Reproductive system

1. Reproductive system-1
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
RDGMC

2. Homeostasis?
 Normal functioning of the reproductive system is not
aimed at homeostasis.
 It is not necessary for survival of an individual.
 But it is essential for survival of the species.

3. Overview of male reproductive system
 The essential male reproductive functions are as
follows:
1. Production of sperm (spermatogenesis)
2. Delivery of sperm to the female

4. Overview of female reproductive system
 The essential female reproductive functions
1. Production of ova (oogenesis)
2. Reception of sperm
3. Transport of the sperm and ovum to a common site for
union (fertilization, or conception)
4. Maintenance of the developing fetus until it can
survive in the outside world (gestation, or pregnancy)
5. Giving birth to the baby (parturition)
6. Nourishing the infant after birth by milk production

5. Sex determination
 Sex determination depends on the combination of sex
chromosomes
 Genetic males have both an X and a Y sex chromosome
 Genetic females have two X sex chromosomes.
 Thus, the genetic difference responsible for all the anatomic
and functional distinctions between males and females is
the single Y chromosome.

6. Sex determination
 During fertilization, combination of an X-bearing sperm
with an X-bearing ovum produces a genetic female, XX
 Whereas union of a Y-bearing sperm with an X-bearing
ovum results in a genetic male, XY.
 Thus, genetic sex is determined at the time of
conception and depends on which type of sex
chromosome is contained within the fertilizing sperm.

7. Genetic sex and gonadal sex
 Genetic sex in turn determines gonadal sex, that is, whether testes
or ovaries develop.
 Gonadal specificity appears during the seventh week of intrauterine
life
 Gonadal ridge (undifferentiated gonadal tissue present in both
males and females) of a genetic male begins to differentiate into
testes under the influence of the sex-determining region of the Y
chromosome (SRY), the gene solely responsible for sex
determination.

8. Phenotypic sex
 Phenotypic sex, the apparent anatomic sex of an
individual, is hormonally mediated and depends on the
genetically determined gonadal sex.

9. Sex determination

10. Sex differentiation
 The term sexual differentiation refers to the embryonic
development of the external genitalia and reproductive tract
along either male or female lines.
 Differentiation into a male type reproductive system is
induced by androgens, which are masculinizing hormones
secreted by the developing testes.
 The absence of these testicular hormones in female fetuses
results in the development of a female-type reproductive
system.
 By 10 to 12 weeks of gestation, the sexes can easily be
distinguished by the anatomic appearance of the external
genitalia.

11. Sex differentiation
 In males, the reproductive tract develops from the
Wolffian ducts and the Müllerian ducts degenerate.
 In females the Müllerian ducts differentiate into the
reproductive tract and the Wolffian ducts regress.
 Both duct systems are present before sexual
differentiation occurs, the early embryo has the
potential to develop either a male or a female
reproductive tract.

12. Sex differentiation
 Development of the reproductive tract along male or
female lines is determined by the presence or absence
of two hormones secreted by two different cell types in
the fetal testes—
1. Testosterone produced by the newly developed Leydig
cells
2. Müllerian-inhibiting factor (also known as anti-
Müllerian hormone), produced by the early Sertoli cells

13. Male reproductive system
Dr. Sai Sailesh Kumar G
Associate Professor
Department of Physiology
RDGMC

14. Learning objectives
 Describe the physiological anatomy of the male sexual
organs
 Describe the steps of spermatogenesis
 List the hormones that stimulates spermatogenesis
 Describe the structure of mature sperm
 Describe the role of prostate gland and seminal vesicle
 Describe the composition of semen
 Define the terms- cryptorchidism, oligospermia,
azoospermia.

15. Some important terms
 Azoospermia – Absence of sperm in the ejaculate
 Cryptorchidism – failure of testes to descent from
abdomen into the scrotum at or near the time of birth
 Spermatogenesis – The proliferation and differentiation
of spermatogonia through definite stages of
development to form sperm
 Spermatogonia – immature germ cells in the testes
 Spermiogenesis – The process by which spermatids
mature into spermatozoa

16. Male reproductive system

17. Male reproductive system
 Testis composed of 900 coiled seminiferous tubules
 Sperms are formed in seminiferous tubules
 Then sperms are emptied into epididymis
 Epididymis leads into vasdeferens
 Vas deferens enlarges into the ampula of the vasdeferens
immediately before the vas enters the body of prostate
gland
 Two seminal vesicles on either side of prostate empty into
prostatic end of ampula
 Then to ejaculatory duct and finally urethra which is last
connecting link from testis to exterior

18. Male reproductive system
 In embryo, testes develop from gonadal ridge located in the
rear of the abdominal cavity.
 Late in the fetal life, they will descent slowly, passing out of
abdominal cavity through the inguinal canal into the
scrotum.
 One testes dropping into each of the scrotal sac.
 Testosterone from the fetal testes initiates the decent of
testes.
 Once the testes descend, the opening in the abdominal wall
through which the inguinal canal passes will be closed.

19. Male reproductive system
 Incomplete closure or rupture of this opening permits
abdominal viscera to slip through, resulting in an
inguinal hernia.
 Although the time varies somewhat, descent is usually
complete by the seventh month of gestation.
 As a result, descent is complete in 98% of full-term
baby boys.

20. Cryptorchidism
 Premature male infants the testes are still within the
inguinal canal at birth.
 In most instances of retained testes, descent occurs
naturally before puberty or can be encouraged with
administration of testosterone.
 Rarely, a testis remains undescended into adulthood, a
condition known as cryptorchidism (crypt means
“hidden”; orchid means “testis”).

21. Scrotal location of testes
 The temperature within the scrotum averages several
degrees celsius less than normal body (core)
temperature.
 Descent of the testes into this cooler environment is
essential because spermatogenesis is temperature
sensitive and cannot occur at normal body
temperature.
 Therefore, a cryptorchid is unable to produce viable
sperm.

22. Scrotal location of testes
 The position of the scrotum in relation to the abdominal
cavity can be varied by a spinal reflex mechanism.
 Reflex contraction of scrotal muscles on exposure to a
cold environment raises the scrotal sac to bring the
testes closer to the warmer abdomen.
 Conversely, relaxation of the muscles on exposure to
heat permits the scrotal sac to become more
pendulous, moving the testes farther from the warm
core of the body.

23. Leydig cells
 The testes perform the dual function of producing sperm
and secreting testosterone.
 About 80% of the testicular mass consists of highly coiled
seminiferous tubules, within which spermatogenesis takes
place.
 The endocrine cells that produce testosterone - the Leydig,
or interstitial, cells - lie in the connective tissue (interstitial
tissue) between the seminiferous tubules.
 Thus, the portions of the testes that produce sperm and
secrete testosterone are structurally and functionally
distinct.

24. Testosterone
 Testosterone is a steroid hormone derived from a
cholesterol precursor molecule.
 Once produced, some of the testosterone is secreted
into the blood, where it is transported to its target sites
of action.
 A substantial portion of the newly synthesized
testosterone goes into the lumen of the seminiferous
tubules, where it plays an important role in sperm
production.

25. Mechanism of action
 Testosterone binds with androgen receptors in the
cytoplasm of target cell.
 The androgen-receptor complex moves to the nucleus
 Where it binds with the androgen response element on
DNA
 Leading to transcription of genes
 Genes will direct synthesis of new proteins
 Proteins carry out the desired cellular response.

26. Functions of testosterone
 The effects of testosterone can be grouped into five
categories:
1. Effects on the reproductive system before birth
2. Effects on sex-specific tissues after birth
3. Other reproduction-related effects
4. Effects on secondary sexual characteristics
5. Non-reproductive actions

27. Effects on the reproductive system before birth
 Before birth, testosterone secretion by the Leydig cells
of the fetal testes
1. masculinizes the reproductive tract and external
genitalia
2. promotes descent of the testes into the scrotum

28. Effects on sex-specific tissues after birth
 After birth, testosterone secretion ceases, and the
testes and remainder of the reproductive system
remain small and nonfunctional until puberty.
 Puberty is the period of sexual maturity and the ability
to reproduce.
 It usually begins between the ages of 10 and 14 in
males (between the ages of 9 and 13, in females).

29. Effects on sex-specific tissues after birth
 Puberty encompasses a complex sequence of
endocrine, physical, and behavioral events.
 In both sexes, the reproductive changes that take place
during puberty are
1. enlargement and maturation of gonads
2. development of secondary sexual characteristics
3. achievement of fertility (gamete production)
4. growth and maturation of the reproductive tract
5. attainment of libido (sex drive).

30. Effects on sex-specific tissues after birth
 At puberty in males, the Leydig cells start secreting testosterone
once again.
 Testosterone is responsible for growth and maturation of the
entire male reproductive system.
 Under the influence of the pubertal surge in testosterone
secretion,
1. the testes enlarge and start producing sperm for the first time
2. the accessory sex glands enlarge and become secretory
3. the penis and scrotum enlarge.
 Ongoing testosterone secretion is essential for spermatogenesis
and for maintaining a mature male reproductive tract throughout
adulthood.

31. Andropause?
 Once initiated at puberty, testosterone secretion and
spermatogenesis occur continuously throughout the male’s
life, although testicular efficiency gradually declines after 45
to 50 years of age.
 However, men in their 70s and beyond may continue to
enjoy an active sex life, and some even father a child at this
late age.
 The gradual reduction in circulating testosterone levels and
in sperm is due to degenerative changes associated with
aging that occur in small testicular blood vessels.
 This age-related gradual decline is sometimes mistakenly
termed “male menopause” or “andropause.

32. Other reproduction-related effects
 Testosterone
1. governs development of sexual libido at puberty
2. helps maintain the sex drive in the adult male.
3. negative-feedback control of gonadotropin hormone
secretion by the anterior pituitary.

33. Effects on secondary sexual characteristics
 These nonreproductive male characteristics induced by
testosterone include
1. The male pattern of hair growth (for example, beard and chest
hair)
2. A deep voice caused by enlargement of the larynx and thickening
of the vocal folds
3. Thick skin
4. The male body configuration (for example, broad shoulders and
heavy arm and leg musculature) as a result of protein deposition.
 A male castrated before puberty (a eunuch) does not mature
sexually, nor does he develop secondary sexual characteristics.

34. Nonreproductive actions
 It has a general protein anabolic (synthesis) effect, thus
contributing to the more muscular physique of males.
 It also plays a role in the pubertal growth spurt.
 Testosterone stimulates bone growth,
 Prevents further growth of bones by sealing the
growing ends of the long bones.
 Induces aggressive behavior

35. Conversion of testosterone to estrogen
 a small portion of testosterone secreted by the testes is
converted to estrogen outside the testes by the enzyme
aromatase.
 Aromatase is most abundant in adipose tissue.
 Estrogen receptors have been identified in the testes,
prostate, bone, and elsewhere in males.
 Estrogen even plays an essential role in male
reproductive health.
 it is important in spermatogenesis and, surprisingly,
contributes to male heterosexuality.

36. Spermatogenesis
 About 250 m (800 ft) of sperm-producing seminiferous
tubules are packed within the testes.
 Two functionally important cell types are present in
these tubules.
1. Germ cells, most of which are in various stages of
sperm development.
2. Sertoli cells, which provide crucial support for
spermatogenesis.

37. Spermatogenesis
 Spermatogenesis is a complex process by which
relatively undifferentiated primordial germ cells, the
spermatogonia (each of which contains a diploid
complement of 46 chromosomes), proliferate and are
converted into extremely specialized, motile
spermatozoa (sperm), each bearing a randomly
distributed haploid set of 23 chromosomes.

38. Spermatogenesis
 Microscopic examination of a seminiferous tubule
reveals layers of germ cells in a progression of sperm
development.
 Starting with the least differentiated in the outer layer
and moving inward through various stages of division
to the lumen,
 Where the highly differentiated sperm are ready for exit
from the testis

39. Microscopic examination of a seminiferous
tubule

40. Spermatogenesis
 Spermatogenesis takes 64 days for development from a
spermatogonium to a mature sperm.
 At any given time, different seminiferous tubules are in
different stages of spermatogenesis.
 Up to several hundred million sperm may reach maturity
daily.
 Spermatogenesis encompasses three major stages: mitotic
proliferation, meiosis, and packaging

41. Mitotic proliferation
 Spermatogonia located in the outermost layer of the
tubule continuously divide mitotically.
 one of the daughter cells remains at the outer edge of
the tubule as an undifferentiated spermatogonium, thus
maintaining the germ-cell line.
 The other daughter cell starts moving toward the lumen
while undergoing the various steps required to form
sperm.
 Four primary spermatocytes will be formed by mitotic
proliferation.

42. Mitotic proliferation

43. Meiosis
 Each primary spermatocyte (with a diploid number of
46 doubled chromosomes) forms two secondary
spermatocytes (each with a haploid number of 23
doubled chromosomes) during the first meiotic division
 Finally yielding four spermatids (each with 23 single
chromosomes) as a result of the second meiotic
division.
 No further division takes place beyond this stage of
spermatogenesis.
 Each spermatid is remodeled into a single
spermatozoon.

44. Packaging
 Production of extremely specialized, mobile
spermatozoa from spermatids requires extensive
remodeling, or packaging, of cell elements, a process
alternatively known as spermiogenesis.
 Sperm are essentially “stripped-down” cells in which
most of the cytosol and any organelles not needed for
delivering the sperm’s genetic information to an ovum
have been extruded.
 Thus, sperm travel lightly, taking with them only the
bare essentials to accomplish fertilization.

45. THANK YOU