Reproductive System Concepts

Question 1

Name the 4 ways to organize male reproductive structures and name which of the 4 is under control of the HP axis

Answer 1

Testes
System of ducts
Accessory glands
Supporting structures

Testes are under the control of the HP axis

Question 2

Describe the scrotum structurally, including the components of the scrotal septum

Answer 2

• Suspended from the root, or base, of the penis
• Externally, the scrotum appears as a single pouch, divided along the midsagittal plane by a ridge of skin called the Raphe
• Internally, the testis is separated by a septum made of subQ tissue and dartos muscle, which is smooth muscle fiber also running through all the subQ tissue of the scrotum surrounding the testes

Question 3

Describe the components of the spermatic cord and their roles in male reproduction

Answer 3

Vas deferens = carrying sperm
Blood Vessels = vascularize
Lymphatics = drain lymph
Nerves = innervate

Question 4

Name, deep to superficial, the layers surrounding the testes

Answer 4

Tunica albuginea
Tunica vaginalis
Internal spermatic fascia
External spermatic fascia
Dartos muscle
Skin

Question 5

Order proximal to distal, the path of newly formed sperm from the seminiferous tubule to the epididymis.

Answer 5

Once sperm is produced in the seminiferous tubules, sperm move to the rete testis, through the efferent ducts, and into the epididymis, where they are stored and matured prior to ejaculation

Question 6

Trace the path of spermatogenesis from spermatogonia to sperm, focusing on the location of each step, relation to the blood-testis barrier, and ploidy of each step.

Answer 6

• Each tubule is wrapped in a basement membrane with spermatogonia, premature cells, superficially, and transform into sperm deeper in the tubule near the lumen
• Superficial cells are “you” but the lumen is “not you”
• To form the blood-testis barrier to separate “you” from “not you,” Sertoli cells lock together via tight junctions to form a barrier ring

Question 7

Detail the roles of the Sertoli cell, and the Leydig cell, focusing on the HP axis where appropriate

Answer 7

Sertoli cell:
- Lock together via tight junctions to form a barrier ring
- Nourish all maturing sperm cells
- Phagocytize excess cytoplasm as sperm mature
- Control movement of spermatogenic cells toward the lumen and their release into the lumen
- Provide fluids for sperm transport
- Regulate the effects of testosterone

Leydig cell:
- Secrete testosterone when triggered by FSH & LH of HP axis

Question 8

Contrast spermiogenesis & spermination to spermatogenesis

Answer 8

Spermiogenesis & spermination:
Structural transformation of spermatids to sperm
No cell division
Immobile sphere to mobile, elongated shape
Reaching and penetrating an oocyte is key

Spermatogenesis:
About 70 days of:
Mitosis
Meiosis I
Meiosis II
Structural development or spermiogenesis
Migration to lumen
Maturation and storage
ejaculation

Question 9

Describe a sperm structurally, focusing on the roles of each important structure

Answer 9

• At the head, the Acrosome forms on top of the nucleus which narrows and elongates. The acrosome holds enzymes to penetrate an oocyte
• Flagellum develops at the tail end for motility
• Centriole forms at the neck. Centrioles build microtubules that form the principal piece
• Mitochondria proliferate in the middle piece to make ATP to fuel motility

Question 10

Review negative feedback on testosterone levels within the HP axis.

Answer 10

The increase in testosterone levels is detected by the hypothalamus.

The neurosecretory cells in the hypothalamus respond by inhibiting the secretion of GnRH in the anterior pituitary and LH and FSH in gonadotropic cells to decrease testosterone levels.

Question 11

BRIEFLY, contrast the role of LH & FSH in testosterone homeostasis

Answer 11

LH
Stimulates testosterone secretion in Leydig cells

FSH
Works synergistically with testosterone to keep testosterone high in the lumen of seminiferous tubules and ISF around spermatogenesis cells

Question 12

Trace the path of sperm from the ductus epididymis through the rest of the reproductive tract, focusing on the direction of travel of the vas deferens from the testes to the junction with the seminal vesicles

Answer 12

Ductus epididymis
Vas deferens
Ampulla of vas Deferens
Ejaculatory duct
Prostatic, membranous, spongy urethra

The vas deferens runs from the epididymis superiorly and then laterally and posteriorly through the inguinal canal and into the pelvic cavity

Question 13

Compare and contrast the 3 male accessory sex glands, focusing on location, size, and components of secretion into the reproductive tract

Answer 13

Seminal Vesicles:
- Posterior and inferior to the ampulla of the vas deferens
- Produce and secrete the majority of seminal fluid (60%)
- Secrete through the seminal vesicle duct, into the ejaculatory duct just distal to the merger with the ampulla of the vas deferens
- Seminal fluid is slightly alkaline to neutralize the acidity of urethra
- Fructose for sperm ATP production and coagulate sperm post ejaculation

Prostate:
- Donut-shaped gland inferior to the bladder
- Multiple prostatic ducts secrete menial fluid that makes up 25% of the volume of semen
- Its seminal fluid is slightly acidic but is offset by the other 2 glands
- Citric acid for sperm ATP production (Krebs cycle)
- Seminal fluids contain proteolytic enzymes that break down clotted semen and liquefy it
- Contains seminal plasmin, an antibiotic against microbes in semen

Bulbourethral (Cowper’s) Glands:
- Paired pea-sized glands laying inferior to the prostate and posterior to the root of the peen, and within deep muscles of the perineum
- Seminal fluid is slightly alkaline and contains mucous to lubricate passage through the urethra and external urethral opening (tip of the penis)

Question 14

Describe semen components, role & clotting/unclotting

Answer 14

• A mixture of sperm from the testes and seminal fluid contributions from the 3 glands
• Fluid is a transport medium for sperm, nourishes the sperm, and protects against acidic environments of the male urethra and female vagina
• Once ejaculated, semen clots in about 5 minutes from the clotting factors in seminal vesicle fluid
• Then 15 minutes after that the hydrologic enzymes of prostatic seminal fluid break up the clot and liquefy the semen

Question 15

Detail the anatomy of the penis, focusing on 3 parts proximal to distal, erectile tissue components, transverse sectional components, attachment & associated musculature, and suspensory ligaments

Answer 15

Proximal root
- The bulb lies medially and is the posterior extension of the corpus spongiosum. Attached to the inferior surface of deep muscles of the perineum and is enclosed by bulbospongiosus
- The Crust of the penis is the posterior extension of the 2 more lateral corpora cavernosa of the penis. They flare laterally and attach to the inferior ischial and pubic rami and are surrounded by ischiocavernosus

Middle “body” section
- Composed of 3 cylindrical tubes: singular corpus spongiosum runs medially and ventrally, paired corpora cavernosa run dorsolaterally
- All 3 are enclosed in layers of tunica albuginea and contain erectile tissue
- The corpus spongiosum holds the spongy urethra
- Skin and subQ layer lay superficial to all 3

Distal “glans penis”
- Entirely corpus spongiosum, enlarged into an acorn shape, with a margin called the corona
- The spongy urethra dilates at the most distal margin, forming the slit-like external urethral orifice
- Prepuce, or foreskin, covers the glans in uncircumcised males

The suspensory ligament, along with the fundiform ligament, suspends the weight of the penis

Question 16

Contrast erection & ejaculation, anatomically & physiologically

Answer 16

Erection:
- Sexual arousal triggers parasympathetic output at the sacral spinal region which produces and releases nitric oxide into the erectile tissues of the penis. NO relaxes smooth muscles of the arterioles feeding erectile tissue, increasing blood flow, and relaxes smooth muscle fibers within erectile tissues to widen blood sinuses to fill with incoming blood

Ejaculation:
- Sympathetic reflex from the lumbar spinal region
- The internal urethral sphincter closes to prevent entry of urine into the urethra, and backflow of semen into the urinary bladder
- Pre-ejaculation, peristalsis moves semen
- May cause emission, a discharge of a small amount of semen that will contain sperm
- Contraction of bulbospongiosus, ischiocavernosus, and superficial transverse perineus triggers ejaculation
Post stimulation, afferent arterioles constrict, blood sinuses shrink, efferent veins re-dilate, blood leaves the penis and it returns to a flaccid state

Question 17

Name the 4 ways to organize female reproductive structures and name which of the 4 is under the control of the HP axis

Answer 17

Ovaries
Uterine tubes
Uterus/vagina
External Structures

Ovaries are responsible for hormone (progesterone and estrogen) production within the HP axis

Question 18

Describe the anatomy of the ovaries in detail, including location, associated ligaments, and internal structure.

Answer 18

• Paired ovaries lie within the peritoneal cavity, about the size and shape of an almond
• Lateral to the uterus and inferior to the uterine tube
• Hilum is the media portion where blood vessels, lymphatics, and nerves enter and exit
• Ovarian follicles are embedded in the ovarian cortex and work to hold the primary (and eventually secondary) oocytes inside the follicle

Suspension in the pelvic cavity:
- The ovarian ligament runs medially from the ovary to anchor it to the uterine, it runs through the broad ligament
- The broad ligament is the flat sheet anchoring the uterus to the pelvic wall, but it also grabs a bit of the ovary to hold it in place
The suspensory ligament hangs the ovaries from the pelvic wall

Question 19

Describe oogenesis, focusing on relevant structures, timing, and relationship to meiosis.

Answer 19

• Each primary oocyte that forms in the ovaries prenatally (and freezes in meiosis I) gets surrounded by a primordial follicle
• At the onset of puberty, FSH and LH from the HP axis stimulate the development of primordial follicles into primary follicles
• With continued monthly maturation the primary follicle develops into a secondary follicle
• To end each monthly cycle of follicular development, a secondary follicle develops into a mature follicle. That primary pre-natally ovulation in meiosis I that got paused 14 years ago continues to produce a secondary oocyte and a smaller first polar body
• Mature follicle fuses with the ovarian mesothelium and ruptures - ovulating the secondary oocyte into the pelvic cavity
• Potentially sperm penetrates the secondary oocyte, which triggers the final step of meiosis II which produces the mature haploid ovum which will soon be a zygote

Question 20

Contrast primordial, primary, secondary, and mature follicles in terms of size, location, type of oocyte, and structural & functional aspects

Answer 20

Primordial follicle:
- Largest oocyte
- Primary oocyte
- Follicular cells deep to the basement membrane and stromal cells superficial to it

Primary follicle:
- 2nd largest oocyte
- Primary oocyte
- Granulosa cells, zona pellucida, theca folliculi

Secondary follicle:
- 3rd largest oocyte
- Primary oocyte
- Granulosa cell, fluid-filled antrum, theca externa and theca interna, corona radiata, zona pellucida

Mature follicles:
- Smallest oocyte
- primary oocyte
- Granulosa cell, zona pellucida, corona radiata, fluid-filled antrum, theca externa and theca interna
- Ruptures upon ovulation to expel the secondary oocyte into the pelvic cavity

Question 21

Describe ovulation, in the context of follicular structure, ovarian structure & ongoing meiosis

Answer 21

The process by which mature follicle fuses with ovarian mesothelium and expels the secondary oocyte into the pelvic cavity

Swept into uterine tubules, and if sperm is present, the sperm will potentially penetrate the secondary oocyte, which triggers the final step of meiosis II which produces the mature haploid ovum - soon to be a zygote

Question 22

Describe the uterine tubes anatomically, focusing on location, associated ligaments, sections of the tube, histology, and role in oocyte migration

Answer 22

A route for sperm to reach a secondary oocyte and transport of secondary oocytes and fertilized ova to the uterus

Sections of tube laterally to medially:
Fimbriae = tethers tube to the ovary
Infundibulum = inferiorly pointed funnel part holding the fimbriae
Ampulla = lateral ⅔ and widest part
Isthmus = narrower and thicker medial 1/3rd connects to the lateral wall of the uterus

Histologically:
Mucosa
- Simple ciliated columnar to “sweep” oocytes toward the uterus
- Some non-ciliated Peg cells with microvilli to secrete fluid to nourish ova
- Lamina propria to underlie the epithelium

Muscularis
- Standard circular and longitudinal layer of smooth muscle (movement by peristalsis)

Serosa
- The uterus is the most inferior organ of the peritoneum, so uterine tubes are wrapped superficially in simple squamous mesothelium plus loose areolar CT = serosa

Question 23

Describe the role of the uterus. Describe it anatomically, focusing on shape, location, associated ligaments, sections, and histological layers.

Answer 23

The size and shape of an inverted pear laying medially at the very inferior aspect of the pelvic cavity

Roles:
Pathway for sperm to reach the uterine tubules
Site of implantation of a fertilized ovum
Site of fetal development during pregnancy
Source of menstrual flow

Anchored by:
Broad ligaments
Round ligaments
Uterosacral ligaments
Cardinal ligaments

Structurally:
Fundus = dome-shaped superior portion
Body = central portion tapering inferiorly
Isthmus = short section inferior to the body connecting to the more inferior cervix
Cervix = narrow, most inferior portion

Histologically:
Endometrium = mucosa
Myometrium = muscularis
Perimetrium = serosa

Question 24

Contrast the two endometrial layers in terms of the structure & function of the uterus, focusing on location, vasculature, associated glands, and fate during the menstrual cycle

Answer 24

Stratum functionalis
- More superficial
- Heavily vascularized (spiral arterioles)
- The functional layer is sloughed off each month during menstruation

Stratum basalis
- Deeper
- Mitotically replaces the sloughed-off functional layer

Question 25

Name the functions of the vagina, and describe it anatomically & histologically.

Answer 25

The superior aspect meets the much narrower cervix and forms a fornix (vault)

A passage for:
- Sperm to reach the uterine tubes
- Menstrual flow to be excreted
- Childbirth

Histologically:
Mucosa
- non-keratinized stratified squamous
- Lamina propria
- arranged in transverse ridges of rugae
- Packed with glycogen that decomposes to organic acids, which acidifies the vaginal canal

Muscularis
- Standard circular and smooth layer
- Lamina propria has elastic fibers for extensibility and elasticity

Adventitia
- Anchors the vagina to the rectum posteriorly and to the urinary bladder and urethra anteriorly

Question 26

Contrast the anteflexion & retroflexion of the junction of the uterus & vagina

Answer 26

In the anteflexion position, the vagina meets the cervix at about a 90-degree angle
- vesicouterine pouch

In the retroflexion position, they meet in a straight line
- rectouterine pouch

Question 27

Give the function of the vulva & accessory sex glands, including mons pubis, labia majora, labia minora, clitoris, vestibule of the vagina, vestibular bulb, and Bartholin’s glands.

Answer 27

Mons pubis = cushioning pubic symphysis
Labia majora = surrounds the vaginal orifice laterally and houses sebaceous and sudoriferous glands
Labia minora = surrounds the vaginal orifice
Clitoris = erection during arousal
Vestibule = house vaginal orifice, external urethral orifice, and clitoris
Vestibular bulb = exerts pressure on the penis during intercourse
Bartholin’s glands = secrete mucous

Question 28

Understand the concept of homologous structures, between male & female reproductive anatomy, and be able to describe ONE homologous pair of structures.

Answer 28

The ovaries of females is homologous to the testes of males.
Both are gametes (oogenesis in female spermatogenesis in males)

Question 29

Describe the perineum, the two components of it, and the structures found in each component

Answer 29

• A diamond-shaped area bordered by 4 elements of the skeletal system (anterior pubic symphysis, posterior coccyx, and lateral two ischial tuberosity)
• Anterior triangle in the female (urogenital triangle) houses the vulva
• The posterior (anal triangle) houses the anus

Question 30

Describe the location, structure, and role of the mammary glands in producing and secreting breast milk.

Answer 30

• Milk is produced in glandular alveoli, enters secondary tubules within a lobe, moves anteriorly through the mammary ducts, and into lactiferous sinuses or terminal dilations of lactiferous ducts
• Prolactin from the HP axis has a huge role in milk production (with the help of estrogen and progesterone)
• Oxytocin from the posterior pituitary stimulates the ejection of milk via positive feedback

Question 31

Name the 3 locations of the female reproductive cycle, and the 7 molecules involved, focusing on hypothalamic & ovarian hormones

Answer 31

3 locations:
Hypothalamus and adenohypophysis
Ovary
Uterus

7 molecules:
GnRH
FSH
LH
Estrogen
Progesterone
Inhibin
Human chorionic gonadotropin

Question 32

Give a general overview of the HP axis, hypothalamic hormones, adenohypophyseal hormones, and effector hormones.

Answer 32

HP axis = body’s main stress response between the hypothalamus and pituitary

Hypothalamic hormones = 5 releasing hormones and 2 inhibiting hormones that either stimulate the release of trophic hormones or inhibit their release

Adenohypophyseal hormones = 5 trophic areas that secrete 7 different anterior pituitary hormones that go out to act on effectors

Effector hormones = organs that release their own hormones (ovaries releasing estrogen and progesterone in females and testes releasing testosterone in males)

Question 33

Contrast the 3 phases of the ovarian cycle, focusing on average length (based on the 28-day average), hormones involved, locations, and key events. Trying at each phase to link ovarian hormone production to simultaneous events going on in the uterus, as part of the uterine, or menstrual, cycle

Answer 33

Follicular (Days 1-14):
- A couple of primary follicles grow and develop into secondary follicles, driven by FSH and LH, however, only one is needed
- Over the first 6 or so days the couple of growing follicles secrete estrogen, which starts to rise in the blood
- About the 6th day, one follicle becomes dominant and the rising estrogen for the next 4-5 days inhibits FSH and LH release by the anterior pituitary
- From about days 1–14 estrogen levels keep rising as the dominant follicle continues to secrete estrogen that cuts off FSH and LH for a few days
- Rising estrogen reaches levels that stimulate FSH and huge amounts of LH as the secondary follicle grows to become a mature follicle ready to ovulate

Ovulatory (Days 14-15):
- LH surge at days 14-15 takes over and drives meiosis of primary oocyte to secondary oocyte and ovulation
- After 14 days of actively growing follicles secreting estrogen, follicular development is over and estrogen level drops quickly

Luteal (Days 15-28):
- Post ovulation, the corpus luteum secretes inhibin which heads back to the anterior pituitary and inhibits secretion of FSH and LH
- Remaining LH transforms the empty follicle into the corpus hemorrhagic and then the corpus luteum, which then produces 11-12 days of high progesterone to prepare the uterus for ovum implantation
- If fertilization does not occur, the corpus luteum slowly starts to drop progesterone production
- If fertilization occurs, the chorion of the developing embryo secretes human chorionic gonadotropin, which heads back to the corpus luteum and green-lights it to keep producing progesterone for the next 10-12 weeks to support pregnancy

Question 34

Describe the role of relaxin in facilitating uterine implantation

Answer 34

Calm down contractions of the Myometrium during the time most likely for a fertilized ovum to implant in the uterine wall

Question 35

Describe the 28-day profiles of LH, FSH, estrogen & progesterone, tying hormone profiles into physiological events in the ovarian & uterine cycles

Answer 35

Uterine Cycle:
For the first 14 days, estrogen is pumped from the developing follicles of the ovary, then for the next 14 days, it’s bombed with progesterone from the corpus luteum

Question 36

Describe the uterine cycle in terms of locations & molecules involved!

Answer 36

Locations:
Ovary
Uterus

3 molecules:
Estrogen
Progesterone
Human chorionic gonadotropin

Question 37

Contrast the 3 phases of the uterine cycle, focusing on average length (based on the 28-day average), hormones involved, locations, and key events. Trying at each phase to link uterine events back to ovarian cycle events

Answer 37

Menstruation (Days 1-5):
- If fertilization doesn’t happen progesterone levels from the corpus luteum will drop
- Progesterone keeps the spiral arterioles feeding the endometrium in a normal balance of vasoconstriction and vasodilation
- For about 5 days, excessive alternating vasodilation and vasoconstriction aren’t good. Spiral arterioles will fatigue and rupture. Without adequate blood supply, the functional layer will die. - Dead cells, tissue, and blood from ruptured vessels become menstrual flow. The basal layer stays.
- Estrogen will rebuild the functional layer in 8 days until ovulation day (angiogenesis= building blood vessels, mitosis = building cells & tissues)

Proliferation (Days 6-14):
- Estrogen builds female reproductive structures, secondary sex characteristics, and uterine (exocrine) glands
- It will create a thin mucous layer in the cervix to facilitate the passage of sperm into the uterus
- With the degeneration of mature follicles, estrogen levels will plummet and there’s no anabolic growth via estrogen in the uterine wall
- A little bit of relaxin will be secreted by the corpus luteum to relax the uterine wall and prepare it for possible implantation

Secretory (Days 15-28):
- Progesterone and estrogen stay elevated above background levels, functional layer will continue to develop
- Angiogenesis to further vascularize the endometrium, and more mitotic growth to further thicken it
- Uterine glands secrete “broth” rich in macromolecules
- If implantation happens, the chorion of the implanted embryo will secretion human chorionic gonadotropin (hCG) to go back to the corpus luteum and stimulate more progesterone
- Without fertilization, the corpus luteum cuts off the progesterone supply
- Without progesterone, spiral arteries start to spasm

Question 38

Describe the role of hCG in dictating the fate of the corpus luteum

Answer 38

Stimulates the corpus luteum to secrete progesterone