Physiology of Drugs Affecting Fertility and Reproduction Flashcards
Name the 3 categories of steroids secreted by the gonads
- Estogens: Estradiol, Estrone and Estriol
- Progestins: Progesterone
- Androgens: Testosterone
Biosynthesis of the sex steriods
Pregnenolone is a precursor of progesterone and it is responsible for the maintenance of pregnancy during the female sexual cycle.
It is also the precursor to dehydroepiandrosterone and Androstenedione(Two androgens which are secreted by the adrenal gland)
What is Aromatase
Aromatase is responsible for converting Adrenal and gonadal androgens to Estrogen-by forming an aromatic A-ring for the selective high affinity binding of Estradiol, Estriol and Estrone
Secretion of Testosterone in Males and in Females
In Females, Ovarian Thecal cells secrete small quantities of Testosterone.
In Males, The Leydig cells in the testes secrete about 95% of Testosterone and about 5% is derived from the Adrenal cortex.
5alpha-Reductase
Converts Testosterone to dihydrotestosterone(DHT) and it is found within the prostate, hair follicles and skin.
In plasma, T is bound to a sex-steroid-binding globulin.
In the liver, it is converted to Androstenedione and other metabolites, including sulfate and glucuronide conjugates of T-90% excreted in urine.
Both T and DHT active androgen receptors,DHT has a greater receptor affinity and forms a more stable receptor-ligand complex than T,If DHT formation is inhibited, this significantly reduces androgenic stimulation to the prostate and hair follicles
Hormonal actions of Es and Progesterone
Estrogen is secreted by the granulosa cells of the ovary.
Progesterone is primarily produced by the corpus luteum in response to LH stimulation
Hormonal actions of Es and Prog:
The Follicular Phase
Ovarian follicles are recruited and a dominant estrogen-secreting follicle develops.
Es levels gradually increase, whereas Prog levels remain very low.
A surge of Lh is released midcycle in response to the positive estrogen feedback to the pituitary gland and this LH surge triggers ovulation
Hormonal actions of Es and Prog:
The Luteal Phase and pregnancy
The follicle becomes the corpus luteum that screted both Prog and Es in response to LH.
Both hormones prepare the uterus for implantation of a fertilized egg as the endometrium becomes more vascular and secretory.
If pregnancy does not occur: The corpus luteum ceases to produce Es and Prog resulting in endometrial sloughing and menstruation
If pregnancy does occur: The placenta produces human chorionic gonadotropin, which maintains the production of Prog by the corpus luteum for about 3 months, after that the placenta becomes the dominant source of prog-serves to maintain pregnancy and prevent endometrial sloughing and miscarriage
Physiological effects of Estrogen
Sensitize myometrium to oxytocin at parturition this facilitates labour.
Stimulate protein synthesis in the brain and may thereby affect mood and emotions
Influences the distribution of body fat and thereby contribute to the development of feminine body contours.
They enhance blood coagulation by increasing the synthesis of clotting factors.
Prevent osteoporosis by inh bone reabsorption.
Epiphyseal closure in both males and females which halts linear bone growth
Decrease the levels of LDL cholesterol and lipoprotein a which increasing HDL cholesterol
Physiological Effects of Progesterone
Produce a dose related increase in LDL levels and decrease in HDL levels
Increase basal body temperature by 0.5 to 0.8C at ovulation during the luteal phase.
Affect emotional state
Mild mineralocorticoid(salt) retaining properties
Hormonal actions of Testosterone
LH stimulates T synthesis in Leydig cells and FSH promotes spermatogenesis by Sertoli cells in the seminiferous tubules.
Sertoli cells also produce a protein called-Inhibin, which acts in concert with DHT as a feedback regulator of FSH secretion by the PG
Physiological effects of T
Development of primary and secondary sex characteristics in males during puberty.
Promotes sexual function by stimulating growth of the penis, scrotum, seminal vesicles and prostate gland as well as the growth of the larynx, thickening of the vocal cords, growth of facial, axillary and pubic hair
Increase lean body mass and skeletal growth and eventually accelerate epiphyseal closing
Contributes to the development of acne in both sexes by increasing sabaceous gland activity and sebum production.
Androgens also increase the production of EPO in the kidneys and decrease the levels of HDL cholesterol
