Blood

Question 1

Average circulating blood volume in a typical adult male

Answer 1

5L; 1L in the lungs, 3L systemic venous circulation, 1L heart and arterial circulation.

Question 2

Functions of blood

Answer 2

1. Carriage of physiological active compounds (hormones, enzymes, nutrients)
2. Clotting (prothrombin and fibrinogen)
3. Defence (WBCs/ leukocytes)
4. Carriage of gas (O2 and CO2 in RBCs)
5. Thermoregulation
6. Maintenance of ECF pH

Question 3

Plasma

Answer 3

Accounnts for approx 4% body weight comprised of 92% water, 7% proteins and 1% organic molecules, ions, trace elements and vitamins.
It circulates biologically active molecules and compounds and its composition is nornally kept within strict limits.

Question 4

Plasma proteins

Answer 4

Albumin (60%, contributes to colloid osmotic pressure, carriers), globulins (alpha and beta are clotting factors, enzymes and carriers/ gamma - antibodies), fibrinogen (forms fibrin thread for clotting and other clotting factors), transferrin (transports iron).

Question 5

Oncotic pressure/colloid osmotic pressure

Answer 5

Plasma proteins, mainly albumin, make the osmotic pressure of blood higher than that of interstitial fluid. This osmotic gradient pulls water from the interstitial fluid alongside ions, Glc etc. The concentration of fluid remains unchanged but the volume of plasma and fluid alters.
Net fluid movement is subject to 2 forces;
1. Capillary hydrostatic pressure (>IHP) favours movement of fluid out of the capillary.
2. Plasma protein concentration (high) favours movement of fluid into the capillary. The oncotic pressure determines the direction of met movement.

Question 6

Hypoproteinaemia

Answer 6

Low levels of circulating plasma proteins characterised by oedema as loss of oncotic pressure.

Question 7

Circulating levels

Answer 7

RBCs - 4-6x10^(12)/L
WBCs - 1x10^(10)/L
Platelets - 140-400x10^(9)/L

Question 8

Life span of blood cells

Answer 8

RBC - 120 days
WBC - 13-20 days
Platelets - 10 days

Question 9

Red blood cells

Answer 9

Used for gas transport - densely packed with haemoglobin containing O2. It removes CO2 from the body via the lungs to be exhaled.

Question 10

Erythropoietin

Answer 10

It promotes the formation of RBCs by the bone marrow.
It is a hormone produced by the kidneys (85%) and hepatocytes (15%).
Low O2 delivery to kidneys due to haemorrhage, anaemia, cardiac dysfunction, lung disease etc will increases its secretion with a 2-3 day delay.

Question 11

Lymphocytes

Answer 11

Eliminate the antigen. B lymphocytes produce/release antibodies. Cytotoxic/killer T cells release cytotoxic granules. Helper T cells signal to other immune cells for help.

Question 12

Monocytes

Answer 12

After 72 hours of circulation they migrate to connective tissue to become macrophages. Macrophages are used for phagocytosis and recruitment of lymphocytes as they are antigen presenters to T cells.
Dendritic cells are antigen presenting cells. They are messengers between innate and adaptive immune systems.

Question 13

Neutrophils

Answer 13

The first line of defence. They are circulatory and sense signals of infection. Phagocytes (68%) have a 6.5 hour life expectancy and they phagocytose bacterial infections, trapping bacteria in nets.

Question 14

Eosinophils

Answer 14

Attack pathogens too large for other leukocytes. They increase in allergic reactions.

Question 15

Basophils

Answer 15

Respond in inflammatory responses by releasing histamine and heparin.

Question 16

Leukopoiesis

Answer 16

The formation of WBCs. Controlled by a cocktail of cytokines (proteins/peptides released from 1 cell type which act on another) which is dynamic depending upon infection. Colony stimulating factors such as granulocyte CSF stimulatethe bone marrow to producegranulocytes and stem cells and release them into the bloodstream.
Interleukins mediate communication between WBCs.

Question 17

Platelet function

Answer 17

They adhere to damaged vessel walls and expose connective tissue to mediate blood clotting by forming a scaffolding for clotting factors to produce the clot.

Question 18

Platelet formation

Answer 18

Megakaryocytes mix with thrombopoietin and membrane bound cell fragments to form platelets.

Question 19

Haematocrit

Answer 19

The ratio of the volume of RBCs to the total volume of blood expressed as a percentage. Diagnostic tool through centrifugation.
Normal values;
- male; 40-54%
- female; 37-47%
Decreased by anaemia, bleeding, leukemia, malnutritiom, low iron, high H2O. Increased in people living at altitude as less O2 in the air, congenital heart disease, bone marrow disease and dehydration.

Question 20

Blood viscosity

Answer 20

How thick/sticky blood is compared to water.
Plasma - 1.8 (x thicker than water)
Whole blood - 3-4
Viscosity is not an absolute value and depends on; the haematocrit as a 50% increase leads to a 100% increase in viscosity and temperature as an increase leads to a decrease in viscosity. A 1degree change changes viscosity by 2%.