Body defence mechanisms (12) Flashcards
(31 cards)
Why do we have defence mechanisms?
To protect us against pathogenic organisms
What are the different lines of defence?
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
What is resistance?
Our ability to ward off disease through our defences
What is susceptibility?
Vulnerability/lack of resistance
What is the innate non-specific defence system?
> 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
What is the adaptive specific defence system?
> This is the 3rd line of defence
Specialised lymphocytes- B and T cells
Antibodies
How does the skin protect entry against microorganisms?
> 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
What is the lacrimal apparatus?
> 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
What protects mucous membranes- saliva?
Dilutes no. of microorganisms and washes them from teeth and mucous membranes of the mouth
What are mucous membranes?
Line all body cavities that open to the exterior
What protects mucous membranes- muco-ciliary escalator?
> Viscous mucus traps microorganisms that enter the respiratory tract
Mucous membranes contain mucus coated hair which filter air; trap microorganisms, dust and pollutants
What protects mucous membranes- cilia?
> 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
What protects mucous membranes- epiglottis?
> Microorganisms are prevented from entering the lower respiratory tract by the closing of a small lid of cartilage called the epiglottis
What protects mucous membranes- urine?
> Normal acid pH inhibits bacterial growth
> Cleanses the lower urinary tract as it flushes from body
What protects mucous membranes- vaginal secretions?
Slightly acidic which prevents growth of microorganisms
What is the role of sebum?
> An antimicrobial substance
Forms a protective film over the skin
Slightly increases the acidity of the skin which prevents growth of microorganisms
What is the role of perspiration?
> An antimicrobial substance
Eliminates waste
Flushes microorganisms from the surface of the skin
Contains lysosyme (an enzyme with antimicrobial properties)
What is the role of gastric juice?
> An antimicrobial substance
Mixture of HCL, enzymes (pepsin and renin) and mucus
Very acidic (pH 1.2-3)
Destroys almost all microorganisms
What is the role of normal skin flora?
> 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
What is phagocytosis?
> 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
What are phagocytes?
> When infection occurs, neutrophils and monocytes move to the area
As infection progresses, macrophages dominate as they scavenge and clear up dead cells
What is inflammation?
> 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
What are the functions of inflammation?
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
What is stage 1 of inflammation?
VASODILATION
> Increased blood supply to the area= redness and heat
> Caused by chemicals released by damaged cells
> Histamine, kinins, prostaglandins
