Human Embryonic Development Quiz

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Questions and Answers

What is responsible for the pigmentation of the areolas in females?

Testicular androgens

Estrogens (correct)

Growth hormones

Pregnancy hormones

What is the result of meiotic division in males?

Four sperms, two with X and two with Y chromosome (correct)

One sperm with X and one sperm with Y chromosome

Two sperms with XX and two sperms with YY chromosome

Two sperms, one with X and one with Y chromosome

What is the characteristic pattern of pubic hair in females?

Triangular

Irregular

Circular

Flat-topped (correct)

What is the reason for the female distribution of fat in the breasts and buttocks?

Absence of testicular androgens Signup and view all the answers

What is the outcome of fertilization in a female zygote?

22 pairs of autosomes plus XX Signup and view all the answers

What is the function of estrogen receptor α (ERα) in the body?

It binds to DNA and alters its transcription Signup and view all the answers

What develops from the medulla in genetic males?

Testis Signup and view all the answers

What is the primary hormone responsible for the growth of pubic and axillary hair in both sexes?

Androgens Signup and view all the answers

What is the function of MIS in genetic males?

Regression of the mullerian duct Signup and view all the answers

What is the characteristic of the female larynx?

It retains its prepubertal proportions Signup and view all the answers

What occurs in male fetuses before birth?

A burst of testosterone secretion Signup and view all the answers

What triggers the final maturation of the reproductive system?

Gonadotropins from the pituitary Signup and view all the answers

What is the primary function of Human Chorionic Somatomammotropin (hCS) during pregnancy?

To regulate maternal glucose utilization Signup and view all the answers

How soon can Human Chorionic Somatomammotropin (hCS) be detected in the blood after conception?

6 days Signup and view all the answers

What is the similarity between Human Chorionic Somatomammotropin (hCS) and human growth hormone?

They have similar structures and evolutionary history Signup and view all the answers

Why is low Human Chorionic Somatomammotropin (hCS) levels a concern during pregnancy?

It may indicate placental insufficiency Signup and view all the answers

What happens to the maternal pituitary growth hormone secretion during pregnancy?

It decreases to compensate for hCS Signup and view all the answers

What is the average duration of pregnancy in humans?

270 days from fertilization Signup and view all the answers

What is the primary function of the secretory phase of the menstrual cycle?

Preparation of the uterus for implantation of the fertilized ovum Signup and view all the answers

What proportion of menstrual blood is of venous origin?

25% Signup and view all the answers

What is the average amount of blood lost during menstruation?

30 mL Signup and view all the answers

What is the length of the secretory phase of the menstrual cycle?

14 days Signup and view all the answers

What is the purpose of fibrinolysin in menstrual blood?

To lyse clots Signup and view all the answers

What is an abnormal amount of blood lost during menstruation?

More than 80 mL Signup and view all the answers

What is the primary function of oxytocin during labor?

To directly act on uterine smooth muscle cells to make them contract Signup and view all the answers

What is the role of prostaglandins in labor?

To enhance oxytocin-induced contractions Signup and view all the answers

What is the primary role of prolactin in lactation?

To stimulate the formation of milk droplets Signup and view all the answers

What is the role of human chorionic somatomammotropin (hCS) in lactation?

To have mild lactogenic properties Signup and view all the answers

What is the primary hormone responsible for the development of the mammary ducts?

Estrogens Signup and view all the answers

What is the role of spinal reflexes and voluntary contractions of the abdominal muscles during labor?

To aid in delivery Signup and view all the answers

What is the first event in girls during adolescence?

Development of breasts Signup and view all the answers

What is the period when the endocrine and gametogenic functions of the gonads have first developed to the point where reproduction is possible?

Puberty Signup and view all the answers

What is the term for the increase in the secretion of adrenal androgens during adolescence?

Adrenarche Signup and view all the answers

What is the approximate age range for the peak of DHEA values in women?

25 years Signup and view all the answers

What is the approximate age range for puberty in boys?

9-13 years Signup and view all the answers

What is the characteristic of initial menstrual periods in girls?

Anovulatory Signup and view all the answers

What determines the differentiation of primitive gonads into testes or ovaries in humans?

Genetic factors Signup and view all the answers

What is the primary function of gonadotropins from the anterior pituitary during adolescence?

Activating the gonads and triggering sexual development Signup and view all the answers

What is the outcome of ovarian function regression in human females?

The cessation of sexual cycles Signup and view all the answers

What is the dual function of the gonads in both sexes?

Gametogenesis and hormone secretion Signup and view all the answers

What is the outcome of the absence of testicular tissue in human development?

The development of female genitalia Signup and view all the answers

What is the primary difference between male and female reproductive systems in most mammals?

A single chromosome Signup and view all the answers

What is the primary location where the enzyme aromatase (CYP19) is active?

Fat, liver, muscle, and the brain Signup and view all the answers

What percentage of circulating estradiol is free?

2% Signup and view all the answers

What is the fate of estradiol, estrone, and estriol in the liver?

They are converted to glucuronide and sulfate conjugates Signup and view all the answers

What stimulates estradiol production in granulosa cells?

Both LH and FSH Signup and view all the answers

What is the proportion of estradiol bound to albumin?

60% Signup and view all the answers

What is the result of enterohepatic circulation of estrogen metabolites?

They are secreted into the bile and reabsorbed into the bloodstream Signup and view all the answers

What is the primary function of progesterone in maintaining pregnancy?

Inhibiting prostaglandin production by the uterus Signup and view all the answers

What is the composition of human chorionic gonadotropin (hCG)?

α and β subunits, galactose, and hexosamine Signup and view all the answers

What is the function of the corpus luteum during pregnancy?

Producing estrogen and progesterone Signup and view all the answers

What is the significant decrease in hCG secretion after?

Initial marked rise Signup and view all the answers

What is the function of relaxin during pregnancy?

Inhibiting myometrial contractions Signup and view all the answers

What is the molecular weight of hCG-β?

28,000 Signup and view all the answers

What is the primary reason for the delay in milk secretion in women compared to most animals?

Different hormonal response to childbirth Signup and view all the answers

What is the effect of breastfeeding on menstrual cycles in women?

It delays the onset of menstruation Signup and view all the answers

What is the role of estrogen in lactation?

It inhibits milk production Signup and view all the answers

What is the first fluid secreted by the breasts after childbirth?

Colostrum Signup and view all the answers

What is the effect of prolactin on menstrual cycles?

It inhibits the onset of menstruation Signup and view all the answers

What is the primary function of prolactin in lactation?

Milk production Signup and view all the answers

Which enzyme is involved in the biosynthesis of estrogens?

CYP19 Signup and view all the answers

Where is estradiol primarily secreted into?

Follicular fluid Signup and view all the answers

What percentage of circulating estradiol is free?

2% Signup and view all the answers

What stimulates estradiol production in granulosa cells?

FSH Signup and view all the answers

What happens to estradiol, estrone, and estriol in the liver?

They are converted to glucuronide and sulfate conjugates Signup and view all the answers

What is the result of enterohepatic circulation of estrogen metabolites?

Reabsorption into the bloodstream Signup and view all the answers

What is responsible for breast enlargement at puberty in girls?

Estrogens Signup and view all the answers

What is the result of fertilization in a male zygote?

22 pairs of autosomes plus an X and a Y Signup and view all the answers

What is characteristic of the female body shape?

Narrow shoulders and broad hips Signup and view all the answers

What is the primary function of estrogen receptor α (ERα)?

Altering DNA transcription Signup and view all the answers

What develops from the cortex in genetic females?

An ovary Signup and view all the answers

What is the function of testosterone in male fetuses?

Causes regression of müllerian duct Signup and view all the answers

What is the characteristic of pubic hair growth in both sexes?

Primarily due to androgens Signup and view all the answers

What is the period of quiescence in both sexes?

A period in which the gonads of both sexes are quiescent until they are activated by gonadotropins Signup and view all the answers

What is the characteristic of the female larynx?

It retains its prepubertal proportions Signup and view all the answers

What is the role of gonadotropins in both sexes?

Triggering the final maturation of the reproductive system Signup and view all the answers

What is the primary characteristic of female fat distribution?

Primarily in the lower body Signup and view all the answers

What is the outcome of the development of the medulla in genetic males?

Testis development Signup and view all the answers

What is the primary function of Human Chorionic Somatomammotropin (hCS) in pregnancy?

To regulate maternal metabolism Signup and view all the answers

How soon can Human Chorionic Somatomammotropin (hCS) be detected in the blood?

6 days after conception Signup and view all the answers

What is the average duration of pregnancy in humans?

270 days from fertilization Signup and view all the answers

What is the result of low levels of Human Chorionic Somatomammotropin (hCS) during pregnancy?

Fetal growth restriction Signup and view all the answers

What is the effect of Human Chorionic Somatomammotropin (hCS) on maternal pituitary growth hormone secretion?

It decreases secretion Signup and view all the answers

What is the structural similarity between Human Chorionic Somatomammotropin (hCS) and another hormone?

Human growth hormone Signup and view all the answers

What triggers lactation in women?

The drop in circulating estrogen Signup and view all the answers

What is the primary effect of prolactin on lactation?

Stimulates milk production Signup and view all the answers

What is the primary function of oxytocin in lactation?

Evokes reflex oxytocin release and milk ejection Signup and view all the answers

Why do breastfeeding women typically not menstruate for several weeks?

Prolactin inhibits GnRH secretion Signup and view all the answers

What is the composition of the first fluid secreted during lactation?

Same concentration of protein and lactose as milk, but no fat Signup and view all the answers

What is the effect of estrogen on lactation?

Inhibits milk production Signup and view all the answers

Study Notes

Breast Development and Estrogens

Estrogens produce duct growth in the breasts and are responsible for breast enlargement at puberty in girls
Estrogens are responsible for the pigmentation of the areolas, which becomes more intense during the first pregnancy than at puberty
Breast enlargement at puberty is due to estrogens, known as the growth hormones of the breast

Female Secondary Sex Characteristics

Body changes that develop in girls at puberty are due to estrogens and the absence of testicular androgens
Women have narrow shoulders and broad hips, thighs that converge, and arms that diverge (wide carrying angle)
This body configuration is also seen in castrate males
Women retain their prepubertal larynx proportions and high-pitched voice
They have less body hair and more scalp hair, with a characteristic flat-topped pattern (female escutcheon) of pubic hair
Growth of pubic and axillary hair in both sexes is primarily due to androgens, not estrogens

Mechanism of Estrogen Action

Estrogen binds to estrogen receptor α (ERα) to form homodimers, which bind to DNA, altering transcription
Some tissues contain ERα, while others contain both ERα and ERβ

Human Chorionic Somatomammotropin (hCS)

hCS is a protein hormone secreted by the syncytiotrophoblast, with lactogenic and growth-stimulating activity
hCS structure is similar to human growth hormone, and evolved from a common progenitor hormone
hCS is found in high quantities in maternal blood, but little reaches the fetus
hCS functions as a "maternal growth hormone of pregnancy" to retain nitrogen, potassium, and calcium, and promote lipolysis and decreased glucose utilization
Low hCS levels indicate placental insufficiency

Parturition and Pregnancy

The duration of pregnancy in humans averages 270 days from fertilization (284 days from the first day of the menstrual period preceding conception)
Irregular uterine contractions increase in frequency in the last month of pregnancy
The difference between the body of the uterus and the cervix becomes evident at the time of delivery

Ovarian Hormones: Estrogens

Estrogens are steroids secreted by granulosa cells of ovarian follicles, the corpus luteum, and the placenta
Biosynthesis depends on aromatase (CYP19), which converts testosterone to estradiol and androstenedione to estrone
Theca interna cells supply androstenedione to granulosa cells, which make estradiol when provided with androgens
Granulosa cells have FSH receptors, and FSH facilitates estradiol secretion by increasing aromatase activity
Mature granulosa cells also acquire LH receptors, and LH stimulates estradiol production
2% of circulating estradiol is free, with the remainder bound to protein (60% to albumin, 38% to gonadal steroid-binding globulin)
Estradiol is converted to glucuronide and sulfate conjugates in the liver, excreted in the urine, and secreted in bile with reabsorption into the bloodstream (enterohepatic circulation)### Meiosis and Fertilization
In males, meiotic division results in the formation of four sperms, two containing the X chromosome and two containing the Y chromosome.
Fertilization produces a male zygote with 22 pairs of autosomes plus an X and a Y chromosome or a female zygote with 22 pairs of autosomes and two X chromosomes.

Development of Gonads

A condensation of tissue near the adrenal gland on each side of the embryo develops into a gonad, which has a cortex and a medulla.
Until the sixth week of development, the gonads are identical in both sexes.
In genetic males, the medulla develops into a testis, and the cortex regresses, with the appearance of Leydig and Sertoli cells, and the secretion of testosterone and Müllerian Inhibiting Substance (MIS).
MIS causes regression of the Müllerian duct.
In genetic females, the cortex develops into an ovary, and the medulla regresses, with the Müllerian duct system developing into uterine tubes and a uterus.

Hormonal Regulation

Hormonal treatment of the mother has no effect on gonadal differentiation in humans.
A burst of testosterone secretion occurs in male fetuses before birth, and again in the neonatal period, but the Leydig cells become quiescent thereafter.
In both sexes, the gonads are quiescent until activated by gonadotropins from the pituitary to bring about the final maturation of the reproductive system.

Lactation

Milk is secreted into the ducts as early as the 5th month, but the amount is small compared to the surge of milk secretion that follows delivery.
In women, it takes 1-3 days for the milk to "come in" after delivery.
The drop in circulating estrogen after expulsion of the placenta initiates lactation.
Prolactin and estrogen synergize in producing breast growth, but estrogen antagonizes the milk-producing effect of prolactin on the breast.
Suckling stimulates prolactin secretion, which maintains and augments milk secretion.

Colostrum

The first fluid secreted is the colostrum, which contains the same concentration of protein and lactose as milk but no fat.

Effect of Lactation on Menstrual Cycles

Women who do not breastfeed their infants usually have their first menstrual period 6 weeks after delivery.
Women who breastfeed regularly have amenorrhea for 25-30 weeks.
Breastfeeding stimulates prolactin secretion, which inhibits GnRH secretion, inhibits the action of GnRH on the pituitary, and antagonizes the action of gonadotropins on the ovaries.

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Description

Test your knowledge on the development of gonads and formation of zygotes from meiotic division in males. Learn about the differences in development between males and females. Understand the formation of autosomes and sex chromosomes.