Lymphatic system lecture 15 Flashcards
Capillary hydrostatic pressure (CHP)
forces fluid out of the circulatory system,
but pressure drops moving from arterial to venous end of capillaries
Blood colloid osmotic pressure (BCOP)
tends to pull water and solutes into capillaries
Net filtration pressure (NFP)s
the difference between capillary hydrostatic pressure and blood colloid osmotic pressure
Functions of the lymphatic system
Fluid recovery
Immunity
Lipid absorption
fluid recovery
- Fluid continually filters from capillaries to interstitial spaces
- Capillaries reabsorb c 85% of this
- The remaining 15% would equate to a loss of about 2-4 L of water, and half of the plasma protein, per day
- This would lead to circulatory failure and death within hours
- The lymphatic system returns this fluid to the blood
immunity - lymphatic system
- With the lymph fluid, the lymphatic system inevitably picks up foreign cells and chemicals from the surrounding tissues
- On their way back to the bloodstream, the lymph is passed through lymph nodes, where immune cells cleanse this fluid
lipid absorption- lymphatic system
• Lipids in small intestine are packaged into chylomicrons that are too large to pass into blood via capillary walls but can pass into
special lymphatic capillaries (lacteals)
Components of the lymphatic system
Lymph
Lymphatic vessels
Lymphatic tissues
Lymphatic organs
lymph
• the fluid collected from interstitial spaces and returned to the bloodstream
• Clear, colourless fluid
• Similar to blood plasma but low in protein
• Varies in composition around the body
– after a meal, lymph draining from small intestine is milky, because of high lipid content
lymphatic vessels
the vessels that transport lymph
• Lymph flows through a network of lymphatic vessels that are similar to blood vessels
• The capillaries of these penetrate almost all body tissues except
– central nervous system
– cornea
– cartilage
– bone
– bone marrow
• Closely associated with blood capillaries but – unlike blood vessels – lymphatic capillaries are closed at one end
lymphatic tissues
• aggregates of lymphocytes and macrophages, found in many organs
lymphatic organs
- organs with specially high levels of lymphatic tissue
* separated from surrounding organs by connective tissue capsules
what does the lymph contain?
- Lymphocytes
- Macrophages
- hormones
- Bacteria
- Viruses
- Cellular debris
- Can also contain travelling cancer cells (breast cancer frequently progresses to adjacent lymph nodes)
lymphatic trunks
(4 pairs, plus single intestinal trunk) – jugular – subclavian – bronchiomediastinal – intestinal (single) – lumbar
collecting ducts
– right lymphatic duct (drains r upper arm; right side of head and thorax into right subclavian vein)
–thoracic duct (larger; from rest of body into
left subclavian vein)
right lymphatic duct
• Formed by convergence of – right jugular trunk – right subclavian trunk – right bronchimediastinal trunk • Drains right upper limb and right side of head and thorax • Empties into right subclavian vein
thoracic duct
• Larger and longer (than right lymphatic duct)
• Just below diaphragm, we have the cisterna chyli, formed from
– left and right lumbar trunks
– intestinal trunk
• Thoracic duct then passes superiorly through diaphragm, to be joined by
– left bronchiomediastinal trunk
– left subclavian trunk
– left jugular trunk
flow of lymph
- Lymphatic flow is similar to venous flow, except without a pump – and at even lower speed and pressure
- Flow primarily governed by rhythmic contractions of the lymphatic vessels, produced by skeletal muscles that squeeze the vessels (again like veins)
- Since lymphatic vessels often share a connective sheath with arteries and veins, arterial pulses may also contribute to the contraction of lymphatic vessels
lymphatic vessels structure
Thin, overlapping cells, like fish scales
• Overlapping gaps act as valves, opening when pressure is greater outside, and closing when it is lower
• Gaps are large enough to allow bacteria, lymphocytes and other cells to enter with the interstitial fluid
• Thus, composition of the lymph mirrors that of the ‘upstream’ tissues: a ‘report’
• Often travel alongside arteries and veins and share a common sheath of connective tissue
• At irregular intervals they empty into lymph nodes
Natural killer (NK) lymphatic cells
– attack and kill bacteria, transplanted tissue cells or infected host cells
T lymphocytes (T cells)
lymphatic cells
– ‘T’ for ‘thymus-dependent’
– develop in thymus,
– activity regulated by thymic hormones
– three classes:
– Cytotoxic T (TC) cells: directly attack and kill other cells
– Helper T (TH) cells: coordinate defence mechanisms
– Memory T (TM) cells: ‘remember’ antigens; confer immunity
B lymphocytes (B cells)
lymphatic cells
– differentiate to form plasma cells
– mature in bone marrow
Macrophages
lymphatic cells
– Large, phagocytic cells
– Also transport foreign matter to cell surface to present to T cells
Langerhans cells
lymphatic cells
– Also known as dendritic cells
– Branched macrophages
Reticular cells
lymphatic cells
– Antigen-presenting cells
primary lymphatic organs
• Red bone marrow
• Thymus
where B and T lymphocytes mature and become immunocompetent
secondary lymphatic organs
• Lymph nodes
• Tonsils
• Spleen
populated with lymphocytes that matured in the primary lymphatic organs
red bone marrow
- Soft, highly vascularised material involved in erythropoeisis and immunity
- In children, occurs in most of skeleton
- In adults, limited to axial skeleton plus proximal heads of humerus and femur
- Supplies lymphocytes to immune system
thymus
- Part of both endocrine and lymphatic systems
- Located between heart and base of neck
- Firm and conical in children; red due to rich blood supply
- After age 15 or so, contains less lymphatic tissue and shrinks; becomes yellowish as it accumulates fat
- By old age, difficult to distinguish from surrounding fat
- Site of maturation of T lymphocytes
lymph nodes
• Most numerous lymphatic organ, with several hundred
• Bean-shaped, 2-3cm long
• Dual functions:
– cleanse lymph
– site of activation for T and B lymphocytes
• Lymph enters node via afferent lymphatic vessels entering the node’s convex surface
• Leaves via one of three efferent vessels lead out of its concave surface via an indentation called the hilum
• Macrophages and reticular cells remove about 99% of impurities in lymph
• Lymph flows through one node after another as it is returned to the bloodstream; a thorough cleaning process
Lymph nodes are widespread, but especially concentrated in some areas:
– Cervical lymph nodes – Axillary lymph nodes – Thoracic lymph nodes – Abdominal lymph nodes – Intestinal and mesenteric lymph nodes – Inguinal lymph nodes – Popliteal lymph nodes
tonsils
• Patches of lymphatic tissue at opening of pharynx • Guard against inhaled pathogens 1. Single pharyngeal tonsil (adenoids) – on wall of pharynx behind nasal cavity 2. Paired palatine tonsils – posterior margin of oral cavity 3. Many lingual tonsils – on each side of root of tongue • Palatine tonsils are largest and frequently infected (tonsillitis is an acute Streptococcus infection)
spleen
• Largest lymphatic organ (12cm long; 160g)
• Sits between diaphragm, stomach and kidney
• Erythrocyte graveyard
• Two tissue types
– red pulp
– white pulp
red pulp
- Many erythrocytes
- Capillaries highly permeable, allowing RBCs out
- These accumulate in red pulp; fagile RBCs rupture as they are squeezed through the capillary walls, to be phagocytosed by macrophages
white pulp
• Lymphoctyes and macrophages monitor blood for foreign antigens
