Functions and Composition of Blood

Overview of Blood Functions

Blood is a vital connective tissue responsible for transport, regulation, and protection within the body.

• Transport: Delivers oxygen, nutrients, hormones, and removes waste products.

• Regulation: Maintains pH, temperature, and fluid balance.

• Protection: Involves immune responses and clotting mechanisms.

Key Point: Blood viscosity is influenced by proteins, cells, and hydration status, affecting blood pressure and flow.

Blood Composition

• Plasma: The liquid matrix (~55% of blood), containing water, proteins (albumin, globulins, fibrinogen), nutrients, hormones, and waste.

• Formed Elements: Red blood cells (RBCs), white blood cells (WBCs), and platelets.

• Hematocrit: The percentage of blood volume occupied by RBCs.

Example: A high hematocrit increases blood viscosity, raising cardiac workload.

Red Blood Cells (Erythrocytes)

• Structure: Biconcave discs lacking nuclei and most organelles, optimized for gas transport.

• Hemoglobin: The main protein in RBCs, binds oxygen; each molecule can carry up to four O2 molecules.

• Surface Antigens: Determine blood types (A, B, AB, O) and Rh factor.

Formula: Oxygen-carrying capacity is proportional to hemoglobin content.

White Blood Cells (Leukocytes)

• Types: Neutrophils, lymphocytes, monocytes, eosinophils, basophils.

• Functions: Immune defense, inflammation, and allergic responses.

Example: Eosinophils increase during parasitic infections and allergies.

Platelets (Thrombocytes) and Hemostasis

• Platelets: Cell fragments essential for blood clotting.

• Hemostasis: The process of stopping bleeding, involving vascular spasm, platelet plug formation, and coagulation.

Three Phases of Hemostasis: Vascular spasm, platelet plug formation, coagulation cascade.

Cardiovascular System: Heart Structure and Function

Heart Anatomy

The heart is a muscular organ divided into four chambers: two atria and two ventricles.

• Base and Apex: The base is the superior, broad part; the apex is the pointed inferior tip.

• Pericardium: Double-walled sac enclosing the heart, providing protection and reducing friction.

• Wall Layers: Epicardium (outer), myocardium (muscular middle), endocardium (inner lining).

Heart Valves and Blood Flow

• Atrioventricular (AV) Valves: Tricuspid (right), bicuspid/mitral (left).

• Semilunar Valves: Pulmonary (right), aortic (left).

• Blood Flow Pathway: Right atrium → right ventricle → pulmonary artery → lungs → left atrium → left ventricle → aorta → systemic circulation.

Example: The left ventricular wall is thicker than the right due to higher systemic pressure.

Cardiac Muscle and Conduction System

• Cardiac Muscle Cells: Striated, branched, interconnected by intercalated discs for synchronized contraction.

• Autorhythmicity: The heart generates its own electrical impulses.

• Conduction System: SA node (pacemaker) → AV node → Bundle of His → bundle branches → Purkinje fibers.

ECG Waves: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

Cardiac Cycle and Output

• Cardiac Cycle: Sequence of events in one heartbeat (systole and diastole).

• Stroke Volume (SV): Volume of blood ejected per beat.

• Cardiac Output (CO): Total blood pumped per minute.

Formula:

$\text{Cardiac Output (CO)} = \text{Heart Rate (HR)} \times \text{Stroke Volume (SV)}$

Ejection Fraction: Percentage of end-diastolic volume ejected per beat.

Blood Vessels and Circulation

Types of Blood Vessels

• Arteries: Carry blood away from the heart; thick, elastic walls; high pressure.

• Veins: Return blood to the heart; thinner walls, larger lumen, contain valves.

• Capillaries: Microscopic vessels for exchange of gases, nutrients, and wastes.

Comparison Table:

Special Vascular Structures

• Thoroughfare Channel: Direct capillary connection between arteriole and venule.

• Anastomosis: Connection between blood vessels; can be arterial or venous.

Example: Arterial anastomoses provide collateral circulation to vital organs.

Blood Flow, Pressure, and Resistance

• Blood Flow: Volume of blood moving through a vessel per unit time.

• Blood Pressure (BP): Force exerted by blood on vessel walls.

• Resistance: Opposition to flow, mainly due to vessel diameter, length, and blood viscosity.

Formulas:

$\text{BP} = \text{CO} \times \text{TPR}$

$\text{Pulse Pressure} = \text{Systolic BP} - \text{Diastolic BP}$

$\text{Mean Arterial Pressure (MAP)} = \text{Diastolic BP} + \frac{1}{3}(\text{Pulse Pressure})$

Capillary Exchange and Fluid Movements

• Starling Forces: Capillary hydrostatic pressure (CHP) and colloid osmotic pressure (COP) govern fluid movement.

• Filtration: Movement of fluid out of capillaries at arterial end.

• Reabsorption: Movement of fluid into capillaries at venous end.

Example: Edema occurs if filtration exceeds reabsorption or lymphatic drainage is impaired.

Regulation of Blood Flow and Pressure

Intrinsic and Extrinsic Controls

• Autoregulation: Local control of blood flow by tissues (metabolic and myogenic mechanisms).

• Extrinsic Controls: Neural (sympathetic/parasympathetic) and endocrine (hormones like epinephrine, ADH, angiotensin II) regulation.

Example: During exercise, local vasodilation increases blood flow to active muscles.

Factors Affecting Blood Pressure

• Cardiac Output: Increased by higher heart rate or stroke volume.

• Total Peripheral Resistance (TPR): Increased by vasoconstriction, blood viscosity, or vessel length.

• Elasticity of Arteries: Loss of elasticity (arteriosclerosis) raises systolic pressure.

Pathological Conditions

• Turbulent Flow: Disordered flow increases resistance and risk of vascular damage.

• Circulatory Shock: Inadequate tissue perfusion due to low blood pressure or volume.

• Ineffective Tissue Perfusion: Can result from heart failure, vessel obstruction, or shock.

Summary Table: Key Cardiovascular Concepts

Additional info:

• Some details, such as specific slide numbers and lecture references, were omitted for clarity and generalization.

• Where original notes were fragmented, standard academic context was added to ensure completeness.