Reproduction

1. BMICCT 102 - MODULE IX: REPRODUCTIVE
SYSTEM
Unit 1: Formation of semen & spermatogenesis
Unit 2: Brief account of menstrual cycle
By
Sujoy Tontubay
Assistant Professor of Medical Laboratory Technology, iLEAD

2. • A man’s reproductive system is specifically designed to
produce, store, and transport sperm. Unlike the female
genitalia, the male reproductive organs are on both the interior
and the exterior of the pelvic cavity. They include:
• the testes (testicles)
• the duct system: epididymis and vas deferens (sperm duct)
• the accessory glands: seminal vesicles and prostate gland
• the penis

3. • Sperm production occurs in the testicles. Upon
reaching puberty, a man will produce millions of sperm cells
every day, each measuring about 0.002 inches (0.05
millimeters) long.

4. How is sperm produced?
• There is a system of tiny tubes in the testicles. These tubes, called the
seminiferous tubules, house the germ cells that hormones —
including testosterone, the male sex hormone — cause to turn into sperm.
The germ cells divide and change until they resemble tadpoles with a head
and short tail.
• The tails push the sperm into a tube behind the testes called
the epididymis. For about five weeks, the sperm travel through the
epididymis, completing their development. Once out of the epididymis, the
sperm move to the vas deferens.
• When a man is stimulated for sexual activity, the sperm are mixed with
seminal fluid — a whitish liquid produced by the seminal vesicles and the
prostate gland — to form semen. As a result of the stimulation, the semen,
which contains up to 500 million sperm, is pushed out of the penis
(ejaculated) through the urethra.

5. How long does it take to produce new
sperm?
• The process of going from a germ cell to a mature sperm cell
capable of egg fertilization takes around 2.5 months

7. semen
• semen, also called seminal fluid, fluid that is emitted from
the male reproductive tract and that contains sperm cells, which
are capable of fertilizing the female’s eggs. Semen also contains
liquids that combine to form seminal plasma, which helps keep
the sperm cells viable.
• The total volume of semen for each ejaculation of a human male
averages between 2 and 5 ml . In human beings each ejaculation
contains normally 200 to 300 million sperm. Semen frequently
contains degenerated cells sloughed off from the network of
tubules and ducts through which the semen has passed.

8. testis
• testis, plural testes, also called testicle, in animals, the organ that
produces sperm, the male reproductive cell, and androgens, the male
hormones. In humans the testes occur as a pair of oval-shaped organs.
They are contained within the scrotal sac, which is located directly behind
the penis and in front of the anus.
• Anatomy of the testes
• In humans each testis weighs about 25 grams and is 4–5 cm long and 2–3
cm in diameter. Each is covered by a fibrous capsule called the tunica
albuginea and is divided by partitions of fibrous tissue from the tunica
albuginea into 200 to 400 wedge-shaped sections, or lobes. Within each
lobe are 3 to 10 coiled tubules, called seminiferous tubules, which produce
the sperm cells. The partitions between the lobes and the seminiferous
tubules both converge in one area near the anal side of each testis to form
what is called the mediastinum testis.

9. Spermatogenesis
• The seminiferous tubules, in which the sperm are produced, constitute about 90 percent of the
testicular mass. In the young male the tubules are simple and composed of undeveloped sperm-
producing cells (spermatogonia) and the Sertoli cells. In the older male the tubules become
branched, and spermatogonia are changed into the fertile sperm cells after a series of
transformations called spermatogenesis. The Sertoli cells found in both young and adult males
mechanically support and protect the spermatogonia. Each seminiferous tubule of the adult testis
has a central lumen, or cavity, which is connected to the epididymis and spermatic duct (ductus
deferens). Sperm cells originate as spermatogonia along the walls of the seminiferous tubules.
The spermatogonia mature into spermatocytes, which mature into spermatids that mature into
spermatozoa as they move into the central lumen of the seminiferous tubule. The spermatozoa
migrate, by short contractions of the tubule, to the mediastinum testis; they are then transported
through a complex network of canals (rete testis and efferent ductules) to the epididymis for
temporary storage. The spermatozoa move through the epididymis and the spermatic duct to be
stored in the seminal vesicles for eventual ejaculation with the seminal fluid. Normal men
produce about one million spermatozoa daily. In animals that breed seasonally, such as sheep and
goats, the testes regress completely during the nonbreeding season and the spermatogonia
return to the state found in the young, sexually immature males. Frequently in these animals the
testes are drawn back into the body cavity except in the breeding season, when they again
descend and mature; this process is known as recrudescence.

11. Spermatogenesis
• spermatogenesis, the origin and development of the sperm cells within the male reproductive organs, the testes. The testes are
composed of numerous thin tightly coiled tubules known as the seminiferous tubules; the sperm cells are produced within the
walls of the tubules. Within the walls of the tubules, also, are many randomly scattered cells, called Sertoli cells, that function to
support and nourish the immature sperm cells by giving them nutrients and blood products.
• As the young germ cells grow, the Sertoli cells help to transport them from the outer surface of the seminiferous tubule to the
central channel of the tubule. Sperm cells are continually being produced by the testes, but not all areas of the seminiferous
tubules produce sperm cells at the same time. One immature germ cell takes as long as 74 days to reach final maturation, and
during this growth process there are intermittent resting phases.
• The immature cells (called spermatogonia) are all derived from cells called stem cells in the outer wall of the seminiferous tubules.
The stem cells are composed almost entirely of nuclear material. (The nucleus of the cell is the portion containing the
chromosomes.) The stem cells begin their process by multiplying in the process of cell duplication known as mitosis.
Spermatogonia destined to develop into mature sperm cells are known as primary sperm cells. These move from the outer portion
of the seminiferous tubule to a more central location and attach themselves around the Sertoli cells. The primary sperm cells then
develop somewhat by increasing the amount of cytoplasm (substances outside of the nucleus) and structures called organelles
within the cytoplasm. After a resting phase the primary cells divide into a form called a secondary sperm cell. During this cell
division there is a splitting of the nuclear material. In the nucleus of the primary sperm cells there are 46 chromosomes; in each of
the secondary sperm cells there are only 23 chromosomes, as there are in the egg. When the egg and sperm combine and their
chromosomes unite, the characteristics of both individuals blend and the new organism starts to grow. The secondary sperm cell
still must mature before it can fertilize an egg; maturation entails certain changes in the shape and form of the sperm cell. The
nuclear material becomes more condensed and oval in shape; this area develops as the head of the sperm. The head is covered
partially by a cap, called the acrosome, which is important in helping the sperm to gain entry into the egg. Attached to the
opposite end of the head is the tail piece. The tail is derived from the secondary sperm cell’s cytoplasm. In the mature sperm, it
consists of a long, slender bundle of filaments that propel the sperm by their undulating movement. Once the sperm has matured,
it is transported through the long seminiferous tubules and stored in the epididymis of the testes until it is ready to leave the male
body.

13. Sperm
• sperm, also called spermatozoon, plural spermatozoa, male reproductive cell, produced by most animals. With the
exception of nematode worms, decapods (e.g., crayfish), diplopods (e.g., millipedes), and mites, sperm are flagellated;
that is, they have a whiplike tail. In higher vertebrates, especially mammals, sperm are produced in the testes. The
sperm unites with (fertilizes) an ovum (egg) of the female to produce a new offspring. Mature sperm have two
distinguishable parts, a head and a tail.
•
The head of the sperm varies in shape for each animal species. In humans it is flattened and almond-shaped, four to five
micrometres long and two to three micrometres wide (there are about 25,000 micrometres in an inch). The head
portion is mainly a cell nucleus; it consists of genetic substances, called chromosomes, which are responsible for
transmitting specific characteristics of an individual, such as the colour of eyes, hair, and skin. In each body cell of
healthy humans, there are 46 chromosomes, which are responsible for the individual’s general physical makeup. The
sperm cells have only 23 chromosomes, or half of the usual number. When a sperm cell unites with the ovum, which also
has 23 chromosomes, the resulting 46 chromosomes determine the offspring’s characteristics. The sperm cells also carry
the X or Y chromosome that determines the sex of the future child.
• Covering the head of the sperm is a cap known as the acrosome, which contains enzymes that help sperm to enter an
egg. Only one sperm fertilizes each egg, even though 300,000,000 to 400,000,000 sperm are contained in an
average ejaculation. Each egg and sperm produced has slightly different genetic information carried in the
chromosomes; this accounts for the differences and similarities between children of the same parents.

15. Menstruation – Definition
• In a life cycle, a woman’s body is vulnerable to a variety of changes. The cycle
of these changes occur in women every month, positively for pregnancy is
called the menstrual cycle. When an ovum is unfertilized, the uterus lining
sheds and leads to a hemorrhage, called menstruation.

16. • In a girl, menstruation starts from the age of 10 to 15 when she attains puberty
and this beginning is known as menarche. The ending of menstruation is
known as menopause which takes place at the age range of 50.
• The first day of bleeding is marked as the first day of a menstrual cycle and
the period from one menstrual cycle to another can vary from 28 to 30 days.

17. Phases of the Menstrual Cycle
• The menstrual cycle is divided into four phases, namely:
1.Menstrual phase: Day 1, uterus lining which is prepared for implantation starts to
shed which lasts 3 to 5 days.
2.Follicular phase: In this phase, the primary follicle starts developing into a mature
Graafian follicle. The endometrium also starts proliferating. The uterus starts
preparation for another pregnancy.
3.Ovulatory phase: Mid-cycle phase, this is the phase in which ovulation takes place
i.e., day 13-17. The end of the follicular phase along with the ovulation period
defines the fertilization period.
4.Luteal phase: It is the post-ovulation phase, where the fate of the corpus luteum is
decided. If fertilization occurs, pregnancy starts. If fertilization doesn’t occur, it marks
the onset of another cycle.

19. Role of Hormones in Menstrual Cycle
• The chemical messengers in our body called hormones, released by various
endocrine glands are responsible for many changes in a human body.
Menstruation is a slave to certain hormones. Every phase of the menstrual
cycle is influenced by a female hormones namely estrogen, progesterone,
FSH and LH. The variation in the level of each of these hormones decides the
phase which a girl undergoes.
• Let’s have a look at the role of hormones in the menstrual cycle with the help
of a diagram.

20. • Follicle-stimulating hormone
(FSH) and luteinizing
hormone (LH) are secreted by
the anterior pituitary. FSH
stimulates the growth of
ovarian follicles that secrete
estrogen. Progesterone is
secreted by the corpus
luteum.

21. • As we can see in the above diagram, the secretion of FSH and LH gradually
increases during the follicular phase. They stimulate the development of
follicles and the release of estrogen from them. Estrogen stimulates the
proliferation of the endometrium. The level of LH and FSH peaks in the middle
of the cycle. LH induces ovulation. There is a sudden surge in LH level just
before ovulation. After ovulation, the ruptured follicle develops into the corpus
luteum, which secretes progesterone, hence the level of progesterone
increases in the luteal phase. Progesterone is required for the maintenance of
the endometrium for implantation. In the absence of fertilisation, corpus
luteum regresses and progesterone level decreases. It leads to the
disintegration of the endometrium and menstrual flow occurs.

22. Frequently Asked Questions
• What is the duration of a menstrual cycle?
• The duration of a menstrual cycle is usually 28 days. But, under different
physiological conditions, it may vary anywhere between 20 and 40 days.
• What is ovulation?
• Ovulation is a process by which the Graafian follicle ruptures with the consequent
discharge of the ovum into abdominal cavity. This phase is primarily influenced by
the luteinizing hormone. It occurs on the 14th day of menstrual cycle in a normal
cycle of 28 days. During this process, the ovum enters the fallopian tube.
• What is corpus luteum?
• Corpus luteum is a glandular yellow body developed from the ruptured Graafian
follicle after the release of the ovum.