(a)++Overview+of+human+defence+system


 * __(a) Overview of Human defence system __**

(1) Describe the type of responses against pathogens carried out by each of the following levels of defense  (a) First line of defense  ﻿EXTERNAL DEFENSES 1) Skin :   The tightly packed cells of the dermis and epidermis become a barrier that does not permit pathogens to enter the body. The acidity of the skin (pH 3 to 5) and the sebum create an environment that does not welcome microorganisms. Perspiration helps to wash away microbes from the skin. Similarly, tears wash away foreign bodies from the eyes    2) mucus membranes    Mucous membranes line the epithelial layer of many of the body cavities, such as the nasal passages, respiratory tract, and digestive tract. Since the mucous is viscous and slightly sticky, it traps many microorganisms, preventing them from attaching to the epithelium or entering the tissue. Some of these membranes are also ciliated, which helps to move trapped particles away from the body.   3) Secretions : oil glands and sweat glands,  Lysozyme: enzyme found in tears, saliva and mucous secretions   Characteristics of Human Skin   - Human oil and sweat glands acidify skin (pH around 3-5) which discourages microbial growth  - Saliva, tears, mucous secretions    o Wash away invading microbes  o Contain antimicrobial proteins (Lysozyme) that break down cell walls of many bacteria    - Mucous membrane: Celia* sweep invaders out of trachea and bronchi - Gastric juice of stomach (pH 1.5-2.5) kills most bacteria - Symbiotic bacteria in digestive tract outcompete other organisms that could cause damage (eg. Yeast infection)  *Note: =<span style="font-family: Times,serif; font-size: 14px; line-height: 16px;">Cilium = <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;">**Definition** //noun, plural: cilia// (biology) [|Microscopic], hair-like [|projection] on the surfaces of some [|cells] and of certain organisms. (botany) Any of the hair forming a fringe along the margin or edge of a plant structure, e.g. of a [|leaf]. (anatomy) The [|eyelash]. <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;">brush pathogens up and out in mucus you swallow
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Best way to prevent pathogens such as bacteria and viruses from entering body
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">When unbroken, it is almost impossible for any micro-organism to penetrate the skin

Cilia are generally of two kinds: //[|motile]// cilia (for [[[|locomotion]]]) and non-motile cilia (for [|sensory]). Example of tissue cells with cilia are the [|epithelia] lining the [|lungs] that sweep away fluids or particles. Examples of organisms that have cilia are [|protozoans] that use them for movement. <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;">[]
 * Supplement**

<span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;"> (b) Second line of defense <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;">INTERNAL DEFENSES <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;">1) phagocytic cells <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;">2) antimicrobial proteins <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;">3) inflammatory response <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;">4) natural Killer cell <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;"> White blood cells <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;"> <span style="color: black; direction: ltr; display: block; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;"> - White blood cells: phagocytosis of microbes that pass 1st line defense  o Neutrophils (kamikaze cells)   § Becomes phagocytic in infected tissue   § Attracted by chemical signals   § Only live a few days and destroy self while destroying pathogens   o Monocytes -> macrophages   § Large phagocytic cells   § Found in interstitial fluid or permanently in organs and connective tissue   § Phagocytize pathogens, other foreign cells, neutrophils with pathogens   o Eosinophil   § Limited phagocytic activity   § Contain destructive enzymes : disgorged against outer covering of invading pathogens   § Mainly used against parasitic worms   o Natural killer cells (NK cells)   § Destroy body’s own cells when cells are infected by viruses (c) Third line of defense 1. Cell mediated response (cytoxic lymphocytes) - Involves the activation and clonal selection of cytotoxic T cells, which directly destroy certain target cells 2..(Humoral response) Antibodies <span style="display: block; font-family: Times,serif; font-size: 14px; line-height: 16px;"> - Antigen  o Any molecule, usually a protein or polysaccharide that may be identified as foreign and will elicit an immune response   o Eg. Toxin (insect bite, bacteria) protein coat of a virus molecule unique to a cell membrane of bacteria, worms, pollen, protozoa…   o Each antigen has a unique molecular shape and stimulates production of a particular antibody that defends against that antigen   - Antibody or immunoglobin   o Antigen-binding protein that acts as an effector for immune response   o Secreted by B-lymphocytes
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Immediate but non specific
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Recognise and respond to proteins on pathogens called antigens in a generic way
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Immediate defense against infection
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Does this by phagocytosis (phagocytes engulf and digest micoorganisms and cellular debris)
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Found in nearly all species of life
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Specific immune response
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Stronger than second line
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Not immediate - there is a lag time between exposure and maximal response
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Found only in jawed vertebrates
 * <span style="color: black; direction: ltr; margin-left: 0.375in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Allows for immunological memory - each pathogen is 'remembered' by a signature antigen - these 'memory cells' are used to quickly eliminate the pathogen if it returns to the body

<span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt;">(2) Distinguish between the following categories of resistance to pathogens <span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt;"> (a) Non-specific resistance (b) Specific resistance
 * <span style="color: black; direction: ltr; margin-left: 0.75in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Includes the first and second line of defense
 * <span style="color: black; direction: ltr; margin-left: 0.75in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">They are designed with an acidic surface that usually repels bacteria and are attributable to factors other than specific pathogens
 * <span style="direction: ltr; margin-left: 0.75in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Includes third line of response
 * <span style="direction: ltr; margin-left: 0.75in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">Specialised white blood cells can remember a specific virus or bacteria
 * <span style="direction: ltr; margin-left: 0.75in; margin-top: 0in; unicode-bidi: embed; vertical-align: middle;">When the pathogen returns, these specialised white blood cells are ready to eliminate them

<span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt;">(3) Briefly define the following terms and give a short explanation of their role in internal defense <span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;">(a) Susceptibility <span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;"> <span style="background: #cde5d5; color: black; font-family: Times; font-size: 10.5pt; margin: 0in 0in 0in 0.375in;">Means that there is an inability to resist some extraneous agent, such as a pathogen Can also mean defenselessness, vulnerability, or weakness [] <span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;">(b) Resistance <span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;"> A defense mechanism able to reject and deny diseases. <span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;">(c) Phagocytosis <span style="color: black; display: block; font-family: Times; font-size: 10.5pt; margin: 0in 0in 0in 0.375in;"> The engulfing and ingestion of bacteria or other foreign particles.

<span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;">(d) Inflammation <span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;"> <span style="background: #cde5d5; color: black; font-family: Times; font-size: 10.5pt; margin: 0in 0in 0in 0.375in;">Response of cellular injury--> identified by redness, heat, swelling in the process of eliminating noxious agents. <span style="color: black; display: block; font-family: Times,serif; font-size: 10.5pt; line-height: 115%; margin: 0in 0in 0pt 1in;">(e) Fever <span style="background-clip: initial; background-color: #cde5d5; background-origin: initial; color: black; display: block; font-family: Times; font-size: 10.5pt; margin: 0in 0in 0in 0.375in;">A rise in body temperature as the body fights extraneous agents