Reproductive physiology Flashcards
1
Q
What is the main function of the Pineal gland?
A
The main function of the Pineal gland is the regulation of diurnal cycles (sleep and wake cycles) by producing melatonin.
2
Q
What are the components of the Diencephalon?
A
The Diencephalon consists of the Thalamus, Hypothalamus, and Epithalamus, including the Pineal gland and Habenula (habenular commissure).
3
Q
Why is the Pineal gland sometimes referred to as the third eye?
A
The Pineal gland is sometimes called the third eye due to its association with regulating diurnal cycles and producing melatonin in response to light and darkness.
4
Q
Which nucleus is known as the biological clock?
A
The Suprachiasmatic Nucleus (SCN) is known as the biological clock.
5
Q
How does the Retinohypothalamic Tract (RHT) contribute to the regulation of sleep-wake cycles?
A
The RHT carries action potentials from light receptors in the retina to the SCN, contributing to the regulation of sleeping and waking.
6
Q
What chemicals are released by the SCN to stimulate different organs?
A
The SCN releases specific chemicals, usually glutamate, to stimulate different organs in the body.
7
Q
What is the role of the Paraventricular Nucleus (PVN) in the regulation of the sleep-wake cycle?
A
The PVN is stimulated and sends signals down the spinal cord to the Superior Cervical Ganglion (SCG), contributing to the regulation of the sleep-wake cycle.
8
Q
Which neurotransmitter is secreted by postganglionic motor neurons to signal the Pineal gland?
A
Postganglionic motor neurons secrete norepinephrine (NE) to signal the Pineal gland.
9
Q
What type of receptors do Pinealocytes have for NE?
A
Pinealocytes have specific adrenergic receptors for NE.
10
Q
Describe the intracellular pathway stimulated by adrenergic receptors in Pinealocytes.
A
Adrenergic receptors in Pinealocytes stimulate the intracellular pathway: Tryptophan → 5-hydroxytryptamine → Serotonin → Melatonin.
11
Q
How does light influence the SCN and Pineal gland activity?
A
Light inhibits the SCN, leading to Pineal gland inhibition and decreased melatonin secretion, promoting staying awake.
12
Q
What happens in response to darkness regarding the SCN and Pineal gland activity?
A
Darkness stimulates the SCN, leading to Pineal gland stimulation and increased melatonin secretion, promoting sleep.
13
Q
Where are the receptors for melatonin located, and what effect does increased melatonin have on the SCN?
A
Receptors for melatonin are located in the SCN, and increased melatonin levels rest the biological clock of the SCN.
14
Q
What is the general timeframe for a normal menstrual cycle?
A
A normal menstrual cycle typically lasts around 28 days, with a normal timeframe ranging from 21 to 39 days.
15
Q
Define ovulation in the context of the menstrual cycle.
A
Ovulation is the process where a mature female sex cell (ovum) is released by a Graafian Follicle, traveling to the fallopian tube in preparation for fertilization.
16
Q
What are the two special nuclei in the hypothalamus responsible for releasing Gonadotropin-Releasing Hormone (GnRH)?
A
The two special nuclei in the hypothalamus responsible for releasing GnRH are the Arcuate Nucleus and the Pre-Optic Nucleus.
17
Q
What hormones are synthesized and released by the anterior pituitary in the context of the menstrual cycle?
A
The anterior pituitary controls the synthesis and release of gonadotrophins, specifically Follicular Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
18
Q
In the ovary, what do gonadotropins (FSH and LH) work on?
A
Gonadotropins (FSH and LH) work in the ovary.
19
Q
What hormones are released by the ovary, and what are they converted into?
A
The ovary releases androgens, which are converted to estrogen, followed by the later release of progesterone.
20
Q
What is the role of primordial follicles in the context of ovarian follicle growth?
A
Primordial follicles, which arise from oogoniums, are diploid cells that become necessary stem cells during a female’s reproductive years.
21
Q
How many chromosomes do oogoniums have, and what do they develop into before puberty?
A
Oogoniums have 46 chromosomes (diploid), and before puberty, they develop into primordial cells.
22
Q
What is the status of the first oocyte in a primordial cell, and in which phase is it stationary?
A
The first oocyte in a primordial cell continues to be diploid and is stationary in Prophase I.
23
Q
What are the potential variations in menstruation, and what conditions do they indicate?
A
Menstruation can vary, with conditions like amenorrhea (non-existent menstruation) or menorrhagia (longer and heavier bleeding events) indicating variations in the menstrual cycle.
24
Q
What stimulates primordial follicles to develop into a primary follicle in females after reaching puberty?
A
Local androgens stimulate primordial follicles into developing into a primary follicle.
25
What is the composition of a primary follicle, and what is the status of the primary oocyte within it?
A primary follicle is composed of a single layer of cuboidal or columnar-like epithelial cells, surrounded by thecal cells. The primary oocyte within is still frozen in prophase I and has not undergone meiosis I.
26
How does FSH and LH contribute to estrogen production in the follicular phase?
FSH causes the development of additional layers of granulosa cells surrounded by thecal cells, while LH stimulates thecal cells to convert cholesterol to androgens. Androgens pass from the thecal cells to the neighboring granulosa cells, contributing to estrogen production.
27
What is the glycoprotein layer produced by the early secondary follicle, and what stimulates its formation?
The early secondary follicle produces a glycoprotein layer called the zona pellucida, and its formation is stimulated by FSH.
28
Describe the composition and characteristics of the early secondary follicle.
The early secondary follicle is composed of multiple layers of cuboidal or columnar-like epithelial cells, a zona pellucida, and is surrounded by thecal cells. It is still in prophase I and produces estrogen.
29
How does the late secondary follicle differ from the early secondary follicle in terms of granulosa cell proliferation and fluid production?
The late secondary follicle undergoes further proliferation of granulosa cells and produces follicular fluid pockets rich in hyaluronic acid. It has an almost similar composition to the early secondary follicle but with increased granulosa cell proliferation and fluid pockets.
30
What is the final stage in the follicular phase, and how is it initiated?
The Graafian Follicle, also called the vesicular or tertiary follicle, is the final stage in the follicular phase. It is produced from the stimulation of the late secondary follicle by FSH.
31
What significant events occur in the Graafian Follicle, and what does it undergo in terms of meiosis?
The Graafian Follicle undergoes further proliferation of epithelial cells and continuous production of follicular fluid pockets, forming a large fluid-filled cavity called the antrum. It undergoes meiosis I, resulting in the haploid cell splitting into two daughter cells, one becoming a polar body. Subsequent splits produce a daughter cell and three polar bodies. The daughter cell has a corona radiata.
32
What is the duration of the follicular phase, and what are the key products produced during this phase?
The follicular phase typically occurs from day 1 to 14 and produces multiple layers of granulosa cells, estrogen, zona pellucida, corona radiata, and follicular fluid antrum. It also involves the conversion of a primary oocyte to a secondary oocyte.
33
What characterizes the Mid-Follicular Phase, and when does it occur in the menstrual cycle?
The Mid-Follicular Phase is marked by the rise in estrogen levels entering the bloodstream, starting around the middle of the follicular phase (around day 7-10). The increased estrogen exerts negative feedback on the hypothalamus and anterior pituitary, inhibiting GnRH release and subsequently FSH and LH release.
34
What initiates the Late Follicular Phase, and how does the feedback loop change during this phase?
The Late Follicular Phase is initiated by a change in feedback loop from negative to positive due to increased estrogen levels in the blood. The hypothalamus produces GnRH, and the anterior pituitary releases gonadotropins, leading to an LH surge. This surge stimulates angiogenesis, increasing blood supply to the Graafian follicle, and results in ovulation.
35
Describe the process of ovulation and its timing in the menstrual cycle.
Ovulation usually occurs around mid-cycle, approximately day 14-15, triggered by the LH surge. The fimbriae of the fallopian tubes become stiff, creating fluid-filled currents that pull the secondary oocyte into the fallopian tube's ampulla for potential fertilization.
36
When does the Luteal Phase occur, and what transformations happen to the Graafian follicle during this phase?
The Luteal Phase occurs in the second half of the cycle, approximately day 15-28. The Graafian follicle, now called corpus hemorrhagicum, is stimulated by LH to accumulate cholesterol, lipids, and fats, turning it into the corpus luteum. The corpus luteum produces progesterone.
37
What stimulates the corpus luteum to accumulate cholesterol, lipids, and fats during the Luteal Phase?
LH stimulates the corpus luteum, which was the Graafian follicle that expelled the oocyte, to accumulate cholesterol, lipids, and fats during the Luteal Phase.
38
What is the role of the corpus luteum during the Luteal Phase, and what hormone does it produce?
The corpus luteum produces progesterone during the Luteal Phase. It is formed from the Graafian follicle expelled during ovulation and is further stimulated by LH.
39
What happens during the follicular phase from day 1-14?
Conversion of the primary follicle to a secondary follicle, producing multiple layers of granulosa cells, zona pellucida, corona radiata, follicular fluid antrum, and estrogen.
40
What triggers the events of the ovulatory phase, and when does it occur in the menstrual cycle?
The ovulatory phase is triggered by the LH surge and typically occurs on day 14-15. It involves the release of the secondary oocyte to the fallopian tube for transport to the area of fertilization.
41
What transformations occur during the luteal phase, and when does it take place?
The luteal phase occurs from day 15-28 and involves the formation of the corpus luteum from the Graafian follicle, which produces progesterone.
42
In the follicular phase, what structures and substances are produced from day 1-14?
Multiple layers of granulosa cells, zona pellucida, corona radiata, follicular fluid antrum, and estrogen are produced during the follicular phase from day 1-14.
43
What are the different cells involved in the follicular phase, and what are their characteristics?
- Primordial Cell: Continues to be a diploid cell.
44
What hormones are involved in the production of estrogen in the follicular phase?
d) FSH and LH
45
What produces progesterone during the luteal phase?
c) Corpus Luteum
46
What timeframe does the luteal phase encompass?
a) Day 15-28
47
What timeframes of the menstrual cycle are considered pathological?
c) Less than 20 and more than 40 days
48
In mid-follicular phase, do the levels of estrogen in the blood cause a positive feedback loop on the hypothalamus and anterior pituitary gland?
b) False
49
What is the inner lining of the uterus called?
Endometrium
50
How many sublayers or strata compose the endometrium, and what are they called?
Two sublayers or strata compose the endometrium: Stratum functionalis (green layer) and Stratum basalis (blue layer).
51
During menstruation, which sublayer of the endometrium is shed from the uterus?
The stratum functionalis is shed during menstruation.
52
What is the time frame for the menstrual period, and what factors can influence its duration?
The menstrual period typically occurs from days 1 to 5, but it can vary from person to person, depending on whether they have a regular menstrual period or experience heavy menstruation (menorrhagia).
53
What structures are lost during the shedding of the stratum functionalis in the uterus?
Spiral and coiled arteries are lost during the shedding of the stratum functionalis.
54
Differentiate between the types of arteries found in the stratum basalis and stratum functionalis.
In the stratum basalis, straight arteries are present, while in the stratum functionalis, spiral and coiled arteries are found. These arteries are branches of uterine arteries, which come off the internal iliac artery.
55
What is the significance of losing spirally and coily arteries during menstruation?
The loss of spirally and coily arteries during menstruation results in both tissue and blood loss, contributing to the menstrual flow. The straight arteries in the stratum basalis are retained.
56
Provide a quick recap of what menstruation consists of.
Menstruation consists of the loss of the stratum functionalis, including blood carried by spiral and coiled arteries. The stratum basalis remains intact.
57
What is the primary hormone during the proliferative phase, and what is its role?
The primary hormone during the proliferative phase is estrogen. Its role is to regenerate the stratum functionalis and spiral and coiled arteries in the endometrium.
58
During which days does the proliferative phase occur in the menstrual cycle?
The proliferative phase occurs from days 6 to 14 in the menstrual cycle.
59
What structures are regenerated during the proliferative phase?
During the proliferative phase, the stratum functionalis and spiral and coiled arteries are regenerated.
60
What term is used to describe the process of making new arteries, and what hormone is responsible for this process?
The term used to describe the process of making new arteries is angiogenesis, and estrogen is responsible for this process during the proliferative phase.
61
Besides regenerating the stratum functionalis and arteries, what additional functions does estrogen perform during the proliferative phase?
Estrogen stimulates the production of uterine glands, which secrete specific fluids. It also stimulates the production of thin cervical mucus from specific glands in the cervix, facilitating the movement of sperm through the female reproductive tract during ovulation.
62
Why is the production of thin cervical mucus important during the proliferative phase?
The production of thin cervical mucus is important during the proliferative phase because it allows for easier movement of sperm through the female reproductive tract toward the egg, especially during ovulation when the oocyte is ejected into the ampulla of the Fallopian tubes.
63
What does estrogen do to cervical mucus production during the proliferative phase, and what chemicals are present in the mucus to assist with sperm capacitation?
Estrogen during the proliferative phase stimulates the production of thin cervical mucus, making it easier for sperm to move toward the egg. The mucus contains specific chemicals such as cholesterol and glycoproteins that aid in the capacitation of the sperm.
64
What are the key events occurring during the proliferative phase, and during which days does it take place?
The proliferative phase occurs from days 6 to 14 and involves the regeneration of the stratum functionalis, angiogenesis for more spiral and coiled arteries, production of uterine glands, and the creation of thin cervical mucus to facilitate sperm movement.
65
What is the primary hormone stimulating the secretory phase, and where is it synthesized and secreted?
The primary hormone stimulating the secretory phase is progesterone. It is synthesized and secreted by the corpus luteum, which is formed from the Graafian follicle under the influence of luteinizing hormone (LH).
66
How does progesterone affect the stratum functionalis in the uterus during the secretory phase?
Progesterone causes the stratum functionalis to become thicker during the secretory phase. It also promotes the development of blood vessels, including more spiral and coiled arteries.
67
What is the role of progesterone in the stimulation of uterine glands during the secretory phase, and what does the produced substance contain?
Progesterone stimulates uterine glands to produce a nutrient-rich broth during the secretory phase. This substance is rich in glycogen (a polysaccharide or polymer of glucose), lipids, and specific types of proteins.
68
What are the key roles of progesterone during the secretory phase?
Progesterone during the secretory phase performs the following functions: 1) Proliferating the stratum functionalis to make it thicker, 2) Promoting angiogenesis by enlarging and increasing the number of spiral and coiled arteries, 3) Stimulating the secretion of uterine glands within the endometrium, and 4) Inducing the production of thick cervical mucus to block the cervix.
69
How does progesterone affect cervical mucus production in the case of fertilization and no fertilization?
In the case of fertilization, progesterone stimulates the production of thick cervical mucus to block the cervix and protect the potential embryo. In the absence of fertilization, progesterone maintains the production of thick cervical mucus to prevent substances or organisms from entering the uterus.
70
What is the normal range of menstrual cycle days, and what timeframes are considered pathological?
The normal menstrual cycle is around 28 days on average. Anything less than 21 days or greater than 40 days is considered pathological.
71
What happens in the absence of fertilization concerning the corpus luteum and progesterone production?
In the absence of fertilization, the embryo does not produce human chorionic gonadotropin, leading to a decline in progesterone production by the corpus luteum. This results in the endometrial vessels undergoing spasms, becoming weak, and eventually rupturing, causing blood accumulation in the stratum functionalis.
72
How does the vasoconstriction and vasodilation of spiral and coiled arteries depend on progesterone levels, and what happens if there's no fertilization?
Progesterone stabilizes the vasoconstriction and vasodilation of spiral and coiled arteries. In the absence of fertilization and a decline in progesterone levels, these vessels undergo spasms, leading to weak walls and eventual rupture, causing blood accumulation in the stratum functionalis and ischemia due to inadequate oxygen supply.
73
rogesterone?
In the absence of fertilization, the corpus luteum stops producing progesterone. This leads to the cessation of the cervical plug, and the endometrial vessels undergo spasms, rupturing and causing blood accumulation in the stratum functionalis. As progesterone production ceases, the tissue becomes ischemic, resulting in necrosis (cell death). The necrotic tissue, including the stratum functionalis and ruptured arteries, is shed off during menstruation.
74
How does the corpus luteum respond to the absence of fertilization, and what is the result?
In the absence of fertilization, the corpus luteum does not receive signals from the embryo, leading to its degeneration. The corpus luteum transforms into scarred and fibrous fatty tissue known as corpus albicans. The corpus albicans is incapable of producing progesterone or responding to luteinizing hormone (LH).
75
What initiates the beginning of a new menstrual cycle if fertilization does not occur?
If fertilization does not occur, the degenerated corpus luteum forms corpus albicans, marking the end of the previous ovulatory cycle. The absence of signals from the embryo initiates the beginning of a new menstrual cycle, and the menstrual process restarts on day 1 with the shedding of the stratum functionalis.
76
What is ovulation, and what is the primary purpose of this process?
Ovulation is the process where a mature female sex cell (ovum) is released by a Graafian Follicle to travel to the fallopian tube in preparation for fertilization. The primary purpose of ovulation is to release a viable egg (ovum) for potential fertilization in the fallopian tube.
77
Define the menstrual cycle and its typical duration.
The menstrual cycle is a periodic event lasting approximately 28 days, beginning at puberty and ending at menopause. Reproductively active females secrete an ovum into the fallopian tube during ovulation as part of the menstrual cycle. A normal menstrual cycle duration is considered to be between 21 to 39 days.
78
What timeframes are considered normal, and what is considered pathological in terms of menstrual cycle duration?
A menstrual cycle spanning between 21 to 39 days is considered normal. Timeframes of either 20 days or less, or 40 days or more, are considered pathological.
79
Describe the variations in menstruation events among females.
While menstruation is referred to as a five-day event, it can vary among females. It can be non-existent (amenorrhea) or longer and involve heavier bleeding (menorrhagia).
80
Provide an overview of hormone production and distribution in the hypothalamus, anterior pituitary, and ovaries.
The hypothalamus, consisting of the arcuate nucleus and pre-optic nucleus, is responsible for releasing gonadotropin-releasing hormone (GnRH). GnRH travels to the anterior pituitary, where gonadotrophins, including Follicular Stimulating Hormone (FSH) and Luteinizing Hormone (LH), are synthesized and released. These gonadotrophins act in the ovary, leading to the release of androgens, which are converted to estrogen, followed by the release of progesterone.
81
What is the pre-follicular phase, and what occurs during this phase?
The pre-follicular phase involves the development of primordial follicles, which are primary oocytes surrounded by a single layer of simple squamous cells. These follicles are frozen in prophase 1. By the birth of a female child, the ovary contains all the oogonium required for their reproductive life.
82
Describe the follicular phase, including follicular development and estrogen synthesis.
The follicular phase occurs from day 1 to 14 and is characterized by the development of primordial follicles into primary follicles under the influence of local androgens. This phase involves several stages: early secondary follicle, late secondary follicle, and Graafian follicle. Follicles undergo maturation with the addition of more layers of cells and the production of follicular fluid, filling pockets during the late second phase. Estrogen is synthesized during this phase, stimulated by FSH, LH, and androgens. Estrogen production involves the conversion of cholesterol into androgens, which are then converted to estrogen by granulosa cells.
83
Explain the hormonal changes during the mid-follicular phase.
In the mid-follicular phase (approximately day 7 to 9), estrogen levels rise, causing a negative feedback loop. This inhibits the hypothalamus from producing GnRH and the anterior pituitary from producing FSH and LH, resulting in a reduction of estrogen levels. However, the Graafian follicle continues to produce estrogen during this phase.
84
What happens in the late follicular phase, and how do estrogen levels change?
In the late follicular phase (approximately day 13 to 15), estrogen levels rise again, leading to a change in the feedback loop from negative to positive. The hypothalamus is stimulated to produce a massive amount of GnRH, and the anterior pituitary produces FSH and LH. Around day 14, the Graafian follicle produces inhibin B.
85
Describe the events during the ovulatory phase, specifically the LH surge and its effects.
The ovulatory phase occurs on day 14-15. The LH surge overrides the anterior pituitary signal, shutting off the production of FSH. This results in a large amount of LH, known as the LH surge. The effects of the LH surge include increased permeability of blood vessels, causing more blood to enter and become follicular fluid. Proteolytic enzymes are stimulated to cut around the tissue of the Graafian follicle, allowing the secondary oocyte to be released. The fimbriae of the fallopian tubes become stiff and scrape the ovary's surface, creating fluid-filled currents that pull the oocyte towards the fallopian tubes, where it is caught.
86
What happens during the luteal phase, and how does the corpus hemorrhagicum transform into the corpus luteum?
The luteal phase occurs from day 15-28. The ruptured Graafian follicle, now called the corpus hemorrhagicum, is stimulated by LH to accumulate cholesterol, lipids, and fat, turning yellow. The corpus hemorrhagicum transforms into the corpus luteum, and LH stimulates it to produce progesterone.
87
Explain the events during the menstrual phase, including the structures involved and what is sloughed off.
The menstrual phase, occurring on days 1-5, involves the sloughing off of the endometrial lining, including the stratum functionalis, spiral arteries, uterine glands, and any blood collected from the rupture of spiral arteries. Residual necrosis of the functionalis also occurs. The stratum basalis, being the basal layer with straight arteries, remains within the uterus.
88
Detail the events of the proliferative phase, mentioning the role of estrogen and its effects on the uterus.
The proliferative phase takes place from day 6-14. Estrogen regenerates the stratum functionalis through regrowth, promotes angiogenesis for the regeneration of spiral arteries, and stimulates the formation of new uterine glands. The cervical glands produce a thin cervical mucus at the cervix's entrance, facilitating sperm entry. The mucus contains chemicals that cause capacitation of the sperm, including cholesterol and glycoproteins.
89
Describe the events during the secretory phase, focusing on the effects of progesterone.
The secretory phase occurs from day 15-28. After ovulation on day 14, LH converts the ruptured Graafian follicle into the corpus luteum, which begins producing progesterone. The effects of progesterone during the secretory phase include stimulating the proliferation of the stratum functionalis, promoting angiogenesis to increase the length of spiral arteries, thickening cervical mucus into a cervical plug to prevent entry of unwanted substances in case of fertilization, and stimulating uterine glands to produce a thick fluid rich in glycoproteins, lipids, and proteins as a nutritive source for the developing embryo if implanted. Small amounts of FSH and estrogen can still be produced at this stage.
90
Explain the processes that occur in the case of fertilization, including the role of human chorionic gonadotropin (hCG) and the corpus luteum.
In the case of fertilization, upon implantation of the blastocyst, hCG is produced, stimulating the corpus luteum to continue making progesterone. The corpus luteum produces progesterone until the 12th week of embryology when the placenta takes over progesterone production. At this stage, the corpus luteum will die off.
91
Describe what happens in cases where fertilization does not occur, including the fate of the corpus luteum and the role of progesterone.
In cases where fertilization does not occur, hCG is not released. The corpus luteum degenerates into the corpus albicans and stops producing progesterone. The absence of progesterone leads to abnormal vasoconstriction and vasodilation, weakening the arteries. During vasoconstriction, the capillaries rupture, causing blood to enter the uterus and accumulate within the stratum functionalis. The stratum functionalis cells become ischemic, necrotic, and eventually slough off, leading to another menstruation phase.
92
What is the role of the hypothalamus in the brain-testicular axis?
The hypothalamus is the master endocrine regulator in the brain-testicular axis. It controls the pituitary gland and consists of several grey matter nuclei, including the Preoptic nucleus (PON) and Arcuate nucleus (AN). The Preoptic and Arcuate nuclei secrete Gonadotropin-Releasing Hormone (GnRH), which travels down through the hypophyseal portal system to the anterior hypophysis. GnRH binds to specific receptors on gonadotropes, cells in the anterior hypophysis, triggering the production of Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH).
93
1. What are the two gonadotrophic hormones secreted by the pituitary gland?
- Follicle stimulating hormone (FSH) and Luteinizing hormone (LH)
94
2. In males, what is the primary function of FSH?
- FSH in males causes the testes to produce sperm (spermatogenesis).
95
3. In females, what are the two main effects of FSH?
- FSH in females causes the growth of ovarian follicles (oogenesis) and stimulates the ovary to secrete estrogen.
96
4. What is the role of LH in males?
- LH in males causes the testes to secrete testosterone.
97
5. What are the functions of LH in females?
- LH in females causes ovulation and stimulates the production of progesterone by the corpus luteum.
98
6. Provide a brief description of the image labeled 'Gonadotrophic Hormones Secreted by Pituitary'.
- The image illustrates the roles of FSH and LH in males and females. In males, FSH stimulates spermatogenesis, while LH stimulates testosterone secretion. In females, FSH promotes oogenesis and estrogen secretion, while LH induces ovulation and stimulates progesterone production by the corpus luteum.
99
7. What is the role of Gonadotrophin Releasing Hormone (GnRH) in the hypothalamic-pituitary-gonadal (HPG) axis?
- GnRH is responsible for the release of FSH and LH from the anterior pituitary.
100
8. How is GnRH released, and what is its pulsatile nature regulated by in males and females?
- GnRH is a neuropeptide released from GnRH neurons within the hypothalamus. It is released in a pulsatile manner. In males, GnRH is secreted in pulses at a constant frequency. In females, the frequency of GnRH pulses varies during the menstrual cycle. Although GnRH pulsatility is regulated by estrogen and progesterone/testosterone, GnRH-producing neurons do not contain receptors for these hormones; instead, these hormones act indirectly via kisspeptin neurons, which then influence the hypothalamus.
101
What is the characteristic of the follicular phase?
Variable, typically 14 days +/- 7 days
102
During which phase does the LH surge precede ovulation?
Luteal phase
103
What stimulates the growth of ovarian follicles?
FSH
104
What is responsible for infertile thick mucus?
Progesterone
105
What is the function of oestrogens in the menstrual cycle?
Increase the thickness of the endometrium
106
What occurs under the influence of LH in the menstrual cycle?
Ovulation
107
What phase is characterized by follicular growth?
Follicular phase
108
What hormone inhibits the secretion of LH?
Progesterone
109
What influences the hypothalamus and pituitary to lower FSH levels temporarily?
Rising oestrogen levels
110
What happens during the LH surge in the menstrual cycle?
Progesterone production and secretion
111
What decreases LH secretion by influencing GnRH pulsatility?
Progesterone
112
What characterizes the events in the ovary and endometrium?
A follicle consists of an oocyte surrounded by follicular cells (granulosa cells, theca cells); Growth entails an increase in the number of follicular cells (not oocytes) and accumulation of follicular fluid, both resulting in an increase in the diameter and overall size of the follicle; Endometrium thickens under the influence of oestrogen and becomes a secretory tissue under the influence of progesterone
113
What are the functions of oestrogens in the menstrual cycle?
Increase the thickness of the endometrium; Regulate LH surge; Reduce vaginal pH through an increase in lactic acid production; Decrease viscosity of cervical mucus to facilitate sperm penetration; Mainly acts to negatively feedback to the pituitary and hypothalamus, but sustained high oestrogen midcycle stimulates secretion of LH and FSH (positive feedback)
114
What are the functions of progesterone?
Maintains the thickness of the endometrium; Responsible for infertile thick mucus (prevent sperm transport and help prevent infection); Relaxes the myometrium; Functional progesterone withdrawal thought to regulate birth; Has a thermogenic effect (increases basal body temperature)
115
What is Spinnbarkeit?
Describes the property of cervical mucus that changes in response to high levels of oestrogen around the time of ovulation. It becomes thin, slippery, and very stretchy.
116
How is Spinnbarkeit tested in the lab?
Lab test involves the formation of a thread from the mucus from the cervix uteri when spread onto a glass slide and drawn out by a cover glass; maximum length usually precedes or coincides with the time of ovulation.
117
What do home ovulation kits use to predict ovulation?
Home ovulation kits use the LH surge to predict the onset of ovulation.
118
How reliable are home ovulation kits?
Home ovulation kits are not very reliable, with a ratio of 3:100.
119
How does basal body temperature (BBT) change after ovulation?
BBT shifts by 0.2-0.4 ℃ following ovulation.
120
When should basal body temperature be measured?
BBT should be measured in the morning before moving about or eating after at least 6 hours of sleep.
121
What regulates the sperm's ability to penetrate cervical mucus?
Thickness of the mucus (under hormonal control), motility of the sperm, interaction with reactive oxygen species (ROS) produced by leukocytes, and interaction with mucins.
122
What is the structure of the cervix?
The cervix has stroma (fibroblast cells surrounded by a collagen matrix) and epithelium (columnar epithelial cells, the site of mucus production).
123
What are the hormonal events in pregnancy?
- Follicle produces oestradiol - Corpus luteum, if a fertilized ovum implants, releases progesterone - Implanted embryo produces HCG (pregnancy test) - Placenta produces human placental lactogen (hPL), placental progesterone, and placental oestrogens - Pituitary produces prolactin during pregnancy - Foetal organogenesis starts at 5 weeks (possibly earlier).
124
What stimulates the release of FSH and LH in the male reproductive tract?
FSH and LH are released in response to GnRH (Gonadotropin-Releasing Hormone).
125
What is the role of LH in the male reproductive system?
LH (Luteinizing Hormone) stimulates testosterone production from Leydig cells in the testis.
126
How does testosterone exert its effects on tissues?
Testosterone acts via nuclear androgen receptors, which interact with co-regulatory proteins to produce the appropriate tissue responses.
127
What is the role of FSH in spermatogenesis?
FSH stimulates the Sertoli cells in the seminiferous tubules to produce mature sperm as well as inhibin.
128
What is the feedback mechanism involving inhibin?
Inhibin, produced by Sertoli cells, feeds back to the pituitary to decrease FSH secretion.
129
What is the duration of the entire spermatogenic process?
The entire spermatogenic process takes 70 days.
130
When does spermatogenesis begin, and how long does it occur?
Spermatogenesis begins at puberty and occurs for 60 years or more.
131
Why is the blood-testes barrier important in testicular organization?
The blood-testes barrier restricts contact between postmitotic germ cells and the immune system, preventing the rejection of spermatogenic cells.
132
What are the compartments in testicular organization?
There are extratubular and intratubular compartments. The extratubular compartment includes the interstitial and intravascular components, while the intratubular compartment includes basal and adluminal compartments with Sertoli cells and germ cells.
133
What are the endocrine factors involved in hormone action in the male reproductive tract?
LH and FSH are endocrine factors involved in hormone action.
134
What is the main source of testosterone production in the male reproductive system?
Leydig cells produce testosterone under the control of LH.
135
How is testosterone mostly transported in the bloodstream?
The majority of testosterone is bound to SHBG (Sex Hormone-Binding Globulin) and albumin, with only 0.5%-2% existing in the free form.
136
Where is most of the testosterone taken up in the male reproductive system?
Sertoli cells take up 90% of testosterone, playing a crucial role in spermatogenesis and maintaining the integrity of the blood-testes barrier.
137
What happens to testosterone that reaches other target tissues?
Testosterone reaching other target tissues is converted to dihydrotestosterone (a highly active form) and oestradiol.
