Introduction to the Reproductive System: Physiology Flashcards

Question

Comparing the 2 sex cell types on male and female

Answer 1

a. The male Leydig and female theca cells are interstitial cells and have many features in common. i. These include the presence of LH receptors, the ability to make androgens, and the inability to make estrogens due to the absence of aromatase. b. The male Sertoli and female granulosa cells are immediately adjacent to the developing gametes and also have many features in common. i. These include the presence of FSH receptors, the ability to make inhibin, and the ability to convert androgens into estrogens due to the presence of aromatase.

Answer 2

a. The Leydig cells occupy the interstitial layer surrounding the seminiferous tubules. b. In response to LH, Leydig cells produce around 95% of the testosterone in males. c. LH stimulates the rate-limiting conversion of cholesterol into pregnenolone in two ways: i. by increasing the amount of desmolase and ii. by enhancing the affinity of desmolase for cholesterol. d. The resulting testosterone which acts on the Sertoli cells to support spermatogenesis. i. This testosterone also exerts negative feedback on the hypothalamic – pituitary – testicular axis at both the hypothalamic and pituitary levels.

Answer 3

a. The Sertoli cells in the male are in direct contact with the developing spermatozoa and are regarded as the as the support or nurse cells of the developing spermatozoa. b. Spermatogenesis requires LH, FSH, Leydig cells, Sertoli cells, and testosterone. c. The Sertoli cells are organized into a tubular epithelium known as the seminiferous tubule. i. This general structure is supported by the presence of tight gap junctions between adjacent Sertoli cells. d. Maturing spermatogonia are located between adjacent Sertoli Cells. Gap junctions between Sertoli cells and the adjacent spermatozoa are responsible for the maturation of those gametes.

Answer 4

FSH binding to Sertoli cells has several effects. a. These include increased production of androgen binding protein, enhanced conversion of testosterone from the Leydig cells into estradiol, and the production of inhibin. b. The Sertoli cells are the primary source of inhibin in males. i. Inhibin plays an important role in the negative feedback arm of the hypothalamic-pituitary-testicular axis.

Answer 5

a. The theca cells are located in the ovarian stroma surrounding the follicles and are similar to the Leydig cells in the male. b. In response to LH secretion, theca cells produce progesterone and androgens. c. Theca cells lack aromatase and therefore the capacity to produce estrogens. d. Androstenedione from the theca cells must therefore diffuse into nearby granulosa cells for estrogen to be produced.

Answer 6

a. The ovarian granulosa cells are in direct contact with the oogonia and are similar to the Sertoli cells in the male. b. The gametes and their surrounding granulosa cells are called primordial follicles. i. In reproductive age women, one follicle, called the dominant follicle, matures each month. c. Oogenesis and ovulation require LH, FSH, granulosa cells, theca cells, testosterone and estradiol. d. Granulosa cells lack the enzyme which converts progesterone into androgens. e. Progesterone from the granulosa cells must therefore diffuse to the theca cells where it is converted into androstenedione. f. As mentioned above, theca cells lack aromatase, so the resulting androstenedione diffuses back to the granulosa cells for conversion to estradiol

Answer 7

a. Progestins are the 21-carbon sex steroids derived from cholesterol. b. The progestins synthesized in the human body include pregnenolone, 17-alpha-hydroxy-pregnenolone, progesterone, and 17-alpha-hydroxy-progesterone (17-OH-P). c. In addition to being sex steroids, progestins are also precursors for the production of aldosterone and cortisol by the adrenal gland. i. Like progesterone, cortisol and aldosterone also have 21 carbons. d. The major circulating progestins are progesterone and 17-hydroxy-progesterone, with the former present in higher concentrations in females. i. Clinically, 17-hydroxy-progesterone is an excellent marker for late-onset congenital adrenal hyperplasia, which is discussed in other lectures.

Answer 8

1. Androgens are the 19-carbon sex steroids derived from cholesterol via pregnenolone. i. The major androgens synthesized in the human body include testosterone, dehydroepiandrosterone (DHEA), dehydroepiandrosterone-sulfate (DHEA-S), dihydrotestosterone (DHT), and androstenedione. ii. Approximately 95% of the testosterone which circulates in the male is produced in the testes. iii. The other major source of androgens is the adrenal cortex. 2. Estrogens are the 18-carbon sex steroids derived from cholesterol via pregnenolone. i. Pregnenolone is converted into other progestins, and then into the androgens. ii. Androgens are converted into the estrogens via an enzyme known as aromatase. iii. The estrogens synthesized in the human body include estrone (E1), estradiol (E2) and estriol (E3). They have one, two, and three hydroxyl groups, respectively. iv. Of these, estradiol is the most potent and estriol is the least. v. Estradiol is the major circulating estrogen and is produced by the granulosa cells of the ovary in females and by the Sertoli cells of the testes in males

Answer 9

1. Progestins affect almost all tissues in the body, most notably the uterus, the ovaries, and the breasts. i. Key functions of progesterone include the growth and development of the tissues and organs related to ovulation, menses, pregnancy, and lactation. ii. Progesterone levels fluctuate during the normal menstrual cycle. iii. Within the context of the hypothalamic – pituitary – ovarian axis, progesterone acts as a key feedback inhibitor at the levels of hypothalamus and pituitary. 2. Androgens-->Testosterone affects almost all tissues in the body. i. The effects are classified into two major categories: androgenic and anabolic. ii. Androgenic impacts include the growth and development of the internal and external genitalia, the development and maintenance of secondary sex characteristics, spermatogenesis, and sexual fantasies and libido. iii. Anabolic effects can be summarized as the growth-promoting effects on somatic tissues such as bone and muscle. iv. Within the hypothalamic – pituitary – testicular axis, testosterone acts as a key feedback inhibitor at the levels of hypothalamus and pituitary. 3. Estrogens affect almost all tissues in the body, most notably the uterus, the ovaries, and the breasts. i. Key functions of estradiol include the growth and development of the tissues and organs related to ovulation, menses, pregnancy, and lactation. ii. Estradiol levels fluctuate during the normal menstrual cycle. iii. Within the context of the hypothalamic – pituitary – ovarian axis, estradiol acts as a key feedback inhibitor at the levels of hypothalamus and pituitary.

Answer 10

a. Sex steroids are steroid hormones that interact with vertebrate androgen or estrogen receptors. b. Their effects are mediated by slow genomic mechanisms through nuclear receptors as well as by fast nongenomic mechanisms through membrane-associated receptors and signaling cascades. i. The term sex hormone is nearly always synonymous with sex steroid. c. In many contexts, the two main classes of sex steroids are androgens and estrogens, of which the most important human derivatives are testosterone and estradiol, respectively. i. Other contexts will include progestogens as a third class of sex steroids, distinct from androgens and estrogens. ii. Progesterone is the most important and only naturally-occurring human progestogen. d. In general, androgens are considered "male sex hormones", since they have masculinizing effects, while estrogens and progestogens are considered "female sex hormones" although all types are present in each sex, albeit at different levels.

Answer 11

a. Androgen is any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. b. This includes the activity of the primary male sex organs and development of male secondary sex characteristics. i. Androgens are also the original anabolic steroids and the precursor of all estrogens. c. The primary and most well-known androgen is testosterone i. Dihydrotestosterone (DHT) and androstenedione are less known generally, but are of equal importance in male development ii. DHT in the embryo life causes differentiation of penis, scrotum and prostate. iii. Later in life DHT contributes to male balding, prostate growth and sebaceous gland activity. d. Although androgens are described as male sex hormones, both males and females have them to varying degrees, as is also true of estrogens.

Answer 12

The main subset of androgens, known as adrenal androgens, is composed of 19-carbon steroids synthesized in the zona reticularis, the innermost layer of the adrenal cortex.

Answer 13

a. The main subset of androgens, known as adrenal androgens, is composed of 19-carbon steroids synthesized in the zona reticularis, the innermost layer of the adrenal cortex. b. Besides testosterone, other androgens include: 1) Dehydroepiandrosterone (DHEA) is a steroid hormone produced in the adrenal cortex from cholesterol. i. It is the primary precursor of natural estrogens. DHEA is also called dehydroisoandrosterone or dehydroandrosterone. 2) Androstenedione (Andro) is an androgenic steroid produced by the testes, adrenal cortex, and ovaries. 3) Androstenediol is the steroid metabolite thought to act as the main regulator of gonadotropin secretion. 4) Dihydrotestosterone (DHT) is a metabolite of testosterone, and a more potent androgen than testosterone in that it binds more strongly to androgen receptors. It is produced in the skin and reproductive tissue.

Answer 14

a. Estrogen is the primary female sex hormone. It is responsible for the development and regulation of the female reproductive system and secondary sex characteristics. b. The steroid 17β-estradiol is the most potent and prevalent endogenous estrogen, although several metabolites of estradiol also have estrogenic hormonal activity. c. The three major naturally occurring forms of estrogen in women are estrone (E1), estradiol (E2), and estriol (E3). i. Quantitatively, estrogens circulate at lower levels than androgens in both men and women d. While estrogen levels are significantly lower in males compared to females, estrogens nevertheless also have important physiological roles in males. e. Like all steroid hormones, estrogens readily diffuse across the cell membrane. Once inside the cell, they bind to and activate estrogen receptors (ERs) which in turn modulate the expression of many genes

Answer 15

a. The three major naturally occurring estrogens in women are estrone (E1), estradiol (E2), and estriol (E3). b. Estradiol is the predominant estrogen during reproductive years both in terms of absolute serum levels as well as in terms of estrogenic activity. c. During menopause, estrone is the predominant circulating estrogen and during pregnancy estriol is the predominant circulating estrogen in terms of serum levels. d. Though estriol is the most plentiful of the three estrogens it is also the weakest, whereas estradiol is the strongest with a potency of approximately 80 times that of estriol. e. Thus, estradiol is the most important estrogen in non-pregnant females who are between the menarche and menopause stages of life.

Answer 16

a. In the first step in the steroidogenic pathway, cholesterol is converted into pregnenolone (P5), which serves as the precursor to the progestogens progesterone and 17α-hydroxyprogesterone. b. These progestogens, along with another steroid, 17α-hydroxypregnenolone, are the precursors of all other endogenous steroids, including the androgens, estrogens, glucocorticoids, mineralocorticoids, and neurosteroids. c. Thus, many tissues producing steroids, including the adrenal glands, testes, and ovaries, produce progestogens. d. All progestogens are characterized by their basic 21-carbon skeleton, called a pregnane skeleton (C21). i. In similar manner, the estrogens possess an estrane skeleton (C18), and androgens, an andrane skeleton (C19).

Answer 17

a. All progestogens are characterized by their basic 21-carbon skeleton, called a pregnane skeleton (C21). b. In similar manner, the estrogens possess an estrane skeleton (C18), and androgens, an andrane skeleton (C19).

Answer 18

a. The hypothalamic–pituitary–gonadal axis (HPG axis) refers to the hypothalamus, pituitary gland, and gonadal glands as if these individual endocrine glands were a single entity. i. Because these glands often act in concert, physiologists and endocrinologists find it convenient and descriptive to speak of them as a single system. b. The HPG axis plays a critical part in the development and regulation of a number of the body's systems, such as the reproductive and immune systems. i. Fluctuations in this axis cause changes in the hormones produced by each gland and have various local and systemic effects on the body. c. The axis controls development, reproduction, and aging in animals. i. Gonadotropin-releasing hormone (GnRH) is secreted from the hypothalamus by GnRH-expressing neurons. ii. The anterior portion of the pituitary gland produces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the gonads produce estrogen and testosterone. d. The HPA, HPG, and HPT axes are three pathways in which the hypothalamus and pituitary direct neuroendocrine function.

Answer 19

a. The hypothalamus is located in the brain and secretes GnRH. i. GnRH travels down the anterior portion of the pituitary via the hypophyseal portal system and binds to receptors on the secretory cells of the adenohypophysis. b. In response to GnRH stimulation these cells produce LH and FSH, which travel into the blood stream. i. These two hormones play an important role in communicating to the gonads. c. In females FSH and LH act primarily to activate the ovaries to produce estrogen and inhibin and to regulate the menstrual cycle and ovarian cycle. i. Estrogen forms a negative feedback loop by inhibiting the production of GnRH in the hypothalamus. ii. Inhibin acts to inhibit activin, which is a peripherally produced hormone that positively stimulates GnRH-producing cells. iii. Follistatin, which is also produced in all body tissue, inhibits activin and gives the rest of the body more control over the axis. d. In males LH stimulates the interstitial cells located in the testes to produce testosterone, and FSH plays a role in spermatogenesis. i. Only small amounts of estrogen are secreted in males. Recent research has shown that a neurosteroid axis exists, which helps the cortex to regulate the hypothalamus’s production of GnRH

Answer 20

a. In response to GnRH stimulation these cells produce LH and FSH, which travel into the blood stream. i. These two hormones play an important role in communicating to the gonads. b. In females FSH and LH act primarily to activate the ovaries to produce estrogen and inhibin and to regulate the menstrual cycle and ovarian cycle. c. Estrogen forms a negative feedback loop by inhibiting the production of GnRH in the hypothalamus. d. Inhibin acts to inhibit activin, which is a peripherally produced hormone that positively stimulates GnRH-producing cells. i. Follistatin, which is also produced in all body tissue, inhibits activin and gives the rest of the body more control over the axis

Answer 21

a. In response to GnRH stimulation these cells produce LH and FSH, which travel into the blood stream. i. These two hormones play an important role in communicating to the gonads. b. In males LH stimulates the interstitial cells located in the testes to produce testosterone, and FSH plays a role in spermatogenesis. c. Only small amounts of estrogen are secreted in males. d. Recent research has shown that a neurosteroid axis exists, which helps the cortex to regulate the hypothalamus’s production of GnRH

Answer 22

a. Leydig cells are found adjacent to the seminiferous tubules in the testicle. i. They produce testosterone in the presence of luteinizing hormone (LH). b. Leydig cells release a class of hormones called androgens (19-carbon steroids). c. They secrete testosterone, androstenedione and dehydroepiandrosterone (DHEA), when stimulated by the pituitary hormone luteinizing hormone (LH). d. LH increases cholesterol desmolase activity (an enzyme associated with the conversion of cholesterol to pregnenolone), leading to testosterone synthesis and secretion by Leydig cells. e. Prolactin (PRL) increases the response of Leydig cells to LH by increasing the number of LH receptors expressed on Leydig cells.

Answer 23

a. A Sertoli cell is a "nurse" cell of the testicles that is part of a seminiferous tubule and helps in the process of spermatogenesis; that is, the production of sperm. b. It is activated by follicle-stimulating hormone (FSH) secreted by the adenohypophysis, and has FSH receptor on its membranes. i. It is specifically located in the convoluted seminiferous tubules (since this is the only place in the testes where the spermatozoa are produced). ii. Development of Sertoli cells is directed by the testis-determining factor protein.

Answer 24

a. Theca cells are a group of endocrine cells in the ovary made up of connective tissue surrounding the follicle that has many diverse functions during folliculogenesis. b. These roles include synthesizing androgens, providing signal transduction between granulosa cells and oocytes during development by the establishment of a vascular system, providing nutrients, and providing structure and support to the follicle as it matures. c. The theca cells are responsible for the production of androstenedione, and indirectly the production of 17β estradiol, also called E2, by supplying the neighboring granulosa cells with androstenedione that with the help of the enzyme aromatase can be used as a substrate for this type of estradiol. d. FSH induces the granulosa cells to make aromatase that converts the androgens made by the theca interna into estradiol.

Answer 25

a. A granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete (called an oocyte or egg) in the ovary of mammals. b. The major functions of granulosa cells include the production of sex steroids, as well as myriad growth factors thought to interact with the oocyte during its development. c. The sex steroid production consists of follicle-stimulating hormone (FSH) stimulating granulosa cells to convert androgens (coming from the thecal cells) to estradiol by aromatase during the follicular phase of the menstrual cycle. d. However, after ovulation the granulosa cells turn into granulosa lutein cells that produce progesterone. e. The progesterone may maintain a potential pregnancy and causes production of a thick cervical mucus that inhibits sperm entry into the uterus.