Primary Lymphoid Tissue Flashcards
What are primary lymphoid tissues?
They are tissues where lymphocytes develop and mature to a stage where they are able to recognise antigens
What are primary lymphoid tissues also known as?
Central lymphoid organs
What do primary lymphoid tissues consist of?
Bone marrow and the thymus
What are all immune cells derived from?
Haematopoietic stem cells in the bone marrow
What is the bone marrow a site of?
The site of origin of red blood cells and platelets
What are the two main types of bone marrow?
Red and yellow
What is red marrow involved in?
Haempatorpoiesis
What is yellow marrow made up of?
Adipocytes
What is an Adipocyte?
A specialised cell of adipose tissue that stores excess energy in the form of triglyceride droplets and secretes various substances (such as leptin) that plat a role in various physiological processes
What happens when our body requires additional energy?
The droplets of triglyceride contained in Adipocytes undergo enzymatic hydrolysis to produce free fatty acids and glycerol
Where does haematopoiesis take place at birth?
Takes place in all medullary cavities of bone
Where does haematopoiesis take place in adults?
It is restricted to the axial skeleton and all other medullary cavities are left with only Adipocytes
What do lymphocytes descend from?
A common lymphoid progenitor
What do T cells leave the bone marrow as?
Immature progenitors and travel to the thymus, via the blood to complete maturation and undergo selection
What does the thymus sit?
Within the thorax, specifically superior and anterior mediastinum
Where is the thorax positioned?
It is positioned anterior/superficial to the heart and pericardium but posterior to the sternum
What happens to T cells during maturation?
T cells die in the thymus as they fail to produce a T cell receptor that is useful to the immune system
What do pro-T cells do?
They travel to the thymus and enter the cortex
What is positive selection of T cells?
It selects those T cells capable of recognising self MHC molecules and peptides
What do cortical epithelial cells do?
They present antigens to the T cells on MHC 1 and MHC 2
What are major histocompatability complex molecules?
They are the MHC complex molecules responsible for antigen presentation at a cellular level
What are cells that are able to detect MHC-1 go on to become?
Cytotoxic T cells
What are cells that are able to detect MHC class II able to go onto?
Helper-T cells
What happens to the T cell if they don’t recognise the proteins MHC complex?
They will die by apoptosis after four days. 95% of T cells which make it to the thymus fall to this fate
What happens if a T cells successfully recognises the MHC protein complex?
It receives a survival signal which prevents it entering apoptosis
What do surviving T cells advance to?
The medullary region
What happens in the medullary region?
Negative selection takes place - eliminating the T cells which wold recognise self-peptide and therefore be dangerous to the body
What happens in the medulla (dendritic cells)?
The dendritic cells present self antigen to the T cells on MHC1 and MHC2
What happens to the cells that recognise and bind the antigen in the medulla?
They are given the death signal and they are told to undergo apoptosis
What happens to the cells that do not bind after 4 days in the medulla?
They a deemed useful and leave the thymus, entering the bloodstream
