Structure of a Lymph Node

Lymph nodes vary in size and shape but are usually less than 2.5 centimeters long and are somewhat bean-shaped. Figure 16.9 illustrates a section of a typical lymph node.

The indented region of a bean-shaped node is called the hilum, and it is the portion through which the blood

Afferent lymphatic vessel

Subcapsule (macrophages, B cells)

Lymph flow

Trabecula

Germinal

Afferent lymphatic vessel

Subcapsule (macrophages, B cells)

Lymph flow

Trabecula

Germinal

Structure Lymph Node

Sinus Capsule

Hilum

Lymph flow

Figure 16.9

(a) A section of a lymph node. (b) Light micrograph of a lymph node (2.5x micrograph enlarged to 5x).

center (B cells)

Nodule Artery

Sinus Capsule

Hilum

Lymph flow

Efferent lymphatic vessel

Efferent Lymphatic Vessel

Capsule

Lymph node

Figure 16.9

(a) A section of a lymph node. (b) Light micrograph of a lymph node (2.5x micrograph enlarged to 5x).

Capsule

Lymph node vessels and nerves connect with the structure. The lymphatic vessels leading to a node (afferent vessels) enter separately at various points on its convex surface, but the lymphatic vessels leaving the node (efferent vessels) exit from the hilum.

A capsule of connective tissue with numerous fibers encloses each lymph node. The capsule extends into the node and partially subdivides it into compartments called lymph nodules, with lighter staining germinal centers, that contain dense masses of actively dividing lymphocytes and macrophages. These nodules are the structural units of the lymph node.

Nodules also occur singly or in groups associated with the mucous membranes of the respiratory and digestive tracts. The tonsils, described in chapter 17 (pp. 691-692), are composed of partially encapsulated lymph nodules. Also, aggregations of nodules called Peyer's patches are scattered throughout the mucosal lining of the distal portion of the small intestine.

The spaces within the node, called lymph sinuses, provide a complex network of chambers and channels through which lymph circulates as it passes through. Lymph enters a lymph node through afferent lymphatic vessels, moves slowly through the lymph sinuses, and leaves through efferent lymphatic vessels (fig. 16.10).

Superficial lymphatic vessels inflamed by bacterial infection appear as red streaks beneath the skin, a condition called lymphangitis. Inflammation of the lymph nodes, called lymphadenitis, often follows. Affected nodes enlarge and may be quite painful.

Lymph Node Structure

Lymphatic vessels

Lymph node Blood vessels

Muscle

Figure 16.10

Lymph enters and leaves a lymph node through lymphatic vessels.

Lymphatic vessels

Lymph node Blood vessels

Muscle

Figure 16.10

Lymph enters and leaves a lymph node through lymphatic vessels.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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