Reproduction Unit EXAM 3

Difference between NS and ES

Endocrine: Graded response: Amount of hormone circulating and density of receptors on target tissues

Nervous: Graded response: spatial and temporal summation of synaptic inputs

Similarities between ES and NS

Both systems operate by sending out chemical messenger molecules that bind to specific receptors to trigger a response in the target cell

Both have graded responses

What is fertility?

The ability to conceive children. Being infertile is not being able to achieve pregnancy after regular intercourse.

What is the HPG Axis?

Hypothalamus → Anterior Pituitary → Gonads → Effector Tissues

Role of the hypothalamus in the HPG axis

The hypothalamus releases GnRH (gonadotropin releasing hormone), and that hormone binds to receptors in the pituitary gland and stimulates the pituitary to release tropic hormones. GnRH is a tropic hormone.

Gonadotropins are…

Tropic = stimulates another gland to secrete hormones

Ex. LH (luteinizing hormone) and FSH (follicular stimulating hormone) are tropic hormones because they stimulate endocrine glands (ovaries and testes) to secrete sex hormones

What kind of receptors do peptide hormones like gonadotropins usually have?

Extracellular receptors → the hormones will bind to receptors on the outside like G-coupled protein receptors to trigger signaling cascade inside the cell. The receptors would be on the cell membranes of target cells

Role of the anterior pituitary in the HPG axis?

Releases LH and FSH which target cells in the ovaries and testes.

What cells do the LH and FSH stimulate in the ovaries and testes?

LH

• Testes: Leydig cells

• Ovaries: Thecal cells

FSH

• Testes: Sertoli cells

• Ovaries: Granulosa cells

What cell produces testosterone, what cell produces estrogen, what cell produces progesterone?

Testosterone → Leydig cells

Estrogen → Granulosa cells and Theca cells (indirectly)

Progesterone → Theca cells

Why can’t theca cells directly produce estrogen?

They lack the enzyme aromatase which converts androgens into estrogen. They work with neighboring cells using the 2C2G model.

_______________ is a precursor for all steroid hormones.

Cholesterol

Androgens include

Testosterone and DHT

What enzyme converts testosterone to DHT?

5-alpha-reductase

What is sex hormone-binding globulin (SHBG) for?

It binds tightly to sex hormones like testosterone, DHT, and estrogen, and carries them through your bloodstream to control how much of the hormones are free to act on tissues.

Estrogens include

estrone and estradiol

Estrogen target tissues (effectors)

Estrogen can have an action wherever there is a receptor, and many diff. types of tissues have estrogen subtype receptors

Androgen target tissues (effectors)

Androgen can have an action where there is a receptor, and many different types of tissues have ARs

What levels are the lowest in childhood (0-10 yrs)

Gonadotropins are the lowest. Girls are incapable of conceiving AKA infertile

Fertility in puberty (10-15 yrs old)

Becoming physiologically capable of conceiving children (initial menses/growth of testes)

Initiated by onset of pulsatile GnRH

Fertility in adult years (18-45 yrs)

Fertility fluctuates with menstrual cycle, stays relatively high for sperm-producing individuals

Gonadotropin levels continue to increase

Fertility in Climacterium (45-50 years)

Menstruation becomes less frequent, changes in libido, decrease in estrogen levels

Fertility in senescence (50+)

Cessation of mens cycle

Decrease in sperm count and mobility

Gonadotropin levels are the highest

List if LH or FSH is > in each part of the lifespan.

Childhood: FSH > LH

Puberty: LH > FSH

Adult: LH > FSH

Senescence: FSH > LH

The effects of stress axis on reproduction

• Cortisol inhibits HPG axis

• CRH inhibits GnRH (CRH is primary initiator of HPG axis response to stress)

  • Chronic stress → amenorrhea (no period), low libido, erectile dysfunction

LH binds to:

FSH binds to:

LH binds to leydig and theca cells → LLT - Long Live Tom

FSH binds to sertoli and granulosa cells → FSG - Five Stupid Guys