IB Biology Unit 11 Human health and physiology
- Defence against infectious disease
- Distinguish own cells (self) from pathogen (non-self)
- Lines of defence
- First line
- Non-specific
- Both physical and chemical barriers (prevent pathogen from entering)
- Skin, mucus in respiratory passages
- Second line
- Non-specific
- Phagocyte to site of infection
- Clotting factor released when tissue it damagedàcapillaries dilateàmore bloodàphagocytes squeeze through capillary wallàengulf pathogens
- Third line
- Specific to a particular antigen
- B and T lymphocytes
- B lymphocyte: Humoral response
- B cells actively dividedàproduce antibodies which are released into bloodstreamàantibodies bind to the pathogen to prevent it from dividing + allow it to be engulfed by phagocytes
- T lymphocyte: Cell mediated response
- T cells produce chemicals to
- Kill virally infected or cancer cells
- Activate B cells and phagocytes
- Memory cell:
- Few B lymphocytes produced to be remained as memory cells (for future immune response)
- Describe the process of blood clotting
Clotting is the mechanism that prevents blood loss from broken blood vessels
When the tissue is injured,
- Clotting factors (proteins) released from either damaged tissue cells or platelets (platelets are small cell fragments)
- Clotting factors activate Prothrombin (inactive form)àthrombin (enzyme)
- Thrombin turns Fibrinogen (soluble, plasma protein) (removal of sections of peptide containing negative charges)àfibrin (insoluble, fibrous)
- Fibrin binds platelets and blood cells together to form a meshà clot
- Outline the principle of challenge and response, clonal selection and memory cells as the basis of immunity (copied from bio ninja)
Challenge and response:
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- When the body is challenged by foreign pathogen, it will respond with both non-specific and specific immune reactions (3 lines of defence)
- The body is capable of recognizing invaders as they do not possess molecular markers that designated to all body cells as ‘self’
- Non-specific immune cells (macrophages/phagocytes) present the foreign antigens to lymphocytes as examples of ‘non-self’
- These lymphocytes can then respond with the production of antibodies to destroy pathogens
Clonal selection
- Each B lymphocyte has a specific antibody on its surface that is capable of recognizing a specific antigen
- When antigens are presented to B cells by phagocytes/macrophages, only the B cell with appropriate antibody will become activated and clone
- The majority of B cell clones will differentiate into antibody-producing plasma cells, a few will become B memory cells
Memory cell
- Because the adaptive immune response is dependent on clonal expansion to create sufficiently large amount of antibodies, there is a delay between initial exposure and production of antibodies (for primary response)
- When B cell divides and differentiates into antibody-secreting cells, a small portion of clones will differentiate into memory cells (remain in the body for long period of time)
- If a second infection with same antigen occurs, the memory cells react faster and more vigorously (secondary response) than the initial immune response (primary response), hence symptoms of the infection do not normally appear
- No symptoms of infection upon exposure= immune
- Define active and passive immunity
Active immunity: immunity due to the production of antibodies by the organism itself after the body’s defence mechanisms are stimulated by antigens
Passive immunity: immunity due to the acquisition of antibodies from another organism in which active immunity has been stimulated (passive acquisition achieved through placenta, colostrum and injection)
Neutral immunity: immunity due to infection
Artificial immunity: immunity due to inoculation with vaccinef
- Explain antibody production
- Antigens stimulate an immune response through the production of antibodies
- When a pathogen invades the body, it is engulfed by phagocyte (macrophage) which present the antigenic fragments on its surface
- The macrophage becomes an antigen-presenting cell, present the antigen to T helper cell
- T helper cells bind to antigen and become activated, and then activate B lymphocyte with the specific antibody for the antigen
- This B cell clones and differentiates into plasma cells and memory cells
- Plasma cells produce high quantities of specific antibody to the antigen, whereas memory cells remain in the bloodstream for an extended period of time
- Upon re-exposure to the antigen, memory cells initiate a faster and more vigorous secondary immune response (long term immunity)
- Describe the production of monoclonal antibodies and their use in diagnosis and treatment
Production
- Monoclonal antibodies are antibodies derived from a single B cell clone
- An animal (mouse) is injected with an antigen and produces specific plasma cells
- The plasma cells are removed and fused (hybridized) with tumour cells capable of endless division (immortal cell line)
- The resulting hybridoma is capable of synthesizing large quantities of monoclonal antibodies, for use in diagnosis and treatment
Diagnosis use (checkup)
- Monoclonal antibodies can be used to test pregnancy through the presence of HCG (Human chorionic gonadotrophin)
- An antibody specific to HCG is made and tagged to an indicator molecule (pigment)
- When HCG is presented in the urine it will bind to anti-HCG monoclonal antibody and this complex will move in the fluid until it reaches a second group of fixed antibodies which is specific to anti-HCG monoclonal antibody
- When the complex binds to the fixed antibodies, they will appear as a blue line (positive result)
Treatment use
- Monoclonal antibodies can be used for emergency treatments of rabies
- Because the rabies virus is potentially fatal in non-vaccinated individuals, injecting purified quantities of antibody is an effective emergency treatment for a very serious viral infection
- Explain the principle of vaccination
- Vaccinations induce artificial active immunity by stimulating the production of memory cells
- A vaccine contains weakened or attenuated forms of the pathogen and is injected into the bloodstream
- Because a modified form of pathogen is injected, the individual should not develop disease symptoms
- The body responds to the vaccine by initiating a primary immune response, resulting in the production of memory cells
- When exposed to the actual pathogen, the memory cells trigger a secondary immune response that is much faster and vigorous
- Vaccine confer long term immunity, however because memory cells may not survive a life time, booster shots may be required
- Discuss the benefits and dangers of vaccination
Benefits
- Vaccination results in active immunity
- Limit the spread of infectious disease (pandemic/epidemic)
- Diseases maybe eradicated entirely (smallpox)
- Vaccination program may reduce the mortality rate and protect vulnerable groups
- Decreases health care cost (prevention cheaper than cure)
Risks
- Produce mild symptoms of the disease
- Human error in preparation, storage or administration of the vaccine
- Individuals may react badly to vaccines (allergic reactions)
- Immunity may not be lifelong (requires booster shots)
- Toxic effects of mercury-based preservatives used in vaccine
Muscle and Movement
- State the role of bones, ligaments, muscles, tendons and nerves in human movement
Bones: Provide a hard framework for stability and act as a lever
Ligaments: Hold bones together
Muscles: provide the force required for movement by moving one bone (point of insertion) in relation to another (point of origin)
Tendons: Connect muscles to bones
Nerves: motor neurons provide the stimulus for muscle movement and coordinate sets of antagonistic muscle
- Label a diagram of the human elbow joint, including cartilage, synovial fluid, joint capsule, named bones and antagonistic muscles (biceps and triceps)
- Outline the function of the structures in the human elbow joint named in 10.
Biceps: arm flexor
Triceps: arm extensor
Humerus: Anchors (stabilizes) muscle
Radius/Ulna: forearm levers (radius: lever for biceps; ulna: lever for triceps)
Cartilage: allows easy movement, shock absorbance and distributes load
Synovial fluid: provide nutrients, oxygen and lubrication to cartilage
Joint capsule: seals the joint space and provides passive stability by limiting range of movement
- Compare (and contrast) the movement of the hip joint and knee joint
Similarities
- Both are synovial joints
- Involved in movement of the leg
Differences
- Describe the structure of striated muscle fibers, including the myofibrils with light and dark bands, mitochondria, the sarcoplasmic reticulum, nuclei and the sarcolemma.
- Many nuclei (long fibers, fusing of multiple muscle cells, hence multinucleated)
- Large no. of mitochondria (muscle contraction requires ATP)
- Tubular myofibrils (divided into sections known as sarcomeres, made of two myofilaments (protein responsible for contraction)
- Actin: thin (light band)
- Myosin: thick (H zone)
- Two myofilaments overlap: A band (dark band)
- Sarcolemma: membrane surrounding a muscle fiber
- Sarcoplasmic reticulum: internal membranous network (specialized for muscle contraction, high level of Ca2+ ions)
- Draw and label a diagram to show the structure of the sarcomere, including Z lines, actin filaments, myosin filaments with heads, and the resultant light and dark bands
- H zone: only myosin
- I band: only actin
- A band: overlap of both myofilaments
- Z line: extremities of a single sarcomere
- M line: middle
- Explain how skeletal muscles contract, including the release of calcium ions from the sarcoplasmic reticulum, the formation of cross-bridges, the sliding of actin and myosin filaments, and the use of ATP to break cross-bridges and reset myosin heads
- An action potential from a motor neuron triggers the release of Ca2+ ions from the sarcoplasmic reticulum
- Ca ions expose the myosin heads by binding to a blocking molecule (troponin complexed with tropomyosin) and causing it to move
- Myosin heads form cross-bridges with actin binding sites
- ATP binds to myosin heads and breaks the cross-bridge
- The hydrolysis of ATP causes the myosin heads to change shape and swivel (this moves them towards the next actin binding site)
- The movement of myosin of myosin heads cause the actin filaments to slide over the myosin filaments, shortening the length of the sarcomere
- Through the repeated hydrolysis of ATP, the skeletal muscle will contract
- Analyze electron micrographs to find the state of contraction of muscle fibers
Muscle fibers
- Fully relaxed, slightly contracted, moderately contracted and fully contracted
- Sarcomere gets shorter when the muscle contracts (A band does not: filaments do not contract)
- Filaments sliding over each other and increasing their overlap: gradual reduction in the H zone
