Cardiovascular control 2 Flashcards
How do you calculate stroke volume?
How do you calculate cardiac output?
How do you calculate blood pressure?
Describe the 2 circuits of the circulatory system
The 2 circuits- pulmonary (to the lungs) and systematic (to the body)
Pulmonary- RA-RV- lungs- heart (LHS)
Systematic- LHS heart- body
What is the venous volume distribution affected by?
Venous volume distribution affected by peripheral venous tone, gravity, skeletal muscle pump and breathing.
What does the central venous pressure (mean pressure in the RA) determine?
It determines the amount of blood flowing back to the heart.
What determines the stroke volume?
The amount of blood flowing back to the heart
How is blood flow controlled?
Constriction of veins reduces compliance and venous return.
In arterioles, constriction determines:
- Blood flow to downstream organs
- Mean arterial blood pressure
- The pattern of blood flow to organs
Flow is primarily changes by the radius
What are the 2 mechanisms to regulate blood flow?
1) Local mechanisms are intrinsic to the smooth muscle. Important for local blood flow regulation
2) Systemic mechanisms that are extrinsic to the smooth muscle.
Hormones (catecholamines) affect constriction and dilation of vessel.
Autonomic nervous system can stimulate contraction of smooth muscles.
What are the local mechanisms for regulating blood flow?
- Autoregulation
- Myogenic theory
- Metabolic theory
- Injury
What is autoregulation?
It is the intrinsic capacity to compensate for changes in perfusion pressure by chnaging vasculae resistance
What is the myogenic theory?
It states that smooth muscle fibres respond to tension in the vessel wall (as pressure rises, fibres contract; stretch sensitive channels are involved)
What is the metabolic theory?
As blood flow decreases, metabolites accumulate and the vessels dilate; subsequent increased flow will dilate diluting the effect of the xs electrolytes.
Describe the injury mechanism to regulating blood flow
If vessels are injured, there are clumping platelets to produce clot. Serotonin will constrict vessel around injured site.
Hormones can be local or circulating: what’s the difference and give some examples
Local- endothelium derived
Circulating- non-endothelium derived
What are the 2 branches of the autonomic nervous system? What are the differences between them?
Parasympathetic- rest and digest. Important for controlling the HR.
Sympathetic- fight or flight. Important for controlling circulation
PARASYMPATHETIC: Pre ganglion fibres are long and short post-ganglionic. Uses ACh
SYMPATHETIC: short pre ganglionic and long post ganglionic. Uses noradrenaline. Important for controlling ciruculation and size of vessels.
Sympathetic nervous system innervation to blood vessels
The SNS innervates the heart and all vessels except capillaries and precapillary sphincters and some metarterioles.
SNS innervation elsewhere is variable:
Heavy innervation: kidneys, gut, spleen and skin
Poorly innervated: skeletal muscle and brain
Noradrenaline preferentially binds to alpha1 adrenoreceptors to cause smooth muscle contraction and vasoconstriction
What is the vasomotor centre and where is it located?
It is located bilaterally in the reticular substance of the medulla and the lower third of the pons (midbrain-pons-medulla)
The VMC has a vasoconstrictor (pressor) area and a vasodilator (depressor) area. There is also a cardioregulatory inhibitory area.
The VMC transmits impulses distally through the spinal cord to almost all blood vessels.
What has effects over the vasomotor centre?
Many higher centres of the brain, like the hypothalamus cna have powerful excitatory or inhibitory effects on the VMC.
What do the different parts of the VMC do?
Lateral portions of the VMC control the heart activity by influencing heart rate and contractility.
Medial portion of VMC transmits signals via vagus nerve to heart that tend to decrease HR.
How is blood vessel diameter affected by nervous control?
Blood vessels receive SNS post-ganglionic innervation by noradrenalin neurotransmitter.
There is always some level of tonic activity which can be increased (vasoconstriction) and decreased (vasodilation). More tonic acitivity- constriction, less tonic activity- dilation
Generally, there is no PNS innervation to vasculture.
What will innervate the heart (i.e. what will increase the heart rate?)
- Increase in SNS activity
- Increase in plasma adrenaline
- Decrease in PNS activity
What is the controlling force of contraction?
Ca2+ channels allow Ca2+ influx in the cardiac cell.
The uptake carries into intracellular stores. The sarcoplasmic reticulum is stimulated to release internal stores of Ca2+
NB- beta 1 receptors are in the heart
alpha one receptors in skeletal muscle
How can you increase stroke volume?
- Increase SNS efferents to the heart
- Increase end diastolic volume
- Increase plasma adrenaline
End diastolic volume can be increased by higher venous return and arterial pressure. Also a greater respiratory movement (and therefore decreased intrathoracic pressure), contributes to a higher end diastolic volume.
