University:
Kentucky State University
Course:
BIO 111 | Principles of Biology
Academic year:

2024
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141

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22
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teespagmaxrtf

Chapter 45 Animal reproductive system Both asexual and sexual reproduction occurs in the animal kingdom • Reproduction is either sexual or asexual. • In sexual reproduction, the fusion of haploid gametes forms a diploid cell, the zygote. • The animal that develops from a zygote can give rise to gametes by meiosis. • Two types of gametes: • The female gamete (egg): large and nonmotile. • The male gamete (sperm): much smaller and motile. Both asexual and sexual reproduction occur in the animal kingdom • In asexual reproduction, new individuals are generated without the fusion of egg and sperm. • Reproduction relies entirely on mitotic cell division. Human male reproductive anatomy Seminal vesicle (behind bladder) (Urinary bladder) Prostate gland Bulbourethral gland Urethra Scrotum Erectile tissue of penis Vas deferens Epididymis Testis (Urinary bladder) Seminal vesicle (Urinary duct) (Rectum) Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland (Pubic bone) Erectile tissue Urethra Vas deferens Epididymis Testis Scrotum Glans Prepuce Penis Epididymis Gametogenesis Seminiferous tubule Testis • Gametogenesis: is the production of gametes. Primordial germ cell in embryo Cross section of seminiferous tubule Mitotic divisions Spermatogonial stem cell 2n Mitotic divisions Sertoli cell nucleus Spermatogonium • Spermatogenesis: the formation and development of sperm, is continuous and prolific in adult human males. 2n Mitotic divisions Primary spermatocyte 2n Meiosis I Secondary spermatocyte • Acrosome: a special vesicle which contains enzymes that help the sperm penetrate an egg. Lumen of seminiferous tubule Neck Tail Plasma membrane n n Meiosis II Spermatids (two stages) Early spermatid n n n n Differentiation (Sertoli cells provide nutrients) Midpiece Head Acrosome Nucleus Mitochondria Sperm cell n n n n Human female reproductive anatomy Ovaries Oviduct Follicles Funnel-like opening Corpus luteum Uterus Uterine wall Endometrium Cervix Vagina Mammary gland • Mammary glands are not part of reproductive system, but important for reproduction. • Mammary glands present in both sexes, but produce milk only in females. • Within the glands, small sacs of epithelial tissue secrete milk that drains into ducts which open at the nipple. • The breasts contain connective and fatty tissues in addition to the mammary glands. Gametogenesis Primary oocyte within follicle Ovary Primordial germ cell Growing follicle In embryo Mitotic divisions Gametogenesis: is the production of gametes. 2n Oogonium Mitotic divisions • Oogenesis: the development of mature oocyte (egg), is a prolonged process in human female. Primary oocyte (present at birth), arrested in prophase of meiosis I 2n First polar body Completion of meiosis I and onset of meiosis II n n Secondary oocyte, arrested at metaphase of meiosis II Ovulation, sperm entry Completion of meiosis II Mature egg containing a sperm head Second polar n body n Mature follicle Ruptured follicle Ovulated secondary oocyte Corpus luteum Fertilized egg Degenerating corpus luteum • Fertilization: is the fusion of haploid nuclei of the sperm and secondary oocyte, although the term is often used loosely to mean the entry of sperm head into the egg. • The raptured follicle left behind after ovulation develops into the corpus luteum. • Corpus luteum secretes estradiol as well as progesterone, a hormone that helps maintain the uterine lining during pregnancy. • If the egg is not fertilized, the corpus luteum degenerates, and a new follicle matures during the next cycle. Spermatogenesis and oogenesis differ in three significant ways: • Only in spermatogenesis do all four products of meiosis develop into mature gametes. In oogenesis, cytokinesis during meiosis is unequal, with almost all the cytoplasm segregated to a single daughter cell. Spermatogenesis and oogenesis differ in three significant ways: • Only in spermatogenesis do all four products of meiosis develop into mature gametes. In oogenesis, cytokinesis during meiosis is unequal, with almost all the cytoplasm segregated to a single daughter cell. • Spermatogenesis occurs throughout adolescence and adulthood. In contrast, mitotic divisions that occur in oogenesis in human females are thought to be completed before birth. Spermatogenesis and oogenesis differ in three significant ways: • Only in spermatogenesis do all four products of meiosis develop into mature gametes. In oogenesis, cytokinesis during meiosis is unequal, with almost all the cytoplasm segregated to a single daughter cell. • Spermatogenesis occurs throughout adolescence and adulthood. In contrast, meiosis divisions that occur in oogenesis in human females are thought to be completed before birth • Spermatogenesis produces mature sperm from precursor cells in a continuous sequence, whereas there are long interruptions in oogenesis. The interplay of tropic and sex hormones regulates mammalian reproduction • Endocrine control of reproduction begins with the hypothalamus, which secretes gonadotropin releasing hormone (GnRH). • GnRH directs the anterior pituitary to secrete the gonadotropins: • Follicle stimulating hormone (FSH). • Luteinizing hormone (LH). • The gonads produce and secrete three major types of steroid sex hormones: • Androgens (testosterone). • Estrogens (estradiol and progesterone). Functions of androgens in males • During embryogenesis, they direct the appearance of the structures directly involved in reproduction (ducts, seminal vesicles, external reproductive organs). • Induce formation of secondary sex characteristics. Cause voice to deepen. Cause facial and pubic hair to develop and muscles to grow. • Promote sexual behavior and sex drive as well as an increase in aggressiveness. Functions of estradiol in females: • Simulates breast and pubic hair development. • Influences female sexual behavior. • Induces fat deposition in breasts and hips. • Increases H2O retention and alter Ca2+ metabolism. Hormonal Control of the Male Reproductive System − Hypothalamus Gonadotropin releasing hormone − − Anterior pituitary FSH LH Follicle stimulating hormone Luteinizing hormone Leydig cells Sertoli cells Inhibin Spermatogenesis Testis Testosterone Negative feedback • These signals coordinate the activity of reproduction with growth, metabolism, homeostasis, and behavior. GnRH Negative feedback • Leydig cells produce testosterone and other hormones and local regulators, including oxytocin, renin, angiotensin, corticotropin-releasing factor, growth factors, and prostaglandins. Hormonal control of female reproductive cycles • Two reproductive cycles in human females: • Ovarian cycle. • Uterine (Menstrual) cycle. • In menstrual cycle, endometrium thickens and develops a rich blood supply before being shed through the cervix and vagina if pregnancy does not occur. • Menstruation: the cyclic shedding of the blood-rich endometrium from the uterus which occurs in a flow through the cervix and vagina. The ovarian cycle * • High level of estradiol increases the sensitivity of LH-releasing cells in the anterior pituitary to GnRH. ➢ which causes further release of LH. Several follicles begin to grow The uterine (menstrual) cycle Low LH and FSH Stimulated by LH -ve FSH, LH Progesterone, estradiol After ovulation Enlargement of blood vessels & growth of endometrial glands • Endometriosis: is a disorder in which some cells of the uterine lining migrate to an abdominal location that is abnormal or ectopic (away from a place). • In this abdominal location that can be an oviduct, ovary or large intestine, the ectopic tissue responds to hormones in the bloodstream. • Like the uterine endometrium, the ectopic tissue swells and breaks down during each ovarian cycle. Menopause Menopause: the cessation of ovulation and menstruation after about 500 cycles in a woman. • During this interval, the ovaries lose responsiveness to FSH and LH resulting in a decrease in estradiol production. Menstrual versus estrous cycles • The estrous cycle is a reproductive cycle characteristic of female mammals except humans and certain other primates, in which the non pregnant endometrium is reabsorbed rather than shed, and sexual response occurs only during the period surrounding ovulation, known as estrus. • The length, frequency and nature of estrous cycle vary widely among mammals.

Chapter 45 Animal Reproductive System

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