REPRODUCTIVE SYSTEM PHYSIOLOGY pkl 2414437kptx

REPRODUCTIVE SYSTEM
PHYSIOLOGY
I

„INTRODUCTION
Reproductive system ensures the continuation
of species.
 Gonads are the primary reproductive organs
which produce the gametes.
a pair of testes produces sperms in males
a pair of ovaries produces ovum in females.
Normally, most of the animals including humans
are either definite males or definite females.

Sexual Differentiation
Sexual differentiation includes the development of
the gonads, the internal genital tract, and the
external genitalia. "Maleness" or "femaleness"
can be characterized in three ways:
(1) genetic sex, whether the sex chromosomes are
XY or XX
(2) gonadal sex, whether the gonads are testes or
ovaries
(3) phenotypic or genital sex, whether the person
looks like a male or a female

Reproductive organs include:
1. Primary sex organs
2. Accessory sex organs.

Testes are the primary sex organs or gonads in
males.

Accessory sex organs in males are:
1. Seminal vesicles
2. Prostate gland
3. Urethra
4. Penis.

The male gonads are the testes, which have two
functions: spermatogenesis and secretion of
testosterone.
Normally, the testes occupy the scrotum, which lies
outside the body cavity and is maintained at 35°
to 36°C, or 1° to 2°C below body temperature.
This lower temperature, essential for normal
spermatogenesis, is maintained by a
countercurrent arrangement of testicular arteries
and veins, which facilitates heat exchange.

Eighty percent of the adult testis is composed of
seminiferous tubules, which produce the
sperm.
The seminiferous tubules are convoluted loops,
120 to 300 μm in diameter, which are
arranged in lobules and surrounded by
connective tissue.

The epithelium lining the seminiferous tubules
consists of three cell types:
1. Spermatogonia which are the stem cells
2. Spermatocytes which are cells in the process
of becoming sperm
3. Sertoli cells, which support the developing
sperm.

The Sertoli cells
Lining the seminiferous tubules have three
important functions that support
spermatogenesis.
(1) The Sertoli cells provide nutrients to the
differentiating sperm (which are isolated from
the bloodstream).
(2) Sertoli cells form tight junctions with each other,
creating a barrier between the testes and the
bloodstream called the blood-testes barrier.

The blood-testes barrier imparts a selective
permeability, admitting "allowable"
substances such as testosterone to cross but
prohibiting noxious substances that might
damage the developing sperm.
(3) Sertoli cells secrete an aqueous fluid into the
lumen of the seminiferous tubules, which
helps to transport sperm through the tubules
into the epididymis.

The remaining 20% of the adult testis is
connective tissue interspersed with Leydig
cells.
The function of the Leydig cells is synthesis and
secretion of testosterone, the male sex steroid
hormone.

Testosterone has both local (paracrine) effects
that support spermatogenesis in the testicular
Sertoli cells and endocrine effects on other
target organs (e.g., skeletal muscle and the
prostate).

FUNCTIONS OF TESTES
Testes performs two functions:
1. Gametogenic function: Spermatogenesis
2. Endocrine function: Secretion of hormones

SPERMATOGENESIS
Spermatogenesis occurs continuously
throughout the reproductive life of the male,
from puberty until senescence.

Stages of spermatogenic cells
Different stages of spermatogenic cells seen
from periphery to the lumen of seminiferous
tubules are:
1. Spermatogonium
2. Primary spermatocyte
3. Secondary spermatocyte
4. Spermatid.

GAMETOGENIC FUNCTIONS OF
TESTES – SPERMATOGENESIS
Spermatogenesis is the process by which the male
gametes called spermatozoa (sperms) are
formed from the primitive spermatogenic cells
(spermatogonia) in the testis .
It takes 74 days for the formation of sperm from a
primitive germ cell. Throughout the process of
spermatogenesis, the spermatogenic cells have
cytoplasmic attachment with Sertoli cells.
Sertoli cells supply all the necessary materials for
spermatogenesis through the cytoplasmic
attachment.

STAGES OF SPERMATOGENESIS
Spermatogenesis occurs in four stages:
1. Stage of proliferation
2. Stage of growth
3. Stage of maturation
4. Stage of transformation.

1. Stage of Proliferation
Each spermatogonium contains diploid
number (23 pairs) of chromosomes. One
member of each pair is from maternal origin
and the other one from paternal origin. The
23 pairs include 22 pairs of autosomal
chromosomes and one pair of sex
chromosomes.
Sex chromosomes are one X chromosome and
one Y chromosome.

During the proliferative stage, spermatogonia
divide by mitosis, without any change in
chromosomal number. In man, there are
usually seven generations of spermatogonia.
The last generation enters the stage of growth
as primary spermatocyte.
During this stage, the spermatogonia migrate
along with Sertoli cells towards the lumen of
seminiferous tubule.

2. Stage of Growth
In this stage, the primary spermatocyte grows
into a large cell. Apart from growth, there is
no other change in spermatocyte during this
stage.

3. Stage of Maturation
After reaching the full size, each primary
spermatocyte quickly undergoes meiotic or
maturation division, which occurs in two phases:
First phase
In the first phase, each primary spermatocyte
divides into two secondary spermatocytes. The
significance of the first meiotic division is that
each secondary spermatocyte receives only the
haploid or half the number of chromosomes. 23
chromosomes include 22 autosomes and a X or a
Y chromosome.

Second phase
During this phase, each secondary spermatocyte
undergoes second meiotic division, resulting
in two smaller cells called spermatids. Each
spermatid has haploid number of
chromosomes.

4. Stage of Transformation
There is no further division. Spermatids are
transformed into matured spermatozoa
(sperms), by means of spermeogenesis and
released by spermination.

Spermeogenesis
Spermeogenesis is the process by which
spermatids become matured spermatozoa.
Changes taking place during spermeogenesis:
i. Condensation of nuclear material
ii. Formation of acrosome, mitochondrial spiral
filament and tail structures
iii. Removal of extraneous (extra volume of
nonessential) cytoplasm.

Spermination
Spermination is the process by which the
matured sperms are released from Sertoli cells
into the lumen of seminiferous tubules.

FACTORS AFFECTING
SPERMATOGENESIS
Spermatogenesis is influenced by:
1. Sertoli cells
2. Hormones
3. Other factors.

2. Role of Hormones in
Spermatogenesis
Spermatogenesis is influenced by many hormones, which
act either directly or indirectly gives the hormones
essential for each stage of spermatogenesis.
Hormones necessary for spermatogenesis are:
i. Follicle-stimulating hormone (FSH)
ii. Testosterone
iii. Estrogen
iv. Luteinizing hormone (LH)
v. Growth hormone (GH)
vi. Inhibin
vii. Activin.

i. Follicule-stimulating hormone
Responsible for the initiation of
spermatogenesis.
It binds with Sertoli cells and spermatogonia
and induces the proliferation of
spermatogonia. It also stimulates the
formation of estrogen and androgen-binding
protein from Sertoli cells

ii. Testosterone
Testosterone is responsible for the sequence
of remaining stages in spermatogenesis. It is
also responsible for the maintenance of
spermatogenesis.
Testosterone activity is largely influenced by
androgen-binding protein.

iii. Estrogen
Estrogen is formed from testosterone in Sertoli
cells. It is necessary for spermeogenesis.
iv. Luteinizing Hormone
In males, this hormone is called interstitial
cellstimulating hormone. It is essential for the
secretion of testosterone from Leydig cells.

v. Growth Hormone
Growth hormone is essential for the general
metabolic processes in testis. It is also
necessary for the proliferation of
spermatogonia. In pituitary dwarfs, the
spermatogenesis is severely affected.

vi. Inhibin
Inhibin plays an important role in the regulation
of spermatogenesis by inhibiting FSH
secretion through feedback mechanism.

vii. Activin
Activin is also a peptide hormone secreted in
gonads along with inhibin. The exact location
of its secretion in testis is not known. It is
suggested that activin is secreted by Sertoli
cells and Leydig cells.
Activin has opposite actions of inhibin. It
increases the secretion of FSH and accelerates
spermatogenesis.

STORAGE OF SPERM, EJACULATION,
AND FUNCTION OF SEX ACCESSORY
GLANDS
Sperm leave the testes through ducts that carry
them to the epididymis, the primary location
for the maturation and storage of sperm. They
remain viable in the epididymis for several
months.

During sexual arousal, contractions of the
smooth muscle around the ducts advance
sperm through the epididymis.
At ejaculation, sperm are expelled into the vas
deferens and then into the urethra.
The ampulla of the vas deferens provides an
additional storage area for sperm and secretes
a fluid rich in citrate and fructose, which
nourishes the ejaculated sperm.

The seminal vesicles secrete a fluid rich in
fructose, citrate, prostaglandins, and
fibrinogen.
As the vas deferens empties its sperm into the
ejaculatory duct, each seminal vesicle
contributes its secretions, which also will be
nutritive for the ejaculated sperm.

The prostaglandins present in seminal fluid may
assist in fertilization in two ways:
(1) Prostaglandins react with cervical mucus to
make it more penetrable by sperm; and
(2) prostaglandins induce peristaltic contractions
in the female reproductive tract (i.e., the
uterus and fallopian tubes) to propel the
sperm up the tract.

The prostate gland adds its own secretion to the
ejaculate, a milky aqueous solution rich in citrate,
calcium, and enzymes.
The prostatic secretion is slightly alkaline, which
increases sperm motility and aids in fertilization
by neutralizing acidic secretions from the vas
deferens and the vagina.
Collectively, the combined secretions of the male
sex accessory glands compose 90% of the volume
of semen, and sperm compose the remaining
10%.

Pathway for the passage of sperms

„HORMONES SECRETED BY TESTES
Testes secrete male sex hormones, which are
collectively called the androgens.
Androgens secreted by testes are:
1. Testosterone
2. Dihydrotestosterone
3. Androstenedione.

REPRODUCTIVE SYSTEM PHYSIOLOGY pkl 2414437kptx

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