Various Mechanisms that Prevent Blood Loss

Question 1

Hemostasis

Answer 1

(a) A sequence of responses that stops bleeding when blood vessels are injured.
(b) Be sure not to confuse the two words hemostasis and homeostasis.
(c) The hemostatic response must be quick, localized to the region of
damage, and carefully controlled.

Question 2

Three mechanisms can reduce loss of blood from blood vessels

Answer 2

(a) Vascular spasm
(b) Platelet plug formation
(c) Blood clotting (coagulation)

Question 3

When successful, hemostasis prevents hemorrhage

Define hemorrhage

Answer 3

(a) Hemorrhage is the loss of a large amount of blood from the vessels.
(b) Hemostasis can prevent hemorrhage from smaller blood vessels, but
extensive hemorrhage from larger vessels usually requires medical
intervention.

Question 4

. Vascular spasms.
Define
Timeframes

Answer 4

(1) When a blood vessel is damaged, the smooth muscle in its wall contracts
immediately, a response called a vascular spasm.
(2) Vascular spasm reduces blood loss for several minutes to several hours, during
which time the other hemostatic mechanisms begin to operate.

Question 5

Platelet Plug Formation.
Define
Process of platelet plug formation

Answer 5

(1) When platelets come into contact with parts of a damaged blood vessel, their
characteristics change drastically and they quickly come together to form a
platelet plug that helps fill the gap in the injured blood vessel wall.
(2) Platelet plug formation occurs as
follows:
(a) Initially, platelets contact and stick to parts of a damaged blood vessel, such as collagen fibers.
(b) Then, they interact with one another and begin to liberate the chemicals.
(c) The chemicals activate nearby platelets and sustain the vascular spasm,
which decreases blood flow through the injured vessel.
(d) The release of platelet chemicals makes other platelets in the area sticky,
and the stickiness of the newly recruited and activated platelets causes them to stick to the originally activated platelets.
(e) Eventually, a large number of platelets forms a mass called a platelet plug.
(f) A platelet plug can stop blood loss completely if the hole in a blood vessel
is small enough.

Question 6

Blood Clotting.
Define plasma
Process of clot formation

Answer 6

(a) The straw-colored liquid, called serum, is simply plasma minus the clotting
proteins.
(b) The gel is called a clot and consists of a network of insoluble protein fibers
called fibrin in which the formed elements of blood are trapped
(3) The process of clot formation, called clotting (coagulation).
(a) Coagulation is a series of chemical reactions that culminates in the
formation of fibrin threads.
(b) If blood clots too easily, the result can be thrombosis, clotting in an
unbroken blood vessel.
(c) If it takes too long to clot, hemorrhage can result.

Question 7

Clotting is a complex process in which various chemicals known as clotting
factors activate each other.

Name the chemicals

Answer 7

(a) Clotting (coagulation) factors include:
1) Calcium ions (Ca2+)
2) Several enzymes that are made by liver cells and released into the blood
3) Various molecules associated with platelets or released by damaged tissues

Question 8

Clotting occurs in three stages

Answer 8

1) Step 1 – Prothrombinase is formed.
2) Step 2 – Prothrombinase converts prothrombin (a plasma protein formed in the liver with the help of vitamin K) into the enzyme thrombin.
3) Step 3 – Thrombin converts soluble fibrinogen (another plasma protein
made by the liver) into insoluble fibrin.
a) Fibrin forms the threads of the clot (lattice structure like a net).
b) Cigarette smoke contains substances that interfere with this step.

Question 9

Explain clot/fibrin clot

Answer 9

(e) Clot retraction is the consolidation or tightening of the fibrin clot. The fibrin
threads attached to the damaged surfaces of the blood vessel gradually
contract as platelets pull on them.
(f) As the clot retracts, it pulls the edges of the damaged vessel closer together,
decreasing the risk of further damage. Permanent repair of the blood vessel
can then take place.

Question 10

Whats fibroblasts part in all of this

Answer 10

In time, fibroblasts form connective tissue in the ruptured area, and new
endothelial cells repair the vessel lining

Question 11

Fibrinolysis

Answer 11

occurs simultaneously as coagulation occurs