8
Hormones

The endocrine system consists of a series of tissues, glands, and cells found throughout the body that secrete certain chemicals. When active, these chemicals, called hormones, exert specific effects on specific cells and tissues. Some hormones have the potential to significantly affect other parts of an organism's body.

Both plants and animals produce hormones. Those produced by plants emanate primarily from where most of the growth occurs, such as in the buds, seeds, new shoots, and at the root tips. The plant hormone-producing areas have other functions as well. In animals, the sole function of these hormone-producing tissues, or endocrine glands, is hormone production. In animals, hormones are distributed through the body via the circulatory system. In vascular plants, hormones are transported by the phloem from the site of synthesis to where they are used.

PLANT HORMONES

Plant hormones have been of considerable interest to researchers because of their many potential practical applications. For instance, when storing fruits, vegetables, and grains, it would be helpful to understand what makes them remain dormant for long periods of time. And because some hormones stimulate the rapid growth of specific plant parts, such as the seeds, or even specific parts of a seed, by manipulating plant hormones it is possible to increase the value of a cereal crop considerably.

AUXINS

The auxins represent one of the most widely understood groups of plant hormones. They have been shown to be important in controlling cell elongation in plant stems, especially with regard to varying types of stimuli. For instance, light reduces the auxin supply to the side of a plant it strikes. Since the plant has more auxins on the shaded side, the cells grow faster there, causing the stem to bend toward the light. This bending toward light is known as the phototropic response.

Plant tropisms usually refer to the turning or bending of a plant part in response to a particular stimulus, such as light, gravity, water, or other nutrients, producing different growth patterns. One such tropism in which auxins are implicated is geotropism, which has to do with the direction plant parts grow in response to gravity. A negative geotropic response involves a shoot growing away from the direction in which gravity pulls.

Shoot tips are not only sensitive to light, but they can also detect gravity. When there is an unequal distribution of gravitational pull on all sides, they increase the concentration of auxins on the lower side. This stimulates the cells on the lower side to elongate faster than the cells on the upper side, which gets the plant to grow up again. Roots, unlike shoots, have a positive geotropic response. That is, they turn toward the pull of gravity. Root growth direction is also affected by the concentration gradient of water and specific nutrients.

Auxins are also involved in the inhibition of lateral buds. Those auxins produced in the terminal bud, the bud at the tip of the shoot, move down the shoot and inhibit the development of the nearby buds, while also stimulating the stem to elongate.

It has been demonstrated that the rapid growth of many types of fruit is stimulated by auxins released from the pollen grains that fertilized the ovule (egg), and that, as the seeds develop, they continue to produce more auxins. Auxins are also involved in preventing leaves, flowers, and fruits from falling off the plant. Then, when it is time, hormonal changes, such as those triggered by shorter day length, colder temperatures, or drier conditions, can stimulate the growth of what are known as abscission layers, which result in specific plant parts falling off.

In addition to being important in cell elongation and in forming abscission layers, auxins are also involved in cell division. In the early spring, when the auxins move down from the buds, they stimulate the cambium to divide, forming a new layer of xylem. Toward autumn, the buds produce less auxin until eventually the production of new buds, leaves, and xylem slows down or stops. Toward the end of winter, renewed auxin production stimulates the resumption of growth.

GIBBERELLINS

The gibberellins, another group of plant hormones, probably function in conjunction with, rather than separately from, the auxins. Gibberellins have a dramatic effect on stem elongation, particularly on those plants that are normally known for their “dwarf” varieties. Unlike auxins, gibberellins do not produce the bending movements typical of the phototropic and geotropic responses of shoots and roots. Gibberellins do not inhibit the growth of lateral buds, and they do not prevent leaf abscission. While auxins stimulate the cambium to produce new xylem cells, gibberellins stimulate the cambium to produce new phloem cells. Gibberellins have also been implicated in ending seed dormancy, and they have been shown to induce some biennials, which normally take two years to flower, to flower during their first year of growth. Gibberellins also affect the time when plants flower, depending on both timing and duration of the dark periods of a day (see the section on Photoperiodism below).

CYTOKININS AND INHIBITORS

Both auxins and gibberellins have been shown to affect cell division, though they appear to work in conjunction with other substances more directly involved in this process. The cytokinins are the compounds known to promote cell division. Other compounds, known as inhibitors, are important in inhibiting or blocking cell division activity, thereby maintaining the dormancy of buds, seeds, and shoots.

One such hormone is abscisic acid, which has been shown to be involved in inducing abscission. Abscission is caused from the growth of thin-walled cells that result in the falling of a leaf or fruit from the plant. Abscisic acid has also been implicated in plant dormancy, stomatal closure, and growth inhibition.

ETHYLENE

Ethylene is a very volatile compound that has a number of different activities in plants. This plant hormone is involved in fruit ripening. It contributes to leaf abscission and to lateral bud inhibition. In addition, it has been shown that when some trees are attacked by herbivorous insects, ethylene is released, which may trigger nearby trees to manufacture chemicals that will protect them from the insects. Ethylene is also involved in the plant's aging process.

PHOTOPERIODISM

The response by an organism to the duration and timing of light and dark is known as photoperiodism. Some plants respond to precise daylight periods. It has been found that rather than day length, it is the length of the night that is critical. But since this was discovered after the following terms were coined, they are still with us.

Short-day plants flower when the day length is below a certain critical value, generally resulting in a plant's blooming either during the spring or the fall. Long-day plants bloom when the day length exceeds a specific critical value, which is usually during the summer. And day-neutral plants can bloom anytime and may respond to other cues besides the length of the daylight or darkness.

Depending on the particular species, a certain day length causes the leaves to manufacture the hormone florigen, which moves to the buds and causes flowering. When leaves are exposed to other specific photoperiods, they destroy florigen, and therefore the plants do not flower. It is not precisely known how gibberellins affect flowering, but it appears to differ with species. In some, the effect of gibberellins is indirect. In others, the gibberellins seem to work in conjunction with florigen to induce flowering. It has been found that plants possess a sensitive pigment, phytochrome, which responds to the presence or absence of light by measuring the time lapse between the onset of darkness until the next exposure to light. Phytochrome is coupled with florigen synthesis.

ANIMAL HORMONES

Hormones are important to animals as well as plants. Among invertebrates and vertebrates, hormones are involved in the regulation of growth, development, and homeostasis. Specific animal organs produce hormones that travel, usually via the blood, to other organs where they coordinate certain bodily functions. In animals, the release of hormones is usually triggered by nervous stimuli.

There are two basic groups of organs that secrete specific substances into the body. These are the exocrine glands, which secrete their products into ducts, which then carry the secretions to the body surface or into the body cavity. Digestive, mucous, sebaceous, and sweat glands are included in this category.

Glands in the other group secrete their products into the general area around the secretory cells, and from this area, the secretions pass into the blood capillaries. These endocrine glands are ductless. They include the adrenals, pancreas, pineal, parathyroids, ovaries, testes, thymus, and thyroid. It is the endocrine glands that produce hormones, which are a protein, an amine, or a steroid (see Figure 8.1).

Location and the general appearance of important hormone-secreting glands in humans, including the adrenals, pancreas, pineal, parathyroids, ovaries, testes, thymus, and thyroid. — **Figure 8.1** Location and general appearance of important hormone-secreting glands in humans.

Regardless of the type of chemical, all hormones, whether protein, amine, or steroid, stimulate cellular changes in target cells, in a target organ, or in a group of organs. Or the hormone may affect the activities of all the cells in the body. See Table 8.1 for a list of human hormones and their functions.

DIGESTION (GASTROINTESTINAL TRACT)

Digestion is the breakdown of large insoluble food into water-soluble molecules that can move into the bloodstream. For food to be properly digested, it is often chewed first and broken down into smaller pieces. As saliva starts to break down starches, the food is swallowed. Peristaltic muscle contractions help move the chewed food and liquids through the esophagus to the stomach. Passing into the stomach, meat stimulates the release of gastrin, a hormone that stimulates the gastric glands to secrete gastric juice, which starts digesting the meat. Both the stomach and intestine produce gastrin. One type of gastrin is called stomach gastrin and the other, intestinal gastrin. When the food is done being processed in the stomach, it passes through the pyloric sphincter, which is a circular muscle that controls the opening at the end of the stomach and the beginning of the duodenum, which is the beginning of the small intestine.

Table 8.1 Major sources of human hormones and their functions.

Source	Hormone	Functions	Deficiency	Excess
Thyroid gland	Thyroxine	Stimulates metabolism: regulates general growth and development	Cretinism	Graves' disease
Thyroid gland	Calcitonin	Lowers blood calcium
Parathyroid	Parathormone	Increases blood calcium; decreases blood phosphate	Muscle spasms	Calcium deposits
Pancreas	Insulin	Lowers blood glucose	Diabetes	Hypoglycemia
Pancreas	Glucagon	Increases blood glucose	Hypoglycemia
Adrenal
medulla	Epinephrine (Adrenalin)	Increases metabolism in emergencies
medulla	Norepinephrine (Noradrenalin)	As above
cortex	Glucocorticoids and related hormones	Controls carbohydrate, protein, mineral, salt, and water metabolism	Addison's disease	Cushing's syndrome
Pituitary
anterior	Thyroid-stimulating hormone	Stimulates thyroid gland function
	Adrenocorticotropic hormone (ACTH)	Stimulates adrenal cortex	Hypoglycemia	Cushing's syndrome
	Growth hormone	Increases body growth	Dwarfism	Gigantism, acromegaly
	Gonadrotropic hormones	Stimulates gonads
	Prolactin	Milk secretion
posterior	Vasopressin (ADH)	Water retention by kidneys
posterior	Oxytocin	Milk production
Testis	Testosterone (Androgens)	Secondary sex characteristics, sperm production	Sterility
Ovary	Estrogens	Secondary sex characteristics
Ovary	Progesterone	Prepares uterus for pregnancy
Hypothalamus	Hypothalamic releasing and inhibiting hormones	Releases of hormones from anterior pituitary gland
Kidney	Renin	Vasoconstriction		Increases blood pressure
Kidney	Erythropoietin	Production of red blood cells in bone marrow
Gut wall	Digestive hormones	Digestion of food
Thymus gland	Thymosin	Maturation of lymphocyte white blood cells

Fats stimulate the wall of the duodenum to release enterogastrone, a hormone that inhibits the secretion of gastric juice. When stimulated by acidic food coming from the stomach, the mucosal cells of the small intestine release the hormone secretin. Secretin stimulates the secretion of pancreatic juice. The small intestine, when stimulated by acids and fats, releases the hormone cholecystokinin (pancreozymin), which stimulates the gallbladder to release bile. Bile aids in fat digestion. It is produced by the liver, stored in the gallbladder, and released into the duodenum.

From the stomach the digesting food passes through the gastrointestinal tract, which is basically a large, muscular tube that extends from the mouth to the stomach to the small intestine, and then through the large intestine, where what has not been absorbed into the bloodstream is passed out through the anus.

HISTAMINE

Damaged tissues release histamine, which dilates, or relaxes, the muscles in the walls of blood vessels, thereby making them more permeable to their contents and enabling more white blood cells and antibodies to move into the damaged area to fight infection.

People with certain allergies, such as hay fever, may develop a reaction that causes the nasal mucosa to release histamine. This dilates the nasal blood vessels so that fluids escape from both the blood vessels and the mucosal glands, thus causing a runny nose. This is why such people take antihistamines.

PANCREAS

The pancreas aids digestion by producing pancreatic digestive enzymes. In addition, the pancreas contains islet cells, or islets of Langerhans, which produce the hormone insulin. This hormone reduces the concentration of glucose in the blood. Too much insulin in one's system, from the rare condition of an overactive pancreas, can produce insulin shock, during which the blood sugar level falls so low that a person may become unconscious and die.

More common is the insulin deficiency, known as diabetes, which results in the inability of the liver and muscles to control the conversion of glucose into glycogen. Sometimes the liver produces too much glucose from glycogen, depleting all its resources and making the body use its proteins and fats. Diabetes often leads to chronic problems affecting many aspects of one's well-being.

The pancreas also secretes glucagon. This has the opposite effect of insulin, causing the amount of glucose in the blood to increase.

ADRENALS AND KIDNEYS

At the anterior (top) end of each kidney is an adrenal gland (sometimes called a suprarenal gland), which is composed of the outer adrenal cortex and the inner adrenal medulla. The cortex produces over 50 different hormones, not all of which are active. All are steroids, as are the hormones produced by the gonads (ovaries and testes). The cortical hormones, those produced by the adrenal cortex, are grouped according to their function. One group, the glucocorticoids, contains hormones that regulate carbohydrate and protein metabolism. Another group, the mineralocorticoids, regulates salt and water balance. A third group, the gonadocorticoids, consists of certain male and female sex hormones, the estrogens and androgens.

The adrenal medulla secretes adrenalin (epinephrine), as well as noradrenalin (norepinephrine). Adrenalin decreases insulin secretion, and it also stimulates pulse and blood pressure. In addition, it stimulates the conversion of glycogen into glucose (in the liver), which is then released into the blood. Adrenalin also increases oxygen consumption and the flow of blood to the skeletal muscles (those that move the body), while decreasing the blood flow to the smooth muscles (those involved in digestion). Many of these reactions, which cumulatively are often referred to as the fight-or-flight response, occur when the body is subjected to pain, fear, anger, or other stress. Noradrenalin has similar effects in that it helps to mobilize the body during times of stress.

The kidneys secrete the protein renin, which reacts with a blood protein to form the hormone hypertensin (also called angiotonin). Hypertensin stimulates the constriction of small blood vessels, increasing blood pressure. This seems to be a response that kidneys use to compensate for reduced blood flow due to blocked arteries. The higher blood pressure can overcome such temporary blockages, allowing the kidneys to filter the necessary amount of blood. Kidneys also secrete erythropoietin, a hormone that stimulates red blood cell production.

THYROID

In humans, the thyroid gland, located just below the larynx, around the front and sides of the trachea, produces the hormone thyroxin, an amino acid altered with four iodine atoms. Thyroxin's primary function involves the regulation of metabolic activity by increasing the rate at which carbohydrates are burned. Also, it stimulates cells to break down proteins for their energy rather than using them to build new tissues.

Iodine is necessary for proper thyroid function; an insufficient amount in the diet produces a condition known as hypothyroidism, resulting in a decrease in energy. Children with this condition can have developmental problems. Hypothyroidism can be treated with more iodine in the diet, or with thyroxin.

Hyperthyroidism is due to a thyroid that produces too much hormone, resulting in an increased metabolic rate, higher than normal body temperature, high blood pressure, and weight loss. Elevated thyroid activity can be inhibited with the prescribed treatment of recently discovered drugs.

The thyroid gland releases two other hormones. Triiodothyronin is similar to thyroxin, except that it is much stronger. Thyrocalcitonin (sometimes called calcitonin) is quite different from the previous two hormones, both structurally and functionally; it helps control the blood calcium level.

PARATHYROIDS

On the thyroid's surface are four small pea-like organs known as the parathyroids, which are functionally distinct from the thyroid. They produce the hormone, parathormone(PTH), which regulates the calcium-phosphate balance between the blood and other tissues. A calcium deficiency caused by hypoparathyroidism results in nervous twitches, spasms, and convulsions.

Hyperparathyroidism results in an increase in parathyroid hormone, which leads to the demineralization of bone tissue, rendering the bones highly susceptible to fracture.

THYMUS

Located in the upper chest and lower neck, the thymus gland is composed of tightly packed lymphocytes. These white blood cells are held in place by fibrous tissue. The thymus is most active from infancy to puberty, after which it atrophies, only to enlarge again in old age. The gland produces thymosin, a hormone that stimulates plasma cells in the spleen, lymph nodes, and other lymphoid tissues to function immunologically. Two of the main types of lymphocytes, the B cells and T cells, are produced in the bone marrow and then migrate to lymphoid tissues. Those that end up in the thymus gland become thymus-dependent lymphocytes, or T cells. It may be the thymosin that affects these cells, enabling them to destroy antigens (foreign microbes and substances). Thymic dendritic cells also reside in the thymus. Like B cells and T cells, dendritic cells are also produced in the bone marrow. Dendritic cells stimulate resting T cells to initiate an immune response. American scientists Ralph Steinman and Zanvil Cohn discovered dendritic cells in 1973, for which Steinman received the Nobel Prize in 2011.

PITUITARY

In the brain is the small gland known as the pituitary, also called the hypophysis, which consists of two lobes: the anterior lobe and the posterior lobe. Both are attached via a stalk, the infundibulum, to the hypothalamus, which is located just above the pituitary (see Figure 8.2).

The anterior pituitary, also called the adenohypophysis, produces many hormones. Most control the activities of other endocrine glands (see Figure 8.3). Of these hormones, prolactin stimulates female mammary glands to produce milk. Growth hormone (somatotrophic hormone, STH) is important in regulating growth. Melanocyte-stimulating hormone (MSH) triggers pigment molecule dispersion in the pigment-containing cells, often called melanophores in some lower vertebrates such as fish, frogs, and lizards. MSH increases skin pigmentation by stimulating the dispersion of melanin granules in mammal melanocytes; mammals, however, lack melanophores.

Thyrotropin, also called thyrotropic hormone, stimulates the thyroid. Adrenocorticotropic hormone (also known as ACTH) stimulates the adrenal cortex. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) act on the gonads. In females, FSH initiates the development of an ovum each month. In males, FSH stimulates the testes to produce more sperm. In females, LH stimulates the ovary to release the developed ovum. It also stimulates the corpus luteum in the ovary to secrete progesterone, which prepares the uterus for receiving the embryo. The posterior lobe, or neurohypophysis, contains neuron fibers that connect with the hypothalamus. The cell bodies of these neurons produce two hormones: oxytocin and antidiuretic hormone (ADH). Oxytocin stimulates the contraction of the uterus as well as the contractile cells around the ducts in the mammary glands. ADH, also called vasopressin, stimulates the kidneys to absorb more water and return it to the blood, thereby decreasing the urine volume. Alcohol inhibits the secretion of ADH, increasing urine output.

A cross section of the human brain depicting the location of the pituitary gland, thalamus, hypothalamus, medulla, and cerebellum. — **Figure 8.2** Location of the pituitary gland and hypothalamus, as illustrated in this cross section of a human brain.

Illustration of the hormones produced by the pituitary gland and the parts of the body where each has its effect - Cortical hormone, growth hormone, throxin, prolactin, testoterone, and estrogen. — **Figure 8.3** The hormones produced by the pituitary gland and the parts of the body where each has its effect.

The pituitary gland also releases thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to make thyroxine (which is released into the bloodstream in this inactive form). Later the liver and kidneys convert it into triiodothyronine, which affects metabolic processes all around the body.

HYPOTHALAMUS

The hypothalamus receives nervous impulses from the body's sense organs and then responds by secreting releasing factors into the blood. The releasing factors, which are hormone-like substances, stimulate the anterior pituitary to secrete specific hormones.

The onset of puberty, the sequence of events that transforms a child into a young adult, begins when the hypothalamus secretes follicle-stimulating hormone-releasing factor (FSHRF), which signals the anterior pituitary to secrete FSH and interstitial cell-stimulating hormone (ICSH), both of which are hormones that stimulate the gonads (testes and ovaries). Hormones released by the gonads are referred to as gonadotropic hormones (see Figure 8.3).

In the female, the menstrual cycle and ovarian cycle are controlled by the FSHRF and the luteinizing hormone-releasing factor (LHRF). FSHRF stimulates the anterior pituitary to release FSH, which stimulates follicular development and estrogen secretion by the follicles.

Luteinizing hormone-releasing factor stimulates the anterior pituitary to release LH, which stimulates the development of ovarian follicles, leading to ovulation. In addition, it stimulates the production of the female growth and maturation hormones, estrogens and progesterone. The hypothalamus gland also produces TSH releasing hormone.

OVARIES

In the ovaries are jackets of cells surrounding the potential egg cells. These are known as follicles. They release estrogens, which are involved in the development and maintenance of the uterus and breasts. Estrogens are also involved in fat distribution and deposition, voice pitch, broadening of the pelvis, and hair growth.

The corpus luteum, which is formed from the follicle after ovulation, secretes both estrogens and progesterone, which prepare the endometrium, the internal layer of the uterus, for implantation of an embryo, and it helps prepare the breasts for milk production.

On average, from the first period, or menses (menarche), to menopause, the termination of menstrual cycles, the menstrual cycle lasts 28 days. The menstrual cycle can be divided into the menstrual phase (menses), the preovulatory phase, ovulation, and the postovulatory phase. The main events that occur in the ovary and uterus with regard to the above hormones are illustrated in Figure 4.10 on page 82.

During birth, estrogen stimulates the contractions of the uterine muscles, and progesterone inhibits these muscular contractions. Oxytocin is thought to be involved in uterine contractions. Another hormone, relaxin, which is secreted by the ovaries and placenta during pregnancy, helps loosen some of the connections between the pelvic bones, making them more flexible to enlarge the birth canal when the baby is being born. This occurs to a lesser extent in humans than in many other mammal species.

TESTES

Follicle-stimulating hormone stimulates the seminiferous tubules to begin spermatogenesis. Interstitial cell-stimulating hormone assists the seminiferous tubules to develop mature sperm and also stimulates the interstitial cells in the testes to secrete testosterone.

Just prior to birth, testosterone stimulates the descent of the testes into the scrotum. Testosterone also controls development, growth, and maintenance of the male sex organs. At puberty, testosterone stimulates the secondary male sex characteristics such as the development of more muscle, more body hair, and deepening of the voice. The anabolic steroids used by many athletes to increase muscle mass are artificially manufactured forms of testosterone. One of their possible side effects may be male sterility.

KEY TERMS

abscisic acid	adrenal medulla	antihistamines
abscission layers	adrenalin	auxins
adenohypophysis	adrenocorticotropic hormone	bile
adrenal cortex	anabolic steroids	oxytocin
adrenal gland	hormones	pancreas
cholecystokinin	hyperparathyroidism	pancreatic juice
corpus luteum	hypertensin	pancreozymin
cortical hormones	hyperthyroidism	parathormone
cytokinins	hypoparathyroidism	parathyroids
day-neutral plants	hypophysis	photoperiodism
diabetes	hypothalamus	phototropic response
endocrine glands	hypothyroidism	phytochrome
endocrine system	infundibulum	pituitary
endometrium	inhibitors	posterior lobe
enterogastrone	insulin	progesterone
erythropoietin	insulin shock	prolactin
estrogen	interstitial cell-stimulating hormone	relaxin
ethylene	islet cells	releasing factors
exocrine glands	islets of Langerhans	secretin
florigen	long-day plants	renin
follicle-stimulating hormone	luteinizing hormone	short-day plants
follicle-stimulating hormone-releasing factor	luteinizing hormone-releasing factor	steroids
gastric glands	melanocyte-stimulating hormone	testes
gastric juice	menarche	testosterone
gastrin	menopause	thymosin
geotropism	menses	thymus gland
gibberellins	menstrual cycle	thyrocalcitonin
glucagon	mineralocorticoids	thyroid gland
glucocorticoids	neurohypophysis	thyrotropic hormone
gonadocorticoids	noradrenalin	thyrotropin
gonadotropic hormones	norepinephrine	thyroxin
gonads	ovaries	triiodothyronin
growth hormone	anterior lobe	tropisms
histamine	antidiuretic hormone	vasopressin

SELF-TEST

Multiple-Choice Questions

Introduction, Plant Hormones, Auxins, Gibberellins, Cytokinins

Chemicals that exert specific
effects on target tissues are called ___________.
1. hormones
2. auxins
3. gibberellins
4. cytokinins
5. all of the above
The following group of plant hormones, ___________, has been shown to be important in controlling cell elongation in plant stems, as well as in roots, and is also involved in the phototropic and geotropic responses.
1. cytokinins
2. gibberellins
3. auxins
4. ethylenes
5. all of the above
A plant ___________ is the term usually used to describe the turning or bending of a plant part in response to a particular stimulus.
1. tropism
2. gibberellin
3. auxin
4. all of the above
5. none of the above
The following group of plant hormones, ___________, has a dramatic effect on stem elongation, particularly on plants that are normally “dwarf” varieties.
1. gibberellins
2. auxins
3. cytokinins
4. all of the above
5. none of the above
While both the auxins and gibberellins have been shown to be involved in stimulating cell division, apparently they work in conjunction with other substances more directly involved in this process. The group of compounds that promote cell division is called ___________.
1. inhibitors
2. ethylenes
3. phytochromes
4. cytokinins
5. all of the above

Animal Hormones, Digestion (Gastrointestinal Tract), Histamine

The following are examples
of endocrine glands:
1. adrenals, pancreas, pineal, mucous
2. parathyroids, ovaries, testes, sweat
3. thymus, thyroid, adrenals, testes, mucous
4. sweat, pancreas, pineal, ovaries, thymus
5. parathyroids, testes, thymus, thyroid, adrenals
Endocrine glands produce hormones that are ___________.
1. proteins
2. steroids
3. amines
4. proteins and amines
5. proteins, steroids, and amines
Certain hormones can stimulate a ___________.
1. cellular change
2. a change in a target organ
3. a change in a group of organs
4. a change in the activities of all the cells in the entire body
5. all of the above
The stomach and intestine produce stomach ____________ and intestinal ___________, hormones carried by the blood to the ___________ glands, which then secrete ___________.
1. enterogastrone, secretin, cholecystokinin, pancreozymin
2. gastrin, enterogastrone, cholecystokinin, pancreozymin
3. cholecystokinin, secretin, gastrin, enterogastrone
4. gastric juice, secretin, gastric, enterogastrone
5. gastrin, gastrin, gastric, gastric juice
Damaged tissues release ___________, which dilates the muscles in the walls of the blood vessels, making them more permeable to their contents, enabling more white blood cells and antibodies to move into the damaged area where they can fight infection.
1. histamine
2. antihistamine
3. insulin
4. glucagon
5. cortisone

Pancreas, Adrenals and Kidneys, Thyroid

The pancreas functions
not only in aiding digestion by producing pancreatic digestive enzymes but also contains ___________ that produce the hormone ___________, which reduces the concentration of ___________ in the blood.
1. islet cells, insulin, glucose
2. islets of Langerhans, insulin, glucose
3. adrenal glands, norepinephrine, glycogen
4. a and b
5. all of the above
An insulin deficiency, known as ___________, results in the inability of the liver and muscles to properly control the conversion of glucose to glycogen.
1. diabetes
2. cretinism
3. hypothyroidism
4. hypertensin
5. hyperthyroidism
The pancreas releases ___________, which has the opposite effect of ___________, causing the amount of blood glucose to increase.
1. insulin, glycogen
2. insulin, glucagon
3. glycogen, insulin
4. glucagon, insulin
5. none of the above
On top of each kidney is a(n) ___________.
1. adrenal gland
2. adrenal cortex
3. adrenal medulla
4. suprarenal gland
5. all of the above
Each adrenal gland is composed of ___________ and___________.
1. an outer adrenal cortex, an inner adrenal medulla
2. an outer adrenal medulla, an inner adrenal cortex
3. a thyroid gland, a parathyroid gland
4. an anterior pituitary gland, a posterior pituitary gland
5. none of the above
___________ hormones regulate carbohydrate and protein metabolism, salt and water balance, and some sexually related functions as well.
1. cortical
2. pancreatic
3. thyroid
4. gastrointestinal
5. digestive
The adrenal medulla
secretes ___________.
1. adrenalin
2. epinephrine
3. noradrenaline
4. norepinephrine
5. all of the above
The kidneys secrete the protein renin that reacts with a blood protein, forming the hormone ___________, which stimulates the contraction of small blood vessels, increasing blood pressure.
1. hypertensin
2. angiotonin
3. erythropoietin
4. a and b
5. all of the above
An amino acid that has been altered by the addition of four iodine atoms and is the primary hormone produced by the thyroid gland is ___________.
1. triiodothyronin
2. thyrocalcitonin
3. thyroxine
4. hypothyroid
5. hyperthyroid
Iodine is necessary for proper thyroid function. With insufficient amounts in the diet, the condition ___________ may develop, resulting in a decrease in energy.
1. hyperthyroidism
2. hypothyroidism
3. diabetes
4. iodinemia
5. parathyroidism

Parathyroids, Thymus, Pituitary, Hypothalamus

Parathormone is the hormone produced by the parathyroids that regulates the ___________ balance between the blood and other tissues.
1. potassium-phosphate
2. calcium-sodium
3. potassium-sodium
4. sodium-phosphate
5. calcium-phosphate
Hyperparathyroidism leads to ___________.
1. a deficiency of calcium
2. nervous twitches
3. spasms
4. convulsions
5. the demineralization of bone tissue
Hypoparathyroidism is or results in ___________.
1. a deficiency of calcium
2. nervous twitches
3. spasms
4. convulsions
5. all of the above
The thymus is
composed of ___________.
1. tightly packed lymphocytes
2. lymphocytes held in place by fibrous tissue
3. T cells
4. all of the above
5. none of the above
The hormone that stimulates female mammary glands to produce milk is ___________.
1. adrenocorticotrophic hormone
2. luteinizing hormone
3. progesterone
4. prolactin
5. follicle-stimulating hormone
The corpus luteum in the ovary secretes ___________.
1. adrenocorticotrophic hormone
2. progesterone
3. antidiuretic hormone
4. oxytocin
5. vasopressin
The following hormone stimulates the kidneys to absorb more water, returning it to the bloodstream, thereby decreasing the urine volume:
1. antidiuretic hormone
2. progesterone
3. oxytocin
4. luteinizing hormone
5. thyrotrophic hormone
Contraction of the uterus is stimulated by ___________.
1. antidiuretic hormone
2. vasopressin
3. oxytocin
4. melanocyte-stimulating hormone
5. growth hormone
The hypothalamus receives nervous impulses from the body's sense organs and then responds by secreting hormone-like substances, known as ___________, into the blood.
1. anticoagulants
2. blood thinners
3. ammonium ions
4. releasing factors
5. all of the above

Ovaries, Testes

The menstrual cycle and ovarian cycle are controlled by follicle-stimulating, hormone-releasing factor and luteinizing hormone-releasing factor, both of which originate in the ___________.
1. anterior pituitary
2. posterior pituitary
3. infundibulum
4. hypophysis
5. hypothalamus
Along with
estrogens, ___________ prepares the endometrium (the internal layer of the uterus) for implantation of an embryo, and it helps prepare the breasts for milk secretion.
1. progesterone
2. follicle-stimulating hormone-releasing factors
3. luteinizing hormone-releasing factor
4. vasopressin
5. oxytocin
___________ are involved in the development and maintenance of female reproductive structures such as the uterus and breasts, as well as being involved in fat distribution and deposition, voice pitch, broadening of the pelvis, and hair growth.
1. estrogens
2. follicle-stimulating hormone-releasing factors
3. luteinizing hormone-releasing factors
4. thyrotrophic hormones
5. all of the above
___________ stimulates the seminiferous tubules to begin spermatogenesis.
1. follicle-stimulating hormone
2. testosterone
3. relaxin
4. estrogen
5. luteinizing hormone
Just prior to birth, ___________ stimulates the descent of the testes into the scrotum.
1. follicle-stimulating hormone
2. testosterone
3. relaxin
4. estrogen
5. luteinizing hormone

ANSWERS

Questions to Think About

What are hormones, and how are they delivered from where they are produced to their target area?
What is the difference between endocrine and exocrine glands?
What are two groups of plant hormones, and how do they affect plants?
What is a plant's photoperiod?
Describe how hormones affect diabetes.
Compare the similarities and differences of male and female sex hormones.