Lecture 16: Introduction to Reproduction Flashcards
What is reproduction?
Reproduction is the process by which new individuals of a species are produced and genetic material is passed through generations
What are the 3 main drivers of sex?
- Want to create new individuals of a species (can occur asexually)
- Genetic information can be passed from one generation to another (can occur asexually)
- to create new individual who is different form their parents and is able to adapt to the environment
What is reproduction like in males?
Constant production of Spermatozoon
300million per day (1500 per second per testicle)
Sperm is the smallest cell in body
Constant fertility from puberty onwards
Gradual decline with age - but fertile most of life
How many spermatozoon are produced per day in a male?
300 million per day
1500 per second per testicle
What is reproduction like in females?
Cyclical fertility from puberty (14/15 - 40), therefore Limited range of fertility
3-5 days per month
In utero, 7 million follicles, declining near to 0 during Menopause (don’t make any more)
Only about 400 follicles will be ovulated
(in Nz) And only about 2 fetilised
carefull controled
only fertile at limited times per month- regulated through reproductive hormones
What is the difference between the relative cell size of gametes between genders?
Sperm = Smallest cell in the body
Egg= Largest cell in the body
17500 sperm weigh as much as 1 female
What is the weight of 1 female Egg equivalent to?
17500 sperm
How far do sperm have to swim to reach a woman’s egg?
15cm swim to reach woman’s egg
human terms = about 16km
When is gamete quality optimum?
Sperm quality = best between 20-45 in men
Egg quality= Narrower range.. About 30 gives rise to More Complications
What is the function of endocrine glands?
To control reproductive processes via releasing hormones
What is the role of hormones?
Hormones released are Circulating hormones which travel through the blood and bind to specific receptors
If no receptor = No effect
What are the 4 main Endocrine glands?
Hypothalamus
Pituitary Gland
Adrenal Gland
Gonads (testes and Ovaries)
What are the two main functions of the Gonads?
- Produce Gametes: Sperm for males, Eggs for females
- Produce reproductive hormones: a. Early development of Genetalia. b. changes in puberty - 2/secondary sexual characteristics. c. adulthood- outgoing maintenance of reproductive function
What are the 2 main types of reproductive hormones?
Water soluble Hormones
Lipid Soluble Homrones
What is an exemplar class of a water soluble hormone?
Peptides and proteins
What is an exemplar class of a Lipid Soluble Hormone?
Steroid Hormones
What are 4 examples of water soluble hormones?
(GNRH) Gonadotrophin releasing Hormone
Follicle Stimulating Hormone (FSH)
Lutenising Hormone (LH)
Oxytocin
Which water soluble hormone is secreted by the hypothalamus?
GNRH
Gonadotropin releasing hormone
What water soluble hormone is secreted by the Anterior Pituitary?
Follicle Stimulating Hormone (FSH) Lutenising Hormone (LH)
What water soluble hormone is secreted by the posterior pituitary?
Oxytocin
is MADE in the hypothalamus, but is SECRETED from the posterior pituitary
What are some features of Water Soluble Reproductive Hormones?
Fast effect
quick changes in activity of different enzymes brings about rapid change in phosphorylation cascade
hormone transported in solution of blood
bind to specific receptor on target tissue
receptors activate G proteins, activate adenylate cyclase, turns ATP –> cAMP
Protein kinase is activated, results in other enzymes being phosphorylated
–> process stops by phosphodiesterase stopping cAMP
What are 3 examples of Reproductive Lipid soluble hormones?
Androgens (2 types)
Oestrogens (3 types)
Progestrogens (mainly 1)
What lipid soluble hormones are secreted from the Testes?
Androgens (2 types)
-not exclusively
What lipid soluble hormones are secreted form the ovaries?
Oestrogen (3 types)
Progesterone (mainly 1)
-not exclusively
What are some features of Lipid Soluble Hormones?
Slow effect
actions are longer lasting
hormones are lipid soluble but water insoluble
hormones transported via transport/carrier proteins through capillaries when in blood
released dissolves through lipid bilayer of target cell - diffuses out
enters nucleus and alters gene expression
newly formed mRNA directs synthesis of specific proteins on ribosomes
changes in activity through producing New protein which alters - cell activity and -gene expression
only 2-3% of hormones free at any one times - if too high/too low can be damaging
What is hormone action like?
Hormone action is complex
can have more than one effect
often many hormones used
What is the hierarchical arrangement of endocrine glands called?
Hypothalamic - Pituitary - Gonadal Axis (HPG)
What does the HPG axis allow for?
Signal amplification
go from peaka gram amounts of products produced in hypothalamus
microgram produced in pituitary
milligram amounts produced in gonads
What is GNRH release like?
Pulsatile release of GNRH
rather than continuous release
Which hormones act to promote spermatogenesis and oogenesis?
LH and FH act to promote spermatogenesis and oogenesis
gonadotropins
Which hormones are regulated by the testes and ovaries and why?
FSH and LH are regulated by the testes and ovaries
they act to produce gametes and stimulate sex steroid hormone production
What is the main function of the hypothalamus?
homeostatic regulator
for: -reproduction, stress, body temp, hunger and thirst, and sleep
provides major integrating link between nervous and endocrine system
when something changes, brings everything back to normal
a neuroendocrine organ as it process both neural and hormonal information
Aggregation of neurons into areas called NUCLEI (areas of neurons)(not nucleus)
What are the 6 things the hypothalamus acts as a homeostatic regulator of?
reproduction stress body temp hunger and thirst sleep
What sort of organ is the hypothalamus called?
Neuroendocrine organ
as it processes both neural and hormonal information
What is the size and shape of the Pituitary gland?
Pear shaped
about 1.5 cm
What are some features of the Pituitary gland?
Attaches to the hypothalamus by stalk called the infundibulum
Down growth of the brain
Two anatomically and functionally separate anterior and posterior lobes –> posterior lobe is smaller (1/2 size)
Both required - if one missing, no hormones produced. -if one is overactive(e.g. tumour) there is adverse effects also
Which lobe in the pituitary gland is smaller?
Posterior Lobe
is about 1/2 the size
What is another name for the posterior pituitary gland?
neurohypophysis
What is the overall function of the neurohypophysis?
hormones released and stored
What are some features nuclei connecting the hypothalamus with the neurohypophysis?
Neurosecretory neurons are aggregated into uncle - cell bodies
regular neurones can conduct a nerve impulse, releasing NEUROTRANSMITTERS
Usane Bolt: Neurosecretory neurons can conduct a nerve impulse, AND SYNTHESIZE, CARRY + release NEUROSECRETORY PEPTIDE HORMONES
Neurosecretory neurons have long axon tracts which pass into the posterior pituitary
Where are neurosecretory peptide hormones synthesised?
in the hypothalamus
Where are neurosecretory peptide hormones travel bound?
travel bound to carrier proteins down the axon terminals
Where are neurosecretory peptide hormones stored?
in secretory vesicles
What happens to nerve impulses involving neurosecretory peptide hormones?
nerve impulses travel along the axon to trigger exocytosis of the secretory vesicle
releasing the peptide hormones at the posterior pituitary
What the two neurosecretory peptide hormones released from the posterior pituitary called?
oxytocin - most exciting antidiuretic hormones (ADH or vasopressin) - renal function
Where are the Where are oxytocin and ADH/vasopressin synthesised?
Oxytocin and ADH synthesised int eh hypothalamus
transported to the posterior pituitary, where they are stored and released
What is the comparison between Oxytocin and ADH?
they have very similar structures but very different specificities of action
-both small peptides
(look similar and only differently two amino acids)
1x controls reproduction and 1x controls renal function
What are some key effects of oxytocin?
major effects on smooth muscle contraction
secretion stimulated in response to stimulation of nipples
-suppling of milk from child
(lactation) or uterine distention
also a “love” hormone, imported for bonding- love, lust, orgasm
Used to induce labour- uterine stretches and development of contractions and eventual arrival of child
What are some key effects of ADH?
acts on kidneys to retain water
What is another name for the anterior pituitary?
Adenhypophysis
-lobe isn’t produced in the brain
What is the overall function of the anterior pituitary?
upgrowth from top of mouth early in development
-lobe not produced in the brain
What are some key features of the anterior pituitary?
Lobe not produced in the brain
Connected to the hypothalamus via a HUMORAL or VASCULAR connection (portal)(rather than neural)
Neurosecretory neurons are short and don’t have hypothalamus
release connects into portal blood vessels
Nuclei present (cell bodies of neurosecretory neurons) and short tons
Portal system- a vascular arrangement - therefore hormones aren’t diluted in blood system -
-AVOIDS DILUTION
vascular arrangement in which blood flows from one capillary bed to another without going through the heart
What happens with hormones in the anterior pituitary gland?
releasing (+ve) and inhibiting (-ve) hromones (9 types) act on specific secretory cells arranges in clumps at the (stored as vesicles in termini) termini of the Hypophyseal Portal Blood Vessels
What do gonadotrophs produce?
2x gonadotropins:
FSH and LH
What is the summary of neurosecretory action in the anterior pituitary gland?
Neurosecretory neurons synthesize releasing and inhibiting hormones in their cell body into vesicles, which travel to the axonal terminus
In response to nerve impulses, these neurosecretory peptide hormones are secreted into linking hypophyseal portal vessels
fast acting –> rapid effects
What is involved in the regulation of the pituitary secretory cells?
homeostatic mechanisms involving negative and positive feedback loops regulate hormone levels
releasing and inhibiting hormones have either a positive of negative effect on anterior pituitary
which determines if it produces inhibiting or releasing hormones
when a hormone acts on a target tissue it seeds out either 1. inhibiting signal (stop hormone production) 2. releasing signal (more of hormone)
What does the regulation of Gonadotropin secretion involve?
Comes above via negative feedback system to ensure relatively constant (homeostasis) supply of FSH/LH
Just before ovulation- –> + feedback
endocrine relationships are complex systems of amplification, controlled by a series of feedback loop
What sort of feedback do sex hormones show?
-ve negative feedback
on the -pituitary and hypothalamus
What are elements of pulsatile release?
hypothalamus secretions are released in discrete burst 9once every 1-2 hours)
seen as pulsatile release of pituitary hormones (FSH/LH)
This prevents receptor desensitisation and down regulation
What is the rate of secretions from the hypothalamus?
once every 1-2 hours
release plus long period of time, to ensure maximum effect
What are the two hormones which regulate gonadal activity?
FSH
LH
What to FSH and LH do?
contact from pituitary –> gonads
bind to receptors in ovary/testes
promote synthesis of sex steroid hormones and gametogenesis
same hormones in boys and girls, but have different target tissues
What is the role of FSH in females?
growth of ovarian follicles
What is the role of LH in females?
Secretion of female sex hormones Stimulates ovulation (LH SURGE) v. important
What is the role of FSH in males?
growth of spermatozoon(oa)
What is the role of LH in males?
stimulates production of testosterone
What are sex steroids?
after puberty, regular production of sex hormones
What are some features of sex steroids?
made from body through cholesterol
-diet
-made endogenously from body
cholesterol converted to different forms of hormones inside cells based on structure
produced by gonads, effect on target tissues
structure is similar to cholesterol - different groups around 4 rings
but very different functions, actions and specificities –> also acts on target tissue
What are some features of Androgens?
mostly associated with male
but females produce androgens, although little compared to males (10-100x more)
Testosterone and 5 alpha Dihydrotestosterone (more potent and more important effect on target tissue)
Testosterone is the main secretory product of the testes
mainly associated with the development and maintenance of male characteristics (external and internal) and fertility, from puberty –> adulthood
What are key properties of Androgens?
male sex development –> early + puberty
external and internal genetalia
spermatogenesis
sexual behaviour
muscle development
-abuse anabolic steroids-precursors in body building
females - for libido/sexual behaviour/interest in sexual activity
What are some key properties of Oestrogens?
female sex development growth of endometrium regulation of menstrual cycle bone growth (men + women) male spermatogenesis
What are some features of Oestrogens?
most females but also males (though females 10-100x more0
main roles is the development and maintenance of female characteristics and fertility
DOESNT play a major role in early sexual development
The main site of oestrogen production is in the granolas cells of the growing follicle
Oestradiol, oestrone, oestriol
What are some important features of Oestradiol?
produced by growing follicle (granolas cell)
main oestrogen
puberty –> menopause vast amount produces
regulates menstrual cycle
What are some important features of oestrone?
weaker
important for male/post-menopause women
-only oestrogen secreted, also produced pre
in adipose (fat)
What is the role of progestagens?
Progesterone are major steroidal hormone of the corpus lutetium and placenta
after ovulation
only act in males
What are prodestagens associated with?
Progestagens are the DRUG OF PREGNANCY
associated with PREPARATIONS of pregnancy and its MAINTENANCE of foetus
What is the main type of hormone?
Water soluble hormones which travel in the blood
How can you stop all reproductive function?
by castrating someone
cutting off one element of the HPG axis
-tiny organs but completely control reproduction
Where does the hypothalamus sit?
in the CNS
what pathway does the hypothalamus take to communicate with the posterior lobe?
Neural direct pathway
What pathway doe the hypothalamus take to communicate with the anterior lobe?
Humoral indirect pathway
Vascular
Portal system
What is the nuclei in the hypothalamus?
A grouping of cell bodies in the hypothalamus
What is the purpose of the portal system, in particular the hypophyseal portal system?
It avoid dilution (of special hormones(bits of perfume- a little drop))
hormones go directly to the secretory hormones, WITHOUT being diluted in the blood system
How many types of secretory cells are present in the anterior pituitary?
5
What are secretory cells like?
Taxis
pick up messages from hormones, through portal system, and secreotry cells will go of an do what they want to do
completely different functions
will produce their own hormones
What is the role of secretory cells?
arranges at the bottom of the portal system
arranged in clumps
go off and perform their own functions (produce their own distinctive pituitary hormones which will have an affect on their target tissue)
then will regulate pituitary and hypothalamus via BOTH NEG and POS feedback by things produced in the target tissue
When is their positive regulation in the HPG axis?
only time of positive feedback
once every month
Why is their homeostasis in the gonads?
constant homeostatic reproductive activity to bring about production of the sex hormones
What is the pathway of regulation of the pituitary secretory cells?
Hypothalamus -+/- -> anterior pituitary –> Pituitary hormone –> Target tissue –(mainly - but once monthly +)–> anterior p and hypothalamus
What is the pathway of regulation of gonadotrophin secretion?
Hypothalamus –GnRHin portal-blood –> Anterior pituitary: Gonadotrophs —> FSH and LH in systemic-blood –> Gonads —Sex hormones NEGve always –> Hypothalamus and anterior p
What is the feedback of sex hormones like?
always negative
back to regulate hypothalamus and anterior pituitary
to regulate ant. pituitary’s gonadotrophin secretion
What are the two types of androgens?
Testosterone
5 alpha dihydrotestosterone (more portent and important - esp in its effect on target tissue)
Which hormone is important for libido?
Androgens
What is libido?
Interest in sexual activity
sex drive
Which oestrogen is most potent?
Oestradiol
therefore will only produce from puberty–> menopause
Why is oestradiol only produced from puberty –> menopause?
as it is the only time there is growing follicles (follicle growth)
will decline dramatically after menopause
What form oestrogen is in males/post menopausal woman?
Oestrone
is weaker than previously oestradiol
IMPORTANT in MALES
When is oestriol important and where is it produced?
Important in the: softening of the cervix during labour (pregnancy hormones)
Produced: by the placenta
Which is the most dimorphic hormone?
Progestagens
only produced in femalse
Which sex hormone is exclusive to women?
Progestagens
What is the need for the pulsatile release of both FSH and LH?
regulate spermatogenisis and oogeneisis
pulsatile, so don’t get sick of hormone, but instead has max effect
What are the testes and ovaries regulated by?
the 2 gonadotropins
FSH and LH
Why are the testes and ovaries regulated?
so they can produce gametes, also stimulate Sex STEROID hormone production
