W7- Lecture 33- Lymphatic system

Question 1

what are the two parts of the circulatory system ?

Answer 1

cardiovascular & lymphatic

Question 2

name the three major components of the lymphatic system

+ purpose

Answer 2

Extensive network of capillaries & collecting vessels: receive fluid from loose connective tissues throughout body and transport to CV system

Lymph Nodes: filter fluid in collecting vessels

Lymphoid organs: include lymphatic nodules, tonsils, spleen & thymus

Question 3

what does a build up of interstitial fluid lead to?

Answer 3

oedema

Question 4

Lymphatic Vessel Types

Answer 4

Capillarys form Collecting Vessel from Trunks form Ducts

Question 5

you find Lymph capillaries occur alongside blood capillaries aside from ?

Answer 5

bone, bone marrow, teeth, and entire central nervous system

Question 6

compare Lymphatic Vessels to capillaries

Answer 6

Like blood capillaries but very permeable.
Two unique structural modifications:
Endothelial cells loosely overlap, open easily, create mini-valves.
Endothelial cells anchored to surrounding structures by fine filaments that separate with  interstitial fluid volume. Expose gaps in capillary wall but close if fluid pressure is > inside capillary, preventing leakage.

Question 7

what are lacteals

Answer 7

Highly specialised lymph capillaries in villi of intestinal mucosa. Lymph here is milky white rather than clear as it contains digested intestinal fats and is aka chyle.

Question 8

compare Collecting Vessels to veins

Answer 8

Collecting Vessels
Three tunics like veins, but:
Thin-walled
More internal valves
More anastomosing(branching )

Question 9

where do the Larger lymphatic vessels receive blood supply from?

Answer 9

vasa vasorum.

Question 10

which vessels do the collecting vessels in the skin travel with ?

which vessels do the deep lymphatics travel with ?

Answer 10

superficial veins

deep arteries

Question 11

what are the purpose of lymphatic trunks?

Answer 11

Drain large areas of body
(named after areas drained
e.g. paired lumbar, bronchomediastinal, subclavian and jugular trunks, single intestinal trunk.)

Question 12

how are lymphatic trunks formed ?

Answer 12

Capillaries collect into vessels which form lymphatic trunks

Question 13

how are lymphatic ducts formed ?

Answer 13

lymphatic trunks form lymphatic ducts

Question 14

describe the location that the right lymphatic duct empties into

+ what it drains

Answer 14

empties at junction of right internal jugular and right subclavian veins

+right arm, thorax

Question 15

describe the location that the thoracic duct empties into

Answer 15

into junction of left internal jugular and left subclavian veins

Question 16

describe the location that the cisterna chyli empties into

Answer 16

most inferior part of the thoracic duct

Question 17

what actions enable lymph transport ?

Answer 17

Milking action of muscles;
Breathing-induced pressure changes in thorax;
Use of valves;
Rhythmic contractions of smooth muscle in the trunks and ducts.

Question 18

what Lymphoid Tissue is important ?

/why

Answer 18

of loose connective tissue (aka reticular connective tissue) in all L. organs except the thymus.

Macrophages live on the fibres & lymphocytes reside temporarily in spaces

Question 19

describe how Lymphoid tissue is “packaged” in different ways

Answer 19

Diffuse - in most body organs especially in mucous membranes & in lymphoid organs.

Follicles/Nodules - solid, tightly packed, spherical bodies with centres (germinal centres via clonal selection ) containing B cells.

Usually found within organs e.g. lymph nodes but also singly in intestine (Peyer’s Patches).

Question 20

why does more fluid leaves capillaries than enters them?

how much is left per day ?

Answer 20

Hydrostatic & osmotic pressures at arterial ends of capillary beds force fluids, with plasma proteins, into interstitial space.

Most is reabsorbed at the venous end, but more than 3 L/day remains

Question 21

name three places where lymphatic vessels converge to form trunks

Answer 21

groin (inguinal),
Arm pit (axillary),
neck (cervical)

Question 22

describe the importance of trabeculae in lymph nodes?

Answer 22

divide node into compartments. Provides stroma of support for ever changing resident lymphatic cells. phagocytes an act on them . and divides lymphnode into two distinct regions outer Cortex & inner Medulla. major site of filtration.

Question 23

what are trabeculae?

Answer 23

Fibrous capsules and some bits extent into centre of centre of lymph node

Question 24

describe the cortex of a lymph node

Answer 24

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 25

describe the medulla of a lymph node

Answer 25

Contains cords inward extensions of the cortex which contain lymphoctes and plasma cells

Question 26

what structure difference enables more time for immune surveillance? where ?

Answer 26

More vessels coming in then out – slows down fluid. Passes through many nodes before returning back to cardiovascular system less at the hilus

Question 27

what cells trap antigens in the lymph nodes ?

Answer 27

Macrophages and dendritic cells trap antigens

Question 28

describe b cell proliferation in lymph nodes after activation

Answer 28

Outer cortex – nodules that contain B cells 1 recognition 2 interaction with helper T cells In the dark zone B cells proliferate undergo clinal selection Only those that can attach to antigens If b cell doesn’t receive help from t cell it undergoes apoptosis

Question 29

what happens when b cells move from the dark zone (aka germinal centre ) to the basal light zone

Answer 29

positive selection for binding to antigen on follicular dendritic cells

Question 30

describe the structure of Lymph Sinuses

Answer 30

Spanned by reticular fibres with resident macrophages, enter the nodes, and phagocytose foreign material. Some leakage of antigens into surrounding reticular tissue that activate lymphocytes.

Question 31

what is the only lymphoid tissue that filters lymph?

Answer 31

Lymph Nodes

Question 32

what side of the lymph nodes do the afferent lymphatic vessels enter ?

Answer 32

convex side

Question 33

what sinus does the lymph pass through that helps it pass from the ’ cortex to medulla

Answer 33

the sub-capsular sinus

Question 34

describe the spleen

Answer 34

Largest lymphoid organ; soft, blood-rich organ, fist size Located on left abdomen under diaphragm. Served by large splenic artery & Saphenous vein that enter hilus on concave side.

Question 35

what are the functions of the spleen ?

Answer 35

Lymphocyte proliferation & immune surveillance/ response Cleans blood e.g. remove old RBC/platelets, bacteria, virus, foreign matter, debris, toxins etc. Storage of red blood cell constituents and release of others to liver Stores platelets Site of RBC production in foetus

Question 36

what are the two distinct areas caused by Trabeculae in the spleen ?

Answer 36

Areas of L on reticular fibres: white pulp and form “cuffs” around central arteries. Areas of red cells, venous sinus, splenic cords, and red pulp. Dispose of effete red blood cells and pathogens.

Question 37

what place in the spleen does RBC degradation take place?

Answer 37

Splenic chord

Question 38

which cells help the degradation of RBC in the spleen ?

Answer 38

Macrophages help break down damaged RBC

Question 39

what is the thymus + structure

Answer 39

Primary lymphoid organ Largest as a child Secretes thymosin, thymopentin to make T L immunocompetent. structure: thymic lobules each with outer cortex and inner medulla. Dark-staining cortex Rapidly dividing, densely packed lymphocytes and few macrophages. Light-staining medulla: fewer lymphocytes, contains bizarre-shaped structures Hassal’s or thymic corpuscles – responsible for the conversion of self-reactive T-lymphocytes into suppressive T-lymphocytes.

Question 40

describe Hassal’s or thymic corpuscles

Answer 40

In medulla of thymus Increased number of epithelial cells that 1provide support to the medulla 2 help negatively select reactive T cells to generate tolerance against self antigens

Question 41

how does the thymus differ from other lymphoid organs (2)

Answer 41

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

Question 42

describe the steps of t cell maturation

Answer 42

please see diagram - 1 Rag caused shuffling of DNA – production of random T cell receptors produced (recombinases ) 2 Binding event occurs(Positive selection ) Binding leads to survival of cells 3 Regulation up/down of cd4 /cd8. 4 Cells bind of MHC 1 or 2 class molecules (negative selection ) If it does react cell undergoes apoptosis

Question 43

name the four types of tonsils | + where they are located

Answer 43

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 44

describe what a tonsil is

Answer 44

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 45

what takes place in the pits of tonsils?

Answer 45

immune surveillance + formation of memory cells

Question 46

describe the germinal centre in the tonsils

Answer 46

immune surveillance + formation of memory cells

Question 47

describe the describe the germinal centre in the tonsils of the tonsils

Answer 47

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.

Question 48

what are Peyer’s Patches?

Answer 48

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

Question 49

where can you find an aggregate of Lymph Nodules?

Answer 49

Appendix & Peyer’s Patches

Question 50

describe what the Appendix & Peyer’s Patches do

Answer 50

Destroy bacteria (many in gut) Generate memory Lymphocytes for long-term immunity. Mucus associated lymph tissue for respiratory and digestive tract protection.

Question 51

where is the Peyer’s Patches placed ? | important for ?

Answer 51

close to the lumen of the ileum and the germinal centre where B-cells proliferate. Important for anti-microbial, antibody production.