Reproductive Flashcards
What is the role of the human male ?
The male human has two major roles with respect to the physiology of reproduction
- manufacturing of sperm (spermatogenesis)
- depositing of Sperm(ejaculation)
Summarize the effects 9f gonadotropin releasing hormone(GRH)?
GRH- a hypothalamic hormone stimulates pituitary hormone lutenizing hormone or FSH
LH targets gonads for androgen production
FSH- targets gonads for follicle maturation, spermatogenesis)
What does dopamine do as a Anterior pituitary hormone?
Dopamine( release inhibitor)
Pitutary target cell hormone: lactotrope
Pituitary hormone: prolactin
Target organ (effects): mammary glands (milk production and letdown)
When is the gonadotrophic axis active?
Before birth and becomes quiescent after parturition, it remains so until puberty
What are the functions of GnRH?
Pulsatile allows for normal reproductive activity. Continued release desensitizes gonadotrope receptors—> decrease FSH & LH
What is the function of FSH?
Develops follicles in the ovaries and regulates spermatogenesis in the testis
What is the function of LH?
Causes ovulation and litenization of ovulated follicle in the ovary of the female and stimulates production of estrogen and progesterone by the ovary. In the male LH stimulates the cells of the testis to produce and secrete testosterone
Where are leydig cells located?
In the testis vascular interstitium produce testosterone
When are leydig cells first active?
In the fetus when testosterone is needed for development of male characteristics, then become inactive until puberty with resumption of lutenizing hormone
What is the effect of DHT and testosterone in the fetus?
Develops male sexual organs
Testosterone -differentiation internal male genital tract (epidydimys, vas deferens, seminal vesicles);
DHT- (testosterone activated to dihydrotestpsterone (DHT) by 5a-reductase in some tissues)- differentiation external male genitalia (penis, scrotum and prostate gland)
-promotes descent of Testes
In most target tissues testosterone is converted to the biologically active derivatives I) DHT by 5 a-reductase and II) estradiol by aromatase
DHT high binding affinity for androgen receptors and is - 2-3 times more potent than testosterone
Describe testosterone
Secreted from leydig cells, it exerts negative feedback on both the hypothalamus to decrease GnRH and the anterior pituitary to decrease both LH and FSH. There is even some evidence to suggest that there may be additional feedback to higher brain centers that can affect axis control
Testosterone also stimulates Sertoli cells to release inhibin
Describe inhibin
Inhibin B provides negative feedback to the anterior pituitary in males, where it decreases secretion of FSH. Sertoli cells also produce activin and follistatin that regulate the secretion of FSH
What is the effect of testosterone on bone?
Increased growth of bone and connective tissue
What is the effect of testosterone on muscle ?
Increased growth of muscle and connective tissue
What is the effect of testosterone on reproductive organs?
Increased growth and development by Testes, prostate, seminal vesicles, and penis
Increased growth of facial, axillary, and pubic hair
Increased growth of larynx
Increased spermatogenesis
What is the effect of testosterone on skin ?
Increased sebaceous gland size and secretions
Summarize the process of spermatogenesis
- mtitotic divisions of spermatogonia (stem cells) which generate the spermatocytes —> ultimately become mature sperm
- two meiotic divisions of spermatocytes - which decrease the chromosome number—> haploid spermatids(N=23). Each primary spermatocyte yields 4 sperm
- Spermiogenesis in which spermatids differentiate into spermatozoa, they lose cytoplasm and develop flagella and are transformed to mature sperm
What is the function of seminiferous tubules?
Produce sperm in avascular tubules of the Testes
As spermatogonia move from the outer edge to the lumen of the tubule as they are converted into spermatozoa
The process takes approximately 64 days
What are the types of cells in seminiferous tubules?
Two types of cells: spermatogonia, Sertoli cells
Sertoli cells between columns of spermatocytes (extend from basal lamina to lumen)
Adjacent Sertoli cells linked by ‘tight junctions’ (blood testis barrier)
Explain Sertoli cells
Sertoli cells are connected by tight junctions, which divide the intracellular space into a basal compartment and an adluminal compartment
- Spermatogonia are in the basal compartment and maturing sperm in the adluminal compartment
- Spermatocytes are formed from the spermatogonia and cross the tight junctions into the adluminal compartment, they mature into spermatozoa
- Sertoli cells- nourishment for the sperm, fluid to transport sperm, forms tight junctions with each other creating blood-testis barrier, synthesize and secrete androgen binding proteins and inhibin B
What are the actions of LH on leydig cells?
Stimulates leydig cells to secrete testosterone by stimulating the enzyme cholesterol desolate (first step in steroid organic pathway)
What are the actions of FSH on Sertoli cells ?
FSH binds to receptors on the Sertoli cells and stimulates spermatogenesis and Sertoli functions
FSH causes the Sertoli cells to secrete inhibin which has a negative feedback on the anterior pituitary for FSH
Summarize testosterone and DHT for adulthood
Throughout adulthood
Testosterone- maintains reproductive organs and spermatogenesis
DHT- male pattern baldness, male hair pattern
What is hypogonadism?
Decreased testosterone release from testicles(primary) or as a result of altered release of hormone from the hypothalamus/pituitary (secondary). Can occur at any age
Increased exogenous testosterone: Abdrogen (anabolic steroids) abuse leads to decreased LH and increased aggression
Describe the epididymis
Epidydmis is a single, tightly coiled, 4-5 meters long duct
Spermatozoa formed in the seminiferous tubules are transported to the epidydimis
Epidydmis is responsible for maturation (especially in the head), storage (in the tail), protection and transport of sperm cells
Sperm become capable of forward mobility when moving through the body of the epidydmis
What are the male accessory organs?
Seminal vesicle, prostate glands and Bulborethral gland
-the accessory organs provide over 90% of volume of semen
What is the flow of ejaculation through the vas deferens?
On the initiation of ejaculation the sperm are moved through the Ductus ‘vas’ deferens to the urethra
- Vas deferens forms a dilated tube, the ampulla, which joins the duct of the seminal vesicle to form the ejaculatory duct prior to entering the prostate
- Ampulla also a storage site for the sperm
What are the functions of seminal vesicles ?
Forms most of semen approx. 60%
-Supply fructose, citrate and some ascorbic acid
- Secrete prostaglandins
- Prostaglandins react with cervical mucous to make it more penetrance by sperm
- Prostaglandins induce contractions in uterus and Fallopian tubes to propel sperm up the tract
- Provides semen clotting precursors. Fibrinogen in seminal fluid forms a weak fibrin coagulum that holds the semen in the deeper areas of the vagina
What are the functions of prostate gland?
Contributes aprox. 30% semen volume
- Surrounds what is called prostatic urethra
- Alkaline, milky fluid (increases sperm motility, neutralizes acid secretion from vas deferens and vagina)
- Includes fibrinolysin- liquefication of the coagulated semen
What is the function of bulborethral gland?
Thick, clear, salty mucus that lubricates the end of the urethra and the vagina and helps to clean urine residues from the penile urethra
- Released after the male becomes sexually aroused and shortly before the release of the semen
- It is possible fir bulbourethral fluid to pick up sperm already present in the urethra, and therefore it may be able to cause pregnancy
What is the role of the female reproductive system?
- Production of the egg
- Ovulation
- Implantation of the egg
- Pregnancy
- Birth
- Lactation
What is oogenesis ?
By middle fetal lofe( 20-24 weeks gestation), all mitotic divusions of the primordial germ cells completed.
- the number of oogonia(immature germ cells) peaks at 6-7 million - Primary oocyte: the oogonia that are surrounded by a single layer of follicular cells and begin their first meiotic division
Meiotic processes continues until ~ fifth month of fetal development at which point most oogonia —> become primary oocytes
-Primary oocytes remain in a state of suspended Prophase 1 until ovulation i.e. the first meiotic division not completed until ovulation
What is a primordial follicle?
The primary oocyte and its single sheath of follicular cells
How many oocytes are there?
At birth only 1-2 million oocytes. At puberty only 2-400,000 oocytes
After puberty one primary oocyte reaches development/month
-As that primary oocyte is being released, it finishes its first meiotic division, becomes a secondary oocyte, and is arrested in the metaphase stage of the second meiotic division
What hormonal changes occur for women in puberty ?
- GnRH activity increases
- Eventually leads to ovarian activity
- Increased estrogen levels stimulate reproductive organ development
Summarize the menstrual cycle
The menstrual cycle is comprised of the ovarian and uterine cycle. Both cycles have 3 phases
The ovarian cycle: has follicular, ovulation and luteal phase. Note follicular and luteal phases can be further split into early mid and late portions
The uterine cycle has menses, proliferative phases and secretory phases. These phases are driven by changes in levels of GnRH, FSH, LH, Estrogen, progesterone and inhibin
What is the function of hypothalamic pituitary- gonadal regulation in the female reproductive system ?
Gonadotropin-releasing hormone (+) fir LH & FSH
I) estrogens circulating in blood inhibits the release of LH & FSH from the anterior pituitary. Estrogens have a negative feedback initially.
II) Granulosa cells release inhibin and inhibits FSH secretion from anterior pituitary
III) Activin stimulates the secretion of FSH
IV) At mid cycle estrogens rise above a certain level and have a +ve feedback resulting in secretion of FSH and LH. Significant in the preovulatory surge
What are the 3 phases of the ovarian cycle?
The phases- follicular, ovulation and luteal
- Follicular phase- period of follicular growth. Dominant steroid hormone is estrogen. Typical ovarian cycle lasts ~28 days
- Primary follicle —> begins at puberty, gonadotropin dependent, secondary follicle—> Graafian follicle —> dominant follicle ruptures and releases oocyte
- Secondary follicle - several layers of granulosa cells; stromal cells near the basement membrane differentiate into theca interna and externa(with blood vessels)
- Granulosa cells acquire FSH receptors (also androgen and estrogen receptors ) produce small amounts estrogen; theca interna cells acquire LH receptors and become steroidogenic
-FSH and estrogens stimulate mitosis of the granulosa cells
What is the LH during menses?
LH are too low to support the corpus luteum
-Corpus luteum produces progesterone
Articulate the early follicular phase
-FSH primarily stimulates growth of ovarian follicles, secretion of estrogen
I. Estrogens cause granulosa cells to form increasing numbers of FSH receptors
II. The increasing estrogens plus the increasing LH act together to increase follicular thecal cells and their secretion III. Circulating levels of estrogen begin to rise
Estrogens have a negative feedback initially
What happens in the late follicular phase?
The FSH and estrogens combine to promote LH receptors on original granulosa cells
II) estradiol levels increase dramatically
The follicular theca cells, under control of LH, produce androgens that diffuse to the follicular granulosa cells, where they are converted to estrogens via a follicle-stimulating hormone- supported aromatization reaction. The dashed arrow indicates that granulosa cells cannot convert progesterone to androstenedione because of the lack of the enzyme 17 a-hydroxylase
What are the chemical changes in the theca cells in late follicular phase?
LH binds and ATP stimulates cAMP causing cholesterol to converted to pregnenolone
Pregnolone converted to 17OH pregnonlone which is converted to dehydroeplandrosterone and then converted to androstenedione and then finally, testosterone
Both of the last two products are sent to the granulosa cell and receives. Estradiol from granulosa cells
What are the chemical changes in a granulosa cell in late follicular phase?
LH binds to granulosa cell and forms ATP to stimulate cAMP to convert cholesterol
Cholesterol converted to pregnenolone which is converted to progesterone converted to androstenedione which is converted to testosterone and estrone
Testosterone stimulated by cAMP to become estradiol
Androstenedione converted to estrione then estradiol and sent to theca cell
Estrione synthesis from Androstenedione and estradiol synthesis from testosterone use cAMP from FSH binding to granulosa cell and producing ATP
What is the hormone ratio of Polycistic ovary syndrome ?
LH: FSH ratio
What is the tertiary follicular stage of ovarian cycle?
Tertiary follicular stage. Fluid filled spaces (or antra) develop around the granulosa cells
- Antra increase in size and coalesce forming a Graafian follicle
- Antral follicles have a unique micro environment in which follicular fluid contains several hormones, growth factors etc.
- A single Graafian follicle achieves dominance, follicle ruptures, releases oocyte
- Typically 14-day period preceding ovulatio. Pre-ovulatory period most variable, last from 10 days to 3 weeks
- Follicle must be exposed to appropriate sequence for hormones I.e. FSH followed by estradiol and then LH fir appropriate maturational and functional development
