Ok, once again – Histology. Tadaaa! =)
Ok, this is just a relax discussion, nothing is too complicated, we can get through in a blink of an eye lol
Let us start
Introduction
Erythrocytes or RBCs are :-
1) Biconcave in shape, makes it paler at the center
2) Lifespan of 120 days
3) Produced in red marrow; regulated by erythropoeitin
4) Consist of protein carrying O2 called haemoglobin
5) Stained by eosin dye, means it is basic in nature, with acidophilic in attraction
6) No nuclei and organelle, so that
+ it will give more space for heamoglobin
+ it wont use O2 that it carries (mitochondria uses O2)
Morphology of Erythrocyte
Red cells are biconcave in shape is due to its complex cytoskeleton arrangement. Let me try to simplify it 1) Vertical filament (Anchor)
+Ankyrin
+ Band 3 protein
+ Band 4 protein 2) Horizontal filament
+ Spectrin 3) Protein links both vertical and horizontal filaments
+ 15 actin monomeres
Formation
Erythrocyte formation is called as eryhtropoeisis. This process is then regulated by a hormone called erythropoeitin which released by peritubular capillary endothelial cells of the KIDNEY.
Erythropoeisis takes place at red marrow of long bone in children while flat bone in adults.
Below is the simplified diagram which might help you to understand the process
This whole process needs 15 days to complete one cycle
Meanwhile, reticulocyte needs 2 days to mature into erythrocyte. During this time, it eliminates its organelles.
Teminologies
1) CFU = Colony Forming Unit
2) BFU = Birth Forming Unit
3) CFU-E = Colony Forming Unit Erythrocyte
4) Stem cell = stem cell is not a comitted cell, means it can give rise to other types of cell. Such as:-
+ CFU-S
+ PHSC
5) Progenitor cell = this cell is a commited cell, means it will only give rise to a single mature cell. All CFU except CFU-S are progenitor cells
6) Precursor cell = immature cell, with ending of ‘blast’. Such as
+ Erythroblast
What a nice day today! =) Thinking of discussing a little bit on Histology of the blood.
To most people, blood is like a taboo, but for us; medical student or doctor its like a best friend – its like almost everyday we need to face it. Therefore, we don’t have choice but to know about it.
Today we will try to cover on definition, function, composition, formation and few terminologies.
Introduction
1) Bright to dark red fluid
2) Slightly alkaline pH 7.4
3) Blood is a specialized connective tissue
4) Consist of formed elements:-
-Erythroctes
-Leukocytes
-Plateletes
5) Suspended in a yellowish fluid called plasma
Functions of blood
1) Transportation of :-
-Oxygen
-Carbon dioxide
-Nutrients
-Waste products such as urea
-Nitrogenous products
2) Regulation of :-
-pH
-Temperature
-Electrolytes
-Glucose and cholesterol level
3) Protection against :- -Infection by immunocytes -Blood lost trough coagulation
Blood cells in general 1) Erythrocytes
-Size = 7.1 – 7.9mcm
-Lifespan = 120 days
-Formation = Erythropoesis in red marrow
-Regulation = Erythropoetin released by peritubular capillary cells of kidney
2) Plateletes
-Size = 2-4mcm
-Lifespan = 10 days
-Formation = Thrombopoesis in red marrow
-Regulation = Thrombopoeitin released by liver
7) Lymphocytes
-Size = 7-16 mcm
-Lifespan = 3 days to 20 years
-Formation = Leukopoeisis
-Regulation = Colony Stimulating Factor (CSF)
Those are few simplified characteristics of formed elements in blood.
Ok, now let me discuss a little bit detail on general ideas of blood cells.
Blood cells formation is called hemopoeisis in which all blood cells came as direct descendents of a single mother cell called Pluripotent Hemapoeitic Stem Cell (PHSC).
In general, all blood cells undergo maturation from PHSC to progenitor cells (commited cells) and next to become precursor cells and finally become the mature cells.
For example
Proerythroblast becomes erythrocyte. It is reguated by hormone called Erythropoeitin released by kidney.
Megakaryoblast become thrombocyte (platelete). It is controlled by Thrombopeitin released by liver.
We have a lot of cells in blood, let us simplify them into few categories which are :- 1) Erythrocytes 2) Thrombocytes 3) Leukocytes which further categorized into:- -Agranuocytes (without granules)
+ Monocytes
+ T and B lymphocytes -Granulocytes
+ Neutrophils
+ Basophils
+ Eosinophils
Ok, now is the tricky part; Heamopoeisis
It must be clear that heamopoeisis can be divided based on its location and period of time.
Hemopoeisis based on location 1)Myeloid Heamopoeisis (red marrow)
-Erythropoeisis
-Thrombopoeisis
-Monocytopoeisis
-Granulocytopoeisis
Heamopoeisis based on period of time 1)Prenatal Heamopoeisis – histogenesis of blood tissue. This hemopoeisis concentrates in forming new tissue that will one day becoming the blood tissue. Thats why it is called histogenesis (formation of new tissue)
2)Postnatal Hemopoeisis – This heamopoeisis concentrates in maintaining the already formed blood tissue. This process is called Physiological Regeneratiom of Blood Tissue.
Let us discuss in detail for Prenatal Heamopoeisis.
Prenatal Heamopoeisis can be further divided into 4 phases which are :-
1) Mesoblastic 2) Hepatic 3) Splenic 4) Myeloid
Mesoblastic Heamopoeisis
1) Begins at 2 weeks
2) In the mesoderm at the blood islands
3) Islands of blood
– Peripheral cells become vessel walls
– Remaining cells become erythroblast which will become NUCLEATED erythrocytes
4) 3rd week, vascular network forms
5) Stem cells formed from the yolk sac.
6) Blood containing stem cell enter primodiums (immature organs) in which one day will become heamopoeitic organs.
Hepatic Heamopoeisis
1) Replaced the mesoblastic during 6th week of gestation
2) Erythrocytes still have nuclei
3) Leukocytes appear during 8th weeks of gestation
4) Upgrade from Mesoblastic, has new genesis :-
-Thrombocytopoeisis
– Monocytopoeisis
– Lymphocytopoeisis
5) Center of hemopoeisis starting from 6th week and peak at 6th month
6) Mainly provides the myeloid hemopoeisis
7) Ceases completely after birth
Splenic Heamopoeisis
1) Starts when liver starts to lessen its hemopoeitic activity
2) 14th week – myeloid hemopoeisis only
3) 18th week – transitional stage goes on
4) 23rd week – T lymphocyte precursors invade spleen and B lympocytopoesis happens
5) Before birth – Lymphoid and Myeloid
After birth – Lymphoid only
Medullary Hemopoesis
1) Starts from 4th month of prenatal life
2) 7th to 8th month – main myeloid heamopoeisis in prenatal
3) Retains activity until senile age
Wow! Thats a lot!!! Lol.. I know, never mind, no pressure. At least you read =).
I will discuss in detail for each blood cells in the future. Until then, thank you so much. Good luck by the way!!
Virtual Medic 