B9 Transport in Animals

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9.1 Circulatory System

The circulatory system is a system of blood vessels with a pump and valves to ensure one-way flow of blood.

The single circulation of a fish

One function of the blood is to carry oxygen. This occurs at what is known as the animal's respiratory surface. In fish, this is provided by the gills.

Blood is pumped by the heart to the gills

It picks up oxygen

It travels under relatively low pressure, distributing oxygen to all the internal organs

It returns to the heart containing carbon dioxide

The heart pumps the blood under pressure to the gills where it loses its carbon dioxide and picks up a fresh supply of oxygen

In one circulation of the body, the blood therefore passes once through the heart and the fish is said to have a single circulation

Double circulation

During one complete circulation of the human body, blood travels twice through the heart.

Once on its way to the lungs after having arrived in the heart from the other organs in the body

Once on its way to the other organs having arrived from the lungs

The heart is divided into two halves. The right side deals with de-oxygenated blood an the left side deals with oxygenated blood.

Since the distance the blood has to travel to reach the lungs is short in comparison with how far it may travel in order to reach other parts of the body, blood leaving the heart in the lesser circulation ( to the lungs ) is not under so much pressure.

A double circulation ensures that oxygenated blood is sent quickly, under high pressure, to all the organs of the body.

It is also quickly returned to the heart and then to the lungs to lose its carbon dioxide and become fully oxygenated again.

There is no mixing of oxygenated and de oxygenated blood

Double circulation advantages

Double circulatory systems have advantages over single circulatory systems. When blood flows through a fish gills or a mammals lungs, it loses a lot of pressure that was given to it by the pumping of the heart. In a mammal however this low pressure blood is delivered back to its heart which raises its pressure again before sending it off to the rest of the body. In a fish, though, the low pressure blood just travels through the body,this means blood travels much slower in a fish than in a mammal.

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9.2 The heart

Key facts about the heart :

It is a muscular pump

Has four chambers, two atria on top and two ventricles on the bottom

Atria receive blood in veins

Ventricles have thick muscular walls to pump the blood out of the heart into the arteries under pressure.

The left ventricle has the thickest walls because it sends blood around the whole body. The blood is first pumped into the aorta, which takes blood around the body

The right ventricle pumps blood into the pulmonary artery, which takes it to the lungs.

A system of valves ensure one way flow of blood through the heart

When the ventricles contract, the mitral (aka bicuspid) and tricuspid valves are slammed shut. ( this causes the lubb sound of the heart bead)

The heart muscle then relaxes and as the ventricles do so, the semi-lunar valves close to stop blood being drawn back into the ventricles. ( this causes the dupp sound of the heart beat)

The left and right sides of the heart are separated by a wall called a septum to ensure oxygenated and de oxygenated blood do not mix

blood is pumped away from the heart into arteries and returns to the heart in veins

The heartbeat

When the heart beats, a wave of contraction passes through the heart from the atria to the ventricles. It is triggered by electrical impulses from a structure in the wall of the right atrium made of muscle and nerve endings called the pacemaker. The atria contract before the ventricles.

During one heart beat ( or cycle ) the following happens

The walls of the atria contract

Blood passes into the ventricles through the tricuspid and bicuspid valves that are forced open by the pressure of the blood

The ventricles contract

Blood pressure closes the tricuspid and bicuspid valves and opens the semi-lunar valves

De oxygenated blood is forced out of the right ventricle and travels to the lungs via the pulmonary artery

At the same time, oxygenated blood is forced out of the left ventricle and sent off round the body in the aorta

The atria relax, drawing a fresh supply of de oxygenated blood from the venae cavae into the right atrium and oxygenated from the pulmonary vein into the left atrium

The ventricles relax ready to receive blood from the atria

Monitoring the activity of the heart

There are various ways to check if the heart is beating normally

Feeling the pulse. This gives an idea of how strongly & quickly the heart is beating. (the average rate in an adult human is 70 beats per minute)

Listening for the sounds of valves closing. If you can hear another sound accompanying the normal 'lupp-dupp' sound, the valves may not be closing properly, allowing blood to leaf into the atria or ventricles. This additional sound is called a heart murmer

By taking a ECG. This is a recording of the electrical impulses that control the contraction of the heart muscles and can detect abnormalities that may need to be treated via drugs or surgery.

The effect of exercise on the heart

The heart beats quicker during exercise because use of muscles during exercise increases the amount of carbon dioxide in the blood.

Higher levels of carbon dioxide in the blood are detected by the part of the brain that controls heart rate; it responds by stimulating the pace maker situated in the heart muscle to increase the rate at which it sends out impulses to the muscles that surround it. The heart thus beats faster. Other factors also increase the heart rate including a higher pressure of blood reaching the heart and an increase in the hormone adrenaline in the bloodsteam. The faster heart rate ensures:

Faster removal of extra carbon dioxide from the blood travelling to the lungs

A faster rate of uptake of oxygen to supply the increased activity in the muscles

a more rapid supply of glucose to muscle cells for greater energy release during increased respiration

Coronary heart disease

The heart muscle needs a constant supply of nutrients and oxygen so that it can continue to contract and relax. The coronary artery supplies this.

If the coronary artery gets blocked, then the cardiac muscle will run short of oxygen. They cannot respire, and therefore cannot obtain energy to allow them to contract. The heart therefore stops beating. This is called cardiac arrest ( heart attack ). Blockage of the coronary heart disease or CNS.

To decrease the risk of heart disease take the following precautions, especially if there is a history of heart disease in you family as deficiencies affecting the heart are often inherited:

Restrict intake of animal products containing fat, as they deposit on the artery walls - restricting blood flow.

Avoid obesity - puts extra strain on the heart

Do not smoke - nicotine encourages the depositing of fat on the artery walls

Settle for a less stressful life-style - stress causes the release of raised levels of the hormone adrenaline which constricts artery walls which may already be partially blocked, further increasing blood pressure.

Take regular exercise

Exercise and heart disease

A large proportion of the fats found in meat and meat products are known as saturated fats and cholesterol. With time, saturated fats and cholesterol build up on the walls of our arteries forming atheroma, and causing occlusion of the blood vessel ( block the flow of blood ). If this happens in the coronary artery it prevents oxygen reaching the heart muscle, cuasing a heart attack.

Activities that raise the heart rate are recommended in order to maintain a healthy heart

The treatment of heart disease

Drugs

Drugs (heparin, warfarin and aspirin) may be used to prevent or break down blood clots clocking the coronary artery. 'ACE inhibitors' help widen blood vessels supplying the heart, decreasing blood pressure. Other drugs can be given to correct the rate and rhythm the heart beats

Surgery

The most common forms of heart surgery are

Inserting a small balloon into the coronary artery, then inflating it to stretch the walls of the artery allowing blood to flow more easily

Placing a stent (wire cage) into the coronary artery to hold it open

Performing a bypass operation in which a blood vessel is used to divert blood round the blocked part of the coronary artery. In extreme cases a heart transplant may be needed if a suitable donor is available.

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9.03 Blood and lymph vessels

Arteries

Arteries take oxygenated blood with blood sugar and other materials to all organs - must maintain blood pressure so it can reach, the thick muscular walls help to maintain this pressure.

Blood leaves the heart in arteries - vessels with thick muscular walls to withstand high pressure of blood

The largest artery us the aorta

A small artery is called a arteriole

Veins

Blood returns to the heart under much lower pressure in thinner walled vessels called veins

Veins carry blood that has lost its pressure after passing through capillaries. They rely on their one-way semi lunar valves and on their thin walls to allow the effect of muscular contractions to be passed to blood within pushing it from one set of valves to the next.

The largest vein is the vena cava

Small veins are called venules

Capillaries

Blood passes from arterioles to venules through microscopic blood vessels called capillaries

Path of blood

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9.04 Blood

Blood is made up of four basic components

Red blood cells

Their role is to transport

White blood cells

Platelets

Plasma