Reproduction Lectures 2021 - MALE REPRODUCTIVE SYSTEM Flashcards
Reproductive organs/gonads in males
Testes
- paired organ that contains gametes
Reproductive organs/gonads in females
ovaries
- paired organ that contains gametes
Gametogenesis
process by which sperm or ova are produced
Gametes have an endocrine role:
– Androgens in males
– Estrogens and progesterones in females
Reproductive tracts
house and transport gametes
What are the reproductive tracts in females?
fallopian tubes
What are the reproductive tracts in males?
vas deferens (for the most part)
Accessory sex glands in males
– Seminal vesicles
– Prostate
– Bulbourethral (Cowper’s) glands
What is the seminal vesicles a major site of?
gamate production in males
What are the Prostate & Bulbourethral (Cowper’s) glands largely responsible for?
producing fluids that aid in the survival of those gametes, but also assist in the sexual act or transmission or capacitation of sperm
Capacitation
process where sperm are not fully viable until they hit the female reproductive tract
Accessary sex glands in females
– Bartholin’s glands
– Clitoris
– Breasts
Bartholin’s glands, Clitoris & the Breasts are sex glands but also…
related to reproduction in general & associated with the Bartholin’s glands in assisting with the sexual act
Prostate gland
produce fluids that either support survival of sperm or capacitation of that sperm just prior to ejaculation; entry into the female reproductive tract
Vas deferens
- tubule structure
- comes into close association with the seminal vesicles & the prostate gland
What is the 2nd most common cancer next to lung cancer in males?
Prostate cancer
Corpora cavernosa
spongy, leaky tissue that aids in the flow of blood into the penis & essentially an erection is caused by an imbalance in blood flowing in vs. blood flowing out
Prostaglandins
a hormone found throughout the body, were 1st identified in the prostate gland
- but it turns out the seminal vesicles actually produce as much if not more prostaglandins into the sperm & the fluid surrounding the sperm & so those prostaglandins aid in the reproductive act & can promote both constriction within an ejaculation (sperm into the female reproductive tract) but also contractile forces within the female reproductive tract, promoting the advance sperm further in the female reproductive tract
Describe testes development
- testes develop from the GONADAL RIDGE during development
- descend through the INGUINAL CANAL usually complete before 7 months of gestation (within the mother’s womb)
Cryptorchidism
occurs in 1-3% of newborn males
- where the testis have failed to descend properly through inguinal canal & are essentially trapped within the body
- this has huge implications for fertility in those males (tend to be infertile)
Why do the testes lie external to the body?
- testis are ~3% lower than body core temp
- so they lie in a cooler area
- those cooler temps promote development & increase mitochondria in particular
- with increase mitochondria, that provides more energy for individual sperm & therefore better transfer for fertilization
- therefore 1 reason is b/c of the reduced temp & increased viability of the sperm at that reduced temp
What is the route in order to form an ejaculation?
Epididymis tubule –> through canal –> into vas deferens –> seminal vesicles, prostate glands –> penis for ejaculation
Head of epididymis
gathers all the seminiferous tubules within the testicle itself
Epididymis
- lots of storage
- sperm not yet fertile (infertile) at this stage (has to be capacitated)
- # of events are req. to promote fertility of that sperm
In terms of testicular mass:
the seminiferous tubules comprise of ~80% of testicular mass within each testicle
What are Leydig cells extremely imp. in?
extremely imp. in communicating gamete dev. within males & communicate with sertoli cells
Sertoli cells location
- INSIDE seminiferous tubule
- surrounded by layers of connective tissue & smooth muscle
Leydig cells location
- OUTSIDE seminiferous tubule
- produce testosterone
- communicate with the sertoli cells within the internal area of the seminiferous tubule & the dev. spermatids
Sertoli & Leydig cells…
support those dev. gametes (critical in terms of gamete dev.)
Blood Testis Barrier
- this barrier, the basal lamina that separates the internal environment of the seminiferous tubule with the external environment of the body is critical & essentially acts v. similar to a blood brain barrier as the blood testis barrier that stops the immune system from attacking what would be otherwise unknown cells (the gametes that develop within the seminiferous tubule)
- therefore, critical in gamete dev.
- blood testis barrier is by the basal lamina
Myoid cells
are found within the basal lamina
- these specific cell types are really critical for communicating b/t the leydig cells & the sertoli cells within the seminiferous tubule
- also help in movement of fluids from the external environment to the internal environment across that basal lamina
*specific cell type around the basal lamina that aid in the communication b/t sertoli & leydig cells & also production of fluids
What does the tight junction b/t sertoli cells do?
essentially separates the development of these spermatids b/t each other on either side
You get columns of spermatogonia at varying stages of dev. as you move from the…
& what will support & aid all of these?
outside (periphery of the seminiferous tubule) to the internal region of the seminiferous tubule
sertoli cells will support & aid all of these
The fluid within the seminiferous tubule, in which the mature spermatids are bathing (a water based fluid) is…
High K+ ions & high in steroids (partic. testosterone)
Why is the fluid within the seminiferous tubule high in K+ ions?
- related to motility of sperm
- with a higher K+ concen. the sperm tend to be less mobile or motile
- as a conseq. are not needlessly burning energy that would be req. once released into the female reproductive tract
- so they have a lower metabolic rate in the presence of high ECF K+ concens.
Testosterone is…
lipid soluble (won't dissolve easily within this water based fluid in the lumin of the seminiferous tubule) - so as a conseq. of that there are ABP, that is also released into the lumen of the seminiferous tubule
What is ABP & describe the importance of it
- imp. to facilitate the concen. of testosterone in the seminiferous tubule fluid
- b/c it is a water fluid environment & testosterone is a steroid so it’s lipophilic
- binds to the testosterone in the seminiferous tubules so that more testosterone can come in from the outside/is available
- total concen. of testosterone within the fluid of the seminiferous tubule is higher b/c you have a large proportion bound to the BP & a small proportion that is free
Basal lamina
barrier to prevent the immune system from attacking these unknown cells
What is within the lumen of the seminiferous tubule?
tails of spermatids within the lumen of the seminiferous tubule & diff. cell types that might support dev. of those sperm cells at diff stages
In theory, males can keep producing testosterone & sperm all their lives, but as males age things do slow down & usually through blood vessel degradation can result in:
Androgen Deficiency in Aging Males (ADAM)
Androgen Deficiency in Aging Males (ADAM)
a degradation in the blood vessels supplying the testis & as a result, an imperfect balance b/t leydig & sertoli cell communication as a conseq. of an imperfect release of antigens that can lead to a reduction in fertility in those males
Leydig cells
lie within the interstitium b/t seminiferous tubules
1 of the things Leydig cells are responsible for is:
the production of testosterone primarily
Testosterone acts to:
– Influence the reproductive system prior to birth
– Influence sex-specific tissues after birth (requires LH
stimulus)
* has a link to HPG axis
– Additional reproductive effects
* libido
– Development of secondary sexual characteristics
– Non-reproductive actions
- bone growth - males don’t produce a lot of estrogen but there is aromatase expressed within the blood tissue that converts those androgens (testosterone in partic.) to estrogens to facilitate & regulate bone growth)
- aggression - increased testosterone is known to induce a more aggressive phenotype in males
At puberty there is a surge in…
testosterone that regulates the growth of the reproductive system & the secondary sexual characteristics in males
Testosterone helps dev. of…
libido (sexual drive), but isn’t essential for maintenance of that libido
Before ppl thought that a vasectomy in males can…
reduce their sexual drive & that is not true
- actually males who had one report a greater sexual drive
What are the prepubertal biological effects of testicular androgens
Accessory sex glands - Wolffian duct differentiation and growth
External genitalia - Growth and differentiation (scrotum and penis)
What are the pubertal biological effects of testicular androgens?
Skeleton & muscle - Masculine physique, epiphyseal closure
Vocal cords - Voice deepening
Skin - Facial hair growth and/or cranial hair loss
Testis - Sertoli cell maturation and androgen binding protein synthesis
External genitalia - Penile and scortal growth
Accessory sex glands - Prostate, seminal vescile and bulbourethral growth
CNS - libido
hypothalamus/pituitary - Inhibition of LH secretion (-ve feedback)
What is the Wolffian duct differentiation imp. for?
sex determination
Spermatogonia
Undifferentiated germ cells containing a diploid complement of 23 pairs of chromosomes (1 paternal and 1 maternal)
- post puberty
Spermatozoa
fully differentiated sperm cells containing a random haploid set of 23 chromosomes
Three key steps of Spermatogonia
– Mitotic proliferation
– Meiosis
– packaging
How long does the whole process of spermatogonia take in males?
~64 days
- constant, ongoing within the seminiferous tubules
- have huge amount of viable sperm throughout their lifetime
How many MATURE sperm do males have avail. on a daily basis?
~2 million
- massive production & energy req. within males (not near energy req. in females in terms of their role in reproduction)
How many MATURE spermatozoa do each daughter cell produce?
~16
- but that’s not always the case (upwards of 40-60% of these cells might die in the process of gamete dev.)
- this is another job of SERTOLI CELLS, that they will scavenge that material & clean it up & get rid of the cells that have divided & gone wrong
Spermatid development
• Meiotic division and the development of the secondary spermatocyte CROSSING OVER occurs between paired chromosomes
- get the unique genetic code to each of those final spermatozoa
- The cytoplasm of spermatids is always JOINED until complete differentiation and sperm development has occurred
- Half the spermatids have an X and half have a Y chromosome
Why is “the cytoplasm of spermatids is always joined until complete differentiation and sperm development has occurred”?
there are key genes on the X chromosome that are absolutely critical for development & final dev. (maturation) & that’s why they remained joined right up until that last little bit
The Y chromosome DOESN’T…
doesn’t express as many of the genes that are critical for dev.
- hence why they’re joined just prior to that separation
The Y chromosome DOES…
does express the SRY gene, & that SRY gene is critical for sexual dev.
List the 4 main parts to sperm:
- Head
- Acrosome
- Mid Piece
- Tail
Head in sperm
contains nucleus with DNA
Acrosome in sperm
contains enzymes req. for breaking through the corona radiata in the egg & ultimately fertilizing the egg
Mid Piece in sperm
mitochondria rich
- maybe at a lower temp like 3 degrees lower than core body temp
- promotes generation of those mitochondria that will promote capacity for that sperm to swim
Tail in sperm
swimming
- flagellum - beating of the tail can promote potential fertilization
List the 6 functions of Sertoli cells:
- Protect sperm cells
- Feed sperm cells
- Remove unwanted cells
- Secrete seminiferous tubule fluid
- ABP secretion
- Endocrine feedback regulation - inhibin
Why is “feed sperm cells” an imp. function of sertoli cells?
imp. as those sperm are stored prior to release
Why is “remove unwanted material” an imp. function of sertoli cells?
a single daughter cell in theory can produce 16 mature spermatozoa, but that doesn’t happen & so those dead cells are reabsorbed & reprocessed by the sertoli cells (the sertoli cells will also secrete fluid into the seminiferous tubule to aid in supporting cell viability & life & it will also secrete ABP)
Why is “secrete seminiferous tubule fluid” an imp. function of sertoli cells?
creates a (+) pressure
- as fluid builds up within the seminiferous tubule
- the (+) pressure pushes sperm down the length of the seminiferous tubule into the epididymis (storage area just prior to the vas deferens)
- that fluid buildup is imp. for transporting sperm that are otherwise non-motile at this stage (higher concen. of K+ limiting motility of the sperm within the seminiferous tubule)
Why is “ABP secretion” an imp. function of sertoli cells?
BP req. for testosterone to bind & promote concen. of testosterone within the lumen of the seminiferous tubule
Why is “endocrine feedback regulation - inhibin” an imp. function of sertoli cells?
imp. hormone in syn. & release by the sertoli cells
- will selectively inhibit FSH over LH
- this is key in terms of the endocrinology of male gametogenesis & dev.
Male reproductive endocrine axis
Direct (-) feedback inhibition of LH, but an indirect (-) feedback inhibition of both FSH & LH through inhibiting GnRH
Testosterone is critical for…
sertoli function & viability of sperm
Testosterone has…
NO androgen receptors on male gametes & so testosterone is converted to estrogen & there are estrogen receptors on male gametes that promote dev. of the gamete
There is a higher amount of avail. testosterone within the…
fluid of the seminiferous tubule
Epididymis
- prior to arriving in the epididymis sperm are non-motile and infertile
- concentrates sperm through reabsorption of seminiferous fluid. Also protects sperm with defensin
Within the epididymis there is a…
Low pH
- due to CO2 production by infertile sperms
- so that lowers the pH of the fluid
If the sperm is NOT ejaculated & dies, then it is…
reabsorbed by phagocytotic mechanisms
Onset of Capacitation
sperm obtain the ability to fertilise the egg and become somewhat mobile in the epididymis (this is completed in the female reproductive tract)
- with the help of defensin & changes in chemistry of the surrounding fluid within the epididymis
Ductus deferens
storage site can be days in length (prior to those sperm dying & becoming infertile)
- semi-motile sperm are stored
Seminal vesicle
empties into the ejaculatory duct
- fructose, PG’s, ~50% of the seminal fluid, fibrinogen
Seminal fluid is produced by the…
seminal vesicle
Fibrinogen
aids in the retention of sperm within the female reproductive tract
- promote clotting of the sperm
- ejaculation of sperm into female repro. tract is associated also with clotting enzymes, so the fibrinogen aids in that clotting
Prostate
- alkaline fluid, clotting enzymes & fibrinolysin
Alkaline fluid promote…
viability of sperm
Fibrinolysin
aids in the BREAKDOWN of that fibrinogen & that clotting & the release of the sperm into the female repro. tract
As the sperm is deposited into the female repro. tract, initially as a more clotted group of cells, it (fibrogen?)…
promotes the retention of the viable sperm within the female repro. tract
- then the fibrinolysin quickly gets to work on the fibrinogen breaking that up & releasing the sperm within the female repro. tract
Bulbourethral gland
- mucus like substance
- aids in sexual act as a lubricant
List the 4 principle phases of the male sexual act in humans:
- Excitement
- Plateau phase
- Orgasmic phase
- Resolution phase
The principle phases of the sexual act b/t males & females is similar with 1 distinct diff. & that is the 3rd & 4th phase b/c…
females can repeatedly go through the orgasmic phase (phase 3), males cannot (so they then go to phase 4, the resolution phase)
- Excitement phase:
arousal & erection
Erection is largely due to…
an imbalance b/t blood flow & blood out flow
- inflow is more b/c the penis has to be engorged with blood
- get an inhib. of vasoconstricted neurons & sympathetic neuons that synpase with the penile arterioles (blood flows into the penis, it can’t flow out quite as well & so an erection enforms)
- parasympathic via nitrogenous (nitric?) oxide will dilate penile arterioles
- Plateau phase:
continued arousal includes increased heart rate, mean arterial blood pressure, respiration rate and muscle tension
- Orgasmic phase:
ejaculation and muscle contraction combined with intense physical pleasure
- females can repeatedly go through this phase, males cannot
- Resolution phase:
return to pre-arousal state
Erection
state of vasocongestions
- blood flow within the penis itself
Erection reflex
Stimulation of mechanoreceptors in the glans penis
- STIMULATES PARAsympathetic supply to BULBOURETHRAL & URETHRAL GLANDS
- -> mucus –> lubrication - STIMULATES PARAsympathetic supply to PENILE ARTERIOLES
- -> penile arterioles dilate –> erection –> compresses veins –> erection - INHIBITS SYMpathetic supply to PENILE ARTERIOLES
- -> penile arterioles dilate –> erection –> compresses veins –> erection
Ejaculation
- Emission: preparatory phase a few seconds prior to ejaculation
- Expulsion of seminal fluid and sperm from the penis
What is the average volume produced during an ejaculation?
• Average volume approximately 3ml but can range considerably
Average sperm concentration:
~ 66million.ml-1
Clinically infertile:
< 20million.ml-1
- shows what a huge req. is needed from males to produce a huge # of sperm & to ensure successful reproduction
Erectile Dysfunction
- NOT an infertile individual, but they’re not capable of the sexual act
- ~50% suffer from this (normally in older men in 40-70’s)
- viagra can sustain an erection (not able to cause it), but can combat that dysfunction
Sildenafil: What does it do?
• Nitric oxide is released in response to parasympathetic stimulation
• NO acts through an enzyme linked receptor pathway that uses cGMP as a second messenger
• cGMP initiates the PKG pathway which leads to the activation of SR Ca2+-ATPase (SERCA)
* • cGMP is broken down by the cellular enzyme phosphodiesterase 5
- Sidenafil INHIBITS the action of phosphodiesterase 5
- so it maintains cGMP, maintaining the activation of SR Ca2+-ATPase, so it maintains the erection in the individual (*but cannot initiate the erection)
