lecture 6: cardiovascular control 2 Flashcards
what is the equation for stroke
end diastolic volume - end systolic volume
what is the equation for cardiac output?
heart rate x stroke volume
what is the equation for Mean Systemic Arterial Pressure
Cardiac Output (CO) x Total Peripheral Resistance (TPR)
what are the two types of circulation?
pulmonary and systemic
what do veins have
capacitance and they act as reservoirs
what is volume distribution determined by?
- venous tone,
- gravity,
- skeletal muscle pump
- respiratory muscle pump.
what determines venous return?
central venous pressure determines venous return which determines stroke volume
what mechanisms determine blood flow?
intrinsic and extrinsic
what is the intrinsic mechanism for?
- intrinsic to the smooth muscle
- important for local blood flow to an organ
what is extrinsic mechanism for?
- consists of systemic regulation of hormones
- autonomic nervous system
what is auto regulation? as part of the intrinsic mechanism
the intrinsic capacity to compensate changes
in perfusion pressure by changing vascular resistance.
what does the myogenic theory state?
smooth muscle responds directly to tension changes in the vessel wall
what does the metabolic theory state?
as blood flow decreases metabolites accumulate and vessels dilate in response
what does the injury theory state?
this happens if a vessel is injured
Serotonin release from platelets causes
vasoconstriction.
what do the extrinsic mechanisms consist of?
- the systemic regulation of hormones
what hormones are involved as part of the extrinsic mechanism?
- kinins eg. bradykinin
- ANP - vasodilator
- circulating vasoconstrictors
ADH
NE from adrenal medulla
angio tension ii from renin secretion
what substances are released from the endothelium?
as part of the intrinsic mechanism?
- nitric oxide
2.Prostacyclin & Thromboxane A2 – vasodilator and
constrictor respectively
- endothelins
what is the sympathetic nervous system needed for?
controlling circulation
fight or flight
what is the para-sympathetic nervous system needed for?
regulating heart rate
rest and digest
what is sympathetic innervation to blood vessels?
- SNS nerve fibres supply all vessels with nerves apart from capillaries pre capillary sphincters and some metarterioles
what tissues do more fibres innervate nerves to?
kidney
gut
spleen
skin
what tissues do less fibres innervate nerves to?
skeletal muscles
the brain
what is the vasomotor system composed of?
where is it located?
- a pressor
- a depressor
- a cardioregulatory inhibitor arrea
it is in the pons and the medulla
what do the lateral portions of the VMS control?
what do medial portions of the VMS control?
heart rate
signals via vagnus nerves ot decrease heart rate
what is the nervous control of the blood vessel diameter?
- vessels always receive sympathetic post-ganglionic nerve
innervation to maintain vascular tone.
This means nerve activity can dilate OR constrict vessels
there is no PSN innervation to the vascular system
Summary of the control of blood vessel radius.
insert
show a graph of the sympathetic and parasympathetic nerve activity?
insert graph
how can we get an increase in heart rate?
- Increased SNS activity.
- Increased plasma levels of adrenaline.
- Decreased PNS activity
how can we control the force of contraction?
contractility is controlled by starlings law
- SNS controls contractility
- PSM has no action on the contractility of the heart
what is the process of controlling the force of contraction?
- NE binds to adrenoceptors to increase cAMP.
- cAMP activates PKA to phosphorylate LTCC, SR Calcium release
channels and SERCA. - More Ca2+ influx and more Ca2+ reuptake.
- Heart rate and contractility altered.
how to control stroke volume extrinsically?
- increased sympathetic activity to the heart
- increased plasma adrenaline
how to control stroke volume intrinsically?
- a greater EDV
what are baroreceptors
they are needed for maintenance of blood pressure
where are the baroreceptors located?
carotid sinus
aortic arch
at what range do carotid sinus receptors respond to pressures?
where are they MOST sensitive?
60 and 180 mmHg
90 -100 mmHg
what is reciprocal innervation?
- when the baroreceptors sense increase in pressure they fire more
- this means more PNS stimulation
- there is also an inhibitory neurone which stimulates the SNS arm to decrease SNS activity
overall what are the results of reciprocal innervation?
- PNS stimulation of the heart via vagus nerve = decreased HR
- decreased SNS stimulation means lower HR and stroke volume
- decreased SNS to the blood vessels also causes dilation
what does an increased blood pressure result in?
- this means a huge increase in firing from the baroreceptors
- more pressure means more firing
what does BR activity trigger?
- more traffic in vagus nerve from the VMC
what directly reflects the BR activity?
- the PNS activity
what does an increase in PSN activity mean?
Increase in PNS activity → more ACh production in
SinoAtrialNode → decreases gradient of pacemaker potential →
decrease in heart rate
what does less SNS activity result in?
decrease in contractility and
increase in vessel radius (vasodilation).
what does a change in HR contractility and dilation mean?
decrease in blood pressure
what happens in great blood loss?
= less arterial pressure
= less baroreceptors firing
= reflexes
= decrease in para sympathetic discharge to the heart
= increase in sympathetic to the heart
= increased contractility and heart rate and cardiac output
show a diagram of how arterial pressure is maintained:
INSERT
