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Anatomy & Physiology: Cardiovascular System - Blood Vessels and Blood Flow

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  • What is tissue perfusion?

    Tissue perfusion is the blood flow through body tissues, essential for delivering O2 and nutrients, removing wastes, gas exchange in lungs, nutrient absorption in the digestive tract, and urine formation in kidneys.

  • What controls the rate of blood flow?

    Blood flow rate is controlled by extrinsic factors (sympathetic nervous system and hormones) and intrinsic factors (autoregulation/local control by tissues).

  • What is extrinsic control of blood flow?

    Extrinsic control involves nerves and hormones acting on arteriolar smooth muscle to reduce blood flow to less needed regions, regulating flow through the whole body.

  • What is intrinsic control (autoregulation) of blood flow?

    Intrinsic control or autoregulation is local adjustment of blood flow by tissues themselves, modifying arteriole diameter to meet specific tissue needs.

  • How does blood flow redistribute during exercise?

    During exercise, skeletal muscle arterioles dilate (intrinsic control) increasing blood flow to muscles, while extrinsic controls reduce flow to organs like kidneys and digestive system.

  • What are the two types of intrinsic mechanisms regulating blood flow?

    The two intrinsic mechanisms are metabolic controls and myogenic controls, both determining the autoregulatory response.

  • What triggers metabolic controls in blood flow autoregulation?

    Increased tissue metabolism lowers O2 and raises metabolic products (H+, K+, adenosine, prostaglandins), causing arteriole relaxation and nitric oxide release for vasodilation.

  • What role do endothelins play in blood flow regulation?

    Endothelins are potent vasoconstrictors released by endothelium, balanced with nitric oxide; when blood flow is inadequate, nitric oxide predominates causing vasodilation.

  • How do myogenic controls regulate blood flow?

    Myogenic controls respond to changes in mean arterial pressure (MAP): increased stretch causes vasoconstriction, decreased stretch causes vasodilation to maintain constant perfusion.

  • What is long-term autoregulation?

    Long-term autoregulation occurs when short-term control fails, involving angiogenesis and vessel enlargement to increase blood supply over weeks or months.

  • How does blood flow vary in skeletal muscles?

    At rest, myogenic and neural mechanisms maintain flow (~1 L/min); during activity, local controls override sympathetic vasoconstriction, increasing flow up to 10 times.

  • What controls cerebral blood flow?

    Brain blood flow is tightly regulated by metabolic controls (pH, CO2 levels) and myogenic controls responding to MAP changes to prevent ischemia or edema.

  • How does skin blood flow help regulate body temperature?

    Skin blood flow is neurally controlled; vasodilation occurs with heat to radiate warmth, vasoconstriction occurs with cold to conserve heat, also serving as a blood reservoir.

  • How is pulmonary blood flow regulated differently from systemic circulation?

    Pulmonary arteries have low pressure and resistance; low O2 causes vasoconstriction, high O2 causes vasodilation, directing blood to oxygen-rich lung areas.

  • How does coronary blood flow change during the cardiac cycle?

    During systole, coronary vessels are compressed stopping flow; during diastole, high aortic pressure forces blood through coronary circulation.

  • What is the velocity pattern of blood flow through systemic circulation?

    Blood flow velocity is fastest in the aorta, slows down in capillaries due to large cross-sectional area, then increases again in veins.

  • What is vasomotion?

    Vasomotion is the intermittent flow of blood through capillaries caused by the opening and closing of precapillary sphincters.

  • What are the four routes molecules use to cross capillaries?

    Molecules cross capillaries by diffusion through endothelial membranes, passing through intercellular clefts, fenestrations, or active transport via pinocytotic vesicles.

  • What forces drive bulk fluid flow across capillary walls?

    Bulk flow is driven by hydrostatic pressure (fluid pushing out) and colloid osmotic pressure (protein pulling fluid in), determining fluid movement at arterial and venous ends.

  • What is net filtration pressure (NFP) and its formula?

    NFP is the net force driving fluid out or into capillaries: \(NFP = (HP_c + OP_{if}) - (HP_{if} + OP_c)\).

  • What causes edema?

    Edema is caused by increased capillary hydrostatic pressure, increased interstitial osmotic pressure, decreased capillary osmotic pressure, or lymphatic blockage, leading to excess interstitial fluid.

  • What are the two main circulations in the vascular system?

    The vascular system has pulmonary circulation (heart to lungs and back) and systemic circulation (heart to body and back).

  • How do systemic arteries and veins differ in location?

    Arteries run deep only, while veins can be deep or superficial; superficial veins do not correspond to arteries by name.

  • What is unique about venous pathways compared to arterial pathways?

    Venous pathways are more interconnected, can have multiple names, and include special drainage systems like dural venous sinuses and the hepatic portal system.

  • What is the hepatic portal system?

    The hepatic portal system is a vein connecting two capillary beds, transporting blood from digestive organs to the liver for filtering before systemic circulation.

  • Why is blood filtered through the liver before entering systemic circulation?

    Blood from digestive organs is filtered in the liver to remove toxins and microorganisms using hepatocytes and phagocytes in sinusoid capillaries.

  • What is the function of the hepatic portal vein?

    The hepatic portal vein carries nutrient-rich blood from digestive organs to the liver for processing before it enters the general circulation.

  • How does net filtration pressure affect fluid movement at capillary ends?

    At the arterial end, NFP causes fluid to move out (filtration); at the venous end, NFP causes fluid to move in (reabsorption).