Repro 2 Flashcards
Bipotential parts of external genitalia
Genital tubercle, urethral groove, urethral fold, labioscrotal swelling
If female genital tubercle
Forms clitoris
If female urethral folds and grooves
Form labia minora, opening of vagina and urethra
If female labioscrotal swellings
Form labia Majora
If male genital tubercle
Forms glans penis
If male urethral folds and grooves
Form shaft of penis
If male labioscrotal swellings
Form shaft of penis and scrotum
External genitalia development is driven by
Presence or absence of androgens (DHT)
At 10 weeks of female growth (external)
In absence of androgens external genitalia is feminized
At 10 weeks of male growth (external)
DHT causes development of male external genitalia
At birth males (external)
Testosterone causes Testes to descend from abdominal cavity into scrotum
When did importance of DHT come to light
Studies of male pseudohermaphrodites
What do pseudohermaphrotdites lack
Have defective gene for 5a reductase
Needed for conversion of testosterone to DHT
What does no DHT cause for pseudohermaphrodites
Despite having testosterone
- failure of male external genitalia and prostate development
- appear female at birth, male internal
- at puberty testes begin to secrete testosterone causing masculinzatin of external genitalia
Testis and ovaries both produce
Hormones and gametes
Ovum
- some of largest cells in body
- nonmotile, move via smooth muscle contraction or cilia
What are all females born with
All oocytes, cyclically released during reproductive years
After ~40 years in ceases
Sperm
- quite small
- only flagellated cells in body
- highly motile
- continuously produces after reaching reproductive maturity
- sperm and testosterone production dismisses with age but not cease
Gametogenesis
Production of gametes
What does gametogenesis begin with
Mitosis in utero to increase germ cell numbers
Female germ cells
Oogonia
Male germ cells
Spermatogonia
How many viable gametes does 1 sperm cell produce
4
How many viable gametes does 1 female germ cell produce
1
Steps of gametogenesis
- Germ cells in embryonic gonads undergo mitosis divisions to increase number
- Meiosis: Duplication of chromosomes (92 chromatids)
- One primary gamete divides into 2 secondary gametes (each with 46 chromosomes)
- Secondary gametes divide again to produce haploid gametes (23 chromatids)
Female gametogenesis
- significant mitosis in embryonic and fetal development (lots of oogonia)
- enter meiosis and create large pool of primary oocytes
- stay arrested until reproductive age
At birth ~ how many primary oocytes in each ovary
5000
When does second meiotic division occur for females
Ovary releases egg and it does not until Fertilization
When does mitosis and first stage of meiosis occur by in females
Fifth month of fetal development
When does meiosis resume in females
Puberty
First meiotic division in females
Produces large secondary oocyte and tiny first polar body (46 chromosomes)
What happens when egg begins second meiotic division
Polar bodies break down
How many chromosomes does secondary oocyte contain
46
Once sperm begins to fertilize secondary oocyte what does it undergo
Meiotic division shedding a polar body containing 23 chromosomes
Leaves 23 in ovum and 23 new chromosomes enter sperm
Why dont polar bodies survive
Uneven division
Very small with very little cytoplasm and few organelles
In both males and females gametogenesis is under control of
Hormones from brain and from endocrine cells in gonads
When does significant mitosis happen for males
Once reach reproductive age
At birth what do testes contain
Only immature germ cells and remain quiescent
At puberty what happens to germ cells in males
Mitosis resumes producing spermatogonia
What happens to spermatogonia if they do not continue in mitosis
Some enter meiosis producing primary spermatocytes, secondary spermatocytes, spermatid then sperm
What directs resproduction
Brain
For both male and female what doses reproduction begin with
Secretion of peptide hormones from hypothalamus and anterior pituitary that control gonadal secretion of sex hormones
- androgens, estrogens, progrestorone
What sex hormones do both sexes produce
Androgens, estrogens, progesterone
Males primarily secrete
Androgens
95% testes, 5% adrenal cortex
Most converted in periphery to DHT
Females primarily secrete
Estrogens and progesterone (ovaries)
What is the sex hormone precursor
Cholesterol
What is the main control pathway for the reproductive system
Hypothalamic pituitary gonadal axis
Gonatropin releasing hormone (GnRH)
Produces in hypothalamic neurons
Controls secretion of 2 anterior pituitary gonadotropins from gonadotropes
What are the 2 ant. Pit. Gonadotropins
Follicle stimulating hormone (FSH)
Luteinizing hormone (LH)
Act on gonads
What regulates GnRH
Kisspeptin
What does LH act on
Endocrine cells
In females gamete production
What does FSH act on
Gamete production
How does GnRH get to anterior pituitary
Hypophyseal portal system
How does hypophyseal portal system work
GnRH secreted enters capillary bed at base of hypothalamus
Travels through portal veins to 2nd capillary bed in ant. Pit.
GnRH stimulates gonadotropes
LH and FSH enter 2nd capillary bed and travail via blood stream to gonads
What is short loop negative feedback
Involves LH and FSH inhibiting GnRH release from hypothalamus
Low estrogen or androgen(testosterone)
Absence of negative feedback
Increases in GnRH, LH and FSH
Moderate estrogen or androgen
Negative feedback
Decreases GnRH
High androgen
Negative feedback
Decreases
Sustained high estrogen
Positive feedback
Increases to drive LH
Why is estrogen negative feedback to a point
Flips to positive driving GnRH and LH even higher
Plays role in female reproductive cycle
What does feedback at anterior pituitary affect
Gonadotropes
What does feedback at hypothalamus act on
Directly on GnRH neurons or via kisspeptin
How is GnRH released from hypothalamus
In pulsatile fashion every 1-3 hours in both sexes
Females have a surge of GnRH release
Corresponding with ovulation
Children with GnRH deficiency
Not mature sexually without gonadotropin stimulation
Synthetic GnRH must be delivered in pulsatile manner
What does constant delivery of GnRH lead to
Down regulation of receptors in pituitary gonadotropes
- receptors internalize
- must be pulsatile
