Haemotology I - components of Blood with a focus on red blood cells

What is blood?

A fluid connective tissue and a component of the cardiovascular system.

What makes up the cardiovascular system?

The heart and blood vessels.

What is the average adult blood volume?

Approximately 5 litres.

What percentage of body weight is blood?

Approximately 7% of body weight.

What are the two main components of blood?

Plasma and formed elements (blood cells and cell fragments).

What percentage of blood is plasma?

Approximately 55%.

What is the normal range of plasma volume?

46–63% of total blood volume.

What is plasma?

The liquid component of blood that transports substances, formed elements and heat.

What percentage of plasma is water?

Approximately 92%.

What percentage of plasma consists of proteins?

Approximately 7%.

What percentage of plasma consists of other solutes?

Approximately 1%.

What are the main plasma proteins?

Albumin, globulin, fibrinogen and regulatory proteins.

What are the other solutes found in plasma?

Electrolytes, organic nutrients and waste products.

What is the function of plasma?

Transports inorganic and organic molecules, formed elements and heat.

What is albumin?

A plasma protein.

What are globulins?

Plasma proteins.

What is fibrinogen?

A plasma protein involved in blood clotting.

What are the main transport functions of blood?

Transporting gases, nutrients, excretory products and heat.

Which gases does blood transport?

Oxygen (O2) and carbon dioxide (CO2).

What nutrients does blood transport?

Nutrients required by body tissues.

What excretory products does blood transport?

Waste products that need to be removed from the body.

What is the role of blood in temperature regulation?

Transports heat around the body.

What are the main defence functions of blood?

Protection through antibodies, white blood cells and clotting factors.

What are antibodies?

Defence substances involved in protecting the body.

What are the three main functions of blood?

Transport, defence and clotting-related protection.

What is haematopoiesis (haemopoiesis)?

The formation and production of blood cells.

What is erythropoiesis?

The production of red blood cells (erythrocytes).

What hormone stimulates erythropoiesis?

Erythropoietin (EPO).

What is erythropoietin (EPO)?

A hormone that stimulates red blood cell production in the bone marrow.

What are the requirements for erythropoiesis?

EPO, iron, vitamins B12 and B9 (folic acid), intrinsic factor and amino acids.

Why is iron required for erythropoiesis?

Iron is required for haemoglobin production.

Which vitamins are required for erythropoiesis?

Vitamin B12 and folic acid (vitamin B9).

What is intrinsic factor?

A substance secreted by the stomach that is required for vitamin B12 absorption.

Why are amino acids required for erythropoiesis?

They are needed for protein synthesis, including globin chains.

Where does erythropoiesis occur in the early foetus?

In the yolk sac.

Where does erythropoiesis occur later in foetal development?

In the liver and spleen, followed later by the bone marrow.

Where does erythropoiesis occur in infants?

Throughout the bone marrow.

Where does erythropoiesis occur in adults?

Only in red bone marrow.

Where is red bone marrow found in adults?

Ribs, vertebrae, skull and upper ends of long bones.

How many red blood cells are produced per second?

Approximately 2–3 million.

What are red blood cells also called?

Erythrocytes.

What is the main function of red blood cells?

Transporting oxygen from the lungs to body tissues.

What is a major structural characteristic of red blood cells?

They are highly flexible and deform readily.

What is the average size of a red blood cell?

Approximately 7.2–8.4 µm.

How many red blood cells are present in the average adult body?

Approximately 25 trillion.

What is the main substance contained in red blood cells?

Haemoglobin.

How many haemoglobin molecules are in each red blood cell?

Approximately 280 million.

What is haemoglobin (Hb)?

A protein in red blood cells responsible for transporting respiratory gases.

When does haemoglobin synthesis begin?

At the proerythroblast stage.

What percentage of haemoglobin is synthesised at the erythroblast stage?

Approximately 65%.

What percentage of haemoglobin is synthesised at the reticulocyte stage?

Approximately 35%.

Is haemoglobin synthesis completed before a red blood cell is fully mature?

Yes, haemoglobin synthesis occurs before full red blood cell maturation.

What is the approximate haemoglobin concentration in blood?

Approximately 15 g/dL.

What is the normal haemoglobin concentration in females?

12–16 g/dL.

What is the normal haemoglobin concentration in males?

13.5–17.5 g/dL.

What is adult haemoglobin called?

HbA.

How many subunits does adult haemoglobin (HbA) contain?

Four subunits.

What are the subunits of adult haemoglobin (HbA)?

Two alpha (α) chains and two beta (β) chains.

What are the two components of each haemoglobin subunit?

A haem group and a long polypeptide chain called globin.

What is the haem group?

The part of haemoglobin containing a central ferrous iron atom.

What type of iron is found in the haem group?

Ferrous iron (Fe2+).

What does Fe2+ bind to?

One molecule of oxygen (O2).

How does oxygen bind to haemoglobin?

Reversibly, allowing oxygen to bind and be released.

What does reversible oxygen binding mean?

Oxygen can attach to and detach from haemoglobin.

What are the main gases and substances carried or involved in haemoglobin transport?

Oxygen, carbon dioxide, carbon monoxide and hydrogen ions (H+).

What does haemoglobin transport from the lungs to tissues?

Oxygen (O2).

What does haemoglobin transport from tissues to the lungs?

Carbon dioxide (CO2).

What is hypoxia?

A condition in which oxygen availability is insufficient.

What are the causes of hypoxia listed in the lecture?

Increased exercise, high altitude, smoking and bleeding.

What is erythrocyte homeostasis?

The regulation of red blood cell numbers in response to the body's oxygen requirements.

What happens to EPO production during hypoxia?

EPO production increases.

What happens to the bone marrow during increased EPO stimulation?

The bone marrow is stimulated to produce more red blood cells.

How does the body respond to hypoxia through negative feedback?

Hypoxia increases EPO production, stimulating bone marrow and increasing the red blood cell count.

How long does it take for the red blood cell count to increase following EPO stimulation?

Approximately 3–4 days.

What is anaemia?

A haemoglobin concentration in whole blood below the accepted normal range.

How does the WHO definition describe anaemia?

Haemoglobin concentration in whole blood below the accepted normal range.

What haemoglobin concentration indicates anaemia in men according to the lecture?

Less than 13.5 g/dL.

What haemoglobin concentration indicates anaemia in women according to the lecture?

Less than 12.0 g/dL.

Approximately how much of the world's population is affected by anaemia?

Approximately one-third.

What are the three main causes of anaemia?

Decreased red blood cell production, increased red blood cell destruction and blood loss.

What is iron deficiency anaemia?

Anaemia caused by insufficient iron, affecting haemoglobin production.

What is the most common type of anaemia worldwide?

Iron deficiency anaemia.

What does hypochromic mean?

Red blood cells have reduced haemoglobin content and appear paler.

What does microcytic mean?

Red blood cells are smaller than normal.

What is the red blood cell appearance in iron deficiency anaemia?

Hypochromic and microcytic.

What happens to mean cell volume (MCV) in iron deficiency anaemia?

It decreases.

What is MCV?

Mean cell volume; a measurement of the average size of red blood cells.

What are the causes of iron deficiency anaemia?

Pregnancy, gastrointestinal bleeding, malabsorption, menorrhagia and dietary malnutrition.

What gastrointestinal conditions can cause iron deficiency anaemia?

Ulcers and malignancy causing bleeding from the gastrointestinal tract.

What is menorrhagia?

Heavy menstrual bleeding.

How can pregnancy contribute to iron deficiency anaemia?

Increased iron requirements can contribute to iron deficiency.

How can malabsorption cause iron deficiency anaemia?

Reduced absorption of iron can lead to iron deficiency.

Why is diagnosing iron deficiency alone insufficient?

The underlying cause of the iron deficiency must always be investigated.

What is a normal blood film used for?

Providing a reference for comparing normal blood cell appearance with abnormal blood films.

What is megaloblastic anaemia?

A type of anaemia caused by vitamin B12 deficiency or folate deficiency.

What are the two main deficiencies causing megaloblastic anaemia?

Vitamin B12 deficiency and folate (vitamin B9) deficiency.

What is the red blood cell appearance in megaloblastic anaemia?

Macrocytic red blood cells.

What does macrocytic mean?

Red blood cells are larger than normal.

What happens to MCV in megaloblastic anaemia?

It increases.