Ch 24 Body Defence Mechanism

Question 1

Physical barrier

Answer 1

1. The skin
   It prevents the entry of pathogens by forming a tough and impermeable barrier and covers the whole body
2. Blood clotting
   At the damaged blood vessel, the blood platelets starts off a series of reaction converting soluble protein fibrinogens in plasma into a net of insoluble fibrin. Blood platelets, Red blood cells and white blood cells are trapped in the net. This forms a blood clot, which then dries up to become a scab. The blood clot prevents further bleeding ,seals the wound to prevent the entry of pathogens and protect the underneath injured tissue while new skin grows.
3. Inner wall of respiratory tract
   The cells are closely packed to form a barrier, mucus secreted by mucus secreting cells can trap pathogens in inhaled air and cilia of ciliated epithelial cells beat to sweep the mucus with trapped pathogens towards the pharynx. The mucus is then coughed up or swallowed into the stomach where most of the pathogens will be killed by hydrochloric acids.

Question 2

Chemical barrier

Answer 2

1. Tears and saliva, it contains lysozyme and kills pathogen.
2. Sebum secreted by sebaceous glands kills pathogens
3. Gastric juice
   It has hydrochloric acid and kill pathogen
4. Vaginal secretion
   It is acidic and can inhibit the growth of pathogen.

Question 3

Phagocytosis

Answer 3

Phagocytes is a type of white blood cell. It will engulf the pathogens by phagocytosis and then the pathogen are then digested by enzymes.

Question 4

Inflammatory responses

Answer 4

Our damaged cells release chemicals called histamine to initiate an inflammatory response. These chemicals cause nearby arterioles to dilate ,increasing blood flow to the injured tissue. They also increased the permeability of capillaries. As a result, more phagocytes comes out of capillaries to engulf and digest pathogens. This process speeds up tissue repair.
Inflammatory response results in a condition called inflammation and here is the following symptoms:
Redness: dilation of arterioles increases blood flow to the injured tissue, making it red
Hotness: the increased blood flow, causes a rise in temperature
Swelling: increased permeability of capillaries results in the formation of more tissue fluid. Its accumulation leads to swelling.
Pain : more tissue fluid presses against nerve endings. Pain receptors in the skin are stimulated, causing pain
A yellowish liquid called pus may which consists of the remains of killed pathogens and worn-out phagocytes may form at inflamed tissue.

Question 5

What are the four non- specific body defences?

Answer 5

Physical barrier, chemical barrier, phagocytosis and inflammatory response

Question 6

What is lymphocytes?

Answer 6

Foreign antigens are identified by lymphocytes, a type of white blood cell. Each lymphocytes has only one type of receptor .

Question 7

The two types of lymphocytes:

Answer 7

B cells: They are formed and mature in the bone marrow
T cells: They are formed in the bone marrow and mature in the thymus gland.

Question 8

Antibody:

Answer 8

Antibody is a Y-shaped protein molecules. It has 2 antigen binding sites. The binding results in the formation of an antigen-antibody complex.

Question 9

The ways the antibodies act against pathogens:

Answer 9

1. Some antibodies bind to antigens on pathogens. This attracts certain proteins in the blood to cause lysis of the pathogens.
2. Some antibodies bind with antigens on several pathogen at the same time. This clumps several pathogens together in a process called agglutination. Agglutination facilitates phagocytosis of the pathogens. The phagocytes engulf the pathogen and digest them by enzymes.
3. Some antibodies act as antitoxins to neutralize toxins by binding to them. The toxins become harmless.

Question 10

Immune response of B cells

Answer 10

B cells are activated when antigens on the surface of pathogen or circulating freely, bind to their receptors, divide and differentiate into plasma cells and memory B cells.

Question 11

Function of plasma cell in B cell

Answer 11

Release antibodies into the blood to act against pathogens, having that antigen 

Question 12

Function of memory B cells

Answer 12

Remember the type of antigen so that they can respond quickly in any subsequent invasion by the same type of antigen 

Question 13

Plasma cell or memory B cell live longer?

Answer 13

Memory B cell

Question 14

Immune response of T cells

Answer 14

Helper T cells are activated when antigens of pathogens are presented to them by certain phagocytes, helper T cells secrete lymphokines, which activates T cells to divide and differentiate into killer T cells and memory T cells.

Question 15

Function of Killer T cells

Answer 15

Bind to infected cells and kill them directly by making holes in their cell membranes 

Question 16

Function of Memory T cells

Answer 16

Remember the type of antigen so that they can respond quickly in any subsequent invasion by the same type of antigen.

Question 17

Does the helper T cells or lymphokines activated other T cells to divide and differentiate into Killer T cells and Memory T cells? What are the other cells it activates?

Answer 17

Lymphokines. Activates B cells and phagocytes.

Question 18

What are the characteristics of specific defence mechanisms?

Answer 18

Specificity and immunological memory.

Question 19

Principle of vaccination

Answer 19

Vaccines contains the antigens of pathogens, which stimulates the lymphocytes to produce memory cells for that antigens (primary response) when the same type of antigens enters the body again the memory cells can produce a larger amount of antibodies and killer T cells for that antigens in a shorter time. (Secondary response)

Question 20

What characteristics does a vaccination make use of?

Answer 20

Vaccination makes use of specificity and immunological memory . 

Question 21

natural method of passive immunity

Answer 21

Antibodies in maternal blood passes through the placenta into the foetal blood
Obtain antibodies in the mother’s milk via breast feeding