Biology Lesson 10: Male Reproductive System

Male Reproductive System

• Located mostly outside the body, with some parts inside the abdomen
• Responsible for sexual function and urination
• Produces, maintains, and transports sperm and semen (protective fluid)

Testes

• Primary sex glands, located in the scrotum
• Produce male gametes (spermatozoa) and male sex hormone (testosterone)
• Each testis is about 5 cm long, 2.5 cm wide, and weighs 10-15 grams
• Has a dense connective tissue capsule called tunica albuginea
• Divided into about 250 pyramidal compartments or testicular lobules by septa

Seminiferous Tubules

• Highly coiled, tightly packed tubules in the testes
• Sites of spermatogenesis (sperm production)
• Lined with specialized stratified germinal epithelium (seminiferous epithelium)
• Epithelium consists of two distinct populations: spermatogenic cells and Sertoli cells

Sertoli Cells

• Tall columnar cells that extend from the basement membrane to the lumen of the seminiferous tubules
• Provide structural and metabolic support to spermatogenic cells
• Have distinct oval nuclei with well-developed nucleoli
• Joined together by tight junctions, forming the blood-testis barrier
• Secrete components of testicular fluid, androgen-binding protein (ABP), and inhibin

Spermatogenesis

• Process by which spermatogonia develop into mature spermatozoa
• Takes place in the seminiferous tubules

Spermatozoa

• Elongated motile male gametes found in close association with Sertoli cells
• Each spermatozoon is about 60 μm in length, consisting of a head, neck, and tail
• The head contains a dark elongated nucleus with a haploid number of chromosomes
• The neck contains the centriole from which the flagellum arises
• The tail consists of a middle piece, principal piece, and end piece

Epididymis

• A comma-shaped structure on the posterolateral aspect of the testis
• A 6-meter long, highly coiled tube, supported by vascular connective tissue
• Divided into a head, body, and tail
• Lined with pseudostratified columnar epithelium, which bears long microvilli (stereocilia)
• Functions: storage of spermatozoa, maturation of spermatozoa, and absorption of testicular fluid

Genital Ducts

• Conduct sperm to the urethra
• Consist of epididymis, ductus deferens, and ejaculatory duct
• Ductus deferens is a muscular tube that stores spermatozoa and conveys them to the urethra during ejaculation### Male Reproductive System
• Accessory sex glands include seminal vesicle, prostate, and bulbourethral glands, which secrete fluids that make up seminal fluid
• Seminal fluid provides a medium for transport and nourishment of sperm
• Bulbourethral glands secrete a clear mucus-like substance that coats and lubricates the urethra in preparation for sperm passage

Female Reproductive System

Internal Female Reproductive Organs

• Consist of ovaries, fallopian tubes, uterus, and vagina
• Fallopian tubes, also known as uterine tubes or oviducts, transfer mature ovum from ovaries to uterus
• Each fallopian tube is about 10-12 cm in length and divided into four major regions:
  • Infundibulum (closest to ovaries) with finger-like projection called fimbriae
  • Ampulla (longest region) where fertilization of ovum most likely occurs
  • Isthmus
  • Intramural part (travels through uterine wall to transport ovum)

Uterus

• Hollow, pear-shaped, muscular organ that nourishes and supports embryonic growth during pregnancy
• Divided into three main parts:
  • Fundus (curved top/superior part)
  • Body (largest middle section)
  • Cervix (bottom/cylindrical part)

Fallopian Tube Layers

• Mucosa (inner layer):
  • Lined with simple columnar epithelium
  • Two types of cells: ciliated cells with visible cilia to help ovum movement, and secretory peg cells with apical bulge
• Muscularis:
  • Two layers of smooth muscle: inner circular/spiral layer, and outer longitudinal layer
• Serosa (outer layer):
  • Composed of single layer of basophilic/simple cuboidal cells and thin layer of supporting connective tissue

Endometrium

• Inner mucosal layer of uterus
• Divided into two zones:
  • Functional layer (upper surface portion, sheds during menstruation)
  • Basal layer (underlying portion, remains attached during menstruation and regenerates functional layer)
• Endometrial stroma (supportive tissue):
  • Contains extensive microvasculature, stellate cells, macrophages, and lymphocytes

Ovaries

• Almond-shaped structures producing steroid hormones (estrogen and progesterone) and female gametes (oocytes)
• Each ovary is about 3 cm long, 1.5 cm wide, and 1 cm thick with a thin outer capsule
• Cortex (outer region):
  • Where oocytes and ovarian follicles develop
  • Highly cellular connective tissue
• Medulla (inner region):
  • Loose fibroelastic connective tissue with large tortuous blood vessels, lymphatic vessels, and nerve fibers

Ovarian Follicles

• Fluid-filled structures containing oocytes
• Primordial follicles develop during fetal life and remain arrested until needed for ovulation
• Primary oocyte:
  • Large round cell making up majority of primordial follicle
  • Diameter: 25-30 micrometers
• Follicular cells:
  • Flattened cells surrounding primordial follicle
• Zona pellucida:
  • Thin pink/eosinophilic layer of glycoproteins between primary oocyte and follicular cells

Menstrual Cycle

• 3 phases:
  • Proliferative phase: functional layer regenerates after menstruation
  • Secretory phase: uterine glands accumulate and secrete glycogen
  • Menstrual phase: functional layer sheds, leading to menstrual bleeding