Lymphatics

Question 1

What is an overview of the lymphatic system?

Answer 1

System of thin walled lymph vessels which drain XS ISF fluid from tissues, through a series of lymph nodes, back into circulation (cranial end of thorax, usually thoracic inlet)

Question 2

What are the roles of the lymphatic system?

Answer 2

1. Removal XS water from ISF
2. Removal of infectious agents and dead cells
3. Antigen presentation- takes infectious agents to lymph nodes
4. Movement of lymphatic cells- WBC
5. Transport of some proteins
6. Transport of dietary lipids from the gut - chylomicrons

Question 3

How is the lymphatic system arranged?

Answer 3

1. Starts with blind ending capillaries- v leaky, discontinuous basement membrane
2. these join together and together to form
3. larger lymph vessels - larger develop some scarce smooth muscle = some contractile ability.

Question 4

How is the lymphatic vessel arranged

Answer 4

1. thin walled endothelium with some adventitial connective tissue
2. other travel with BV
3. large vessles have some smooth msucle ans possess valves similar to veins
4. Capillaries blind endidn = single endothelial layer with discontinuous BM

Question 5

What is the different between afferent and efferent lymphvessels

Answer 5

1. Afferent blood vessels = coming towards

2. Efferent = going away

Question 6

What are haemolymph nodes and haemal nodes

Answer 6

haemolymph nodes- lymph nodes with some red blood cells in and look red rather than pale adn beigy
2. Haemal = only found in sheep dorsal abdomen = similar function to spleen, red with lot of vascular tissue!

Question 7

What are lymphocentres?

Answer 7

1. a collection of important lymph nodes in an area

Question 8

Name the key lymphocentres in the:

1. Head
2. Neck
3. Thorax
4. Abdomen
5. Hindquarters
6. Formelim

Answer 8

1. Head - retrioharyngeal, parotid, mandibular
2. Neck - superficial and deep cervical
3. Thorax - Dorsal and ventral thoracic, mediastinal and bronchial
4. Abdomen - lumbar, coeliac, cranial and caudal mesenteric
5. Hindquarters - popliteal, ischial, deep inguinal, superficial inguinal, iliosacral
6. Forelimb - axillary

Question 9

What are the palpable LN in a dog?

Answer 9

all potentially palpable if enlarged.
1. mandibular = under chin
2. Parotid = ears
3. pre scapula = infront of shoulder blade
4. Axillary and accessory axillary = armpit
popliteal = behind back knee

Question 10

What are the palpable lymph nodes in a horse

Answer 10

1. normally only the submandibular lymph nodes

Question 11

What are the palpable lymph nodes in a OX

Answer 11

1. Pre scapular and prefemoral lymph nodes are usually palpable in the normal animal

Question 12

What is the significance between lymph nodes adn lymphatic vessels?

Answer 12

1. all lymph nodes are connected up by lymphatic vessels and all have to get to venous circulation

Question 13

1. where does the lymph system develop in the early embryo

2. what are the first few stages

Answer 13

1. Develops in mesoderm of embryo
2. initially 6 sacs:
   a) paired jugular sacs - cranial
   b) Cisterna chyli
   c) paired iliac sacs - caudal
   d) 6th retroperitoneal sac - abdominal cavity
3. islands join together = lymph vessels. Sacs turn into lymphocentres (except CC)
4. lymphatic vessels extend = colonise = lymph vessels

Question 14

What is the thymus

Answer 14

1. a lymphoid tissue, where T lymphocytes come from
2. in cranial mediastinum
3. once adult = useless = becomes fatty tissue

Question 15

Explain how the lymphatic system acts to maintain fluid balance in the body

Answer 15

1. In most caps, most of time = net filtration of fluid from blood caps: HDS pressure difference outweighs oncotic pressure difference for most of length of cap
2. fluid moves into ISF
3. BULK flow of fluid (HDS pressure difference) into lymph : greater pressure in ISF than lymph cap
4. Lymphatic caps also uptake protein from ISF = lowers oncotic pressure of ISF, inc in lymphatic caps
5. Once fluid in lymph, flow within tubes = by bulk flow (HDS pressure differences)
6. pressure in venous system must be lower than lymph for lymph to flow down pressure gradient

Question 16

Do blind ended capillareis favour absorption or filtration?

Answer 16

favour absorption from ISF and oppose filtration

Question 17

What helps flow within the lymphatic system by bulk flow?

Answer 17

1. Overall hydrostatic pressure gradient leading into venous system
2. external pressure from skeletal muscle
3. SMooth msucle in walls of larger lymph (can constrict to some degree)
4. Valves prevent backflow

Question 18

Why could there be failure of the lymphatic drainage?

Answer 18

1. disease of the lymphatic system
2. Capacity of lymphatic system overwhelmed = produce so much ISF
3. derangement of hydrostatic pressure gradient - no gradient = no lymph flow = no flow = can’t take up more ISF

Question 19

How could raised vena cava pressure cause fluid in pleural cavity? (pleural effusion)

Answer 19

1. VC high pressure = reduced or reversed pressure gradient

2. fluid can’t be removed by lymphatic

Question 20

Which node drains the deep structures of the forelimb?

Answer 20

1. Axillary

Question 21

When examining a normal horse, which are the only readily palpable lymph nodes?

Answer 21

2. Submandibular

Question 22

A dog presents with a mass on its right dorsal metatarsal area. in addition to a biopsy from the mass, which lymph node should you sample to check for local metastasis?

Answer 22

(top of back foot)

1. popliteal

Question 23

Where does the thoracic duct originate?

Answer 23

1. Cisterna chyli

Question 24

What causes bulk flow into lymphatic capillaries?

Answer 24

1. high hydrostatic pressure in ISF compared to lymphatic capillaries

Question 25

What type of lymphoid tissue is the spleen?

Answer 25

secondary- for filtering blood

Question 26

What are the histological features of the spleen

Answer 26

1. connective tissue capsule surrounds 2. Red pulp - all the red bits: pretty much everything 3. white pulp - nodular folicular structure bluish whitish circular structure 4. Trabecula = connective tissue that invaginated into spleen (secta = thinner in spleen = T) 5. Trabecular vein = RBC within

Question 27

What do the trabeculae look like in certain species

Answer 27

1. in certain = smooth muscle = when splenci contraction = inc blood volume 2. Cigar shaped elongated nuclei in smooth muscle

Question 28

What are the circular structures you can identify in the spleen?

Answer 28

1. lymphatic follicles = larger | 2. smaller arterioles that associated with individual follicles

Question 29

What is the structure of a secondary lymph follicle

Answer 29

WHITE PULP Germinal centre Mental zone = darker Marginal zone of entire follicle = around 1. middle = densely populated with B cells = lighter 2. Darker zone = T cell population around