Lecture 35 - Male reproductive system II Flashcards
Flow of sperm
Production of sperm in the testes which are transported via the rete testis and efferent ductless into the head of the epididymis and then the tail of the epididymis which is continuous with the ductus deferns, passing through the inguinal canal posterior to the bladder where it widens to form an ampulla then there is a short ejaculatory duct which goes on to form the urethra which is separated into 3 parts called the prostatic, membranous and spongy/penile urethra
The scrotum contains
Two testes (singular is testis) - the two testes are separated by a fibrous septum Two epididymides (singular is epididymis) - each one is associated with the posterior border of the testes Two spermatic cords (with part of the ductus deferens) - run from the testis up through the inguinal canal which passes up to the abdominal cavity
The scrotum is the sack of skin that encloses the testes and it is quite thin skin which is lined with a superficial fascia
Inguinal canal
The inguinal canal is a short passage that extends inferiorly and medially through the inferior part of the abdominal wall. The canal serves as a pathway by which structures can pass from the abdominal wall to the external genitalia.
Why is the scrotum outside of the body?
The scrotum hoses the testes away from the body to maintain temperature at 34 degrees
Optimum temperature for spermatogenesis is 34 degrees which is several degrees lower than the normal body temperature
By housing the testes outside within the scrotum, it gives the body a mechanism by which it can control differences in temperature
3 mechanism for heat transfer - the scrotum
Scrotum is lined by the dartos muscle - lines the skin of the scrotum and what happens when this muscle contracts is that it wrinkles the skin which changes the surface area available for heat exchange so when it is all wrinkled up, less heat exchange occurs, helps to maintain and keep temperature (the opposite can occur too)
Cremaster muscle that contracts for heat conservation - Muscle that encloses the testis and spermatic cord, when this muscle contracts it draws the testis up closer to the body which allows the warming up of the testis if this is required. Contracts for heat conservation and it also contraction during arousal which brings the testes closer to the body which offers protection during sexual intercourse
Venous plexus or pampiniform plexus - veins form a net structure around the artery known as a venous plexus which provides an increased surface area to allow heat transfer between the warmer blood coming down from the body in the artery and the cooler blood being returned from the testes back up towards the body
Dartos muscle
Scrotum is lined by the dartos muscle - lines the skin of the scrotum and what happens when this muscle contracts is that it wrinkles the skin which changes the surface area available for heat exchange so when it is all wrinkled up, less heat exchange occurs, helps to maintain and keep temperature (the opposite can occur too)
Cremaster muscle
Cremaster muscle that contracts for heat conservation - Muscle that encloses the testis and spermatic cord, when this muscle contracts it draws the testis up closer to the body which allows the warming up of the testis if this is required. Contracts for heat conservation and it also contraction during arousal which brings the testes closer to the body which offers protection during sexual intercourse
Venous plexus
Venous plexus or pampiniform plexus - veins form a net structure around the artery known as a venous plexus which provides an increased surface area to allow heat transfer between the warmer blood coming down from the body in the artery and the cooler blood being returned from the testes back up towards the body
The spermatic cord
Two spermatic cords
Within the scrotum
Runs between the abdomen and testes (run between the superior part of the testes and up into the inguinal canal)
Contains the ductus deferns, blood vessels - testicular arteries and veins, nerves and lymphatics
The penis
Dual function of urination and copulation (sexual intercourse)
Cylindrical organ
Root (bulb) (this is the part that adheres to the body wall)
Body (mobile part)
Glans covered by prepuce/foreskin (removed if a male is circumcised)
Three cylindrical erectile tissues in the penis
Two corpora cavernosa (singlar = corpus cavernosum)
This is the main erectile tissue and it is located on the Doral aspect
One corpus spongiosum
Contains the urethra, forms the bulb and the glans (starts at the root, goes through the body and also widens and expands to form the glans penis)
Ventral aspect of the penis
Corpora cavernosa (corpus cavernosum)
Two corpora cavernosa (singlar = corpus cavernosum)
This is the main erectile tissue and it is located on the Dorsal aspect
Corpus spongiosum
One corpus spongiosum
Contains the urethra, forms the bulb and the glans (starts at the root, goes through the body and also widens and expands to form the glans penis)
Ventral aspect of the penis
Dorsal aspect of the penis
When erect, the dorsal side lies on the body
Dorsal vasculature - arteries, veins and nerves coming into the penis
Ventral aspect of the penis
When erect, the ventral side lies outwards. The ventral side lies on the scrotum
Optimum temperature for the scrotum
34 degrees
What vessels supply the testes?
Testicular artery
Venous plexus
Lymphatic vessels
And nerves supply the testes
Three accessory glands
Seminal vesicles
Prostate gland
Bulbourethral glands
Seminal fluid
Spermatozoa are carried to the female reproductive tract in the seminal fluid (together called semen)
Seminal fluid has some very important functions in terms of when it is ejaculated into the female reproductive tract, things the seminal fluid is responsible for is providing a transport medium for the sperm, provide a nutrient and energy source for the sperm, provide protection (specifically to the acidity of the male urethra but also within the vagina of the female) and they also help to activate the spermatozoa which gets the flagella to start beating so that the sperm can become motile
Seminal vesicles
Two glands that are located posterior to the bladder, and lateral to the ampulla of the ductus deferens
Produce viscous secretion which makes up 60% of semen, alkaline pH which protects the sperm against the acidic environment in the urethra and vagina
Prostate gland
Located inferior to the bladder, wraps around the prostatic urethra
Procduces secretion - 30% of semen, it is slightly acidic and milky fluid, contains PSA which is prostate specific antigen, contributes to sperm activation, viability and motility
Bulbourethral glands
Two glands located in the urogenital diaphragm
Open into the spongy/penile urethra
Contributes 5% of semen volume - released first, about lubricating the urethra and neutralises/removing residual urine and therefore any residual acidity that was left
Secretions lubricate and neutralise the acidity in the urethra prior to ejaculation
Components of semen
60% from the seminal vesicles
30% from the prostate
5% from the bulbourethral glands
Last 5% is made up of sperm which is what is being transported from the testes to the epididymis
Vasectomy
Surgical method of sterilisation in males
Cut the ductus deferens - ends are tied or cauterised
If you have a vasectomy you are not going to get the transport of sperm up from the testes up into the ampulla so that 5% that makes up the semen is no longer to be there so it is a minor reduction
Gametogenesis
Formation of the gametes (sex cells)
Spermatogenesis in males, oogenesis in females
Under hormonal control
Occurs via mitosis (somatic cell division) and meiosis (cell division that produces daughter cells that are haploid) - cells need to be haploid i.e. contain 23 chromosomes
Brief overview of meiosis
Same basic process for males and females
Original cell has 46 chromosomes (diploid = 2n)
Two cycles of cell division to produce gametes (23 chromosomes which is haploid = n)
Meiosis 1 - 2 haploid cells produced from 1 original diploid cell
Meiosis 2 - Each cell produced from meiosis 1 dives to produce two haploid cells with 23 chromosome cells
Meiosis 1
Meiosis 1 - 2 haploid cells produced from 1 original diploid cell
Meiosis 2
Meiosis 2 - Each cell produced from meiosis 1 dives to produce two haploid cells with 23 chromosome cells
Spermatogenesis
Formation of the male gamete
The process by which spermatogonia are transformed to mature spermatozoa (sperm)
Occurs continuously from puberty onwards
Occurs in the seminiferous tubules
Spermatogenesis process
Works from the basement membrane and then works outwards to form spermatozoa in the lumen
Part 1 Spermatogonia divide by mitosis into 2 daughter cells (diploid = 46 chromosomes) One spermatogonium (type A) stays at the basement membrane of the seminiferous tubule - in order to allow the process to keep on repeating and to initiate the next round of mitosis
Part 2
The second spermatogonia (type B) differentiates into a primary spermatocyte (diploid) which undergoes meiosis I
Forms 2 secondary spermatocytes (haploid therefore 23 chromosomes)
Part 3
These undergo meiosis II to form spermatids (haploid)
Spermatids differentiate into spermatozoa with a head, body and tail via spermiogenesis
Spermatozoa are released into the lumen
Mature sperm features
Head, neck, mid piece and tail
The head encloses a very condensed nucleus
Acrosome is a sac of enzymes that lies over the nucleus within the head of the spermatozoa - these enzymes are important in penetrating the oocyte during fertilisation
Get rid of excess cytoplasm in order to become streamline
When the spermatozoa are ejaculated up into the female vagina they have to be able to make their way into the uterine tube which requires energy and therefore need mitochondria which are found concentrated in the mid piece of the spermatozoa
Name the reproductive hormones
GnRH = gonadotropin releasing hormone produced by the hypothalamus (note - gonadotropin = hormone that acts on the gonads) LH = Lutenizing hormone (a gonadotropin) produced by the anterior pituitary FSH = Follicle stimulating hormone (a gonadotropin) produced by the anterior pituitary
Gonadotropin
gonadotropin = hormone that acts on the gonads
GnRH
GnRH = gonadotropin releasing hormone produced by the hypothalamus
LH
LH = Lutenizing hormone (a gonadotropin) produced by the anterior pituitary
FSH
FSH = Follicle stimulating hormone (a gonadotropin) produced by the anterior pituitary
Hormones in males
Inhibin
Testosterone
Inhibin
Important role is negative feedback regulating spermatogenesis
From the nurse (Sertoli) cells
Testosterone
Produced by interstitial endocrine (Leydig) cells
Type of androgen - a group of steroid hormones, group of hormones that have effects on stimulating male reproductive mechanisms, responsible for male characteristics (such as maturation of sex organs, spermatogenesis, secondary sec characteristics that include hair growth and deepening of the voice, libido (sex drive)), synthetic androgens (steroids) have therapeutic purposes and they are also abused for sporting purposes
Negative feedback loop with FSH and LH and testosterone
LH stimulates production of testosterone (intersitial endocrine (Leydig) cells)
FSH and testosterone control spermatogenesis
FSH stimulates inhibin production (nurse (sertoli) cells) - Inhibin is released into the circulation and provides negative feedback back up to the anterior pituitary regulating the production of specifically FSH
Negative feedback:
Inhibin suppresses FSH
Testosterone surpasses LH and GnRH
General process ….
- Hypothalamus produces GnRH
- Release of GnRH stimulates the release of LH and FSH from the anterior pituitary gland
- LH acts on the interstitial endocrine cells and stimulates the production of testosterone and testosterone acts locally within the semifernous tubules and other ducts within the male reproductive system but it also is released into the circulation where it can have its effects all around the body and one of these effects is to take messages back up to the hypothalamus and anterior pituitary as negative feedback so lots of restoring going back up which reduces the amount of testosterone which decreases the of production of LH and FSH
______ spermatozoa are produced from _____ primary spermatocyte
Four
One
Spermatogenesis
Maturation of spermatid into spermatozoa (head, midpiece, tail)
Sperm formation - names flow chart
Spermatozoa to spermatozoon (plural of this is spermatozoa) (round spermatic cells to structurally mature spermatozoon)
