Lecture 29: Hormones and reproduction Flashcards Preview

1060 Human form and function > Lecture 29: Hormones and reproduction > Flashcards

Flashcards in Lecture 29: Hormones and reproduction Deck (28):
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Reproductive life history??

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where is  the hypothalamus??

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The hypothalamic-pituitary-gonadal (HPG) axis

 

Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH) are released together into the circulation from the anterior pituitary in response to GnRH 

 

Luteinising Hormone

Stimulates production of steroid hormones

Follicle Stimulating Hormone

Stimulates production of gametes (eggs, sperm) 

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Two main roles of the gonads??

Two main roles:

Production of gametes.
Production and release of steroid hormones. 

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3 main types of steroids when it comes to reproduction??

Progestagens

Androgens

Oestrogens

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Steroid hormone function??

Androgens??

Pass through cell membranes to act on intracellular receptors.

Receptor activation leads to changes in gene transcription. 

 

Androgens

Steroid hormones that stimulate male physical and reproductive characteristics

Testosterone is the primary biological androgen

Mainly synthesised and released by the testes and the adrenal gland

Can be converted into oestrogens 

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Steroid hormone function??

Oestrogen??

Pass through cell membranes to act on intracellular receptors.

Receptor activation leads to changes in gene transcription. 

 

Steroid hormones that function as the primary female reproductive hormones

In non-pregnant women the primary naturally occuring oestrogen is oestradiol

Mainly synthesised from androgens and released by the ovaries 

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Steroid hormone function?

Progestagens ??

Pass through cell membranes to act on intracellular receptors.

Receptor activation leads to changes in gene transcription. 

 

Steroid hormones derived from the same precursor as testosterone and oestrogen.

Involved in the menstrual cycle and pregnancy. 

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Anatomy of testes

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Effects of Testosterone ??

Male hormone - anabolic

Primary and secondary male sexual characteristics

Libido and sexual behaviour

Stimulates spermatogenesis 

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Spermatogenesis ??

Spermatogenesis occurs within the seminifous tubules 

Seminiferous tubules contain both sertoli cells and spermatogonial stem cells 

 

Spermatogonial stem cells

Sperm production

Sertoli cells

Support
Nutrition

 

Spermatogenesis :

Starts at puberty

Maintains species

Mitosis followed by Meiosis

120 million sperm / day or 1,500 / sec

Regulated by FSH 

Protection

Regulation 

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The male hypothalamic-pituitary-gonadal (HPG) axis 

LH stimulates testosterone release from the Leydig cells.

FSH and testosterone stimulate production of sperm in the seminiferous tubules. 

 

The leydig cells and the seminiferus tubules work together to maintain male reproductive function

 

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Male 

New sperm produced continuously throughout adult life

testosterone released at a constant level

 

Female?

unlike in males, female reproductive function is cyclic with one oocyte released per cycle

 

A limited supply of eggs which are released in cycles until the menopause

Oestradiol and progesterone levels change in cycles 

 

However, both are controlled by the HPG axis 

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histology of ovaries ??

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Effects of Oestradiol ??

Female hormone

Primary and secondary female sexual characteristics

Effects on bone development and growth

Controls the ovarian cycle and ovulation 

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The Ovarian Cycle phases??

3 Phases:

Follicular phase: Days 1-10

A follicle grows in preparation for ovulation • The growing follicle releases oestradiol

Ovulatory phase: Days 11-14

High oestradiol causes the LH surge • Ovulation

Luteal phase: Days 14-28

Remains of the follicle release progesterone – Corpus Luteum 

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Follicular phase (days 1-10) ??

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FSH causes follicles to grow.

LH stimulates the release of oestradiol from the follicles.

As the follicles grow oestradiol levels increase... 

 

Primordial follicle (40μm)

- Immature dormant oocytes.
- Surrounded by flat granulosa cells. 

 

Mature follicle (20mm)

- Dependant on FSH to grow.

- Competition for limited FSH means that only one follicle is left by day 10.

- As the follicle grows the theca cells and granulosa cells release oestradiol in response to LH. 

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Ovulatory phase (days 11-14) ??

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Normally oestradiol has a negative feedback effect on LH release.

BUT – during ovulation oestradiol stimulates LH causing the “LH surge”.

The LH surge triggers ovulation. 

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Luteal phase (days 15-28) 

The follicle becomes the corpus luteum and releases oestradiol and progesterone to prepare for pregnancy.

If the egg is not fertilised the corpus luteum degenerates. 

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The female hypothalamic-pituitary-gonadal (HPG) axis 

Ovulatory Phase 

High oestradiol switches to a positive feedback effect.

“LH surge” in response to positive feedback causes ovulation. 

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The female hypothalamic-pituitary-gonadal (HPG) axis 

Follicular Phase 

FSH causes follicle growth.

Increased oestradiol release as follicle grows. 

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The female hypothalamic-pituitary-gonadal (HPG) axis

Luteal Phase

The follicle collapses forming the corpus luteum and releasing oestradiol and progesterone. 

 

End of Luteal Phase

The corpus luteum degenerates.

The cycle starts again...

 

 

 

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Controlling reproductive function - contraception 

Female

Progestogen-only pills

Progesterone inhibits GnRH, LH and FSH

No follicle growth and no ovulation

 

Combined oral contraceptive pill (Oestrogen and Progesterone)

Oestrogen added to help control cycles

 

Male

Currently not available – ongoing research

Synthetic testosterone works, but not 100% 

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Clinical problems with reproductive function

The HPG axis is complex and steroid hormones affect many different tissues.

Clinical problems can occur at many points. 

Hypothalamus: Kallman syndrome
Target tissues: Androgen insensitivity syndrome 

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Kallmann syndrome ??

The GnRH neurones originate from the olfactory region of the brain.

Genetic mutations affecting the development of the olfactory bulb also stop GnRH neurones developing 

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Androgen insensitivity syndrome ??

Genetic defects in the androgen receptors reduce sensitivity to testosterone.

Complete androgen insensitivity can result in female body development despite XY chromosomes. 

 

The individuals on the picture are XY

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