What does the cardiovascular system do?

The cardiovascular system (CVS) consists of the heart, lungs and blood vessels. It is responsible for transportation of vital nutrients, gases and hormones throughout the body. The heart functions as the central pump with the blood vessels the pipes of the body. The CVS is controlled by a number of internal and external systems, which keep the CVS in balance with the needs of the body.

The heart is a pear shaped organ positioned centrally within the chest cavity with the apex extending over to the left nipple.  The heart is a divided into a right and left side, each side has an atrium and ventricle.  Heart valves and the contraction of the heart muscle control blood flow through the heart. The right side receives de-oxygenated blood from the major veins of the body and pumps this blood into the lungs.  The left side of the heart then receives oxygen rich blood from the lungs and pumps this blood into the Aorta and arteries of the body.  This pumping action is a complex well-coordinated activity that cannot be fully explained here.    The heart receives its blood supply via the left and right coronary arteries. 

Poor or abnormal function of the cardiovascular system

May be a result of:

• Insufficient blood supply due to dehydration, bleeding or swelling;
• A poor blood supply to the heart, where there is not enough oxygen and other nutrients for its work;
• Poor lung function or obstruction to blood flow in the lungs, which places a strain on the heart muscle;
• Too many or too few electrolytes (eg. potassium, magnesium) that cause irregular heartbeats or dangerous rhythms in the heart.
• Weakness of blood vessel walls.
• Heart muscle weakness

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Shock has different causes.

Shock caused by a loss of large amounts of blood or body fluids is known as hypovolaemic shock. It occurs in serious accidents, with major surgery, in burns and with medical conditions where there is severe vomiting and diarrhoea. The patient’s heart will pump faster to try and compensate for the decreased blood volume. This is seen as a high heart rate or pulse. This is called tachycardia.

Shock due to heart muscle damage is known as cardiogenic shock. It can occur as a result of a heart attack or when the heart muscle has a severe infection. The damaged heart muscle often results in abnormal heart rates. The heart may beat too fast (tachycardia) or too slow (bradycardia). Drugs (inotropes) may be needed to help the heart muscle to pump with more force.

Shock caused by severe infection is known as septic shock. Septic shock is triggered by the body’s reaction to the toxins (poison) released by the bacteria into the blood. In severe septic shock blood vessels may dilate or constrict. Drugs (vasoconstrictors) can be used to narrow the blood vessels whilst other drugs (vasodilators) can be used to open the blood vessels.

Shock caused by a severe allergic reaction is known as anaphylactic (pronounced: ‘ana-fil-actic’) shock. In a severe allergic reaction the small blood vessels known as capillaries ‘leak’ fluid and the blood vessels dilate. Usual treatment for this type of shock includes adrenaline.

Shock caused by damage to the nervous system (brain or spinal cord) is known as neurogenic shock (also called ‘spinal’ shock). The (autonomic) nervous system keeps the muscles of blood vessels slightly contracted, when a part of this system is damaged, those blood vessels lose the ability to constrict and instead they dilate causing shock.

Severe shock requires admission to an intensive care unit. Doctors will monitor the blood pressure via an arterial line and the heart rate by a cardiac (heart) monitor. If more technical monitoring is required doctors can use measuring devices such as a central venous pressure (CVP) line, a pulmonary artery (PA or Swan-Ganz) catheter or a peripherally introduced continuous cardiac output (PICCO) monitor.

Medical treatment includes:

1. Oxygen (either by mask or ventilator). Fluids – given into veins located peripherally (arm or leg) or centrally (neck, chest, groin). Fluids that can be given include:
   • Crystalloids – salt, water and electrolyte solutions
   • Colloids – ‘plasma’ like solutions
   • Blood and blood products
2. Drugs – to restore abnormal body functions.
   1. Inotropes – to assist the heart to pump with more force at the right rate
   2. Vasodilators – to open up blood vessels
   3. Vasoconstrictors – to narrow blood vessels
   4. Antibiotics – to fight infection caused by bacteria
3. Surgery – to control bleeding (haemorrhage) due to severe injuries