Blood vessels and circulation
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Transcript of Blood vessels and circulation
Blood Vessels and Circulation
Chapter 13
Pgs 389-403
Overview
• Introduction• The Anatomy of Blood
Vessels– Structure of vessel walls– Arteries– Capillaries – Veins
• Cardiovascular Physiology– Pressure – Resistance– Circulatory pressure
• Cardiovascular Regulation– The autoregulation of blood
flow– The neural control of blood
pressure and flow– Hormones and
cardiovascular regulation
Capillary Bed
Circulatory Physiology
• 2 factors affect blood flow through capillaries:– Pressure– Resistance
• Vascular resistance• Viscosity• Turbulence
Pressure
• Hydrostatic pressure• Circulatory pressure
– Overall pressure difference between base of aorta and entrance to RA
• Avg is 100 mm Hg– Needed to force blood along
– Divided into 3 components• Arterial pressure = blood pressure• Capillary pressure = pressure in caps• Venous pressure = pressure in veins
Resistance
• For blood to flow:– Circulatory pressure must be great enough to
overcome total peripheral resistance• But pressure low in veins so focus on arterial system (called
peripheral resistance)
• Neural and hormonal controls• Sources of peripheral resistance:
– Vascular resistance– Viscosity– Turbulence
Vascular Resistance
• Resistance of the blood vessels
• Most important factor is friction between the blood and the vessel walls– Friction depends on:
• Length• Diameter
Viscosity
• Resistance to flow caused by interactions among molecules and suspended materials in a liquid
• Viscosity of blood 5xs that of water
• Remains constant
Turbulence
• Blood flow smooth– Slowest flow near the walls; fastest at the
center
• High flow rates, irregular surface, sudden changes in vessel diameter = turbulent flow (swirls and eddies created)
• Slows the flow, increases resistance
Circulatory Pressure
• Where would you expect to find pressure the:– Highest?– Lowest?
• Arterial blood pressure– Systolic pressure– Diastolic pressure– Pulse pressure
Capillary Pressures
• Unlike other arteries because capillary walls permeable– Most reabsorbed– Some water and solutes enter lymphatic
vessels
• This continuous movement plays important role in maintaining homeostasis
Capillary Exchange
• 4 important functions– Maintain constant communication between plasma
and ISF– Speeds the distribution of nutrients, hormones, and
dissolved gases throughout tissues– Assists the movement of insoluble lipids and tissue
proteins that are impermeable– Flushes bacterial toxins and other chemical stimuli to
lymphoid tissue and organs that provide immunity from disease
Venous Pressure
• Veins become larger– Drops resistance, increases flow rate
• 2 factors overcome gravity– Muscular compression– Respiratory pump
Cardiovascular Regulation
• Tissue perfusion—tissue blood flow• Homeostatic mechanisms regulate
cardiovascular activity to ensure tissue perfusion meets demand for oxygen and nutrients
• 3 variable factors that influence tissue perfusion:– Cardiac output– Peripheral resistance– Blood pressure
Cardiovascular Regulation
• Cells become active = increased circulation to region • Goal of cardiovascular regulation is to ensure that these
blood flow changes occur:– At an appropriate time– In the right area– Without drastically altering blood pressure and blood flow to vital
organs
• Factors involved in regulation of cardiovascular function include:– Local factors– Neural mechanisms– Endocrine factors
Autoregulation of Blood Flow
• Precapillary sphincter – Respond automatically to alterations in local
environment• Increased or decreased levels of oxygen and/or
carbon dioxide
– Dilation caused by vasodilators– Contraction caused by vasoconstrictors
Neural Control of Blood Pressure (BP) and Blood Flow (BF)
• Cardiovascular (CV) centers in medulla responsible– Includes a cardioaccelerator center and cardioinhibitory center
• Vasomotor center (part of CV)– Primarily controls diameters of arterioles– Inhibition of center leads to vasodilation
• Will this increase or decrease peripheral resistance?
– Stimulation of center leads to vasoconstriction
• CV centers detect changes in tissue by monitoring:– Arterial blood (esp bp)– pH– Dissolved gas concentrations
Baroreceptor Reflexes
• Monitor degree of stretch in walls of expandable organs
• Located in:– Carotid sinuses– Aortic sinuses– Wall of RA
• Initiate baroreceptor reflexes– Autonomic reflexes that adjust CO and peripheral
resistance to maintain normal arterial pressures
Chemoreceptor Reflexes
• Respond to changes in carbon dioxide levels, oxygen levels, or pH in blood and CSF
• Found in:– Carotid bodies– Aortic bodies – Medulla (CSF)
Hormones and Cardiovascular Regulation
• Provides both short term and long term regulation
• E and NE immediately stimulate CO and peripheral vasoconstriction
• ADH, angiotensin II, EPO, and ANP– Affect long term regulation of blood volume