Lymphatic & Immune System – Comprehensive Study Notes

Hilum & Gross Anatomy of a Lymph Node

• Hilum (“doorway”)
  • Indentation where all vessels enter/exit.
  • Easy landmark: “right by the blue tube” in most textbook diagrams.
• Vessel arrangement
  • \textbf{1 efferent} vessel exits the hilum.
  • \textbf{Many afferent} vessels pierce the convex capsule and converge toward the hilum.
  • Mnemonic offered in class: “One way out, many ways in.”
• Other internal structures (implied although not labelled in demo)
  • Cortex (B-cell–rich nodules)
  • Paracortex (T-cell zone)
  • Medulla (medullary cords & sinuses)
• Professor’s humor: “If you start asking me about the cisterna chyli we’re going to fight—save that for advanced anatomy.”

Lymphatic System ↔ Cardiovascular System Connection

• Ultimate job: return escaped plasma (now called lymph) to the bloodstream.
• Where it empties
  • Thoracic duct → left subclavian vein.
  • Right lymphatic duct → right subclavian vein.
• Equals a near-mirror of the venous tree: “For every vein you basically have a lymphatic capillary following it.”
• Orientation reminder: left/right always refers to patient left/right, not the observer’s.

Composition of Lymph

• Largely water.
• Dissolved solutes: electrolytes, phospholipids (mis-heard as “fossils” in transcript), plasma proteins.
• Possible cargo: pathogens, cancer cells, cell debris—“the stuff that’s not supposed to be there.”

Lymphatic Capillaries & Fluid Dynamics

• Microscopic, closed-ended, finger-like vessels woven through nearly every tissue that has blood capillaries.
• Anchored by collagen filaments; endothelial flaps act as one-way mini-valves.
• Driving forces at blood capillaries
  • Arterial side: P_{hydrostatic} pushes fluid out.
  • Venous side: \pi_{oncotic} (colloid osmotic pressure) pulls most fluid back.
  • The ≈10 % left behind becomes interstitial fluid → lymph.

Transport & Immune Surveillance Functions

• Fluid return—prevents edema.
• Cellular taxi service
  • Transports lymphocytes & APCs to nodes for immune activation.
  • “Keeps your cancers at bay” by ferrying errant tumor cells to immune hubs.
• Note on immunosuppression: lower immune vigilance → higher cancer incidence.

Venous/Lymph Flow Mechanics

• No pump; relies on:
  • Skeletal muscle contraction (“muscle pump”).
  • One-way valves.
  • Thoracoabdominal pressure changes during breathing.

Clinical Correlate—Metastasis & Surgical Oncology

• Malignant cells often hitchhike in lymph → first stop = regional lymph nodes.
• Breast cancer example:
  • Axillary nodes are commonly excised with the primary tumor.
  • Rationale: node acts like a “trap”; remove the whole trap before cells escape.
• Friend anecdote: “My friend’s getting her lymph nodes removed.”

Major Lymphatic Duct Drainage Map

• Thoracic duct (larger, left-side)
  • Drains entire body except right arm, right thorax, right side of head/neck.
• Right lymphatic duct (smaller)
  • Drains the “right upper quadrant” described above.

MALT – Mucosa-Associated Lymphoid Tissue

• Found in mucous membranes; mucus traps invaders → local immune cells destroy them.
• Example organs: tonsils, Peyer’s patches, appendix, bronchi.

Hematopoiesis Through the Life Span

• Adults
  • Red bone marrow limited to axial skeleton (vertebrae emphasized), proximal epiphyses of humerus/femur.
• Children
  • Nearly all bones remain hematopoietic.
• Fetus
  • Primary site = liver (review from Term 1).

Miscellaneous Instructor Tips & Exam Hints

• Jugular veins are neck structures; don’t mis-label abdominal items “jugular.”
• Upcoming schedule: only one 40-slide chapter this week; another single chapter over the next two weeks.
• Likely quiz question (pulled straight from poor class performance): recognize that P{hydrostatic} drives filtration, \pi{oncotic} drives re-absorption.
• Cute metaphor: student’s baby “needs a bubble”—illustrates mucosal barriers & immunity.