Cardiovascular systems 6 - Cardiovascular control 2 Flashcards
What three factors does constriction of arterioles determine?
- Bloodflow to downstream organs
- Mean arterial blood pressure
- Pattern of blood flow to organs
What is the local method of regulating blood flow?
Autoregulation - changing diameter in response to flow.
What are the local hormones that affect radius of arterioles?
- Nitric oxide (vasodilator)
- Prostacylin (vasodilator)
- Thromboxane (vasoconstrictor)
- Endothelins (vasoconstrictors)
What are the circulating hormones that affect the radius of arterioles?
- Kinins (vasodilator)
- Atrial natriuretic peptide (vasodilator)
- Vasopressin (vasoconstrictor)
- Noradrenaline (vasoconstriction)
- Angiotensin II (vasoconstrictor)
What are the primary roles of the SNS and PNS of the cardiovascular system?
- SNS controls circulation
- PNS controls heartbeat
Where do parasympathetic nerves arise from?
- Cranial part of the spinal chord
- Sacral part of the spinal chord
Where do sympathetic nerves arise from?
- Thoracic vertebra
- Lumbar vertebra
What neurotransmitters are used in pre-ganglionic fibres?
Acetylcholine
What neurotransmitters are used in post-ganglionic fibres?
- PNS uses acetylcholine
- SNS uses noradrenaline
Where does noradrenaline bind on smooth muscle?
- a1 adrenoreceptors
- Causes vasoconstriction
Describe the location and structure of the vasomotor centre.
- Located in the medulla
- Contains a vasoconstrictor (pressor) area, and a vasodilator (depressor) area, as well as a cardioregulatory inhibitory area
What is the function of the vasomotor centre?
- Controls blood vessels
- Influences heart rate and contractility
- Controlled by hypothalamus
What are the locations of baroreceptors?
- Mechanoreceptors in the carotid sinus, which change their firing rate due to pressure changes
- Mechanoreceptors in the aortic arch change their firing rate due to changes in pressure
What pressures are baroreceptors most sensitive to?
90-100mmHg
What is the consequence of increased baroreceptor activity?
- Parasympathetic nerves are stimulated
- Sympathetic nerves are inhibited, this is by inhibiting the basal tonic activity of sympathetic nerves
What is the consequence of hemorrhage?
- Blood volume decreases
- Venous pressure and atrial pressure decrease
- Cardiac output and blood pressure decreases. This is detected by baroreceptors, which increases venous pressure.
- This results in increased loss of blood.
When is afferent activity highest in baroreceptors?
When systolic blood pressure is high, and pulse pressure is high
Do sympathetic efferent nerves or parasymapathetic nerves have shorter post ganglionic fibres?
Parasympathetic nerves have the shorter postganglionic fibres.
What is the myogenic mechanism hypothesis for autoregulation?
Smooth muscle fibres respond to tension in the vessel wall
What is the metabolic mechanism hypothesis for autoregulation?
Metabolites accumulate as blood flow decreases, causing vessels to dilate so metabolites are washed away.
What do local molecules which affect vascular smooth muscle contraction respond to?
Respond to local stimuli - metabolism and shear stress
What determines resting heart rate?
PNS and SNS stimulation
How are blood vessels innervated?
- By SNS efferents only
- Capillaries recieve no innervation
