Exam 4 - Reproduction System

Question 1

Functions of reproduction system

Answer 1

1) Gametogenesis: The reproductive system is responsible for producing gametes in the gonads

2) Fertilization: It facilitates the meeting of sperm and egg.

3) Development and Nourishment of a New Individual: The female reproductive system supports the development of the fetus during pregnancy and provides nourishment after birth through breastfeeding.

4) Production of Reproductive Hormones: The system produces hormones that regulate reproductive function and influence the development of sex-specific physical traits and reproductive behaviors.

Question 2

Functions of reproduction system: Male vs. Female

Answer 2

1) Gametogenesis: The reproductive system is responsible for producing gametes (sperm in males and eggs in females) in the gonads—testes in males and ovaries in females.

2) Fertilization: It facilitates the meeting of sperm and egg. In males, the duct system helps mature and transport sperm. In females, the reproductive tract receives the sperm and enables its movement toward the egg for fertilization.

3) Development and Nourishment of a New Individual: The female reproductive system supports the development of the fetus during pregnancy and provides nourishment after birth through breastfeeding.

4) Production of Reproductive Hormones: The system produces hormones that regulate reproductive function and influence the development of sex-specific physical traits and reproductive behaviors.

Question 3

Scrotum and role in regulating temperature in testes

Answer 3

The scrotum is a saclike structure that houses the testes and is divided into two compartments by a connective tissue septum. Externally, a midline ridge called the raphe marks the division. The wall of the scrotum consists of skin, connective tissue, and two types of muscles: the dartos muscle (smooth muscle) and the cremaster muscle (skeletal muscle from the abdominal wall).

These muscles regulate testicular temperature, which is vital for healthy sperm development. In cold temperatures, the dartos muscle contracts, causing the scrotal skin to wrinkle and tighten, while the cremaster muscle pulls the testes closer to the body—both actions help conserve heat. In warm conditions, both muscles relax, allowing the scrotum to become loose and the testes to hang further from the body, facilitating cooling. This temperature regulation mechanism ensures that sperm cells, which are highly temperature-sensitive, develop under optimal conditions.

Question 4

Structure of testes

Answer 4

The testes are small, oval-shaped organs (4–5 cm long) located within the scrotum. They serve as both exocrine glands (producing sperm) and endocrine glands (secreting testosterone). Each testis is enclosed by a thick, white connective tissue capsule known as the tunica albuginea, which extends inward to form septa. These septa divide the testis into 300–400 lobules, each containing tightly coiled seminiferous tubules, where sperm production takes place.

Surrounding the seminiferous tubules is loose connective tissue containing interstitial (Leydig) cells, which secrete testosterone. The seminiferous tubules lead into straight tubules called the tubuli recti, which drain into a network called the rete testis. From there, sperm travels through 15–20 efferent ductules, which pass through the tunica albuginea to exit the testis. These ductules are lined with ciliated epithelium to help transport sperm efficiently.

Question 5

Specialized cells of testes: Spermatogenic cells

Answer 5

The testes contain specialized spermatogenic (germ) cells within the seminiferous tubules that are responsible for the continuous production of sperm. These cells undergo several stages of development, beginning as spermatogonia at the base of the tubule. Through a series of mitotic and meiotic divisions, they develop into spermatocytes, then spermatids, and finally mature into spermatozoa. This entire process, known as spermatogenesis, allows the testes to produce millions of sperm daily, crucial for male fertility.

Question 6

Specialized cells of testes: Sertoli cells

Answer 6

Among the developing sperm cells are Sertoli cells, also called sustentacular cells, which play a vital supportive role. These cells nourish and protect the developing sperm by forming the blood-testis barrier, which prevents immune cells from attacking the genetically distinct sperm. Sertoli cells also secrete inhibin, which helps regulate sperm production through feedback to the pituitary gland, and androgen-binding protein, which maintains high testosterone levels in the seminiferous tubules necessary for sperm development.

Question 7

Specialized cells of testes: Sertoli cells: Leydig cells

Answer 7

Surrounding the seminiferous tubules in the connective tissue are the interstitial cells, or Leydig cells, which are responsible for producing the hormone testosterone. Testosterone is essential not only for stimulating and maintaining spermatogenesis but also for the development of male secondary sexual characteristics such as increased muscle mass, body hair, and a deeper voice. Together, spermatogenic cells, Sertoli cells, and Leydig cells ensure the proper function of the testes in both sperm production and hormone regulation.

Question 8

Process of spermatogenesis

Answer 8

Spermatogenesis is the process by which sperm cells are produced and matured in the seminiferous tubules of the testes. During the final phase, called spermiogenesis, each developing spermatid undergoes a transformation to become a mature sperm cell. This involves forming three main parts: the head, which contains the nucleus and the acrosome (an enzyme-filled vesicle that helps the sperm penetrate the egg); the midpiece, which is packed with mitochondria to supply energy; and the tail or flagellum, which enables motility through its microtubule-based movement.

As spermiogenesis concludes, the developing sperm align themselves with their heads positioned toward the sustentacular (Sertoli) cells and their tails facing the lumen of the seminiferous tubules. This orientation ensures that once mature, sperm can be efficiently released into the lumen. From there, they continue their journey through the male reproductive tract. The entire process ensures the production of motile and functional sperm capable of fertilizing an egg.

Question 9

Ducts of male reproductive system and their functions

Answer 9

After sperm cells are released into the seminiferous tubules, they travel through a series of ducts. First, they move through the tubuli recti into the rete testis. From there, they pass through the efferent ductules, which transport them out of the testis and into the epididymis, where they mature and are stored.

Once mature, the sperm travel through the ductus deferens, then into the ejaculatory duct, and finally through the urethra, which carries them to the exterior of the body during ejaculation

Question 10

Ducts of male reproductive system and their functions: Epididymis

Answer 10

The epididymis is a coiled tube attached to the back of each testis that plays a crucial role in sperm maturation and storage. It receives immature sperm from the testis and gradually transports them through its long duct, where they undergo structural and functional changes. Over 12–16 days, sperm lose excess cytoplasm, mature their acrosome, and gain the ability to swim and fertilize an egg. The stereocilia lining the duct absorb fluid and aid in concentrating the sperm. By the time sperm reach the tail of the epididymis, they are fully mature and ready for ejaculation.

Question 11

Ducts of male reproductive system and their functions: Ductus deferens

Answer 11

The ductus deferens (also known as the vas deferens) is a muscular tube that transports sperm from the tail of the epididymis to the ejaculatory duct. It ascends along the posterior side of the testis, joins with blood vessels and nerves to form the spermatic cord, and passes through the inguinal canal into the pelvic cavity. The ductus deferens travels over the ureter and loops behind the bladder toward the prostate gland. Near the prostate, it widens to form an ampulla, where sperm is temporarily stored. Its inner lining contains pseudostratified columnar epithelium surrounded by smooth muscle, and peristaltic contractions help propel sperm forward during ejaculation.

Question 12

Ducts of male reproductive system and their functions: Ejaculatory duct

Answer 12

The ejaculatory duct is formed where the ampulla of the ductus deferens merges with the duct from the seminal vesicle. Each ejaculatory duct is about 2.5 cm long and travels through the prostate gland to join the urethra. During ejaculation, sperm from the ductus deferens mixes with seminal fluid from the seminal vesicles in the ejaculatory duct. This pathway ensures the sperm is delivered into the urethra, where it can then be expelled from the body.

Question 13

Ducts of male reproductive system and their functions: Urethra

Answer 13

The male urethra is a 20 cm long tube that serves as a dual-purpose passageway for both urine and reproductive fluids. It extends from the urinary bladder to the tip of the penis and is divided into three regions: the prostatic urethra, which passes through the prostate and receives secretions from the prostate gland and ejaculatory ducts; the membranous urethra, the shortest section that runs through the perineum; and the spongy (penile) urethra, which is the longest portion extending through the penis to the external urethral orifice. The urethra is lined with different types of epithelium depending on the region and also contains mucus-secreting urethral glands that help lubricate the passage. Its primary role is to transport urine and semen out of the body, making it essential for both excretory and reproductive functions in males.

Question 14

Structure and function of penis

Answer 14

The penis is the male organ of copulation, responsible for transferring sperm to the female reproductive system. Structurally, it contains three columns of erectile tissue: two corpora cavernosa on the dorsum and sides, and one corpus spongiosum on the ventral side. The corpus spongiosum surrounds the spongy urethra and expands at the tip to form the glans penis, and at the base to form the bulb of the penis. During erection, blood fills the spaces in the erectile tissue, causing the penis to enlarge and become firm. The root of the penis is anchored to the pelvic bones by structures called the crura, while the external urethral orifice at the glans allows for the exit of semen and urine.

The skin of the penis is loosely attached, with a specialized fold called the prepuce or foreskin covering the glans in uncircumcised males. This skin is rich in sensory receptors. In some cultures, the prepuce is removed through circumcision, which may reduce the risk of infection and penile cancer. The penis also contains numerous nerves, arteries, and veins, mainly located along its dorsal surface. Dorsal arteries and nerves provide blood supply and sensation, while deep arteries run within the erectile tissues. Altogether, the penis’s structure supports its functions in reproduction and urination, while also being highly sensitive to touch.

Question 15

Structure and function of three major glands in male reproductive system: Seminal vesicles

Answer 15

The seminal vesicles are sac-shaped glands located near the ampullae of the ductus deferens. Each gland is approximately 5 cm long and tapers into a short duct that merges with the ductus deferens to form the ejaculatory duct. Structurally, the seminal vesicles are enclosed in a capsule made of fibrous connective tissue and smooth muscle cells, which aids in the expulsion of their contents during ejaculation.

The seminal vesicles produce thick, mucous-like secretions that serve multiple essential functions in reproduction. These secretions contain fructose, citric acid, and other nutrients that nourish sperm cells, providing the energy needed for their movement and survival. They also include fibrinogen, a protein that contributes to the coagulation of semen shortly after ejaculation, helping it to stay within the female reproductive tract. Additionally, prostaglandins in the seminal fluid stimulate uterine contractions, which aid in moving sperm toward the site of fertilization. Overall, the seminal vesicles play a vital role in enhancing sperm viability and facilitating successful fertilization.

Question 16

Structure and function of three major glands in male reproductive system: Prostate gland

Answer 16

The prostate gland is a walnut-shaped organ approximately 4 cm long and 2 cm wide, located at the base of the urinary bladder and surrounding the prostatic urethra and ejaculatory ducts. Structurally, it is made up of both glandular and muscular tissue, enclosed in a fibrous connective tissue capsule. Inside, numerous fibrous partitions contain smooth muscle and are lined with columnar epithelial cells that form saccular dilations. These cells secrete prostatic fluid, which is delivered into the prostatic urethra through 15 to 30 small ducts.

The prostate gland produces a thin, milky, alkaline secretion that plays several important roles in reproduction. This secretion, along with fluids from the seminal vesicles, bulbourethral glands, and urethral mucous glands, helps neutralize the acidic environment of the urethra and the vagina, creating a more favorable condition for sperm survival. The prostate also contributes to the coagulation of semen immediately after ejaculation by supplying enzymes that convert fibrinogen (from the seminal vesicles) into fibrin, making semen sticky. This sticky consistency helps semen stay in place temporarily within the female reproductive tract. Later, the enzyme fibrinolysin, also from the prostate, dissolves this coagulated mass, freeing the sperm cells to move toward the egg for fertilization.

Question 17

Structure and function of three major glands in male reproductive system: Bulbourethral glands

Answer 17

The bulbourethral glands, also known as Cowper glands, are a pair of small, pea-sized glands located near the membranous urethra at the base of the penis. Each gland is a compound mucous gland, meaning it produces a thick, slippery secretion. These glands are more prominent in younger males but become smaller and harder to detect with age. Their small ducts merge to form a single duct that empties into the spongy urethra.

The bulbourethral glands, along with the urethral mucous glands, produce an alkaline mucous secretion just before ejaculation. This secretion plays a crucial supportive role in reproduction by performing four main functions: it lubricates the urethra to ease sperm movement, neutralizes the acidity of the spongy urethra to protect sperm, provides additional lubrication during intercourse, and reduces vaginal acidity, creating a more favorable environment for sperm survival. These functions help ensure the successful transport and viability of sperm within the male and female reproductive tracts.

Question 18

Hormones that influence male reproductive system and their functions: GnRH

Answer 18

The gonadotropin-releasing hormone (GnRH) is produced by the hypothalamus and acts on the anterior pituitary to stimulate the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These two pituitary hormones are critical for the functioning of the testes. Chronically elevated GnRH levels in the blood cause anterior pituitary cells to become insensitive to stimulation by GnRH molecules, and little LH or FSH is secreted. Long-term administration of synthetic GnRH can reduce sperm cell production, causing infertility

Question 19

Hormones that influence male reproductive system and their functions: FSH

Answer 19

Follicle-stimulating hormone, also released from the anterior pituitary, acts on the seminiferous tubules, specifically targeting sustentacular (Sertoli) cells, to support spermatogenesis, the process of sperm production. This action ensures that sperm cells are produced and mature properly within the testes.

Question 20

Hormones that influence male reproductive system and their functions: Testosterone

Answer 20

Testosterone, produced by the interstitial cells, plays a broader role. It supports spermatogenesis and is also responsible for the development and maintenance of male reproductive organs. Additionally, testosterone influences the development of secondary sexual characteristics such as increased muscle mass, deeper voice, and facial hair. It also provides negative feedback to the hypothalamus and anterior pituitary to regulate the secretion of GnRH, LH, and FSH, maintaining hormonal balance within the male reproductive system.

Question 21

Hormones that influence male reproductive system and their functions: LH

Answer 21

Luteinizing Hormone targets the interstitial cells (Leydig cells) in the testes, stimulating them to produce and secrete testosterone, the primary male sex hormone.

Question 22

Changes that occur in males during puberty

Answer 22

During male puberty, which typically begins between ages 12 and 14, significant hormonal and reproductive changes occur that enable sexual maturity. Before birth, the placenta produces human chorionic gonadotropin (hCG) to stimulate testosterone production in fetal testes. After birth, this stimulation ceases, and testosterone levels remain low until puberty. At puberty, the hypothalamus becomes less sensitive to the inhibitory effects of androgens, leading to an increase in gonadotropin-releasing hormone (GnRH) secretion. This rise in GnRH stimulates the anterior pituitary to release more luteinizing hormone (LH) and follicle-stimulating hormone (FSH). FSH promotes the formation of sperm cells, while LH stimulates interstitial cells in the testes to produce larger amounts of testosterone, which is essential for the development of secondary sexual characteristics. Although testosterone begins to exert negative feedback on GnRH, it cannot completely suppress its secretion, allowing puberty to progress and the male reproductive system to fully mature.

Question 23

Events that occur during the male sex act: Erection

Answer 23

Erection is the first phase of the male sex act and is triggered by parasympathetic nerve impulses originating in the spinal cord. These impulses travel through the pudendal nerve to the arteries of the penis, causing the release of acetylcholine and nitric oxide (NO). These substances relax smooth muscle cells and dilate the blood vessels, allowing blood to fill the sinusoids of the erectile tissues. As a result, venous outflow is restricted, and blood pressure within the penis rises, causing it to become enlarged and rigid. This vascular engorgement allows for penetration during intercourse.

Question 24

Events that occur during the male sex act: Secretion of Mucus

Answer 24

At the same time that erection occurs, parasympathetic action potentials stimulate the mucous glands of the penile urethra and the bulbourethral glands at the base of the penis. These glands secrete alkaline mucus into the urethra. This mucus serves multiple purposes: it lubricates the urethra, helps neutralize acidic urine residue, and prepares the urethral passage for the safe movement of sperm.

Question 25

Events that occur during the male sex act: Emission

Answer 25

Emission refers to the accumulation of sperm cells and secretions from the accessory glands (seminal vesicles, prostate gland, and bulbourethral glands) into the prostatic urethra. This phase is controlled by sympathetic nerve impulses from the spinal cord (T12–L1), which cause peristaltic contractions of the reproductive ducts. These contractions help move semen components into the urethra, where they are held temporarily in preparation for ejaculation. This stage also generates sensory signals that contribute to sexual arousal.

Question 26

Events that occur during the male sex act: Ejaculation

Answer 26

Ejaculation is the forceful expulsion of semen from the urethra. It is triggered by somatic motor action potentials that stimulate rhythmic contractions of the skeletal muscles in the pelvic floor, the urogenital diaphragm, and the base of the penis. These contractions propel semen out through the urethra. Simultaneously, sympathetic impulses cause the internal urinary sphincter to constrict, preventing urine from mixing with semen during ejaculation.

Question 27

Events that occur during the male sex act: Orgasm

Answer 27

Orgasm is the climactic sensation associated with ejaculation. It involves intense physical pleasure, heightened muscle tension, and rapid involuntary contractions in the pelvic region. The experience is a result of the integration of sensory, sympathetic, and somatic nerve activity during the ejaculation process and serves as the emotional and physical peak of the male sexual response.

Question 28

Events that occur during the male sex act: Resolution

Answer 28

Resolution is the final stage, occurring after ejaculation and orgasm. During this phase, the penis returns to a flaccid state as blood drains from the erectile tissues. There is an overall feeling of satisfaction, and the body enters a refractory period during which another erection or ejaculation is temporarily not possible. This period varies in duration depending on age and individual factors.

Question 29

Organs of female reproductive system and their functions: Ovaries

Answer 29

Ovaries: The ovaries are paired organs responsible for producing oocytes (egg cells) and secreting the female sex hormones estrogen and progesterone. These hormones regulate the menstrual cycle, prepare the uterus for pregnancy, and influence the development of female secondary sexual characteristics.

Question 30

Organs of female reproductive system and their functions: Uterine tubes

Answer 30

Uterine Tubes (Fallopian Tubes): These tubes transport oocytes from the ovaries to the uterus and are typically the site where fertilization occurs. Cilia and smooth muscle contractions within the tubes help move the egg toward the uterus for potential implantation.

Question 31

Organs of female reproductive system and their functions: Uterus

Answer 31

Uterus: The uterus is a muscular organ that serves as the site for implantation of a fertilized egg. It supports the growth and nourishment of the developing fetus throughout pregnancy and contracts during labor to aid in childbirth.

Question 32

Organs of female reproductive system and their functions: Vagina

Answer 32

Vagina: The vagina is a muscular canal that connects the uterus to the exterior of the body. It functions as the birth canal during delivery, receives the penis during sexual intercourse, and provides an outlet for menstrual flow.

Question 33

Organs of female reproductive system and their functions: External genital organs

Answer 33

External Genital Organs (Vulva): This includes structures such as the labia, clitoris, and vestibule. These organs protect internal reproductive structures and contribute to sexual arousal and stimulation.

Question 34

Organs of female reproductive system and their functions: Mammary glands

Answer 34

Mammary Glands: Located in the breasts, the mammary glands are specialized to produce and secrete milk after childbirth. This milk nourishes and supports the infant during early life.

Question 35

Organs of female reproductive system and their functions: Ligaments

Answer 35

Ligaments (e.g., Broad Ligament): A group of ligaments holds the internal reproductive organs in place. The broad ligament, in particular, is a large peritoneal fold that supports the uterus, ovaries, and uterine tubes, helping to stabilize them within the pelvic cavity.

Question 36

Anatomy and histology of ovaries

Answer 36

The ovaries are the female gonads, small almond-shaped organs measuring approximately 2–3.5 cm long and 1–1.5 cm wide. They are held in place within the pelvic cavity by several ligaments. The mesovarium, part of the broad ligament, attaches each ovary to its posterior surface. The suspensory ligament extends from the mesovarium to the body wall, while the ovarian ligament connects the ovary to the uterus. Blood vessels, lymphatic vessels, and nerves reach the ovaries via the suspensory ligament and enter through the mesovarium. Histologically, the ovary is covered by a layer of simple cuboidal cells called the ovarian epithelium, beneath which lies a dense fibrous capsule known as the tunica albuginea. Internally, the ovary is divided into the cortex and the medulla. The cortex is the outer, denser region containing ovarian follicles, each housing an oocyte (immature egg cell). The medulla, located at the center, is composed of looser connective tissue and houses blood vessels, lymphatics, and nerves. The stroma, or connective tissue of the ovary, supports the follicles within the cortex, playing a key role in oocyte development and hormone production.

Question 37

Development of oocyte

Answer 37

Oogenesis is the process of egg cell development in females that begins before birth. By the fourth month of fetal development, the ovaries contain around five million oogonia, which multiply and then begin to degenerate. The remaining cells become primary oocytes, which start meiosis I but pause at prophase I until puberty. At puberty, hormonal signals trigger some primary oocytes to resume meiosis I. This produces a large secondary oocyte and a small first polar body. The secondary oocyte begins meiosis II but pauses at metaphase II, only completing division if fertilization occurs. If fertilized by a sperm cell, the secondary oocyte finishes meiosis II, forming a mature ovum and another polar body. The sperm and ovum each contribute 23 chromosomes, forming a zygote with 46 chromosomes. The zygote undergoes mitotic divisions, and about seven days later, the resulting blastocyst may implant in the uterus, marking the beginning of pregnancy.

Question 38

Development of follicle

Answer 38

Follicle development begins before birth when primordial follicles, each containing a primary oocyte, form in the ovaries. At birth, females have about 2 million oocytes, but this number drops to 300,000–400,000 by puberty. Only about 400 of these will mature and be released during a woman’s reproductive years. At puberty, some primordial follicles become primary follicles. The oocyte grows, and the surrounding granulosa cells become cuboidal and multiply. These follicles then develop into secondary follicles, where fluid-filled spaces called vesicles appear, and supportive layers called the theca interna and theca externa form around them. As the fluid spaces merge, a large cavity called the antrum forms, creating a mature (Graafian) follicle. The oocyte is pushed to one side, surrounded by cumulus cells. At ovulation, the mature follicle ruptures, releasing the secondary oocyte. After ovulation, the remaining follicle tissue forms the corpus luteum, which secretes estrogen and progesterone to prepare the uterus for pregnancy. If fertilization doesn't occur, the corpus luteum degenerates into the corpus albicans, a small white scar, and hormone levels fall, restarting the cycle.

Question 39

Ovulation

Answer 39

Ovulation is the process in which a secondary oocyte is released from the ovary. Once released, the oocyte begins meiosis II but pauses at metaphase II and will only complete this division if fertilization occurs. Fertilization begins when a sperm cell binds to and penetrates the oocyte's membrane. This triggers the oocyte to complete meiosis II, forming two cells, each with 23 chromosomes. One of these is the second polar body, a small, nonfunctional cell that degenerates. The other, larger and functional cell becomes the ovum, ready to support early embryonic development if fertilization is successful.

Question 40

Location and result of fertilization

Answer 40

Fertilization most likely occurs in the uterine tube, specifically within the ampulla, which is the widened section of the tube near the ovary. It begins when a sperm cell penetrates the membrane of a secondary oocyte, triggering the completion of meiosis II and the formation of a mature ovum and a second polar body. The 23 chromosomes from the sperm then unite with the 23 chromosomes of the ovum, forming a zygote with a full set of 46 chromosomes. The zygote then undergoes mitotic divisions, forming a cluster of cells. Around seven days after ovulation, this cluster, now a blastocyst, may implant in the uterine wall, initiating pregnancy. Over the next nine months, the blastocyst continues to develop into a new individual.

Question 41

Structure and function of uterine tubes

Answer 41

The uterine tubes, also called fallopian tubes or oviducts, are paired structures that extend from the ovaries to the uterus. Each tube is positioned along the superior margin of the broad ligament, with a specific region of the ligament, the mesosalpinx, supporting it. The tube opens directly into the peritoneal cavity near the ovary to receive the secondary oocyte during ovulation. The tube begins with the infundibulum, a funnel-shaped section fringed with fimbriae—fingerlike projections lined with ciliated mucosa that help sweep the oocyte into the tube. Following the infundibulum is the ampulla, the longest and widest part of the uterine tube where fertilization usually occurs. The isthmus is the narrower region closer to the uterus, and the final segment, the uterine (intramural) part, passes through the uterine wall and opens into the uterine cavity. Together, these sections guide the oocyte—or a developing embryo—toward the uterus. Structurally, each uterine tube has three layers: the outer serosa (from visceral peritoneum), a middle muscular layer (smooth muscle that aids movement), and the inner mucosa (lined with ciliated columnar epithelium and folded into ridges). The mucosa plays a crucial role in nourishing the oocyte or embryo and assisting its transport by ciliary motion and muscular contractions. These functions ensure that fertilization can occur and that the embryo can reach the uterus for implantation.

Question 42

Structure of uterus

Answer 42

The uterus is a pear-shaped, muscular organ in the pelvic cavity, consisting of the fundus, body, and cervix. It connects to the vagina through the cervical canal and is supported by ligaments that help maintain its position. Normally anteverted, it can shift in orientation, and weak pelvic muscles may cause prolapse, where the uterus descends into the vagina. The uterine wall has three layers: the perimetrium (outer serous layer), myometrium (middle smooth muscle layer for contractions), and endometrium (inner mucous membrane). The endometrium includes a basal layer, which regenerates, and a functional layer, which thickens and sheds during menstruation. Spiral arteries supply the functional layer and regulate the cycle. The cervical mucous glands secrete a protective mucus. Around ovulation, this mucus becomes thinner to help sperm pass into the uterus, aiding fertilization.

Question 43

Anatomy and histology of vagina

Answer 43

The vagina is a 10 cm muscular tube that connects the uterus to the body’s exterior. It functions in intercourse, menstrual flow, and childbirth. Its inner surface has columns and rugae, allowing for expansion, and the fornix surrounds the base of the cervix. The vaginal wall has two layers: an outer smooth muscle layer for flexibility and an inner mucosa of moist, stratified squamous epithelium for protection and lubrication. Lubrication comes from cervical and external gland secretions, especially during arousal. The hymen is a thin membrane partially covering the vaginal opening. Its shape and presence vary and can change from physical activity or tampon use. It is not a reliable sign of virginity.

Question 44

Anatomy of female external genitalia

Answer 44

The female external genitalia, or vulva, includes structures that surround the vaginal and urethral openings. These include the labia minora, labia majora, clitoris, and vestibule. The clitoris is a small, sensitive organ involved in sexual arousal, while the labia protect internal structures. The vestibule houses the vaginal and urethral openings and contains glands that secrete lubricating fluids. The bulbs of the vestibule swell during arousal, enhancing sensation. The labia majora are fatty folds that enclose and protect the rest of the vulva. The mons pubis lies above the pubic bone, and the pudendal cleft is the space between the labia majora.

Question 45

Changes that occur in females during puberty

Answer 45

During female puberty, which typically starts between ages 11 and 13, significant physical and hormonal changes occur, driven largely by maturation of the hypothalamus. The first visible sign is menarche, the onset of menstruation. Other changes include the growth and maturation of the vagina, uterus, uterine tubes, and external genitalia, along with increased fat deposition in the breasts and hips. Pubic and axillary hair also begin to grow, and sexual drive develops. These physical changes are triggered by increased secretion of estrogen and progesterone by the ovaries. Before puberty, these hormones are present only in small amounts, but with puberty, a cyclical adult hormone pattern begins to form. This change is facilitated by the increased secretion of GnRH from the hypothalamus and LH and FSH from the anterior pituitary. Before puberty, estrogen and progesterone strongly inhibit these hormones through negative feedback. However, during puberty, this inhibition decreases, allowing hormone levels to rise and establish the menstrual cycle.

Question 46

Changes in the ovary during ovarian cycle

Answer 46

The ovarian cycle is a hormonally regulated process that involves the development and release of an oocyte and the preparation of the ovary for potential pregnancy. It includes two main phases: the follicular phase and the luteal phase. During the follicular phase (days 1–14), a primordial follicle matures into a secondary follicle, and then into a mature (Graafian) follicle containing a secondary oocyte. Ovulation occurs around day 14, when the mature follicle ruptures and releases the secondary oocyte into the uterine tube. This event marks the beginning of the luteal phase (days 15–28), during which the ruptured follicle transforms into the corpus luteum, an endocrine structure that secretes progesterone and a small amount of estrogen to prepare the uterus for potential implantation.

Question 47

Changes in uterus during uterine cycle

Answer 47

The uterine cycle is the monthly process in which the uterus prepares for a potential pregnancy. It includes three phases: menses, the proliferative phase, and the secretory phase. Menses is when the functional layer of the endometrium is shed, resulting in menstrual bleeding. After this, during the proliferative phase, the endometrium regenerates and thickens. Spiral glands and blood vessels begin to grow, preparing the uterus to support a fertilized egg. In the secretory phase, after ovulation, the endometrium becomes thicker and spiral glands secrete nutrients. This phase gets the uterus ready to accept an embryo. If fertilization does not happen, hormone levels drop and the cycle starts over with menstruation.

Question 48

List hormones of female reproductive system and explain their functions: GnRH

Answer 48

Gonadotropin-releasing hormone (GnRH) is produced by the hypothalamus and targets the anterior pituitary. Its primary role is to stimulate the secretion of two key hormones—luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This hormone plays a central role in initiating and regulating the menstrual and ovarian cycles.

Question 49

List hormones of female reproductive system and explain their functions: LH

Answer 49

Luteinizing hormone (LH) is secreted by the anterior pituitary and acts on the ovaries. It is responsible for triggering ovulation—the release of a mature secondary oocyte from the follicle. It also causes the ruptured follicle to transform into the corpus luteum, which then secretes hormones necessary for maintaining the uterine lining.

Question 50

List hormones of female reproductive system and explain their functions: FSH

Answer 50

Follicle-stimulating hormone (FSH) is also secreted by the anterior pituitary and targets the ovaries. FSH promotes the development of ovarian follicles, particularly the growth and maturation of the primary oocyte and surrounding follicular cells.

Question 51

List hormones of female reproductive system and explain their functions: Prolactin

Answer 51

Prolactin, produced by the anterior pituitary, targets the mammary glands. Its main function is to stimulate milk production following childbirth, ensuring nourishment for the newborn.

Question 52

List hormones of female reproductive system and explain their functions: Estrogen

Answer 52

Estrogen, secreted primarily by the follicles of the ovaries, has multiple target tissues. It stimulates the proliferation of endometrial cells in the uterus, contributes to the development of the mammary glands (especially duct systems), and is essential for the development of female secondary sexual characteristics. Estrogen also plays a role in feedback regulation: it enhances LH and FSH secretion before ovulation but suppresses their secretion afterward in cooperation with progesterone.

Question 53

List hormones of female reproductive system and explain their functions: Progesterone

Answer 53

Progesterone, produced mainly by the corpus luteum of the ovaries, supports pregnancy by promoting the hypertrophy of endometrial cells and increasing secretion from uterine glands. It also aids in the development of mammary alveoli and works with estrogen to provide negative feedback to reduce LH and FSH secretion after ovulation. Additionally, it contributes to the development of female secondary sexual traits.

Question 54

List hormones of female reproductive system and explain their functions: Oxytocin

Answer 54

Oxytocin, from the posterior pituitary, targets the uterus and mammary glands. It induces strong uterine contractions during childbirth and also causes the contraction of myoepithelial cells in the breast, facilitating milk letdown during lactation.

Question 55

List hormones of female reproductive system and explain their functions: hCG

Answer 55

Human chorionic gonadotropin (hCG) is secreted by the placenta during early pregnancy. It maintains the corpus luteum and stimulates increased progesterone secretion during the first trimester, which is vital for sustaining the uterine lining and pregnancy. In male fetuses, it also promotes testosterone production in the testes.

Question 56

Regulation of hormones secreted by female reproductive system: GnRH

Answer 56

Gonadotropin-releasing hormone (GnRH): GnRH is secreted by the hypothalamus and regulates the release of two key anterior pituitary hormones—luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Before puberty, low estrogen and progesterone levels exert a strong negative-feedback effect, suppressing GnRH secretion. At puberty, this inhibition is reduced, allowing for increased GnRH release, which initiates the menstrual cycle. GnRH secretion continues in a pulsatile pattern, modulated by estrogen and progesterone feedback loops throughout the ovarian and uterine cycles.

Question 57

Regulation of hormones secreted by female reproductive system: FSH

Answer 57

Follicle-stimulating hormone (FSH): FSH is released from the anterior pituitary in response to GnRH and stimulates the growth and maturation of ovarian follicles. During the follicular phase, FSH promotes the proliferation of granulosa cells and increases the number of LH receptors. As follicles grow, they release inhibin, which exerts a negative-feedback effect on FSH secretion, reducing its levels even as follicle development continues.

Question 58

Regulation of hormones secreted by female reproductive system: LH

Answer 58

Luteinizing hormone (LH): LH is also stimulated by GnRH and plays a critical role in ovulation and corpus luteum formation. As estrogen levels rise during the follicular phase, they initially inhibit LH secretion. However, when estrogen reaches a high threshold, it switches to exert a positive-feedback effect, leading to a sharp LH surge that triggers ovulation. After ovulation, the corpus luteum forms and secretes progesterone and estrogen, which again switch to a negative-feedback effect, reducing LH secretion.

Question 59

Regulation of hormones secreted by female reproductive system: Estrogen

Answer 59

Estrogen: Produced by developing follicles, estrogen supports the proliferative phase of the uterine cycle by promoting endometrial growth and preparing the tissue for implantation. High estrogen levels before ovulation cause a surge in LH and FSH through positive feedback. After ovulation, estrogen works with progesterone to suppress further GnRH, LH, and FSH secretion via negative feedback.

Question 60

Regulation of hormones secreted by female reproductive system: Progesterone

Answer 60

Progesterone: Secreted primarily by the corpus luteum after ovulation, progesterone maintains the uterine lining during the luteal (secretory) phase. It inhibits GnRH, LH, and FSH secretion, preventing additional ovulation during the same cycle. If fertilization does not occur, the corpus luteum degenerates, leading to a drop in progesterone levels, which causes menstruation and allows GnRH levels to rise again, restarting the cycle.

Question 61

Events that occur during female sex act

Answer 61

During the female sex act, multiple physiological and neurological processes occur, largely influenced by parasympathetic and sympathetic stimulation. Sexual desire and arousal begin with sensory and psychological stimuli, influenced in part by hormones like androgens and estrogens acting on the brain. These stimuli trigger action potentials sent from the genitalia to the spinal cord, particularly the sacral region. Ascending pathways carry sensory information to the brain, and descending pathways relay motor signals back to modulate reflexes involved in sexual activity. These signals activate reproductive organs via parasympathetic and sympathetic nerves and skeletal muscles via somatic motor nerves. During sexual excitement, parasympathetic stimulation leads to increased blood flow to erectile tissues such as the clitoris and vaginal opening, causing them to become engorged. The nipples may also become erect. Lubrication begins as small amounts of mucus are secreted from the vestibular glands, and a mucous-like fluid is released into the vagina through its wall, aiding in reducing friction and easing penetration. Tactile stimulation and psychological arousal usually lead to orgasm. During orgasm, there are rhythmic contractions of the vaginal, uterine, and perineal muscles, as well as widespread muscle tension. This response is accompanied by intense pleasure. Following orgasm, the resolution phase is marked by muscle relaxation and an overall sense of satisfaction. Unlike males, females can often experience multiple orgasms in succession and do not require orgasm for fertilization to occur.

Question 62

Events that occur following fertilization of oocyte

Answer 62

Fertilization: Fertilization typically occurs in the ampulla of the uterine tube. A single sperm cell enters the secondary oocyte, triggering the completion of meiosis II and resulting in the formation of a zygote. The oocyte remains viable for about 24 hours after ovulation, and sperm cells can survive in the reproductive tract for up to 6 days, although most become nonviable after 24 hours. Thus, for fertilization to occur, intercourse must typically take place within a window of about 5 days before to 1 day after ovulation. Early Development and Implantation: Following fertilization, the zygote undergoes a series of cell divisions (cleavage) as it travels through the uterine tube toward the uterus. By 7 to 8 days after ovulation, which corresponds to days 21–22 of a typical 28-day cycle, the endometrium has been hormonally primed by estrogen and progesterone to support implantation. The developing embryo, now a blastocyst, attaches to and begins to embed itself into the thickened and secretory endometrium, initiating pregnancy.

Question 63

Process of implantation of embryo

Answer 63

After fertilization, the developing embryo begins a journey through the uterine tube toward the uterus. During this time, it undergoes several mitotic divisions. By 7 or 8 days after ovulation, the endometrium—previously thickened and made secretory by estrogen and progesterone—is ready for implantation. The embryo, now a blastocyst, begins to implant in the uterine lining. The outer layer of the blastocyst, called the trophoblast, releases enzymes that digest the endometrial tissue, allowing the embryo to embed itself and form the early stages of the placenta, the organ of nutrient and waste exchange between mother and embryo. Following implantation, the trophoblast and developing placenta begin to secrete human chorionic gonadotropin (hCG), which maintains the corpus luteum. This continued function of the corpus luteum ensures the ongoing secretion of progesterone and estrogen, preventing the onset of a new uterine cycle. hCG levels rise rapidly, peaking around 8 to 9 weeks after fertilization, and can be detected in urine for pregnancy testing. After peaking, hCG levels decline and stabilize by the 16th week.

Question 64

Menopause

Answer 64

Menopause is defined as the permanent cessation of menstrual cycles, typically occurring between the ages of 40 and 50 in females. During this transition, menstrual cycles become increasingly irregular, and ovulation becomes inconsistent. Eventually, menstruation ceases entirely, marking the end of a woman's reproductive years. The term menopause specifically refers to this complete stopping of menstrual cycles. The period leading up to menopause, when irregular cycles begin and continue until their final cessation, is known as perimenopause or the female climacteric. This transitional phase generally spans 3 to 5 years.

Question 65

Changes that menopause cause

Answer 65

1. Ovarian Function Decline: Menopause is primarily due to changes in the ovaries. As females age, the number of ovarian follicles decreases significantly. By around age 50, most oocytes and follicles have been lost. The few remaining follicles become less responsive to LH and FSH stimulation, which reduces the production of mature follicles and corpora lutea, leading to the eventual cessation of ovulation and menstruation. 2. Hormone Level Decrease: The drop in ovarian hormone production, particularly estrogen and progesterone, contributes to most of the physical and physiological changes seen in menopause. Lower estrogen levels lead to various symptoms and reduce the feedback inhibition on the hypothalamus and pituitary, affecting the release of gonadotropins and disrupting the menstrual cycle. 3. Menstrual Cycle Irregularity: Approximately 5 to 7 years before menopause, the menstrual cycle becomes irregular due to reduced follicular development. Ovulation occurs less frequently, and eventually stops. As a result, menstruation becomes inconsistent and ceases entirely, marking the onset of menopause. 4. Reproductive Organ Changes: Postmenopausal changes also affect the uterus and vagina. The uterus undergoes atrophy, and the endometrial lining becomes thinner. In the vagina and external genitalia, tissues lose elasticity, the epithelium thins, pubic hair decreases, and reduced secretions lead to vaginal dryness and increased susceptibility to infections. 5. Skin and Cardiovascular Effects: Estrogen plays a role in maintaining healthy skin and cardiovascular function. After menopause, the skin becomes thinner, and melanin synthesis increases. Cardiovascular changes include increased risks of hypertension and atherosclerosis, partially due to the loss of estrogen’s protective effects on blood vessels. 6. Vasomotor Instability: Hot flashes and increased sweating are classic symptoms of menopause, caused by vasodilation of cutaneous blood vessels. These symptoms are not due to FSH or LH secretion changes, but instead to lowered estrogen levels affecting the hypothalamus. 7. Changes in Sexual Function: Sex drive may temporarily fluctuate during menopause, with some women experiencing decreases or, in some cases, increases. These variations are influenced by hormonal changes and psychological factors related to aging and fertility concerns. 8. Fertility Reduction: Fertility naturally begins to decline about 10 years before menopause. As the follicle pool diminishes, chances of conception drop, and by menopause, reproductive capability ends altogether due to the near-total depletion of viable oocytes.

Question 66

Blastocyst

Answer 66

A blastocyst is a fluid-filled structure that develops in the early stages of embryonic development, typically around five to six days after fertilization. It represents a critical phase in the reproductive process because it is the form the embryo must reach in order to implant successfully into the uterine wall. At this stage, the fertilized egg, or zygote, has undergone several rounds of cell division and has formed a hollow ball of cells with a distinct cellular organization. The blastocyst is composed of three main components. The outer layer of cells, known as the trophoblast, plays a key role in implantation and will eventually form the placenta, the organ responsible for nutrient and waste exchange between mother and embryo. Inside the blastocyst is the inner cell mass (ICM), which will develop into the actual embryo and later give rise to all the tissues and organs of the body. Between these layers is the blastocoel, a fluid-filled cavity that allows the structure to expand and supports the separation of cells for further development. When the blastocyst reaches the uterus, it undergoes implantation, a process where it attaches to and embeds into the endometrium, the lining of the uterus. Successful implantation marks the beginning of pregnancy. The trophoblast cells secrete enzymes to break down part of the uterine lining and allow the blastocyst to nestle in securely. This stage is essential because it initiates the interaction between the maternal tissues and the embryo, allowing for the formation of the placenta and continued embryonic development.

Question 67

Process of implantation of placenta

Answer 67

After fertilization, the developing embryo travels to the uterus and implants into the thickened endometrial lining around day 7 or 8 post-ovulation. The outer layer of the embryo, called the trophoblast, releases enzymes that help it embed into the uterine wall. This embedded embryo becomes part of the placenta. The placenta begins producing key hormones—hCG, estrogen, and progesterone—that maintain the pregnancy. Initially, the corpus luteum provides these hormones, but by the end of the first trimester, the placenta takes over. Once formed, the placenta functions both as the site of nutrient and waste exchange between mother and fetus and as an endocrine gland. It continues to secrete estrogen and progesterone in increasing amounts to support fetal growth and maintain the uterine lining for the remainder of the pregnancy.

Question 68

Overview of reproduction system (NOTES)

Answer 68

Gonadal activity in both sexes is tightly regulated to ensure successful fertilization. While male activity is constant, female reproductive activity is cyclic. Both processes are initiated in the central nervous system (CNS) and controlled by hormonal signals originating from the hypothalamus, pituitary gland, and gonads. These hormones orchestrate the maturation of gametes and the functioning of reproductive organs.

Question 69

Male reproductive anatomy and physiology: Structures and ducts (NOTES)

Answer 69

The male reproductive system includes the testes, epididymis, vas deferens, ejaculatory duct, seminal vesicles, prostate gland, bulbourethral glands, penis, and the urethra. The testes are enclosed by the tunica vaginalis and tunica albuginea. Blood is supplied via testicular arteries and drained through the pampiniform plexus. Sperm production occurs in the seminiferous tubules, which are housed in lobules within the testes. From the seminiferous tubules, sperm travel through the tubulus rectus, rete testis, efferent ductules, and into the epididymis.

Question 70

Male reproductive anatomy and physiology: Epididymis and sperm maturation (NOTES)

Answer 70

The epididymis consists of a head, body, and tail, and functions in sperm storage and maturation. Non-motile sperm acquire motility over about 20 days and can be stored for approximately 100 days. Stereocilia in the epididymis absorb testicular fluid and supply nutrients. Sperm pass from the epididymis to the vas deferens.

Question 71

Male reproductive anatomy and physiology: Scrotum and temperature regulation (NOTES)

Answer 71

The scrotum is a skin sac that houses the testes and epididymis. It maintains the testes at a temperature 3°C below body temperature via the dartos and cremaster muscles. These muscles contract in cold conditions to conserve heat and relax in warmth to cool the testes.

Question 72

Male accessory glands (NOTES)

Answer 72

The accessory glands include the seminal vesicles, prostate gland, and bulbourethral glands. Seminal vesicles produce about 60% of semen, containing fibrinogen and a high pH. The prostate adds about 30%, producing a milky secretion with clotting factors and fibrinolysin. The bulbourethral glands contribute ~5%, secreting mucus just before ejaculation to neutralize vaginal acidity.

Question 73

Penis structure (NOTES)

Answer 73

The penis contains three erectile tissues: two corpora cavernosa and one corpus spongiosum, which surrounds the urethra. The glans penis is covered by the prepuce (foreskin), and the external urethral orifice is at the tip.

Question 74

Male sexual function (NOTES)

Answer 74

Erection is triggered by sexual stimuli and involves a parasympathetic reflex that releases nitric oxide (NO), which relaxes vascular smooth muscle. This dilation allows blood to fill erectile tissues, particularly the corpora cavernosa, compressing veins and sustaining erection. Ejaculation is under sympathetic control, involving contractions of reproductive ducts and accessory glands, closure of bladder sphincters, and rhythmic contractions of the bulbospongiosus muscles. This process is accompanied by systemic effects like muscle contraction, increased heart rate, blood pressure, and pleasure.

Question 75

Spermatogenesis and Hormonal Regulation (NOTES)

Answer 75

Spermatogenesis, taking about 24 days, transforms spermatogonia into motile sperm. Sertoli (sustentacular) cells support this process, providing nutrients, secreting testicular fluid, and forming the blood-testis barrier to protect developing sperm from immune attacks. Luteinizing hormone (LH) stimulates interstitial cells to produce testosterone, while follicle-stimulating hormone (FSH) acts on Sertoli cells to promote spermatogenesis and secondary sexual traits.

Question 76

Male development (NOTES)

Answer 76

By week 5 of embryonic development, Wolffian ducts and primordial germ cells appear. By week 7, male internal structures form, including testes near the kidneys. Testosterone drives development of the penis and scrotum. By the eighth month, testes descend into the scrotum—a process that may be disrupted in cryptorchidism. At puberty, reproductive organs mature, and secondary characteristics like facial hair and penis growth occur.

Question 77

Female Reproductive Anatomy and Functions (NOTES)

Answer 77

The internal genitalia include the ovaries, fimbriae, infundibulum, uterine tubes, uterus, cervix, and vagina. External structures include the mons pubis, labia majora and minora, clitoris, hymen, and vestibular glands. The ovaries produce gametes and sex hormones and are supported by the ovarian, suspensory, and broad ligaments. Blood supply comes from ovarian arteries and uterine branches.

Question 78

Uterine Tubes and Uterus (NOTES)

Answer 78

The uterine tubes receive oocytes during ovulation and are the site of fertilization. The fimbriae generate currents to draw the oocyte into the infundibulum, and cilia and peristalsis transport it to the uterus. Non-ciliated cells nourish the oocyte. The uterus consists of the fundus, body, isthmus, and cervix and is supported by several ligaments. Its wall includes three layers: perimetrium, myometrium (smooth muscle), and endometrium (functional and basal layers). The endometrium is hormonally regulated and supports implantation.

Question 79

Vagina and External Genitalia (NOTES)

Answer 79

The vagina extends from the cervix to the outside and functions in childbirth, menstruation, and copulation. Its wall includes adventitia, muscularis, and mucosa. The hymen partially covers the vaginal orifice. The external genitalia, or vulva, include the labia, clitoris, vestibule, and associated glands. The clitoris contains erectile tissue similar to the penis and is involved in female sexual arousal.

Question 80

Female Sexual Response (NOTES)

Answer 80

Arousal causes engorgement of the clitoris, breasts, and vaginal mucosa, while vestibular glands lubricate the vestibule. Orgasm involves uterine contractions, elevated heart rate and blood pressure, and no refractory period, allowing for multiple orgasms.

Question 81

Female reproduction system development and aging (NOTES)

Answer 81

Development begins around week 5 with Mullerian duct formation and progresses with external genital development in the absence of testosterone. Ovaries descend but are halted by the broad ligament. At puberty, reproductive organs mature and secondary traits (e.g., breast development, menstruation) appear. Aging causes scarring of ovaries, reduced fertility, and eventually menopause, marked by estrogen decline, reproductive organ atrophy, hot flashes, and mood changes.

Question 82

Oogenesis and Ovarian Cycle (NOTES)

Answer 82

Oogenesis begins in fetal life when oogonia divide and form primary oocytes, which stall in prophase I. At puberty, each cycle yields a secondary oocyte (and a polar body). Ovulation releases the secondary oocyte, which completes meiosis II only if fertilized. The ovarian cycle includes: Follicular phase: Primordial follicle matures to Graafian follicle. Ovulation: Release of the secondary oocyte. Luteal phase: Corpus luteum forms, secretes progesterone and estrogen, and degenerates into corpus albicans if no pregnancy occurs. If pregnancy ensues, the corpus luteum maintains hormone production until the placenta takes over.

Question 83

Hormonal Regulation of the Menstrual Cycle (NOTES)

Answer 83

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) regulate the cycle. Estrogen promotes endometrial thickening, and progesterone supports the luteal phase. Positive feedback from estrogen triggers the LH surge, causing ovulation. If fertilization does not occur, progesterone falls, the endometrium deteriorates, and menstruation begins.

Question 84

Conception and Fertilization (NOTES)

Answer 84

Fertilization is possible during a 3–6 day window before ovulation and up to 24 hours after. Sperm viability is 24–72 hours. The oocyte is protected by the corona radiata and zona pellucida. Capacitation (6–8 hours) makes sperm capable of fertilization. Sperm penetrate the corona radiata and zona pellucida, aided by enzymes. A single sperm fuses with the oocyte membrane, triggering fast (Na⁺) and slow (Ca²⁺) blocks to polyspermy.

Question 85

Implantation and Early Development (NOTES)

Answer 85

The blastocyst, only slightly larger than the zygote, begins implantation 6–7 days post-ovulation, typically completing by day 14. Trophoblasts secrete enzymes and growth factors to penetrate the endometrium. These cells differentiate into cytotrophoblasts and syncytiotrophoblasts, which invade maternal tissue. hCG from the trophoblast maintains the corpus luteum until the placenta forms. Delayed implantation results in failure of pregnancy.