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Chapter 41: The human reproductive system

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1 Chapter 41: The human reproductive system
Leaving Certificate Biology Higher Level

2 Structure of Female Reproductive Tract

3 Structure of Female Reproductive Tract

4 Structure of Male Reproductive Tract

5 Functions of Female Reproductive Organs:
Ovaries: Where eggs develop Produce sex hormones: oestrogen and progesterone that are responsible for the onset of puberty and the maintenance of secondary sexual characteristics Fallopian tubes (oviducts): Collect the egg following ovulation and direct it towards the womb using muscular contractions Uterus (womb): Has a delicate lining called the endometrium that is shed once a month Fertilised egg develops in the uterus to become an embryo and then a foetus

6 Functions of Female Reproductive Organs:
Cervix: Located at the bottom of the womb and is the region where the sperm enter following intercourse Vagina: Muscular tube that receives the penis during intercourse Serves as the birth canal during parturition

7 Functions of Male Reproductive Organs:
Testes: Located outside the body so that the temperature is lower as sperm require a lower temperature of 35 ˚C for proper formation Where sperm develop and mature before being released Produce testosterone that is responsible for the onset of puberty and the maintenance of secondary sexual characteristics

8 Functions of Male Reproductive Organs:
Epididymis: Located at the top of each testes and sperm are stored until they are released – if they are not released then they are broken down and reabsorbed Sperm ducts (vas deferens): Where sperm are carried to the urethra and then out of the body

9 Functions of Male Reproductive Organs:
Glands: There are three glands associated with the male reproductive system: Seminal vesicles Prostate Cowper’s gland They all contribute to seminal fluid that is the medium for the sperm to swim in and contains nutrients for the sperm that will help nourish sperm while they are within the female reproductive tract

10 Functions of Male Reproductive Organs:
Penis: The penis is a muscle that is capable of swelling with blood in order that it can be inserted into the vagina It is responsible for delivering the sperm at the cervix

11 Meiosis and Gamete Formation
Meiosis has an important function: Meiosis halves the number of chromosomes in the formation of 4 haploid daughter cells from one diploid parent cell Halving the number of chromosomes is critically important in propagating the species as it ensure that the resulting offspring (the next generation) will have the correct number of chromosomes in every cell

12 Secondary Sexual Characteristics
Secondary sexual characteristics are those features that distinguish males from females, apart from the sex organs themselves

13 Secondary Sexual Characteristics in Males:
Pubic hair Underarm, body and facial hair Enlarged pharynx Larger muscles and bones Wide shoulder girdle Large body size in comparison to females Sebum secretion

14 Secondary Sexual Characteristics in Females:
Pubic hair Underarm and body hair Breasts Wide pelvic girdle Higher body fat in comparison to males Sebum secretion

15 Oestrogen Oestrogen is one of the female sex hormones that is made in the ovaries and secreted into the bloodstream Oestrogen affects a wide variety of tissues throughout the body – the most common ones including: breast, brain, adipose, and uterine tissue Oestrogen has a very important role in the menstrual cycle – see forthcoming slides

16 Progesterone Progesterone is the other sex hormone in females that has a similar structure as oestrogen and similar effects but the timing of the effects is different Progesterone is also secreted by the ovary

17 Testosterone Testosterone is the male sex hormone that is secreted by cells within the testes Testosterone: General growth Growth of the male reproductive system early in life Development of secondary sexual characteristics Maintenance of secondary sexual characteristics Sperm production

18 The Menstrual Cycle The menstrual cycle biorhythm in females that takes approximately 28 days The menstrual cycle begins at puberty (ages 11 to 16) and usually lasts until menopause (ages 45 to 55) The menstrual cycle is controlled by four hormones: Follicle-stimulating hormone (FSH) Oestrogen Luteinising hormone (LH) Progesterone The menstrual cycle can be divided up into three main stages or events: Menses and follicular phase Ovulation Luteal phase

19 1. Menses and the follicular phase
Menses: occurs between days 1 and 5: Involves the shedding of the lining of the uterus Follicular phase: FSH secretion from the pituitary increases and causes a number of Graafian follicles to form Only one of these follicles normally survives and a new egg develops within the Graafian follicle The Graafian follicle secretes oestrogen As the Graafian follicle enlarges the amount of oestrogen secreted increases Only one Graafian follicle normally develops so that only one egg will be produced each month

20 1. Menses and the follicular phase (continued)
Repair of the endometrium occurs over days 6 to 13 where the developing Graafian follicle is secreting oestrogen which causes the endometrial cells to start dividing again As oestrogen levels are increasing it inhibits FSH secretion by negative feedback – ensuring no more Graafian follicles develop

21 2. Ovulation Oestrogen levels keep increasing until they reach a critical concentration When this concentration is reached it stimulates the release of a hormone from the pituitary called luteinising hormone (LH) LH causes ovulation Ovulation occurs on day 14 and involves the release of the egg from the ovary into the funnel and onto the oviduct

22 3. Luteal phase When the egg is released from the ovary the Graafian follicle turns into a yellow structure called the corpus luteum Oestrogen levels drop The corpus luteum secretes progesterone which maintains the endometrium in preparation for fertilisation In addition progesterone maintains the inhibition on FSH and LH ensuring no further eggs develop If fertilisation does not occur then the corpus luteum dies and progesterone levels drop causing the beginning of menstruation

23 Menstrual Disorder Fibroids:
Fibroids are benign tumours within that develop within the uterus as the female gets older Most are very small but some can grow large enough to cause symptoms Symptoms of large fibroids are pain, prolonged menstrual bleeding, infertility and anaemia (through loss of blood) Their cause is thought to be due to abnormal responses to oestrogen Most fibroids do not need any medical treatment, however, large fibroids may require surgery (hysterectomy may be carried out)

24 Stages of Copulation Sexual arousal: Copulation:
Males: blood flows into the penis and the penis becomes erect Females: blood flow to vagina increases causing it to becomes longer and mucous secreting cells ensure the vagina is lubricated Copulation: Penis is inserted into the vagina

25 Orgasm and Insemination
Copulations causes physical and mental sensations in both the female and male These sensations are collectively called orgasm During orgasm in the male, semen is released into the female at the site of the cervix The release of sperm at the cervix is called insemination

26 Survival Time for Sperm and Ova
Sperm can survive for up to 3 days within the female reproductive tract The egg cell survives for 2 days following ovulation

27 Fertilisation Fertilisation is the fusion of an egg cell and a sperm cell to produce a diploid zygote Fertilisation normally occurs in the fallopian tube

28 Sequence of Development of Zygote
After fertilisation the diploid zygote divides by mitosis into 2 cells, 4 cells, 8 cells etc. After approximately 3 days a clump of cells between 32 and 128 cells is formed – this is called the morula After 1 week a hollow structure of a few hundred cells (inner cell mass) has formed and this is called the blastocyst The outer layer of cells is called the trophoblast and it is this structure that will enable implantation to occur

29 Early Sequence of Zygote Development

30 Implantation Implantation is the embedding of the blastocyst into the lining of the uterus Implantation occurs approximately 1 week following fertilisation Once implanted the blastocyst continues to grow and the trophoblast extends projections into the uterine tissue The interaction between the uterine tissue and the trophoblast will eventually give rise to the placenta The implanted embryo continues to grow and the placenta begins to form The embryo is recognisably human after about 8 weeks post-fertilisation – at this stage it is called a foetus

31 Placenta The placenta is an organ made of two tissues: mother’s uterine tissue and foetal tissue The bloodstream of the foetus and mother DO NOT mix, but come into close contact so that materials can be exchanged The placenta is only fully formed and fully functional after about 3 months The placenta is the foetus’ life support The foetus gains its nourishment from the mother via the placenta Examples of materials that pass from mother to foetus are: oxygen, water, glucose, amino acids, hormones, antibodies Examples of materials that pass from foetus to mother are: carbon dioxide and urea

32 Embryo Development – Germ Layers
Ten days following fertilisation the inner cell mass give rise to an embryonic disc The embryonic disc gives rise to three layers of cells called: Endoderm: gives rise to liver and pancreas and to inner lining of digestive, respiratory and excretory systems Mesoderm: gives rise to internal organs such as heart, lungs, kidneys, muscles, skeleton Ectoderm: gives rise to skin, hair, nails, nervous system

33 Embryo Development – First 8 Weeks
First 4 weeks: heart forms and begins to beat and brain develops as well as the umbilical cord Week 5: limbs begin to form Week 6: eyes are visible and face is forming Week 7: tail begins to disappear and all the internal organs are now formed Week 8: ossification starts to occur

34 Embryo Development – First 8 Weeks
Week 8 onwards: the embryo rapidly increases in size By week 12: eyes are low in the face and bone continues to replace cartilage; nerves become coordinated and the embryo begins to move For the rest of pregnancy, the foetal organs increase in size, become stronger and mature so that they will be able to function independently following birth

35 Birth During pregnancy, oestrogen and progesterone are produced in high amounts by the placenta – inhibiting the release of FSH and also inhibiting contractions of the uterus However, these hormones stop being secreted towards the end of pregnancy and then the walls of the uterus begin to contract Pituitary gland then begins to secrete oxytocin which causes further stronger contractions of the uterus

36 Birth (continued) Birth is subdivided into three parts:
Labour: lasts approx 12 hours: Waters break and baby moves down towards the cervix Parturition: lasts 20 minutes to 1 hour: Cervix dilates Baby is pushed out through cervix and vagina head first Umbilical cord is clamped and cut Afterbirth: 30 minutes: Continuing uterine contractions expel the placenta from the uterus

37 Lactation Lactation is the production and secretion of milk by the mammary glands of the female Following birth the pituitary begins to secrete prolactin Prolactin stimulates the breasts to secrete milk For the first few days of the baby’s life the mother produces a thick yellow fluid called colostrum For as long as the baby suckles prolactin will continue to be produced and milk will continue to be secreted

38 Benefits of Breast-Feeding
Ideal balance of nutrients Contains antibodies – helps baby’s immunity Helps mother bond with the baby Helps the mother’s body recover from pregnancy Evidence suggests it may reduce the risk of developing breast cancer later in life

39 Birth Control Birth control is any mechanism whereby pregnancy is prevented Birth control can be carried out by the use of contraception or by carrying out an abortion after fertilisation has occurred Both methods of birth control are disallowed by the Catholic Church and abortion is illegal in many countries

40 Birth Control (continued)
There are four main types of contraception: Natural: involves not having intercourse or by using the rhythm of the menstrual cycle to predict when ovulation is likely to occur Mechanical: use of a condom or diaphragm to prevent entry of the sperm through the cervix Chemical: use of the contraceptive pill (contains oestrogen and progesterone) prevents ovulation Surgical: involves usually irreversible sterilisation of the male or female whereby the vas deferens or the fallopian tubes are cut or tied to prevent the sperm and the egg reaching each other

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