Anatomy of the immune system

Question 1

What are the different components of the lymphatic system ?

Answer 1

• primary and secondary lymphoid organs e.g. thymus, bone marrow and spleen
• lymph nodes
• lymph vessels
• mucosa associated lymphoid tissues e.g. adenoids and tonsils
• thousands of immune cells

Question 2

Briefly describe the function of the lymph nodes

Answer 2

They are checkpoints consisting of macrophages and dendritic cells which deal with minor threats directly by phagocytosis or they activate the immune system to deal with severe threats

Question 3

What are the 3 major components of the lymphatic system ?

Answer 3

• lymph fluid
• lymph vessels and lymph nodes
• lymphoid organs

Question 4

What is the lymph fluid ?

Answer 4

It is a watery fluid that originates from the blood plasma and circulates the lymph vessels

Question 5

What are the lymph vessels and lymph nodes ?

Answer 5

A network of vessels that recirculate lymph fluid and there 600-700 lymph nodes that act as checkpoints

Question 6

What are the lymphoid organs ?

Answer 6

primary : thymus and bone marrow
secondary : spleen, tonsils, Peyer’s patches and mucosa associated lymphoid tissues (MALTs)

Question 7

Where does the lymph fluid come from ?

Answer 7

• ~20 litres of fluid is forced out of the arteriolar through the capillary beds to allow the exchange of nutrients and gases everyday
• the vast majority of the interstitial fluid is reabsorbed at the venous end of the capillary beds due to osmotic pressure
• 3 litres is not reabsorbed and this becomes the lymph fluid
• this is taken up by capillaries of the lymph system
• these capillaries wrap their way between capillaries
• they are made of overlapping endothelial cells which form a series of flat like bowels which only open in one direction allowing the interstitial fluid to flow into the lymph vessels
• once in the lymphatic system it moves towards the area of lowest pressure in the blood circulatory system so it can be returned to the blood
• this is important to maintain blood volume

Question 8

What is the role of the valves in lymph vessels ?

Answer 8

They prevent the lymph fluid from flying back down the vessel

Question 9

Describe the structure of the lymph nodes

Answer 9

• contains medullary cords, paracortical areas and primary lymphoid follicles
• surrounded by an outer capsule
• contains arteries and veins
• the afferent lymph vessels bring in lymph fluid
• the efferent lymph vessels remove lymph fluid

Question 10

What is the role of the medullary cords, paracortical areas and primary lymphoid follicles of the lymph nodes ?

Answer 10

• medullary cords and sinuses contain macrophages
• paracortical areas contain T cells and dendritic cells
• primary lymphoid follicles contain B cells

Question 11

Other than lymph nodes, give some other checkpoints of the lymphatic system

Answer 11

• thymus
• spleen
• MALTs e.g. Peyer’s patches

Question 12

What is the main function of the thymus ?

Answer 12

It is the site of early T lymphocyte development

Question 13

Describe the location of the thymus

Answer 13

Sits directly above the heart
Most active during infancy
Shrinks in size as we age

Question 14

Describe the structure and location of the spleen

Answer 14

• largest lymphatic organ
• it is the size of a fist
• it sits around the region of the stomach
• contains red and white pulp regions

Question 15

What are the 2 main functions of the spleen ?

Answer 15

2 main functions :
1) To remove old red blood cells from circulation - red pulp region
2) Filter pathogens and immune complexes from blood - white pulp region

• it only filters blood and not lymph fluid
• it has a reserve of monocytes and platelets

Question 16

What is the function of the macrophages found in the red pulp of the spleen ?

Answer 16

They destroy pathogens which are circulating in the blood