Anatomy and Physiology - Lymphatic System

Overview

The lymphatic system returns interstitial fluid to blood, absorbs lipids (lacteals), and provides immune surveillance. Master drainage pathways and organ functions.

Vessels and flow

• Blind‑ended capillaries with flap‑like minivalves; flow aided by skeletal muscle, valves, and pressure gradients; obstruction causes lymphedema.

Organs

• Primary: bone marrow (B‑cell development), thymus (T‑cell maturation; cortex/medulla; Hassall corpuscles).
• Secondary: lymph nodes (cortex follicles with B cells; paracortex T cells; medulla cords/sinuses), spleen (white pulp immune, red pulp filter/ RBC clearance), MALT (tonsils, Peyer patches, appendix).

Drainage (survey)

• Right lymphatic duct drains right upper quadrant; thoracic duct drains rest into left subclavian vein; cisterna chyli origin.

Immune interface

• Antigen capture in tissues → afferent lymphatics → node; dendritic cells present antigen to naïve T cells; germinal centers support B‑cell maturation.

Worked micro‑examples

1. Node architecture

• Enlarged, tender nodes with prominent germinal centers suggest active B‑cell response; painless, firm nodes may suggest alternative pathology (scope awareness only).

2. Post‑mastectomy lymphedema

• Disrupted axillary drainage → arm swelling; compression and lymphatic therapy as management concepts.

Pitfalls

• Confusing drainage territories of thoracic vs right lymphatic ducts.
• Ignoring spleen dual roles (immune vs filtration) and vulnerability to encapsulated organisms after splenectomy (vaccination considerations).

Practice prompts

• Map drainage from small intestine lacteals to venous angle.
• Label node microanatomy and cell populations.
• Explain thymic selection outcomes (positive/negative) conceptually.

References

• SciOly Wiki – Anatomy & Physiology (Lymphatic)
• OpenStax Anatomy & Physiology (Lymphatic and immune systems)