Reproductive and Urinary Systems

what are gonads, and how do they differ in males and females?

sex organs that contain germ cells and produce gametes and sex hormones

males = testes, produce sperm

females = ovaries, produce eggs

what is the principle male sex hormone?

testosterone, a potent androgen

where is testosterone synthesised?

within the Leydig cells of the testes (in males) and some from adrenal cortex (in both sexes)

which androgens other than testosterone are synthesised within the adrenal cortex in both sexes, and what is their role?

Dehydroepiandrosterone (DHEA) and androstenedione - weak androgens

activate oestrogen receptors

responsible for early development of pubic/body hair due to DHEA

testosterone takes over in boys to complete puberty

label testes

which enzymes metabolise testosterone in men and in women, and what is the resultant product?

men: 5-alpha-reductase, dihydrotestosterone

women: aromatase, estradiol

describe the functions of testosterone

stimulates enlargement of testes and male accessory organs

stimulates development of male secondary sex characteristics:

• increased growth of body hair

• enlargement of the larynx and thickening of vocal cords

• thickening of the skin

• muscle growth, widening of shoulders, narrowing of waist

• thickening and strengthening of bones

how does dihydrotestosterone act on androgen receptors?

binds to cytoplasmic androgen receptors, promoting release of heat shock protein (hsp)

steroid receptor complex migrates to nucleus and binds to specific regions of DNA containing androgen response elements (ARE)

this drives expression of genes that determine male phenotype

how do testosterone levels change throughout a lifespan?

always a circulating level

mini puberty at ~6 months then levels unchanged until puberty

maintained throughout adult life, decline in old age

describe the effect of testosterone on muscle, liver, fat, brain, bone and bone marrow

muscle - increase in strength and volume

liver - synthesis of serum proteins

fat - decrease fat mass

brain - libido, aggression, cognition

bone - accelerated linear growth, maintains bone mineral density

bone marrow - stimulation of stem cells

via what hormones does the brain control reproduction in both sexes?

GnRH (gonadotropin-releasing hormone) and pituitary gonadotropins (FSH and LH)

what is the role of GnRH?

stimulates anterior pituitary to release LH and FSH

what is the role of LH?

lutenizing hormone

released from anterior pituitary

triggers ovulation in women and sperm production in men

targets endocrine cells to release steroid and peptide hormones

what is the role of FSH?

follice-stimulating hormone

released from anterior pituitary

stimulates growth and maturation of ovarian follices (containing immature eggs) in women

promotes spermatogenesis in men

what is the role of ovaries?

produce female sex hormones and female germ cells

differentiate between gonadotrophic and ovarian hormones

gonadotrophic - LH and FSH

ovarian - estrogen, inhibin and progesterone