Human Reproductio1.docx

Human Reproduction Male Anatomy and Functions (2) - Sperm: The male gamete and can survive for up to five days - Epididymis: A tubular structure on the outside of each testis which stores immature sperm until ejaculation - Sperm duct (Vas deferens): Sperm that leave the epididymis during ejaculation...

Human Reproduction Male Anatomy and Functions (2) - Sperm: The male gamete and can survive for up to five days - Epididymis: A tubular structure on the outside of each testis which stores immature sperm until ejaculation - Sperm duct (Vas deferens): Sperm that leave the epididymis during ejaculation is passed along the sperm duct by peristalsis to the urethra Seminal Vesicles: Add sugar solution to sperm in the sperm duct to feed them on their journey to the fallopian tube to fertilise the egg. Seminal fluid makes up 60% of sperm - Semen: A milky white sticky liquid of sperm and fluids from the seminal vesicles, the prostate gland, and the Cowper’s gland - Cowper’s Gland: Adds a thick and slippery fluid to the penis for lubrication during intercourse. Flushes the urethra before sperm arrives - Penis: Made of erectile tissue. When the male becomes sexually excited, blood vessels leaving the penis constrict, causing the penis to engorge with blood and become erect. After stimulation, ejaculation occurs and the penis deposits sperm around the opening of a female’s cervix to allow it to enter the uterus as quickly as possible Female Anatomy and Functions (3) - Ovaries: One ovary releases an egg every 28 days on average. The egg is the female gamete and survives for about two days - Oestrogen and progesterone: Hormones produced by the ovaries from puberty until menopause - Fallopian tubes: Lined with cilia with beat in unison to waft the egg towards the uterus. Fertilisation occurs in the top third of the fallopian tube - Uterus: A muscular sac which holds and nourishes the developing embryo - Endometrium: The innermost lining of the uterus and is the site of implantation and placenta formation. Thickens in preparation for the arrival of a fertilised egg. If a fertilised egg does not arrive, the lining is shed through the cervix and vagina in menstruation (a period) - Menstruation: A woman will lose approximately 30 to 90 ml of fluid over three to seven days - Cervix: Neck of the womb, blocked by a mucus plug for most of the month. Around the time of ovulation, the mucus thins out to allow sperm to swim through and enter the uterus - Vagina: During copulation, the vagina stimulates the penis to ejaculate and ensures sperm is deposited against the cervix. Lubricated with acidic mucus to prevent the growth of pathogenic microorganisms - Vulva: Outer lips of the vagina Meiosis in the Production of sperm and eggs Sperm The sperm-producing cells (diploid) in the tubules of the testes divide by meiosis and produce sperm(haploid). - Head: Contains the haploid nucleus consisting of one set of chromosomes. The acrosome is a bag of digestive chemicals is to help penetrate the egg - Midpiece: Contains mitochondria which supply the energy necessary to complete the journey from the vagina to the top of the fallopian tube - Tail: Spins and produces the force necessary to propel the sperm and make them motile Egg After puberty, approximately 20 eggs are produced by meiosis each month. Usually only one continues to grow and the rest die off. After meiosis, a haploid egg is surrounded by a Graafian follicle. An egg can live for 24 - 48 hours (5) - Haploid nucleus - Cytoplasm: Contains mitochondria and cell organelles - Non-cellular layer: The area where sperm burrows its way into the egg Sexual Characteristics - Primary sexual characteristics: Any body structures directly involved with reproduction e.g., penis, vagina, uterus, testes - Secondary sexual characteristics: Features, both physical and behavioural, that develop at puberty under the influence of sex hormones and further distinguish males from females - Males: Main hormone involved is testosterone. Features that develop include a deepening of the voice, broadening of the shoulders, increased muscle mass, and the growth of facial, pubic, and underarm hair - Females: Main hormone involved is oestrogen. Features include enlargement of the breasts, widening of the hips, development of pubic and underarm hair and thickening of the layer of subcutaneous fat giving a more rounded figure. Progesterone keeps the endometrium built up and stops the uterus from contracting The Menstrual Cycle The menstrual cycle involves changes in the ovaries and uterus that makes pregnancy possible. The cycle starts between the ages of nine and fifteen at puberty. The first period, which marks the beginning of a woman’s reproductive life, is called the menarche, and she will continue having periods until the menopause in her late forties or early fifties. Process of Menstruation - Day one of the cycle is when menstruation occurs and lasts for four or five days - Day five marks the beginning of the build-up of the endometrium in preparation for the possible arrival of a fertilised egg during the fertile period. The Graafian follicle produces oestrogen which travels through the blood stream from the ovary to the uterus - The fertile period is when fertilisation is possible. Days 9 to 15 are the most fertile - Day 14 is when ovulation occurs. The egg is released when the Graafian follicle bursts. Follicle- stimulating hormone (FSH) and luteinising hormone (LH) concentrations peak just before ovulation due to a rapid rise in oestrogen levels, and cause the follicle to swell and burst - Days 15 to 21 is when the empty follicle transforms into a corpus luteum. This secretes the hormone progesterone, which maintains the endometrium, and makes it soft and spongy so that a developing embryo can easily embed in it - In days 21 to 28, if fertilisation has not occurred, the egg passes out of the uterus. The corpus luteum breaks down and progesterone production ceases. This causes the endometrium to begin to degenerate, and by day 28 is ready to break down and pass out through the cervix and vagina - If pregnancy occurs, the endometrium is maintained by a hormone called Human chorionic gonadotrophic hormone (hCG), produced by the placenta. It is the presence of hCG that is detected in pregnancy tests (6) Hormones and the Menstrual Cycle - Follicle- stimulating hormone (FSH), produced by the anterior pituitary, starts the process by stimulating a primary oocyte to develop into an ovum inside the Graafian follicle - The developing Graafian follicle produces the hormone oestrogen, which travels around the body in the blood - Oestrogen does three things a. Repairs and thickens the endometrium b. Tells the anterior pituitary gland to stop producing FSH. This is called a feedback system because the production of one substance influences the production of another. This is negative feedback as it stops the other substance from being produced c. Tells the anterior pituitary to start producing luteinising hormone (LH). This is positive feedback since it causes an increase in production of the other substance - The day before ovulation, there is a marked increase in LH which causes the final maturation of the Graafian follicle and ovulation. This makes the female more receptive to the sexual advances of the male, but in humans it is not very marked since sexual activity is not tied to fertility - LH continues the inhibition of FSH, and a sudden surge in its production stimulates ovulation. It also stimulates the subsequent change of the remains of the Graafian follicle into the yellow-coloured corpus luteum - The corpus luteum produces progesterone. Progesterone inhibits both FSH and LH, and thickens the endometrium - If fertilisation does not occur, the lack of LH results in the corpus luteum degenerating and this stops the production of progesterone - If pregnancy occurs, hGC is produced by the placenta and maintains the corpus luteum and thus the production of progesterone, which keeps the endometrium built up Menstrual Disorders - Benign growths in the wall of the uterus which can range in size - Symptoms include heavy bleeding, prolonged periods and abdominal pain - Caused because some cells have more oestrogen and progesterone receptors than others - Treatments can vary from painkillers in mild cases, to surgery in severe cases Pregnancy Copulation - The natural process of using the erect penis to deposit semen at the top of the vagina beside the cervix. - If sperm is collected from a donor and placed into the vagina or the uterus using a medical implement, this is called artificial insemination Ovulation - The release of an egg from an ovary on day 14 of the cycle. The egg can survive for two days - Sperm can survive in the fallopian tube for up to five days, if it meets an egg fertilisation can take place Fertilisation - The fusion of the haploid male and female gamete nuclei to form a diploid zygote - Takes place in the top third of the fallopian tube Infertility - If a couple cannot conceive a child after a year of trying, they are infertile. - Doctors can provide assistance such as in vitro fertilisation In vitro fertilisation In vitro fertilisation is the fertilisation of eggs outside the womb, usually in a petri dish. - Early in the menstrual cycle, the woman is given hormones to cause the production of several eggs - The developing follicles are monitored by ultrasound scanning - Immediately before ovulation, the eggs are removed through a narrow needle and transferred to a nutrient fluid in a petri-dish - The man’s sperm is mixed with the eggs and incubated - After a few days, if fertilisation has taken place and the embryos have begun to grow, several embryos are placed in the uterus and hopefully one will implant and develop Causes of Infertility Males - Low sperm count can be caused by smoking or excess consumption of alcohol - Low sperm mobility due to malformed sperm - Low testosterone levels due to endocrine gland failure can be overcome using hormone replacement therapy with testosterone - High temperature, from wearing tight underwear, can cause sperm to die Females - Fallopian tube blockage due to injury or infection caused by untreated subclinical infections such as chlamydia - Endocrine gland failure due to disease, injury or malformation can be treated by hormone replacement therapy (HRT) Stages of Development Morula and blastocyst - Immediately after fertilisation, the zygote begins to divide by mitosis, forming two, then four and then eight cells - By day three after fertilisation, it is a solid ball of 16 cells called a morula - As cell division continues, a cavity starts to form, which produces a hollow ball of cells called a blastocyst - Cells begin to change in structure and function, a process called differentiation - Around 7 days after fertilisation, the blastocyst has travelled as far as the uterus - It begins to make connections with the uterus that will eventually form the placenta. This is called implantation - A group of cells at one end of the blastocyst forms three distinct layers, each called a germ layer - Each germ layer develops into different tissues depending on its location. This is called a triploblastic arrangement The three layers that some of the tissues that develop from each are; - Endoderm: Innermost layer that forms the lining of the gut, the respiratory and the urinogenital system - Mesoderm: Middle layer that forms blood, bone and muscle - Ectoderm: Outermost layer that forms the skin, epidermis and the nervous system Up to 8 weeks old, the developing baby is called an embryo. From week 9 onwards it is called a foetus The amnion is a sac that forms around the embryo, and by the fourth week is filled with amniotic fluid. The amniotic fluid acts as a shock absorber and protects the baby. It allows the baby to move freely, especially in the later stages of pregnancy. (7) Placenta - The placenta is a disc-shaped structure which is formed partly from the cells of the embryo, and partly from cells of the womb wall, and is connected to the foetus by the umbilical cord - It takes approximately 3 months to form - Foetal blood is carried to the placenta in two arteries in the umbilical cord and a vein carries the foetal blood back from the placenta to the foetus - The blood of the mother and foetus do not mix. Functions of the placenta - Gaseous exchange: Oxygen diffuses from the mother’s blood into the baby’s blood, while Carbon dioxide diffuse from the baby’s blood to the mother’s blood - Antibodies: Can be passed from the mother to the baby to give passive acquired immunity - Nutrition: Glucose, amino acids, fats, vitamins, and minerals pass from the other to the baby - Endocrine gland: Makes progesterone and hCG to maintain the pregnancy and diffuses into the bloodstream - Excretion: Metabolic waste such as carbon dioxide and urea pass into the mother’s blood from the baby and are excreted by the mother - Protection: The placenta prevents the energy of many pathogens Birth The process of birth, called labour, occurs in three distinct stages Cervical dilation - Contractions of the uterus progress and strengthen for longer periods with a decreasing interval between them - The cervix dilates, and the mucus plug breaks free and passes out of the vagina as a sticky, jelly-like pink mucus - The amniotic sac bursts and passes out through the vagina - When the cervix has dilated to 10 cm wide, the second stage of birth begins Delivery - The contractions of the uterine muscle become stronger causing the baby to move slowly through the pelvis - The mother must push as the baby’s head descends through the birth canal, then one shoulder followed by the other, then the rest of the baby slides out - Umbilical cord is clamped and cut - Baby breathes air. Placental delivery - The placenta and the rest of the umbilical cord (afterbirth) pass out of the body through the birth canal Milk Production and Breastfeeding - Suckling the baby stimulates the anterior pituitary to produce two hormones, prolactin and oxytocin -Prolactin stimulates lactation while oxytocin stimulates the expression of milk from the breasts - Milk produced at the start of lactation is called colostrum, which is yellow in colour and rich in nutrients and antibodies - Milk produced later is white, thinner in consistency, and not as rich in antibodies (8) Benefits of Breastfeeding - Breast milk is the perfect food at correct temperature - It has a lot of advantages for the baby’s growth and development - It has the correct level of sodium, phosphate, and essential amino acids in contrast to cow’s milk - Sterile at room temperature. - Breast milk contains antibodies which protect against many diseases and allergies - Allows bonding of mother and baby - Can delay the return of the menstrual cycle if prolactin level is maintained high - Reduced risk of breast cancer Birth Control Methods The availability of contraception results in a decrease in population and some contraceptives can decrease sexually transmitted infections (STI). Natural Methods - Abstinence: Avoiding sexual intercourse prevents pregnancy and STI’s - Withdrawal: Removing the penis from the vagina before ejaculation, only 75% effective at best Artificial Methods – Mechanical - Condoms: Form a latex barrier between the sperm and the egg. They give protection against STI’s once they are put on before any sexual contact. 99% reliable is used properly - Diaphragm: A rubber cap that fits over the cervix and blocks sperm from entering. No protection against STI’s. Only 80 – 95% effective as it can dislodge Artificial Methods – Chemical - Contraceptive pill: Contains progesterone and oestrogen which prevent ovulation. 99% effective if correctly taken every day - Implants: Rods that are implanted under the skin which release chemicals thar prevent ovulation and make cervical mucus thicker. 99% effective Surgical Methods - Vasectomy: Involves cutting a man’s sperm ducts and tying off the cut ends. 100% effective but difficult to reverse - Sterilisation: Involves cutting a woman’s Fallopian tubes and tying off the cut ends - Intrauterine device (IUD): A copper t-shaped device is inserted into the uterus and prevents fertilization and implantation (9)