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Gametogenesis

Gametogenesis is the development of gametes from primordial germ cells. This process differs between the sexes. In males, spermatogenesis produces spermatozoa. In females, oogenesis results in an ovum. The process starts with the migration of primordial germ cells from the yolk sac Yolk Sac The first of four extra-embryonic membranes to form during embryogenesis. In reptiles and birds, it arises from endoderm and mesoderm to incorporate the egg yolk into the digestive tract for nourishing the embryo. In placental mammals, its nutritional function is vestigial; however, it is the source of intestinal mucosa; blood cells; and germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg. Embryoblast and Trophoblast Development to the gonadal ridge Gonadal ridge Development of the Urogenital System. Oogenesis starts during the embryonic and fetal periods, whereas spermatogenesis starts at puberty Puberty Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11-19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Puberty. However, the phases of gametogenesis are similar, with germ cells progressing through mitosis Mitosis A type of cell nucleus division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. Cell Cycle, meiosis I Meiosis I Following DNA replication, meiosis I creates 2 daughter cells containing half the genetic information of the mother cell (1n) but the same number of chromosomes (2c) by segregating sister chromatids into the same daughter cell Meiosis, meiosis II Meiosis II Meiosis II is a cellular division event wherein the number of chromosomes in the daughter cells is halved from that of the mother cell. Meiosis II: similar to meiosis I but not preceded by interphase (DNA replication) Meiosis, and maturation. This process results in gametes that are haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics, with 23 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure.

Last updated: Sep 1, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Overview

Emigration of germ cells

  • Primordial germ cells (PGCs) originate from the endoderm Endoderm The inner of the three germ layers of an embryo. Gastrulation and Neurulation of the yolk sac Yolk Sac The first of four extra-embryonic membranes to form during embryogenesis. In reptiles and birds, it arises from endoderm and mesoderm to incorporate the egg yolk into the digestive tract for nourishing the embryo. In placental mammals, its nutritional function is vestigial; however, it is the source of intestinal mucosa; blood cells; and germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg. Embryoblast and Trophoblast Development.
  • Journey along the hindgut Hindgut Development of the Abdominal Organs → reach gonadal ridge Gonadal ridge Development of the Urogenital System → cells now called gametogonia 
  • Take up association with primordial sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria cords

Gametogenesis

  • Gametogonia and gametogenesis differ between sexes:
    • Females: oogonium → oogenesis
    • Males: spermatogonium → spermatogenesis
  • Cells generally follow the same phases:
    • Mitosis Mitosis A type of cell nucleus division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. Cell Cycle
    • Meiosis I Meiosis I Following DNA replication, meiosis I creates 2 daughter cells containing half the genetic information of the mother cell (1n) but the same number of chromosomes (2c) by segregating sister chromatids into the same daughter cell Meiosis
    • Meiosis II Meiosis II Meiosis II is a cellular division event wherein the number of chromosomes in the daughter cells is halved from that of the mother cell. Meiosis II: similar to meiosis I but not preceded by interphase (DNA replication) Meiosis
    • Maturation/differentiation
  • These phases lead cells through the following development:
    • Gametogonium ( diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics, 46 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure)
    • Primary gametocyte ( diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics, 46 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure)
    • Secondary gametocyte ( haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics, 23 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure)
    • Gametid ( haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics, 23 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure)
    • Gamete ( haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics, 23 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure)
Gametogenesis in males and females

Gametogenesis in males and females:
Diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics gametogonia undergo mitosis Mitosis A type of cell nucleus division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. Cell Cycle. Some daughter cells will remain as gametogonia, while others differentiate into primary gametocytes Gametocytes Plasmodium/Malaria. From there, meiosis I Meiosis I Following DNA replication, meiosis I creates 2 daughter cells containing half the genetic information of the mother cell (1n) but the same number of chromosomes (2c) by segregating sister chromatids into the same daughter cell Meiosis occurs, resulting in secondary gametocytes Gametocytes Plasmodium/Malaria that are haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics. Meiosis II Meiosis II Meiosis II is a cellular division event wherein the number of chromosomes in the daughter cells is halved from that of the mother cell. Meiosis II: similar to meiosis I but not preceded by interphase (DNA replication) Meiosis leads to gametids, with 1 representative strand of DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure from each chromosome Chromosome In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. Basic Terms of Genetics. Gametids undergo a separate process for differentiation/maturation to produce mature gametes.

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Oogenesis

Oogenesis is the process of ovum production from PGCs. 

Note: This animation does not have sound.

Formation of ovum

  • Phases of oogenesis:
    • Mitosis Mitosis A type of cell nucleus division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. Cell Cycle
      • Oogonium → primary oocyte
      • Ploidy: diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics
      • 46 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure
    • Meiosis I Meiosis I Following DNA replication, meiosis I creates 2 daughter cells containing half the genetic information of the mother cell (1n) but the same number of chromosomes (2c) by segregating sister chromatids into the same daughter cell Meiosis
      • Primary oocyte → secondary oocyte and 1st polar body
      • Ploidy: diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics
      • 46 → 23 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure
    • Meiosis II Meiosis II Meiosis II is a cellular division event wherein the number of chromosomes in the daughter cells is halved from that of the mother cell. Meiosis II: similar to meiosis I but not preceded by interphase (DNA replication) Meiosis
      • Secondary oocyte → ootid and 2nd polar body
      • Ploidy: haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics
      • 23 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure
    • Maturation: ootid → ovum
  • Note: Unlike in spermatogenesis, cell division Cell Division A type of cell nucleus division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. Cell Cycle is uneven in oogenesis, resulting in a single ovum and polar bodies.
  • Time line:
    • Initiated in the embryonic and fetal periods.
    • Halts in prophase Prophase The first phase of cell nucleus division, in which the chromosomes become visible, the cell nucleus starts to lose its identity, the spindle apparatus appears, and the centrioles migrate toward opposite poles. Cell Cycle of meiosis I Meiosis I Following DNA replication, meiosis I creates 2 daughter cells containing half the genetic information of the mother cell (1n) but the same number of chromosomes (2c) by segregating sister chromatids into the same daughter cell Meiosis
    • Resumes during puberty Puberty Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11-19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Puberty
    • A 2nd arrest occurs in the metaphase Metaphase The phase of cell nucleus division following prometaphase, in which the chromosomes line up across the equatorial plane of the spindle apparatus prior to separation. Cell Cycle of meiosis II Meiosis II Meiosis II is a cellular division event wherein the number of chromosomes in the daughter cells is halved from that of the mother cell. Meiosis II: similar to meiosis I but not preceded by interphase (DNA replication) Meiosis.
    • Resumes again after fertilization Fertilization To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur. Fertilization and First Week
    • Process continues monthly until menopause Menopause Menopause is a physiologic process in women characterized by the permanent cessation of menstruation that occurs after the loss of ovarian activity. Menopause can only be diagnosed retrospectively, after 12 months without menstrual bleeding. Menopause.

Follicle development

Folliculogenesis Folliculogenesis Ovaries: Anatomy is a complex process in which an ovarian follicle, containing an oocyte, matures through several stages.

  • Primordial follicle Primordial follicle Ovaries: Anatomy:
    • Develops in ovaries Ovaries Ovaries are the paired gonads of the female reproductive system that contain haploid gametes known as oocytes. The ovaries are located intraperitoneally in the pelvis, just posterior to the broad ligament, and are connected to the pelvic sidewall and to the uterus by ligaments. These organs function to secrete hormones (estrogen and progesterone) and to produce the female germ cells (oocytes). Ovaries: Anatomy during the fetal period Fetal period Prenatal and Postnatal Physiology of the Neonate
    • Oogonia become surrounded by somatic epithelial cells from the genital ridge.
  • Primary follicle Primary follicle Ovaries: Anatomy:
    • Contains a primary oocyte
    • A glycoprotein layer is created ( zona pellucida Zona pellucida A tough transparent membrane surrounding the ovum. It is penetrated by the sperm during fertilization. Fertilization and First Week).
    • Follicular cells proliferate to become the granulosa cell Granulosa cell Supporting cells for the developing female gamete in the ovary. They are derived from the coelomic epithelial cells of the gonadal ridge. Granulosa cells form a single layer around the oocyte in the primordial ovarian follicle and advance to form a multilayered cumulus oophorus surrounding the ovum in the graafian follicle. The major functions of granulosa cells include the production of steroids and LH receptors. Puberty layer.
  • Secondary follicle Secondary follicle Ovaries: Anatomy
    • This stage is responsive to gonadotropins.
    • Granulosa cell Granulosa cell Supporting cells for the developing female gamete in the ovary. They are derived from the coelomic epithelial cells of the gonadal ridge. Granulosa cells form a single layer around the oocyte in the primordial ovarian follicle and advance to form a multilayered cumulus oophorus surrounding the ovum in the graafian follicle. The major functions of granulosa cells include the production of steroids and LH receptors. Puberty layer grows.
    • Recruitment Recruitment Skeletal Muscle Contraction of thecal cells → surround basement membrane Basement membrane A darkly stained mat-like extracellular matrix (ecm) that separates cell layers, such as epithelium from endothelium or a layer of connective tissue. The ecm layer that supports an overlying epithelium or endothelium is called basal lamina. Basement membrane (bm) can be formed by the fusion of either two adjacent basal laminae or a basal lamina with an adjacent reticular lamina of connective tissue. Bm, composed mainly of type IV collagen; glycoprotein laminin; and proteoglycan, provides barriers as well as channels between interacting cell layers. Thin Basement Membrane Nephropathy (TBMN)
  • Tertiary follicle Tertiary follicle Ovaries: Anatomy:
    • Granulosa cells produce:
      • Secretions → create an antrum
      • Estrogen Estrogen Compounds that interact with estrogen receptors in target tissues to bring about the effects similar to those of estradiol. Estrogens stimulate the female reproductive organs, and the development of secondary female sex characteristics. Estrogenic chemicals include natural, synthetic, steroidal, or non-steroidal compounds. Ovaries: Anatomy
    • Granulosa cells around the oocyte become the cumulus oophorus.
    • Thecal cells differentiate into:
      • Theca interna: contains small vessels and glandular cells; produce testosterone Testosterone A potent androgenic steroid and major product secreted by the leydig cells of the testis. Its production is stimulated by luteinizing hormone from the pituitary gland. In turn, testosterone exerts feedback control of the pituitary LH and FSH secretion. Depending on the tissues, testosterone can be further converted to dihydrotestosterone or estradiol. Androgens and Antiandrogens → converted to estrogen Estrogen Compounds that interact with estrogen receptors in target tissues to bring about the effects similar to those of estradiol. Estrogens stimulate the female reproductive organs, and the development of secondary female sex characteristics. Estrogenic chemicals include natural, synthetic, steroidal, or non-steroidal compounds. Ovaries: Anatomy by granulosa cells
      • Theca externa: stabilizes follicles; derived from connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology
  • Mature (graafian) follicle:
    • Only 1 follicle will reach this stage each cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation.
    • Primary oocyte → secondary oocyte just before ovulation Ovulation The discharge of an ovum from a rupturing follicle in the ovary. Menstrual Cycle
    • Antrum enlarges (makes up most of the follicle)
    • Innermost layer of the cumulus oophorus → corona radiata
  • Corpus luteum Corpus Luteum The yellow body derived from the ruptured ovarian follicle after ovulation. The process of corpus luteum formation, luteinization, is regulated by luteinizing hormone. Ovaries: Anatomy:
    • Formed after oocyte release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology
    • Center contains a blood clot formed after ovulation Ovulation The discharge of an ovum from a rupturing follicle in the ovary. Menstrual Cycle.
    • Granulosa and theca cells Theca cells The flattened stroma cells forming a sheath or theca outside the basal lamina lining the mature ovarian follicle. Thecal interstitial or stromal cells are steroidogenic, and produce primarily androgens which serve as precursors of estrogens in the granulosa cells. Puberty produce progesterone Progesterone The major progestational steroid that is secreted primarily by the corpus luteum and the placenta. Progesterone acts on the uterus, the mammary glands and the brain. It is required in embryo implantation; pregnancy maintenance, and the development of mammary tissue for milk production. Progesterone, converted from pregnenolone, also serves as an intermediate in the biosynthesis of gonadal steroid hormones and adrenal corticosteroids. Gonadal Hormones.
    • Atrophies if pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care does not occur.
The stages of folliculogenesis

The stages of folliculogenesis Folliculogenesis Ovaries: Anatomy:
Note the progression of follicular cell proliferation, thecal cell differentiation, and antrum enlargement.

Image by Lecturio.

Ovulation Ovulation The discharge of an ovum from a rupturing follicle in the ovary. Menstrual Cycle

  • Occurs when luteinizing hormone ( LH LH A major gonadotropin secreted by the adenohypophysis. Luteinizing hormone regulates steroid production by the interstitial cells of the testis and the ovary. The preovulatory luteinizing hormone surge in females induces ovulation, and subsequent luteinization of the follicle. Luteinizing hormone consists of two noncovalently linked subunits, alpha and beta. Within a species, the alpha subunit is common in the three pituitary glycoprotein hormones (TSH, LH, and FSH), but the beta subunit is unique and confers its biological specificity. Menstrual Cycle) and follicle-stimulating hormone ( FSH FSH A major gonadotropin secreted by the adenohypophysis. Follicle-stimulating hormone stimulates gametogenesis and the supporting cells such as the ovarian granulosa cells, the testicular sertoli cells, and leydig cells. Fsh consists of two noncovalently linked subunits, alpha and beta. Within a species, the alpha subunit is common in the three pituitary glycoprotein hormones (TSH, LH, and FSH), but the beta subunit is unique and confers its biological specificity. Menstrual Cycle) levels peak
  • Cumulus oophorus cells loosen → allows oocyte and corona radiata to detach from the follicle
  • Proteolytic enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes weaken the follicle wall.
  • Rupture of the follicular wall → release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology of the oocyte

Related videos

Spermatogenesis

Spermatogenesis is the process of sperm production from PGCs.

Note: This animation does not have sound.

Location

Overview:

  • Spermatogenesis takes place in the seminiferous tubules Seminiferous Tubules The convoluted tubules in the testis where sperm are produced (spermatogenesis) and conveyed to the rete testis. Spermatogenic tubules are composed of developing germ cells and the supporting sertoli cells. Testicles: Anatomy in the testes Testes Gonadal Hormones
  • Prepuberty, seminiferous tubules Seminiferous Tubules The convoluted tubules in the testis where sperm are produced (spermatogenesis) and conveyed to the rete testis. Spermatogenic tubules are composed of developing germ cells and the supporting sertoli cells. Testicles: Anatomy consist of:
    • Sertoli cells Sertoli Cells Supporting cells projecting inward from the basement membrane of seminiferous tubules. They surround and nourish the developing male germ cells and secrete androgen-binding protein and hormones such as anti-mullerian hormone. The tight junctions of sertoli cells with the spermatogonia and spermatocytes provide a blood-testis barrier. Testicles: Anatomy
    • PGCs (spermatogonia)

Sertoli cells Sertoli Cells Supporting cells projecting inward from the basement membrane of seminiferous tubules. They surround and nourish the developing male germ cells and secrete androgen-binding protein and hormones such as anti-mullerian hormone. The tight junctions of sertoli cells with the spermatogonia and spermatocytes provide a blood-testis barrier. Testicles: Anatomy:

  • Control the environment within the seminiferous tubules Seminiferous Tubules The convoluted tubules in the testis where sperm are produced (spermatogenesis) and conveyed to the rete testis. Spermatogenic tubules are composed of developing germ cells and the supporting sertoli cells. Testicles: Anatomy
  • Help regulate spermatogenesis
  • Contain FSH FSH A major gonadotropin secreted by the adenohypophysis. Follicle-stimulating hormone stimulates gametogenesis and the supporting cells such as the ovarian granulosa cells, the testicular sertoli cells, and leydig cells. Fsh consists of two noncovalently linked subunits, alpha and beta. Within a species, the alpha subunit is common in the three pituitary glycoprotein hormones (TSH, LH, and FSH), but the beta subunit is unique and confers its biological specificity. Menstrual Cycle and androgen receptors Receptors Receptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell. Receptors → necessary for stimulating spermatogenesis
  • Secrete:
    • Antimüllerian hormone ( AMH AMH A glycoprotein that causes regression of mullerian ducts. It is produced by sertoli cells of the testes. In the absence of this hormone, the mullerian ducts develop into structures of the female reproductive tract. In males, defects of this hormone result in persistent mullerian duct, a form of male pseudohermaphroditism. Primary Amenorrhea) → regression Regression Corneal Abrasions, Erosion, and Ulcers of müllerian ducts during embryonic development
    • Inhibin B → inhibits FSH FSH A major gonadotropin secreted by the adenohypophysis. Follicle-stimulating hormone stimulates gametogenesis and the supporting cells such as the ovarian granulosa cells, the testicular sertoli cells, and leydig cells. Fsh consists of two noncovalently linked subunits, alpha and beta. Within a species, the alpha subunit is common in the three pituitary glycoprotein hormones (TSH, LH, and FSH), but the beta subunit is unique and confers its biological specificity. Menstrual Cycle secretion Secretion Coagulation Studies → helps with regulating hormone levels
  • Form the blood–testis barrier → protects sperm development from:
    • Immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs
    • Other substances in the blood (e.g., toxins, hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types)

Formation of spermatozoa

  • Onset: puberty Puberty Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11-19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Puberty
  • Induced by FSH FSH A major gonadotropin secreted by the adenohypophysis. Follicle-stimulating hormone stimulates gametogenesis and the supporting cells such as the ovarian granulosa cells, the testicular sertoli cells, and leydig cells. Fsh consists of two noncovalently linked subunits, alpha and beta. Within a species, the alpha subunit is common in the three pituitary glycoprotein hormones (TSH, LH, and FSH), but the beta subunit is unique and confers its biological specificity. Menstrual Cycle and testosterone Testosterone A potent androgenic steroid and major product secreted by the leydig cells of the testis. Its production is stimulated by luteinizing hormone from the pituitary gland. In turn, testosterone exerts feedback control of the pituitary LH and FSH secretion. Depending on the tissues, testosterone can be further converted to dihydrotestosterone or estradiol. Androgens and Antiandrogens (produced by Leydig cells Leydig Cells Steroid-producing cells in the interstitial tissue of the testis. They are under the regulation of pituitary hormones; luteinizing hormone; or interstitial cell-stimulating hormone. Testosterone is the major androgen (androgens) produced. Testicles: Anatomy in response to LH LH A major gonadotropin secreted by the adenohypophysis. Luteinizing hormone regulates steroid production by the interstitial cells of the testis and the ovary. The preovulatory luteinizing hormone surge in females induces ovulation, and subsequent luteinization of the follicle. Luteinizing hormone consists of two noncovalently linked subunits, alpha and beta. Within a species, the alpha subunit is common in the three pituitary glycoprotein hormones (TSH, LH, and FSH), but the beta subunit is unique and confers its biological specificity. Menstrual Cycle)
  • Occurs in phases:
    • Mitosis Mitosis A type of cell nucleus division by means of which the two daughter nuclei normally receive identical complements of the number of chromosomes of the somatic cells of the species. Cell Cycle
      • Spermatogonia → primary spermatocyte
      • Ploidy: diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics
      • 46 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure
    • Meiosis I Meiosis I Following DNA replication, meiosis I creates 2 daughter cells containing half the genetic information of the mother cell (1n) but the same number of chromosomes (2c) by segregating sister chromatids into the same daughter cell Meiosis
      • Primary spermatocyte → secondary spermatocyte
      • Ploidy: diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics
      • 46 → 23 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure
    • Meiosis II Meiosis II Meiosis II is a cellular division event wherein the number of chromosomes in the daughter cells is halved from that of the mother cell. Meiosis II: similar to meiosis I but not preceded by interphase (DNA replication) Meiosis
      • Secondary spermatocyte → spermatid
      • Ploidy: haploid Haploid The chromosomal constitution of cells, in which each type of chromosome is represented once. Symbol: n. Basic Terms of Genetics
      • 23 chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure
    • Spermiogenesis (maturation): spermatid → spermatozoa
  • Mature spermatozoa are released into the lumen of the seminiferous tubules Seminiferous Tubules The convoluted tubules in the testis where sperm are produced (spermatogenesis) and conveyed to the rete testis. Spermatogenic tubules are composed of developing germ cells and the supporting sertoli cells. Testicles: Anatomy → stored in the epididymis Epididymis The convoluted cordlike structure attached to the posterior of the testis. Epididymis consists of the head (caput), the body (corpus), and the tail (cauda). A network of ducts leaving the testis joins into a common epididymal tubule proper which provides the transport, storage, and maturation of spermatozoa. Testicles: Anatomy
  • Entire process takes approximately 2 months
The process of spermatogenesis

The process of spermatogenesis as the cells progress from primary spermatocytes to secondary spermatocytes to spermatids to sperm

Image: “Illustration from Anatomy & Physiology, Connexions” by OpenStax College. License: CC BY 4.0

Structure of spermatozoa

Spermiogenesis results in characteristic morphologic changes associated with spermatozoa.

  • Head:
    • Nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles
      • Contains chromosomes Chromosomes In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. DNA Types and Structure
      • Condensed
    • Acrosome: 
      • Cap-like structure covering the anterior head region
      • Produced by transformation Transformation Change brought about to an organism’s genetic composition by unidirectional transfer (transfection; transduction, genetic; conjugation, genetic, etc.) and incorporation of foreign DNA into prokaryotic or eukaryotic cells by recombination of part or all of that DNA into the cell’s genome. Bacteriology of the Golgi apparatus
      • Contains enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes needed for fertilization Fertilization To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur. Fertilization and First Week
  • Body (mid-piece):
    • Contains mitochondria Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive ribosomes, transfer RNAs; amino Acyl tRNA synthetases; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs. Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. The Cell: Organelles
    • Provides ATP for movement of the flagellum
  • Tail (flagellum): 
Structure of sperm

Structure of sperm

Image: “Structure of Sperm: Sperm cells are divided into a head, containing DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure; a mid-piece, containing mitochondria Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive ribosomes, transfer RNAs; amino Acyl tRNA synthetases; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs. Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. The Cell: Organelles; and a tail, providing motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility. The acrosome is oval and somewhat flattened.” by OpenStax College. License: CC BY 4.0

Capacitation

  • Spermatozoa are functionally immature after spermiogenesis.
  • A final maturation process is required to: 
    • Become metabolically active
    • Fertilize an ovum
  • Process:
    • Begins in the epididymis Epididymis The convoluted cordlike structure attached to the posterior of the testis. Epididymis consists of the head (caput), the body (corpus), and the tail (cauda). A network of ducts leaving the testis joins into a common epididymal tubule proper which provides the transport, storage, and maturation of spermatozoa. Testicles: Anatomy
    • Ends in the female reproductive tract
  • Changes include:
    • Motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility
    • Enzyme content of the acrosome
    • Cell surface proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis

Clinical Relevance

  • Trisomy Trisomy The possession of a third chromosome of any one type in an otherwise diploid cell. Types of Mutations 21 ( Down syndrome Down syndrome Down syndrome, or trisomy 21, is the most common chromosomal aberration and the most frequent genetic cause of developmental delay. Both boys and girls are affected and have characteristic craniofacial and musculoskeletal features, as well as multiple medical anomalies involving the cardiac, gastrointestinal, ocular, and auditory systems. Down syndrome (Trisomy 21)): chromosomal disorder that can result from an error Error Refers to any act of commission (doing something wrong) or omission (failing to do something right) that exposes patients to potentially hazardous situations. Disclosure of Information in meiosis Meiosis The creation of eukaryotic gametes involves a DNA replication phase followed by 2 cellular division stages: meiosis I and meiosis II. Meiosis I separates homologous chromosomes into separate cells (1n, 2c), while meiosis II separates sister chromatids into gametes (1n, 1c). Meiosis during gametogenesis. Affected individuals have characteristic craniofacial and musculoskeletal features, as well as multiple medical anomalies involving the cardiac, GI, ocular, and auditory systems. Ultimately, karyotyping Karyotyping Mapping of the karyotype of a cell. Chromosome Testing confirms the diagnosis in the prenatal or postnatal period Postnatal period Prenatal and Postnatal Physiology of the Neonate. There is no cure for Down syndrome Down syndrome Down syndrome, or trisomy 21, is the most common chromosomal aberration and the most frequent genetic cause of developmental delay. Both boys and girls are affected and have characteristic craniofacial and musculoskeletal features, as well as multiple medical anomalies involving the cardiac, gastrointestinal, ocular, and auditory systems. Down syndrome (Trisomy 21). Treatment is based on the clinical manifestations present. 
  • Trisomy 18 Trisomy 18 Edwards syndrome, or trisomy 18, is a genetic syndrome caused by the presence of an extra chromosome 18. The extra chromosome is either from 3 full copies of chromosome 18 or an additional segment of chromosome 18. As the 2nd most common trisomy, Edwards syndrome is seen in 1 out of every 5,500 live births. Edwards Syndrome (Trisomy 18) ( Edwards syndrome Edwards syndrome Edwards syndrome, or trisomy 18, is a genetic syndrome caused by the presence of an extra chromosome 18. The extra chromosome is either from 3 full copies of chromosome 18 or an additional segment of chromosome 18. As the 2nd most common trisomy, Edwards syndrome is seen in 1 out of every 5,500 live births. Edwards Syndrome (Trisomy 18)): chromosomal disorder that can result from an error Error Refers to any act of commission (doing something wrong) or omission (failing to do something right) that exposes patients to potentially hazardous situations. Disclosure of Information in meiosis Meiosis The creation of eukaryotic gametes involves a DNA replication phase followed by 2 cellular division stages: meiosis I and meiosis II. Meiosis I separates homologous chromosomes into separate cells (1n, 2c), while meiosis II separates sister chromatids into gametes (1n, 1c). Meiosis during gametogenesis. Trisomy 18 Trisomy 18 Edwards syndrome, or trisomy 18, is a genetic syndrome caused by the presence of an extra chromosome 18. The extra chromosome is either from 3 full copies of chromosome 18 or an additional segment of chromosome 18. As the 2nd most common trisomy, Edwards syndrome is seen in 1 out of every 5,500 live births. Edwards Syndrome (Trisomy 18) is the 2nd most common trisomy Trisomy The possession of a third chromosome of any one type in an otherwise diploid cell. Types of Mutations, with a predominance in girls. Characteristic features include intrauterine growth restriction, cardiac defects, clenched fists with overlapping fingers, and rocker bottom feet. Diagnosis is made by karyotype Karyotype The full set of chromosomes presented as a systematized array of metaphase chromosomes from a photomicrograph of a single cell nucleus arranged in pairs in descending order of size and according to the position of the centromere. Congenital Malformations of the Female Reproductive System analysis. No treatment is available, and most affected individuals do not survive beyond 1 year of life.
  • Trisomy 13 Trisomy 13 Trisomy 13, or Patau syndrome, is a genetic syndrome caused by the presence of 3 copies of chromosome 13. As the 3rd most common trisomy, Patau syndrome has an incidence of 1 in 10,000 live births. Most cases of Patau syndrome are diagnosed prenatally by maternal screening and ultrasound. More than half of the pregnancies result in spontaneous abortions. Patau Syndrome (Trisomy 13) ( Patau syndrome Patau syndrome Trisomy 13, or Patau syndrome, is a genetic syndrome caused by the presence of 3 copies of chromosome 13. As the 3rd most common trisomy, Patau syndrome has an incidence of 1 in 10,000 live births. Most cases of Patau syndrome are diagnosed prenatally by maternal screening and ultrasound. More than half of the pregnancies result in spontaneous abortions. Patau Syndrome (Trisomy 13)): chromosomal disorder that can result from an error Error Refers to any act of commission (doing something wrong) or omission (failing to do something right) that exposes patients to potentially hazardous situations. Disclosure of Information in meiosis Meiosis The creation of eukaryotic gametes involves a DNA replication phase followed by 2 cellular division stages: meiosis I and meiosis II. Meiosis I separates homologous chromosomes into separate cells (1n, 2c), while meiosis II separates sister chromatids into gametes (1n, 1c). Meiosis during gametogenesis. Trisomy 13 Trisomy 13 Trisomy 13, or Patau syndrome, is a genetic syndrome caused by the presence of 3 copies of chromosome 13. As the 3rd most common trisomy, Patau syndrome has an incidence of 1 in 10,000 live births. Most cases of Patau syndrome are diagnosed prenatally by maternal screening and ultrasound. More than half of the pregnancies result in spontaneous abortions. Patau Syndrome (Trisomy 13) is the 3rd most common trisomy Trisomy The possession of a third chromosome of any one type in an otherwise diploid cell. Types of Mutations. Clinical features include brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification and spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: Anatomy malformations, cardiac defects, eye defects, cleft lip Cleft lip The embryological development of craniofacial structures is an intricate sequential process involving tissue growth and directed cell apoptosis. Disruption of any step in this process may result in the formation of a cleft lip alone or in combination with a cleft palate. As the most common craniofacial malformation of the newborn, the diagnosis of a cleft is clinical and usually apparent at birth. Cleft Lip and Cleft Palate/ palate Palate The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates. Palate: Anatomy, and hypotonia Hypotonia Duchenne Muscular Dystrophy. Diagnosis is made by karyotype Karyotype The full set of chromosomes presented as a systematized array of metaphase chromosomes from a photomicrograph of a single cell nucleus arranged in pairs in descending order of size and according to the position of the centromere. Congenital Malformations of the Female Reproductive System analysis. No treatment is available, and most affected individuals do not survive beyond 1 year of life.

References

  1. Gilbert, S.F. Spermatogenesis (2000). In Developmental Biology, 6th ed. Sunderland (MA): Sinauer Associates. https://www.ncbi.nlm.nih.gov/books/NBK10095/
  2. Matsumoto, A.M., Anawalt, B.D. (2020). Male reproductive physiology. UpToDate. Retrieved September 5, 2021, from https://www.uptodate.com/contents/male-reproductive-physiology
  3. Suede, S.H., Malik, A., Sapra, A. (2021). Histology, spermatogenesis. StatPearls. Retrieved September 5, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK553142/
  4. Waters, M., Tadi, P. (2020). Genetics, female gametogenesis. StatPearls. Retrieved September 9, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK555917/
  5. Holesh, J.E., Bass, A.N., Lord, M. (2021). Physiology, ovulation. StatPearls. Retrieved September 9, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK441996/
  6. Desai, N., Ludgin., et al. (2013). Female and male gametogenesis. Chapter 3 of Falcone, T., Hurd, W.W. (Eds.), Clinical Reproductive Medicine and Surgery. Springer Science+Business Media New York. https://www.clevelandclinic.org/ReproductiveResearchCenter/docs/publications/180_Female_and_male_gametogenesis.pdf
  7. Swerdloff, R.S., Wang, C. (2020). The testis and male hypogonadism, infertility, and sexual dysfunction. In: Goldman, L., Schafer, A. I. (Eds.), Goldman-Cecil Medicine, 26th ed., pp. 1537–1547. Elsevier.

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