What are the 3 components of the reproductive system?
Components of Reproductive System
A. Primary Reproductive Organs: gonads (testes - male, ovaries - female)
B. Secondary Reproductive Organs: reproductive tract and accessory sex glands
C. Brain and Nervous System: autonomic, pituitary/hypothalamus, sexually dimorphic nuclei
What are the functions of gonads?
1. endocrine function: secretion of testosterone (m), estrogen (f), progesterone (f), inhibin (m & f)
2. production of gametes: sperm (m), ovum (f)
What are the functions of secondary reproductive organs?
Functions of Secondary Reproductive Organs
1. transport and maturation of gametes
2. union of gametes
3. secretion of various fluids for lubrication, nourishment, and transport of gametes
4. development of embryo
What are the functions of the brain and nervous system in reproduction?
1. endocrine function
a. hypothalamus (e.g. secretion of GnRH)
b. anterior pituitary (e.g. secretion of LH, FSH, prolactin) and posterior pituitary (secretion of oxytocin)
2. neural function
a. autonomic nervous system (erection, ejaculation)
b. sexual behavior (libido, sexual orientation)
What enzyme interconverts testosterone and estradiol?
What is sexual differentiation?
Explain the differences btwn genetic sex, gondal sex, and phenotypic sex.
Sexual differentiation: the differences between genetic sex, gonadal sex and phenotypic sex
A. Genetic sex is determined by the Y chromosome (present in the male, and absent in the female)
B. The determinant of gonadal sex (development of testes or ovaries) follows from the presence or absence of a Y chromosome
C. Phenotypic sex, the formation of a male or female reproductive tract, is then determined by the presence (male) or absence (female) of testosterone
What region on the Y chromosome determines sex? What is one thing this region codes for?
•SRY – sex-determining region Y. SRY region codes for TDR – testes determining factor
What do germ cells, coelomic epithelium, and mesenchymal cells differentiate into in males and females?
Why is female sex the default sex?
What 2 chemicals must be present in males for a male phenotype?
1. germ cells: spermatogonia in males, oogonia in females
coelomic epithelium: Sertoli cells in males, granulosa cells in females
mesenchymal cells: Leydig cells in males, Theca cells in females
2. Female sex is the default sex. In males, anti-mullerian hormone (produced by Sertoli cells) and testosterone must be present for male phenotypic sex (formation of male genital tract and male external genitalia). Without the production of these hormones, female sex results. Note that in the streak gonad (XO) the sex is female but the gonads are fibrous and non-functional.
Explain the hypothalamic pituitary control of the reproductive system in females and males.
Control of the Reproductive System
A. Control is achieved by endocrine feedback systems (negative, and in some instances, positive) between the gonads, the anterior pituitary, and the hypothalamus
B. Control of the male reproductive system involves negative feedback from the testes onto the pituitary and hypothalamus
C. Control of the female reproductive system involves negative, and sometimes positive, feedback from the ovaries onto the pituitary and hypothalamus. The feedback of estradiol can become positive during a portion of the female ovarian cycle.
inhibin: important for regulation of reproduction
activin: stimulates FSH release. is less well understood
note that there is negative feedback at all levels
T or F: Reproduction requires a complex interaction between the nervous system and the Endocrine system. The sex hormones have widespread effects outside of the reproductive Tract and therefore influence all of the normal physiology of the body.
What type of circulation exists btwn the hypothalamus and pituitary?
Describe the chronology of sexual development.
Chronology of endocrine changes in reproductive system
Unlike other physiological functions, which begin essentially at conception and operate continually until death, sexual functions wax and wane throughout the course of life.
A. Embryonic development
1. sexual differentiation
2. development of Wolffian ducts and Mullerian ducts
B. Childhood: sexual quiescence
C. Puberty: resumption of sexual development
1. Start of menstruation in female
D. Adulthood: sexual maturity
puberty: encompasses the physiological, morphological and behavioral changes that occur as gonads change from the infantile to the adult state
What physical change occurs in both males and females during puberty?
What is the difference of time of occurrence in males and females?
What hormones is this phyiscal change dependent on?
Physical changes include:
1. In both male and female there is an adolescent growth spurt
a. on average, males gain 28 cm while females gain 25 cm
b. growth spurt occurs later in males (allowing more time before the growth plates of the long bones close) accounting for greater height of males
c. growth spurt dependent on growth hormone (GH) and gonadal hormones (testosterone and estrogen)
What physical changes occur in males during puberty? What hormones are responsible for these changes?
In the male there occurs:
a. enlargement of male genitalia (penis, testicles, scrotum); first sign of puberty. note that in attached figure, plasma testosterone increases once testicles reach a certain size
b. enlargement of larynx (development of Adams’ apple and deepening of voice) due to action of testosterone on thyroid and cricoid cartilages and on the laryngeal muscles
c. development of facial hair
d. broadening of shoulders and increased muscle mass
What physical changes occur in females during puberty? What hormones are responsible for these changes?
In the female there occurs:
a. breast development (dependent on ovarian estrogen)
b. growth of pubic and axillary hair (dependent on androgens secreted by adrenal cortex and ovaries)
c. enlargement of labia (dependent on estrogen)
d. broadening of hips (redistribution of adipose tissue)
Describe the differences in pattern and levels of plasma LH in pre-puberty, puberty, and adulthood.
The changes that occur during puberty are driven by significant changes in the temporal pattern of hormone secretion and the levels of sex hormones that are present
1. During puberty there develops a circadian rhythm in gonadotrophin secretion although no such pattern is present before puberty or in the adult
2. Increased GnRH during sleep produces increased levels of LH, FSH and testosterone and estrogen
The mechanism underlying the initiation of puberty is not completely understood.
What part of the reproductive system is thought that puberty is dependent on the maturation of?
Once the maturation of this part occurs, what is the result?
1. Puberty seems to be dependent on the maturation of the central nervous system, specifically the hypothalamus, since:
a. The immature pituitary can respond to GnRH with pulses of LH and FSH.
b. In turn, the immature gonads can respond to LH and FSH.
c. Thus, it appears that hypothalamic release of GnRH is low before puberty and as a result the levels of gonadal hormones are low.
2. One model that has been proposed is that the initiating event at the start of puberty is a decrease in the sensitivity of the hypothalamus and the pituitary to the negative feedback produced by testosterone and estrogen.
What hormones are thought to be involved in the initiation of puberty? What are the effects of these hormones in this process? (basically, what is believed to be the mechanism for puberty initiation?)
A more recent model suggests a different mechanism in the hypothalamus for the initiation of puberty.
1. There is considerable data from a number of species that show that puberty only begins when the individual’s energy reserves (basically body fat) is adequate to support the metabolic demands of reproduction (which is considerable for the female).
a. Leptin is a hormone released from adipose cells.
b. The occurrence of puberty is related to a sufficiently high level of leptin. c
. However, whether this is the “timing” mechanism that triggers puberty is still not clear.
Kisspeptin is a newly discovered transmitter-like substance released from hypothalamic neurons. GnRH secreting hypothalamic neurons have a receptor for this peptide. In the absence of kisspeptin, or its receptor, puberty does not occur.
a. Observed in knock-out mice lacking the gene to produce the kisspeptin receptor
b. A similar phenomenon is also observed in human families with a genetic defect that blocks the kisspeptin-receptor system.
3. It has been proposed that as the child grows and matures, leptin (or some other “growth related” signal) increases in concentration, GnRH neurons increase their sensitivity to kisspeptin. At some level of activation by kisspeptin the release of GnRH is high enough to initiate puberty (increases in LH, FSH leading to increases in sex hormones). It is thought that kisspeptin decreases the sensitivity of GnRH neurons to negative feedback by testosterone and estrogen.
What is menopause? What is a result of?
• Cessation of reproductive (not sexual) function in female
• It arises from a cessation of function in the ovaries
What are targets for estrogen in the body?
Targets for estrogen
• Reproductive organs
– Male reproductive tract: Efferent ductule fluid absorbtion, germ cells, differentiation
– Female reproductive tract
• Bone (osteoblasts stimulation)
• Vascular system (vasodilation, plaque protection)
• CNS (growth, neuroprotection, perfusion)
What are the 3 most important androgens? (just list)
Which is the most potent?
DHT (dehydroxytestosterone). most potent
What percentage of testosterone is free in plasma? What plasma proteins does testosterone bind to?
What enzyme converts testosterone to the more potent DHT?
Which of the 3 androgens is the most abundant in circulation?
Which of the 3 androgens has the lowest affinity for androgen receptors?
– Testosterone (~2% free, 44% Sex Hormone Binding Protein; SHBP, 54% albumin/CBG)
– DHT (most potent, converted to DHT from testosterone by 5-alpha reductase in target tissue)
– DHEA (most abundant circulating). Also has lowest receptor affinity
What are the 3 most important estrogens? (just list)
What plasma proteins does estradiol bind to? During what time is estradiol must abundant?
During what time is estrone most abundant?
During what timne is estriol must abundant?
– Estradiol (Important non-pregnant, 2% free, 38% SHBP, 60% Albumin )
– Estrone (most abundant in menopause)
– Estriol (important during pregnancy)