BLOOD

The blood vascular system is responsible for transport of:

- oxygene, carbon dioxide

- nutrients, metabolities, hormones and vitamins

- regulation of body temperature, acid-base and osmotic balance

Development: mesenchyme – pluripotential hematopoietic stem cell

Blood consists of two parts:

- formed elements (blood cells- BC) - erythrocytes (red BC), leukocytes (white BC), platelets

- plasma (the liquid in which are suspended blood cells) – contains water, inorganic salts,

proteins, amino acids, vitamins, hormones, lipoproteins

Hematocrit: estimation of the volume of formed elements per unit volume of blood: 42-47%

Volume: about 5,5 l in adult human body

Department of Histology and Embryology, P. J. Šafárik University, Medical Faculty, Košice

BLOOD: Syllabus for dental and general medicine students

Author: doc. MVDr. Iveta Domoráková, PhD.

Hematocrit: estimation of the volume of erythrocytes per unit volume of blood. The normal value in the

adult men is 40-50% and 35-45% in the adult women.

If anticoagulants (heparin or citrate) are added to the glass tube with blood, than centrifuged, blood is

separated into:

lower, red coloured layer – consists of erythrocytes (45% of entire volume of blood in the glass tube),

thin layer immediately above, grayish in colour (buffy coat) – consists of leukocytes and platelets (1% of

the blood volume)

and on the top is translucent, yellowish, viscous supernatant – blood plasma (54%).

Blood removed from circulatory system will clot. This clot contains formed elements and separated yelow

liquid is called serum.

45%

1%

54%

blood in the glass tube

after centrifugation

RED BLOOD CELLS (Erythrocytes)Shape:

- biconcave shape, without nuclei, life span: 120 days

- never leave the circulatory system!

Diameter:

• normocytes: 7,5 µm in diameter, 2,6 µm thick at the

rim, 0,8 µm in the centre

• macrocytes grater than 9 µm

• microcytes smaller than 6 µm

Anisocytosis – presence of Ec with varying size

The normal concentration of Ec in blood

- 5,5 milion / µl in men

- 4,5-5,5 mil/µl in women

Decreased concentration of Ec - anemia

Increased number of Ec – erythrocytosis or polycythemia

Ec contain a 33% solution of hemoglobin, oxygen-carrying protein (basic protein,

- acidophilia of Ec)

Hemoglobin + oxygen = oxyhemoglobin

Hemoglobin + carbon dioxide = carbaminohemoglobin

Hemoglobin + carbon monoxide = carboxyhemoglobin - is irreversible!

Mature Ec - no organells

Younger Ec - reticulocytes (1% of the volume of circulating Ec) = immature

stages of Ec released by the bone marrow into bloodstream, contain ribosomal

RNA - basophilic granules.

PLASMALEMMA of erythrocytes:

40% lipid, 50 % protein and 10 % carbohydrate

Specific peripheral membrane proteins are responsible for special

shape and flexibility of Ec: fibrilar proteins spectrin and actin are bind to

peripheral proteins with ankyrin and serves as membrane skeleton.

LEUKOCYTES (white blood cells)

Number: 6.000-10.000 /µl

Leukocytes are classified to two groups:

GRANULOCYTES (polymorphonuclear Lc)

- segmented nucleus - 2 and more lobes

- specific granules : neutrophilic, eosinophilic, basophilic

- azurophilic granules (stained purple) are considered to be primary lysosomes

contain: acid phosphatase, lysozyme, myeloperoxidase

AGRANULOCYTES (mononuclear Lc)

- no specific granules

- presence of azurophilic granules - bind the azure dyes

- nucleus round or kidney shaped

Function: cellular and humoral defense of organism against foreign material

(antigens - Ag)

Leukocytes leave blood capillaries by diapedesis and enter the connective tissue!

1.GRANULOCYTES

a / NEUTROPHILS: 60-70%

Diameter 12-15 µm

2 types of small granules, invisible in the LM

Specific granules: membrane limited 0,3 µm,

contain enzymes : alkaline phosphatase, collagenase,

lactoferrin, lysozyme

Azurophilic granules: primary lysosomes

Nucleus:

segmented 2-5 lobes (usually 3 lobes – 41%) linked

by chromatin bridges

nonsegmented (band form) - the immature

neutrophil

Life span: 6-7 hours in blood, 1-4 days in connective

tissue

Function:

phagocytosis of small particles (bacteria)

neutrophils are called microphages

b / EOSINOPHILS: 2-4 %

Diameter : 12 – 15 µm

Nucleus : bilobed, glass-shaped

Specific granules - eosinophilic: 0,3 – 1,0 µm,

(200 granules per cell)

Granules contain enzymes: acidic phosphatase,

hydrolytic enz., peroxidase, major basic protein

Increased number of eosinophils is associated

with allergic reactions and parasitic infection

Function: eosinophils modulate inflammation by

inactivation of the leukotriens and histamine,

phagocytosis of Ag-Ab complex

c / BASOPHILS: less than 1 %

Diameter : 12 – 15 µm

Nucleus : less heterochromatic, divided into

irregular lobes, S-shaped or kidney shaped

Basophilic specific granules: 0,5 µm,

irregular in shape and size, stained

basophilic or metachromatically

Granules contain: heparin and histamine

(similarity with mast cells)

- production of leukotrienes

- immediate hypersensitivity reaction

2. AGRANULOCYTES

a / LYMPHOCYTES: 25-30%spherical shape

Nucleus – spherical with condensed

chromatin (heterochromatin, dark basophilic

nucleus)

Cytoplasm - thin rim, slightly basophilic with

azurophilic granules (lysosomes)

Size: small 6-8 µm, medium 10-12 µm, large

18 µm (activated by specific Ag)

Life span: some live a few days, others for

many years

The site of lymphocyte development and differentiation

into immunocompetent cells with specific integral

membrane proteins:

T – lymphocytes develop in the thymus;

Function: cellular imunity

B - lymphocytes develop in the bone marrow;

Function: humoral imunity (immunoglobulins)

T - LYMPHOCYTES: 80% of lymphocytes, very long life

After activation by specific antigens (Ag) - proliferate and differentiate into effector

cells:

1. helper T cells - positively regulate the activity T and B cells, produce lymphokines

(MQ)

2. supressor T cells - inhibition of T and B cells, supress autoimmune diseases

3. cytotoxic cells / killer - secrete substances that kill tumor cells, viruses-infected cells

and foreign grafts

B - LYMPHOCYTES: 15%

After activation by specific Ag differentiate into effector cells - plasma cells (Ig)

NULL CELLS - 5%

circulating stem cells that have neither T nor B lymphocyte surface antigens

Immunologic memory -

T and B lymphocytes after activation by specific Ag remain inactive - memory cells

Upon subsequent exposure to the specific Ag - effector cells

Detailed study of lymphocytes (types, function in lymphatic system

– Junqueira: Basic histology)

b / MONOCYTES: 3-8% of leukocytes

Diameter: 12-20 µm

Nucleus: pale oval, horse-shoe or kidney-

shaped

Cytoplasm: basophilic with fine azurophilic

granules (lysosomes) giving it blueish color

Function: They represent precursors of the

monocyto-macrophage system

histiocytes, chondroclasts, osteoclasts,

microglia in the nerve tissue, alveolar

macrophages in the lung, Kupffer cells in the

liver...

After crossing of the capillary wall they enter

to the connective tissue - differentiation into

MACROPHAGES and Ag presenting cells

PLATELES (Thrombocytes)

200-400 000/µl

Diameter 2-4 µm

Life span: 10 days

nonnucleated disc-like cell fragment originated from the

fragmentation of megakaryocytes (bone marrow cells)

LM + EM:

LM: Peripheral hyalomere - light blue, pale basophilic

EM:

- open canalicular system,

- marginal bundles of microtubules keep ovoid shape,

- actin microfilaments - platelet movement and

aggregation

- Mitochondria

LM: Central granulomere – dark purple

EM:

- purple, azurophilic alpha granules - fibrinogen (visible

in LM)

- delta granules - Ca2+, ADP, ATP, pyrophosphate,

serotonin (visible in EM like dense granules)

- lambda granules - lysosomal enzymes

Function: promote blood clotting

help repair injury in the blood vessel walls

dark purple

granulomere

PLATELES (Thrombocytes) formation:

- nonnucleated disc-like cell fragments, originated from the fragmentation of large cells -

megakaryocytes that are present in the bone marrow

- parts of megakaryocyte cytoplasm cross through the capillary endothelium,

- fragments of cytoplasm cleave and become platelets flowing in the blood

Activated platelets change in shape to become more spherical, and

pseudopods form on their surface. Thus they assume a stellate shape.

platelets+ erythrocytes+fibrin

Postnatal blood cell development

Red bone marrow lies entirely within the spaces of bone, in the medullary cavity of young, long bones and

the spaces of spongy bone (short bones, skull). Active hemopoiesis.

Bone marrow consists of:

1. blood vessels, capillary sinusoids

2. supporting rericular cells, macrophages

3. small amount of adipocytes

4. hemopoietic tissue = developing blood cells arranged in cords

• development of blood cells occurs strictly in the bone marrow;

• matured cells cross the wall of capillary sinosoids and enter to the blood.

Location of red bone marrow

in adults (black)

Cavities in the spongy bone are

filled with bone marrow

Yellow bone marrow – innactive bone marrow, lies in the

medullary cavities of the long bones of the arms, legs, fingers

it is composed of adipocytes & reticular connective tissue,

blood vessels

hemopoiesis is stopped, but when necessary: e.g. severe

loss of blood, it can revert to active red bone marrow

Prenatal blood cell development

1. Mesoblastic period - in the wall of yolk sac; red blood cells develop from mesenchymal cells.

2. Hepato-lienal period - in the liver and spleen.

3. Medullary period – starts in the bones, when bone marrow is created.

For development of erythrocytes are essential substances: hormone erythropoietin (produced in the

kidney), iron, folic acid, vitamine B12.

Red blood cell maturation, a cell undergoes a series of differentiations (find why the cytoplasm change the

staining – accumulation of ribosomes (cytoplasm is basophilic), hemoglobin synthesis , releasing of the

nucleus out of the cell).

The following stages of development - within the bone marrow:

1. HEMOCYTOBLAST a multipotent hematopoietic stem cell

2. PROERYTHROBLAST

3. BASOPHILIC ERYTHROBLAST (early erythroblast; lot of ribosomes)

4. POLYCHROMATOPHILIC ERYTHROBLAST (late erythroblast; ribosomes + increase of hemoglobin)

5. ORTHOCHROMATIC ERYTHROBLAST (normoblast; high content of hemoglobin) + nucleus is expelled

normoblast becomes a RETICULOCYTE (small amount of polyribosomes, which are lost soon)

. reticulocytes

(1% )