Histology of the Blood |Histology|


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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

3) Neutrophils
-Size              = 9-12 mcm
-Lifespan      = 1-2 days
-Formation   = Leukopoeisis
-Regulation  = Colony Stimulating Factor (CSF)

4) Eosinophils
-Size              = 10-14 mcm
-Lifespan       = 1-2 days
-Formation   = Leukopoeisis
-Regulation   = Colony Stimulating Factor (CSF)

5) Basophils
-Size              = 8-10 mcm
-Lifespan       = Hours to days
-Formation   = Leukopoeisis
-Regulation   = Colony Stimulating Factor (CSF)

6) Monocytes
-Size               = 15-20 mcm
-Lifespan        = 3 days
-Formation    = Leukopoeisis
-Regulation    = Colony Stimulating Factor (CSF)

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

2)Lymphoid Heamopoeisis (Lymphoid Tissue)
-B lymphocytes (Bursae Fibricious)
-T lymphocytes (Thymus)

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!!

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2 responses to “Histology of the Blood |Histology|

  1. 1. cfu n csf – are they the same ?
    2. ape yg dmaksudkan dgn ‘transitional stage goes on’ on 18th w of splenic hemopoiesis? ape yg berubah ?
    3. kalau kat dlm module guide, the last objective is about the comparative ch. of prenatal n postnatal. kalau keluar soalan tu, is that kte kne ckp yg prenatal have 4 phases n so on, while postnatal hemopoiesis happen in BM…is it ?

    thanx, sory byk soalan .. =)

    • Dear Anis
      1 – CFU is NOT the same with CSF. CFU (Colony Forming Unit) is a progenitor cells meanwhile CSF (Colony Stimulating Factor) is a cytokine released to control the rate pf leukocytopoeisis
      2 – Trnastitional period on Splenic Heomopoeisis means that the Spleen is at first having only MYELOID HEMOPOEISIS but after the invasion of Lymphocytes into the Spleen and start to generate there, LYMPHOID HEMOPOIESIS is now happening. At this time Spleen is transiting from MYELOID to MYELOID and LYMPHOID and eventually ONLY LYMPHOID UNTIL WE DIE
      3 – YUP, just to remind you, never forget that PRENATAL is considered to be HISTOGENESIS HEMOPOEISIS (formation of new cells) and POSTNATAL is considered to be PHYSIOLOGICAL REGENERATION OF BLOOD TISSUE

      Good luck! =)

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