Chapter 13: Endocrine System
Endocrine System:
The endocrine system is made up of the cells, tissues, and organs that secrete
hormones into body
fluids such as the blood stream. What is its function? To control physiological
activities and help maintain homeostasis.
What is the difference between an endocrine gland and an exocrine gland?
Endocrine glands secrete hormones into the body fluids; excrine glands secrte homromes
outside of the body.
Each hormone acts only on specific cells in the body; these are called Target cells.
Hormone Action:
Steriod hormones are lipid-soluble and can pass through cell membranes.
Their receptors are located in the target cell's nucleus.
The hormone-receptor complex binds with the DNA and activate specific genes.
Transcription of a specific gene results in the synthesis of a molecule of mRNA, which in
turn, directs the synthesis of a specific protein.
Non-steriod hormones combine with receptors on target cell membranes; the receptors have
a binding site and a/an activity site. The hormone-receptor complex (as first messenger)
triggers a cascade of biological activity. The complex activates a protein in the cell
membrane, called a G-protein.
What is the name of a common second messenger? cAMP
Prostaglandins are locally-produced lipids that affect the organ in which they are
produced, with a variety of
effects. What are some of these effects? Relax or contract smooth muscle, stimulate
secretion,influence blood pressure, affect reproductive physiology.
Control of Hormone Secretion:
There are several ways in which hormone release is very closely regulated. All of
these mechanisms use negative feedback.
The hypothalamus regulates the anterior pituitary gland’s release of hormones.
The nervous system influences certain endocrine glands directly with impulses.
Other glands respond directly to changes in the composition of the internal
environment.
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Explain in general how negative feedback works.
When the concentration of a regulated substance rechease a certain level, the gland is
inhibited from secreting more hormone.
Pituitary Gland:
The pituitary gland is attached to the base of the brain and has a front lobe called the
anterior pituitary
and a rear lobe called the posterior pituitary
The brain controls the activity of the pituitary gland in two ways:
Releasing hormones from the hypothalamus control the secretions of the anterior
pituitary and are
carried in the bloodstream byhypophyseal portal veins.
The posterior pituitary releases hormones into the bloodstream in response to nerve
impulses from the hypothalamus.
Anterior Pituitary:
The anterior pituitary consists mostly of epitheal tissue arranged around blood vessels
and
enclosed in a capsule of collagenous connective tissue.
How many hormones does it secrete? Six
What function do most of them have in common? Stimulate other endocrine glands.
Growth Hormone (GH):
What is the function of GH? It stimulates body cells to grow and reproduce.
What factors influence growth besides GH? Nutritional status, genetics
Which hormones from the hypothalamus control the levels of GH? GH-Releasing
Hormone and GH- Release Inhibiting Hormone.
What disorders may result from a lack of or too much GH? Pituitary dwarfism,
gigantism, acromegaly.
Prolactin (PRL):
What is the function of PRL? Promotes milk production in lactating women
What is its target tissue? The breast
Which hormones of the hypothalamus control the secretion of PRL? Prolactin
release-inhibiting hormone, and prolactin releasing factor.
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distribution in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in
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Thyroid Stimulating Hormone (TSH):
What is the function of TSH? To stimulate the thyroid gland to secrete thyroid
hormones. What is its target organ? Thyroid gland
What hypothalamic hormones affect its release Thyrotropin- Releasing Hormone.
How are these hormones from the hypothalamus regulated? As the level of
circulating thyroid hromones faqll, the hypothalamus secretes TRH. When the levels
of circulating thyroid hormones are at a rising level, the hypthalums stops screting
TRH.
Adrenocorticotropic Hormone (ACTH):
What is the target organ for ACTH? Adrenal cortex
What hormone does it affect the release of? Cortisol
What is the name of the hormone from the hypothalamus that controls the release of
ACTH? Corticotropin- releasing hormone.
Follicle Stimulating Hormone (FSH):
What are the target organs for FSH? Testes or ovaries
What effect does it have on males? Stimulates sperm production
On females? Stimulates ovarian follicles. Which hormone from the hypothalamus
affects its release? Gonadotropin-Releasing Hormone
Luteinizing hormone (LH):
What does it do? Causes ovulation and formation of corpus luteum in the ovaries.
How is it different in males than in females? Stimulates the testes to release
testosterone.
What is its controlling hormone from the hypothalamus called? GonadotropinReleasing Hormone
Posterior pituitary:
The posterior lobe consists of nerve fibers and supporting neurological cells arising in
the
hypothalamus.
What structure actually produces the hormones released by the posterior pituitary?
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Hypothalamus
Antidiuretic Hormone (ADH):
What is the function of this hormone? Causes kidneys to conserve water
What disorder may result if ADH is not secreted in sufficient quantities? Diabetes
insipidus
Oxytocin:
What are the functions of this hormone ? It causes contraction of the uterine walls
during childbirth, and milk letdown during breast feeding.
Thyroid Gland:
The thyroid gland is located below the larynx and consists of two broad lobes
connected by an isthmus.
The thyroid consists of secretory parts called follicles filled with hormone-storing
colloid.
Thyroxine (T4): How many iodine atoms does it contain? 4
Triiodothyronine (T3): How many iodine atoms does it contain? 3
What is the function of these two hormones? Increase metabolic rate in cells
Which of these hormones is more potent? T3
How does TSH affect their release? When these hormones reach a high level, the
release of TSH is inhibited.
What is a goiter and what may cause one? A goiter is an enlarged thyroid gland that is
caused by a lack of iodine.
Calcitonin:
What is the function of this hormone? Lowers blood levels of calcium and phosphate
ions.
What part of the thyroid secretes it? Extrofollicular cells
Parathyroid Glands:
How many are there and where are they found? 4 and on the back of the thyroid gland
Parathyroid hormone PTH:
What is the function of this hormone? Increase blood calcium levels
How does it achieve this function? Stimulates osteoclasts in bone which break down
bone tissue and relause calcium into the blood.
How is it related to calcitonin from the thyroid? PTH and calcitionin have opposite effects
and work together to maintain the correct levels of calcium ions in the blood.
Adrenal Gland:
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The adrenal glands sit atop the kidneys, enclosed in a layer of fat.
Adrenal medulla:
The adrenal medulla is made up of modified post-ganglionic neurons that are connected
to the sympathetic nervous system.
The hormones secreted are the same as neurotransmitters of this system, but are called
hormones because they are secreted into the blood.
Epinephrine & Norepinephrine:
What effects do these have on the body? Similar effects to those of the sympathic
division of the autonomic nervous system; increase in heart rate and breathing rate, decrease
in digestive activities.
What are they secreted in response to? stress
Adrenal cortex:
The adrenal cortex makes up most of the adrenal glands and consists of epithelial cells
in three layers—
an outer, middle, and an inner zone. Several groups of steroid hormones are secreted by
the cortex.
Mineralocorticoids:
The hormone aldosterone controls the levels of sodium ions by conserving them in the
kidneys. It also causes the excretion of potassium ions.
Why is this important? Homeostasis of the body
Which zone secretes mineralocorticoids? Outer zone
Glucocorticoids:
These hormones influence the metabolism of glucose, protein, and fat in response to
conditions that stress.
the body and require a greater supply of glucose in the bloodstream.
How does negative feedback control the release of these hormones? CRH from the
hypothalmus causes the pituitary to release ACTH.
What else can trigger their release? Stress, injury
Name an important Glucocorticoid. Cortisol
Which zone secretes these hormones? Middle zone
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Adrenal sex hormones:
Sex hormones, produced in the inner zone, are mostly of the male type, called
androgens but can be converted to female hormones, called estrogens, in the skin, liver, and
adipose tissues.
These hormones supplement those released by the gonads, and may stimulate early
development of reproductive organs.
Pancreas:
The pancreas secretes hormones as an endocrine gland, and digestive juices into the
digestive tract as an
Exocrine gland. Where is the pancreas located? Behind and beneath the stomach
Its endocrine portions are the pancreatic islets that include two cell types—alpha cells
that secrete glucagon, and beta cells that secrete insulin.
Glucagon increases the blood levels of glucose by stimulating the breakdown of
glycolgem and the conversion of noncarbohydrates into glucose.
What controls the levels of glucagon in the blood? Negative feedback system
Insulin decreases the blood levels of glucose by stimulating the liver to form glycogen
increasing protein synthesis, and stimulating adipose cells to store fat.
What controls the blood level of insulin? High blood glucose level
Pineal gland:
The pineal gland, near the upper portion of the thalamus, secretes melatonin which is
involved in the
regulation of circadian rhythms of the body.
Thymus gland:
The thymus gland, lying between the lungs under the sternum secretes thymosins which
affect production and differentiation of T lymphocytes that are important in immunity
Reproductive Glands:
The ovaries produce what two hormones? Estrogen, progesterone
What hormones does the placenta produce? Estrogen, progesterone, and gonadotropin.
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The testes produce Testosterone
Digestive Glands and Other Hormone Producing Organs:
The digestive glands secrete hormones associated with the processes of digestion.
The heart secretes atrial natriuretic peptide, which affects sodium excretion, and the
kidneys secrete erythropoietin for red blood cell production.
Stress:
Factors that serve as stressors to the body produce stress and threaten homeostasis.
Stress may be physical, psychological, or some combination of the two.
What effects does physical stress have on the body? Threatens the survival of tissues and
life
What does psychological stress result from? Stress, anger, fear, anxiety
Responses to stress are designed to maintain homeostasis.
The hypothalamus controls the general stress syndrome, which involves increased
sympathetic activity and increased secretion of which hormones?
Epinephrine, cortisol, glucagon, growth hormone, antidiuretic hormone.
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distribution in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in
whole or part.