TRANSPORT OF MATERIALS IN LIVING THINGS
Introduction
The basic characteristics of all
living things are nutrition, respiration, excretion, growth and development,
movement, reproduction and sensitivity. In order for these life processes to
take place, there must be transportation of materials. Materials are
transported either from the environment into the organism or from one part of
the organism to another. They can also be transported from the organism into
the environment.
For example, during nutrition,
organisms take in food substances that they need to provide them with energy.
The food must also be transported to all parts of the organism. Respiration
requires oxygen, which must be taken in from the environment. During excretion,
waste materials from the organism are transported to the excretory organs and
removed from the body. Growth requires the production and transportation of
growth hormones to the growing parts of the organism. Movement and locomotion
are made possible by the transportation of impulses to the relevant organs.
Reproduction requires the movement of gametes (sex cells) or the transportation
of genetic material. Sensitivity is made possible by the transportation of
messages about the presence of a certain thing in the environment.
Transportation is therefore very
important for the survival of living things.
Transportation is therefore very
important for the survival of living things.
Ways of transportation of materials
Life processes in organisms take
place at the cell level. Therefore, it is necessary for substances to move in
and out of the cells. There are two ways through which substances can move
across the cell membrane:
Passive transport; which occurs spontaneously without the need of energy to
transport materials through the cell membrane.
Active transport; where the cell has to use energy to move materials across
the cell membrane.
Processes like diffusion, osmosis
and mass flow involve passive transport.
Diffusion
Diffusion is the movement of
particles from an area of high concentration to one of low concentration.
A difference in the concentration of a substance between two regions is known as a concentration gradient. Diffusion causes particles to move from the area of high concentration to a low concentration area. This process continues until the particles are distributed evenly throughout the liquid. Figure below shows the diffusion of potassium permanganate in water.
FACTORS AFFECTING RATE OF DIFFUTION
- Concentration gradient: high diffusion rate with higher concentration and
vice versa
- Surface area to volume ratio: the higher it faster the diffusion rate.
- Distance over which diffusion takes place: example a thin layer of cells increases diffusion
rate
Osmosis
Osmosis is a form of passive
transport considered as a special form of diffusion involves movement of water
molecules through semi-permeable membrane.
Osmosis defined as the process by
which water move from a weak solution into a strong through a semi-permeable
membrane. The semi permeable membrane is only permeable to some solutes
(dissolved substances).
For osmosis to take place there must
be two separated solution by a semi-permeable membrane. One solution should
have greater water and a lesser quantity of solute than other solution. This
solution is hypotonic, it has a lower water potential. The second should have a
lesser volume of water andvolume of solute than the other solution. This
solution is hypertonic, meaning it has greater water potential.
Two solutions have the same water potential are said to be isotonic
Effects of osmosis in living
organisms
Osmosis and animal cells
When an animal cell is put in a
hypotonic solution, it absorbs water. If it remains in the solution for a long
time, it absorbs excess amounts of water. A cell that does not have a mechanism
for removing the excess water bursts due to the excessive internal pressure.
When an animal cell is placed in a
hypertonic solution, it loses water. If it remains in the solution for a long
time, it loses a lot of water, shrinks and shrivels.
These effects of osmosis on animal
cells can be observed in red blood cells. Under normal conditions, the osmotic
pressure of red blood cells is equal to that of the blood plasma, i.e. they are
isotonic. Thus, there is equal movement of water in and out of the cells. This
helps to maintain the disc shape of these cells.
When red blood cells are put in a
hypotonic solution, they absorb water, causing the cell volume to increase.
Excessive amounts of water cause haemolysis (bursting).
When red blood cells are put in a hypertonic solution, they lose water, leading to shriveling of the cell. This is referred tocrenation
Osmosis is important for the
reabsorption water in the colon and the kidneys. This help to maintain the
body's water balance.
Osmosis and plant cells
In an isotonic solution,
plant cells neither lose nor gain water. In a hypotonic solution cells absorb
water, causing the cell membrane to push against the cell wall. The cell is to
be turgid. It does not burst because membrane exerts pressure on the cell wall
restricts additional intake of water. Turgid plants to maintain their shape.
In a hypertonic solution, plant
cells lose water this causes the vacuole to shrink and their cell membrane to
pull away from wall, making the cell flaccid. Such a cell is to be
plasmolyzed and the process plasmolysis.
If a plasmolyzed cell is placed in a hypotonic solution, it absorbs water and becomes turgid.
Osmosis is importantforthe absorption of water by plant roots. Opening and closing of stomata also depend on osmosis. When guard cells absorb water the stomata open and when they lose water the stomata close.
Osmosis and unicellular organisms
Unicellular organisms that live in fresh water, for example amoeba and euglena, are hypertonic to surrounding so water enters the organisms by osmosis. These organisms have a contractile vacuole. The contractile vacuole collects the excess water and removes it from the cell. This prevents the cells from bursting
Mass flow
Mass flow is the bulk movement of substances from one region to
another due to the difference in pressure between the two regions. Mass flow
occurs within a cell or along a vessel.
This mode of transport is important
in large complex organisms where substances are required in large amounts and
also have to be transported over large distances.
Examples of systems where mass flow
occurs are:
- The circulatory system (flow of blood) in animals.
- The lymphatic system (flow of lymph) in animals.
- Transport of manufactured food material in plants from the site of manufacture (mostly leaves) to the point of use (all plant parts) through the phloem. This process is called translocation
Differences between diffusion,
osmosis and mass flow
The following table gives a summary
of the differences between diffusion, osmosis and mass flow.
Differences between diffusion,
osmosis and mass flow
|
Characteristics |
Diffusion |
Osmosis |
Mass flow |
|
Substance transported |
liquids and gases |
Water molecules |
Solids and liquids |
|
Transportation |
None structure |
Semi permeable membrane |
Cytoplasm and vessel |
|
Causes of movement |
Diffusion gradient |
Osmotic pressure |
Different in pressure |
Chapter summary
- Transport is necessary for the movement of substances
within, into and out of cells so as to enable vital life processes to
occur.
- Transport can be carried out through diffusion, osmosis
or mass flow.
- Diffusion is the movement of particles from a region of
high concentration to a region of low concentration.
- Osmosis is the movement of water molecules from a weak
solution to a strong solution through a semi-permeable membrane.
- A hypotonic solution has a lower water potential.
- A hypertonic solution has a higher potential.
- A red blood cell haemolysis in a hypotonic solution and
crenates in a hypertonic solution.
- A plant cell becomes turgid in a hypotonic
solution and plasmolyzed in a hypertonic solution.
- Mass flow is the bulk movement of substance due to
pressure differences in two regions.
TRANSPORTATION IN MAMMALS
Introduction
Mammals are complex multicellular
organisms. Their bodies are made up of numerous cells and tissues. Hence,
diffusion alone is not enough to ensure efficient carrying out of life
processes. Mammals therefore have an elaborate transport system called the
circulatory system. The circulatory system is made up of the heart, the blood
and the blood vessels.
The mammalian heart
An example of the mammalian heart is
the human heart. The human heart is approximately the size of a clenched fist.
It is located in the chest cavity between the two lungs.
The external structure of the mammalian heart
The wall of the heart is made up of the cardiac muscles. Cardiac muscle is never fatigued (tired). It works continuously as long as a person is alive. This type of muscle is found only in the heart.
The wall of the heart has three
layers:
The epicardium is the outer protective layer.
The myocardium is the middle layer.
The endocardium is the inner most layer. This layer is continuous with the
lining of the blood vessels attached to the heart.
The coronary artery supplies the
heart with oxygenated blood. The coronary vein carries blood containing waste
materials away from the heart.
The vena cava and pulmonary vein
bring blood from the rest of the body to the heart. The aorta and pulmonary
artery transport blood from the heart to the rest of the body.
The internal structure of the mammalianheart
Figure shows a longitudinal section
of the mammalian heart
The heart has four chamber right auricle, right ventricle, left auricle and left ventricle. The auricles are also called atria (singular: atrium). The walls of the ventricles are thicker than those of the auricles. This is because the ventricles pump blood to a greater distance than the auricles. Auricles pump blood to the ventricles. Ventricles pump blood to all other parts of the body. The left ventricle is thicker than the right ventricle because the right ventricle pumps blood to the lungs while the left ventricle pumps blood to the rest of the body.
The heart has several valves. Valves
have flaps that ensure that blood flows in one direction only. The tricuspidvalve
is found between the right auricle and right ventricle. The bicuspid valve
is found between the left auricle and left ventricle. Semi lunar valves are
located at the bases of the pulmonary artery and aorta to prevent blood from
flowing back into the ventricles.
Valves close when blood tries to
flow back.
The left and right sides of the
heart are separated by the septum. The septum is a thick muscular wall
that prevents mixing of oxygenated and deoxygenated blood.
The flow of blood through the heart;
The vena cava brings deoxygenated
blood to the heart. Deoxygenated blood contains low amounts of oxygen.
The vena cava has two branches:
The superior vena cava which transports deoxygenated blood from the upper parts of the body such as head, neck and upper limbs.
The inferior
vena cava which
transports deoxygenated blood from the lower parts of body such as the lower
limbs, kidney, liver, stomach and intestines.
The inferior vena cava and the
superior vena cava unite to form the vena cava; the vena cava is
connected to the right auricle.
When the right auricle relaxes, it
fills up with deoxygenated blood from the vena cava. There is increased
pressure in the right auricle when the muscles contract. This pushes the blood
trough the tricuspid valve. The muscles of the
Right ventricles relax and it fills
up with blood. The tricuspid valve closes to prevent blood from owing back into
the right auricle. When the right ventricle is full, the increased pressure
causes the muscles to contract and the Semi lunar valve in the pulmonary artery
to open. The blood flows into lie pulmonary artery and the bicuspid valve
closes prevent back flow of blood.
The pulmonary artery transports
blood to the lungs. Blood absorbs more oxygen in the lungs, and thus becomes
oxygenated.
Oxygenated blood flows to the heart
through the pulmonary vein. This vein is connected to the left auricle. When
the left auricle relaxes, the semi lunarvalve opens and blood from the
pulmonary veinflows in. Pressure increases in the left auricle as itfills up
with blood. The pressure causes the musclesof the auricle to contract and pump
blood throughthe bicuspid valve into the left ventricle.
The muscles of the left ventricle
contract, allowing blood to flow in. The bicuspid valve closes to prevent blood
from flowing back into the left auricle. Pressure builds up in the left
ventricle as blood flows in.
The muscles of the left ventricle
contract, pumping blood through the semi lunar valve into the aorta. The aorta
branches into smaller arteries that transport blood to all parts of the body.
The heart beats in such a way that when the auricles contract, the ventricles
relax and vice versa.
In the right atrium, there is a
small patch of muscle called the sinoatrial node (SAN). This node acts
as a pacemaker, setting the time and rate of cardiac muscle contraction.
Adaptations of the heart to its
functions
Table below shows how the heart is adapted to its functions.
Adaptations of the heart
|
Adaptation |
Function |
|
Muscular
walls |
Contract to pump blood |
|
Cardiac muscle |
Contract and relax continuously
without being fatigued. This ensures continuous pumping of blood |
|
Valves |
Ensure blood flows in only one
direction |
|
Septum |
Separates oxygenated blood from
deoxygenated blood |
|
Connection to large blood vessels |
Enables transportation of deoxygenated
blood from all parts of the body to the heart and transportation of
oxygenated blood from the heart to all parts of the body |
|
Sinoatrial node |
Sets time and rate of contraction
of cardiac muscle |
|
Coronary artery and coronary vein |
The coronary artery nourishes the
heart and supplies it with oxygen, The coronary vein
removes wastes which would harm the heart if left to accumulate |
Blood vessels
Mammals have three types of blood
vessels: arteries, veins and capillaries.
Arteries
Arteries are thick-walled, muscular and elastic vessels that transport blood from the heart to all parts of the body. All arteries transport oxygenated blood, except the pulmonary artery which transports deoxygenated blood from the heart to the lungs
The endothelium is the
innermost layer of the artery. It has only one layer of cells. The endothelium
surrounds the lumen (the central tube of the vessel). The lumen of an
artery is narrow and smooth so that it can transport blood at high pressure.
The muscular layer is made of smooth
muscle and elastic fibres. Smooth muscle is arranged in circles round the
endothelium. This layer makes it possible for the artery to contract and relax
for the efficient movement of blood.
The outermost layer is the fibrous
layer made of connective tissues such as collagen. The fibres are arranged
parallel to the length of the vessel. They enable the artery to withstand the
pressure caused by the blood coming from the heart.
When the ventricles contract, the
arteries relax allowing blood from the heart to flow into them. When the
ventricles relax, the arteries contract, forcing the blood forward. This
contraction and relaxation of arteries is felt as a pulse.
Pulse rate is the number of pulses
per minute. The pulse rate reflects the heartbeat. An adult human’s heart beats
at an average of 72 times a minute. However, this can increase or
decrease due to physical activity, emotional state or health factors
Arteries branch to form arterioles.
Arterioles in turn branch to form capillaries. Capillaries are joined at
the other end by venules which join to form veins.
Veins
Veins are vessels that transport
blood to the heart from all parts of the body. All veins transport deoxygenated
blood except the pulmonary vein. The pulmonary vein transports oxygenated blood
from the lungs to the heart
Veins have a larger lumen and less muscular walls compared to arteries. This is because the blood in the veins flows at low pressure.
Vein have valves at regular
intervals. The valves prevent the back flow of blood.
The muscles next to the veins squeeze the veins and help to force blood to flow towards the heart. The contraction of the ribs during breathing also helps to squeeze some veins and keep blood flowing.
Capillaries
Capillaries are the smallest blood vessels. They are narrow and have walls that are one cell thick
Capillaries are in direct contact
with the tissues of the body. They form a network for the efficient diffusion
of substances. Their thin walls maximize the rate of diffusion.
The thin walls of the capillaries enable oxygen and nutrients to diffuse from the blood to the cells, carbon dioxide and other waste products to diffuse from the cells into the blood and white blood cells to reach sites of infection.
Capillaries join to form venules (small veins) which join to form veins.
Differences between arteries, veins
and capillaries
Table below gives a summary of the
structural and functional differences between arteries, veins and capillaries.
Differences between arteries, veins and capillaries
|
Arteries |
vein |
Capillaries |
|
Have narrow smooth
lumens |
Have wide irregular lumens |
Have narrow smooth lumens |
|
Have thick muscular walls |
Have thin, less muscular walls |
Have one cell ' thick walls |
|
Lack valves except where they
are connected to the heart |
Have valves at regular intervals |
Lack valves |
|
Transport blood at high pressure |
Transport blood at low pressure |
Transport blood at low pressure |
|
Transport blood away from the
heart |
Transport blood towards the heart |
Transport blood within the tissues |
|
Transport oxygenated blood, except
the pulmonary artery |
Transport deoxygenated blood,
except the pulmonary vein |
Transport either oxygenated or
deoxygenated blood |
|
Contract and relax to create a
pulse |
Blood flows smoothly |
Blood flows smoothly |
Blood
Blood is a fluid tissue. It consists
of cells (red blood cells and white blood cells) and platelets (fragments of
cells) suspended in a fluid called plasma. An adult human has 4 to 6 liters of
blood. The pH of blood is 7.4.
Plasma
Plasma is a pale-yellow fluid.
Approximately 55% of the blood is plasma. Plasma is mostly made up of water but
it also has dissolved substances such as food nutrients, metabolic wastes,
oxygen, proteins and mineral ions. These solutes make up 8% of the plasma while
water makes up 92%.
The major functions of plasma are
the transportation of:
- nutrients from the digestive system to the whole body
- red blood cells containing oxygen to the tissues
- wastes such as carbon dioxide and urea to the excretory
organs
- white blood cells and antibodies to sites of infection
- hormones to the target organs
- mineral ions such as sodium, potassium and chlorides
- Platelets to sites of bleeding.
Plasma is also important for
distributing heat to all parts of the body, regulating the pH of body fluids
and it is where the exchange of nutrients and waste products takes place in the
body.
Red blood cells
Another name for the red blood cells is erythrocytes. They are red, round biconcave cells with no nucleus. One milliliter of blood has approximately 5 to 6 million red blood cells
Red blood cells are formed in the bone marrow. Their lifespan is about 120 days. The liver and the spleen destroy old red blood cells and release haemoglobin for the formation of new cells.
Haemoglobin is the red pigment in erythrocytes. It has a high affinity for oxygen.
The function of red blood cells is
to transport oxygen and carbon dioxide. The adaptation red blood cells that
make them suited forthis function are the presence of haemoglobin, their large
numbers, biconcave shape and the lack of nucleus which increases the total
surface area of gaseous exchange.
Transport of
oxygen
In the lungs (where there is a high
concentration of oxygen), haemoglobin combines with oxygen to form
oxyhaemoglobin. This is an unstable compound which releases oxygen when it
reaches tissues that have a low concentration of oxygen. The formation of
oxyhaemoglobin and release oxygen and haemoglobin can be shown using the
following equation.
Haemoglobin + oxygen =
Oxyhaemoglobin
Oxygen diffuses out of the red blood
cells, through the capillary walls to the tissues.
Transport of carbon dioxide
In the red blood cells, carbon
dioxide combines with haemoglobin to form carbominohaemoglobin. This compound
is transported to the lungs where carbon dioxide is released and expelled from
body.
White blood cells
Another name
for the white blood cells is
leucocytes. These cells have irregular shapes; milliliter of blood has
approximately 5000 to 10 white blood cells.
White blood cells are produced in
the bone marrow and in the lymph nodes.
The function of white blood cells is to protect body against infection. They perform this function by:
- Engulfing and destroying pathogens (a process called
phagocytosis).
- Producing substances that neutralize toxins produced by
pathogens.
- Causing clumping
together of foreign materials in the body.
- Killing infected body cells.
- Preventing clotting in damaged tissues.
The effect of HIV on white blood
cells
The Human Immunodeficiency Virus
(HIV) attacks a type of white blood cells called helper-T cells. These cells
are essential for body immunity. When they encounter an antigen, the helper-T
cells divide themselves to form new cells. This increases the number of cells
available to fight the infection. After the infection, some cells remain as
memory cells to activate an immune response if the infection happens again, in addition
helper-T cells activate other cells in the immune system.
HIV has a protein envelope that can only bind to its receptor called CD4 found on the cell membrane of the helper-T cell. When it enters the human body, HIV fuses its protein envelope with the CD4 then enters the cell. Once inside the cell, the virus becomes part of the helper-T cell and replicates together with it as it undergoes division. This increases the amount of HIV in the blood. The HIV destroys helper-T cells resulting in the reduction of the number of helper-T cells and reducing the CD4 count.
HIV destroys helper-T cells in the
following ways:
- It reproduces inside the helper-T cell, and then
ruptures the cell's membrane and the new viruses are released.
- It alters the helper T-cells so that when it responds
to an infection, it kills itself instead of dividing to form new cells.
- It marks helper-T cells as targets for
destruction by other cells in the immune system.
- It causes the fusion of many helper-T cells to form a
giant' cell. Such a cell can survive but it cannot perform normal helper-T
cell functions.
Thus, HIV lowers the body's immunity
significantly making it vulnerable to opportunistic infections.
Platelets
Platelets at the site of an injury
produce thromboplastin which starts off the clotting process.
Thromboplastin, with the help of vitamin K and calcium neutralizes heparin,
an anticoagulant in blood.
Heparin converts prothrombin
(which is an inactive plasma protein) to thrombin (an active plasma
protein).
Thrombin catalyzes the conversion of soluble fibrinogen to insoluble fibrin. Fibrin forms a network of fibres that traps debris and blood cells. The result is a clot at the site of the wound preventing further loss of blood.
Blood Groups and Blood Transfusion
Grouping of human blood is done using the ABO system and the Rhesus factor.
The ABO system
The ABO system of grouping blood
depends on two things. First is the presence or absence of antigen A or antigen
B on the membranes of the red blood cells. Second is the presence of antibody
A or antibody B in the blood plasma.
A person cannot have a certain
antigen membrane of the red blood cell and also have the corresponding antibody
in the plasma. For example, you cannot have both antigen A antibody a. This
would cause agglutination clumping together of red blood cell. Agglutination
can cause fatal
The various blood groups and the
antigens a antibodies present in them are summarized
|
Blood group |
Antigen on the membrane of the
blood cell |
Antibody in the plasma |
|
A |
A |
A |
|
B |
B |
B |
|
AB |
A and B |
(none) |
|
O |
(none) |
a and b |
Rhesus factor
This factor is named after the
Rhesus monkey in which it was first observed. When the rhesus factor is present
on the red blood cell membrane, a person is said to be rhesus positive. This is
abbreviated as Rh+. If it is absent, the person is rhesus negative this is
abbreviated as Rh-. Thus, a person’s blood is said to be A+ if it is blood
group A and has the Rhesus factor or A- if it is blood group A but lacks the
Rhesus factor. There is also B+ or B-, O+ or 0- and AB+ or AB- blood groups.
If a rhesus negative woman marries a rhesus positive man, their children are highly likely to be rhesus positive. During the last months of pregnancy, the rhesus antigen from the foetus passes into the mother's blood. This causes the mother's body to produce antibodies which destroy some of the foetus's red blood cells. This destruction is minimal in the first child but in the children that follow, a lot of destruction could take place, killing the foetus. This is called haemolytic disease of the newborn or erythroblastosis foetalis. To prevent this, the mother is treated with anti-rhesus globulin. This prevents her body from forming antibodies against the rhesus antigen.
Blood transfusion
Blood transfusion is the transfer of blood from one person (the donor) to another (the recipient). It is necessary to replace blood when the recipient has a blood disorder or has lost a lot of blood due to surgery or an accident.
In order for blood transfusion to be
successful, the blood of the donor and that of the recipient must mix without
agglutination. When this happens, the blood is said to be compatible. If the
blood is incompatible, agglutination occurs.
Blood compatibility depends on the
blood groups of the donor and the recipient. For example, if a person of blood
group A receives blood from a person of blood group B, the recipients’ body
produces antibodies against antigen B. This is because the antigen is seen as
foreign material.
Individuals with blood group AB are
called universal recipients. They can receive blood from people of any blood
group. However, they can only donate blood to someone with blood group AB.
Those with blood group O are universal donors. They can donate blood to people
of all blood groups. On the other hand, they can only receive blood from
someone with blood group O.
The following is a compatibility
table for the different blood groups.
Compatibility of blood groups
Donor's blood group Recipient's blood group
|
|
A |
B |
AB |
O |
|
A |
√ |
× |
√ |
× |
|
B |
× |
√ |
√ |
× |
|
AB |
× |
× |
√ |
× |
|
O |
√ |
√ |
√ |
√ |
Key:
v - Means compatible
X - Means incompatible.
If blood from a rhesus positive
person is transfused to a rhesus negative person, the recipient produces rhesus
antibodies. If such a transfusion is done a second time, massive agglutination
can occur. This can lead to loss of life.
Precautions taken during transfusion
- Blood from the donor must be checked for compatibility
with blood from the recipient in terms of both ABO blood group and Rhesus
factor in order to avoid agglutination.
- The donor's blood must be screened to ensure that it
does not have pathogens that can cause diseases such as HIV and AIDS,
syphilis and hepatitis B.
- Donated blood is stored in special bags and an
anticoagulant is added to prevent it from coagulating.
- Donated blood is kept in a refrigerator for a maximum
of 21 days. After that it expires and should not be used.
- Transfusion should be done only when extremely
necessary.
Advantages of blood transfusion
- It ensures rapid replacement of blood lost from the
body, for example during surgery or due to an accident.
- Blood transfusion is used to treat diseases such as
sickle-cell anaemia
Disadvantages of blood transfusion
- There are no exact blood matches. Blood is a complex
tissue that contains many different. One person's blood cannot be exactly
the same as another's. Hence, there are chances of developing a reaction
to transfused blood.
- Transfused blood may not always be 100% free of
infections.
Blood circulation in human being
Blood circulation is the movement of blood from the heart to all part of the body and back to the heart. Human being exhibit double circulation where by the blood passes through the heart twice for each complete circulation
In other less complex
organisms like the fish, blood goes through the heart only once; this is known
as single circulation.
Pulmonary circulation
- During pulmonary circulation, deoxygenated blood is
brought to the heart through the vena cava. This blood is emptied into the
right auricle. The right auricle pumps blood to the right ventricle. When
the right ventricle contracts, it pumps blood to the lungs through the
pulmonary artery.
- In the lungs, the blood is oxygenated. It then flows
back to the heart through the pulmonary vein. The movement of blood
between the heart and the lungs is called the pulmonary cycle.
Systemic circulation
- In systemic circulation, the pulmonary vein transports
blood to the left auricle. The left auricle then pumps the blood into the
left ventricle. The left ventricle has strong muscles that pump blood to
all parts of the body through the aorta.
-
- After the tissues have derived their requirements from
the blood, it flows back to the heart through the vena cava. This movement
of blood between the heart and the various parts of the body is called the
systemic cycle.
Formation of tissue fluid
The aorta is the largest artery in
the body. It braches into smaller arteries, which in turn branch into even
smaller vessels called arterioles. Arterioles branch into capillaries which are
in contact with the tissue of the body. The capillaries have tiny pores that
allow some components of blood to filter into the tissues.
At the arterial end of the capillary,
there is high blood pressure. This forces fluid out through the any pores in
the capillaries
The fluid is composed of water,
oxygen, hormones and nutrients. This fluid bathes the cells. It is called
tissue fluid or interstitial fluid.
At the venous end of the capillary,
blood pressure is low; water potential is also low. The pressure of the tissue
fluid is higher. This forces the tissue fluid back into the capillaries.
Diffusion also helps in the re-entry of tissue fluid to the capillary. However,
some tissue fluid remains within the cells. This later enters the lymphatic
system to form lymph.
The capillaries join to form
venules. Venules join to form veins. The veins transport blood back to the heart.
Veins in the lower part of the body unite to form the inferior vena cava while
veins in the upper part of the body unite to form the superior vena cava. These
two large veins join to form the vena cava which transports blood to the right
auricle of the heart.
Importance of blood circulation
- It enables the transportation of cell requirements such
as oxygen and nutrients to all the body tissues.
- It ensures that waste products from the cells are
removed in order to prevent accumulation. Accumulation of waste products
is harmful to the body.
- Blood circulation is important for the regulation of
body temperature. Body heat is transported to all parts of the body
through this system.
- Blood circulation also transports hormones from the
organs that produce them to the organs where they are needed. For example,
insulin from the pancreas is a hormone necessary for the regulation of
blood sugar levels
Blood pressure
Blood pressure is measured by
considering the systolic pressure and the diastolic pressure.
Systole occurs when the ventricles contract and pump blood into the
arteries.
Diastole is the phase when the auricles contract to pump blood into
the ventricles.
The pressure developed during these
actions can be felt in the arteries. It is measured in millimeters of mercury
(mmHg).
For example, if the pressure during
systole is 120 mmHg and the pressure during diastole is 80 mmHg, the blood
pressure is 120/80 mmHg. This is the average blood pressure in a normal human
being. A sphygmomanometer is the instrument used to measure blood
pressure.
Diseases and disorders of the human
circulatory system
The diseases and disorders of the
human circulatory system are increased by eating habits and lifestyles. Eating
food with high levels of cholesterol and fat causes narrowing of blood vessels
due to deposition in blood vessels. Lifestyles such as smoking, lack of
exercise, stress and taking alcohol also put one in danger of developing heart
problems such as coronary heart disease and high blood pressure.
Arteriosclerosis
Arteriosclerosis is the hardening of
arteries. It happens when there are fat deposits on the wall of the artery or
when fibrous tissues form in the artery wall or artery walls degenerate;
Arteriosclerosis hinders the arteries from pulsating normally. The lumen is narrowed, affecting the efficiency of blood flowAs a result, the heart has to pump harder in order to supply the tissues with enough blood. The result of this is high blood pressure (hypertension). High blood pressure usually has no specific symptoms. However, it can cause headaches, dizziness and ringing in the ears.
Causes of arteriosclerosis
Arteriosclerosis is mainly caused by
excessive alcohol and smoking, stress, too much fat in the jet, lack of
exercise or old age,
Effects of arteriosclerosis
Arteriosclerosis causes swelling of
part of a blood vessel and rupturing of the artery walls. It also causes total
blockage of an artery, thus depriving some tissues of oxygen. This can cause
the affected tissue to become severely damaged or to die.
Prevention and treatment of arteriosclerosis
People can prevent themselves from
arteriosclerosis by avoiding alcohol and smoking, reducing stress, minimizing
intake of fatty foods and engaging in regular exercise. Arteriosclerosis can be
treated by medication or surgery.
Sickle-cell anaemia
This condition is a genetic disorder which causes production of abnormal haemoglobin and malformed red blood cells. The effect is a reduction of the blood's capacity to transport oxygen. The disease gets its name from the crescent or sickle shape of the red blood cells.
Signs and symptoms of sickle-cell anaemia
Sickle-cell anaemia is characterized
by fatique or excessive tiredness, shortness of breath during exercise,
headaches, dark-coloured urine, abdominal pain, abnormal heartbeat and general
body weakness.
Treatment and prevention of
sickle-cell anaemia
Sickle-cell anaemia has no cure. It
is difficult to prevent since it is inherited. However, patients can be helped
by making sure that they avoid excessive physical exercise and eat a
well-balanced diet that is rich in minerals and vitamins.
Leukemia
Leukemia is a type of blood cancer.
It is caused by the over production of white blood cells and the suppressed
production of red blood cells
The excess white blood cells infiltrate body organs, for example the liver and the spleen. This causes reduced efficiency in the functioning of these organs and their abnormal enlargement.
Signs and symptoms of leukemia
Leukemia is characterized by
abnormally high numbers of white blood cells, abnormal bleeding, e.g. nose
bleeding, bleeding even from minor cuts, extreme body weakness, anaemia, and
throat and mouth infections that may be recurrent.
Treatment of leukemia
Leukaemia cannot be cured. However,
it is controlled by frequent blood transfusions, radiotherapy and chemotherapy
to kill the abnormal cells, and bone marrow transplants
High blood pressure (Hypertension)
The blood pressure of a normal human
being is 120/80 mmHg. Very high blood pressure (over 140/90)
strains the blood vessels and causes hypertension and sometimes heart failure.
Increase in blood pressure may be caused by high fat levels due to over-consumption
of fatty foods, lack of exercise, obesity, high emotional stress, alcoholism
and smoking, and arteriosclerosis.
Signs and symptoms of hypertension
The signs and symptoms of
hypertension include feeling dizzy, ringing sound in the ear and severe
headaches.
Prevention and treatment of hypertension
Hypertension can be prevented by
engaging in regular exercises, avoiding alcohol and smoking, eating a balanced
diet with less fat to control weight and reducing stress as much as possible.
Hypertension can be treated using drugs.
Coronary thrombosis
Coronary thrombosis occurs when
there are blood clots in the blood vessels that supply blood to the heart
(coronary arteries). This prevents blood from reaching some tissues of the
heart. The affected tissues lack adequate amounts of oxygen and waste materials
accumulate in the cells to toxic levels.
Symptoms of coronary thrombosis
Coronary thrombosis is characterized
by uncomfortable pressure or sharp pain in the chest, sometimes extending to
the neck, shoulders and arms, excessive sweating, dizziness or fainting, nausea
or a feeling of severe indigestion and shortness of breath.
Effects of coronary thrombosis
Coronary thrombosis can cause death
of some cardiac tissue or sudden death.
Prevention and treatment of coronary thrombosis
People can avoid coronary thrombosis
by doing regular exercise, avoiding sudden strenuous activity, avoiding alcohol
and smoking, minimize intake of fatty foods and avoiding excessive stress
Thrombosis can be treated by drugs.
Stroke
A stroke occurs when there is
interference in the amount of blood flowing to the brain. Such interference can
be due to blockage or rupture of an artery supplying blood to the brain. This
causes some brain cells to lack adequate oxygen and nutrients.
Symptoms of stroke
Symptoms of a stroke include sudden
numbness or weakness especially on one side of the body, sudden confusion or
trouble in understanding or speaking and sudden poor vision in one 01 both
eyes. The patient also experiences sudden dizziness, loss of balance, trouble
when walking 01 lack of coordination, and sudden severe headaches
Effects of a stroke
A stroke has severe effects on the
victim such as weakness or paralysis on one side of the body, leading to
difficulties in movement and coordination. It also causes lack of feeling on
one side of the body, speech or language problem; and loss of memory. Other
effects are behaviour changes, difficulty when swallowing and exhaustion.
Prevention and treatment of a stroke
A stroke can be avoided by avoiding
drinking and smoking, ensuring your blood pressure remains it the normal range
and exercising regularly. Eating a low-fat, low-salt diet can also prevent a
stroke Medication can help in the treatment of a stroke.
The Lymphatic system
The lymphatic system closely
resembles the blood circulatory system. It consists of lymph, lymph vessels
through which lymph travels, and lymphoid organs and tissues such as thymus,
adenoids, tonsils, lymph nodes and spleen.
Lymphatic system connects with the
blood circulatory system at the superior vena cava
After cells get their requirements from tissue fluid, not all the fluid flows back into the capillaries, Part of it flows into lymph vessels. Once in these vessels, the fluid is called lymph. Lymph is a pale yellow fluid. It has the same components as tissue fluid, but more fatty substances.
Lymph vessels unite to form larger vessels called lymph ducts. There are two main lymphatic ducts; the right lymphatic duct empties into the right subclavian vein while the left lymphatic duct drains into the left subclavian vein. The two veins join to form the superior vena cava. In this way, the contents of lymph enter the blood circulation system
Lymphatic ducts form nodule-like
structures called lymph nodes. These nodes are found in the abdomen,
groin, armpits and neck. Lymph nodes are important sites for the production of white
blood cells. They also filter out foreign materials such as bacteria and dead
tissue before they enter the bloodstream.
The flow of lymph depends greatly on the squeezing of lymph vessels by breathing movements, intestinal movements and muscular movements. The lymph vessels have valves to prevent back flow of lymph.
Importance of the lymphatic system
- Lymph nodes produce lymphocytes (white blood cells)
which help the body to fight diseases.
- Lacteals enable absorption of fatty acids after
digestion.
3.
It provides a way of getting tissue fluid back to the circulatory system.
4. The
spleen destroys worn out red blood cells.
5. The
spleen, the adenoids and the tonsils produce antibodies which help in
fighting disease-causing microorganisms
Disorders and diseases of the lymphatic system
There are many diseases and
disorders that affect the lymphatic system. Some of these diseases and
disorders are explained below.
Elephantiasis
This is a disease that is caused by
worms (filaria) that block the lymph vessels causing accumulation of lymph
which leads to swelling of the arms or legs
Filaria worms are transmitted by
mosquitoes. Elephantiasis is treated by destroying the parasites. One way of
preventing it is by eliminating breeding areas of mosquitoes, for instance
bushes and stagnant water.
Oedema
This is the swelling of body tissues
due to excessive lymph. It is caused by increased blood pressure in the
capillaries, causing the production of large amounts of lymph that the lymphatic
system cannot transport efficiently, pregnancy, obesity and protein deficiency.
Oedema can be controlled by taking
measures to reduce blood pressure, pregnant women keeping the feet slightly
raised when sitting or lying down eating a well-balanced diet and taking
measures to reduce body weight, for example by exercising and avoiding eating
excessive amounts of food.
Lymphoma
Lymphoma is the term used to refer
to cancers that affect the lymphatic system. These cancers cause abnormal
growth or functioning of the components of the lymphatic system. The result is
weakened immune response in the body.
Symptoms of lymphoma include swollen
and painful lymph nodes, fatigue, weight loss, night sweats and itching.
Lymphomas are treated using
chemotherapy and radiation therapy. Severe cases may call for bone marrow
transplants
Tonsillitis
This is an infection and swelling of
the tonsils. It is caused by bacteria or viruses that enter the body through
the mouth or sinuses.
Symptoms include red and swollen
tonsils, sore throat, fever or chills, muscle ache and tiredness.
Mild cases of tonsillitis are
treated by having adequate rest and taking plenty of fluids. More severe cases
may require medical treatment; frequent tonsillitis is sometimes solved by
tonsillectomy (surgical removal of the tonsils).
Summary:
- The mammalian heart is responsible for pumping blood to
all parts of the body. It has four chambers: two auricles (or atria) and
two ventricles.
- Valves in the heart and veins prevent the back flow of
blood.
- The flow of blood in the heart is as follows
(a) Deoxygenated blood from the body
enters the right auricle through the vena cava
(b) The right auricle pumps blood to
the right ventricle.
(c) The right ventricle pumps blood
to the lungs through the pulmonary artery.
(d) Oxygenated blood from the lungs
enters the left auricle through the pulmonary vein.
(e) The left auricle pumps blood to
the left ventricle.
(f) The left ventricle pumps blood
to all parts of the body through the aorta.
4.The main blood vessels are
arteries, veins and capillaries.
5. Arteries are muscular vessels
that transport blood away from the heart. Arteries contract and relax, creating
a pulse.
6. Veins are less muscular than arteries. They transport blood
towards the heart.
10. Red blood cells are biconcave in
shape, lack a nucleus and contain haemoglobin. Their function is to transport
oxygen and carbon dioxide.
11. White blood cells are
irregularly shaped. They are important for immunity.
12. Platelets are fragments of
cells. They help in blood clotting.
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