Chapter 28 Reproductive System

Question 1

Homologues

Answer 1

1. Ovary/Testis Produces gametes and sex hormones
2. Clitoris/Glans of Penis Contains erectile tissue that is stimulated during sexual arousal and orgasm
3. Labia Minora/Body of Penis Contains erectile tissue that is stimulated during sexual arousal and orgasm.
4. Labia Marjora/Scrotum Protect and cover some reproductive structures
5. Greater Vestibular Gland/Bulbourethral Gland Secretes for lubrication

Question 2

Gametes Female/Male

Answer 2

Both females and males have paired primary reproductive organs called gonads. These are ovaries in females and testes in males. The gonads produce gametes. Gametes are oocytes in females and sperm in males, which unite at fertilization to initiate the formation of a new individual.

Question 3

Sex Hormones

Answer 3

The gonads also produce relatively large amounts of hormones, which affect maturation, development, and changes in the activity of the reproductive system.

Question 4

Accessory Reproductive Organs

Answer 4

Both sexes also have accessory reproductive organs, including ducts to carry gametes away from the gonads toward the site of fertilization (in females) or to the outside of the body (in males).

Question 5

Sexual Maturation: Females/Males

Answer 5

Both the female and male reproductive systems are primarily nonfunctional and dormant until a time in adolescence known as puberty. At puberty, external sex characteristics become more prominent, such as breast enlargement in females, pubic hair growth in both sexes, and full functional reproductive organs in both sexes. The gonads start to secrete their sex hormones and gametes begin to mature within the gonads.
Puberty is initiated when the hypothalamus begins secreting gonadotropin releasing hormone (GnRH). GnRH acts on specific endocrine cells in the anterior pituitary and stimulates them to release the gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH). (**Both FSH and LH are not produced in the body before puberty.) As levels of FSH and LH increase, the gonads produce significant levels of sex hormones and start the processes of both gamete and sexual maturation.
The female typically produces and releases only a single gamete, termed an oocyte, monthly, whereas the male produces large numbers of gametes, or sperm, daily-about 100 million per day. These male gametes are stored for a short time, and if they are not expelled from the body within that period, they are reabsorbed.

Question 6

Anatomy: Perineum

Answer 6

Diamond-shaped area between thighs that is delineated by the pubic symphysis anteriorly, the ischial tuberosities (of the hip bones) laterally, and the coccyx posteriorly.
The anterior triangle, called the urogenital triangle, contains the urethral and vaginal orifices in females and the base of the penis and the scrotum in males. Within the urogenital triangle are the muscles that surround the external genitalia, called ischiocavernosus, bulbospongiosus, and superficial transverse perineal muscles. Deeper muscles in the triangle include the deep transverse perineal muscle and the external urethral sphincter.
The posterior triangle, called the anal triangle, contains the anus, which is surrounded by the external anal sphincter
The external anal sphincter, bulbospongiosus, and superficial transverse perineal muscles are partly anchored by a dense connective tissue structure called the perineal body.

Question 7

Gametogenesis

Answer 7

Is the process of forming human sex cells, called gametes. Female gametes are called secondary oocytes (commonly referred to as “eggs”) , whereas male gametes are called sperm. The process of gametogenesis begins with a specific type of cell division called meiosis. The events of meiosis generally are similar in both females and males, with a few differences.

Question 8

Heredity

Answer 8

Humans pass on their traits to a new individual when they reproduce. This hereditary information is carried on chromosomes. Human somatic (body) cells contain 23 pairs of chromosomes -22 pairs of autosomes and 1 pair of sex chromosomes, for a total of 46 chromosomes.
Autosomes contain genes that code for cellular functions. These genes also help determine most human characteristics, such as eye color, hair color, height, and skin pigmentation. A pair of matching autosomes is called homologous chromosomes.
The pair of sex chromosomes consists of either two X chromosomes or an X and a Y chromosome. These chromosomes primarily determine whether an individual is female (XX) or male (XY), although they also contain genes that code for cellular functions.

Question 9

Diploid

Answer 9

A cell that contains 23 pairs of chromosomes

Question 10

Haploid

Answer 10

The gametes from either sex contain 23 chromosomes only, not 23 pairs.

Question 11

Meiosis vs. Mitosis

Answer 11

Sex cell division that starts off with a diploid parent cell and produces haploid daughter cells called gametes. Mitosis (somatic cell division,) and meiosis (sex cell division) differ:
1. Mitosis produces two daughter cells that are genetically identical to the parent cell. Meiosis produces up to four daughter cells that are genetically different.
2. Mitosis produces daughter cells that are diploid, whereas meiosis produces daughter cells that are haploid.
3. Meiosis includes a process called crossing over, whereby genetic material is exchanged between homologous chromosomes. Crossing over does not occur in Mitosis.

Question 12

Meiosis

Answer 12

Begins with a diploid parent cell located in a gonad (ovary or testis). In this cell, 23 chromosomes came from the organism’s mother (23 maternal chromosomes), and 23 from the father (23 paternal chromosomes). To produce haploid gametes, this parent cell must undergo meiosis.

Question 13

Interphase

Answer 13

The cell cycle phase called interphase occurs prior to meiosis. During interphase, the DNA in each chromosome is replicated, or duplicated exactly, in the parent cell. These replicated chromosomes are composed of two identical structures called sister chromatids. Each sister chromatid contains an identical copy of DNA at this point. The sister chromatids are attached at a specialized region- centromere.
**Sister chromatids are not the same as a pair of chromosomes. A chromosome composed of sister chromatids resembles a written letter X, whereas a homologous pair of chromosomes is composed of a matching maternal chromosome and paternal chromosome, which are not attached at the centromere. After interphase, there are 23 pairs of replicated chromosomes.
Once the DNA is replicated in interphase, the phases of meiosis begin. Meiosis is comprised of 2 separate sequential events: Meiosis I and Meiosis II

Question 14

Prophase I

Answer 14

Homologous replicated chromosomes in the parent cell pair up to form a tetrad. (Each chromosome here consists of two sister chromatids.) The process by which homologous chromosomes pair up is called synapsis.
As the maternal and paternal chromosomes come close together, crossing over occurs. The homologous chromosomes within each tetrad exchange genetic material at this time. A portion of the genetic material in a sister chromatid of a maternal chromosome is exchanged with the same portion of genetic material in a sister chromatid of paternal chromosome. This shuffling of the genetic material ensures continued genetic diversity in new organisms. (Note that after crossing over, the sister chromatids in a replicated chromosome are no longer identical.) Prophase I ends with the breakdown of the nuclear envelope.

Question 15

Metaphase I

Answer 15

Spindle fibers formed by microtubules extend from centrioles at opposite ends of the cell and attach to the centromere of each homologous replicated chromosome.
The spindle fibers align the homologous pair of each tetrad on either side of the midline or equator of the cell, forming a double line of chromosomes. This alignment of paired chromosomes is random with respect to whether the original maternal or paternal chromosome of a pair is on one side of the equator or the other.

Question 16

Anaphase I

Answer 16

The homologous pairs of chromosomes separate as they are pulled by the spindle fibers to the opposite ends of the cell. A maternal chromosome consisting of two sister chromatids is pulled to one side of the cell, while the homologous paternal chromosome is pulled to the opposite side. The process by which maternal and paternal chromosome pairs are separated and move to opposite ends of the cell means that each daughter cell receives only one-half the starting number of chromosomes (only 23 chromosomes of the original 23 pairs). **The pairs of chromosomes are no longer together; however, each replicated chromosome still consists of two sister chromatids. In addition, recognize that not all maternal chromosomes are pulled to the same side of the cell; because of independent assortment in metaphase I, there is a random alignment of maternal and paternal chromosomes.

Question 17

Telophase I and Cytokinesis

Answer 17

The replicated chromosomes arrive at the opposite ends of the cell, and then a nuclear membrane may re-form around these chromosomes. A cleavage furrow forms in the cell, and the cell cytoplasm divides (called cytokinesis) to produce two new cells. Each daughter cell now contains 23 replicated chromosomes only, but each replicated chromosome is still composed of two sister chromatids bound together.
The two cells formed in this stage must undergo another round of cell division, meiosis II, to separate the sister chromatids.

Question 18

Meiosis II

Answer 18

After meiosis I, the two daughter cells formed each contain 23 replicated chromosomes consisting of two connected sister chromatids. In meiosis II, these chromatids are separated and become single chromosomes in haploid cells.

Question 19

Prophase II

Answer 19

The second prophase event of meiosis resembles the prophase stage of mitosis. In each of the two new cells, the nuclear envelope breaks down, and the chromosomes collect together. Crossing over does not occur in this phase because no homologous chromosome pairs are present; the pairs were previously separated in anaphase I.

Question 20

Metaphase II

Answer 20

Spindle fibers extend from the centrioles to the centromere of each replicated chromosome (consisting of sister chromatids). The replicated chromosomes (composed of two sister chromatids) are aligned to form a single line along the equator in the middle of the cell.

Question 21

Anaphase II

Answer 21

The sister chromatids of each replicated chromosome are pulled apart at the centromere and are now separated. Each sister chromatid will form its centromere, at which point the chromatid is renamed as a single chromosome. The single chromosomes are pulled to opposite poles of the cell.

Question 22

Telophase II and Cytokinesis

Answer 22

The single chromosomes arrive at opposite ends of the cell. Nuclear membranes re-form, and a cleavage furrow forms during telophase II. Cytokinesis overlaps with telophase II as the cytoplasm in both cell divides.
The two divisions of meiosis produce four daughter cells from the original single cell. These daughter cells are haploid, because they contain 23 chromosomes only, not 23 pairs. Twenty-two of the chromosomes are autosomes, and one is a sex chromosome.
The final structures formed are secondary oocytes or sperm.

Question 23

Ovaries

Answer 23

Primary female reproductive organs.

Question 24

Accessory Reproductive Organs: Female

Answer 24

Uterine tubes, uterus, vagina, external genitalia, and mammary glands

Question 25

Ovaries

Answer 25

The ovarian follicles are the site oocyte production and release of the sex hormones estrogen and progesterone.
They are paired, oval organs located within the pelvic cavity lateral to the uterus.
Include several cords and sheets of tissue:
1. Ovarian ligament - fibrous connective tissue, anchors each ovary to the lateral wall of the uterus.
2. Mesovarium - double fold of peritoneum, attaches to each ovary at its hilum. It secures each ovary to a broad ligament - a drape of peritoneum that hangs over the uterus.
3. Suspensory ligament - connective tissue, attaches the lateral edge of each ovary and projects superolaterally to the pelvic wall. The ovarian blood vessels and nerves are housed within each suspensory ligament.

Question 26

Ovarian Follicles

Answer 26

Consist of an oocyte surrounded by follicle cells, which support the oocyte.
1. Primordial -primary oocyte- single layer of flattened follicular cells surround an oocyte- fetal period
2. Primary - primary oocyte- single layer of cuboidal granulose cells surround an oocyte- puberty.
3. Secondary - primary oocyte- multiple layers of granulose cells surround the oocyte- puberty
4. Antral - primary oocyte- many layers of granulose cells surround the oocyte and a small antrum develops within layers of granulosa cells - puberty
5. Mature- secondary oocyte-many layers of granulose cells surround the oocyte and a very large antrum- puberty
6. Corpus luteum - no oocyte - yellowish, collapsed folds of granulosa cells - puberty
7. Corpus albicans - no oocyte - whitish connective tissue scar, remnant of a degenerated corpus luteum - puberty.

Question 27

Oogenesis

Answer 27

The maturation of a primary oocyte to a secondary oocyte. Oogenesis begins in a female fetus, when primary oocytes form in primordial follicles. The ovary and these follicles remain inactive in childhood. At puberty, a select number of primordial follicles each month are stimulated to develop. One mature folic (that houses a secondary oocyte) forms each month.

Question 28

Oogenesis: Before Birth

Answer 28

The process of oogenesis begins in the fetus. At this time, the ovary cortex contains primordial germ cells called oogonia, which are diploid cells (they have 23 pairs of chromosomes). (The oogonia are within the primordial follicles.) During the fetal period, the oogonia divide by mitosis to produce primary oocytes. Prior to starting meiosis, the primary oocytes replicate their DNA (a step necessary for all types of cell division). Primary oocytes then start the process of meiosis, but soon they are arrested in prophase I. At this point, the cells are the primary oocytes described in the preceding section. At birth, the ovaries an infant are estimated to contain a total of 1.5 million primordial follicles within its cortex. The primary oocytes in the primordial follicles remain arrested in prophase I until after puberty.

Question 29

Oogenesis: Childhood

Answer 29

During childhood, the ovaries are relatively inactive. The continuing event that occurs during childhood is atresia, in which some primordial follicles regress. By the time the child reaches puberty, only about 200,000-400,000 primordial follicles remain in the ovaries.

Question 30

Oogenesis: Puberty to Menopause

Answer 30

When a child reaches puberty, folliculogenesis, or follicle development, begins. Folliculogenesis is regulated in part by the secretion of GnRH (gonadotropin-releasing hormone) from the hypothalamus, which stimulates secretion of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) from the anterior pituitary.
folliculogenesis may be subdivided into a preantral stage and an antral stage. The preantral stage lasts for approximately 290 days and consists of the development from primordial follicle to a late secondary follicle. Follicular development in the preantral stage occurs due to local molecular signals directly from the ovarian follicle cells, and thus follicular development is largely independent from gonadotropin secretion. (**FSH plays a small role in preantral follicle development.
In contrast, the antral stage of folliculogenesis is dependent on FSH and LH secretion. The antral stage lasts for approximately 65 days and begins with the origin of the antral follicle, its development into a mature follicle that can be ovulated. After ovulation, the follicular cells left in the ovary enter a luteal phase. This cyclical patter composes the ovarian cycle, which consists of the follicular phase (the last 13 days of the antral stage), ovulation, and the luteal phase.

Question 31

Follicular Phase

Answer 31

The follicular phase of the ovarian cycle is typically shown as days 1-13 of an approximate 28-day ovarian cycle. The follicular phase is the last 13 days or so of the antral stage of folliculogenesis. Folliculogenesis actually begins up to one year prior, when molecular signals from the oocyte and follicle cells stimulate up to about 20 primordial follicles to develop into primary follicles. As the ovarian follicles develop, their granulose cells release the hormone inhibin. Inhibin (and the initial low levels of estrogen secreted by the primary follicles) help inhibit FSH production, preventing excessive ovarian follicle development and allowing the current primary follicles to mature. After, a few of these primary follicles mature and become secondary follicles. The primary follicles that do not mature undergo atresia.
The later stages of follicular development (secondary to antral to mature follicle) are more directly dependent on increased FSH and LH levels. FSH and LH now directly acts on the secondary follicles. Only one secondary follicle in an ovary develops into an antral follicle. Late in the follicular phase, this antral follicle develops into a mature follicle. The volume of fluid increases within the antrum of this follicle, and the oocyte is forced toward one side of the follicle, where it is surrounded by the cumulus oophorus. The innermost later of the cumulus oophorus cells is the corona radiate.
As the antral follicle develops into a mature follicle, its primary oocyte finishes meiosis I (where pairs of replicated chromosomes are separated), and two cells form. One of these cells receives a minimal amount of cytoplasm and forms a polar body, which is a nonfunctional cell that later regresses. The other cell receives the bulk of the cytoplasm and becomes the secondary oocyte, which continues to develop and reaches metaphase II of meiosis before it is arrested again. This secondary oocyte does not complete meiosis II (where sister chromatids are separated) unless it is fertilized by a sperm. If the oocyte is never fertilized, it breaks down and regresses about 24 hours later.

Question 32

Ovulation

Answer 32

Occurs on day 14 of a 28-day ovarian cycle and is defined as the released of the secondary oocyte from a mature follicle. Only one ovary ovulates each month. Ovulation is induced only when there is a peak in LH secretion. As the time of ovulation approaches, the granulose cells of the mature follicle increase their rate of fluid secretion into the antrum, forming a larger antrum and causing further swelling within the follicle. The edge of the follicle that continues to expand at the ovarian surface becomes quite thin and eventually ruptures, expelling the secondary oocyte through the mature follicle and the ovary wall.

Question 33

Luteal Phase

Answer 33

The luteal phase occurs during days 15-28 of a 28-day ovarian cycle, when the remaining follicle cells in the ruptured mature follicle become the corpus luteum.
The corpus luteum is essentially a temporary endocrine gland. It secretes progesterone and estrogen that stabilize and build up the uterine lining, and prepare for possible implantation of a fertilized oocyte. It also secretes inhibin, which, along with the high levels of estrogen and progesterone, inhibits the hypothalamus and anterior pituitary from secreting their reproductive hormones.
The corpus luteum has a life span of about 10 to 13 days if the secondary oocyte is not fertilized. After this time, the corpus luteum regresses and becomes a corpus albicans. As the corpus luteum regresses, its levels of secreted progesterone and estrogen decrease dramatically, causing the uterine lining to be shed in a process called menstruation. The shed lining is called menses or a period. This marks the end of the luteal phase. A person’s first menstrual cycle, called monarch, indicates the culmination (end point) of female puberty and typically occurs around age 11-12.

Question 34

Menopause

Answer 34

The time nearing menopause is called perimenopause. During perimenopause, estrogen levels begin to drop and a woman may experience irregular periods, skip some periods, or have very light periods. The timing of perimenopause varies, but it can occur as early as age 35 years or as late as the late 50s. It may last for a period of months to several years. When a woman has stopped having monthly menstrual cycles for 1 year and is not pregnant, or has a medical condition that leads to a cessation of menstruation-such as extremely low body fat or in cases of anorexia nervosa - she is said to be in menopause.
The age at normal onset of menopause varies considerably, but typically it is between 45-55 years. Menopause begins either when there are no more ovarian follicles remaining, or ovarian follicle maturation has halted. As a result, the uterine lining does not grow, and menses no longer occurs.

Question 35

Regulation: Ovarian Cycle

Answer 35

1. Hypothalamus initiates the ovarian cycle by secreting GnRH, which stimulates the anterior pituitary to secrete FSH and LH.
2. FSH and LH target the ovaries and affect ovarian follicle growth.
   3a. The maturing preantral ovarian follicles secrete inhibin and low levels of estrogen.
   3b. Estrogen also assists with the development of the ovarian follicle.
3. The antral follicle develops, and its growth is now dependent on FSH and LH secretion.
4. The mature follicle produces a large threshold amount of estrogen, which stimulate the hypothalamus and anterior pituitary.
5. Positive feedback results in an LH surge from the anterior pituitary, which induces ovulation.
6. A corpus luteum forms from the ovulated follicle
7. The corpus luteum secretes large amounts of progesterone, estrogen, and inhibin.
8. The ovarian cycle repeats.

Question 36

Human Chorionic Gonadotropin (hCG)

Answer 36

if the secondary oocyte is fertilized, and if it successfully implants in the uterine lining, this fertilized structure, now called a pre-embryo, starts secreting hCG, a hormone that enters the mother’s blood and acts on the corpus luteum. Essentially, hCG mimics the effects of LH and continues to stimulate the corpus luteum. As a result, the corpus luteum continues producing progesterone and estrogen, which maintains and continues building the uterine lining. After 3 months, the placenta of the developing fetus starts producing its own progesterone and estrogen. By the end of the third month the corpus luteum has usually regressed into a corpus albicans.

Question 37

Uterine Tubes

Answer 37

Fallopian tubes or oviducts, extend laterally from both sides of the uterus toward the ovaries. They function to transport the ovulated oocyte to the uterus, and are the site of fertilization of an oocyte.
infundibulum
ampulla
isthmus
Uterine part
mucosa
Muscularis
serosa

Question 38

Uterus

Answer 38

Is a hollow, pear-shaped, thick-walled, muscular organ within the pelvic cavity. It has a lumen (internal space) that connects to the uterine tubes superolaterally and to the vagina inferiorly.
anteverted
retroverted
fundus
body
isthmus
Cervix

Question 39

Vagina

Answer 39

A thick-walled, fibromuscular tube that forms the inferior most region of the female reproductive tract. Connects the uterus with the outside of the body and functions as the birth canal.
vaginal orifice
hymen

Question 40

Uterine Cycle

Answer 40

The cyclical changes in the endometrial lining occur under the influence of estrogen and progesterone secreted by the developing follicles and the corpus luteum. The uterine cycle (or menstrual cycle) consists of three phases of endometrium development: the menstrual phase, proliferative phase, and secretory phase. The length of the uterine cycle may vary greatly among females.

Question 41

Ovarian Cycle Phase/Uterine Cycle Phase

Answer 41

1-5 days - follicular phase/menstrual phase
6-13 -follicular phase/proliferative phase
14 ovulation/proliferative phase
15-28- luteal phase/secretory phase

Question 42

Influence of Hormones: Ovarian vs Uterine Cycles

Answer 42

1. GnRH-Hypothalamus-stimulates anterior pituitary to produce and secrete FSH and LH
2. FSH-Anterior Pituitary-stimulates growth of ovarian follicles
3. LH-Anterior Pituitary- stimulates ovulation (when there is a peak in LH)
4. Estrogen- ovarian follicles(before ovulation), corpus luteum (after ovulation), or placenta (during pregnancy)- initiates and maintains growth of the functional layer of the endometrium
5. Progesterone- Corpus luteum or placenta (during pregnancy) - primary hormone responsible for functional layer growth after ovulation; causes increase in uterine blood vessel distribution, uterine gland size, and nutrient production.
6. Inhibin - Ovarian follicles- inhibits FSH secretion so as to prevent excessive follicular development

Question 43

Testes

Answer 43

primary male reproductive organs. Produce sperm and androgens

Question 44

Accessory Reproductive Organs

Answer 44

set of ducts and tubules, accessory glands, penis.

Question 45

Seminiferous tubules

Answer 45

Each lobule contains up to 4 thin, elongated, and extremely convoluted seminiferous tubules. They contain 2 types of cells a.)a group of non dividing support cells called sustentacular cells, b) a population of dividing germ cells (spermatogonia) that, beginning at puberty, continuously replicate and develop by the process of meiosis into sperm.
The sustentacular cells provide a protective environment for the developing sperm, and their cytoplasm helps nourish the developing sperm. In addition, sustentacular cells release the hormone inhibin when sperm count is high. Inhibin inhibits FSH secretion and regulates sperm production. When sperm count declines, inhibin secretion decreases.
the sustentacular cells are bound together by tight junctions, which form a blood-testis barrier that is similar to the blood-brain barrier. The blood-testis barrier helps protect developing sperm from materials in the blood. It also protects the sperm from the body’s leukocytes, which may perceive the sperm as foreign because they have different chromosome numbers and proteins. (In comparison, the oocyte likely is protected from materials in the blood by the ovarian follicle structures that surround the oocyte.)
The spaces surrounding the seminiferous tubules are called interstitial spaces. Within these spaces reside interstitial cells. Luteinizing hormone stimulates the interstitial cells to produce hormones called androgens. There are several types of androgens; the most common one is testosterone. Although the adrenal cortex secretes a small amount of androgens in all individuals, the vast majority of androgens release is via the interstitial cells in the testis, beginning at puberty.

Question 46

Hormone Regulation: Spermatogenesis & Androgen Production

Answer 46

1. GnRH secreted by the hypothalamus stimulates the anterior pituitary to secrete FSH and LH
2. LH stimulates interstitial cells to secrete testosterone. FSH stimulates sustentacular cells to secrete androgen-binding protein (ABP), which keeps testosterone levels high in the testis
3. Testosterone stimulates spermatogenesis but inhibits GnRH secretion and reduces the anterior pituitary’s sensitivity to GnRH
4. Rising sperm count levels cause sustentacular cells to secrete inhibin, which further inhibits FSH secretion.
5. Testosterone stimulates libido and development of secondary sex characteristics.

Question 47

Spermatogenesis vs. Spermiogenesis

Answer 47

Spermatogenesis - is the process of sperm development that occurs within the seminiferous tubule of the testis. Spermatogenesis does not begin until puberty, when significant levels of FSH and LH stimulate the testis to begin gamete development.
In the final stage of spermatogenesis, a process called spermiogenesis, the newly formed spermatids differentiate to become anatomically mature spermatozoa or sperm. During spermiogenesis, the spermatid sheds excess cytoplasm and its nucleus elongates. A structure called the acrosome cap forms over the nucleus. This structure contains digestive enzymes that help penetrate the secondary oocyte for fertilization. As the spermatid elongates, a tail, also called the flagellum, forms from the organized microtubules within the cell. The tail attached to a mid piece or neck region containing mitochondria. These mitochondria provide the energy to move the tail.

Question 48

Spermatogenesis: Process

Answer 48

1. Germ cells that are the origin of sperm are diploid cells (containing 46 chromosomes, or 23 pairs) called spermatogonia. Mitotic divisions of these cells produce a new germ cell a committed cell. The committed cell is a primary spermatocyte.
2. Meiosis I begins with the diploid primary spermatocytes. The haploid cells (containing 23 replicated chromosomes only) produced during meiosis I are called secondary spermatocytes.
3. Meiosis II originates with the secondary spermatocytes and produces spermatids (haploid cells which contain 23 single chromosomes).
4. The process of spermatogenesis begins with spermatids and results in morphologic changes needed to form sperm that will be motile.

Question 49

Stages of Spermatogenesis

Answer 49

1. Spermatogonium -23 pairs (46)-diploid- divides by mitosis to produce a new spermatogonium and a primary spermatocyte
2. Primary spermatocyte- 23 pairs (46) of replicated chromosomes-diploid- completes meiosis I to produce secondary spermatocytes
3. Secondary spermatocyte- 23 replicated chromosomes only- haploid-completes meiosis II to produce spermatids
4. Spermatid- 23 single-stranded chromosomes only- haploid- undergoes spermiogenesis, where most of its cytoplasm is shed and a mid piece, tail, and head form.
5. Spermatozoon- 23 single-stranded chromosomes only- haploid- leaves seminiferous tubule and matures in epididymis

Question 50

Male/Female Gametogenesis

Answer 50

Both female and male gametogenesis events share some similarities and have some notable differences. Both female and male gametes undergo meiosis, but only a single viable secondary oocyte is produced, whereas four sperm are produced. All oocytes have initiated (and then become arrested in) meiosis in the fetus. In contrast, spermatogonia do not start spermatogenesis until puberty, but after this time they can divide and produce spermatocytes throughout an individual’s adult lifetime.

Question 51

Rete Testis vs. Efferent Ductules

Answer 51

Is a meshwork of interconnected channels in the mediastinum testis that receive sperm from the seminiferous tubules via straight tubules. The rete testis is lined by simple cuboidal epithelium with short microvilli covering its luminal surface. The channels of the rete testis merge to form the efferent ductules.
Efferent ductules connect the rete testis to the epididymis. They are lined with both ciliated columnar epithelia that propel the sperm toward the epididymis and conciliated columnar epithelia that absorb excess fluid secreted by the seminiferous tubules. The efferent ductules provide passage fro the sperm from the rete testis into the epididymis. The formation of sperm is within the seminiferous tubules, and the pathway for the sperm from the seminiferous tubules is: straight tubules, rete testis, and efferent ductule to the epididymis, where the sperm are stored.

Question 52

Epididymis

Answer 52

Is a comma-shaped structure composed of an internal duct and an external covering of connective tissue. Its head lies on the superior surface of the testis, whereas the body and tail are on the posterior surface of the testis. Internally, the epididymis contains a long, convoluted duct of the epididymis, which is approximately 4-5 meters in length and lined with pseudostratified columnar epithelium that contains sterocilia (long microvilli).
The epididymis stores sperm until they are fully mature and capable of being motile. If sperm are not ejected from the male reproductive system within a few months, these sperm degenerate and are reabsorbed by cells lining the duct of the epididymis.

Question 53

Ductus Deferens

Answer 53

When sperm leave the epididymis during ejaculation, they enter the ductus deferent (vas deferens). The ductus deferent is a thick-walled tube that extends from the epididymis superiorly through the spermatic cord (a structure that passes through the inguinal canal). Emerging from the spermatic cord, the ductus deferent enters the pelvic cavity, where it separates from the other spermatic cord components and continues posteriorly along the super-lateral surface of the bladder. It then extends inferiorly and terminates close to the region where the bladder and prostate gland meet. As the ductus deferent approaches the superoposteriar edge of the prostate gland, it enlarges and forms the ampulla of the ductus deferent. The ampulla of the ductus deferent unites with the proximal region of the seminal vesicle to form the terminal portion of the reproductive duct system, called the ejaculatory duct.
mucosa
muscularis
adventitia

Question 54

Ejaculatory Duct

Answer 54

Is between 1 and 2 cm long. The epithelium of the ejaculatory duct is a pseudo stratified ciliated columnar epithelium. The ejaculatory duct conducts sperm ( from the ductus deferent) and a component of seminal fluid (from the seminal vesicle) into the prostatic urethra.

Question 55

Urethra

Answer 55

The urethra transports semen from both ejaculatory ducts to the outside of the body. The urethra is subdivided into prostatic urethra that extends from the bladder through the prostate gland, a membranous urethra that is surrounded by the external sphincter, and a spongy urethra that extends through the penis.

Question 56

Seminal Fluid

Answer 56

The vagina has a highly acidic environment to prevent bacterial growth. Sperm cannot survive in this type of environment, so an alkaline secretion called seminal fluid is needed to neutralize the acidity of the vagina. In addition, as the sperm move through the female reproductive tract (a process that can take hours to several days), they are nourished by nutrients within the seminal fluid. The components of seminal fluid are produced by the accessory glands that include the seminal vesicles, the prostate gland, and the bulbourethral glands.

Question 57

Seminal Vesicles

Answer 57

The paired seminal vesicles are located on the posterior surface of the urinary bladder lateral to the ampulla of the ductus deferent. Each seminal vesicle is an elongated, hollow organ approximately 5-8 cm long. The wall of each vesicle contains mucosal folds of pseudo stratified columnar epithelium. The medial (proximal) portion of the seminal vesicle merges with a ductus deferent to form the ejaculatory duct.
The seminal vesicles contribute to the seminal fluid. These glands secrete a viscous, whitish-yellow, alkaline fluid containing both fructose and high levels of prostaglandins. Fructose nourishes the sperm as they move through the female reproductive tract. Prostaglandins are hormone-like substances that promote the widening and slight dilation of the external os of the cervix, which facilitates sperm entry into the uterus. Prostaglandins also promote smooth muscle contraction of the uterus. Sexual intercourse close to a pregnant woman’s due date has the potential to facilitate the beginning true labor.

Question 58

Prostate Gland

Answer 58

The prostate gland is a compact, encapsulated organ that weighs about 20 grams and is shaped like a walnut, measuring approx. 2cm by 3cm by 4 cm. It is located immediately inferior to the bladder. The prostate gland includes submucosal glands that produce mucin and more than 30 tubuloacinar glands that open directly through numerous ducts into the prostatic urethra. Together, this aggregate of secretory structures contributes a component to the seminal fluid.
The prostate gland secretes a slightly milky fluid that is weakly acidic and rich in citric acid, seminalplasmin, and prostate-specific antigen (PSA). The citric acid is a nutrient for sperm health, the seminalplasmin is an antibiotic that combats urinary tract infections in the male, and the PSA acts as an enzyme to help liquefy semen following ejaculation. (**the slightly acidic prostate secretion of the prostate is not sufficient to cause seminal fluid to be acidic, and thus seminal fluid is alkaline and so it helps neutralize the acidity of the vagina.)

Question 59

Bulbourethral Glands

Answer 59

Paired, pea-shaped (Cowper glands) are on the lateral sides of the membranous urethra and surrounded by fibers of the external urethral sphincter. Each gland has a short duct that projects into the bulb (base) of the penis and enters the spongy urethra. Bulbourethral glands are tubuloacinar glands that have a simple columnar and pseudo stratified columnar epithelium. Their secretory product is a clear, viscous mucin that forms mucus. This mucus coats and lubricates the urethra for the passage of sperm during sexual intercourse.

Question 60

Semen

Answer 60

Seminal fluid from the accessory glands combines with sperm from the testes to make up semen. When released during intercourse, semen is called ejaculate, and it normally measures about 3-5 ml in volume and contains approx. 200-500 million sperm. In a sexually active male, the average transit time of human sperm-from their release into the lumen of the seminiferous tubules, passage through the duct system (including their storage time in the epididymis), and presence of seminal fluid, an individual who is very active sexually may have a reduced sperm count because there are fewer sperm to be released from the epididymis; however, the total semen volume remains close to normal for that individual.