form 5 biology chapter 1 transport (b).docx

Form 5 Biology Chapter 1 Transport (b)

Mechanism of Blood Clotting

Question 4: What is the importance of blood clotting for human body system?

Blood Clotting Mechanism – A Minor Cut

1. The collagen fibres in the connective tissue at the wall of the vessel are exposed

to blood.

2. The platelets stick rapidly to the collagen fibres and release chemicals that make

the platelets sticky

3. The aggregation of platelets forms a plug called a platelet plug to stop blood

loss.

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Blood Clotting Mechanism – A Major Cut

When the damage in the vessel is severe, the plug is reinforced by a clot of

fibrin which is formed through a series of steps

a) The clumped platelets, the damaged cells and clotting factors in the plasma

form activators (thromboplastins).

b) These activators or thromboplastins, together with calcium ions and vitamin

K, convert the prothrombin (an inactive plasma protein) to thrombin (an

active plasma protein).

c) Thrombin, in turn, catalyses the conversion of the soluble protein fibrinogen

in blood plasma into the insoluble fibrin. Fibrin is a fibrous protein which

combines to form a mesh of long threads over the wound, trapping red

blood cells and sealing the wound.

d) The resulting blood clot hardens when exposed to air to form a scab.

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Problem related to blood clotting

1. Some people suffer from the disease haemophilia. They lack the gene

necessary for the production of certain clotting factors, for example, Factor

VIII. This is an example of impaired clotting mechanism.

2. Haemophilia causes serious bleedling particularly in the joints. In severe cases,

haemophiliacs may die of internal or external bleeding.

3. Certain clotting factors such as Factor VIII can now be produced by genetic

engineering and is used in the treatment of haemophilia.

4. A blood clot is sometimes formed on the damaged rough inner wall of an

artery. This clot is called thrombus.

5. The thrombus may cause blockage of the artery and the condition is known as

thrombosis.

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6. When the thrombus dislodges and is transported away by the bloodstream, it is

known as an embolus. The embolus may be trapped in a small artery and it

may block the flow of blood. The condition is called embolism.

7. If the coronary artery is partially blocked, the condition is called angina. It

may cause chest pains especially during strenuous physical exercise.

8. A total blockage cuts off the supply of oxygen and nutrients to the heart

muscles. It causes a heart attack (myocardial infarction) and the affected

muscles are damaged. If only a small area of muscle cells dies, the patient can

recover.

9. A stroke occurs if there is a blockage of arteries carrying blood to the brain

cells.

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[SBP 2015]

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Signs of Heart Attack & Stroke (Extra Reading)

Heart Attack

The most common heart attack symptom is chest pain or discomfort. This

includes new chest pain or discomfort or a change in the pattern of existing

chest pain or discomfort.

Most heart attacks involve discomfort in the centre or left side of the chest that

often lasts for more than a few minutes or goes away and comes back. The

discomfort can feel like uncomfortable pressure, squeezing, fullness, or pain.

The feeling can be mild or severe.

Heart attack pain sometimes feels like indigestion or heartburn. Chest pain or

discomfort that doesn't go away or changes from its usual pattern (for example,

occurs more often or while you're resting) can be a sign of a heart attack. All

chest pain should be checked by a doctor.

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Other Common Signs and Symptoms

Upper body discomfort in one or both arms, the back, neck, jaw, or upper part

of the stomach

Shortness of breath , which may occur with or before chest discomfort

Nausea (feeling sick to your stomach), vomiting, light-headedness or sudden

dizziness, or breaking out in a cold sweat

Sleep problems, fatigue (tiredness), or lack of energy

Stroke

Face Drooping: Does one side of the face droop or is it numb? Ask the person

to smile.

Arm Weakness: Is one arm weak or numb? Ask the person to raise both arms.

Does one arm drift downward?

Speech Difficulty: Is speech slurred, are they unable to speak, or are they hard

to understand? Ask the person to repeat a simple sentence, like "the sky is blue."

Is the sentence repeated correctly?

Time to call 9-1-1: If the person shows any of these symptoms, even if the

symptoms go away, call 9-1-1 and get them to the hospital immediately.

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Lymphatic System

The Formation of Interstitial fluid and Lymph

1. The minute spaces between tissue cells are called interstitial spaces.

2. The interstitial spaces are filled with a colourless liquid called interstitial fluid

or tissue fluid.

3. The formation of interstitial fluid and lymph:

a. Blood enters the arterial ends of the capillary network under high

pressure.

b. Endothelial cell walls of the capillaries act as filter, holding back relatively

the large cellular components (such as red blood cells) and the large

protein molecules of the blood, but allowing water and other dissolved

substances of the plasma (oxygen, products of digestion and hormones)

to pass through.

c. Hence, at the arterial end of these capillaries, blood plasma is filtered through

the capillary walls into the interstitial spaces to form interstitial fluid.

d. This process of producing interstitial fluid from the blood is called

ultrafiltration.

e. The interstitial fluid once formed, circulates among the tissue cells and

returns to the blood circulatory system in two ways:

f. Passes into the venous end of the capillaries

g. Drains into the lymph capillaries as lymph

h. Lymph and interstitial fluid have the same composition; the difference is

that interstitial fluid is found between cells, while lymph is found inside the

lymph vessels.

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The composition and Importance of Interstitial fluid

1. The composition of tissue fluid is similar to plasma, but without proteins

(which remain in the blood capillaries).

2. The importance of interstitial fluid:

(a)The interstitial fluid is the internal environment of the body.

b) Exchange of substances occurs between the interstitial fluid and the body

cells

c) Dissolved nutrients and oxygen diffuse into the cells and are used by the

cells metabolism, and the waste products and carbon dioxide from the cells

diffuse into the interstitial fluid.

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Structure of the Lymphatic System

1. The lymphatic system is a network of lymph vessels running alongside the

veins.

2. Lymph is found inside the lymph vessels.

3. The composition of lymph is similar to tissue fluid but with more fats (from the

digestive system).

4. Main structures of the lymphatic system:

(a)Lymphatic capillaries are:

i. microscopic closed-ended vessels

ii. larger in diameter than the blood capillaries

iii. located next to blood capillaries in tissue spaces

iv. very permeable to tissue fluid – the cells forming the walls of the lymph

capillaries are loosely fitted together

(b) Lymphatic vessels

i. are formed from the convergence lymph capillaries

ii. resemble veins (have 3-layered walls) but have thinner walls and more

valves

iii. carry lymph away from the tissues

(c)Lymph node

i. is a cluster of small round or oval structures

ii. contains a network of fibres and irregular channels acting like a filter

iii. filters lymph when it flows through the nodes

iv. eliminates bacteria and cellular debris by phagocytosis

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(d) Spleen

i. is an organ located on the left side of the abdomen near the stomach.

ii. produces lymphocytes, filters the blood, stores blood cells and destroys old

blood cells

(e)Lymphatic ducts

i. are the parts of the body where the lymph vessels drain their contents back

into the blood stream

ii. are the left lymphatic duct and right lymphatic duct

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5. The movement of lymph within the lymphatic system:

a) Interstitial fluid drains into the lymph capillaries to form lymph.

b) Lymph capillaries join together to form larger lymphatic vessels.

c) The walls of the lymphatic vessels contain valve-like pores that allow the

entry of cell debris and bacteria.

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d) The contraction and relaxation of the surrounding skeletal muscles

(when the body moves) squeezes and relaxes the lymphatic vessels, pushing

lymph along to the lymph nodes.

e) Numerous semilunar valves within the lymphatic vessels keep the flow of

lymph in one direction.

f) The lymph nodes remove any suspended solids and bacteria from the lymph

by phagocytosis.

g) The lymphatic vessels return the lymph to the heart via two ducts:

(i) the right lymphatic duct drains lymph from the right arm, the right side

of the head and the thorax and opens into the right subclavian vein near

the heart

(ii) the thoracic duct drains lymph from the rest of the body into the left

subclavian vein near the heart.

6. Lymph is moved along the lymph vessels in the following ways:

a) Hydrostatic pressure of the interstitial fluid leaving the blood capillaries

pushes the lymph along the lymphatic capillaries.

b) Lymph is squeezed along the lymphatic vessels as the surrounding skeletal

muscles contract during movement.

c) Valves within the lymphatic vessels ensure that lymph inside them flows

away from the tissues towards the heart.

d) During inhalation, the expansion of the thorax reduces pressure within it,

drawing lymph towards the thorax and away from the tissues.

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The Functions of the Lymphatic System

1. The lymphatic system complements the circulatory system in the following

ways:

(a)Transports interstitial fluid back to the bloodstream.

(b) Distributes fluids and nutrients in the body and drains excess fluids and

protein so that tissues do not swell up.

(c)Transports absorbed fats and fat-soluble vitamins from the small

intestine into blood circulation.

(d) Provides immunological defenses against diseases by:

(i) producing lymphocytes and antibodies to fight and destroy

microorganisms

(ii) filtering out microorganisms and other foreign substances from the

lymph by the lymph nodes and from the blood by the spleen.

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When Interstitial Fluid Fails to Return to the Circulatory System

1. Sometimes too much interstitial fluid is produced, but little or none is re-

absorbed back into the circulatory system.

2. The increase of interstitial fluid causes the organs and tissues of the body to

swell up, causing a condition called oedema.

3. Oedema can be caused by:

(a)an increase in the capillary blood pressure forcing an excess fluid leakage

into the interstitial spaces

(b) a blockage of the lymphatic vessels which slows down the drainage of

excess interstitial fluid

4. Elephantiasis is a disease caused by the blockage of the body’s lymphatic

system by certain parasitic round worms leading to oedema.

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[Terengganu 2013]

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[Perlis 2012]

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[SBP 2012]

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[SBP 2009]

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form 5 biology chapter 1 transport (b).docx

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