THE ENDOCRINE SYSTEM

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THE ENDOCRINE SYSTEM

• Chapter 33

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• The endocrine system
• interacts with the nervous system to maintain
  homeostasis.
• consists of endocrine glands isolated cells
  that secrete hormones.

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• A. Hormones
• Chemicals synthesized in one part of an organism
  transported to another, where they affect
  target cells.

Target cells have receptors on or in them that
bind only to certain hormones.
Hormones
Target cells
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• 1. Classes of Hormones
• Peptide hormones
• water-soluble
• bind to receptors on target cells surface
• Steroid hormones
• lipid-soluble
• bind to receptors in target cells cytoplasm or
  nucleus

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• 2. Hormone Regulation
• Positive feedback loop
• Accumulation of a certain biochemical stimulates
  an increase in its production.
• Ex. release of oxytocin during childbirth
• Negative feedback loop
• Accumulation of a certain biochemical stimulates
  a decrease in its production.
• Ex. release of most hormones

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• B. Diversity of Endocrine Systems
• All animals produce hormones.
• 1. Invertebrate Hormones
• Most are secreted by neurosecretory cells.
• Invertebrate hormones regulate
• regeneration (Hydra, flatworms, annelids)
• color change (crustaceans)
• gonad maturation (flatworms, mollusks,
  arthropods)
• molting metamorphosis (insects)

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• 2. Vertebrate Hormones
• Secreted by neurosecretory cells endocrine
  glands.
• All vertebrates produce the same basic hormones,
  but may have different functions in different
  species.
• Ex. Thyroxine
• sets pace of metabolism in humans
• controls metamorphosis in frogs
• controls heat production oxygen consumption in
  birds.

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• All vertebrate endocrine systems are regulated by
  the hypothalamus and the pituitary gland.

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• C. The Human Endocrine System
• Consists of neurosecretory cells, endocrine
  glands scattered hormone-secreting cells.

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• 1. Pituitary Gland
• Anterior Pituitary (regulated by releasing
  inhibiting hormones of hypothalamus)

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• Growth hormone (GH)
• targets all cells ? promotes growth development
• Hyposecretion in children causes pituitary
  dwarfism.
• Hypersecretion in children causes pituitary
  gigantism.
• Hypersecretion in adults causes acromegaly.
• Prolactin
• targets mammary glands ? stimulates milk
  production

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• Follicle-stimulating hormone (FSH)
• targets ovaries ? initiates development of
  ovarian follicles, oocyte maturation, and release
  of estrogen
• targets testes ? promotes development of testes
  production of sperm
• Luteinizing hormone (LH)
• targets ovaries ? stimulates ovulation
• targets testes ? stimulates production of
  testosterone

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• Thyroid-stimulating hormone (TSH)
• targets thyroid gland ? stimulates release of
  thyroxine triiodothyronine
• Adrenocorticotropic hormone (ACTH)
• targets adrenal cortex ? stimulates release of
  glucocorticoids
• FSH, LH, TSH ACTH are tropic hormones.

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• Intermediate lobe of pituitary (regulated by
  releasing inhibiting hormones of hypothalamus)

• Melanocyte-stimulating hormone (MSH)
• targets melanocytes in skin of many vertebrates ?
  causes color changes

Intermediate lobe is poorly developed in humans.
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• Posterior Pituitary (stores releases hormones
  produced by hypothalamus)

• Antidiuretic hormone (ADH)
• targets kidneys ? stimulates reabsorption of
  water
• targets blood vessels ? regulates blood pressure

• Oxytocin
• targets uterus ? stimulates contraction
• targets mammary glands ? stimulates release of
  milk when baby nurses

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• 2. Thyroid Gland
• Thyroxine (T4) Triiodothyronine (T3)
• target all cells of body ? increase metabolic
  rate
• Dietary iodine is required to produce these two
  hormones.
• How does the body respond to a lack of iodine in
  diet?
• Why is iodine-deficient goiter rarely encountered
  in the US today?

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TRH thyroid releasing hormone
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• Hyposecretion in infants causes cretinism.
• - physical mental retardation
• Hyposecretion in adults causes myxedema.
• - low metabolic rate, weight gain, lethargy,
  puffy face
• Hypersecretion causes hyperthyroidism.
• - high metabolic rate, weight loss,
  irritability, elevated blood pressure
• Calcitonin
• targets bones, kidneys intestines ? reduces
  level of calcium in blood

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• 3. Parathyroid Glands
• Parathyroid hormone (PTH)
• targets bones, kidneys intestines ? increases
  level of calcium in blood

Calcitonin PTH are antagonistic - interact to
maintain normal blood calcium levels.
Regulation of blood calcium level
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• 4. Adrenal Glands
• Adrenal Medulla
• Epinephrine Norepinephrine

• target heart, blood vessels, muscles, liver
• ? increase heart rate, breathing rate, blood
  glucose
• ? redirect blood flow toward brain muscles

Epinephrine norepinephrine help body cope with
emergencies (fight-or-flight response).
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• Adrenal Cortex
• Mineralocorticoids (aldosterone)
• targets kidneys ? retains sodium ions water
  (increases blood volume/pressure)

• Glucocorticoids (cortisol)
• targets all cells ? increases glucose synthesis
  suppresses immune system

Mineralocorticoids Glucocorticoids help body
cope with long term stress.
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• Hyposecretion of adrenal cortex hormones causes
  Addisons disease.
• - dehydration, low blood pressure, mental
  fatigue, weakness, impaired resistance to stress,
  darkening of skin
• Hypersecretion of adrenal cortex hormones causes
  Cushings disease.
• - redistribution of body fat, depresses immune
  system

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• 5. Pancreas
• Classified as exocrine endocrine gland.

• Exocrine portion secretes digestive enzymes.

• Endocrine portion (islets of Langerhans) secretes
  hormones.

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• Insulin (secreted by beta cells of islets)
• targets all cells ? decreases blood glucose
  levels stimulates conversion of glucose to
  glycogen
• Glucagon (secreted by alpha cells of islets)
• targets all cells ? increases blood glucose
  levels stimulates breakdown of glycogen to
  glucose
• Insulin Glucagon are antagonistic - interact to
  maintain normal blood glucose levels.

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• Diabetes mellitus
• Blood glucose level is too HIGH.
• Type I (insulin-dependent)
• autoimmune disease - immune system destroys beta
  cells
• usually develops during childhood
• treated with daily injections of insulin
• Type II (insulin-independent)
• defective insulin receptors
• usually develops in adulthood
• treated with diet exercise

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• Gestational diabetes
• temporary - develops during pregnancy
• placental hormones interfere with insulin action
• Hypoglycemia
• Blood glucose level is too LOW.
• excess insulin production
• treated by following diet of frequent, small
  meals low in carbohydrates high in protein

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• 6. Gonads
• Ovaries
• Estrogen
• targets most cells ? develops maintains sexual
  characteristics in females stimulates growth of
  uterine lining
• Progesterone
• targets uterus ? stimulates growth of uterine
  lining maintains pregnancy

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• Testes
• Testosterone
• targets most cells ? develops maintains sexual
  characteristics in males promotes sperm
  formation
• Inhibin
• targets anterior pituitary ? inhibits FSH release
  (decreases sperm formation)