Male Reproductive System

Question 1

Define the four major functional components of the male reproductive system. Describe their functions and indicate if these structures are paired or unpaired.

Answer 1

• Synthesis: the site of sperm production (spermatogenesis) – facilitated by the testes (paired)
• Transport and storage: of sperm from the testes to a storage site – efferent ducts, epididymis, vas deferens (paired structures)
• Semen production: production of the fluid that contains sperm and other factors – seminal vesicles, bulbourethral glands, prostate (paired, paired, unpaired)
• Secretion: secretion of semen into the female reproductive tract – penis (unpaired)

Question 2

Describe the structure and divisions of the penis (externally as a whole structure). Indicate if they are located internal or external to the body.

Answer 2

• Root – the attached region that connects to the rest of the male reproductive structures inside the body (Internal)
• Shaft – the free region and main body of the penis (external)
• Glans penis – the enlarged tip (external)

Question 3

Describe the key structural elements of the penis in cross-section

Answer 3

• It is heavily vascularised and innervated
• It is made up of three columns of erectile tissue:
  – 2x Corpus cavernosa (plural: corpora cavernosa) – located adjacent to one another superior to corpus spongiosum
  – 1x Corpus spongiosum – located centrally and inferior to corpus venosum. This contains the urethra

Question 4

Why is the penis heavily vascularised and innervated? What happens during blood vessel constriction and dilation?

Answer 4

The penis is heavily vascularised and innervated because this allows it to carry out its function of being erect to facilitate copulation.
- Sympathetic innervation
of blood vessels via release of nitric oxide (noradrenaline) –> Contract smooth muscle around blood vessels –> Blood vessel constriction –> decreased blood flow to erectile tissues –> penis is flaccid
- Parasympathetic innervation
of blood vessels via release of nitric oxide (NO) –> Relax smooth
muscle around blood vessels –> Blood vessel dilation –> increased blood flow to erectile tissues –> Penis is erect

Question 5

What are the three main structures associated with the penis that are part of the external genitalia?

Answer 5

• Scrotum: (superficial –> deep)
  (–Skin –> Superficial fascia + dartos muscle –> External spermatic fascia –> cremaster muscle)
• Tunics
  – Tunica albuginea (inner)
  – Tunica vaginalis (outer)
• Blood supply
  – Arteries
  – Veins

Question 6

What are the two types of muscles located in the scrotum? What are their functions (include how they react to the cold).

Answer 6

Dartos muscle (outer muscle) – smooth muscle
- Function: to keep the testes at a 34 degrees Celsius, which is the required temperature for spermatogenesis
- How does it carry out this function? COLD STIMULATION –> Dartos muscle contracts and wrinkles –> Reduces heat loss and keeps testes warm

Cremaster muscle (inner muscle) – skeletal muscle
- Function: to keep the testes at a 34 degrees Celsius, which is the required temperature for spermatogenesis
- How does it carry out this function? COLD STIMULATION –> Dartos muscle contracts –> Elevates testes closer to body –> Reduces heat loss and keeps testes warm

Question 7

What are the two tunic layers associated with the testes? What are their functions?

Answer 7

The functions of the tunics is to facilitate blood supply to the testes and create a partition between spematogenic portion of the testes from non-spermatogenic portion.
The two layers are:
- tunica vaginalis (outer layer): derived from peritoneum
- tunica albuginea (inner layer): a layer of connective tissue that directly covers the testes and divides it into lobules

Question 8

Describe blood supply to the testes. Which structure encloses blood vessels, nerves and lymphatic supplying the testes?

Answer 8

• Arteries ~ arise from abdominal aorta
• Veins ~ arise from pampiniform venous plexus
  – Surrounds arteries to absorb heat from them and thus keep the testes cool

Blood vessels, nerves and lymphatic supplying the testes are enclosed by the spermatic cord.

Question 9

Describe the structure of the testes and the movement of sperm through the testes and associated structures.

Answer 9

• The testes are divided into lobules by fibrous septa (invaginations of the tunica albuginea).
• Each lobule contains 1-4 seminiferous tubules (containing Sertoli cells and developing germ/sperm cells) and interstitial space (contain Leydig cells). Seminiferous tubules are the site of spermatogenesis.

Sperm produced in seminiferous tubules –> Move to rete testis (network of tubes) –> Move into efferent ductules (these pierce tunica albuginea and drain into a common duct: –> epididymis –> sperm drains into the vas deferens/ductus deferens

Question 10

Describe the structures of the lobules in the testes. Which cells are contained in and around this structure?

Answer 10

The lobule is made up of the:
- seminiferous tubules – contain Sertoli cells and developing sperm cells
- interstitial space/compartment – contain Leydig cells

Question 11

Describe the structure of the seminiferous tubules (SNT). What structures are present? How are they arranged?

Answer 11

The cross-section of the SNT is a circle. The outer border is made of the basement membrane. The innermost part of the seminiferous lumen. Between the basement membrane and lumen are Sertoli cells which are connected to each other through gap/tight junctions and form and interconnected ring through the SNT.
- The positioning of the gap junctions divides the SNT into the:
— Basal compartment ~ which spans from the basement membrane to the gap junctions.
— Adluminal compartment ~ which spans from the gap functions and includes the lumen
- These compartments are micro-environments within the SNT and thus facilitate development of sperm during different stages.

Question 12

What are the functions of Sertoli cells? (6)

Answer 12

• Provide structural support to sperm cells
• Release nutrients for developing germ/sperm cells
• Blood-testis barrier formed by the luminal compartment and prevents chemicals from entering the SNT lumen, thus maintaining its integrity.
• Secrete luminal fluid
• Respond to stimulation by FSH and testosterone
• Produce inhibin – inhibits FSH production from pituitary gland

Question 13

Outline the steps of spermatogenesis? Which steps are occurring in the basal and adluminal compartments?

Answer 13

Steps 1-3: Basal compartment
Steps 5-7: Adluminal compartment

1) Type A spermatogonium are present in the basal compartment of the SNT (between basement membrane and tight junctions)
2) Type A spermatogonium –> Type B spermatogonium via mitosis (and limited differentiation)
3) Type B spermatogonium –> Primary spermatocyte via mitosis and differentiation
4) Tight junction (TJ) remodeling ~ TJ will break down –> allowing primary spermatocyte to move into adluminal compartment –> TJ will reform
5) Primary spermatocyte –> 2 Secondary spermatocytes via 1st meiotic division
6) Each Secondary spermatocyte –> 2 spermatids via 2nd meiotic division
7) Spermatid –> Spermatozoa via differentiation, which is called “spermiogenesis” (24 days)

Question 14

Name the general flow of spermatogenesis in terms of cell types.

Answer 14

Type A spermatogonium –> Type B spermatogonium –> Primary spermatocyte –> Secondary spermatocyte –> Spermatid –> Spermatozoa

Question 15

Do Type A spermatogonia always differentiate into Type B spermatogonia

Answer 15

Not every single clone produced by Type A spermatogonia differentiates into Type B spermatogonia. One of these clones remains undifferentiated (Type A spermatogonia) to maintain the pool of Type A spermatogonia, ensuring that the sperm stem cell pool is not exhausted

Question 16

Outline the change in genetic composition of sperm cells during spermatogenesis

Answer 16

Spermatogonium (46 diploid chromosomes)
Primary spermatocyte (46 diploid chromosomes)
Secondary spermatocyte (23 diploid chromosomes)
Spermatid (23 haploid chromosomes)
Spermatozoa (23 haploid chromosomes)

Question 17

What is spermiogenesis? Where does it occur? Outline the process and how long it takes.

Answer 17

• Spermiogenesis: differentiation of spermatid –> spermatozoa
• Location: Spermatid is embedded into adluminal compartment of Sertoli cells –> spermatozoa is released into lumen
• Process: ~ 24 days
  1) Packaging of acrosomal (hydrolytic) enzymes into acrosomes by the golgi apparatus
  2) Acrosome is positioned at anterioir end of nucleus and centrioles are positioned on opposite side of spermatid
  3) Microtubules elongate to form teh flagellum (from centrioles)
  4) Mitochondria multiply and surround the flagellum
  5) Excess cytoplasm is sloughed off, leaving the immature spermatid
  6) Immature sperm/mature spermatids (non-motile) released by Sertoli cells into lumen via spermiation
  7) Immature sperm matures in epididymis by gaining motility
  8) Final functional maturation occurs in the female reproductive tract

Question 18

Describe the structure and functions of different areas of the sperm

Answer 18

• Head – contains acrosomes (the enzymes inside it will facilitate entry of sperm into eff) and nucleus
• Midpiece – contains mitochondria to provide energy for motility
• Tail – propels flagella through female reproductive tract

Question 19

Differentiation between spermatogenesis, spermiogenesis and spermiation. Indicate the locations of each.

Answer 19

Spermatogenesis – production of sperm cells in the seminiferous tubules
Spermiogenesis – differentiation of spermatid –> sperm in adluminal compartment of Sertoli cells (seminiferous tubules)
Spermiation – the release of immature sperm/mature spermatids from the adluminal compartment of Sertoli cells into the lumen of the seminiferous tubules.

Question 20

Describe the role of the hypothalamus and pituitary gland in the regulation of spermatogenesis. What is the process of hormones release from these structures? What is the effect of them? (think hypothalamo-pituitary-gonadal axis)

Answer 20

Parvocellular neurons receive stimulus and fire action potential –> Release GnRH into hypothalamo hypophyseal portal vessels –> Travel to anterior pituitary and bind receptors of gonadotrophe cells –> release of LH and FSH (Activin also acts with GnRH to promote FSH release) –>
- LH –> Leydig cells (interstitium of seminiferous tubules) –> stimulate steroidogenic enzymes in Leydig cells –> Production of testosterone –> Testosterone travels to Sertoli cells and promotes spermatogenesis –> Rising testosterone levels inhibit LH production by acting on the hypothalamus and anterior pituiatary
- FSH –> Sertoli cells (seminiferous tubules) –> Production of paracrine factors (eg. Androgen binding protein (ABP)) which bind and maintain high concentrations of testosterone near spermatogenic cells to promote spermatogenesis
– FSH –> Sertoli cells –> Production of inhibin –> Feeds back to pituitary to suppress FSH production

Question 21

What are the functions of the epididymis?

Answer 21

1) Monitors and adjusts
composition of sperm produced by seminiferous tubules
2) Stores and protects spermatozoa while facilitating functional maturation of sperm (Immotile –> Motile ~ takes 20 days)
3) Acts as a recycling centre for damaged sperm (if not recovered and matured in 20 days, these are phagocytosed and absorbed by the body)
4) Sperm: epididymis –> vas deferens

Question 22

How does a vasectomy as a birth control method?

Answer 22

Vasectomy – cut and ligation of vas deferens which inhibits the transport of sperm
- Sperm is still produced, but cannot exit body and remains in epididymis. If there for > 20 days, sperm is phagocytosed.

Question 23

Function of vas deferens? What is its relationship with the seminal vesicles?

Answer 23

• It is a tube that runs from scrotal sac and descends towards the urethra – thus it is a pathway for sperm.
• The vas deferens joins with the seminal vesicles to form the ejaculatory duct – a structure which delivers sperm to the urethra, whilst adding molecules that promote sperm function:
  – Seminal vesicles release a viscous fluid which makes up 70% of semen volume and contains substances that enhance sperm motility and ability to fertilise. For example:
  — fructose – energy for sperm
  — prostaglandins – facilitate smooth muscle constraction
  — coagulating enzyme (vasiculase)

Question 24

What is the function of the prostate in sperm maturation?

Answer 24

The prostate activates sperm by producing a fluid that accounts for one third of semen volume and contains:
– citrate ~ nutrients for sperm
– enzymes
– prostate specific antigen (detected in blood during prostate cancer)

Question 25

Which structures contribute to semen production? to what proportion?

Answer 25

Seminal vesicles – contributes to ~70% of semen volume
Prostate – contributes to ~30% of semen volume