinic choline receptors on sympathetic nerves inhibiting release of noradrenaline
Hence reduction in sympathetic stimulation = ↓ TPR, ↓cardiac contractility (SV) ↓ HR
Thus ↓ BP
Outlined the coordinated reflex response in the cardiovascular system, when acute BP rises.
↑circulating volume -->
↑ preload --> causes myocardium to stretch thus stronger contraction thus ↑SV (Starlings Law) --> ↑ Cardiac output therefore ↑ CO x TPR = ↑MAP
How does increasing plasma volume increase MAP?
What regulates plasma volume?
Renin is produced by a specialised area of the kidney in response to low renal perfusion.
What is Renin produced in response to?
Renin converts the peptide angiotensinogen to angiotensinogen I, which is converted by ACE to angiotensinogen II - causes vasoconstriction of arterioles and venules - causing ↑ TPR thus ↑ MAP
Causes adrenal cortex to release the hormone aldosterone - causes the kidney to retain Na+ thus H2O causing ↑Plasma volume thus ↑CO due to starlings law
Causes posterior pituitary gland to release vasopressin/ADH acts as both vasoconstrictor and causes kidney to retain water
all causing BP to increase
How does the production of Renin increase BP?
Low pressure receptors located in the atria, where the pressure is lower.
Baroreceptors located in the aortic arch and carotid sinus where pressure is high
How do low pressure stretch receptors and baroreceptors differ?
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