Reproductive system 1.pdf

Page 4: Human Reproductive System Essential features of human reproduction o Liberation of an ovum at a specific time o Internal fertilization of the ovum by spermatozoa o Transport of the fertilized ovum to the uterus o Implantation of the blastocyst in the uterus o Formation of a placenta and main...

Page 4: Human Reproductive System Essential features of human reproduction o Liberation of an ovum at a specific time o Internal fertilization of the ovum by spermatozoa o Transport of the fertilized ovum to the uterus o Implantation of the blastocyst in the uterus o Formation of a placenta and maintenance during gestation o Birth of the child and maternal organ return Page 5: Unfertilized egg The corona radiata is an outer layer made up of follicular (granulosa) cells that form around a developing oocyte in the ovary and remain with it upon ovulation. The zona pellucida is a specialized extracellular matrix surrounding the developing oocyte Page 11: Fetal Reproductive System Development Reproductive system development post-fertilization The development of the reproductive systems within the fetus begins soon after fertilization of the egg, at 3 weeks of development, Germ cells migrate from the yolk sac to the genital ridge. Females as the "fundamental" sex in development without much chemical prompting, al fertilized eggs would develop into females. Page 13: Sexual Organs Development (SRY Protein) Bipotential tissue: In both male and female embryos, the same group of cells has the potential to develop into either the male or female gonads. The SRY protein actively recruits other genes that begin to develop the testes (4-8 weeks) and suppresses genes that are important in female development. As part of this SRY-prompted cascade, germ cells in the bipotential gonads differentiate into spermatogonia. Without SRY, different genes are expressed, oogonia form, and primordial follicles develop in the primitive ovary. Spermatogonia: A large unspecialized germ cell that in spermatogenesis divides by mitosis to form primary spermatocytes. To become a male you need the SRY gene, because females do not have a Y chromosome, they do not have the SRY gene. Page 14: Male Reproductive System Development Scrotum formation at 9 weeks Testosterone induces development of the mesonephric (Wolfian) duct to form the epididymis, vas deferens and seminal vesicles. During this stage of development, the testis moves from the genital ridge across the pelvis to lie at the internal inguinal ring. Leydig cells' testosterone secretion Testosterone can influence tissues that are bipotential to become male reproductive structures. For example, with exposure to testosterone, cells that could become either the glans penis or the glans clitoris form the glans penis. Cryptorchidism: One or both of testes does not descend (Occurs in 3% of full term and 30% of premature births Page 19: Oogenesis Creation of an egg in the female fetus Oogenesis starts in the fetus at around 7 weeks' gestation ,when primordial germ cells (PGC) colonize the newly formed ovary. They are now referred to as oogonia. Oogonia undergo mitosis. The number of oogonia is estimated to increase rapidly from about 43,000 at 7 weeks' gestation to about 140,000 at 9 weeks' gestation to about 7 million at 14–15 weeks' gestation. After the seventh month of embryonic development, the number of germ cells drops precipitously. Most oogonia die during this period, while the remaining oogonia enter the first meiotic division. These latter cells, called the primary oocytes, progress through the first meiotic prophase I stage, at which point they are maintained until puberty. Goes from Oogonium (granulosa cells). This is prenatal. Mitosis and growth. to Page 21: Reproductive System Development Minimal changes in the reproductive system between infancy and puberty Page 22: Gonadal Changes during Puberty Puberty-related gonadal changes In children, LH and FSH levels are insufficient to initiate gonadal function Between 9-12 years blood levels of LH and FSH increase High levels of LH, FSH initiate gonadal development Nocturnal GnRH pulsatility (LH secretion) preceded phenotypic changes by several years First phenotypic changes: breast development/ testicular enlargement Page 25: Folliculogenesis Process of ovarian follicle growth and development Page 26: Changes during Puberty (Tanner Stages) Puberty First change: At age 8, the hypothalamus increases its production of gonadotropin-releasing hormone (GnRH) Second change: GnRH triggers the anterior pituitary to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH) Third change: LH and FSH trigger testosterone production in the testes and estrogen production in the ovaries. Testosterone release leads to Spermatogenesis. Fourth change: Effects of hormone release: Leads to Penis and scrotum grow, facial hair grows, larynx elongates leading to lowering voice. Shoulders broaden, Body; armpit; and pubic hair grow, musculature increases body-wide. Estrogen release leads to: breasts develop and mature, hips broaden, pubic hair grows. As well as folliculogenesis which is the process of growing and developing of ovarian follicle in the ovary. Fifth change: Before puberty, the hypothalamus and pituitary are sensitive to negative feedback signals from testosterone and estrogen. During puberty, the sensitivity of the hypothalamus and pituitary to this negative feedback decreases to levels typically seen in adults. This change allows an increase in production of testosterone and estrogen that stimulates the development of secondary sex characteristics. Puberty and Factors Affecting Onset Factors affecting puberty onset: genetics, environment, psychological stress Nutrition's impact on puberty onset: better nutrition led to decreased age of menarche in girls in the US Link between puberty onset and stored fat, especially in girls but is present in both sexes o Leptin hormone's role in determining menarche Delay in puberty onset in lean and highly active girls like gymnasts Male Reproductive System Hormonal Control Hypothalamus secretes Gonadotropin releasing hormone (GnRH) Anterior pituitary secretes FSH and LH FSH stimulates Sertoli cells to secrete Androgen Binding Protein (ABP) and inhibin LH causes interstitial cells to secrete testosterone ABP and testosterone stimulate spermatogenesis Negative feedback control by increased testosterone and inhibin Anatomy Gonads, ducts, sex glands, and supporting structures Functions of various parts like penis, testis, epididymis, scrotum, prostate, seminal vesicle, urethra Spermatogenesis Sperm forming cells go through two meiotic divisions Each of four spermatids develop into a sperm Second meiosis division give four spermatids, each with 23 single stranded chromosomes First meiosis division give two secondary spermatocytes, each with 23 chromosomes that become double stranded. Primary spermatocyte with 2n=46 chromosomes Spermatogonium with 2n=46 chromosomes multiply by mitosis Seminiferous tubules contain: Sperm forming cells, Sertoli cells (supporting cells) Interstitial or Leydig cells in between tubules secrete testosterone Sertoli cells; extend from basement membrane to lumen: form blood-testis barrier support developing sperm cells produce fluid & control release of sperm into lumen secrete inhibin which slows sperm production Semen Mixture of sperms and seminal fluid 60% from seminal vesicles, 30% from prostate. Slightly alkaline, milky appearance and sticky Contains nutrients, clotting proteins & an antibiotic to protect the sperms Typical ejaculate is 2.5 to 5 ml in volume Normal sperm count is 50 to 150 millions/mL Actions of many sperm are needed for one to enter If less than 20 millions/mL, sterile Scrotum and Testes Scrotum's role in temperature regulation for sperm survival. Sperm survival requires 2 -3 degrees lower temperature than core body temperature Muscle in scrotum: Elevates testes on exposure to cold & during arousal Warmth reverses the process The scrotum is sac of loose skin, fascia & smooth muscle divided into two pouches by a septum. Fascia is a thin casing of connective tissue that surrounds and holds every organ, blood vessel, bone, nerve fiber and muscle in place. The tissue does more than provide internal structure; fascia has nerves that make it almost as sensitive as skin Testes: Paired oval glands measuring ~2 in by ~1in Surrounded by dense white capsule, tunica albuginea About 200 - 300 compartments called lobules (separated by septum) Each lobule is filled with 2 or 3 seminiferous tubules where sperm are formed Sperm Morphology Adaptations of sperm for fertilization and reaching the egg. Head contains DNA and the acrosome with hyaluronidase enzyme for penetrating the egg Midpiece contains mitochondria to form ATP for energy Tail is flagellum used for locomotion Male Glands Functions and secretions of seminal vesicles, prostate, and Cowper’s glands Seminal Vesicles: Secrete 60% of clear, alkaline seminal fluid, with fructose sugar, ATP and prostaglandins for normal sperm nutrition & function Chemicals for coagulation of semen Prostate: Secretes 30% of milky, slightly acidic seminal fluid with an antibiotic to kill bacteria Cowper’s Glands: Secrete clear, alkaline mucus to buffer and lubricate urethra Penile Erection Blood is supplied to the penis by the cavernosal arteries (branches of the penile artery), which drain directly into the cavernous space. The cavernous space (corpus cavernosum) contains sinusoids that are surrounded by trabecular smooth muscle. Upon sexual stimulation, the increase in parasympathetic activity results in nitric oxide (NO) synthesis and dilatation of the cavernosal arteries and increased blood flow into these vascular spaces. At the same time, relaxation of the trabecular smooth muscle by NO increases the compliance of the cavernous spaces, which facilitates entry of the blood. The increase in blood volume and the compression of the relaxed trabecular muscle results in collapse of the venules and obstruction of venous outflow. Once this occurs, a rigid erection occurs Role of nitric oxide in dilatation of cavernosal arteries and trabecular smooth muscle relaxation Emission and Ejaculation Emission: Muscle contractions close sphincter at base of bladder Fluids propelled through vas deferens, seminal vesicles, & ejaculatory ducts into bulb of penis Prostatic fluid secreted into urethra. Ejaculation: Sympathetic nervous system reflex Skeletal muscles squeeze semen out through urethra