Blood Vessels and Blood Notes

Blood Vessels and Blood

Blood Flow to Organs

  • Arterial Circuit:
    • Large Artery: Has tunica externa, tunica media, lumen, and tunica interna with an elastic layer and endothelium.
    • Medium-sized Artery: Has tunica externa, tunica media, and tunica interna.
    • Arteriole: Leads to capillaries.
  • Venous Circuit:
    • Large Vein: Has tunica externa, tunica media, and tunica interna with endothelium.
    • Medium-sized Vein: Has tunica externa, tunica media, and tunica interna with a valve.
    • Venule: Receives blood from capillaries.
  • Capillaries:
    • Types: Fenestrated (with capillary pores) and Continuous (with endothelial cells and basement membrane).
    • Precapillary sphincters control blood flow into capillaries.

Blood Pressure

  • Pressure Variation:
    • Blood pressure is very low once the blood reaches the veins.
    • Systolic and diastolic pressures are key indicators.
  • Circulation:
    • Systemic Circulation: Arteries experience systolic and diastolic pressures.
    • Pulmonary Circulation: Lower pressure compared to systemic.

Importance of Blood Pressure

  • Blood Flow Rate: The higher the blood pressure, the faster the blood flows to the capillaries.

Factors Affecting Blood Pressure

  • Fick's Law: Describes the relationship between blood flow, pressure, and resistance.
    • Blood Flow = \frac{\Delta P \times r^2}{8\eta l}
      • \Delta P represents the pressure gradient.
      • r represents the radius of the blood vessel.
      • \eta represents the viscosity of the blood.
      • l represents the length of the blood vessel.

Mean Arterial Pressure (MAP)

  • Formula:
    • MAP = \frac{systolic pressure + 2(diastolic pressure)}{3}
  • Control of MAP:
    • MAP = CO \times TPR where:
      • CO is Cardiac Output
      • TPR is Total Peripheral Resistance
  • Factors Affecting Cardiac Output:
    • Heart Rate
    • Stroke Volume
    • EDV (End-Diastolic Volume)
    • ESV (End-Systolic Volume)
  • Factors Affecting Total Peripheral Resistance:
    • Constriction of muscular arteries and arterioles increases resistance.
    • Sympathetic activity increases overall constriction.

Response to Positional Changes

  • Standing Up:
    • Venous return decreases.
    • End-diastolic volume decreases.
    • Stroke volume decreases.
    • Blood pressure decreases.
  • Compensation Mechanism:
    • Stimuli: Decrease in blood pressure.
    • Sensor: Baroreceptors detect the change.
    • Integrating Center: Medulla oblongata.
    • Effector:
      • Sympathetic nervous system increases cardiac rate and vasoconstriction of arterioles.
      • Parasympathetic nervous system adjusts the response.
    • Response: Increased cardiac output and total peripheral resistance leading to increased blood pressure via negative feedback.

Blood Flow Distribution During Exercise and Rest

  • Cardiac Output:
    • Rest: 5 L/min
    • Heavy Exercise: 25 L/min
  • Blood Flow Distribution at Rest:
    • Kidneys: 20-25% (~0.75 L/min)
    • Abdomen: 20%
    • Muscles: 15-20%
    • Brain: 15%
    • Skin: 3-5%
    • Heart: 4-5%
    • Other: 3-5%
  • Blood Flow Distribution During Heavy Exercise:
    • Muscles: 80-85% (~20 L/min)
    • Skin: 3-5%
    • Heart: 4-5%
    • Brain: 3-4%
    • Kidneys: 3-5%
    • Other: 0.5-1%

Vascular Diseases

  • Atherosclerosis:
    • Plaque builds up inside arteries.
  • Arteriosclerosis:
    • Vessel walls harden and lose elasticity.

Microcirculation

  • Components:
    • Arteriole, metarteriole, thoroughfare channel, capillaries, venule.
  • Control:
    • Precapillary sphincters regulate blood flow into capillary beds.
    • Arteriovenous anastomosis allows blood to bypass the capillary bed.
  • Blood Flow Types:
    • Continuous blood flow.
    • Variable blood flow.

Local Control Mechanisms

  • Active Hyperemia and Flow Autoregulation:
    • Both result in the production of local signals that provoke vasodilation.

Capillary Types and Permeability

Capillary TypePermeabilityLocation
ContinuousLeast permeableSkin, connective tissues, muscles, lungs
FenestratedMost permeableKidneys, intestine
SinusoidalMost permeableLiver, bone marrow, spleen

Fluid Exchange in Capillaries

  • Pressures Involved:
    • CHP (Capillary Hydrostatic Pressure)
    • BCOP (Blood Colloid Osmotic Pressure)
    • NFP (Net Filtration Pressure)
  • Fluid Movement:
    • CHP > BCOP: Fluid forced out of capillary (Filtration).
    • CHP = BCOP: No net movement of fluid.
    • BCOP > CHP: Fluid moves into capillary (Reabsorption).
  • Net Filtration Pressure Examples:
    • Arteriole end: NFP = +10 \, mm Hg (Filtration of 24 L/day)
      • CHP = 35 \, mm Hg
      • BCOP = 25 \, mm Hg
    • Middle: NFP = 0 (No net fluid movement)
      • CHP = 25 \, mm Hg
      • BCOP = 25 \, mm Hg
    • Venule end: NFP = -7 \, mm Hg (Reabsorption of 20.4 L/day)
      • CHP = 18 \, mm Hg
      • BCOP = 25 \, mm Hg

Blood Composition

  • Components
    • Formed elements (37-54%)
    • Plasma (46-63%)

Plasma Components

  • Water: 92%, transports organic and inorganic molecules, formed elements, and heat.
  • Plasma Proteins: 7%
    • Albumins (60%): Major contributors to osmotic pressure, transport lipids and steroid hormones.
    • Globulins (35%): Enzymes, proenzymes, hormones; transport ions, hormones, lipids; immune function.
    • Fibrinogen (4%): Essential for clotting; can be converted to insoluble fibrin.
    • Regulatory Proteins (<1%)
  • Other Solutes: 1%
    • Electrolytes: Essential for vital cellular activities; contribute to osmotic pressure.
      • Major Plasma Electrolytes: Na^+, K^+, Ca^{2+}, Mg^{2+}, Cl^–, HCO3^– , HPO4^– , SO_4^{2–}
    • Organic Nutrients: Used for ATP production, growth, and maintenance of cells.
      • Lipids (fatty acids, cholesterol, glycerides), carbohydrates (primarily glucose), and amino acids.
    • Organic Wastes: Carried to sites of breakdown or excretion.
      • Urea, uric acid, creatinine, bilirubin, ammonium ions.

Formed Elements of Blood

  • Red Blood Cells (RBCs): 99.9%
  • White Blood Cells (WBCs): 0.1%
    • Neutrophils (50–70%)
    • Lymphocytes (20–30%)
    • Monocytes (2–8%)
    • Eosinophils (2–4%)
    • Basophils (<1%)
  • Platelets

Red Blood Cells (RBCs)

  • Size:
    • Diameter: 7.2-8.4 µm
    • Thickness: 0.45-1.16 µm and 2.31-2.85 µm
  • Rouleau: A stack of RBCs
    • The sectional view of capillaries and blood vessels shows red blood cells (RBC) and rouleau in longitudinal section with the nucleus of endothelial cell
  • Hemoglobin:
    • Composed of heme and polypeptide chains (alpha and beta).

White Blood Cells (WBCs)

  • Neutrophil:
    • Pinkish-purple colored granules
    • U-shaped or multilobed nucleus
    • Phagocytic for bacteria and fungi
  • Basophil:
    • Dark bluish-purple granules in cytoplasm
    • Production of histamines
  • Eosinophil:
    • Dark red granules in cytoplasm
    • Fights parasitic infection
  • Monocyte:
    • Largest WBC (3-4x larger than RBC)
    • Horseshoe-shaped nucleus
    • Primary phagocytic cell
  • Lymphocyte:
    • Smallest WBC; usually about the same size as RBC
    • Big, round nucleus fills most of the cell
    • B-cells and T-cells; creates antibodies and activates immune system

Hemopoiesis

  • Hematopoietic Stem Cells:
    • Hemocytoblasts give rise to myeloid and lymphoid stem cells
  • Myeloid Stem Cells:
    • Under the influence of Multi-CSF, GM-CSF, EPO, G-CSF, and M-CSF, gives rise to:
      • Proerythroblast → Erythroblast stages → Reticulocyte → Erythrocyte (Red Blood Cells)
      • Megakaryocyte → Platelets
      • Myeloblast → Promyelocyte → Myelocytes → Band Cells → Granulocytes (Neutrophil, Eosinophil, Basophil)
      • Monoblast → Promonocyte → Monocyte
  • Lymphoid Stem Cells:
    • Lymphoblast → Prolymphocyte → Lymphocyte

Platelet Plug Formation

  • Process:
    • Platelet adhesion to the cut edge of the vessel wall
    • Release of chemicals (ADP, thromboxane A2, Ca^{2+}, platelet factors)
    • Platelet aggregation leading to the formation of a platelet plug

Coagulation Phase

  • Extrinsic Pathway:
    • Tissue damage leads to the release of tissue factor (Factor III).
    • Ca^{2+} is involved.
    • Factor VII and tissue factor form a complex.
  • Intrinsic Pathway:
    • Activated proenzymes (usually Factor XII).
    • Ca^{2+} is involved.
    • Clotting Factors VIII, IX.
  • Common Pathway:
    • Factor X activator complex is formed.
    • Prothrombinase converts prothrombin to thrombin.
    • Thrombin converts fibrinogen to fibrin.
    • Platelet factor (PF-3) is involved.

Blood Types

  • Antigens and Antibodies:
    • Type A: Surface antigen A, Anti-B antibodies in plasma.
    • Type B: Surface antigen B, Anti-A antibodies in plasma.
    • Type AB: Surface antigens A and B, Neither anti-A nor anti-B antibodies in plasma.
    • Type O: Neither A nor B surface antigens, Anti-A and anti-B antibodies in plasma.
  • Agglutination:
    • Occurs when antigens and opposing antibodies interact, leading to clumping and hemolysis.