Lecture 4

Question 1

Reproductive Development:

Answer 1

the formation, from conception to adulthood, of sexual characteristics specific to the sex of an individual

Question 2

Sexual Characteristics(2)

Answer 2

Primary = gonads
Prenatal

Secondary = all other sexually dimorphic characteristics
Internal and external genitalia
Variation in body structure, physiology, function
Two major stages of development
Pre- and postnatal
Pubertal

Question 3

Sexual Dimorphism(3)

Answer 3

Morphism: the form of a structure or substance

Dimorphism: having two different forms

Sexual Dimorphism: having two different forms, one for each of two sexes

Question 4

Sexual Differentiation

Answer 4

Differentiation: the process of going from a non-specific state (monomorphic) to a specific state

Sexual Differentiation: the process of going from a sexually monomorphic state to a sexually dimorphic state

Question 5

Undifferentiated (Bipotential) Fetal Reproductive Structuresat Approximately Six Weeks Development

Answer 5

IMAGE

Question 6

Primary (Gonadal) Sex Determination is Chromosomal

Answer 6

Y chromosome = SRY gene = ♂ = testes

No Y chromosome = no SRY gene = ♀ = ovaries

Question 7

Many Genes on Different Chromosomes are involved in Primary Sex (gonadal) Differentiation (short list)

Answer 7

X = ATRX; Dax1

Y = SRY

Question 8

Overview of Genetics of Gonad Formation

Answer 8

Testes form around week seven.

Ovaries form around week sixteen.t

Question 9

SRY present?

Answer 9

If SRY is present, TESTES form around week seven. The testes begin to produce and secrete TESTOSTERONE. If no SRY is present, OVARIES form. Ovaries form around week sixteen.

Question 10

Proper Development of the Ovary Needs Autosomal Genes

Answer 10

Genes needed

Wnt4 (Chromosome 1) to prevent male characteristics in gonad

Gdf9 (Chromosome 5) and FoxL2 (Chromosome 3) are required for proper follicular development

Two copies of DAX1 (X-Chromosome) yield ovaries even in the presence of SRY

Two X-chromosomes are needed for fully functional ovaries

Question 11

Differentiation of Bipotential Gonad

Answer 11

Primordial Germ Cells become Oogonia or Spermatogonia

 Primordial Germ Cells (PGCs) develop OUTSIDE of the embryo, but migrate to (invade) the gonad once gonadal sex is determined.

Question 12

Hormones of Sex Differentiation

Answer 12

Androgens

Testosterone: secreted by Leydig cells of testis

5α-Dihydrotestosterone (DHT): testosterone is converted to DHT at the cells on which it acts

AntiMüllerian Hormone (AMH); aka Müllerian Inhibiting Hormone (MIH, MIS, MRF): secreted by Sertoli cells

Question 13

If Androgens & AMH present….

Answer 13

If androgens and AMH are present, structures are male.If no androgens or AMH, structures are female.

Question 14

SRY & DAX1?

Answer 14

SRY = testis determining factor
DAX1 = 2 copies are needed to form ovaries

Question 15

Anatomical Homologies

Answer 15

Structures are “homologous” in two different sexes (or two different species) if they develop from the same embryonic tissue/structure.

In two different species, they represent common ancestry.

Question 16

Some final words on prenatal development… descent of the testes.

Answer 16

Gonads form at the posterior body wall of the abdominal cavity. Both ovaries and testes descend. But only testes navigate through the pelvic floor.

Question 17

Descent of the testes

Answer 17

Descent occurs in two stages:
Transabdominal descent (cranial suspensory ligament and gubernaculum)
Inguinal-scrotal descent (androgen dependent)

Question 18

Puberty

Answer 18

Puberty begins approximately ten to twelve years following birth.

Question 19

Steroid Hormones(2)

Answer 19

Androgens
Testosterone
DHT (5α-dihydrotestosterone)
Androstenedione

Estrogens
Estradiol
Estriol
Estrone

Question 20

Puberty is? Changes?

Answer 20

The period marking the end of childhood and the attainment of sexual maturity.

Somatic changes = changes in non-reproductive tissues

Reproductive changes = development of secondary sexual characteristics

Question 21

Major Events(4)

Answer 21

Adrenarche:  adrenal gland activation results in steroid hormone synthesis
  produces weak androgens
  promotes pubic and axillary hair growth
Gonadarche:  enlargement of gonads
  more significant in testes
  marks beginning of male puberty
Thelarche:  breast enlargement
  not significant in males
  marks beginning of female puberty
Menarche:  onset of menstrual cycle
  exclusive to females
  last obvious stage of female maturation

Question 22

GnRH Pulse Generator signals the onset of puberty in both males and females

Answer 22

GnRH: gonadotropin releasing hormone
quiescent since birth
triggers LH and FSH secretion by the pituitary

Question 23

GnRH activation is…

Answer 23

GnRH Activation is an orchestration of internal and external signals

Question 24

Factors implicated in pubertal activation of GnRH are divided into two groups

Answer 24

Permissive signals: allow puberty to proceed
Integration of multiple signals may or may not be required

Independent “Master” signal is probably an innate developmental clock

Question 25

Permissive signals implicated in pubertal activation of GnRH – may be different in males and females:

Answer 25

adequate nutritional intake adequate fuel reserves available calories bottom line may actually be “energy balance” (less important in males) adequate body size circadian clock activity (nocturnal melatonin increases)

Question 26

Developmental Clock is now thought to involve two important signaling hormones directly related to energy balance. (2)

Answer 26

Leptin = adipose (fat) derived hormone that controls energy intake and expenditure signals nutritional status Kisspeptin = protein expressed in neurons of control regions in hypothalamus functions through GPR54 receptor no GPR54 receptor – NO PUBERTY!!! neurons express kisspeptin production at GnRH producing cells many kisspeptin neurons have leptin receptors

Question 27

Adrenarche is NOT controlled by GnRH:

Answer 27

Since pubertal onset and duration varies between boys and girls, control of activation of GnRH may differ in males and females There are probably more signals, besides leptin, acting through the Kisspeptin pathway regulating the variation in males and females

Question 28

Male Secondary Sex Characteristics of Puberty in order of appearance (time span ~8 years)

Answer 28

Initiation of androgen production Fat deposition begins Skeletal growth begins; spontaneous erections; seminal vesicles and prostate grow larger Spontaneous nocturnal ejaculations Growth of vocal cords & deepening of voice; axillary, pubic and upper lip hair grow

Question 29

Male Secondary Sex Characteristics of Puberty in order of appearance (time span ~8 years)(continued)

Answer 29

First fertile ejaculation Appearance of chest, body and facial hair; sweat and oil glands increase production; loss of body fat Muscle growth; increase of muscle strength; broadening of shoulders Adult height may be reached (sometimes growth continues into 20s)

Question 30

GRAPHS

Answer 30

Understand graphs!

Question 31

Female Secondary Sex Characteristics of Puberty in order of appearance (time span ~5 years)

Answer 31

Growth spurt and deposition of fat Widening of pelvis Growth and maturation of uterus, uterine tubes and vagina Growth of pubic and axillary hair Skeletal growth increases then decreases; sweat and oil glands increase production; first ovulation occurs Voice deepens slightly Adult height is reached

Question 32

Differences in LH & FSH

Answer 32

GRAPH!

Question 33

Estrogens Fluctuations through life in femal

Answer 33

graph!!

Question 34

Effects of LH & FSH on Estrogen & Progesterone

Answer 34

Graph!

Question 35

Range of Ages of Onset of Puberty (on 4)

Answer 35

Adrenarche is prepubertal Menarche = 8.5 to 17 years of age Thelarche = 8 to 14 years of age Gonadarche = 8.5 to 16

Question 36

Variation in individuals at puberty stages.

Answer 36

All females in image are 12.75 years old. All males are 14.75 years old.