Lymphatic system lecture 15

Question 1

Capillary hydrostatic pressure (CHP)

Answer 1

forces fluid out of the circulatory system,

but pressure drops moving from arterial to venous end of capillaries

Question 2

Blood colloid osmotic pressure (BCOP)

Answer 2

tends to pull water and solutes into capillaries

Question 3

Net filtration pressure (NFP)s

Answer 3

the difference between capillary hydrostatic pressure and blood colloid osmotic pressure

Question 4

Functions of the lymphatic system

Answer 4

Fluid recovery
Immunity
Lipid absorption

Question 5

fluid recovery

Answer 5

• 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

Question 6

immunity - lymphatic system

Answer 6

• 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

Question 7

lipid absorption- lymphatic system

Answer 7

• 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)

Question 8

Components of the lymphatic system

Answer 8

Lymph
Lymphatic vessels
Lymphatic tissues
Lymphatic organs

Question 9

lymph

Answer 9

• 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

Question 10

lymphatic vessels

Answer 10

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

Question 11

lymphatic tissues

Answer 11

• aggregates of lymphocytes and macrophages, found in many organs

Question 12

lymphatic organs

Answer 12

• organs with specially high levels of lymphatic tissue

* separated from surrounding organs by connective tissue capsules

Question 13

what does the lymph contain?

Answer 13

• Lymphocytes
• Macrophages
• hormones
• Bacteria
• Viruses
• Cellular debris
• Can also contain travelling cancer cells (breast cancer frequently progresses to adjacent lymph nodes)

Question 14

lymphatic trunks

Answer 14

(4 pairs, plus single intestinal trunk)
– jugular
– subclavian
– bronchiomediastinal
– intestinal (single)
– lumbar

Question 15

collecting ducts

Answer 15

– 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)

Question 16

right lymphatic duct

Answer 16

• 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

Question 17

thoracic duct

Answer 17

• 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

Question 18

flow of lymph

Answer 18

• 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

Question 19

lymphatic vessels structure

Answer 19

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

Question 20

Natural killer (NK) lymphatic cells

Answer 20

– attack and kill bacteria, transplanted tissue cells or infected host cells

Question 21

T lymphocytes (T cells)

Answer 21

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

Question 22

B lymphocytes (B cells)

Answer 22

lymphatic cells
– differentiate to form plasma cells
– mature in bone marrow

Question 23

Macrophages

Answer 23

lymphatic cells
– Large, phagocytic cells
– Also transport foreign matter to cell surface to present to T cells

Question 24

Langerhans cells

Answer 24

lymphatic cells
– Also known as dendritic cells
– Branched macrophages

Question 25

Reticular cells

Answer 25

lymphatic cells

– Antigen-presenting cells

Question 26

primary lymphatic organs

Answer 26

• Red bone marrow
• Thymus
where B and T lymphocytes mature and become immunocompetent

Question 27

secondary lymphatic organs

Answer 27

• Lymph nodes
• Tonsils
• Spleen
populated with lymphocytes that matured in the primary lymphatic organs

Question 28

red bone marrow

Answer 28

• 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

Question 29

thymus

Answer 29

• 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

Question 30

lymph nodes

Answer 30

• 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

Question 31

Lymph nodes are widespread, but especially concentrated in some areas:

Answer 31

– Cervical lymph nodes
– Axillary lymph nodes
– Thoracic lymph nodes
– Abdominal lymph nodes
– Intestinal and mesenteric lymph nodes
– Inguinal lymph nodes
– Popliteal lymph nodes

Question 32

tonsils

Answer 32

• 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)

Question 33

spleen

Answer 33

• Largest lymphatic organ (12cm long; 160g)
• Sits between diaphragm, stomach and kidney
• Erythrocyte graveyard
• Two tissue types
– red pulp
– white pulp

Question 34

red pulp

Answer 34

• 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

Question 35

white pulp

Answer 35

• Lymphoctyes and macrophages monitor blood for foreign antigens