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sec 3 biology 🩺🥼💉🧬🧫 > chapter 8: transport in humans > Flashcards

chapter 8: transport in humans Flashcards

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1
Q

what are the percentages of the components in blood?

A
  • about 55% of the volume of blood is made up of plasma
  • 45% is made up of blood cells and platelets
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2
Q

what is plasma and what does it contain?

A
  • it is a pale yellowish liquid
    > about 90% water and a complex mixture of dissolves substances such as:
  1. soluble proteins like fibrinogen and prothrombin and antibodies
    > fibrinogen and prothrombin play an important part of clotting blood
    >antibodies help fight diseases
    > these proteins are made in the liver
  2. dissolved mineral salts:
    > hydrogen carbonates, chlorides, sulfates and phosphates of calcium, sodium and potassium
    > all these are ions in plasma
    > calcium is essential for blood clotting
  3. food substances like: glucose, amino acids, fats and vitamins
  4. excretory products: urea, uric acid and creatinine
  5. hormones like insulin
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3
Q

how many red blood cells or erythrocytes do we have and what are they?

A
  • about 5 mill of erythrocytes in each cubic milimeter of blood
    > number varies according to gender and state of health of a person
  • each mammalian blood has these features:
    1. contains the pigment haemoglobin
    > a special kind of iron-containing protein
  • haemoglobin combines reversibly with oxygen
    > enables red blood cells to transport oxygen from the lungs to all cells in the body
  1. circular, flattened biconcave disc
    > centre of the cell is thinner than the edge
    > this increases the cell’s surface area to volume ratio
    > cell can thus absorb and release oxygen at a faster rate
  2. it does not possess a nucleus, enabling it to carry more haemoglobin and thus more oxygen
  3. it is elastic and can turn bell shaped- in order to squeeze through blood vessels smaller than itself in diameter
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4
Q

where are red blood cells produced and how long do they last?

A
  • red blood cells are produced by the bone marrow
  • have a lifespan of about 3 to 4 months
  • when they are worn out, they are destroyed in the spleen
  • haemoglobin that is released from destroyed red blood cells is brought to the liver and broken down
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5
Q

what are white blood cells (leucocytes) and what is its ratio to red blood cells?

A
  • leucocytes are larger than red blood cells but are fewer in number
  • ratio of RBC: WBC > 700:1
  • in each cubic millimeter of of blood, only 50,000-10,000 WBC but about 5 million RBC
    white blood cells have:
  • colourless and does not contain haemoglobin
  • irregular in shape and contains a nucleus
  • it can move, change shape and squeeze through walls of the thinnest blood capillaries into the spaces among the tissue cells

two main kind of white blood cells:
> lymphocytes and phagocytes
- white blood cells plays a vital role in keeping the body healthy by fighting diseases
- although they contain a nucleus
> lifespan in the bloodstream is only a few days

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6
Q

what are lymphocytes?

A
  • each lymphocyte has a large, rounded nucleus and a relatively small amount of non-granular cytoplasm
  • tend to be round in shape and only show limited movements
  • they produce antibodies that may protect the body from disease-causing microorganisms
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7
Q

what are phagocytes?

A
  • they can ingest
    > which is to take in and digest foreign particles such as bacteria
  • it has a lobed nucleus and granular cytoplasm
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8
Q

what are blood platelets(thrombocytes?)

A
  • they are not true cells
    > they are membrane-bound fragments of cytoplasm from certain bone marrow cells
  • they play a part in clotting of blood
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9
Q

what causes clumping of red blood cells?

A
  • the surfaces of your red blood cells contain special proteins
    > antigens
  • the same antigens are found on all your red blood cells
  • your blood plasma contains antibodies which are always present in the blood
  • these natural antibodies will not react with the antigens on your blood cells but may with the red blood cells of another person
    > this causes agglutination

eg: agglutination will occur when
> antigen A mixes with antibody a
> antigen B mixes with antibody b

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10
Q

what is a blood group?

A
  • you can be classified into a blood group based on the types of antigens and antibodies present in your blood
  • antigens are represented by A and B
  • antibodies against antigens A and B may be represented by a and b
  • antibody a reacts with antigen A and clumping occurs
    > blood test will tell you which blood group you belong to
    > A, B, AB or O
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11
Q

just read:
if you belong to blood group A, your red blood cells possess antigen A and your serum contains antibody b
- your serum could not contain antibody a or your own red blood cells would agglutinate

A

“When you have a dream, you’ve got to grab it and never let go.”

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12
Q

what are the 3 functions of blood?

A
  • acts as a transport medium carrying various substances from one part of the body to another
  • it protects the body against disease-carrying organisms (pathogens)
  • blood clotting at wounds prevents excessive loss of blood
    > clotting seals the wound and prevents the entry of bacteria into the bloodstream
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13
Q

what digested food does blood transfer?
( + carried from where and to where)

A
  • glucose, amino acids, mineral salts, fats and vitamins are carried
    > from intestines
  • to other parts of the body
  • excess mineral salts are transported to the kidneys for excretion
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14
Q

what excretory products does blood transfer?
( + carried from where and to where)

A
  1. nitrogenous wastes
    > urea, uric acid, creatine
    > from all parts of the body
    - to the kidneys
  2. carbon dioxide
    > carried as hydrogencarbonate ions in plasma
    > from all parts of the body to
    - lungs, where hydrogencarbonate ions are converted to carbon dioxide and expelled
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15
Q

where do blood carry hormones from and to where?

A
  • carries hormones from glands to target organs
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16
Q

where does blood carry heat from and to?

A
  • carries heat from respiring body tissues
    > eg muscles
  • to all parts of the body to maintain a uniform body temperature
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17
Q

where does blood carry oxygen from and where to?

A
  • blood carries oxygen from lungs to all parts of the body for cellular respiration
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18
Q

how does blood transport oxygen to the cells of the body?

A
  • as blood passes through the lungs,
    > oxygen diffuses from the alveoli into the blood
  • haemoglobin has a great affinity for oxygen, haemoglobin can combine reversibly with oxygen
    > in lungs, where oxygen level is high, haemoglobin in the red blood cells combine with the oxygen to form oxyhaemoglobin
  • red blood cells then transports oxyhaemoglobin to all the tissues of the body
  • as blood passes through tissues ( containing very little oxygen), oxyhaemoglobin releases its oxygen
    > the oxygen then diffuses in solution into the tissue cells
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19
Q

what is coagulation of blood?
( what happens when someone’s blood doesn’t clot?)

A
  • blood exposed to air will form a solid lump
  • the clot seals the wound to prevent the loss of excessive blood
    > clot also prevents foreign particles from entering the bloodstream
  • when people suffer from a heredity disease called haemophilia
    > the normal blood-clotting mechanism is greatly impaired
    > slight injuries may cause such a person to bleed to death or die of internal bleeding
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20
Q

describe the process of blood clotting.

A
  • when blood vessels are damaged, damaged tissues and blood platelets release an enzyme known as thrombokinase
  • thrombokinase converts the protein prothrombin, usually present in plasma into thrombin
    > ( calcium ions need to be present before this can take place)
    -thrombin is also an enzyme which catalyses the conversion of the soluble protein fibrinogen into insoluble threads of fibrin

> fibrin threads entangle blood cells and the whole mass forms a clot or a scab
clot seals the wound to prevent the entry of microorganisms

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21
Q

does blood clot in undamaged blood vessels?

A
  • normally, it does not clot
    > dues to presence of anti-clotting substance (heparin)
    > heparin is produced in the liver
  • when thrombokinase is released, it neutralises the action of heparin > so clotting takes place
  • when blood clots, a yellowish liquid called serum in left behind
    > serum has the same composition as plasma except that it lacks the clotting factors
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22
Q

what are the three reactions of the clotting process?

A
  1. damaged tissues and platelets > (produce) > thrombokinase
  2. prothrombin inactive > (thrombokinase and calcium ions) > thrombin active
  3. fibrinogen > (thrombin) . insoluble fibrin threads form mesh to trap blood cells
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23
Q

what are the two blood circulation systems? explain.

A

pulmonary circulation:
- deoxygenated blood is transported from the heart to the lungs, and returns oxygenated blood back to the heart
systemic circulation:
- oxygenated blood is transported from heart to the body, and returns deoxygenated blood back to the heart

24
Q

describe adaptations at high altitudes

A
  • there is a lower concentration of oxygen at higher altitudes
  • people living at high altitudes have more red blood cells to compensate for these low concentrations
  • increasing the number of red blood cells increases the amount of haemoglobin in the blood
  • thus more oxygen can be transported to the body cells per unit time
  • this is known as acclimatisation
25
Q

how are antibodies produced? and how do they act?

A
  • when disease causing organisms ( pathogens) such as bacteria and viruses gain entry into the bloodstream
    > they stimulate the lymphocytes to produce certain chemical substances called antibodies
  • antibodies protect our bodies against diseases
  • they act by:
    > destroying the bacteria (eg. by attaching to them, causing the bacterial surface membrane to rupture
    > causing the bacteria to clump together or agglutinate so that they can be easily ingested by the phagocytes
    > neutralising the harmful substances ( toxins) produced by bacteria
26
Q

how are antibodies used?
(the possible sources of antibodies)

A
  • antibodies may stay in the blood long after the disease has been overcome
    > thus, a person who has recovered becomes immune or resistant to that infection
  • some types of dead bacteria are sometimes injected into the bodies of certain animals
    eg. horses, to induce the formation of antibodies in the blood
  • antibodies are extracted from the animal’s serum and injected into human beings to protect them from certain diseases
  • antibody production may also be directly induced in the human body by exposing the person to dead or weakened forms of the pathogen
    > process: immunisation / vaccination
  • the dead or weakened form of pathogen stimulates the person’s immune system to produce antibodies against the pathogen
  • your immune system includes white blood cells and their products (eg. antibodies)
  • immune system causes an immune response to foreign particles
    > helps keep body free from diseases
27
Q

what is organ transplant and tissue rejection?

A
  • when a person’s tissue or organ is damaged or diseased, it can be replaced by a healthy tissue or organ from a donor
    > called: organ or tissue transplant
  • organ transplanted must not be rejected by the recipient’s immune system
  • any organ from another person can be treated as a foreign body by the recipient’s immune system
    > recipient’s lymphocytes may respond by producing antibodies to destroy the transplanted organ
  • tissue rejection will not be a problem is the tissue to be transplanted comes from the same person
28
Q

how can people prevent tissue rejection?

A

-a tissue match is necessary to reduce the risk of rejection
> the tissues of both the donor and recipient must be as genetically close as possible
> siblings, parents and close relatives of a recipient are likely to have similar genes

  • immunosuppressive drugs can also be used
    > it inhibits the responses of the recipient’s immune system
  • however there are problems such as:
    > the recipient has a lower resistance to many kinds of infections
    > the recipient has to continue taking the drug for the rest of his or her life
29
Q

what is a circulatory system and what does it consist of?

A
  • it is a closed system of blood vessels
  • when blood flows in the circulatory system, it is called blood circulation
  • it consists of:
    1. heart
    2. arteries
    3. arterioles
    4. blood capillaries
    5. venules
    6. veins
30
Q

what is the heart and what does it do?

A
  • it is a muscular pump which keeps blood circulating throughout the body
  • when the heart relaxes, it fills up with blood
  • when it contracts, blood is squeezed out with great force
    >the blood then circulates through the blood vessels which direct the blood flow round the body
31
Q

what are arteries and what is its function?

A
  • it is a blood vessel that carry blood away from the heart
  • the large artery that leaves the left side of the heart is the aorta
    > branches to form smaller arteries
32
Q

what are arterioles?

A
  • the arteries branch again to form tiny vessels called arterioles
  • arterioles divide and ultimately their branches become very tiny blood vessels called capillaries
33
Q

what are blood capillaries and what are its functions?

A
  • capillaries are microscopic blood vessels that are found between cells of almost all tissues
    >they have walls that are only a single layer of flattened cells called the endothelium
    > endothelium is partially permeable which enables certain substances to diffuse quickly through the capillary walls
  • capillaries branch repeatedly
    > the numerous branches provide a large surface area for the exchange of substances between blood and tissue cells
    > when an arteriole branches into capillaries, the total cross-sectional area increases
    > this lowers the blood pressure in the capillaries
    >the flow of blood is slowed down, giving more time for the exchange of substances
34
Q

what are venules?

A
  • before the capillaries leave an organ or tissue they unite to form small veins called venules
35
Q

what are veins?

A

venules in turn join to form bigger veins
> veins carry blood back into the heart

36
Q

what are arteries?
( structure and function)

A
  • arteries receive blood directly from the heart
  • need to withstand the immense pressure of the blood as it is forced out of the heart
  • arteries have walls which are thick, muscular and elastic
  • the elastic layer is much thicker in the arteries nearest to the heart
  • thick elastic walls help to withstand the high blood pressure in the artery
  • this elasticity enables the artery wall to stretch and recoil or spring back
    > this helps push the blood in spurts along the artery and also gives rise to the pulse
  • the contraction and relaxation of muscles in the arterial wall
    > contraction and dilation of the artery
  • when the artery constricts, its lumen becomes narrower and less blood flows through it per unit time
  • on the other hand, when an artery dilates, its lumen becomes wider and more blood flows through it per unit time
  • most arteries carry oxygenated blood
    > EXCEPT for the pulmonary artery which carry deoxygenated blood from the heart to the lungs
37
Q

what are veins?
( blood pressure)
(valves)

A
  • the blood pressure in the veins is much lower than the blood pressure in the arteries
  • blood flows more slowly and smoothly
  • the walls of the veins need not be as this and muscular than the arteries
  • veins contain less elastic tissue
  • the have valves along their length to prevent backflow of blood
  • valves are folds of the inner walls, shaped like half-moons
    > semi lunar valves
  • the movement of blood along the veins is assisted by the action of skeletal muscles on the veins
  • exercising the muscles increases the pressure exerted on the veins
    > moves blood along more quickly
  • veins carry deoxygenated blood
    > EXCEPT pulmonary veins which carry oxygenated blood from the lungs to the heart
38
Q

what is tissue fluid?

A
  • the tiny spaces between tissue cells contain a colourless liquid
    > tissue fluid (intercellular or interstitial fluid)
  • the tissue cells are bathed with tissue fluid which carries substances in solution between the tissue cells and the blood capillaries
39
Q

how are substances transferred between capillaries and tissue cells?
( dissolved food substances and oxygen)
(excretory waste products)

A
  • dissolved food substances and oxygen diffuses from the blood in the blood capillary into the tissue fluid
    > and then into the cells
  • metabolic ( or excretory) waste products diffuse from the cells into the tissue fluid
    > then through the blood capillary walls into the blood
  • the blood transports these to the excretory organs for removal
40
Q

what are the advantages of red blood cells changing shape as they flow through blood capillaries?

A
  • since blood capillaries are narrow, the red blood cells can only move through the lumen of the blood capillaries in a line
    > one behind the other
  • the red blood cells may become bell-shaped as they pass through narrow blood capillaries

advantages of changing shape:
- the diameter of the red blood cell is reduced so that it can easily pass through the lumen of the capillaries
- the cell increases its surface area to speed up absorption or release of oxygen
- rate of blood flow is reduced, giving more time for, and thus increasing the efficiency of, exchange of materials between the blood and the tissue cells

41
Q

what do the double circulation in mammals consist of?

A
  • pulmonary circulation and the systemic circulation
42
Q

what is the pulmonary circulation?

A
  • blood flows from the main circulation of the body to the heart, then to the lungs and back to the heart again before it is pumped back to the main circulation
  • pulmonary circulation: the circulation linking the hear to the lungs
  • from the heart, the pulmonary artery carry the blood to the lungs
  • oxygenated blood is returned to the heart by the pulmonary veins
43
Q

what is the systemic circulation?

A
  • the circulation of blood around the body
  • oxygenated blood leaves the left side of the heart and is distributed by arteries to all parts of the body
    ( except lungs)
  • veins carry blood from all parts of the body back to the right side of the heart
44
Q

what are the advantages of a double circulation in mammals?

A
  1. the blood entering the lungs is at a lower pressure compared to the blood leaving the heart
    > this ensures that the blood flows more slowly through the lungs, allowing sufficient time for the blood to be well-oxygenated before it is returned to the heart
  2. the heart pumps oxygenated blood at high pressure to the rest of the body (through the systemic circulation)
    > so the oxygenated blood is distributed to the body tissues more quickly
    > helps maintain the high metabolic rate in mammals
45
Q

what is the bag that surrounds the heart?

A
  • the heart is surrounded by a bag called pericardium
  • it is made of two layers of membrane
  • the inner membrane is in contact with the tissues making up the heart
  • between the two pericardial membranes is a fluid while helps reduce friction when the heart is beating
46
Q

what are the four chambers of the heart?
and the muscular wall in between them

A
  1. the upper two chambers are called auricles or ATRIA
    (singular: atrium)
    - the atria have comparatively thin muscular walls since they only force blood into the ventricles which do not require high pressure
  2. the two larger lower chambers are called VENTRICLES
    - ventricles have comparatively thick muscular walls especially the left ventricle
    > it needs to pump blood around the whole body which requires high pressure
    - the right ventricle has thinner walls than the left ventricle
    > it only pumps blood to the lungs which is close to the heart
  3. the right and left sides of the heart are separated by a muscular wall called the MEDIAN SEPTUM which runs down the middle of the heart
    - median septum prevents the mixing of deoxygenated blood in the right side with the oxygenated blood on the left side
    - mixing of deoxygenated with oxygenated blood will reduce the amount of oxygen carried to the tissue cells
47
Q

what paths do the blood take through the heart?
( six steps)
name all the veins and arteries as well

A
  1. deoxygenated blood from various parts of the body is returned to the right atrium
    - deoxygenated blood from the head, neck and arms are returned to the right atrium by a large vein
    > the ANTERIOR or SUPERIOR VENA CAVA
    - blood from the other parts of the body ( excluding lungs) is brought back by the
    >POSTERIOR or INFERIOR VENA CAVA
  2. when the right atrium contracts, blood flows into the right ventricle
    - between the right atrium and right ventricle
    >TRISCUPID VALVE
    > opens when the pressure in the right ventricle becomes lower than the right atrium
    - consists of three flaps
    - these flaps are attached to the walls of the right ventricle by cord-like tendons called CHORDAE TENDINEAE
    - the flaps point downwards to permit easy flow of the blood from the atrium in the ventricle
  3. when the right ventricle contracts
    > the blood pressure forces the flaps of the tricuspid valves to close
    > prevents backflow of blood into the atrium
    - the CHORDAE TENDINEAE prevent the flaps from being reverted into the atrium when the right ventricle contracts
    - blood leaves the right ventricle through the PULMONARY ARCH
    - the pulmonary arch leaves the heart and divide into two pulmonary arteries (one to each lung)
    - semi-lunar valves in the pulmonary arch prevents the backflow of blood into the right ventricle
    • the blood in the pulmonary arteries is slower than the pressure of the blood in the AORTA
      > slows down the rate of blood flow to give more time for gas exchange in the lungs
  5. oxygenated blood is brought back to the left atrium by the PULMONARY VEINS
    - when the left atrium contracts, the blood pressure is higher than in the ventricle
    - this causes the bicuspid valve to open and blood enters the left ventricle
    - the BISCUPID or MITRAL VALVE separates the left atrium from the left ventricle
    - similar to the tricuspid valve except that it has two flaps instead of three
    - when the ventricle contracts, the blood leaves through a large artery, the AORTA
  6. from the aorta, blood is distributed to all parts of the body ( except lungs)
    - the aorta curves upwards from the left ventricle as a U-shaped tube
    - it also possesses semi-lunar valves to prevent backflow of blood into the left ventricle
    - blood entering the aorta is at a very high pressure
    - two small CORONARY ARTERIES emerge from the aorta
    > bring nutrients to the heart muscle
48
Q

what is a cardiac cycle? describe what happens during each cycle.

A
  • cardiac cycle: refers to the sequence of events that takes place in one heartbeat
  1. the atria contract, forcing blood into the relaxed ventricles
  2. after a short pause, the ventricles contract
    - the rise in pressure causes the atrio-ventricular valves ( tricuspid and bicuspid) to close to prevent backflow of blood into the atria
    - this produces a ‘lub’ sound
    - the semi-lunar valves open
    > blood flows from the right ventricle and the left ventricle into the pulmonary arch and aortic arch respectively
  3. as the ventricles contract > atria relaxes
    - the right atrium receives blood from the venae cavae while the left atrium receives blood from the pulmonary veins
    • the ventricles relax
      > the fall in pressure causes the semi-lunar valves to close to prevent backflow of blood from the two arches into the ventricles
      - this produces a softer ‘dub’ sound
      - the AV valves also open and blood flows from the atria into the ventricles
  5. the atria contract again and the whole cycle repeats
49
Q

what is the contraction and relaxation of the ventricles called?

A
  • contraction of ventricles
    > VENTRICULAR SYSTOLE
  • relaxation of ventricles
    > VENTRICULAR DIASYSTOLE
50
Q

what is blood pressure and how is it measured?
( + where is blood pressure the lowest and highest)

A
  • blood pressure: is the force that the blood exerts on the walls of the blood vessels
  • can be measured using an instruments called
    >SPHYGMOMANOMETER
  • the sphygmomanometer consists of an inflatable cuff, a pump and a mercury level gauge
  • the level of mercury in the gauge indicates the blood pressure in the arteries
  • blood pressure is thus always measured in terms of millimeters of mercury
    > blood pressure in the arteries is the highest during ventricular systole when blood is forced into the arteries
    > decreases during the ventricular diastole
  • blood pressure varies in different parts of the body
  • the highest near the aortic arch and becomes weaker the further the arteries are away from the heart
  • blood pressure is low in veins
  • reaches almost 0mm of mercury in the venae cavae just before the venae cavae open into the right atrium of the heart
51
Q

what are the main arteries of the body?

A

the arteries leaving the heart are:
- the pulmonary arteries from the right ventricle
- the aorta from the left ventricle

from the aortic arch, the following arteries are:
- arteries to the head, neck and arms
- the aortic arch curls backward to the left side of the heart and continues downwards as the dorsal aorta

the dorsal aorta distributes blood to regions of the body below the heart
for example, it supplies oxygenated blood through:
-the HEPATIC ARTERY to the liver
-the ARTERIES to the stomach and intestines
- the RENAL ARTERIES one to each kidney

52
Q

what are the main veins of the body?

A

-blood is returned to the heart by the main veins as follow:
- the pulmonary veins bring blood from the lungs to the left atrium of the heart
- the superior (anterior) vena cava returns blood from the head, neck and arms to the right atrium
- the inferior vena cava runs upwards parallel to the dorsal aorta and brings blood to the right atrium

the inferior vena cava collects blood from various veins from the lower parts of the body:
- the RENAL VEIN bring blood from the kidneys
- the HEPATIC vein bringing blood from the liver

the veins from the gut do not open directly into the inferior vena cava
- they unite to form the HEPATIC PORTAL VEIN
> enters the liver and branches into numerous capillaries there
- a ‘portal’ vein is so called because it carries blood from one capillary network to another
- thus the hepatic portal vein arises from capillaries in the gut wall at one end
> and gives rise to the capillaries in the liver at the other end

53
Q

what is coronary heart disease?

A
  • coronary arteries lie on the outside of the heart and carry blood to the muscles in the walls of the heart
  • blood supply to the heart muscles can be greatly reduced due to the occlusion or blockage of the coronary arteries
    > causes heart attack
54
Q

what is a heart attack?

A
  • during a heart attack,
    > blood flow to a particular part of the heart may be completely blocked
    >due to the blocked flow, that part of the heart does not receive sufficient oxygen and nutrients
  • that region of the heart muscle dies
  • extensive heart muscle damage is often fatal
    > as the heart is no longer able to pump blood to various parts of the body
55
Q

what are the causes of the coronary heart disease?

A
  • fatty substances such as cholesterol and saturated fats may be deposited on the inner surface of the coronary arteries
    > atherosclerosis
  • narrows the lumen of these arteries and increases blood pressure
  • such an affected artery develops a ROUGH inner surface
    > increases the risk of a blood clot being trapped in the artery
  • when a blood clot is formed in the artery >THROMBOSIS
  • if it occurs in the coronary arteries, the supply of blood and oxygen to the heart muscles may be completely cut off
    > oxygen needed in aerobic respiration to release energy for the activities of the muscle cells
  • heart muscle cells may be damaged without oxygen and heart attack occurs
  • diet rich in cholesterol and saturated animal fats
  • emotional stress
    -smoking
56
Q

what are the preventive measures against coronary heart disease?

A
  1. a proper diet reduces the risk of atherosclerosis
    - polyunsaturated plant fats should substitute animal fats
    > they do not stick to the inner surface of the arteries and may lower the cholesterol level in the blood
  2. proper stress management helps reduce the risk of a heart attack
  3. avoid smoking
    - cigarette smoke contains nicotine and carbon monoxide that increase the risk of coronary heart disease
  4. regular physical exercise has long term beneficial effects on the circulatory system
    > strengthens heart and maintains the elasticity of the arterial walls
    - the risk of high blood pressure ( hypertension ) can be greatly reduced

sec 3 biology 🩺🥼💉🧬🧫 (20 decks)

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