Lymphoid Organs

Question 1

What is the innate immune system?

Answer 1

Immune system that retains the phagocytic system in the form of monocytes/macrophages and neutrophils
Lacks immunological memory

Question 2

What is the adaptive immune system?

Answer 2

The innate immune system with an added form of defence that has high specifity and memory.
Based on the presence of trillions of lymphocytes and cell surface recptors
Slower to react but highly flexible and very specific

Question 3

Components of innate immune system

Answer 3

Barriers against invasion: skin, mucosa, stomach acid
Phagocytes: macrophages and neutrophils
Complement: plasma proteins that form an enzyme system to defend against bacteria
Extracellular killers: natural killer lymphocytes and eosinophils

Question 4

What do extracellular killer lymphocytes kill?

Answer 4

Virus infected cells

Some tumour cells

Question 5

What do extracellular killer eosinophils do?

Answer 5

Attack larger parasites

Question 6

What is the main role of the adaptive immune system?

Answer 6

Destruction

Question 7

What skill is critical for destruction?

Answer 7

The ability to distinguish ‘self’ from ‘non-self’

Question 8

What happens when the immune system fails to distinguish between self and non-self?

Answer 8

It attacks the body resulting in autoimmune disease

Question 9

What tissue is attacked from rheumatoid arthritis?

Answer 9

Synovial joints

Question 10

What tissue is attacked in addison’s disease?

Answer 10

Adrenal cortex

Question 11

What tissue is attacked in multiple sclerosis?

Answer 11

CNS myelin

Question 12

What tissue is attacked in Hashimoto’s disease?

Answer 12

Thyroid gland

Question 13

What tissue is attacked in grave’s disease?

Answer 13

Thyroid gland

Question 14

What tissue is attacked in myasthenia gravis?

Answer 14

Neuromuscular junction

Question 15

What is a primary lymphoid organ?

Answer 15

An organ which is the site of lymphocyte production and maturation
In humans - bone marrow and thymus

Question 16

What is a secondary lymphoid organ?

Answer 16

Sites to which lymphocytes migrate and where they aggregate in large numbers
In humans - spleen, lymph nodes, lymph nodules

Question 17

What forms do lymphocytes come in?

Answer 17

B lymphocytes - produce antibodies
T lymphocytes - participate in cellular immunity, found in 3 forms
Natural killer cells - kill virus infected cells and some tumor cells

Question 18

Development of lymphocytes

Answer 18

B and T cells produced from stem cells in the bone marrow
B cells remain in the bone marrow to continue their development
Immature T cells migrate to the thymus to mature and be ‘educated’
Both then move through the bloodstream to secondary lymphoid organs

Question 19

Properties of bone marrow

Answer 19

Compact bone
Endosteum
Hemopoietic cells embedded in reticular fibres
Blood sinusoids

Question 20

Properties of the thymus

Answer 20

Located in mediastinum
Increases in size from birth to puberty then regresses and gets more and more fatty
Has two lobes subdivided by septa
Lobules have outer highly cellular cortex and a less cellular inner medulla

Question 21

What does the thymus cortex contain?

Answer 21

Large numbers of T cells
Epithelioreticular cells
Macrophages

Question 22

What does the thymus medulla contain?

Answer 22

Mainly T cells but larger and less densely packed

Epithelioreticular cells

Question 23

What happens when T cells first enter the thymus?

Answer 23

Begin proliferation, maturation and selection processes.

Those that fail (98%) will undergo apoptosis and be phagocytosed by macrophages

Question 24

What happens to T cells that survive the cortex?

Answer 24

They enter the medulla and interact with the epithelioreticular cells
They’re presented with ‘self’ antigens and any cells which become activated are destroyed (clonal deletion)

Question 25

What happens to T cells that survive the medulla?

Answer 25

Enter the blood cells

Question 26

What is a Hassals corpuscle?

Answer 26

Whorls of epithelial cells with keratin at their core

Accumulate in the medulla

Question 27

What is positive selection?

Answer 27

In the cortex T cells must express correct surface antigens and recognise self and foreign antigens to survive

Question 28

What is negative selection?

Answer 28

In medulla T cells that recognise self antigens are eliminated

Question 29

What are the functions of the lymphatic system?

Answer 29

Drainage of lymph into vascular system
Surveillance of tissue for signs of antigens from foreign invaders e.g. bacteria
Delivery of absorbed fats from small intestine into vascular system

Question 30

Structure of lymph vessels

Answer 30

Thin walled
Lined by endothelium
Anchored to tissue by filaments

Question 31

Structure of lymph nodes

Answer 31

Encapsulated
Highly organised structures
Interposed along larger lymph vessels
Found in clusters in areas like neck, axillae and groin

Question 32

How lymphocytes enter lymph nodes?

Answer 32

Via incoming lymph

Via bloodstream

Question 33

What are lymph follicles?

Answer 33

Circular aggregations containing mostly B cells found beneath the capsule

Question 34

What are primary follicles?

Answer 34

Uniformly, densely packed follicles

Unstimulated

Question 35

What are secondary follicles?

Answer 35

Less densely packed centres consisting of actively dividing B cells = germinal centre
Outer mantle zone containing resting B cells
Active follicles

Question 36

What populates the paracortical region of a lymph node?

Answer 36

Mostly T cells

Question 37

What does the medulla of a lymph node contain?

Answer 37

Medullary sinuses

Medullary cords that contain plasma cells and macrophages

Question 38

What is MALT?

Answer 38

Aggregations of lymph tissue associated with the GI tract, respiratory tract and genitourinary tract
Mucosa-associated lymphatic tissue
e.g. palatine tonsil, payer’s patch in ileum

Question 39

What lines the crypts in the palatine tonsil?

Answer 39

Stratified squamous epithelium

Question 40

Functions of the spleen

Answer 40

Produce immune response against blood-borne antigens
Removal of particulate matter and aged blood cells
Production of blood cells during fetal life

Question 41

What is white pulp?

Answer 41

Whitish nodules in spleen made of T cells or B cells

Question 42

What is red pulp?

Answer 42

Deep red tissue in spleen containing mostly blood filled capillaries

Question 43

What happens to old RBCs when leaving the spleen?

Answer 43

Because they cannot deform to fit through the small spaces, they will lyse and be phagocytosed by macrophages within the wall of the sinuses