Cardiovascular and Lymphatic/Immune Systems: Study Guide (Chapters 17–20)

Blood: Composition and Function

Functions of Blood

Blood is a vital connective tissue with several essential functions:

• Transport: Delivers oxygen (O2), carbon dioxide (CO2), nutrients, hormones, and metabolic wastes throughout the body.

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

• Protection: Provides clotting (hemostasis) and immune defense via white blood cells (WBCs).

Composition of Whole Blood

• Plasma (55%): Mostly water (92%), plasma proteins (7%: albumin, globulins, fibrinogen), and other solutes (electrolytes, nutrients, gases, wastes).

• Formed Elements (45%):

  • Erythrocytes (RBCs): 99% of formed elements; transport O2 and CO2.

  • Leukocytes (WBCs): Immune defense; five types (see table below).

  • Platelets: Cell fragments essential for blood clotting.

• Hematocrit: Percentage of RBCs in whole blood (normal: ~45% men, ~42% women).

Erythrocytes (RBCs)

• Shape: Biconcave disc increases surface area for gas exchange.

• Structure: No nucleus or organelles in mature RBCs; filled with hemoglobin (Hb), which binds O2 (each Hb has 4 heme groups with Fe2+).

• Lifespan: ~120 days; removed by spleen and liver.

• Erythropoiesis: RBC production in red bone marrow, stimulated by erythropoietin (EPO) from kidneys in response to hypoxia.

• Clinical: Anemia (low RBC/Hb) causes fatigue; polycythemia (excess RBCs) increases blood viscosity.

Leukocytes (WBCs): Types and Functions

WBCs are crucial for immune defense. The five main types are:

Type	Function	% of WBCs
Neutrophil	Phagocytize bacteria	50-70%
Lymphocyte	Immune response (B cells, T cells)	20-40%
Monocyte	Become macrophages	2-8%
Eosinophil	Kill parasites; allergy response	1-4%
Basophil	Release histamine (inflammation)	<1%

• Clinical: Leukocytosis (high WBC) suggests infection; leukopenia (low WBC) may indicate bone marrow suppression.

Platelets and Hemostasis

• Platelets: Small fragments from megakaryocytes; lifespan 5–9 days.

• Hemostasis Steps:

  1. Vascular spasm (vasoconstriction)

  2. Platelet plug formation (adhesion and aggregation)

  3. Coagulation (clotting factors form fibrin mesh)

• Clotting factors: Mostly produced in the liver; require vitamin K.

• Fibrinolysis: Plasmin breaks down clots after healing.

• Clinical: Thrombocytopenia (low platelets) increases bleeding risk; hemophilia is a genetic clotting factor deficiency; thrombosis is abnormal clot formation.

Blood Typing (ABO & Rh)

• Antigens: A, B, and Rh (D antigen) on RBC surface.

• Antibodies: Anti-A and anti-B in plasma; anti-Rh only if sensitized.

• Universal donor: O negative (no antigens).

• Universal recipient: AB positive (no antibodies).

• Transfusion reaction: Incompatible donor RBCs agglutinate.

• Hemolytic disease of the newborn: Rh- mother, Rh+ fetus; maternal anti-Rh antibodies cross placenta.

Heart: Anatomy and Physiology

Heart Anatomy

• Coverings:

  • Fibrous pericardium (outer sac)

  • Serous pericardium: parietal (lines sac) and visceral (epicardium) layers

  • Pericardial cavity: contains serous fluid for lubrication

• Wall Layers (superficial to deep): Epicardium, myocardium (cardiac muscle), endocardium (inner lining)

• Chambers:

  • Right atrium: receives deoxygenated blood (SVC, IVC, coronary sinus)

  • Right ventricle: pumps to lungs (via pulmonary valve)

  • Left atrium: receives oxygenated blood (pulmonary veins)

  • Left ventricle: pumps to body (via aortic valve); thickest wall

• Valves:

  • Atrioventricular (AV): tricuspid (right), bicuspid/mitral (left)

  • Semilunar: pulmonary (right), aortic (left)

  • Chordae tendineae and papillary muscles prevent AV valve prolapse

Cardiac Conduction System

• Pathway:

  1. SA node (pacemaker, 60–100 bpm)

  2. Atrial syncytium (gap junctions)

  3. AV node (delays impulse ~0.1 sec)

  4. AV bundle (Bundle of His)

  5. Bundle branches (right & left)

  6. Purkinje fibers (ventricular myocardium)

• Intrinsic Rates: SA node: 60–100 bpm; AV node: 40–60 bpm; Purkinje fibers: 15–40 bpm.

• Autonomic Regulation: Sympathetic (β1 receptors) increases HR and contractility; parasympathetic (vagus nerve, ACh) decreases HR.

Cardiac Cycle and Heart Sounds

• Systole: Ventricular contraction and ejection.

• Diastole: Ventricular relaxation and filling.

• S1 ("lub"): AV valve closure (start of systole).

• S2 ("dub"): Semilunar valve closure (start of diastole).

• Murmur: Turbulent flow due to valve stenosis or regurgitation.

• Cardiac Output (CO): $CO = HR \times SV$

• Stroke Volume (SV): $SV = EDV - ESV$

• Ejection Fraction: $EF = \frac{SV}{EDV}$ (normal 55–70%)

• Factors Affecting SV: Preload (venous return), contractility (strength of contraction), afterload (resistance to ejection).

Clinical Connections – Heart

• Ischemic heart disease: Coronary artery blockage causes angina or myocardial infarction (MI).

• Heart failure: Decreased CO leads to edema and fatigue.

• Arrhythmias: Abnormal rhythms (e.g., atrial fibrillation, heart block).

• Murmurs: Indicate valvular problems (e.g., mitral regurgitation, aortic stenosis).

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

Blood Vessels and Circulation

Vessel Structure (Three Tunics)

• Tunica intima: Endothelium; smooth, reduces turbulence.

• Tunica media: Smooth muscle and elastic fibers; regulates diameter.

• Tunica externa (adventitia): Connective tissue; anchors vessel.

Arteries vs. Veins

Feature	Artery	Vein
Wall thickness	Thick	Thin
Lumen	Small, round	Large, irregular
Pressure	High	Low
Valves	No	Yes (especially limbs)
Blood volume	~10–15%	~60–70% (reservoir)

Capillaries and Exchange

• Types: Continuous (most common), fenestrated (pores), sinusoid (gaps).

• Exchange Forces:

  • Hydrostatic pressure (pushes fluid out)

  • Osmotic pressure (pulls fluid in)

  • Arterial end: net filtration (fluid out)

  • Venous end: net reabsorption (fluid in)

  • Excess fluid (~3.6 L/day) is returned via the lymphatic system

• Edema: Accumulation of interstitial fluid due to high hydrostatic or low osmotic pressure.

Hemodynamics – Blood Flow and Resistance

• Blood flow velocity: Fastest in aorta, slowest in capillaries, increases in veins.

• Peripheral resistance (PR): Main factor is vessel diameter ($PR \propto \frac{1}{r^4}$); also affected by length, viscosity, obstructions.

• Blood pressure: $BP = CO \times PR$

• Baroreceptors: Detect pressure (carotid sinus, aortic arch).

• Chemoreceptors: Detect O2, CO2, pH (carotid and aortic bodies).

Major Blood Vessels – Arterial System

• Aorta:

  • Ascending aorta → coronary arteries

  • Aortic arch → brachiocephalic trunk (right common carotid & right subclavian), left common carotid, left subclavian

  • Descending aorta → thoracic → abdominal → common iliac

• Arterial Branches:

  • Common carotid → internal (brain) & external (face) carotid

  • Subclavian → axillary → brachial → radial/ulnar → palmar arches

  • Abdominal aorta → celiac trunk (liver, stomach, spleen), superior mesenteric (small intestine), renal, inferior mesenteric (large intestine), common iliac → external iliac (leg) & internal iliac (pelvis)

  • Femoral → popliteal → anterior/posterior tibial → dorsalis pedis

Venous System and Hepatic Portal

• Major Veins: Superior vena cava (upper body), inferior vena cava (lower body), coronary sinus (heart); veins often parallel arteries.

• Hepatic Portal System: Blood from digestive tract (nutrient- and toxin-rich) flows to liver via hepatic portal vein for processing, then to hepatic veins and IVC. First-pass metabolism occurs here for oral drugs.

Special Circulations and Clinical Correlations

• Coronary circulation: Left and right coronary arteries supply heart; fill during diastole; drained by coronary sinus.

• Cerebral circulation: Circle of Willis provides redundancy to protect brain.

• Pulmonary circulation: Right heart → lungs → left heart.

• Hypertension: Chronic high BP increases risk for heart disease and stroke.

• Atherosclerosis: Plaque buildup in arteries reduces flow, causing ischemia.

• Varicose veins: Valve failure leads to blood pooling and tortuous veins.

Pulse and Blood Pressure Measurement

• Pulse: Wave of arterial expansion from left ventricular systole; measured at pulse points (radial, carotid, brachial, femoral, popliteal, dorsalis pedis, posterior tibial).

• Blood pressure: Systolic/diastolic (normal ~120/80 mmHg).

• Korotkoff sounds: Heard during BP measurement; first sound = systolic, disappearance = diastolic.

• Mean Arterial Pressure (MAP): $MAP = Diastolic + \frac{Pulse\ Pressure}{3}$

Lymphatic System and Immunity

Lymphatic System: Functions

• Fluid balance: Returns excess interstitial fluid (~3.6 L/day) to blood, preventing edema.

• Fat absorption: Lacteals in small intestine absorb dietary lipids (chyle).

• Immunity: Filters pathogens; houses lymphocytes (B cells, T cells).

Lymphatic Organs and Structures

• Lymphatic capillaries: Blind-ended, highly permeable.

• Lymphatic vessels: Contain valves; converge into trunks.

• Lymph nodes: Bean-shaped, filter lymph; cortex (germinal centers), medulla, hilus; found in cervical, axillary, inguinal, thoracic, abdominal regions.

• Thoracic duct: Largest; drains lower body, left arm, left head/neck; empties into left subclavian vein.

• Right lymphatic duct: Drains right upper quadrant; empties into right subclavian vein.

• Spleen: Filters blood (not lymph); white pulp (lymphocytes), red pulp (RBCs); stores platelets; removes old RBCs.

• Thymus: T-lymphocyte maturation; atrophies with age; in mediastinum.

• Tonsils: Pharyngeal, palatine, lingual; trap pathogens at entrances.

• Peyer's patches: Lymphoid tissue in ileum of small intestine.

• Lymph flow: Interstitial fluid → lymphatic capillaries → vessels → nodes → trunks → ducts → subclavian veins.

Immunity: Innate and Adaptive

Innate Immunity (Nonspecific, Immediate)

• External barriers: Skin, mucous membranes, secretions (lysozyme, acid).

• Internal defenses:

  • Phagocytes: neutrophils, macrophages, dendritic cells

  • Natural killer (NK) cells: destroy virus-infected and tumor cells

  • Antimicrobial proteins: interferons (antiviral), complement (lyse bacteria)

  • Inflammation: redness, heat, swelling, pain; promotes healing

  • Fever: inhibits microbial growth, enhances immune response

Adaptive Immunity (Specific, Memory)

• Antigens: Molecules that trigger an immune response.

• Antigen-presenting cells (APCs): Dendritic cells, macrophages, B cells.

• Lymphocytes:

  • B cells: Humoral immunity; differentiate into plasma cells (produce antibodies).

  • T cells: Cell-mediated immunity.

• Humoral Immunity (B cells):

  • Antibodies (immunoglobulins): IgG (most abundant), IgA (secretions), IgM (first response), IgE (allergy), IgD (B cell receptor).

  • Primary vs. secondary response: Secondary is faster and stronger due to memory cells.

• Cell-mediated Immunity (T cells):

  • Helper T cells (CD4+): Activate B cells, cytotoxic T cells, and macrophages.

  • Cytotoxic T cells (CD8+): Kill infected cells.

  • Regulatory T cells: Suppress immune response.

  • Memory T cells: Provide long-term protection.

Clinical Connections – Lymphatic & Immunity

• Lymphedema: Swelling due to lymphatic blockage (e.g., after mastectomy).

• Lymphadenopathy: Swollen lymph nodes (infection, cancer).

• Splenomegaly: Enlarged spleen (mononucleosis, trauma).

• Autoimmune diseases: Immune system attacks self (e.g., rheumatoid arthritis, lupus, type 1 diabetes).

• Immunodeficiency: HIV/AIDS destroys helper T cells.

• Allergies: Overreaction to harmless antigens (IgE, histamine release).

• Vaccination: Induces memory cells for faster secondary response.

• Monoclonal antibodies: Used in cancer treatment (target specific antigens).

Key Pathways and Values

Blood Flow Through the Heart

Body (deoxygenated) → SVC/IVC → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary trunk → pulmonary arteries → lungs (gas exchange) → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → body

Lymph Flow Pathway

Interstitial fluid → lymphatic capillaries → vessels → lymph nodes → lymphatic trunks → thoracic duct (or right lymphatic duct) → subclavian veins → blood circulation

Normal Values to Memorize

• Heart rate: 60–100 bpm

• Blood pressure: 120/80 mmHg

• Cardiac output: 5–6 L/min

• Hematocrit: ~45% men, ~42% women

• WBC differential: Neutrophils 50–70%, Lymphocytes 20–40%

• RBC lifespan: 120 days

• Platelet lifespan: 5–9 days

• Ejection fraction: 55–70%

Sample Calculations and Equations

• Cardiac Output: $CO = HR \times SV$

• Stroke Volume: $SV = EDV - ESV$

• Ejection Fraction: $EF = \frac{SV}{EDV}$

• Peripheral Resistance: $PR \propto \frac{1}{r^4}$

• Blood Pressure: $BP = CO \times PR$

• Mean Arterial Pressure: $MAP = Diastolic + \frac{Pulse\ Pressure}{3}$

Quick Reference Table: Leukocytes

Type	Function	% of WBCs
Neutrophil	Phagocytize bacteria	50-70%
Lymphocyte	Immune response (B cells, T cells)	20-40%
Monocyte	Become macrophages	2-8%
Eosinophil	Kill parasites; allergy response	1-4%
Basophil	Release histamine (inflammation)	<1%

Additional info:

• For exam preparation, focus on tracing blood and lymph flow, understanding the differences between innate and adaptive immunity, and memorizing normal physiological values.

• Clinical correlations help connect physiological concepts to real-world health scenarios.