THE HUMAN CIRCULATORY SYSTEM

Rosalie Crawford - Veronica RevelFondazione Liceo Linguistico Courmayeur

WHY???

• Why are we told not to go swimming for an hour after eating?

• Why is it important to warm up before doing any sport?

• Why do we turn red when we’re embarassed?• Why do we go pale when frightened?

BECAUSE…• the blood flow through our bodies is under

micromanagement, adapting and moving according to internal and external events.

Circulation The human circulatory or cardiovascular system is composed of :

THE HEART, situated on the left side of the thorax and

A NETWORK OF BLOOD VESSELS, of varying dimension (arteries, veins and capillaries), through which blood flows.

The heart pumps blood so that it flows into increasingly smaller blood vessels as far as single cells.

http://www.innerbody.com/anatomy/cardiovascular/upper-torso

Composition of our blood

Blood is composed of……

Plasma (55%), which is chiefly water where nutrients, waste products, ions, antibodies, hormones, enzymes, plasma proteins and other substances are dissolved or suspended.

Red blood cells or erythrocytes (45%) which transport oxygen to all the tissues of the body. There are about 25 trillion (25 x 10¹²) red blood cells in the adult human body. Because red blood cells, lacking a nucleaus, cannot repair themselves, their life span is short, about 120-130 days. At this moment in our bodies, about 2 million red blood cells are dying per second!

Blood is composed of……

• White blood cells or leukocytes and platelets (<1%) which defend the body against invaders such as viruses and bacteria. They are colourless, contain no hemoglobin, have a nucleus and are often destroyed in the course of fighting infection. New white blood cells are formed constantly in the spleen, in bone marrow and in certain other tissues.

• Platelets play an essential role in initiating the clotting of blood and in plugging breaks in the blood vessels.

The function of blood

Transports-nourishment from digestion and hormones from glands.

-oxygen from the lungs to body tissue

-carbon dioxide from body tissue to the lungs

-disease fighting substances to the tissue and waste to the kidneys

Regulates-pH levels

-blood and pulse pressure (heart rate)-body temperature- water and saline levels

Protects -the immune system--emostasi

The structure of blood vessels

Types of blood vesselshttp://www.bbc.co.uk/schools/gcsebitesize/pe/appliedanatomy/0_anatomy_circulatorysys_rev1.shtml

ArteriesCarry oxygenated blood away from the heart (except for the pulmonary

artery which goes to the lungs)

Have thick muscular walls

Have small passageways for blood (internal lumen)

Contain blood under high pressure

Arterioles Smaller arteries, have thinner walls and a reduced layer of muscle

VeinsCarry de-oxygenated blood to the heart (except for the pulmonary vein

which goes from the lungs to the heart)

Have thin walls

Have larger internal lumen

Contain blood under low pressure

Have valves to prevent blood flowing backwards

Types of blood vesselsCapillariesFound in the muscles and lungs

Microscopic – one cell thick

Very low blood pressure

Where gas exchange takes place. Oxygen passes through the capillary wall and

into the tissues, carbon dioxide passes from the tissues into the blood

DID YOU KNOW THAT…?

» The total length of capillaries in a human adult is more than 80,000 kilometres.

» No cell in the human body is farther than 130 micrometres – a distance short enough for rapid diffusion – from a capillary.

» Even the cells in the walls of the large veins and arteries depend on capillaries for their blood supply, as do the cells of the heart itself.

Anatomy of the human heart and systematic circulationBlood returning from the systematic circulation through the superior and inferior venae cavae enters the right atrium and passes to the right ventricle, which propels it through the pulmonary arteries to the lungs, where it is oxygenated. Blood from the lungs enters the left atrium through the pulmonary veins, passes to the left ventricle and then is pumped through the aorta to the body tissues.http://www.bbc.co.uk/schools/gcsebitesize/pe/appliedanatomy/0_anatomy_circulatorysys_rev2.shtml

Regulation of heartbeat

• The contraction of cardiac muscle is initiated by a special area, the sinoatrial node, located in the right atrium. Acting as a pacemaker, this region of tissue can spontaneously initiate its own electrical impulse.

• Intercalated disks conduct electrical impulses across the heart to the right atrium (the atrioventricular node). From here, impulses are carried by special muscle fibres (bundle of His) to the walls of the right and left ventricles, which then contract almost simultaneously.

• As a consequence, there is a delay between the atrial and ventricular contractions, ensuring that the atrial beat is completed before the beat of the ventricles begins.

Regulation of heartbeat

• When impulses travel across the heart, electric current generated on the heart’s surface is transmitted to body fluids and thus to the body surface. Electrodes placed on the skin and connected to a recording instrument can measure the heart’s ability to initiate and transmit impulses.The output is an electrocardiogram.

• Parasympathetic stimulation has a slowing effect on the pacemaker and therefore decreases the rate of heartbeat.

• Sympathetic nerves stimulate the pacemaker, increasing the rate of heartbeat.

• Adrenaline affects the heart in the same way as stimulation by the sympathetic nerves.

Blood flow

• As blood flows through the circulatory system, its pressure gradually drops as a consequence of the resistance of arterioles and capillaries. Thus, blood pressure is not the same throughout the body. It is highest in the aorta and other large systematic arteries, much lower in the veins and lowest in the right atrium.

• Veins, with their relatively thin walls and large diameters, offer little resistance to flow and allow blood to return to the heart despite its low pressure.

• Valves in the veins prevent backflow. • The return of blood to the heart is enhanced by the

contractions of skeletal muscles

How is blood pressure measured?Your blood pressure is measured with a device that uses the pressure in the artery to push up a coloumn of mercury and registers two numbers.

The first number, which is higher, is taken when the heart beats during the systole phase. The second number is taken when the heart relaxes during the diastole phase. A column of mercury rises and falls with the beat of the heart. The height of the column is measured in millimeters. Normal blood pressure in a young adult is about 120 mm of mercury when the ventricles are contracting (systolic pressure) and 80 mm when the ventricles relax (diastolic pressure).

The greater the blood pressure, the greater the rate of flow. Similarly, the larger the diameter of the vessel, the larger the volume of blood that can flow through it.

Diseases of the heart and blood vessels

Cardiovascular diseases cause 18.65% of all deaths in Italy.

A heart attack is the result of an insufficient supply of blood (ischemia) to an area of heart muscle. A heart attack can be caused by a blood clot – a thrombus – that forms in the coronary arteries, the blood vessels that supply the heart itself. Or it can be caused by a wandering clot – an embolus – that forms elsewhere in the body and travels to the heart and lodges in a coronary artery. Thirdly, by a blockage of a coronary artery due to artherosclerosis

• Look at these statistics from the World Health Organization

http://www.nationmaster.com/graph/hea_hea_dis_dea-health-heart-disease-death

Diseases of the heart and blood vessels

• Angina pectoris is a similar condition whose symptoms, like those of a heart attack, are pain in the centre of the chest, between the shoulder blades of the back and often in the left arm and shoulder.

• A stroke is caused by interference with the blood supply to the brain which may be caused by a thrombus, an embolus or the bursting of a blood vessel in the brain.

• Atherosclerosis contributes to both heart attacks and strokes. This disease occurs when the linings of the arteries thicken due to the accumulation of abnormal smooth muscle cells, and their inner surfaces become roughened by deposits of cholesterol, fibrin and cellular debris.

• Hypertension- chronically increased arterial blood pressure-affects 15 million people in Italy. It places additional strain on the arterial walls and increases the chances of emboli.

Regulation of blood cholesterolHow does cholesterol cause heart

attacks?

The key organ in cholesterol regulation is the liver which not only synthesizes needed cholesterol from fatty acids but also degrades excess cholesterol circulating in the blood as a result of a diet rich in meat, cheese and egg yolks. Like other lipids, it is insoluble in plasma. Low density lipoproteins (LDLs) function as the delivery trucks, transporting cholesterol to various destinations in the body, including the liver and hormone synthesizing organs.

Regulation of blood cholesterol• Normally the system is in

balance. However, a number of factiors can throw it out of balance.

• If the dietary intake of cholestreol is high, the liver becomes flooded and cannot degrade all of the excess. If the quantities of LDLs taken up by the cells are high – a sign that blood cholesterol levels are high – the cells stop synthesizing cholesterol.

• When the quantities of circulating LDLs are greater than can be absorbed by the liver and hormone-synthesizing organs, they are taken up by cells lining the arteries supplying the heart. This can lead eventually to a total blockage of an artery and thus to a heart attack.