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Biology 30
Module 2
Lesson 7
Transport System
Copyright: Ministry of Education, Saskatchewan
May be reproduced for educational purposes
Biology 30
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Lesson 7
Biology 30
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Lesson 7
Lesson 7
Transport Systems
Directions for completing the lesson:

Text References for suggested readings :
BSCS Biology 8th edition
Chapter 16 Pages 403-415
Chapter 14 Pages 357-358
OR
Nelson Biology
Chapter 6 Pages 139-156
Chapter 7 Pages 165-168, 171-181

Study the instructional portion of the lesson.

Review the vocabulary list.

Do Assignment 7.
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Lesson 7
Vocabulary
AIDS
antibody
antigen
artery
atherosclerosis
atrium
autoimmune disease
B-cell
capilliary
closed circulatory system
cyclosis
double-loop circulatory system
heart attack
hemoglobin
homeothermic
hypertension
lymph
open circulatory system
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plasma
platelets (thrombocyles)
polkilothermic
pseudohearts
red blood cells (erythrocytes)
S-A node
septum
serum
single-loop circulatory system
sinuses
stroke
T-cell
three-chambered heart
two-chambered heart
vein
ventricle
vessels
white blood cells (leukocytes)
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Lesson 7
Lesson 7 – Transport Systems
Introduction
The importance of each of the processes of respiration, ingestion-digestion and waste
removal was commented upon when each of these actions was described. Obtaining
and then using nutrients, whether they are gases, minerals, organic matter or other
substances requires that these substances be moved. Processing and making use of
the nutrients results in waste materials. These wastes must eventually be moved out
of cells or bodies. Every living cell must receive sufficient nourishment and have its
wastes removed if it is to survive. If these conditions are not met, the continued
survival of the cell is not likely. Unless the well-being of the individual cells is
maintained, the ultimate survival of the entire organism could be in doubt. For this
reason, internal transportation, distribution and collection must accompany other
cell and body activities.
Transport of matter must occur within the cytoplasm of unicellular organisms and
becomes especially critical within the bodies of complex, multicellular organisms.
For the latter, simple diffusion or active transport cannot supply nutrients or remove
wastes to and from all cells fast enough. Such organisms have developed transport
systems which could include tubes, vessels and other parts for moving substances.
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Lesson 7
After completing this lesson you should be able to:
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•
explain the importance of transport within unicellular
and multicellular organisms.
•
list some of the types of substances which are
transported within cells or bodies.
•
explain some of the processes by which molecules pass
through cellular membranes.
•
list the general components which may make up
transport systems.
•
distinguish between the open and closed circulatory
systems in animals.
•
describe the main features of the circulatory systems in

worms

arthropods

fish

amphibians

reptiles

warm-blooded vertebrates
•
provide a detailed description of the circulatory system of
a homeothermic organism (with specific references to
humans).
•
discuss the importance of the human circulatory system
as part of a body's immune or defense system.
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Lesson 7
Transported Substances
Some of the general types of substances moving in and out or within organisms were
identified previously and include:





Nutrients or compounds including water, minerals, and carbon are required
by both plant and animal cells.
Gases for photosynthesis and cellular respiration.
Animal cells require organic nitrogen, 8 to 10 essential amino acids,
essential fatty acids and vitamins.
Chemical messengers in the form of plant or animal hormones move about in
plant sap or animal fluids.
More complex animals commonly have antibodies moving about, defending
against infections.
Other matter becomes significant if it is not transported out of cells or bodies. Waste
matter, largely as a byproduct of metabolic processes, could become toxic above
certain levels of concentration. Organisms must move wastes to body areas where
they can be safely stored permanently or temporarily until they can be eliminated
completely.
Possible Functions of Transport Systems
A summary of the different actions in which transport systems may be involved can
be developed, in large part, from the previous paragraph. These actions can all be
generally regarded as taking part in homeostasis, where stable, internal conditions
are maintained. The functions or actions include:
•
dispersal of necessary nutrients to all living cells.
•
removal of wastes.
•
transport of hormones or chemical "messengers".
•
assisting in cell or body defenses, as in the movements of antibodies or the
active participation of special blood cells.
•
serving as signal mechanisms. This is especially noticeable in complex
animals, where particular conditions of the blood can be detected by special
receptors. Nervous or hormonal systems can then affect breathing rates,
feelings of hunger or fullness, body temperatures and other body conditions.
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Molecular Movements Through Cell Membranes
Movements of molecules through cell membranes may occur either by means of
passive transport or by active transport. These were looked at previously and will
only be mentioned briefly here.
Passive movements depend on the movements of molecules themselves. Osmosis is
the movement of liquid (usually water) molecules from areas of higher to lower
concentrations through differentially permeable membranes. Diffusion is a
molecular movement of gases, liquids or solids. As far as living cells are concerned, it
is important that substances be dissolved in order to pass through their
membranes. This condition does not necessarily mean a substance will move
through a cell's surface automatically. Conditions such as the size of membrane
pores or their chemical structures, could cause membranes to prevent molecular
movements through them.
Active transport requires cells to use up some of their own energy in moving
molecules through membranes. Actively moving toward, surrounding and then
engulfing food particles in vacuoles occurs during phagocytosis. Somewhat less
active is pinocytosis, where molecules make contact with membranes and are
gradually worked through channels which slowly form through the membranes.
Components of Transport Systems
Transport or circulatory systems vary in their complexities through the various
phylum classifications. Some of the following parts may or may not be present
depending on the phylum group.
Transport Medium
All organisms require a substance to move molecules about. This could range from
the streaming cytoplasm of unicellular life forms to plant sap or animal fluids.
Transport Vessels
Larger, multicellular organisms cannot rely only on cytoplasmic movements and
diffusion to move molecules from areas where they were first absorbed. Special tubes
or vessels have appeared to make movements faster and more efficient and to move
substances to or from all body areas.
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Lesson 7
Pumping Organs
Size increases of multicellular organisms, as well as higher rates of activity, could
require even further developments in transport systems to increase speed and
efficiency in movements. Methods of moving fluids along, either by contractions of
body muscles (sometimes called "muscle pumps") or by special pumping organs
(hearts), add to the general efficiency.
Transport systems will be examinated in the following groups:



Unicellular organisms
Multicellular organisms without vessels
Multicellular organisms with vessels including: worms, arthropods, fish,
amphibians, reptiles, birds and mammals.
Transport in Unicellular Organisms
Single-celled organisms, ranging from bacteria to protists, absorb and release
nutrients and wastes either actively or passively through their cell membranes. Once
nutrients enter cells, it is still important that they move about inside the cells. In
this way they become available to all parts of the cytoplasm or to all organelles
present in the cell.
Movement within unicellular organisms is largely accomplished by cyclosis. The
exact manner or mechanism involved in cyclosis or cytoplasmic streaming is still not
fully understood, although it does seem to require energy on the part of the organism.
Transport in Multicellular Organisms Without
Apparent Vessels
Elodea and Hydra are just two representatives of multicellular organisms in which
successive osmosis or diffusion and cyclosis are the means by which substances
move. Fungi and mosses are land organisms employing the same methods. Such
organisms, especially those found on land, are limited in size by the slowness in
movement of substances from cell to cell. Cells farther away from actual sites of
absorption may not receive enough nutrients. For this reason, multicellular
organisms without vessels tend to remain small in size.
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Lesson 7
Multicellular Animals
Studies of animal transport or circulatory systems have been going on from very early
times. From the Greek Galen's 2nd century ideas of blood simply "ebbing and flowing
like the tides" in animal bodies, we have been adding to our knowledge continuously.
Notable landmarks were achieved in the 17th century when dissections allowed
William Harvey and Marcello Malpighi to separately begin uncovering details about
the circulatory system. Their works first disclosed that blood flowed in closed
vessels, making a circuit through arteries, capillaries and veins. Since that time,
information has been increasing in the area of circulatory functionings and also in
the field of medicine. Some of the more dramatic work has centered around
pacemakers, artificial hearts, artificial blood and heart transplants.
Increases in cell numbers and overall body sizes made
it difficult for the processes of diffusion and osmosis
to alone handle substance movements within animal
bodies.
The types and natures of the circulatory and transport systems possessed by various
animal groups are closely related to the degree of complexity of their bodies and to
their activity levels. Regardless of the kind of system developed, it should be
remembered that at the cellular level, where movements must occur through
membranes, the processes of diffusion, osmosis and active transport are still very
important.
In phylum groups including multicellular "animals" which are relatively small,
diffusion and osmosis are sufficient to take care of all movements. The phylum
Cnidaria (sometimes called Coelenterata) shows the beginnings of various systems,
including muscular and nervous. However, the proximity of most cells to circulating
fluids makes it unnecessary for the development of any transport or circulatory
system.
Similar to the discussion of the waste system, the transport system will be examined in
the following progression:
Worms
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arthropods
fish
amphibians
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reptiles
birds and mammals
Lesson 7
Worms
Vessels and circulatory systems adapted specifically for carrying substances in
animal bodies made their first appearance in worms. Annelids, such as the
earthworm, have dorsal and ventral blood vessels carrying blood forward and back in
the body. Capillaries close to the body surface connect these two major vessels all
along the body. It is through these capillaries that exchanges of food and other
substances between the blood and body cells occur. In addition, gases are also
exchanged (by diffusion) between these capillaries and the nearby moist body
surfaces. Worms do not have a separate system for carrying gases.
At the anterior end of a worm are five pairs of muscular, aortic arches which function
like hearts. (They are sometimes called pseudohearts, which means "false" hearts.)
Arthropods
The blood in annelids, some molluscs and all vertebrates is confined throughout its
circuit in vessels. This is not to say that substances do not enter or leave the blood
through the vessel walls, because they do. However, a major portion of the fluid
blood does remain inside vessels and for this reason these are called closed
circulatory systems.
Arthropods such as crustaceans, insects and arachnids have a type of circulatory
system which is somewhat different. Blood does flow through vessels, but it is not
confined to the vessels in the entire circuit. In places, vessels empty into body
cavities which may or may not be divided into smaller chambers called sinuses.
These cavities or sinuses are the main areas where exchanges of substances occur.
Contraction of adjacent body muscles may continue the movement of blood into other
vessels and sinuses. One of these sinuses commonly contains a tubular kind of
heart with openings in it to allow blood to enter it and to be pumped ahead once
more.
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Compared to a closed system, movement of blood is not as rapid in an open system.
In sinuses, some blood may be moved along for fairly long periods of time. To
overcome this inefficiency, two factors are present:


open circulatory systems are confined to organisms with small bodies or small
body cavities, which require smaller amounts of blood to move dissolved gases
and other substances.
In one class of arthropods, the insects, there is also another separate transport
system consisting of tracheal tubes. These tubes conduct gases in and out and
throughout insect bodies.
The remaining animal groups described in this lesson possess either body sizes or
activity levels which make them all dependent on closed circulatory systems. These
circulatory systems will be looked at from the point of view of the different developments
and major differences which have appeared in and among the groups. A more detailed
look at the parts of circulatory systems, their nature and their functioning will be
undertaken when humans are used as representatives of warm-blooded vertebrates.
Fish
Of the vertebrates, fish have the least complex circulatory system in terms of heart
and vessel development.
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A fish heart is two-chambered, with an atrium receiving deoxygenated blood from
some part of the body and a stronger ventricle pushing it on through a ventral aorta
to the gills. The entire circulation pattern is known as a single-loop circulatory
system, since the blood passes through the heart once every time it makes a circuit
through the body.
Amphibians
Frogs, toads and salamanders show a heart type with 3 chambers – two atria leading
into a single ventricle. The right atrium receives deoxygenated blood from the body
and the left atrium receives oxygenated blood from the pulmonary veins (the only
veins to carry oxygenated blood). Both atria contract at the same time, sending blood
into the single ventricle. Contraction of the ventricle pushes the mixture of
deoxygenated and oxygenated blood through arteries to the rest of the body.
Amphibians exhibit a closed,
incomplete double loop circulatory
system. It is an incomplete, double
loop as some blood may make one
circuit through the lungs upon one
complete heart contraction and then
another circuit through the body upon
the next complete contraction. Mixing
of some oxygenated and deoxygenated
blood does occur in the ventricle.
However, this apparent inefficiency may be offset by two conditions: 1) The manner
in which blood enters the ventricle and the ridges in its walls seem to prevent
complete mixing and a large amount of deoxygenated blood is deflected into the
pulmonary-skin arteries 2) the large numbers of blood vessels in and near the
amphibians’ thin, moist skins aids in the process of diffusion of considerable
amounts of gases between the skin and blood vessels.
When temperatures are low and
body metabolism has been greatly
reduced, gas needs may be
completely satisfied through the
skin. This enables some
amphibians to hibernate
completely submerged under
water.
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Lesson 7
Reptiles
Reptiles show different degrees of heart development which are advancements over
the type shown by amphibians. The advancement is in the appearance of a partial
muscular partition or septum in the ventricle. This means that, even though the
heart is still basically three-chambered, a septum partially divides the ventricle,
preventing the mixing of blood.
In some reptiles the septum is large enough so that when the ventricle contracts, the
opening between the sides does close. One reptilian division, the Crocodilian order,
demonstrates the greatest advancement in reptiles by actually having a completely
divided heart ventricle. Beginning with crocodilians then, there is the appearance of
the first closed, complete double loop circulatory system and a four-chambered
heart.
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Birds and Mammals
Of all vertebrates, birds and mammals show the greatest levels of both internal body
processes and rates of body actions. High metabolic rates and warm-blooded or
homeothermic (sometimes spelled homoiothermic) body conditions are related to
and especially important for such characteristics. Cold-blooded or poikilothermic
animals have their actions, metabolic rates and hence, body temperatures,
fluctuating with external environmental temperatures. Maintaining high metabolic
rates and homeothermy require efficient transport systems and the most complex
developments have appeared in these animal groups.
The circulatory system of mammals is an efficient closed, double loop system where
deoxygenated and oxygenated blood are kept in separate circuits. This system is
powered by an efficient, four-chambered heart pump, shown in the following
diagram.
The flow of blood through the heart.
The muscular development of the ventricles in the heart, especially the left ventricle,
also generates a blood pressure high enough to move blood with force and speed
through all the blood vessels. Blood pressures in other animal groups before this
had not been high.
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Lesson 7
The circulatory system is comprised of three cycles or circuits:
1.
2.
3.
Cardiac or coronary circuit – this is the travel of blood within the heart
muscle.
Pulmonary circuit – the path of the blood from the heart to the lungs and
back.
Systemic circuit – the path of the blood from the heart to the rest of the body.
Note: The exact ways vessels leave or enter the heart, and their locations in the
body, have been "simplified" to show directions of blood flow more clearly.
As mentioned earlier, a circulatory system must have transport vessels. There are
three types of vessels which make up a blood circulatory circuit: the artery, the vein
and the capilliary.
Arteries:
 carry blood away from the heart. (generally oxygenated blood)
 have a thick layer of smooth muscle, making them elastic. (As a person ages,
some of an artery’s elasticity is lost.)
 smaller inner diameter than veins
 arteries divide, leading into smaller branches called arterioles which will then
lead to the capillaries
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Lesson 7
Capilliaries:
 thin walled – consist of single surrounding layers of epithelial cells
 Location of exchanges or movements of dissolved nutrients, wastes, and gases,
as well as hormones, white blood corpuscles and blood plasma which becomes
tissue fluid.
 Connect arteries and veins
Veins
 capillaries veins or venules which gradually form larger veins.
 Carry blood toward the heart (generally de-oxygenated blood)
 Thin walled. These vessels have a greater internal diameter and less elasticity
than arteries. (An absence of blood causes a collapse of vein walls.)
 Have valves which prevent back flowing of blood
While it is true that arteries generally carry oxygenated blood while veins transport
deoxygenated blood, the opposite scenario exists with the pulmonary arteries and
veins.
Transport Medium: Blood
Blood is the transport medium in the mammalian circulatory system. A common
impression is that blood is fairly uniform in its composition, however this is not the
case. The average 4 to 6 litres of blood in a human adult may be made up of the
following parts:



Nutrients and wastes
Hormones
Blood cells
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Lesson 7
Nutrients and Wastes
Blood vessels and blood are the main means of moving substances about in the
bodies.
Nutrients
Oxygen; the common organic
compounds of sugars, amino
acids and lipids; and, salts and
minerals, such as calcium,
magnesium and potassium
Wastes
gases; byproducts of metabolism
(such as urea); or excesses of some
vitamins and minerals which are
not required and could even be
harmful in larger amounts.
Hormones
The chemical "messengers" produced by the ductless glands in various parts of a
body move about by means of the circulatory system. Since all body areas are close
to some capillaries, it does not usually take long for a hormone to affect its "target"
organ.
Blood Cells
Distinct and solid blood cells are common in the "river" of blood passing through a
vessel. An illustration of the three types of blood cells is below, followed by
characteristics and functions of each type.
Red Blood Cells (or, erythrocytes)

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

the most numerous of the blood cells.
produced in bone marrow, particularly in that of ribs and vertebrae.
initially have nuclei, but in humans the nuclei are lost as the cells mature.
Under higher magnification, each round cell appears “dished in” near its
middle.
as the nuclei disappear, the blood cells form an iron-containing, red-colored
protein called hemoglobin.
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Lesson 7




in some animal groups, another metal – such as copper, may help form the
pigment. Different metal molecules could result in shades of blood ranging
from blue to green to our more familiar red.
Hemoglobin is responsible for the transport of oxygen as oxygen is not very
soluble in the liquid portion of blood, particularly at higher (body)
temperatures. However, hemoglobin has a good attraction for it and most of
the oxygen transported in blood is joined to this protein in red blood cells. A
lack of red blood cells or hemoglobin to carry oxygen can cause a condition
called anemia.
average life expectancies range from two to four months. Most are destroyed
when their cell membranes rupture as they are forced through capillary walls.
the spleen and liver process the remains of most of these cells and the
hemoglobin yields back much of the iron. Some of the remaining waste
products form the bile pigments.
Platelets (or, thrombocytes)


smaller, irregular-shaped cells which seem to float passively in the blood.
responsible for clotting: when vessel walls and platelets are ruptured during
some injury, the platelets release a chemical or enzyme. This enzyme begins a
step-like series of actions on certain proteins carried in the blood plasma. The
series of changes eventually produce threads of protein called fibrin. Acting
like screens, these threads begin trapping blood cells and forming a clot..
White blood cells (or, leukocytes)






produced in bone marrow and in lymph tissue or lymph glands.
important components of a body’s defense or immune system.
five different types of white blood cells have so far been recognized and
described, according to sizes, shapes of nuclei and cytoplasmic characteristics.
although found in the circulatory system, many more white cells are in other
fluids, body tissues and organs (especially the spleen and thymus gland). The
circulatory system is a convenient way for them to travel in the body.
they move about in amoeboid fashion, squeezing through capillary walls and in
between body cells. In their movements they engulf bacteria and other foreign
protein particles using the process of phagocytosis. Lysosomes (“suicide sacs”)
in these cells, containing protein-digesting enzymes, destroy the foreign
particles and often the leukocytes themselves. Remains of these white blood
cells and the foreign particles may form pus.
other white cells defend against infections with immune responses.
Encounters with foreign proteins (or antigens) will cause these cells to begin
multiplying mitotically fairly quickly. The large numbers of these new cells
form and release their own special soluble proteins or antibodies. These
defensive proteins attach to foreign cells and, if they do not destroy them
directly, “mark” them for destruction by other white cells. The individual
antibodies seem to be able to direct other white cells in the manner of
destroying the antigens. Some white blood cells, such as macrophages, may
engulf and digest certain antigens. Other white cells may be directed to bore
holes in the antigens’ membranes, causing the foreign cells to rupture.
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Lesson 7

Lymphocytes (so called because many are in the lymph fluid) function in a
number of ways. Initially, a lymphocyte appears to be an undifferentiated cell
ready to change into a more specialized cell such as a red blood cell (a cell
taking part in forming connective tissue) or a certain kind of plasma cell (Bcells or T-cells) producing important antibodies or taking part in defensive
reactions.
B-Cells and T-Cells and Body Defenses
The critical importance of body defenses, or lack of, against foreign "invaders"
deserves more attention. Differentiation of lymphocytes can produce two types of
cells called B lymphocytes (or B-Cells) and T lymphocytes (or T-Cells).
B-Cells
Usually, a body initially has a large and varied population of B-cells. Each of these
generally has only one antibody on its surface which is capable of combining with
only one kind of antigen which it may chance to encounter. If this occurs, the
antibody can take the foreign cell apart. The B-cell can take some of the protein
"pieces" of the foreign cell and incorporate them into its own outer membrane.
Particular kinds of (helper) T-cells encountering these protein pieces will bind to the
B-cell and release certain molecules. These cause the B-cell to grow and undergo
divisions to produce a mass of B-cells, each having more antibodies against the
particular antigen.
From the initial entrance into a body and possible increase in numbers of a certain
antigen (virus, bacteria...), it takes the body about 5 to 10 days to produce enough of
the specific B-cells (and antibodies) to combat it. While most of the B-cells are used
in trying to control an antigen, some are formed which are known as memory cells.
These move about in the body and are also stored in the spleen. Should the same
type of antigen ever invade body tissues again, the memory cells would initiate much
faster responses in the body's defense. Since the proteins of some pathogens do not
change, a body will retain the defense mechanisms (memory cells) to deal with those
pathogens in the future. These memory cells are the basis of developing permanent
immunities against certain diseases. Not all defenses or immunities are permanent.
Due to mutations, some of the antigens change. When this happens and a slightly
different form of antigen enters a body, the entire immunity response must be gone
through again. This is fairly common with pathogens causing colds and influenzas.
T-cells
The T-cells, which mature after passing through the thymus gland, can differentiate
into three types of cells.
 Helper T-cells, mentioned earlier, cause increases of particular B-cells and
antibodies, as required.
 Suppressor T-cells slow B-cell and antibody production once an antigen has
been overcome.
 "Killer" T-cells take direct part in the destruction of cells.
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Lesson 7
Viruses or other antigens which enter bodies can often enter host cells before meeting
any white blood cells. Once this happens, an antigen cannot be attacked by
engulfing white cells or by antibodies. Should the antigen, such as a virus, begin
directing the host cell to produce viral particles, some of those viral particles may
make their way into the host's outer membrane. Passing "killer" T-cells could
recognize these particles and bind to the surface of the host cell. The T-cell destroys
the cell and either kills the antigen or exposes it to destruction by other white cells.
T-cells are also very important for the many protein "messengers" which they send
out to direct the defensive actions of other white cells.
The Body’s reaction to Proteins
How is the body or the immune system able to distinguish between its own cells or
proteins and those that are foreign?
A current theory is that a developing fetus contains a large assortment of T-cells,
some capable of attacking a body’s own proteins and cells. Possibly sometime before
birth and shortly after, the thymus gland displays cells containing sample body
proteins (or marker proteins) in their membranes. Any T-cells binding to these cells
with the intention of destroying them, are themselves destroyed by the thymus gland.
This means that shortly after birth, a body should not contain any T-cells that would
harm its own cells.
Sometimes, over time and for various reasons, an immune system will begin to fail to
recognize marker proteins of some of its own body cells and the antibodies or T-cells
begin to attack and destroy their own cells. These instances are referred to as
autoimmune diseases. Multiple sclerosis is one example, where the protective
myelin surrounding nerve cells is destroyed. Another example is in rheumatoid
arthritis, in which cells in joints begin to be destroyed by a body’s own immune
system.
In some situations, certain bodies may tend to "overreact" to particular proteins
entering them. These allergic reactions occur as antibodies react to certain marker
proteins on pollen, hair or other matter. An antibody will attach to the antigen,
triggering reactions in certain mast cells. Mast cells are ameoba-like cells scattered
throughout various tissues. Some tissues include the linings of respiratory passages
and various ducts. Mast cells release a substance called histamine, which causes
cells to experience inflammation. This can lead to such conditions as "runny" nose;
itchy, teary eyes; or, breathing difficulties, as in asthma. Antihistamine drugs can
relieve some of these symptoms, although they do not correct the original problem.
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Lesson 7
Human Immunodeficiency Virus (HIV), T-Cells and AIDS
A parasitic virus which has aroused great concern is one which actually uses white
blood cells themselves as hosts. The HIV enters T-cells mainly, but also uses
macrophage cells and some non-blood (often epithelial) cells. Once inside a cell, the
virus can direct that host cell to produce the virus' own proteins. These viral proteins
can become incorporated into the white blood cell's nucleus or into its membrane, or
be set free to infect other cells. As with other viruses, HIV can remain in latent or
inactive form inside cells, although the viral protein is reproduced each time a host
cell reproduces. This inactive period can apparently last from a few weeks to l5 to 20
years from the time of infection. In humans, studies seem to indicate an average
time of about 8 years from infection to when the HIV becomes active.
When HIV does become active, the host T-cells are eventually destroyed as they are
taken over in the production of the viral proteins. The reduction in T-cell and
macrophage numbers, as well as the loss of the directing influences of the messenger
proteins normally sent out by T-cells, eventually lead to AIDS. AIDS, or acquired
immune deficiency syndrome, develops as a body's defences are destroyed. This
leaves the body open to other infections. These other infections, normally easily
defended against, will ultimately cause death. At this particular time, there is no
cure for AIDS, although some drugs do slow its progress. The HIV inhabits white
blood cells and also various epithelial cells. Epithelial cells are those which line the
surfaces of some body cavities and secretory canals. This means that infections can
occur from two major sources.


Transfer of HIV infected blood is one of these. Transfer of such blood can occur
by transfusion, through a mother's placenta, the use of a contaminated syringe
or even from dental equipment.
The other source of infection is through sexual intercourse, as certain body
secretions (such as semen) can include HIV infected cells. In all instances,
certain precautions and procedures can be utilized to minimize the chances of
infection.
Blood Plasma
Much of the blood of a vertebrate is made up of a straw-colored fluid portion called
plasma.
Plasma has the following components:
 about 90%, without the red and white cells, is water.
 Remaining 10% are nutrients, such as fats and glucose; vitamins and
minerals; and, hormones.
 plasma also contains various proteins. Some of these are clotting agents,
defensive agents against foreign proteins and agents in maintaining blood
volume and blood pressure
 carries waste materials such as nitrogen byproducts (ammonia, uric acid,
urea…).
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Blood fluid can make its way through capillary walls into tissue spaces and around
cells. This liquid forms the lymph or interstitial fluid surrounding the cells and
collecting in body cavities. Lymph is somewhat paler in color than the plasma from
which it came, as some materials were screened in the passage through capillary
walls.
The liquid portion of blood could be refined further into what is called a serum. The
serum portion is not only missing the various blood cells, but also has none of the
clotting agents or proteins. Medical laboratories frequently prepare sera from animal
bloods which have developed antibodies useful for human immunities.
Lymph Circulation
In this lesson, three transport or circulatory systems will have been mentioned.
1.
Blood circulation
2.
A brief reference was made to the tracheal transport system common to
insects. This system of trachea or air tubes enables gases to be circulated
throughout organisms' bodies without the use of circulating fluid or blood,
although this is present as well.
3.
Another transport system found in mammals and only in a few other groups, is
the lymphatic circulatory system.
The lymphatic circulatory system is a network of glands and vessels, containing a
fluid called lymph (pale or yellowless). This system helps maintain the balance of
fluids in the body.
Lymph originates from blood
fluids which pass through
capillary walls to bathe
surrounding cells. These fluids
are important in having
nutrients reach all cells, while
at the same time removing
wastes from those cells. Some
lymph makes its way back into
the blood circulatory system
through the capillary walls.
Much of it collects in lymph
vessels which are found all over the body but are largest in size in the abdominal and
thoracic regions. Besides serving individual cells, lymph also absorbs lipids or fat
molecules through the villi of the intestine. Smaller lymph "capillaries" join into
larger lymph vessels. Some of the larger ones contain valves, just as veins do. As
with veins, movement in these lymph vessels appears to occur by contractions of
nearby muscles.
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Many of the lymph vessels join finally into a large thoracic duct which empties into a
vein in the left shoulder region. A smaller lymph duct also joins a vein in the right
shoulder area. Joining of lymph ducts and veins results in the return of lymph to the
blood circulatory system.
The lymphatic system also works to help guard against infection. At various points
along lymph vessels there are enlargements called lymph nodes or glands. Greater
concentrations of these exist in the groin, armpit and throat areas. Tonsils and
adenoids are lymph node areas in the head. Concentrations of white blood cells –
especially lymphocytes, are found in lymph nodes. These white blood cells
destroy bacteria and other foreign proteins which have entered the system. Serious
infections could result in nodes swelling up and becoming very painful.
Blood and Lymph as Transport Systems
There are a number of ways in which substances are carried about by the blood and
lymph.
Since a large portion of the fluid is water, which is a good solvent, many nutrients
and wastes are simply dissolved in it. Other molecules are small enough to float in
the fluid or to break apart into charged ions which can then dissolve (as most
minerals do).
Although many organic nutrients and wastes can dissolve easily in the fluids, oxygen
is not very soluble in blood plasma. Only about 2% of the oxygen transported by the
blood is in dissolved form in the plasma. When oxygen molecules diffuse through the
alveoli of the lungs and into the lining capillaries, most of them are attracted and
joined to the iron-containing protein in the red blood cells. Union of oxygen with
hemoglobin produces oxyhemoglobin, giving blood a bright, cherry-red color. The
strength of attraction between oxygen and hemoglobin can vary and appears to be
related to two conditions:


oxygen molecule concentrations
acidity levels
(Both of these conditions function in the release of oxygen from blood in tissue and cell areas where it
is needed.)
1. Concentration of oxygen molecules: A higher number of oxygen molecules
causes more to join with hemoglobin molecules, or more oxygen molecules
to join with a single hemoglobin molecule. Fewer oxygen molecules in the
tissue or the environment mean that fewer join with the iron pigment and
could actually cause oxygen to separate from hemoglobin.
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DID YOU KNOW…
In mountainous areas, where higher altitudes mean lower oxygen concentrations,
hemoglobin of a red blood cell carries fewer oxygen molecules. During strenuous or
prolonged activity, oxygen starvation can occur. Human and other mammals make a
special adjustment for this. The adjustment is a production of more red blood cells
which, although carrying fewer oxygen molecules individually, make up for the
difference with their numbers. Athletes preparing for events at higher altitudes than
what they are used to, will often go to these areas ahead of time so that their bodies will
form extra blood.
2. Acidity: A higher acidity level weakens the attraction and could cause a
separation of the two molecules. A buildup of carbon-dioxide cause
carbonic acid to be formed. This, along with lactic acid, weakens the bond
and causes oxygen to be released. About 70% of the carbonic acid, formed
from carbon-dioxide is also more soluble than oxygen and approximately 5
to 10% of it can be carried in dissolved form in the plasma. Another 20%
can join to the hemoglobin . Waste carbon-dioxide can then be carried by
the blood to the lung capillaries where, in reverse processes, it can be
diffused out through the alveoli.
DID YOU KNOW…
While carbon-dioxide can combine more readily with blood than oxygen can, carbonmonoxide has an even greater attraction with hemoglobin. In areas where carbonmonoxide is produced in excessive amounts (as from running cars, trucks or tractors in
enclosed areas), this gas quickly binds to the red blood cells and prevents oxygen from
doing so. Oxygen starvation and death can occur quickly during carbon-monoxide
poisoning, unless preventive or corrective measures are speedily adopted.
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In addition to increases in concentration, increases in pressure also cause more
gases to dissolve in the blood or to bind to hemoglobin. Diving in fresh or ocean
water increases surrounding pressure on a body and can cause more oxygen and
carbon-dioxide to be dissolved in the blood. A more significant gas under pressure is
nitrogen, which also dissolves in blood. When divers return to the surface too
quickly (or, when pilots in unpressurized cockpits go to higher altitudes too quickly),
nitrogen bubbles develop in the blood. The effects of these can range from a tingling
sensation to muscular aches and pains and possible blackouts as the bubbles stop
blood movements. Death can result unless proper depressurizing techniques or
proper air mixtures in tanks are used.
The Heart in Action
The mammalian heart consists of four chambers:


a left and right atrium and
a left and right ventricle.
The atria and ventricles are separated by valves. Blood enters the heart through the
atria and exits through the ventricles. The double pumping action results from the
simultaneous contraction of the two ventricles. It is vital that the contractions are
not interrupted or stopped. Complete stoppage or a loss in the rhythm of heart
muscle contractions can lead to quick death. Partial destruction of heart muscle can
lead to a loss of overall energy, breathlessness, kidney damage and other symptoms
of a failing circulatory system.
The regular contraction and relaxation, or heartbeat, of an "average" human adult
takes place about 70 times a minute. This is not a constant rate, however.
Heartbeats can range from 40 to 180 and can be affected by age and physical fitness,
activity levels, drugs or chemicals, excitement and other factors. Conditions
affecting heart rate may originate externally, but the natural control
mechanisms are internal.
Aside from complications, contractions of
the heart are continuous. This
continuous contraction is controlled
within the heart itself, is a bundle of
specialized muscle tissue found in the
right atrium. This area is called the sinoatrial (S-A) node, or the sinoauricular
node.
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Contractions and relaxations begin at the S-A node and spread across the heart
muscle. Since the basic rhythm of the heart originates at the S-A node, it is
considered the heart's natural "pacemaker". Both an electrical stimulus and
contraction move from the S-A node to an atrial-ventricular (A-V) node in an area
between the atria and ventricles. Stimulation of this area causes electrical impulses
and contractions to travel to all parts of the ventricles and cause their contractions.
After a short period of relaxation, the process is repeated. Damage to a portion of the
heart muscle or damage to a pacemaker itself may destroy the uniformity of the
impulses and contractions as they travel across the heart muscle. Instead of
contractions moving evenly or uniformly through the heart muscles, they may
become disorganized so that random twitching replaces the regular beat.
People who are accidentally electrocuted may have the same thing happen to their
hearts. An external electric current can disrupt the regular electric impulses
travelling across their hearts, leading to disorganized twitching or ventricular
fibrillation. In such conditions, blood flow is stopped. Some individuals who may
have experienced heart damage and are susceptible to fibrillation, have artificial
pacemakers implanted (usually just under the skin). Wires transmit electrical
impulses from these artificial devices to the heart so that regular beats are
maintained. These pacemakers can also adjust impulse frequencies to activity levels.
Natural heart rates can be modified by a number of body controls. The control center
seems to be the medulla, at the base of the main brain. Different sets of nerves,
which can stimulate and inhibit, connect the medulla and the S-A region of the heart.
The medulla detects chemicals or changes in the blood and acts accordingly. Some
examples of body controls are:
1.
2.
3.
Higher carbon-dioxide concentrations in the blood, due to increased activities,
may be noticed by the medulla itself or by special receptors in the aorta or
arteries which then send impulses to the medulla.
Stretch receptors in the muscle walls of the right atrium may also detect more
blood than usual returning from the body as a result of more muscle
contractions. This would lead to impulses that could be sent to the medulla.
Sudden stress or strong emotions could trigger the release of certain hormones
(such as epinephrine or adrenalin from the adrenal gland) which could be
detected by the medulla.
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In all these situations, the medulla responds by stimulating the heart, causing it to
beat at a higher frequency. Opposite changes or conditions would result in the
medulla slowing down the heart rate.
Blood Types
In the course of developing certain medical procedures, blood transfusions were used
as a way of trying to save individuals who had lost considerable amounts of blood.
Successful in some cases, in other instances they seemed to hasten death. Around
1900, it was discovered that the protein nature of blood could be different enough to
clearly establish distinct blood types. A body has its own unique kinds of proteins
and any other kinds, whether they are viruses, bacteria, pollen grains or blood of
another type are treated as "invaders". The body's natural tendencies in such
situations is to produce antibodies to destroy the foreign proteins.
A considerable amount of protein is found in the cellular membranes of red blood
cells. The kind of protein a red blood cell has is identified by its reactions with
antibodies of other individuals. The term "antigen" applies to a foreign protein, but it
is also used to identify the protein of a blood cell resulting in the four common types
of blood – A, B, AB and O.
Blood type or
group
A
B
AB
O
Antigen
present
A
B
A, B
None
Antibody in
plasma
Anti-B
Anti-A
None
Anti A, Anti B
A red blood cell can be identified as carrying antigen (or protein) A on its surface. A
different protein can classify another blood cell as antigen B. If the A-antigen or Type
A blood was introduced into a Type B person, the recipient would produce anti-A
antibodies, which cause clumping and destruction of A blood cells. A transfusion of
antigen B blood into an A person would cause clumping and destruction of the B
cells. The clumping of blood could be fatal to the recipient as it blocks flow of blood.
Two other blood types have been identified as Type AB (having both types of antigens
or proteins) and Type 0 (having neither antigen A nor antigen B).
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A different type of protein in blood establishes some people as Rh positive (Rh+)
and others as Rh negative (Rh-). Rh+ blood (having that particular protein)
transfused into a Rh- individual (not having the protein) will cause that recipient
to form anti-Rh+ antibodies. While an initial transfusion may be uneventful
(since the life span of the blood cells is short), antibodies are built up so that
future transfusions can cause clumping, or agglutination, and death.
Differences in the Rh protein characteristics of blood have also had an impact on
child-bearing between Rh+ fathers and Rh- mothers. Normally, a mother's and her
unborn child's circulations are largely kept separate by membranes; however,
seepage may sometimes occur between mother and child.
Seepage takes place most commonly from a few days before birth to the time
during birth. (This seepage does not happen as much as once thought.) If a
child is Rh+ and the mother is Rh-, seepage of the child's blood into the mother's
would initiate the formation of anti-Rh+ antibodies. If early seepage occurred in
another future pregnancy where the child was Rh+, antibodies from the mother
would begin destroying the child's blood. Death and abortion of the fetus could
take place. If death does not occur, a shortage of red blood cells and improper
nutrient (oxygen) circulation could lead to brain damage and a mental deficiency.
If the seepage begins shortly before or during birth and complications develop,
the problem may be corrected with the child receiving a transfusion of Rh- blood
without the antibody. This blood would temporarily replace the child's Rh+ blood
which was being agglutinated. Since their life span is not long, the Rh- blood
cells would soon be replaced by newly produced, normally functioning Rh+ cells.
Another recent treatment involves the injection of an Rh factor into the mother's
blood several weeks before a child's birth. This factor destroys all possible Rh+
cells which may enter the mother's system. In this way she does not develop an
antibody against those cells.
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Circulatory System Irregularities
The preceding section and some before pointed out various difficulties or diseases
which could develop with aspects of, or related to, the human circulatory system.
This lesson will conclude with brief comments or descriptions of others.
Atherosclerosis
An artery wall is normally fairly elastic, allowing for easy movement of blood. The
movement is powered by a contraction of the heart and also by the pulse which
develops and then works its way along the artery. As a person ages, arteries become
less elastic, a condition known as atherosclerosis.
Smoking and a diet rich in (saturated or high cholesterol) fats contribute to this
condition. Deposits of fat streaks or plaque on the inside walls of arteries reduces
elasticity and also internal diameter. The condition makes it necessary for the heart
to work harder in forcing blood through the less elastic, smaller diameter vessels.
Atherosclerosis also contributes to high blood pressure and increases risks of heart
attacks and strokes.
High Blood Pressure
In order to pump blood through less elastic and smaller diameter arteries, the heart
must exert greater force. This becomes evident by the greater or higher blood
pressure against the arterial walls during both contraction of the heart (systole) and
relaxation (diastole). A higher than the average blood pressure of 120/80 over an
extended period of time is often referred to as hypertension. Factors contributing to
hypertension:



Prolonged emotional stress associated with school, family, work or with other
matters.
Being overweight and "out of shape" commonly increase both heart rate and
blood pressure.
A faulty diet can lead to obesity and can also increase the volume of blood if
foods contain excess salts. Too much salt causes a body to retain more fluids
in its tissues, including blood. The extra load on the heart due to high blood
pressure can tire the heart muscle more easily and can cause damage,
especially in times of increased physical demands.
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Heart Attacks
Atherosclerosis, where internal diameters of arteries are reduced, increases the
possibilities of blood clots (which probably occur more frequently than once thought)
completely blocking certain vessels. Should this happen in one or more of a heart's
coronary arteries, muscle areas normally receiving oxygen and nutrients from those
arteries will begin to die. Death of heart muscle can eventually lead to sudden,
intense pain and then heart failure, or a heart attack.
Strokes
Sudden blockages of arteries due to clots can occur anywhere in the body. Should
one happen in the brain, a stroke results. Deaths of nerves in brain areas will affect
body conditions or body actions normally controlled by those brain areas. The degree
or extent to which body actions such as sight, speech, memory or muscle coordination are affected, depends on the locations and amounts of brain areas
damaged.
Organ Transplants
Partial or complete failures of vital organs can have crippling or fatal consequences if
not corrected. Attempts to transplant parts of, or entire, organs have been met with
different degrees of success.
A body's immune system recognizes marker proteins on cell membranes and their
degree of relatedness to the body. T-cells, macrophages and other white cells will
begin destroying any cells or tissues with marker proteins different from those of the
body. Success rates of transplants increase if related donors, or careful tissue
typings, are used so that marker proteins are similar between donor and recipient.
Drugs can also be used to suppress an immune system's recognition of the protein
markers on cells.
Varying degrees of success have also accompanied attempts to implant or to use
artificial devices to take the places of various tissues and organs. Implants of
artificial hearts have not been successful for any extended time. Circulatory
problems with clots and resulting strokes and other body seizures have ended each
attempt so far. More encouraging, dialysis units are being used much more
successfully by individuals with failing or non-functional kidneys. The present size
and design of the units requires that individuals come to the units to be attached for
treatments on a regular basis. Circulation machines are also used to maintain blood
conditions and movements during (open) heart surgeries. However, these are for only
relatively short time periods and under very careful and continuous monitoring.
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Summary
The movements of substances into and out of cells or bodies of organisms, as well as
within multicellular bodies, is one of the essential processes of life. At the cellular
level for all organisms, unicellular or multicellular, movements of substances through
or across membranes may occur by diffusion, osmosis or active transport. As
organisms become larger, the major problem becomes one of having all cells serviced
properly. Diffusion or osmosis from cell to cell may be sufficient to move substances
in smaller organisms, but become inefficient when cell numbers and body sizes
become large. In such groups of organisms, adaptations have taken place with the
appearance of special cells and tissues designed specifically for transport. Tracheal
transport systems consist of tube networks with circulating gases. Other tube
networks in plants and animals are filled with moving fluids, which could be water
and dissolved minerals, plant sap, blood or lymph. Forces responsible for moving
substances in tubes could be physical (without much effort by the organism itself) as
they largely are in plant xylem and phloem. In animals, such forces are replaced by
mechanisms or "pumps" designed to improve the efficiency of circulatory systems
which must maintain higher body temperatures or activity levels.
Increasing complexities in the circulatory systems, which include the pumping
organs or hearts, can be observed in the adaptations which have appeared in
different animal groups. Open circulatory systems, with blood flowing partly through
vessels and partly through body cavities or sinuses, along with very simple "heart"
structures, are common to smaller, less complex organisms. Larger, more complex
animal groups have closed circulatory systems, with blood making complete circuits
through arteries, capillaries and veins by the pumping actions of hearts.
Developments of additional heart chambers and valves, from the fish through to the
birds and mammals, show increasing efficiency in the direction and speed of blood
movements. This efficiency is supported by the ability to maintain separate circuits
between deoxygenated and oxygenated blood.
Mammals, of which humans are a part, have highly developed and complex
circulatory systems. Not only are these circulatory systems involved in movements of
nutrients and wastes, but they play very significant roles in other ways. By
transporting enzymes, hormones and other chemical messengers, regulation and
monitoring of many body conditions and activities are continually taking place. As
well, body defenses or immunities are centered around components of blood and
their actions and movements. The parts which make up circulatory systems and the
manners in which they function have long been a source of interest and marvel. Yet,
for all their complexities, transport systems are just one of many body processes
trying to maintain steady body states or homeostasis, and the condition of life.
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Miscellaneous Facts
•
An average person living to age 75 will have a heart which has beat 2.8 billion
times and will have pumped 390 million liters of blood.
•
The lowest recorded human heartbeat was 28 beats per minute.
•
Well-conditioned athletes can have heartbeats of about 40 per minute, during
inactive periods.
•
A reduction of about 10 beats per minute can save a heart 18 to 19 days of
work over a year.
•
It takes blood about 1 minute to make a circuit in an inactive person.
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