BLOOD ANATOMY AND PHYSIOLOGY

BLOOD

HUMAN ANATOMY AND PHYSIOLOGY

Lecturers: REUBEN AZIE, OKONKWO GABRIEL

Learning Objectives

• By the end of this session, you will be able to:

  • Describe physical characteristics & functions of blood

  • Differentiate plasma composition & formed elements

  • Explain erythrocyte structure & oxygen transport mechanisms

  • Interpret the O₂-Haemoglobin dissociation curve & shifts

  • Identify leukocyte types & clinical significance

  • Outline the 4 stages of haemostasis & coagulation labs

  • Relate blood physiology to nursing assessments & interventions

Introduction – The River of Life

• WHAT IS BLOOD?

  • Specialized Connective Tissue (Mesoderm origin)

  • Formed elements suspended in extracellular matrix (Plasma)

  • The body's transport system

PHYSICAL CHARACTERISTICS

• Temperature: ~38°C (100.4°F)

• pH: 7.35 – 7.45 (Tightly regulated)

• Viscosity: 3–4x thicker than water

• Volume: 4–6 Litres (7–8% of body weight)

  • Men: 5–6 L

  • Women: 4–5 L

Functions of Blood (TDR)

1. TRANSPORT

   • O₂, CO₂, Nutrients, Hormones, Waste

   • The "Highway" of the body

2. DEFENSE

   • WBCs patrol for pathogens

   • Antibodies neutralize invaders

   • Clotting prevents blood loss

3. REGULATION

   • Body Temperature (Heat distribution)

   • Acid-Base Balance (pH 7.35–7.45)

   • Fluid Balance (Capillary exchange)

THREE BROAD PHYSIOLOGICAL ROLES

Composition of Blood

• CENTRIFUGED BLOOD SEPARATION:

  • Plasma: The top, clear liquid layer (contains clotting factors if anticoagulants are used).

  • Buffy Coat: A thin, middle white layer containing white blood cells and platelets.

  • Red Blood Cells (RBCs): The dense, bottom layer.

BLOOD PLASMA VS SERUM

• Serum

  • Anti-coagulant

  • 
    

• Plasma

  • Buffy coat (white blood cells and platelets)

  • Blood clot

  • Red blood cells

Plasma & Plasma Proteins

• PLASMA COMPOSITION

  • 90–92% Water

  • 8–10% Solutes (Proteins, Electrolytes, Nutrients)

• MAJOR PLASMA PROTEINS (Liver Production):

  • ALBUMIN (54%)

  • GLOBULINS (38%)

  • FIBRINOGEN (<1%)

Major Types:

• Albumin (60%)

  • Major component of osmotic pressure of plasma

• Globulins (35%)

  • Antibodies (immunoglobulin) and transport proteins

• Fibrinogens (4%)

  • Functions in blood clotting

• Other (<1%)

  • Various roles (a-1-antitrypsin, coagulation factors, etc.)

ALBUMIN (54%)

• A vital protein produced by the liver that constitutes the main protein in blood plasma

• Key Functions & Importance

  • Fluid Balance: Keeps blood inside vessels, preventing edema (swelling) in tissues.

  • Transportation: Acts as a carrier for hormones, vitamins, enzymes, and drugs.

  • Tissue Growth: Assists in nourishing tissues and repairing damage.

GLOBULINS (38%)

• A protein produced by the liver and immune system (alpha, beta, and gamma groups) that fight infections, aid blood clotting, and transport nutrients.

• The normal concentration of serum globulin in adults is generally 2.0 to 3.5 g/dL (20 to 35 g/L).

FIBRINOGEN (<1%)

• A vital plasma glycoprotein produced by the liver which is crucial for blood clotting, acting as the precursor to fibrin

• It is the primary structural component of blood clots.

• Healthy adults typically have levels between 200–400 mg/dL

OTHER PLASMA PARTS

• Electrolytes: (Na⁺, K⁺, Ca²⁺, etc.)

• Nutrients: (glucose, amino acids)

• Hormones, dissolved gases, waste: (urea, creatinine)

• Role reminder: Plasma proteins also keep blood thick enough and help buffer pH.

Clinical Alert: Albumin & Edema

• WHY ALBUMIN MATTERS TO NURSES MECHANISM:

  • Albumin stays in blood vessels → Pulls water in (Oncotic Pressure)

  • Low Albumin → Water leaks into tissues → EDEMA

• CAUSES OF HYPOPROTEINEMIA:

  • Liver Disease (Cirrhosis)

  • Kidney Disease (Nephrotic Syndrome)

  • Severe Malnutrition

• NURSING ACTION:

  • Assess for pitting edema, ascites, pulmonary edema

  • Monitor albumin levels in swelling cases

FORMED ELEMENTS & HEMATOCRIT

• 45 % of blood = RBCs + WBCs + platelets

• Hematocrit (Hct) = % of packed RBCs

  • Men: 42–54 %

  • Women: 37–47 %

• Quick rule: Hct ≈ 3 × Hb

Erythrocytes (RBCs)

• Number: 4.5–5.5 million per microlitre

• Lifespan: 120 days

• Destroyed in spleen & liver by macrophages

RBC Structure

• Biconcave disc shape – genius design!

  • Huge surface area for gas exchange

  • Flexible – squeezes through tiny capillaries

  • No nucleus, no mitochondria → more room for haemoglobin + does NOT use the O₂ it carries!

Haemoglobin (Hb) – The Oxygen Hero

• Each RBC packed with ~280 million Hb molecules

• 4 polypeptide chains + 4 heme groups with iron (Fe)

• 1 Hb carries 4 O₂ molecules

• Oxyhaemoglobin = bright red

• Deoxyhaemoglobin = dark red

• Normal values:

  • Men: 13.5–17.5 g/dL

  • Women: 12–15.5 g/dL

Oxygen-Haemoglobin Dissociation Curve

• S-shaped (sigmoid) curve – beautiful!

  • Lungs (PO₂ ~100 mmHg) → 98 % saturated

  • Resting tissues (PO₂ ~40 mmHg) → ~75 % saturated (25 % unloaded)

  • Exercising tissues (PO₂ ~20 mmHg) → even more unloaded

Right Shift = More O₂ Released to Tissues

• Mnemonic:

• CADET

  • ↑ CO₂

  • ↑ Acidity (↓ pH) – Bohr effect

  • ↑ 2,3-DPG

  • ↑ Exercise / Temperature

• Real-life example:

  • Patient with fever 39.5 °C or running a marathon → tissues hot & acidic → automatic right shift → more O₂ delivered exactly where needed!

Left Shift & Important Nursing Scenarios

• Left shift = Hb holds O₂ tighter

• Causes: alkalosis, low temperature, stored blood (low 2,3-DPG)

• Nursing scenarios you MUST know:

  • Stored blood transfusion → left shift → tissues may still be hypoxic even if SpO₂ = 100 %

  • Hyperventilating patient (respiratory alkalosis) → left shift

  • Severe anaemia → SpO₂ 100 % but total O₂ content very low

Carbon Dioxide Transport

• Three ways:

  • 70 % as bicarbonate (HCO₃⁻) inside RBCs (carbonic anhydrase + chloride shift)

  • 20–25 % bound to Hb (carbaminohaemoglobin) – Haldane effect

  • 5–10 % dissolved in plasma

• Equation to remember:
  $CO₂ + H₂O <br>ightleftharpoons H₂CO₃ <br>ightleftharpoons H^+ + HCO₃⁻$

RBC Destruction

• Red blood cells (RBCs) have a lifespan of approximately 120 days.

• As they age, they become less flexible and are eventually filtered out and dismantled in a highly efficient recycling process.

• Majority of RBC destruction (90%) happens extravascularly (E.g. Spleen, liver and bone marrow).

• About 10% of RBCs rupture directly within the bloodstream due to mechanical stress or damage.

Where Destruction Occurs

• The Spleen "RBC graveyard":

  • Acts as a mechanical filter.

  • Old RBCs must squeeze through narrow gaps (3 micrometers) in the splenic pulp.

  • Fragile, aged cells that cannot deform properly are trapped and engulfed by specialized white blood cells called macrophages.

Breakdown and Recycling

• Once a macrophage engulfs an RBC, the hemoglobin inside is broken down into its three main components:

  • Globin

  • Iron

  • Heme

Globin (The Protein)

• Once the macrophage (the "cleanup" cell) digests the red blood cell, it uses enzymes called proteases to break the Globin chains down into amino acids through a process of hydrolysis

• The body does not waste these amino acids.

  • They have three primary destinations:

  • Many travel back to the red bone marrow to be reassembled into brand-new hemoglobin for the next generation of red blood cells.

  • They may be used by other cells to build different proteins, such as muscle tissue, enzymes, or antibodies.

  • If the body is in a state of starvation or high demand, these amino acids can be deaminated (the nitrogen is removed) and processed to create ATP (energy).

Iron (Fe²⁺)

• This is the most "precious" component.

• It is released from the heme and transported by a protein called transferrin back to the bone marrow for new RBC production

• It can also be stored in the liver as ferritin.

Heme (The Pigment)

• The non-iron portion of heme cannot be recycled for new cells.

• It is converted into:

  • Biliverdin (green pigment).

  • Bilirubin (yellow pigment), which travels to the liver.

• Excretion: The liver secretes bilirubin into bile, which enters the intestines.

  • It is eventually converted into stercobilin (giving feces its brown color) and urobilin (giving urine its yellow color).

Leukocytes (White Blood Cells)

• Total: 4,500–11,000 per microlitre

• Granulocytes (have granules) vs Agranulocytes (no granules)

• Mnemonic order (most to least common):

  • Never Let Monkeys Eat Bananas

• Neutrophils → Lymphocytes → Monocytes → Eosinophils → Basophils

Classification of WBC Types

• Granulocytes

  • Neutrophils (50–70%)

  • Eosinophils (1–4%)

  • Basophils (<1%)

• Agranulocytes

  • Lymphocytes (20–30%)

  • Monocytes (2–8%)

Granulocytes Detail

1. NEUTROPHILS (50–70%)

   • Multi-lobed nucleus

   • First responders to BACTERIA

   • Phagocytosis

2. EOSINOPHILS (1–4%)

   • Bilobed nucleus, Red-orange granules

   • Combat PARASITES

   • Mediate ALLERGIC reactions

3. BASOPHILS (<1%)

   • Dark blue granules obscure nucleus

   • Release HISTAMINE & Heparin

   • Inflammation & Allergy

Agranulocytes Detail

• MONOCYTES (2–8%)

  • Kidney/Horseshoe shaped nucleus

  • Become MACROPHAGES in tissues

  • Major phagocytes & Antigen Presentation

• LYMPHOCYTES (20–30%)

  • Large round nucleus, thin cytoplasm rim

  • ADAPTIVE IMMUNITY

  • T Cells: Kill infected cells

  • B Cells: Produce Antibodies

  • Rise in VIRAL infections

The Five WBC Types (Table)

WBC Differential & Nursing Interpretation

• Left shift = more immature neutrophils (bands) → severe bacterial infection

• Right shift = hypersegmented neutrophils → B12/folate deficiency

• Common patterns:

  • ↑ Neutrophils → bacterial infection

  • ↑ Lymphocytes → viral (flu, COVID, mono)

  • ↑ Eosinophils → allergy or parasites

  • Low WBC (<4500) → neutropenic precautions!

Blood Grouping

• It is the classification of blood based on inherited antigens on red blood cells

• The ABO and Rh systems are the main blood grouping systems used, determining compatibility for transfusions.

• The four main types (A, B, AB, O), further split by Rh factor (positive or negative), define if blood is compatible, with O-negative as a universal donor and AB-positive as a universal recipient.

The ABO Blood Group System

• This system is determined by two carbohydrate antigens, A and B.

• The unique feature is that individuals naturally possess preformed antibodies against the antigens they lack, even without prior exposure to foreign blood.

  • Type A: Has A antigens on RBCs and anti-B antibodies in the plasma.

  • Type B: Has B antigens on RBCs and anti-A antibodies in the plasma.

  • Type AB: Has both A and B antigens; contains no ABO antibodies (Universal Recipient).

  • Type O: Has neither A nor B antigens; contains both anti-A and anti-B antibodies (Universal Donor).

The ABO Blood Group System

The Rh (Rhesus) Blood Group System

• The Rh system involves over 50 antigens, but the D antigen is the most clinically significant and highly immunogenic.

• Rh Positive (Rh+): RBCs express the D antigen.

• Rh Negative (Rh-): RBCs lack the D antigen.

• Antibody Production:

  • Unlike the ABO system, Rh-negative individuals do not naturally have anti-D antibodies.

  • These are only produced after sensitization—exposure to Rh+ blood through transfusion or pregnancy.

The Eight Common Blood Types

• Combining ABO and Rh systems results in eight common types:

  • A+, A- , B+, B-, O+, O-, AB+, and AB-

  • O+: 36% (Most common)

  • A+: 28%

  • O-: 14%

  • A-: 8%

  • B+: 8%

  • B-: 3%

  • AB+: 2%

  • AB-: 1% (Least common)

Clinical Significance

• Transfusions: Receiving incompatible blood can trigger fatal immune reactions. Rh-negative individuals should generally receive Rh-negative blood.

• Pregnancy: If a mother is Rh-negative and the fetus is Rh-positive, the mother's immune system might attack the fetus's blood cells (Hemolytic Disease of the Fetus and Newborn).

• Inheritance: Blood type is inherited from parents.

Platelets (Thrombocytes)

• Tiny fragments from megakaryocytes

• Normal: 150,000–400,000 per microlitre

• Low (<20,000) = spontaneous bleeding (petechiae)

• HAEMOSTASIS

  • Process of stopping bleeding

  • Maintains flow in intact vessels

  • 4 Stages (Orchestrated Sequence)

Hemostasis – Stopping the Bleed

• Four-act play:

  • Act 1 Vascular spasm (immediate)

  • Act 2 Platelet plug formation (adhesion → activation → aggregation)

  • Act 3 Coagulation cascade (extrinsic + intrinsic → common pathway → fibrin)

  • Act 4 Clot retraction & fibrinolysis (plasmin dissolves clot later)

Hemostasis

• Vascular Spasm (Vasoconstriction): Immediate contraction of the smooth muscle in the damaged vessel wall to reduce blood flow

• **Platelet Plug