Blood Characteristics and Functions

Blood Characteristics

  • Volume of Blood:
    • Adult women: approximately 4.5 liters
    • Adult men: approximately 5 liters
  • Normal pH of Blood:
    • Average pH: ~7.4, range: 7.35-7.45
  • Average Temperature of Blood:
    • Blood temperature: 100.4°F
    • Average body temperature: 98.6°F

Blood Functions

  • Transportation Functions of Blood:
    • Carries:
    • Oxygen (O2)
    • Nutrients
    • Ions
    • Enzymes
    • Hormones
    • Buffers for acids
    • Transports wastes:
    • Carbon dioxide (CO2)
    • Various wastes and toxins to:
      • Lungs (for excretion of CO2)
      • Kidneys
      • Digestive System
      • Liver
    • Temperature Regulation:
    • Heats or cools different body parts as needed
    • Immune Function:
    • White blood cells and antibodies travel to areas invaded by pathogens to aid in conflict

Blood Clotting

  • Formation of Clots:
    • Blood clots form in injured blood vessels
    • Involved Components:
    • Red blood cells
    • Platelets
    • Fibrin
    • Function: Patch up damaged vessels and form clots

Blood Composition

  • Major Components of Blood:
    • 55% Plasma
    • 45% Formed Elements
    • Red blood cells (RBCs or erythrocytes): ~99.9% of cells
    • White blood cells (WBCs or leukocytes): ~0.1% of cells
    • Platelets: fragments of megakaryocytes (approximately 6 per 100 RBCs)

Plasma Composition

  • Plasma consists of:
    • 92% Water
    • 7% Plasma Proteins
    • 1% Other Solutes

Plasma Proteins

  • Types of Plasma Proteins:
    • Albumins (60%):
    • Major contributors to osmotic pressure of plasma
    • Transport lipids and steroid hormones
    • Globulins (35%):
    • Transport ions, hormones, lipids
    • Play a role in immune function
    • Fibrinogen (4%):
    • Key component of the clotting system
    • Converts to insoluble fibrin
    • Regulatory Proteins (
    • Include enzymes, proenzymes, and hormones

Other Solutes in Plasma

  • Electrolytes:
    • Essential for vital cellular activities
    • Major plasma electrolytes:
    • Sodium (Na+)
    • Potassium (K+)
    • Calcium (Ca2+)
    • Magnesium (Mg2+)
    • Chloride (Cl-)
    • Bicarbonate (HCO3-)
    • Phosphate (HPO4^2-)
  • Organic Nutrients:
    • Needed for ATP production, growth, and cellular maintenance
    • Nutrients include:
    • Lipids (fatty acids, cholesterol, glycerides)
    • Carbohydrates (primarily glucose)
    • Amino acids
  • Organic Wastes:
    • Carried to sites for breakdown or excretion, includes:
    • Urea
    • Uric acid
    • Creatinine
    • Bilirubin
    • Ammonium ions

Plasma Circulation

  • Flow of Plasma, Interstitial Fluid and Lymph:
    • Plasma circulates from blood into interstitial fluid and then into lymph
    • Interstitial Fluid:
    • Fluid in the interstitium, the space between tissue cells
    • Lymph Composition:
    • Interstitial fluid, solutes, and proteins draining into lymph vessels

Diffusion of O2 and CO2

  • Concentration Differences and Effects:
    • Plasma has a higher O2 concentration than interstitial fluid; thus,
    • O2 diffuses from plasma to interstitial fluid to cells
    • Plasma has a lower CO2 concentration than interstitial fluid; thus,
    • CO2 diffuses from interstitial fluid into plasma and is transported to the lungs

Plasma Circulation in Relation to Cells

  • Plasma and interstitial fluid have similar ion concentrations but different protein concentrations:
    • Plasma has a much higher protein concentration than interstitial fluid
    • Most proteins are too large to diffuse from plasma into interstitial fluid and thus are retained in systemic capillaries

Plasma Proteins Overview

  • Plasma proteins constitute about 7% of plasma
    • Approximately 90% of these proteins are synthesized in the liver
    • Major Classes of Plasma Proteins Include:
    • Albumins (60%)
    • Globulins (35%)
    • Fibrinogen (4%)
    • Other proteins (

Albumin

  • Characteristics and Function:
    • Smallest plasma protein
    • Carries a negative charge
    • Cannot pass through a cell membrane
    • Holds water inside capillaries due to solute concentration differences
    • Transports insoluble substances, including unconjugated bilirubin (breakdown product of hemoglobin) to the liver
    • Also transports lipids, some steroid hormones, and thyroid hormone

Globulins

  • Categories of Globulins:
    • Transport Globulins:
    • Transport insoluble substances, such as ions and hormones
    • Example: Sex hormone-binding globulin carries testosterone or estrogen
    • Immunoglobulins (Antibodies):
    • Integral to immune function, interacting with pathogens

Fibrinogen

  • Fibrinogen is the largest plasma protein:
    • Type: Glycoprotein
    • Function:
    • Converted to fibrin during the clotting cascade
    • Forms a web that traps platelets and red blood cells to stabilize blood clots
    • Note: Serum is plasma devoid of clotting proteins

Plasma's Role in Transportation

  • Plasma plays a vital role in transporting:
    • Gases:
    • Oxygen, carbon dioxide
    • Electrolytes:
    • Comprising sodium, chloride, bicarbonate, calcium, magnesium, phosphate
    • Nutrients and Wastes:
    • Nutrients include carbohydrates, proteins, and lipids
    • Wastes comprise urea, creatinine, uric acid, and bilirubin

Formed Elements of Blood

  • Components of Formed Elements:
    • Comprise approximately 45% of blood volume:
    • Red Blood Cells (RBCs or erythrocytes)
    • White Blood Cells (WBCs or leukocytes)
    • Platelets
  • Distribution in Blood:
    • 99.9% of formed elements are RBCs
    • Less than 0.1% are WBCs

Types of Blood Cells and Platelets

  • Blood Cell Types:
    • Erythrocytes (Red Blood Cells)
    • Leukocytes (White Blood Cells):
    • Neutrophils
    • Lymphocytes
    • Eosinophils
    • Basophils
    • Monocytes
    • Platelets
  • Platelet Characteristics:
    • Fragments of megakaryocytes
    • Life span: 1-2 weeks
    • Approximately 350,000 platelets per microliter of blood

Red Blood Cells (RBCs)

  • Physical Structure:
    • Biconcave disc shape: large surface area to volume ratio allowing gas exchange
    • Flexibility enables passage through capillaries; can form rouleau ("stacks" of coins)
  • Lifespan and Replacement:
    • Lifespan: approximately 120 days (4 months)
    • 1% of old RBCs replaced daily
    • About 3 million new RBCs produced every second

Characteristics of Hemoglobin

  • Hemoglobin Structure:
    • Composed of:
    • 2 Alpha chains and 2 Beta chains
    • Each chain has a heme group that contains an iron ion (Fe2+)

Oxygen Transport by Hemoglobin

  • Each iron ion can bind a single O2 molecule, allowing a single RBC to carry over 1 billion O2 molecules due to approximately 280 million hemoglobin molecules within 1 RBC
  • Color Variation:
    • Arterial blood appears bright red when oxygenated
    • Venous blood appears dark red when deoxygenated
  • Carbon Dioxide Transport:
    • Approximately 23% of CO2 binds to hemoglobin; most CO2 is transported as bicarbonate (HCO3-)

Platelets

  • Structure and Characteristics:
    • Fragments of megakaryocytes, devoid of nuclei
    • Life span: 1-2 weeks
  • Count in Blood:
    • Approximately 350,000 platelets per microliter
    • Ratio: about 6 platelets for every 100 RBCs
  • Storage:
    • 66% circulate in blood, 33% stored in spleen and other organs
    • In case of injury, spleen releases platelets into circulation

Platelet Functions

  • Involved in hemostasis (blood clotting)
    • Form a platelet plug at injury sites
    • Release chemicals that kickstart clotting pathways
    • Contract and pull fibrin fibers to shrink blood clots

White Blood Cells (WBCs)

  • Definition and Overview:
    • White blood cells are less than 0.1% of blood volume
    • Approximately 1000 times more RBCs than WBCs present in blood
  • Immune Function:
    • Essential in the defense against pathogens
    • WBCs multiply in response to infections and remove damaged cells

Types of WBCs

  • Distribution:
    • Most WBCs found in tissues, with a smaller number circulating in blood
  • Chemotaxis:
    • Body cells release chemicals that attract WBCs to infection sites, guiding their movement
  • Diapedesis:
    • Process by which WBCs exit capillaries near infection sites

Classification of WBCs

  • Granulocytes:
    • Neutrophils
    • Eosinophils
    • Basophils
    • Contain granules in cytoplasm
  • Agranulocytes:
    • Monocytes
    • Lymphocytes
    • Lack granules

Neutrophils

  • Characteristics:
    • Constitute 50-70% of WBCs, twice the size of RBCs
    • Multilobed nucleus
    • Stain lavender/lavender-pink with common hematoxylin/eosin stains
  • Function:
    • Actively phagocytize pathogens, particularly bacteria
    • Typically the first responders to infections, consuming 10-25 bacteria before dying within 10 hours

Eosinophils

  • Characteristics:
    • Represent 2-4% of WBCs, bilobed nucleus
    • Stain red due to eosin dye
  • Function:
    • Phagocytes that also target parasites and are involved in allergic reactions

Basophils

  • Characteristics:
    • Account for less than 1% of WBCs, difficult to discern their nuclei due to numerous granules
  • Function:
    • Contain granules with histamine (which dilates blood vessels) and heparin (which facilitates blood flow to infection sites)

Monocytes

  • Characteristics:
    • Comprise 2-8% of WBCs, the largest WBCs with a kidney-shaped nucleus
  • Convert into macrophages and can reside in tissues for prolonged periods

Macrophages

  • Differentiation:
    • Monocytes differentiate into macrophages either prenatally or postnatally
    • Macrophages are key players in the immune response, releasing chemicals that recruit other WBCs and fibroblasts to infection sites

Lymphocytes

  • Characteristics:
    • Make up 20-30% of WBCs, slightly larger than RBCs
    • Possess a large round nucleus with a small rim of cytoplasm
  • Types of Lymphocytes:
    • Natural Killer (NK) Cells: part of the innate immune system, present at birth
    • T Lymphocytes: part of the adaptive immune system, develop throughout life, activate other immune components, some attack specific pathogens
    • B Lymphocytes: produce antibodies to target specific pathogens

Lifespan of Lymphocytes

  • Lymphocytes generally have longer lifespans compared to other blood cells:
    • 80% have a lifespan of four years, with some surviving up to 20 years
    • In comparison, RBCs survive approximately 120 days and neutrophils from hours to a few days

Clinical Correlation

  • WBC Count with Differential:
    • A common medical test providing the percentage of each type of white blood cell in a patient's blood

Hemopoiesis

  • Definition:
    • Hemopoiesis is the formation of blood cells, occurring in red bone marrow
  • Stem Cell Differentiation:
    • Hematopoietic stem cells differentiate into two main lineages:
    • Myeloid Stem Cells
    • Lymphoid Stem Cells

Myeloid Stem Cells and Their Differentiation

  • Myeloid stem cells produce:
    • Erythropoiesis: Formation of red blood cells
    • Thrombopoiesis: Formation of platelets
    • Leukopoiesis: Formation of granulocytes and monocytes

Erythropoiesis

  • Definition:
    • Erythropoiesis is the process of forming red blood cells
  • Sequence of Development:
    • Hematopoietic Stem Cells → Myeloid Stem Cells → Reticulocytes → Erythrocytes
    • Only erythrocytes (RBCs) and some reticulocytes circulate in blood

Conditions for Erythropoiesis

  • Occurs in the red bone marrow within specific regions of adults:
    • Locations include the axial skeleton, pectoral girdle, pelvic girdle, and proximal long bones
  • Stimulated by erythropoietin from the kidneys in response to low oxygen levels
  • Requires nutrients including iron and Vitamin B12

Thrombopoiesis

  • Definition:
    • Thrombopoiesis is the process of forming platelets
  • Sequence of Development:
    • Hematopoietic Stem Cell → Myeloid Stem Cell → Megakaryocyte → Platelets

Leukopoiesis

  • Definition:
    • Leukopoiesis refers to the formation of white blood cells:
    • Granulocytes: neutrophils, eosinophils, basophils
    • Monocytes: differentiate into macrophages and dendritic cells

Lymphopoiesis

  • Definition:
    • Lymphopoiesis is the formation of lymphocytes from lymphoid stem cells
  • Sequence of Development:
    • Occurs in red bone marrow, where lymphoid stem cells differentiate into NK cells and B lymphocytes
    • Lymphoid stem cells migrate to the thymus to develop into T lymphocytes

Lymphatic Tissue Formation

  • Overview:
    • Involves the red bone marrow, thymus, and peripheral lymphatic tissues
    • Hematopoietic stem cells produce lymphatic stem cells with two fates:
    • Group remains in bone marrow, maturing into NK and B cells via interleukin-7
    • Group migrates to thymus, developing T cells influenced by thymic hormones
  • Lymphocytes eventually enter bloodstream and migrate to lymphatic tissues, red bone marrow, spleen, and other targeted areas for immune activities.