Costanzo | Physiology | Chapter 10 | Reproductive Physiology | Study Guide
Chapter 10: Reproductive Physiology Notes
I. Sexual Differentiation
Genetic Sex: Determined by the sex chromosomes: XY for males and XX for females.
Gonadal Sex: Refers to the presence of either testes or ovaries. The development of testes is directed by the Y chromosome; in its absence, ovaries develop.
Phenotypic Sex: Defined by the physical characteristics of the internal genital tract and external genitalia.
Male Phenotype: Includes the prostate, seminal vesicles, vas deferens, and epididymis (internal), and the scrotum and penis (external). This requires testosterone and antimüllerian hormone.
Female Phenotype: Includes the fallopian tubes, uterus, and vagina (internal), and the clitoris and labia (external). This develops in the absence of male hormones.
II. Puberty
Hormonal Changes: GnRH, FSH, and LH levels are low during childhood. At puberty, there is a pulsatile increase in GnRH secretion, and the GnRH receptor in the anterior pituitary becomes up-regulated.
FSH and LH Ratios: During childhood, FSH is higher than LH; during the reproductive years, LH is higher than FSH.
Clinical Signs: In girls, the first sign is usually breast budding, followed by menarche (onset of menses) about two years later. Pubic and axillary hair development (adrenarche) is dependent on adrenal androgens.
III. Male Reproductive Physiology
Testes: Composed of Sertoli cells (support spermatogenesis) and Leydig cells (secrete testosterone).
Spermatogenesis: A 64-day cycle occurring in the seminiferous tubules. Mature sperm (spermatozoa) possess an acrosome containing enzymes needed to penetrate the ovum.
Hormonal Control:
FSH: Stimulates spermatogenesis and Sertoli cell function.
LH: Stimulates Leydig cells to synthesize testosterone by increasing cholesterol desmolase activity.
Androgens: Testosterone is the primary androgen, but in some target tissues, it must be converted to dihydrotestosterone by the enzyme 5α-reductase.
IV. Female Reproductive Physiology
Ovaries: Site of oogenesis (ova production) and steroid hormone synthesis.
Follicular Development: Follicles progress through stages, with a single graafian follicle achieving dominance and rupturing during ovulation on day 14.
Ovarian Steroidogenesis:
Theca cells produce testosterone (stimulated by LH).
Granulosa cells convert testosterone to 17β-estradiol via the enzyme aromatase (stimulated by FSH).
Menstrual Cycle: Averaging 28 days, it includes a variable follicular phase (estrogen-dominant) and a constant luteal phase (progesterone-dominant).
Pregnancy: Fertilization occurs in the ampulla of the fallopian tube. The corpus luteum is "rescued" from regression by human chorionic gonadotropin (HCG) secreted by the trophoblast (placenta).
Parturition (Labor): Near term, an increased estrogen/progesterone ratio and the action of prostaglandins and oxytocin increase uterine contractility to expel the fetus.
Lactation: Prolactin stimulates milk production, while oxytocin stimulates milk letdown.
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Chapter 10 Study Guide
I. Glossary of Key Terms
Acrosome: A structure on the sperm head containing enzymes necessary for penetrating the ovum.
Adrenarche: The onset of increased adrenal androgen secretion, leading to pubic and axillary hair development.
Aromatase: The enzyme that converts androgens to estrogens in granulosa cells.
Corpus Luteum: The structure formed from a ruptured follicle that secretes progesterone and estrogen to maintain early pregnancy.
Graafian Follicle: The dominant ovarian follicle that ruptures during ovulation.
HCG: A hormone from the placenta that maintains the corpus luteum in early pregnancy.
Menarche: The first occurrence of menstruation.
Spermatogenesis: The process of sperm production in the testes.
Trophoblast: The outer layer of the blastocyst that develops into the placenta.
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II. 50 Question-and-Answer Quiz
What determines genetic sex? Sex chromosomes (XY or XX).
Which chromosome directs the development of testes? The Y chromosome.
What are the two primary cell types in the testes? Sertoli and Leydig cells.
Which hormone do Sertoli cells secrete to inhibit female tract development? Antimüllerian hormone.
Which cells in the testes secrete testosterone? Leydig cells.
What defines phenotypic sex? The physical characteristics of the internal and external genitalia.
What are the components of the internal male genital tract? Prostate, seminal vesicles, vas deferens, and epididymis.
What are the components of the internal female genital tract? Fallopian tubes, uterus, and upper one third of the vagina.
When do GnRH, FSH, and LH levels first begin to rise significantly? At puberty.
What is the pattern of GnRH secretion during puberty? Pulsatile.
Which pituitary hormone is higher during reproductive years: FSH or LH? LH.
What is the first sign of puberty in girls? Breast budding.
What is the term for the first menstrual period? Menarche.
How long is one full cycle of spermatogenesis? 64 days.
How many sperm are produced daily by a healthy male? 128 million.
What is the function of the sperm's acrosome? It contains enzymes to penetrate the ovum.
Which hormone stimulates the first step of testosterone synthesis in Leydig cells? LH.
Which enzyme converts testosterone to dihydrotestosterone? 5α-reductase.
What happens in 5α-reductase deficiency? External genitalia do not develop normally in genotypic males.
Which androgen is responsible for the male pubertal growth spurt? Testosterone.
Which androgen is responsible for male pattern baldness? Dihydrotestosterone.
Where does fertilization typically take place? In the ampulla of the fallopian tube.
How long after ovulation does the blastocyst arrive in the uterine cavity? 4 days.
Which hormone prevents the regression of the corpus luteum if fertilization occurs? HCG.
What is the primary source of HCG? The trophoblast (placenta).
Which cells in the ovary produce androgens? Theca cells.
Which cells in the ovary convert androgens to estrogen? Granulosa cells.
Which hormone stimulates aromatase in granulosa cells? FSH.
What is the primary estrogen produced by the ovaries? 17β-estradiol.
What are the primary actions of progesterone? Maintenance of pregnancy and secretory activity of the uterus.
Which hormone has a thermogenic action that increases basal body temperature? Progesterone.
What is the average length of the menstrual cycle? 28 days.
Which phase of the menstrual cycle is constant in length? The luteal phase.
What causes menses (menstrual bleeding)? Regression of the corpus luteum and loss of estradiol/progesterone.
What is the typical duration of human pregnancy? 40 weeks.
How does estrogen affect uterine contractility? It increases it.
How does progesterone affect uterine contractility? It decreases it (raises the threshold).
Which substances increase uterine contractility near term? Prostaglandins and oxytocin.
Which hormone is a powerful stimulant of uterine contractions used to induce labor? Oxytocin.
Which hormone stimulates milk production? Prolactin.
Which hormone stimulates milk letdown (ejection)? Oxytocin.
What effect does suckling have on ovulation? It suppresses it by inhibiting GnRH.
Which estrogen is the major form produced during the third trimester? Estriol.
What does the fetal liver contribute to estriol synthesis? 16-OH DHEA-sulfate.
What happens to GnRH receptors at the onset of puberty? They are up-regulated.
Which adrenal enzyme is missing in the most common form of congenital adrenal hyperplasia? 21β-hydroxylase.
What is the result of 21β-hydroxylase deficiency in a female infant? Masculinization of external genitalia.
Which cells in the testes are the site of FSH action? Sertoli cells.
What happens to the follicle that doesn't become the graafian follicle? It regresses.
What marks the end of the reproductive period in females? Menopause.
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III. Short Answer Questions
Explain the "Two-Cell, Two-Gonadotropin" hypothesis for ovarian steroidogenesis.
Answer: LH stimulates theca cells to synthesize testosterone from cholesterol. This testosterone then diffuses into the granulosa cells, where FSH stimulates the enzyme aromatase to convert it into 17β-estradiol.
How does the body distinguish between genetic, gonadal, and phenotypic sex?
Answer: Genetic sex is determined by chromosomes (XY or XX). Gonadal sex is the presence of testes or ovaries. Phenotypic sex is the physical appearance of internal and external genitalia, which is determined by the hormones produced by the gonads during development.
Describe the role of HCG in early pregnancy.
Answer: HCG is secreted by the trophoblast starting about 8 days after ovulation. It acts like LH to "rescue" the corpus luteum from regression, ensuring continued production of progesterone and estrogen to maintain the pregnancy until the placenta can take over.
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IV. Essay Questions
Describe the hormonal feedback mechanisms that regulate the human menstrual cycle.
Focus: Discuss negative feedback by estrogen and progesterone during the follicular and luteal phases to inhibit FSH and LH. Highlight the critical positive feedback event where a high level of estrogen triggers the LH surge required for ovulation.
Compare the physiological roles of testosterone and dihydrotestosterone in males.
Focus: Explain that both are androgens but act on different tissues. Testosterone is responsible for the internal male tract, muscle mass, and the pubertal growth spurt. Dihydrotestosterone (converted by 5α-reductase) is required for the external genitalia, male hair patterns, and prostate growth
