ANATOMY - Histology Of Immune Sytsem Flashcards
What are primary lymphoid organs ?
Organs in which immature lymphocytes acquire receptors to recognise antigens - they mature lymphocytes
What are the primary lymphoid organs? (2)
-thymus
-bone marrow
Where are T lymphocytes matured?
Thymus
Where are B lymphocytes matured?
Bone marrow
What are secondary lymphoid tissues ?
Tissues where lymphocytes are activated in response to an antigen.
Give 3 examples of secondary lymphoid tissues
-lymph nodes
-spleen
-MALT
Where is blood screened for pathogens?
Spleen
Where is lymph screened for pathogens?
Lymph nodes
Where are antigen activated lymphocytes found?
In blood, lymph and lymphoid organs - continuously circulating
What are 3 lymphoid cells?
-lymphocytes
-antigen presenting cells (APCs)
-reticular cells
What is a reticulocyte?
An immature red blood cell
What are 3 types of lymphocytes?
- b lymphocytes
- T lymphocytes
- natural killer cells (NK)
What are the different types of T cells ?
- helper T cells
- Cytotoxic T cells
- Suppressor T cells
- Memory T cells
What is the function of antigen presenting cells?
-display antigens on MHC
- help to activate T cells
What are examples of APCs?
- macrophages
- dendritic cells
- B lymphocytes
What do reticular cells do
Produce stroma which supports other cells in lymphoid organs
What is stroma?
Scaffolding
What are the 2 sections of the thymus?
Medulla and cortex
What is found in the medulla of the thymus ?
More mature T cells
Hassall’s corpuscles
Macrophages
What is found in the cortex of the thymus?
Less mature T cells
What kinds of cells are found in the thymus?
- lymphocytes
- macrophages
- reticular cells
Where are macrophages found in the thymus
In the cortex and the medulla
What are reticular cells called in the thymus?
Epithelial cells
What do reticular cells do in the thymus ?
They form a cellular network
Describe the scaffolding of the thymus
Epithelial cells form a cellular network - they line up together to form scaffolding
What is unusual about the scaffolding in the thymus?
Reticular fibres are not common in the thymus - instead linked cells form the scaffolding
What is a significant feature found in the medulla of the thymus?
Hassall’s / thymic corpuscles
What are Hassall’s / thymic corpuscles?
-keratinised epithelial cells
- look like swirls
- found in medulla of thymus
What cells are found in lymph nodes?
- B cells
- T cells
- APCs e.g macrophages
- reticular cells
What do reticular cells do in lymph nodes?
They produce reticular fibres (collagen) which form a network
What is the function of the scaffolding in the lymph nodes?
Keeps the sinuses open
What is in the centre of follicles in lymphoid tissue?
Germinal centres - actively dividing B cells
What surrounds the centre of the follicle in lymphoid tissues?
resting B cells
What is the paracortex of the lymph nodes?
Deep cortex
What is contained in the paracortex of lymph nodes?
T cells
What type of lymphocyte is contained in the medulla of lymph nodes?
Plasma B cells
What is the largest lymphoid organ?
Spleen
What are the 2 blood cleansing functions of the spleen?
- removal or blood borne antigens
- removal and destruction of old/defective RBCs
Where does haemopoeisis occur in an adult?
Bone marrow
Where does haemopoeisis occur in the foetus?
In the spleen
What are the 2 types of substance in the spleen?
-white pulp
-red pulp
What is white pulp?
Thick sleeves of lymphoid tissue
What is red pulp composed of?
- venous sinuses
- splenic cords
Where is red pulp found?
In the spleen, surrounding white pulp
What are the blood vessels which supply/ drain the spleen called?
Splenic artery & splenic vein
Does the spleen have trabeculae?
Yes
What is the composition of white pulp?
- lymphoid tissue
- central arteries
- sheathed capillaries surrounded my macrophages
- T cells surround arteries
- B cells form follicles
What is red pulp composed of ?
- splenic sinusoids
- splenic cords (composed mainly of macrophages and reticular cells)
What are splenic cords?
Sheets of reticular CT
Found in red pulp
What are PALS? In the spleen
PeriArterial Lymphoid Sheaths
- white pulp surround central arteries in the spleen
How is blood passed from artery to vein in the spleen?
Splenic artery -> central arteries -> sheathed capillaries -> splenic cords of red pulp -> splenic sinusoids -> veins of red pulp -> splenic vein
Where are central arteries located?
White pulp
What surrounds sheathed capillaries?
Macrophages
What part of the red pulp do sheathed capillaries empty blood into?
Splenic cords
What kind of cells line the splenic sinusoids?
Endothelial cells
What surrounds the tonsils?
1/2 surrounded by stratified squamous epithelium
1/2 surrounded by Hemi-capsule
What are the invaginations found on the tonsils called?
Crypts
What happens to crypts during infection?
Pus collects in the crypts
Why is only half of the tonsil surrounded by a capsule?
So that antigens can come into contact with the tonsils on the part which doesn’t have hemi -capsule i.e epithelial cell covered part
Do tonsils have follicles?
Yes
Where are Peyer’s patches found?
Distal end of small intestine in the wall
Describe structure of a Peyer’s patch
Clusters of lymphoid follicles with germinal centres
What is immunity?
Resistance to disease
What are the two intrinsic systems of the immune system?
- innate immunity (non-specific)
- adaptive immunity (specific)
What are the innate defences?
-surface Barriers
-internal defences
What are the types of surface barrier that play a role in innate immunity ?
Skin
Mucous membranes
What are the internal defences which play a role in innate immunity ? (5)
-phagocytes
- natural killer cells
- inflammation
-antimicrobial proteins
-fever
What are the 2 types of adaptive immmunity ?
- Humoral/antibody mediated immunity
- cellular immunity
What cells are involved in humoral immunity ?
B cells
what kind of cells are active in cellular immunity ?
T cells
What are the 3 types of phagocytes involved in innate immunity?
Macrophages
Neutrophils
Eosinophils
What do natural killer (NK) cells do?
Cause apoptosis in cancer/virus infected cells
What happens to B lymphocytes during humoral immunity?
-they become plasma cells
-they secrete antibodies
What do antibodies do?
Mark cells for destruction by macrophages
What are memory B cells?
Some B cells which are activated during humoral immunity do not become plasma cells.
They are primes to respond to the same antigen upon second infection
What do cytotoxic T cells do?
- bind to antigen presenting cells
-perforate the cell membrane - this signals the cell to undergo apoptosis
What do dendritic cells do?
Capture antigens and deliver them to lymph nodes
In lymph nodes, what are medulllary cords?
Found in the medulla between medullary sinuses.
Filled with plasma cells & macrophages
What is the capsule of a lymph node composed of?
Connective tissue
What are trabeculae in the lymph nodes made of?
Connective tissue
