Circulatory System

Cardiac, pulmonary and systemic circulationCardiac circulation:route taken by the blood to supply the heart. The heart is a muscle. It needs oxygen and nutrients and the removal of waste.

Pulmonary circulation:pathway of blood from heart to lungs and back

Systemic circulation:route from the heart to the tissues of the body and back

Coronary (cardiac) circulation

Circulatory facts:

• the average adult man has about 5 to 6 litres of blood, while the average woman has about 4 to 5 litres• of your blood right now 80 – 90 % is in systemic

circulation and the rest is in the pulmonary circulation• three main elements of the circulatory system:

• A - transport medium (blood)• B – transport vessels (arteries, arterioles, capillaries,

venules, veins)• C – pumping mechanism (heart)

Transport Vessels

3 main blood vessels:

arteries, capillaries and veins

• small artery = arteriole

• small vein = venule

ARTERIESARTERIES carry blood away from the heart. Arteries have muscular walls that have a lot of elasticity. They are able to expand when the heart pushes blood out of the heart, and then snap back as the ventricles relax and fill. This helps to direct blood flow in the right direction (away from the heart).

Arteries generally carry oxygenated blood, with the exception of the pulmonary artery, which carries deoxygenated from the heart to the lungs.

ARTERIOLES

ARTERIOLES are small arteries. As the arteries carry blood toward the tissues, the arteries reduce in circumference to become arterioles. This helps reduce the pressure of the blood as it comes to the capillary beds in the body tissues.

CAPILLARIES

These are the smallest blood vessels. Their diameter is just large enough to allow a red blood cell to pass through.The walls of capillaries are one cell thick. This allows materials to be able to diffuse rapidly through the cells to go into or leave the cells of the body.

A venule is a very small blood vessel that allows blood to return from the capillary beds to the larger blood vessels called veins. Venules are formed when capillaries unite (come together).Venules are blood vessels that drain blood directly from the capillary beds. Many venules unite to form a vein.

VENULES

VEINS

Veins are large blood vessels that return the blood to the heart to be pumped.

Veins have thinner walls than arteries, but have a larger inner diameter. They are not elastic, so the veins must rely on other mechanisms to ensure blood flows in the correct direction:

a. interior valves (one-way) that keep blood flowing against gravity

b. rely on contraction of skeletal muscles around the veins to keep blood moving in the correct direction.

Most veins carry deoxygenated blood, except the pulmonary veins.

VEINS

Vessel Name Direction of blood flow

O2/CO2 Exceptions valves walls Blood pressure

arteries Away from heart

high/low pulmonary artery

no thick, elastic, muscular

high

arterioles Same as arteries but smaller capillaries Start away

then to the heart, true whether in the systemic or pulmonary circulations

Starts high/low in systemic, but then becomes low/high after gas exchange in the systemic; opposite in the pulmonary circ.

no One cell thin. A rolled sheet of simple squamous

Very low

venules Same as veins but smaller

veins toward heart low/high pulmonary vein

Use unidirectional (one-way)

Thinner, not as elastic – that’s why people can get varicose veins or hemorrhoids – the walls get pushed out and can not spring back

Lower than arteries

Components of the blood• blood is considered a tissue because it is specialized to perform a set

of specific functions

• blood consists of two distinct elements: plasma and cells

• 55% is plasma, consisting of water, gases, proteins, sugars, vitamins, minerals, waste

• the remaining 45% is cells

• when centrifuged (separated), the three layers are (from least to most dense): plasma, white blood cells (leukocytes) and platelets, and red blood cells (erythrocytes)

PLASMAThis is the fluid portion of the blood. It is pale yellow and clear. The plasma is 92% water, 7% dissolved blood protein (albumin, globulin, fibrinogen), and 1% dissolved organic and inorganic materials.

Water – dissolves and transports materials

Plasma protein – albumin - maintain fluid balance in the body fibrinogen – important in blood clotting globulins – antibodies – important in immunity

Salts – maintain fluid balance, assist in nerve and muscle function, maintain alkaline pH (blood is slightly basic)

WHITE BLOOD CELLS (LEUKOCYTES)These cells play an important role in the immune function. They make up only about 1% of the total blood volume, but they multiply rapidly during infections.

Phagocytes (macrophages) – engulf and destroy pathogens (disease or illness-causing agents)

Lymphocytes – produce antibodies (proteins that incapacitate pathogens)

White blood cell

PLATELETS (THROMBOCYTES)These are fragments of cells that play a major role in blood clotting. Blood clotting is an important process that helps to prevent blood loss when a blood vessel is broken. It involves a complex series of steps.

Blood clotting• When a blood vessel is broken, chemicals are released from

cells that attract platelets.• Platelets break open releasing chemicals that combine with

some plasma proteins to make the enzyme thromboplastin.• In the presence of calcium ions (Ca2+), thromboplastin reacts

with prothrombin (a protein made in the liver) to produce the enzyme thrombin.

• Thrombin reacts with fibrinogen (plasma protein) to form fibrin – the insoluble protein that forms the mesh of a clot.

RED BLOOD CELLS (ERYTHROCYTES)These cells are specialized for oxygen transport. They have a disc-like shape that allows them to bend slightly as they move through capillaries. Erythrocytes have no nuclei and are packed with iron containing molecules called hemoglobin, to which the oxygen molecules bind chemically. The hemoglobin is also able to carry a small amount of carbon dioxide, though only about 10% of the total blood CO2 is carried this way.

Flow of blood through the heart – pt 1• Deoxygenated blood returns from the body tissues to the right

side of the heart through the superior vena cava and inferior vena cava.

• It enters the right atrium• It flows through the right atrioventricular valve (tricuspid)• Blood enters the right ventricle• When the right ventricle contracts, the right av valve closes

and the pulmonary semilunar valve opens• Blood is pushed up into the pulmonary trunk which branches

into 2 pulmonary arteries (right and left), which carries blood to the lungs

• Blood is oxygenated in the lungs

Flow of blood through the heart – pt 2• Oxygenated blood is carried back to the left side of the heart

by 2 sets of pulmonary veins (right and left)• Blood enters the left atrium• It flows through the left atrioventricular valve (bicuspid, or

mitral)• Blood enters the left ventricle• When the left ventricle contracts, the left av valve closes and

the aortic semilunar valve opens• Blood is pushed out of the left ventricle and into the aorta,

which carries it toward the body tissues

VasodilationVasodilation: The widening of blood vessels. Muscles in the walls of blood vessels relax so the blood vessels get bigger in diameter. This causes more blood to flow down these ones.

Conversely, bodies can “purposefully” lose heat from the extremities in hot weather by sending blood there due to vasodilation. Many dessert animals have huge thin ears with lots of blood vessels in them, that they vasodilate in the day to lose body heat so they don’t overheat.

VasoconstrictionVasoconstriction: The narrowing of blood vessels. Muscles in the walls of blood vessels contract so the blood vessels get smaller in diameter.

With the interplay of both of these, blood can be kept away from extremities in cold temperatures by vasoconstriction so heat is not lost (from the fingertips for example) and can be kept closer to the middle of the body by vasodilation in central body parts so it stays where it is warmer and further away from the cold outside.

Control of Heartbeat

The heartbeat that you can hear (the "lub-DUB" sound) can be divided into 2 phases.

1. the atria contract (the "lub" part) while the ventricles are relaxed.2. then the ventricles contract (the "-DUB" part) while

the atria relax.The actual sound you hear is caused by the vibrations of the heart when the valves close.

"lub" = closing of atrioventricular valves"DUB" = closing of the semi-lunar valves.Beating heart animation

Control of Heartbeat

Systole: Heart contraction – pushing blood out of the ventricles.

Diastole: Heart relaxing – ventricles filling with blood.

DiastoleUnder the control of the medulla oblongata, the sinoatrial (SA) node releases electricity at a rate of 60 – 100 times per minute at rest. This electricity moves through the right atrial and left atrial muscle tissue, causing them to contract. This causes blood to move into the ventricles as the atrioventricular valves open

Control of Heartbeat

SYSTOLEThe wave of electricity then reaches the atrioventricular (AV) node found just above both ventricles, where it jump starts it to send out its own electrical signals at the same rate.

These signals move down the Bundle of His, which traverses through the interventricular septum. This insulated bundle of nerve fibres moves the electrical signal to the bottom of each ventricle, where the fibres become uninsulated and are now called Purkinje fibres. These fibres allow the electrical signal to leak out into the cardiac muscle of each ventricle, starting at the bottom. The wave of electricity spreads upwards. The blood is pushed up into the aorta (from the left ventricle); and into the pulmonary artery (from the right ventricle).

Blood pressure

Blood pressure is caused from blood pushing outwards on the inside wall of arteries (and veins and other tubes - but measured mostly in arteries).

.

Measuring blood pressureMeasuring blood pressure. An inflatable cuff is wrapped around the upper left arm of a person, while a stethoscope is placed over the brachial artery pulse. The cuff is inflated to about 220 mmHg. This is enough pressure to stop blood flowing down the brachial artery. Then while watching the pressure monitor, the cuff is deflated slowly until you can hear a thud or tapping noise in the stethoscope. This is the sound of blood getting past the constriction caused by the cuff. As soon as you can hear this that means the pressure in the cuff at that time is the same as the pressure in the artery. This is called the SYSTOLIC BLOOD PRESSURE. It is normally 120 mmHg at rest. The cuff is continued to be deflated while watching the pressure monitor, until the sound of the blood in the brachial artery tapping on the stethoscope changes a lot, or stops completely. The number on the pressure monitor at this time is the DIASTOLIC BLOOD PRESSURE. It is normally 80 mmHg

High blood pressure (Hypertension)

HYPERTENSION (High blood pressure) is caused due to two main reasons. 1) too much fluid in the tubes

a) may be due to problems with kidneys causing less than normal amounts of urine (which used to be fluid in the blood) to be eliminated.

b) eating too much salt, causing fluid to stay in the blood or move into the blood because of osmosis

2) tubes are too narrow, or too hard and not elastic enougha) some hormonal problems causing too much vasoconstriction at the wrong

timesb) narrowing of the blood vessels from constant vasoconstriction –

cigarette smoke can cause thisc) hardening of the arteries (becoming less elastic) due to a build up of cholesterol in

the inside wall of the arteries. This can be a dietary issue, but also can be genetic.

Hypertension is dangerous because it forces the heart to work harder to pump blood around the body and it can also rupture blood vessels.

Arteriosclerosis

Literally artery (arteri) combined with (o) hardening (scler) and condition of (osis)

Often caused by the build up of cholesterol and other fatty deposits that then become hardened with.