Human body

UNIT 1
There are many different types of cells in the human body. None of these cells function well on there own and they are part of the much larger systems.
Tissues
Cells group together in the body to form tissues - a collection of similar cells that group together to perform a specialized function. There are 4 primary tissue types in the human body: epithelial tissue, connective tissue, muscle tissue and nerve tissue.
1. Epithelial Tissue - The cells of epithelial tissue pack tightly together and form continuous sheets that serve as linings in different parts of the body. Epithelial tissue serve as membranes lining organs and helping to keep the body's organs separate, in place and protected. Some examples of epithelial tissue are the outer layer of the skin, the inside of the mouth and stomach, and the tissue surrounding the body's organs.
2. Connective Tissue - There are many types of connective tissue in the body. Generally speaking, connective tissue adds support and structure to the body. Most types of connective tissue contain fibrous strands of the protein collagen that add strength to connective tissue. Some examples of connective tissue include the inner layers of skin, tendons, ligaments, cartilage, bone and fat tissue.
3. Muscle Tissue - Muscle tissue is a specialized tissue that can contract. Muscle tissue contains the specialized proteins actin and myosin that slide past one another and allow movement.
4. Nerve Tissue - Nerve tissue contains two types of cells: neurons and glial cells. Nerve tissue has the ability to generate and conduct electrical signals in the body. These electrical messages are managed by nerve tissue in the brain and transmitted down the spinal cord to the body.
Organs
An organ is a structure that contains at least two different types of tissue functioning together for a common purpose. There are many different organs in the body: the liver, kidneys, heart, even our skin is an organ.
Organ Systems
Organ systems are made of two or more different organs that work together to provide a common function. There are few major organ systems in the human body.

SKELETAL SYSTEM
Major Role:
The main role of the skeletal system is to provide support for the body, to protect delicate internal organs and to provide attachment sites for the organs.
Major Organs:
Bones, cartilage, tendons and ligaments.
MUSCULAR/MUSCLE SYSTEM
Major Role:
The main role of the muscular system is to provide movement. Muscles work in pairs to move limbs and provide the organism with mobility. Muscles also control the movement of materials through some organs, such as the stomach and intestine, and the heart and circulatory system
Major Organs:
Skeletal muscles and smooth muscles throughout the body.
NERVOUS SYSTEM
Major Role:
The main role of the nervous system is to relay electrical signals through the body. The nervous system directs behaviour and movement and, along with the endocrine system, controls physiological processes such as digestion, circulation, etc.
Major Organs:
Brain, spinal cord and peripheral nerves.
INTEGUMENTARY SYSTEM
Major Role: The main role of the integumentary system is to cover body with layer of cells which makes skin and keep temperature of body steady and in balance with exterior conditions. Also to receive messages from the outside world and react in response to it.
Major organs:
Skin and senses.
CIRCULATORY, LYMPHATIC/IMMUNE AND ENDOCRINE SYSTEM
Major Role:
The main role of the circulatory system is to transport nutrients, gases (such as oxygen and CO2), hormones and wastes through the body. The main role of the immune system is to destroy and remove invading microbes and viruses from the body. The lymphatic system also removes fat and excess fluids from the blood. The main role of the endocrine system is to relay chemical messages through the body. In conjunction with the nervous system, these chemical messages help control physiological processes such as nutrient absorption, growth, etc.

Major Organs:
Heart, blood vessels and blood; Lymph, lymph nodes and vessels, white blood cells, T- and B- cells; Many glands exist in the body that secrete endocrine hormones. Among these are the hypothalamus, pituitary, thyroid, pancreas and adrenal glands.
RESPIRATORY SYSTEM AND DIGESTIVE SYSTEM
Major Role:
The main role of the respiratory system is to provide gas exchange between the blood and the environment. Primarily, oxygen is absorbed from the atmosphere into the body and carbon dioxide is expelled from the body. The main role of the digestive system is to breakdown and absorb nutrients that are necessary for growth and maintenance.
Major Organs:
Nose, trachea and lungs; Mouth, esophagus, stomach, small and large intestines.
REPRODUCTIVE AND URINARY SYSTEM
Major Role:
The main role of the reproductive system is to manufacture cells that allow reproduction. In the male, sperm are created to inseminate egg cells produced in the female. The main role of the urinary system is to filter out cellular wastes, toxins and excess water or nutrients from the circulatory system.
Major Organs:
Female (top): ovaries, oviducts, uterus, vagina and mammary glands;
Male (bottom): testes, seminal vesicles and penis;
Major organs of urinary system are kidneys, ureters, bladder and urethra.
(Adapted from: http://web.jjay.cuny.edu/~acarpi/NSC/14-anatomy.htm)

UNIT 2
WHERE BONES BREAK
The risk of breaking a bone varies with age and occupation. Children’s bones are more flexible than adults’ and incomplete breaks known as “greenstick fractures” are most common. They frequently occur just above the elbow. In old age bones are more brittle. A mild fall can break the hip. For younger people road accidents and sports involve the greatest risk of breakages.

How a broken arm mends
Blood seeps out of the torn blood vessels. It formes a clot between the broken ends.
Cells in the bone sheath and lining multiply to form a bridge of fibrous tissue.
Within a week, young bone begins to replace the fibrous. By 3-6 weeks the broken ends are linked by bone.
The young bone is replaced by stronger mature bone. By 6-12 weeks the arm can be used again. Over the next year the bone gradually regains its smooth outline in children. A slight bump remains in adults.

UNIT 3
MUSCLES
Altogether the body has about 600 muscles, some large and very powerful, others tiny but precise in action. In a single stride you may use over 100 different muscles. The timing of their actions is perfectly coordinated to make one streamlined movement.
Throughout each movement messages pass along the nerves between muscles and brain. In this way the muscles are controlled with little effort from our conscious minds.

Each muscle is made up of very fine strands of fibres. These contains numerous very fine filaments of two special proteins, actin and myosin. When a muscle fibre gets the signal to contract, the action filaments are pulled along the myosin filaments by electrochemical forces, shortening the muscle.

UNIT 4
THE BRAIN
Inside the human head is a large lump of grayish jelly – it’s called the brain. Here lies the seat of the mind, intelligence and thought. The brain “jelly” is composed of millione of nerve cells which have many branches to receive or transmit information. A single cell may be connected to over 200 others.
All day and night the brain is alive with electrical activity. Messages stream in along the nerves from the eyes, ears, skin, etc. Each message is coded as a series of electrical “bleeps” or impulses.Deeper inside the brain there are centres controlling sneezing, sleeping, hearing and many other activities.
All mental activity depends on many parts of the brain working together. In the simple act of reading aloud one sentence from this book, you would use the centres of visual analysis, hearing, speech, muscle control and various others. The activity of all these regions would be coordinated by numerous connecting nerve cells to produce smooth, clear sound of your voice.

UNIT 5
SKIN
Inside, the skin is made up of two main layers: the epidermis and the dermis. Except on the hand and soles the dermis is very thin, just about 1/10th millimeters deep. At its surface, dead cells are being continually rubbed away, and new cells move out from the living layer inside to replace them.

The dermis is much thicker. It is made up of a meshwork of tough white fibres and springy elastic fibres. Between them run many blood vessels and nerves which are connected to the tiny organs responsible for sensations of touch, pain, warmth and cold.

Hairs are specialized parts of the epidermis and they grow from the base of hair follicles.
The waxy secretion of the sebaceous glands oils the hairs, and also provides food for the follicle mite, a minute spider-like animal that lives ina many people’s eyelashes.

In cold weather tiny muscles pull the hairs upright trapping a film of warm still air around the body. The blood capillaries in the dermis narrow, so that the skin looks pale. In warm weather these cappilaries open fully, to allow more blood to reach the cool surface of the skin, and the sweat glands pour out a clear salty liquid, which evaporates, cooling the body.
In the armpits and genital areas are special sweat glands called apocrine glands, whose products smell strongly under the influence of local bacteria. These may have helped our animal ancestors in sexual attraction. Today, however, man self-consciously suppress them with deodorants.

Birth
At birth baby have a smooth soft skin with very little pigment. A thick layer of fat beneath the skin accounts for the chubby cheeks.

Adolescence
New levels of sex hormones stimulate beard growth in boys and greater activity in the sebaceous glands in both sexes. These may become infected with bacteria, causing pimples.

Middle age
The skin is beginning to show signs of ageing. Furrows from across the brow because of repeated frowning, and where hair pigment production has slowed down, grey hairs appear.

Old age
Wrinkles form as elastic fibres in the dermis lose their “springiness”, and as the production of hair pigment ceases the hair turns white. Though wild whiskers often grow in ears and eyebrows, many scalp follicles produce only fine soft hairs, or cease production altogether, causing baldness.


UNIT 6
CIRCULAR TOUR

The heart is the main pump for the organism. It beats about 70 times a minute.
The left side of the heart deals with oxygen rich blood from the lungs; the right side with oxygen deficient blood from elsewhere. The incoming blood fills the auricles. It is forced
into the ventricles, then into the aorta or pulmonary artery. Valves ensure that the blood does not go the wrong way.
With every beat of a heart about a third of a cup of blood leaves each side of the heart. A single circular journey from the heart to the lungs, back to the heart, out through the arteries to a limb and back to the heart through the veins would take only about half a minute.

UNIT 7
RELEASING ENERGY – RESPIRATION
Once the cells have obtained food, they must be able to release the energy it contains. This is done through respiration. The food substance is gradually broken down and its energy released a little at time. During this ‘reaction’ oxygen is sed up and carbon dioxid left as waste.
Respiration is in many ways like burning of a fire. Burning also requires oxygen and releases energy and carbon dioxide. However, respiration is a slower, less violent process and it takes place at a much lower temperature.
The oxygen needed for respiration is obtained from the air during breathing. The lungs and surrounding parts of the chest pump air in and out of the body. The air coming in is filtered free of dust particles in the nose. It travels down the windpipe to the lungs, then along many branching air passages. In the end it reaches millions of tiny air pockets, or alveoli, surrounded by blood vessels. Oxygen passes through the walls of alveoli into the blood vessels, to be transported around the body.
The very fine air passages in the lungs end up in tiny air sacs or alveoli. Here oxygen enters the bloodstream. Carbon dioxide goes out of the blood vessels into the air sacs and is expelled when air is breathed out.

High in the mountain the air contains less oxygen than down below. The climber breathes faster and deeper than usual. If he stays many weeks in the mountains, his body will make extra haemoglobin to help transport more oxygen.When there is too little oxygen or too much carbon dioxide in the blood, messages are sent from the “breathing centre” in the brain to the diaphragm and chest muscles to raise the rate of breathing.


UNIT 8
GROWING UP
Between nine and fourteen years old of age boys and girls enter a stage called adolescence. The body gradually changes from child-like to adult form. Inside, the reproductive organs begin to mature, so that the person will be capable of having children of his or her own.
In girls these changes start with gradual swelling of the breasts and the growth of hair in the armpits and genital area. Within the next year or two monthly periods begin. In boys the testes enlarge first. Then the moustache and beard develop, the voice breaks and the penis gradually grows to its full size.
All these changes take several years to complete. They are controlled by the brain through chemical messengers called hormones. These are created by reproductive organs and the pituitary gland – the master gland at the base of the brain. Mental changes accompany the physical changes. Gradually boys and girls become attracted to each other, but often experience difficulty in relationships with their parents for a few years.

The menstrual cycle
Once every month the ovaries release a single egg which could develop into a baby. In preparation for this event, the womb grows a new soft lining. If the egg does not meet the sperm within 24 hours of leaving the ovary, it dies. The lining of the womb then breaks down. It is discarded with a little blood during the monthly period. Then the cycle starts again. Just before their periods, many girls feel irritable or find that their skin is more spotty than usual.

The male sex organs
Sperm are produced in the testes which are held in two thin sacs behind the penis. This lets out urine and injects sperm into the woman during intercourse. The seminal vesicles and prostate glands make fluids which help the sperm on their journey.

The female sex organs
The ovaries produce microscopic eggs which travel down the fallopian tubes to a muscular sac called the womb. In pregnant women the womb houses the developing baby. A short tube with stretchy walls, the vagina, links the womb to the outside world.


Source: The Human Body, Janet Noel - Macdonald/Educational 1973.