Haem Week 2 Flashcards
Where does embryological haematopoeisis take place?
The yolk sac
What is the primary site of erythropoiesis in foetal life?
The liver and the spleen
What are the three stages of foetal haematopoeisis?
Mesoblastic (yolk sac)
Hepatic (liver)
Myeloid (bone marrow)
What proportion of the skeleton marrow produces blood cell in a foetus?
All of it
What is red marrow replaced by in adult life in areas where haematopoeisis doesn’t take place?
Adipose tissue (yellow marrow)
Where is bone marrow found?
The medullary cavities of long bone and cavities of cancellous bone
Under what circumstances can yellow marrow be converted to red marrow?
Hypoxia
What are the two most common sites of extra medullary haematopoeisis?
Liver and the spleen
What is the ratio of immature white blood cells to red blood cells in marrow?
How can this be explained?
3:1
The lie span of WBC is much shorter, only hours to a few days. RBC’s Can survive up to 120 days, therefore more WBC must be produced to keep supply in the blood.
What cell gives rise to all types of blood cell?
Pluripotent haematopoetic stem cell
What are the type of progenitor cell gives rise to RBCs and granulocytes?
Myeloid stem cell
What progenitor cell gives rise to lymphocytes?
Lymphoid stem cells
What is a colony forming unit?
A progenitor cell which has developed a committed cell lineage
What cells can the GEMM colony form in unit produced?
Granulocyte, erythrocyte, monocyte and megakaryocyte
What determines the way in which blood stem cells differentiate?
Cytokines (regulatory glycoproteins)
What is the general trend in cell size as it progresses from stem cell to adult committed cell type?
Decreases in size, ratio of cytoplasm to nucleus increases
What are the different stages in RBC maturation?
Proerythropblast, basophilic erythroblast, polychromatic erythroblast, ortho chromic erythroblast, reticulocytes, mature RBC
At what stage of erythropoiesis does haemoglobin begin to appear?
Polychromatic erythroblast
At what stage of erythropoiesis is the nucleus no longer present within the cell?
Reticulocytes
How long does it take for a red blood cell to form from a pluripotent stem cell?
5-9 days
What does an increased level of circulating reticulocytes indicate?
Increased levels of erythropoiesis.
This is because reticulocytes circulate form1-2 days bro becoming mature RBC
What dictates the rate of growth of cells undergoing erythropoiesis?
Growth factors - erythropoietin and thrombopoietin
Where is erythropoietin formed?
Kidneys
What is the stimulus for the release of erythropoietin?
Hypoxia ( which can be caused by low blood volume, low haemoglobin, poor blood pressure etc)
What is the net effect of erythropoietin?
Stimulates all stages of erythropoiesis - including release of reticulocytes into the bloodstream
What role does vitamin B12 and folic acid have in erythropoiesis?
They are essential for the synthesis of DNA as they are cofactors for enzymes which help make DNA building blocks. RBC are rapidly replacing themselves so DNA replication is going on more frequently.
What type of anaemia occurs when vit b12 or folic acid are deficient?
Macrocytic anaemia.
The cells can’t divide as rapidly due to impaired DNA formation, so the cells grow bigger than normal before dividing. Membranes often flimsy and too big to fit through capillaries
Why are the kidneys an appropriate site for determining the release of erythropoiesis?
25% of cardiac output goes through the kidneys, so it has enough blood supply to determine whether oxygen levels in the blood are adequate.
What other hormones can increase the rate of erythropoiesis?
Thyroxin, testosterone, ACTH, Cortisol and Growth hormone
What is haemoglobin composed of?
A haeme group attached to four globin chains
What role does haeme play in RBC?
It is the porphyrin compound which binds the Fe2+ ion and is the site at which oxygen binds during gas exchange
What is the HbA1 and HbA2 haemoglobin composed of?
HbA1 is 2 alpha and 2 beta globin chains (95% of people)
HbA2 is 2 alpha and 2 delta globin chains
What are the proteins which can store iron?
Ferritin and hemosiderin
Which protein transports iron in the blood?
Transferrin
Where is the majority of iron found in the body?
Haemoglobin (65%) and ferritin stores in the liver (15-30%)
How many oxygen molecules can a haemoglobin molecule carry?
4
Does carbon dioxide compete with oxygen for a binding site on the haemoglobin?
No, carbon dioxide binds to a protein side chain - not the iron in the haeme group
Can haemoglobin exist outside of RBCs?
Only in specific places - neurons, liver etc. It cannot survive in the plasma without being inside a RBC
Why is haemoglobin higher in foetal life?
The foetal haemoglobin hasn’t greater affinity for oxygen and somoxygen isn’t released as easily into tissue. Therefore there is a degree of hypoxia which triggers more haematopoeisis and therefore more red blood cells
How much oxygen can one gram of haemoglobin carry?
1.34 mL
Why do red blood cells have a limited life span?
Do not contain nucleus or cell organelles and no ability to synthesise proteins and maintain, repair damage. Membrane loses flexibility and fragments.
Where do most RBC get destroyed?
In the spleen, liver and bone marrow?
In what way do red blood cells get destroyed and reused?
The spleen has very small capillary spaces that act as a sieve which forces blood cells to squeeze through. Old and damaged cells burst. Macrophages clean up, amino acids and iron recycled and haeme reduced to bilirubin
