repro 2 Flashcards
what is the importance of dihydrotestosterone (DHT)?
came to light in studies of male pseudohermaphrodites
-defective gene for 5a-reductase
-despite having testosterone production, lack of DHT results in failure of male external genital and prostate development
-appears to be females at birth
-at puberty the testes begin to secrete testosterone again causing masculinization of external genitalia
what are the basic patterns of reproduction?
the testis and ovaries both produce hormones and gametes and share other similarities but gametes produced are very different
what is the basic description of the ovum?
-some of the largest cells in the body
-nonmotile, move via smooth muscle contraction or cilia
-born with all the oocytes you will have, cyclically released during reproductive years
-after around 40 years, cease
what is the basic description of the sperm cell?
-quite small
-the only flagellated cells in the body and are highly motile
-continuously produced after reaching reproductive maturity
-sperm and testosterone production diminishes with age but do not cease
what is gametogenesis and when does it begin?
-the production of gametes
-mitosis begins in utero to increase germ cell numbers
what are the stages of gametogenesis?
begins in utero
1. germ cells in embryonic gonads undergo mitotic divisions to increase number
2. duplication of chromosomes (92 chromosomes)
3. one primary gamete divides into two secondary gametes (each with 46 chromosomes)
4. secondary gametes divide again to produce haploid gametes (23 chromosomes=23 chromatids)
what is the graph of female gametogenesis?
what is female gametogenesis?
-in females, germ cells are oogonia
-mitosis and the first stage of meiosis occurs by the fifth month of female development
-at birth each ovary 500,000 primary oocytes
-meiosis resumes at puberty
-first division produces large secondary oocyte and a tiny first polar body (46 chromosomes)
-the egg begins second meiotic division, polar bodies break down
-ovaries releases egg and it does not undergo secondary division until fertilized
what is important about the secondary oocytes?
-secondary oocyte contains 46 chromosomes but is preparing to undergo division
-once sperm begins to fertilize secondary oocyte it undergoes meiotic division shredding a polar body containing 23 chromosomes
-this leaves 23 chromosomes in the ovum and 23 new chromosomes enter from the sperm
why don’t polar bodies survive?
-uneven division
-polar bodies are very small with very little cytoplasm and few organelles
in both male and female, gametogenesis is under control of _______________
HORMONES from the brain and from endocrines cells in the gonads
what is the graph of male gametogenesis?
what is male gametogenesis?
-at birth, testes contain only immature germ cells and remain quiescent
-at puberty germ cells mitosis resumes producing germ cells known as spermatogonia
-some spermatogonia continue in mitosis, some enter meiosis producing primary spermatocytes. secondary spermatocytes, spermatids and finally sperm
how does the brain direct reproduction?
the reproductive system has some of the most complex control pathways in the body with multiple hormones interacting in an ever-changing fashion
-begins with secretion of peptide hormones from hypothalamus and anterior pituitary that control gondal secretion of sex hormones including androgens, estrogens and progesterone
what is the percentage of what hormones are in both male and females?
both sexes produce all three: androgens. estrogens and progesterone
-males primarily androgens (95% testes, 5% adrenal cortex) most converted in periphery to DHT
-females primarily estrogens and progesterone (ovaries)
what is the hypothalamic-pituitary-gonadal axis?
-gonadotrophin releasing hormone (GnRH) produces in hypothalamic neurons control secretion of two anterior pituitary gonadotrophins from gonadotropes
-follicles stimulating hormone and luteinizing hormone (both act on gonads)
what is the hypophyseal portal system?
what are feedback pathways?
estrogen is negative feedback up to a point, but once reaching higher concentrations flips to positive feedback driving GnRH and especially LH even higher, plays a significant role in female reproductive cycle
-how? thought to be estrogen influencing GnRH release via kisspeptin
what is the graph of feedback pathways?
what is GnRH release?
-released from hypothalamus in pulsatile fashion every 1-3 hours in both sexes
-females also have a surge corresponding with ovulation
