structure of the lymphoreticular system

Question 1

what is the lymphatic system

Answer 1

• part of the circulatory system
• network of capilaries, vessels, ducts, nodes and tissues
• carries excess tissue fluid (lymph) back to the circulating blood

Question 2

what are the functions of the lymphatic system

Answer 2

1. mechanism for removing excess intersitial (fluid in btwn tissue cells) fluid
2. transportation of fats
3. immune defence - presentation of foreign materials to the immune system and circulation of lymphocytes

Question 3

outline the flow of lymph through the body

Answer 3

1. interstitial spaces
2. lymphatic capillaries
3. lymphatic vessels
4. lymph nodes
5. lymphatic vessels
6. lymphatic ducts
7. cranial vena cava
8. circulatory system
9. repeat

Question 4

describe the function of lymphatic capillaries

Answer 4

• fluid and dissolved gasses are passing out of the circulatory capillaries into tissues
• excess is removed from the tissue by the lyphatic system
• interstitial fluids enter lymph capillaries via openings between adjacent endothelian cells (lymph capillaries have blind endings)

Question 5

describe the structure of lymphatic vessels

Answer 5

• flow of lymph is unidirectional
• lymph vessels are similar in structure to veins but are more delicate (have thinner walls)
• have many valves to prevent backflow
• flow is mainly passive and is maintained by valves, contraction of surrounding skeletal muscles and arteries and respiratory pump (force from artery puts pressure on lymph vessels to push it through)

Question 6

what is oedema

Answer 6

build up of fluid in tissues

Question 7

what is lymphoedema

Answer 7

localised fluid retention due to obstructions/patjology of the system

Question 8

what is pulmonary oedema

Answer 8

build up of fluid in the lungs

Question 9

what is the largest duct of the lymphatic system

Answer 9

the thoracic duct
- originates from the cisterna chyli in dorsal abdomen
- drains into cranial vena cava around vicinity of left brachiocephalic vein

Question 10

how are fats transported through the lymphatic system

Answer 10

• chyle drains into lymphatic capillaries known as lacteals in the small intestine
• lacteals return chyle to chyle cistern, the origin of the thoracic duct

• lymph from the digestive system is called Chyle and contains protein coated lipid droplets called chylomicrons

Question 11

what are the primary lymphoid tissues

Answer 11

where lymphocytes are produced and mature
B-Cells: Bone marrow, Bursa of fabricius (birds), peyers patches (ruminants)
T-Cells: Thymus

Question 12

what are secondary lymphatic tissues

Answer 12

where lymphocytes aer activated
- spleen
- lymph nodes
- mucosa associated lymphoid tissue (MALT)
- peyers patches (in dogs and cats)

Question 13

describe the Thymus’s role in the immune system and the progression as the animal ages

Answer 13

• primary lymphoid organ
• located in caudal neck and cranial thoracic regions
• larger in younger animals to kick-start development of the immune system
• regresses with age and replaced with fat tissue
• varies in appearance between species

Question 14

describe the spleen’s role in the immune system and its functions

Answer 14

• largest of the lymphoid organs
• closely attached to greater curvature of the stomach of left side of cranial abdomen (bean shaped in bird)
• stores blood
• destruction of old red blood cells
• have red and white pulp:
• red pulp removes particulate matter from circulation (filter out bacteria and foreign particles)
• White pulp: division of lymphocytes - secondary lymphoid

Question 15

decribe the histological features of the thymus

Answer 15

• cortext, medulla
• connective tissue capsule and strands form incomplete lobules
• hassalls corpuscle

Question 16

describe the histological features of the spleen

Answer 16

• smooth muscle capsule
• trabeculae
• central arteries
• red and white pulp

Question 17

describe the location of lymph nodes

Answer 17

located at various points along the lymph vessels, acts as elaborate filters
- superficial and deep
- ex. submandibular, popliteal, prescapular, axillary, superficial inguinal

Question 18

describe the structure and function of a lymph node

Answer 18

• enclosed by a capsule
• afferent vessels open into subscapular sinus
• lymph then flows into trabecular sinuses into medulla and medullary sinus
• efferent vessels leave at the hilus
• as lymph passes through the node, lymphocytes are added, and macrophages acts as filters to remove microorganisms in an attempt to halt the spread of infection and tumours
• lymph nodes survey and filter foreign antigens. they mount an immune response and are responsible for specific regions

Question 19

describe the histological features of lymph nodes

Answer 19

• capsule and subscapular sinus
• cortex - B-cell centres
• high endothelial venules (HEVs) (characterised by plump endothelial cells and allow lymphocytes from blood to enter directly into lymph node)

HEV on magnified section looks like tunnel

Question 20

describe lymph drainage and how this can affect the spread of cancerous cells

Answer 20

• lymph nodes drain specific areas and therefore if infections occurs within a drainage area the lymph node will become active
• rapid cell turnover and production of local inflammatory mediators may cuase the node to enlarge and become tender
• because lymph nodes are efficient filters and flow throughour them is slow, cells that have migrated from primary tumours and enter the lymphatic vessels can often lodge and grow as secondary tumours in lymphnnodes (metastasis)