Blood: Structure, Function, and Disorders (Anatomy & Physiology Chapter 17 Study Notes)

Blood: Structure, Function, and Disorders

17.1 Functions of Blood

Blood is the life-sustaining transport vehicle of the cardiovascular system, performing essential roles in transport, regulation, and protection.

• Transport

  • Delivers O2 and nutrients to body cells

  • Transports metabolic wastes to lungs and kidneys for elimination

  • Transports hormones from endocrine organs to target organs

• Regulation

  • Maintains body temperature by absorbing and distributing heat

  • Maintains normal pH using buffers, especially the alkaline reserve of bicarbonate ions

  • Maintains adequate fluid volume in the circulatory system

• Protection

  • Prevents blood loss via plasma proteins and platelets that initiate clot formation

  • Prevents infection via antibodies and white blood cells

17.2 Composition of Blood

Blood is the only fluid tissue in the body and is classified as a connective tissue. It consists of a nonliving fluid matrix called plasma and living cells called formed elements.

• Plasma: Straw-colored, sticky fluid; about 90% water

  • Contains over 100 dissolved solutes: nutrients, gases, hormones, wastes, proteins, inorganic ions

  • Plasma proteins are the most abundant solutes

    • Remain in blood; not taken up by cells

    • Produced mostly by the liver

    • Albumin: Makes up 60% of plasma proteins; functions as a carrier, blood buffer, and contributes to plasma osmotic pressure

• Formed Elements:

  • Erythrocytes (red blood cells, RBCs)

  • Leukocytes (white blood cells, WBCs)

  • Platelets

• Spun tube of blood yields three layers:

  • Erythrocytes on bottom (~45% of whole blood) – measured as hematocrit

    • Normal values: Males 47% ± 5%, Females 42% ± 5%

  • Buffy coat (<1%): thin, whitish layer between RBCs and plasma; contains WBCs and platelets

  • Plasma on top (~55%)

• Physical Characteristics and Volume:

  • Blood is sticky, opaque, with metallic taste

  • Color varies with O2 content: high O2 = scarlet red, low O2 = dark red

  • pH: 7.35–7.45

  • Volume: Males 5–6 L, Females 4–5 L

17.3 Erythrocytes (Red Blood Cells)

Erythrocytes are specialized cells responsible for the transport of respiratory gases, primarily oxygen and carbon dioxide.

• Structural Characteristics:

  • Small-diameter (7.5 μm), biconcave disc shape

  • Anucleate and lack organelles

  • Filled with hemoglobin (Hb) for gas transport

  • Contain plasma membrane protein spectrin and other proteins

  • ATP production is anaerobic; RBCs do not consume the O2 they transport

• Features for Efficient Gas Transport:

  • Biconcave shape offers large surface area relative to volume

  • Hemoglobin makes up 97% of cell volume (excluding water)

  • No mitochondria

• Function:

  • Dedicated to respiratory gas transport

  • Hemoglobin binds reversibly with oxygen

• Hemoglobin Structure:

  • Consists of red heme pigment bound to the protein globin

  • Globin: four polypeptide chains (two alpha, two beta)

  • Each heme group contains central iron atom that binds one O2

  • Each RBC contains ~250 million Hb molecules

• Oxygen and Carbon Dioxide Transport:

  • O2 loading in lungs: produces oxyhemoglobin (ruby red)

  • O2 unloading in tissues: produces deoxyhemoglobin (dark red)

  • CO2 loading in tissues: 20% of CO2 in blood binds to Hb, producing carbaminohemoglobin

• Production of Erythrocytes:

  • Hematopoiesis: formation of all blood cells; occurs in red bone marrow

  • Hematopoietic stem cells: stem cells that give rise to all formed elements

  • Hormones and growth factors push cells toward specific pathways of development

  • Committed cells cannot change

  • New blood cells enter blood sinusoids

• Regulation and Requirements of Erythropoiesis:

  • Too few RBCs lead to tissue hypoxia

  • Too many RBCs increase blood viscosity

  • Balance between RBC production and destruction depends on:

    • Hormonal controls

    • Dietary requirements

  • Erythropoietin (EPO): hormone that stimulates formation of RBCs

    • Released by kidneys (and some by liver) in response to hypoxia (low O2 levels)

    • Testosterone enhances EPO production

• Dietary Requirements:

  • Nutrients: amino acids, lipids, carbohydrates

  • Iron: essential for hemoglobin synthesis

  • Vitamin B12 and folic acid: necessary for DNA synthesis and cell division

• Fate and Destruction of Erythrocytes:

  • Life span: 100–120 days

  • Old RBCs become fragile; hemoglobin degenerates

  • Macrophages in spleen engulf and break down dying RBCs

Erythrocyte Disorders

Most erythrocyte disorders are classified as either anemia or polycythemia.

• Anemia: Blood has abnormally low O2-carrying capacity, insufficient to support normal metabolism.

  • Symptoms: fatigue, pallor, dyspnea, chills

  • Three groups based on cause:

    1. Blood loss

       • Rapid blood loss (e.g., severe wound): treated by blood replacement

       • Chronic hemorrhagic anemia (e.g., bleeding ulcer): treated by addressing primary problem

    2. Not enough RBCs produced

       • Iron-deficiency anemia: microcytes (small, pale RBCs); cannot synthesize hemoglobin due to lack of iron; treated with iron supplements

       • Pernicious anemia: autoimmune disease destroying stomach mucosa that produces intrinsic factor (needed for B12 absorption); results in macrocytes (large RBCs); treated with B12 injections or nasal gel

       • Renal anemia: lack of EPO; treated with synthetic EPO

       • Aplastic anemia: destruction/inhibition of red bone marrow by drugs, chemicals, radiation, or viruses; all formed elements affected; treated with transfusions or stem cell transplants

    3. Too many RBCs destroyed

       • Hemolytic anemias: premature lysis of RBCs due to incompatible transfusions, infections, or genetic abnormalities

       • Thalassemias: typically found in people of Mediterranean ancestry; one globin chain absent or faulty; RBCs are thin, delicate, and deficient in hemoglobin; severity varies

       • Sickle-cell anemia: mutated hemoglobin S; one amino acid wrong in a globin beta chain; RBCs become crescent-shaped under low O2; rupture easily and block small vessels; prevalent in people of African descent; confers resistance to malaria

• Polycythemia: Excess of RBCs increases blood viscosity; can be caused by bone marrow cancer (polycythemia vera) or secondary to low O2 levels (e.g., high altitude)

Table: Comparison of Major Anemia Types

Anemia Type	Main Cause	RBC Appearance	Treatment
Iron-deficiency	Low iron intake or absorption	Microcytic, pale	Iron supplements
Pernicious	Lack of intrinsic factor (B12 absorption)	Macrocytic, large	B12 injections/nasal gel
Aplastic	Bone marrow destruction/inhibition	All formed elements affected	Transfusions, stem cell transplant
Hemolytic	RBC rupture (genetic, infection, transfusion)	Varies	Treat underlying cause
Thalassemia	Faulty globin chain (genetic)	Thin, delicate	Transfusions (severe cases)
Sickle-cell	Mutated hemoglobin S (genetic)	Crescent-shaped	Transfusions, stem cell transplant

Key Equations and Scientific Terms

• Hematocrit: $\text{Hematocrit} = \frac{\text{Volume of RBCs}}{\text{Total Blood Volume}} \times 100\%$

• Oxygen transport by hemoglobin: $\text{Hb} + \text{O}_2 \rightleftharpoons \text{HbO}_2$

• Carbaminohemoglobin formation: $\text{Hb} + \text{CO}_2 \rightleftharpoons \text{HbCO}_2$

Additional info: These notes expand on the provided slides and images, adding definitions, examples, and a comparison table for anemia types to aid in exam preparation.