Human Physiology BIOL3205 PDF

Human Physiology BIOL3205 Cardiovascular system II Prof. Chi Bun C...

Human Physiology BIOL3205 Cardiovascular system II Prof. Chi Bun Chan School of Biological Sciences 5N10 Kadoorie Biological Sciences Building [email protected] http://www.bestinfographics.co/blood-vessels-in-the-body-infographic/ 39173823  Lecture outline Structure of blood vessels Regulation of blood flow Mechanism of material exchanges between cells and capillaries Physical characteristics of blood pressures Regulation of blood pressure Hypertension and hypotension  Parallel flow Blood flows in a parallel arrangement Advantages Receive the same composition Blood flow in each organ can be independently adjusted (e.g. exercise) Blood flow to the brain is constant Heart Organ A Organ C Organ B  Types of blood vessels Hollow interior (lumen) Blood vessels are classified according to the blood flow direction and size There are 5 types of blood vessels: Arteries, arterioles, capillaries, venules, and veins Microcirculation: Arterioles, capillaries, venules Contains: endothelium, elastin fibers, smooth muscle, connective tissues Veins have valves  Arteries Major pathway to transport blood between organs Offer little resistance because of its large radius Contains two types of connective tissues: Collagen fibers – tensile strength Expanding pressure Elastin - elasticity Act as a pressure reservoir to Systole keep blood flow continuously Blood flow Elastic recoil Diastole  Arterioles An artery branches into numerous arterioles within the organ No elastin fibers → no elasticity Have an abundance of circular smooth muscle → control the radius of the vessel Vasodilation – enlargement of the vessel (↑ tone) Vasoconstriction– narrowing of the vessel lumen Arterioles are partially constricted at basal condition (vascular tone), which form the basal resistance (↓ tone)  Change of blood flow distribution Blood does not flow equally to all organs but instead gets distributed based on need Vasoconstriction and vasodilation are important mechanisms to control the distribution of cardiac output Also contributes to the total peripheral resistance (TPR) Aorta Arteriole Organ Fixed Cell no.  Control of blood flow - arteriolar radius The radius of the arteries Active and arterioles can be (Autoregulation) hyperemia Chemical regulated via intrinsic and Intrinsic control Reactive hyperemia extrinsic controls Physical Intrinsic control - local Total peripheral resistance Sympathetic metabolic need Neuronal nerve Extrinsic control - overall Extrinsic control Epinephrine blood pressure Hormonal Norepinephrine Intrinsic control overrides Vasopressin Angiotensin II the extrinsic control (e.g. muscle) Intrinsic control of arteriolar radius – chemical factors Active hyperemia Reactive hyperemia The most important local chemical influences on arteriolar smooth muscle are related to metabolic changes within a given organ When cells are more active metabolically, they need more blood to bring in O2 and nutrients, and to remove metabolic wastes. Increased blood flow (vasodilation) in response to enhanced tissue activity is called active hyperemia Reactive hyperemia - Increased blood flow (vasodilation) in response to lack of blood flow Vasoactive paracrine (e.g. NO and endothelin) is released from the arteriolar endothelial cells in response to metabolic changes  Intrinsic control of arteriolar radius – physical factor Arteriolar smooth muscles are stretch- sensitive that responds to being passively stretched (e.g. high blood pressure) by myogenically increasing their tone (i.e. vasoconstriction) to resist the initial passive stretch During reduced blood flow (e.g. low blood pressure), the arterioles respond to this reduced stretch by myogenically relaxing (i.e. vasodilation) Tends to keep a constant volume of blood flow Together with the chemical mechanism (reactive hyperemia) are called Autoregulation  Arteriole radius and blood flow ↓ muscular tone Increase of blood pressure Vasoconstriction Normal vascular tone Normal vascular tone Blood flow Normal vascular tone Vasodilation Drop of blood pressure ↑ vascular tone  Extrinsic control of arteriolar radius Arteriolar smooth muscle is innerved by Sympathetic nerve sympathetic nerves Release norepinephrine causes the contraction of smooth muscle → vasoconstriction No parasympathetic nerves Ateriole Vasodilation is produced by decreasing Capillary sympathetic vasoconstrictor activity Hormones (norepinephrine and epinephrine, (http://163.178.103.176/Tema3C/APortal/CardioCG/FisoCardio00/ vasopressin, angiotensin II) are released LaUIII/U3Ob10/sympath.html) from other endocrine organs to regulate the arteriolar radius and blood flow Can be overridden by intrinsic control (e.g. exercise)  Capillaries Capillaries are the thinnest and smallest vessels (~ the size of red blood cell) which contains a single layer of endothelial cell Primary function is for the exchange of substances between blood and tissue. Capillary wall is thin and has pores Narrow – O2 exchange from every red blood cell Extensively branched (cells are within 1 mm from the capillaries) → high surface area (~600 m2) Total cross-sectional area is bigger than that of the other blood vessel → slow blood (http://antranik.org/blood-vessels/) velocity (NOT flow rate!) → adequate time for exchange of material Materials exchange between blood and cells Exchange of material between blood and the cells is not made directly – blood → interstitial fluid → cell Blood contains water-soluble substances, lipid-soluble substances, and plasma protein Passive diffusion – solute cross primarily by diffusion down concertation gradients Bulk flow – movement in the bulk of a protein-free plasma across the capillary between the blood and interstitial fluid  Bulk flow is a process that a volume Bulk flow of protein free-plasma filters out of the capillary, mixes with the interstitial fluid, and reabsorbed by the blood The fluid that is pushed out through the capillary pores by ultrafiltration The net inward movement of fluid from the interstitial fluid into the capillaries is known as reabsorption Bulk flow is important in controlling Provide a (https://en.wikipedia.org/wiki/Capillary#/media/File:2108_Capillary_Exchange.jpg) extracellular fluid (Plasma + temporary interstitial fluid) volume mechanism to Controlled by capillary blood help keep plasma pressure (Pc) and plasma-colloid volume fairly osmotic pressure (p) differences in constant between plasma and interstitial fluid  Many capillaries are close under Metarterioles resting conditions Metarterioles – structural intermediates between arterioles and capillaries Contain isolated rings of smooth muscle (precapillary sphincter) that act as gatekeepers at a strategic point Precapillary sphincters are controlled by local metabolic changes Regulation of blood flow in a particular organ Blood flow to a particular tissue at constant blood pressure is controlled by Degree of resistance offered by the arterioles (sympathetic and local factors) Number of open capillaries (local factors)  Veins Veins are thin-walled vessels with little tone and resistance (because of the large radius) Highly stretchable with little elastic recoil It is the pathway to return blood into the heart and is the reservoir of blood Contain valves Venous return – the volume of blood per min entering each atrium Several mechanisms that help the venous return - sympathetic activity, skeletal muscle activity, respiratory pump, cardiac suction  Mechanisms of venous Cardiac suction return Skeletal muscle and valves Respiratory pump  Blood pressure Blood pressure is the force exerted by the blood (http://www.cdc.gov/) against a vessel wall Usually referring to that of arteries Depends on cardiac output, blood volume, arteries compliance/distensibility (how easily they can be stretched), and total peripheral resistance (TPR) Systolic pressure – the max. pressure exerted in the arteries when the blood is ejected into them during systole (~120 mm Hg) Diastolic pressure – the min. pressure within the 120 x (1/3) + 80 x (2/3) = 93.3333 arteries when blood is draining off into the rest of the vessels during diastole (~80 mm Hg) Mean arterial pressure (MAP) – the average pressure driving blood forward into the tissue throughout the cardiac cycle (~93 mm Hg)  Pressure in different blood vessels Blood pressure in arteries is not static - pulsatile Pressure gradient - encourage the blood flow from the heart to the various organs downstream Blood pressure is a function of vessel resistance (the friction between the moving fluid and the stationary vascular walls) Major determinant of resistance to flow is the vessel radius Arteriolar vasoconstriction increases blood pressure Arteriolar vasodilation decreases blood pressure Sphygmomanometer (blood pressure meter) (https://youtu.be/VJrLHePNDQ4) Regulation of blood pressure - baroreceptors Blood pressure fluctuates from time to time, and depends on the external stimuli (e.g. temperature, exercise) Monitored by the baroreceptor reflex Baroreceptors are a type of mechanoreceptor sensory neuron that is excited by the stretch of the blood vessel. Thus, increases in the pressure of blood vessel trigger (http://www.interactive-biology.com/4301/blood-pressure-short-term-and-long-term-control-measures/) increased action potential generation rates and provide information to the central nervous system. The integrating center that receives the afferent impulse is the cardiovascular control center  Regulation of blood pressure Blood pressure is regulated by short-term (within seconds) and long-term (minutes to days) measures Short-term – controls cardiac output (CO) and total peripheral resistance (TPR) Long-term – controls blood volume and TPR Blood pressure can be regulated by the action of hormones Epinephrine - ↑ vasoconstriction Vasopressin and angiotensin II ↑ vasoconstriction ↓urine output - ↑ blood volume Determinants of mean arterial blood pressure Arterial blood pressure is determined by Cardiac output Heart rate Stroke volume Total peripheral resistance Arteriolar radius Blood viscosity/blood volume  Short term regulation of blood pressure CO = HR x SV High blood pressure Low blood pressure  Hypertension Hypertension is the long-term medical condition that the blood pressure in the arteries is persistently elevated (Europe: 140/90; AHA: 130/80 mm Hg) A study by the School of Public Health of the University of Hong Kong in 2012 revealed that about 1 in 3 adults in Hong Kong has hypertension Primary hypertension – hypertension with unknown causes Secondary hypertension - hypertension that occurs as a consequence of other diseases (e.g. kidney disease) Numerous complications Once initiated, hypertension is self- perpetuating (positive feedback) (http://www.fastmed.com/)  Hypotension Hypotension occurs when there is a disproportion between vascular capacity and blood volume when the heart is too weak to drive the blood When the blood pressure falls that no adequate blood flows to the tissues, it causes circulatory shock Hemorrhage (hypovolemic shock) Heart failure (cardiogenic shock) Reversible or irreversible shock After the lecture, you should be able to explain Anatomical differences between different blood vessels Regulation of blood flow – change of arteriole radius Mechanism of material exchanges between cells and capillaries Physical characteristics of blood pressures Regulation of blood pressure Blood pressure disorders