HISTOLOGY 1.7.: THE BLOOD
Blood is a fluid connective tissue that circulates through vascular channels
to carry nutrients and oxygen to the cells and waste products to the excretory
organs and carbon dioxyde to the respiratory organ.
Total volume in percentage of body weight:
large domestic animals: 8-11 %
common laboratory animals: 6-7 %
Components:
cellular (blood corpuscles):
erythrocytes
platelets (thrombocytes)
leukocytes:
neutrophils
eosinophils granulocytes
basophils
lymphocytes agranulocytes
monocytes
ECM: 1./ plasma:
91-92 % water
8-9 % solutes: inorganic: ions, electrolytes
organic:proteins (albumins,globulins)
glucose
lipids, etc.
2./ fibers:
fibrinogen dissolved in plasma – fibrin (clothing)
Microscopic preparation of blood for light microscopic studies
An evaluation is often needed to assess general health, or to diagnose
haematologic and some other diseases.
Blood test is used for this purpose. For light microscopic observation one drop
of blood is enough spread onto the surface a slide.
The blood film is air-dried, fixed in methanol and stained with Giemsa
Blood corpuscles
1. Erythrocytes (red blood cells)
Non-nucleated biconcave discs: dog, cow, sheep.
Shallow concavity: horse, cat
Flat shape: pig, goat
Size and number also varies among species
SEM image of blood
LM image of a blood smear
1. RED BLOOD CELLS (ERYTHROCYTES)
Size:
7 mm the largest (in dog)
4.1 mm the smallest (in goat)
Number in 1 mm3 of blood:
in the range of N x 106
(depending on size)
Origin: red bone marrow
Life span: some months only (120 days)
Destruction: in the spleen
Poikilocytosis: variation in shape (goat, deer)
Rouleaux formation: adherence to each other, forming long chains
Howell-Jolly bodies: small, round, pyknotic DNA fragments
(remnants of the nucleus)
Reticulocyte: immature red blood cell with residual ribosomes
Rouleaux formation
Howell-Jolly bodies (arrows)
Poikilocytosis
Reticulocyte (arrow)
Fine structure of erythrocytes:
Mature erythrocyte lacks nucleus and cell organelles.
It is a membrane-bound container of hemoglobin (33-36 %)
some enzymes and electrolytes in water.
Biconcave shape is maintained by spectrin at the internal surface
of the membrane
TEM
Main function of the erythrocytes: to carry oxygen to the cells and
to carry carbon dioxyde from the cells to the respiratory organ
Molecular structure of hemoglobin
Heme-part
2. Leukocytes (white blood cells) (5000-9000/mm3):
2.1. Polymorphonuclear granulocytes:
2.1.1. Neutrophils (55-60 %)
2.1.2. Eosinophils (1-3 %)
2.1.3. Basophils (0-0.7 %)
2.2. Mononuclear agranulocytes
2.2.1. Lymphocytes (25-33%)
2.2.2. Monocytes (3-7 %)
2.1.1.
2.2.1.
2.1.1. Neutrophils:
The most segmented nuclei (4-5 lobes)
Size: 10-12 mm
Amount: 3000-6000/ml
Moderately stained pale granules
Function: phagocytosis (microphages)
Origin: red bone marrow
Life span: some hours (7-8)
2.1.1. Neutrophils:
Ultrastructure:
Two types of granules:
• Specific: lysosyme,
lactoferritin, alkaline
phosphatase
• Azurophilic: lysosomal
enzymes (acidic phosphatase, peroxidase,
etc.)
Endothelial cell
Neutrophils are able to
migrate through capillary walls (see the image) to the site of bacterial
infection.
There they phagocyte the bacteria.
Pus: phagocyted bacteria and hundreds of thousands dead neutrophils.
2.1.2. Eosinophils:
Bilobed nuclei (spectacle form in
human)
Bright red eosinophilic granules
(species-specific)
Size: 10-12 mm
Amount: 300/ml
Origin: red bone marrow
Life span: 8-12 days
Function:
Control of allergic reactions
Moderate phagocytotic activity
Defense against parasitic worms
2.1.2. Eosinophils:
Fine structure:
Specific granules are
heterogeneous from
species to species
(various crystal structures
inside).
Content of specific granules:
lysosomal hydrolases,
major basophilic protein
MBP, eosinophilic cationic
protein ECP, eosinophil-derived
neurotoxin, antihistamin,
slow reacting substance
SRS)
TEM
2.1.3. Basophils:
U- or kidney-shaped nucleus
Large purple granules
Size: 10 mm
Amount: very rare
Origin: red bone marrow
Function:
They share common
features with the CT mast cells.
Their granules contain
histamine (allergic reactions,
anaphylaxic shock),
heparin (anticoagulant).
Human
2.2.1. Lymphocytes
Large nucleus, thin cytoplasmic rim
Size: 7-12 mm (large-medium-small)
Origin: red bone marrow
No stained granules in the cytoplasm (except small azurophilic ones)
Types: B- and T-lymphocytes (morphologically not distinguishable)
null-cells (somewhat smaller size)
Function: defence - immunity
2.2.2. Monocytes:
Large kidney-shaped eccentric nucleus
No granules in the cytoplasm except azurophilic small granules
Size: up to 17 mm
Origin: red bone marrow
Function: 1-2 days circulation in the blood, then enter the CT
and trasform into macrophages (see there)
TEM
3. Platelets (thrombocytes):
Minute colorless anucleate corpuscles
Thin biconvex discs
Size: 2-3 mm
Number: 150.000-300.000/ml
Origin: megakaryocytes
Function: blood clothing
TEM
LM
TEM
Blood clothing
Thromboplastin
Prothrombin
Thrombin
Fibrinogen
Ca ions are also needed for the process
Fibrin
The avian blood:
Erythrocytes are nucleated ovoid cells
Thrombocytes are nucleated ovoid cells
Granulocytes are called heterophils (arrows)
Please note: all the submammalian vertebrate animals (fish, amphibians, reptiles)
have similar ovoid nucleated red blood cells