Haemotology Flashcards
What are the main components of blood?
Plasma, red blood cells, white blood cells, platelets
Plasma consists of approximately 55% of blood volume. (Ranges 46-63%)
What are the main functions of blood?
Transport, defense, regulation
Blood transports gases, nutrients, waste products, and regulates temperature.
What is haemopoiesis?
The process of blood cell formation
It includes the production of red blood cells, white blood cells, and platelets.
What is erythropoiesis?
The production of red blood cells
Requires erythropoietin, iron, vitamins B12 and folic acid, and amino acids.
Where does erythropoiesis occur?
- Foetus = early yolk sac, then liver & spleen, later in bone marrow (at birth)
- Infant = all bone marrow (as high demand)
- Adults = only in red bone marrow (ribs, vertebrae, skull, upper ends of long bones)
What is the lifespan of a red blood cell?
Approximately 120 days
After this, they undergo breakdown and recycling.
What is haemoglobin?
A protein in red blood cells that carries oxygen
Each red blood cell contains approximately 280 million haemoglobin molecules.
What is the normal range of haemoglobin for men?
13.5 - 17.5 g/dL
For women, it is 12.0 - 16.0 g/dL.
Define anaemia.
A condition characterized by a low level of haemoglobin in blood
Less than 13.5 g/dL for men and less than 12.0 g/dL for women.
What are the causes of anaemia?
Decreased RBC production, increased RBC destruction, blood loss
These factors can lead to a deficiency in oxygen transport.
What is iron deficiency anaemia?
The most common type of anaemia worldwide
Decreased mean cell volume (MVC)
Characterized by hypochromic (pale RBCs), microcytic red blood cells (smaller than normal RBCs)
What are the characteristics of megaloblastic anaemia?
Macrocytic red blood cells (larger than normal RBCs, more oval shaped) & hypersegmented neutrophil
Reduced haemoglobin concentration
Abnormal RBCs
Increased mean cell volume (MVC)
What is pernicious anaemia?
A type of megaloblastic anaemia caused by lack of intrinsic factor
This factor is necessary for vitamin B12 absorption.
What is sickle cell anaemia?
- A hereditary condition characterized by abnormal haemoglobin structure
- Common in African & West Indian backgrounds
- It leads to sickle-shaped red blood cells that can obstruct blood flow (due to deformed shape) causing pain and low O2
Protects against malaria
What are thalassaemias?
Hereditary disorders of abnormal haemoglobin production
Common in Mediterranean & Middle/ Far Eastern backgrounds
Produce alpha and beta thalassaemias - affects number of alpha and beta Hb
What hormone increases red blood cell production during hypoxia?
Erythropoietin (EPO)
Its levels rise in response to low oxygen levels.
Fill in the blank: Blood accounts for approximately _____ of your weight.
7%
The average adult has a blood volume of 5L.
True or False: The average size of a red blood cell is approximately 7.2-8.4 um.
True
This size range is typical for red blood cells.
What is haemolytic disease of the newborn (HDN)?
A condition that occurs when an Rh negative mother gives birth to an Rh positive baby, leading to the mother’s immune system attacking the baby’s red blood cells
This can occur if the mother has been sensitized to Rh positive blood through transfusion or a previous pregnancy.
What determines the Rh blood group?
The presence or absence of the D antigen
An individual can be classified as Rh negative (-) or Rh positive (+) based on this antigen.
What is required for an Rh negative individual to develop anti-Rh (D) antibodies?
Sensitization by exposure to Rh positive red blood cells
This can happen through transfusion or during pregnancy.
What are the components of the intrinsic pathway in coagulation?
Factor IX, co-factor VIII, factor XII, and factor XI
This pathway activates factor X to Xa more slowly than the extrinsic pathway.
What is the common pathway in the coagulation process?
It involves prothrombinase, which consists of FXa and FVa, activating prothrombin to form thrombin
Thrombin then converts fibrinogen to fibrin.
What role do calcium and vitamin K play in coagulation?
They affect almost every aspect of the clotting process
Calcium is necessary for clotting, and vitamin K is essential for the production of certain clotting factors in the liver.
What is the function of antithrombin in coagulation control?
It inhibits thrombin and other clotting factors
This helps regulate the coagulation process.
What is fibrinolysis?
The process of breaking down a fibrin clot
The main enzyme involved is plasmin, which converts plasminogen to plasmin.
Produces fibrin degradation products in different sizes
What are the main components of haemostasis?
Platelets, vasoconstriction, and coagulation
These components work together to form a stable fibrin clot.
What is the ABO blood group system?
A system that classifies blood based on the presence of surface antigens on red blood cells
The most clinically significant blood groups are A, B, AB, and O.
How are ABO blood groups inherited?
A and B genes are dominant, while the O gene is recessive
This results in various combinations of blood types based on parental alleles.
Who can donate blood to whom based on ABO and Rh blood groups?
Rhesus positive can donate to positive and negative; Rhesus negative can only donate to negative
O negative is considered the universal donor.
What is the primary role of platelets in haemostasis?
To form a stable haemostatic plug at the site of vessel injury
Platelets have a normal lifespan of 7-10 days and are produced from megakaryocytes.
What is the endpoint of the coagulation phase?
The conversion of soluble plasma protein fibrinogen to the insoluble rigid polymer fibrin (irreversible fibrin clot)
This process is stabilized by factor XIII.
True or False: The extrinsic pathway of coagulation is faster than the intrinsic pathway.
True
The extrinsic pathway responds more quickly to tissue injury.
What are white blood cells also known as?
Leukocytes
These are nucleated = capable of repair and remain in circulation
What is the normal white blood cell (WBC) count range in litre blood?
Approx 4-11 x 10^9
WBC count can indicate various diseases.
What are the two main types of white blood cells based on their structure?
Agranulocytes and granulocytes
What percentage of WBCs are neutrophils?
50-70%
Neutrophils are the most common type of white blood cell.
What is the primary function of neutrophils?
- First line of defence against bacterial infections
- Phagocytic
- Mobile
- Circulate in blood for approx. 10 hours
- Major constituent of pus
What is the structure of neutrophils?
9-15 µm diameter (varies due to maturity), distinctive nucleus with 2-5 lobes (more mature = more globes), granular cytoplasm
How long do neutrophils circulate in the blood?
Approx 10 hours
But can remain in tissue for 10-12 days
What percentage of WBCs are eosinophils?
2-4%
NOT very common in the body
What is the structure of eosinophils?
10-12 µm diameter, bilobular nucleus (2 lobes)
What are the main functions of eosinophils?
- Circulate in blood for approx. 8-12 hours then migrate to tissues
- Survive for approx. 1-3 days
- Release toxic compounds e.g. NO and cytotoxic enzymes to fight infection
- Allergies, asthma causes eosinophil count to increase
- Combat parasitic infections in particular
- Also help neutrophils in attacking bacteria, Protozoa, debris
What percentage of WBCs are basophils?
> 1%
Basophils are the least common type of white blood cell.
What is the structure of basophils?
8-10 µm diameter, bilobed ‘S’ shaped nucleus, large cytoplasmic granules (obscure the nucleus)
Granules = histamine, heparin (chemicals in inflammatory response and clotting)
What is the main function of basophils?
Inflammatory response
Lifespan unknown
Maybe precursor to mast cells- share a common bone marrow precursor
What percentage of WBCs are monocytes?
2-10%
What is the structure of monocytes?
Largest white cell
Up to 20 µm diameter
Large kidney/horse shoe shaped nucleus (may vary but will have indentation)
Extensive cytoplasm
What is the lifespan of monocytes in circulation?
3-4 days before migrating to tissues where they live forever
What percentage of WBCs are lymphocytes?
20-30%
What is the lifespan of lymphocytes?
Weeks to several years
What are the main types of lymphocytes?
- T cells
- B cells
- NK cells
What is the function of T cells?
Mediate cell-mediated immunity
E.g. transplant rejection
What is the function of B cells?
Differentiate into plasma cells; secrete antibodies
(Humoral immunity)
What is the function of NK cells?
Immune surveillance, important in preventing cancer
What is the process of erythropoiesis?
- Starts as a stem cell (in blood marrow only) = hemocytoblast
- Becomes a committed cell = proerythroblast
- Phase 1 is ribosome synthesis = Erythroblast
- Phase 2 is hemoglobin accumulation = Normoblast
- Phase 3 is ejection of nucleus (as a normoblast)
- Becomes a reticulocyte
- Then finally an erythrocyte (red blood cell)
What is required for erythropoiesis?
- Erythropoietin (EPO) = growth factor for production
- Iron
- Vitamins B12 & folic acid (B9) = essential
- Intrinsic factor = to absorb vitamin B12
- Amino acids = to make ‘globin’ part of heamoglobin
What is the structure and function of red blood cells?
Shape & size
- diameter of 7-8 um
- disc shape
- thick outer membrane and thin inner membrane to allow flexibility
- Highly flexible and deform readily
Contents
- only heamoglobin
- no organelles = prone to damage
What are causes of hypoxia?
low levels of O2 in the blood
- increase in exercise
- high altitude
- smoking (affects ability of O2 binding)
- bleeding
Describe the erythrocyte homeostasis cycle. (5 marks)
- Low O2 blood levels
- Stimulus (hypoxia) received and kidneys increase production of erythropoietin
- Stem cells increase red blood cell production
- O2 blood level returns to normal
- Normal O2 blood level so stimulus is resolved
How is haemoglobin produced?
- Synthesis begins in proerythroblast
- 65% at erythroblast stage
- 35% at reticulocyte stage
- Hb is produced before the red blood cell is fully mature
What is the role of haemoglobin (Hb)?
- transports O2 from lungs to tissues
- transports CO2 from tissues to lungs
What is the structure of haemoglobin adult (HbA)?
- 4 subunits: 2x alpha and 2x beta subunits
- Each subunit has “haem” bound to long polypeptide chain “globin”
- In the centre of Haem group is a ferrous iron atom (Fe2+)
- Fe2+ can reversible bind with one molecule of oxygen (O2)
What causes iron deficiency anaemia?
-Pregnancy
-Bleeding from GI tract (ulcer, malignancy)
-Malabsorption (iron reabsorption)
-Menorrhagia (heavy periods)
-Malnutrition (dietary)
What causes Megaloblastic anaemia?
Vitamin B12 deficiency or folate deficiency (needed for cell division)
What are the elements of heamostatic response?
Vasoconstriction of blood vessels (damage)
Platelet adhesion and aggregation
Clotting - coagulation phase
What are platelets?
- ‘fragments of a cell’
- small, oval, no nucleus
- contains granules (containing clotting factors)
- megakaryocyte cytoplasm (precursor cell)
- lifespan of 7-10 days
Production is controlled by
- No of circulating platelets (negative feedback)
- Thrombopoietin (TBO) release = increase platelet numbers
What initiates the coagulation phase?
EXTRINSIC PATHWAY
- Tissue factor released by damaged tissue
- Binds to factor VII (F7)
- Forming tissue factor-FVIIa complex (‘a’ means activated)
- This binds to FX and activates it to become FXa
What is the intrinsic pathway in the coagulation phase?
- Factor IX (F9) and cofactor VIII (enhances F9)
- Activates FX to FXa
- More slowly than extrinsic pathway but more sustained
- Factor XII —> XIIa
- Which in turn activates factor XI to XIa
- This then activates FIX to IXa
What is the common pathway of the coagulation phase?
- Prothrombinase = consists of FXa and FVa as a co-factor
- Activates prothrombin to form thrombin (important for feedback)
- Thrombin converts fibrinogen to fibrin (forms clot)
What is heparin?
Released by basophils and mast cells- co-factor that accelerates actions of antithrombin
What happens in haemolytic disease of the newborn?
- maternal and fetus tissue is initially separate
- tissues merge
- Rh+ enters mother and immune response is triggered
- this remains in circulation
- haemolysis occurs (break down of red blood cells)
What is the role of white blood cells?
- defence against pathogens
- toxin and waste removal (macrophage)
- removes damaged cells (macrophage)
- act mainly outside in tissues = in transit between sites of activity
What are the characteristics of WBCs?
- all can migrate out of the blood stream = extravasation (diapedesis)
- all are capable of amoeboid movement
- all are attracted to specific chemical stimuli
- neutrophils, eosinophils, and monocytes are capable of phagocytosis
What are the 3 types of ganulocytes?
- neutrophils
- eosinophils
- basophils
What are the 2 kinds of Agranulocytes?
Monocytes and lymphocytes
What is the function of monocytes?
Little function in blood
Tissue macrophages (several months-years)
Phagocytic
What is the structure of lymphocytes?
Smallest white cell
6-15 um diameter
Lifespan = weeks to several years (depends on which type)
What is the function of lymphocytes?
Central role in all immunological defence mechanisms
Circulate between various lymphoid tissues and all other tissues of body via blood and lymphatic vessels
Name the WBCs from most common to least common and their percentage
- Neutrophils = 50-70%
- Lymphocytes = 20-30%
- Monocytes = 2-10%
- Eosinophils = 2-4%
- Basophils = <1%
