Reproductive Endocrinology

Reproductive Endocrinology

Hormones: are chemical agents

which are secreted from endocrine

and ductless glands; and affect

tissue or organs to increase or

decrease their effects in the body.

• From Hypothalamus, hormone releasing factors are secreted. These are; TRF, CRF, GRF, GnRH, PIF, PRF.

• Vasopressin (ADH) and oxytocin are hormones produced in hypothalamus.

They are transported to hypophisis dorsal lobe through neural ports and stored.

Reproductive Endocrinology

• From hypophysis frontal lobe (adenohypophysis); FSH, LH, LTH (luteotrophic hormone), ACTH, TSH, STH (somatotrophic hormone), MSH (melanocyte stimulating hormone), PRL.

• From dorsal lobe

(Neurohypophysis); oxytocin and ADH (vasopressin) are secreted.

Reproductive Endocrinology

• Ovary: Estrogen (theca interna), progesterone (Corpus Luteum), Inhibin.

• Testis: Testosterone (Leydig cells), Androgen Binding Protein, Inhibin.

• Uterus: Prostaglandin F

 (endometrium).

Reproductive Endocrinology

• Placenta:

– PMSG – PMS (Pregnant Mare Serum Gonodotropin)(FSH effect) – HCG(Human Chorionic Gonadotropin) (LH effect)

– Prolactin (LTH luteotrophic effect) – Estrogen

– Testosterone – Progesterone

– HMG (Human Menopausal Gonadotropin) – HCS (Human Chorionic Somatotropin)

Reproductive Endocrinology

• According to their chemical structures Steroid hormones

– Estrogen

– Progesterone – Testosterone – Glucocorticoids

– Mineralocorticoids (aldosterone)

Reproductive Endocrinology

Proteo-hormones

– LTH – ACTH – TSH – STH – MSH – ADH

– Oxytocin

Reproductive Endocrinology

Glucoproteins – FSH – LH – PMSG – HCG

Synthetic hormones

– DES (diethylstilbestrol, estrogen) – Medroxyprogesterone acetate

(progesterone)

– Testosterone propiyonate (testosterone) Anti hormones

– Formed after the induction of a hormone from one species to another species.

Reproductive Endocrinology

• After any stimulus, the neurosecreting neurons in eminentia media of hypothalamus are effected.

• Gonadotropin Releasing Hormones, which are secreted by neurons arrive adenohypophysis by sinusoidal portal veins.

• As a result of stimulation of the basophilic cells in adenohypophysis, FSH and LH, which are gonadotropic complex hormones are formed.

• This mutual interaction between hypothalamus and adenohypophysis is called internal feedback mechanism.

Feedback Mechanism

• The progressive secretion of FSH, causes the estrogen secreted by theka interna and membrana granulosa of follicles to increase progressively.

• When the estrogen hormone reaches a specific level in blood, it causes a positive feedback on adenohypophysis, while causing a negative feedback on hypothalamus.

• While stimulating LH hormone secretion from the gonadotropic complex, it also prevents FSH-RH secretion from hypothalamus. Thus as FSH secretion decreases; the LH which is secreted in increasing proportions in the gonadotropic complex affects the Graaf folicle and causes ovulation to occur.

Feedback Mechanism

• In the concavity formed after the Graaf folicle eruption, a synergy of LH and LTH (prolactin) occurs causing corpus luteum periodicum to form; this new composed structure starts to secrete progesterone.

• The secreted progesterone, causes a negative feedback on adenohypophysis while causing a positive feedback on hypothalamus and stopping FSH secretion in gonadotrapic complex, prevents new follicle formation and development.

• Because of the progesterone secretion decrease resulting from the luteolysis of corpus luteum periodicum, the negative feedback on adenohypophysis will be removed;

resulting in FSH secretion and increase in follicular development.

Feedback Mechanism

Reproductive Endocrinology

Melatonin

• Melatonin is a hormone secreted by the pineal (epiphysis) gland located at the back of hypothalamus.

• It displays its effect by starting and ending the sexually active season in poliestric animals (sheep, goat, horse).

• The impulses regarding light in the eyes are

transformed into neurological impulses in the retina

and these neurological impulses travel to the

suprachiasmatic nucleus located in front of

hypothalamus which determines the secretion

rhythm of the pineal gland directly by retino-

hypothalamic pathway.

Reproductive Endocrinology

Melatonin

• Signals emenating from the suprachiasmatic nucleus are transferred through the preganglionic and postganglionic fibers to the pineolocytes which are the main cells of the pineal gland.

• The pineal gland changes the melatonin secretion levels in accordance with duration of daylight depending on the neural information coming from the eyes.

• Darkness increases the sympathic neural activity on

the pineal gland, thus increasing melatonin secretion

rate.