Cardiovascular System

Anatomy of the Cardiovascular System

Structure

  • Composed of the heart, blood vessels and blood

Function

  • Transport essential materials throughout the body to cells

    • Oxygen

    • Fuel molecules

    • Hormones, etc.

  • Collects waste materials generated by the body's metabolic activity

    • CO2

    • Lactate (lactic acid)

    • Urea, etc)

Divided into 2 second

Pulmonary circuit

  • Blood vessels going to and from the lungs

  • The right ventricle pumps through this circuit

Systemic Circuit

  • Blood vessels going to and from the rest of the tissues of the body

  • The left ventricle pumps through the systemic circuit

Heart

  • Has 4 chambers that are muscular pumps which propels blood

Atria

  • Two upper chambers of the heart

Ventricles

  • The two lower chambers

Septum

  • Divides the left and right sides, divides the two pumps

Walls of the ventricles

  • The wall of the left ventricle is thicker than the wall of the right because the systemic circulation is a much higher pressure system than the pulmonary circulation

  • Systemic circulation must force greater volumes of blood father through the body vs pulmonary circulation

Valves

  • Direction of blood flow through the heart is controlled by unidirectional valves

  • Prevents black flow

Heart Murmur

  • Valve in heart is damaged or doesn't close properly

  • The blood regurgitates causing a noise

Myocardium

  • Specificized type of muscle

  • Cardiac muscle

  • All fibers or cells in cardiac muscle are interconnected - functional syncytium. Individual cells work together with adjacent cells for coordinated action

  • When one fiber contracts, all fibers contract

  • Fibers of the atria are electrically separate from the fibers of the ventricles

  • Heart contracts in sync, cardiac muscle must all fire

Intercalate disk with gap junctions

  • Link cells together. Major portal for cardiac cell to cell communication, required for coordinated muscle contraction and maintenance of circulation

Conduction System of the Heart

Heart's inherent contractile rhythm originates in an area of specialized tissue located in the posterior wall of the right atrium

SA Nodes

  • Has autorhythmic cells, spontaneously firing

  • Fire at set frequency

  • Normal pacemaker of the heart

Path way of conduction of the wave of depolarization

Atrial muscle fibers > contraction of atria > Internodal pathway (only electrical connective atria to ventricle) > AV node > AV bundle > left and right bundle branches > Purkinje fibers travel throughout the ventricles > simultaneous contraction of the left and right ventricle

Delay of the AV Node

  • Delay in wave of depolarization is delayed to give the atria time to contract and empty their contents into the ventricles

Electrocardiogram (ECG)

  • Record the wave of depolarization as it passes across the heart using electrodes on the surface of the body

Components of a normal ECG Wave

P Wave

  • Atrial depolarization

QRS Wave

  • Represents ventricular depolarization

T wave

  • Represents ventricular repolarization

Arrhythmias

  • Irregularity in the rhythm of the heartbeat

Diagnosing arrhythmias

  • Look at heart rate, amplitude and shapes of the components of the ECG waveform and the time intervals

Tachycardia

  • HR is faster than normal

Bradycardia

  • HR is slower than normal

Fibrillation

  • ECG is disorganized

Atrial Fibrillation

  • Atria reacts irregularly, heart is still functional as a mump

  • Needs a pace maker

Ventricular fibrillation

  • Ventricle beats irregularly

  • Heart doesn't function as an effective pump

  • Can't bring enough blood to the brain/body

  • Must defibrillate to reset electrical activity

Blood Supply to the Heart

Heart is suppled by 2 major arteries which originate from the aorta above the aortic valve

  • Left coronary artery

  • Right coronary artery

The large veins of the heart converge and empty into the right ventricle

Cardiac muscle is higher dependent on aerobic metabolism, it must have a rich blood supply

At rest

  • Normal blood flow to the myocardium is 4% of the total cardiac output

During exercise

  • Heart stays at 4% of cardiac output but cardiac output increases with exercise which increases the flow of blood to the heart

70-80% of the oxygen is extracted from blood flowing in the coronary vessels compared to the average 30% in other tissue

Blood Vessel

Arteries

  • Blood vessel that carry blood away from the heart. Range in size from the aorta which is 35mm in diameter to arterioles that are 0.5mm

Large arteries > medium-sized arteries > small arteries > arterioles, less elastic tissue in the wall of the artery and more smooth muscle

Total Blood volume: 5L

Arterioles

  • Arteries under 0.5mm in diameter

  • Contracting or relaxing the thick layer of smooth muscle in the walls of arterioles, blood flow can be increased or decreased to various capillaries

  • During exercise

    • Arterioles leading to working muscles are dilated, directing blood flow to active muscle where oxygen and fuel for contraction are required.

  • Arterioles and arterioles constitute the high pressure part of the circulatory system

Capillaries

  • Tiny, thin walled vessels. Site of exchange of nutrients and gases between blood and tissues

All other organs of the circulatory system exist only to serve the capillary beds

Very large surface area and length = 6000 square meters, 100,000km long and twice the mass of the liver

Venules

  • Small vessels which conducts venous blood from capillaries to veins

  • Pressure is lower compared to arteriosus side

Veins

  • Vessels that convey blood to the heart, thinner-walled than arteries

  • Both superficial and deep veins

  • Also have smooth muscle which allow them to change their diameter

Venules and veins constitute the low-pressure part of the circulatory system

Pulse pressure

  • Difference between the systolic and diastolic pressure readings in arteries

Systolic Pressure

  • Pulse pressure

Diastolic Pressure

  • Relaxes

Valves

  • Found in veins which carry blood against the force of gravity, especially in the veins of the legs

Mechanisms involved in return of blood to the heart:

Pressure

  • Difference between left ventricle and right atrium

  • 120mm Hg- 3mm Hg = 117mm Hg driving pressure

Skeletal Muscle Pump

  • Active muscles squeeze the veins and push the blood towards the heart

Respiratory Pump

  • Decreased pressure in thoracic cavity during inspiration

  • Easier for blood to return from lower portions of body via inferior vena cava

  • Thoracic cavity

  • Right atrium of heart

Blood

Composed of specialized cells (red bloods cells, white blood cells and platelets) suspended in a liquid

plasma which makes up 50-60% of blood by volume

Blood volume

  • Blood volumed of an average adult with a normal body composition is about 8% of body mass

  • A person with a body mass of 70kg has a blood volume of 5.6L

  • Blood volume is greater for larger, more endurance trained and heat acclimatized people

Plasma

  • Composed of about 90% water and 10% solutes

Red Blood Cells (erythrocytes)

  • Biconcave discs about 7 microns in diameter

  • About 5 - 6 million RBC per cubic millimeter of blood

    • Hematocrit

      • The ratio of volume of blood cells to the total volume of blood, expressed as percentage

      • 37-47% in females and 42-52% in males

  • Continuously being formed in red bone marrows in the ends of long bones and flat bones >protect place to produce it

  • Lifespan is 120 days

  • Contains Hemoglobin

    • 4 subunits, each one contains one iron molecule

    • Transports oxygen and carbon dioxide

Values for hemoglobin

Men - 140-160g per 1L of blood

Women - 120-140g per 1L of blood

Blood doping

  • Increasing the RBC count and/or oxygen carrying capacity of the blood

  • Blood transfusion, EPO (stimulate products), synthetic oxygen caries

  • To increase RBC count: hypoxic Tents, altitude training

Gas Exchange and Transport

Diffusion

  • Molecules move from areas of high concentration to low, driven by concentration gradient

  • Movement of molecules across the respiratory membrane are driven but diffusion

Rate of diffusion is increased by

  • Higher concentration gradient

  • Shorter diffusion distance (thinner)

  • Higher temperature (more kinetic energy)

  • Greater surface area (more area to diffuse)

Two sites of gas exchange

  1. Alveolar-capillary membrane in lung

    1. Net diffusion of O2 from alveoli > blood

    2. Net diffusion of CO2 from blood > alveoli

  2. Tissue-Capillary membrane in tissue

    1. Net diffusion of O2 from blood > tissue

    2. Net diffusion of CO2 from tissue >blood

Gas Exchange

Partial pressure of gas

  • The pressure of a specific gas in a gas mixture is dependent on:

    • The total (barometric) pressure

    • The fractional concentration of that gas

Barometric pressure: measurement of air pressure in the atmosphere

At sea level

  • Total pressure of all dry ambient (atmospheric) air gases equals 760mm Hg which equals barometric pressure

Composition of dry ambient air at sea level

Gas

Concentration

Partial Pressure

O2

20.93%

0.2093 * 760 = 159.2 mmHg

N2

79.04%

0.7904 * 760 = 600.7 mmHg

CO2

0.03%

0.0003 * 760 = 0.1 mmHg

Total

100%

760.0 mmHg

Important factor for determining gas exchange is the Partial pressure (concentration) gradients of the gases involved

Sea level: O2 20.93%; 0.2093 * 760 = 159.2 mmHg

Mt. Everest O2 20.93%; 0.2093 * 225 = 46.9 mmHg

Ambient air vs tracheal air vs alveolar air

  • Partial pressure differences

The functional residual capacity servers as a damper so that each incoming breath of air only has a small effect on the composition of the alveolar air

  • Partial pressure of gases in the alveoli remains relatively stable

Partial Pressure of Gases in a liquid (blood)

Henry's Law

  • The amount of gas that dissolve in a fluid is a function of 2 factors:

  1. The pressure of the gas above the fluid, given by the gas concentration * the barometric pressure

  2. The solubility coefficient of the gas - CO2 is 20.3 times more soluble in water than O2

Lung Diffusing Capacity

Diffusing capacity for oxygen

  • Volume of oxygen that crosses the alveolar-capillary membrane per minute me mmHg between the alveolar air and pulmonary capillary blood

Besides partial pressure gradients, diffusing capacity can be affected by other factors

  1. Thickness of respiratory membrane - length of the diffusion path.

    1. Diffusing capacity is decreased in restrictive lung disease like pulmonary fibrosis or pneumonia

  2. Number of red blood cells or hemoglobin concentration or both

  3. The surface area of the respiratory membrane available for diffusion

    1. diffusing capacity is decreased in emphysema

Diffusing capacity can increase up to 3 times resting values during heac aerobic exercises

Mechanisms:

  1. Increase lung volumed during exercise > increase surface area for diffusion

  2. Opening up of more capillaries in the lung and greater volume of blood flowing through the lung

Gas Transport

Transport of Oxygen

  • 98% of the oxygen in blood is carried in red blood cells in chemical combination with hemoglobin

  • Hb + O2 > HbO2 = oxyhemoglobin

O2 carrying capacity of hemoglobin

  • 1g of hemoglobin becomes saturated when combined with 1.34mL of O2

If hemoglobin concentration is 15.0g per 100mL of blood then O2 carrying capacity of the blood would be

15.0g (Hb)/100ml (blood) * 1.34ml O2/g (Hb)

= 20.1 ml O2/100ml of blood

Percent saturation of hemoglobin with O2 (%SO2)

  • Related the amount of O2 actually combined with hemoglobin to the max O2 capacity of hemoglobin

Arterial blood at rest at sea level ( PB = 760 mmHg)

  • Hemoglobin is 97.5% saturated with O2

    • 97.5% * 20.1 = 19.5 O2 per 100ml blood

Venous blood at rest at sea level:

  • Hemoglobin is 75% saturated with O2

    • 75% * 20.1 = 15.1ml per 100ml blood

Arteriovenous oxygen different (a-v)O2

  • 19.5-15.1 = 4.4 ml O2 per 100ml blood

  • Represents how much oxygen is extracted or consumed by the tissues for each 100ml of blood perfusing them

Oxyhemoglobin (HbO2) Dissociation Curve

  • Plot the percent saturation of hemoglobin (%SO2) vs the partial pressure of oxygen (PO2)

  • Affinity

    • Attraction between particles

  • When the graph shifts Left , increased hemoglobin affinity for O2 meaning hemoglobin is less likely to release O2 into tissue

Hemoglobin acts as a tissue oxygen buffer system. The level of alveolar oxygen may vary from 60 mm Hg to more than 500 mm Hg, and still the PO2 in the tissue doesn’t vary more than a few mm Hg from normal due to the shape of the oxyhemoglobin dissociation curve. The flat portion of the curve in the upper right indicates that saturation does not change much down to about 60 mmHg of O2, below that, the curve becomes steeper, and saturation declines below 90% as there are further drops in O2.

Plateau portion : 60mm Hg- 100mm Hg

Steep portion: 0 - 40mm Hg

Bohr Effect

  • Increased body temperature, increase pCO2 and decrease pH shift at the oxyhemoglobin dissociate curve to the right

  • release more oxygen at the tissue for a given O2

Total Blood O2 = dissolved O2 +HbO2

In lungs, PO2 is high

  • Drives O2 exchange into plasma

  • High plasma PO2 drive O2 binding to Hb

In tissues PO2 is low

  • Drives O2 exchange out of plasma

  • Low plasma PO2 drives O2 release from Hb

PO2 – partial pressure of oxygen in ambient air 159 mm Hg

PAO2 - partial pressure of alveolar oxygen 104 mm Hg

Pa O2 – partial pressure of arterial oxygen for blood leaving the left ventricle - 95 mm Hg

PvO2 - partial pressure of venous oxygen 40 mm Hg

PCO2 – partial pressure of carbon dioxide in ambient air .1 mm Hg PACO2 - partial pressure of alveolar carbon dioxide 40 mm Hg

PaCO2 - partial pressure of arterial carbon dioxide 40 mm Hg

PvCO2 - partial pressure of venous carbon dioxide 45 mm Hg