Module 2: Gametogenesis and Hormone Regulation Flashcards
Gametogenesis
-process by which gametes are produced in sexually reproducing organisms
What does gametogenesis ensure
-that the gametes are haploid
-the gametes acquire the specialized characteristics that will allow them to fuse successfully via fertilization
Steps of gamete formation
-mitotic division
-meiotic division
-maturation
Spermatogenesis steps
-mitotic proliferation
-meiosis I
-meiosis II
-maturation
2 types of daughter cells
-type A
-type B
Type A daughter cells
-will continue to replenish the spermatogonial pool
Type B daughter cells
-will divide by mitosis to produce identical primary spermatocytes which enter a resting phase in preparation for meiosis I
Where are spermatogonia located
-closest to the basal membrane of seminiferous tubules in outermost layer
Where are daughter cells located
-move towards the surface of the epithelium to reach the lumen of the tubule
Where are the spermatozoa
-once mature they are released into the lumen of the tubule to be transported out of the testis towards epididymis or maturation and storage
Spermatogenesis waves
-within seminiferous tubules, the local course of spermatogenesis occurs in a wave like pattern
How do the waves move in spermatogenesis
-move in spirals towards the inner part of the lumen
-at the end of the spiral, the fully developed spermatogonia are in the lumen and as they mature they move along the tubule to give way to new cells
How long does the process of spermatogenesis waves take
-64-70 days
Supporting cells of the seminiferous tubules
-leydig cells
-sertoli cells
Leydig cells location
-intertubular regions of the testis
Leydig cells function
-responsible for testosterone production
Sertoli cells function
-provide structural and nutritional support to developing sperm cells until they mature
Blood-testis barrier
-regulates the passage of substances from the circulation into the lumen of seminiferous
Basal compartment of the blood-testis barrier
-the area below the blood-testis barrier
Apical compartment of the blood-testis barrier
-the area above the blood-testis barrier
Immune privileged environment
-meiotic and post meiotic cells develop after the body has established immune tolerance and thus could be recognized as foreign by immune system
-seminiferous tubules are thought to actively exclude immune cells and other factors from entering, mostly from the blood-testis border
Parts of a mature sperm cell
-acrosome
-head
-midpiece
-tail
-end piece
Acrosome
-structure that contains hydrolytic enzymes that the sperm cell will use to enter the egg
Head of sperm
-contains DNA and acrosome
Midpiece of sperm
-contains all of the mitochondria, which create energy used by the tail
Tail of sperm
-typical flagellum
End piece of sperm
-last portion of sperm tail
Teratozoospermia
-sperm with abnormal morphology
Examples of how teratozoospermia can happen
-cryptorchildism
-varioceles
-genetic disorders
Varioceles
-enlargement of veins within scrotum
Steps of oogenesis
-mitotic division
-meiosis I
-meiosis II
Oogenesis mitotic division
-produces primary oocytes
Oogenesis meiosis I
-dormant primary oocyte will complete meiosis I to produce haploid secondary oocyte
Oogenesis meiosis II
-secondary oocyte becomes fertilized to produce ootid
-ootid becomes a mature ovum
Improper formation of polar bodies
-oocytes with a polar body that has been improperly formed are significantly less likely to fertilize
-embryos that do form from them end up having significantly impaired growth
Structure of the ovum
-corona radiata
-zona pellucida
-vitelline membrane
-ooplasm
-germinal vesicle
-germinal spot
Corona radiata
-layer of cells around oocyte that will be released with it during ovulation
-provides vital proteins
Zona pellucida
-hard shell
-binds to head of spermatozoa and helps initiate acrosome reaction
Vitelline membrane
-outer portion of cell membrane
Ooplasm
-yolk of the egg cell
-contains mitochondria
Germinal vesicle
-nucleus of cell
-contains all genetic material
Germinal spot
-nuclueolus of ovum
Timing of oogenesis steps
-fetal period
-childhood
-adulthood
Fetal period oogenesis
-oogonia proliferate and mature into primary oocytes, large portion of which undergo apoptosis
-leaving about 2 million oocytes arrested in prophase I
Childhood
-arrested primary oocytes have been surrounded by somatic cells becoming follicles which will remain dormant until puberty
-a lot of them will undergo cell death, leaving about 40 000
Adulthood
-influence of hormones at puberty
-arrested primary oocytes resume maturation following a monthly cycle
Age and risk of aneuploidy
-the human oocyte can remain in prophase I for several decades
-there may be a risk of segregation errors in older eggs
Ovarian follicles function
-produce the sex hormones that promote oogenesis and regulate pregnancy when fertilization is successful
Cells of the ovarian follicles
-theca cells
-granulosa cells
Theca cells
-surround the follicle
-produce the precursors required by granulosa cells to produce progesterone and estrogen
Granulosa cells
-produce estrogen and progesterone
Follicular phase
-occurs within ovarian follicles
-follicular phase ends with ovulation, the moment when a single secondary oocyte is released
Luteal phase
-changes which occur after ovulation to the empty follicle
-after ovulation the follicle briefly becomes the corpus hemorrgaicum and then the corpus luteum
Corpus luteum
-produces progesterone to prepare body for pregnancy, if fertilization does not occur, it degenerates, becoming the corpus albicans
Folliculogenesis steps
-primordial follicle
-primary follicle
-secondary follicle
-tertiary (graafian) follicle
Primordial follicle
-dormant follicles we are born with
-contain primary oocyte surrounded by singular layer of flattened granulosa cells
Primary follicle
-granulosa becomes cuboidal
-oocyte forms zona pellucida
Secondary follicle
-forms as granulosa cells multiply and theca cells are recruited to surround outermost layer
Tertiary (graafian) follicle
-granulosa and theca cells multiply and follicle grows in diameter
Ovarian cycle
-describes the changes that occur in the ovary
Uterine cycle
-describes the preparation and maintenance of the uterus to receive a fertilized egg
Menstrual cycle
-the ovarian and uterine cycle combined
The HPG axis
-major signalling pathway between hypothalamus, pituitary gland, and the gonads
-regulates production of specific hormones that direct function of reproductive system
Hormones of the HPG axis
-gonadotropin releasing hormone
-lutenizing hormone
-follicle-stimulating hormone
Gonadotropin releasing hormone
-at around age 10-12, these hormones neurons in the hypothalamus receive a signal to start producing GnRH
What does GnRH induce
-the release of gonadotropins
Lutenizing hormone and follicle-stimulating hormone
-once GnRH is released, it travels towards the anterior pituitary and binds secretory cells, causing them to produce gonadotropins
Hormonal effects of HPG axis
-LH and FSH are released by pituitary gland in bloodstream and go on to produce different effects in each sex
HPG axis in males function
-mainly involved in the regulation of testosterone production and process of spermatogenesis
HPG axis in females function
-mainly involved in regulation of menstrual cycle
Regulation of HPG axis
-GnRH is released in a pulsatile manner
-frequency and size of pulses determine the synthesis and secretion of gonadotropins
GnRH pulses in males
-relatively constant frequency throughout the day
GnRH pulses in females
-frequency of pulses depends on stage of menstrual cycle
Inhibin
-protein secreted by granulosa (female) and sertoli (male) cells in response to FSH accumulation
Major action of inhibin
-negative feedback control of pituitary FSH secretion
Hormones of the follicular phase
-FSH
-LH
-estrogen
FSH phase
-FSH levels continue to rise from the last few days of the previous menstrual cycle and peak during the first week of follicular phase
-stimulates 5-7 primary oocytes to begin maturation
LH phase
-before LH levels rise, 1-2 follicles emerge as dominant
-Lh binds to receptors on theca cells to induce production of estrogen precursors which emerge to granulosa cells
-granulosa cells begin to produce estrogen
Estrogen phase
-estrogen secretion of dominant follicle leads to slight decrease in LH and FSH levels causing death of other follicles
-therefore only one follicle will prevail and reach maturity
Hormones of the ovulatory phase
-estrogen
-LH
Estrogen in the ovulatory phase
-continues to rise as follicle matures and exerts a positive feedback action to cause a surge of LH production
Lh in the ovulatory phase
-makes the mature follicle finally rupture
Luteal phase
-FSH and LH now cause the empty follicle to transform into corpus luteum
What does progesterone effect
-the uterine lining and makes it receptive to implantation
What does the corpus luteum become when it degenerates
-corpus albicans
The uterine cycle phases
-menses
-proliferative phase
-secretory phase
Menses of uterine cycle
-stage where cycle restarts
-the uterine lining is shed due to release of prostaglandins
Proliferative phase of uterine cycle
-endometrium consists of only a few layers of cells and is less than 1 mm thick
-estrogen secretion increases due to newly developing follicle which causes the repair and growth of the endometrium to 3-5 mm
Secretory phase of uterine cycle
-this is when the uterine endometrium is receptive to implantation and coincides with the luteal phase
-progesterone increases the blood supply to the uterine lining and reduces the contractility of smooth muscle in the uterus lining
Hormones in the male cycle
-LH
-FSH
LH in the male cycle
-enters the testes and stimulates the interstitial leydig cells to make and release testosterone into the testes and the blood
FSH in the male cycle
-enters testes and stimulates sertoli cells to produce androgen binding protein (ABP) and inhibin
Androgen binding protein (ABP)
-protein that specifically binds testosterone to help concentrate it in the luminal fluid of the seminiferous tubules
How is the male hormonal cycle regulated
-via the negative feedback system
-rising levels of testosterone and inhibin act on the hypothalamus and pituitary
HPG axis disorders
-disruptions in normal sex hormones and metabolism
Types of hormonal imbalances in males
-hypogonadism
-gynecomastia
Hypogonadism
-decreases production of gonadal hormones
-impaired function of gonads and sexual growth
-the body does not produce enough testosterone
Gynecomastia
-excessive development of the male breasts that can be caused by a variety of endocrine disorders
Types of hormonal imbalances in females
-hyperandrogenism
-polycystic ovarian syndrome
Hyperandrogenism
-excessive secretion of androgens by adrenal cortex, ovaries, or testis
Polycystic ovarian syndrome (PCOS)
-results in infrequent or prolonged menstrual periods and development of small collections of fluid in the ovaries leading to failure of egg release
