Lymphatic System Flashcards
Explain the hydrostatic pressure and oncotic pressure effect in a capillary bed and how this allows tissue fluid to enter lymphatic capillary
- In a capillary bed, the hydrostatic pressure of the capillaries in the arteriole side drive fluid into the interstitial space
- Oncotic pressure on the venule side is able to absorb some of the water back
- However little proteins can enter the interstitial space through the small gaps in the capillary
- This takes water with it so not all fluid can be absorbed
- Net filtration of fluid ≠ net reabsorption of fluid
- Tissue fluid (fluid in interstitium) enters the lymphatic capillary
- Walls of lymphatic capillary more porous than blood capillary to allow tiny proteins to enter
What material enters lymph
- Tissue fluid, small proteins, damaged cells, bacteria, cancer cells, lipids (chylomicrons from gut lymphatics)
How much lymphatic fluid is produced per day
- 3-4 L of lymphatic fluid produced per day
- Amount of fluid filtered out of blood capillaries exceeds what is absorbed by 4L/day
Explain passive and intrinsic constriction in lymphatic system
- No central pump but has valves
- Passive constriction - lymph vessels run next to muscle or artery to push fluid
- Valves only allow single direction flow
- Intrinsic constriction - when area fills up, own walls squeeze fluid
Explain how a low pressure system in the lymphatics allows fluid to join the blood
- Low pressure system - higher than venous circulation at point of joining
- Lowest pressure of venous circulation just before it enters heart
- Thoracic duct and right lymphatic duct drain into left and right subclavian veins
Briefly state the structure of lymph nodes
- Tough fibrous outer capsule
- Reticular connective tissue inside (candy floss)
Explain the role of lymph nodes
- Immune surveillance and defense
- Highly organized centres of immune cells - lymphocytes
- Lymph draining into lymph nodes may contain pathogens
- All substances transported in lymph pass through ≥ 1 lymph node
- Physical filter, phagocytic filter
- Full of lymphocytes - activate and proliferate in response to antigens
What is lymphedema
Abnormal collection of protein-rich fluid causing tissue swelling due to compromised lymphatic system
State causes of lymphedema
- Removal or enlargement of lymph nodes
- Infections
- Damage to lymphatic system - eg. Cancer treatments
- Lack of limb movement - muscle contraction assists lymph fluid movement
- Congenital - Milroy’s syndrome
What is lymphadenopathy
- Abnormal size or number of lymph nodes
- Pathogens can enter alongside interstitial fluid
What are causes of lymphadenopathy
- Enlarged lymph nodes mainly caused by infection
- Tender, mobile
- Can also be caused by malignancy
- Hard, matted, non-tender
Distinguish between regional and terminal lymph nodes
- Regional - drain specific areas
- Terminal - receive drainage from number of regional nodes
How are regional and terminal lymph nodes separated in the head and neck
- Superficial (regional) and deep (terminal) lymph nodes separated by investing layer of deep cervical fascia of neck
- Some deep lymph nodes lie within carotid sheath
State the major superficial (regional) lymph nodes of the head
- Submental
- Submandibular
- Pre-auricular
- Post-auricular
- Occipital
- Superficial: EJV
- Posterior: EJV
- Anterior: EJV
State the major deep (terminal) lymph nodes of the head
- Jugulo-digastric
- Jugulo-omohyoid
- Suptraclavicular lymph nodes
