Module 9: Reproduction and Development I Flashcards
Humans are sexually _____, males and females have distinct physical characteristics (determined by _____)
dimorphic, genome
What are the three sets of structures comprising male and female sex organs? Give their roles and examples from both sexes.
-
Gonads: gamete producing organs
- Male: testis
- Female: ovaries
-
Internal genitalia: accessory glands and ducts
- Male: epididymis, vas deferens
- Female: fallopian tubes, cervix
-
External genitalia: external reproductive structures
- Male: penis, scrotum
- Female: labia, clitoris
Genetic males are defined by the presence of what? How are genetic females defined?
Males are defined by the prescence of a Y chromosome. Females only have X chromosome(s).
Are both X chromosomes active in females?
No.
The SRY gene produces this hormone
testis determining factor (TDF)
Describe what happens in X-chromosome inactivation.
In females, after the development of ovaries, one X chromosome is turned off in each cell. Whether the paternal or maternal X chromosome is shut off differs in each cell.
X-linked recessive genetic disorders more commonly affect _____. Why? Give some examples of these diseases.
Males. There is only one X chromosome that cannot be shut off. Muscular dystrophy, color blindness, hemophilia.
The inactivated X chromosome is known as a _____.
Barr body
X chromosome inactivation occurs _____ development of the ovaries
after
What is non-disjunction and when does it occur? Is it limited to sex chromosomes?
It is where chromosomes can be unevenly separated, resulting in sex abnormalities. Can occur at either meiosis I or II. This can also happen with autosomes (ex., T21 [Down’s], T18 [Edwards] and T13 [Patau’s]).
What are the two main sex chromosome disjunction disorders? What are the 3 “others”?
Main
- Klinefelter’s syndrome (XXY): present male
- Turner syndrome (X): present female
Others
- Y: non viable
-
XXX and 3. XYY
- These are not typically diagnosed as there is no real effect to the offspring
When does fetal development start? How long does it last? How long is the embryonic period?
Starts with the formation of a zygote at fertilization. Pregnancy from the moment of conception is 38 weeks long. 8 weeks long.
Reproductive structures do not begin to differentiate until the _____ week of development and prior to this time are considered _____ (both look the same, could be either or)
seventh, bipotential
How do the gonads (outer cortex, inner medulla) in males and females change during fetal development?
Gonad: outer cortex and inner medulla
- Male: cortex regresses, medulla forms testis
- Female: medulla regresses, cortex forms ovary
How do the accessory ducts in males and females change during fetal development? What hormones control the regression or formation?
Accessory ducts: Wolffian duct, Mullerian duct
Male: Wolffian duct forms epididymis, vas deferens, and seminal vesicle (testosterone present), Mullerian duct regresses (AMH)
Female: Wolffian duct regresses (test. abs), Mullerian duct becomes fallopian tube and upper half of vagina (AMH absent)
Male or female development depends on the presence or absence of what gene? What does this do? What cells are eventually formed?
Sex determining region of the Y chromosome (SRY gene). The gene produces testis determining factor (TDF), which activates SOX9, WT1, and SF1 genes, which guide development of gondal medulla into a testis, forming sertoli and laydig cells.
The testes produce three hormones after activation of the SRY gene, what are they, which cell are they produced by and what are their roles?
- Anti-Mullerian hormone (sertoli cells): causes Mullerian ducts to regress
- Testosterone (leydig cells): converts Wolffian ducts into male accessory structures (epididymis, vas deferens, and seminal vesicles)
- Dihydrotestosterone (leydig cells): differentiation of external genitalia
External genitalia development (genital tubercle, urethral folds and grooves and labioscrotal swellings) driven by presence or absence of _____.
Androgens (DHT).
Development of male external genitalia is caused by what? What happens to the genital tubercule, urethral folds and grooves, and labioscrotal swellings?
Male: presence of androgens
- Genital tubercule forms glans penis
- Urethral folds and grooves forms shaft of penis
- Labioscrotal swellings forms shaft of penis and scrotum
Development of female external genitalia is determined by what? What happens to the genital tubercule, urethral folds and grooves, and labioscrotal swellings?
If female: absence of androgens
- Genital tubercule forms clitoris
- Urethral folds and grooves forms labia minora, opening of vagina and urethra
- Labioscrotal swellings forms labia majora
What is the importance of dihydroxytestosterone (DHT)? Which enzyme is involved in its conversion from testosterone?
DHT is involved in the formation of male external genital and prostate development. The enzyme is 5a-reductase.
Oocytes
- Size
- Motility
- Number and release
- Last until
- Some of the largest cells in the body
- Nonmotile, move via smooth muscle contraction or cilia
- Born with all the oocytes you will have, cyclically released during reproductive years
- After ~40 years ceases
Sperm
- Size
- Motility
- Production
- Last until
- Quite small
- Only flagellated cells in the body and are highly motile
- Continuously produced after reaching reproductive maturity
- Sperm and testosterone production diminishes with age but do not cease
Define gametogenesis. What are the 4 steps?
The production of gametes.
- Germ cells in embryonic gonads undergo mitotic divisions to increase number
- Duplication of chromosomes (92 chromosomes)
- One primary gamete divides into two secondary gametes, each with 46 chromosomes
- Secondary gametes divide again to produce haploid gametes (23 chromosomes = 23 chromatids)
In both males and females, gametogenesis under control of _____ from brain and from _____ in the gonads
hormones, endocrine cells
What are the 5 steps of female gametogenesis?
- Oogonia replicates DNA, forming primary oocyte (92 chromosomes)
- Primary oocyte undergoes first division, producing large secondary oocyte and a tiny first polar body (46 chromosomes each)
- The egg begins second meiotic division, polar bodies break down
- Ovary releases egg and it does not undergo secondary division until fertilized
- Secondary oocyte contains 46 chromosomes, preparing to undergo division
- Once sperm begins to fertilize secondary oocyte it undergoes meiotic division shedding a polar body containing 23 chromosomes, leaving 23 chromosomes in the ovum and 23 new chromosomes enter from the sperm
How many eggs are produced from one primary oocyte?
1
Which month of fetal development does mitosis and the first stage of meiosis occur in female gametogenesis?
Occurs by the 5th month of fetal development.
How many oocytes are there at birth and when are all of them made? When does meiosis resume?
About 500,000, all produced by the 5th month. Meiosis resumes at puberty.
Why don’t polar bodies survive?
Uneven division, polar bodies are very small with very little cytoplasm and few organelles, same number of chromosomes. This ensures that everything needed for a zygote to thrive is in the main cell.
What are the 5 steps of male gametogenesis?
- Germ cells (spermatogonium)(2n) proliferate into spermatogonia (2n) (mitosis)
- Spermatogonia DNA replicates with no separation, forming a primary spermatocyte (4n)
- Primary spermatocyte undergoes first meiotic division into a secondary spermatocyte (2n)
- Secondary spermatocyte undergoes second meiotic division into spermatids (n)
- Spermatids mature into sperm
How many sperm are produced from one primary spermatocyte?
4
In male gametogenesis, what cells are present in the testis at birth? What cells are produced during puberty and what happens to these cells?
At birth testes contain only immature germ cells and remain quiescent. At puberty germ cell mitosis resumes producing germ cells known as spermatogonia. Some spermatogonia continue in mitosis, some enter meiosis producing primary spermatocytes, secondary spermatocytes, spermatids and finally sperm.
How do all reproductive control pathways begin?
Begins with secretion of peptide hormones from hypothalamus and anterior pituitary that control gondal secretion of sex hormones including androgens, estrogens and progesterone.
What is the difference between males and females in regards to the main reproductive hormones?
Both sexes produce all three, just in different amounts
-
Males primarily androgens (95% testes, 5% adrenal cortex) most converted in periphery to DHT
- DHT and testosterone both act on the same receptor, but have different effects
- Females primarily estrogens and progesterone (ovaries)
The precursor for androgens, estrogen and progesterone is _____.
Cholesterol.
Describe the hypothalamic-pituitary-gonadal axis control pathway
Gonadotrophin releasing hormone (GnRH) produced in hypothalamic neurons controls secretion of two anterior pituitary gonadotropins from gonadotrophs: follicle stimulating hormone (FSH) and luteinizing hormone (LH)
- FSH and LH act on gonads
- Kisspeptin is believed to influence GnRH
Describe the 3 steps of the hypophyseal portal system.
- Neurons synthesizing trophic neurohormones release them into the capillaries of the portal system
- Portal veins carry them to the anterior pituitary where they act on endocrine cells
- Endocrine cells release their peptide hormones into the second set of capillaries for distribution to the rest of the body
Short-loop negative feedback involves _____ and _____ inhibiting _____ release from the hypothalamus.
Most suppression results from long-loop via _____ and _____ hormones.
LH, FSH, GnRH.
Steroid, peptide.
The offspring is considered bipotential until the _____ week
7th
At low concentrations is estrogen negative or positive feedback? What about at high concentrations? How does this work?
Estrogen is negative feedback up to a point, but once reaching higher concentrations flips to positive feedback driving GnRH and especially LH even higher, plays a significant role in female reproductive cycle. Thought to be estrogen influencing GnRH release.
Long loop feedback is from what to what? What about short loop?
Long: gonads to pituitary or hypothalamus (GnRH)
Short: pituitary (LH and FSH) to hypothalamus (GnRH, kisspeptin)
What are the two sites of feedback pathways in the brain and which cells are involved?
- Anterior pituitary on gonadotrophs
- Hypothalamus directly on GnRH neurons or via Kisspeptin containing neurons
What kind of feedback effects do testosterone, estrogen and progesterone have on the hypothalamus and gonadotrophic cells in the hypophyseal portal system?
Testosterone: negative feedback on hypothalamus and gonadotrophic cells in the hypophyseal portal system
Estrogen and progesterone: positive or negative feedback on hypothalamus and gonadotrophic cells in the hypophyseal portal system
GnRH release occurs how often and in which sex? Which cells direct release?
Every 1-3 hours in both sexes. Directed by pulse neurons in the medial hypothalamus
Females have a surge in GnRH release corresponding with what?
Ovulation.
What happens to children with a GnRH deficiency? How is this treated? Why in this specific way?
Children with a GnRH deficiency will not mature sexually without gonadotropin stimulation of the gonads. Synthetic GnRH must be delivered in a pulsatile manner.
Constant delivery of GnRH leads to down regulation of receptors in the pituitary gonadotrophs
Why can administration of constant GnRH treat breast or prostate cancers?
It suppresses sex hormone production to prevent spread of cancer.
Pulsatile activity in _____ neurons stimulates GnRH neurons to release GnRH. GnRH binds GnRH receptor on gonadotrophs in the anterior pituitary to stimulate the release of _____ and _____. What is the role of these two?
Kisspeptin, LH and FSH.
LH and FSH act on the gonads to stimulate hormone secretion and facilitate gamete production
Studying the effects of environmental factors in men is difficult, and easier in women. Why?
Difficult to study in males as it is hard to tell externally. The normal reproductive cycle in women easier because physiological uterine bleeding during menstrual cycle can be monitored.
What are some environmental factors that are believed to influence reproduction? (4)
- Nutritional status
- Physical activity
- Change of day/light cycles (altering circadian rhythm) (travelling across time zones, night shift work)
- Environmental estrogens
What are environmental estrogens? How do they work in the body? What are they believed to influence?
Estrogens from the environment. Can bind and activate estrogen receptors. Some are anti-estrogens that interfere with second messenger pathways. May influence developing embryo/fetus.
How long does the zygote take to develop into a blastocyst?
1 week
Most GnRH suppression occurs through _____-feedback loops
long
The _____ acts as the GnRH pacemaker
mediobasal hypothalamus
