Nervous tissue – there are two types of tissue in the nervous system, excitable cells (neurones) which initiate, receive, conduct and transmit information; and non-excitable cells (glial cells) and these support the neurones. This tissue is found in the brain, spinal cord and nerves.
Muscle tissue – there are three types of muscle tissue. Cardiac muscle is found in the walls of the heart and its function is involuntary, i.e. it functions without the person thinking about doing anything. Skeletal muscle is used in the movement of the skeletal parts and is voluntary, i.e. the person has to think about using these muscles. Smooth muscle is found in the walls of internal organs and blood vessels, this is an involuntary muscle.
Organs – the organs in the body are made up of different types of tissue. There are many organs in the human body with different functions. These include, the eye (sight), the ear (hearing), the liver (glycogen storage, produces bile), heart (pump oxygen rich blood around the body), lungs (absorbs oxygen and expels carbon dioxide).
Systems – a group of organs together form a system in the human body. There are many systems and a few are:
Skeletal system – consists of bones, cartilage and joints. Its function includes strength, support and shape of the body.
Muscular system – this consists of the different types of muscle and its function is the movement of body parts.
Nervous system – this consists of the brain, spinal cord, nerves and nerve endings. Its role is to control and co-ordinate the body functions.
Respiratory system – this includes the lungs, nose, trachea, bronchi and bronchioles. The function is gaseous exchange (enable input of oxygen and output of carbon dioxide).
There are other systems in the body covering digestion (digestive system), protection (lymphatic system), reproduction (male and female reproduction systems).
1.2
Homeostasis is the maintenance of a stable internal environment in the human body, without this the body would not operate correctly and we would die.
There are 6 things that are essential for health need to be controlled:
Carbon dioxide – too much carbon dioxide and the body becomes too acidic. This is mainly lost through the air that is breathed but a little is lost in the urine that is past. The amount of carbon dioxide is controlled by the hypothalamus in the brain and the lungs help to get rid of excess.
Urea – is the waste chemical produced when amino acids are digested in the liver. This is removed via urine and some lost by sweat.
Ions – including sodium, potassium and phosphate need to be kept at the right balance or the integrity of the cells could be compromised. These are controlled by the amount of water we drink and through the urine we pass.
Sugar – having enough glucose for respiration and adequate glycogen is critical to the body. If the blood sugar level falls too low death could occur.
Water – the majority of the body is water, having the right amount can be fatal. The kidneys control the amount of water in the body.
Temperature – the body functions at the optimum temperature of 37 degree Celsius.
As already mentioned various glands and organs help with the homeostasis of the body.
The hypothalamus in the brain monitors the water levels, the body’s temperature and carbon dioxide content of the blood.
The pituitary gland at the base of the brain secretes a number of hormones
The liver helps to control glucose content of the body by storing it as glycogen.
The muscles of the body can help to maintain a stable body temperature as muscular activity and shivering help to generate heat.
The skin is the largest organ and has a central role in maintaining a constant temperature.
1.3
All cells whether plant or animal share the same basic structure, cell membrane, cytoplasm and nucleus. Inside the cytoplasm are various organelles which perform different tasks. The nucleus is the control centre it determines how the cell will function. The cell is enclosed by a cell membrane it maintains the shape of the cell and controls what goes in and out of it.
Thinking in terms of the origins of human life, the human body develops from a single cell (zygote) which has come from the fusion of two other cells, the ovum (female egg cell) and spermatozoon (male sex cell). The nucleus contains the DNA (the body’s genetic material), upon cell division this information replicates so the DNA is in the nucleus of both cells.
As cell division continues a foetus grows and cells with different structural and functional specializations develop but all have the same DNA as the original zygote.
As the new human life grows the organelles in the various cells continue to have various functions within the cell which could equate to different functions of the body.
The nucleus is the brain of the cell and control all active in the cell much like the human brain controlling the body.
The cell membrane holds in the contents of the cell and allows certain elements in and out of the cell, much like the skin on a human which lets substances in and out e.g. sweat.
Like the human body having various organs inside the body, the cell is the same having organelles with different functions.
The ribosomes are the workhorse of the cell; they carry out protein synthesis for the nucleus. The proteins produced are essential to the function of the cell.
The lysosomes are digestive sacs which breakdown macromolecules in the cell; it could be thought of as like the digestive system in the human body.
The aerobic respiration of the cell takes place in the mitochondria similar to the respiratory system.
The endoplasmic reticulum (ER) acts in a similar function to the blood vessels in the body; they transport substances from one part of the cell to another. The ER is also the site of membrane and protein synthesis.
So from a single cell (zygote) the millions of cell divisions produce millions of cells each with the same genetic makeup. The cells coming together to form tissues then into organs but knitted all together into a human body.
