Main functions

1- Delivering O2 and nutrients to the tissues

2- Removing CO2 and waste products from the tissues

Others:

1- Delivering hormones from their glands to their sites of action

2- Regulating body temperature

3- Maintaining adequate blood supply to the body in various stress conditions (e.g. exercise)

Cardiac output at rest is the volume of blood per minute pumped by the left ventricle - 5 Liters/minute

Because the left ventricle (left pump), systemic system, right ventricle (right pump), and pulmonary system are connected in series (as opposed to parallel) the flow (NOT velocity) of blood is the same everywhere in the body

At steady state the cardiac output is equal to the venous return - the amount per minute pumped by the left ventricle is equal to the amount per minute returned to the right atrium by the vena cava

Different levels of pressure are required for blood to flow

Blood will flow from high pressure to low pressure

Left ventricle has the highest pressure because it is pumping to the entire body

Pressure decreases as blood flows from the left ventricle to the arteries to capillaries to veins all the way to the right atrium

Pressure then increases in the right ventricle so the blood can be pumped to the lungs and into the left atrium

Oxygenated blood enters the left ventricle from the left atrium through the mitral valve

Blood enters the aorta through the aortic valve

Blood is distributed throughout the body by arteries and capillaries -

25% of volume each for renal, gastrointestinal, and skeletal systems.

15% for cerebral,

5% each for coronary and skin (all numbers at rest)

Venules collect deoxygenated blood from capillaries and coalesce into veins

Vena cava returns blood to the heart in the right atrium

Blood enters the right ventricle through the tricuspid valve

Blood enters the pulmonary artery through the pulmonic valve

Gas exchange occurs in the lungs and pulmonary vein returns oxygenated blood to the left atrium

In tandem the papillary muscles and chordae tendinae prevent backflow in the aortic and mitral valves

For blood to flow to occur properly it is important that no backflow occurs

The muscle contracts and pulls the tendons which pulls the valve open downward.

It prevents the valve from opening upward

Vena cava returns deoxygenated blood to the right atrium

Blood enters the right ventricle through the tricuspid valve

Blood enters the pulmonary artery through the pulmonic valve

Pulmonary artery (ONLY artery in the body w/ deoxygenated blood) takes blood to the lungs

Pulmonary vein (ONLY vein in the body w/ oxygenated blood) takes blood to the left atrium

Blood enters the left ventricle through the mitral valve

Blood enters the aorta through the aortic valve is distributed all over the body

Compliance = change in volume / change in pressure

Compliance means how easy a vessel can be stretched

a) Not easily stretched -> low compliance ex's - arteries, atherosclerosis or vessels in old age

b) Easily stretched -> high compliance ex - veins

Capacitance means capacity to hold blood

Aorta = low capacitance

Veins = high capacitance

* probably don't have to memorize actual #'s

systemic veins - 60-70%

lungs - 10-12%

systemic arteries - 10-12%

heart - 8-11%

capillaries - 4-5%

Veins are the main reservoir of blood volume because they have a high compliance. They can hold a large blood volume because they can easily stretch

Arterial system

Small change in volume -> large change in pressure Arteries have low compliance so small changes in volume will lead to large changes in pressure

Venous system

Large change in volume -> small change in pressure Veins have high compliance so large (or small) changes in volume will only lead to small changes in pressure The compliance of veins is why the large majority of blood (60-70%) is found in veins

Age or Sympathetic stimulation --> increased vascular smooth muscle tone --> increased pressure at each volume in arteries and veins

Curves shift to the right

Wall tension is how hard the walls of the a vessel are being stretched when there is pressure inside the vessel

Laplace relationship: Tension is proportional to pressure multiplied by radius

Ex - aorta has the highest wall tension because it has the highest pressure and the biggest radius

If blood is flowing in an area where pressure is the same but the radius increase then the wall tension increases

The area with the increased radius is at risk for dissection (i.e. wall tear) more than the other areas

Blood flow is determined by Ohm's law

Q = delta P / R

Q = blood flow delta

P = the pressure difference between two ends of a vessel (P1 and P2)

R = vascular resistance of the vessel

Fluid molecules flow in layers or lamina

Flow is silent

Velocity: Maximum in the center and minimum in the periphery (due to molecules adherence in the vessel wall)

Fluid molecules "bounce around" under certain conditions:

a) Vascular aneurysm,

b) Stenosis (narrowing of the vessels) and arterivenous fistula (abnormal connection or passageway between an artery and a vein)

c) Anemia  *Noisy *Low velocity

A dimensionless number of the flow, can be determined as follows:

Nr = velocity * diameter * density / viscosity

Nr < 2000 --> laminar flow

Nr > 2000 --> turbulent flow

Velocity: (speed) rate of blood displacement with respect to time (e.g. cm/s)

Flow: volume per unit time (e.g. ml/s) - cardiac output (5 L/min) is flow

The velocity is inversely proportional to the cross-section area of blood vessel

Velocity = flow / cross-section area

Flow is constant so velocity is dependent on cross-sectional area

Aorta: 2.5 (smallest) - only one vessel so although it has the largest radius it has the smallest area

Small arteries: 20

Arterioles: 40

Capillaries: 2500 (largest) - individual capillaries have small area but there are millions of capillaries

Venules: 250

Small veins: 80

Venae cavae: 8

*probably don't have to memorize the #'s but understand the differences especially between the aorta and capillaries

Aorta = 33 cm/s vs. Capillaries = 0.3 mm/s under resting conditions

Resistance is calculated as resistance = change in pressure / flow

It can be expressed in mm Hg/ml/min or in Peripheral Resistance Unit (PRU= mm Hg/ml/sec)

Resistance is equal to [(blood viscosity * vessel length)/ radius^4)] * (8/pi)

Radius length is the main determinant of the vascular resistance

Radius decreases by half -> resistance increases 16-fold

Radius doubles -> resistance is 1/16 of original value

increased myogenic activity

increased oxygen

decreased CO2 and other metabolites

increased endothelin

sympathetic stimulation

vasopressin and angiotensin II

Cold

decreased myogenic activity

decreased O2

increased C02 and other metabolites

increased NO

decreased sympathetic stimulation

histamine release

heat

R total = R1 + R2 + R3 +....

Total resistance is simply calculated by adding all individual resistance together.

Total resistance is always greater than any individual resistances

Adding a resistor in series increases the total resistance of the system

Flow is equal at all points in series system

Vessels are arranged in series around the circulation - arteries, arterioles, capillaries, venules and veins.

Pressure decrease according to the resistance that it has to overcome - i.e. the greatest decrease in pressure occurs in the arterioles because arterioles contribute to the highest resistance

If only the central resistance (R2) increases:

Flow decreases equally at all points (series system)

Pressure immediately upstream from R2 increases

Pressure immediately downstream from R2 decreases

Thus an increase in resistance leads to an increase in the pressure difference

if only the central resistance (R2) decreases:

a) Flow increases equally at all points (series system)

b) Pressure immediately upstream from R2 decreases

c) Pressure immediately downstream from R2 increases decreased resistance leads to decreased difference in pressure remember R = delta P/ Q

The reciprocal of the total resistance is the sum of the reciprocals of individual resistances

Total resistance is always smaller than any individual resistances

Adding a resistor in parallel decreases the total resistance of the system.

However, increase resistance in an individual resistance will increase total resistance

Flow in individual resistance can be adjusted independently

Vessels are arranged in parallel in various organs e.g. coronary, cerebral, renal, etc.

There is no loss of pressure in parallel resistance arrangement

Viscosity = internal "stickiness" of the fluid.

Viscosity of the blood changes with hematocrit (amount of blood cells)

Anemia causes decreased hematocrit which causes decreased viscosity

Polycthemia causes increased hematocrit which causes increased viscosity

In general

Force = Pressure / Area

Blood pressure: the force exerted by the blood against any unit area of the vessel wall

Systolic pressure (SP): is the peak aortic pressure, occurs duringthe ejection of the blood from the left ventricle into aorta

Diastolic pressure (DP): is the minimum aortic pressure

Pulse pressure = Systolic Pressure - Diastolic Pressure

Mean arterial pressure (MAP) = Diastolic Pressure + 1/3 Pulse Pressure = 2/3 Diastolic Pressure + 1/3 Systolic Pressure

MAP = CO x TPR 

MAP = mean arterial pressure (mmHg)

CO = cardiac output (ml/min)

TPR = total peripheral resistance (mmHg/ml/min)

Aorta & large arteries = 100 mmHg

Capillaries = 17 mmHg

Veins = almost 0 mmHg

Pulmonary arteries = 16 mmHg

Pulmonary capillaries = 7 mmHg

1. increase stroke volume

2. decrease compliance of the arterial tree

3. decrease heart rate (via increased stroke volume)

1. decrease in total peripheral resistance (TPR)

2. decrease in heart rate

3. decrease in stroke volume

Major factors that increases pulse pressure:(systolic increases and diastolic decreases)

1. increase in stroke volume

2. decrease in compliance of the arterial tree

3. decrease TPR

The progressive diminishment of the pulse pressure in the peripheral circulation

Causes:

1) the resistance to blood movement in the vessels

2) The compliance of the vessels

Degree of damping is proportional to resistance * compliance

Arteries have a higher systolic pressure but a lower mean arterial pressure

The lower mean arterial pressure is needed for blood to flow from the aorta to the arteries

Arteriosclerosis - blockage causes increased systolic pressure and increased pulse pressure

Aortic stenosis - narrowing of aorta decreases stroke volume which decreases systolic pressure and thus pulse pressure

Patent ductus arteriosus - connection between aorta and pulmonary artery causes increased systolic pressure and decreased diastolic pressure

Aortic regurgitation causes similar but larger effects

Systolic and diastolic blood pressure increase with age due to change of the pressure control mechanisms

Two main control mechanisms change with age:

1) Kidney, long term regulation of the blood pressure

2) Arteries, decrease elasticity -> increase in systolic blood pressure

Central venous pressure is the pressure in the right atrium, normally = 0 mmHg

Regulation: balance between the heart’s ability to pump the blood out of the right atrium and ventricle into the lung and the flow back of the blood from peripheral veins into the right atrium

1) Increased blood volume

2) Decreased ability of the heart to pump the blood

3) Increased vessel tone -> increased peripheral venous pressure

4) Dilatation of the arterioles -> decreases the peripheral resistance -> increased flow of the blood from arteries to veins

1) Decreased blood flow into the heart

2) Increased pumping of the blood by the heart

The pressure results from the weight of the blood

Venous Pressure (mmHg):

right atrium = 0

veins of the feet = 90

veins inside the skull = -10

Arterial pressure (mmHg):

Heart level = 100

Arteries of the feet = ~ 190

Arteries inside the skull = 90