Endocrine System Chemical Communcations in the Body

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Endocrine System Chemical Communcations in the
Body

• Endocrine system composed of hormone-secreting
  glands (I.e., internal secretions)
• Secreted hormones enter blood stream and target
  specific tissues organs
• Exocrine system composed of glands which secrete
  substances into a duct network (I.e., external
  secretions)

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Endocrine (Internal-Secretions)
Gland
Hormone
Target Tissue (activated by the hormone)
Blood Stream
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Exocrine (External-Secretions)
Exterior
Secreted Substances E.g., milk tears
saliva sweat sebum
G/I juice semen
Duct system
Gland
Interior
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A Little History

• Early study of endocrine glands paralleled early
  study of vitamins
• Questions? What is the function of glands? What
  is the function of components of our food?
• Answers? Obtained by applying the scientific
  method of inquiry
• Experimental approach with vitamins hormones
  remove something and see what happens

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Early Vitamin Research
Mice fed whole-grain milled-grain rice
Whole-grain
Body weight
Milled-grain
Whole-grain
Milled-grain
Conclusions whole- grain had components
necessary for growth B-complex vitamins
Weeks
Seed coat removed
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Early Hormone Research
Surgically remove pancreas
Diabetic symptoms (blood sugar rise, etc)
inject
Extract insulin from pancreas
For example Banting Best experiments with
dog model for diabetes
Blood sugar returns to normal
CONCLUSIONS?
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How Do Hormones Work?

• Glands produce 2 types of hormones proteins and
  steroids
• Both types of hormones H target tissues by
  binding to specific receptor sites R
• Once a HR complex is formed, the target tissue
  responds in some way
• Each type of hormone influences the target tissue
  differently

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Protein Hormone Mechanism
GLAND
TARGET CELL
Hormone
HR
Receptor
cyclase
ATP
cAMP
(2nd Messenger)
Activate cell component

• E.g., Glucagon forms HR complex leading to
  formation of cAMP
• which activates phosphorylase breaking glycogen
  down to glucose

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Steroid Hormone Mechanism
GLAND
TARGET CELL
Hormone
Receptor
HR
Note steroids enter cells while protein
hormones bind to surface receptors
Activate Gene expression
Proteins
(Change fate of cell)
E.g., Estrogen and testosterone target gonads to
produce egg sperm as well as targeting other
tissues accounting for gender differences
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Major Glands Hormones

• Pituitary
• Adrenal Cortex
• Thyroid
• Parathyroid
• To be covered later glands hormones involved
  in Stress Response, Control of Blood Sugar, and
  Reproduction
• Also, cells and tissues producing hormone-like
  factors (e.g., cytokines from white cells and
  atrial naturetic factors from heart muscle)

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Pituitary
Sensory stimuli
HYPOTHALAMUS
BRAIN
Vessels
Anterior Lobe
Nerves
Magnified to right
PITUITARY
Posterior Lobe
Pituitary Hormones
Note Anterior lobe stimulated by tropic
factors, posterior lobe by innervation
Target Tissues
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Anterior Hormones - TSH

• TSH (thyroid stimulating hormone)
• Clinical conditions a.Hypothyroidism - BMR
  low
• b.Hyperthyroidism - BMR high

• Targets thyroid gland to produce thyroxin (which
  targets body cells to increase rate of
  metabolism BMR)
• Increases rate of breakdown of sugar and fat
  (yielding ATP and heat energy)

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Anterior Hormones - GH

• GH (growth hormone)
• Clinical conditions a.dwarfism underproduction
  of GH b. giantism
  overproduction of GH

• Targets all cells and tissues of the body
• Causes increases in cell division, and rates of
  protein synthesis
• Most active during active growth periods infancy
  adolescence

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Human Growth Periods
Periods E embryonic F fetal I infancy C
childhood Adolescence Adulthood
Birth
Growth Rate
Female
Male
E F I C Adol Adulthood
Major GH input
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Anterior Hormones - ACTH

• ACTH (adrenalcorticotropic hormone)

• Targets outer cortex of adrenal gland
• Gland responds with glucocorticoids and
  mineralocorticoids
• Stress response gluco mobilizes sugar and
  mineralo targets kidney to retain water

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More Anterior Hormones

• FSH (follicle-stimulating hormone) targets
  ovaries to produce eggs, and testes to produce
  sperm
• LH (luteinizing hormone) targets ovaries to
  produce estrogens, and testes to produce
  androgens (subsequently estrogens and androgens
  account for secondary gender differences)
• Prolactin targets mammary glands to produce
  milk

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Posterior Hormones

• ADH (anti-diuretic hormone vasopressin)
  targets kidney to reabsorb salt, thereby retain
  water stabilizes blood pressure
• Oxytocin targets the smooth muscle of the
  uterus (myometrium) during childbirth also
  targets smooth muscle of the mammary gland ducts
  to expel milk during lactation

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Regulation of Blood Calcium

• Blood levels of calcium are kept constant by
  thyroid and parathyroid glands
• Calcium homeostasis is hormonally-regulated
  (thyrocalcitonin parathyroid h)
• Calcium is critical to most body functions
• Calcium comes from the diet if not enough from
  the diet calcium comes from the bones (causing
  osteoporosis symptoms)

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Calcium Homeostasis
Dietary Calcium
Thyrocalcitonin causes calcium to be released
deficiency
BLOOD CALCIUM
digestion
Blood vessels
Parathyroid Hormone causes uptake of calcium
Calcium-rich bones
Note chronic dietary Deficiency leads to
osteoporosis
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Other Glands ( their hormones)?

• White blood cells secrete cytokines which
  control immune and inflammatory responses
• Heart tissue atrial naturetic factor which
  targets CV system to reduce blood pressure
• Kidney erythropoeitin bone marrow (rbc)
• Cancer tissue endothelial growth factor
  targets proliferation of capillary bed
• List of cells tissues making hormone-like
  chemicals is greatly expanding (re-defines what
  an endocrine gland is to be considered in the
  future)

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Future Hormone Research?

• 1. Reverse Pharmacology First find the hormone
  receptor, then test drugs of best fit (e.g.,
  orexins block uptake of fat)
• 2. Chemical Exploration Screen chemicals in
  nature for drug effects (e.g., taxol used to
  treat estrogen-sensitive cancers)
• 3. Pharmacogenomics Use info from Human Genome
  Project ( Proteonomics) to develop new classes
  of drugs
• 4. Recombinant DNA Technology Use to make rare
  human hormones (e.g., Humulin, Procrit)