Ovarian Cycle, Menstrual Cycle, Fertilisation, and Early Embryonic Development

Vocabulary flashcards covering the key structures, hormones, processes, and developmental stages of the ovarian cycle, menstrual cycle, fertilisation, and early embryology.

Follicle-Stimulating Hormone (FSH)

A hormone secreted by the anterior pituitary gland that stimulates the growth and development of ovarian follicles in the ovaries.

Luteinising Hormone (LH)

A hormone secreted by the anterior pituitary gland that promotes maturation of the ovarian follicle, triggers ovulation, and causes the formation of the corpus luteum.

Oestrogen

A hormone secreted by developing ovarian follicles that causes the endometrium to repair and rebuild, decreases FSH secretion via negative feedback, and develops female secondary sex characteristics.

Progesterone

A hormone secreted by the corpus luteum that maintains, repairs, and thickens the endometrium for pregnancy and inhibits the release of FSH and LH to prevent other follicles from maturing.

Human Chorionic Gonadotropin (HCG)

A hormone produced by the chorion/placenta in a pregnant woman that maintains the corpus luteum until the placenta can secrete oestrogen and progesterone.

Corpus Luteum

A temporary endocrine structure formed from the ruptured follicle in the ovary after ovulation that secretes progesterone and oestrogen.

Corpus Albicans

Scar tissue formed in the ovary when the corpus luteum degenerates $8\text{ to }10\text{ days}$ after ovulation if fertilisation does not occur.

Primary Follicle

An immature egg (primary oocyte) enclosed by a single layer of surrounding cells, formed from precursor primordial follicles.

Secondary Follicle

A growing follicle containing a fluid-filled space (antrum) created by surrounding cell secretions, which gradually forces the secondary oocyte to the edge.

Mature Follicle (Graafian Follicle)

A fully enlarged follicle that reaches the surface of the ovary, producing a bulge, prior to rupturing during ovulation; development takes $10\text{ to }14\text{ days}$.

Ovulation

The release of a secondary oocyte into the fallopian tube caused by a surge in LH triggered by high oestrogen levels, typically occurring around Day 14 of the cycle.

Follicular Phase

The phase of the ovarian cycle (Days 0 to 14) characterized by FSH-stimulated growth and maturation of the follicle and egg, along with oestrogen secretion.

Luteal Phase

The phase of the ovarian cycle following ovulation in which the ruptured follicle forms the corpus luteum to secrete progesterone and oestrogen.

Menstrual Cycle

A series of monthly changes in the uterine lining (endometrium) and vagina controlled by oestrogen and progesterone to prepare for potential embryo implantation, averaging $28\text{ days}$ in length.

Menarche

The onset of the first menstrual period in females, commencing around puberty.

Menopause

The permanent cessation of reproductive hormone production by the ovaries resulting in the absence of menstruation for $12\text{ months}$.

Menstruation (Menses)

The shedding of the endometrial lining, blood capillaries, mucous secretions, and cell debris through the vagina during Days 1 to 4 of the cycle, caused by falling progesterone and oestrogen levels.

Proliferative Phase

Days 5 to 12 of the menstrual cycle in which gradual increases in oestrogen from developing follicles cause the endometrium to repair, thicken, and become softer.

Secretory Phase

Days 16 to 28 of the menstrual cycle where progesterone from the corpus luteum maintains a thick endometrium and stimulates glands to secrete glycogen-rich watery mucus.

Secondary Sexual Characteristics

Physical features associated with a specific sex that develop due to reproductive hormones (testosterone in males; oestrogen and progesterone in females) but are not directly involved in reproduction.

Insemination

The release of semen containing millions of spermatozoa from an erect penis into the vagina during sexual intercourse.

Fertilisation

The fusion of the haploid nuclei of a viable sperm and ovum in the fallopian tube to form a diploid zygote, initiating pregnancy.

Corona Radiata

An outer layer of follicle cells surrounding the zona pellucida of the secondary oocyte, cemented by acid to provide protection and nourishment.

Zona Pellucida

A glycoprotein matrix surrounding the plasma membrane of the oocyte that controls sperm binding and hardens post-fertilisation to prevent polyspermy.

Acrosome Reaction

The exocytosis of hydrolytic enzymes (such as hyaluronidase and acrosin) from the acrosome of the sperm head to digest the corona radiata and zona pellucida.

Cleavage

Rapid mitotic cell divisions occurring during Days 1 to 3 post-fertilisation that increase cell numbers without increasing the overall size of the zygote.

Morula

A solid ball of $16\text{ to }32$ cells formed by Day 4 post-fertilisation as the developing embryo reaches the entrance of the uterus.

Blastocyst

A hollow ball of cells formed around Days 5 to 6 consisting of an outer trophoblast layer and an inner cell mass.

Trophoblast

The outer layer of cells of the blastocyst that secretes enzymes to digest endometrial cells during implantation and eventually forms the placenta.

Inner Cell Mass

The internal cluster of pluripotent cells inside the blastocyst that develops into the embryo proper.

Implantation

The process occurring around Days 7 to 8 where the blastocyst burrows deeply into the endometrial lining of the uterus using digestive enzymes.

Totipotent Stem Cells

Stem cells capable of forming all cell types in the body as well as extra-embryonic tissues like the placenta; located in the zygote and early morula.

Pluripotent Stem Cells

Stem cells that can differentiate into nearly all cell types belonging to the three germ layers but cannot form extra-embryonic tissues; located in the inner cell mass of the blastocyst.

Multipotent Stem Cells

Stem cells that can only differentiate into a limited range of closely related cell families; located in adult tissues (e.g., bone marrow) and umbilical cord blood.

Yolk Sac

An extra-embryonic membrane formed around Day 9 that produces blood cells before the liver and bone marrow develop.

Amniotic Cavity

A fluid-filled space enclosed by the amnion (formed around Day 11) that acts as a shock absorber, maintains constant temperature, and allows free fetal movement.

Chorion

The outermost extra-embryonic membrane (formed around Day 13) that secretes HCG and forms the fetal portion of the placenta.

Allantois

An extra-embryonic membrane formed around Day 16 that forms the structural basis of the umbilical cord linking the embryo to the placenta.

Ectoderm

The outermost primary germ layer that develops into the epidermis of skin, hair, nails, glands of skin, and the entire nervous system.

Mesoderm

The middle primary germ layer that develops into muscles, bones, cartilage, blood, blood vessels, dermis, and the urogenital system.

Endoderm

The innermost primary germ layer that develops into the epithelial lining of the alimentary canal, liver, pancreas, lungs, thyroid, and urinary bladder.