Male Reproductive System Quiz

Male Reproductive System

• The male reproductive system consists of four major components: testes, ducts, exocrine glands, and the penis.
• The testes are responsible for producing sperm and androgens.
• The ducts collect, store, and transport sperm.
• The exocrine glands secrete fluids that make up semen.
• The penis delivers semen to the female reproductive tract.

The Penis

• The penis is composed of three main parts: the root, shaft, and glans penis.
• The glans penis is the enlarged tip covered by the foreskin (prepuce).
• It contains three cylindrical columns of erectile tissue: two corpora cavernosa and one corpus spongiosum.
• The urethra runs through the middle of the corpus spongiosum.
• The penis is highly vascularized and innervated.

Erection

• During sexual stimulation, parasympathetic nerves release nitric oxide (NO) which causes relaxation of smooth muscles in the penile arteries.
• This leads to vasodilation, increased blood flow, and engorgement of the vascular channels, resulting in an erection.

The Scrotum

• The scrotum is a sac of skin and superficial fascia that houses the testes.
• It maintains the testes at a lower temperature (around 34 degrees Celsius) which is essential for sperm production.
• The dartos and cremaster muscles regulate temperature.
• The dartos muscle contracts in cold temperatures, wrinkling the scrotal skin and decreasing heat loss.
• The cremaster muscle contracts in cold temperatures, elevating the scrotum and moving the testes closer to the body.

The Testes

• Each testis is divided into lobules by fibrous septa that project inwards from the tunica albuginea.
• Each lobule contains 1-4 seminiferous tubules, where spermatogenesis (sperm production) takes place.
• Seminiferous tubules converge to form the rete testis, which leads to the efferent ductules and then the epididymis.
• The epididymis is a long, coiled tube that stores and matures sperm.
• The vas deferens is a large, thick-walled tube that carries sperm from the epididymis to the urethra.

Spermatogenesis

• Spermatogenesis is the process of sperm production.
• It occurs in the seminiferous tubules and begins at puberty.
• It is a continuous process throughout adult life, with each mature sperm taking approximately 10 weeks to form.
• Each seminiferous tubule has a basement membrane, a fluid-filled lumen, and a tubular wall made of germ cells and supporting cells (Sertoli cells).
• Sertoli cells form tight junctions that create a blood-testis barrier.
• The barrier prevents chemicals from moving from the blood into the seminiferous tubule lumen and helps maintain the correct conditions for germ cell development.

Spermatogenesis Pathway

• Spermatogenesis begins with stem cells in the testes, located in the basal compartment.
• Type A spermatogonia divide through mitosis to produce Type B spermatogonia.
• Type B spermatogonia differentiate and divide to form two primary spermatocytes.
• Primary spermatocytes move into the adluminal compartment and undergo meiotic division.
• Each primary spermatocyte forms two secondary spermatocytes.
• Each secondary spermatocyte then forms two spermatids.
• Spermatids differentiate into spermatozoa during spermiogenesis.

Spermiogenesis

• Spermiogenesis is the process of transforming spermatids into functional sperm, taking approximately 24 days.
• It involves extensive cellular remodeling and no further cell division.
• During spermiogenesis, the Golgi apparatus packages hydrolytic enzymes into the acrosomal vesicle, the acrosome forms at the anterior end of the nucleus, microtubules elongate to form the flagellum, mitochondria multiply and move to the proximal portion of the flagellum, and excess cytoplasm is sloughed away.
• Immature sperm are released from Sertoli cells in the process of spermiation.
• Sperm mature and become motile in the epididymis.

Sperm Structure

• Sperm have a head, midpiece, and tail.
• The head contains the nucleus and the acrosome which contains hydrolytic enzymes that help the sperm penetrate an egg.
• The midpiece contains mitochondria that provide energy for the flagellum.
• The tail propels the sperm through the female reproductive tract.

The Spermatogenic Cycle

• Spermatogenesis is cyclic, occurring sequentially along the length of the seminiferous tubules, resulting in a continuous release of spermatozoa.
• Different stages of germ cell development occur at different levels of the tubule.

Sperm Transport

• Sperm travel through the epididymis, where they mature and gain motility.
• The vas deferens carries sperm from the epididymis to the urethra.
• During ejaculation, sperm and seminal fluid mix in the ejaculatory duct and enter the prostatic urethra.

Seminal Vesicles

• The seminal vesicles attach to the vas deferens to form the ejaculatory duct.
• They secrete a viscous fluid that makes up 70% of semen volume.
• This fluid contains substances that enhance sperm motility and fertilizing ability.
• These substances include fructose (energy source), prostaglandins (smooth muscle contractions), and vesciculase (coagulating enzyme).

Prostate

• The prostate is a donut-shaped gland that produces approximately 1/3 of semen volume.
• It secretes a milky, acidic fluid that contains citrate (nutrient source), prostate-specific antigen (PSA), and enzymes like hyaluronidase.

Bulbourethral Glands

• The bulbourethral glands line the urethra and secrete thick mucus to lubricate the glans penis and neutralize traces of acidic urine.

Hormonal Control of Male Reproductive Function

• Spermatogenesis is controlled by the hypothalamic-pituitary-gonadal (HPG) axis.
• The hypothalamus secretes gonadotropin-releasing hormone (GnRH) which stimulates the anterior pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• LH binds to Leydig cells in the testes and stimulates testosterone production.
• Testosterone feeds back to the hypothalamus and pituitary gland, inhibiting GnRH and LH secretion.
• FSH binds to Sertoli cells and stimulates spermatogenesis.

Testosterone Function

• Testosterone stimulates the differentiation and function of male accessory organs, induces male secondary sex characteristics, opposes estrogen action, stimulates protein anabolism and bone growth, enhances sex drive, stimulates erythropoietin (EPO) secretion, and increases basal metabolic rate.

Regulation of FSH Levels

• Sertoli cells produce inhibin in response to FSH action.
• Inhibin inhibits FSH secretion from the pituitary gland.

Inhibin

• Inhibin is produced by Sertoli/granulosa cells in response to follicle stimulating hormone (FSH), released and acts on gonadotroph cells in the pituitary, blocking activin signalling and hence FSH production.

Female Reproduction

• The female reproductive system produces gametes and nurtures a developing fetus for 9 months before childbirth.
• The ovaries are the primary reproductive organs, producing female gametes (ova/eggs) and synthesizing/secreting estrogen and progesterone.
• The production of eggs and their release from the ovaries is cyclical unlike continuous sperm production in men.
• The structure and function of elements of the female reproductive system are synchronized with the ovarian cycle (menstrual cycle).
• The hypothalamic-pituitary-gonadal axis regulates the cyclical changes in the ovaries and uterus.
• The ovary changes prepare the uterus to receive the developing embryo.

Anatomy

• The ovaries and the duct system are located in the pelvic cavity.
• Accessory ducts from adjacent to the ovary to the exterior of the body include the fallopian tubes, uterus and vagina.
• The vagina provides a passageway for menstrual fluid, the penis during intercourse, and the expulsion of the fetus during childbirth.
• At the upper end of the vagina, it connects to the uterus (latin for womb).

Uterus

• The uterus is a hollow, thick-walled muscular organ that receives, retains and nourishes the fertilized ovum.
• The uterus has three layers:
  • Perimetrium (outermost layer).
  • Myometrium – bulky layer of smooth muscle.
  • Endometrium – mucosal inner layer.
• The endometrium has two strata:
  • Stratum functionalis – undergoes cyclical changes depending on ovarian hormones, allows for implantation of a fertilized egg and is shed during menstruation.
  • Stratum basalis – unresponsive to ovarian hormones, generates a new functional layer after menstruation ends.

Fallopian Tubes

• Also known as oviducts or uterine tubes.
• Each fallopian tube extends from the fundus of the uterus to the ovaries.
• Finger-like projections (fimbriae) sweep over the ovary to capture the oocyte.
• The oocyte travels through the infundibulum and then the ampulla, where fertilization usually takes place.
• The egg is carried to the uterus through a mixture of muscular peristalsis and beating of mucosal cell cilia.

Ovaries

• Produce female gametes (oocytes/eggs) and female sex hormones: estrogen and progesterone.

Ovarian Cycle

• A series of changes in the ovary during which a follicle matures, an ovum is shed and a corpus luteum develops.
• Consists of two phases:
  • The follicular phase (days 1-14) during which follicles grow, ending in ovulation.
  • The luteal phase (days 15-28) during which the corpus luteum is active.

Oocyte Development

• At birth, ovaries contain 1-2 million eggs (female lifetime supply).
• Many oocytes degenerate during development leaving 300k and less than 1000 at menopause.
• Only 400 oocytes are released in a woman's lifetime.
• Oocytes remain in structures known as follicles throughout their life in the ovary.

Follicle Growth

• Primordial follicles – one oocyte surrounded by a single layer of granulosa cells.
• Primary follicles – cells around the oocyte become cuboidal, the zona pellucida forms and the oocyte enlarges.
• Secondary follicles – granulosa cells proliferate and form a stratified epithelium around the oocyte.
• Early antral follicle – a fluid-filled space forms between the granulosa cells.
• Mature follicle – antrum expands with follicular fluid and a mound of the oocyte with its surrounding granulosa cells forms.

Ovulation

• The mature follicle bulges from the ovarian surface.
• Ovulation occurs when the follicle walls rupture and the secondary oocyte is released into the peritoneal cavity.
• The follicular fluid provides a medium to carry the oocyte and protects and nourishes it.

Corpus Luteum

• The ruptured follicle collapses around the antrum and develops.
• Granulosa cells enlarge and combine with thecal cells to form the corpus luteum (yellow body).
• The corpus luteum secretes progesterone and some estrogen (for 3 months if pregnancy occurs).
• If the egg is not fertilized, the corpus luteum degenerates 10 days after ovulation and its hormonal output ends.
• The corpus luteum degeneration results in the formation of a scar, the corpus albicans (white body).

Hormonal Control of Ovarian Function

• Hormonal regulation is similar to that of the testes.
• GnRH secretion from hypothalamic neurons into the hypothalamo-hypophyseal portal vessels regulates LH and FSH, which control female reproductive cycles.
• The frequency and amplitude of GnRH pulses changes across the cycle in women.

Hormonal Levels

• FSH increases in the early follicular phase, decreasing throughout the cycle except for a small mid-cycle peak.
• LH remains constant throughout most of the follicular phase but increases dramatically mid-cycle (LH surge).
• Estrogen levels are low and stable for the first week but increase rapidly in the second week as the dominant follicle grows.
• Progesterone is not secreted by the ovaries until just before ovulation.

Inhibin

• Inhibin A and B are produced in a discordant way.

Hormonal Control of the Ovarian Cycle

• Inhibin B is primarily produced by granulosa cells of small follicles, while inhibin A is predominantly produced by large follicles and the corpus luteum.
• Inhibin B levels are inversely correlated with FSH levels in the follicular phase.
• FSH and LH are released from the anterior pituitary gland, stimulated by GnRH from the hypothalamus.
• FSH promotes the growth of preantral and early antral follicles, while LH stimulates theca cells to produce androgens.
• Granulosa cells convert androgens into estrogen using aromatase.
• Rising estrogen levels in the follicular phase exert negative feedback on the hypothalamus and anterior pituitary, suppressing FSH and LH release.
• Inhibin also exerts negative feedback on FSH synthesis.
• Only one dominant follicle typically survives the FSH dip, becoming more sensitive to FSH and producing large amounts of estrogen.
• High estrogen levels from the dominant follicle briefly exert a positive feedback effect, inducing the LH surge.
• The LH surge triggers ovulation and the transformation of the ruptured follicle into the corpus luteum.

Corpus Luteum and Hormonal Changes

• The corpus luteum produces progesterone and some estrogen.
• Progesterone helps maintain the endometrium and is essential for pregnancy.
• Progesterone exerts strong negative feedback, suppressing LH and FSH synthesis.
• Without fertilization, the corpus luteum regresses within two weeks, causing a decrease in progesterone and estrogen levels.
• This decline in ovarian hormones stimulates FSH, LH, and potentially GnRH release, initiating a new cycle.

Uterine Cycle

• The endometrium undergoes cyclic changes in response to ovarian hormones.
• The endometrium consists of a functional layer (shed during menstruation) and a basal layer.
• During menses, the functional layer is shed due to vasoconstriction of spiral arteries and uterine contractions, mediated by prostaglandins.
• The proliferative phase rebuilds the endometrium under the influence of estrogen, thickening the functional layer and developing spiral arteries.
• Estrogen promotes progesterone receptor expression, preparing the endometrium for the secretory phase.
• The secretory phase is characterized by the dominant influence of progesterone, leading to glandular development, coiling of spiral arteries, and a thick cervical plug.
• Progesterone inhibits uterine contractions.
• Without fertilization, progesterone levels fall, triggering menstruation and a new uterine cycle.

Fertilization

• Oogenesis, the development of oocytes, begins with all oogonia developing into primary oocytes.
• Only oocytes destined for ovulation complete the first meiotic division, forming a secondary oocyte and a first polar body.
• The secondary oocyte undergoes a second meiotic division, but only completes it if fertilization occurs.
• In vitro oocyte production from mouse pluripotent stem cells has successfully produced viable offspring.
• Sperm transport and capacitation are essential for fertilization.
• Capacitation involves changes in the sperm membrane that make it capable of fusing with the oocyte.
• Sperm must penetrate the cumulus granulosa cells and zona pellucida to reach the oocyte.
• The acrosomal reaction releases enzymes that digest the zona pellucida.
• The zona pellucida mediates species-specific fertilization and prevents polyspermy.
• The cortical reaction, triggered by calcium surges, prevents further sperm entry by hardening the zona pellucida.
• After fertilization, the egg completes its second meiotic division, forming a mature ovum and a second polar body.
• The sperm and egg nuclei fuse, forming the diploid zygote.
• The zygote undergoes its first mitotic division, marking the start of embryogenesis.
• Ectopic pregnancies occur when a fertilized egg implants outside the uterus, typically in the fallopian tube.

Test your knowledge of the male reproductive system with this quiz. Explore key structures, processes, and functions integral to male reproduction. Answer questions regarding hormones, sperm development, and anatomical features.