Human Reproduction - 1 Flashcards
describe the external features of testes
The testes are situated outside the
abdominal cavity within a pouch
called scrotum. The scrotum helps
in maintaining the low temperature
of the testes (2–2.5o C lower than
the normal internal body
temperature) necessary for
spermatogenesis. In adults, each
testis is oval in shape, with a length
of about 4 to 5 cm and a width of
about 2 to 3 cm. The testis is
covered by a dense covering( connective tissue).
describe the internal structure of the testes
Each
testis has about 250 compartments
called testicular lobules
(Figure 2.1b).
Each lobule contains one to
three highly coiled seminiferous
tubules in which sperms are
produced. Each seminiferous tubule
is lined on its inside by two types
of cells called male germ cells
(spermatogonia) and Sertoli cells
(Figure 2.2 ). The male germ cells
undergo meiotic divisions finally
leading to sperm formation, while
Sertoli cells provide nutrition to the
germ cells.
what cells are found in the interstitial spaces of testes
The regions outside the
seminiferous tubules called
interstitial spaces, contain small
blood vessels and interstitial cells
or Leydig cells (Figure 2.2). Leydig
cells synthesise and secrete
testicular hormones called
androgens. Other immunologically
competent cells are also present.
describe the accessory ducts of the male repro system
The male sex accessory ducts include rete testis, vasa efferentia,
epididymis and vas deferens (Figure 2.1b). The seminiferous tubules of
the testis open into the vasa efferentia through rete testis. The vasa efferentia
leave the testis and open into epididymis located along the posterior surface
of each testis.
journey of vas deferens
The epididymis leads to vas deferens that ascends to the
abdomen and loops over the urinary bladder. It receives a duct from seminal
vesicle and opens into urethra as the ejaculatory duct (Figure 2.1a). These
ducts store and transport the sperms from the testis to the outside through
urethra. The urethra originates from the urinary bladder and extends
through the penis to its external opening called urethral meatus.
describe male external genitalia
The penis is the male external genitalia (Figure 2.1a, b). It is made up
of special tissue that helps in erection of the penis to facilitate insemination.
The enlarged end of penis called the glans penis is covered by a loose fold
of skin called foreskin
describe secretions of the male repro glands
The male accessory glands (Figure 2.1a, b) include paired seminal
vesicles, a prostate and paired bulbourethral glands. Secretions of these
glands constitute the seminal plasma which is rich in fructose, calcium
and certain enzymes. The secretions of bulbourethral glands also helps
in the lubrication of the penis.
define spermatogenesis and outline its steps
In testis, the immature male germ cells
(spermatogonia) produce sperms by spermatogenesis that begins at
puberty.
i)The spermatogonia (sing. spermatogonium) present on the
inside wall of seminiferous tubules multiply by mitotic division and
increase in numbers. Each spermatogonium is diploid and contains 46
chromosomes.
ii) Some of the spermatogonia called primary
spermatocytes periodically undergo meiosis. A primary spermatocyte
completes the first meiotic division (reduction division) leading to
formation of two equal, haploid cells called
secondary spermatocytes, which have
only 23 chromosomes each.
iii)The secondary
spermatocytes undergo the second meiotic
division to produce four equal, haploid
spermatids (Figure 2.5). What would be the
number of chromosome in the spermatids?
iv)The spermatids are transformed into
spermatozoa (sperms) by the process
called spermiogenesis.
v) After
spermiogenesis, sperm heads become
embedded in the Sertoli cells, and are finally
released from the seminiferous tubules by
the process called spermiation.
describe the hormonal control of spermatogenesis in males
Spermatogenesis starts at the age of
puberty due to significant increase in the
secretion of gonadotropin releasing hormone
(GnRH). This, if you recall, is a hypothalamic hormone. The increased
levels of GnRH then acts at the anterior pituitary gland and stimulates
secretion of two gonadotropins – luteinising hormone (LH) and follicle
stimulating hormone (FSH). LH acts at the Leydig cells and stimulates
synthesis and secretion of androgens. Androgens, in turn, stimulate the
process of spermatogenesis. FSH acts on the Sertoli cells and stimulates secretion of some factors which help in the
process of spermiogenesis.
describe the structure of human sperm
It
is a microscopic structure composed of a head,
neck, a middle piece and a tail (Figure 2.6).
A plasma membrane envelops the whole body
of sperm. The sperm head contains an elongated
haploid nucleus, the anterior portion of which
is covered by a cap-like structure, acrosome.
The acrosome is filled with enzymes that help
fertilisation of the ovum. The middle piece
possesses numerous mitochondria, which
produce energy for the movement of tail that
facilitate sperm motility essential for fertilisation.
what is the condition of sperms required for assured fertilisation
The human male ejaculates about 200 to 300
million sperms during a coitus of which, for
normal fertility, at least 60 per cent sperms
must have normal shape and size and at least
40 per cent of them must show vigorous
motility.
to escape acidic nature amd leucocytes of vagina
what is semen
Sperms released from the seminiferous
tubules, are transported by the accessory
ducts. Secretions of epididymis, vas deferens, seminal vesicle and
prostate are essential for maturation and motility of sperms. The seminal
plasma along with the sperms constitute the semen. The functions of
male sex accessory ducts and glands are maintained by the testicular
hormones (androgens).
