11.4 Reproduction Essential idea: Sexual reproduction involves the development and fusion of haploid gametes.

Understandings Statement Guidance 6.6 U.1 A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone. 6.6 U.2 Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty. 6.6 U.3 Estrogen and progesterone cause pre-natal development of female reproductive organs and female secondary sexual characteristics during puberty 6.6 U.4 The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones. 11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. 11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm. 11.4 U.3 Fertilization in animals can be internal or external Fertilization involves the acrosome reaction, fusion of the plasma membrane of the egg and sperm and the cortical reaction. 11.4 U.4 Fertilization involves mechanisms that prevent polyspermy 11.4 U.5 Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy 11.4 U.6 HCG stimulates the ovary to secrete progesterone during early pregnancy. 11.4 U.7 The placenta facilitates the exchange of materials between the mother and fetus. 11.4 U.8 Estrogen and progesterone are secreted by the placenta once it has formed. 11.4 U.9 Birth is mediated by positive feedback involving estrogen and oxytocin.

Applications and Skills Statement Guidance 6.6 A.1 The use in IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy. 6.6 A.2 William Harvey’s investigation of sexual reproduction in deer 6.6 S.1 Annotate diagrams of the male and female reproductive system to show names of structures and their functions 11.4 A.1 The average 38-week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals. 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis. 11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions.

11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Oogenesis Oogonium (2n) divide by mitosis to produce many oogonia Each oogonia grows within the follicle of cells. Meiosis begins but stops at prophase I. The oogonia are found within the primary follicles. There are approx 400,000 primary follicles present in the ovary prior to puberty. Primary Follicles (prophase I) may develop to secondary follicles (metaphase II) under the influence of FSH. Note that the first polar body ( haploid set chromosomes) does not progress beyond metaphase II. The Oocyte does not progress to the end of meiosis unless fertilization takes place.

11.4 U.1 Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation. Spermatogenesis It is a process by which spermatogonia are transformed into spermatozoa. It begins at puberty.

Spermatogenesis creates 4 small gametes 11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm. Oogenesis creates 1 gamete with large amounts of cytoplasm and organelles Spermatogenesis creates 4 small gametes

The male sex cell is designed to deliver just DNA. 11.4 U.2 Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm. Spermatogenesis The male sex cell is designed to deliver just DNA. The sperm cell contains no cytoplasm and delivers no organelles

11.4 U.3 Fertilization in animals can be internal or external Sexual Reproduction – Frogs External fertilization

11.4 U.3 Fertilization in animals can be internal or external External Fertilization Internal Fertilization Egg shed by female, fert. by male in water Environmental cues / courtship behavior Large # gametes  low survival Eg. fish, amphibians Sperm deposited in female reprod. tract Cooperative behavior Dry environment Fewer gametes, fewer zygotes  greater survival   External Devel. Tough eggshell Eg. reptiles, birds, platypus Internal Devel. High parental care Eg. placentals, sharks, some reptiles

Sperm maneuvers through cells of the corona radiata 11.4 U.4 Fertilization involves mechanisms that prevent polysperm Sperm maneuvers through cells of the corona radiata Sperm use their acrosome enzymes to digest the zona pellucida 1st sperm through attaches to the plasma membrane and enters the cell This causes the cortical reaction where cortical granules form an impenetrable wall that will allow no other some to enter

Zygote the fused sperm and egg cell Zygote the fused sperm and egg cell. This cell undergoes rapid mitotic cell division, but these do not increase the size of the zygote Morula Cleavage produces a solid sphere of cells, still surrounded by zona pellucida. Blastocyst At 4.5 to 5 days, cells have developed into a hollow ball, & enters the uterus.

Human embryonic development Conception: in oviduct 11.4 U.5 Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy . Human embryonic development Conception: in oviduct Implantation: in uterus Hormones: Human Chorionic Gonadotropin (hCG): maintain estrogens in early pregnancy; pregnancy test Human gestation (pregnancy) = 40 weeks Egg lodged in oviduct = ectopic (tubal) pregnancy

Formation of Zygote Cleavage starts Cleavage continues Ovary Fertilization occurs The blastocyst implants Uterus Ovulation Endometrium From ovulation to implantation

Early Postfertilization Events Endo- metrium Inner cell mass Cavity Trophoblast Blastocyst Implantation of blastocyst

6.6.U8 Many hormones are involved in the menstrual cycle Follicle stimulating hormone (FSH): causes a follicle to become dominant Triggers increased estrogen LH causes ovulation (egg release to occur) Estrogen causes thickening of uterine wall Progesterone maintains uterine wall Cycle ends in pregnancy or decreased progesterone levels cause menstruation to begin

Prevents breakdown of endometrium so embryo can grow into a fetus 11.4 U6 HCG stimulates the ovary to secrete progesterone during early pregnancy. Human Chorionic Gonadotrophin (HCG) Implantation of blastocyst: secretion of human chorionic gonadotrophin (hCG) into maternal blood. The concentration doubles every 2-3 days and reaches a peak at 8-10 wk's. d) hCG targets ovary and corpus luteum, secretes high levels od progesterone and estrogen Inhibits FSH & LH secretion from pituitary. (no new ovualtion). Prevents breakdown of endometrium so embryo can grow into a fetus

Human Chorionic Gonadotrophin (HCG)

11.4 U.7 The placenta facilitates the exchange of materials between the mother and fetus. Functions of the placenta: 1. Transfer gases 2. Transport nutrients 3. Excretion of wastes 4. Hormone production – temporary endocrine organ – estrogen and progesterone 5. Formation of a barrier – incomplete, nonselective – alcohol, steroids, narcotics, anesthetics, some antibiotics and some organisms can cross

Placenta The placenta grows from the embryonic tissue. It attaches to the endometrium of the uterus. Unlike other mammals the human placenta invades the endometrium very deeply.

11.4 U.8 Estrogen and progesterone are secreted by the placenta once it has formed. As the placenta forms and grows, it develops the ability to produce hormones. Between weeks 6-9 of pregnancy, the placenta takes over from the ovaries as the main producer of progesterone and estrogen, vital to the establishment of pregnancy. Progesterone has many functions during late pregnancy, including: Preventing womb muscles contracting until labor Preventing lactation until after pregnancy Strengthening pelvic muscles for labor Estrogen Stimulate growth of myometrium (uterine muscles) and oxytocin receptors. Stimulate mammary gland development.

11.4 U.9 Birth is mediated by positive feedback involving estrogen and oxytocin.

11.4 A.1 The average 38-week pregnancy in humans shows correlation between animal size and the development at birth for other mammals. Altricial “requiring nourishment”organisms which are incapable of moving around on their own soon after hatching or being born Precocial refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. These are usually have large body masses.

Structure of the Testis 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis Structure of the Testis Each testis is composed of a tubular structure. It is from these seminiferous tubules where sperm are produced. From puberty these tubules will produce sperm cells throughout the life of the man. Note the basement membrane which surrounds each tubule. Inside the basement membrane can be seen various cells which are the stages of the developing spermatozoa.

Leydig cells are responsible for the production of testosterone 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis Micrograph of testis This light micrograph shows the cross section of seminiferous tubules, blood vessels and also the interstitial Leydig cells. Leydig cells are responsible for the production of testosterone

Please Sing a Song for Me 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis Each testis is composed of a tubular structure. It is from these seminiferous tubules that sperm are produced. From puberty these tubules will produce sperm cells throughout the life of the man. Note the basement membrane which surrounds each tubule. Inside the basement membrane can be seen various cells which are the stages of the developing spermatozoa. Between the seminiferous tubules are groups of cells called interstitial or Leydig cells that produce the male sex hormone, testosterone. Please Sing a Song for Me

This image is of the wall of a seminiferous tubule. 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis This image is of the wall of a seminiferous tubule. a) Basement membrane b) Germinal epithelium (2n) which divide by mitosis to produce c) Spermatogonium (2n) which grow and enlarge d) Primary spermatocytes (2n) go through Meioses I (n) converting into Secondary Spermatocytes . e) Secondary Spermatocytes go through Meiosis II to produce spermatids (n) *Sertoli cells nourish and allow the spermatids to differentiate to spermatozoa. These are released into the lumen

Spermatogonium are found at or near the basement membrane. 11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis Spermatogenesis Spermatogonium are found at or near the basement membrane. •They have a high rate of cell division by mitosis to produce spermatogonia. •Primary Spermatocytes are large diploid cells which form from rapidly growing spermatogonia. •The Primary spermatocytes separate the homologous pairs of chromosomes in meiosis I(reduction division) to form the haploid Secondary Spermatocytes. •The spermatids are formed from the separation of the sister chromatids in meiosis II.

Spermatogenesis (continued) The spermatids are found in association with the sertoli cells which nourish the spermatids as they differentiate into spermatozoa. •The rate of spermatozoa is high and continuous throughout the life on the sexually mature male. •The average number of spermatozoa in ejaculated semen is 32 x 106 ml-1

11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis

Hormonal Control of Spermatogenesis

11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions Structure of Sperm The acrosome vesicle contains the enzymes required to digest its way though the ovum wall. Haploid nuclei (n=23) containing the paternal chromosome s The 'mid-section' of the sperm contains many mitochondria which synthesis ATP to provide the energy for the movement of the tails structure. Protein fibers add longitudinal rigidity and provide a mechanism of propulsion.

11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions Structure of Sperm

11.4 S.1 Annotation of diagrams of seminiferous tubule and ovary to show the stages of gametogenesis Ovary structure

A) Primary follicles in the medulla region (center) each one contains an oogonia arrested at prophase I. b) Sequence showing the development of the primary follicle (PI) into the secondary follicle (MII). c) The mature secondary follicle is also known as a graffian follicle. The size of this follicle will make the wall of the ovary bulge prior to ovulation. Note the exclusion of the 1st polar body that will degenerate

d) Ovulation, with the rupture of the follicle wall the oocyte is released into the oviduct. e) The Oocyte moves into the oviduct. This oocyte is at metaphase II and will complete meiosis only with fertilization. f) The Corpus luteum forms from the now empty secondary follicle. This structure is responsible for the production of higher levels of progesterone.

Cortical granules involved in the acrosome reaction at fertilization. 11.4 S.2 Annotation of diagrams of mature sperm and egg to indicate functions Mammalian Oocyte During follicle development unequal division of the cell during meiosis produces the 1st polar body that can be seen outside the plasma membrane. This will not develop be continues to be part of the follicle. Zona pellucida surrounds the structure and is composed of glycoproteins. Cortical granules involved in the acrosome reaction at fertilization. Follicular cells found round the outside are the follicle.

https://www.youtube.com/watch?v=gZ5q9dzEJ6s Polyspermy – Harry Potter Polyspermy Polyspermy – https://www.youtube.com/watch?v=7G2rL5Cutd4 Menstrual summary https://www.youtube.com/watch?v=l_wX285vrrU Oogenesis https://www.youtube.com/watch?v=gTSUWHWe70Q