Lecture 36 - Immune System Overview

Question 1

What is the immune system?

Answer 1

It’s a diffuse collection of cells and organs that are responsible for the ability to resist infection and disease

Question 2

Name 3 examples that the immune system protect the body against?

Answer 2

1. Pathogens
2. Toxic material
3. Own misfunctioning cells

Question 3

Function of physical barriers against infection

Answer 3

Anatomical and physiological mechanisms prevent entry of foreign organisms and substances

Question 4

Function of cell-mediated immune responses

Answer 4

Innate and adaptive defence responses that rely on WBC activity

Question 5

What are physical barriers made of?

Answer 5

Structural features - work to prevent a pathogen from entering the body (ex. skin and hair)

Chemical secretions - used to neutralize and destroy pathogens (ex. lysozyme, stomach acid)

These defences are created by non-immune cells

Question 6

What is the most important physical barrier of the body? Why?

Answer 6

The integument. It has:

1. Secretions - washes away/destroys potential pathogens
2. Hair - keeps away potential hazards away from the skin surface
3. Stratified squamous epithelium - many closely interlocked layers which keep intruders out

Question 7

What is the purpose of mucous membranes?

Answer 7

It lines the digestive, respiratory, urinary, and reproductive tracts and provide protection against foreign substances and pathogens

Question 8

What are immune system responses mediated by?

Answer 8

WBCs - both innate and adaptive immune responses rely on the activation and signalling of specialized immune cells

Question 9

Where do WBCs come from and how are different WBCs divided?

Answer 9

They all come from red bone marrow

WBCs are divided based on:
- Function
- Anatomy
- Developmental history

Question 10

What are the 3 functions of immune responses that are mediated by WBCs?

Answer 10

1. Detection/recognition of invaders or abnormality
2. Secretion of chemicals that alter the local environment or signal to other cells
3. Destruction of foreign particles, pathogens, and diseased cells

No one type of WBCs performs all of these functions, but some are involved in more than one

Question 11

What are the 2 types of immune responses

Answer 11

Innate responses - nonspecific responses that react to any threat they detect. They are present from birth

Adaptive responses - specific and powerful responses triggered by exposure to particular antigens. They must be “learned” over the lifetime

Question 12

What does the lymphatic system consist of?

Answer 12

It consist of vessels that move lymph through the body, and tissues that produce or house lymphocytes

Question 13

What is lymph?

Answer 13

It’s a connective tissue that resembles blood, but lacks most of the cells and plasma proteins

Question 14

T/F? The lymphatic system is synonymous with the immune system

Answer 14

False - it is not synonymous with the immune function

Question 15

What are the 2 main non-immune functions of the lymphatic system?

Answer 15

1. Return of filtered fluid from ISF to plasma
2. Transport of digested and absorbed lipids

Question 16

What are similarities of lymphatic vessels and blood vessels?

Answer 16

• blood and lymph vessels have an endothelial wall around a lumen
• larger vessels have a smooth muscle layer and contain valves that keep lymph flowing one way

Question 17

What are 3 differences of lymphatic vessels and blood vessels?

Answer 17

• lymph capillaries have blind ends
• all lymph vessels are typically more permeable along their length
• there is no equivalent of a heart to create pressure gradients to move lymph; it relies on smooth muscle contraction (and skeletal muscle pumps)

Question 18

What does the lymphatic system consist of?

Answer 18

Lymphocytes, lymph nodes, and lymphoid tissues and organs

Question 19

T/F? Lymphoid organs and lymphoid tissues all belong to the immune system and contain lymphocytes (a subset of WBCs)

Answer 19

True

Question 20

Examples of primary organ/tissue and their function

Answer 20

They are involved in production and maturation of lymphocytes

• Bone marrow
• Thymus

Question 21

Examples of secondary organ/tissue and their function?

Answer 21

Contains mature and functional lymphocytes

• Lymphoid tissue
• Lymph nodes

Question 22

Characteristic of tissues and organs

Answer 22

Tissues - lack a distinct capsule
Organs - have a distinct fibrous capsule

Question 23

Are all WBCs lymphocytes? Why?

Answer 23

No:
Lymphocytes are a developmental classification; all lymphocytes come from lymphoid stem cells

All other WBCs develop from myeloid stem cells (like RBC and platelets)

Question 24

T/F? All lymphocytes are associated with adaptive immune responses

Answer 24

False - Most are, but not all, lymphocytes are associated with adaptive immune responses

Ex. T and B cells are associated with the adaptive immune response, but NK cells are associated with the innate immune response

Question 25

Describe the structural make up of lymph nodes

Answer 25

They are encapsulated structures which are connected to lymph vessels and house mature lymphocytes

Question 26

How does lymph flow in lymph vessels?

Answer 26

Lymph within lymph vessels flows through lymph nodes, which are often clustered at joints and where peripheral lymph vessels meet the torso

Question 27

How do lymph nodes stimulate immune responses?

Answer 27

They filter lymph and act as staging posts for generating adaptive immune responses to antigens detected by the innate immune system

Question 28

Where do antigens that WBCs have detected enter?

Answer 28

They enter the lymph node through afferent vessels and encounter B and T cells in the cortex and paracortex

Question 29

What are activated lymphocytes?

Answer 29

Activated lymphocytes that have acquired specific adaptive immune responses leave the lymph nodes through efferent vessels

Question 30

Function of marcophages and where are they located?

Answer 30

They are in the medulla and help destroy pathogens that make it into the lymph vessels, before they reach the bloodstream

Question 31

What are secondary lymphoid tissues?

Answer 31

They are mature lymphocytes that are not associated with lymph nodes. These tissues contain aggregations of lymphocytes that act like lymph nodes, but possess structural differences

Question 32

What are lymphoid nodules?

Answer 32

Regions of lymphoid tissue that are typically associated with mucosa

Question 33

What are Mucosa Associated Lymphoid Tissue (MALT)?

Answer 33

They are lymphoid nodules that are aggregations of lymphocytes. They lack a distinct capsule

Question 34

What are 4 ways lymphoid nodules distinguished from lymph nodes?

Answer 34

Lymph nodules: - have no capsule - no afferent vessels - are found in areolar tissue within mucous membranes - have the highest density where there are many live pathogens in the lumen (ex. colon)

Question 35

How do lymph nodes and lymph nodules generate adaptive immune responses?

Answer 35

They contain B and T cells that generate the adaptive immune responses

Question 36

What is the spleen?

Answer 36

It is a secondary lymphoid organ containing large amounts of lymphoid tissue that filters and monitors the blood

Question 37

What are the 3 functions of the spleen?

Answer 37

1. It has non-lymphoid functions, such as recycling old RBCs in its red pulp 2. Like a lymph node, it contains clusters of lymphocytes within its white pulp, which can generate adaptive immune responses 3. It filters blood plasma, not lymph. It acts like a lymph node for the blood

Question 38

Describe the path of lymph flow through a lymph node

Answer 38

Afferent lymphatics -> Subcapsular space -> Outer cortex -> Paracortex -> Medullary sinus -> Efferent lympathics