Leaving Certificate Agricultural Science The Reproductive System Introduction
- Slides: 27
Leaving Certificate Agricultural Science The Reproductive System
Introduction � Reproduction is the formation of new individuals of the same species. � Sexual reproduction is the only method of reproduction in our species. � Sexual reproduction involves the fusion of specialised haploid sex cells. � The fusion of sperm and egg cell is called fertilisation. � Fertilisation results in the formation of a diploid zygote from which a new individual develops.
Sperm Cells Sperm � Sperm is really just a haploid nucleus with a flagellum that propels it towards the egg cell. � The middle piece or neck contains mitochondria producing the ATP to supply energy for propulsion. � The head contains the nucleus with the genetic material. � It also has a large digestive enzyme sac, called the acrosome. � The digestive enzymes help the sperm to make their way to the surface of the egg cell.
Human Sperm Cell
Secondary Sexual Characteristics � These are the features that distinguish the sexually mature individual from the immature. � They appear at puberty as a result of new higher levels of oestrogen in females and testosterone in males. � Primary Sexual Characteristics are the basic forms that distinguish between male and female i. e. the presence or absence of a penis!
Male Secondary Sex Characteristics � Hair growth on the face, underarm, chest and pubic region � Enlarged � Wider shoulders � Greater � Taller larynx producing a deeper voice skeletal musculature
Female Secondary Sex Characteristics � Hair growth in the pubic region and underarm � Enlarged � Wide breasts hips � Greater � Taller fat deposits under the skin
The Menstrual Cycle � The menstrual cycle is the repeating series of changes in the uterine lining of a fertile female if fertilisation and implantation does not happen. � This cycle ranges from 24 to 35 days, commonly 28 days.
Stages of the Menstrual Cycle Day 1 to day 5 � Day 1 is the first day of menstruation. � The corpus luteum of the previous cycle has disintegrated. � The levels of oestrogen and progesterone declined greatly. � Low progesterone level leads to the menstruation. � Menstruation is the breakdown and discharge of the outer layer of the uterine lining. � Low oestrogen and progesterone levels permit the secretion of FSH (follicle stimulating hormone) by the pituitary gland.
Stages of the Menstrual Cycle Day 6 to day 13 � FSH stimulated the formation and maturation of a Graafian follicle. � The maturing follicle secretes oestrogen. � Oestrogen inhibits FSH secretion preventing other follicles maturing. � Oestrogen also stimulates repair of the uterine lining. � Oestrogen brings about a surge of LH (luteinising hormone) just before ovulation.
Stages of the Menstrual Cycle Day 14 � The surge of LH stimulates ovulation. � Ovulation is the release of the egg cell from the mature Graafian follicle at the ovary’s surface. � The egg cell is drawn into the Fallopian tube.
Stages of the Menstrual Cycle Day 15 to day 26 � A corpus luteum (yellow body) develops from the ‘empty’ Graafian follicle. � The corpus luteum secretes progesterone and oestrogen. � These hormones stimulate the final maturation of the uterine lining. � High levels of theses hormones also inhibit FSH and LH secretion from the pituitary. � If implantation does not take place by day 26 the corpus luteum disintegrates.
Stages of the Menstrual Cycle Day 26 to day 28 � The degeneration of the corpus luteum causes he levels of oestrogen and progesterone to decline rapidly. � The degenerated corpus luteum becomes a small scar in the ovary.
Fertilisation � Fertilisation is the fusion of the male gamete (sperm cell) and the female gamete (egg) to form a diploid zygote. � Fertilisation occurs in the Fallopian Tube usually. � Only one sperm cell can fertilise an egg and a chemical change occurs in the membrane of egg once fertilisation has taken place. � The most motile sperm will reach the egg first!
Pregnancy and Implantation � The usual first sign that pregnancy has occurred is that menstruation does not happen. � Implantation is the embedding of the blastocyst (early developing embryo) into the uterine lining (endometrium). � Implantation occurs about six days after fertilisation. � The developing embryo releases a hormone into the mother’s blood. � This hormone maintains the corpus luteum. � The surviving corpus luteum continues to secrete progesterone and oestrogen. � As a result the endometrium (uterine lining) does not break down and the pregnancy continues. � Conception is fertilisation followed by successful implantation.
Lactation is breastfeeding the baby with milk. The placenta produced very high levels of oestrogen and progesterone. � After the birth of the baby these hormone levels fall rapidly. � This decline allows the pituitary to secrete prolactin hormone. � Prolactin stimulates the glands in the breasts to produce milk. � The suckling of a baby at the breast also stimulates the mother’s pituitary to release prolactin. � The regular presence of prolactin maintains milk production. � Suckling also stimulates the pituitary to secrete oxytocin. � Oxytocin causes the milk ducts to contract ejecting the milk from the breast. � �
Family Planning and Contraception � Family planning is a conscious action to control the number of and interval between children. � Contraception is the deliberate prevention of fertilisation or implantation. Natural Methods � Abstinence: no sexual intercourse. 0% failure rate. � Temporary abstinence: no sexual intercourse during the most fertile period of the menstrual cycle: 24% failure rate. � Withdrawal: penis is removed from the vagina before ejaculation: 25% failure rate.
Family Planning and Contraception Male Contraceptive Methods � Condom: a thin impermeable sheath covering the penis; semen cannot be deposited in the vagina: 10% failure rate. � Vasectomy: cutting, sealing or tying off the sperm ducts; sperm will not be in the semen: 0. 4% failure.
Family Planning and Contraception Female Contraceptive Methods � Cervix Barriers: diaphragm or cap – prevents sperm entering the uterus: 15% failure rate. � Intrauterine Devices (IUD): these are plastic or metal loops or coils, prevents implantation: 5% failure rate. � Oral contraceptive pill: prevents ovulation as the follicles do not mature 6% failure rate. � Spermicides: these chemicals are placed in the vagina to kill sperm: 20% failure rate. � Tubal ligation: the Fallopian tubes are cut and sealed preventing sperm and egg cells meeting: 0. 4% failure rate.
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