Female reproduction D3.1.4-D3.1.7

• What is the menstrual cycle?

  The menstrual cycle is a pattern of changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The typical menstrual cycle is 28 days.

  Unless pregnant, the menstrual cycle begins at puberty and stops at menopause. The menstrual cycle is the combination of both the ovarian cycle and the uterine cycle.
• What is the ovarian cycle?

  The ovarian cycle is divided into two main phases:

  - Follicular

  - Luteal
• What is the follicular phase?

  - The follicular phase is stimulated by Follicle stimulating hormone (FSH).

  - FSH is released from the pituitary gland, triggered by gonadotropin releasing hormone (GnRH) from the hypothalamus. It then travels through the blood to the ovaries.

  - At the ovaries, FSH stimulates granulosa cells in the follicles to secrete oestradiol and increase in size in preparation for ovulation.

  - On day 14, ovulation marks the end of the follicular phase.
• What is ovulation?

  - Ovulation is the rupture of a developed follicle to release the egg into the oviduct.

  - Ovulation is triggered by a rise in Luteinising hormone (LH). LH rises and FSH drops when oestradiol rises.

  - LH is released from the pituitary gland, triggered by gonadotropin releasing hormone (GnRH) from the hypothalamus. It then travels through the blood to the ovaries.

  - At the ovaries, LH causes partial digestion of the follicle wall, allowing it to burst open to release the egg.

  - If sperm is present, the egg cell may be fertilised in the oviduct.
• What is the luteal phase?

  - The luteal phase is stimulated by Luteinizing hormone (LH).

  - LH is released from the pituitary gland, triggered by gonadotropin releasing hormone (GnRH) from the hypothalamus. It then travels through the blood to the ovaries.

  - In the ovaries, LH stimulates the development of a corpus luteum from the remains of the ruptured follicle. A corpus luteum is a temporary mass of hormone producing cells that form from the follicle after ovulation.

  - The cells of the corpus luteum then secrete oestradiol and progesterone, which causes the thickening of the uterus endometrium. Progesterone inhibits FSH and LH, in a negative feedback loop.

  - If fertilisation does not occur, then the corpus luteum will be broken down, causing a drop in oestradiol and progesterone.
• What does FSH do, and where is it secreted?

  Stimulates follicle growth in ovary.

  - Pituitary
• What does LH do, and where is it secreted?

  Triggers ovulation and corpus luteum formation.

  - Pituitary
• What does oestradiol do, and where is it secreted?

  Promotes growth of uterine lining; exerts positive feedback to increase LH before ovulation; later, negative feedback inhibits FSH and LH.

  - Ovary
• What does progesterone do, and where is it secreted?

  Maintains uterine lining; provides negative feedback on FSH and LH to prevent new follicle development.

  - Ovary
• What is the uterine cycle?

  - The uterine cycle is the changes that occur to the endometrium (the lining of the uterus) during each menstrual cycle.

  - During the luteal phase, stimulated by progesterone, the endometrium becomes thicker and more richly supplied with blood.

  - During menstruation, this thicker lining is shed.
• What is one example of negative feedback in the ovarian cycle?

  Oestradiol provides negative feedback to the hypothalamus, which lowers the levels of FSH and LH that are secreted, and subsequently, the levels of oestradiol that are produced.
• What is one example of positive feedback in the ovarian cycle?

  During days 12- 14 of the cycle, oestradiol provides positive feedback to the hypothalamus. This causes an increase in LH secretion, resulting in ovulation.
• What does the female reproductive system include?

  - Ovary

  - Oviduct

  - Uterus with endometrium

  - Cervix

  - Vagina

  - Vulva
• What is the function of the ovaries?

  Produce eggs (ova) and hormones (oestrogen, progesterone)
• What is the function of the fallopian tubes/oviduct?

  Transport eggs from ovaries to uterus and is the site of fertilization
• What is the function of the uterus?

  Site of embryo implantation and foetal development
• What is the function of the cervix?

  Narrow opening to uterus; allows passage of sperm and childbirth
• What is the function of the vagina?

  Canal receiving sperm and is the birth canal
• What is the function of the vulva?

  External genitalia protecting internal organs
• What is fertilisation?

  - Fertilisation is the fusion of two haploid nuclei from parents to form a new diploid organism. It is the mechanism of inheritance in eukaryotes with a sexual life cycle. It may either be internal or external.

  - Once released, egg and sperm will die unless they meet and fuse in the process of fertilisation.

  - Fertilisation is only complete when the two haploid nuclei come together and combine their chromosomes into a single diploid nucleus.

  - Sperm can live for five days within the female reproductive tract.

  - The egg can live for 12 to 24 hours after ovulation.
• What is the movement of sperm after ejaculation?

  After ejaculation, sperm move through the cervix, into the uterus and swim towards the egg that is in the oviduct.

  Sperm move through thermotaxis and chemotaxis

  - Thermotaxis- sperm swim according to a temperature gradient- towards warmer temperature

  - Chemotaxis- sperm swim according to a chemical gradient. Sperm plasma membranes have receptors that detect chemicals that are released by the egg.
• What is the acrosome reaction?

  Once at the egg, the sperm manoeuvre through the cells of the corona that radiate around the egg.

  The corona cells secrete hormones that trigger the acrosomal reaction in the sperm, where enzymes in the sperm's head digest the zona pellucida of the egg.
• What is the significance of membrane fusion in fertilisation?

  Fertilisation occurs with the fusion of the sperm plasma membrane with the egg plasma membrane. After the membranes fuse, the sperm nucleus enters the egg cell. The tail and mitochondria do not enter the egg.
• What is the cortical reaction?

  When the sperm and egg membranes fuse, the zona pellucida around the egg hardens to prevent entry of more sperm. This cortical reaction ensures that the egg is not fertilised by multiple sperm, and that the zygote will have the correct number of chromosomes.
• What are the two types of fertilisation?

  - In vivo fertilisation occurs in the oviduct during natural conception.

  - In vitro fertilisation is a form of medically assisted reproduction. Fertilisation occurs outside of the body, in controlled laboratory conditions.
• What are the key components of in vitro fertilisation?

  - Down regulation

  - Ovarian stimulation

  - Egg retrieval

  - Fertilisation

  - Endometrial preparation

  - Embryo transfer
• What is down regulation?

  Injection of drugs that stop the pituitary from secreting FSH and LH, to control timing.
• What is ovarian stimulation?

  - High doses of FSH are prescribed. This triggers development of multiple follicles (superovulation).

  - hCG is injected to stimulate follicle maturation
• What is egg retrieval?

  Needle with a vacuum suction draws eggs from matured follicles, using an ultrasound
• What is fertilisation (during IVF)?

  Egg is mixed with sperm sample in a shallow dish. This is incubated for 1-2 days for zygote formation.
• What is endometrial preparation?

  Oestradiol and progesterone are prescribed to stimulate the thickening of the endometrium.
• What is embryo transfer?

  Embryos are placed in the uterus, where they implant into the endometrium and continue to grow.