Category Zoology

When does the heart stop beating?

Your heart is a muscular pump that never stops beating. It has its own timing device that produces tiny electrical signals. These signals cause the heart muscle to contract rhythmically. The pump on the right side of the heart receives blood that has been pumped around the body. This blood is dark red and has used up most of its oxygen. The right pump sends it on a short circuit through the lungs that surround the heart. The blood comes back bright red and rich in oxygen, to the heart’s left side, ready for its journey around the body. When the heart stops beating, body tissues no longer receive fresh blood carrying oxygen and nutrients. So life ends.

However, in a hospital, the cardiopulmonary machine can take over the job of heart and lungs. This means doctors can resuscitate people or carry out operations on the heart, such as replacing diseased valves.

Fact File:

When the body is very active, the heart can pump 20 gallons of blood each minute. That would fill a bathtub within two minutes.

 

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When do people get heart attacks?

Your heart is a powerful muscle which pumps blood around your body. It is only the size of your fist and weights less than half a kilogram. Each and every day it pumps about 18,000 litres of blood around your body, and yet you are not normally aware that it is even beating. Run quickly upstairs, though, and you will soon feel it thumping away inside your rib cage.

A heart attack can occur when either or both sides of the heart are unable to pump sufficient blood to meet the needs of our body. Other prominent causes of a heart attack are abnormally high blood pressure (hypertension), coronary atherosclerosis (the presence of fatty deposits in the lining of the coronary arteries), and rheumatic heart disease.

A person with left-sided heart failure experiences shortness of breath after exertion, difficulty in breathing while lying down, spasms of breathlessness at night, and abnormally high pressure in the pulmonary veins. A person with right-sided failure experiences abnormally high pressure in the systemic veins, enlargement of the liver, and accumulation of fluid in the legs. A person with failure of both ventricles has an enlarged heart that beats in gallop rhythm – that is, in groups of three sounds rather than two.

Fact File:

An electrocardiogram, or ECG, measures the electrical signals that the heart produces as it beats. These signals change when a person is suffering from certain medical conditions that affect the heart.

 

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When was Haemophilia discovered in the royal line?

Haemophilia  is an inherited deficiency whereby the substance necessary for blood clotting is missing. The transmission of this condition is sex linked, being present mostly in males but carried solely by females. Sons of a haemophilic male are normal, but daughters, although outwardly normal, may transmit this deficiency to half their sons.

The existence of haemophilia in certain royal families of Europe is well known. Working from family trees it seems probable that Queen Victoria naturally produced the gene for haemophilia.

Fact File:

When we look at other human bodies, we usually concentrate on the face. Our features are largely inherited, under control of the gens, which is why we resemble our parents.

 

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When were genes discovered?

In the 1800s a monk named Gregor Mendel experimented with characteristics in pea plants by cross-fertilizing plants with different traits. He kept a careful track of the traits displayed by the pea plants produced by cross-fertilization, discovering that the characteristics from the parent plants were inherited by the progeny (off-spring) plants in specific patterns.

Mendel also discovered during his experiments that certain genes seemed more dominant than others. For example, if a pea with a white flower is cross-fertilized with a pea with a pink flower, the resulting flowers will all be pink.

This is clear in human beings. A parent with brown-brown genes produces only children with brown eyes, while a parent with brown-blue genes could produce children with eyes other than brown.

Fact file:

Chromosomes are tiny threads that are present in all cells apart from red blood cells. They contain all the information for an entire person to develop. There are46 chromosomes in each cell. They come in 22 pairs, plus another special pair that determine the person’s sex.

 

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When does mitosis occur?

As well as being packed with information, the DNA of chromosomes also has the ability to reproduce itself. Without this, the cells could not pass on information from one generation to the other. The process of cell division in which the cell duplicates itself is called mitosis, which works as follows:

1 the chromosomes become shorter and the nuclear envelope breaks,

2 the chromosomes are released, which duplicate and attach themselves to a cytoplasmic network,

3 they are then drawn apart

4-7 to form two new cells with reformed nuclear envelopes.

Mitosis is absolutely essential to life because it provides new cells for growth and for replacement of worn-out cells. Mitosis may take minutes or hours, depending upon the kind of cells and species of organisms. It is influenced by time of day, temperature, and chemicals. Strictly speaking the term mitosis is used to describe the duplication and distribution of chromosomes, the structures that carry our genetic information.

Fact File:

DNA strands look like a twisted ladder. Sections of DNA are called genes. All the instructions for growing a new human being are coded into the DNA molecule.

 

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What is migration?

            Migration is a fascinating phenomenon that Nature repeats every year. It is the seasonal movement of some animals, from one place to another, year after year, usually across vast distances.

            Birds, fishes, mammals, insects and reptiles all migrate. Animals migrate for many reasons. It may be to find food, or to escape harsh weather. Some may travel thousands of miles in the spring, and then, thousands of miles back in the fall.

            Animals also migrate in search of better food supplies, or a safe place to give birth to their young. Such migrations happen on a regular basis. Irregular migrations are sometimes triggered by famine or over-population.

            The Arctic tern, the sea bird, travels from one end of the world to the other end every year! This is the longest migration undertaken by any bird. This bird flies in zigzagging routes between breeding grounds in the Arctic and Antarctica each year, a distance of around 70,900 kilometres. They will spend about four or five months in Antarctica, before heading back to the Arctic. Scientists have extensively studied the evolution of migration. But no single theory has been fully accepted.

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