MALE REPRODUCTIVE SYSTEM

• Reproduction/Procreation

  • production of a new individual
  • most important of the biological processes
• Sexual reproduction

  • requires the gametes (germ cells) of the male and the female to unite to form a zygote or fertilized ovum
  • male gamete - sperm cell (spermatozoon)
  • female gamete - egg cell (ovum)
• Gamete

  • unique among the numerous cell types in the body in that they one haploid (21 chromosomes)
  • all the others are diploid (i.e., they contain 46 chromosomes)
• Fertilization

  • sperm cell and an ovum unite
  • resulting cell (zygote) is diploid because it inherits all the chromosomes in both gametes
  • undergoes mitotic divisions (cleavage)
  • soon becomes an embryo
• Fetus

  • developing human individual from the end of the eighth week after fertilization until birth
• Gametogenesis

  • the production of male (spermatogenesis) and female gametes(oogenesis)
• Male reproductive system

  • consists
  • pair of testes
  • corresponding duct system of each testis
  • copulatory organ (penis)
  • accessory glands
• Primordial germ cells

  • earliest recognizable stem cells of the male and female gametes
  • arise from the endoderm of the yolk sac from the 2nd to the 8th week 8 intrauterine life
  • 4th - 5th week - gonads
• Oogonia

  • developing gonads (ovaries) of genetic female that will differentiate into
  • precursor cells of ova
• Spermatogonia

  • developing gonads (testes) of genetic males, they promptly differentiate into
  • precursor cells of spermatozoa
• Spermatogenesis

  • differentiation of the spermatogonia into spermatozoa, which occurs in the, seminiferous tubules of the testes
  • starts at puberty and continues until old age
  • 3 stages:
  • spermatocytogenesis
  • meiosis
  • spermiogenesis
• Spermatocytogenesis

  • refers to the development of spermatogonia into primary spermatocytes
• Meiosis

  • refers to the two successive cell divisions that the primary spermatocytes and their daughter cells respectively undergo to give rise to haploid cells called' spermatids
• Spermiogenesis

  • refers to the transformation of spermatids into spermatozoa
• Stages of Spermatogenesis

  A) primordial germ cell

  B) type Ad spermatogonium

  C) type Ap spermatogonium

  D) type B spermatogonium

  E) primary spermatocyte

  F) secondary spermatocyte

  G) spermatid

  H) spermatozoon

  
• Spermatocytoqenesis

  • several types of spermatogonia in the testes
  • dark type A spermatogonium (type Ad spermatogonium)
  • pale type A spermatogonium (type Ap spermatogonium)
  • type B spermatogonium
• Type Ad spermatogonium

  • a relatively small cell (about 12 um in diameter)
  • not entered the spermatogenic cell cycle yet
  • flattened ovoid nucleus contains dense chromatin material
  • rarely divide in adults
  • dormant reserve stem cells
• Type Ap spermatogonia

  • have entered the spermatogenic cycle
  • divide (mitose) actively either to renew their numbers or to produce type B spermatogonia
  • cytokinesis or division of the cytoplasm that occurs during telophase (the last stage of mitosis) is not completed (to produce type B spermatogonia
  • paler nucleus
  • lightly-staining, finely granular chromatin
  • contains a couple of nucleoli
• Type B spermatogonia

  • resemble type Ap spermatogonia
  • nucleus is more rounded
• A type B spermatogonium

  • undergoes further mitosis after which all its progenies increase in size and differentiate into primary spermatocytes
• Primary spermatocyte

  • largest cell in the spermatogenic cycle
  • a large nucleus whose chromatin material is in the form of fine threads or clumps, and abundant cytoplasm
• Meiosis

  • involves two successive cell divisions:
  • Meiosis I
  • Meiosis II
  • chromosomes replicate only once
• Meiosis I

  • undertaken by the diploid primary spermatocyte and results in the formation of two haploid cells (secondary spermatocytes)
  • has 22 pairs of homologous somatic chromosomes and a pair of male sex chromosomes (X and Y)
  • interphase (preleptotene stage) - its chromosomes replicate resulting in the production of two sister chromatids
  • 4 stages:
  • prophase
  • metaphase
  • anaphase
  • telophase
• Prophase (meiosis I)

  • 5 stages:
  • leptotene stage
  • zygotene stage
  • pachytene stage
  • diplotene stage
  • diakinesis
  • takes about 22 days to complete
• Leptotene stage

  • chromatin material starts to condense and form fine threads within the nucleus
• Zygotene stage

  • chromatin material condenses further and the homologous and sex chromosomes approach each other to form 23 pairs
  • replicates in the preleptotene stage
• Pachytene stage

  • chromosomes become thicker by condensing even further, rendering the sister chromatids recognizable as distinct entities
  • corresponding segments of the non-sister chromatids of each pair of homologous chromosomes are exchanged, a process called crossing-over or genetic recombination, which ensures that the genome of the resulting offspring is unique
• Diplotene stage

  • homologous and sex chromosomes begin to separate
• Diakenesis

  • nuclear membrane disappears and the homologous and sex chromosomes move a little further from each other
• Metaphase

  • homologous and sex pairs of chromosomes align themselves in parallel fashion at the center of the cell
• Anaphase

  • one member of each of the 22 pairs of homologous somatic chromosomes; and the Y chromosome move to one pole
  • other member of each of the 22 pairs of homologous somatic chromosomes and the X chromosome move to the opposite pole
  • homologous and sex pairs of chromosomes part company, but the sister chromatids of each chromosome stay together
• Telophase

  • each of the two groups of chromosomes that have migrated to the opposite ends of the cell acquires a nuclear envelope
  • cytoplasm of the mother cell is divided equally between the two daughter cells
  • secondary spermatocytes
  • two daughter cell
  • has 22 somatic chromosomes plus the Y chromosome while the other has 22 somatic chromosomes plus the X chromosome
  • chromatids
• Second Meiosis (Meiosis II)

  • completes in just a matter of hours
  • secondary spermatocytes are difficult to find
  • prophase - chromosomes condense
  • metaphase - move to the equatorial phase
  • anaphase - sister chromatids of each chromosome are pulled away from each other
  • telophase - each set of chromatids acquires a nuclear envelope and the cytoplasm of the mother cell is divided equally between the two daughter cells (spermatids)
  • spermatids
  • contain 23 chromosomes
  • none of them is identical to any of the chromosomes
  • smallest and most numerous of the immature gametes
• Spermiogenesis

  • haploid spermatid undergoes radical change in form and becomes a sperm cell (spermatozoon)
  • nucleus condenses and elongates
  • forms an acrosome (acrosomal cap)
  • acquires a tail (flagellum)
  • 3 stages:
  • Golgi phase
  • acrosomal phase
  • maturation phase
  • ends with spermiation
  • takes about 64 days for the spermatogonia to develop into spermatozoa
• Golgi phase

  • Golgi complex produces numerous small, membrane-bound granules (proacrosomal granules) that later coalesce to form a Single, large, membrane-bound structure (acrosomal vesicle)
  • nucleus condense and elongate
  • centrioles move towards the surface of the cell that is opposite the acrosomal vesicle
  • align with the long axis of the nucleus and start to elongate to form a tail (flagellum)
  • continuous production of proacrosomal granules by the Golgi complex and fusion of these granules with the acrosomal vesicle
• Acrosomal phase

  • acrosomal vesicle transforms into an acrosome
  • nucleus elongates further and its chromatin material condenses
  • tail continues to lengthen
  • cytoplasm
  • migrates
  • forms middle piece
• Acrosome

  • a caplike structure that coversa bigpart ofthe nuclear surface
• Maturation phase

  • transformation of the spermatid into a spermatozoon is completed
  • residual cytoplasm is shed and phagocytosed by the Sertoli cells
  • mitochondria get arranged in a helical manner around the middle piece forming what is known as a mitochondrial sheath
• Spermiation

  • release of the spermatozoon into the fluid-filled lumen of the seminiferous tubule
  • additional maturation - ductus epididymis
  • physiologically mature - female genital tract
• Spermatozoon

  • 2 parts:
  • head
  • tail