Body defence mechanisms (12)

Question 1

Why do we have defence mechanisms?

Answer 1

To protect us against pathogenic organisms

Question 2

What are the different lines of defence?

Answer 2

1st- block entry of microorganisms into the body
2nd- seek out and destroy microorganisms that enter the body
3rd- detect and react rapidly to antigens that are foreign

Question 3

What is resistance?

Answer 3

Our ability to ward off disease through our defences

Question 4

What is susceptibility?

Answer 4

Vulnerability/lack of resistance

Question 5

What is the innate non-specific defence system?

Answer 5

> 1st line of defence consists of surface barriers- skin; mucous membranes and their secretions; normal flora of the body
2nd line of defence includes phagocytosis; inflammation; fever; antimicrobial substances

Question 6

What is the adaptive specific defence system?

Answer 6

> This is the 3rd line of defence
Specialised lymphocytes- B and T cells
Antibodies

Question 7

How does the skin protect entry against microorganisms?

Answer 7

> Has to be intact
Epidermis- layers of tightly packed epithelial cells which forms a physical barrier
There are specialised cells in the epidermis which are part of the immune system e.g. Granstein cells assist helper T cells
Top layer is dead but contains a waterproof protein called keratin which provides resistance against acids, alkalis and bacterial enzymes
Dryness of skin inhibits microorganisms settling

Question 8

What is the lacrimal apparatus?

Answer 8

> Produces and drains away tears
Tears spread over the entire surface of eyeball
Continual washing of tears prevents microorganisms settling on the eye
If irritating substances or microorganisms get onto the eye, the over production of tears dilutes and washes away the irritant

Question 9

What protects mucous membranes- saliva?

Answer 9

Dilutes no. of microorganisms and washes them from teeth and mucous membranes of the mouth

Question 10

What are mucous membranes?

Answer 10

Line all body cavities that open to the exterior

Question 11

What protects mucous membranes- muco-ciliary escalator?

Answer 11

> Viscous mucus traps microorganisms that enter the respiratory tract
Mucous membranes contain mucus coated hair which filter air; trap microorganisms, dust and pollutants

Question 12

What protects mucous membranes- cilia?

Answer 12

> Cells of lower respiratory tract are covered with cilia which propel inhaled debris towards the throat and nose
Muco-ciliary blanket moves at 1-3cm/hr
Coughing/sneezing speeds up muco-ciliary escalator
Chemicals in cigarette smoke are toxic to cilia and seriously impair their functioning

Question 13

What protects mucous membranes- epiglottis?

Answer 13

> Microorganisms are prevented from entering the lower respiratory tract by the closing of a small lid of cartilage called the epiglottis

Question 14

What protects mucous membranes- urine?

Answer 14

> Normal acid pH inhibits bacterial growth

> Cleanses the lower urinary tract as it flushes from body

Question 15

What protects mucous membranes- vaginal secretions?

Answer 15

Slightly acidic which prevents growth of microorganisms

Question 16

What is the role of sebum?

Answer 16

> An antimicrobial substance
Forms a protective film over the skin
Slightly increases the acidity of the skin which prevents growth of microorganisms

Question 17

What is the role of perspiration?

Answer 17

> An antimicrobial substance
Eliminates waste
Flushes microorganisms from the surface of the skin
Contains lysosyme (an enzyme with antimicrobial properties)

Question 18

What is the role of gastric juice?

Answer 18

> An antimicrobial substance
Mixture of HCL, enzymes (pepsin and renin) and mucus
Very acidic (pH 1.2-3)
Destroys almost all microorganisms

Question 19

What is the role of normal skin flora?

Answer 19

> It is microorganisms that establish permanent residence in the body, but in normal circumstances do not produce disease
Fight for resources against pathogenic microorganisms
All animals do not have this in-utero
At birth, microbial populations begin to become established
Lactobacilli from Mothers vagina becomes the first and predominant organism in the neonates intestines
After birth, E.Coli and other bacteria from food inhabit the large intestine and remain there throughout life and may cause disease

Question 20

What is phagocytosis?

Answer 20

> The ingestion of a microorganism by a cell
2nd line defence mechanism
1) Phagocyte adheres to pathogen
2) Phagocyte forms pseudopods which eventually engulf the particles, forming a phagosome
3) Lysosome fuses with phagosome, forming a phagolysosome
4) The hydrolytic enzymes inside the lysosome destroy the pathogens
5) Vesicles move to plasma cell membrane, fuse with it and release its contents by exocytosis

Question 21

What are phagocytes?

Answer 21

> When infection occurs, neutrophils and monocytes move to the area
As infection progresses, macrophages dominate as they scavenge and clear up dead cells

Question 22

What is inflammation?

Answer 22

> A non-specific response to damage to body tissues
Causes include microbial infections, heat, electricity, chemical agents or physical trauma
Produces redness, pain, heat, swelling and loss of function

Question 23

What are the functions of inflammation?

Answer 23

1) To destroy injurious agent and to remove it and its by-products from the body if possible
> If destruction is not possible, it will limit its effects on the body by confining/walling off the agent
2) To repair/replace tissue damaged by the agent or its by-products

Question 24

What is stage 1 of inflammation?

Answer 24

VASODILATION
> Increased blood supply to the area= redness and heat
> Caused by chemicals released by damaged cells
> Histamine, kinins, prostaglandins

Question 25

What is stage 2 of inflammation?

Answer 25

PHAGOCYTE MIGRATION
> Within 1 hour, large numbers of phagocytes move to the area, engulf large numbers of microorganisms and then die
> After a few days, an area containing dead phagocytes/damaged tissue forms (this is pus)

Question 26

What is stage 3 of inflammation?

Answer 26

REPAIR
> The process where tissues replace dead/damaged cells
> Repair begins during the active period of inflammation but does not complete until all toxins have been neutralised

Question 27

How can microorganisms affect our body temperature?

Answer 27

> We maintain a body temperature within a fairly constant range
Many microorganisms produce chemicals which enter the bloodstream and directly/indirectly stimulate the hypothalamus (the body’s thermostat), resulting in fever

Question 28

What is complement?

Answer 28

> This refers to a groups of at least 20 plasma proteins that normally circulate in the blood in an inactive form
These are numbered C1-C9, factors D, B and P and regulatory proteins
It provides a major mechanism for destroying foreign substances in the body
Its activation unleashes inflammatory chemicals which amplify nearly all aspects of the inflammatory process
Activated complement also kills bacteria and other cell types
Enhances the effectiveness of both non-specific and specific defences

Question 29

What are the types of immunity?

Answer 29

1) Natural active- infection
2) Natural passive- antibodies pass from mother to baby via placenta and breastfeeding
3) Artificial active- Vaccine
4) Artificial passive- injection of immune serum

Question 30

What is immunity?

Answer 30

> When someone is protected against an infection
This can occur due to memory cells- if they have had it before, the next time the person comes in contact with the same antigen, the immune system is ready to destroy it
Immunity can be strong, weak, short-lived or long-lasting
Can be influenced by inherited genes
Vaccines contained weakened or dead forms of bacteria which can provoke an immune response so that the body becomes familiar with that antigen

Question 31

What is an injection of immunity serum?

Answer 31

> Rich in antibodies against a particular microbe
Antiserum is given to protect travellers to countries where Hep A is widespread
Typically only lasts a few weeks/months
Infants born with weak immune system but are protected by antibodies they receive from their Mothers in-utero
Breast feeding also gives them antibodies to help protect their GI tracts