1. 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.

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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

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

10. 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.

11. 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

12. 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

13. 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

14. 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

15. 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

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

17. 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

18. 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

19. 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

20. 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.

21. 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

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

23. 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

24. 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

25. 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

26. Spleen

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

29. 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

30. 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

31. Ileum & Peyer’s Patch

32. 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

33. 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