chapter 15: Blood: Functions, Composition, Hemostasis, and Blood Types

Transport: Blood is responsible for transporting various substances throughout the body, including nutrients, gases, hormones, and waste products.
Regulation:
- Fluid and Electrolyte Balance: Helps maintain the balance of fluid and electrolytes in the body.
- Acid-Base Balance: Regulates pH levels within the body to prevent acidosis or alkalosis.
- Body Temperature: Aids in regulating body temperature through vasodilation and vasoconstriction.
Protection:
- Infection Defense: Blood contains white blood cells that protect the body from pathogens and infections.
- Clotting Factors: Prevents excessive blood loss through the coagulation process.

General Characteristics:
- Type: Blood is considered a connective tissue that consists of blood cells suspended in a liquid matrix.
- Color: Ranges from bright red (oxygenated) to darker blue-red (deoxygenated) depending on the oxygen content.
- Volume: Typically, an adult has about 4 to 6 liters of blood.
- pH: Healthy blood pH ranges from 7.35 to 7.45.
- Viscosity: Blood is three to five times more viscous than water.
Components: Blood consists of two main parts:
- Plasma (55%): The liquid component that contains water, electrolytes, proteins, hormones, and waste products.
- Formed Elements (45%): This includes blood cells such as erythrocytes, leukocytes, and thrombocytes (platelets).

Erythrocytes (Red Blood Cells):
- Functions to transport oxygen and carbon dioxide.
- Shape: Large, round, doughnut-shaped cells that lose organelles as they mature.
- Contains hemoglobin, composed of globin (protein) and heme (iron-containing substance).
- Erythropoiesis: The process of red blood cell production is regulated by erythropoietin.
Leukocytes (White Blood Cells):
- Function: Protect the body against infections by destroying pathogens and clearing dead tissues through phagocytosis.
- Count: Normal range is 5,000 to 10,000 WBCs per microliter of blood.
- Lifespan: WBCs circulate for less than 12 hours.
Thrombocytes (Platelets):
- Function: Involved in blood clotting to prevent blood loss.
- Count: Each microliter of blood contains approximately 150,000 to 450,000 platelets.

Origin: Blood cells are formed in two primary pathways:
- Myeloid Pathway: Produces RBCs, platelets, and some types of WBCs.
- Lymphoid Pathway: Produces certain types of WBCs, mainly lymphocytes.

Bone Marrow Depression (Myelosuppression): Can lead to conditions such as aplastic anemia and leukopenia.
Bone Marrow Overactivity: Conditions like polycythemia vera can cause thickened blood, burdening the heart, with symptoms such as a ruddy complexion.

Removal: Damaged RBCs are detected and phagocytosed by macrophages in the spleen and liver.
Component Recycling: Hemoglobin is broken down, and excess bilirubin can lead to jaundice when excessively deposited in the skin.

Process: Hemostasis stops bleeding through a series of steps:
1. Blood Vessel Spasm: Constriction of blood vessels in response to injury.
2. Platelet Plug Formation: Platelets adhere to the injury site and each other to form a temporary seal.
3. Blood Clotting (Coagulation): Involves a cascade of clotting factors leading to the formation of a stable clot.

Stages:
- Stage I: Injury activates various clotting factors.
- Stage II: Calcium and platelet chemicals facilitate the conversion of prothrombin to thrombin.
- Stage III: Thrombin converts fibrinogen into fibrin.
Clot Retraction: Consolidation of the clot to close the wound.

Mechanisms to prevent excessive clot formation include natural fibrinolytic processes and medical interventions.

ABO Blood Grouping: Blood types A, B, AB, and O are determined by the presence of specific antigens on RBC membranes.
- Antigens: Molecules that trigger immune responses if mismatched.
- Antibodies: Plasma contains specific antibodies that react against incompatible blood types.
Agglutination: The clumping of red blood cells that occurs when antigens and antibodies interact, which can lead to hemolysis.

Classification: The Rh factor is another antigen that determines if blood is Rh-positive (+) or Rh-negative (−).
Clinical Relevance:
- Erythroblastosis Fetalis: A condition occurring when an Rh-negative mother has an Rh-positive baby.
- Hemolytic Disease of the Newborn: Caused by Rh factor incompatibility between mother and child, leading to severe complications during or after pregnancy.