Category Human Body

What are tissues?

Millions of cells that do the same job are grouped together into tissues, so they can be put to work by the body. There are many different types of tissue, for example muscle tissue. Muscle is built up from millions of thread-like muscle cells.

What do cells need to survive?

Cells need food, oxygen and a watery environment in order to survive. Food and water are supplied by the blood and other body fluids, which also carry away wastes. Blood also contains all of the food substances and chemicals needed by the cell.

What are organs?

Organs are made up from different types of tissue that are grouped together to carry out a particular body function.

The heart, for example, is a collection of muscle tissue, connective tissue and nervous tissue. These tissues work together to pump blood around the body.

Different types of organs are in turning grouped together to form systems, such as the circulatory system. It includes the heart and all the body’s blood vessels. The digestive system includes the mouth, gullet, stomach and intestines, while the nervous system includes the brain, spinal cord and nerves extending throughout the body. The human body also has a skeletal system, a muscular system, an endocrine system (glands), a respiratory system, a urinary system and a reproductive system.

What is the body made of?

More than half of the human body is made of water. The rest of the body is built from a huge number of complicated chemicals. These chemicals, together with water, are assembled into tiny building blocks called cells. Each cell is self-contained and has a particular function in the body. There are more than 50,000 billion cells in your body.

What do cells look like?

The shape and appearance of a cell depends on what job it does. Nerve cells are long and thread-like so they can carry messages around the body along the nervous system. Red blood cells are like flattened discs that are pinched in at the centre. White blood cells are shapeless so they can squeeze between other cells and attack invaders such as bacteria.

What’s inside a cell?

Cells consist mostly of a watery jelly-like material called cytoplasm. Each cell is held together by a very thin flexible membrane, rather like a balloon filled with water inside the cell the cytoplasm is organized into special areas called organelles. These control the functioning of the cell, for example, the production of essential substances called proteins. Tiny grains called mitochondria use oxygen to break down food and release the energy that powers the cell. An area called the nucleus contains 46 thread-like chromosomes that control the working of the cell. Some cells, such as those lining the intestines, only live for a few days, while other nerve cells within the brain can survive throughout your entire life.

The coccyx is the lower end of the spinal column of man and consists of four nodules of bone, like tiny vertebrae, corresponding to the tail, which is found in lower animals. The bones are deeply buried in muscle tissue, but occasionally they jut backwards and are surrounded by a fold of skin, so as to form an actual tail.

    The name coccyx was given by the Greek physician Galen (c. A.D. 130-200) and free comes from the Greek word for “cuckoo”, as the bone rather resembles a cuckoo’s bill.

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Cardiac pacemakers are used by sufferers from “heart-block”. They do the work normally performed by the body’s natural pacemaker in controlling the rate and rhythm of the heart beats. This natural pacemaker is a small collection of specialized nervous tissue situated at the base of the heart. It forms the starting point for the impulses that initiate the heartbeats.

    “Heart-block” is a serious condition in which the conducting mechanism between the cavities of the heart (atrium and ventricle) is impaired or destroyed. When this happens, the atrium and ventricle beat at different rates independently of each other because the impulse from the pacemaker is not reaching all parts of the heart. Fainting, convulsive attacks or complete stoppage of the heart may follow, but the condition can be overcome by the use of an artificial pacemaker.

      This acts as a battery to stimulate the heart, allowing it to beat regularly at normal speed, about 70-80 impulses a minute. The pacemaker is either fixed to the outside of the chest or implanted in the armpit and connected to an electrode tube, which is passed through the main vein in the neck into the heart.

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Muscles are the body tissue which, because it has the power of contraction, enables the higher animals to move their bodies. Muscles are divided into two great groups, voluntary and involuntary, the former being controlled by the will, while the latter act independently

     Most voluntary muscles are attached to the skeleton and range in size and shape to suit the particular jobs they perform. They can get into action within a few hundredths of a second, exert an enormous pull on the bone to which they are attached and, if necessary, support 1,000 times their own weight. Involuntary muscles include heart muscle and the muscles of the digestive system, and the fibers of which they are composed are very much smaller than those of voluntary muscle.

    Because of its exceptionally rich blood supply, muscle is the most infection-free of the body’s basic tissues. If it is over-taxed it tires and will stop contracting altogether, but if used normally will give little trouble.

Picture credit: google