Blood Overview and Functions

Blood Overview

• Blood is a fluid component of the cardiovascular system
• It flows through a closed network of blood vessels
• Arteries carry blood away from the heart to tissues
• Capillaries allow nutrient, gas, and waste exchange
• Veins return blood to the heart

Blood Functions

• Transportation: Oxygen, carbon dioxide, metabolic waste, nutrients, heat, and hormones
• Regulation: pH, water, ion content of interstitial fluids, body temperature
• Protection: Blood/fluid loss, disease (white blood cells and antibodies)

Blood Characteristics

• More viscous than water; flows slower (specific gravity 1.050-1.060)
• Beneficial due to its role in transportation
• Temperature: 38°C
• pH: 7.4 (7.35-7.45)
• 8% of total body mass
• Volume: 5-6L (males), 4-5L (females)
• Hormonal negative feedback systems maintain constant blood volume and osmotic pressure
• Hematopoiesis: Formation of blood cells

Blood Composition

• Blood Plasma (55%): Primarily water (91.5%), proteins (7%), and other solutes (1.5%)
  • Proteins: Albumins (54%), Globulins (38%), Fibrinogen (7%), others (1%)
  • Other solutes: Electrolytes, nutrients, gases, regulatory substances, waste
• Formed Elements (45%):
  • Red blood cells (erythrocytes): 4.8-5.4 million per μL *
  • White blood cells (leukocytes): 5,000-10,000 per μL (neutrophils, lymphocytes, monocytes, eosinophils, basophils)
  • Platelets (thrombocytes): 150,000-400,000 per μL

Blood Plasma Details

• 92% water
• Extracellular fluid (combination of interstitial fluid plus blood plasma)
• Plasma proteins synthesized in the liver and confined to the bloodstream
  • Albumin: maintains blood osmotic pressure
  • Globulins: transport and immunoglobulins (IgG, IgM, IgA)
  • Fibrinogen: clotting
• Other substances: electrolytes, nutrients, hormones, gases, waste products

Formed Elements - Red Blood Cells

• Also called erythrocytes
• Formed in red bone marrow (erythropoiesis)
• Biconcave disk, 8 μm diameter
• Shape allows a large surface area to volume ratio
• Stacking for smooth blood flow
• Smooth/flexible shape to enter capillaries
• Lifespan: approximately 120 days
• No nucleus or other organelles; no division or mitochondrial ATP formation.
• Primed for gas transport
• Short life span (120 days)
• Hematocrit levels: Females (38-46%), Males (40-54%)
• 1/3 of weight is haemoglobin
• Flexible internal protein scaffold

Formed Elements - White Blood Cells

• Also called leukocytes
• Defence mechanism
• Contain nuclei and other organelles
• Do not contain haemoglobin
• Many types: monocytes, lymphocytes, eosinophils, neutrophils, basophils
• Lymphocytes (T, B, natural killer (NK))
• Increase in number during infections
• Phagocytosis: engulf and destroy microbes and damaged tissue

Haemostasis

• Blood's ability to seal leaks, cuts, and breaks in blood vessels to limit blood loss
• Three basic mechanisms:
  • Vascular spasm (within seconds)
  • Platelet plug formation (after 30 seconds)
  • Blood clotting (coagulation)

Vascular Spasm

• Smooth muscle contracts
• Constricts blood vessels, decreasing blood flow
• Important initial step to decrease blood loss

Platelet Plug Formation

• Platelets carry chemicals (Ca²⁺, ADP, ATP, clotting factors, serotonin) producing thromboxane A2
• Thromboxane A2 and serotonin act as vasoconstrictors, restricting blood flow through the injured vessel
• Tiny cell fragments
• No nucleus
• 5-9 days survival
• Help in stopping blood loss: form platelet plug, release chemicals to promote blood clotting, release chemicals to promote vascular spasms.

Clotting (Coagulation)

• Permanent repair
• Complex cascade of reactions
• Coagulation factors activate each other
• Conversion of fibrinogen into fibrin
• Vitamin K: required by the liver to synthesize clotting factors
• Calcium: essential for blood clotting; low blood calcium impairs clotting

Transport Function

• Blood transports various substances throughout the body

Haemoglobin (Hb)

• Composed of 4 protein chains (2 alpha and 2 beta)
• Iron (Fe²⁺) at the center of each heme group binds oxygen reversibly
• Oxyhaemoglobin: makes blood bright red
• Deoxyhaemoglobin: no oxygen bound to iron; blood is dark red/burgundy

Carbon Dioxide Transport

• Occurs in three ways:
  • Dissolved in plasma (7%)
  • Combined with globin part of Hb molecule, forming carbaminohaemoglobin (23%)
  • As part of bicarbonate ion in plasma (70%)

Oxygen Transport

• 98.5% of oxygen combines chemically with haemoglobin inside red blood cells (oxyhaemoglobin)
• 1.5% dissolves in blood plasma
• Oxygen dissociation curve shows levels of saturation and oxygen partial pressures

Oxygen-Dissociation Curve

• Relates haemoglobin saturation to oxygen partial pressure at normal blood pH (7.4) and temperature (38°C)
• Cooperative binding method: Binding of oxygen to haemoglobin is a reversible reaction.
• Blood almost fully saturated at pO₂ of 60 mmHg
• Implications at high altitudes and diseases. Between 20 and 40 mm Hg oxygen released in areas of need (e.g., contracting muscles).

Factors Affecting Haemoglobin-Oxygen Affinity

• pH/Acidity:
  • High blood pH favors oxygen binding.
  • Low blood pH favors oxygen release (Bohr effect). Increased CO₂ levels (meaning lower pH) means decreased oxygen capacity. Decreased CO₂ levels (meaning higher pH) means higher oxygen capacity.
• Exercise and metabolism acidity of blood; as acidity increases, O₂ affinity of Hb decreases
• Exercise and metabolism, blood, acidity, as acidity increases, O₂ affinity of Hb decreases

External Respiration

• Calculate % oxygen saturation of blood passing through pulmonary capillaries on its way to the left heart (98%)
• Calculate % oxygen saturation of blood in pulmonary artery before entering the lungs (75%)

Explore the essential overview of blood, its functions, and characteristics within the cardiovascular system. This quiz covers aspects such as transportation, regulation, and protection, along with the composition and physiological properties of blood. Delve into the vital role blood plays in maintaining homeostasis.