Non-specific animal defences

What are primary defences?

The initial barriers that prevent pathogens entering the body

What happens when pathogens enter the body?

The secondary defences are triggered

What are the two types of secondary response?

1. specific

2. non specific

What are the primary defences of the body?

• Skin

• Eyes

• Mucous membranes

• Stomach

• Expulsive reflexes

• Blood clotting

How does the skin act as a primary defence against pathogens?

• Physical barrier - blocks pathogens from entering the body

• Chemical barrier - produces antimicrobial chemical that destroy / slow the growth of organisms

How do the eyes act as a primary defence against pathogens?

• Tears contain antibodies

• Also contain the enzyme lysozyme

How do mucous membranes act as a primary defence against pathogens?

• Protect body openings from environment

• Secrete mucus that traps pathogens

• Secretes antimicrobial chemicals

How does the stomach act as a primary defence against pathogens?

• Contains stomach acid (HCl)

• Too acidic for pathogens to survive

How do expulsive reflexes act as a primary defence against pathogens?

• e.g. coughing and sneezing

• happen automatically

• sneeze = mucus membrane in the nostrils is irritated

• cough = irritation in the respiratory tract

How does blood clotting act as a primary defence against pathogens?

• prevents entry of pathogens

• prevents further blood loss

How does blood clotting occur?

• platelets are released in response to a cut

• they cause the formation of fibrin

• fibrin forms a network - trapping platelets

• this forms a clot

What are platelets?

• irregularly shaped, colorless bodies that are present in blood

• sticky surface lets them, along with other substances form clots to stop bleeding

How does wound repair occur after initial clotting?

• clot dries out to form a scab

• epidermal cells below scan start to grow

• damaged blood vessels regrow

• collagen fibres are deposited to strengthen tissue

• once new epidermis reaches normal thickness, the scab sloughs off and the wound is healed

What are the secondary non-specific responses to pathogen?

• inflammation

• phagocytosis

What is the inflammatory response?

• a localised response to pathogens

• signs include swelling, pain, heat and redness

What causes the inflammatory response?

• It is caused by histamines and cytokines

• Which are released from activated mast cell

What do histamines do?

1. blood vessels dilate

• this increases blood flow to affected area

• results in heat and redness

• helps prevent pathogens reproducing

2. increase permeability of blood cells

• start to leak fluid into the surrounding area

• more tissue fluid forms

• results in swelling and pain

What are phagocytes?

• White blood cells involved in the non-specific response

• They ingest foreign particles and microorganisms form their surroundings

What are the different types of phagocytes?

• neutrophils

• monocytes

• macrophages

What is a neutrophil?

short lived phagocytes that travel round the body, squeezing in and out of capillaries

What is a monocyte?

travel in the blood, then develop into macrophages once they leave the blood and settle in organs

What is a macrophages?

long lived large phagocytes that are found in organs

What do cytokines do in the inflammatory response?

Attract phagocytes to the site of injury

What happens during phagocytosis?

• pathogens invade body

• cells under attack release chemicals that attract phagocytes

• phagocytes attracted by chemotaxis

• these phagocytes bind to the pathogen

• pathogen engulfed by endocytosis

• pathogen is trapped within a vacuole in the phagocyte called a phagosome

• lysosomes migrate towards the phagosome - fusing with it to give a phagolysosome

• digestive enzymes are released into the vacuole

• pathogen is digested and breakdown products are released

What do phagocytes that have engulfed pathogens release?

• Cell signalling molecules called cytokines

• They attract more phagocytes to the area

What do cytokines released by phagocytes that have engulfed a pathogen do?

• increase body temperature

• stimulate the specific immune system

What are opsonins?

Molecules that bind to pathogens and tag them for recognition by phagocytes

How do phagocytes interact with opsonins?

• Phagocytes have receptors on their cell membranes that bind to common opsonins

• Phagocyte then engulfs the pathogen