Central Control of Circulation Flashcards
what is the main goal of control of circulation?
to maintain mean systemic arterial pressure (MAP) - the average blood pressure in the arteries during the cardiac cycle
what is the equation for MAP?
MAP = DP [diastolic pressure] + 1/3 (SP - DP) [pulse pressure]
what are the effectors for control of circulation?
blood vessels, heart and kidney
What is the Presser region?
Is it sympathetic/parasympathetic?
How does it work?
located in medulla; responsible for raising blood pressure
sympathetic
increases blood increasing vasoconstriction, cardiac output (by increasing heart rate and stroke volume), and contractility
pressor region –> sympathetic route –> medulla –> spinal cord –> synapses at T1-L2 –> heart
What is the Depressor region
Is it sympathetic or parasympathetic?
How does it work?
also located in medulla, responsible for lowering blood pressure
parasympathetic
decreases blood pressure by inhibiting pressor region
depressor region –> medulla –> vagus nerve –> heart
what do the central chemoreceptors in the medulla primarily respond to?
decrease in pH (due to CO2 diffusing across the blood brain barrier and thereby reducing pH)
where are cardiopulmonary baroreceptors located? What do they do?
atria, ventricles and pulmonary artery
when stimulated (high blood pressure), lead to inhibition of pressor region/vasoconstrictor centre in medulla –> blood pressure falls (due to vasodilation and fluid loss)
also inhibits renin-angiotensin and aldosterone system
also inhibits vasopressin/ADH
what does peripheral control of circulation (peripheral resistance) mainly depend on?
arteriole resistance
what do arterioles respond to?
- Respond to blood pressure - When the muscle of the arteriole contracts the radius
↓ causing the resistance to flow to ↑ thus causing blood flow to ↓ - and vice versa - local factors
a. Vasoconstrictors
- smooth vascular muscle constricts
- Endothelin-1 (ET-1) - released by endothelium cells results in vasoconstriction [POTENT]
- Increase in internal blood pressure, resulting in myogenic contraction (when smooth muscle is stretched there will be automatic contraction until diameter is normalised or slightly reduced) due to the blood pressure increase - this is autoregulation
b. vasodilators
- Hypoxia: when O2 supply decreases, there will be an accumulation of vasodilator
metabolites which will dilate vessels to increase local blood flow
- Increased CO2
- Decreased pH
- Bradykinin
- Nitric oxide: released by endothelial cells - triggers vasodilation [POTENT]
- Increased K+
- H+
- Tissue breakdown products e.g. lactic acid
- Prostacyclin/ Prostaglandin I2 (PGI2): released by endothelial cells - triggers vasodilation [POTENT]
- respond to hormonal factors
what are examples of vasoconstrictors and vasodilators?
- Vasoconstrictors: angiotensin II, vasopressin & adrenaline
- Vasodilators: Atrial Natriuretic Peptide, adrenaline
what is another name for adrenaline? is adrenaline a vasoconstrictor or vasodilator?
epinephrine
both, depending on which receptors are present
where are peripheral chemoreceptors found? What are they stimulated by?
In the aortic arch & carotid sinus
stimulated by a fall in PaO2 & a rise in PaCO2 & a fall in pH causing blood pressure to increase
what do arterial baroreceptors respond to?
respond to pressure
they are stretch receptors
where are the arterial baroreceptors found
Two found where the left and right common carotid divide into two smaller arteries (internal & external carotid) - this portion of the artery is known as the CAROTID SINUS (found at the base of the internal carotid): carotid sinus > sinus nerve > glossopharyngeal > medulla: ↓ sympathetic & ↑ parasympathetic = ↓ in blood pressure
