Worksheet II:
Circulatory System-Blood
1. Give 2 basic functions of the circulatory system.
_______________________________
_______________________________
2. List 6 things that are distributed by the circulatory system.
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
3. List 2 things that our circulatory systems protects us
from. _______________________________
_______________________________
4. Name the 2 major divisions of the Circulatory
System. _______________________________
_______________________________
5. The cardiovascular division includes the ___________________ and
________________________.
6. The lymphatic system includes the ___________________,
_______________, and _____________.
7. Fluid derived from plasma as it leaks out of the capillary walls and
surrounds cells (filling tissue spaces) is called:
_______________________________.
8. Give 5 functions of blood.
_______________________________
_______________________________
_______________________________
_______________________________
_______________________________
9. Give the statistical information about blood requested below.
a. Normal pH range.
_______________________________
b. Mean temperature.
_______________________________
c. Viscosity range.
_______________________________
d. % of body weight.
_______________________________
e. Average volume of blood in
females.______________________________
f. Average volume of blood in males.
_______________________________
g. Salinity.
_______________________________
10. When a sample of blood is centrifuged for several minutes, the
blood separates into two components:
__a__ and __b__. The per cent of blood occupied by cellular
components is called the __c__. __a__ is a
straw-colored liquid
that contains ions, proteins, and dissolved gases and nutrients.
There are 3 kinds of
__b__: __d__, __e__, and __f__. __d__
have a biconcave shape and account for most __b__ averaging
__g__
% and __h__ % of the total blood volume in males and females,
respectively. __e__ are one of the
body's main lines of defense
against foreign agents. __f__ are important in the circulatory
system to be self-sealing.
a. ______________________________
e. _______________________________
b. ______________________________
f. ________________________________
c. ______________________________
g. ________________________________
d. ______________________________
h. ________________________________
11. Plasma and interstitial fluid have __a__
(similar/markedly different) amounts of electrolytes while
plasma
has __b__ (more/fewer) dissolved proteins than interstitial
fluid. Oxygen is in __c__ (higher/ lower)
concentration while
(and) carbon dioxide is in __d__ (higher/lower) concentration in plasma
than interstitial fluid.
a. ______________________________
c. ________________________________
b. ______________________________
d. ________________________________
12. Name the 3 primary classes of proteins found in
plasma.
______________________________
______________________________
______________________________
13. Identify the plasma protein based on the information given below.
a. 7% of plasma proteins; important in
clotting.
______________________________
b. Antibodies and transport proteins are
examples. ______________________________
c. Help maintain osmotic pressure.
______________________________
d. Accounts for 60% of plasma proteins.
______________________________
14. Name 2 kinds of globulins and give their functions.
______________________________________
______________________________________
15. Give the specific names of 2 kinds of transport
proteins. ______________________________
______________________________
16. Most plasma proteins are synthesized by the:
______________________________.
17. Identify the kind of formed element based on the descriptions given
below and if the formed
element is a leukocyte, give the specific kind
described.
a. Volume is ~ 33% hemoglobin.
______________________________
b. Formed as cytoplasmic fragments of a larger
cell.
______________________________
c. Anucleate and biconcave in shape.
______________________________
d. Nucleus is polymorphic; accounts for 2/3 of all
WBCs.______________________________
e. The most abundant formed element.
______________________________
f. Releases histamine; absorbs basic
stains.
______________________________
g. Second most abundant WBC.
______________________________
h. Smallest formed element.
______________________________
i. Largest formed element.
______________________________
j. ~ 5 million/mm3 in blood.
______________________________
k. ~ 8,000/mm3 in blood.
______________________________
l. ~ 300,000/mm3 in blood.
______________________________
m. Stem cell is a megakaryocyte.
______________________________
n. Absorb acidic stains.
______________________________
o. Absorb both acidic and basic stains.
______________________________
p. Nucleus resembles telephone receiver; elevated in
parasitic worm infections.
______________________________
q. Nucleus large, appears round, but is slightly
indented. ______________________________
r. First line of defense against bacteria at an
injury.
______________________________
s. Large U-shaped nucleus; second line of defense at
an injury. _________________________
t. Granulocyte; but granules very fine.
_______________________________
u. The rarest WBC.
_______________________________
v. Most are housed in lymph nodes and
organs.
_______________________________
w. Granulocyte; granules reddish.
_______________________________
x. Largest agranulocyte.
_______________________________
y. Known as Langerhans cells, macrophages,
etc.
_______________________________
18. Name 3 modifications of RBCs that allow them to carry oxygen
efficiently.
_______________________________
_______________________________
_______________________________
19. Males have _______________ (more/less) erythrocytes per cubic
mm than females.
20. __a__ is a quarternary-structured protein composed of 2
parts: a(n) __b__ unit made up of a
porphyrin ring and __c__ ion
and 4 globular proteins called __d__. It is the __c__ ion that
binds
__e__ forming a chemical called __f__. There are 4 __d__ ,
2 __g__ chains and 2 __h__ chains.
The __b__ sits in the center
of each __d__; therefore, each __a__ molecule can bind __i__ (How
many?) __e__ molecules.
a. ______________________________
e. _______________________________
b. ______________________________
f. ________________________________
c. ______________________________
g. ________________________________
d. ______________________________
h. ________________________________
i.
________________________________
21. The process of RBC formation from myeloid tissue in the __a__ is
called: __b__. This process
is regulated by a hormone called __c__ and
this hormone is released by the __d__ (Give organ.).
a. ______________________________
c. _______________________________
b. ______________________________
d. ________________________________
22. List 3 factors that stimulate erythropoiesis.
____________________________
____________________________
____________________________
23. List, in the correct sequence, 6 kinds of cells formed during
erythropoiesis.
_____________________________
_____________________________
_____________________________
_____________________________
_____________________________
_____________________________
24. Identify the cell type of erythropoiesis described below.
a. Stem cell for RBCs.
______________________________
b. Nucleus absent; rough ER still
present.
______________________________
c. Nucleus, ER, mitochondria all absent.
______________________________
d. The stage that begins synthesis of ribosomes and
hemoglobin.
______________________________
e. Stem cell for all blood cells.
______________________________
f. Nucleus present; hemoglobin concentration
peaking. ____________________________
25. How long does it take to go from a hemocytoblast to an
erythrocyte? ________________________
26. How long do RBCs last in the
body? Males: ________________ Females:
_______________.
27. Erythrocytes that begin leaking cytoplasm are detected by
__a__ and __b__ (Process). Once
inside the __a__ the hemoglobin
molecule is disassembled into 3 parts: the __c__, the __d__
minus
the Fe ion, and the __e__. The __c__ is metabolized into amino
acids which are used by
the __a__ or released to other __f__. The
__d__ is stripped of the __g__ ion and converted to __h__.
The
__h__ is picked up by the __i__ (Organ) and released as a component of
__j__. The __g__ ion
is stored or released into the general
circulation where it binds to a transport protein called __k__.
Developing RBCs absorb the __g__ ion from these __k__. Excess
__g__ ions are stored in the __l__
(Organs) as __m__ (Give both
molecules.).
a. ______________________________
h. _______________________________
b. ______________________________
i. ________________________________
c. ______________________________
j. ________________________________
d. ______________________________
k. ________________________________
e. ______________________________
l. _______________________________
f. ______________________________
m. ________________________________
g. ______________________________
28. Identify the disorder of the blood based on the information given
below.
a. Genetic disorder of mostly Negroid
population; results from a
single amino acid substitution in the hemoglobin
molecule. _____________________________
b. Results from the body's response to high altitude
or exercise; not really a disorder.
_______________________________
c. Production of large numbers of poorly formed WBCs;
mostly lymphocytes.
_______________________________
d. Caused by bone marrow cancer; hematocrit may be
80%; blood viscosity is very high.
_______________________________
e. Caused by lack of vitamin B12; RBCs very
large
and shape varies.
_______________________________
f. An abnormally low count of WBCs; anticancer
drugs
and glucocorticoids can cause.
_______________________________
g. A clot in an unbroken vessel.
_______________________________
h. A moving clot.
_______________________________
i. Deficiency of circulating platelets; spontaneous
bleeding all over body.
_______________________________
j. Caused by missing factors VIII and IX in clotting
pathway. _____________________________
k. WBC count above 11,000 cells/mm3; normal response
to an infection.
________________________________
l. Production of large numbers of poorly formed WBCs;
mostly descendents of myeloblasts.
________________________________
m. Caused by lack of dietary proteins needed to make
Hb. ______________________________
n. Caused by severe bleeding; very low
hematocrit.
________________________________
o. Failure of bone marrow to produce RBCs; caused by
radiation exposure.
________________________________
p. An Rh- women becomes pregnant with her second
Rh+ child; the child dies of:
________________________________
q. Renal failure; agglutination of RBCs; small
vessels
blocked by damaged cells.
________________________________
r. Sac of pus that gets wall off by
collagen.
________________________________
s. A tumor-like growth containing infectious and
resistant
bacteria.
________________________________
29. Answer the questions about the blood groups given below.
a. A person with blood type A has what kind of
antigen(s)? ______________________________
b. A person with blood type B has what kind of
antigen(s)? ______________________________
c. A person with blood type AB has what kind of
antigen(s)? _____________________________
d. A person with blood type O has what kind of
antigen(s)? ______________________________
e. A person that is Rh+ has what kind of antigen(s)?
______________________________
f. A person that is Rh- has what kind of
antigen(s)?
______________________________
g. A person with blood type B has what kind of
antibody(ies)? ____________________________
h. A person with blood type A has what kind of
antibody(ies)? ____________________________
i. A person with blood type O has what kind of
antibody(ies)? ____________________________
j. A person with blood type AB has what kind of
antibody(ies)? ___________________________
k. A person that is Rh+ has what kind of
antibody(ies)?
____________________________
l. A person that is Rh- has what kind of
antibody(ies)?
____________________________
m. An antigen is what kind of molecule?
______________________________
n. An antibody is what kind of molecule?
______________________________
o. A person with Type A blood can, in theory,
receive blood
from type(s):
______________________________
p. A person with Type B blood can, in theory,
receive blood
from type(s):
______________________________
q. A person with Type AB blood can, in theory,
receive blood
from type(s):
______________________________
r. A person with Type O blood can, in theory,
receive blood
from type(s):
______________________________
s. A person with Type O blood can, in theory, donate
blood
to type(s):
______________________________
t. A person with Type A blood can, in theory, donate
blood
to type(s):
______________________________
u. A person with Type B blood can, in theory, donate
blood
to type(s):
______________________________
v. A person with Type AB blood can, in theory,
donate blood
to type(s):
______________________________
w. When antibody A reacts with antigen A what
reaction occurs? _________________________
x. How is erythroblastosis fetalis
prevented?
_______________________________
30. Identify the characteristic of WBCs based on the descriptions given
below.
a. Cytoplasmic extensions form; used for movement and
feeding.
________________________________
b. A form of endocytosis that involves particulate
matter. ________________________________
c. The ability to identify and follow a chemical
trail to the
site of an infection.
________________________________
d. Squeezing between capillary cells and out into
tissue
spaces.
________________________________
e. Clinging to the inner endothelial
wall.
________________________________
f. Antibodies coat a foreign body making it easier
for a
WBC to bind to and engulf.
________________________________
31. Name the 3 kinds of granulocytes.
________________________________
________________________________
________________________________
32. Name 2 kinds of agranulocytes.
________________________________
________________________________
33. List the 5 kinds of WBCs from greatest to least
abundant.
________________________________
________________________________
________________________________
________________________________
________________________________
34. List 4 symptoms of inflammation.
________________________________
________________________________
________________________________
________________________________
35. Identify the chemical mediator based on the information given below.
a. Released from basophils; promotes
vasodilation and
increased permeability of capillaries.
________________________________
b. A group of 20 circulating proteins that pierce and
cause bacteria cells to leak; also enhance effects of
other mediators.
________________________________
c. Induces chemotaxis; causes WBCs to release enzymes
that make kinins; induce pain.
________________________________
d. Formed from the plasma protein
kininogen.
________________________________
e. Sensitize cells to chemical mediators; Released
from
cell membranes.
________________________________
36. During the inflammatory response damaged cells release __a__
that cause diameter increase
of vessels called __b__. __b__
allows __c__ (more/less) blood to flow into the injured area
causing
__d__ (Give symptoms.). Other __a__ increase the
permeability of __e__ and attract
leukocytes by __f__ (Give
process.). Arriving leukocytes cling to the endothelial lining, a
process
called __g__, and squeeze between endothelial cells, a process
called __h__, into the injured area.
As more fluids enter the
area, blood flow gradually __i__ (increases/decreases) causing __j__
(Give symptoms.). Clotting proteins begin to seal the wound. As
more leukocytes aggregate, the
damaged cells are removed and __k__
destroyed.
a. ______________________________
g. _______________________________
b. ______________________________
h. ________________________________
c. ______________________________
i. ________________________________
d. ______________________________
j. ________________________________
e. ______________________________
k. _______________________________
f. ______________________________
37. List, in the correct sequence, 6 major events of
hemostasis and wound healing.
_____________________________
_____________________________
_____________________________
_____________________________
_____________________________
_____________________________
38. The stoppage of blood flow is called __a__. An injury by a blunt
blow initiates an initial
vaso__b__ (constriction/dilation) response by
blood vessels called the __c__. This event __d__
(increases/ reduces) blood loss. A smooth, undamaged,
endothelial
lining has a __e__
(positive/negative/neutral) charge and naturally
repels platelets which are __f__ (positively/negatively/
neutrally)
charged. Damaged vessels have exposed __g__ fibers that create a
__h__ (positive/negative/
neutral) charge in the area and thus __i__
(attract/repel) the __f__ (positively/negatively/neutrally)
charged
platelets. The platelets become sticky and swell, releasing chemicals
such as __j__, __k__,
and __l__. __j__ enhances the __c__, __k__
causes platelets to aggregate, and __l__, a prostaglandin,
also causes
platelet aggregation. Within one minute, platelets fill the
exposed area forming the __m__.
Tissue damage also causes
prothrombin activator to be formed.
The __n__ stage is next in the sequence, but starts
simultaneously with formation of the __m__.
Tissue damage causes __o__
activator to form. __o__ activator converts __p__ to __q__. __q__
converts __r__ to __s__, a long stringy protein that forms a net
trap. This net trap captures escaping
__t__ and also helps stop
the bleeding. The __u__ is formed within 30 to 60 minutes.
__v__, a
protein in platelets, contracts and pulls the __s__ strands
inward and seals the broken vessel. Another
chemical released by
platelets, called __w__, stimulates smooth muscle and fibroblasts to
divide,
rebuilding the vessel wall. After __a__, is __x__, a
process that removes the clot after healing.
This stage is both
important externally because it removes the scab, but even more
important internally
because it prevents the clot from expanding and
blocking blood flow. This clot would be called a(n) __y__.
a. ______________________________
n. _______________________________
b. ______________________________
o. ________________________________
c. ______________________________
p. ________________________________
d. ______________________________
q. ________________________________
e. ______________________________
r. _______________________________
f. ______________________________
s. ________________________________
g. ______________________________
t. ________________________________
h. ______________________________
u. ________________________________
i. ______________________________
v. _______________________________
j. ______________________________
w. ________________________________
k. ______________________________
x. ________________________________
l. ______________________________
y. ________________________________
m. ______________________________
39. In coagulation there are 2 pathways. Name
them.
_______________________________
_______________________________
40. Give 3 similarities between the 2 pathways in question
#39.
_______________________________
_______________________________
_______________________________
41. Give 2 differences between the pathways in question
#39.
_______________________________
_______________________________
42. In fibrinolysis, __a__ is activated by __b__ forming __c__.
a. ______________________________
c. _________________________________
b. ______________________________
43. What 3 factors help prevent clot formation in undamaged vessels.
_____________________________________________
_____________________________________________
_____________________________________________
44. A substance that helps form a blood clot is classified as a(n):
_______________________________.
45. A substance that helps prevent a clot from forming is classified as
a(n): _______________________.
46. Give 3 examples of the answer to question #44.
________________________________
________________________________
________________________________
47. Give 3 examples of the answer to question #45.
________________________________
________________________________
________________________________
48. Why is Vitamin K important in hemostasis?
______________________________________________
49. What is the difference between plasma and serum?
_______________________________________
____________________________________________________________________________________
50. For a bone marrow transplant, which kind of blood cell would be the
most important to transfer? Why?
___________________________________________________________________________________
51. What would happen to the blood and tissue cells if the
albumins were removed? _______________
___________________________________________________________________________________
___________________________________________________________________________________
52. What is blood doping?
_____________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
53. Why is blood doping not always beneficial to the person
trying it? ____________________________
___________________________________________________________________________________
___________________________________________________________________________________
54. Why is it not a serious problem for a type O person to donate
blood to a type A or B individual even
though the person giving the
type O blood possesses A and B antibodies? ________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
55. What would an elevated eosinophil count in a patient
suggest about the patient's condition to a physician?
__________________________________________________________________________
56. What factors prevent clot formation in an undamaged vessel?
_______________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
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Worksheet II:
Answers
1. Distribution of substances and protection.
2. Oxygen, carbon dioxide, nutrients, enzymes, hormones, heat, wastes.
3. Injury (it is self-sealing) and Disease-causing agents.
4. Cardiovascular and Lymphatic
5. Heart/blood vessels
6. lymph vessels, lymph nodes, lymphoid organs
7. interstitial fluid
8. Transports dissolved gases, nutrients, and wastes/Delivers Ez and
hormones/Regulates pH,
temperature, and electrolyte
composition/restricts fluid losses/Defends the body against toxins
and
pathogens/and, if your desperate, maintains homeostasis.
9. a. 7.35-7.45
e. 4-5
liters
b. 100 F or 38 C
f. 5-6
liters
c. 4.5-5.5
g. .90%
d. 7-8%
10. a. plasma
e.
leukocytes (WBCs)
b. formed
elements
f. thrombocytes or platelets
c. hematocrit
g.
42-48%
d. erythrocytes
(RBCs) h. 38-44
%
11. a. similar
c. higher
b. more
d. lower
12. Albumins/globulins/fibrinogen
13. a. Fibrinogen
c.
Albumins
b.
Globulins
d.
Albumins
14. Immunoglobulins (also called antibodies) attack foreign proteins
and pathogens./
Transport proteins carry ions, hormones, and other
substances in the blood.
15. Thyroid-binding globulin/transferrin.
16. liver
17. a. Erythrocyte
n.
Leukocyte, Eosinophil
b. Thrombocytes (=
platelets)
o. Leukocyte, Neutrophils
c.
Erythrocyte
p. L,
Eosinophil
d. L,
Neutrophil
q. L, Lymphocyte
e.
Erythrocyte
r. L,
Neutrophils
f. L,
Basophil
s. L,
Monocyte
g.
Lymphocyte
t. L,
Neutrophil
h.
Thrombocyte
u.
Basophils
i. L,
Monocyte
v. L,
Lymphocyte
j.
Erythrocyte
w. L,
Eosinophil
k. Leucocytes
(Neutrophils)
x. L, Monocyte
l.
Thrombocyte
y. L,
Monocyte
m. Thrombocyte
18. Biconcave shape gives more surface area./Lack of most
organelles allows them to
carry more Hb./Shape also allows stacking and
more efficient transport through small
vessels./They are very flexible.
19. more
20. a. Hemoglobin
f.
oxyhemoglobin
b. heme
g. alpha
c. Fe
h. beta
d. globins
i.
4
e. oxygen
21. a. bone marrow
c.
erythopoietin
b.
erythropoiesis
d. kidney
22. High altitude/hemorrhage/exercise
23.
Hemocytoblasts-->proerythroblasts-→erythroblasts-->normoblasts-->reticulocytes--->erythrocytes
24. a. proerythroblast
d. Erythroblasts
b.
Reticulocyte
e.
Hemocytoblast
c.
Erythrocyte
f.
Normoblast
25. 5-8 days
26. 120 days males; 109 days females.
27. a. leukocytes
h.
bilirubin
b.
phagocytized
i. liver
c. globin
j. bile
d. heme
k.
transferrin
e. Fe
l. liver and bone marrow
f. cells
m. ferritin and hemosiderin
g. Fe
28.a. Sickle-cell anemia
k.
Leukocytosis
b. Secondary polycythemia
l. Myelogenous leukemia
c. Lymphogenous leukemia
m. Nutritional anemia
d. Polycythemia vera
n. Hemorrhagic anemia
e. Pernicous anemia
o. Aplastic
anemia
f. Leukopenia
p.
Erythroblastosis fetalis
g. Thrombus
q.
Transfusion reaction
h. Embolus
r. Abcess
i. Thrombocytopenia
s. Granulomas
j. Hemophilia
29.a. Antigen A
m.
Glycoprotein
b. Antigen B
n.
Protein
c. Both antigens A and B
o. Type A and type O
d. No antigens
p. Type
B and type O
e. Rh+ antigen
q. Types
A, B, AB, and O.
f. Has no Rh antigen
r. Type O
g. Antibody A
s. Types
A, B, AB, and O
h. Antibody B
t. Types
A and AB
i. Antibodies A and B
u. Types B and AB
j. No antibodies to A or B
v. Type AB
k. No antibodies to Rh
w.
Agglutination
l. Antibody to Rh factor
x.
Rhogam shots
30. a. Ameboid motion
d.
Diapedesis
b.
Phagocytosis
e.
Pavementing
c.
Chemotaxis
f.
Opsonization
31. Neutrophils, basophils, eosinophils.
32. Lymphocytes and monocytes.
33. Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils.
34. Redness, heat, swelling, pain.
35. a. Histamine
d. kinins
b. Complement
system e. Prostaglandins
c. Kinins
36.a. chemical mediators
g.
pavementing
b. vasodilation
h.
diapedesis
c. more
i. decreases
d. heat and redness
j.
swelling, heat, &
redness
e. blood vessels
k.
bacteria
f. chemotaxis
37. Vascular spasm,Platelet plug, Coagulation, Clot formation, Clot
retraction, Fibrinolysis.
38.a. hemostasis
n.
coagulation
b. constriction
o.
prothrombin
c. vascular spasm
p. prothrombin
d. reduces
q.
thrombin
e. positive
r.
fibrinogen
f. positively
s. fibrin
g. collagen
t. blood
cells (formed elements)
h. negative
u. clot
i. attract
v. Actomyosin
j. serotonin
w.
platelet-derived growth factor
k. ADP
x.
fibrinolysis
l. Thromboxane
y.
thrombus
m. platelet plug
39. Extrinsic and intrinsic
40. Both are trigger by a damaged vessel./Both depend on Ca++ and
Vitamin K./
Both are the same after factor X is formed.
41. The extrinsic pathway is activated by external tissue damage, the
intrinsic
pathway is activated by damage to the vessel wall. The
intrinsic pathway has
more steps-this makes it less likely to form a
thrombus.
42. a. plasminogen
c. plasmin
b. plasminogen
activator
43. Clotting factors are in inactive state./Clotting factors are
diluted away from injury site./
anticoagulants prevent clot formation.
44. procoagulant
45. anticoagulant
46. prothrombin activator, thrombin, fibrin, factors I through XII.
47. Heparin, Protein C, Antithrombin, etc.
48. It is required by the liver for making clotting factors.
49. Serum is plasma without fibrinogen present; therefore serum does
not clot, but still contains the antibodies.
50. A hemocytoblast would be the most important because it can give
rise to all other blood cell types.
51. Albumins help maintain osmotic forces in the blood. If the
albumins, a solute, were removed the
blood would become hypotonic
relative to the tissues and water would move out into the tissues
causing
them to swell. Blood volume and therefore pressure would
decrease.
52. Blood doping is when an individual has blood removed and then at a
time after their blood cell levels
have returned to normal have the
removed blood returned. This procedure greatly elevates the
oxygen
carrying capacity of the blood for athletic events.
53. A problem with blood doping is that blood volume, viscosity,
and pressure are elevated. The heart has
to work harder to move
blood through the vessels.
54. The best donation is between a type O and a type O (or between A
and A, etc.). Only in emergencies
it is acceptable to for a type
O to become the universal donor. Type O have both antibodies and
these antibodies,
if given to another blood type would attack the
recipient’s blood cells. As long as the donation is small, the
antibodies are very diluted and don't cause coagulation.
55. A parasitic infection.
56. Several things prevent clots from forming in a undamaged
vessels. 1) Coagulation factors are inactive
or inhibited.
2) Clotting factors are diluted in undamaged areas when they are
released.
3) PGI2 (Prostacyclin) prevents platelet aggregation.