(b)++Details+of+the+human+defence+system


 * __(b) Details of Human defence system __**

(4) Describe the functional role of the following defense mechanisms (a) Skin (including sweat and sebum products): The skin is the largest organ of the human body. The skin prevents disease and pathogens from entering the body. When unbroken, it is almost impossible for micro-organisms to penetrate the skin. The skin is also an organ of regulation; it regulates the body temperature through sweating. Sweating coolds down the body. through sweat we also gets rid of unwanted fluids in the body. Physical component of skin’s defense: - Epidermis  o Composed of multiple layers of tightly packed cells which few pathogens can penetrate on their own   o Natural shedding of dead skin cells removes many attached microorganisms   o Cells called epidermal dendritic cells engulf and digest pathogens  - Dermis   o Contains protein fibers called collagen. Collagen is a tough and fibrous protein which gives the skin the strength to resist cuts that could introduce microorganisms

<span style="color: #00b050; font-family: 'Cambria','serif'; font-size: 12pt;">Chemical components of the skin’s defense: <span style="display: block; line-height: normal; margin: 0in 0in 0pt 0.5in; mso-add-space: auto; mso-list: l0 level1 lfo1; mso-outline-level: 2; text-indent: -0.25in;"><span style="color: #00b050; font-family: 'Cambria','serif'; font-size: 12pt;">- Perspiration <span style="display: block; line-height: normal; margin: 0in 0in 0pt 1in; mso-add-space: auto; mso-list: l0 level2 lfo1; mso-outline-level: 2; text-indent: -0.25in;"> o <span style="color: #00b050; font-family: 'Cambria','serif'; font-size: 12pt;">Secreted by the skin’s sweat gland and contains salt and enzymes  <span style="display: block; line-height: normal; margin: 0in 0in 0pt 1in; mso-add-space: auto; mso-list: l0 level2 lfo1; mso-outline-level: 2; text-indent: -0.25in;"> o <span style="color: #00b050; font-family: 'Cambria','serif'; font-size: 12pt;">Few microbes can live in a highly saline environment like this and the lysozyme in sweat are a type of enzyme that destroy the cell walls of bacteria  <span style="display: block; line-height: normal; margin: 0in 0in 0pt 0.5in; mso-add-space: auto; mso-list: l0 level1 lfo1; mso-outline-level: 2; text-indent: -0.25in;"><span style="color: #00b050; font-family: 'Cambria','serif'; font-size: 12pt;">- Sebum  <span style="display: block; line-height: normal; margin: 0in 0in 0pt 1in; mso-add-space: auto; mso-list: l0 level2 lfo1; mso-outline-level: 2; text-indent: -0.25in;"> o <span style="color: #00b050; font-family: 'Cambria','serif'; font-size: 12pt;">Secreted by skin sebaceous (oil) glands  <span style="display: block; line-height: normal; margin: 0in 0in 0pt 1in; mso-add-space: auto; mso-list: l0 level2 lfo1; mso-outline-level: 2; text-indent: -0.25in;"> o <span style="color: #00b050; font-family: 'Cambria','serif'; font-size: 12pt;">This oil enables to skin to be less likely to break or tear and also lowers the pH of the skin to a more acidic level that inhibits the growth of many types of bacteria

<span style="color: black; font-family: 'Times','serif'; font-size: 10.5pt; line-height: 115%;">(b) Phagocytosis by white blood cells (phagocytic leucocytes)://Draw a diagram & include the word phagocytosis.// The phagocytic white bloodcells are attracted by chemicals produced at the sites of infection and move to these sites. they engulf and digest the pathogens. The soluble products are absorbed and assimilated by the phagocytes. They may also be destroyed by toxins produced by the pathogens. the number of leucocytes(white blood cells) increase to try to destroy the pathogen and neutralise the toxin. ( [])

<span style="color: black; font-family: 'Times','serif'; font-size: 10.5pt; line-height: 115%;">(c) Mucus secreting and ciliated membranes: The trachea and bronchi is lining with cilia. Micro-organisms and undesirable substance can be caught by the mucus which then are removed by the beating cilia toward the glottis and then to the throat. It is then either swallowed or cough out.

<span style="color: black; font-family: 'Times','serif'; font-size: 10.5pt; line-height: 115%;">(d) Defence secretions: tears, urine, saliva, gastric juice: tears: tears secreted by tear gland and acidic sebum (sebaceous gland)- contain lysozymes which destroy some bacteria urine:to eliminate soluble wastes, which are toxic, most animals have excretory systems. In humans soluble wastes are excreted by way of the urinary system, which ocnsists of the kidneys, ureters,urinary bladder and urethra. The kidneys extract the soluble wastes from the bloodstream, as well as excess water, sugars, and a variety of other compounds. Remaining fluid contains high cioncentrations of urea and other substances, including toxins. Urine flows through these structures; the kidney, ureter, bladder, and finally the urethre. Urine is produced by a process of filtration, readsorption and tubular secretion. saliva: produced by the salivary glands, washes microbes from the surface of the teeth and the mucuous membrane of the mouth starts the digestion of starches.A thick transparent liquid rich in digestive [[enzymes like [[amylase, used to break down foodstuff. Saliva is produced by the salivary glands of the mouth and the volume of saliva produced depends on the type of the food being eaten. gastric juice: Gastric juice is a collection of Hydrochloric acid, enzymes and mucus secreted by the stomach. The high acidity of gastric juice (pH 1.2 - 3.0) destroys bacteria and almost all important bacterial toxins.

<span style="color: black; font-family: 'Times','serif'; font-size: 10.5pt; line-height: 115%;">(e) Antibody production <span style="color: black; display: block; font-family: 'Times','serif'; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;">* Anibody's are also called 'immunoglobin', are soluable proteins* Are produced by lymphocytes, as a response to an antigen* An antibody recoginzes an antigen and neutralizes it* each different lymphocyte will recognize a different type of antigen* the lymphocyte will divide many times, forming a clone (a group of lymphocytes that all produce the same antibody)*all the antibodies will attach to the antigen and make it harmless (f) Fever *inanate immune system of body*if temperature is elevated to above the optimum growth temperature for many micro-organism, they will repoduce more slowly, allowing the body an advantage in time to work to destroy the antigens*stimulates the production of heat-shock proteins resulting in the production of infammation-promoting cytokines*elevates temperature in body, increasing rate of enzyme reactions, resulting in a faster metabolism*this speeds up production of phagocytes and lymphocytes and tissue repair (g) Cell-mediated immunity *does not require antibodies; instead uses macrophages and natural killer cells *most effective in removing virus-infected cells* generates T lymphocytes that are reactive against specific antigens (h) The inflammatory response *to increase blood circulation around the area; *blood vessels around area dilate*allowing more phagocytes, macrophytes and lymphocytes to reach the area