Chapter 9 The Endocrine System
The Endocrine System and Hormone Function Overview
• The endocrine system coordinates and directs the activity of the body’s cells.
• The major processes
influenced by hormones are reproduction, growth and development,
mobilizing defenses, maintaining electrolyte and nutrient balance, cellular metabolism and energy balance.
The Endocrine System and Hormone
• Endocrine organs lack the structure and continuity of typical organ
systems.
• Hormones are chemical substances secreted by cells into extracellular fluids that regulate metabolic activity of other cells in the body.
• Hormones can be classified into amino acid-based or steroids.
• Prostaglandins are localized
hormones made from lipids of the plasma membrane.
Testosterone
Progesterone
The Endocrine System and Hormone
• Hormones only affect certain tissues or organs called
target cells or target organs.
• Hormones must bind with membrane receptors to influence cells.
• Hormones affect cells by altering cellular activity to:
1) Changing plasma membrane permeability
2) Synthesis of proteins or regulatory molecules
3) Activation or non-activation of enzymes
4) Stimulation of mitosis.
Thyroid Gland
Adrenal Gland
Ovary
The Endocrine System and Hormone Function Overview
• There are two mechanisms by which hormones trigger changes in cells
The Endocrine System and Hormone
• What prompts the endocrine
glands to release their hormones?
• Negative feedback mechanisms are the chief means of regulating blood levels of nearly all hormones.
• In this system rising hormone levels inhibit further hormone release.
• Major stimuli of the endocrine system fall into 3 categories:
1) Hormonal 2) Humoral 3) Neural
The Major Endocrine Organs
• The hypothalamus plays a dual role in both the endocrine and nervous system.
• Releasing and inhibiting hormones secreted into portal circulation from the hypothalamus control the secretions of the anterior pituitary gland.
• Endocrine glands release
hormones into blood or lymph, whereas exocrine glands
release their products at the body’s surface or into body cavities through ducts.
The Pituitary Gland
• The pituitary gland hangs from the inferior surface of the hypothalamus.
• The anterior pituitary is comprised of glandular tissue, whereas the
posterior pituitary is comprised of nervous tissue.
• GH and PRL effect non-endocrine targets.
• The 4 tropic hormones (TH, ACTH, FSH, & LH) stimulate their target
organs to secrete their hormones
which in turn exert an effect on other organs or tissues.
• All anterior pituitary hormones are:
1) Proteins
2) Act through 2nd messengers 3) Regulated by hormonal stimuli
Hormones of the Anterior Pituitary
• Growth hormone (GH) is a anabolic hormone.
• It directs growth of skeletal muscle and long bones.
• It causes the break down of fats for energy while sparing blood glucose levels.
• Hyposecretion of GH during childhood leads to pituitary dwarfism.
• Hypersecretion of GH during childhood results in gigantism.
• Acromegaly is the result of GH hypersecretion after long bone growth has ended.
• Other cases of hypersecretion result from pituitary tumors.
• Prolactin (PRL) stimulates and maintains milk production after childbirth.
• Adrenocorticotropic hormone (ACTH) stimulates cells of the adrenal cortex to produce glucocorticoids,
mineralocorticoids, and androgens.
• Thyroid-stimulating hormone (TSH) a.k.a thyrotropic hormone (TH)
stimulates the release of thyroxine T4 from the thyroid gland.
• Gonadotropic hormones FSH and LH (ICSH in males) regulate hormonal
activity of the ovaries and testes (gonads).
• Hyposecretion of FSH or LH results in sterility.
Hormones of the Anterior Pituitary
Hormones of the Posterior Pituitary
• The posterior pituitary is a storage site for oxytocin and antidiuretic hormone produced by
neurosecretory cells of the hypothalamus.
• Oxytocin stimulates powerful
contractions of the uterine muscle during childbirth and causes milk ejection in nursing women.
• Antidiuretic hormone (ADH)
inhibits urine production causing a drop in urine volume and an
increase in blood volume.
• Hypersecretion of ADH causes diabetes insipidus (continual thirst).
Thyroid Gland
• The thyroid gland consists of two lobes connected by a mass called the isthmus at the base of the throat.
• Thyroid hormone is two active
iodine-containing hormones thyroxine or T or triiodothyronine or T3. 4
• T
3 is formed by conversion of T
4 at the target tissue.
• Thyroid hormone controls rate of glucose oxidation.
• A goiter is an enlargement of the thyroid gland resulting from an iodine deficient diet.
• In early childhood, hyposecretion results in cretinism.
• Myxedema causes physical and mental sluggishness in adults with hyposecretion.
• Tumors of the thyroid generally cause
hyperthyroidism such as Grave’s disease or exophthalmos.
Thyroid Gland and the Parathyroid Gland
• Calcitonin or thyrocalcitonin produced by the thyroid gland decreases blood calcium levels.
• Calcitonin lowers blood calcium by causing calcium to be deposited in bone.
• The parathyroid glands are small masses of tissue on the posterior surface of the thyroid gland.
• Parathryoid hormone or PTH
stimulates bone cell destruction to release calcium into the
bloodstream in response to low blood calcium levels.
• Tetany is a condition caused by low blood calcium levels.
Hormones of the Adrenal Glands
• The adrenal glands are composed of endocrine tissue (adrenal cortex) and neural tissue (adrenal medulla) that sits atop of the kidneys.
• The adrenal cortex produces 3 major groups of steroid hormones:
1) Mineralocorticoids such as aldosterone help regulate mineral (salt) content of the blood by targeting uptake at the kidneys.
2) Glucocortocoids such as cortisone and cortisol help resist long-term stressors by increasing blood glucose levels and also help control inflammation.
3) Sex hormones such as androgens (male hormones) and estrogens (female hormones)
• Addison’s disease is caused by hyposecretion of adrenal cortex hormones leading to muscle
weakness, hypoglycemia, and a suppressed immune system.
• Cushing’s syndrome is the result of a tumor in the middle of the cortex causing a excessive output of glucocortocoids.
Sara Elizabeth with Addison’s disease
Hormones of the Adrenal Glands
• The adrenal medulla is stimulated by the sympathetic nervous system to release epinenphrine
(adrenaline) and norepinephrine (noradrenaline).
• Upon stimulation the adrenal
medulla pumps its hormones into the bloodstream to enhance and prolong the effects of the
catecholines.
• These hormones increase heart
rate, blood pressure, blood glucose levels, and dilate lung
passageways.
Pancreatic Islets
• The pancreas is a mixed gland.
• Pancreatic islets are little masses of hormone-producing tissue
scattered throughout the pancreas.
• Glucagon and insulin are the products of the islet cells.
• Beta cells of the islets release insulin in response to high blood glucose levels.
• Alpha cells of the islets release glucagon in response to low blood glucose levels.
• Diabetes mellitus is a condition caused by dehydration due to inability to produce insulin.
Hormones of the Pineal Gland and Thymus
• The pineal gland also called the pineal body is found in the 3rd ventricle of the brain.
• The hormone melatonin produced in the pineal gland is believed to be the “sleep trigger”.
• In some animals melatonin is believed to regulate mating behavior and rhythms.
• Melatonin may also coordinate hormones of fertility in humans.
• The thymus is located in the upper
thorax and decreases in size throughout adulthood.
• Thymosin is a hormone that aids in maturation of white blood cells in childhood.
Hormones of the Ovaries
• The ovaries produce estrogens and progesterone.
• Estrone and estradiol stimulate the development of secondary sex
characteristics in females and help maintain pregnancy and prepare for lactation.
• Progesterone acts with estrogen to coordinate the menstrual cycle.
• The ovaries are stimulated to release their cyclic products by anterior pituitary gonadotropic hormones.
Hormones of the Testes
• The testes produce male sex hormones a.k.a androgens.
• Testosterone is made by
interstitial cells of the testes which causes development of secondary sex characteristics.
• Continuous production of
testosterone is necessary for sperm production.
• Hyposecretion of testosterone leads to sterility.
