The Lymphatic System

Front 1

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

Back 1

Lymphatic - extend into almost all tissues of body (not CNS, splenic pulp, bone marrow, avascular tissues like teet, bones, cartilage, epidermis)
Differences: larger lumen, more permeable walls; cells in wall allow fluid in, but not out (the mini-valves formed by the overlapping endothelial cells)

Front 2

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

Back 2

- about 3 L/day (very slow)
- interstitial fluid exerts hydrostatic pressure against capillaries, separating flaps of lymphatic walls (the mini-valves)
- when hydrostatic pressure is greater inside, flaps are pressed closed

Front 3

How does the lymphatic system contribute to fluid ballance in the body?

Back 3

- returns any escaped plasma proteins from ICF to circulation
- if not removed, they would create osmotic press, which would cause edema in the tissue

Front 4

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

Back 4

- veins - b/c of the low pressure adaptations etc.
- thinner than veins with more internal valves; still 3 tunics
- usually run parallel to the blood vessels supplying the same area of the body
- lymphatic capillaries to collecting vessels to trunks to ducts

Front 5

How is lymph moved through the lymphatic vessels?

Back 5

- lymphatic capillaries to collecting vessels to trunks to ducts
- pumpless; low pressure conduits
- skeletal muscle pump
- respiratory pump
- internal valves to prevent backflow of lymph
- very slow - 3L/day

Front 6

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

Back 6

- Right lymphatic duct - drains right arm and right side of hear and r. thorax; empties into r. subclavian vein at jct with internal jugular vein
- Thoracic duct - drains the rest of the body; begins at superior end of cysterna chyli (a dilated sac at L1/L2), empties into L. subclavian vein @ jct with internal jugular vein

Front 7

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

Back 7

Diffuse lymphatic tissue (larger collections in lamina propria of mucous mem. and lymphoid organs)
Lymphoid nodules/follicles (have centers/germinal centers which make B cells):
- Tonsils - R+L palatine, R+L linguinal, pharyneal
- MALT - Peyer's patches in illium; in wall of GI tract

Front 8

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

Back 8

- primary (where lymphocytes develop and mature: bone marrow and thymus
- secondary (sites to which lymphocytes migrate when they are mature enough): lymph nodes and spleen

Front 9

What are the general functions of the lymphatic system?

Back 9

- Maintain fluid ballance - collects excess interstitial fluid and returns it to circulation
- Defend body against disease - produces and supports lymphcytes
- Transport dietary fats - specialized lymphatic capillaries (lacteals) in small intestine wall collect absorbed fats and carry them to systemic circulation

Front 10

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

Back 10

Plasma - has plasma proteins, circulates as part of the blood
Interstitial fluid - generally doesn't have p. proteins, the plasma that leaks out of the vessels
lymph fluid - called this as soon as the interstitial fluid enters the lymphatic vessels; probably no plasma proteins, but if some accidentally got into the IF, then they are transported back to the plasma via the lymph fluid

Front 11

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

Back 11

- areas where lymphatic vesels converge to form trunks
- ex. inguinal cervical and axilary regions

Front 12

Describe the structure of a lymph node.

Back 12

- enclosed in a capsule of dense CT
- trabeculae - collagen strands go inward from capsule and partition the node into compartments
- Cortex - outer part has densely packed follicles where B cells formed;with germinal centers that present antigens to B cells to activate them; inner part where T cells in transit are housed
- Medula - has mature B and plasma cells that have migrated from the cortex,k anchored to medullary cords

Front 13

What cells of the immune system are located in each region of a lymph node?

Back 13

Cortex:
- Outer - B cells made in folicles and perform their functions there; germinal centers (middle of follicle): follicular dendritic cells, macrophages, B cells
Deep cortex - T cells in transit, DC to activate them
Medulla - B cells and plasma cells`

Front 14

Describe the lymph pathway through a lymph node.

Back 14

- afferent lymphatic vessels on convex side
- through large sinuses (ex. suscapular sinus)
- smaller sinuses
- out of node through hillum via lymphatic vessels

Front 15

What structural feature(s) help insure that lymph flows slowly through lymph nodes?

Back 15

- valves, so one-directional flow
- fewer efferent vessels than afferent vessels = forced stagnation/slow

Front 16

What is the function of lymph nodes?

Back 16

- filter lymph (macrophages remove/destroy microorganisms + debris)
- site of immune system activation

Front 17

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

Back 17

lymphocytes - 25% of wbcs; T + B lymphocytes, NK cells
- Macrophages and dendritic cells - phagocytizing foreign substances, activate T lymphocytes
- Reticular cells - produce the stroma of lymphoid organs (stroma supports lymphoid cells) (b/cells anchored to their network)

Front 18

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

Back 18

Lymphocytes - B cells formed in follicles, activated in germinal centers, and work in the medulla; T cells are activated in the deep cortex during transport through the node
- Dendritic cells are found in the germinal centers of the outer cortex, and in the deep cortex - activates B and T cells
- Macrophages - clean up the mess and devour the remnants of dead cells; found in the germinal centers

Front 19

Describe the structure and location of the spleen.

Back 19

Location: L. abdominal cavity/hypochondriac region; just below diaphragm, posterior and lateral to stomach
- Structure - surrounded by thin fibrous capsule, partitioned by trabeculae; Two regions: white pulp regions of lymphocytes syspended on ret. fibers; red pulp regions of venous sinuses filled with blood and cords of tissue, with lots of Macrophages and rbcs

Front 20

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

Back 20

White pulp - immune functions; has lymphocytes suspended on reticular fibers around central arteries
Red pulp - disposes worn out rbcs and blood born pathogens; venous sinuses with blood and cords of splenic tissue (regions of ret. CT with large numbers of macrophages); high proportion of macrophages and rbcs in this area

Front 21

What body fluid is cleansed and processed by the spleen?

Back 21

- the blood

NOT lymph

Front 22

What functions are served by the spleen?

Back 22

- filters and cleanses blood
- removes wornout blood cells and platelets from circulation
- stores breakdown products of rbcs (iron for hemoglobin)
- stores platelets
- participates in blood cell formation during fetal development

Front 23

Describe the location and structure of the thymus.

Back 23

Location - bi-lobed organ in mediastinum; just deep to sternum
Structure - surrounded by CT capsule which divides it into 2 lobes; septa divides each lobe into 2 lobules;
lobule has outer cortex and central medulla
- outer cortex: densely packed lymphocytes arranged in clusters (surrounded by reticuloepithelial cells for blood-thymic barrier, so that T lymphocytes aren't prematurely activated)
Medulla - macrophages and DC which help T cells to mature

Front 24

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

Back 24

Thymopoietin and thymosin
- stimulate stem cell division and T cell development

Front 25

What functions are served by the thymus?

Back 25

- blood-thymic barrier - prevent lymphocyte exposure to antigens and premature activation
- hormones stimulate stem cell division and T cell development - develop them into immunocompetent cells/functional lymphocytes

Front 26

Describe the structural and functional changes that occur in the thymus over one's lifespan.

Back 26

- grows until puberty then undergoes involution (decreases in size and tissue becomes fibrous)
- reticuloepithelial cells of medulla (that form blood-thymic barrier) cluster into concentric rings (thymic/hassall's corpuscles) as degenerating cells and cell remnants
- more and more of these corpuscles as you age

Front 27

What is the largest lymphoid organ?

Back 27

- the spleen

Front 28

immunocompetant

Back 28

- means they are mature and functional

Front 29

hillus

Back 29

- on the concave side of the lymph node
- the efferent lymphatic vessels attatch here and carry lymph out of the node

Front 30

stroma

Back 30

- supporting network of reticular cells and fibers in the sinuses of the lymph nodes
- physically supports the macrophages, DCs and lymphocytes that are present in the sinus

Front 31

trabeculae

Back 31

partitions that divide the lymph node into a number of compartments
- the spaces b/w the trabeculae are called the sinuses

Front 32

capsule

Back 32

- found around lymph nodes and organs
- made of Dense CT
- collagen strands/trabeculae extend inward from the capsule and form partitions/divide the node into compartments

Front 33

parenchyma

Back 33

- the tissue that makes up the specialized parts of an organ, rather than the blood vessels and connective or supporting tissue
- in the spleen it's made up of the red pulp and the white pulp

Front 34

lymphedema

Back 34

persistent local tissue swelling: a form of edema resulting from the loss of normal lymph channel drainage of the affected part.

Front 35

dendritic cells

Back 35

- found in the germinal centers of the follicles in the outer cortex (present antigens to B cells); and in the deep cortex (activate T cells)

Front 36

Aereolar CT

Back 36

functions: supporting an binding other tissues; holding body fluids; defending against infection;storing nurtients as fat
- a loose CT; loowe arangement of fibers, reservoirfor water and salts; most widely distributed CT;

Front 37

Elastic CT

Back 37

- a dense regular connective tissue, but much more elastic
- bundles of collagen fibers runing in the same direction; parallel to direction of pull; very strong in one direction
- tendons; aponeuroses, ligaments (specifically the ligamenta nuchae and flava connecting adjacent vertebrae, b/c they're so elastic

Front 38

Dense fibrouse CT

Back 38

- overall; includes dense regular and dense irregular CT
- fibers are prominent element

Front 39

Simple squamous ET

Back 39

- flattened, sparse cytoplasm, thin and permeable
- found where filtration/exchange of substances by rapid diffusion is a priority (kidneys, lungs, endothelium, capillaries, mesothelium)