Functions and Composition of Blood

Functions of Blood

• Blood transports gases, nutrients, waste products, processed molecules, regulatory molecules, and helps to regulate pH, osmosis, body temp and protects against foreign substances.
• Blood helps clot to prevent blood loss.

Composition of Blood

• Blood is composed of plasma (55%) and formed elements (45%).
• Plasma is 91% water, 7% protein and 2% other.
• Plasma contains albumin (58%), globulins (38%), and fibrinogen (4%) which aid in maintaining water balance, immune system health, and clot formation.
• Formed elements are made up of cells and cell fragments (erythrocytes, leukocytes, thrombocytes).

Hematopoiesis

• The process of blood cell formation is hematopoiesis.

Erythrocytes

• Erythrocytes are red blood cells (RBCs) with a disk-shaped structure, a thick edge, and no nucleus.
• RBCs live for 120 days and are responsible for oxygen transport.

Hemoglobin

• Hemoglobin, the main component of erythrocytes is used to carry oxygen.
• It contains four globin proteins and four heme molecules.
• Each heme molecule contains an iron atom and one oxygen molecule can bind to each iron atom.
• Oxyhemoglobin is hemoglobin that has bound oxygen.

Production of Erythrocytes

• Erythrocytes are produced in red bone marrow by megakaryocytes.
• Lost blood is replaced by new blood or a transfusion.

Preventing Blood Loss

• Three mechanisms prevent blood loss: vascular spasm, platelet plug formation, and blood clotting.
• Vascular spasm is the immediate constriction of a blood vessel in response to injury and helps seal small breaks in blood vessels.
• Platelets are responsible for forming a platelet plug that helps to stop blood loss.

Platelet Plug Formation

• Platelet adhesion occurs when platelets stick to exposed collagen at the site of injury.
• Activated platelets change shape and release chemicals that attract more platelets.
• Fibrinogen bridges between fibrinogen receptors on platelets form a platelet plug.

Blood Clotting

• Blood clotting is the transformation of blood from a liquid to a gel.
• Clot formation is dependent on clotting factors, which are proteins in plasma only activated by injury.
• Clotting factors need Vitamin K and are made in the liver.

Steps in Clot Formation

• Injury to a blood vessel activates clotting factors by exposing connective tissue or releasing thromboplastin.
• Prothrombinase is formed and converts prothrombin into thrombin.
• Thrombin activates fibrinogen, converting it to fibrin.
• Fibrin forms a network that traps blood cells and creates a clot.

Clot Formation Control

• Anticoagulants prevent clots from forming, and examples include heparin and antithrombin.
• An adequate amount of clotting factors are needed for coagulation, and anticoagulants can’t inhibit clotting in that area of the body.

Clot Retraction and Fibrinolysis

• Clot retraction is the tightening of a clot, which pushes out serum and enhances healing.
• Fibrinolysis is the process of dissolving a clot.
• Plasminogen breaks down fibrin to dissolve clots.

Blood Grouping

• Blood transfusions are necessary following injury or surgery.
• Transfusion reactions/agglutination are clumping of blood cells that occur when blood is incompatible.
• Antigens are molecules on erythrocyte surfaces, and antibodies are proteins in plasma.
• Blood is named based on the antigens present. (ABO)

ABO Blood Groups

• The ABO system has antigens called A and B on erythrocyte surfaces.
• The ABO blood group system has antibodies present in plasma against antigens, and the specific antibody depends on the blood group.