Control of reproduction Flashcards
Neural control
- Nerves release neurotransmitters directly onto the target tissue
- Usually operates via the spinal cord
- Quick response
Neuroendocrine control
- Combined efforts of nerves and hormones
- Usually operates via spinal cord
- Relies on transport of hormone through circulatory blood
- Faster than just endocrine response
Endocrine control
- Hormones operating independent of the nerves
* Relies on transport of hormones through circulatory blood
Example of neural response
Ejaculation:
- Sensory stimulation of glans penis (temperature & pressure)
- Afferent neuron to spinal cord
- Motor neuron to target tissue
- Sudden & powerful contraction of urethralis, bulbospongiousus and ischiocavernousus muscles
- Expulsion of semen
- Very quick response
Neuroendocrine reflex
Message sent to brain
Triggers release of hormones
Hormones affect target tissue
Example of neuroendocrine control
Milk Ejection:
Suckling stimulates udder
Neural response goes up to brain
Causes release of oxytocin from the posterior lobe of the pituitary
Oxytocin travels through circulation down to mammary gland
Causes contractions of the muscle basket around mammary alveoli
Squeezes the milk out through ducts
Initially fast response - slows down a bit when hormone has to travel through circulation (takes roughly 30 sec for milk ejection)
Endocrine control
Stimulation of hormone release into circulation
Travels to target tissue
Binds to appropriate receptors
Start to initiate response in cells
Example of endocrine control
Spontaneous ovulation:
Follicles on ovary produce oestrogen
As follicles get bigger they produce more oestrogen
Oestrogen concentration in bloodstream increases
Feeds back to the surge centre of the hypothalamus (positive feedback)
Hypothalamus releases GnRH
GnRH travels to anterior pituitary
Causes the release of LH into circulation
Travels back down to ovary
Causes follicle to burst open and release its egg = ovulation
Slow process - can take hours to a couple of days depending on species
Where is GnRH produced?
Hypothalamus
GnRH function
Controls release of gonadotropins from anterior pituitary:
- Follicle stimulating hormone (FSH)
- Luteinising hormone (LH)
Tonic release of GnRH
Occurs in males & females
Small pulsatile GnRH release throughout reproductive life
Surge release of GnRH
Occurs in females only
High amplitude, high frequency pulses of GnRH when stimulated by high oestrogen levels
FSH function
Follicle stimulating hormone
Stimulates follicular growth in females - hence increases production of oestrogen
Stimulates Sertoli cells in males - hence initiates spermatogenesis
Lh functions
Lutenizing hormone
Induces ovulation of mature follicles - hence formation of the corpus luteum & production of progesterone
Stimulates testosterone production in males
Where are gonadotropins released?
Anterior pituitary
GnRH is released in hypothalamus - travels to anterior pituitary - causes release of gonadotropins
List the steroid hormones
Testosterone
Progesterone
Oestrogen
Where is testosterone released in males?
In the testes
What cells produce testosterone in males?
Interstitial cells/ Leydig cells in the seminiferous tubule
Production of sex steroids are under the control of what?
The hypothalamohypophyseal tract
Via positive & negative feedback or GnRH
Hypothalamo-hypophyseal tract
- A capillary system connecting the hypothalamus with the anterior pituitary
- Allows small amounts of GnRH to have an immediate effect on the pituitary before being diluted into the blood
- One of the ways the body has adapted to speed up the endocrine response allows GnRH to travel very quickly from hypothalamus to anterior pituitary to trigger the release of another hormone
Negative feedback
Suppression of release, therefore maintained concentration of target hormone, this is used in homeostasis
- Product later in pathway suppresses release of hormones earlier in pathway
- Negative feedback drives control of testosterone in males
Positive feedback
Stimulation of release therefore increase in concentration of targeted hormone
Positive feedback = high levels of hormone release
• E.g. Release of oestrogen in high levels from late stage follicles causing huge release of LH
Testosterone function
Male behaviour & aggression
Spermatogenesis
Growth of secondary sex glands and muscle
Development of typical male characteristics, e.g. antlers
Oestrogen functions
Increases blood flow in the uterus
Growth of uterine endometrial glands
Secretory activity of oviduct
Smooth muscle motility
Sexual receptivity
Closure of epiphyseal growth plate in bones
Mammary duct growth
Progesterone functions
Uterine endometrial gland growth - getting ready for implantation
Secretory activity of oviduct and endometrial glands
Mammary lobular growth
Quiescence of uterus
Progesterone = pregnancy hormone
Is the hypothalamus the same in males and females?
No it is structurally different
female has surge area
How do primary follicles differ from primordial follicles?
- Primary follicles differ to primordial follicles as they are bigger and can be receptive to gonadotropins (primordial follicles lack LH & FSH receptors)
Inhibin
Key role in the control of follicular growth
Inhibits the releases of FSH
Switches the release of gonadotropins from being preferential for FSH to preferential to LH – inducing ovulation
How does an egg remove excess chromosomes?
By exuding a polar body
It does this twice
Microscopically how do you know if an egg is ready to be fertilised?
if you see an egg with a polar body you know that egg is ready to be fertilized
