Blood Composition and Function

• There are 7 ways blood helps to maintain homeostasis in the body.

Blood Homeostasis

• Transports gases like oxygen, nutrients, and waste products
• Transports processed molecules, such as vitamin D precursors from the skin to the liver and then the kidneys
• Transports regulatory molecules.
• Regulates pH and osmosis
• Normal pH of body tissues should be between 7.35 and 7.45
• Maintains body temperature through the shunting of warm blood to the body's interior
• Protects against foreign substances through antibodies
• Facilitates clot formation

Blood Plasma Components

• Plasma is the liquid part of blood, constituting 55% of its volume
• Plasma contains colloids, which are suspended substances that do not settle
• Proteins make up 7% of plasma
• Albumins are the most abundant plasma proteins (58%) and are vital for viscosity, osmotic pressure, buffering, and transport of fatty acids, bilirubin, and thyroid hormones
• Globulins transport lipids, carbohydrates, hormones, ions, antibodies, and complement
• Fibrinogen, the least abundant plasma protein (4%), is essential for blood clotting
• Water constitutes 91% of plasma and serves as a solvent and suspending medium
• Ions (electrolytes) are involved in osmosis, membrane potentials, and acid-base balance
• Nutrients include glucose, amino acids, triglycerides, cholesterol, and vitamins
• Waste products include urea, uric acid, creatinine, and ammonia salts, which are byproducts of protein metabolism
• Bilirubin, a breakdown product of red blood cells, and lactic acid, an end product of anaerobic respiration, are also waste products
• Gases like oxygen, carbon dioxide, and inert nitrogen are present
• Regulatory substances include hormones and enzymes

Formed Elements

• The three kinds of formed elements are red blood cells, white blood cells, and platelets.
• Red blood cells (erythrocytes) are biconcave discs without a nucleus (anucleate) and contain hemoglobin
• Erythrocytes transport oxygen and carbon dioxide and are the most abundant formed element, but die quickly due to lack of a nucleus
• White blood cells (leukocytes) protect the body against microorganisms and remove dead cells and debris
• Granulocytes are leukocytes with large granules in the cytoplasm and multi-lobed nuclei, divided into neutrophils, eosinophils, and basophils
• Agranulocytes are leukocytes with small granules and unlobed nuclei, divided into lymphocytes and monocytes
• Platelets (thrombocytes) are cell fragments that form platelet plugs and release chemicals necessary for blood clotting and growth factors

Hemoglobin Structure and Function

• Embryonic and fetal hemoglobin have a greater affinity for oxygen than adult hemoglobin
• Fetal hemoglobin production stops after birth
• Adult hemoglobin types:
• Oxyhemoglobin transports oxygen
• Deoxyhemoglobin is ready and looking to bind oxygen
• Carbaminohemoglobin transports carbon dioxide
• Red blood cells transport oxygen
• Oxygen from lungs to tissues is 98.5% bound to hemoglobin and 1.5% dissolves in plasma
• Carbon dioxide transport from tissues to lungs:
  • 7% dissolves in plasma
  • 23% combines with hemoglobin
  • 70% is transported as bicarbonate ions, facilitated by carbonic anhydrase within red blood cells
  • CO2 + H2O ↔ H2CO3 ↔ H⁺ + HCO3-
• Hemoglobin consists of four globin molecules (polypeptide chains) that transport carbon dioxide and nitric oxide
• Nitric oxide induces smooth muscle relaxation, which lowers blood pressure
• Four heme molecules transport oxygen with each containing one iron atom
• Iron is required for oxygen transport
• Iron is absorbed in the upper small intestine, aided by stomach acid and vitamin C, and is lost in urine, feces, and menstrual fluid

Red Blood Cell Life History

• Erythropoiesis is the production of red blood cells
• Erythropoietin, a hormone mainly produced by the kidneys, stimulates red bone marrow to produce more red blood cells when blood oxygen levels are low
• Hematopoiesis/hemopoiesis is the process of blood cell production
• All formed elements derive from a single population of stem cells (hemocytoblasts)
  • Proerythroblasts develop into red blood cells
  • Myeloblasts develop into basophils, neutrophils, and eosinophils
  • Lymphoblasts develop into lymphocytes
  • Monoblasts develop into monocytes
  • Megakaryoblasts develop into platelets
• Production of red blood cells requires B12, folic acid, and iron
  • Stem cells become proerythroblasts, then progress through early, intermediate, and late erythroblast stages, and finally become reticulocytes
• Red blood cell production is higher in males due to testosterone
• A reticulocyte is an immature red blood cell that enters the bloodstream from the bone marrow
• Reticulocytes consist of ⅓ hemoglobin and ⅔ lipids, ATP, and carbonic anhydrase

White Blood Cell Types (Leukocytes)

• Neutrophils: first line of defense

  • Leaving bone marrow, they circulate for 10-12 hours before moving to tissues
  • They become motile and phagocytize bacteria, antigen-antibody complexes, and other foreign matter
  • Neutrophils secrete lysozyme and last 1-2 days
  • Neutrophils account for 60-70% of white blood cells (majority of WBCs)

• Eosinophils:

  • Leave circulation and enter tissues during inflammatory responses and are prevalent in allergic reactions
  • Destroy inflammatory chemicals like histamine and release chemicals that help destroy tapeworms, flukes, pinworms, and hookworms
  • Eosinophils account for 2-4% of white blood cells

• Basophils:

  • Least common, they leave circulation and migrate through tissues, playing a role in inflammatory and allergic reactions
  • Produce histamine and heparin (a blood-thinning agent) and account for less than 1% of white blood cells

• Lymphocytes:

  • Produced in red bone marrow but migrate to lymphatic tissues to proliferate
  • Responsible for antibody production and studied extensively within the immune system
  • Lymphocytes account for 20-25% of the white blood cells

• Monocytes:

  • Remain in circulation for 3 days, then leave to become macrophages
  • They are phagocytic cells that break down antigens and present them to lymphocytes for recognition
  • Monocytes account for 3-8% of the white blood cells

Platelets

• Platelets originate from cell fragments pinched off from megakaryocytes in red bone marrow, derived from larger stem cells
• They have surface glycoproteins and proteins that allow adhesion to other molecules, such as collagen
• Platelets are important in preventing blood loss
  • forming platelet plugs that promote the formation and contraction of clots

Hemostasis

• Hemostasis is the process of arresting bleeding and involves three stages to prevent excessive blood loss

1. Vascular spasm: vasoconstriction of damaged blood vessels, which can occlude small vessels and is caused by thromboxanes from platelets and endothelin from damaged endothelial cells
2. Platelet plug formation
3. Coagulation or blood clotting: two pathways including extrinsic and intrinsic pathways, involving fibrin fibers (from fibrinogen) and requiring vitamin K

• A thrombus is a blood clot attached to a blood vessel wall
• An embolus is a thrombus that has broken off and is circulating in the bloodstream

ABO Blood Group Incompatibilities

• Blood grouping is determined by antigens (agglutinogens) on the surface of red blood cells
• Antibodies (agglutinins) can bind to red blood cell antigens, leading to agglutination (clumping) or hemolysis (rupture)

Rh blood group

• Rh positive: Have Rh antigens present on the surface of RBCs
  • Does not have Rh antibodies
• Rh negative: Do not have Rh antigens present
  • Have Rh antibodies

Hemolytic Disease of the Newborn

• Hemolytic disease of the newborn occurs when an Rh positive fetus has an Rh negative mother
• Late in pregnancy: Rh antigens from the fetus cross the placenta, leading the mother to create anti-Rh antibodies (primary response)
• Second Rh positive pregnancy: the mother's antibodies might cross the placenta and attack the new fetus
  • Potentially fatal to the fetus. It is called HDN
• Rhogam: Contains antibodies against Rh antigens. This injection of Rh antigens destroys any Rh-positive baby cells in the mother’s circulation

Key Definitions

• Plasma: The liquid part of blood
• Erythropoiesis: Red blood cells that last 120 days in circulation. RBCs lose their nucleus during the transformation
• Proerythroblast: Develop into red blood cells
• Megakaryoblast: Develop into platelets
• Bilirubin: waste product
• Chemotaxis: Movement of white blood cells to histamine
• Diapedesis: Cells become thin and move through capillaries
• Thrombus: A blood clot attached to a blood vessel wall
• Embolus: A thrombus is in the bloodstream
• Agglutination: Clumping of red blood cells
• Antigen: Protein identifiers
• Antibody: Marks foreign bodies for destruction
• Reticulocyte: Immature red blood cell that enters the bloodstream from bone marrow

This quiz explores the role of blood in maintaining homeostasis, transporting nutrients, and buffering pH levels. It covers key functions such as hormone transport, vitamin D processing, and red blood cell production, focusing on blood's role for overall health.