12.1 Male Reproductive System - Introduction Flashcards
List the functions of the male reproductive system
- Sperm production
- Storage and transfer of sperm into female
- Male sex hormone production
Primary vs Secondary Sex Organs
Primary: Gonads; produce gametes and hormones
Secondary: Sustain and transfer gametes
Describe the structure of the scrotum
- Thin layer of smooth muscle called dartos muscles beneath scrotal skin
- Two skeletal cremaster muscles that descends from the abdomen and covers each testis like a muscular net.
- A rich blood and nerve supply.
What are the functions of the scrotum?
- Support
- Protection
- Thermoregulation
Are the testes located externally in an embryo?
- No
- Develop with the abdomen, and migrate down into scrotum
What are some negative effects of core body temperature on testicular function?
- Arrested/abnormal spermatogenesis
- Abnormal metabolism
- Increased risk of testicular cancer
If a man’s testicular temperature is radically decreased or increased, what changes would we see in his testosterone levels?
- Probably none
- Temp doesn’t influence endocrine activity of testes; as long as nothing is burnt or frozen off, he’s fine in that regard
Other than being located out of the pelvic cavity, how else is testicular temperature maintained?
- Sweat glands in scrotal skin
- Cremaster muscles contract when cold and relax when warm (like in Red Dead)
Where is are the cremaster muscles located relative to the scrotal skin?
Under dermis
Where is the dartos muscle located relative to the scrotal skin?
Within dermis
What causes regular wrinkling of scrotal surface?
Resting tone of dartos muscle
Describe the contraction and relaxation of the dartos muscle
Cold: Contract -> more wrinkling, more surface area for heat loss
Hot: Relax -> less wrinkling, more surface area for heat loss
Describe countercurrent heat exchange in the testicular blood supply
Heat is removed from testicular arteries as blood descends to the veins. Like passing contraband.
Function of testes
Sperm cell and sex hormone production
Approximate length of testis
4-5cm
How many lobules per testis?
200-300 compartments
What are the two membranes within the scrotum
- Tunica vaginalis
- Tunica albuginea
What type of membrane is the tunica vaginalis? What is its function?
- Serous membrane
- Secretes protein-rich fluid that decreases friction
What type of membrane is the tunica albuginea? What is its function?
- Dense connective tissues capsule
- Separates each testis into 200-300 lobules, each of which contains seminiferous tubules
Where is the site of spermatogenesis?
Seminiferous tubules, which are in lobules, which are in a testis, which are in the scrotum
What two cell types are located in the seminiferous tubules?
- Spermatogenic cells
- Sertoli cells
Why is it important that there are blood vessels running between seminiferous tubules?
Because hormones are also produced in the testis, and they travel in the blood
Which cells are responsible for testosterone production
Leydig cells
What happens to testosterone once it it produced in the leydig cells between seminiferous tubules?
- Some goes into STs to stimulate sperm production
- Some goes into blood vessels and enters systemic circulation
Where do sertoli cells span from? How are they connected to one another?
- Span from basement membrane to lumen of Seminiferous tubule
- Connected by tight junctions
Why are the tight junctions between sertoli cells important?
- They stop some substances from diffusing through the cells
- Prevents immune cells from recognising the developing sperm cells as “foreign”, which would result in it launching an attack
Can substances diffuse directly to and from developing sperm cells?
- No
- They pass through the sertoli cells as intermediaries
What hormone do sertoli cells release to slow sperm production?
Inhibin
Functions of sertoli cells
- Control release and movement of sperm cells
- Nourish sperm cells
- Prevent self-immune reaction
- Secrete inhibin to slow sperm production
What is it called when testicles fail to descend from the abdomen?
Cryptorchidism
How long does spermatogenesis take?
65-75 days
Outline the process of spermatogenesis in three main steps
- Mitotic proliferation of spermatogonia
- Meiotic division (primary and secondary spermatocytes)
- Spermiogenesis (morphological change)
What is the name of the cells that result from secondary spermatocytes undergoing Meiosis II?
Spermatid
How many sperm does a man produce per day?
300 mil
How long is a sperm?
60 micrometers
What is the functional purpose of the elongated shape of sperm?
Adapted for reaching (flagellum) and penetrating (acrosome etc.) the egg
What are the four key events of spermiogenesis?
- Acrosome development
- Flagellum Development
- Nucleus Condensation
- Shedding of excess cytoplasm
Why is the nucleus of a spermatid condensed during spermiogenesis?
Protects DNA against damage -> protects against shearing forces during ejaculation
Why do sperm shed cytoplasm during spermiogenesis? What isn’t shed?
- Streamlined; better motility
- Mitochondria remain for motility
Are spermatogonia stem cells?
Indeed they are
Can sperm fertilize an oocyte directly from the testes?
No; it needs to undergo maturation to gain motility
What is the purpose of ducts in the male reproductive system?
- Functional maturation
- Nourishment
- Storage
- Transport
What is the name of the tubule network that collects sperm from the seminiferous tubules?
Rete testis
Where does sperm travel after making its way through the rete testis? What about after that?
- From the rete testis, it moves to the efferent ducts
- From here, it enters the epididymus
What is another name for the vas deferens?
Ductus deferens
How long is the epididymus?
7 fucking metres
What are the functions of the epididymus?
- Monitors and adjusts fluid composition
- Recycling centre for damaged sperm (resorb and break down)
- Stores and protects sperm
- Concentrates sperm
- Functional sperm maturation
What part of sperm maturation occurs in the female reproductive tract?
Capacitation
Proteins are secreted by the epididymus that bind to sperm and…
- Stabilise sperm (withstand shearing forces)
- Trigger flagellum to develop motility
What class of hormones is sperm maturation dependent on? Why?
- Androgens
- Andorgens bind to epididymal cells which trigger protein release in sperm maturation
How long is the vas deferens?
40-45cm
What is the bulbous end of the ductus deferens called?
Ampulla of ductus deferens (like Roman Ampulla)
How is sperm propelled along the ductus deferens?
The force comes from contraction of a thick layer of smooth muscle in the ductus deferens itself
How long is the ejaculatory duct?
2cm
Where is the ejaculatory duct located? What happens there?
Connects the ampulla of the ductus deferens and the seminal vesicle, and joins them to urethra.
What are the three parts of the urethra, and where do they sit?
- Prostatic (in prostate)
- Membranous (in pelvic floor)
- Spongy (in penis)
What are the three accessory glands in the male reproductive system
- Seminal vesicles (x2)
- Prostate
- Bulbourethral glands (x2)
How long are seminal vesicles?
5cm
Where are the seminal vesicles located relative to the bladder
Posterior wall of bladder
What volume of semen is made of secretions from the seminal vesicles?
60%
Describe the pH of seminal vesicle mucus-like fluid. Why is this the case?
- Alkaline
- Neutralise male urethra and female reproductive tract
What are the key components of seminal vesicle fluid?
- Fructose (sperm metabolism)
- Prostaglandins (smooth muscle contractions in male and female reproductive tracts + motility and stability)
- Fibrinogen (coagulate semen straight after ejaculation to protect from acidic environments)
What is the prostate composed of (under a microscope)?
- Cluster of 30-50 glands
- Each drain into prostatic urethra
- Surrounded by smooth muscle
Prostate growth before puberty
Slow
Prostate growth from puberty-30
Rapid
Prostate growth 30-45
Slow & Steady
Prostate growth 45+
May enlarge
What volume of semen comes from prostatic secretions?
25-30%
What are some key substances secreted from the prostate during ejaculation?
- Citric acid (used for ATP production)
- Proteloytic enzymes
- Seminalplasmin (antibiotic; prevents bacterial infections)
Describe the acidity of prostatic fluid
Slightly acidic (balanced by alkaline seminal vesicle secretions) -> makes sense: citric acid
What proteolytic enzymes are in prostatic secretions?
- Fibrinolysin (breaks down clotting proteins from seminal vesicles)
- Prostate-specific antigen (can be used to test for enlarged prostate)
What do the bulbourethral glands secrete, and why?
Secrete thick, alkaline mucus prior to ejaculation to:
- Neutralises urethra
- Lubricates glans penis
What percentage of semen is seminal fluid, and what percentage is sperm?
Sperm: 10%
Seminal fluid: 90%
What are the three main sections of a sperm?
- Head
- Mid-Piece
- Tail
Erection mech
- Stimulation
- Parasympathetic neurons release nitric oxide, dilating nearby arteries and causing increased bloodflow to cavernosal arteries is corporus cavernosa
- Veins are compressed; blood accumulates in corporus cavernosa
- Erection is maintained until parasympathetic contraction of arteries and smooth muscle, removing blood from penis
Functions of testosterone
- Spermatogenesis
- Secondary sex traits
- Libido
Testosterone production and circulation mech
- GnRH from hypothalamus
- LH and FSH from Ant. Pituitary
- LH stimulated Leydig cells to release testosterone, and FSH stimulated sertoli cells to serete androgen binding protein (and Inhibin)
- ABP binds to testosterone, increasing local levels and causing spermatogenesis
[note: high T levels have negative feedback on GnRH secretion] - Circulating testosterone (entering from nearby blood vessels in the testes) increase libido and develop 2° sex traits
