Endocrine System

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Chapter 14

• Endocrine System

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Outline

• Endocrine Glands
• Hypothalamus and Pituitary
• Posterior vs. Anterior
• Thyroid Gland
• Parathyroid Glands
• Adrenal Glands
• Pancreas
• Other Endocrine Glands
• Homeostasis

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Endocrine Glands

• ductless glands and tissues that secrete hormones
  directly into the bloodstream
• Hormone secretion by an endocrine gland is often
  controlled by negative feedback
• Actions of a hormone can also be controlled by an
  antagonistic hormone

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The Endocrine System
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Hypothalamus Neuroendocrine junction

• regulates homeostasis by controlling two systems
• the autonomic nervous system
• the endocrine system via control of the pituitary
  gland

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Hypothalamic Pituitary
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Pituitary Gland

• Anterior Pituitary
• makes its own hormones
• hypothalamus controls their secretion with
  releasing/inhibiting hormones

• Posterior Pituitary
• hormones made in hypothalamus
• hypothalamus controls their secretion via nerve
  impulses

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Posterior Pituitary

• releases two hormones produced by the
  hypothalamus
• Antidiuretic hormone (ADH)
• Causes water reabsorption
• Negative feedback control
• Oxytocin
• Causes uterine contraction during childbirth and
  milk letdown
• Positive feedback control

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Anterior Pituitary

• controlled by hypothalamic-releasing and
  -inhibiting hormones
• Secretes
• Thyroid Stimulating Hormone (TSH).
• Adrenocorticotropic Hormone (ACTH).
• Gonadotropic Hormones (FSH and LH).
• Prolactin (PRL).
• Melanocyte-Stimulating Hormone (MSH).
• Growth Hormone (GH).

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Effects of Growth Hormone

• Growth hormone is produced in greater quantities
  during childhood and adolescence
• Too little GH produced during childhood may lead
  to pituitary dwarfism
• Too much GH produced during childhood may lead to
  gigantism
• Too much GH produced as an adult may lead to
  acromegaly

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Pituitary gigantism and dwarfism

• hypersecretion in childhood gigantism
• hyposecretion in childhood drwarfism

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Acromegaly

• hypersecretion of growth hormone in adulthood

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Thyroid Gland

• secretes thyroxins (triiodothyronine and
  thyroxine) and calcitonin
• enwraps trachea

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goiter

• enlarged thyroid due to dietary iodine deficiency

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Cretinism

• may result if the thyroid fails to develop
  properly

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Hypothyroidism in adults

• Myxedema lethargy, weight gain, loss of hair,
  low body temp., thickness and puffiness of skin

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Hyperthyroidism in Adults

• Graves Disease (exopthalamic goiter)
  hyperactivity, nervousness, irritability,
  insomnia, etc.

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Thyroid Calcitonin

• helps regulate blood calcium level

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parathyroid glands

• secrete parathyroid hormone
• increases blood calcium
• Antagonistic action of calcitonin and parathyroid
  hormone maintain blood calcium levels within
  normal limits
• decreases blood phosphate

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Blood Calcium Homeostasis
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Adrenal Glands

• consist of central adrenal medulla and peripheral
  adrenal cortex

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Adrenal Medulla

• functions as part of sympathetic division of the
  autonomic nervous system
• secretes epinephrine/norepinephrine during E
  situations

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Adrenal Cortex

• Mineralocorticoids regulate salt and water
  balance
• glucocorticoids regulate metabolism
• gonadocorticoids mostly male sex hormones
  (androgens) tha stimulate libido

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Addisons Disease

• Hyposecretion of glucocorticoids and
  mineralocorticoids
• dehydration, low blood pressure

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Cushings Disease

• Hypersecretion of adrenocorticoids
• hyperglycemia, loss of muscle and bone protein,
  water and salt retention

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Pancreas

• Exocrine digestive juices
• Endocrine pancreatic islets, produces and
  secretes insulin and glucagon directly into the
  blood.

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Diabetes Mellitus

• body cells are unable to take up and/or
  metabolize glucose
• Type I - Pancreas is not producing insulin
• Type II - Pancreas produces insulin, but the
  liver and muscle cells do not respond in the
  normal fashion

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Regulation of Blood Glucose
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Glycosuria
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Testes

• produce androgens (testosterone)
• _at_ Puberty secondary sexual characteristics
• produce sperm

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Ovaries

• produce estrogens and progesterone
• _at_ Puberty secondary sexual characteristics
• produce eggs

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Steroid Abuse
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Thymus Gland

• Secretes thymosins, aid the differentiation of
  lymphocytes

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Pineal Gland

• Secretes melatonin, involved in regulating
  sleep-wake cycle

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Hormones from Other Tissues

• Leptin
• Protein hormone produced by adipose tissue.
• Growth Factors
• Stimulate cell division and mitosis.
• Prostaglandins
• Chemical signals produced within cells from
  arachidonate (fatty acid).
• Act locally.

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Chemical Signals

• Peptide hormones bind to a receptor on cell
  membranes and activate an enzyme producing cyclic
  AMP
• Leads to enzyme cascade
• Steroid hormones enter cells and form
  hormone-receptor complexes that activate DNA
  (genes) leading to protein synthesis

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Examples of Endocrine Homeostasis

• Hypothalamus produces ADH and thus regulates
  blood osmolarity
• Endocrine system controls secretion of
  epinephrine and norepinephrine and thus controls
  fight or flight responses
• Controls blood calcium levels
• Muscle contraction
• Insulin encourages uptake of glucose by cells and
  storage of glucose as glycogen in the liver and
  muscles

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Review

• Endocrine Glands
• Hypothalamus and Pituitary
• Posterior vs. Anterior
• Thyroid Gland
• Parathyroid Glands
• Adrenal Glands
• Pancreas
• Other Endocrine Glands
• Homeostasis

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