1 Sylvia S Mader Immagini e concetti della

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Sylvia S. Mader Immagini e concetti della biologia 2 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

C 11 Reproduction and development 3 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Reproduction in animals is varied Both asexual and sexual reproduction occur among animals. Asexual reproduction (some invertebrates, sponges, cnidarians, flatworms, annelids and echinoderms): single parent gives rise to offspring that are identical to the parent. 4 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Reproduction in animals is varied Sexual reproduction (some invertebrates, earthworms, plants and animals): sex cells, or gametes, produced by the parents unite to form a genetically unique individual. Copulation is the sexual union to facilitate the reception of sperm and to protect sperm from drying out. 5 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The male reproductive system The gonads are the organs that make gametes. Testes are male gonads. The human male reproductive system also includes epididymides, vasa deferentia, ejaculatory duct and urethra. 6 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The human reproductive system The penis is the organ of sexual intercourse. The semen is composed of sperm and secretions from the seminal vesicles, prostate gland bulbourethral glands. Orgasm (sexual climax) is the discharge of accumulated sexual tension resulting from ejaculation of semen and ending in rhythmic muscular contractions in the pelvic region. 7 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Production of sperm Testes contain seminiferous tubules where spermatogenesis occurs. Seminiferous tubules produce: • Sperm • Interstitial cells 8 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Spermatogenesis is the process by which spermatozoon (male sperm cell) are produced through meiosis. 9 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Sex hormones The anterior pituitary secretes hormones that: 1. trigger the spermatogenesis, as the follicle-stimulating hormone (FSH); 2. control the production of testosterone, as the luteinizing hormone (LH). Testosterone is a steroid hormone that influences the sex organ function, sperm maturation and male secondary sex characteristics. 10 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The female reproductive system The female gonads are the ovaries and the reproductive system also includes oviducts, uterus and vagina. 11 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The female reproductive system The clitoris is a sexual organ located near above the opening of the urethra. Unlike the penis, the clitoris is the female’s most sensitive sexual organ. The female external genital area also includes the vaginal opening, labia minora and labia majora. Female orgasm culminates in uterine and oviduct contractions. 12 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Production of oocytes The production of an egg occurs as an ovarian follicle (aggregation of cells) changes from primary to secondary to a vesicular follicle. 13 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Production of oocytes Before ovulation, the oocyte maturation requires the oogenesis, a meiotic process whose completion is triggered by the fertilization by a spermatozoon. When the two gamete nuclei melt, the zygote (46 chromosomes) forms. 14 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Female sex hormones Ovaries produce: • Estrogen: promotes the development of female secondary sexual characteristics. • Progesterone: involved in the menstrual cycle, pregnancy and embryogenesis. 15 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The ovarian cycle starts with the production of folliclestimulating hormone (FSH) in the anterior pituitary. • FSH causes maturation of a follicle that secretes estrogen and some progesterone. • During the luteal phase, LH promotes development of the corpus luteum. 16 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The uterine cycle starts with menstruation, the endometrium cleavage occurs and the blood vessels break. • During the proliferative phase estrogen causes uterine lining to thicken. • Progesterone causes the lining to become secretory. 17 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

The ovarian cycle 18 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Sexually transmitted diseases AIDS: disease of the immune system caused by the human immunodeficiency virus (HIV). Herpes Simplex Virus (HSV): transmitted during reactivation phase of the virus. Human Papilloma Virus (HPV): causes infections of the skin or mucous membranes. Other STD are chlamydial infection, syphilis and gonorrhea. 19 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Contraceptives Numerous birth control methods are available before and after sexual intercourse. 20 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Technologies to help fertility Assisted reproductive technologies include: • artificial insemination by a donor • in vitro fertilization • gamete intra-fallopian transfer • intra-cytoplasmic sperm injection 21 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Embryonic development The first step of the embryogenesis is the cellular stages. The zygote undergoes rapid mitotic divisions. This cleavage results in a multicellular mass (called morula) and then a singlelayered blastula forms. 22 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Embryonic development The second embryogenesis step is the tissue stages. The gastrulation leads to the formation of a three-layered structure called gastrula 23 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Gastrulation A mature gastrula has three germ layers: ectoderm, mesoderm and endoderm. 24 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Gastrulation The three germ layers will develop into specific organs. 25 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Extraembryonic membranes The amnion protects and moisturize the embryo in a sac filled with amniotic fluid. The yolk sac contains the source of food until hatching. The chorion is below the shell and provides gas exchanges with the outside air. The allantois collects metabolic wastes of the embryo. 26 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Embryonic development spans the first two months of the gestation, from fertilization through the acquisition of organ systems. 27 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Embryonic development 28 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Embryonic development Eight weeks after fertilization the embryo is completed and becomes fetus. It has recognizable external features. 29 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Fetal development occurs after the third month. Exchanges at the placenta supply the fetus with O 2 and nutrients and collect CO 2 and wastes. During the third and fourth month, the skeleton ossifies and the fetus sex becomes distinguishable. During the fifth, sixth and seventh month fetal movements begin, the fetus continues to grow and gain weight. 30 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Fetal development Nine months after the fertilization, the pregnancy ends with the birth of the newborn. 31 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

Childbirth 1. Dilatation: uterine contractions begin. 2. Expulsion: uterine contractions occur every 1 -2 minutes. The baby is born and the umbilical cord is cut. 3. Dislodging: uterine muscle contractions shrink the uterus and dislodge the placenta, which is expelled. 32 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018