The Endocrine System

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Chapter 10

• The Endocrine System

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Overview

• We have already seen how the nervous system
  regulates body functions by means of nerve
  impulses and integration of information by the
  spinal cord and brain.

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Overview

• The other regulating system of the body is the
  endocrine system, which consists of endocrine
  glands that secrete chemicals called hormones.
• Fig. 10-1 pg 224 Know this table

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Hormones

• Hormones are chemicals that speed up or slow down
  physiologic processes.
• Hormones are chemical substances secreted by
  glands in response to stimulation.

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Major Glands of the Endocrine System

• Pituitary gland
• Thyroid gland
• Parathyroid glands
• Adrenal glands
• Pancreas
• Thymus
• Pineal gland
• Gonads (ovaries and testes)
• Hypothalamus

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Overview

• Endocrine glands are ductless, that is, they do
  not have ducts to take their secretions to
  specific sites.
• Instead, hormones are secreted directly into
  capillaries and circulate in the blood throughout
  the body.

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Overview

• Each hormone then exerts very specific effects on
  certain organs, called target organs or target
  tissues.
• Some hormones, such as insulin and thyroxine,
  have many target organs.
• Other hormones, such as calcitonin and some
  pituitary gland hormones, have only one or a few
  target organ.

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Overview

• In general, the endocrine system and its hormones
  help
• Regulate growth
• Use of foods to produce energy
• Resistance to stress
• The pH of body fluids and fluid balance
• reproduction

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Chemistry of Hormones

• Hormones may be classified into 3 groups
• Amines
• Proteins
• Steroids

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Chemistry of Hormones

• 1. Aminesthese simple hormones are structural
  variation of the amino acid tyrosine.
• This group includes thyroxine from the thyroid
  gland and epinephrine and norepinephrine from the
  adrenal medulla

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Chemistry of Hormones

• 2. Proteinsthese hormones are chains of amino
  acids.
• Insulin from the pancreas, growth hormone from
  the anterior pituitary gland, and calcitonin from
  the thyroid gland antidiurectic hormone and
  oxytocin, synthesized by the hypothalamus are all
  proteins.
• .

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Chemistry of Hormones

• 3. Steroidscholesterol is the precursor for the
  steroid hormones, which include cortisol and
  aldosterone from the adrenal cortex, estrogen and
  progesterone from the ovaries, and testosterone
  from the testes.

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Regulation of Hormone Secretion

• Hormones are secreted by endocrine glands when
  there is a need from them, that is, for their
  effects on their target organs.
• The cells of endocrine glands respond to changes
  in the blood, or perhaps to other hormones in the
  blood.

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Regulation of Hormone Secretion

• These stimuli are the information they use to
  increase or decrease secretion of their own
  hormones.
• When a hormone brings about its effects, the
  stimulus is reversed, and secretion of the
  hormone decreases until the stimulus reoccurs.

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Regulation of Hormone Secretion

• Ex. Insulin is secreted by the pancreas when the
  blood glucose level is high, that is,
  hyperglycemia is the stimulus for secretion of
  insulin.
• Once circulating in the blood, insulin enables
  cells to remove glucose from the blood to use for
  energy production and enables the liver to store
  glucose as glycogen.

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Regulation of Hormone Secretion

• As a result of these actions of insulin, the
  blood glucose level decreases, reversing the
  stimulus for secretion of insulin.
• Insulin secretion then decreases until the blood
  glucose level increases again.

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Regulation of Hormone Secretion

• Hormone levels are controlled by a feedback loop.
• Feedback can be either negative or positive.
• Most endocrine disorders result from
  overproduction or underproduction of specific
  hormones.

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The Pituitary GlandSmall but Mighty

• Also called the hypophysis or master gland.
• It is called the master gland because it
  regulates the function of other endocrine glands.
• The pituitary has 2 main regions
• The anterior pituitary
• The posterior pituitary

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The Pituitary Gland

• The anterior pituitary is the larger region and
  produces at least 6 hormones
• Growth hormone (GH)
• Thyroid-stimulating hormone (TSH)
• Corticotropin (ACTH)
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• prolactin

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The Pituitary Gland

• The posterior pituitary makes up about 25 of the
  gland
• It serves as a storage area for antidiuretic
  hormone (ADH), or vasopressin, and oxytocin,
  which are produced by the hypothalamus.

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Antidiurectic Hormone (ADH)

• ADH increases the reabsorption of water by kidney
  tubules, which decreases the amount of urine
  formed.
• The water is reabsorbed into the blood, so as
  urinary output is decreased, blood volume is
  increased, which helps maintain normal blood
  pressure.

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Antidiurectic Hormone (ADH)

• The stimulus for secretion of ADH is decreased
  water content of the body.
• Any type of dehydration stimulates the secretion
  of ADH to conserve body water.

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Antidiurectic Hormone (ADH)

• Ingestion of alcohol inhibits the secretion of
  ADH and increases urinary output.
• If alcohol intake is excessive and fluid is not
  replaced, a person will feel thirsty and dizzy
  the next morning.
• The thirst is due to the loss of body water, and
  the dizziness is the result of low blood
  pressure.

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Oxytocin

• Oxytocin stimulates contraction of the uterus at
  the end of pregnancy and stimulates release of
  milk from the mammary glands.
• Oxytocin causes strong contractions of the smooth
  muscle of the uterus to bring about delivery of
  the baby and the placenta.

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Table 10-1 pg 228

• Hormones of the posterior pituitary gland,
  function, and regulation of secretion.

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Anterior Pituitary Gland

• The anterior pituitary is the larger region and
  produces at least 6 hormones
• Growth hormone (GH)
• Thyroid-stimulating hormone (TSH)
• Corticotropin (ACTH)
• Follicle-stimulating hormone (FSH)
• Luteininzing hormone (LH)
• prolactin

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Growth Hormone (GH)

• May also be called somatotropin.
• Stimulates bone and muscle growth
• Promotes protein synthesis and fat
  metabolization.

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Thyroid-Stimulating Hormones

• May also be called thyrotropin and its target
  organ is the thyroid gland.
• TSH stimulates production and secretion of
  thyroid hormones.

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Adrenocorticotropic Hormone (ACTH)

• Stimulates the secretion of cortisol and other
  hormones by the adrenal cortex.

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Prolactin

• Is responsible for lactation.
• Initiates and maintains milk production by the
  mammary glands.

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Follicle-Stimulating Hormone (FSH)

• FSH is one of the gonadotropic hormones, that is,
  it has its effects on the gonads the ovaries or
  testes.
• Stimulates development of ovum (egg cells) in
  ovaries and sperm in testes.

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Luteinizing Hormone (LH)

• Luteinizing hormone (LH) in females
• Interstitial cell-stimulating hormone (ICSH) in
  males
• Initiates ovulation and the secretion of sex
  hormones in both genders.

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Thyroid Gland

• Located on the front and sides of the trachea
  just below the larynx.
• Its two lobes are connected by a middle piece
  called the isthmus which gives it a butterfly
  shape.

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Thyroid Gland

• The two lobes of the thyroid function as one
  unit.
• The thyroid concentrates iodine from food and
  uses it to synthesize tetraiodothyronine (T3),
  thyroxine (T4).
• T3 and T4 regulate the bodys metabolic rate.

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Thyroid Gland

• T3 T4 increases oxygen consumption and heat
  production.
• Stimulates, increases, and maintains metabolic
  processes.

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Thyroid Gland

• The third hormone produced by the thyroid gland
  is calcitonin.
• Calcitonin inhibits the release of calcium from
  bone thus lowering blood calcium levels.
• Also maintains a stable strong bone matrix.

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Parathyroid Glands

• There are four parathyroid glands
• 2 on the back of each lobe of the thyroid gland.
• The hormone they produce is called parathyroid
  hormone.

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Parathyroid Hormone (PTH)

• Increases blood calcium by stimulating calcium
  release from bone.
• Decreases blood phosphate level

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Pancreas

• Located in the upper left quadrant of the
  abdominal cavity
• The hormone-producing cells of the pancreas are
  called Islets of Langerhans which contain
• Alpha cells that produce glucagon
• Beta cells that produce Insulin

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Glucagon

• Glucagon stimulates the liver to change glycogen
  to glucose and to increase the use of fats and
  excess amino acids for energy production.
• The overall effect of glucagon is to raise the
  blood glucose level and to make all types of food
  available for energy production.

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Insulin

• Lowers blood sugar
• Increases glycogen storage in liver
• Stimulates protein synthesis
• The brain, liver, and kidney cells, are not
  dependent on insulin for glucose intake.

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Insulin

• Insulin is a vital hormone we cannot survive for
  very long without it.
• A deficiency of insulin or in its functioning is
  called diabetes mellitus (DM)

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Insulin

• As glucose is absorbed from the small intestine
  into the blood, insulin is secreted to enable
  cells to use the glucose for immediate energy.
• At the same time, any excess glucose will be
  stored in the liver and muscles as glycogen.

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Adrenal Glands

• The two adrenal glands are located one on top of
  each kidney, which gives them their other name of
  suprarenal glands.
• Each adrenal gland consists of two parts an
  inner adrenal medulla and an outer adrenal
  cortex.
• The hormones produced by each part have very
  different functions.

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Adrenal Medulla

• The cells of the adrenal medulla secrete
  epinephrine and norepinephrine, which
  collectively are called catecholamines, and are
  sympathomimetic.
• (mimetic means to mimic)

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Adrenal Cortex

• The adrenal cortex secretes three types of
  steroid hormones mineralocorticoids,
  glucocorticoids, and sex hormones.
• The sex hormones, female estrogens and male
  androgens (similar to testosterone), are produced
  in very small amounts, and their importance is
  not known with certainty.

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Adrenal Cortex

• They may contribute to rapid body growth during
  early puberty.
• They may also be important to supply estrogen to
  women after menopause, and to men throughout life.

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Aldosterone

• Aldosterone is the most abundant of the
  mineralocorticoids.
• Aldosteroneincreases reabsorption of sodium and
  excretion of potassium by the kidneys.
• Results maintains normal blood pH, blood
  volume, and blood pressure (electrolyte balance)

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Aldosterone

• Activates the renin-angiotensin mechanism of the
  kidneys.

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Cortisol

• Cortisol is a representative of the group of
  hormones called Glucocorticoids
• Glucocorticoids maintain the carbohydrate reserve
  of the body by promoting the conversion of amino
  acids into glucose (sugar) instead of protein.

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Cortisol

• The production of these hormones increases in
  times of stress to aid the body in responding to
  unfavorable conditions.
• Stress disease, physical injury, hemorrhage,
  fear or anger, exercise, and hunger.

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Cortisol

• Glucocorticoids also have the ability to suppress
  the inflammatory response (anti-inflammatory
  effect) and are often administered as medication
  for this purpose.
• The major hormone of this group is cortisol,
  which is also called hydrocortisone.

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Cortisol

• Too much cortisol, however, decreases the immune
  response, leaving the body susceptible to
  infection and significantly slowing the healing
  of damaged tissue.

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Ovaries

• The ovaries are located in the pelvic cavity, one
  on each side of the uterus.
• The hormones produced by the ovaries are the
  steroids estrogen and progesterone, and the
  protein inhibin.

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Testes

• The testes are located in the scrotum, a sac of
  skin between the upper thighs.
• Two hormones, testosterone and inhibin, are
  secreted by the testes.

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Other Hormones

• Melatoninsecreted by the pineal gland during
  darkness brings on sleep.
• Prostaglandinsare involved in inflammation and
  pain, reproduction, nutrient metabolism, changes
  in blood vessels, blood clotting.

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Aging

• Most of the endocrine glands decrease their
  secretions with age, but normal aging usually
  does not lead to serious hormone deficiencies.
• Unless specific pathologies develop, however, the
  endocrine system usually continues to function
  adequately in old age.