Blood

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Functions of the Blood

The blood transports dissolved gases, nutrients, hormones and metabolic waste.

It regulates the pH and electrolyte composition of interstitial fluids throughout the body.

It restricts fluid loss

It defends against toxins and pathogens

It stabilizes the body temperature

Compostion

The blood volume is ~5L

3L Plasma:

water

Ions

Trace elements and vitamins

Gases: O2 + CO2

Organic molecules:

Amino acids

Proteins: albumins synthesized by the liver (osmotic pressure and transport hormones) Globulins (ion transport and immune system) and Fibrinogen (coagulation)

Glucose

Lipids

Nitrogenous waste

2L Blood Cells

Red Blood Cells

White Blood Cells: lymphocytes, monocytes, neutrophils, Eosinophils, basophils.

Platelets

Haematopoiesis: Blood cell formation from a stem cell. Undifferentiated cells capable of becoming any blood cell.

Bone marrow contails the cells in different stages of development and supporting tissue

Red Blood Cells (erthrocytes): gas transport

Red blood cells are the most abundant blood cell, they contains haemoglobin which binds and transports O2 and CO2. Each RBC is a biconcave disc ~8micrometres x 2.5micrometres with a high SA to volume ratio. Short life span of 120 days as they have no nuclei or organelles. Bilirubin is the major breakdown product.

Haemoglobin is a large protein consisting of 4 polypeptide chains each containing a single molecule of haem which contains an iron pigment. The iron ion in haem is able to reversibly bind to an oxygen molecule so Hb can bind O2 in the lungs and release it in the tissues. Iron is stored in the liver bound to a protein called ferritin.

Leukocytes

Neutrophils: They are the first line of defense for the immune system as they are phagocytic and engulf bacteria. Enter tissues during infections.

Lymphocytes: B cells and T cells they secrete antibodies as part of the immune system.

Eosinophils: found in blood and mucosal surfaces to fight invasions by eukaryotic parasites.

Monocytes: circulate in the blood and mature into macrophages in the tissue.

Macrophages: engulf viruses and bacteria in the tissue.

Basophils: secrete heparin which is an anti clotting factor.

Placelets

Produced when large portions of the bone marrow cells break off.

Regulation of blood cell maturation:

Different stimuli (haematopoietic growth factors) will increase certain cell types:

Erthyropoiesis: one example

Low oxygen levels release erythropoietin from the kidney, this acts on bone marrow to stimulate red blood cell production. It is usually secreted in samll amounts in order to produce erythrocytes at a rate to replace the usual loss.

Polycythemia (high RBC count) occurs at high altitudes and with bronchitis and emphysema. It is caused by an increase in erythropoietin production at low oxygen levels to the kidney. It increases oxygen delivery.

Anaemia

This is when blood can't transport enough oxygen to tissues. This can be because of a decrease in number of erythrocytes or a low concentration of haemoglobin per erythrocyte or a combination of the two.

Sickle Cell Disease is due to a genetic mutation that cause the BRC to become sickle shaped at low oxygen levels

Haemostasis

This keeps blood from being lost from the vascular system by clots forming at tissue repair.

Placelet plug and Clot Formation

Exposed collagen binds to and activates placelets causing the release of platelet factors attracting more, causing a plug. Activated blood factors activate a cascade of enzymes this results in the generation of fibrin from fibrinogen by action of thrombin. Thrombin catalyses a reaction which splits several polypeptides from fibrinogen. Fibrin then forms bridges between aggregated placelets. factor XIII stabilizes fibrin

Haemophilia: insufficient clotting

Thrombosis: inappropriate clotting