Male Reproductive System Microanatomy

• Objectives are to understand the microanatomy of the male reproductive system

Connective Tissue Layers

• Identify the different connective tissue layers surrounding and within the testes.

Testicular Blood Supply

• The collective name for blood vessels in the testes

Tunica Albuginea

• A tunica albuginea surrounds the testes, epididymis, and penis.

Testicular Cells

• Differentiate between somatic and germ cells within the testes.
• Identify the cells within the seminiferous tubules, those surrounding the basement membrane of the seminiferous tubules, and those in the interstitium.

Somatic Cell Differences

• Understand the differences in somatic cells in terms of location and function.

Germ Cell Identification

• Identify the different types of germ cells.
• Categorize germ cells as diploid or haploid.
• Locate germ cells in the basal vs. adluminal compartments.

Sperm Production: The Processes

• Know the cell that enters and results from spermatogenesis, spermatocytogenesis, meiosis, and spermiogenesis.

Spermiogenesis

• Describe all germ cell changes that occur during spermiogenesis.

Spermatozoa Maturation

• Elongated spermatids (spermatozoa) released from the convoluted seminiferous tubules are not capable of fertilization until they reach the cauda epididymis.

Spermatozoa Structure

• Know the structures spermatozoa will enter after leaving the convoluted seminiferous tubules.

Rete Testis

• Understand the location and function of the rete testis.

Sertoli and Leydig Cells

• Know the functions of Sertoli and Leydig cells.
• Know which pituitary hormones regulate these cells and their hormonal and other products.

Testicular Tumors

• Know the different types of testicular tumors.
• Know which type can result in gynecomastia and urinary incontinence.

Cryptorchid Testes

• Cryptorchid testes will still contain Sertoli and Leydig cells.
• Cryptorchid testes can have increased incidence of Sertoli cell tumors and elevated testosterone concentrations.

Epididymis

• Describe the type of epithelium found in the various portions of the epididymis.
• Describe the luminal contents of the epididymis.
• Describe how the luminal contents change from the corpus to cauda epididymis.
• Describe the organ function.

Testes and Epididymis

• Realize that the testes and epididymis can be given together on a single slide.

Ductus Deferens

• Understand the different layers of the ductus deferens.
• Know how to distinguish the ductus deferens from the uterine tube.
• Recognize that the ductus deferens can be part of the spermatic cord.

Spermatic Cord

• Understand the different connective tissue layers that surround the structures of the spermatic cord and what structures are part of it.

Accessory Glands

• Know how to identify the accessory glands.
• Know which species lack a given accessory gland.
• Know the function of each accessory gland.
• Know which organs may be seen in combination together, such as the prostate gland and male urethra.

Male Urethra

• Know which organs may be seen in combination with the male urethra.

Penis

• Know the origin of the corpus cavernosum.
• Identify the various erectile tissues and other structures that may be found in the body or glans region.

Tom Cat Anatomy

• Know which male reproductive structures are unique in the tom cat.
• Understand the differences in penile anatomy/microanatomy in the tom cat.

Urethral Transitions

• Know where the pelvic urethra ends and penile urethra begins.

Scrotal Structures

• Know the structures present in the scrotum.

Male Reproductive Components

• Male genital organs:
  • Testis
  • Epididymis
  • Ductus deferens
• Accessory genital glands:
  • Ampulla of ductus deferens
  • Seminal vesicles (vesicular glands)
  • Prostate
  • Bulbourethral gland
• External genitalia:
  • Penis
  • Male urethra
  • Scrotum

Male Reproductive Functions

• Production and transport of spermatozoa
• Production of testosterone and other hormones

Testis Layers

• Tunica vaginalis
  • Visceral lamina: CT and mesoathelium, Closely associated with T. albuginea
  • Parietal lamina

Testis Stroma

• Tunica albuginea:
  • Covers testis and epididymis
  • Dense irregular C.T., appears white
• Tunica vasculosa:
  • Branches of testicular artery and vein
  • Penetrates deep into the testis
• Septula:
  • Connects tunica albuginea with mediastinum
  • Divides testes into lobules
• Mediastinum
  • Rete testis - functional (sperm move through, and add fluid component)

Testis Parenchyma

• Convoluted seminiferous tubules (lobules)
• Straight seminiferous tubules
  • Not prominent except in stallion
  • Initial portion lined by Sertoli cells only which may act as a valve to prevent backflow of sperm
  • Remainder lined by simple cuboidal epithelium
• Rete testis
  • Within mediastinum
  • Adds fluid to spermatozoa

Convoluted Seminiferous Tubules

• Spermatogenic epithelium
  • Sustentacular cells (Sertoli cells)
• Myoid cells
  • Long elliptical nuclei
  • Contractile properties
• Presumable help to release sperm into the lumen

Spermatogenesis Defined

• The entire process from spermatogonia to spermatozoa (haploid)

Spermatogenesis Phases

• Spermatocytogenesis (Diploid)
• Meiosis (Haploid)
• Spermiogenesis (Haploid)

Spermatocytogenesis Details

• Spermatogonia (mitosis) divide at puberty
  • Spermatogonia A remain at the basement membrane to continue to divide
  • Spermatogonia B become primary spermatocytes

Primary Spermatocytes

• 4n DNA content(Diploid content)
• Largest spermatogenic epithelial cell
• Enters first stage of meiosis
• One primary spermatocyte gives rise to 4 spermatids

Meiosis Details

• One primary spermatocyte (2N, where N = number of chromosomes)
  • Diploid DNA duplication like mitosis
  • Some use N to refer to amount of DNA, which means these cells are 4N in terms of amount of DNA
• Two Secondary spermatocytes (1N)
  • 2N in terms of DNA
  • Chromosomes are still double stranded
  • These cells divide rapidly
  • Meiosis II = mitosis
• Four Spermatids (1N)
  • 1N in terms of DNA (Haploid)

Spermiogenesis

• Spermatids develop into mature spermatozoa
• Acrosome formation
  • RER → Golgi complex → cap of digestive enzymes over nucleus
  • Helps spermatozoa penetrate corona radiata and zona pellucida (ZP)
• Chromatin condensation
  • Large spherical nucleus becomes streamlined because of condensation (not pyknotic)
• Flagellum formation
  • Develops from one of the centrioles
  • Mitochondria orient around flagellum to give power for movement
• Shedding excess cytoplasm, now called the residual body, phagocytosed by Sertoli cells

Spermatozoan Structure

• Head
  • Acrosome - light cap that surrounds nucleus (help penetration)
  • Nucleus
• Flagellum

Sertoli Cell Morphology

• Sertoli Cells
  • Cannot see cytoplasmic boundaries
  • Oval nuclei oriented perpendicular to seminiferous tubules
  • Prominent nucleolus that may not be seen in all cells because of plane of section
  • Span entire length of seminiferous epithelium

Sertoli Cell Functions

• Support, protection, & nutritional regulation of developing germ cells
• Phagocytosis - ingest excess cytoplasm of spermatids & dead germ cells
• Secretion of Androgen Binding Protein (ABP) in response to pituitary FSH
  • Concentrates testosterone for normal spermatogenesis
  • Primarily remains in convoluted seminiferous epithelium
• Secretion of Inhibin in response to FSH
  • Provides negative feedback in male to decrease FSH
• Secretion of Estrogen
  • Produced by pre-pubertal Sertoli cells
• Sertoli cell tumors can revert to producing estrogen leading to feminization, including enlarged mammary glands (gynecomastia)
• Blood-seminiferous tubular barrier via occluding junctions between Sertoli cells
  • Separates basal (spermatogonial) and adluminal compartment (other spermatogenic cells)
  • Function:
• Protects other germ cells that were not present at the time of immune maturation against immune attack
• Primary spermatocytes are capable of moving past tight junction and afterwards tight junction returns to normal
• Production of Anti-Mullerian Hormone (AMH)= Mullerian Inhibiting Substance (MIS)
  • Causes regression of the Mullerian (paramesonephric) duct in the male embryo

Interstitial Cells (Leydig Cells)

• Location: Interstitium
• Appearance: Foamy or acidophilic
• Boar and stallion have abundant Leydig cells
• Functions:
  • Testosterone production in response to pituitary hormone LH = Interstitial Cell Stimulating Hormone (ICSH)
  • Produce estrogen, particularly in mature animals

Testicular Tumors

• Testicular tumors don't metastasize a lot of the time
• Seminoma
  • Derived from germ cells
  • Mitotically active (likely to become malignant)
  • Most likely of all three testicular tumors to become malignant
• Sertoli cell tumor
  • Many produce high amounts of estrogen
  • Can result in feminization, including enlarged mammary glands (gynecomastia), which may produce milk
  • May also cause urinary incontinence
  • Seen commonly in cryptorchid testes
• Interstitial (Leydig) cell tumor
• Cryptorchidism and Sertoli cell tumors
  • Undescended testes can be as far cranial as the kidneys
  • Leads to higher incidence of Sertoli cell tumors

Epididymis Structure

• Efferent ductules
  • Simple columnar epithelium with true cilia (kinocilia), motile
• Ductus epididymidis - three main portions, epithelial height decreases
  • Caput (Head) + initial segment
  • Corpus (Body)
  • Cauda (Tail) fertile

Epididymis Function

• Storage and maturation of spermatozoa
• Spermatozoa are incapable of fertilization when they enter the epididymis, and are fully mature once they reach the tail

Ductus Epididymis Description

• Pseudostratified columnar epithelium with stereocilia (long microvilli), not motile
• Epithelium height decreases from initial segment to caudal region (storage of spermatozoa)

Ductus Deferens

• Gross Structure - leads away from tail of epididymis
• Transport sperm to pelvic urethra via peristalsis
• Typical tubular organ with pseudostratified columnar epithelium
• Thick tunica muscularis
  • Not organized into well-defined inner circular, instead courses in all directions
• Histological mimic for oviduct
  • Method to distinguish: oviduct has true motile cilia and more mucosal folds than ductus deferens
  • Spermatozoa in lumen

Accessory Genital Glands Function

• Produce fluid portion of the ejaculate that nourishes, protects, and buffers the spermatozoa

Accessory Sex Glands - Species Differences

• Seminal vesicles - absent in dog and tom cat
• Bulbourethral gland - absent in dog
• Ampulla of ductus deferens - absent in boar and tom cat
• Prostate - present in all but some may not have prostate body

Seminal Vesicles (Vesicular Glands)

• Not present in carnivores
• Pseudostratified columnar epithelium with large irregular alveoli
• Basal cells present in ruminants and in boar that may accumulate large lipid droplets
• Secretion rich in fructose to nourish the spermatozoa
• Prostaglandin originally purified from ovine seminal vesicles

Ampulla of Ductus Deferens

• Not present in tom cat and boar
• In the dog, see a slight increase in diameter of ductus deferens
• Easiest to identify under low magnification
• Large irregular alveolar cells that look similar to vesicular gland, minus the capsule
• Lamina propria-submucosa and thick tunica muscularis with ill-defined layers
• Produce high concentrations of fructose for energy

Prostate Gland Description

• Most substantial in the dog, sections in lab from the canine prostate
• Present in all species to a certain extent
• Gross anatomy: Body and Disseminate part
  • The disseminate part is in lamina propria-submucosa of pelvic urethra
  • The epithelium looks the same as that in lobes
  • Main portion in the boar
• Microscopic anatomy: Glandular epithelium transitions to simple cuboidal, very acidophilic
  • Secretion neutralizes acidity of semen

Bulbourethral (Cowper's) Gland

• Not present in dog
• Present in other species at junction of pelvic urethra and penis
• Glandular epithelium transitions to simple columnar
  • Either tubules or alveoli/tubuloalveolar
  • Nuclei toward base
• Mucous secretion
  • May see droplets within cells
  • Lubricates urethra prior to ejaculation
• May see skeletal muscle externally
• Histological mimic for salivary glands
  • No striated ducts like in salivary glands

Genitalia: Penis

• Three parts:
  • Root, Body, and Glans
• Body:
  • Corpora cavernosa penis (erectile tissue) surrounded by Tunica albuginea (connective sheath)
  • Corpus spongiosum penis (erectile tissue)
  • Abundance of elastic fibers

The Glans Description

• Bulbus glandis
• Pars longa glandis
  • Corpus spongiosum glandis
• Os penis
  • Present in carnivores: dogs, cats, otters, raccoons, and walruses
• In tom cats, obstruction is caused by bone traps calculi which end up inside the caudal end of the penis

Tom Cat Penis Specifics

• Penis directed caudoventrally in non-erect state and moves cranioventrally
• Glans penis is conical and undivided
• Small os penis with urethra on dorsal side
• Cornified spines on glans
• May help to induce ovulation
• Size is not as large for castrated cats

Male Urethra Makeup

• Pelvic part: neck of urinary bladder to bulb of the penis
• Spongy part: penile urethra in corpus spongiosum of penis
• External urethral ostium
  • Surrounded by corpus spongiosum
  • Typical tubular organ
  • Transitional to stratified squamous epithelium
• Distal end may have portions that are stratified cuboidal/columnar

Scrotum Description

• Scrotal skin looks like typical skin
• Tunica dartos is a subcutaneous layer containing smooth muscle which forms scrotal septum

Explore the microanatomy of the male reproductive system, identifying connective tissue layers, testicular blood supply, and the tunica albuginea. Differentiate between somatic and germ cells within the testes and understand their functions. Learn about spermatogenesis and sperm production.