Cardiovascular System Part 3 Flashcards
What does the regulation of circulation hinge on?
Controlling the arterial blood pressure; making sure it delivers adequate blood supply to the heart and brain (survival mode), and supply blood to other organs. Controlling capillary pressure is done by tissue volume and composition of interstitial fluid.
What mechanisms are involved in the regulation of circulation?
Autoregulation, autonomic nervous system, and humoral control.
How does the Parasympathetic Nervous System affect Cardio Output?
By slowing heart rate; rest and digest.
How does the Sympathetic Nervous System affect Cardio Output?
By increasing the heart rate; fight or flight.
What do veins serve as?
A blood reservoir and return blood to the heart. Veins are large in diameter with little elasticity and low myogentic tone. They easily distend to accommodate additional volumes of blood with no recoil (capacitance vessels).
Mammalian veins contain more than 60% of the total blood volume.
Sympathetic stimulation constricts veins, enhancing venous return and increasing stroke volume.
What are arterioles?
The major resistance vessels due to their small radii. There is a large drop in pressure through the arterioles (93 mmHg -> 37 mmHg), and they eliminate pulsatile pressure swings (making blood flow smoothly).
What are the vein’s smooth muscle innervated with?
The thick layer of smooth muscle is innervated by sympathetic nerve fibres. Vasoconstiction results from smooth muscle contraction; decreased radius, increased resistance, decreased blood flow. Vasodilation results from smooth muscle relaxation; increased radius, decreased resistance, increased blood flow.
What is Vasodilation caused by?
Decreased myogenic activity, decreased oxygen, increased CO2, increased nitric oxide, decreased sympathetic stimulation (heat).
How is blood flow distributed?
The amount of blood flow received by each organ is determined by the number and diameter of its arterioles.
Local (intrinsic) controls are changes within a tissue that alter the radii of arterioles.
What are examples of local (intrinsic) controls of the arterioles?
Some are instantaneous, some are not.
- Local metabolic changes produce relaxation of arteriolar smooth muscle to increase blood flow to the organ (active hyperaemia; changes in oxygen)
- Histamine release causes vasodilation as an inflammatory response; triggers an expansion of the arterioles, more blood to capillary beds
- Exposure to heat or cold (heat = expand, cold = contract)
- Stretch produces myogenic vasoconstriction
What is important about the autoregulation of organ blood flow?
It is most important in the brain, heart, and kidney. It is independent of neural or hormonal influences, the cerebral circulation autoregulates almost perfectly between 60-130mmHg.
Blood flow is not constant along pressure.
What does extrinsic control of the arterioles include?
Neural and hormonal influences with the sympathetic nervous system dominating.
What does sympathetic stimulation cause blood flow?
It redistributes blood flow to the heart and skeletal muscle at the expense of other organs.
Vasoconstriction of most arterioles is due to the activation of a1-adrenergic receptors by NE or epinephrine.
Lung and brain arterioles do not have a1-receptors and do not constrict.
Epinephrine activates B2-adrenergic receptors in the arterioles of skeletal muscle and heart to cause vasodilation.
What is arterial pressure regulated at?
It’s well regulated at about 100 mmHg, thanks to the cardiovascular centre. Body sense where pressure is on the body; aortic baroreceptor -> carotid arteries -> carotid artery baroreceptor -> nerves -> medulla oblongata.
What do baroreceptors do?
Sense stretch of elastic artery wall in systole. Nerve impulses from baroreceptors increase as mean arterial pressure increases and decrease is mean arterial pressure decreases.
