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General Anatomy: Lymphatic System & Cardiovascular System

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PART I — LYMPHATIC SYSTEM

1. Overview & Function

• Fluid return: Collects interstitial fluid (lost from vascular capillary beds during nutrient exchange) and returns it to the venous circulation
• Immune surveillance: Transports pathogens, lymphocytes, macrophages, cell products (hormones), and cell debris
• Fat absorption: In the small intestine, special lymphatic capillaries called lacteals absorb dietary fats packaged as chylomicrons; this fluid (called chyle, which is opaque and milky) is transported to the venous system in the neck
• Protein rescue: Returns plasma proteins from the interstitial space to the bloodstream — without this function, life could not be sustained beyond ~24 hours (Guyton)

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2. Lymphatic Vessels

• Contraction of skeletal muscles (indirect compression)
• Arterial pulsations from adjacent arteries
• Valves maintain unidirectional flow toward the venous system

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3. Major Lymphatic Trunks & Drainage Areas

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4. Cisterna Chyli & Thoracic Duct

• The right and left lumbar trunks (from lateral aortic/para-aortic nodes) and the intestinal trunk (from pre-aortic nodes around the celiac, superior mesenteric, and inferior mesenteric arteries) converge on the posterior right side of the abdominal aorta.
• Their confluence sometimes forms a saccular dilation called the cisterna chyli.
• The thoracic duct arises from the cisterna chyli, ascends through the posterior mediastinum, and empties into the left venous angle.

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5. Lymph Nodes

• Small (0.1–2.5 cm), encapsulated structures that interrupt lymphatic channels
• Contain lymphocytes and macrophages organized into nodules
• Act as elaborate filters — trap and phagocytose particulate matter; detect and respond to foreign antigens
• Because flow through nodes is slow, metastatic tumor cells frequently lodge and grow here → used clinically to track disease spread
• Nodes that drain infected or diseased areas become enlarged, hard, or tender — clinically detectable

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6. Lymphatics of the CNS (Glymphatic System)

• Cerebrospinal fluid flowing into perivascular spaces around cerebral blood vessels (formed by astrocytic glia)
• CSF enters the brain parenchyma along periarterial spaces, exchanges with interstitial fluid, and exits via perivenous routes
• Waste products and macromolecules (including potentially amyloid-β) are cleared into meningeal lymphatics → ultimately enter the blood

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7. Areas Without Lymphatics

• Bone marrow
• Avascular tissues (epithelia, cartilage)
• Superficial skin epidermis
• Endomysium of muscle
• Bones

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PART II — CARDIOVASCULAR SYSTEM (CVS)

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1. Overview

• The heart — a muscular pump
• Blood vessels — a closed network of arteries, veins, and capillaries

• Pulmonary circulation: Right heart → pulmonary arteries → lungs → pulmonary veins → left heart (gas exchange)
• Systemic circulation: Left heart → aorta → body tissues → venae cavae → right heart (nutrient/waste exchange)

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2. Blood Vessel Wall Structure

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3. Classification of Arteries

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4. Classification of Veins

• Thinner tunica media (lower pressure)
• Larger luminal diameter
• Often paired as venae comitantes alongside arteries in peripheral regions
• Contain valves (especially in limb veins inferior to the heart) — paired cusps to prevent backflow and assist venous return

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5. Capillaries

• Smallest vessels — 1 cell thick (endothelium only)
• Site of gas exchange, nutrient delivery, and waste removal between blood and tissues
• Connect arterioles (arterial side) to venules (venous side)

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6. The Heart

• Located in the middle mediastinum, within the pericardial sac
• Oriented obliquely: base faces superiorly/posteriorly; apex points inferiorly/anteriorly toward the left (5th intercostal space, midclavicular line)

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7. Key Vessels of Systemic Circulation

• Aorta → Aortic arch (brachiocephalic trunk, left common carotid, left subclavian) → Thoracic aorta → Abdominal aorta → Common iliac arteries

• Superior vena cava (SVC): drains head, neck, upper limbs, thorax
• Inferior vena cava (IVC): drains abdomen, pelvis, lower limbs
• Coronary sinus: drains the heart wall itself → right atrium

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8. Coronary Circulation

• Right coronary artery (RCA): Supplies right ventricle, SA node (in ~60% of people), AV node (in ~80%), and the inferior/posterior left ventricle in right-dominant systems
• Left coronary artery (LCA): Divides into:
  • Left anterior descending (LAD): Supplies anterior left ventricle and interventricular septum
  • Circumflex (LCx): Supplies lateral and posterior left ventricle
• Venous drainage: mostly via coronary sinus into the right atrium; anterior cardiac veins drain directly

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9. Clinical Correlations

• Chronic inflammatory reaction in arterial walls with cholesterol/fatty protein deposition → secondary calcification → reduced lumen diameter
• Plaque may cause distal embolism or fissure to form acute thrombus
• Clinical impact depends on which vessel is affected (coronary → MI; carotid → stroke; peripheral → limb ischemia)

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Relationship Between the Two Systems

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