Lymphatic System

Question 1

The Lymphatic System

Answer 1

Consists of two semi-independent parts:
o Lymphatic vessels
o Lymphoid tissues and organs

Lymphatic system functions
o Transports escaped fluids from the cardiovascular system back to the blood
o Plays essential roles in body defence and resistance to disease

Without the lymphatic system –> cardiovascular and immune systems wouldn’t function properly

Question 2

Lymphatic Vessels - General

Answer 2

As blood circulates around the body –> nutrients, wastes and gases are exchanged between blood and interstitial fluid
o Remaining fluid (up to 3L) becomes part of the interstitial fluid

• Lymph consists of excess tissue fluid and plasma proteins carried by lymphatic vessels back to blood

If fluids are not picked up, edema (swelling) occurs as fluid accumulates in tissues
o Excessive edema impairs cell ability to make exchanges with the interstitial fluid and blood

Question 3

Lymphatic Vessels - Flow System

Answer 3

Pick up excess fluid (lymph) and return it to the blood
o Form a one-way system
o Lymph flows only toward the heart

Question 4

Lymphatic Vessels Relation to Veins of the Cardiovascular System

Answer 4

o Thin-walled
o Larger vessels have valves
o Low-pressure, pumpless system

Question 5

Lymph Transport is Aided By:

Answer 5

o Milking action of skeletal muscles
o Pressure changes in thorax during breathing
o Smooth muscle in walls of lymphatics pump rhythmically

Question 6

Lymph Capillaries

Answer 6

• Weave between tissue cells and blood capillaries in loose CT of body and absorb the leaked fluid
• Walls overlap to form flaplike minivalves
• Fluid leaks into lymph capillaries
• Capillaries are anchored to connective tissue by filaments
• Higher pressure on the inside closes minivalves  prevents lymph from leaking back out
• Fluid is forced along the vessel
• Highly permeable

Question 7

Lymphatic Collecting Vessels

Answer 7

• Collect lymph from lymph capillaries
• Carry lymph to and away from lymph node

Return fluid to circulatory veins near the heart
o Right lymphatic duct drains the lymph from the right arm and the right side of the head and thorax
o Thoracic duct drains lymph from rest of body

• Both ducts empty into the subclavian vein

As lymph is transported to the heart
o It is filtered through thousands of lymph node which cluster along lymphatic vessels
 Inguinal, Axillary and Survival regions

Question 8

Lymph Nodes

Answer 8

• Lymph nodes filter lymph before it is returned to the blood
  o Important for immunity

Harmful materials that are filtered 
o	Bacteria
o	Viruses 
o	Cancer cells 
o	Cell debris

Question 9

Defence Cells within Lymph Nodes

Answer 9

Macrophages
o Engulf and destroy bacteria, viruses, and other foreign substances in lymph

Lymphocytes
o Respond to foreign substances in lymph

Question 10

Lymph Node Structure

Answer 10

Most lymph nodes are kidney-shaped, less than 1 inch long, and buried in connective tissue
o Surrounded by a fibrous capsule
o Divided into compartments by trabeculae (CT strands)

o Internal is a network of soft reticular tissue
 Provides space for ever changing population of lymphocytes to reside as they monitor lymphatic stream

Question 11

Lymph Node Structure Cortex

Answer 11

o Contains follicles
 Collections of lymphocytes

o Germinal centers enlarge when B-lymphocytes are creating daughter cell which release antibodies

o Rest of cortical cells (lymphocytes in transit)
 Circulate continuously between blood and lymph nodes and the lymphatic stream

Question 12

Lymph Node Medulla

Answer 12

o Contains phagocytic macrophages

o Medullary Cords
 Inward extensions of cortical tissue that contain both B and T cells
 Phagocytic macrophages are located in the central medulla of the lymph node

Question 13

Flow of Lymph Through Nodes

Answer 13

• Lymph enters the convex side through afferent lymphatic vessels
• Lymph flows through a number of sinuses inside the node
• Lymph exits through efferent lymphatic vessels
• Because there are fewer efferent than afferent vessels, flow is slowed

Question 14

Other Lymphoid Organs: Spleen

Answer 14

o Located on the left side of the abdomen
o Filters and cleans blood of bacteria, viruses, debris
o Provides a site for lymphocyte proliferation and immune surveillance
o Destroys worn-out blood cells
 Returns broken down fragments to the liver
o Forms blood cells in the fetus
o Acts as a blood reservoir
o During haemorrhage, both spleen and liver contact to provide their blood into circulation

Question 15

Other Lymphoid Organs: Thymus

Answer 15

o Found overlying the heart
o Functions at peak levels only during youth
o Largest during childhood –> shrinks during puberty
o Majority of lymphocytes are formed within marrow –> transfer to thymus –> mature to T-cell

Question 16

Other Lymphoid Organs: Tonsils

Answer 16

o Small masses of lymphoid tissue deep to the mucosa surrounding the pharynx (throat)
o Trap and remove bacteria and other foreign pathogens
o Tonsillitis results when the tonsils become congested with bacteria
 Become red, swollen and sore

Question 17

Other Lymphoid Organs: Peyer’s Patches

Answer 17

o Found in the wall of the small intestine
o Similar lymphoid follicles are found in the appendix
o Macrophages capture and destroy bacteria in the intestine

Question 18

Other Lymphoid Organs: Mucosa-Associated Lymphoid Tissue (MALT)

Answer 18

Includes:
 Peyer’s patches
 Tonsils
 Appendix

o Acts as a sentinel to protect respiratory and digestive tracts from constant attacks from foreign matter entering the cavities