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Function of the gonads

The organs that produce gametes, the eggs & sperm that unite to form a new individual


What are the male & female gonads

Male-Testes, which produce sperm (spermatozoa)
Female- Ovaries, which produce eggs or ova (singular ovum)


What is sexually dimorphic?

(di-two + amorphous, form), meaning that males & females are physically distinct. This distinction can be blurred by dress & hairstyle, but these are cultural acquisitions


The male & female organs consist of 3 sets of structures

1) The gonads
2) The internal genitalia
3) The external genitalia


The internal genitalia consist of?

Accessory glands & ducts that connect the gonads with the outside environment


The external genitalia consist of?

All external reproductive structures


Sexual development is programmed in the?

Humane genome


Each nucleated cell of the body except eggs & sperm contains?

46 chromosomes. This set of chromosomes is called the diploid number because the chromosomes occur in pairs: 22 matched or homologous, pairs of autosomes plus one pair of sex chromosomes


Humans have 23 pairs of chromosomes which consist of?

22 pairs of autosomes and one pair of sex chromosomes. X & Y chromosomes means that these came from a male


What do the chromosomes do?

The 22 pairs of autosomal chromosomes direct development of the human body form & of variable characteristics such as hair color & blood type. The two sex chromosomes, designated as either X or Y, contain genes that direct development of internal & external sex organs


Which one is larger, X or Y?

The X chromosome is larger than the Y chromosome & includes many genes that are missing from the Y chromosome


Eggs & sperm are haploid cells meaning?

They have 23 chromosomes, one from each matched pair & one sex chromosome. When the eggs & sperm unite, the resulting zygote then contains 46 chromosomes of each matched pair coming from the mother & father


XX means



XY means



What happens to a zygote that inherits only a Y chromosome (YO)?

They will die because the larger X chromosome contains essential genes that are missing from the Y chromosome


What happens to a zygote that gets only one X chromosome (XO)?

Known as Turner's syndrome. It will develop into a female. Two X chromosomes are needed for normal female reproductive function however


Having an extra chromosome on #21 causes?

Down syndrome


Reproductive structures do not develop until?

The 7th week of development


What directs some single cell zygotes to become males and others to become females?

Sex determination depends on the presence or absence of the sex-determining region of the Y chromosome, or SRY gene


In the presence of sex-determining region of the Y chromosome (SRY) what happens? (Y means only male)

The bipotential gonads develop into testes


What happens in the absence of sex-determining region of Y chromosome (SRY)?

In the absence of the SRY gene and under the direction of multiple female specific genes, the gonads develop into ovaries


Before differentiation, the embryonic tissues are considered bipotential because they?

Cannot be morphologically identified as male or female


Tissues that can become either male or female



The bipotential gonad has an outer cortex & an inner medulla. Under the influence of the appropriate developmental signal, the medulla will develop into?
In the absence of the signal, the cortex will differentiate into?

Presence of signal, medulla develops into a testis
Absence of signal, cortex develops into ovarian tissue


The bipotential internal genitalia consist of 2 pairs of accessory ducts

1) Wolffian ducts (mesonephric) derived from the embryonic kidney
2) Mullerian ducts (paramesonephric ducts)
As development proceeds along either male or female lines, one pair of ducts develops while the other degenerates


Where is SRY gene found?

Only in males only on their Y chromosome


The SRY gene produces a protein (testis-determing factor or TDF) that does what?

Binds to DNA & activates additional genes, including SOX9, WT1, & SF1. The protein products of these genes direct development of the gonadal medulla into testis


Once the testes differentiate, they begin to secrete there hormones that influence development of the male internal & external genitalia.

1) Testicular Sertoli cells secrete glycoprotein anti-Mullerian hormone
2) Leydig cells secrete testosterone & its derivative dihydrotestosterone. These two androgens are the dominant steroid hormones in males


Essential for production of testosterone

Leydig cells


Anti-Mullerian hormone causes?

Regression of Mullerian duct


Testosterone controls?

1) Development of Wolffian duct into accessory structures
2) Development of male external genitalia (via DHT)


In the developing fetus, anti-Mullerian hormone causes the embryonic Mullerian ducts to?



In the developing fetus testosterone converts?

The Wolffian ducts into male accessory structures: epididymis, vas deferens, & seminal vesicle


Later in fetal development, testosterone controls migration of?

The testes from the abdomen into the scrotum, or scrotal sac. The remaining male sex characteristics, such as differentiation of the external genitalia, are controlled primarily by DHT


The enzyme that catalyzes the conversion of testosterone to DHT



In females, embryos, which have no SRY gene, the cortex of the bipotential gonad develops into?

Ovarian tissue


Symptoms of turner syndrome?

Infertile b/l streak gonads/ovarian agenesis
-primary amenorrhea
-short stature
-sexual infantilism
-high risk of congenital heart defects
-webbed neck


- Female sex
- May only exist in some of the body’s cells
- 1 in 2500 girls
- Infertile & tend to be short in stature, but other symptoms vary extensively

XO = Turner’s syndrome


During gamete development each daughter cell takes? of

- One of each homologue
- Creates haploid cells
- 23 chromosomes


In the absences of testicular AMH (anti-Mullerian hormone) what happens?

The mullerian ducts develop into the upper portion of the vagina, the uterus, & the fallopian tubes


Also called oviducts

Fallopian tubes


Without testosterone, the Wolffian ducts?



Without DHT, the external genitalia?

Take on female characteristics


Week 0-8



Week 8 - birth



Differentiation is (basic points)

1) Developing specific sex characteristics
2) Takes place in 2nd month of embryonic development
3) Development of different sex organs
- Gonads (organs that produce sex cells)
- Internal genitalia (glands and ducts that connect the gonads to external genitalia)
- External genitalia (external reproductive structures)


Presence or absence of SRY (basic points)

Presence of SRY:
- Production of TDF
- Indifferent gonads become testes
Absence of SRY
- No TDF
- Indifferent gonads become ovaries


- Stimulates development of Wolffian duct



- Aka: Mullerian Inhibition Factor
- Stimulates regression of Mullerian duct

Anti-Mullerian Hormone


Female genitalia

Mullerian duct


Male genitalia

Wolffian duct


What happens in the bipotential stage: 6 week fetus

The internal reproductive organs have the potential to develop into male or female structures


Mullerian duct becomes?

Fallopian tube, uterus, cervix, & upper 1/2 of vagina (AMH absent)


If female:
Gonad (Cortex)-
Gonad (Medulla)-
Wolffian duct-
Mullerian duct-

Gonad (Cortex)- forms- Ovary
Gonad (Medulla)- Regresses
Wolffian duct- Regresses (testosterone absent)
Mullerian duct- Becomes fallopian tube, uterus, & upper 1/2 of vagina (AMH absent)


If male:
Gonad (Cortex)-
Gonad (Medulla)-
Wolffian duct-
Mullerian duct-

Gonad (Cortex)- Regresses
Gonad (Medulla)- Form testis
Wolffian duct-Forms epididymis, vas deferens, & seminal vesicle (testosterone present)
Mullerian duct- Regresses (AMH present)


Development of internal organs in females:
10 weeks what happens?
At birth?

1) Gonadal cortex becomes ovary in the absence of SRY protein & under the influence of female-specific genes
2) Absence of testosterone causes Wolffian duct to degenerate
3) Absence of anti-Mullerian hormone to become the fallopian tube, uterus, & upper part of the vagina


Development of internal organs in males:
10 weeks what happens?
At birth?

1) SRY protein in male embryo directs the medulla of the bipotential gonad to develop into testis
2) Anti-Mullerian hormone from testis causes the Mullerian ducts to disappear
3) Testosterone from testis coverts Wolffian duct into seminal vesicle, vas deferens, & epididymis. DHT controls prostate development


Biologically there is sexually dimorphism meaning there are two distinct sexes, male & female, and its biologically based on?

Gonads because that is where the gametes are produced


What determines sex is what is?



Autosomes code for?

Everything else in the body other than sex


The sex chromosomes can be?
During gamete development?

X and/or Y
Each daughter cell takes half of the sets from one parent and half the set from the other & combines them


During development, the gametes are developed into?

Haploid cells then when fertilization occurs the egg becomes a diploid cell because it takes in the DNA from the sperm


The female parent can only give an?

X chromosome because female is XX


The male parent can give?

Has an X & Y so can pass on either one. If it is a Y chromosome it will be a male offspring


Not all zygotes end up with 46 chromosomes. Sometimes in cell division to form gametes occasionally there is a mix up where?

24 of the chromosomes might go to where only 23 were supposed to go leaving one with 22 instead of 23.
Sometimes what is passed on isn't exactly 23 pairs & so you end up with chromosomal disorders


During gametogenesis homologous chromosomes may
separate or sister chromatids may not separate.
Example is?

Down’s syndrome- there is an extra chromosome #21 (47 total chromosomes instead of 46)


sex chromosome variations § XXY = male (Klinefelter’s syndrome)

sex chromosome variations § XXY = male (Klinefelter’s syndrome)


sex chromosome variations with XXY

Male Klinefelter’s syndrome
- Y chromosome leads to development of male
- Most common sex chromosome disorder
- 1 in 500 males have XXY, only about half have syndrome
-Small testicles, reduced fertility


Testis determining factor



Where is the gene for the protein TDF (testis determining factor)?

On the Y chromosome. So if you don't have a Y chromosome (males) you're not going to have a TDF/YDF


Leydig cells that secrete



Sertoli cells secrete?

Anti-Mullerian hormone (AMH)



Testis-determining factor signal molecule is going to bind to receptors
Anti-mullerian hormone


For the male, because testosterone is present from developing gonads that then leads to?

The development of the internal structures. Whereas the male is also producing the anti-Mullerian hormone.


In the female because there is no anti-Mullerian hormone

The Mullerian duct developed into the female structures


Initially because of the presence of the Y chromosome (SRY protein) the development of which part of the gonadal tissue (cortex or medulla) will develop?
What happens in the absence?

In the absence of the SRY/TDF protein the cortex will develop into ovaries


Anti-Mullerian causes which duct to regress or degenerate?
In the absence of anti-Mullerian?

Mullerian duct
Absence of anti-Mullerian- Mullerian duct develops


Which duct does disintegrate in the female?

Wolffian because there is no testosterone to stimulate growth


What had to be present for the development of external male genitalia?

Dihydrotestosterone (DHT)


What does 5a-reductase catalyze?

The conversion of testosterone to DHT


What does aromatase do?

An enzyme that converts androgens to estrogens, the female sex hormones


Sex development is also referred to as



The signal molecules, receptors and enzymes involved in sex development

1) Signal molecules: testosterone, DHT, anti-Mullerian hormone, SRY protein
2) Receptors for these signal molecules
3) Enzymes: 5-alpha reductase, aromatase


In addition to chromosomal disorders, there are genetic disorders that can influence development of?

Any organ system


Variations in sex development is?

Having mis-matched internal and external sex organs or inconsistent gonads


Biologically we refer to sex based on the presence of?
What happens if certain tissues of the embryonic tissue develop differently? What if there are lack of receptors in certain cells but not in others?

Specific gonads


True Hermaphroditism (having the sex organisms of both sexes)

From a biological perspective means they have both gonad types. So something in the signaling pathway is different in some cells than others


True Hermaphroditism (basic points)

1) Expression of SRY gene in some embryonic cells but not others
2) Extremely rare
3) Possible types
- One ovary, one testis
- Ovotestes (part ovary, part testis on both sides) (certain cells were converted to ovaries so the cortex developed & in other cells the medulla developed)
- Ovotestes on one side only, testis or ovary on the other (most common)


Pseudohermphroditism is

For example growing up a girl then finding out at puberty that your genitals are developing into males. These men have the internal sex organs of a male but inherit a gene that causes a deficiency in one of the male hormones. They are bone with external genitalia that appear feminine, & they are raised as girls. At puberty the period when a person makes the transition from being non reproductive to being reproductive, pseudohermaphrodites begin to secrete more male hormones. As a result they develop some, but not all, of the characteristics of men.


Female congenital adrenal hyperplasia is an example of?



- Gonads and external genitalia don’t match
- Have testes or ovaries (not both)
- Underdeveloped penis or overdeveloped clitoris



Besides the gonads where else in the body (males & females) do we produce estrogen, progesterone, testosterone?

The adrenal cortex


Steroid hormones are produced here including the sex

Adrenal cortex


What happens if there is excess tissue growth in the female of the adrenal cortex?

Congenital Adrenal Hyperplasia (excess tissue growth) so there would be increased sources of the steroid hormones like estrogen, progesterone, testosterone. Because of this she will end up having androgens (male sex hormones) & it will end up during embryonic development as having masculinized genitalia, so the clitoris will be enlarged & the labia will be underdeveloped


- Excessive secretion of androgens from adrenal cortex
- “Masculinized” genitalia
- Enlarged clitoris, under developed labia

Female Congenital Adrenal Hyperplasia
Can be treated with a reduction in adrenal tissue


Males Testicular Feminization Syndrome

A male will have normal testes but they never descend, they remain inside the body & the reason because they are lacking the gene, therefore they are lacking the receptors for testosterone. They have female genitalia developed. They have a vagina without a uterus. Develop breasts. But because they have a vagina they are thought from birth to be females & its not until they reach puberty that they are unable to have a menstrual cycle & are infertile


Males Testicular Feminization Syndrome (main points)

1) Have normal testes that remain in the body cavity
2) Lack testosterone receptors
3) Female genitalia develop
4) Vagina without uterus
5) Testosterone converted to estrogen at puberty, breast development
6) Appears to be female who does not menstruate and is infertile


The condition in males 5-a-reductase deficiency

Males that lack the enzyme5-a-reductase which converts testosterone to DHT, so lacking this enzyme is what is responsible for the external genitalia so even though everything is normal inside there is a poorly developed penis & scrotum



Convertes testosterone to DHT males need DHT for the external genitalia


5-α-reductase deficiency main points

1) Lacking the enzyme that converts testosterone to dihydroxytestosterone (DHT)
2) DHT is the active form of the hormone for external genitalia
3) Normal epididymides, vas deferens, seminal vesicles, ejaculatory ducts
4) Poorly developed penis and scrotum


In the presence of aromatase testosterone can become?

Estradiol which is estrogen (high concentration of estrogen & the most potent form of estrogen in the female)


- Sex cell production
- In utero to puberty



Describe the gametogenesis process main points

1) Primary gamete
- Cells with 46 chromosomes, each with sister chromatids
- Diploid cells, duplicate copies of DNA
2) Secondary gamete
- Cells with 23 chromosomes, each with sister chromatids
- Haploid, duplicate copies of DNA
3) Final stage gamete
- Cells with 23 chromosomes, single chromatid
- Haploid, single copy of DNA


What is secreted from the hypothalamus for hormonal control of spermatogenesis

GnRH (gonadotropin-releasing-hormone) which controls secretion of two anterior pituitary gonadotropins: follicle-stimulating hormone (FSH) & Luteinizing hormone (LH)


In which structure are the receptors for GnRH?

Anterior pituitary


What does the anterior pituitary release?

Both Lutenizing hormone (LH) & Follicle stimulating hormone (FSH)


Development of sperm is stimulated by?



The LH stimulates the?

Leydig cells to secrete testosterone


Testosterone not only influences secondary sex characteristics but it also enhances the?

Activity of the sertoli cells for sperm production


Steroid hormone synthesis for the ovaries & testis

Ovary- Progesterone & Estrogen
Testis- Testosterone


Process of GnRH to spermatocyte maturation

GnRH > FSH > Sertoli cells > spermatocyte maturation


Process of GnRH to sex characteristics

GnRH > LH > Leydig cells > testosterone > sex characteristics


The female does not only have to produce games but she has to develop the?

Whole environment in which another organism can grow. Its not just egg development, its building the housing for potential pregnancy


How many days generally are in a ovarian phase?

28 days


The very first day of the ovarian phase/cycle is noted by the onset of?

Menses (the sleuthing off, the bleeding) of the uterine wall within the first 5-7 days then it starts to grow again in case of pregnancy


Why is it called the follicular phase of the menstraul cycle?

Because it is when the follicle is really developing (the follicle is a bunch of supported cells around egg)


Granulosa cells secrete?



Why is it called luteal phase of the menstrual cycle?

(FIG. 26.10)
Because that the leftover of the follicle becomes the corpus luteum so thats why its called the luteal phase


The cells that make up the follicle & then the corpus luteum are really important for?

Steroid hormone production


Which structure is responsible for producing estrogen the first two weeks?
What are the cells called?

The follicle
Cells that produce estrogen- granulosa cells


Granulosa cell

Cell of ovarian follicle that secretes estrogen


FSH is secreted from?

Anterior pituitary


During the menstrual cycle FSH is lowest during?

(FIG. 26.10)
Lowest-Luteal phase
Highest- Follicular phase because its helping the follicle develop & the more the follicle develops the more granulosa cells there are and the more granulosa cells there are the more estrogen & there reaches a critical point in estrogen feeding back to the hypothalamus & the anterior pituitary that stimulates the surge in lutenizing hormone (LH) which stimulates ovulation


Responsible for the development of the menstrual follicle

FSH (follicle stimulating hormone


3 phases of the menstrual Cycle

1) Follicular phase
2) Ovulation
3) Luteal phase


Follicle growth in ovary (egg matures)

Follicular phase


Ripened follicles and release of oocyte(s)



Luteal phase

Ruptured follicle into corpus luteum in preparation for pregnancy


What happens during menses?

No pregnancy & Bleeding from uterus


What happens during proliferative phase?

New layer of endometrium in preparation of pregnancy


What happens during secretory phase?

Conversion of endometrium to secretory structure


Surge in LH stimulates?



Progesterone is coming from the?

corpus luteum


As the corpus luteum develops & matures it produces & secretes?

(FIG. 26.10) Both progesterone and estrogen which is why there is another spike after estrogen came back down.


Progesterone takes over during which phase?

The luteal phase as being really important for the endometrium & preparing it in case of pregnancy


What causes/stimulates menses?

The drop in hormones progesterone, & estrogen


Produce androgens that are converted to estrogen by granulosa cells

Theca cells


Hormone regulation in females

1) Begins with onset of bleeding (menses)
2) GnRH release
3) LH release steady
4) FSH release gradually increases
5) Growth of follicle
6) Granulosa cells secrete estrogen
-Autocrine: estrogen to increase FSH receptors and growth of granulosa cells
- Negative feedback to hypothalamus by estrogen
- Negative feedback by AMH to other follicles (limits a
single follicle development)


Granulosa cell growth leads to?

1) Very high estrogen production and release
2) Peak in estrogen stimulates LH release (surge)
3) LH surge is the primary stimulus for ovulation
4) Estrogen has begun preparing the uterus for pregnancy
5) The cervix produces stringy mucus- to create channels for the sperm to follow up into the uterus
6) Ovulation within 1 day of the LH surge


Corpus luteum formed from?

1) Granulosa and theca cells of the follicle
2) Produces progesterone in larger, then more estrogen during the luteal phase
- Negative feedback to hypothalamus and anterior pituitary
- Prevents signals that would lead to development of new follicle
3) Progesterone
- stimulates further development of endometrium in case of pregnancy
- Increased vasculature
- Storage of fuels ( glycogen, lipids)
- Stimulates thickening of mucus to block cervical opening (reduce entry of bacteria or sperm)


What happens during the Corpus luteum phase

1) No pregnancy
2) Becomes corpus albicans (about 12 days after ovulation
3) Stops producing steroid hormones
- After 2 days without steroids to maintain the endometrium, menstruation begins
- Slough off the cells of the endometrium
- Start new cycle
4) Also, without steroid hormone negative feedback gone, hypothalamus begins secreting GnRH
5) Start of the new cycle (menstruation = day 1)
6) Pregnancy
- Secretion of human chorionic gonadotropin (hCG) by the placenta keeps corpus luteum active secreting progesterone (placenta takes over after several weeks)


Hormonal control follicular phase

1) FSH stimulates follicular development
2) Maturation to secondary and tertiary follicle
3) Granulosa cells produce estrogen
- Low to moderate levels of estrogen provide negative feedback- decreases FSH and LH secretion
- Late in the phase, high estrogen levels increase GnRH release (positive feedback loop)
4) LH stimulates thecal cells to produce androgens


Hormonal control ovulation

1) High levels of estrogen
2) LH surge and FSH spike
3) Egg release
4) High levels of inhibit which Inhibits production of FSH
5) Decrease new follicle development
6) Low levels of progesterone
7) Positive feedback
8) GnRH and LH


Hormonal control luteal phase

1) Granulosa & theca cells form corpus luteum which Secretes progesterone & estrogen
2) High levels of progesterone (and estrogen) maintain
3) Inhibin continues to limit new follicular development


Hormonal control late luteal phase

1) Pregnancy
- Corpus luteum maintains high levels of progesterone,
estrogen, and inhibin
2) No pregnancy
- Corpus luteum regresses and disintegrates
- Decreased levels of progesterone, estrogen, and inhibit 3) Menses
- High levels of FSH and LH
- New follicle development