Blood, Cardiovascular, Lymphatic & Integrated Systems: Anatomy & Physiology Study Guide

Blood Composition & Hemostasis

Blood: Structure and Properties

Blood is a specialized connective tissue, serving as the body's only fluid tissue. It plays a vital role in transport, regulation, and protection. The average adult has 5–6 liters of blood, accounting for about 8% of body weight. Blood is slightly alkaline, with a pH of 7.35–7.45, and a temperature of approximately 38°C (100.4°F).

• Plasma: The nonliving fluid matrix, making up 55% of blood volume. Composed of ~90% water, electrolytes, plasma proteins (albumin for osmotic balance, fibrinogen for clotting, globulins for antibodies), nutrients, and wastes.

• Buffy Coat: Less than 1% of blood volume. Contains leukocytes (white blood cells) for defense and platelets for clotting.

• Erythrocytes: 45% of blood volume (hematocrit). Red blood cells responsible for oxygen transport via hemoglobin.

Table: Components of Centrifuged Blood

Layer	Percentage	Components & Major Functions
Plasma	55%	Nonliving fluid matrix (~90% water), electrolytes, plasma proteins, nutrients, wastes
Buffy Coat	<1%	Leukocytes (defense), Platelets (clotting)
Erythrocytes	45%	Red blood cells (oxygen transport)

Formed Elements & Leukocyte Types

Formed elements are produced in the red bone marrow via hematopoiesis from a common hemocytoblast stem cell. Leukocytes are classified by their structure and function:

• Neutrophils (40–70%): Granulocytes with 3–7 lobed nucleus; active phagocytes during acute infections.

• Lymphocytes (20–45%): Agranulocytes with large dark nucleus; B cells produce antibodies, T cells direct attack.

• Monocytes (4–8%): Agranulocytes, largest WBC with kidney-shaped nucleus; become macrophages for chronic cleanup.

• Eosinophils (1–4%): Granulocytes with bilobed nucleus; attack parasitic worms and act in allergy response.

• Basophils (0–1%): Granulocytes releasing histamine (vasodilator) and heparin (anticoagulant) at inflammation sites.

Mnemonic: 'Never Let Monkeys Eat Bananas' (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils) for leukocyte abundance order.

Normal WBC count: 4,800–10,800 cells/mm³.

Hemostasis: Stopping Blood Loss

Hemostasis is the process that stops bleeding from damaged vessels, involving three sequential phases:

1. Vascular Spasms: Immediate vasoconstriction to reduce blood flow.

2. Platelet Plug Formation: Platelets adhere to exposed collagen at injury site.

3. Coagulation: Clotting cascade forms a fibrin mesh to seal the break.

Example: When a blood vessel is cut, hemostasis prevents excessive blood loss by rapidly forming a clot.

Cardiovascular System & Cardiac Cycle

Heart Structure and Circuits

The cardiovascular system is a closed network where the heart pumps blood through two main circuits: pulmonary and systemic. The heart is located in the thoracic cavity, with its apex pointing toward the left hip and its base toward the right shoulder.

Table: Dual Circuit Architecture

Circuit	Pump Side	Blood Flow Pathway	Function
Pulmonary Circuit	Right Heart	Right Ventricle → Pulmonary Trunk & Arteries → Lung Capillaries → Pulmonary Veins → Left Atrium	Delivers oxygen-poor blood to lungs for gas exchange
Systemic Circuit	Left Heart	Left Ventricle → Aorta → Systemic Arteries → Body Capillaries → Vena Cavae → Right Atrium	Pumps oxygen-rich blood to all body tissues

Additional info: The left ventricular wall is thicker to generate higher pressure for systemic circulation.

The Cardiac Cycle

A complete heartbeat (cardiac cycle) lasts about 0.8 seconds at a resting rate of 75 bpm, involving coordinated contraction (systole) and relaxation (diastole).

1. Atrial Diastole (Ventricular Filling): Heart is relaxed, AV valves open, blood fills ventricles passively.

2. Atrial Systole: Atria contract, pushing remaining blood into ventricles.

3. Isovolumetric Contraction: Ventricles contract; AV valves close, producing the first heart sound ('Lub').

4. Ventricular Systole (Ejection Phase): Semilunar valves open, blood is ejected into aorta and pulmonary trunk.

5. Isovolumetric Relaxation: Ventricles relax; semilunar valves close, producing the second heart sound ('Dup').

Heart Sounds: 'Lub' = closing of AV valves at start of ventricular systole; 'Dup' = closing of semilunar valves at end of ventricular systole.

Lymphatic System & Body Defenses

Lymphatic Vessels & Drainage

The lymphatic system returns fluid lost from blood capillaries back to the cardiovascular system and houses defense cells for immunity. Lymph flows toward the heart, propelled by skeletal muscle contraction, thoracic pressure changes during breathing, and smooth muscle in vessel walls.

Table: Lymph Ducts and Drainage

Duct Name	Drainage Territory	Venous Entry Point
Right Lymphatic Duct	Right arm, right side of head, right thorax	Right subclavian vein
Thoracic Duct	Rest of body (left side & lower limbs)	Left subclavian vein (arises from Cisterna Chyli)

Lymph Nodes & Lymphoid Organs

Lymph nodes filter bacteria, viruses, cancer cells, and cell debris before returning lymph to the blood. Nodes are kidney-shaped, with an outer cortex containing lymphocyte-rich follicles and an inner medulla with phagocytic macrophages. Lymph enters via multiple afferent vessels and exits via fewer efferent vessels at the hilum, slowing flow for thorough filtration.

• Spleen: Filters blood, destroys worn-out RBCs, stores platelets.

• Thymus: Produces thymosin to program T lymphocytes; most active in youth.

• Tonsils: Trap and remove pathogens entering pharynx in food or air.

• Peyer's Patches & Appendix: Capture and destroy bacteria in digestive tract (MALT).

Integrated Core Systems Quick Reference

Overview of Key Systems

This section summarizes the main mechanisms and functions of several core systems in human anatomy and physiology.

Table: Integrated Core Systems

System	Key Anatomy / Physiology Mechanisms	Primary Function / Concept
Nervous System	Resting potential (-70mV), Depolarization (Na+ influx), Repolarization (K+ efflux). CNS vs PNS.	Rapid electrical communication & signal processing
Respiratory System	Boyle's Law ($P_1V_1 = P_2V_2$) governs pulmonary ventilation. O2 transported on Hemoglobin; CO2 as Bicarbonate.	Gas exchange (O2 uptake & CO2 elimination)
Musculoskeletal System	Sliding Filament Theory: Ca2+ binds troponin, myosin heads bind actin cross-bridges. Osteoblasts build bone, Osteoclasts resorb.	Locomotion, structural framework & mineral homeostasis

Example: The nervous system uses rapid electrical signals to coordinate muscle contraction, while the respiratory system exchanges gases essential for cellular metabolism.

Additional info: Boyle's Law ($P_1V_1 = P_2V_2$) explains how changes in thoracic volume affect air pressure and movement during breathing.