ANHB1101 Lecture Notes - Lecture 29: Gamete, Autocrine Signalling, Estrogen
3 Jun 2018
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Lecture 29
Thursday, 19 May 2016
8:24 am
Hormonal Control of Reproduction
Hormone Action:
• Hormones - chemical messengers
• Reproductive messengers - involved in all aspects of reproductions
• Used for communication
• Messages are secreted in the blood
• Produced by endocrine glands/cell
• Act on target cells/tissues
• Target cells express specific receptors - membrane bound or intracellular
Chemical Structures of Reproductive Hormones:
• Peptides
o Relatively simple chain of amino acids
o E.g. GnRH, LH, FSH, hCG, inhibin, oxytocin, prolactin
• Steroids
o Derived from a common precursor - cholesterol
o Specific biochemical pathway
o E.g. testosterone, oestradiol, progesterone, cortisol
• Eicosanoids
o Derived from fatty acids liberated from cell membranes
o Reasonably simple in structure
o E.g. prostaglandins
Receptors:
• Peptide hormones
o Peptides are relatively large - find it difficult to cross biological
membranes
o Bind to membrane-bound receptors
o Require action of second messengers
o E.g. GnRH, LH and FSH
• Steroid hormones
o Small molecules derived from lipids
o No problem crossing biological membranes
o Have nuclear receptors - found within nucleus of a given cell
o Hormones bind to receptors in the nucleus - receptor/ligand-hormone
complex
o Complex takes role of transcription factor - alter gene expression within
cell
o E.g. oestradiol, progesterone, testosterone
Types of Hormone Action:
• Endocrine
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o Classically method of hormone action
o Endocrine gland produces hormone, enters the blood stream and is
received by target cells with specific receptor
o E.g. LH or FSH from anterior pituitary
• Paracrine
o Relates to a hormone producing cell (paracrine cell) producing a hormone
that diffuses into interstitial fluid/space to get to a relatively close-by cell
(target cell)
o E.g. testosterone
• Autocrine
o The cell producing the hormones will also have receptors for that
hormone
o Still secreted to interstitial fluid, but taken up by receptors in the cell of
origin
o E.g. oestradiol
• Exocrine
o Gland/organ secretes a substance into a duct/organ
o Make their way to the target organ
o E.g. upon ovulation, follicular fluid accompanies oocyte enters oviduct -
contains prostaglandin and other hormones that act on the uterine
tube/epithelium to facilitate transport of oocyte
Control of the Endocrine System:
• Negative feedback
o Relatively simple mechanism
o Designed to promote homeostasis - keeping level of hormones at a
relatively stable set point
o Negative feedback at gland of origin - reduction of hormone action in
target tissue
o
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Document Summary
Chemical structures of reproductive hormones: peptides, relatively simple chain of amino acids, e. g. Gnrh, lh, fsh, hcg, inhibin, oxytocin, prolactin: steroids, derived from a common precursor - cholesterol, specific biochemical pathway, e. g. testosterone, oestradiol, progesterone, cortisol, eicosanoids, derived from fatty acids liberated from cell membranes, reasonably simple in structure, e. g. prostaglandins. Receptors: peptide hormones, peptides are relatively large - find it difficult to cross biological membranes, bind to membrane-bound receptors, require action of second messengers, e. g. Types of hormone action: endocrine, classically method of hormone action, endocrine gland produces hormone, enters the blood stream and is received by target cells with specific receptor, e. g. Hierarchy of control - hormonal axis: hpg axis, hypothalamus - base of brain, gonadotrophin releasing hormone (gnrh, pituitary, gonadotrophins (lh and fsh, gonads - ovary and testis, oestradiol, progesterone, testosterone. Important for gametogenesis and development of secondary sex characteristics: environmental cues has important stimulatory/inhibitory effects on the axes.
