22.3 The Cells and the Lymphatic Organs

Three short movements: the case, the anatomyThe study of the structure of the human body. and physiologyThe study of how the body functions., then the tie back to Stina. Each links to the scene where you’ll see it move.

I · A swelling that comes with the fever

Every flare, the nodes in her neckNarrow region just below the head; common fracture site. and groin rise to a centimetre or two, tender, and sink back inside a week. At fifteen a surgeon took out her appendix on a textbook picture — fever, right-lower-quadrant pain, a white count up — and the pathology report called the organ unremarkable. Nobody remarked on it. At forty the immunologist’s workup found her lymphocyte subsets normal and her immunoglobulins normal apart from a single sharp spike. Her spleen is a little large and does its job. “Reactive nodes,” the chart says, “nothing to biopsy” — which is correct, and which this chapter will earn.

See it move: Scene 1 · Three Litres a Day · Scene 2 · The Lymph Node on Slide 142

II · From the vessels to the organs

Twenty litres of plasmaThe liquid component of blood. leave the capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. each day; seventeen come back by the veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge and three return through the lymphatics — blind-ended capillaries whose overlapping endothelial flaps, held open by anchoring filaments, admit fluid, protein and whatever else is loose in the tissue and let none of it back. In the small intestine those capillaries are lacteals, and the fat they absorb turns the lymph to chyle. The vessels run up like veins — three tunics, semilunar valves so close together the vessel looks beaded, driven by muscle, breathing and the pulse of the arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr they follow — through trunks into the cisterna chyli below the diaphragm, then the thoracic duct to the left subclavian vein, with the right lymphatic duct draining the right headRounded proximal end that fits into the acetabulum of the hip bone., thorax and arm into the right. Block the vessels and protein-rich fluid pools: lymphedema. Along the way the lymph passes through five or six hundred nodes, bean-shaped filters with many afferent vessels in and one efferent out, so the flow slows and everything in it is inspected. Lymphoid tissue is reticular connective tissue packed with lymphocytes; gathered without a capsule under a mucosaThe innermost lining of the digestive tract that contains mucus-secreting cells for protection and a — tonsils, Peyer’s patches, the appendix, bronchial and nasalTwo small rectangular bones forming the bridge of the nose. patches — it is MALT, the border posts at every mucous membrane. The capsuled organs the lecture builds in order: red marrowBone marrow that produces blood cells. and thymus, the primary organs where B and T cellsThe basic structural and functional units of life. are made and schooled; nodes, spleen and tonsils, the secondary organs where they meet antigen and work.

See it move: Scene 1 · Three Litres a Day · Scene 2 · The Lymph Node on Slide 142 · Scene 3 · The Filter of the Blood · Scene 4 · Where Lymphocytes Are Schooled · Scene 5 · MALT, the Tonsil, and the Appendix That Was Unremarkable

III · Reading the organs on a slide

On slide 142 a lymph node has a capsule sending trabeculae inward, a subcapsular sinus just beneath it where the afferent lymph first spreads, a cortex of round folliclesStructures in the ovaries that contain developing oocytes. — primary follicles are dense and uniform; a secondary follicle has a pale germinal centre where B cells are dividing, which is what “reactive” looks like — a paracortex of T cells threaded with high endothelial venulesSmall veins that collect blood from capillaries and transport it to larger veins. where lymphocytes enter from the blood, and a medulla of cords (B cells, plasma cellsImmune cells that develop from B cells and produce antibodies., macrophages) and sinusesAir-filled spaces in the skull that lighten it and help humidify air. that drain to the hilum. On slide 301 the spleen filters blood instead of lymph: white pulp wrapped around a central arteriole (T cells in the sheath, B-cell follicles beside it), red pulp of sinusoids and Billroth’s cords where old red cells are read and recycled, a marginal zone between them where particulate antigen is caught, three hundred litres a day. On slide 140 the thymus is lobules of dark cortex and pale medulla, epithelial reticular cells that teach, Hassall’s corpuscles in the medulla, and a student body of which ninety-eight percent die — positive selection for reading self-MHC, negative selection against binding self too well — before it involutes from puberty, three percent a year, into fat. On slide 050 red marrow is cords of blood-forming cells between sinusoids, megakaryocytes giving the scale, where B cells run their own school — pro-B, pre-B, immature B — and central tolerance removes the ones that bind self. On slide 138 a palatineL-shaped bones forming posterior part of hard palate and floor of nasal cavity. tonsil shows stratified squamous epithelium diving into crypts over follicles, one post in Waldeyer’s ring. A reactive node is one that has done this work: germinal centres up, paracortex thick, architecture intact, and in a week quiet again. A node that is the disease loses its architecture and does not quiet.

See it move: Scene 2 · The Lymph Node on Slide 142 · Scene 3 · The Filter of the Blood · Scene 4 · Where Lymphocytes Are Schooled · Scene 5 · MALT, the Tonsil, and the Appendix That Was Unremarkable

5 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.

Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: Reactive lymphoid organs doing their job, Neither on its own, or Lymphoid organs that are the disease. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.

Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.