Chapter 11 Reproductive system

• survival of species depends on 


  reproduction, and human species is no exception
• to ensure the continuation of our species 


  some members must produce new individuals to replace those who inevitably die
• humans reproduce sexually 


  process involving the joining of males and female sex cells to produce a zygote, that develops to produce a new individual
• gonads 


  primary sex organs

  produce gametes
• secondary sex organs 


  essential for reproduction

  store gametes, bring them together for fertilisation and support the developing baby
• reproductive system of humans is different than 


  other systems of body

  organs making up system in the male are quite unlike those of the female
• gonads of female 


  two ovaries
• ovaries produce 


  female gametes, ova (eggs)

  each ovary is almond-shape gland approx. 3cm in length

  located completely within the body, one on each side of abdominal cavity supported by ligaments
• stroma 


  mass of connective tissue that composes each ovary

  surrounded by a layer of cells containing numerous germ cells
• each germ cell is enclosed 


  by a follicle, numerous in various stages of development

  as follicle matures, moves to surface of the ovary and ruptures

  egg is expelled into funnel-like opening of uterine tube
• uterine tubes (fallopian tubes/oviducts)


  two, one extending from each ovary

  carry the egg from ovary to uterus
• funnel-like opening near ovary is fringed with


  fimbriae (finger-like projections) that appear to just touch the surface of the ovary

  help guide egg into uterine tube
• lining of tube contains 


  cilia whose movement carries the egg towards uterus

  contraction of smooth muscles in wall of uterine tube also aids in movement of egg
• uterus (womb)


  single, hollow, pear-shaped organ situated behind urinary bladder and in front of rectum

  held in position in pelvic cavity by broad ligaments that allow some movement

  normally tipped forwards over the bladder
• wall of uterus 


  made of mainly smooth muscle with soft mucous lining called endometrium
• uterus has major role to play in

  protecting and nourishing the developing foetus during pregnancy
• cervix

  lower end of uterus/neck of uterus

  protrudes into vagina, a canal leading outside of body that is capable of considerable stretching
• vagina 


  muscular structure around 10cm in length

  lined with mucous membranes

  receives the penis during sexual intercourse

  enlarges to form the birth canal during pregnancy
• hymen 


  fold of tissue that partially covers the external opening of the vagina

  stretched and torn when sex occurs for the first time, but may be torn by other means

  may also remain in place after sex

  presence or absence is not reliable sign of virginity
• vagina opens to the exterior in a region called

  vulva

  made up of external genital organs: labia majora, labia minor and clitoris
• labia majora


  two fleshy folds of skin, made up of fat and fibrous tissue, counting a large number of glands that produce an oily secretion

  outer surfaces are pigmented and, after puberty, covered in hair

  inner surfaces are smooth, lack hair and are moist from oil secretions
• labia minora 


  beneath and between labia majora

  two small folds of skin, pinkish in colour, without fat, lacking pubic hair

  surround space in which urethra and vagina open
• clitoris 


  upper end of labia minor surround clitoris

  contains erectile tissue, blood vessels and nerves

  very sensitive to touch, becoming enlarged with blood when stimulated
• male gonads 


  two testicles

  this is where male gametes, spermatozoa (sperm) are produced
• scrotum


  skin covered pouch that holds and supports the testes

  appears to be single pouch of skin, but internally divided into two sacs, each containing a single testis
• production and development of sperm requires

  temperature that is 2 degrees lower the normal body temperature

  testes lie in the scrotum, outside the body cavity
• with exposure to the cold 


  contraction of smooth muscle fibres in the wall of the scrotum moves the testes closer to the body, where temperature is slightly higher

  if necessary, the same muscles can relax, moving the testes away from the body to keep them cooler
• testis 


  oval shape approx. 4.5cm long and 2.5cm wide and 3cm thick

  internally they are divided between 200-300 lobules, or compartments, filled with fine tubes called seminiferous tubules
• seminiferous tubules 


  are lined with cells that produce the male gametes

  join to form a short, straight tubule

  straight tubules eventually join into ducts, which leave the testies and enter a structure celled the epididymis
• interstitial cells 


  between seminiferous tubules

  secrete male hormone testosterone
• epididymis 


  highly folded tubule that fits against the rear surface of each testis

  sperm from testis enter the tubule of the epidermis where they are stored for up to a month while they mature

  5-6m in length is unravelled, so plenty space for the storage of sperm
• vas deferens 


  tubule of epididymis continues to become vas deferent

  carries the sperm away from the testis

  extends upwards from testis, passes into the abdominal cavity and crosses the upper surface of the bladder , then turns downwards, looping behind the bladder
• urethra

  two vasa deferentia, one from each testis, join urethra which runs from the bladder, through the penis to the exterior

  urethra is a duct for transporting both urine and sperm
• seminal fluid (semen) 


  for the transfer into females body and to reach the egg for fertilisation the sperm must be in a liquid

  this liquid, the semen, nourishes and aids the transport of sperm
• semen is a mixture from

  three glands:

  seminal vesicles

  prostate gland

  bulbo-urethral glands (Cowper's glands)
• seminal vesicles 


  pair of pouch like organs about 5cm in length located behind urinary bladder

  secrete a thick fluid that is rich in sugars and makes up about 60% of the volume of semen
• prostate gland 


  two vasa deferentia join the urethra

  single gland, shaped like a doughnut, which surrounds the urethra just below the bladder

  secretes a thin, milky, alkaline fluid that also becomes part of semen
• bulbo-urethral glands

  two small yellow glands each abut the size of a pea

  located beneath the prostate on either side of the urethra

  secrete clear mucus, carried to the urethra by a duct from each gland

  acts like a lubricant, much of it precedes the emission of the seminal fluid with only a small amount included in the semen
• urethra carries sperm and semen through


  penis to a slit-like opening at the tip

  in reproduction, penis is used to transfer sperm from the male to the vagina of the female
• penis contains 


  connective tissue that has a very rich blood supply

  this erectile tissue has a large number of sponge-like spaces, which fill with blood during sexual arousal

  causes penis to enlarge, stiffen and become erect

  only when penis is erect that to can be successfully introduced into vagina