Biology of Reproduction Summers |
Endocrinology Homeostasis/Feedback Adult Female Steroid Production Ovulation |
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Adult Male Gonadal Axis Regulation Sexual Differentiation Sexual Behavior Puberty |
Reproductive Cycling Estrous Cycles Menstrual Cycle Menopause Fertilization |
Fertilization Systems Gamete Interaction Pregnancy Labor and Parturition Lactation |
Sexual Response & Behavior Pheromones STDs text: Human Reproductive Biology2nd Edition- RE Jones & KH Lopez,: pp 3-28 Acronyms/Abbreviations end |
I. Endocrinology A. Exocrine glands 1. secrete products via a duct to the surface 2. e.g. sweat glands, digestive glands, uterine glands B. Endocrine (ductless) Gland 1. no duct 2. secretes hormone into blood a. Chemical Messenger i. chemical mediation ii. acting at target cell C. Paracrine/Autocrine/Neurotransmitter Secretion 1. no blood vector 2. local action 3. secretory cells not organized into a gland 4. target cells a. paracrines/neurotransmitters = cells nearby b. autocrines = same cells II. Receptors A. Peptide or protein hormones (short (peptide) or long chains of amino acids) 1. defined as a target cell because it has receptors for the hormone a. receptors for peptide hormones are proteins in the membrane (protrudes to surface) of the cell i. membrane receptors activate G proteins ® 2nd messenger systyems ® activate enzymes ® cell response 2. no target cell is responsive to just one hormone a. Antagonism i. one hormone inhibits or blocks the effect of the other b. Synergism/facilitation i. the response of 2 hormones is greater than the sum B. Steroid Hormones (derived from cholesterol) 1. receptors (proteins) are in the cytoplasm or nucleus a. steroid-receptor complex binds to DNA i. stimulates transcription, and therefore protein synthesis b. Steroids may also have, or bind to, membranal receptors 2. steroid hormones may interact with other hormones 3. receptors for thyroid hormones are also in the nucleus C. Paracrines 1. also have membranal receptors III. Brain A. The brain regulates hormonal control of reproductive events 1. Environmental cues (includes social input) are converted by neural mechanisms into meaningful physiological (including hormonal) responses B. Olfactory (gustatory?) cues are mediated by GnRH neurons innervating the limbic (emotions, memory) areas of the brain (especially amygdala and hippocampus) which in turn innervate GnRH neurosecretory neurons in the hypothalamus 1. GnRH acts both as a neurotransmitter/neuromodulator and as a hormone 2. visual cues via the optic nerve have effects through the limbic system and the brain's rhythmic centers (especially SCN = suprachiasmatic nucleus and pineal) 3. tactile cues may travel via the spinal cord and be enhanced by hormones (E2) and neuromodulators (GnRH) C. NE from the locus coeruleus (in brainstem) directly stimulates hypothalamic GnRH 1. Epi will also stimulate GnRH release 2. excitatory amino acid transmitters (glutamate = Glu) regulate preovulatory surges of GnRH and LH 3. Opiates (endorphins/enkephalins) mediate the timing of GnRH/LH surge D. Endocrine Axes 1. Hypothalamus: Releasing Hormones (e.g. GnRH) stimulate 2. Pituitary: Tropic Hormones (e.g. gonadotropins = LH, FSH) a. which in turn stimulate 3. Hormones (e.g. E2 or T) from peripheral glands (e.g. ovary, testis) IV. Hypothalamus A. Produces Releasing Hormones 1. Hypophysiotropic area a. stimulates release of tropic or hypophyseal (pituitary) hormones b. also Release-Inhibiting Hormones c. neurons which conduct electrical signals (slowly) i. release product into the blood instead of synapse (1) electrical signal traveling along axon stimulates release 2. secretion mediated by inputs from other areas of the brain a. e.g. locus coeruleus, amygdala, thalamus i. modulated by environmental stimuli b. and by feedback to the brain from released hormones 3. neurons from the hypothalamus also project to other areas of the brain a. may modify/regulate related behaviors 4. RH's travel via the blood to the pituitary a. HTA b. Axons c. Median Eminance d. Primary capillary plexus e. Hypothalamo-hypophyseal Portal Veins f. Secondary Capillary Plexus g. Anterior Pituitary cell B. Releasing Hormones 1. Gonadotropin-Releasing Hormone (GnRH - also called LHRH) a. only releasing hormone that releases two hormones i. LH ii. FSH b. decapeptide i. > 14 different forms of GnRH exist (1) differences found in the 5th, 7th, & 8th amino acids (a) named for the animal first discovered in ii. mammals (inlcuding humans) have chicken II and mammalian GnRH's (1) c2GnRH acts as a neuromodulator and is found in most vertebrates (a) lizards have c2GnRH and s1GnRH c. GnRH is made in the arcuate and preoptic nuclei of the hypothalamus i. stimulation by NE from the locus ceruleus causes release of GnRH 2. DA (PRIH) and TRH (PRH) a. Prolactin has releasing (TRH) and release inhibiting hormones (DA) b. DA (PRIH) has stronger influence i. PRL is under tonic inhibitory control c. suckling stimulates PRL release facilitated by TRH i. neuroendocrine reflex d. receptors for each releasing hormone i. separate receptors for RIH and RH 3. some other hypothalamic hormones: TRH (release of TSH), CRH (ACTH), GHRH and GHRIH (GH), V. Pituitary Gland - Hypophysis A. "Pituita" - slime or flem in Greek 1. it was thought that the pituitary secreted saliva or flem B. Situated just below the brain (particularly the hypothalamus) 1. Infundibulum = Stalk 2. Anterior Pituitary = Adenohypophysis a. Pars Distalis b. Pars Tuberalis (ring around infundibulum) c. Pars Intermedia (sparse or absent as distinct structure in adult humans) d. adeno = glandular i. derived from Rathke's pouch e. hormones of the adenohypophysis (mostly pars distalis) i. basophils - mostly glycoproteins (1) gonadotropins: (a) Follicle-Stimulating Hormone (FSH) (b) Luteinizing Hormone (LH) (2) also TSH and ACTH (a polypeptide) ii. acidophils - large proteins (1) Prolactin (PRL) (2) GH iii. chromophobe - polypeptides (1) Endorphins and Enkephalins (2) a-MSH 3. Posterior Pituitary = Neurohypophysis = Pars Nervosa a. like the HTA, neurohypophysis is made up of a special kind of neurons = Neurosecretory Neurons i. they don't conduct electrical signals very well ii. synapses not with another neuron, but with capillary bed (1) neurohemal organ iii. neural message causes the release of a hormone b. islands of neurosecretory cell bodies (perikarya) in the hypothalamus = Neurosecretory Nuclei (SON, PVN) i. axons and terminals compose neurohypophysis c. Oxytocin (Oxy) i. milk ejection ii. contractions of the uterus d. Arginine Vasopressin = Antidiuretic Hormone i. blood pressure, water reabsorption ii. AVT combines effects of both AVP + OXY (1) putative evolutionary precursor (2) found in fish, amphibians, reptiles and birds (3) other uterotonic forms include MST, IST LVT, GLT, AST, VAT