1
Q
What are the primary reproductive organs called?
A
Gonads (male: testes, female: ovaries), this is where the gametes, as well as the primary sex hormones, are produced.
2
Q
What is the reproductive tract?
A
The system of ducts that are specialized to transport or house the gametes once they are produced.
3
Q
What are gametes?
A
Reproductive, or germ cells, each containing a half set of chromosomes.
4
Q
What are the two essential reproductive functions of males?
A
- Production of sperm - produced in the testes.
- The delivery of sperm to the female - sperm leave the testes and are mixed with secretions from the seminal vesicles, prostate, and bulbourethral glands, which support sperm viability and enable their delivery to the female reproductive system via the penis.
5
Q
What are the functions of female reproductive system?
A
- The production of ova: Ova or eggs are produced in the ovaries and individual ova undergo cyclical maturation.
- Reception of sperm: Occurs in the vagina, which is a muscular tube that connects the uterus, via the cervical canal, to the external environment.
- Transport of ovum and sperm to a common site for fertilization: The ova leave the ovaries and move into the Fallopian tubes, where they can be fertilized by sperm that have travelled from the vagina, through the cervical canal, into the uterus, and ultimately into the Fallopian tubes.
- Maintenance of the developing fetus: This occurs within the uterus for about 9 months.
- Birth of the baby (parturition)
- Nourishing the baby by milk production (lactation)
6
Q
What is sexual differentiation, and at what levels does it occur?
A
Sexual differentiation is the embryonic development of external genitalia and the reproductive tract. It occurs at three levels: genetic, gonadal, and phenotypic.
7
Q
How is genetic sex determined, and how does it influence gonadal and phenotypic sex?
A
Genetic sex is determined by the sex chromosome combination at conception. Gametes are produced through meiosis, where diploid parent cells divide to form haploid gametes. Sperm carry either an X or Y chromosome, while all ova carry a single X chromosome. Fertilization creates a diploid zygote: XX results in a female embryo, and XY results in a male embryo. Genetic sex determines gonadal sex (presence or absence of a Y chromosome), which then influences phenotypic sex.
8
Q
Diploid vs. Haploid
A
Diploid = Containing two complete sets of chromosomes, with one chromosome from each pair being derived from the sperm cell, and one from the ova. 46 chromosomes, 23 pairs
Haploid = Having a single set of unpaired chromosomes. 23 individual chromsomes
9
Q
How is gonadal sex determined during early gestation, and what role does the H-Y antigen play?
A
Gonadal sex is determined by the presence or absence of a Y chromosome. During the first six weeks of gestation, the H-Y antigen on the Y chromosome stimulates the gonads to develop into testes. In the absence of H-Y antigen (no Y chromosome), the gonads develop into ovaries.
10
Q
True or False: Male and female external genitalia and reproductive tracts develop from the same embryonic tissue.
A
False. Male and female external genitalia develop from the same tissue, but the reproductive tracts do not.
11
Q
What determines an individual’s phenotypic (anatomical) sex, and how do androgens influence its development?
A
Phenotypic sex is determined by gonadal sex. Embryos initially have the potential to develop either male or female genitalia and reproductive tracts. Androgens from developing testes promote male reproductive system development, while the absence of androgens results in a female reproductive system.
12
Q
How does meiosis differ from mitosis, and what are the main outcomes of meiosis I and II?
A
Unlike most body cells that divide by mitosis, specialized germ cells undergo meiosis to produce haploid gametes (sperm and ova) with 23 unpaired chromosomes.
Meiosis I: Homologous chromosomes pair and separate, producing two daughter cells, each with a single set of chromosomes (haploid) where each chromosome still has two sister chromatids.
Meiosis II: Sister chromatids separate, resulting in four haploid daughter cells, each with one chromatid per chromosome.
13
Q
What are the two primitive duct systems in the undifferentiated embryo?
A
The Wolffian and Mullerian ducts
14
Q
What is the placenta?
A
An organ that connects the developing fetus to the uterine wall to allow nutrient uptake, thermo-regulation, waste elimination, and gas exchange via the mother’s blood supply.
15
Q
How do Wolffian ducts develop into the male reproductive system, and what roles do testosterone, dihydrotestosterone, and Müllerian-inhibiting factor play?
A
The placenta secretes hCG, which stimulates the testes to produce testosterone. Testosterone causes the Wolffian ducts to develop into the male reproductive system. Testosterone is also converted to dihydrotestosterone (DHT), which drives the development of male external genitalia. Meanwhile, the testes secrete Müllerian-inhibiting factor, which causes the Müllerian ducts to regress.
16
Q
What is responsible for the development of male external genitalia?
A
Dihydrotestosterone
17
Q
How are female reproductive tract and external genitalia developed?
A
Without testosterone, the Wolffian ducts degrade and the Müllerian ducts develop into the female reproductive tract and external genitalia. Although embryos are exposed to high levels of female sex hormones during gestation, testosterone is required to induce male sexual differentiation; without it, fetuses develop female characteristics by default.
18
Q
What would be the observed result if a genetic male whose testes fail to develop or target tissues lack testosterone receptors?
A
An apparent phenotypic female that is sterile due to lack of ovaries.
19
Q
What would be the observed result if a deficiency in the enzyme that converts testosterone to DHT?
A
An individual having a male reproductive tract with female external genitalia.
20
Q
What would be the observed result if a genetic female with excessive adrenal secretion of DHEA during fetal development?
A
Reproductive tract and external genitalia are masculinized, the extent of which depends on
how much dehydroepiandrosterone is secreted.
21
Q
Where are the testes located, and when do they normally descend?
A
The testes are located outside the abdominal cavity in the scrotal sac. They typically descend into the scrotum in the last months of fetal life. In premature males, descent may occur in early childhood.
22
Q
What is cryptorchidism?
A
If the testes remain undescended into adulthood, which can lead to sterility because spermatogenesis cannot occur at normal body temperature.
23
Q
Why the location of the testes is important?
A
The scrotal location of the testes is crucial for spermatogenesis, which requires a temperature several degrees below core body temperature. In cryptorchidism, sperm production is impaired. Cremaster and dartos muscles, along with a spinal reflex, adjust scrotal position to help regulate testicular temperature.
24
Q
How do the scrotal muscles regulate testicular temperature for spermatogenesis?
A
When the testes are too cold, the cremaster and dartos muscles contract to bring them closer to the body for warmth. When the testes are too hot, the muscles relax to move them away from the body.
25
What is the main structure of the testes where sperm are produced?
Coiled seminiferous tubules
26
What are Leydig cells?
These are the cells that produce and secrete testosterone under the control of luteinizing hormone. They are also known as interstitial cells.
27
What cells produce and secrete testosterone?
Leydig cells
28
Where are Leydig cells located, and what are the roles of the testosterone they produce?
Leydig cells are located in the connective tissue between the seminiferous tubules. They secrete testosterone, some of which enters the bloodstream to act on distant target cells, while most enters the lumen of the seminiferous tubules to support sperm production.
29
What are the actions of testosterone (5 categories)?
1. Effects before birth - it causes the masculinization of the reproductive tract and external genitalia + the descent of the testes into the scrotum
2. Effects on sex-specific tissues after birth - it maintains the reproductive tract throughout adulthood, promotes spermatogenesis, and promotes maturation of the reproductive system at puberty
3. Other reproductive effects - develops sex drive at puberty and controls the secretion of gonadotropin hormone
4. Effects on secondary sexual characteristics - causes voice to deepen, development of male pattern of body hair, and promotion of muscle growth (protein anabolism)
5. Non-reproductive actions - promotes bone growth at puberty and plays a role in the closing of the epiphyseal plates. May also induce aggressive behaviour
30
The majority of the seminiferous tubules are composed of what cell types?
Germ cells and Sertoli cells
31
What is spermatogenesis?
The process in which diploid (46 chromosomes) primordial germ cells are converted into motile sperm cells with a haploid (23 chromosomes) set of chromosomes
32
What are the main stages involved in producing mature sperm?
Mitotic Proliferation: Spermatogonia (in the outer layer of seminiferous tubules) divide mitotically to maintain a germ cell pool. One daughter cell remains at the edge, while the other moves toward the lumen and undergoes two more mitotic divisions to form four primary spermatocytes, which enter a resting phase before meiosis.
Meiosis: Each primary spermatocyte forms two secondary spermatocytes (23 double-stranded chromosomes). Meiosis II produces two spermatids from each secondary spermatocyte (23 single-stranded chromosomes). Overall, one spermatogonium can produce 16 spermatids.
Packaging (Spermiogenesis): Spermatids mature into spermatozoa by shedding cytosol and most organelles, streamlining the cell for motility.
33
The primordial germ cells are called?
Spermatogonia
34
Indicate whether the following cells at each step of spermatogenesis is haploid or diploid, and whether the chromosomes are single or double stranded? (spermatogonium, spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, spermatozoa)
Spermatogonium: diploid, single
Spermatogonia: diploid, single
Primary spermatocytes: diploid, double
Secondary spermatocytes: haploid, double
Spermatids: haploid, single
Spermatozoa: haploid, single
35
A mature spermatozoa has which four parts?
Head: Consists of the nucleus
Acrosome: Enzyme-packed vesicle at the tip of the head that is needed to penetrate the ovum
Midpiece: Packed full of mitochondria to provide energy for locomotion
Tail (flagellum): Movement of this provides propulsion (a process that requires lots of ATP)
36
Which part of the spermatozoa has mitochondria?
Midpiece
37
What makes up the walls of the seminiferous tubules?
A single layer of Sertoli cells
37
What roles do Sertoli cells play during spermatogenesis?
During spermatogenesis, developing sperm cells pass between and are partially engulfed by Sertoli cells as they migrate toward the lumen. The sperm head remains embedded in Sertoli cells until the sperm is fully mature.
38
What are the six functions of Sertoli cells for spermatogenesis?
1. The tight junctions which exist between the Sertoli cells form the blood-testes barrier. For a substance to reach the intratubular fluid, it must pass through the Sertoli cells. This allows the Sertoli cels to control the intratubular environment optimal for developing spermatozoa.
2. Nourish sperm cells.
3. Absorb developing sperm cytoplasm and remove any defective germ cells.
4. Secrete seminiferous tubule fluid into the lumen to flush released sperm into the epididymis for storage.
5. Secrete androgen-binding protein that helps to concentrate testosterone in the lumen.
6. The site of action for testosterone and FSH to regulate spermatogenesis.
39
The testes are under the control of which hormones?
LH and FSH
40
What are the roles of LH and FSH in males?
LH stimulates the Leydig cells to secrete testosterone and FSH acts on the Sertoli cells to stimulate spermatogenesis and to secrete inhibin. Testosterone has a direct negative feedback pathway at the level of both the hypothalamus to decrease GnRH release and at the anterior pituitary to decrease LH and FSH release. The inhibin released by the Sertoli cells feeds back to the anterior pituitary to decrease FSH release.
41
What is the role of inhibin? What releases it?
It's released by the Sertoli cells and it feeds back to the anterior pituitary to decrease FSH release.
42
The male reproductive tract consists of?
The epididymis and ductus deferens, the accessory sex glands, and the penis
43
What is the role of the epididymis and ductus deferens in sperm transport and storage?
After sperm are produced in the seminiferous tubules, they enter the epididymis, a tightly coiled tube (~5 m long) where sperm are not yet motile due to the low pH. The epididymal ducts converge to form the ductus deferens, which empties into the urethra. Sperm can be stored in the epididymis for months until ejaculation.
44
What are the three primary accessory sex glands whose secretions make up the bulk of semen? What are their functions?
Seminal vesicles, prostate gland, and bulbourethral glands.They function to provide support for the continuing viability of sperm inside the female reproductive tract.
45
What is fibrinogen?
A precursor of the protein fibrin, which forms the meshwork of a clot.
46
What are the seminal vesicles, and what roles do they play in semen composition and sperm function?
There are two seminal vesicles, each emptying into a ductus deferens just before the urethra. They contribute the bulk of semen, provide fructose as an energy source for sperm, secrete prostaglandins to stimulate smooth muscle contractions in both male and female reproductive tracts, and secrete fibrinogen.
47
What contributes to the bulk of semen?
Seminal vesicles
48
What is the prostate gland, and what are its two primary purposes?
It's a large gland that surrounds the ejaculatory ducts and urethra. Two main purposes:
1. To secrete an alkaline fluid to neutralize the acidic environment of the vagina.
2. Secretes clotting enzymes which act on the fibrinogen from the seminal vesicles to produce fibrin, which clots the semen and keep it within the female reproductive tract
49
What are the bulbourethral glands? What is their role?
Aka Cowper's glands. They are a pair of glands that both empty into the urethra, one on each side, before the urethra enters the penis. They secrete a clear substance during sexual arousal and this fluid helps to lubricate the urethra for sperm to pass through.
50
What are the granulosa cells?
The layer of cells immediately surrounding a developing oocyte within an ovarian follicle.
51
What are the steps of oogenesis?
1. Fetal Development: Undifferentiated primordial germ cells in the ovaries undergo mitosis. By ~5 months of gestation, 6–7 million primary oocytes are formed, each arrested before meiosis I and surrounded by granulosa cells forming a primordial follicle. By birth, only ~2 million remain.
2. Follicle Development: Primordial follicles give rise to primary follicles. Most undergo atresia, but after puberty, about 400 follicles will mature and release ova. By menopause, all follicles are exhausted.
3. Meiotic Division I: During each menstrual cycle, some primary follicles develop into secondary follicles. The primary oocyte grows, accumulates cytoplasm, and undergoes meiosis I just before ovulation, producing a secondary oocyte (most cytoplasm) and a first polar body (degenerates).
4. Ovulation and Meiosis II: The secondary oocyte is released during ovulation. If fertilization occurs, it undergoes meiosis II, forming a second polar body and a haploid ovum, which combines with the sperm’s haploid chromosomes to form a diploid zygote.
52
Primordial follicle VS. Primary follicle
Primordial follicle: Forms during fetal life and consists of a primary oocyte arrested before meiosis I, surrounded by a single layer of granulosa cells. It represents part of the fixed lifetime supply of potential ova, most of which will undergo atresia.
Primary follicle: Forms when a primordial follicle begins to develop. It increases in size as the oocyte accumulates cytoplasm and will either continue toward ovulation or undergo atresia, with only about 400 follicles ovulating after puberty.
53
Primary vs. Secondary oocyte
Primary oocyte: A diploid cell (46 chromosomes) that is formed before birth and remains arrested in prophase I of meiosis until puberty. During each menstrual cycle, one primary oocyte resumes meiosis I just before ovulation.
Secondary oocyte: Produced when the primary oocyte completes meiosis I. It is haploid (23 chromosomes, still duplicated as sister chromatids), receives most of the cytoplasm, and is released during ovulation. The secondary oocyte is arrested in metaphase II and will only complete meiosis II if fertilization occurs.
54
First vs. Second polar body
First polar body: Formed when the primary oocyte completes meiosis I. It is haploid (23 chromosomes, still duplicated) and contains very little cytoplasm. Its role is to discard excess genetic material, and it usually degenerates.
Second polar body: Formed when the secondary oocyte completes meiosis II, which only happens after fertilization. It is also haploid (23 single chromatids), contains minimal cytoplasm, and degenerates. Its purpose is the same—to eliminate extra chromosomes while preserving cytoplasm for the ovum.
55
Indicate whether the cell at each step of oogenesis is haploid or diploid, and whether they are single or double stranded (Oogonium, primary oocytes, primary oocyte, secondary oocyte, mature ovum)
Oogonium: diploid, single
Primary oocyte (2nd step): diploid, double
Primary oocyte (3rd step): diploid, double
Secondary oocyte: haploid, double
Mature ovum: haploid, single
56
What are the two female reproduction cycles?
The ovarian cycle (occurs in the ovaries and prepares an ova for release) and the uterine cycle (prepares the uterus for implantation)
57
At the onset of puberty, the ovarian cycle alternates between which two phases?
The follicular phase (prepares a mature egg) and the luteal phase (prepares the reproductive tract for potential implantation)
58
The follicular phase lasts for how many days? How about the luteal phase.
Follicular phase - first 14 days of the ovarian cycle
Luteal phase - last 14 days
59
What happens during the follicular phase?
1. The follicular phase begins with the proliferation of granulosa cells in a primary follicle, forming multiple layers around the oocyte.
2. Granulosa cells secrete glycoproteins that form the zona pellucida, separating the oocyte from the granulosa cells. At the same time, ovarian connective tissue differentiates into thecal cells that surround the granulosa cells. Together, these are called follicular cells. Development of the primary follicle occurs under the influence of FSH and estrogen.
3. As the follicle enlarges, it becomes a secondary follicle, which is capable of secreting estrogens, primarily estradiol. This stage is mainly due to FSH and estrogen.
4. A fluid-filled cavity (antrum) forms within the granulosa cells. Expansion of the antrum increases follicle size and estrogen secretion increases.
5. Each cycle, one follicle develops faster and becomes a mature follicle by around day 14. The oocyte completes its first meiotic division to become a secondary oocyte, which is located to the side of the follicle.
6. Under the influence of LH and FSH, ovulation occurs around day 14. The follicle ruptures, releasing the ovum into the abdominal cavity, and antral fluid helps move it into the oviduct. This marks the end of the follicular phase.
60
During the follicular phase, when does the follicle become capable of secreting estrogens, primarily estradiol?
Secondary follicle
61
When does ovulation occur?
Around day 14 under the influence of LH and FSH.
62
What represents the end of the follicular phase?
The release of the ovum
63
Describe the luteal phase.
1. Once the ovum has been released, the remaining follicular cells undergo a process called luteinisation to form the corpus luteum. The corpus luteum becomes highly vascularized and it becomes very active in secreting hormones, mainly progesterone with some estrogens.
2. If within around 14 days the ovum is not fertilized and implanted, the corpus luteum rapidly degenerates to form the corpus albicans, which is essentially a fibrous scar tissue. This signifies the end of one ovarian cycle and the follicular phase begins again.
64
What signifies the end of one ovarian cycle and the follicular phase begins again?
If within around 14 days the ovum is not fertilized and implanted, the corpus luteum rapidly degenerates to form the corpus albicans
65
The ovarian cycle is under the control of which hormones?
FSH, LH and estrogen
66
How do FSH, LH, and estrogen regulate the ovarian cycle during the follicular phase?
FSH and estrogen stimulate early follicular development and formation of the secondary follicle, while LH contributes to estrogen production by the developing follicle. During most of the follicular phase, rising estrogen levels inhibit FSH secretion by reducing the response of FSH-secreting cells to GnRH, leading the anterior pituitary to preferentially release LH. As estrogen levels continue to rise, estrogen shifts to a positive feedback effect, triggering a surge in LH secretion, which has several downstream actions.
67
When LH surge occurs during the follicular phase?
During ovulation
68
What are the actions of LH surge?
* It stops estrogen synthesis by follicular cells
* It reinitiates meiosis in the oocyte
* It triggers release of local factors that increase the swelling of the follicle and weaken the wall
* It differentiates the follicular cells into luteal cells
69
Which hormones control the luteal phase?
LH continues to maintain the corpus luteum. Corpus luteum begins secreting large amounts of progesterone in preparation of a potential pregnancy. Progesterone causes changes in the uterine lining to prepare for potential implantation of an embryo to establish a pregnancy. If no implantation occurs, the rapid degradation of the corpus luteum results in a rapid drop in circulating progesterone.
70
Which hormone causes changes in the uterine lining to prepare for potential implantation of an
embryo to establish a pregnancy?
Progesterone
71
Which hormone is important in the production of estrogen which is secreted in increasing quantities
by the secondary follicles?
LH
72
Which hormone exerts a positive feedback action to cause a surge in LH secretion?
Estrogen
73
Which hormone is important for stimulating early follicular development and formation of the secondary follicle?
FSH
74
Which hormone inhibits the production of LH and FSH by the pituitary gland?
Inhibin
75
Which hormone is released by Sertoli cells, feeds back to the anterior pituitary to decrease FSH release?
Inhibin
76
Which hormone stimulates the Leydig cells to secrete testosterone?
LH
77
Which hormone has a direct negative-feedback pathway at the level of both the hypothalamus and the anterior pituitary?
Testosterone
78
Which hormone acts on the Sertoli cells to stimulate spermatogenesis and to secrete inhibin?
FSH
79
Which hormone stimulates the anterior pituitary to release LH and FSH?
GnRH
80
How long does the uterine cycle last?
Lasts around 28 days. During this cycle, the uterus is prepared for the possible implantation of a fertilized ovum. If this does not occur, the uterus is stripped clean to prepare for the next cycle.
81
Myometrium vs. Endometrium
Myometrium = an outer layer comprised of smooth muscle
Endometrium = the inner lining that is highly vascularized and also has many glands
82
What are the roles of estrogen and progesterone in preparing the uterus for implantation?
Estrogen stimulates growth of the endometrium and myometrium and induces the expression of progesterone receptors in the endometrium. Progesterone then acts on the endometrium to transform it into a lining suitable for implantation and reduces uterine contractility to support implantation and embryo development.
83
What are the three phases of the uterine cycle?
1. The menstrual phase: With decreased estrogen at the end of the luteal phase, the endometrial growth ceases. As well, the decrease in estrogen and progesterone results in the local release of prostaglandins. These prostaglandins constrict the blood supply to the endometrium and cause the myometrium to rhythmically contract. The endometrial lining then sloughs off and is expelled out through the vagina. During menstruation, the newly developing follicles are secreting enough estrogen to begin repair of the endometrium.
2. The proliferative phase: Begins when the menstrual flow ceases and it coincides with the later stages of the ovarian follicular phase. At the end of the menstrual phase, the endometrium consists only a few layers of cells less than 1 mm in thickness. Under the influence of estrogen, these cells proliferate and there is an ingrowth of glands and blood vessels until the lining is 3-5 mm in thickness. Ovulation occurs during this phase, in which the ovum leaves the ovary and begins travelling through the oviduct towards the uterus.
3. The secretory phase: With the formation of the corpus luteum and the beginning of the ovarian luteal phase, the secretory phase begins. The large amounts of progesterone and estrogen convert the endometrium into a richly vascularized and glycogen-filled tissue necessary to support an early embryo. By this phase, the ovum has made its way to the uterus. Without implantation, the corpus luteum degrades and triggers the next menstrual phase.
84
Ovulation occurs during which phase of the uterine cycle?
The proliferative phase
85
Which parts of the ovarian and uterine cycles align?
* The menstrual phase coincides with the end of the luteal and beginning of a new follicular phase. Thus, the ovarian and uterine cycles begin at the same time.
* The proliferative phase coincides with the later stages of the ovarian follicular phase.
* The secretory phase coincides with the beginning of the luteal phase and the formation of the corpus luteum.
86
What is endometriosis?
A disorder in which the endometrium grows outside of the uterus, commonly on the ovaries, fallopian tubes, connective tissues such as the ligaments stabilizing the uterus and ovaries, and other tissues lining the pelvis. Less commonly it can spread to tissues beyond the pelvic region, such as to the large and small bowl or the abdomen.
87
What are the long-term consequences of endometriosis?
- Increased risk of ovarian cancer
- Fertility problems (as the lesions that form from the outer uterine tissue can prevent the sperm from penetrating and fertilizing the egg)
88
What would be the result of the ectopic tissue in case of endometriosis?
- Endometrial tissue becomes trapped outside the uterus with no way to exit the body
- Trapped tissue causes irritation, leading to scar tissue and adhesions
- When the ovaries are involved, cysts (endometriomas) can form
89
What is osteoporosis?
A disease characterized by low bone mass and deterioration of bone tissue, which can lead to increased risk of fracture
90
What is a notable consequence of menopause?
Without monthly follicular development, there is a dramatic decrease in estrogen secretion. This decrease affects other body systems such as the skeletal and cardiovascular systems. Estrogen helps to promote strong bones by inhibiting osteoclast activity. Bone decay happens to both men and women with aging. After menopause, osteoclast activity increases and can result in osteoporosis.
91
The male sex act involves which two components?
Erection and ejaculation
92
The erectile tissue of the penis is made up of three columns of sponge-like vascular spaces, which are known collectively as?
Corpora cavernosa
93
What happens during erection?
During arousal, the arterioles that supply the corpora cavernosa dilate. The result is that the penis enlarges and becomes rigid and allow entry into the vagina.
94
What is Glans penis?
The sensitive bulbous structure at the end of the human penis (aka the head of the penis)
95
What kind of reflex is the erection reflex?
Spinal reflex. The erection generating centre lies in the lower spinal cord.
96
Activation of the erection reflex has which three actions?
1. Inhibiting the sympathetic supply to the penile arterioles. This removes the tonic vasoconstrictor actions of the sympathetic system.
2. Activates the parasympathetic supply to the penile arterioles to cause vasodilation via a NO-mediated mechanism.
3. Activates the parasympathetic supply to the bulbourethral glands to secrete mucus for lubrication.
97
What is erectile dysfunction?
Aka impotence. The inability to obtain and maintain an erection rigid enough for sex. If erectile dysfunction is an ongoing issue, it could be a sign of an underlying health condition that requires treatment.
98
What kind of reflex is the ejaculation reflex?
Spinal reflex mediated by the same tactile and psychological stimuli as for erection.
99
What are the two steps of ejaculation?
1. Emission: Increased sympathetic activity causes smooth muscle contractions in the prostate, reproductive ducts, and seminal vesicles. The timing is coordinated such that prostatic fluid, then sperm, then seminal vesicle fluid is delivered into the urethra. Collectively, this mixture is called semen. The sphincter at the neck of the bladder is also contracted to prevent urine release.
2. Expulsion: The filling of the urethra with semen triggers the activation of skeletal muscles at the base of the penis. This increases the pressure and forcibly expels the semen.
100
What are the four stages of male sexual response cycle?
1. The excitement phase: This includes a heightened sexual awareness and erection.
2. The plateau phase: This has more generalized responses such as increased heart rate, blood pressure, and respiratory rate.
3. The orgasmic phase: This includes ejaculation as well as other physical and emotional responses.
4. The resolution phase: The return of the body to its pre-arousal stage.
101
Ordering the events from arousal to ejaculation.
1. Parasympathetic stimulation and sympathetic inhibition of penile arterioles.
2. Bulbourethral glands secrete lubricating mucus
3. Smooth muscle contraction in prostrate
4. Smooth muscle contraction in reproductive ducts
5. Smooth muscle contraction in seminal vesicles
6. Semen collects in the urethra
7. Skeletal muscles at the base of the penis contract
8. Semen is forcibly expelled
102
Describe the four phases of the female sexual response cycle.
1. Excitement: Stimuli can be both psychological or physical. Stimulation of the clitoris and the surrounding area activates a spinal reflex that activates the parasympathetic system to dilate the arterioles throughout the vagina and external genitalia. The nipples become erect and there is an increased blood supply to the skin. The clitoris contains erectile tissue and become erect. Dilation of arterioles in the vaginal walls causes vasocongestion of the capillaries, which forces fluid out of the vessels and into the vagina. This fluid, along with secretions from Bartholin's gland, serves as the primary lubricant for intercourse.
2. Plateau: The uterus raises upward, lifting the cervix and enlarging the upper portion of the vagina. This tenting effect creates space for ejaculated semen. Breathing, heart rate, and blood pressure of the female also continue to increase.
3. Orgasm: If erotic stimulation continues, the sexual response culminates in orgasm, as sympathetic impulses lead to rhythmic contractions of the pelvic musculature.
4. Resolution: After orgasm, heart rate, blood pressure, and breathing return to normal. This phase is marked by a general sense of well-being, enhanced intimacy, and, often, fatigue.
Some women are capable of a rapid return to the plateau phase with further sexual stimulation.
103
Ordering of the events in female sexual response.
1. Parasympathetic activity dilates the arterioles throughout the vagina and external genitalia
2. Nipples and clitoris become erect
3. The arterioles in the vaginal walls cause vasocongestion of the capillaries.
4. Vasocongestion causes fluid to be forced into the vagina
5. Fluid from Bartholin’s gland is released
6. The uterus raises upwards and the vagina expands
7. Uterus and muscles of the vagina contract
104
Where does fertilization most commonly occur?
The ampulla of the Fallopian tube
105
Describe the process of fertilization in humans (part 1: ovum transport and sperm transport)
1. Ovum transport to the oviduct:
At the end of the ovarian follicular phase, an ovum is released into the abdominal cavity. Fimbriae guide the ovum into the oviduct, and peristaltic contractions move it toward the ampulla, where fertilization usually occurs.
2. Sperm transport to the oviduct:
After ejaculation into the vagina, sperm must pass through the cervical canal. Progesterone causes cervical mucus to be thick and restrictive, but around ovulation, high estrogen levels thin the mucus, allowing sperm to pass for only a few days each cycle. In the uterus, myometrial contractions rapidly disperse sperm and help propel them to the oviducts. Peristaltic contractions then move sperm to the ampulla, which they can reach within about 30 minutes.
106
Describe the process of fertilization in humans (part 2: fertilization and implantation)
3. Fertilization: When sperm and ovum meet in the ampulla, fertilization can occur. The sperm must penetrate the corona radiata and then the zona pellucida. Sperm enzymes help digest the corona radiata. Binding of the sperm protein fertilin to ZP3 on the zona pellucida triggers the acrosome reaction, releasing enzymes that digest the zona pellucida. The first sperm to fuse with the ovum membrane triggers a rise in intracellular Ca²⁺, which:
Inactivates ZP3; Hardens the zona pellucida to prevent polyspermy; Triggers completion of the ovum’s second meiotic division. Within about an hour, the sperm and ovum nuclei fuse, forming a zygote.
4. Implantation: The zygote remains in the ampulla for several days, undergoing mitotic divisions to form a morula. Progesterone from the corpus luteum relaxes the oviduct, allowing the morula to enter the uterus. The embryo floats freely for several days, nourished by endometrial secretions. It then becomes a blastocyst, which attaches to and penetrates the endometrium. By about one week after ovulation, implantation is complete and the blastocyst is fully embedded in the uterine lining.
107
What are “zinc sparks” in human eggs, and why are they important?
Zinc sparks are bursts of zinc released by an egg at fertilization. They may be used as a marker to assess embryo health before IVF.
108
True or False: Sperm start to arrive in the ampulla around 30 minutes following ejaculation
True
109
True or False: The zygote remains in the ampulla for a few hours.
False
110
True or False: The release of intracellular Ca2+ in the ovum causes the zona pellucida to harden.
True
111
True or False: Fertilization normally happens in endometrium of the uterus.
False
112
True or False: After implantation, the corpus luteum is secreting large amounts of estrogen which
helps to relax the oviduct and allow the morula to move to the uterus.
False
113
What happens during fertilization and implantation in case of identical twins and fraternal twins?
Identical twins occur when a single egg is fertilized with a sperm cell, forms one zygote, and then spontaneously divides into two separate embryos.
Fraternal twins occur after two eggs are released from the ovary. Both eggs are fertilized by two different sperm cells, which are implanted in the uterine wall at the same time.
114
Ectopic pregnancy most often occurs where?
In the fallopian tubes, which is known as tubal pregnancy. It can also occur in the abdominal cavity, the ovaries, or the cervix (neck of the uterus).
115
Why is the placenta necessary for pregnancy, and how does it develop and function over time?
Endometrial glycogen can nourish the embryo for only a few weeks, so a placenta must develop to support the rest of pregnancy. By day 12, the embryo is fully implanted and contributes to placental formation. By about 5 weeks after implantation, the placenta is functional, though immature. By 12–13 weeks, maternal blood supply to the placenta is complete, allowing full support of the fetus. Throughout pregnancy, the placenta continues to grow and acts as the fetus’s digestive, respiratory, and excretory system, enabling nutrient and waste exchange between maternal and fetal blood.
116
True or False: Placenta secretes hormones without any external control
True
117
What are the hormones of placenta?
Human chorionic gonadotropin (HCG), estrogen, and progesterone
118
What is the role of HCG for placenta?
hCG is the first hormone secreted by the developing placenta. It is similar to LH and maintains the corpus luteum, allowing continued secretion of estrogen and progesterone until the placenta takes over around 10 weeks of gestation. hCG also stimulates Leydig cells in male fetuses to produce testosterone for reproductive tract development. Its production coincides with early pregnancy symptoms like morning sickness, and because it appears early in maternal urine, it is used as the marker for pregnancy tests.
119
How is estrogen produced during pregnancy, and what are its main roles?
The placenta cannot make estrogen directly from cholesterol, so the fetal adrenal cortex produces DHEA, which the placenta converts into estrogen—mainly estriol—and releases into maternal blood. Because fetal DHEA production takes time, the corpus luteum of pregnancy is the main estrogen source during the first trimester. Estriol levels can be used to assess fetal viability. During pregnancy, estrogen increases myometrial growth to support uterine expansion and promotes mammary duct development in preparation for lactation.
120
What is the main source of estrogen during the first trimester?
Corpus luteum
121
Can the placenta make estrogen directly?
No
122
How is progesterone produced during pregnancy, and what are its main functions?
The placenta begins secreting progesterone shortly after implantation, but it takes about 10 weeks for placental progesterone production to fully replace the corpus luteum. As the placenta grows throughout pregnancy, maternal progesterone levels continue to rise. Progesterone maintains the cervical mucus plug, stimulates milk gland development, and suppresses uterine contractions to support pregnancy.
123
How does estrogen contribute to uterine contractions during childbirth?
Near the end of pregnancy, rising estrogen levels help prepare the uterus for labor by enabling effective contractions. Estrogen stimulates the formation of gap junctions between myometrial smooth muscle cells, allowing synchronized uterine contractions, and increases the number of oxytocin receptors in the myometrium, making the uterus more responsive to oxytocin during childbirth.
124
What role does oxytocin play in childbirth, and how does it contribute to the positive feedback cycle of labor?
Oxytocin, released by the posterior pituitary, stimulates uterine smooth muscle contractions. Although its levels remain relatively constant during pregnancy, the late estrogen-driven increase in oxytocin receptors makes the uterus responsive to oxytocin. During labor, fetal pressure on the cervix triggers a neuroendocrine reflex that releases more oxytocin, strengthening contractions. This creates a positive feedback cycle: stronger contractions push the fetus further, increasing cervical pressure and oxytocin release, continuing until birth.
125
Why positive feedback is necessary for parturition, and what would happen if it did not occur?
During parturition, positive feedback loops are necessary as they increase the release of oxytocin, which strengthens uterine contractions. These contractions put pressure on the cervix, necessary for the opening of the birthing canal, which in turn increases the amount of oxytocin released. Without this increasing level of oxytocin, there would not be enough cervical pressure, and birth would not occur.
126
How are the mammary glands prepared for lactation during gestation, and which hormones are involved?
During gestation, the mammary glands develop a branching ductal system ending in alveoli, the milk-producing glands. Estrogen promotes duct development, progesterone stimulates alveoli formation, and prolactin along with hCG stimulate enzymes for milk synthesis. By mid-gestation, the breasts are capable of producing milk, but high estrogen and progesterone suppress prolactin, preventing milk secretion until after birth.
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Which hormones are involved in lactation?
Estrogen, progesterone, prolactin and hCG
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How is lactation stimulated, and what roles do prolactin and oxytocin play in milk production and ejection?
Lactation is triggered by the suckling reflex, which activates nerve endings to the hypothalamus. The hypothalamus then:
- Stimulates the posterior pituitary to release oxytocin, causing contraction of myoepithelial cells around alveoli and milk ejection.
- Reduces prolactin-inhibiting hormone (PIH) and releases prolactin-releasing hormone (PRH) to stimulate the anterior pituitary to secrete prolactin, which triggers alveolar epithelial cells to synthesize new milk.
This neuroendocrine reflex ensures milk is produced and ejected in response to the infant’s suckling.
129
The stimulation of lactation is under the control of which hormones?
Prolactin and oxytocin
PHGY 216
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