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Reproductive hormones. What is a hormone? Definition of hormone Hormone –Greek “I excite” or “I arouse” First used by Starling in 1895 –Classical definition.

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Presentation on theme: "Reproductive hormones. What is a hormone? Definition of hormone Hormone –Greek “I excite” or “I arouse” First used by Starling in 1895 –Classical definition."— Presentation transcript:

1 Reproductive hormones

2 What is a hormone?

3 Definition of hormone Hormone –Greek “I excite” or “I arouse” First used by Starling in 1895 –Classical definition Chemical signals that travel via bloodstream to affect the function of the distant organ –Regulatory factor Secretory organ Target organ/tissue

4 Definition of hormone Hormones –Contemporary definition Much broader Local factors (produced and used without being carried in the bloodstream) –Autocrine (produced and used by the same cell/tissue) –Paracrine (produced by the neighboring cells and transported via the interstitial fluid)

5 LH FSH Estradiol Hypothalamus Pituitary gland GnRH Ovary

6 Antrum Granulosa cells Theca interna Theca externa Basement membrane Oocyte

7 Granulosa cells (GC) Theca cells (TC) Basement membrane

8 Classes of hormones Three general classes –Lipids Cholesterol derivatives (steroids) 12-C fatty acid derivatives (eicosanoids) –Proteins and polypeptides –Monoamines

9 Cholesterol and its derivatives Cholesterol –Large molecule Hydrocarbon ring –Highly hydrophobic –Source Diet De Novo synthesis –Found in cell membrane

10 Cholesterol and its derivatives Derivatives –Vitamin D –Bile acid Lipid digestion –Steroid hormones Sex steroids Adrenal steroild –All cholesterol derivatives contain sterol ring

11 Steroid hormones Commonly called sex steroid hormones –Produced mainly by the gonads Ovaries and testis Some production by placenta, adrenal gland, and brain –Water-insoluble but lipid soluble Easily move across the plasma membrane Bound to Steroid hormone-binging globulin during transport

12 Three classes of sex steroid hormones –Progestin/progestagens –Estrogens –Androgens Produced through metabolic process –Steroidogenesis

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14 Steroidogenesis Source of cholesterol –Acetate De Novo Synthesis –Lipoproteins HDL (humans and rodents) LDL (cattle) Common pathway –Conversion of cholesterol to pregnenolone

15 Splits into two different pathway with the same outcome –Delta-4 pathway Conversion of pregnenolone to progesterone Conversion of progesterone to androstenedione –Delta-5 pathway Conversion of pregnenolone to androstenedione

16 Production of estrogens –Final destination of steroidogenesis in the ovary Conversion of androgens (testosterone) to estradiol-17 beta –Some species (i.e. rats) use delta-4 pathway, whereas others (i.e. cows) prefer delta-5 pathway

17 General function of steroid hormones Development of physical characteristics –Male and female sex characteristics Primary (reproductive organs) Secondary (physical) Reproductive success –Sexual behavior and libido –Fertility –Pregnancy

18 Eicosanoids Derivative of 12-C fatty acid (Arachidonic acid) –Prostaglandins (more important for reproduction) –Leukotriens Arachidonic acid released from phospholipid component of the cell membrane –Phospolipase A –Phospholipase C

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20 Prostaglandins –Produced from leukotriens through cyclooxygenases –No specific organ of production Originally isolated from prostate gland Many reproductive organs produce prostaglandins –Quickly metabolized Lungs

21 Protein hormones Three subclasses –Glycoproteins –Proteins Growth hormone Prolactin Placental lactogens –Cytokines (immune system) –Polypeptdes

22 Glycoproteins Produced by the anterior pituitary –Gonadotropins Follicle-stimulating hormone (FSH) Luteininzing hormone (LH) –Thyroid-stimulating hormone (TSH) Less important for regulation of gonadal function Produced by placenta –Chorionic gonadotropins (CG) Human (hCG) Horse (eCG/PMSG)

23 Structural similarity –Two subunits Alpha –Universal Beta –Unique to each hormone Linked together non-covalently (disulfide bridges) –Glycosylated Attachment of carbohydrate moiety onto the subunits –Unique among hormones

24 Proteins Pituitary hormones –Growth hormone (GH) –Prolactin (PRL) Placental hormones –Unique to humans, rodents, and ruminants Placental lactogen (PL) GH-Variant (GH-V) Affect metabolism and lactation Affect ovarian functions

25 Cytokines Different from hormones –No specific organ/cells produce Immune response Inflammation –Multiple targets –Interactions to modulate activities of other cytokines –Redundant functions –Auto/paracrine factor rather than endocrine factor

26 Ovarian proteins –Inhibins –Activins –Mullerian inhibitory substance/hormone (MIS) –Two subunits (alpha and beta) Different combination determines the nature of proteins

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28 Polypeptides Small proteins –Short in length compared to proteins –Produced by cleaving large preprohormone peptides

29 Hypothalamic neuropeptides –Gonadotropin- releasing hormone (GnRH) Regulates secretion of LH and FSH Composed of 10 amino acids

30 Posterior pituitary hormones –Oxytocin Composed of 9 amino acids Produced by the neurons within the hypothalamus but secreted by the posterior pituitary gland Induces contraction of smooth muscles Critical for milk let-down

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