Download Microsoft Word 97

Biology 30
Module 2
Lesson 9
Body Actions and Systems:
Maintaining Life
Chemical Control and Coordination
Copyright: Ministry of Education, Saskatchewan
May be reproduced for educational purposes
Biology 30
267
Lesson 9
Biology 30
268
Lesson 9
Lesson 9
Transport Systems
Directions for completing the lesson:
Text References for suggested reading:

Read BSCS Biology 8th edition
Sections 17.7 – 17.10, pages 443-450
OR
Nelson Biology
Chapter 10, pages 223-236

Study the instructional portion of the lesson.

Review the vocabulary list.

Do Assignment 9.
Biology 30
269
Lesson 9
Vocabulary
ACTH
ADH
adrenal cortex
adrenal glands
biofeedback
diabetes mellitus
endocrine
estrogen
exocrine
FSH
glucagons
gonads
HGH
hypothalamus
insulin
Islets of Langerhans
Biology 30
LH
MSH
neurosecretory cells
ovaries
oxytocin
parathyroid
pheromones
pituitary gland
progesterone
prolactin
testes
testosterone
thymus
thyroid
TSH
270
Lesson 9
Lesson 9 – Chemical Control and
Coordination
Introduction
Studies of the internal natures of living organisms have indicated the ongoing actions
of different processes. Gas exchanges during respiration, food and waste processing
and movements, internal transport and body movements, are just some of the
life-sustaining actions. Usual methods of study have been to look at these
individually. In doing so, one may form a mistaken impression that all of these
processes are going on at the same time, but independently of each other. Yet, just
the opposite relationship exists. All the different systems and processes are closely
tied in with each other and variations in individual ones almost always affect the
others. Increased muscular action in a vertebrate animal brings about a higher
respiration rate, increased heart action and circulatory movement, production of
more wastes and many other changes. The ability of individual systems to work
closely together requires some sort of close communication with each other. How
some communication occurs has already been looked at in the lesson on nervous and
sensory systems. Many organisms have other or additional ways of having their cells
or body parts interact.
Changes in rates of cell or body respiration as well as in various body developments
take place continuously. Variations in developments and processes are commonly
highlighted by differences in the growths and behaviors of organisms during their
daily and life cycles. An animal's body processes may be directed to growth and
maintenance for much of a year. During part of that year, the same animal could
experience changes in body activities during a reproduction phase which sharply
alter both body appearance and behavior. The exact manners in which changes in
cell or body actions occur are not always clear. However, the main mechanisms or
agents bringing about those changes are known.
Coordination and regulation of metabolic rates and body processes take place by
means of "messengers". In an animal, a nervous system helps to detect surrounding
conditions or stimuli and then to carry out appropriate responses by sending
impulses along nerve networks. Coordination of body systems within an animal also
relies on the uses of chemicals produced by certain cells and released to travel to
other locations. This particular lesson will concentrate on coordination and regulation
by hormones.
Biology 30
271
Lesson 9
After completing this lesson you should be able to:
Biology 30
•
explain the importance of regulating metabolic rates and
coordinating body systems.
•
name the two major mechanisms involved in controlling
body processes.
•
describe the general nature of hormones and explain how
they may affect cell and body actions.
•
indicate some of the major differences between controls in
animal bodies.
•
distinguish between duct and ductless glands.
•
explain the role of neurosecretory cells.
•
describe the locations and functions of various endocrine
glands in a vertebrate body system.
•
explain some of the ways in which hormonal actions are
coordinated.
272
Lesson 9
Hormones
Hormones are organic chemicals or chemical "messengers" which can affect certain
cell processes. They are produced within cells. In multicellular organisms, they are
produced either in specialized cells or in particular areas of the organisms.
Molecular structures of these chemicals vary considerably, but for the most part they
are modifications of the same amino acids and lipids used in forming other organic
matter (proteins and fats).
In a multicellular plant or animal, a hormone is commonly
released from one area and moves by diffusion or through an
existing transport system to affect another area.
Not all cells or tissues are affected by a hormone, even though all are exposed to it.
Instead, there are "target" areas where only certain cells react in some way. Target
cells have receptors or molecules which combine with specific hormones. These
receptor or attaching molecules can be located on the surface membranes of cells or
they can be inside cells, either in the cytoplasm or right in nuclei.
Many researchers think that hormones, as chemical "messengers", simply start a
certain sequence of already planned events or responses in target cells. A
comparison sometimes used is that a hormone merely pushes a "starter button" for
some reaction. Pushing a certain button in a poultry feeding operation may cause a
hopper to dump a measured amount of feed onto a conveyor belt. The button could
also have started the conveyor belt in motion past a series of bird cages. As the
conveyor moves along, it deposits measured amounts of feed in front of or into each
cage. After a certain programmed time, the system may shut itself off.
How hormones push the "starter buttons" or begin events may vary.



A particular hormone may attach to the receptor molecule in the membrane of a
certain (target) cell.
The receptor-hormone combination could activate a particular enzyme, causing a
second messenger to be produced in the cytoplasm. This second compound can
then initiate the production of other proteins or it can enter the nucleus.
Inside a nucleus this messenger or even a hormone itself could attach to other
receptors in specific regions of DNA or chromatin. The messenger-receptor or
hormone-receptor combination can then either activate or shut down the actions
of some genes and the cell processes which those genes control.
Biology 30
273
Lesson 9

A hormone may also affect a cell membrane's permeability to certain substances.
By doing this, enzymes may enter to start various metabolic actions. The sizes or
complexities of the hormone molecules could determine which actions take place.
Larger, more complex polypeptide (protein-based) hormones are more likely to
remain on the outside of cell membranes. Steroid or lipid hormones can pass
fairly easily through membranes and their effects are more likely to be initiated
right in a cell's cytoplasm or nucleus.
Regardless of the way in which reactions are started or
stopped, only extremely small amounts of hormones need
to be present. Many are effective in concentrations of just
a few parts per million.
Chemical Messengers in Animals
Coordination of metabolic rates and body processes is probably more critical in
animals than it is in plants. The ability to move about results in changes which often
occur more rapidly or to a greater degree both internally and externally for animals.
Animals have adapted by developing an additional "messenger" system in the form of
nerves and nerve networks. However, chemical messengers or hormones still play
major roles in body functions.
In vertebrates, hormones are involved in some way in almost all body actions. Not
only are hormones involved in what could be considered as moment-by-moment
ongoing actions, but they are also responsible for the various developmental stages
from embryo to old age. Some of the more obvious results of this are the
developments of secondary sexual characteristics in organisms and the distinct
reproductive cycles of species.
Biology 30
274
Lesson 9
The Endocrine System
Plant hormones are produced in various organs by cells which are the same as other
cells in that tissue. That is, there are no cells in plants which are specifically
adapted or designed for producing hormones. This is different in multicellular
animals, as there are secretory cells specialized for hormone production alone. In
addition, the more complex multicellular organisms have these cells in distinct
groupings or glands which are located in specific areas of bodies.
There are two common types of glands: endocrine and exocrine glands.
Endocrine glands are ductless glands, that is they do not have any tubes or ducts
leading out of them to other body areas or to transport systems. Endocrine glands
secrete hormones directly into the bloodstream by diffusion. Most often, these
hormones enter circulatory systems and are eventually transported to all body areas.
Glands have blood vessels running through them so that hormones do not find it
difficult to enter the circulatory system. All the ductless glands, whose hormones
remain inside a body, make up an endocrine system.
In contrast, exocrine glands utilize ducts or tubes to transport their secrections to
specific areas of the body, which could include outside surfaces. Examples are
sweat glands, salivary glands and tear glands. The secrete such substances as
sweat, milk, digestive enzymes and other materials.
The Nerve-Endocrine Relationship
Coordination of cellular and body functions is accomplished by the nervous and
endocrine systems working very closely together. Although there are direct
attachments of nerves to glands in only two instances, the two systems affect one
another indirectly in many ways. For the most part, nerves receive external and
internal stimuli and transmit them to various parts of the body, with the most
important being the brain. Parts of the brain, the hypothalamus in particular, can
"interpret" the various stimuli and send directions to response networks like the
endocrine glands. The glands of the endocrine system then regulate many of the
internal responses which the body makes to these stimuli. The light-dark interval, or
photoperiodism, affects hormonal and behavioral changes in many animals, just as it
does in plants. Migratory and reproductive behaviors, growing more fur or shedding
it and changing fur colors, are some events resulting from nerve-endocrine
interactions.
Biology 30
275
Lesson 9
Neurosecretory Cells
An important "indirect" link between the nervous and endocrine systems is the
presence of neurosecretory cells. These are nerve cells which produce secretions at
their ends. The nerve ends are long fibres which are close to, or are even embedded
in, capillary networks. The secretions or hormones produced by the nerves can
diffuse into the circulatory system and be carried throughout the body. These
hormones can either affect other glands or can affect certain cells directly.
Insects, annelids (worms), mollusks and other invertebrates regulate internal body
conditions almost entirely with neurosecretory cells. Well-defined glands are not
apparent in these groups. Most of the neurosecretory cells are concentrated in the
brain areas of these organisms. Light stimulations received by the eyes and
transferred to the neurosecretory cells in the brains of octopuses and squids, cause
cells to release hormones into the circulatory systems. The hormones cause various
pigment bodies in skin cells to expand or contract, changing the colors of the
organisms. Neurosecretory cells and hormones are responsible for other actions
such as periodic molting of exoskeletons and the timing of the different parts of
reproductive and life cycles.
Biology 30
276
Lesson 9
Neurosecretory cells are also present in vertebrates. In this group, nerves,
neurosecretory cells and glands of the endocrine system are closely connected.
Stimulations and responses can take place both ways between nerves and hormones.
An important linking area in vertebrates occurs in the hypothalamus. There is a
concentration of neurosecretory cells in this area of the brain. The cells release a
number of hormones which affect an adjacent pituitary gland. This gland, in turn,
affects almost all the other endocrine glands.
Biology 30
277
Lesson 9
The Vertebrate Endocrine System
The types of endocrine glands present, the kinds of hormones they produce and the
effects these have on bodies, are very much the same in all vertebrates. Therefore,
the human example will be used as an illustration of the system.
INSERT DIAGRAM OF ENDOCRINE SYSTEM HERE
Hypothalamus
The hypothalamus is not an endocrine gland itself, but is a portion of the brain just
above the pituitary gland. There are actual nerve connections between the
hypothalamus and part of the pituitary. Neurosecretory cells provide a chemical link
between the hypothalamus and the other portion of the pituitary. The hypothalamus
is sensitive to various body conditions, including chemical concentrations, and can
transmit neural or chemical signals to the pituitary and other glands to control these.
Biology 30
278
Lesson 9
The Pituitary Gland
About the size of a pea, the structure of this gland has three parts with: an anterior
lobe, an intermediate part and a posterior lobe. In adults, the intermediate portion
has almost disappeared. The lobes or parts indicate different origins during their
formation. The posterior lobe developed as an apparent extension of a portion of the
hypothalamus. This is probably why there are neural connections between the two.
The anterior lobe developed from a different kind of embryonic tissue and is
considered as a true endocrine gland (while the posterior lobe is not generally
considered as such).
Approximately eight hormones have been recognized as being produced by the
pituitary gland and are as follows:
Hormones produced in Pituitary
Released by
Biology 30
Human Growth Hormone
(HGH)
anterior pituitary
Gonadotrophic hormones such as
FSH and LH
anterior pituitary
Prolactin
anterior pituitary
Thyroid-stimulating hormone
(TSH)
anterior pituitary
Adrenocorticotrophic hormone,
(ACTH)
anterior pituitary
Melanocyte-stimulating hormone
(MSH)
anterior pituitary
Oxytocin
posterior pituitary
Antidiuretic hormone,
(ADH or vasopressin)
posterior pituitary
279
Lesson 9
With the exception of oxytocin and ADH which are released by the posterior pituitary,
the hormones are secreted by the anterior pituitary. The release of these hormones
into the blood is controlled by the hypothalamus. Neurosecretory cells in the
hypothalamus add releasing chemicals to blood vessels which pass through the
hypothalamus and the anterior pituitary. These neurosecretions cause the anterior
lobe to release various amounts of its hormones into the circulatory system. Most of
the pituitary hormones influence other glands, causing them to produce and release
secretions. For this reason, the pituitary is often called the "master gland", even
though the hypothalamus usually initiates responses.
When hormones appear to be involved in "messenger"
roles to other glands, they are referred to as trophic or
tropic hormones. That term will be at the endings of the
names. For instance, gonadotrophic hormone is produced
by the pituitary gland and it affects the ovaries (or
gonads).
A closer look at the hormones produced in the Pituitary
1.
Human Growth hormone indirectly controls skeletal and muscular
development. An excess of this hormone can lead to a pituitary giant
(sometimes called giantism or gigantism), with individuals ranging in height
from two and one-half to nearly 3 meters. A deficiency of the hormone results
in dwarfism, with individuals being about one meter tall. Excess HGH in
adults produces acromegaly, symptoms of which include excessive thickening
of bone tissue, leading to abnormal growth of head, hands and feet.
2.
Gonadotrophic hormones act upon the sex organs (gonads) of females and
males. A number of sex hormones have been recognized. FSH
(Follicle-stimulating hormone) stimulates the formation of sperm producing
tubules in testes. In females, FSH promotes follicle development in ovaries (for
egg development) and also estrogen secretions. Estrogen is responsible for
secondary female sex characteristics and also affects female reproductive
cycles. Luteinizing hormone (LH) induces ovulation, or release of eggs, from
the ovary and acts with FSH in causing estrogen secretions. In males, LH acts
upon cells in the testes causing them to release other sex hormones. In
humans, these sex hormones lead to the onset of puberty and the development
of secondary sexual characteristics – such as growth of extra body hair and a
deepening voice. In other male animals, the sex hormones lead to seasonal or
annual changes in sexual behavior and possibly even appearance.
3.
Prolactin in mammals is produced during and after pregnancy. It stimulates
the development of mammary glands and milk production. In non-mammals,
it seems to bring about some reproductive behaviors in females (such as
broodiness in hens).
Biology 30
280
Lesson 9
4.
TSH (Thyroid-stimulating hormone) activates the thyroid gland. The thyroid
gland will be examined in more detail later.
5.
ACTH (Adrenocorticotrophic hormone) activates the cortex of the adrenal
gland.
6.
MSH (melanocyte-stimulating hormone) affects cells containing a black
pigment called melanin. In humans, it seems to play minor roles in the
development of freckles or the darkening of some body areas under conditions
such as pregnancy. MSH is much more important in the reptilian and
amphibian groups. The hormones can cause melanin to be concentrated in
small areas of cells or spread throughout. These, respectively, cause lighter
and darker skin colors, enabling organisms to better blend in with their
surroundings. This is why fish or frogs change colors.
The posterior pituitary functions as a storage area for the neurosecretions from the
hypothalamus.
7.
Oxytocin hormone stimulates smooth muscle contraction. In female
mammals, this hormone causes contraction of the uterine walls during birth
and the contraction of muscle fibres in the mammary glands during nursing.
8.
ADH or Antidiuretic hormone (sometimes called vasopressin), causes
contraction of arterial walls. This increases blood pressure. ADH, as the name
implies, also acts as an antidiuretic. It increases the permeability of the kidney
tubules, causing the kidneys to reabsorb much of the water originally removed
from the blood. Occasionally, the pituitary may not form and release very
much of this hormone. If this happens, there would not be very much
reabsorption of water by the kidney. A person would be excreting or urinating
large amounts of fluids. This action would lead to body dehydration and
excessive thirst. Such a condition is called Diabetes insipidus. This should not
be confused with the more commonly known Diabetes mellitus, which will be
described shortly and relates to blood glucose levels. Even if a pituitary is
functioning properly under ordinary circumstances, consumption of alcohol
will begin suppressing the production of ADH. This is what increases the
frequency of urination when a person drinks alcohol, and is not merely due to
the intake of fluids. The resulting dehydration can be evident in a person's
thirst and drinking of larger amounts of water some time after an (alcohol)
drinking session.
Biology 30
281
Lesson 9
The Thyroid Gland
The thyroid gland is a two-lobed structure which encircles the trachea near the
larynx.
Thyroxine is an iodine-containing hormone which controls the rate of body
metabolism. Often, this hormone may be undersecreted or oversecreted, leading to
medical complications.
Hypothyroidism: undersecretions of thyroxine. This may be caused by iodine
shortages in the environment and diet, leading to reduced body developments in
young animals. Amphibians may never develop beyond the larval or tadpole stage.
Some varieties of salamanders even become sexually active and reproduce in these
larval or axolotl forms. Undersecretion or hypothyroidism in humans also stops
physical development. Cretinism, where an individual remains very short, is the
resulting abnormality or disease. Individuals are not only small physically, but are
poorly developed mentally (a difference from pituitary dwarfism). Shortages of the
hormone after adulthood has been reached also result in abnormalities. Conditions
such as being overweight, being mentally and physically sluggish and showing
puffiness or coarsening of features could develop.
Hyperthyroidism: overproduction of thyroxine. Excessive amounts of the hormone
may lead to a doubling of the metabolic rate. Individuals may be hyperactive or
irritable, unable to sleep and show such body symptoms as trembling, sweating,
weight losses and protruding eyes. Often, a malfunction of the pituitary gland and
its TSH is the problem.
Goiter, or swelling of the thyroid gland, can be associated with either hypothyroidism
or hyperthyroidism. Hypothyroid goiter can occur when there is not enough
thyroxine to turn off TSH production. Hyperthyroid goiter can occur when the
thyroxine levels are high, the feedback mechanisms fail to tell the thyroid cells to
stop thyroxine production.
Diagnosing thyroid problems is frequently carried out by measuring oxygen
consumption. Since metabolic rates, cellular respiration and respiration are all
related, excessively high or low metabolic rates would be reflected in high or low
oxygen use.
Biology 30
282
Lesson 9
The Parathyroids
Embedded within the thyroid gland itself are four
parathyroids. Parathyroid hormone tries to
maintain a particular concentration of calcium
ions in the blood. The hormone causes cells to
release calcium into surrounding blood vessels.
Calcium ions are used in bone formation and are
also particularly important in muscle contractions
and nerve impulses. Low calcium levels can lead
to muscle twitchings, convulsions and death. A
reduced amount of calcium in the diet causes
parathyroid hormone to remove more of the
mineral from the bones. This can cause the bones
to be weak, deformed and prone to breaking easily.
The Thymus Gland
A two-lobed gland, which is prominent in the early years but becomes reduced in size
in adulthood, is the thymus gland. This gland is located high in the chest area, just
over the heart. Testings and observations indicate that this gland is important in the
early development years when the body is first setting up an immune system.
Hormones from the thymus may stimulate the formation of antibody-producing
lymphocytes in lymph glands.
The Pancreas and the Islets of Langerhans
The pancreatic organ, next to the stomach, was
mentioned for its part as a duct gland in the process of
digestion. Pancreatic juice makes its way from the gland
and into the duodenum. There are isolated clusters of
cells throughout the pancreas, called islets of
Langerhans, which function as ductless glands. Two
kinds of cells make up the islets of Langerhans:

Biology 30
One type produces the hormone glucagon. Glucagon
stimulates a particular enzyme to convert glycogen,
carbohydrates and fats into glucose, which enters the
blood stream.
283
Lesson 9

The second kind of cell releases the hormone insulin. This hormone alters the
permeability of membranes to glucose, allowing extra amounts of it to be absorbed
by cells and to be metabolized into glycogen for storage or for incorporation into
other organic compounds. In most diabetics, there is a shortage of insulin
(although an excess of glucagon is also possible) and the body begins excreting
abnormal amounts of blood sugar through the urine. The high sugar
concentration of blood through the kidneys also reduces the abilities of these
organs to reabsorb water from the nephrons back into the body system.
Therefore, an individual is losing high amounts of both glucose and water. At the
same time, glycogen and organic compounds in body tissues are being broken
down into glucose which enters the blood. The breaking down or catabolism of
carbohydrates, fats and proteins produces high levels of toxic matter, which can
be the actual cause of diabetic coma and death.
Diabetes mellitus, the condition commonly resulting from a shortage of insulin, is
treated with injections of insulin from animal extracts. Taking insulin too soon after
strenuous physical activity or after a long time without nourishment or simply in too
large a quantity, can create another problem called insulin reaction or shock. In
this situation, low blood-sugar levels are decreased even further, leading to collapse,
loss of consciousness and possible coma. Diabetics or people associated with
diabetics should be familiar with the differences between diabetic coma and insulin
shock. Symptoms leading up to diabetic coma are excessive thirst, nausea, vomiting
and breathing difficulty. Symptoms prior to insulin shock are hunger, sweating,
irritability and fatigue.
The Adrenal Glands
An adrenal gland is located on the top of each kidney.
A darker central area or adrenal medulla is surrounded
by a lighter outer part called the adrenal cortex. These
two parts have different origins and functions.
Biology 30
284
Lesson 9
1.
The adrenal cortex produces many secretions which are steroid in nature.
The hormone, ACTH (adrenocorticotrophic hormone), that is produced in the
anterior pituitary, is sent out to the adrenal cortex to regulate these secretions.
Steroids are in the same group as lipids and other fat-related compounds. The
chemicals which make up the steroids are generally called corticoids and
these can be divided into three groups according to function.
Glucocorticoids promote the conversion of fats and amino acids or proteins
into glucose and glycogen. Cortisol is the main glucocorticoid steroid hormone
secreted by the adrenal cortex. The steroids thus provide bodies with extra
energy. Under natural conditions, physical or emotional stresses can cause
rapid drops in blood glucose levels and blood pressure. This is when the
adrenal cortex is signalled by the ACTH of the pituitary gland to release
glucocorticoids into the blood and bring glucose levels up. Steroids, such as
cortisone, are sometimes used to reduce swellings or inflammation by their
actions on membranes (which are based on fat or lipid structures.)
Mineralocorticoids encourage reabsorption of sodium and chlorine ions from
the kidneys into the blood. This is done by Aldosterone, the main
mineralocorticoid steroid hormone secreted by the adrenal cortex. These ions
help to keep blood volume and pressure up. A deficiency of these hormones
cause excessive excretions of the salts in the urine. At the same time, the
blood draws phosphate and potassium ions from body tissues. These ions
make the blood acidic. Undersecretions of the hormones can cause Addison's
disease, which is marked by a low blood pressure, weakened muscles and a
listless condition. Applying cortical steroids or ACTH can help to maintain a
normal life. Lack of treatment generally leads to death in one to two years.
There are a number of cortical sex hormones (sex steroids) produced which
may add their effects to those of the sex hormones produced by ovaries or
testes. An overactive adrenal cortex can lead to early sexual development in
young animals and children. In human females, overactivity can result in the
appearance of secondary sexual characteristics normally associated with
males. These may include extra facial hair and a deeper voice.
2.
The central adrenal medulla may have originated from nerve cells and is under
the control of the nervous system (by neurosecretory cells). This is the
"emergency gland" which produces hormones in response to "fight or flight"
situations. In conditions of anger, fear, pain or other kinds of stress, the
medulla releases two hormones: adrenaline (epinephrine) and noradrenaline
(norepinephrine). Both of these hormones induce changes or conditions
designed to prepare a body for some type of action. The liver converts glycogen
into glucose and releases it into the blood, as an available source of energy.
Breathing rates increase, with pulmonary bronchi increasing in diameter to
allow the passage of more air. Blood vessels to "non-emergency" areas or
organs (skin and digestive system) constrict, sending blood to the heart, liver
and muscles where it is needed more. Vessels to these particular areas expand
slightly and the heart rate goes up.
Biology 30
285
Lesson 9
The Gonads
Female or male gonads are normally associated with the production of either eggs or
sperm. While this is so, ovaries and testes also have cells which produce and release
hormones. The hormones from these ductless gland cells may contribute to the
formation of eggs or sperm, but they also give rise to secondary sexual
characteristics.
The Testes
When testes are stimulated by the LH or lutenizing hormone from the pituitary gland,
they produce and release a number of hormones called androgens. One of the more
important of these is a steroid called testosterone. This hormone leads to a further
development of the male gonads and to a development of the "male" features common
to a species. In many species, the hormone also initiates a reproductive drive in male
animals, which could include aggressive behaviors. Livestock producers commonly
emasculate or castrate many male animals at a young age. This changes their
growth patterns so that musculature (meat) is different and the animals have
subdued temperaments, in addition to being sterile. Some synthetic androgens or
steroids are sometimes utilized by human athletes to promote the development of
extra musculature and strength.
The Ovaries
Estrogens and progesterones are two types of hormones produced by the ovaries
when they are influenced by the FSH (follicle-stimulating hormone) and LH
(lutenizing hormone) from the pituitary gland.
Estrogens lead to the development of
secondary sexual characteristics of female
mammals. These hormones also take part
in regular reproductive cycles of females
during their fertile periods. Estrogens are
released by the follicle cells in which eggs
develop. The hormones cause the uterus
to begin adding more glandular cells and
blood vessels, in preparation for the
possibility of a fertilized egg embedding in its wall.
Once the follicle ruptures and the egg is released (ovulation), the follicle is
transformed into a group of glandular cells called the corpus luteum.
Biology 30
286
Lesson 9
The corpus luteum now releases the hormone progesterone which has two main
actions.


It completes the preparation of the uterus.
It also prevents the development of any other follicles (and eggs).
If fertilization does not occur, progesterone and estrogen production begins to decline
and the corpus luteum begins to break down, as does the lining of the uterus. The
inner uterine lining is then discharged during a four or five day period of
menstruation. Even as this occurs, the level of progesterone will have fallen so that
another follicle will have begun developing to repeat the cycle. In the fertile human
female this cycle occurs about once every 28 days, unless there is a pregnancy or if
there is some irregularity. These cycles continue until an individual is about 42 to 52
years of age. During this time period, follicles are affected less and less by FSH and
LH and they release less estrogen. Ovulations and menstruations become irregular
and finally stop at a time known as menopause.
Other Glands and Hormones
The endocrine glands described so far are some of the major or more noticeable ones
(especially during a malfunction). However, there are other gland cells which are part
of other tissues or organs and are scattered throughout various parts of the body.






The placenta of a pregnant mammal has cells which also produce the hormones
estrogen and progesterone, which affect the uterine wall.
Gland cells in the stomach and small intestine produce hormones involved with
digestion.
A small pineal gland in the brain may produce hormones in animals which
regulate reproductive cycles according to photoperiods or light-dark intervals.
A group of lipid-like hormones called prostaglandins, initially isolated from semen,
are produced in a number of body areas. Original studies showed these
prostaglandins to be responsible for smooth muscle contractions. Further
research is revealing these chemicals to be responsible for many more actions,
including regulations of blood pressure, pain levels and immune responses.
Certain cells in the heart muscle have been found to release a hormone affecting
kidneys and their elimination of sodium (salt) and water.
Some kidney cells also release a hormone which affects red blood cell formation by
bone marrow.
Expectations are that continuing investigations will reveal more hormone-producing
cells in tissues and organs previously regarded as nonendocrine.
A summary of glands, their hormones and actions are presented in the following
table.
Biology 30
287
Lesson 9
Endocrine Gland
Pituitary Gland:
Posterior lobe
Pituitary Gland:
Anterior lobe
Hormone
Major Functions
Oxytocin
Stimulates smooth muscle contraction.
ADH - Antidiuretic hormone
Promotes reabsorption of water in the kidneys.
ACTH - Adrenocorticotropic hormone
TSH - Thyrotrophic
hormone
(also called Thyroid
Stimulating Hormone)
GH - Growth hormone
LH - Lutenizing hormone
Stimulates adrenal cortex
Stimulates thyroid and production of thyroxin.
Stimulates growth - especially of skeleton.
Stimulates follicle in ovary and stimulates the
corpus luteum.
Stimulates testes in males.
Stimulates milk production in mammaries.
Regulates pigment concentrations in skin cells.
Prolactin
MSH - Melanophore stimulating hormone
Thyroid
Thyroxin
Increases metabolic rate.
Suppresses TSH.
Parathyroid
Parathyroid hormone
Increases calcium levels in the blood.
Thymus
Thymus hormone
May be responsible for development of lymphocytes
and therefore, antibody production.
Pancreas: Islets of
Langerhans
Insulin
Enables body cells to convert glucose to (storable)
glycogen.
Causes body cells to convert glycogen to glucose.
Glucagon
Adrenal cortex
Corticoid (steroid) hormones
Regulate metabolism of carbohydrates, water and
minerals.
Affect connective tissue.
Stimulate appearance of secondary sex
characteristics.
Adrenal medulla
Adrenaline,
Noradrenaline
Stimulate actions designed to prepare body for
"fight or flight".
Testes
Androgens
(testosterone)
Stimulate metabolism (respiration) and blood
circulation. Promote development of male
secondary sex characteristics. Stimulate
reproductive or sex drive.
Inhibits FSH.
Ovaries: Follicle
Estrogen
Corpus luteum
Progesterone
Stimulate development of uterine lining.
Promote development of female secondary sex
characteristics.
Inhibits FSH.
Encourages ovulation.
Promotes and maintains uterine lining before and
after pregnancy.
Inhibits LH.
Stomach
Gastrin
Stimulates secretion of gastric juices.
Duodenum
Secretin
Stimulates secretion of pancreatic and bile juices.
Biology 30
288
Lesson 9
Balancing Hormonal Actions
The concept of a steady state or homeostasis has been continually emphasized in the
descriptions of cell and body processes. Actions involving the production and
interplay of hormones is no different. Hormones are the chemical messengers for
controlling body actions and a fine balance often exists between too little stimulation
or too much. Going too far in either direction can result in poor functioning, disease
and even death.
A number of different conditions are responsible for controlling gland actions:
1.
Stimuli received.
All glands regulate their production of hormones by the stimuli which they
receive. Some glands respond to stimuli which have nothing to do with other
glands. These may come from:

external stimuli. Many animals have photoperiodic responses or
behaviors, just as plants do. (Some scientists feel that photoperiods are
among the most important external stimuli for most animals.) As an
example, in following through on the reproductive behaviors of organisms,
the following sequence likely occurs in many species.
Biology 30
289
Lesson 9
Light-dark intervals of particular amounts, which occur over a certain
period of time, will stimulate some nerve centers in organisms' brains.
These nerve stimulations eventually reach the hypothalamus portion of the
brains. A hypothalamus has cells which produce chemicals that affect one
of the more central glands in the body – the pituitary. In this way, an
external stimulus (which is light in this instance) triggers a response in the
pituitary gland.

internal body conditions
Some glands also respond to internal stimuli. Some of these internal
stimuli are "triggering" or trophic hormones from other glands. The
illustration on light-dark effects on reproductive behavior shows that after
the pituitary is stimulated, it sends out (trophic) hormones which affect the
testes or ovaries of individuals. These gonads are prompted to produce their
own hormones which then bring about various changes in reproductive
characteristics. In whitetail deer, androgens in bucks increase the sizes of
testes and cause the production of sperm.
(Most bucks are actually infertile for much of a year.) These male hormones
cause a swelling of the neck muscles and of scent glands on the legs.
Behavior is sharply modified as bucks enter a "rutting" or reproductive
behavior. This includes an expansion of territorities, active searching for
does and possible aggressive actions towards other animals, especially rival
males.
Internal stimuli could also include the levels or concentrations of
particular substances in the blood or tissues. The amount of glucose in
the blood affects the islets of Langerhans and their production of the
hormones insulin and glucagon. Higher amounts of glucose will result in a
greater production of insulin, which causes some cells to take up glucose
and convert it to glycogen (in the liver and muscles) and fat (in body cells).
Low glucose levels in the blood cause a drop in insulin production and a
release of glucagon. Glucagon reverses the actions of insulin, causing cells
to form glucose and release it into blood vessels.
Biology 30
290
Lesson 9
Glucose levels in blood demonstrate yet another way in which regulation of hormone
production and body activities occurs. Some hormones exist as antagonistic pairs.
The levels of some substances in the body could be very critical. The body is very
sensitive to the amounts of glucose in the blood and severe damage to cells and
tissues can occur if there are excesses or shortages. If insulin alone controlled
glucose levels, increasing or decreasing the production of that hormone probably
would not bring about fast enough adjustments. The other hormone produced by the
pancreas has an opposing action, or negative feedback, to insulin. When glucose
levels in the blood become low due to the actions of insulin, glucagon tries to negate
or to correct the imbalance. Its actions cause liver and muscle cells to convert
glycogen and, if necessary, amino acids and fats into glucose. The antagonistic
actions between such pairs of hormones are able to bring about faster adjustments.
Imbalances between such pairs of hormones or in the glands themselves could lead
to malfunctions, such as Diabetes mellitus which was described earlier.
Blood – Glucose Cycle
Insulin and glucagons function together to maintain
a fairly stable level of blood glucose
Again, the type of action in which a hormone causes the production of another
hormone and then this second hormone suppresses the first, illustrates a feedback
action. To be more precise, it is negative feedback.
Feedback actions occur on a continuous basis. The hypothalamus part of the brain
is sensitive to many of these feedbacks. The hypothalamus then passes on
neurosecretions or neural messages to the pituitary gland which changes its own
actions.
A more careful examination of the human female reproductive cycle and its
illustration of negative feedback will be looked at more closely in Lesson 11.
Biology 30
291
Lesson 9
Biofeedback
The "feedback" described with respect to hormones should not be confused with
another term or action called biofeedback.
Biofeedback refers to techniques or actions where some
individuals try to consciously control internal body
actions normally under the influence of the autonomic
nervous system.
Individuals try to (develop techniques to) control various body conditions by using
monitoring devices. By observing and concentrating on such things as his or her
own blood pressure, heart rate, electrical impulses (on electroencephalographs) or
other conditions, a person tries to consciously regulate those very conditions. Any
success in achieving any degree of extra control could possibly be used in treating
high blood pressure, migraine headaches, epileptic seizures or other undesirable
conditions. The difficulties in trying to explain how or why conscious controls could
work, or how to measure if they really do work, make biofeedback an uncertain area
of study.
Pheromones
Pheromones are a group of chemicals that are designed to affect other members of the
same species. These chemicals are secreted by duct glands and are released to the
outside. The chemicals which had been previously described were hormones which
are distributed internally and affect internal actions of an individual.
Pheromones are especially noticeable in social insect groups. A queen bee releases a
pheromone from glands in her body into the atmosphere around her. This chemical
affects the female worker bees and prevents any of them from developing an
egg-laying ability. Ants can leave pheromone "trails" on the ground behind them and
use these to retrace their way or to serve as "markers" for others to follow. Ants also
release another type of pheromone from glands in their heads when they are alarmed.
In smaller concentrations, the chemical attracts others toward it.
In larger concentrations, the chemical causes concern and alarm in others
and induces them to scurry about looking for the source of disturbance.
If the disturbance has disappeared, the chemical eventually loses its
concentration in the air and the ants resume normal activities.
Biology 30
292
Lesson 9
Pheromones are also released by individuals during reproduction, enabling males
and females to locate each other over long distances. (Scientists have duplicated
some of these to use as lures in attracting some organisms to traps.)
Just as hormones can be looked at as chemicals which co-ordinate and regulate
individual internal actions, pheromones can be regarded as chemicals which regulate
activities among a group of organisms. For some species – especially social groups,
close communications or regulations among individual members by means of
pheromones are important in maintaining group numbers and social structures.
Pheromones may be just as important for group survival as hormones are for
individual survival.
Summary
To sustain living conditions, organisms must be able to respond to external and
internal stimuli. A response, however, does not necessarily ensure survival. It must
be the right response, in such things as timing and possibly direction and degree or
level of reaction. As the complexities of organisms increase, there are increasing
numbers of body processes going on at the same time. While some may appear to
function independently, many complex interrelationships are actually present. This
makes responses much more complex than what they may seem to be. An action of
one body part or in one area may mean a whole series of actions in other parts or
systems. Simply being startled by a loud noise could result in responses or changes
in heart rate, breathing rate, glucose levels in the blood, sizes of blood vessels and
blood pressure.
The ability to make proper responses, which occur at the right times and in harmony
with each other, has to be under some sort of control. Coordination and regulation of
responses in animal bodies is carried out, in part, by chemical messengers. In an
animal body, these hormones are produced in secretory cells usually organized into
distinct groupings to make up endocrine glands. Ductless, these glands release their
hormones into the blood which then transports them around the body. While
hormones may have some effect on all body cells, specific ones generally have a
"target" area or a group of cells on which they have more influence.
Hormones have some control in almost all body actions or responses. A question
which often arises has to do with what "turns the glands on or off" or what
determines their level of output. External stimuli can do this through their
stimulation of nerve cells and neurosecretory cells in the hypothalamus or other
areas. The hypothalamus can also respond to internal stimuli, particularly to the
levels of substances in the blood or tissues. Once certain glands are stimulated to
release hormones, those hormones may themselves serve as triggering agents for
other glands. Some hormones can exert negative feedback by suppressing the
production of the agent which caused their formation in the first place. All these
influences on hormone production mean that there is usually a fine line or balance
between too little or too much. Extremes in either direction can lead to consequences
ranging from "mild" body disturbances to possible death.
Biology 30
293
Lesson 9