lecture 10,11,12 cardiovascular system, cardiac function, arteries & arterioles

the goal of cardiovascular system 

maintain adequate delivery of oxygen and nutrients and removal or wastes from all tissues in the body

also

• monitor tissue integrity

• avenue for signaling

know these:

• total blood volume = 5.5 L

• hemocrit = 45%

• hemoglobin = 15 g/dL per micro liter

• red cell count = 5 million per micro liter

• total white cell count = several thousand

plasma

• mostly water; ions like interstitial fluid

• gases, nutrients, wastes

• hormones and messenger molecules 

• proteins 7% (4.5 albumin, 2.5 globulins, 0.3 fibrinogen)

• plasma vs serum = absence of clotting factors

reference table for plasma constituents

erythrocytes (red blood cells)

• 7 microns in diameter

• optimal shape for diffusion 

• 5 mill per micro liter blood

• 2 mill hemoglobin molecules per RBC, or about 15g/100mL blood

• no nucleus or ribosomes (in mature state)

anemia = reduced oxygen carrying capacity of the blood 

due to: 

• too few red blood cells 

• not enough hemoglobin per red blood cell

erythropoetin

a hormone released by the kidney, stimulated production of red blood cells

general organization of the cardiovascular system

flow of blood

• blood will only flow if there is a pressure gradients: blood will flow from higher pressure to lower pressure

• consider the flow of blood through one of these vessels

  • flow is proportional to the pressure gradient

  • flow is inversely proportional to resistance

• flow = ΔPressure/resistance

• ΔPressure = flow x resistance

• resistance = ΔPressure/flow

resistance to flow

• viscosity is not changing much in body

• length stays same in adult body 

• radius is adjustable and is how body regulates modifiable pressure

basic principles about flow:

• blood flows if there is pressure gradient, from high → low pressure

• flow is opposed by resistance 

• flow rate & velocity are different beings; flow rate (or simply flow) is the volume of blood passing a point in the circulation per unit time (i.e. ml/min) whereas velocity is the distance the blood travels per unit time (i.e. cm/min)

• the larger the cross-sectional diameter of the vessel, the slower the velocity of flow

• flow rate = volume of blood passing a point in a given amount of time 

• flow = volume per time

diagram about flow

flow resistance causes a pressure drop

out of all these vessels the arterioles are providing the greatest amount in resistance

diagrams of heart, heart wall etc

flow of blood in heart

valve opened vs valve closed

valve opened: 

• when pressure is greater behind the valve (atrium) , it opens

valve closed:

• when pressure is greater in front of the valve, it closes

Note that when pressure is greater in front of the valve, it doesn’t open in the opposite direction; its a one-way valve

tricuspid and mitral (bicuspid) valves

prevents blood from flowing backwards from the ventricles into the atria during ventricular contraction

semilunar valves

prevents blood from flowing backwards from the aorta and pulmonary artery into the ventricles 

cardiac muscle

structure of intercalated disk

two types of cardiac cells

contractile and autorhythmic (pacemaker)

overview of cardiac myocite contraction 

ventricular myocyte action potential

refractory periods

SA Node action potential

conduction system of the heart

comparison of action potentials in cardiac & skeletal muscle

ANS can alter the rate of the pacemaker potential (not the shape of the action potential)

overview of ECG

cardic cycle

wiggers diagram

stroke volume (SV)

amount of blood pumped by one ventricle during a contraction

stroke volume = end diastolic volume - end systolic volume

SV = EDV - ESV

70 mL = 135 mL - 65 mL

cardiac output (CO)

volume of blood pumped per unit time (by the left heart) 

cardiac output = heart rate x stroke volume 

CO = HR - SV

CO = in liters per minute

HR = in beats per minute

SV = in liters

5 L/min = 72 b/min x 0.07 L/b

CO = HR x (EDV - ESV) ← all of these parameters are regulated

autonomic control of the heart rate

• SA node innervated by both sympathetic and parasympathetic and important for regulating heart rate

• AV node also innervated by both, but not very important 

• ventricular muscle innervated by sympathetic (but not parasympathetic) and important for regulating force of contraction

starling law of the heart

stroke volume increases in proportion with EDV

sympathetic nervous system influences cardiac contractility altering the starling curve and ESV

pulmonary circulation diagrams

cardiac output (resting conditions)

cardiac output (resting conditions) - 5 L/min - thats flow

• flow = ΔPressure/resistance

• the vasculature provides resistance

functional model of the cardiovascular system

• amount of flow through any level of this system (e.g, arteries, capillaries, veins) is the same 

• as resistance varies, pressure gradients vary 

• pressure falls across a resistance

• as relative resistance of different arterioles changes, so too does flow

• as total cross-sectional area changes, flow velocity changes 

blood vessel structure

endothelial cells lining blood vessels serve several functions:

only need to know:

• physical lining of blood vessels

• secrete substances that influence vascular smooth muscle

[main point is that the vascular endothelium is more than a passive lining]

arteries

• large diameter, low resistance 

• serve as low resistance conduit to distribute blood around body

systemic circulation pressures 

arteries are not rigid, but rather somewhat compliant (C= dV/dP)

→ as a result of compliance, arteries serve to keep blood flowing during diastole 

arterial pressure pulse

Mean Arterial pressure = diastolic pressure + 1/3 of the pulse pressure

what factors influence arterial blood pressure?

here we mean the average arterial pressure across the cardiac cycle; mean arterial pressure 

dPressure = flow * resistance 

what factors influence pulse pressure?

• stroke volume and heart rate

• arterial compliance

myogenic tone

(muscle tone in the arterioles)

can be regulated by:

• local mechanisms

  • active hyperemia

  • flow autoregulation

  • endothelial factors

• extrinsic

  • sympathetic neural control

  • hormones 

    • epinephrine 

    • angiotensin 

    • vasopressin (antidiuretic hormone)

    • atrial natriuretic hormone (and many more) 

local mechanisms: active hyperemia and flow autoregulation

adrenergic receptors and arteriolar resistance: 

• alpha receptors are constrictor (primarily NE from sympathetic nerves)

• beta receptors are dilatory (primarily E from the adrenal medulla) and these only exist in arterioles in a few tissues like skeletal and heart

arteriole diameter is controlled by tonic release of norepinephrine

chemicals mediate vasoconstriction and vasodilation (CHART)

tissue metabolic activity 

reference summary of arteriolar control in specific organs (CHARTS)