CH.17- Blood

The Cardiovascular System: Blood Composition

Blood Composition

  • Definition: Blood is a fluid connective tissue composed of several components, which include:
      - Plasma
      - Formed Elements
        - Erythrocytes (Red Blood Cells or RBCs)
        - Leukocytes (White Blood Cells or WBCs)
        - Platelets

Hematocrit

  • Definition: The hematocrit is the percentage of blood volume that is made up of red blood cells.

  • Normal Values:
      - Males: 47% ± 5%
      - Females: 42% ± 5%

Physical Characteristics and Volume

  • Characteristics: Blood is a sticky, opaque fluid with a color range from scarlet to dark red.

  • pH Level: Normal pH ranges from 7.35 to 7.45.

  • Temperature: Blood is usually around 38°C.

  • Body Weight Percentage: Blood constitutes approximately 8% of body weight.

  • Average Volume: The average blood volume is 5-6 L for males and 4-5 L for females.

Functions of Blood

  • Distribution of:
      - Oxygen (O2) and nutrients to body cells.
      - Metabolic wastes to the lungs and kidneys for elimination.
      - Hormones from endocrine organs to target organs.

  • Regulation of:
      - Body Temperature: By absorbing and distributing heat.
      - Normal pH Levels: Maintained using buffers.
      - Adequate Fluid Volume: Maintains fluid volume in the circulatory system.

  • Protection Against:
      - Blood Loss: Plasma proteins and platelets initiate clot formation.
      - Infection: Antibodies and complement proteins; WBCs defend against foreign invaders.

Blood Plasma

  • Composition:
      - 90% water.
      - Proteins (mostly produced by the liver):
        - 60% Albumin
        - 36% Globulins
        - 4% Fibrinogen
      - Nitrogenous By-products of Metabolism: Lactic acid, urea, creatinine.
      - Nutrients: Glucose, carbohydrates, amino acids.
      - Electrolytes: Na⁺, K⁺, Ca²⁺, Cl⁻, HCO₃⁻.
      - Respiratory Gases: O2 and CO2.
      - Hormones.

Formed Elements

  • Definition: Formed elements of blood consist of:
      - Only WBCs are fully functional with nuclei.
      - RBCs: Anucleate and lack organelles.
      - Platelets: Formed as cell fragments.

  • Lifespan of Blood Cells: Most formed elements survive only a few days in the bloodstream and originate in the bone marrow, where they do not divide.

Erythrocytes (Red Blood Cells)

  • Structure: Biconcave discs that are anucleate and contain no organelles. They are filled with hemoglobin (Hb) for gas transport.

  • Key Characteristics:
      - About 5 million RBCs per microliter of blood.
      - Biconcave shape allows for high surface area relative to volume.
      - Composed of greater than 97% hemoglobin (excluding water).
      - No mitochondria; ATP production is anaerobic, utilizing no O2 during ATP generation.
      - Exemplary of the complementarity of structure and function.

Erythrocyte Function

  • Main Role: RBCs are dedicated to respiratory gas transport.

  • Hemoglobin Binding: Hemoglobin binds reversibly with oxygen.

  • Hemoglobin Structure: Consists of:
      - Globin: Composed of two alpha and two beta chains.
      - Heme Pigment: Bonded to each globin chain, with an iron atom capable of binding to one O2 molecule.
      - Each Hb molecule can transport four O2 molecules.

Hemoglobin (Hb)

  • O2 Loading and Unloading:
      - In the Lungs: O2 loading produces oxyhemoglobin (ruby red).
      - In the Tissues: O2 unloading produces deoxyhemoglobin (dark red).

  • CO2 Transport: Hemoglobin can also carry carbon dioxide, known as carbaminohemoglobin (carries 20% of CO2 in the blood).

Hematopoiesis

  • Definition: Hematopoiesis (or hemopoiesis) is the formation of blood cells.

  • Location: Occurs in the red bone marrow of the axial skeleton, girdles, and the proximal epiphyses of the humerus and femur.

Fate and Destruction of Erythrocytes

  • Lifespan: Approximately 100-120 days.

  • Deterioration: As RBCs age, they become fragile; hemoglobin begins to degenerate.

  • Macrophages: Engage in engulfing dying RBCs mainly in the spleen.

  • Iron Salvage: Iron is salvaged for reuse, while heme is degraded into bilirubin (a yellow pigment).
      - Liver Role: The liver secretes bilirubin into bile, which is transported into the intestines.
      - Excretion: Degraded pigments exit the body in feces as stercobilin.
      - Globin Metabolism: Globin is broken down into amino acids.

Erythrocyte Disorders

  • Anemia: Abnormally low O2-carrying capacity of blood. It is a sign rather than a standalone disease.
      - Symptoms: Fatigue, paleness, shortness of breath, chills.
      - Common Types:
        - Iron-deficiency anemia (most prevalent).
        - Vitamin-deficiency anemia (B12 and folate deficiency).

Leukocytes (White Blood Cells)

  • Proportion in Blood: Comprise less than 1% of total blood volume.

  • Functionality: WBCs can exit capillaries via diapedesis and move through tissue spaces by ameboid motion and positive chemotaxis.

  • Leukocytosis: A condition where WBC count exceeds 11,000 per microliter, typically a response to bacterial or viral infections.

  • Classification: Two groups:
      - Granulocytes
      - Agranulocytes

Granulocytes

  • Types: Neutrophils, eosinophils, basophils.

  • Characteristics: Granulocytes possess cytoplasmic granules that stain specifically with Wright’s stain. They are larger and shorter-lived than RBCs and have lobed nuclei.

  • Function: These cells are phagocytic, meaning they can engulf and digest pathogens.

Neutrophils

  • Description: The most numerous type of WBC, also known as polymorphonuclear leukocytes (PMNs).

  • Appearance: Have fine granules that take up both acidic and basic dyes, giving a cytoplasm a lilac color.

  • Function: Contains hydrolytic enzymes or defensins and is considered very phagocytic—commonly referred to as "bacteria slayers."

Eosinophils

  • Description: Characterized by red-staining bilobed nuclei and coarse, lysosome-like granules.

  • Function: Primarily involved in digesting parasitic worms that are too large to be phagocytized, and they modulate the immune response.

Basophils

  • Description: The rarest type of WBC with large, purplish-black granules that contain histamine.

  • Function: Histamine is an inflammatory chemical acting as a vasodilator, attracting other WBCs to inflamed sites. Basophils are functionally similar to mast cells.

Agranulocytes

  • Types: Include lymphocytes and monocytes.

  • Characteristics: Lack visible cytoplasmic granules and possess spherical or kidney-shaped nuclei.

Lymphocytes

  • Description: Large, dark-purple spherical nuclei with a thin rim of blue cytoplasm; primarily located in lymphoid tissue, with some circulating in the blood.

  • Crucial to Immunity:
      - T Cells: Act against virus-infected cells and tumor cells.
      - B Cells: Differentiate into plasma cells that produce antibodies.

Monocytes

  • Description: The largest type of leukocyte, with abundant pale-blue cytoplasm and dark purple-staining U or kidney-shaped nuclei.

  • Function: Leave circulation to enter tissues and differentiate into macrophages. They are actively phagocytic, playing a critical role against viruses, intracellular bacterial parasites, and chronic infections, and they help activate lymphocytes for immune responses.

Disorders of Leukocytes

  • Leukopenia: A condition characterized by too few leukocytes.

  • Leukemia: A type of cancer resulting in an abundance of leukocytes.

  • Lymphoma: A malignant condition where T/B lymphocytes accumulate inappropriately.

Platelets (Thrombocytes)

  • Description: Small fragments derived from megakaryocytes, featuring a blue-staining outer region with purple granules.

  • Function: Form a temporary platelet plug that aids in sealing breaks in blood vessels.

Platelet Disorders

  • Thrombocytosis: A condition characterized by an excess number of platelets.

  • Thrombocytopenia: A condition defined by a deficiency of platelets.

Summary Notes

  • What is the composition of the whole blood?

    • The composition of the whole blood is plasma and formed elements. (erythrocytes, leukocytes, and platelets.)

  • What are formed elements?

    • Formed elements are the cellular components of blood, which include red blood cells (erythrocytes), white blood cells (leukocytes), and cell fragments known as platelets (thrombocytes).

  • Which of the formed elements are nucleated?

    • The formed elements that are nucleated are

  • What is hematocrit?

    • Hematocrit is the ratio of the volume of red blood cells to the total volume of blood, expressed as a percentage.

  • What is a normal hematocrit level in a healthy person?

    • The normal hematocrit level in a healthy person is men 47% +- 55 and for females 42%. The average is 45%.

  • What are the physical characteristics of blood?

    • Physical characteristics of blood include sticky, opaque fluid, red, and a neutral leaning towards a basic pH of 7.35 -7.45.

  • What is the average volume of blood in a body?

    • The average volume of blood in a body is approx. 5 L.

  • What are the functions of blood?

    • The functions of blood include the distribution of oxygen and nutrients, regulating body temperature, transporting hormones, and removing waste products from cells, as well as protecting against blood loss and infection.

  • What is the composition of blood plasma?

    • The composition of blood plasma is 90% water, with proteins where 60% albumon, 36% globulins, and 4% fibrinogen. Additionally, having nitrogenous by-products of metabolism, nutrients, electrolytes, respiratory gases, and hormones.

  • Plasma composes about ________ percent of whole blood and water composes ________ percent of the plasma volume.

    • 10;90

  • Learn the structural characteristics of erythrocytes.

    • The structural characteristics of erythrocytes are characterized by their biconcave disc shape, which increases surface area for efficient gas exchange, and the absence of a nucleus and organelles, allowing for more hemoglobin to be present for oxygen transport.

  • Learn the structure of hemoglobin

    • The structure of hemoglobin consists of protein globin and heme pigment.

  • How many atoms of Fe does each hemoglobin contain?

    • There is 1 iron atom in each heme group, resulting in a total of 4 iron atoms per molecule of hemoglobin.

  • What is the percentage of hemoglobin (not counting water) in a red blood cell?

    • The percentage of hemoglobin in a red cell is approximately 33%.

  • What are oxyhemoglobin, deoxyhemoglobin, and carbaminohemoglobin? Where are they formed?

    • Oxyhemoglobin occurs when oxygen in the lungs binds to hemoglobin in the red blood cells, allowing efficient transport of oxygen throughout the body. Deoxyhemoglobin is the form of hemoglobin after it has released its oxygen to the tissues. Carbaminohemoglobin, on the other hand, is formed when carbon dioxide binds to hemoglobin, primarily within the tissues.

  • Where does hematopoiesis occur?

    • Hematopoiesis occurs in red bone marrow of the axial skeleton, girdles, and proximal epiphyses of the humerus and femur.

  • What is the average life span of a red blood cell?

    • An RBC has a 100-120 day lifespan.

  • Where are damaged red blood cells removed from circulation?

    • Damaged RBCs are primarily removed from circulation by the spleen and liver, where they are phagocytized by macrophages.

  • What is anemia?

    • Anemia is when blood has a low oxygen-carrying capacity due to a deficiency in red blood cells or hemoglobin, which can result from various factors, including nutritional deficiencies, bone marrow disorders, or chronic diseases.

  • What components of blood increase in number in response to the presence of an infectious agent?

    • The components of blood that increase in number in response to the presence of an infectious agent are white blood cells, specifically leukocytes, which play a crucial role in the immune response to fight off infections and foreign invaders.

  • Learn the relative concentration of the leucocytes in blood.

    • The relative concentration of leukocytes in blood is <1%.

  • What is a normal WBC count?

    • A normal WBC count is over 11,000.

  • Learn the structure and functions of neutrophils

    • Neutrophils are the most numerous of WBCs, act as the first line of defense, give cytoplasm a lilac-like color, and play a crucial role in responding to infections by engulfing pathogens through a process known as phagocytosis. They have a multilobed nucleus, and their unique structure enables them to move through blood vessels and tissues with ease, allowing them to quickly reach sites of infection or inflammation.

  • Learn the structure and functions of eosinophils

    • Eosinophils are the red-staining, bilobed nuclei and are involved primarily in combating parasitic infections and mediating allergic responses. They contain granules filled with enzymes and chemokines that are released during inflammatory reactions, contributing to the immune response.

  • Learn the structure and functions of basophils

    • Basophils are the rarest WBCs, characterized by their large blue-staining granules that contain histamine and heparin, which are released during allergic reactions and inflammatory responses. They are large, purplish-black granules containing histamine. Basophils play a crucial role in the regulation of blood flow and the amplification of the inflammatory response, helping to attract other immune cells to sites of infection or injury.

  • Learn the structure and functions of lymphocytes

    • Lymphocytes are large, dark purple, circular nuclei with a thin rim of blue cytoplasm. Found mostly in lymphoid tissue, they are crucial to immunity. They are divided into two different types, T and B cells.

  • What are the functions of B and T lymphocytes?

    • The functions of B cells are to give rise to plasma cells, to produce antibodies, and T cells act as virus-infected cells and tumor cells.

  • Learn the structure and functions of monocytes.

    • Monocytes are a type of white blood cell that circulate in the bloodstream and migrate into tissues, where they differentiate into macrophages and dendritic cells, playing crucial roles in phagocytosis and antigen presentation. They’re dark purple, U-shaped or kidney-shaped nuclei. activate lymphocytes to mount an immune response. Additionally, monocytes help in the removal of dead or damaged cells, thus contributing to tissue repair and inflammation regulation.

  • Learn the structure and functions of platelets.

    • Platelets are small fragments of megakaryocytes, forming a temporary platelet plug that helps seal breaks in blood vessels. They play a crucial role in hemostasis, preventing excessive bleeding during injury by promoting blood clotting through the release of various chemical signals.

  • A mnemonic device to remember the order of white blood cells is Never let Monkeys Eat Bananas.