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Nature of hormones. What is a hormone?. Hormone Greek “I excite” or “I arouse” Classical definition Chemical messenger released by one type of cells and carried in the bloodstream to act on specific target cells Modern definition

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what is a hormone
What is a hormone?
  • Hormone
    • Greek “I excite” or “I arouse”
    • Classical definition
      • Chemical messenger released by one type of cells and carried in the bloodstream to act on specific target cells
    • Modern definition
      • Includes factors produced and used locally without entering the blood stream
slide3
Endocrine factors
    • Released and carried in the blood
    • Classical hormones
  • Autocrine factors
    • Released and used by the same cells
  • Paracrine factors
    • Affect function of neighboring cells without entering the blood stream
      • Interstitial fluid
slide4

GnRH

Hypothalamus

FSH

LH

Estradiol

Pituitary

gland

Ovary

slide5

Granulosa cells

Basement

membrane

Antrum

Oocyte

Theca externa

Theca interna

slide6

Granulosa

cells (GC)

Theca

cells (TC)

Basement membrane

general characteristics of hormones
General characteristics of hormones
  • Very low in concentrations
    • Ppb (ng/ml) or ppt (pg/ml)
  • Very specific receptor
    • One hormone, one receptor
chemical nature of hormones
Chemical nature of hormones
  • Classes
    • Lipids
      • Steroids
      • Eicosanoids
    • Proteins
      • Short polypeptides
      • Large proteins
        • Chemical modification through glycosylation
    • Amino acid derivatives
steroid hormones
Steroid hormones
  • Derivative of cholesterol
    • Large molecule
      • Hydrocarbon ring
    • Highly hydrophobic
    • Source
      • Diet
      • De Novo synthesis
    • Found in cell membrane
cholesterol and its derivatives
Cholesterol and its derivatives
  • Derivatives
    • Vitamin D
    • Bile acid
      • Lipid digestion
    • Steroid hormones
      • Sex steroids
      • Adrenal steroild
    • All cholesterol derivatives contain sterol ring
steroid hormones1
Steroid hormones
  • Origins
    • Adrenal
      • Mineralocorticoids
        • Affect mineral homeostasis
      • Glucocorticoids
        • Affect glucose metabolism and immune function
    • Gonads (testis and ovaries)
      • Estrogens
      • Progestins/progestagens
      • Androgens
eicosanoids
Eicosanoids
  • Metabolites of 12-C fatty acid
    • Arachidonic acid
  • Prostaglandins
    • Produced by numerous tissues and organs
      • Originally isolated from prostate gland secretion
      • Inflammatory reaction
      • Reproduction
  • Thromboxanes, leukotriens, and prostacyclins
protein hormones
Protein hormones
  • Short chain of amino acids
    • Neurohormones
      • GnRH (10)
      • Oxytocin (9)
      • TRH (3)
protein hormones1
Protein hormones
  • Large polypeptides
    • Linear chain
    • Subunits
      • Linked by disulfide bridge(s)
    • 3-D structure
      • Critical for interaction with receptor
slide19
Chemical modification
    • Glycosylation
      • Common in gonadotropins (LH, FSH, hCG, eCG)
    • Sulfation
    • Acetylation
protein hormones2
Protein hormones
  • Isoform and variants
    • Amino acid substitution
    • Gene duplication
amino acid metabolites
Amino acid metabolites
  • Tyrosine metabolites
    • Thyroid hormones
      • Thyroxine
      • Triiodothyronine
    • Adrenal medulla
      • Epinephrine
      • Norepinephrine
      • Dopamine
      • Often used as neurotransmitters
endocrine glands
Endocrine glands
  • Composition
    • Parenchyma (mass of cells)
      • Secretory cells
    • Blood vessels
      • Highly vasucualized
    • No ducts
  • Permanent or transient
    • Pituitary, adrenal, pancreas etc
    • Ovarian follicle and corpus luteum
cells that produce hormone
Cells that produce hormone
  • Specialized secretory cells
    • Usually one type of cells produce one hormone
  • Neurons
    • Hypothalamus
    • Posterior pituitary
    • Adrenal medulla
hormone synthesis
Hormone synthesis
  • Protein hormones
    • Transcription
    • Translation
    • Physical/chemical modification
      • Cleaving of long amino acid chain (preprohormones) to generate small peptide hormones (GnRH, oxytocin, TRH)
      • Interaction and linking of subunits
      • 3-D structure
slide27
Metabolism
    • Cholesterol (steroids)
      • Smooth ER
      • Mitochondria
    • Tyrosine
      • Thyroid follicular cells (thyroid hormones)
        • Thyroglobulin
      • Adrenal medulla
      • Nerve terminals
control of synthesis and secretion
Control of synthesis and secretion
  • Neural inputs
    • Brain
    • Hypothalamus
  • Hormonal stimulation/inhibition
    • Releasing factors/hormones
    • Inhibitory factors
    • Feedback system
  • Metabolic status
    • Stress
    • Blood concentrations of substances
      • Ca
      • Glucose
      • Water
hormones in circulation
Hormones in circulation
  • Peptides and some protein hormones (i.e. insulin)
    • Very short half-life
      • Degraded by proteolytic enzymes
  • Large protein hormones
    • Longer half-life
slide30
Steroids
    • Water-insoluble
    • Bound to binding globulins (SHBG or CBG) and albumin
    • Some steroids exist as free form
      • Short half-life
  • Thyroid hormones
    • Thyroxine-binding globulin (TBG)
    • Transthyretin
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