L18 Lymphatic System

Question 1

What are the lymphoid organs?

Answer 1

Lymphatic nodules, tonsils, spleen, and thymus

Question 2

Which of the following is the correct sequence?

a) capillary - duct - trunk - collecting vessel
b) collecting vessel - capillary - trunk - duct
c) capillary - collecting vessel - trunk - duct
d) duct - capillary - collecting vessel - trunk

Answer 2

c) capillary - collecting vessel - trunk - duct

Question 3

Lymph capillaries generally occur alongside blood capillaries. Where would this NOT be the case?

Answer 3

Bone, bone marrow, teeth, and the entire CNS

Question 4

Lymph capillaries and blood capillaries are very similar. In what 2 ways are the lymph capillaries structurally unique?

Answer 4

1) Permeability: endothelial cells loosely overlap, open easily, create mini-valves. If pressure inside capillary is lower than outside, the pores open. If pressure inside is greater than outside, the pores close to prevent leakage.
2) Filaments: Endothelial cells are anchored to surrounding structures by fine filaments.

Question 5

What is chyle?

Answer 5

Chyle is a kind of lymph found in lacteals. It is milky white rather than clear because it contains digested intestinal fats.

Question 6

What are lacteals?

Answer 6

Lacteals are highly specialized lymph capillaries in villi of intestinal mucosa.

They contain chyle.

Question 7

True or false, lymphatic collecting vessels have 3 tunics.

Answer 7

True.

They are structurally similar to veins, but they are thin-walled, they have more internal valves, and they are more anastomosing.

Question 8

Do lymphatic vessels have a blood supply?

Answer 8

Yes, larger lymphatic vessels receive blood supply from vasa vasorum. It is a shared supply with the cardiovascular vessels, not their own independent supply.

Question 9

Collecting vessels in the skin travel with __1__. Deep lymphatics travel with __2__.

Answer 9

1) superficial veins

2) deep arteries

Question 10

What are lymphatic trunks?

Answer 10

They drain large areas of the body,

e.g. lumbar, bronchomediastinal, subclavian, and jugular trunks. Single intestinal trunk.

Question 11

What are the two lymphatic ducts called?

Answer 11

1) Right lymphatic duct
(drains right upper arm, right side of head, thorax)

2) Thoracic duct
(drains rest of body, arises from cisterna chyli)

Question 12

Where do the lymphatic ducts meet the venous circulation?

Answer 12

Each duct empties lymph into the venous circulation at the junction of the internal jugular vein and subclavian vein.

Question 13

Where are macrophages found in lymphoid tissue?

Answer 13

Macrophages live on the reticular fibres.

Reticular fibres are like branches of trees. Macrophages sit like birds on the twigs of the branches.

Question 14

Lymphoid tissue can be “packaged” in different ways.

In most body organs (esp. in mucous membranes and lymphoid organs) it is __1__.

It can also be found as __2__ or nodules, which are solid, tightly packed, spherical bodies with centres. These centres are called __3__ and contain __4__. They can be found singly within the intestine, where they are known as __5__.

Answer 14

1) diffuse
2) follicles
3) germinal centres
4) B-cells
5) Peyer’s Patches

Question 15

What are germinal centres?

Answer 15

Centre of a lymphoid follicle/nodule. Germinal centres contain B cells.

Question 16

What are Peyer’s Patches?

Answer 16

Large isolated clusters of nodules similar to tonsil, located in wall of ileum (intestine)

Question 17

What are the 2 regions of a lymph node?

Answer 17

Outer cortex and inner medulla.

Question 18

Describe the cortex of a lymph node.

Answer 18

Outer region of the LN: contains densely-packed follicles, many with germinal centres. Dendritic cells wrap around follicles to separate from transit T-cell rich interspaces.
T cells circulate between blood, lymph and LNs for immune surveillance

Question 19

Describe the medulla of a lymph node.

Answer 19

Contains cords (inward extensions of the cortex) which contain Ls and plasma cells

Question 20

Describe the spleen.

Answer 20

Largest L. organ; soft, blood-rich organ, fist size Located on left abdomen under diaphragm.

Thin capsule with Trabeculae, contains lymphocytes & macrophages.

Served by large splenic artery & S. vein that enter hilus on concave side.

Question 21

What are the functions of the spleen?

Answer 21

1) L proliferation & immune surveillance/ response
2) Cleans blood eg. remove old RBC/platelets, bacteria, virus, foreign matter, debris, toxins etc.
3) Storage of RBC constituents and release of others to liver
4) Stores platelets
5) Site of RBC production in fetus

Question 22

Where do you find red pulp and white pulp?

Answer 22

In the spleen:

2 distinct areas:

1) Areas of L on reticular fibers: white pulp and form “cuffs” around central arteries.
2) Areas of red cells, venous sinus, splenic cords, and red pulp. Dispose of effete RBC and pathogens

Question 23

How do T lymphocytes become mature/immunocompetent?

Answer 23

The thymus secretes thymosin and thymopentin to mature the T cells.

Question 24

What is the structure of the thymus?

Answer 24

It’s like a cauliflower head, each floret is a thymic lobule - each one with it’s own cortex and inner medulla.

Question 25

True or false: the thymus cortex contains few lymphocytes but is packed full of macrophages.

Answer 25

False.

The cortex of the thymic lobules is full of rapidly-dividing, densely packed lymphocytes; there are relatively few macrophages.

Question 26

Where are Hassal’s corpuscles found and what are they responsible for?

Answer 26

Found in the thymic medulla. Responsible for the conversion of self-reactive T-lymphocytes into suppressive T-lymphocytes.

Hassal’s corpuscles are also known as thymic corpuscles.

Question 27

True or false: the thymic medulla contains fewer lymphocytes than the cortex, and contains bizarre-shaped structures?

Answer 27

True

Question 28

In what 2 ways does the thymus differ from other lymphoid organs?

Answer 28

1) Functions only in T cell maturation, does not fight antigens directly - blood-thymus barrier - prevents premature activation of immature lymphocytes
2) Stroma (framework) consists of star-shaped epithelial cells, not reticular cells, which aid lymphocytes by secreting stimulating hormones

Question 29

Tonsils

Answer 29

Simplest lymphoid organs - ring of tissue around entrance to throat (pharynx). Part encapsulated as swellings in mucosa

Gather/remove pathogens entering in inhaled air/food

Question 30

Where are the tonsils found?

Answer 30

1) Palatine:, largest tonsils and are located on either side of posterior end of oral cavity. Most often infected.
2) Lingual: Located at base of tongue
3) Pharyngeal: (adenoids) in posterior wall of nasopharynx.
4) Tubal: surround opening of auditory tubes into pharynx.

Question 31

How do tonsils function?

Answer 31

Contain nodules with germinal centers surrounded by diffusely scattered lymphocytes.

Exterior surface: Covered by squamous epithelium that invaginates deep into tonsil to form blind-ended crypts that trap bacteria & particles.

Bacteria killed in lymphoid tissue. Produces ‘memory’ immune cells.