Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)

BLOOD

INTRODUCTION TO BLOOD


Blood
 Viscous fluid pumped around the body by the heart and the vascular system
 Contains RBC’s, white cells (immunology), platelets (anucleate; clotting)
 Contains plasma (liquid fraction; clotting and complement systems)
 Blood is not involved in paracrine signalling

Circulatory system
 Arteries: heart to organs and tissues (generally oxygenated)
 Veins: returns blood from the organs and tissues to the heart, followed by the lungs for re-oxygenation (generally
de-oxygenated)
 Pulmonary artery – deoxygenated blood to lungs to be oxygenated
 Pulmonary vein – oxygenated blood from lungs to heart to be pumped around body
 Arterioles, venules, capillaries: small blood vessels which have a small diameter and therefore maximise blood-
tissue interaction

The heart
 The human heart consists of 2 atria and 2 ventricles and pumps around 5 L blood per
minute
 De-oxygenated blood in vena cava into the right atrium  right ventricle  pumps
blood into pulmonary artery  reoxygenation in lungs  pulmonary vein  left
atrium  left ventricle  aorta
 Valves prevent “backflow”

Functions of the blood
 Hydration of tissues and organs
 Delivery of oxygen to tissues and organs
 Provision of nutrients to tissues and organs
 To fight infection: Innate and adaptive immune responses
 Regulation of body temperature and pH
 Distribution of (endocrine) hormones
 To prevent its own (blood) loss

, Oxygen delivery  RBC’s contain haemoglobin which is regulates oxygen transport
Fight infection  White blood cells contribute to the immune response against infection (all white cells) and to
allergic reactions (eosinophils and basophils)
 In the blood plasma, the complement system is activated to fight infection by pathogens
Hormone Endocrine hormones are secreted by specific endocrine glands into the blood to be circulated to
distribution remote target tissues.
 Insulin (beta cells in pancreas)
 Thyroid stimulating hormone (anterior pituitary lobe)
 Oestrogen, progesterone, testosterone (ovary/testes)
 Vasopressin (posterior pituitary lobe)
 Adrenaline (adrenal medulla)
Preventing blood  Platelets – small anucleate blood cells that clump together
loss  Blood Coagulation Pathway – Through the formation of thrombin a fibrin clot is formed


Blood cells
 Blood cells are derived from one progenitor cell in the bone marrow: the multipotential haematopoietic stem cell
 Two major lineages: myeloid (other types of blood cells) and lymphoid (lymphocytes and natural killer cell)
 These two lineages produce 11 different types of blood cell




Blood plasma
 55% of the blood volume is plasma (liquid fraction of the blood)
 Most abundant blood plasma proteins are:
1. Albumin (35-50 g/L), “filler”
2. Immunoglobulins (15 g/L), involved in fighting infection
3. Fibrinogen (3-5 g/L), involved in clotting

Serum and plasma
 Serum = Plasma – Clotting Factors (blood is allowed to clot before it is centrifuged)
 Plasma = Serum + Clotting Factors (+ clotting inhibitor)
 45% of blood volume is taken up by blood cells

Blood incompatibility
 If blood of incompatible blood groups are mixed, antibodies react with antigens on the red blood cell (RBC)
membrane, causing haemolysis (RBC rupture)