Blood and Cardiovascular System: Study Notes for ANP College Students

BLOOD

Components of Blood

Blood is a specialized connective tissue composed of plasma and formed elements (cells and cell fragments). It performs vital functions in the body, including transport, regulation, and protection.

• Formed Elements: Includes erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).

• Plasma: The liquid matrix of blood, containing water, proteins, nutrients, hormones, and waste products.

Functions of Blood

• Distribution: Transports oxygen, carbon dioxide, nutrients, hormones, and waste products.

• Regulation: Maintains body temperature, pH, and fluid volume.

• Protection: Prevents blood loss (hemostasis) and fights infection (immune response).

Hematopoiesis

Hematopoiesis is the process of blood cell formation, occurring primarily in the red bone marrow. The number of formed elements is regulated by hormones and growth factors.

• Stem Cells: All blood cells originate from hematopoietic stem cells (hemocytoblasts).

• Regulation: Controlled by factors such as erythropoietin (EPO) and hypoxia-inducible factors (HIFs).

Erythrocytes (Red Blood Cells)

• Structure: Anucleated, biconcave discs containing hemoglobin and the protein spectrin for flexibility.

• Hemoglobin: The oxygen-carrying protein. Formula: $\text{Hb} + \text{O}_2 \rightarrow \text{HbO}_2$

• Erythropoiesis: The process of RBC formation from stem and committed cells.

• Regulation: EPO (from kidneys) stimulates erythropoiesis in response to hypoxia.

• Disorders: Include anemia (low RBCs or hemoglobin) and polycythemia (excess RBCs).

Leukocytes (White Blood Cells)

• Granulocytes:

  • Neutrophils: Contain lysozymes; phagocytize bacteria.

  • Eosinophils: Attack parasitic worms, modulate allergic responses, and handle antigen-antibody complexes.

  • Basophils: Release histamine and heparin; involved in inflammation.

• Agranulocytes:

  • Lymphocytes: T cells (cell-mediated immunity) and B cells (humoral immunity).

  • Monocytes: Phagocytic; become macrophages in tissues; arrive last at infection sites.

Hemostasis

Hemostasis is the process that stops bleeding after vessel injury, involving three main steps:

1. Vascular Spasm: Vasoconstriction reduces blood flow.

2. Platelet Plug Formation: Platelets adhere and release ADP, serotonin, and thromboxane A2 to attract more platelets.

3. Coagulation (Blood Clotting):

   1. Formation of prothrombin activator

   2. Conversion of prothrombin to thrombin

   3. Conversion of fibrinogen to fibrin (forms the clot mesh)

• Clot Retraction & Fibrinolysis: The clot contracts and is eventually dissolved.

Blood Groups

Blood types are determined by the presence of antigens (agglutinogens) and antibodies (agglutinins) on RBCs.

Blood Type	Antigen(s)	Antibody(ies)
A	A	Anti-B
B	B	Anti-A
AB	A, B	None
O	None	Anti-A, Anti-B
Rh+	Rh	None
Rh-	None	Anti-Rh (if sensitized)

CARDIOVASCULAR SYSTEM: HEART

Heart Anatomy

• Coverings: Pericardium (fibrous and serous layers)

• Heart Wall: Epicardium (outer), myocardium (muscle), endocardium (inner)

• Chambers:

  • Right and Left Atria: Receive blood from systemic and pulmonary circuits

  • Right and Left Ventricles: Pump blood to pulmonary and systemic circuits

• Valves: Ensure unidirectional blood flow

  • Atrioventricular (AV) Valves: Tricuspid (right), Bicuspid/Mitral (left)

  • Semilunar Valves: Pulmonary (right), Aortic (left)

Blood Flow Through the Heart

1. Blood enters right atrium via superior vena cava, inferior vena cava, and coronary sinus

2. Passes through tricuspid valve to right ventricle

3. Pumped through pulmonary valve to pulmonary trunk and lungs

4. Returns via pulmonary veins to left atrium

5. Passes through mitral valve to left ventricle

6. Pumped through aortic valve to aorta and systemic circulation

Coronary Circulation

• Coronary Arteries: Supply oxygenated blood to heart muscle

• Cardiac Veins: Drain deoxygenated blood from heart muscle

Cardiac Muscle Physiology

• Cardiac Muscle Twitch: Features a plateau phase that prolongs the refractory period, preventing tetanus.

• Ion Distribution: Involves Na+, K+, and Ca2+ movement during action potentials.

• Intercalated Discs: Contain gap junctions (electrical coupling) and desmosomes (mechanical strength).

• Functional Syncytium: Cardiac cells contract as a unit due to electrical connectivity.

Conduction System of the Heart

1. Sinoatrial (SA) node

2. Atrioventricular (AV) node

3. AV bundle (Bundle of His)

4. Right and left bundle branches

5. Purkinje fibers

Electrocardiogram (ECG)

• P wave: Atrial depolarization

• QRS complex: Ventricular depolarization

• T wave: Ventricular repolarization

Cardiac Cycle

The cardiac cycle describes the sequence of events in one heartbeat, including blood flow, valve actions, and pressure changes.

• Isovolumetric Contraction: Ventricles contract with all valves closed.

• Blood Ejection: Semilunar valves open, blood is pumped out.

• Isovolumetric Relaxation: Ventricles relax, all valves closed.

Cardiac Output

• Definition: Volume of blood pumped by each ventricle per minute.

• Formula: $\text{CO} = \text{HR} \times \text{SV}$

• Stroke Volume (SV): $\text{SV} = \text{EDV} - \text{ESV}$

• Frank-Starling Law: Increased preload (EDV) increases stroke volume.

• Afterload: The resistance the ventricle must overcome to eject blood.

Autonomic Control of the Heart

• Cardiac Centers: Located in the medulla oblongata.

• CAC (Cardioacceleratory Center): Sympathetic; releases epinephrine and norepinephrine to increase HR and contractility.

• CIC (Cardioinhibitory Center): Parasympathetic; releases acetylcholine to decrease HR and contractility.

CARDIOVASCULAR SYSTEM: BLOOD VESSELS

Blood Vessel Anatomy

• Tunica Interna (Intima): Endothelial lining

• Tunica Media: Smooth muscle and elastic fibers

• Tunica Externa (Adventitia): Connective tissue

Types of Blood Vessels

• Arteries: Carry blood away from the heart

• Arterioles: Small branches of arteries

• Capillaries: Sites of exchange between blood and tissues

• Venules: Collect blood from capillaries

• Veins: Return blood to the heart

Venous Return Mechanisms

• Valves prevent backflow

• Skeletal muscle pump assists movement

• Respiratory pump aids venous return during breathing

Blood Flow and Pressure

• Arterial Blood Pressure: Determined by cardiac output (CO), blood volume (BVol), and peripheral resistance (PR)

• Formulas:

  • $\text{CO} = \text{HR} \times \text{SV}$

  • $\text{PR}$ depends on blood viscosity, vessel length, and vessel diameter

Regulation of Blood Pressure

• Vasomotor Center: Sympathetic control of vessel diameter

• Chemical Controls:

  • Adrenal catecholamines (norepinephrine, epinephrine)

  • ANF (Atrial Natriuretic Factor)

  • ADH (Antidiuretic Hormone)

  • Endothelin, PDGF (vasoconstrictors)

  • Nitric oxide (vasodilator)

  • Aldosterone, renin-angiotensin system

  • Alcohol (vasodilator)

Shock

Shock is a condition of inadequate tissue perfusion due to decreased blood pressure, cardiac output, or venous return.

• Types:

  • Hypovolemic (blood loss)

  • Cardiogenic (heart failure)

  • Neurogenic (loss of vascular tone)

  • Vasogenic (widespread vasodilation, e.g., anaphylaxis)

Special Circulations

• Systemic

• Coronary

• Hepatic portal

• Pulmonary

• Fetal

• Cerebral

CARDIOVASCULAR SYSTEM: BLOOD VESSELS (CONTINUED)

Blood Flow Regulation

• Autoregulation: Local control of blood flow by tissues

• Metabolic Control: Changes in tissue metabolism alter blood flow

• Myogenic Control: Vascular smooth muscle responds to pressure changes

Special Areas of Circulation

• Skeletal muscle

• Skin

• Heart

• Brain

• Lungs

Capillary Dynamics (Additional info: for advanced study)

• Bulk Fluid Movements: Governed by hydrostatic and osmotic pressures

• Pressures:

  • HPc: Hydrostatic pressure of the capillary

  • OPc: Osmotic pressure of the capillary

  • HPi: Hydrostatic pressure of the interstitium

  • OPi: Osmotic pressure of the interstitium

Fluid Compartments

Compartment	Volume (L)
Intracellular	25
Extracellular	15
Interstitial	12
Plasma	3

Edema

• Definition: Accumulation of excess fluid in interstitial spaces

• Causes: Increased capillary hydrostatic pressure, decreased plasma osmotic pressure, increased capillary permeability, lymphatic obstruction