Sexual Reproduction (11.4) Flashcards
Describe the Soil and Seed theory.
The soil and seed theory proposed by Aristotle described how animals were thought to reproduce sexually. The male produced a seed which formed an egg when mixed with menstrual blood (the soil). The egg would then develop into a fetus inside the mother.
Who debunked the Soil and Seed theory and how?
William Harvey debunked the soil and seed theory by studying the sexual organs of female deer after mating. He was unable to detect a growing embryo until 6-7 weeks after mating had occurred. So he concluded that Aristotle’s soil and seed theory was incorrect and menstrual blood did not contribute to the development of a fetus. However, Harvey was unable to identify the correct mechanism of sexual reproduction and incorrectly stated that the fetus did not develop by a mixture of male and female ‘seeds’.
How was the modern theory of sexual reproduction developed?
Our current understanding of sexual reproduction is based on evidence discovered with the use of light microscopes (invented after William Harvey’s death).
What is the purpose of the female reproductive system?
To produce eggs, receive the sperm, develop the embryo in the uterus and to give birth.
Give the function of the following structures:
Ova
Ovary
Fallopian tube
Uterus
Cervix
Vagina
Ova: The female sex cell.
Ovary: Where oocytes mature prior to ovulation. Responsible for the secretion of oestrogen and progesterone.
Fallopian tube: The tube through which the ova travels to reach the uterus. Fertilisation occurs here.
Uterus: Where a fertilised egg will implant and develop into an embryo.
Cervix: The passage between the uterus and the vagina.
Vagina: The passage through which the semen enters the female reproductive system. The baby passes through here.
What are the female and male sex hormones?
Female sex hormones:
Oestrogen, progesterone.
Male sex hormones:
Testosterone.
What determines sex in humans?
Females possess two X chromosomes (XX) while males possess one X chromosome and one Y chromosome (XY).
The Y chromosome contains a gene called the SRY gene (Sex determining Region Y) which codes for TDF (Testis Determining Factor). The TDF causes the embryonic gonads to develop into testes.
In the absence of the TDF protein (i.e. no Y chromosome), the embryonic gonads will develop into ovaries.
What is the role of oestrogen and progesterone in female sex development?
Oestrogen and progesterone are secreted by the ovaries. The pituitary gland produces Follicle Stimulating Hormones (FSH) which stimulate the ovaries to produce oestrogen. It also produces the Lutenising Hormone (LH) which stimulates the follicles to become mature and release their egg and then develop into the corpus luteum.
Oestrogen and progesterone promote the pre-natal development of the female reproductive organs (primary sex characteristic) and are responsible for the development of secondary sex characteristics (body hair and breast development). They are also involved in monthly preparation of egg release following puberty.
What are the two key groups of hormones that control the menstrual cycle?
Pituitary hormones (FSH, LH)
- Act on the ovaries to develop follicles.
Ovarian hormones (oestrogen, progesterone)
- Act on the uterus to prepare for pregnancy.
Describe the follicular phase of the menstrual cycle.
The pituitary gland releases the follicle stimulating hormone (FSH) which stimulates the production of follicles on the ovary. The ovarian follicles secrete oestrogen. When oestrogen peaks there is a surge in the lutenising hormone which intiates ovulation.
Describe the ovulation phase of the menstrual cycle.
The ovary releases an egg. The egg travels down the fallopian tube where it waits to be fertilised by sperm.
Describe the luteal phase of the menstrual cycle.
The dominant follicle that released the egg in ovulation changes into a structure called the corpus luteum. This produces oestrogen and progesterone which help to thicken the lining of the uterus.
If fertilisation does not occur the corpus luteum breaks down. Progesterone production decreases and the endometrial lining is shed.
What is IVF?
Fertilisation that occurs outside of the body (in vitro). It occurs via the usage of drugs to stop the normal menstrual cycle and hormone treatments to harvest multiple eggs (super ovulation).
Give a summary of the key stages of IVF.
SHE’S FIT
Stop normal menstrual cycle via drugs
Hormone treatments for superovulation
Extract multiple eggs from the ovaries
Sperm collected
Fertilisation occurs externally (in vitro)
Implantation of multiple embryos into the uterus
Test for pregnancy
What are the primary and secondary sex characteristics of females?
Primary sex characteristics: The prenatal development of the vagina, uterus, fallopian tubes, clitoris and cervix and the ability to menstruate after maturity and give birth.
Secondary sex characteristics: Breast development, wider hips and fat deposition, body hair and external genitalia development.
What are the primary and secondary sex characteristics of males?
Primary sex characteristics: The prenatal development of male genitalia, including a penis.
Secondary sex characteristics: An enlarged penis, growth of skeletal muscle, pubic hair, facial hair, sperm production, larynx enlargement.
What is the purpose of the male reproductive system?
To produce sperm in the testes and to deliver the sperm into the female reproductive system.
Give the function of the following structures:
Testes
Scrotum
Epididymis
Vas deferens
Prostate gland
Seminal vesicle
Urethra
Penis
Testes: Where sperm is produced.
Scrotum: Where the testes are located. Keeps the testes at a slighter lower temperature than the body.
Epididymis: Where sperm mature and develop motility.
Vas deferens: The tube through which the sperm cells travel from the testes to the penis.
Prostate gland: Secretes an alkaline liquid that neutralises vaginal acid (needed to maintain sperm viability).
Seminal vesicle: Secretes a fluid containing enzymes, proteins, sugar and vitamins.
Urethra: Tube inside the penis through which semen leaves the body. Also used for urine.
Penis: Semen is ejected from this into the vagina.
Define gametogenesis.
The process by which diploid (2n) cells undergo meiotic division to become haploid (n) gametes (sex cells). In males this is called spermatogenesis and in females this is oogenesis.
Explain the function of the following structures in the sperm:
- Head
- Mid-piece
- Tail
The head contains the acrosome, nucleus and centrioles. The acrosome cap contains enzymes which help the sperm to penetrate the jelly coat of the egg. The nucleus contains the paternal DNA. The centrioles are needed by a zygote in order to divide.
The mid-piece contains mitochondria which provides the energy (ATP) needed for the tail to move.
The tail (flagellum) is composed of a microtubule structure called the axoneme which bends to facilitate movement.
Explain the function of the following structures in the egg:
- Corona radiata
- Zona pellucida
- Cortical granule
- Nucleus
The corona radiata is an external layer of follicular cells which provide support and nourishment to the egg cell.
The zona pellucida (jelly coat) is a glycoprotein matrix which acts as a barrier to sperm entry.
The cortical granules release their contents upon fertilisation to prevent polyspermy from occurring.
The nucleus contains the maternal DNA.
Explain the process of oogenesis.
During foetal development a large number of primordial cells are formed by mitosis. These cells undergo a period of cell growth and become primary oocytes. The primary oocytes undergo meiosis but the process stops at prophase I. It resumes during puberty. Each month FSH triggers some of the primary oocytes to continue meiosis and form secondary oocytes and polar bodies. After meiosis I, the secondary oocyte undergoes meiosis II which stops at metaphase II until fertilisation occurs. When this happens, meiosis II continues and an ootid and a polar body are created. The polar bodies disintegrate and the ootid undergoes maturity, eventually forming an ovum.
Explain the process of spermatogenesis.
During puberty, the germline epithelium of the seminiferous tubules of the testes divide by mitosis forming spermatogonia. The spermatogonia undergo a period of cell growth and form spermatocytes. The spermatocytes undergo meiosis and form four haploid daughter cells (spermatids). The spermatids differentiate and become functional sperm cells. They are released into the tubule and transported to the epididymis.
What are the hormones involved in spermatogenesis and what is their role?
FSH: Produced in the pituitary gland. Stimulates primary spermatocytes to undergo the first division of meiosis and form secondary spermatocytes.
LH: Produced in the pituitary gland. Stimulates the secretion of testosterone by the testis.
Testosterone: Produced by the interstitial (Leydig) cells in the testis. Stimulates the development of secondary spermatocytes into mature sperm.
