Module 4: Blood and Immune

Question 1

How much blood is in the average human adult?

Answer 1

5 L

Question 2

How much blood does the heart pump per heartbeat and per day?

Answer 2

70mL per pump, 14,000 L per day

Question 3

How long does it take for blood to do a circuit of the body?

Answer 3

1 minute

Question 4

How much blood does a newborn have?

Answer 4

300 mL

Question 5

How long are our blood vessels?

Answer 5

100,000 km.

Question 6

What is the path of blood?

Answer 6

It is pumped through our arteries, capillaries and veins before returning to the heart. Some components are passed through the capillary walls into the tissue, becoming interstitial fluid which circulates and returns to the blood through the ducts of the lymph system.

Question 7

What are the functions of blood?

Answer 7

Transport, regulation, protection

Question 8

What is the transport function of blood?

Answer 8

Carries O2, CO2, hormones, nutrients, waste, heat, drugs and vaccines around the body

Question 9

What is the regulatory function of blood?

Answer 9

Regulates homeostasis, temperature, salinity, osmolarity and the hormones it carries regulate cell processes

Question 10

What is the protective function of blood?

Answer 10

Carries antibodies and immune system cells/molecules to prevent infection. It also has a clotting function to prevent bleeding out.

Question 11

What is the composition of blood?

Answer 11

55% plasma.
Of plasma, 1.5% solutes, 7% proteins, 91.5% water.
Of proteins, 54% albumins (serum albumin) and 38% globulins
45% formed elements
Of formed elements, 99% RBCs. The rest are WBCs and platelets

Question 12

What is the composition of white blood cells?

Answer 12

60-70% Neutrophils
20-25% lymphocytes
3-8% monocytes
2-4% eosinophils
.5-1% basophils

Question 13

What is the structure of a RBC?

Answer 13

They are biconcave, with a diameter of about 8um.
Each cell contains approx. 280 million haemoglobin molecules which can each bind 4 oxygen molecules- each RBC can transport about 1 billion O2 molecules!

Question 14

What is the structure of haemoglobin?

Answer 14

It is a quaternary protein with 4 polypeptide chains- 2x alpha and 2x beta. Each chain binds 1 haem molecule. It is the most prevalent protein in blood, at about 15% (150mg/mL). One blood cell is approx. 34% haemoglobin

Question 15

What is the basic structure of a haem group?

Answer 15

It has an iron atom at its center, enabling it to bind to an O2 molecule. Surrounding it are 4 Nitrogen connected to ring structures etc

Question 16

What is serum albumin?

Answer 16

A polypeptide which carries small insoluble molecules like lipids, hormones and drugs.

Question 17

What is the structure of serum albumin?

Answer 17

It’s a single stranded polypeptide of 585 amino acids.

Question 18

Why is the structure of serum albumin important?

Answer 18

When designing drugs it must be ensured that they will be able to bind to serum albumin.

Question 19

What is an immunoglobulin?

Answer 19

There are millions of different types with different specific antigen binding sites. This means they can ‘tag’ other cells for destruction by binding to them until a leukocyte finds them. It comprises about 20mg/mL of plasma

Question 20

What is the structure of immunoglobulin?

Answer 20

It is made up of 12 domains, and the predominant class is called IgG. It is comprised entirely of B pleated sheets arranged in 4 chains: 2 heavy and 2 light. The heavy chains are each 434 amino acids long, while the light are 213. They are arranged in a Y shape, with the two heavy chains making the tail and inside of the V of the Y, and the two light chains lining the V’s outside. These are held together with disulfide bonds. Each heavy chain has 4 domains, and each light has 2. At the ends of the V, where the H and L chains meet (the variable region) there is an antigen binding site, specific to a single antigen.

Question 21

How can there be so many types of IgG?

Answer 21

The ‘variable’ regions are created by both inherited and ‘random’ sequences of DNA, resulting in a large number of know and unknown antigens to be identified.

Question 22

What is the difference between leukocytes and erythrocytes?

Answer 22

RBCs have DNA, a nucleus, organelles and complex functions

Question 23

Where do leukocytes come from?

Answer 23

Haemopoietic stem cells

Question 24

What are monocytes?

Answer 24

They are produced in the red bone marrow, spending 5-8 days in the blood before moving into the tissues and becoming macrophages.

Question 25

What are macrophages?

Answer 25

They act as the neighborhood watch, reporting foreign bodies to the lymph nodes. They recognize common infections and can ingest and destroy antigens they don't recognize- they aren't specific to an antigen.

Question 26

What is an antigen?

Answer 26

Anything which stimulates the immune system

Question 27

What are B & T lymphocytes?

Answer 27

T- helper cells assist B cells in developing a response by activating them. Killer T-cells identify and kill infected body cells, rather than just foreign bodies. B cells are activated by T cells and differentiate into plasma cells (to produce specific antibodies) and memory cells (which ensure the body can generate a faster response if attacked by this antigen again) Both have antigen-specific receptors. B cells can also circulate in the blood and move into tissue and destroy antigens IF they come across their specific antigen.

Question 28

What are phagocytes?

Answer 28

Cells which digest other cells. They include neutrophils, monocytes and B cells. B cells are antigen specific, but the others are generalized.

Question 29

How do phagocytes become attracted to an infection site?

Answer 29

Mast cells in the infected tissue produce histamine, and dilate the blood vessels. This attracts neutrophils and macrophages. NB neutrophils die after consuming their antigen, while macrophages relay the broken molecule back to the lymph nodes.

Question 30

How do macrophages 'report' their kill?

Answer 30

First, they ingest the antigen through their plasma membrane via phagocytosis, in a bubble which is, when internalized, binds to a lysosome. (The antigen/lysosome complex is called a phagolysosome). The bacteria is broken up by enzymes. Some pieces are excreted by exocytosis, while some get expressed through the plasma membrane through a molecule called MHCII, which holds it in place and enables it to be read by T-cells in the lymph nodes.

Question 31

What is the structure of the lymph nodes?

Answer 31

They are a sort of mosaic of B and T cells, with different regions specific to different antigens.

Question 32

What is the first step in an immune response?

Answer 32

For a first infection: Localised swelling (due to histamine). Some corresponding antibodies may be present, and they tag the bacteria. Phagocytes are attracted and move from the blood vessel into the tissue, consuming and breaking down the bacteria. If by chance a B cell passes with the right specificity, it will also help.

Question 33

What is the second step in an immune response?

Answer 33

Macrophages heralding their kill move back through the lymph, passing through the lymph nodes until they find one which matches their antigen. The MHCII matches the T-cell receptor on the T cell, which interact and are held together by CH4. The binding of the two together causes the T cell to divide, assisting others with antibody production. There are now more T-cells specific for this infection.

Question 34

What is the third step in an immune response?

Answer 34

If the infection persists, a corresponding B cell will stumble across it, and present it with MHCII like the macrophage. When it reaches the corresponding T cell in the lymph node, the T cell is activated, which re-activates the B cell, allowing it to divide and form active B cell clones, which differentiate into plasma cells to produce antibodies, and memory cells.

Question 35

What is the fourth step in an immune response?

Answer 35

A while later, B cells have produced vast numbers of antibodies specifically for the infection. T cells are also proliferating, to activate more B cells. This causes the lymph nodes to swell. Eventually all antigens have been tagged and destroyed.

Question 36

What is the fifth and final step of the immune response?

Answer 36

'Memory cells' remain in the lymph nodes, and some specific antibodies may remain in circulation, ready to respond again if needed.

Question 37

What is the difference between the immune response for a first and second infection?

Answer 37

In a second infection, the response will be much faster and effective because: There are large numbers of the specific T and B cells in the lymph nodes, so memory alert is very fast - There may still be some antibodies in the blood, allowing recognition to occur sooner. The second infection may be cleared before the host is aware of its presence.

Question 38

How do antibodies help to rid an infection?

Answer 38

- Neutralization: antibodies block the antigen's binding site, coats the bacteria, or opsonizes (identifies) the antigen. - Agglutination: the antibodies join into a long 'wheel', with antibodies in the centre and the bacteria facing outward (helps the phagocyte to get it all in one go) - Precipitation: If the antigen is soluble, the antibodies bind them into long chains, forcing them to precipitate.

Question 39

What is HIV?

Answer 39

A retrovirus and a slow virus, meaning it has a long incubation period. It is transmitted through body fluids (semen, blood and breastmilk), and affects all population groups worldwide. It's the leading cause of death in Africa, and new cases are constantly being recorded.

Question 40

What is the internal structure of HIV?

Answer 40

As a retrovirus, it contains RNA. It is a spherical cell with a lipid bilayer membrane, a matrix, a conical caspid and surface proteins. The conical caspid contains 2 identical strands of RNA, which contain 9 genes coding for 19 proteins. It also contains reverse transcriptase and proteinase. The surface proteins are GP120, which attaches to a GP41 stalk.

Question 41

How do HIV's 9 genes produce 19 proteins?

Answer 41

The enzyme called proteinase cleaves the polypeptides the gene codes for into smaller functional ones. Eg. one polyproteinase creates env, gag and pol proteins.

Question 42

What is the process of HIV infection?

Answer 42

When HIV arrives in the body, it is tagged for destruction and a normal immune response results. Killer T cells kill infected cells, but often, the HIV has inserted itself into the DNA of helper T-cells. It does this by binding to CD4 with GP120, after which the virus's cell membrane attaches to the T-cell and its caspid opens, depositing the two RNA strands and reverse transcriptase into the cytoplasm of the t-cell. Reverse transcriptase converts the 2 RNA to a DNA double helix, while the protein integrase inserts this new DNA into the DNA of the T cell, where it waits for activation.

Question 43

How do killer T cells know which cells to kill?

Answer 43

Cells advertise small pieces of their internal proteins on their surface, which allows the killer T cells to know if it's 'norma' or 'not normal'.

Question 44

Why can't killer T-cells identify the integrated HIV/T cells?

Answer 44

The virus is in the DNA, which is not advertised on the cell surface, allowing it to go undetected.

Question 45

How does HIV proliferate?

Answer 45

When the T cell is activated by an antigen, the HIV hijacks the cell and replicates, producing more HIV particles. While killer T-cells will take out some infected cells (pre-integration), the rate of HIV generation outstrips the killer T-cells' abilities.

Question 46

What happens once you have less than 20% of your normal T-cell count?

Answer 46

The number of antibodies you have begins to decrease, AIDS develops, allowing any and all infections, cancers and diseases full scope of the body. It is fatal.

Question 47

Why is HIV important?

Answer 47

It is worldwide There is currently no cure It is difficult to eliminate infected cells without triggering an immune response (and generating more HIV) The drugs are currently expensive, inconvenient and have many side effects. There is no vaccine, so behavior is the only thing able to prevent it.