50 Fun Facts About Reproductive System

Which paired organs produce the egg cells and secrete the main female hormones?

They sit on either side of the uterus and work as endocrine glands as well as gamete factories.

What is the lining of the uterus called?

It thickens each cycle to receive an embryo and is shed during menstruation if none implants.

Fertilisation of the ovum usually happens inside which structure?

The fertilised egg then travels on to the uterus and implants in its lining.

What is the narrow neck of the uterus, where it joins the vagina, called?

It dilates during labour to let the infant pass from the uterus into the birth canal.

What is a fertilised ovum called?

Only one sperm is needed to fertilise the egg and create it.

What is the release of an egg cell from the ovary called?

It usually happens in just one of the two gonads each cycle.

What is the median length of the menstrual cycle, in days?

Normal cycles run anywhere from 21 to 35 days.

Menarche, the first period, usually occurs around what age?

Cycles then continue for roughly 30 to 45 years until menopause.

Which hormone stimulates the uterus lining to thicken each cycle?

The thickened lining's blood supply feeds an embryo if one implants.

Menstruation is triggered by falling levels of which hormone?

The shed lining is a sign that pregnancy has not occurred.

The hypothalamus controls the cycle by releasing which hormone?

It prompts the nearby anterior pituitary to release FSH and LH.

What does FSH stand for?

Its cyclical rise and fall prompts the growth of oocytes.

A surge of what from the pituitary triggers release of the mature oocyte?

The same hormone regulates testosterone release in males.

How many chromosomes does a human gamete carry?

Two gametes fuse to restore the diploid count of 46.

Which type of cell division halves the chromosome number to make gametes?

It turns diploid germ cells into haploid ones.

Gamete production within the gonads is known as what?

In males it is called spermatogenesis and in females oogenesis.

Each primary oocyte ultimately forms how many mature ova?

The rest of the division products become polar bodies that cannot be fertilised.

Each primary spermatocyte forms how many functional gametes?

That is the key contrast with oogenesis, which yields a single egg per germ cell.

In which structure do immature sperm gain their tails and the ability to move?

Sperm also mature and are concentrated there before moving into the sperm duct.

Sperm are produced in which fine coiled tubes inside the testes?

Germ cells lining them develop into sperm from puberty through old age.

Which interstitial cells of the testes produce testosterone?

Their androgens drive puberty, facial hair, sexual behaviour and libido.

Which supporting cells of the sperm-producing tubules secrete the hormone inhibin?

Inhibin dampens FSH release from the pituitary, helping regulate sperm production.

The scrotum keeps the testes roughly how many degrees Celsius below core body temperature?

Sperm production and survival need that slightly cooler environment.

Which tube, also called the sperm duct, carries sperm toward the ejaculatory duct?

It is about 30 centimetres long and runs from the epididymis into the pelvic cavity.

Which gland below the bladder produces seminal fluid and helps regulate urine flow?

It develops from the urogenital sinus in the embryo.

Which two glands behind the bladder secrete many of the components of semen?

They form from lateral outgrowths of the mesonephric ducts.

The bulbourethral glands are also known by what other name?

They add fluid to semen during ejaculation.

A sperm carrying which chromosome results in a male child?

The egg always carries an X, so it is the sperm that decides the sex.

Which enzyme converts testosterone into DHT inside target cells?

DHT, not testosterone itself, mediates the androgen effect in the developing external genitalia.

Which embryonic structure forms the fallopian tubes, uterus and vagina?

It essentially disappears in the male embryo.

The Wolffian duct persists to form the internal ducts of which sex?

It becomes the epididymis, sperm duct, ejaculatory duct and seminal vesicle.

The adult male or female pattern is determined in which week of early development?

Endocrine hormones are the critical controlling factor in that differentiation.

The gonads and external genitals develop from which embryonic tissue?

The Wolffian and Müllerian ducts and the gonads are the three main precursors of the reproductive organs.

The testes usually descend into the scrotum around which week of development?

A cord called the gubernaculum shortens and pulls each testis down.

For about 85% of men, which testis hangs lower in the scrotum?

The asymmetry comes from differences in the blood vessel anatomy.

What is the tough fibrous shell that covers each testis called?

The same name is used for the capsule around the ovaries.

From start to finish, producing a sperm cell takes roughly how long?

The process runs constantly, from spermatogonia through spermatocytes and spermatids.

What is the tail of a sperm cell called?

Some red algae and fungi make non-motile sperm with no tail at all.

The word 'sperm' comes from a Greek word meaning what?

The Greek is sperma.

How much mitochondrial DNA does a human sperm typically pass on to offspring?

Mitochondrial DNA is degraded as sperm mature, so it comes almost entirely from the egg.

The fertilised egg divides to form which structure that implants in the uterine wall?

Its implantation marks the start of gestation.

The developing human is called an embryo until the end of which week of pregnancy?

From week 9 until delivery it is called a fetus.

Which glands produce the mucous fluid for vaginal lubrication?

Skene's glands, the other vestibular glands, lubricate the urinary opening.

The uterus is usually described as having what shape?

Its muscular wall contracts powerfully to push out the fetus at birth.

How many suspensory ligaments help hold the uterus in position?

They are the uterosacral, round and cardinal ligaments.

What pushes the ovum along the oviduct toward the uterus?

The trip takes hours or days.

The word 'ovary' comes from a Latin word meaning what?

The Latin is ōvārium.

After releasing its egg, the ruptured follicle becomes which hormone-secreting body?

It sits in the ovarian cortex alongside follicles at every stage of maturation.

A period typically lasts about how many days?

Day one of the period is counted as day one of the whole cycle.

Around which day of the menstrual cycle is an egg usually released?

That splits the ovarian cycle into a follicular phase before and a luteal phase after.