4.1: Human reproduction

Testis

Testis

Where male hormones and sperm are produced. Comprised of germinal epithelial and sertoli cells, seminiferous tubules, vasa efferentia, epididymis and connected to the vas deferens.

Vasa efferentia

Where the spermatozoa collects from the seminiferous tubules. Then move to the head of epididymis.

Seminiferous tubules

In the testes, and where spermatogenesis occurs. They move from the walls lining the outside, comprised of germinal epithelial cells, to the inner lumen.

Head of epididymis

Where sperm move from the vasa efferentia. Remain here until they are motile, and then move to the vas deferens during ejaculation.

Vas deferens

Tube carrying the spermatozoa from the head of epididymis to the penis. Receives secretions from the seminal vesicles and prostate, which are alkali and provide nutrients.

Seminal vesicles

There are two, which secrete mucus, known as seminal fluid, into the vas deferens which contains chemicals such as fructose, which is respired by spermatozoa for energy. These are alkali to neutralise urine and the vaginal tract.

Prostate gland

Passed through via the ejaculatory duct, and secretes fluid which contains zinc. This is alkali to neutralise urine and the vaginal tract.

Ejaculatory

Duct that passes over the prostate.

Semen

Made up of spermatozoa, seminal and prostate fluid.

Ovaries

Where female hormones and oocytes are produced. There are two, and they alternate ovulation. Have follicles and germinal epithelial cells. Links to the oviducal funnel.

Oviducal funnel

Contains ciliated epithelium which sweep the secondary oocyte to the oviduct from an ovary.

Uterus

Where an egg is implanted and an embryo is developed. Has three layers, and opens into the vagina via the cervix.

Perimetrium

Outermost uterine layer. A thin layer around the outside.

Myometrium

Middle layer of the uterus, made up of muscle.

Endometrium

Innermost uterine layer. A mucous membrane with a good blood supply, which is shed monthly unless and oocyte is fertilised.

Cervix

A narrow ring of connective tissue and muscle that separates the vagina and uterus. Dilates during childbirth and holds the baby in.

Gametogenesis

Word for the creation of gametes, encompasses spermatogenesis and oogenesis.

Germinal

Type of epithelial cells in ovaries and testes, which develop into the first stages of gametogenesis; respectively, oogonia and follicles, and spermatogonia.

Spermatogonia

Created from mitosis of germinal epithelial cells, which can also make more germinal epithelial cells. Diploid. Divide and enlarge to make primary spermatocytes.

Primary spermatocytes

Created from multiple mitoses and enlargement of spermatogonia, which can also make more spermatogonia. Diploid. Undergo mitosis 1 to create secondary spermatocytes.

Secondary spermatocytes

Made from mitosis 1 of primary spermatocytes. Haploid. Undergo mitosis 2 to create spermatids.

Spermatozoa

Made from maturation of spermatids. Final stage of spermatogenesis, move towards the lumen of the seminiferous tubules.

Spermatids

Made from meiosis 2 of secondary spermatocytes. Mature into spermatozoa.

Sertoli

Cells which nourish spermatids and protects them from the male’s immune system.

Leydig

Cells also known as interstitial cells. These secrete testosterone, which is the male sex hormones with roles in sperm formation and maturation, and the development of male secondary sex characteristics.

Oogonia

Created from mitosis of germinal epithelial cells, which can also make more germinal epithelial cells. Diploid. Divide and enlarge to make primary oocytes.

Primary oocyte

Created from the multiple mitoses and enlargement of oogonia, which can also make more oogonia. Diploid. These undergo meiosis 1, but stop at prophase 1 before creating secondary oocytes and the first polar body.

Follicles

Created by mitosis of germinal epithelial cells. They then surround primary oocytes to make primary follicles.

Primary

Follicle that surrounds the primary oocyte. Matures into a secondary follicle, or Graafian follicle. This is stimulated by hormones. Each month several begin to develop, but normally, only one fully matures.

Secondary oocyte

Created once primary follicles are stimulated by hormones at the beginning of puberty, causing primary oocytes to complete meiosis 1. Have a protruding first polar body. Haploid. Undergo meiosis 2, stopping at metaphase 2 until fertilisation occurs, and then creates an ovum and the second polar body.

Graafian follicle

AKA secondary follicle. Surrounds the secondary oocyte, and bursts at the surface of the ovary to release the secondary oocyte, a process known as ovulation. It then becomes the corpus luteum, which releases hormones if fertilisation occurs.

Ovulation

When a Graafian follicle bursts at the surface of the ovary to release the secondary oocyte into the oviducal funnel. Triggered by LSH.

Polar body

Secondary product of oogenesis meiosis. Oocytes take most of the nutrients, such as the cytoplasm.

Corpus luteum

AKA yellow body. Made from the Graafian follicle after ovulation. Releases progesterone and oestrogen, but regresses if implantation does not occur.

Zona pellucida

Clear glycoprotein layer which surrounds the cell membrane of the secondary oocyte. Broken down by acrosin released by the rupturing of the acrosome membrane during the acrosome reaction. Converted into the fertilisation membrane by cortical granules.

Cortical granules

Secondary organelles which surround the cytoplasm periphery of secondary oocytes. They prevent polyspermy by releasing enzymes into the cell membrane which cause the zona pellucida to convert into the fertilisation membrane.

Corona radiata

Surround the secondary oocyte and provide nutrients. Partly made up of cumulus cells. Broken down when the acrosome releases proteases during the acrosome reaction.

Antrum

Fluid filled space in the Graafian follicle, therefore around the secondary oocyte.

Theca

Cells that make up the outer layer of the Graafian follicle, which produce oestrogen in order to rebuild the endometrium, trigger LH production for ovulation and inhibit FSH so only one Graafian follicle is made.

Acrosome

Lysosome at the anterior head of the sperm. Contains proteases, such as acrosin, to break through the corona radiata and zona pellucida during the acrosome reaction.

Urethra

Where both urine and semen leave a male via the penis.

Metaphase 2

Where a secondary oocyte stops meiosis 2 until fertilisation occurs.

Prophase 1

Where primary oocytes stop meiosis 1 until stimulated by puberty-released hormones.

Capacitation

Process sperm undergo in the vagina or uterus. Cholesterol and glycoproteins are removed from the sperm head over the acrosome, making it more fluid and permeable to calcium ions. Takes several hours.

Acrosome reaction

Process where the acrosome releases proteases to digest the corona radiata, and once the zona pellucida is reached the acrosome ruptures and releases acrosin, another protease, which hydrolyses the zona pellucida.

Acrosin

Special protease released to digest the zona pellucida, releases when the acrosome membrane is ruptured.

Ovum

What the secondary oocyte becomes once a sperm enters and their cell membranes fuse, triggering the second meiotic division and second polar body to be released.

Cortical reaction

Occurs once the sperm attaches to the secondary oocyte to prevent polyspermy. Calcium ions are released by the secondary oocyte’s smooth ER, causing cortical granules to fuse with the cell membrane and release their enzymes via exocytosis, making a fertilisation membrane from the zona pellucida.

Fertilisation membrane

Formed when cortical granules release their enzymes via exocytosis once fused with the cell membrane, causing the zona pellucida to be chemically modified, expand and harden to prevent polyspermy.

Zygote

What the ovum becomes known as after the first mitotic division occurs along with the sperm, combining their genetic material.

Oviduct

The tube which carries the fertilised egg into the uterus for implantation. Receives the egg from the oviducal funnel.

Morula

Term for the embryo when it is a solid ball of 16 cells formed via cleavage. Formed within 3 days while moving down the oviduct.

Cleavage

Term for the rapid mitotic division of the embryo as it moves down the oviduct. Ends once a blastocyst is produced.

Blastocyst

Occurs by around day 7, when the embryo becomes hollow with cells on the outside known as trophoblasts, which divide to make an inner cell mass on one side. It moves from the oviduct to the uterus.

Implantation window

Lasts for 6-10 days after ovulation, when progesterone and oestrogen maintain the endometrium for the implantation of a blastocyst.

Trophoblasts

Cells surrounding the hollow part of a blastocyst, which divide to make an inner cell mass on one side. Have trophoblastic villi on the outside.

Trophoblastic villi

Protrusions from trophoblasts which penetrate the endometrium. Increase surface area for nutrient absorption. This is implantation.

Placenta

An organ grown by the mother during pregnancy, which is made up of tissues from the embryo and the mother. It connects the foetus to the uterine wall, is an endocrine organ, protects weak foetal capillaries from the high and fluctuating mother’s blood pressure, and provides passive immunity to foetal cells while attacking any pathogens they incur.

Chorion

Developed from the trophoblast - an outer membrane which surrounds the embryo. Have chorionic villi.

Chorionic villi

Formed when chorion cells move into trophoblastic villi. These are much larger, and develop blood capillaries which connect the embryo to the uterine wall via the umbilical cord. Have microvilli.

Lacunae

Intervillous spaces which surround chorionic villi and contain the mother’s blood. Only 5 um distance between the two blood sources, and a counter current flow.

Syncytium

Formed by cell walls of the chorionic villi fusing, which leaves no room for migratory immune cells to enter the foetal blood. Does not protect from Rhesus disease, pre-eclampsia (abnormally high blood pressure which can be caused by a mother’s immune response), Rubella, or drugs such as nicotine and heroin.

Umbilical cord

Develops from the placenta and transfers blood between the foetus and mother. Two umbilical arteries enter the placenta via this, and after material exchange at chorionic villi the blood returns via the single umbilical vein.

Oestrus

Had by most mammals, such as dogs. Has a period of sexual activity, known as heat, followed by the reabsorption of endometrium and an anoestrus period.

Menstrual

Cycle which occurs in most primates, which occurs monthly. Involves the ovaries, uterus and brain with four key hormones, FSH, LH, oestrogen and progesterone.

Follicle stimulating (FSH)

Hormone which is released by the anterior pituitary gland, and stimulates the development of a primary follicle into a Graafian follicle. Inhibited by oestrogen once this occurs successfully, and is stimulated by LH and inhibits oestrogen after ovulation. When levels fall, the corpus luteum degenerates. In men, is used in sperm development.

Gonadotropin

AKA GnRH. Secreted by the hypothalamus on day 1 of a period, which stimulates the anterior pituitary gland to release FSH.

Luteinising (LH)

Hormone which is stimulated by oestrogen, released in the pituitary gland, and stimulates ovulation. Also stimulates FSH to inhibit oestrogen, and inhibits progesterone. When levels fall, the corpus luteum degenerates. In men, stimulates Leydig cells.

Oestrogen

Produced by thecal cells around the Graafian follicle and the corpus luteum. This stimulates LH, inhibits FSH and prolactin, triggers endometrium reconstruction, stimulates uterine growth and mammary gland growth and blood supply (especially during 3rd trimester). It is inhibited by FSH.

Progesterone

Released by the corpus luteum to maintain the endometrium. Once it is degenerated, its levels fall. Inhibits LH, prolactin and oxytocin.

Amnion

Membrane derived from the inner cell mass of a blastocyst. Initially touches the foetus, but as it’s fluid accumulates it increases in volume. Contains amniotic fluid.

Amniotic fluid

Fluid that contains 98% water, urea, salts, a little protein, trace amounts of sugar and sloughed off foetal cells. Made by the mother and foetal urine. 500cm³ is swallowed a day. Maintains foetal temperature, lubrication to prevent webbed fingers and toes, contributes to lung development, allows for movement to improve muscle and bone development and acts as a shock absorber.

Human chorionic gonadotropin

AKA hCG. Secreted from the blastocyst 6 days after fertilisation, and made by the chorion. A glycoprotein which maintains the corpus luteum for the first 16 weeks of pregnancy to maintain progesterone levels, to ensure the placenta develops.

Prolactin

Inhibited by oestrogen and progesterone. Released in the anterior pituitary once oxytocin contracts muscles around the milk gland. Stimulates glandular tissue in mammary glands to synthesise milk. This hormone continues after birth, for as long as milk is needed.

Oxytocin

Inhibited by progesterone, and released in the posterior pituitary gland once it’s levels fall pre birth. It causes myometrial and milk gland contractions. Contractions cause more to release, causing more contractions - positive feedback. Occur from the top down.

Embryo

What the blastocyst becomes known as until around 10 weeks into pregnancy, when organs begin development.

Blastocoele

The hollow part of a blastocyst, surrounded by trophoblasts and with an inner cell mass.

Flagellum

Makes lashing movements to move the sperm. Requires many mitochondria, which spiral around microtubules in the middle of the sperm.