Chapter 26 Flashcards
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
Female
XY means
Male
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
Bipotential
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?
Regress
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
5a-reductase
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?
Degenerate
Without DHT, the external genitalia?
Take on female characteristics
Week 0-8
Embryo
Week 8 - birth
Fetus
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
Testosterone
- 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?
10 WEEKS
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
AT BIRTH
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?
10 WEEKS
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
AT BIRTH
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