Reproductive System

• Reproductive system


  The human species could not survive without functional male and female reproductive systems
• Reproductive system


  • Plays essential roles in the development of the structural and functional differences between males and females
  • Influences human behavior
  • Produces offspring
• A reproductive system, unlike other organ systems, is not necessary for the survival of an individual human
• Reproductive system functions


  • Production of gametes
  • Fertilization
  • Development and nourishment of a new individual
  • Production of reproductive hormones
• Gametes


  Sex cells, sperm in males, oocytes (eggs) in females
• Meiosis


  A special type of cell division that leads to formation of sex cells
• Meiosis


  1. Before meiosis begins, all the chromosomes are duplicated

  2. At the beginning of meiosis, each of the 46 chromosomes consists of 2 chromatids connected by a centromere

  3. The chromosomes align as pairs in a process called synapsis

  4. Genetic material is exchanged on occasion, when a part of a chromatid of 1 chromosome breaks off and is exchanged with part of another chromatid from the other chromosome, in a process termed, crossing over

  5. Meiosis I produces 2 cells, each having 23 chromosomes composed of 2 chromatids joined at a centromere

  6. During Meiosis II, each of the 2 cells divide into 2 cells and the centromere breaks, giving separate chromosomes

  7. The final result from meiosis are four cells, each having 23 chromosomes

  
• From Fertilization to Fetus

  1. Fertilization: union of sperm and oocyte

  2. Zygote: what develops after fertilization, develops into an embryo 3 to 14 days after fertilization

  3. Embryo: 14 to 56 days after fertilization

  4. Fetus: 56 days after fertilization

  
• Male reproductive system structures

  • Testes
  • Epididymis
  • Ductus deferens
  • Urethra
  • Penis
  • Seminal vesicles
  • Prostate gland
  • Bulbourethral gland
  • Scrotum

  
• Scrotum


  Contains testes, contains dartos muscle that moves scrotum and testes close to and away from body depending on temp, sperm must develop at temp. less than body temp
• Testes


  Primary male reproductive organ, produces sperm, contain seminiferous tubules where sperm is produced, contain interstitial cells that secrete testosterone, contain germ cells that sperm cells arise from, contain sustentacular cells that nourish germ cells and produce hormones

  
• Epididymis


  Thread-like tubules on side of each testis, where seminiferous tubules empty new sperm, where sperm continue to mature develop ability to swim and bind to oocytes

  
• Ductus deferens


  Extends from epididymis and joins seminal vesicle, cut during a vasectomy
• Urethra


  Extends from urinary bladder to end of penis, passageway for urine and male reproductive fluids

  
• Penis


  Corpus cavernosum, corpus spongiosum, spongy urethra: 3 columns of erectile tissue which fill with blood for erection, transfer sperm from male to female, excrete urine

  
• Male reproductive system glands

  • Seminal vesicles
  • Prostate gland
  • Bulbourethral gland

  
• Seminal vesicles


  Next to ductus deferens, helps form ejaculatory duct, provide fructose, contain prostaglandins which decrease mucus thickness around cervix and uterine tubes and help sperm move through female repro. tract, contains coagulants that help deliver semen into female

  
• Prostate gland


  Surrounds urethra, size of a walnut, contains enzymes to liquefy semen after it is inside female, neutralizes acidity of vagina
• Bulbourethral gland


  Small mucus secreting glands near base of prostate gland, neutralize acidity of male urethra and female vagina
• Semen


  Mixture of sperm and secretions from glands, provides a transport medium and nutrients that protect and activate sperm
• Semen composition


  • 60% from seminal vesicles
  • 30% from prostate gland
  • 5% from bulbourethral gland
  • 5% from testes

  
• Path of sperm


  1. Sperm develop in seminiferous tubules (testes)

  2. Epididymis (mature)

  3. Ductus deferens

  4. Receive secretions from seminal vesicles, prostate gland, and bulbourethral gland

  5. Urethra where semen (sperm) exit body
• Spermatogenesis


  Formation of sperm cells, begins at puberty, interstitial cells increase in number and size, seminiferous tubules enlarge, seminiferous tubules produce germ cells and sustentacular cells

  
• Production of sperm cells

  1. Germ cells

  2. Spermatogonia

  3. Primary spermatocytes

  4. Secondary spermatocytes

  5. Spermatids

  6. Sperm cells
• Sperm cell structure


  • Head: contain a nucleus and DNA
  • Midpiece: contain mitochondria
  • Tail: flagellum for movement

  
• Male sex hormones


  • Gonadotropin-releasing hormone (GnRH)
  • Luteinizing Hormone (LH)
  • Follicle-stimulating hormone (FSH)
  • Testosterone
  • Inhibin
• Male puberty


  Sequence of events in which a boy begins to produce male hormones and sperm cells, begins at 12 to 14 and ends around 18, testosterone is major male hormone, secondary sexual characteristics develop
• Male sex act


  1. Emission: movement of sperm cells, mucus, prostatic secretions, and seminal vesicle secretions into the prostatic, membranous, and spongy urethra

  2. Ejaculation: forceful expulsion of the secretions that have accumulated in the urethra to the exterior

  3. Resolution: after ejaculation in which the penis becomes flaccid, an overall feeling of satisfaction exists, and the male is unable to achieve erection and a second ejaculation
• Penile erection


  Neural stimuli cause the penis to enlarge and become firm, parasympathetic action potentials from the sacral region of the spinal cord cause the arteries that supply blood to the erectile tissues to dilate, blood then fills small venous sinuses called sinusoids in the erectile tissue and compresses the veins, which reduces blood flow from the penis
• Penile ejaculation


  Ejaculation results from the contraction of smooth muscle in the wall of the urethra and skeletal muscles surrounding the base of the penis, just before ejaculation, action potentials are sent to the skeletal muscles that surround the base of the penis, rhythmic contractions are produced that force the semen out of the urethra, resulting in ejaculation, in addition, muscle tension increases throughout the body
• Female reproductive organs


  • Ovaries
  • Uterine tubes
  • Uterus
  • Vagina
  • External genitalia
  • Mammary glands
• Penile Ejaculation


  1. Arteries that supply blood to the erectile tissues dilate

  2. Blood fills small venous sinuses called sinusoids in the erectile tissue and compresses the veins, reducing blood flow from the penis

  3. Contraction of smooth muscle in the wall of the urethra and skeletal muscles surrounding the base of the penis

  4. Action potentials sent to the skeletal muscles that surround the base of the penis, producing rhythmic contractions that force the semen out of the urethra

  5. Muscle tension increases throughout the body
• Female Reproductive System


  • Ovaries, uterine tubes, uterus, vagina, external genitalia, and mammary glands
  • Internal reproductive organs located within the pelvis, between the urinary bladder and the rectum

  
• Ovaries


  • Primary female reproductive organ
  • Produces oocytes and sex hormones
  • One on either side of uterus
  • Ovarian ligaments anchor ovaries to uterus
  • Suspensory ligaments anchor ovaries to pelvic cavity
  • Ovarian follicle: cells in ovaries that contain oocytes
• Uterine (Fallopian) Tubes


  • Part of uterus which extends toward ovaries and receive oocytes
  • Fimbriae are fringe-like structures around opening of uterine tubes that help sweep oocyte into uterine tubes
  • Tubal ligation (sterilization of female)
• Uterus


  • Pear sized structure located in pelvic cavity
  • Functions: receive, retain, and provide nourishment for fertilized oocyte, where embryo resides and develops
  • Body: main part
  • Cervix: narrow region that leads to vagina
• Uterus Wall Layers


  • Perimetrium (serous): outermost layer
  • Myometrium (muscular): middle layer composed of smooth muscle
  • Endometrium: innermost layer that is sloughed off during menstruation

  
• Vagina


  • Extends from uterus to outside of body
  • Female copulation organ that receives penis during intercourse
  • Allows menstrual flow
  • Involved in childbirth
  • Contains very muscular walls and a mucous membrane
  • Very acidic to keep bacteria out
• External Female Genitalia


  • Vulva: mons pubis, labia majora and minora, clitoris, and vestibule
  • Mons pubis: fatty layer of skin covering pubic symphysis
  • Labia majora: larger, outer folds of skin, equivalent to male scrotum
  • Labia minora: thin, inner folds of skin
  • Clitoris: small erectile structure located in vestibule, equivalent to male penis
  • Prepuce: where 2 labia minora unite over clitoris
  • Vestibule: space in which vagina and urethra are located
• Ovulation


  1. Release of an oocyte from the ovary

  2. Due to LH secreted from the anterior pituitary

  3. Corpus luteum: mature follicle after ovulation, degenerates if egg is not fertilized