Immunology - Haematology Flashcards
Define haematopoeisis? Erythropoiesis?
- The production of cells that circulate in the bloodstream.
- Specifically, erythropoiesis is the process by which red blood cells (erythrocytes) are produced.
Where does erythropoiesis occur:
- in the very early foetus?
- from 2-5 months gestation
- from 5 months gestation
- in the yolk sac
- in the liver and spleen
- in the bone marrow
When erythropoiesis is inadequate in the bone marrow, what can this trigger? Where is this commonly seen?
- This can trigger extramedullary haematopoiesis – i.e. haematopoiesis occurring outside the marrow
- This is commonly seen in haemoglobulinopathies, in particular thalassaemias and myelofibrosis.
What does the production of all blood cells begin with?
- A multipotent haematopoietic stem cell –> a haemocytoblast
- Haemocytoblasts differentiate into common myeloid progenitor cells OR common lymphoid progenitor cells The
- The common myeloid progenitor cells –> these then differentiate into erythrocytes and other cells
What cell line are erythrocytes from?
Common myeloid progenitor
What cell line are T and B lymphocytes from?
Common lymphoid progenitors
What cell line are natural killer cells from?
Common lymphoid progenitors
What cell line are macrophages, mast cells, basophils, neutrophils and eosinophils from?
Common myeloid progenitors
Which hormone drives erythropoiesis? What secretes this hormone?
- Erythropoietin (EPO), which is a glycoprotein cytokine
- Secreted by the kidney
- It is constantly secreted at a low level, sufficient for the normal regulation of erythropoiesis.
If the erythrocyte level becomes inadequate, what happens to the O2 levels in the blood? How does this then affect EPO levels?
- The blood becomes relatively hypoxic
- When there is a reduced partial pressure of oxygen (pO2) in the kidney, this is detected by the renal interstitial peritubular cells.
- In response, there is a surge in EPO production, which acts in the bone marrow to stimulate increased red blood cell production.
- This causes haemoglobin levels to increase, subsequently causing the pO2 to rise and therefore EPO levels to fall.
What is the mononuclear phagocyte system (MPS)?
- An important part of the innate immune system.
- It serves as a network of phagocytic cells in the blood and lymphatic system as well as the lymph nodes, liver and spleen.
What is the main role of the MPS?
- Identify foreign antigens and mount an appropriate immune response.
- These antigens are phagocytosed before they have a chance to cause further harm to the body.
- Additionally, the MPS plays a key role in the destruction of old and dysfunctional cells
- Allows the body to recycle key materials such as iron.
What is the primary cell of the MPS?
The phagocyte
What are common phagocytes?
- Macrophages
- Dendritic cells (derived from monocytes)
- Granulocytes
Monocytes are formed in the bone marrow and circulated in the blood, from where they migrate into surrounding tissues. Here, what do they mature into?
Either tissue histiocytes or macrophages.
How are macrophages further classified?
According to the organ they reside in
What are macrophages called in the:
- CNS
- Liver
- Lungs
- Skin and mucosa
- Microglial cells
- Kupffer cells
- Alveolar macrophages
- Langerhans cells
What is the function of the spleen?
- The spleen is formed from both red pulp and white pulp.
- Red pulp: endothelial macrophages
- Play a key role in ensuring that defective or ageing red blood cells are phagocytosed
- White pulp: contains B and T lymphocytes
- Any antigen presenting cell passing through the spleen can stimulate activation of the lymphocytes to mount an appropriate immunological response.
- Red pulp: endothelial macrophages
- Spleen serves as pool for platelets and red blood cells
- Can be rapidly mobilised when needed
What does the lymphatic system consist of?
-
Lymphatic vessels and lymph nodes which act to filter tissue fluid from the blood
- Lymph nodes house B and T lymphocytes
What are the macrophages in the liver called? Where do they reside?
-
Kupffer cells
- Reside in the vessels forming the capillary beds of the liver, known as sinusoids.
As blood enters the liver via the portal vein and drains into the sinusoids, what is role of Kupffer cells?
- Remove foreign materials through phagocytosis
- They stimulate a local inflammatory responses using cytokines and oxygen radicals.
How are Kupffer cells also involved in the metabolism of red blood cells and haemoglobin?
- The haem portion is further broken down into iron for immediate reuse or for storage, whilst the globin chains are reused
- Bilirubin is conjugated here and secreted in the bile.
