Reproductive System
Similarities of Sexes
Homologues: Varied Structures that preform a common function.
Reproductive Homologues
Female Ovaries/Male Testis: Produce gametes and sex hormones.
Produce cells called gametes; referred to as oocytes in females and sperm in males.
Sex Hormone production which influences maturation, development, and changes in activity of reproductive organs.
Female Clitoris/Male Glans of Penis: Contains erectile tissue that is stimulated during sexual arousal and orgasm.
Female Labia Minora/Male Body of Penis: Contains erectile tissue that is stimulated during sexual arousal and orgasm.
Female Labia Majora/Male Scrotum: Protect and cover reproductive structures.
Female Greater vestibular gland/ Male bulbourethral gland: Secretion of mucin for lubrication.
Both sexes also exhibit accessory reproductive organs, which include ducts to carry gametes/oocytes from gonads towards fertilization in uterus and subsequently to deliver sperm, thereby facilitating successful reproduction.
Sexual union or reproduction, is also known as co-population, coitus or sexual intercourse.
Sexual Maturation in both Sexes
Puberty (grown up): phase of time in development where external sex characteristics become more prominent.
Females: breast enlargment, onset of menstruation, and the widening of hips.
Males: increased muscle mass, deepening of the voice, and growth of facial and body hair.
Shared: pubic hair growth and gonad secrection.
Gonadotropin-releasing hormone (GnRH): Hypothalamus hormone which initiates puberty. GnRH acts on specific endocrine cells in anterior pituitary to release gonadotropins.
Follicle-stimulating hormone (FSH): Hormone produced by the anterior pituitary that stimulates sperm production in males and egg development in females.
Luteinizing Hormone (LH): Hormone produced by the anterior pituitary that triggers ovulation in females and stimulates testosterone production in males.
Gamete production: Males roughly produce around 100 million sperm a day versus females only one oocyte a month.
Perineum
Diamond-shaped area between the thighs that is delineated by the pubic symphysis anteriorly, ischial tuberosities laterally, and coccyx posteriorly.
Urogenital triangle: Anterior triangle containing urethral and vaginal orifices in females. In males, the scrotum and base of penis.
Anal triangle: Posterior triangle containing the anal opening, bordered by the ischial tuberosities laterally and the coccyx posteriorly.
Gametogenesis
Gametogenesis: process of forming human sex cells (gametes).
Female Gametes: Secondary oocytes produced during oogenesis, which occur in the ovaries and are released during ovulation.
Male Gametes: Spermatozoa produced through spermatogenesis, which takes place in the testes and are released during ejaculation.
Heredity Fun
Human somatic cells contain 23 pairs of chromosomes. 22 pairs of autosomes and 1 pair of sex chromosomes, totally 46.
Autosomes: Genes for cellular functions. Determine most human characteristics such as eye color, hair color, height, and skin pigmentation.
Homologous chromosomes: Chromosomes that are similar in size, shape, and genetic content; one from each parent, they carry alleles for the same genes.
Sex chromosomes: XX (female) or XY (male) chromosomes. Mainly determine sex, but also contain genes which code for cellular functions.
Meiosis again
Meiosis: Sex cell division; Starts from a diploid parent cell and produces haploid daughter cells called gametes.
Meiosis versus Mitosis: While meiosis results in four genetically diverse gametes, mitosis produces two identical daughter cells, maintaining the original cell's genetic makeup.
“Crossing over” - Unique to meiosis to shuffle the cards.
Site of Meiosis: Gonads.
Interphase: The preparatory phase where DNA is replicated and centrioles are duplicated, setting the stage for cell division.
Replicated DNA/Chromosomes: Composed of two identical structures called sister chromatids attached at the centromere, which are separated during meiosis to ensure genetic diversity among gametes. It forms a X
Pair of Chromosomes: Homologous maternal chromosome and paternal chromosome. Two sticks not the X.
Meiosis I: First stage; Homologous pairs of replicated chromosomes are separated when cell divides. Resulting in two cells, which contain 23 chromosomes that consist of replicated sister chromatids.
Prophase I: Homologous replicated chromosomes (in this case two sister chromatids present so X/Two sticks) in parent cell pair up to form a tetrad through a process called synapsis (two Xs come together). As maternal and paternal chromosomes align, crossing occurs, exchanging genetic material. This stage ends with nuclear envelope break down.
Metaphase I: Homologous tetrads line up along the metaphase plate, and spindle fibers attach to the centromeres of each homologous chromosome, preparing them for separation.
Anaphase I: The spindle fibers shorten, pulling the homologous chromosomes apart toward opposite poles of the cell (breaking the tetrad), with each chromosome consisting of two sister chromatids still attached at their centromeres. This stage ensures that each resulting daughter cell will receive one chromosome from each homologous pair.
Telophase I & Cytokinesis: Replicated chromosomes arrive at the poles of the cell, and the nuclear envelope begins to reform around each set of chromosomes. Subsequently, cytokinesis occurs, resulting in the division of the cytoplasm and the formation of two haploid daughter cells, each containing one chromosome from each homologous pair.
Meiosis II: During meiosis I, two daughter cells formed each containing 23 replicated chromosomes consisting of two connected sister chromatids. In meiosis II, the chromatids are separated and become single chromosomes in haploid cells.
Prophase II: Nuclear envelopes of daughter cells break down, and replicated chromosomes cluster together. No crossing over occurs here.
Metaphase II: Spindle fibers extend from centrioles, connecting to each chromosome, dragging them to the equatorial plane of the cell, ensuring proper alignment for the separation of sister chromatids.
Anaphase II: Sister chromatids of each replicated chromosome are pulled apart at centromere, becoming single chromosomes that migrate to opposite poles of cell.
Telophase II: Nuclear division finishes as nuclear envelopes re-form around chromosomes. Two divisions of meiosis form four distinct daughter haploid (containing 23 chromosomes not 23 pairs) cells.
Female Reproductive System
Anterior vesicouterine pouch: space between urinary bladder and uterus;
Posterior rectouterine pouch: space between rectum and uterus
Ovaries
Ovarian follicles: site of oocyte production and release of sex hormones estrogen and progesterone.
Ovaries: Paired oval organs located within pelvic cavity lateral to uterus.
Ovarian ligament: cord of fibrous connective tissue, anchoring each ovary to lateral wall of uterus.
Mesovarium: double fold of peritoneum, attaching to ovary’s hilum. meso-ovarium secures each ovary to a broad ligament.
Broad ligament: Drape of peritoneum that hangs over uterus.
Suspensory ligament: Formed from connective tissue of broad ligament, forms superior lateral edges of the ovaries, containing blood vessels and nerves that supply the ovaries.
Ovarian artery and associated vein: Extends through suspensory ligament, entering ovary at its hilum.
Ovarian Tissue Layers: Consists of three layers.
Germinal epithelium: Outer-most layer, it is a thin simple cuboidal epithelial layer.
Tunica albuginea: Dense connective tissue layer beneath the germinal epithelium, providing structural support to the ovary.
Outer cortex and inner medulla: Cortex contains connective tissue and ovarian follicles, whereas medulla contains connective tissue and branches of ovarian blood vessels, lymph and nerves.
Ovarian follicles: Structures in cortex which consist of an oocyte surrounded by follicle cells, which support the oocyte.
Primordial follicle: Initial stage of follicular development, consisting of a primary oocyte surrounded by a single layer of flattened follicle cells.
Primary Oocyte: Arrested in prophase I of meiosis until the individual reaches puberty, when hormonal changes trigger the maturation of some oocytes.
Primary Follicle: Development stage which comes from maturation. Cuboidal cells become Granulosa cells, which secrete estrogen and provide support for the developing oocyte, thus preparing it for eventual ovulation. Zona pellucida forms.
Zona pellucida (new): A glycoprotein layer that surrounds the oocyte and plays a crucial role in fertilization by facilitating the binding of sperm.
Secondary Follicle: Granulosa cells proliferate, expanding in layers, and a outer layer of connective tissue-derived cells called Thecal cells proliferate.
Thecal Cells: Secrete androgens, which are converted into estrogen by granulosa cells.
Antral follicle: Fluid-filled space called Antrum develops within granulosa cells. Fluid increases in volume as ovulation nears, forcing oocyte toward against one side of follicle. Clusters of follicle cells called Cumulus oophorus surround
Antrum appears: Fluid-filled space which increases as ovulation occurs.
Cumulus Oophorus: Clusters of follicle cells that hug the pushed oocyte and support its development, providing essential nutrients and signaling molecules necessary for oocyte maturation.
Corona radiata: Inner most layer of the cumulus oophorus, consisting of tightly packed granulosa cells that provide structural support and enhance the oocyte's developmental environment.
Mature follicle: Final stage of follicle development. Contains a secondary oocyte surrounded by zona pellucidum and corona radiaita, cumulus oophorus, numerous external layers of granulosa cells, thecal cells, and large antrum.
Seconday oocyte: A cell that is derived from the primary oocyte and resumed meiosis during ovulation, ultimately capable of being fertilized by sperm.
Ovulation: Rupture of mature follicle, expelling secondary oocyte into fallopian tube where it may encounter sperm for fertilization.
Mature Follicle becomes a corpus luteum post-ovulation, which secretes hormones such as progesterone to support early pregnancy.
Corpus Luteum: Yellowish remnant structure from site of ovulation; it acts as a endocrine gland, secreting estrogen and progesterone.
Corpus albicans: Degenerated form of the corpus luteum, leading to a decrease in hormone production and marking the end of the luteal phase if fertilization does not occur.
Oogenesis and Ovarian Cycle
Oogenesis: Maturation of a primary oocyte into a secondary oocyte.
Before birth:
Oogonia: Diploid germ cells which contain 23 pairs of chromosomes.
Oogonia divided by mitosis to produce primary oocytes, which then enter prophase of meiosis I and begin their development, but remain arrested until puberty.
Roughly 1.5million primordial follicles will be made in a infant.
Childhood
Ovaries are relatively inactive during childhood, causing atresia of many primordial follicles. Only 200,000-400,000 remain by puberity.
Atresia: regression and reabsorption of unutilized ovarian follicles, resulting in a significant reduction in the total number of follicles available for future ovulation.
Puberty to Menopause
Folliculogenesis: Development of Folliucles.
Preantral stage: the phase in which primordial follicles grow into primary follicles, characterized by the formation of the zona pellucida and the proliferation of granulosa cells. Lasts roughly 290 days.
Antral stage: the phase where primary follicles develop into secondary follicles and antrum formation occurs, allowing for further maturation and selection of the dominant follicle.
This stage is dependent upon FSH and LH secretion.
Lasts for roughly 65 days.
Ovarian Cycle: the series of events involving the maturation of ovarian follicles, ovulation, and the formation of the corpus luteum, which can be divided into the follicular phase, ovulation, and luteal phase.
Follicular phase: Last ~13 days of antral stage of Folliculogenesis and first 13 days of 28 ovarian cycle.
Inhibin: a hormone produced by the ovarian follicles that helps inhibit release of follicle-stimulating hormone (FSH) from the anterior pituitary gland, preventing excessive ovarian development.
Primary follicles that do not become secondary follicles undergo atresia.
Typically only one secondary follicle develops into an antral follicle, due to FSH and LH stimulating the maturation process, while others regress and undergo atresia.
Antral follicle → Mature follicle. Primary oocyte finishes meiosis I, and two cells form. One of these cells becomes the secondary oocyte, while the other, called the polar body, is a non-functional cell that eventually degenerates.
Ovulation (Day 14): Occurs due to a peak in LH secretion, which instructs granulosa cells to produce increasing amounts of fluid into antrum. This forces the secondary oocyte to break through the ovarian wall and be released into the pelvic cavity, where it may be captured by the fimbriae of the fallopian tube.
Luteal Phase (Day 15-28): Ruptured follicle becomes corpus luteum, which produces progesterone and estrogen to build up the uterine lining for potential implantation of a fertilized egg. Inhibin also secreted.
Corpus luteum has a life-span of roughly 10-13 days if secondary oocyte is not fertilized. If not fertilized, corpus luteum regresses and uterine lining is shed in response (Mensuration).
Menopause: The natural decline in reproductive hormones, typically occurring between ages 45 and 55, marking the end of a woman's menstrual cycles and fertility.
Perimenopause: The transitional phase leading up to menopause, characterized by irregular menstrual cycles, fluctuating hormone levels, and various physical and emotional symptoms such as hot flashes and mood changes.
Rundown of Ovarian Cycle:
Hypothalamuses releases GnRH, which causes anterior pituitary to release FSH and LH.
FSH and LH target the ovaries and affect ovarian follicle growth.
Note: little effect in preantral ovarian follicles.
Split into two parts
Maturing preantral ovarian follicles secrete inhibin and low levels of estrogen.
Inhibin inhibits FSH release and low levels of estrogen inhibit production of GnRH, FSH, and LH via negative feedback loop.
Estrogen assists in development of ovarian follicle. In addition to local molecular signals, estrogen helps facilitate ovarian follicle growth from primary to secondary to antral follicle.
Antral follicle develops, growth determined by FSH and LH levels.
Follicular phase/Antral phase of Ovarian Cycle.
Mature follicle produces large threshold amount of estrogen, which stimulates the hypothalamus and anterior pituitary.
Positive feedback results in LH surge, which induces ovulation.
LH surge is essential for the release of the mature egg from the ovary, marking the transition to the luteal phase of the ovarian cycle. Oral contraceptives regulate levels to prevent LH surge.
Corpus luteum forms from ovulated follicle. LH induces remaining granulosa cells to develop into lutem cells.
Corpus luteum secretes large amounts of progesterone, estrogen and inhibin.
Inhibits hypothalamic release of gonadotropin-releasing hormone (GnRH), thereby reducing the secretion of FSH and LH, which helps to prevent ovulation.
Also promotes uterine lining build up.
'Corpus luteum degenerates if oocyte not fertilized in 10 to 13 days.
If fertilization happens, pre-embryo (fertilized egg) secretes Human chorionic gonadotropin (hCG) which acts like LH, keeping the corpus luteum functional and ensuring the continuation of progesterone production to maintain the uterine lining for implantation.
Negative feedback loop restarts Ovarian cycle.
Uterine Tubes (Fallopian Tubes)
Serve as the pathway for the oocyte to travel from the ovary to the uterus.
Site where fertilization typically occurs, allowing sperm to meet the egg.
Uterine Tube Composed of these contiguous segments:
Infundibulum: Free, funnel-shaped, lateral margin of uterine tube. Has numerous finger-like folds called fimbriae. Fimbriae envelop ovary at time of ovulation.
Ampulla: expand region medial to infundibulum.
Isthmus: Constricted region that extends medially from ampulla toward lateral wall of uterus. Forms one-third of the length of uterine tube.
Uterine part/intramural part: extends medially from isthmus and penetrates wall of uterus.
Uterine Tube contains a mucosa, muscularis and a serosa.
Mucosa: Simple ciliated columnar epithelium w/ underlying areolar connective tissue. Thrown in linear folds, reducing the luminal diameter and increasing the surface area for secretions and absorption. Cilia beat on apical surface to move the ovum towards the uterus, facilitating fertilization and transport.
Muscularis: inner circular and outer longitudinal layer of smooth muscle. Peristaltic contractions in this muscularis layer help propel the ovum through the uterine tube, ensuring timely delivery to the uterus.
Serosa: thin layer of areolar connective tissue and an external serous membrane.
Uterus
Uterus: Hollow, pear-shaped, muscular organ within pelvic cavity. It’s lumen connects to uterine tubes supero-laterally and to vagina inferiorly.
Anteverted vs retroverted: The terms describe the orientation of the uterus, with an anteverted uterus tilting forward towards the bladder and a retroverted uterus tilting backward towards the rectum.
Uterus functions:
Supports, protects and nourishes pre-embryo in uterine lining after implantation through a vascular connection which later becomes the placenta, facilitating exchange of nutrients and waste between the mother and developing fetus.
Uterus ejects fetus at birth after maternal oxytocin levels increase to initiate uterine contractions of labor. Without fertilization, contracts to shed uterine lining.
Uterus segments:
Fundus: Superior region.
Body: Middle major area.
Isthmus: Narrow, constricted inferior region of the body superior to cervix.
Cervix: narrow inferiormost portion of uterus that projects into vagina.
Cervical canal: connects to vagina and allows the passage of menstrual fluid and the birth canal during delivery.
Internal and external os: the openings of the cervical canal; the internal os opens into the uterine cavity, while the external os opens into the vagina.
Mucin-secreting glands present that form a mucus plug to protect the uterus from infections and to provide a barrier during pregnancy.
Structural components which support uterus:
Muscles of pelvic floor.
Round ligaments: These ligaments help to anchor the uterus in place, allowing for limited movement and providing stability during pregnancy.
Transverse cervical ligaments: These ligaments support the uterus by connecting it to the lateral pelvic walls, playing a crucial role in maintaining its position and ensuring proper alignment during various stages of life.
Uterosacral ligaments: These ligaments provide posterior support to the uterus, extending from the uterus to the sacrum, thereby helping to stabilize its position and preventing displacement.
RISK: Prolapse: A condition where the uterus slips from its normal position into the vaginal canal, which can occur when the supporting ligaments weaken due to factors such as aging, childbirth, and hormonal changes.
Uterine Wall Make-Up:
Perimetrium: Outer serosa.
Myometrium: thick, middle smooth muscle layer.
Endometrium: intricate mucosa composed of simple columnar epithelium and underlying lamina propria.
Lamina Propria: filled with compound tubular glands, which enlarge during uterine cycle.
Basal layer (Stratum Basalis) and Functional layer (Stratum Functionalis): the functional layer undergoes cyclical changes during the menstrual cycle, being shed during menstruation and regenerated following each cycle.
Vagina
Vagina: Thick-walled, fibromuscular tube that forms the inferior most region of the female reproductive tract. Serves as a canal from the uterus to outside world.
Intercourse, and menstruations.
Three tunics: inner mucosa, middle muscularis, and outer adevntitia.
Mucosa: nonkeratinized stratified squamous epithelium that provides lubrication and protection against friction during intercourse.
Acidic secretion to prevent pathogenic infection.
Muscularis: Composed of smooth muscle that allows for expansion and contraction during sexual activity and childbirth.
Adventitia: Connective tissue layer that anchors the vagina to surrounding structures, providing support.
Inferior region exhibits numerous transverse folds/rogue.
Vaginal orifice: the opening of the vagina, which serves as the entry point for the penis during intercourse and as the exit for menstrual fluid and childbirth.
Uterine Menstrual Cycle
Influenced by estrogen and progesterone. Lasts around 28 days.
Uterine cycle consists of three phases of endometrium development:
Menstrual phase (day 1-5): sloughing of functional layer of endometrium and lasts through period of bleeding.
Proliferative phases (day 6-14): regeneration of the functional layer of the endometrium, where estrogen levels rise, promoting thickening and preparation for a potential implantation.
Secretory phase (day 15-28): after ovulation, the endometrium further thickens and becomes more vascular as progesterone rises, facilitating nutrient supply for a potential embryo.
During this phase, if fertilization does not occur, hormone levels drop, leading to the breakdown of the endometrial lining and the commencement of the next menstrual phase.
External Genitalia/Vulva
Mons pubis (mountain): expanse of skin and subcutaneous connective tissue anterior to pubic symphysis. Hairy in postpuberty.
Labia Majora (labium majus; labum = lip, majus = larger): paired, thickened folds of skin and connective tissue.
Homologous to scrotum of male.
Labia Minora: paired folds internal to labia majora, devoid of hair and very vascular. With numerous melanocytes.
Vestibule: the space between the labia minora, which contains the openings of the urethra and the vagina, providing access to internal reproductive structures.
Greater vestibular glands: posterolateral walls of vestibule and secrete mucin, lubricating vagina.
Clitoris: Small erectile body located at the anterior junction of the labia minora, highly sensitive and plays a key role in sexual arousal.
Corpora cavernosa: two cylindrical erectile structures within the clitoris that facilitate engorgement with blood during arousal, contributing to the overall sensation and swelling of the clitoral tissue.
Crus of Clitoris: The bilateral extensions of the corpora cavernosa that anchor the clitoris to the pubic symphysis, enhancing stability and support during sexual arousal.
Glans: The external portion of the clitoris, covered by the prepuce, it contains numerous nerve endings, making it a key area for sexual pleasure.
Mammary glands
Nipple: The protruding structure that facilitates breastfeeding by delivering milk from the mammary glands to the infant, also playing a role in sexual arousal.
Areola: The pigmented area surrounding the nipple, which contains small glands that help lubricate the nipple during breastfeeding.
Nulliparous Woman: Woman who haven’t given birth, it exhibits rosy or light brown color. While parous typically exhibit darker color.
Suspensory ligaments: thin bands extending from skin to deep fascia that support the breast tissue and help maintain its shape and position.
Lobes/Lobules of Mammary Glands: Lobes subdivided into lobules. Lobules contain alveoli which produce milk in lactating female. They become numerous during pregancy.
Tiny ducts of lobules merge to form 10-20 larger channels called lactiferous ducts, which drains breast milk from lobules to lactiferous sinus.
Lactiferous sinus holds milk prior to release.
Lactation: The process of milk secretion from the breasts, which is stimulated by hormones such as prolactin and oxytocin.
Female Sexual Response
Cascade of physiologic events that occur during stimulation of female reproductive organs.
Responses begins with the excitement phase and ends with the resolution phase, during which physiological arousal gradually decreases and the body returns to its resting state.
Excitement phase: parasympathetic innervation of the genitalia leads to increased blood flow, resulting in the engorgement of erectile tissues such as the clitoris and vaginal walls.
Nipples become erect due to blood engorgement, vaginal wall starts producing mucin and uterus shifts from an anteverted position to erect position.
Erectile tissue of the clitoris swells as it engorges with blood, becoming sensitive to tactile stimuli. Inferior portion of vagina wall contracts.
Woman’s heart rate, blood pressure, and respiratory rate increases as orgasm approaches.
Orgasm: Climax of sexual excitement, characterized with feelings of released tension, feeling of warmth, and some pelvic throbbing. Vagina and uterus contract for many seconds.
We don’t know the purpose of the female orgasm.
Resolution phase: Uterus returns to normal position and vaginal wall relaxes. Excess blood returns from reproductive organs , leading to a decrease in heart rate and blood pressure as the body transitions back to its resting state. Female sexual response does NOT have a refractory period.
Male reproductive System
Primary reproductive organ of the male is the Testes. Accessory reproductive organs include complex set of ducts, glands and penis.
Scrotum
Scrotum is a skin-covered sac between thighs, allowing for 2-3C temperature regulation essential for optimal sperm production.
Raphe: A ridge of tissue that divides the scrotum into two compartments, providing structural support and aiding in temperature regulation.
Outer external layer of skin, thin layer of superficial fascia and a layer of smooth muscle consisting of the dartos muscle, which helps to contract or relax the scrotum based on temperature changes.
Spermatic Cord: Multilayered structure originating in inguinal canal (tubelike passageway through inferior abdominal wall) which provides conduits for nerves, blood vessels, and lymphatics essential for testicular function and support.
External spermatic Fascia: Layer of connective tissue surrounding the spermatic cord, providing additional support and protection to the structures contained within.
Cremaster muscle and cremasteric fascia: Bands of internal oblique fibers and adjacent aponeurosis.
Internal spermatic fascia: Membranous layer of connective tissue that envelops the spermatic cord and aids in anchoring it to surrounding structures, enhancing stability and protecting the spermatic vessels and nerves.
Testicular artery: Direct branch from abdominal aorta.
Surrounded by plexus of veins called pampiniform plexus which help with thermoregulation.
Testes and Spermatogenesis
Testis are small oval-shaped organs housed in the scrotum.
Tunica vaginalis: External serous membrane consisting of a outer parietal layer, middle serous fluid-filled space and a inner visceral layer.
Tunica albuginea: Lies deep to tunica vaginalis, it is a thick, white, fibrous capsule.
Mediastinum testis: The area within the testis that contains blood vessels, lymphatics, and nerves, playing a crucial role in testicular function.
Septa: Internal projection of tunica albuginea, which subdivides internal space into ~250 lobules.
Lobules: contain up to four thin, elongated, convoluted seminiferous tubules.
Lobules/Seminiferous tubules: Split up by Septa. These contain seminiferous tubules which are made of two distinct cells:.
Sertoli/Sustentacular/nurse cells: Support and nourish developing sperm cells.
Release inhibin when sperm count is high.
Cells bound together to form a blood-testis barrier.
Leydig/interstitial cells: Within spaces surrounding tubules (interstitial space). Luteinizing Hormone causes them to produce androgens such as testosterone.
Hormonal Regulation of Androgen and Sperm
Hypothalamus initiates spermatogenesis by secreting GnRH< which causes anterior pituitary to release FSH and LH.
FSH & LH target testes and stimulate spermatogenesis and androgen production.
FSH: Stimulates sustentacular cells to secrete androgen-binding protein and promotes the maturation of sperm cells.
LH stimulates interstitial cells to produce testosterone.
Increased levels of testosterone have various immediate effects on the body. High testosterone facilitate spermatogenesis. Due to negative feedback, it also inhibits GnRH secretion.
Sustentacular cells respond to rising sperm count levels and secrete inhibin as well. Inhibin inhibits FSH secretion, serving as a additional negative feedback loop.
Circulating testosterone stimulates libido and development of secondary sex characteristics. Testosterone acts on the brain to increase desire for sexual stimulation.
Development of Sperm
Spermatogenesis: process of sperm development which occurs within seminiferous tubules of testes. Does not occur until puberty, when significant levels of FSH and LH are present.
Spermatogonia: Primordial diploid (23 pairs of chromosomes (46 total)) that are the precursor cells to spermatozoa, undergoing mitosis and meiosis during spermatogenesis to ultimately produce haploid sperm cells.
Mitosis: One becomes a primary spermatocyte, while the other one becomes a new spermatogonium, ensuring a continuous supply of precursor cells for ongoing sperm production.
Primary spermatocyte: Diploid cell that undergoes meiosis I, resulting in two secondary spermatocytes, each of which is haploid (23 chromosomes).
Secondary spermatocytes: Haploid cells formed from the division of primary spermatocytes during meiosis I, which subsequently undergo meiosis II to produce a total of four spermatids.
Spermatids (circular appearance): Haploid cell formed from Meiosis II of secondary spermatocytes; it is a haploid cell with 23 single chromosomes and is embedded within sustentacular cell cytoplasm, next to the lumen of the seminiferous.
Spermiogenesis: Newly formed spermatids differentiate into mature spermatozoa or sperm. Excess cytoplasm shed and nucleus elongates.
Acrosome cap: Structure containing digestive enzymes that help penetrate oocyte for fertilization. Forms over nucleus.
Tail/flagellum: Whip-like structure that provides motility to the sperm, allowing it to swim through the female reproductive tract in search of the oocyte.
Midpiece/neck: Region that connects the head and tail, containing mitochondria that supply energy needed for the sperm's motility.
Head: Contains the genetic material from the male and is capped by the acrosome, which aids in the fertilization process.
Duct System in Male Reproductive System
Ducts within the Testis: Rete
Rete testis: network of interconnected channels in mediastinum testis that receive sperm from seminiferous tubules via straight tubules.
Simple cuboidal epithelium with short microvilli
Efferent ductulus: Merge from channels of rete testis to form 12-15 larger ducts which connect to the epididymis.
Ciliated columnar epithelia help propel sperm to epididymis while non-ciliated columnar epithelia absorb excess fluid secreted in tubules.
Epididymis: comma-shaped/squid paw structure composed of an internal duct and an external covering of connective tissue. Stores sperm until maturation and motility.
Duct of epididymis: 4-5 meters long and lined with pseudostratified columnar epithelium which contain stereocilia.
Head: the upper portion of the epididymis, where sperm mature and are stored before entering the vas deferens.
Body: the midsection of the epididymis that continues the maturation process of sperm and assists in their transport.
Tail: the lower section of the epididymis that leads to the vas deferens, acting as the final storage area for mature sperm before ejaculation.
Ductus Deferens: Thick-walled tube which extends from epididymis superiorly through spermatic cord up around bladder then back down where it terminates near where bladder and prostate border.
Ampulla: the enlarged end of the ductus deferens that provides a storage site for sperm and is where sperm is mixed with seminal fluid prior to ejaculation.
Composed of inner mucosa (lined by a pseudostratified ciliated columnar epithelium), middle muscularis, and an outer adventitia. Muscularis contains a inner longitudinal, middle circular, and outer longitudinal layer.
Ejaculatory Duct: 1-2 cm long, is a duct formed by the union of the ductus deferens and the seminal vesicle, opening into the prostatic urethra. Pseudo-stratified ciliated columnar epithelium
Urethra: Transports semen from both ejaculatory ducts to outside of the body.
Prostatic Urethra: Extends from bladder through prostate gland.
Membranous urethra: short segment, surrounded by external urethra sphincter.
Spongy Urethra: longest, extending through the penis.
Accessory Glands and Semen Production
Seminal fluid needed to neutralize acidity of vagina and to nourish sperm.
Seminal Vesicles: two glands on posterior urinary bladder later to ampulla of ductus deferens. Elongated, hollow organ 5-8 cm long. Mucosal folds of pseudostratified columnar epithelium line lumen.
Medial portion merges with ductus deferens to form ejaculatory duct.
Secretion: viscous, whiteish-yellow, alkaline fluid containing fructose and high levels of prostaglandins.
Fructose for energy to sperm cells; prostaglandins are local hormones which promote smooth muscle contractions in the female reproductive tract, aiding in sperm transportation.
Prostate Gland: Compact, encapsulated organ that is shaped like a walnut (~2cm by ~3cm by ~4cm). Immediately inferior to bladder.
Submucosal glands that produce mucin and tubuloacinar glands which open directly into prostatic urethra.
Secretion: slightly milky fluid that is weakly acidic, rich in citric acid (sperm health), seminalplasmin (antibiotic) and prostate-specific antigen (liquefy semen).
Bulbourethral Glands/Cowper glands: Paired pea-shaped and sized glands on lateral sides of membranous urethra. Surrounded by fibers of external urethral sphincter as well
Short ducts which project into bulb/base of penis, where it enters spongy urethra.
Tubuloacinar glands containing simple columnar and psuedostratified columnar epithelium.
Secretion: clear, viscous mucin which forms mucus. Coats and lubricates urethra for passage of sperm.
Semen: Seminal fluid and sperm combined. After ejaculation, it is called ejaculate. Sperm roughly takes two weeks from seminiferous tubules to ejaculation.
Penis: Biggest external reproductive organ in males.
Root: Internal attached portion of the penis.
Bulb: Internal dilated portion of the root, which goes posterior. Attaches penis to bulbospongious muscle (inner circular muscle of penis) in urogenitial triangle.
Crus: The pair of elongated structures that extend from the bulb to the pubic arch, helping in the formation of the penis.
Body/Shaft: External elongated, movable portion.
Tunica Albuginea: Thick dense layer of connective tissue covering erectile tissue of penis.
Corpora cavernosa: paired dorsolateral cylindrical erectile tissue. Proximal end forms a crus of the penis and distal end terminates in shaft.
Corpus spongiosum: single ventral, midline erectile cylindrical tissue which contains spongy urethra. Continues within glands/
Glans & External urethral orifice: Glans is the tip of the penis while the external urethral orifice is the opening through which urine and semen exit the body, located at the distal end of the penis.
Male Sexual Response
Venous Spaces: complex network of spaces within erectile bodies of penis which surround central artery. Blood enters erectile bodies and fill venous spaces, leading to engorgement and erection.
Erectile Tissue prevents veins from returning blood until excitement ends.
Phases: Excitement, Orgasm and resolution.
Excitement/Erection: Parasympathetic system causes release of local nitric oxide into erectile tissue, causing filling of venous spaces. Increase in HR, BP and RR near end.
Orgasm: Climax of sexual pleasure, feeling of release of tension, and expulsion of semen.
Early burst of oxytocin: Ductus deferens undergoes peristalsis and moves sperm to urethra. Glands release secretions later subsequently.
Internal urethral sphincter contracts, to inhibit urine flow during ejaculation.
Ejaculation (final stage of phase): Semen expelled from penis through rhythmic contractions of smooth muscle in wall of urethra. Strangely, controlled by sympathetic innervation.
Resolution phase: Exhibited by feelings of intense relaxation. Sympathetic division stimulated to contract central artery of penis and small muscles around erectile tissue, to expel engorged blood to restore the penis to its flaccid state, culminating the process of sexual response.
Refractory period: A time following ejaculation during which the male is unable to achieve another erection or orgasm, typically lasting from a few minutes to several hours, influenced by age and individual physiological factors.
Development of the Reproductive System
Genetic versus Phenotypic Sex
Genetic Sex or Genotypic sex: Sex of of an individual based on chromosomes inherited. Female: XX; Male XY.
Phenotypic sex: Sex of an individual as expressed through physical characteristics and secondary sexual traits, influenced by genetic sex and hormonal factors.
Y chromosome or male determines all: Sex-Determining region Y (SRY) gene located within larger testis-determining factor region on the Y chromosome, SRY gene properly expressed, gene produces proteins which stimulate production of androgens which initiate male phenotypic development.
If NO Y chromosome present, defaults to a female phenotypic sex.
Formation of Neutral Gonads and Genitals
Genital ridges/gonadal ridges: Appear at fifth week of embryonic development and form from intermediate mesoderm. Will form the gonads.
Primordial germ cells: Week 5-6, primordial germ cells migrate from yolk sac to genital ridges, forming two sets of duct systems.
Mesonephric ducts/Wolffian ducts: End up forming the majority of male duct system and connect mesonephros to developing urinary bladder.
Paramesonephric ducts/Mullerian ducts: form most of the female duct system, developing into the fallopian tubes, uterus, and part of the vagina.
All HUMAN EMBYROS develop both duct systems, however only one remains.
Male —> Mesonephric ducts grow and differentiate into male reproductive structures —> paramesonephric ducts degenerate.
Female —> Paramesonephric ducts develop and mesonephric ducts degenerate.
Internal Genitalia Development
Females: No SRY proteins present, therefore gonad differentiates into an ovary at week seven and mesonephric ducts degenerate. Week 8-20 of development, superior paramesonephric ducts remain separate and form two uterine tubes. Inferior ducts form, forming the uterus and superior portion of vagina. Remaining portion formed from urogenital sinus.
Males: SRY genes present. Gonads become testes, which form sustentacular cells and interstitial cells. Sustentacular cells secrete anti-Mullerian hormone, preventing development of paramesonephric ducts, resulting in DEATH and DEGENERATION. Weeks 8-12, mesonephric ducts begin to form male duct system- efferent ductules, epididymides, vasa deferens, seminal vesicles, and ejaculatory ducts.
Prostate and bulbourethral glands form as endodermal outgrowths of developing urethra between weeks 10 and 12.
External Genitalia Development
External genitalia form from same primordial structures. By sixth week, these structures are seen:
Urogenital folds: Paired, elevated structures on either side of urogenital membrane, a thin partition which separates urogenital sinus from outside of the body.
Genital Tubercle: rounded structure anterior to urogenital folds.
Forms into glans of penis or clitoris
Labioscrotal swellings: paired elevates structures lateral to urethral folds.
Testosterone causes external reproductive structures to differentiate.
Labioscrotal swelling become scrotum shocker. The urogenital folds develop into the shaft of the penis in males and the labia minora in females.