The many physical changes seen during development and puberty that lead to sexual differentiation are primarily caused by two groups of steroid hormones. What are they?
Androgens + Oestrogens
What are 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 oestrogen
What are Oestrogens?
- Steroid hormones that function as the primary female reproductive hormones
- In non-pregnant women the primary naturally occuring oestrogen is oestradiol
- Synthesised from androgens and released by the ovaries
what are the different reproductive organs between the sexes
what is the process of sexual differentiation into males?
what is the male phenotype and female phenotype
XY and XX
XY in a male cannot cross over like a matching chromosome pair. What is different about the Y chromosome and what signals the production of the male characteristics?
Non pairing and pairing region is made on Y Chromosome. The non pairing region has the sry gene activation of this gene results in primordial gonads being formed
what is the process of sexual differentiation into Females?
what are the pubertal changes
1) Adolescent growth spurt • involving skeleton, muscle and viscera
2) Sex specific increases in growth rate • leads to phenotypic sexual dimorphism
3) Changes in body composition • particularly muscle and fat
4) The development of reproductive function • gonadal activity, secondary sexual characteristics
What scale is used to define the stages of puperty?
The Tanner scale
A 1-5 scale of physical development
5 stages of physical development are defined, based on measurements of external primary and secondary sex characteristics such as breast development, genital development and pubic hair.
What are the two events that cause an increase in reproductive hormones and pubertal changes.
Adrenarche: Increased secretion of Androgens from adrenal gland. This is a process of early sexual maturation
Then following this is the inceased HPG axis activity: increased hormone secretions from ovaries/testes
these two events are independent!
where are androgens released from in the adrenal glands
zona reticularis in the adrenal cortex
What do the adrenal glands release during adrenarche and name some examples?
What happens to them?
Weak androgens
- DHEA
- DHEA-sulphate
- Androstenedione
They are then converted peripherally in the body to stronger androgens - testosterone and dihydrotestosterone which results pubertal changes
androgens released from testes are responsible for
facial hair (high levels needed)
describe the HPG axis activity before puberty?
- low levels of GnRH, FSH and LH
- Ovarier/Testes release low levels of sex steroids
- Axis is not stimulated enough to release eggs/sperm
describe the HPG activity after puberty
- Hypothalamus releases - GnRH
- Anterior Pituitary - releases FSH and LH
- Ovary/Testis - releases egg or sperm and oestrogen and testosterone
what are kiss peptins?
a family of peptides encoded by the kiss-1-gene that control the ontset of puberty
It is a g-protein coupled receptor ligand for GPR54 . Mutation of GPR54 - hypogonadotrophic hypogonadism (lack of reprodutive function)
What is LH and FSH? What do they do and where are they released?
Released from the Anterior Pituitary Glands, Stimulated by GnRH.
LH - Luteinising Hormone
in Males: Stimulates production of testosterone in testes
In Females: controls the reproductive cycle and ovulation. stimulates oestrogen
FSH - Follicule Stimulating Hormone
In males: Stimulates the growth and maturation of the testes and spermatogenesis
in Females: stimulates the growth and maturation of ovarian follicles.
increased testosterone released from the growing testes drives...
formation of secondary sexual characteristics deep voice, facial hair
What are some causes of irregular menstrual cycles?
Anovulatory (ain't no ovulation)
Missing luteal phase
Variable oestrogen levels from developing follicles
where in the Hypothalamus is GnRH released from?
The preoptic area in the hypothalamus releases GnRH into the pituitry gland via the median eminence in regular pulses
Where is LH and FSH released from?
gonadotroph cells in anterior pituitary in regular pulses
state the anatomy of the testes
comprised of seminiferous tubules and leydig cells
Outline the HPG axis for males
Leydig cells stimulated by LH which secrete testosterone
Setroli cells are stimulated by FSH which secrete androgen-binding globulin which binds to testosterone making it less lipophilic to stimulate spermatogenesis. It concentrates testosterone in the lumen increasing fertility They also secrete inhibin which signals to the HPG axis to decrease sperm production.
What cells do FSH stimulate in the males and where are they found?
Sertoli cells - found in seminiferous tubules of the testes
What is the main precursor of testosterone?
Pregenolone
main effects of Testosterone?
• Male hormone - anabolic
• Primary and secondary sexual characters
• Libido and sexual behaviour
• Stimulates spermatogenesis
Where does spermatogenesis occur?
Seminiferous tubules
What cells are found in the Seminiferous tubules and what are their roles?
Spermatogonial stem cells:
• Sperm production
Sertoli cells
- Secretes supporting fluid into lumen
- Nutrition
- Protection
- Regulation
- forms blood-testes barrier
when does spermatogenesis occur?
starts at puberty
Outline the process of spermatogenesis
Golgi phase
- The golgi apparatus creates a vesicle of enzymes around the nucleus.
- Mitochondria start to move to the other side of the cell.
- The centriole starts to form an axoneme, the cytoskeletal core of the tail.
Cap phase
- Spermatid DNA is condensed in the nucleus.
- The golgi apparatus surrounds the nucleus and the enzyme vesicle forming the acrosomal cap
Acrosome phase
- The axoneme extends to become the tail of the sperm.
- Temporary cytoskeleton structures called manchettes support the growing tail.
Maturation phase
- Excess cytoplasm is phagocytosed by Sertoli cells to produce mature sperm
What part of the reproductive system are sperm not motile in, and in which part to they gain motility
not motile in seminiferous tubules
gain motility when non-motile sperm transported to epididymis where they are stored and gain motility
how is the blood-testis barrier
Tight junctions between serteoli cells forms a barrier between blood and lumen of seminiferous tubules. allows sertoli cells to control the environment within the lumen.
prolactin role
released from the pituitary and increases LH receptor expression on leydig cells, which increases testosterone release.
What happens in sperm capacitation?
Takes place in the uterus
Switching on of sperm via increased calcium influx causing increased intracellular cAMP levels- increased motility
Cholesterol and gycoproteins are removed from the sperm cell surface by enzymes such as heparin in the uterus
what is the acrosome reaction? what is oocyte activation?
triggered by contact of sperm with oocyte
Interaction with zona pellucida 3 protein (ZP3) on oocyte membrane prevents cross-species fertilisaition and cortical granules are relased that makes the oocyte impereable to other sperm
Acrosome releases hyaluronidase and acrosin enzymes break though egg coating allowing fertilisation
what Non-Hormonal factors can affect testosterone levels?
• Environment
• Climate (heat)
• Radiation
• Air pollution
• Food chain pollution
• Stress
what is klinefelter syndrome
- A genetic disorder in which a male with X and Y chromosomes also has an additional X chromosome.
- Individuals will have 47 chromosomes instead of the normal 46 with XXY.
- Effects vary between individuals, many people will not show any symptoms, but it can result in hypogonadism and reduced fertility.
what is hyperprolactinaemia and what causes it?
Abnormally high levels of circulating prolactin which inhibits GnRH.
Can be caused by pituitary tumours.
Also often a side-effect of various prescription drugs that affect dopamine.
at what week of foetal development does foetal development start to occur?
4-8 weeks
what are primary oocytes?
- Diploid cells with 46 chromosomes.
- Start meiosis, but stop at prophase I.
- Become dormant, halted at this stage of development.
At birth, no further oocytes can be generated
Outline the 5 stages of the Menstrual Cycle
Menstrual phase (day 1-5)
Uterine lining sloughs off and is removed from the body.
Once the uterine lining is removed the endometrium starts to proliferate again.
Proliferative phase (day 5-13)
Endometrium, the lining of the uterus, begins to proliferate and thicken, tubular glands and arteries form.
Stimulation of progesterone receptors synthesis in endometrial cells.
Late-Proliferative phase (day 13-14)
The glands are long and tortuous due to active growth. Stroma is gradually becoming oedematous.
Secretory phase (day 15-22)
The growing endometrium becomes dependant on progesterone released from the corpus luteum.
Enlargement of tubular glands which begin secreting mucus and glycogen in preparation for implantation of the fertilized ovum.
Late-secretory phase (day 23-28)
If fertilization does not occur, the corpus luteum degenerates, progesterone levels fall and the endometrium degenerates.
Uterine glands are wide. Arteries begin contracting and capillary beds begin leaking blood into the endometrium and uterus.
what happens during fertilisation?
Secondary oocyte is fertilised by sperm cell
Polar body and zygote (46 chromosomes) is formed
Polar body degenerates.
The zygote starts to divide as it travels along the fallopian tube towards the uterus (8 cells within it)
what is Blastocyst
formed after 5 days Zygote
Wihin the blastocyst, there are 3 components:
1. inner cell mass (that will become the embryo),
2. blastocoele (fluid space)
3. trophoblast (surrounds the inner cell mass and will become the placenta)
Implantation
The trophoblast layer (that will become placenta) attaches to the surface of the endometrium.
The blastocyst invades the endometrium.
Trophoblast cells release human chorionic gonadotropin which maintains the corpus luteum during early pregnancy. This is to ensure appropriate progesterone release so the endometrial lining can grow.
