The Reproductive System PDF

The Reproductive System Ms. Colette Gouveia Lecture 14  Reproduction The primary function of the productive system is to produce the special cells (Ova and Sperms) necessary to propagate the next generation. There are two forms of reproductive system: 1. Fema...

The Reproductive System Ms. Colette Gouveia Lecture 14  Reproduction The primary function of the productive system is to produce the special cells (Ova and Sperms) necessary to propagate the next generation. There are two forms of reproductive system: 1. Female reproductive system (produces ova) 2. Male reproductive system (produces sperms) Both reproductive systems have primary sex organs called gonads (ovaries in female and testes in male). The gonads produce sex cells called gametes. Female gametes are called oocytes. Male gametes are called sperms. Reproduction is accomplished when the egg cell (female gamete) is fertilized by the sperm cell (male gamete) The Male Reproductive System The Male Reproductive System The organs of the male reproductive system consist of the testes and a number of ducts (tubes), and glands. In the man, the reproductive role is to produce viable sperm, and to deliver the sperm to the female reproductive system.  Male Reproductive Structures External genitalia Penis contains erectile tissue, deposits sperm into vagina of female Urethra conducts semen to exterior Scrotum surrounds testes  Male Reproductive Structures Internal genitalia Ductus deferens conduct sperm between epididymis and prostate Seminal gland secretes fluid making up much volume of semen. Prostate secretes fluid and enzymes Bulbo-urethral gland a pair of pea- sized glands that produce a clear mucus to neutralize acidic urine and lubricate the urethra during ejaculation it also lubricate tip of penis Epididymis is the site of sperm maturation  Main Structures in the Male Reproductive System The SPERM are cells that have a tail, head, and neck. The sperm are produced in the TESTICLES. The testes produce sperm throughout the life of the male. (Unlike the female, who are born with all the eggs they will ever have.) On the top of the testicle is a comma- shaped organ called the EPIDIDYMIS. This structure stores and propels the sperm toward the urethra during ejaculation. Sperm transport relies on ducts, glands, and related structures of the scrotum and testes Path of sperm Main Structures in the Male Reproductive System The testes (singular, testis), also called testicles are paired oval glands that descend into the SCROTUM. Each is approximately 5 cm long; 3 cm wide; 2.5 cm thick and weighs 10–15 g At the onset of puberty, the testes produce TESTOSTERONE. This is the male sex hormone. Testosterone stimulates and promotes Main Structures in the Male Reproductive System Scrotum and associated structures 1. Scrotal cavities House the testes Scrotal septum separates right and left cavities – Marked by a raised thickening (raphe of scrotum) in the scrotal surface 2. Dartos muscle Smooth muscle in the skin of the scrotum Elevates testes and wrinkles scrotal surface 3. Cremaster muscle Contracts to pull testes closer to body during  Main Structures in the Male Reproductive System Scrotum and associated structures 1. Spermatic cords Contains nerves, blood and lymph vessels, and the vas deferens (a coiled tube that carries sperm out of the testicle). Extend through the inguinal canals between testes and abdominopelvic cavity and connects to the testicle in the scrotum (external sac). Each contains layers of fascia and muscle – Layers enclose the ductus deferens, blood vessels, nerves, and lymphatic vessels 2. Superficial inguinal ring Entrance to the inguinal canal 3. Inguinal canal Extends from the inguinal ring to the scrotal cavity Presence of spermatic cords creates weak points in the abdominal wall – Inguinal hernias Main Structures in the Male Reproductive System Epididymis Start of the male reproductive tract Coiled tube bound to posterior border of each testis Lined with pseudostratified columnar epithelium Sperm undergo functional maturation here Regions of the epididymis Head – Receives spermatozoa from efferent ductules Body – Extends inferiorly along the posterior surface of the testis Tail – Starts near the inferior border of the Main Structures in the Male Reproductive System Ductus deferens (or vas deferens) 40–45 cm (160–16 in.) long Passes through inguinal canal as part of spermatic cord Transports sperm from the epididymis Can store sperm for several months in a state of suspended animation Main Structures in the Male Reproductive System Seminal glands (also called seminal vesicles) Sandwiched between the posterior wall of the urinary bladder and the rectum Secretion ejected by smooth muscle lining gland Stimulates flagellum movement in sperm First step of capacitation Produce ~60 percent of semen volume Semen Contains sperm and seminal fluid Fluid is a combination of secretions from: Seminal glands Nurse cells Epididymis Prostate Bulbo-urethral glands Main Structures in the Male Reproductive System Prostate Encircles the proximal urethra as it leaves the bladder Produces 20–30 percent of semen volume Secretions contain seminalplasmin - Antibiotic that may help prevent urinary tract infections in males Bulbo-urethral glands (Cowper’s glands) Located at the base of the penis Duct of each gland empties into the urethra Secrete thick, alkaline mucus - Helps neutralize acids in the urethra Main Structures in the Male Reproductive System Accessory organs secrete various fluids into the reproductive tract Seminal glands, prostate, and bulbo- urethral glands secrete various fluids into ejaculatory duct and urethra Urethra passes through the penis to exit the body. From the epididymis, sperm enters the vas deferens (ductus deferens). This structure transports sperm to the urethra. During its trip toward the outside world, sperm picks up fluids from the Cowper's glands, also known as the bulbourethral glands,  Spermatogenesis This word means to make or produce sperm. Involves three processes 1. Mitosis and cell division (cytokinesis) – Process producing two identical daughter cells – Since daughter cells contain 23 pairs of chromosomes (or two sets of chromosomes), they are called diploid. – In seminiferous tubules, stem cells undergo mitosis to form two daughter cells. – One cell remains in contact with the tubule basement membrane. – The other is a primary spermatocyte 16 days from spermatogonium to primary  Spermatogenesis This word means to make or produce sperm. Involves three processes 2. Meiosis – Special form of cell division involved in gamete production. – Two cycles of cell division (meiosis I and II) – Produces four haploid (haplo, single) cells, each with 23 individual chromosomes. – Synapsis Corresponding material and paternal  Spermatogenesis Meiosis I Each primary spermatocyte begins with 46 chromosomes diploid Daughter cells produced are called secondary spermatocytes – Each contains 23 chromosomes haploid – Each chromosome has pair of duplicate chromatids 24 days from primary spermatocyte to secondary spermatocyte Meiosis II Secondary spermatocytes divide to produce spermatids – Each spermatid contains 23 chromosomes – Each primary spermatocyte produces four spermatids  Spermatogenesis 3. Spermiogenesis – Differentiation of immature male gametes into physically mature spermatozoa Physical maturation of sperm Each spermatid matures into a single sperm 24 days from spermatid to sperm  Structure of a Sperm Specialized to deliver chromosomes to female gamete Acrosome - Membranous compartment containing enzymes essential to fertilization Head - Contains nucleus with densely packed chromosomes Neck - Contains both centrioles of the original spermatid - Microtubules of distal centriole are continuous with those of the middle piece and tail Middle piece - Contains mitochondria to provide ATP for tail movement Tail (flagellum)- Whiplike  Activation of Sperm Sperm released from testes are physically mature Immobile and incapable of fertilizing an oocyte Other parts of male reproductive system are responsible for functional maturation, nourishment, storage, and transport of spermatozoa. Capacitation Process enabling sperm to become motile and fully functional Usually occurs in two steps 1. Sperm become motile when mixed with seminal gland secretions 2. Sperm become capable of fertilization when exposed to the female reproductive tract  The Penis The PENIS is the male sex organ. A slightly enlarged region at the tip of the penis is called the GLANS. The glans of the penis is covered by a fold of skin called the PREPUCE or FORESKIN. Two functions of the penis 1. Conduct urine to the exterior 2. Introduce semen into the female’s vagina during sexual intercourse  Hormonal Interactions Testosterone plays a key role in establishing and maintaining male sexual function Hypothalamus - Secretes gonadotropin-releasing hormone (GnRH) – Released at a steady rate and pace Targets the anterior lobe of the pituitary gland Anterior lobe of the pituitary Responds by producing two gonadotropins – Luteinizing hormone (LH)  Hormonal Interactions Luteinizing hormone (LH) Targets the interstitial cells of the testes – Interstitial cells secrete testosterone and other androgens Testosterone levels are regulated by negative feedback – High testosterone level inhibits release of GnRH Follicle-stimulating hormone (FSH) Targets nurse cells of seminiferous tubules Nurse cells – Promote spermatogenesis and spermiogenesis – Secrete androgen-binding protein (ABP) o Stimulates maturation of – Secrete inhibin o Inhibits FSH o Provides feedback control of spermatogenesis  Hormonal Interactions Peripheral effects of testosterone Maintains libido (sexual drive) and related behaviors Stimulates bone and muscle growth Establishes and maintains male secondary sexual characteristics Maintains accessory glands and organs of the male reproductive system  Procedures Vasectomy A surgery where surgeon cuts (Ligation)the vas deferens (tube connecting the testis to the urethra). This blocks mature sperm from being able to leave the penis. Castration Castration is the removal or destruction of the testicles or ovaries, or the use of drugs to suppress their function: Surgical castration: The surgical removal of the testicles (orchiectomy) or ovaries (oophorectomy). Chemical castration: The use of drugs to deactivate the testes. Castration can be used to stop the production of sex hormones, which may stop the growth of The Female Reproductive System Anatomy of Female Reproductive System The female reproductive system is composed of internal and external organs of reproduction. The female reproductive system (or female genital system) contains two main parts: the uterus, which hosts the developing fetus, produces vaginal and uterine secretions, and can pass sperm through to the Fallopian tubes; and the ovaries, which produce the female's egg  Overall Functions The overall functions of the female reproductive system Produces sex hormones Produces functional gametes Protects and supports developing embryo Maintains growing fetus Nourishes newborn infant  Female External Organs The external organs are collectively known as GENITALIA. This is for both sexes. Female External Reproductive Organs Female external genitalia Vulva- outer genitals and urethra - The external genital organs include the mons pubis, labia majora, labia minora, Bartholin glands ,clitoris and urethra. Female internal genitalia - Ovaries, uterine tubes, uterus, and vagina Mammary gland of breast - Produces milk to nourish infants The external genital organs have three main functions: 1. Enabling sperm to enter the body 2. Protecting the internal genital organs from  Female External Reproductive Organs The mons pubis is a rounded mound of fatty tissue that covers the pubic bone. It contains oil secreting (sebaceous) glands that release substances that are involved in sexual attraction (pheromones) The labia majora (large lips) are relatively large, fleshy folds of tissue that enclose and protect the other external genital organs. They contain sweat and sebaceous glands, which produce lubricating secretions. During puberty, hair appears on the labia majora. The labia minora (small lips) can be very small or up to 2 inches wide. The labia minora lie just inside the labia majora and surround the openings to the vagina and urethra. A rich supply of blood vessels gives the labia minora a  Female External Reproductive Organs The clitoris, located between the labia minora at their upper end, is a small protrusion that corresponds to the penis in the male. It is very sensitive to sexual stimulation and can become erect. Stimulating the clitoris can result in an orgasm. The area between the opening of the vagina and the anus, below the labia majora, is called the perineum. It varies in length from almost 1 to more than 2 inches (2 to 5 centimeters) The opening to the vagina is called the introitus. The vaginal opening is the entryway and the exit Bartholin glands (located beside the vaginal opening) secrete a thick fluid that supplies lubrication for intercourse.  Female Reproductive Structures The internal genital organs form a pathway (the genital tract). This pathway consists of the following: 1. Vagina (site of sperm deposition) - Birth canal during delivery - Passageway for fluids during menstruation 2. Female reproductive tract - Uterus, where an embryo can develop into a fetus. Also, site of exchange between maternal and embryonic/fetal bloodstream - Fallopian tubes (oviducts), where a sperm can fertilize an egg. Deliver oocyte or embryo to the uterus  The Vagina At the beginning of the tract, just inside the opening of the vagina, is the hymen, a mucous membrane. The hymen helps protect the genital tract but is not necessary for health. The vagina is a is a muscular tube about 4 to 5 inches long in an adult woman. that extends from the cervix (neck of the uterus) to the the external genital organs of the body. - functions: sexual intercourse, receptor of semen, discharge of menses, and  Major Female Reproductive Organs Ovary Paired almond-shaped organs near the lateral wall of the pelvic cavity Three main functions 1. Production of immature female gametes (oocytes) 2. Secretion of female sex hormones (estrogens and progesterone) 3. Secretion of inhibin (inhibits FSH production in the anterior pituitary gland)  Major Female Reproductive Organs Uterine tube Expanded funnel (infundibulum) opens into the pelvic cavity along the surface of the ovary The other end opens into the uterine cavity Uterus Inferior to the ovaries Usually angled anteriorly above the urinary bladder Vesico-uterine pouch Pocket between uterus and posterior bladder wall. Recto-uterine pouch  Oogenesis Oogenesis occurs in the ovaries, and ovulation occurs during the 28-day ovarian cycle. It involves Formation and development of the oocyte Begins before birth, accelerates at puberty, ends at menopause Nuclear events are the same as with spermatogenesis Oogenesis and the Ovarian Cycle Steps in oogenesis Mitosis of oogonium (plural, oogonia)— female reproductive stem cells Mitosis completed prior to birth For each oogonium, produces one oogonium and one primary oocyte Oogenesis and the Ovarian Cycle Steps in oogenesis (continued) Meiosis I Begins between 3rd and 7th month of fetal development Primary oocytes begin meiosis I but stop at prophase I until puberty – Rising FSH levels trigger start of the ovarian cycle – Each month, some of the primary oocytes are stimulated to complete meiosis I Yields haploid secondary oocyte and a polar body – Secondary oocyte gets the majority of cytoplasm Ovary releases a secondary oocyte (not a mature ovum) Oogenesis and the Ovarian Cycle Steps in oogenesis (continued) Meiosis II Secondary oocyte begins meiosis II – Suspended in metaphase II at ovulation At fertilization, the secondary oocyte divides into a second polar body and a mature ovum (both haploid) Oogenesis and the Ovarian Cycle Ovarian cycle Involves changes in ovarian follicles Specialized structures where oocyte growth and meiosis I occur About 2 million primordial follicles exist at birth Each containing a primary oocyte By puberty, only about 400,000 primordial follicles remain Others degenerated in a process called atresia Each month, FSH stimulates the  Stages of the Ovarian cycle 1. Primordial follicle in egg nest Primordial follicle – Inactive primary oocyte surrounded by a simple squamous layer of follicle cells Egg nests – Clusters of primary oocytes in the outer portion of the ovarian cortex 2.Formation of primary follicles Follicular cells enlarge, divide, and form several layers around the primary oocyte Follicular cells are now called granulosa cells Zona pellucida ( translucent) – Region that develops around the oocyte Thecal endocrine cells (theca, box) – Layer of cells that form around the follicle  Stages of the Ovarian cycle 3. Formation of secondary follicles Follicle wall thickens, and follicular cells secrete fluid Fluid-filled pockets expand and separate the inner and outer layers of the follicle 4. Formation of tertiary follicle Occurs about day 10–14 of cycle One secondary follicle becomes a tertiary follicle, or mature graafian follicle – Roughly 15 mm in diameter Expanded central chamber (antrum) is filled with follicular fluid – Oocyte projects into the antrum  Stages of the Ovarian Ovulation cycle Tertiary follicle releases secondary oocyte and corona radiata into the pelvic cavity Marks end of follicular phase and start of luteal phase. Formation of corpus luteum (lutea, yellow) Empty tertiary follicle collapses Remaining granulosa cells proliferate Secrete progesterone and estrogens – Progesterone stimulates maturation of the uterine lining Formation of corpus albicans Knot of pale scar tissue produced by fibroblasts Formed by degeneration of the corpus Stages of the Ovarian cycle  The Uterine Tubes and Uterus The uterine tubes are connected to the uterus, a hollow organ with thick muscular walls. Uterine tubes (fallopian tubes) Hollow, muscular structures ~13 cm long Lined with ciliated epithelium Distal portion connects to the uterus Infundibulum Funnel-like expansion adjacent to the ovary Has numerous fingerlike projections (fimbriae) – Extend into the pelvic cavity – Drape over the surface of the ovary  Uterine Tubes Ampulla Muscular middle segment of the uterine tube Isthmus Short segment connected to the uterine wall  Oocyte Transport Involves combination of ciliary movement and peristaltic contraction of smooth muscle in the uterine tube Takes 3–4 days for a secondary oocyte to travel from infundibulum to the uterine cavity Fertilization must occur within the first 12–24 hours after ovulation The Uterine Tubes and Uterus Uterus Hollow, muscular organ Provides mechanical protection, nutritional support, and waste removal for embryo (weeks 1–8) and fetus (>8 weeks) Contractions in the muscular wall are important in delivering the fetus at birth  Layers of the Uterus Layers of the uterine wall Perimetrium (peri, around + metra, uterus) Outer surface Incomplete serosa continuous with the peritoneal lining Myometrium (myo-, muscle) Thick muscular middle layer Smooth muscle layer provides force for childbirth Endometrium Glandular inner lining whose characteristics change with each  Cavities of the Uterus Uterine cavity, or uterine lumen Large, superior cavity continuous with isthmus of uterine tube Internal os (os, opening or mouth) Opening connecting the uterine cavity to the cervical canal Cervical canal Constricted passageway at the inferior end of the uterine cavity Begins at internal os; ends at external os External os  Regions of the Uterus Fundus Rounded portion superior to the openings of the uterine tubes Body Largest portion of the uterus (two-thirds of the organ) Ends at the constriction encircling the internal os Cervix Inferior portion of the uterus Surrounds the cervical canal  The Uterine Cycle The uterine (menstrual) cycle involves changes in the functional layer of endometrium. Monthly changes in the functional zone of the uterus in response to sex hormone levels Averages 28 days in length (range 21–35 days) First cycle (menarche) begins ~11–12 years of age Cycles continue until menopause (~45– 55 years of age)  The Uterine Cycle –Phase 1 Menstrual phase Degeneration of the functional zone of the endometrium Caused by constricted spiral arteries Process of endometrial sloughing (menses, or menstruation) – Lasts ~1–7 days – ~35–50 mL blood lost  The Uterine Cycle Proliferative phase Uterine gland basal cells multiply and spread, restoring uterine epithelium Stimulated and sustained by estrogens secreted from developing ovarian follicles Builds the functional zone to several millimeters thick Uterine glands manufacture  The Uterine Cycle Secretory phase Uterine glands enlarge – Increased secretion of glycoproteins to support embryo Arteries supplying uterine wall elongate and spiral through the functional zone Stimulated by both progesterone and  The Mammary Glands Each breast contains a mammary gland that secretes milk Mammary glands Provide nourishment (milk) for developing infant Milk production (lactation) controlled by hormones released by the reproductive system and the placenta Located on the anterior chest, directly over the pectoralis major muscle  Structure of a Mammary Gland tissue of the Embedded in the subcutaneous pectoral fat pad deep to the skin Suspensory ligaments of the breast Bands of dense connective tissue Surround the duct system and form partitions between lobes and lobules Glandular tissue divided into lobes Each lobe has several secretory lobules Each lobule is composed of secretory alveoli Ducts from the lobules converge into one lactiferous duct per lobe Each lactiferous duct expands near the nipple to form a lactiferous sinus Nipple Conical projection where 15–20 lactiferous sinuses open onto the body surface. Areola Reddish-brown skin around the nipple Grainy texture from sebaceous glands deep to the  Hormonal Interactions The ovarian and uterine cycle are regulated by hormones of the hypothalamus, pituitary gland, and ovaries Ovarian and uterine cycles Ovarian and uterine cycles are controlled by cyclical changes in hormones Two cycles must operate synchronously for proper reproductive function  Ovarian Cycle Steps in ovarian cycle hormonal regulation 1. Release of gonadotropin-releasing hormone (GnRH) – From hypothalamus – Causes production and secretion of FSH – Causes production (not secretion) of LH 2. Follicular phase of the ovarian cycle – Begins when FSH stimulates some secondary follicles to become tertiary follicles – As follicles develop, FSH levels decline (as a result of negative feedback effects of inhibin) – Developing follicles also secrete estrogens (especially estradiol) Low levels of estrogens inhibit LH secretion Inhibition decreases as estrogen levels climb  Ovarian Cycle 3. Luteal phase – GnRH and elevated estrogen levels stimulate LH secretion – Massive surge in LH on or around day 14 triggers: o Completion of meiosis I by the primary oocyte o Forceful rupture of the follicular wall o Ovulation (~9 hours after LH peak) o Formation of corpus luteum – Luteal phase begins after ovulation – Corpus luteum secretes progesterone o Stimulates and sustains endometrial development – Progesterone levels increase, and estrogen levels fall o Suppresses GnRH