IB Biology HL: health and disease

nb. that this set contains a mixture of SL content (6.3) and HL content (11.1)

What is a pathogen?

A disease causing agent that disrupts the normal functioning of an organism (the pathogen could be an organism, a virus or a prion)

What features of skin make it a good barrier against pathogens (represented by TWO CDS)?

Tough, Waterproof, Oily, Clotting (when cut), Dry and Shreds

What features of the mucous membranes make them good barriers to pathogens (represented by SALE)?

Sticky, Acidic, contain Lytic Enzymes

What is blood clotting more technically known as?

Haemostasis

What are the two key components of a blood clot?

• Platelets undergo a structural change and form a sticky plug at the site of damage (primary haemostasis)

• Fibrin strands form an insoluble mesh of fibres (secondary haemostasis)

A blood clot is dissolved by which enzyme when an injury is repaired?

Plasmin

What starts the process in the blood clotting cascade?

Clotting factors released from damaged cells (extrinsic pathway) and platelets (intrinsic pathway)

What causes the conversion of prothrombin to thrombin?

Clotting factors

What does Thrombin do in the coagulation cascade?

Catalyses the conversion of soluble fibrinogen fibres to insoluble fibrin

What does fibrin do in the coagulation cascade?

Forms a mesh of fibres around the platelet plug and traps blood cells to form a temporary clot

What is coronary thrombosis?

The formation of a clot within the blood vessels that supply and sustain the heart tissue (coronary arteries)

What is an atheroma?

Fatty deposits that develop in the arteries and causes stenosis (reduced diameter) of the lumen

What is the innate immune system?

The sum of non-specific immune responses triggered by contact with a pathogen. It does not differentiate between different types of pathogens (non-specific) and it responds to an infection the same way every time (non-adaptive)

What are the components of the non-specific (innate) immune system?

• Phagocytic white blood cells

• Antimicrobial chemicals

• Inflammation and fever

What is phagocytosis?

Literally “cell eating“, phagocytosis is when solid materials such as pathogens are ingested by a cell via endocytosis

What markers on the surface of cells identify them as “self“ (meaning that they won’t be attacked by the immune system)?

MHC (major histocompatibility complex) proteins

What markers on the surface of cells identify them as “foreign“ (meaning that they will be attacked by the immune system)?

Antigens

Which blood group can receive transfusions from any blood group?

Type AB (Rhesus positive)

Which blood group can donate to a person of any blood group?

Type O (Rhesus negative)

What is the consequence of an incompatible blood transfusion?

Agglutination (clumping) of surface antigens and opposing antibodies

Haemolysis (the rupture or destruction of red blood cells)

What is meant by pathogenesis?

The capacity for a pathogen to cause disease

What are zoonoses?

Diseases that can be passed across the species barrier between animals and humans

What are macrophages?

Non-specific immune cells that engulf pathogens non-selectively and break them down internally

What are dendritic cells?

A number of macrophages which present the antigenic fragments of the pathogen to specific lymphocytes

What is the role of T lymphocytes?

T cells are direct fighters of pathogens and also produce cytokines, substances that activate other parts of the immune system

What are the four types of T cell?

• Helper T cells which deploy antibodies in B cells

• Cytotoxic (“killer“) T cells which trigger self-destruction in infected cells

• Regulator T cells which slow and stop the immune response once the pathogen is gone

• Memory T cells which speed up the response when you encounter the pathogen the second time

What is the role of B lymphocytes?

B cells produce antibodies

What happens when a B lymphocyte is activated?

It divides into plasma and memory cells

Plasma cells secrete thousands of antibodies per second into the bloodstream

Memory cells enhance the efficiency of immune response if the pathogen is encountered again

How do antibodies aid in the destruction of pathogens (represented by PANIC)?

• Precipitation – Soluble pathogens become insoluble and precipitate 

• Agglutination – Cellular pathogens become clumped for easier removal

• Neutralisation – Antibodies may occlude pathogenic regions (e.g. exotoxins)

• Inflammation – Antibodies may trigger an inflammatory response within the body

• Complement activation – Complement proteins perforate membranes (cell lysis)

What is opsonization?

The process by which a specific pathogen is tagged for destruction

What is immunity?

When pathogen exposure is unable to make a disease occur in an organism, that organism is said to be immune.

What do memory cells do?

They remain in the blood for several years after primary exposure to a disease, producing low levels of circulating antibodies. This triggers a faster response the second time the pathogen is encountered, so quick that the disease cannot cause symptoms.

Which cells does HIV attack?

Helper T lymphocytes

What is the structure of an antibody?

• Antibodies are also called IGs (immunoglobulins)

• Two long (heavy) and two short (light) polypeptide chains held together by disulfide bridges

• Variable region which facilitates binding to a specific antigen

How do macrophages bridge the innate and adaptive immune system?

They process and present on their surface antigens from the pathogen, stimulating helper T cells

What is the difference between a fixed and a wandering macrophage?

• A wandering macrophage is transported around in the blood

• A fixed macrophage is fixed somewhere in the body which is more susceptible to a disease (for example in the lungs)

Why are some viruses unable to be eradicated via vaccination like smallpox was?

Genetic drift: some viruses such as smallpox have a very small number of antigens on their surface and are less likely to mutate than others such as coronavirus or HIV

What is an attenuated pathogen?

A dead or inactive form of a pathogen used in vaccinations.

What is the normal function of histamines in the body?

They cause the dilation of blood vessels and fluid to leak out containing immune components (specific: antibodies and non-specific: phagocytes)

What are the two type of white blood cell that infection sensitizes?

Mast cells (found in connective tissues) and basophils (found in blood)

What symptoms can exposure to allergens cause?

Overproduction of histamine causes over-dilation of blood vessels, symptoms such as itchy eyes and runny nose

What processes do antibiotics block?

Metabolic pathways/ cell wall formation/ protein synthesis

Why are antibiotics effective against bacteria but not against viruses?

Antibiotics block metabolic pathways in bacteria; viruses are non-living and they do not carry out metabolic processes

Outline the diversity of structure in viruses

Viruses consist of a protein coat and genetic material, the genetic material can be single-stranded RNA or double-stranded DNA (retroviruses have RNA), protein coat contains specific receptors for target organism

What are bacteriostatic medications?

Unlike bactericidal antibiotics which kill bacteria, bacteriostatic antibiotics just inhibit the spread of bacteria infection to give the immune system a better chance at fighting it off

What is clonal selection?

The process of matching the antigens on an antigen presenting cells with the antigen receptors on B and T lymphocytes.

Erythrocytes

Red blood cells

Leukocytes

White blood cells

What is a vector?

An intermediary organism that transmits a disease without developing symptoms itself