Blood, Cardiovascular System, and Hemostasis: Study Notes for Anatomy & Physiology

Blood and Its Components

Functions and Composition of Blood

Blood is a specialized bodily fluid that performs essential functions such as transport, regulation, and protection. It consists of plasma and formed elements (red blood cells, white blood cells, and platelets).

• Function of Blood: Transports oxygen, nutrients, hormones, and waste products; regulates pH, temperature, and fluid balance; protects against pathogens and blood loss.

• Plasma: The liquid component of blood, containing water, proteins (albumin, globulins, fibrinogen), electrolytes, and nutrients.

• Formed Elements: Includes erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets).

• Hemoglobin: The protein in RBCs responsible for oxygen transport.

• Myoglobin: An oxygen-binding protein found in muscle cells, facilitating oxygen storage and release during muscle contraction.

Red Blood Cells (RBCs)

Red blood cells are the most abundant cells in blood, specialized for oxygen transport.

• Structure: Biconcave disc shape increases surface area for gas exchange.

• Lifespan: Approximately 120 days.

• Production: Occurs in red bone marrow via erythropoiesis, stimulated by erythropoietin (EPO).

• Breakdown: Old RBCs are removed by the spleen and liver; hemoglobin is broken down into heme and globin.

• Color of Urine and Feces: Breakdown of heme produces bilirubin, which is excreted in bile and gives feces its brown color; urobilin gives urine its yellow color.

White Blood Cells (WBCs)

White blood cells are involved in immune defense and are classified into granulocytes and agranulocytes.

• Granulocytes: Neutrophils, eosinophils, basophils.

• Agranulocytes: Lymphocytes, monocytes.

• Function: Protect the body against infection and foreign invaders.

Platelets

Platelets are cell fragments essential for blood clotting (hemostasis).

• Function: Initiate clot formation by adhering to damaged blood vessels and releasing clotting factors.

Hemostasis and Blood Clotting

Hemostasis

Hemostasis is the process that prevents and stops bleeding, involving three main steps.

• Vascular Spasm: Immediate constriction of blood vessels after injury.

• Platelet Plug Formation: Platelets adhere to exposed collagen and aggregate.

• Coagulation: Cascade of clotting factors leads to conversion of fibrinogen to fibrin, forming a stable clot.

Fibrin: The protein that forms the meshwork of a blood clot.

Clotting Factors: Proteins in plasma that are activated in sequence during coagulation.

Spleen and Lymphatic System

Spleen

The spleen is an organ involved in filtering blood, immune response, and recycling old RBCs.

• Functions: Removes old and damaged RBCs, stores platelets, and initiates immune responses.

Cardiovascular System

Heart Structure and Function

The heart is a muscular organ that pumps blood throughout the body via the circulatory system.

• Chambers: Four chambers—right atrium, right ventricle, left atrium, left ventricle.

• Valves: Ensure unidirectional blood flow (tricuspid, bicuspid/mitral, pulmonary, aortic).

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

Blood Vessels

Blood vessels transport blood to and from the heart and tissues.

• Arteries: Carry blood away from the heart; thick muscular walls.

• Veins: Carry blood toward the heart; thinner walls, valves present.

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

• Types of Capillaries: Continuous, fenestrated, and sinusoidal.

Blood Pressure

Blood pressure is the force exerted by circulating blood on vessel walls.

• Systolic Pressure: Pressure during ventricular contraction.

• Diastolic Pressure: Pressure during ventricular relaxation.

• Pulse Pressure: Difference between systolic and diastolic pressure.

• Mean Arterial Pressure (MAP): Average pressure in arteries during one cardiac cycle.

Formula for MAP:

$\text{MAP} = \text{Diastolic Pressure} + \frac{1}{3}(\text{Systolic Pressure} - \text{Diastolic Pressure})$

Regulation of Blood Pressure

• Baroreceptors: Sensory receptors in arteries that detect changes in blood pressure.

• Chemoreceptors: Detect changes in blood chemistry (O2, CO2, pH).

• Autonomic Nervous System: Sympathetic and parasympathetic divisions regulate heart rate and vessel diameter.

Cardiovascular Centers and Reflexes

Cardiovascular Centers

Located in the medulla oblongata, these centers regulate heart rate, blood pressure, and vessel tone.

• Cardioacceleratory Center: Increases heart rate via sympathetic stimulation.

• Cardioinhibitory Center: Decreases heart rate via parasympathetic stimulation.

• Vasomotor Center: Controls blood vessel diameter.

Adrenergic and Cholinergic Receptors

Adrenergic Receptors

Adrenergic receptors respond to catecholamines (epinephrine, norepinephrine) and mediate sympathetic effects.

• Alpha Receptors: Cause vasoconstriction and increased blood pressure.

• Beta Receptors: Beta-1 increases heart rate and contractility; Beta-2 causes vasodilation and bronchodilation.

Cholinergic Receptors: Respond to acetylcholine and mediate parasympathetic effects (e.g., decreased heart rate).

Pathophysiology: Anemia, Polycythemia, and Hyperemia

Anemia

Anemia is a condition characterized by a deficiency of RBCs or hemoglobin, leading to reduced oxygen-carrying capacity.

• Causes: Blood loss, decreased production, increased destruction, nutritional deficiencies.

• Symptoms: Fatigue, pallor, shortness of breath.

Polycythemia

Polycythemia is an abnormal increase in RBC count, which can increase blood viscosity and risk of thrombosis.

Hyperemia

• Active Hyperemia: Increased blood flow due to increased metabolic activity.

• Reactive Hyperemia: Increased blood flow following a period of reduced blood supply.

Additional Key Terms and Concepts

• Filtration and Reabsorption: Processes in capillaries that regulate fluid movement between blood and tissues.

• Endothelial Cells: Line blood vessels and regulate vascular tone and permeability.

• Nitric Oxide: A vasodilator produced by endothelial cells.

• Albumin: Major plasma protein responsible for maintaining osmotic pressure.

• EPO (Erythropoietin): Hormone that stimulates RBC production.

• Fibrillation: Rapid, irregular contractions of the heart (e.g., atrial fibrillation).

Table: Comparison of Blood Vessel Types

Vessel Type	Structure	Function	Pressure
Artery	Thick, muscular walls	Carry blood away from heart	High
Vein	Thinner walls, valves present	Carry blood toward heart	Low
Capillary	Single cell layer	Exchange of gases/nutrients	Very low

Example: Calculation of Pulse Pressure and MAP

• Given: Systolic Pressure = 120 mmHg, Diastolic Pressure = 80 mmHg

• Pulse Pressure: $120 - 80 = 40$ mmHg

• MAP: $80 + \frac{1}{3}(120 - 80) = 80 + 13.3 = 93.3$ mmHg

Additional info: Some context and definitions have been inferred and expanded for clarity and completeness.