Chapter 23 Lymphoid system A parasite called filarial worm can lodge itself inside lymph vessel, blocking flow of fluid. Excessive edema may ensue, called elephantiasis.

I. Functions: 1. Fluid balance 3. Lipid absorption 2. Produce & mature lymphocytes 3. Lipid absorption 4. Alternate route for transport

II. Parts of lymphatic system A. Lymph capillaries Located near blood capillaries in loose CT. - Simple squamous cells, Edges of adjacent cells overlap: allows larger substances into capillaries - Blind end: one way route for lymph Different from vascular capillaries: 1) larger diameter 2) thinner walls 3) endothelium lacks continuous basal lamina 4) flat or irregular outline

Figure 23.1 Lymphoid System Tonsil Lymphatics of upper limb Cervical lymph nodes Right lymphatic duct Thymus Axillary lymph nodes Thoracic duct Thoracic (left lymphatic) duct Lymphatics of mammary gland Cisterna chyli Spleen Lumbar lymph nodes Mucosa-associated lymphoid tissue (MALT) Pelvic lymph nodes Inguinal lymph nodes Lymphatics of lower limb 4

Figure 23.2a Lymphatic Capillaries Smooth muscle Lymphatic capillary Arteriole Blood capillaries Endothelial cells Venule Loose connective tissue Interstitial fluid Lymph flow A three-dimensional view of the association of blood capillaries and lymphatic capillaries. Arrows show the direction of blood, interstitial fluid, and lymph movement. 5

Figure 23.2b Lymphatic Capillaries Lymphocyte Lymph flow Incomplete basal lamina To larger lymphatics Loose connective tissue Interstitial fluid Interstitial fluid Lymphatic capillary Blood capillary Sectional view through a cluster of lymphatic capillaries 6

Figure 23.3a Lymphatic Vessels and Valves Vein Artery Lymphatic vessel Lymphatic valve From lymphatic capillaries A diagrammatic view of loose connective tissue showing small blood vessels and a lymphatic vessel. Arrows indicate the direction of lymph flow. 7

B. Lymph vessels 1. Have the same 3 tunica layers of blood vessels, but much thinner. Lumens larger than arteries or veins Base of each valve, the vessels bulge, fluid collects & forces valve closed. “String of beads.” 2. movement through vessels: skeletal muscle contraction 3. Path of body fluid: blood capillaries  tissue fluid  lymphatic capillaries (lymph)  lymphatic vessels lymph nodes  lymphatic trunks  Rt & Lt Lymphatic ducts venous blood stream

blood capillaries  tissue fluid  lymphatic capillaries (lymph)  lymphatic vessels lymph nodes  lymphatic trunks  lymphatic duct venous blood stream.

C. Lymph nodes 1. cervical, axillary, popliteal, inguinal, thoracic, abdominal ~500 lymph nodes in the body! 1mm-3cm. Superficial nodes cervical, axillary & inguinal regions. Vs Deep nodes Capsule (dense CT). CT of all lymphatic organs is reticular CT. Difference btwn. node vs nodule: “ nodules” don’t have tough CT covering whereas “nodes” do. Lymph is usually free of pathogens by the time it leaves the last node & enters the veins.

2. Structures to identify of lymph node:. Hilum 2. Structures to identify of lymph node: Hilum Cortex (Inner cortex T cells, outer cortex B cells) Afferent vessel (many) Medulla with medullary sinuses (openings) Efferent vessel (one) Lymph sinus Capsule & subcapsular space reticular CT, macrophages Germinating centers (B, T, macrophage, Dendritic cells) Trabeculae

Figure 23.9 Structure of a Lymph Node (Part 1 of 2) Lymph vessel Lymph nodes Efferent vessel Lymph node artery and vein Hilum Lymph nodes Medullary sinus Trabeculae Medulla Outer cortex (B cells) Cortex Deep cortex (T cells) Capsule Medullary cord (B cells and plasmocytes) Afferent vessel 12

Figure 23.4 Lymphatic Ducts and Lymphatic Drainage Left internal jugular vein Right internal jugular vein Left jugular trunk Right jugular trunk Brachiocephalic veins Thoracic duct Right lymphatic duct Left subclavian trunk Right subclavian trunk Left bronchomediastinal trunk Right subclavian vein Left subclavian vein Right bronchomediastinal trunk Superior vena cava (cut) First rib (cut) Highest intercostal vein Rib (cut) Thoracic duct Azygos vein Drainage of right lymphatic duct Thoracic lymph nodes Drainage of thoracic duct Hemiazygos vein Parietal pleura (cut) Diaphragm Inferior vena cava (cut) Intestinal trunk Right lumbar trunk Left lumbar trunk The thoracic duct collects lymph from tissues inferior to the diaphragm and from the left side of the upper body. The right lymphatic duct drains the right half of the body superior to the diaphragm. The collecting system of lymph vessels, lymph nodes, and major lymphatic collecting ducts and their relationship to the brachiocephalic veins 13

Figure 23.10 Lymphatic Drainage of the Head and Neck Orbicularis oculi muscle Periauricular lymph node Infraorbital lymph node Retroauricular lymph node Parotid salivary gland Buccal lymph node Occipital lymph node Mandibular lymph node Parotid lymph node Submental lymph node Superficial cervical lymph node Submandicular lymph node Deep cervical lymph node Sternocleidomastoid muscle 14

Figure 23.11 Lymphatic Drainage of the Upper Limb Deltoid muscle Deltopectoral lymph node Pectoralis major muscle Axillary lymph nodes Pectoralis major muscle (cut) Axillary vein Cephalic vein Subclavian lymph node Axillary lymph nodes Basilic vein Supratrochlear lymph node Central lymph node Subscapular lymph node Parasternal lymph node Pectoral lymph node Mammary gland Superficial lymphatic vessels and nodes that drain the upper limb and chest of a male Superficial and deeper lymphatic vessels and nodes of the upper limb and chest of a female 15

Figure 23.12 Lymphatic Drainage of the Lower Limb Superficial inguinal lymph nodes Deep inguinal lymph nodes Great saphenous vein Popliteal lymph nodes 16

Figure 23.14a Lymphatic Drainage of the Inguinal Region Inguinal ligament Femoral artery Deep inguinal lymph nodes Great saphenous vein An anterior view of a dissection of the inguinal lymph nodes and vessels 17

Figure 23.9 Structure of a Lymph Node (Part 2 of 2) Subcapsular space Germinal center Outer cortex Capsule Dividing B cell Capillary Dendritic cells Nuclei of B cells 18

Lymphocytes are produced and stored in which of the following? a. spleen and thymus b. lymph nodes c. tonsils d. the lacteals of the small intestine Answer: a

D. Thymus 1. Posterior to the sternum, superior to the heart. 2 lobes & smaller lobules 2. Blood-thymus barrier: keeps antigens out, prevent premature stimulation T cell maturation (Only 5% of cells leave thymus & go into circulation!) 3. Different from other lymphatic tissue because: not reticular CT based- it is epithelial glandular tissue. At age 20: 80% functional tissue, at 40: 5% functional tissue. Still produces T cells, but fewer as we age.

Figure 23.16a Anatomy and Histological Organization of the Thymus Thyroid gland Trachea THYMUS Right lobe Left lobe Left lung Right lung Heart Diaphragm The location of the thymus on gross dissection; note the relationship to other organs in the chest 21

Figure 23.16b Anatomy and Histological Organization of the Thymus Right lobe Left lobe Septa Lobule Anatomical landmarks on the thymus 22

E. Spleen 1. Largest mass of lymphatic tissue in the body. It is situated in left superior abdomen. Thin capsule Can you live without a spleen? . Size varies among people. Functions: Removes blood-borne pathogens- blood enters the spleen (not lymph) Remove and destroy old or defective blood cells. Site of hematopoiesis in the fetus & stores platelets for life. 2. White pulp: thick sleeve of lymphatic tissue around the blood vessels - immune screening 3. Red pulp: surrounds white pulp. Has venous sinuses: wide areas where blood leaks  macrophages can engulf any defective or dead cells. Red pulp gives spleen’s ability to destroy old blood cells

Figure 23.17a Anatomy and Histological Organization of the Spleen Parietal peritoneum Visceral peritoneum Stomach Diaphragm Rib Gastrosplenic ligament Liver Pancreas Gastric area Aorta Diaphragmatic surface Spleen SPLEEN Hilum Renal area Kidneys The shape of the spleen roughly conforms to the shapes of adjacent organs. This transverse section through the trunk shows the typical position of the spleen within the abdominopelvic cavity (inferior view). 24

Figure 23.17b Anatomy and Histological Organization of the Spleen SUPERIOR Gastric area Hilum Splenic vein Renal area Splenic artery Splenic lymphatic vessel INFERIOR External appearance of the visceral surface of the intact spleen showing major anatomical landmarks. This view should be compared with that of part (a). 25

Spleen

Lymphoid Tissues Lymph nodules (no capsule) Tonsils MALT (mucosa associated lymphoid tissue)

F. Lymphatic nodules- 1. MALT eg. Peyer’s Patches in intestinal wall 2. Tonsils - -crypt (crevice) - Palatine (2), pharyngeal (adenoid) (1), tubal tonsils (2), lingual (2) at base of tongue

Figure 23.8c Histology of Lymphoid Tissues How many tonsils are in the pharynx? Pharyngeal epithelium Pharyngeal tonsil Germinal centers within nodules Palate Palatine tonsil Lingual tonsil Pharyngeal tonsil LM  50 The location of the tonsils and the histological organization of a single tonsil 30

Ileum & Peyer’s Patch

a. capsule; megakaryocytes b. germinal center; erythrocytes Typical lymphoid nodules often have a pale central zone, called a ____, which contains activated, dividing ____. a. capsule; megakaryocytes b. germinal center; erythrocytes c. medulla; lymphocytes d. germinal center; lymphocytes Answer: d

a. declines; natural killer b. increases; T cells c. declines; tumor The increased incidence of cancer in the elderly reflects the fact that lymphoid surveillance ______, and ______ cells are not eliminated as effectively. a. declines; natural killer b. increases; T cells c. declines; tumor d. increases; antigens Answer: c