Lecture 23 Flashcards
What is the size of the human egg?
100-159 micrometers
How long is the sperm? How wide is the sperm?
6 micrometers, 4 micrometers
What is syngamy?
When sperm head is incorporated into egg
What does syngamy allow?
Protects genetic material from the sperm from leukocytes (if sperm genetic material is damaged, if can affect ovarian genetic material as well)
When does syngamy occur?
12-24 hours after ovulation
What allows sperm to swim in the right direction?
Chemoattractants (and maybe temperature changes)
What does the female tract do in regards to sperm filtration?
Weeds out sperm as some are underdeveloped
What happens when decapacitation factors of the sperm head brushes off?
Reveals receptors that bind to egg membrane
Can attach to egg
How are the decapacitation factors removed?
Mucous holes just big enough for sperm to pass through
- mucus scrapes off decapacitation molecules
- reveals receptors
- ready to fertilize
How does IVF work in regards to capacitation of the sperm?
Make sperm swim through artificial mucous membrane
What are the two stages of capacitation?
- Acrosome reaction
2. Motility changes
How is acrosome reaction controlled?
DNA is arrowhead shape but also contains acrosomes (in acrosomal cap) covers 2/3 of head
- Double layered bag pulled over head
- Develops from Golgi apparatus
- There are 60 different hydrolytic enzymes
- acrosome reaction involves holes that release
- enzymes erode membrane surrounding the egg for penetration
- collar that surrounds the head is where receptors are that binds to the egg
- side of head (collar) binds to egg NOT THE TIP
How is motility controlled?
Sperm dances around (starspin) to increase chance to meet egg
Cholesterol in membrane of tail allows change of motility
Eggs only complete meiosis when fertilized
What does pronuclei contain?
Half of the genes
What does the pronuclei do?
Give rise to paternal/maternal chromosomes which mix on metaphase plate
Embryo - Morula - Blastocyst
What does the blastocyst contain?
Contains uterine cavity (84-96 hours after ovulation)
What does the blastocyst do?
Attaches to endometrium then forms placenta
Where does fertilization occur?
in the ampulla of the female tract
How does fertilization allow for diversity?
Provides half (chromosomes from each parent) Randomly selects which paternal chromosome enters gamete Exchange of genetic information during gametogenesis
How long is the gestation length of males and females?
Male: 265 days Female: 266 days
or 38 calendar weeks (9months)
What does sexual phenotype depend on?
GONADS
What develops the male phenotype?
testes present
What develops the female phenotype?
ovaries are present or no gonads
Are oocytes needed for normal ovary development?
yes
Are sperm needed for normal testes development?
no
Where do gonads develop?
gonadal ridges
What do gonadal ridges contain?
Mesonephros (primitive kidney)
Internal tubes and ducts
Where do gonadal ridges form?
Posterior abdominal wall within a few weeks of fertilization
- has presumptive cells that develop into tubular kidney systems (develop close to midline after a few weeks post-fertilization)
What are Gonadal ridges close to?
Allantois germ cells (appear like primordial germ cells)
What do primordial germ cells become when they differentiate at 5 weeks?
Gonia
How many primitive oogonia develop by 7 months of gestation?
9 million cells
How many oogonia are left by birth?
half a million
Why does the number of oogonia decrease after it reaches its peak number?
Degeneration of oogonia (decrease in FSH)
Transformation into oocytes
Oogonia produce my mitosis but oocytes by meiosis
Meiosis Inducing Substance (MIS) needed to transform oogonia to oocytes
Where are Meiosis Inducing Substance from?
Mesonephric ducts in BOTH males and females
What do males produce that counteracts the effects of MIS?
meiosis Preventing substance (MPS)
What becomes the testes during puberty?
testis cordis
How long does it take to produce sperm?
60-70 days
How long does it take to produce oocytes?
can take decades
How many oocytes are there at birth and how many are lost during menstruation?
400 000-500 000
400-500
What happens when all the oocytes are lost?
menopause
What is the name for primitive sperm producing cells?
spermatozoa
What do the testis cords transform into?
Semeniferous tubules
What do the semeniferous tubules do?
produce sperm
What chromosome combination leads to Turner’s syndrome?
X0
How many genes are there on the Y-chromosome?
60 genes
Which gene induces testes information?
Sry
What hormone does the testes produce?
Anti-Mullerian hormone (AMH) (also known as Mullerian Inhibiting Substance (MIS)
Testosterone (several types)
What protein is a product of Sry?
SRY
What does SRY do?
Triggers Sertoli cell fate?
What are sertoli cells?
Supporting cell of testis
Sperm form inside vesicles in sertoli cells
Semeniferous tubules are long
- on surface is where they develop
- sperm develop in vacuoles in sertoli cells
What happens when SRY is absent?
Follicle cell fate develops (becomes female)
What does SRY protein contain?
HMG box-type of DNA binding protein
What does the HMG domain bind to?
Minor groove of DNA altering its configuration so influencing transcription by affecting neighboring interactions between proteins and DNA
Which gene is probably involved in long term maintenance?
SOX9
Acts as the electricity that is controlled by the switch
SOX 9 increases in Sertoli cells a few days after Sry is activated in males
What happens to SOX 9 in females?
decline
What can SOX9 mutations cause?
Male-female reversal
What is the steroidal cell in males and females?
Male: Leydig cell Female: Theca cell
What are the connective tissue cells in males and female?
Male: testicular cords, myoid cells
Female: Stroma cells
What does 5 alpha reductase do?
Converts testosterone to more active 5 dihydroxytestosterone (5DHT)
What are features of 5DHT?
5 times more potent than testosterone itself used to trigger male phenotype pathway
A gradient of response can be obtained
- varying concentration can affect the development of male genitalia
- if lacking, male genitalia do not differentiate properly
What can be seen in Testicular Feminization syndrome?
Karyotype 46/XY
Normal male phenotype but genotype female
Testes present to produce normal levels of testosterone
Low levels of cytosolic carrier protein for hormone prevents actions
Female phenotype is due to unopposed action of (smell) amounts of estrogen from testes/adrenal cortex
- testosterone has no effect to counteract the “female” hormones
Female genitalia generally underdeveloped
How is assignment sex assessed?
External genitalia at birth and on birth certificate
Until when is internal genitalia undifferentiated?
at 8 weeks
What happens by 10 weeks?
AMH starts to take effect
- paramesonephric (Mullerian) duct degenerates in mae
- mesonephric (Wolffian) duct degenerates in female
When are clear differences seen in external genitalia?
12 weeks
By when does the fetus have a normal infant appearance?
34 weeks
In which sex does the paramesonephric duct degenerate?
male
In which sex does the mesonephric duct degenerate?
female
What does the seminal vesicle become?
prostate
What do Leydig cells do?
promote male phenotype
What are the three levels of development?
Undifferentiated
- identical
Partly developed
- male and female still look similar
- Labio scrotal swelling becomes scrotum/labial majora
Fused:
- males: Flap of tissue closes up
- females: Closes but not the whole way (has an opening, that’s why urethra meatus is in the middle)
- Hypospadias: A condition in which males have an opening in middle of scrotum instead of the tip (pretty common)
Fully developed
What comprises the male genitalia?
Glans penis
Urethral meatus: opening of urethra in penis
- urethra is horizontal but tip is vertical - spiral motion of urine
Linear alba: line of skin on ventral surface between testes to the opening of anus
What comprises the female genitalia?
Labia majora
Labia minora: same tissue as linear alba
Glans clitoris and head of penis under microscope look similar
How are the clitoris and the penis similar?
Spongy tissue
Enlarged from sexual arousal
How are the clitoris and the penis different?
Clitoris does not become rigid but is still homologous to penis
Where are the testes in the 8-week baby and 8-month baby?
8-week: abdomen
8-month: scrotal sac
How does the testes move?
Pop through posterior abdominal wall
lie outside of body cavity
men are more likely to have hernia at the hips than women
