Cardiovascular Physiology P-1

Cardiovascular Physiology

Introduction

  • Lecturer: Dr. R. Ahangari

  • Institution: University of Central Florida, Orlando

  • Reference Text: Human Physiology by Linda S. Constanzo

  • Additional Resource: Medline Plus

Overview of the Circulatory System

  • Functions of the Circulatory System:

    1. Transportation:

    • Carries respiratory gases (e.g., O2 and CO2)

    • Transports metabolites

    • Distributes nutrients

    1. Regulation:

    • Hormonal regulation

    • Temperature regulation

    1. Protection:

    • Clotting mechanisms protect against blood loss from injury

    • Immune protection against foreign microbes or toxins

  • Blood Volume:

    • Males: 5-6 liters

    • Females: 4-5 liters

Blood Composition

  • Definition: Blood is a specialized connective tissue containing cellular and liquid components.

  • Components:

    • Blood Cells (Formed Elements)

    • Plasma (fluid portion)

  • Hematocrit: Percentage of blood volume consisting of red blood cells:

    • Males: 42–52%

    • Females: 37–47%

Blood Plasma

  • Characteristics: Straw-colored, sticky fluid,

    • Approximately 90% water

  • Components:

    • Ions (e.g., Na+)

    • Nutrients

    • Hormones

    • Enzymes

    • Antibodies

    • Wastes

    • Proteins

  • Main Plasma Proteins: All produced by the liver

    • Albumin (60-80%): Produced by the liver, provides osmotic pressure necessary to draw water into capillaries from surrounding tissues.

    • Globulins (Alpha, Beta, Gamma):

      • Alpha & Beta: Produced by the liver, transport lipids and fat-soluble vitamins, function in immunity.

    • Fibrinogen: Important clotting factor produced by the liver. When clotted, the fluid is called serum.

  • Formed Elements:

    • Erythrocytes (Red blood cells)

    • Leukocytes (White blood cells)

    • Platelets

Erythrocytes

  • Function: Contains 280 million hemoglobin molecules, which give blood its red color.

    • Hemoglobin Structure: Each hemoglobin molecule consists of four protein chains (globins), each bound to one heme, which contains iron. 4:1 ratio

    • Role: The iron group of heme binds oxygen in the lungs and releases it in the tissues.

  • Origin: Erythrocytes originate in the bone marrow.

Erythropoiesis (Production of RBCs)

  • Mechanism: Mainly controlled by hormonal mechanisms.

  • Initiating Event: Cellular O2 deficiency stimulates the release of the hormone erythropoietin (90% produced in glomeruli of the kidney, the rest mainly in the liver).

  • Life Span: RBCs have a life span of about 120 days. Aged RBCs are removed from circulation in the spleen and degraded.

Leukocytes (White Blood Cells)

  • Characteristics: Contain nuclei and mitochondria, can move in amoeboid fashion.

    • Can squeeze through capillary walls and move to infection sites (Diapedesis or Extravasation).

  • Types of WBCs:

    1. Agranular Leukocytes:

    • Lymphocytes

    • Monocytes

    1. Granular Leukocytes:

    • Eosinophils

    • Basophils

    • Neutrophils

Summary of Formed Elements of Blood

  • Table of WBC Features:

    • Basophils: Nucleus bilobed; diameter 10-12 μm; function: release histamine and mediators of inflammation; lifespan 3-7 days.

    • Lymphocytes: Spherical or indented nucleus; diameter 5-17 μm; composed of 20–45% of WBCs; involved in immune response.

    • Monocytes: Kidney-shaped nucleus; diameter 14-24 μm; function: phagocytosis and develop into macrophages; lifespan months.

Lymphocytes

  • Composition: 20–45% of WBCs; critical for the immune system.

  • Functions:

    • Attack specific foreign molecules (antigens).

  • Main Classes:

    1. T cells: Attack foreign cells directly.

    2. B cells: Multiply to become plasma cells and secrete antibodies.

Monocytes

  • Composition: 4-8% of WBCs; largest leukocytes.

  • Functions:

    • Phagocytic cells that transform into macrophages.

Platelets (Thrombocytes)

  • Role: Vital in blood clotting by releasing serotonin, stimulating blood vessel constriction, and reducing blood flow to injured areas.

  • Additional Functions: Secrete growth factors and act as autocrine regulators.

Hematopoiesis

  • Definition: The formation of blood cells.

  • Origin: Initially arises in the yolk sac of the human embryo, migrates to the fetus's liver, and eventually to bone marrow.

  • Types of Hematopoiesis:

    • Erythropoiesis: Formation of erythrocytes;

    • Leukopoiesis: Formation of leukocytes.

Types of Tissues in Hematopoiesis (Post-Birth)

  • Myeloid Tissue: Red bone marrow of long bones, sternum, pelvis, vertebrae.

  • Lymphoid Tissue: Includes lymph nodes, tonsils, spleen, thymus.

  • Bone Marrow: Produces all different blood cell types.

Blood Cell Formation Stages

  • Stages of Differentiation: Begins from a blood stem cell to various types including proerythroblast, myeloblast, monoblast, etc.

  • Reticulocyte Stage: Reticulocytes remain for 1-2 days in circulation and make up about 1-2% of all erythrocytes.

  • Genesis of Erythrocytes:

    • Committed cells are proerythroblasts.

    • The production of red blood cells requires iron, Vitamin B12, and folic acid.

Disorders Related to Blood Cells

  • Erythrocytes:

    • Polycythemia: Excess of erythrocytes.

    • Anemia: Low erythrocyte levels or hemoglobin concentrations. Specific types include:

    • Normocytic anemia (blood loss)

    • Microcytic anemia (iron deficiency)

    • Macrocytic anemia (Vit B12 or Folate deficiency)

    • Sickle Cell Disease: Inherited condition with defective hemoglobin.

  • Leukocytes:

    • Leukemia: Cancer classified as lymphoblastic or myeloblastic.

  • Platelets:

    • Thrombocytopenia: Low platelet concentration.

Blood Development Over Life

  • Initial Development: First blood cells are developed from mesenchyme cells clustering into blood islands.

  • Liver and Spleen: Take over blood formation late in the second month of fetal development.

  • Bone Marrow: Becomes the major hematopoietic organ by the seventh month.

Sickle Cell Disease Details

  • Characterization: An inherited blood disorder affecting red blood cells.

    • People with this condition have hemoglobin S, leading to sickle-shaped RBCs that struggle to pass through small blood vessels.

    • Normal RBCs contain hemoglobin A, are soft and round, living for approximately 120 days.

  • Clinical Signs & Symptoms:

    • Anemia, jaundice, pigment gallstones, and episodes of pain (crises) affecting various bones and organs.

    • Additional symptoms such as breathlessness, delayed growth and puberty, fatigue, fever, paleness, rapid heart rate, and leg ulcers.

  • Treatment: Involves folic acid supplementation, antibiotics, vaccines for infection prevention.

Leukemia Overview

  • Definition: Cancer of blood cells, begins in bone marrow where abnormal WBCs (leukemia cells) are produced excessively.

  • Types of Leukemia:

    • Acute: Rapidly progressing.

    • Chronic: Slowly progressing.

    • Lymphocytic (or Lymphoblastic): Affects lymphocytes with an increase in mature cells.

    • Myelogenous: Affects myelocytes with an increase in both immature and mature WBCs.

Symptoms and Treatment of Leukemia

  • Symptoms: Fever, night sweats, headache, bleeding easily, bone or joint pain, swollen lymph nodes, frequent infections, weight loss, and weakness.

  • Treatment Options:

    1. Chemotherapy to kill leukemia cells using strong anti-cancer drugs.

    2. Interferon-alpha (INFa) therapy to slow down leukemia cell reproduction and promote immune reactions.

    3. Radiation therapy to kill cancer cells using high-energy radiation.

    4. Stem cell transplantation (SCT) for treatment with high-dose chemotherapy and radiation.

Blood Vessels Structure

  • Composition: Blood vessels consist of three tunics:

    1. Tunica Intima: Composed of simple squamous epithelium.

    2. Tunica Media: Sheets of smooth muscle allowing vasoconstriction and vasodilation.

    3. Tunica Externa: Composed of connective tissue.

  • Lumen: The central blood-filled space of a vessel.

Types of Blood Vessels

  • Arteries: Carry blood away from the heart.

  • Veins: Carry blood toward the heart.

  • Capillaries: The smallest blood vessels where exchange of molecules occurs.

Types of Arteries

  1. Elastic Arteries: Largest arteries with high elastin, diameters ranging from 2.5 cm to 1 cm (e.g., aorta and major branches).

  2. Muscular (Distributing) Arteries

  3. Arterioles: The smallest arteries with elastin.

Types of Veins

  • Conduct blood from capillaries toward the heart; lower blood pressure compared to arteries.

  • Venules: Smallest veins, diameters ranging from 8–100 µm.

    • Postcapillary Venules: Smallest venules that join to form veins.

  • Tunica Externa: Thickest tunic in veins; some contain valves.

  • Skeletal Muscle Pump: Skeletal muscles help push blood through veins toward the heart.

Capillary Characteristics

  • Dimensions: Smallest blood vessels, diameters from 8–10 µm, RBCs pass through in single file.

  • Capillary Bed: Networks of capillaries run through tissues.

    • Low Permeability Capillaries: Examples include those forming the blood-brain barrier, selectively allowing vital substances.

    • Sinusoids: Widespread and leaky capillaries found in the spleen and liver.

Erythrocyte Removal and Hemoglobin Breakdown

  • Erythrocyte Lifespan: Roughly 120 days, with removal occurring in the liver.

  • Kupffer Cells: Phagocytic cells in the liver engulf erythrocytes and release hemoglobin to hepatocytes.

  • Hemoglobin Breakdown:

    1. Globin: Hydrolyzed by peptidases to form amino acids for protein synthesis or metabolism.

    2. Heme Group: Broken down to remove iron which is stored in the liver; bilirubin is the other by-product that has no function and is modified by hepatocytes before being secreted as part of bile.

  • Bilirubin: Stored in the gall bladder and modified by bacteria in the duodenum to form stercobilin, coloring feces.

  • Iron: Transported to bones for hematopoiesis (blood cell formation).