This document discusses platelets and the process of hemostasis. It notes that platelets form from megakaryocytes in the bone marrow, do not have nuclei, and play an important role in clotting. When platelets come into contact with collagen in damaged blood vessels, they swell, adhere to collagen, and secrete substances that activate nearby platelets, forming a platelet plug to stop bleeding. Blood coagulation further involves the conversion of prothrombin to thrombin and fibrinogen to fibrin fibers that trap platelets and blood cells to form a clot.

1.  Agranulocyte
 20-45% of WBCs
 Spherical, dark-staining nucleus
 Thin rim of blue staining
cytoplasm
 Each lymphocyte recognizes and
acts against a specific antigen

2.  T lymphocytes can attack foreign cells directly
(17.6)

3.  B lymphocytes transform into plasma cells and secrete
antibodies

4.  Hemostasis means prevention of blood loss and this
achieved by:
1. Vascular constriction
2. Formation of a platelet plug
3. Formation of blood clot
4. Growth of fibrous tissue into the blood clot

5.  After blood vessel has been cut, the smooth muscle
wall contract; this immediately reduces the flow of
blood from the ruptured vessel

6.  Platelets or thrombocytes
 Formed in the bone marrow from megakaryocytes
 Do not have nuclei
 Function in the clotting process.
 Normal value – 150,000 to 300,000/cubic millimeter.
 It has a half life in the blood of 8 – 12 days, its functional
process run out over several weeks
Formation of platelet plug

8. 1. Contractile protein thrombosthenin that can cause
the platelet to contract
2. Endoplasmic reticulum that store Calcium ions
3. Mitochondria capable of forming ATP
4. Enzymes that can synthesize prostaglandins which
involves in local tissue reactions
5. Contain fibrin stabilizing factor
6. Growth factors that causes vascular cells to grow and
multiply

9.  Platelet begin to swell and assume irregular forms
when comes in contact with collagen fibers
 They become sticky so that they adhere to collagen in
the tissue
 They secrete ADP and form thromboxane which
activate nearby platelets
 The damaged vascular wall activates increasing
numbers of platelets thus forming platelet plug. (In
small vessels the platelet plug is all that is
necessary to stop the bleeding).

10. 1. Exposed collagen binds
and activate platelets
2. Release of platelet
factors
3. Attract more platelets
4. Aggregate into platelet
plug

11.  Blood coagulation take place in three steps
1. As result of rupture blood vessels, formation of
prothrombin activator (protein manufacture in the
liver)
2. Conversion of prothrombin to thrombin in the
presence of calcium
3. The thrombin acts as enzyme to convert fibrinogen
(blood protein) into fibrin fibers that enmesh platelet,
blood cells and plasma to form clot
 Note: vitamin K is required by liver for formation of
prothrombin

12. Prothrombin
Prothrombin Ca
Activator
Thrombin
Fibrinogen Fibrinogen monomer
Ca
Fibrin fibers
Activated fibrin
Stabilizing factor
Cross linked fibrin fibers

13.  SEM of a clot with platelet, fibrin mesh, rbc’s
The clot composed of meshwork of fibrin fibers entrapping blood
cells, platelets and plasma

15.  Prothrombin activator is generally formed in two ways
1. Extrinsic pathway (begins with trauma to the
vascular wall)
2. Intrinsic pathway (begin with the blood)

17.  Preventing blood clotting in vascular system is
1. Smoothness of the endothelial cell surface
2. Layer of glycocalyx on the endothelium
3. Protein bound with the endothelial membrane
thrombomodulin which binds thrombin

18.  The most important anticoagulant in the blood
1. Fibrin fibers
2. Antithrombin III or antithrombin-heparin cofactor
 Both fibrin fibers and antithrombin acts as
antithrombin
 About 85-90% of thrombin becomes adsorbed to the
fibrin fibers
 The thrombin that does not adsorb combines with
antithrombin III which block the effect of thrombin

19.  Heparin is anticoagulant, low concentration in the
blood
 Effectiveness of antithrombin III increases when it
combines with heparin
 Heparin is formed by basophilic and mast cell

20.  Plasma protein contain euglobulin called plasminogen
when activated becomes plasmin
 Plasmin resemble trypsin
 Plasmin digest fibrin fibers and other protein
coagulants
 Plasmin caused lysis of a clot

21.  Injured tissue release activator called tissue
plasminogen activator (t-PA) which convert
plasminogen to plasmin

23. Red blood cells White blood cells Platelets
1 Site of
formation
formed in bone
marrow,
life-span:
4 months
formed in bone
marrow or thymus
formed in
blood
marrow
2 Shape biconcave discs,
no nucleus,
red colour
phagocytes:
irregular,
lobed nucleus &
granular cytoplasm
irregular
shape,
no nucleus,
tiny pieces
of cell
fragments,

24. Red blood cells White blood cells Platelets
3 Size small in size some large &
some small
tiny cell
fragments
4 Number 5,000,000 /mm3
7,000 /mm3 250,000/mm3
5
Function
contain
haemoglobin to
carry oxygen
from lungs to
all parts of
body
phagocytes kill
pathogens &
digest dead cells
lymphocytes
produce
antibodies for
killing pathogens
for blood
clotting

25.  Albumin
 Helps control osmotic pressure
 Helps control diffusion of water
 Globulin
 Includes antibodies (Abs)
 Transport proteins (lipids, iron, copper, etc.)
 Fibrinogen
 Involved in clotting

26.  All the albumin and fibrinogen and 50 – 80% of
globulin are formed in the liver
 The reminder of the globulin are formed in the
lymphoid tissues

27. Total protein: 4.2 - 5.6 g/dl
Albumin: 2.3 - 3.5 g/dl
Globulin: 1.9 – 2.1 g/dl

28. 66 kDa
ALBUMIN
Accounts for ~50% of the total plasma protein and ~ 50%
of the total liver protein production
 Half-life ~ 20 days
 Highly polar
 At pH 7.4 it is anionic with 20 negative charges per molecule

30. Functions of albumin
Maintenance of the osmotic pressure of plasma
Transport of free fatty acids

31. Globulin is made up of different proteins called alpha,
beta, and gamma types.
Some globulins are made by the liver, while others are
made by the immune system.
Other globulins transport metals, such as iron, in the
blood and help fight infection.