lymphatic system

Question 1

1. What are the functions of the lymphatic system?

Answer 1

Maintain fluid balance - collects excess interstitial fluid and returns it to the systemic circulation (helps maintain blood volume too)

Defense against disease - lymph contains pathogens and is filtered in the lymph nodes

Transportation - lacteals (specialized lymphatic capillaries) collect absorbed dietary fats in intestines which are returned into the blood

Question 2

2. Describe the relationship between lymph fluid, interstitial fluid, and plasma.
   Distinguish between the composition of the three fluids.

Answer 2

Lymph Fluid- interstitial fluid once it enters the blood

Interstitial Fluid - fluid that surrounds tissue

Plasma - non-living component of blood

All composed of the same thing - plasma proteins and water

Question 3

3. Describe the structure of lymphatic capillaries. Compare and contrast the structure of
   lymphatic and blood capillaries.

Answer 3

Lymphatic capillaries are highly permeable; they consist of epithelial cells that are staggered on top of one another to create flaplike minivalves. Collagen fibers anchor the cells to surrounding structures.

Lymphatic capillaries are more permeable than blood capillaries. The lymphatic capillaries are also able to take in the larger particles that the blood capillaries are not able to. The lymphatic capillaries mainly transport pathogens, cell debris, and cancer cells, and blood capillaries mainly transport oxygen and nutrients; however, lymphatic capillaries also transport dietary nutrients (dietary fats via lacteals).

Question 4

4. Describe the process of lymph formation (i.e., how/why fluid enters the lymphatic
   capillaries) .

Answer 4

Blood constantly exchanges products with the interstitial fluid; at the capillary bed, fluid is pushed out of the blood (by hydrostatic and osmotic pressures) and into the interstitial fluid (at the arterial end) with most returning on the venous end. The remaining fluid becomes a part of the interstitial fluid. The fluid enters lymphatic vessels (becoming lymph) with the ultimate goal of re-entering the blood.

Question 5

5. How does the lymphatic system contribute to fluid balance in the body?

Answer 5

The interstitial fluid that is not returned back to the blood at the venous end of the capillary bed is eventually returned to the blood stream (through the lymphatic system). This helps maintain blood volume in the cardiovascular system.

Question 6

6. Describe the structure of the lymphatic vessels. To which vessels of the systemic
   circulation are they most similar?

Answer 6

Lymphatic vessels start at the lymphatic capillaries and get progressively bigger and thicker. They unite to form the five lymphatic trunks (4 are bilateral) which then drain into two ducts. These vessels are most similar to the venous system (lymph is moved via the same mechanisms that stimulate venous blood return [i.e. muscle pump, pulmonary pressure changes, and valves])

Question 7

7. How is lymph moved through the lymphatic vessels?

Answer 7

lymph is moved via the same mechanisms that stimulate venous blood return (i.e. muscle pump, pulmonary pressure changes, and valves)

Question 8

8. Name the two large, lymphatic ducts which conduct lymph into the venous circulation.
   Identify the regions of the body drained by each of these large ducts.

Answer 8

Right Lymphatic Duct - drains the right upper limb, right side of the head, the thorax

Thoracic Duct - drains the rest of the body

Question 9

9. Identify the ways unencapsulated lymphoid tissue is found in the body. List an example
   of each type.

Answer 9

Diffuse lymphoid tissue - (loose arrangement of lymphoid cells and some reticular fibers) found in every organ (example: larger collection found in the lamina propria of the mucous membrane of the the lining of the digestive tract)

Lymphoid follicles - (solid spherical bodies of packed lymphoid cells & reticular fibers) (example: Peyer’s patches and in the appendix and in the lymph nodes)

Question 10

10. Identify whether the following are primary or secondary lymphoid organs: bone
    marrow, lymph nodes, the thymus, the spleen.

Answer 10

Primary Lymphoid Organs - (where the lymphocytes mature) bone marrow; thymus

Secondary Lymphoid Organics - (where mature lymphocytes first encounter antigens) lymph nodes; spleen

Question 11

11. Where along the lymphatic pathway would the greatest number of lymph nodes be expected?

Answer 11

The greatest number of lymph nodes occur near the body surface where the lymphatic vessel converge to form trunks (in the inguinal, axillary, and cervical regions)

Question 12

12. Describe the structure of a lymph node. What cells of the immune system are located
    in each region of a lymph node?

Answer 12

Consists of a cortex and a medulla

Cortex

• Germinal centers heavy with dividing B cells found superficially
• T cells housed in the deep areas of the cortex
• Dendritic cells found throughout the cortex and help prepare both B and T cells to become effective defensive cells
• Macrophages found in the subcapsular sinus (on the crisscrossed reticular fibers within) to phagocytize foreign material

Medulla

• Contains both lymphocytes (B cells and T cells) on medullary cords (thin inward extensions from cortical lymphoid tissue
• Macrophages found in the medullary sinus

Question 13

13. Lymph flows slowly through lymph nodes, ensuring adequate time for filtering and
    cleansing by cells of the immune system. Describe the lymph pathway through a lymph
    node. What structural feature(s) help(s) insure that lymph flows slowly through lymph
    nodes?

Answer 13

Multiple afferent lymph vessels (convex side) → subcapsular sinus → medullary sinus → fewer efferent lymphatic vessels (concave side at the hilum)

More afferent lymph vessels than efferent lymph vessels slows the movement of lymph through lymph nodes –> Allows for effective activation of lymphocytes

Question 14

14. What is the function of lymph nodes?

Answer 14

Cleanses the lymph through macrophages found in the lymph sinuses

Site of immune system activation (lymphocytes encounter antigens here)

Question 15

15. Identify the three main types of lymphoid cells and describe the general function of
    each.

Answer 15

Lymphocytes

• B cells - produce plasma cells (which produce antibodies)
• T cells - manage immune response (and target and kill foreign cells) - think helper T cells and cytotoxic t cells

Macrophages

• Phagocytize foreign material; help activate T cells
• They present the fragments - antigen presenting cells

Dendritic cells

• Capture antigens and bring them to lymph nodes (unless they’re already in the lymph nodes lol)
• Antigen presenting cells

Reticular cells
- Create the reticular fibers that are part of the lymphoid tissue - network that supports the other cell types in lymphoid organs and tissues

Question 16

16. What are the roles of the lymphocytes, dendritic cells, and macrophages present in
    lymph nodes?

Answer 16

Lymphocytes

• B cells - found in the lymphoid nodules; proliferate and produce plasma cells
• T cells - found throughout the blood, lymph nodes, and lymph to surveil for antigens (non-self entities)

Macrophages
- Found in the lymph sinuses; phagocytize foreign material

Dendritic cells
- Travels in the lymph to present antigens to lymphocytes

Question 17

17. Describe the structure and location of the spleen.

Answer 17

Structure

• Surrounded by a fibrous capsule and has trabeculae that extend inward
• Composed of white pulp and red pulp
• About the size of a fist; blood rich

Location
- Found on the left side of the abdominal cavity, curling around the anterior aspect of the stomach

Question 18

18. What is the difference between the red pulp and white pulp of the spleen?

Answer 18

Red Pulp

• site of destruction of old RBCs & bloodborne pathogens (by macrophages)
• Contains huge numbers of RBCs and macrophages

White Pulp

• Site of immune functions
• Composed of lymphocytes suspended on reticular fibers

Question 19

19. What body fluid is cleansed and processed by the spleen?

Answer 19

Blood

Question 20

20. What functions are served by the spleen?

Answer 20

• Recycles the breakdown products of RBCs for reuse (i.e. stores iron as ferritin and transferrin; releases remaining heme group portion to the liver to begin excretion process)
• Stores blood platelets and monocytes for release into blood
• Possible site of erythropoiesis in fetus

Question 21

21. Describe the structure and location of the thymus.

Answer 21

Structure

• Bilobed
• Contains thymic lobules with an outer cortex and an inner medulla
• Cortex - includes densely packed, rapidly dividing lymphocytes; a few monocytes
• Medulla - includes thymic corpuscles (believed to be involved in development of regulatory T cells - think autoimmune diseases, where your T cells aren’t regulated to not kill everything)

Location

• Found in inferior neck and extends into superior thorax
• Overlies the heart (above the heart, slightly overlaps with the top of the heart)

Question 22

22. Name the hormones secreted by the thymus gland. What is the role of these hormones?

Answer 22

Thymus Hormones - involved in the normal development of T cells and the immune response
Stimulate stem cell division too
- Thymulin
- Thymopoietin
- Thymosins

Question 23

23. What function(s) is/are served by the thymus?

Answer 23

Maturation of T lymphocytes precursors

Blood thymus barrier - prevents precursor cells from prematurely being activated by interacting with blood - blood thymus barrier separates thymus from blood

Question 24

24. Describe the structural and functional changes that occur in the thymus over one’s
    Lifespan.

Answer 24

The thymus grows in size during the first year → after puberty, the thymus gradually atrophies → by old age, thymus replaced almost completely by fibrous & fatty tissue

Thymus continues to produce mature T cells throughout life (at declining rates though)

When you’re a small child if you come in contact with more things you will develop more immunity

Question 25

25. What is the largest lymphoid organ?

Answer 25

Spleen