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Title: Human Reproduction
Description: Human reproduction covers male and female reproductive system
Description: Human reproduction covers male and female reproductive system
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Chapter 3
Human Reproduction
Basic Steps in Human Reproduction:
1
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3
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5
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7
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1: Male Reproductive System
The male reproductive system has four main parts:
1
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3
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Testes
Accessory ducts
Glands
External Genitalia
Testes (singular Testis):
•
•
•
Situated in the pelvic region outside the abdominal cavity within a pouch called as scrotum
...
It is a part of the external male
genitalia and is located behind the penis
...
5◦C lower
than the average human body temperature
...
Testis is oval in shape
...
•
Each testis has about 250 compartments called as Testicular lobules
•
•
•
•
Each lobule contains 1-3 highly coiled seminiferous tubules
...
➢ The inner lining of each seminiferous tubule consists of two types of cells: Spermatogonia and
Sertoli cells
...
Each spermatogonium is diploid and contains 46 chromosomes
➢ Sertoli cells provide nutrition to the spermatogonia
➢ Interstitial spaces: These are the regions outside the seminiferous tubules
...
➢ Leydig cells: These are the cells that synthesise and secrete testicular hormones called androgens
...
There are
four accessory ducts in the male reproductive system:
•
•
•
•
Rete Testis
Vasa efferentia
Epididymis
Vas deferens
➢ Rete testis: These are the ducts that connect the seminiferous tubules of the testes to the vasa efferentia
...
➢ Epididymis: It is located on the posterior surface of each testis and opens into the vas deferens
...
It receives
a duct from the seminal vesicle and opens into the urethra as ejaculatory duct
...
➢ Urethra: It is a thin muscular tube
...
It then passes through the penis to
its external opening called as the urethral meatus
...
•
•
•
Seminal vesicles: They contribute approximately 60-75% of the fluid in semen
...
The high fructose
content provides nutrient energy for the spermatozoa
...
This helps in the survival of sperms in the
acidic vaginal environment
...
3
...
The parts of the female reproductive system are:
1
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3
...
5
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7
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It has a narrow lumen and joins the uterus
Uterus:
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•
•
•
•
•
•
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•
It is also called as the womb
It is shaped like an inverted pear
It is attached to the pelvic wall by ligaments
The uterus is the part where the embryo develops into the foetus
The uterus opens into the vagina through a narrow cervix
Uterine wall has three layers of tissues: perimetrium, myometrium and the endometrium
Perimetrium: It is the thin external membranous layer
Myometrium: It is the thick middle layer made up of smooth muscle
...
It undergoes periodic changes during
the menstrual cycle
...
Birth canal: The cervical canal along with the vagina forms the birth canal
External Female Genitalia:
They consist of: mons pubis, labia majora, labia minora, hymen and clitoris
Mons pubis: It is a mass of fatty tissue covered by skin and hair
Labia majora: They are fleshy folds of tissue that extend from the mons pubis and cover the vaginal opening
Labia minora: They are the paired folds of tissue under the labia majora
Hymen: It is a membrane that partially covers the opening of the vagina
...
It can also be broken by active participation in some sports like horseback riding, cycling, etc
...
In some women the hymen can persist even after coitus
...
Clitoris: It is a tiny finger-like projection that lies at the junction of the labia minora above the urethral opening
...
Glandular tissue in each mammary gland consists of 15-20 mammary lobes
...
The milk is stored in the lumen or cavities of the alveoli
The alveoli open into mammary tubules
...
Several mammary ducts join to from a wider mammary ampulla
The mammary ampulla is connected to a lactiferous duct through which milk is sucked out
...
3: Gametogenesis
Gametogenesis is the process by the primary male and female sex organs produce the male and female gametes
respectively
...
The spermatogonia multiply by mitosis to increase in number
...
Each spermatogonium is diploid
...
2
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They contain 23 chromosomes
...
The secondary spermatocytes produce four equal haploid cells after they undergo second meiotic division
...
They contain 23 chromosomes
...
The spermatids undergo spermiogenesis to form spermatozoa or sperms
...
The sperm heads are embedded in the Sertoli cells
6
...
Each
spermatogonium is diploid and contains 46 chromosomes
Primary spermatocytes are spermatogonia that undergo periodic meiosis to form two equal haploid cells
called as the secondary spermatocytes
...
They contain 23 chromosomes
...
They
contain 23 chromosomes
Spermiogenesis is the process by which spermatids mature to form spermatozoa
...
Hormones affecting spermatogenesis:
Gonadotropin releasing hormone (GnRH): It is a hormone secreted by the hypothalamus
...
The increased levels of GnRH stimulates the release of two gonadotropins – Follicle
Stimulating Hormone (FSH) and Luteinizing Hormone (LH), from the anterior pituitary
...
Luteinizing Hormone (LH): LH acts on the Leydig cells and stimulates the synthesis and secretion of androgens
which in turn stimulate the process of spermatogenesis
...
Acrosome is a structure that is filled with digestive enzymes that help in the dissolving the membrane of
the egg cell and help in fertilization of the ovum
...
This
is important for the motility of the sperm which is essential for fertilization
...
At least 60% of them should have normal shape
and size and at least 40% should show vigorous motility
...
It consists of the
sperms and the fluids secreted by the accessory ducts and the accessory glands such as the epididymis,
vas deferens, seminal vesicles, prostate and the bulbourethral glands
...
Oogenesis:
The process of formation of a mature female gamete is oogenesis and it is initiated during the embryonic development
stage
...
No more
oogonia are formed and added after birth
...
The oogonia start the process of meiosis and get arrested at the stage of
Prophase I
...
Each primary oocyte gets surrounded by a layer of granulosa cells and is now called as the primary follicle
...
At puberty, therefore, there
are only about 60,000-80,000 primary follicles in the ovary
...
They now form the secondary follicle
...
The tertiary follicle is characterised by the
presence of a fluid filled cavity called as antrum
...
The primary oocyte grows in size and completes the first meiotic division
...
•
•
•
•
Secondary oocyte retains much of the nutrient rich cytoplasm
...
The secondary oocyte forms a new layer called as the zona pellucida around it
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3
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The cycle of events starting from one menstruation till the next one is called menstrual
cycle
...
The
cycle repeats 28-35 days and normally one egg is released per cycle
...
It is also known as a period or monthly
...
It begins at puberty
...
Menarche signals the beginning of reproductive age in females
...
The age of menopause varies from person to person
...
Phases of the Menstrual Cycle:
Menstrual cycle follows four phases:
1
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3
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Menstrual phase
Follicular phase
Ovulation
Luteal Phase
1
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• It typically lasts from 3-5 days
...
• It occurs when the ovum released by the ovary is not fertilised
...
2
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• The endometrium of the uterus regenerates through proliferation
...
•
•
3
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❖
❖
The levels of gonadotropins gradually increase through the follicular phase
The increased levels of-LH and FSH gonadotropins stimulate follicular development
...
Ovulation/Ovulatory Phase: This is the phase of release of ovum from ovary
• The levels of LH and FSH reach their peak at mid-cycle, around 14th day
...
This induces the rupture of the Graafian follicle and thereby the release of ovum
...
It
is a result of the LH surge which occurs mid-cycle around the 14th day
...
Corpus luteum is
therefore the structure that is formed the ruptured Graafian follicle
...
The endometrium is necessary for the implantation of the fertilised ovum and other
events of pregnancy
...
In absence of pregnancy the corpus luteum degenerates
...
3
...
The motile sperms swim rapidly through the cervix, enter into the uterus and finally reach the
ampullary region of the fallopian tube
...
Fertilisation occurs in the fallopian tube only if the ovum and sperms are simultaneously transferred
into the ampullary region of the fallopian tube
...
During fertilisation the sperm induces changes
in the zona pellucida layer of the ovum that block the entry of additional sperms ensuring that only
one sperm can fertilise an ovum
...
This induces the secondary oocyte to complete meiosis
...
It results in
the formation of a second polar body and a haploid ovum
...
The zygote contains 46
chromosomes
...
As the female is
XX the ovum will always carry the X chromosome
...
Therefore, half of all the sperms carry the X chromosome and the other half carry the Y
chromosome
...
The zygote undergoes mitotic cleavage as it moves along the isthmus of the oviduct towards the
uterus
...
Morula: The embryo with 8-16 blastomeres
...
The blastomeres arrange in
to an outer layer called as the trophoblast
...
The trophoblast attaches to the endometrium
The inner cell mass differentiates to form the embryo
The cells of the uterus divide rapidly and cover the blastocyst
...
This is called as implantation
...
3
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The chorionic villi are surrounded by uterine tissue and maternal blood
...
Placenta supplies oxygen and nutrients to the developing embryo and removes the carbon dioxide and
excretory waste from the foetus
...
The embryo transports nutrients and wastes
to and from the placenta through the umbilical cord
...
It produces several hormones such as human
chorionic gonadotropin (hCG), human placental lactogen (hPL), oestrogens, progesterone, etc
...
During pregnancy production of various hormones is increased
...
High levels of these hormones are essential for supporting
foetal growth, metabolic changes in pregnancy as well as maintenance of pregnancy
...
The
mesoderm develops soon after
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The inner cell mass contains stem cells that have the ability to give rise to all the tissues and organs in the
body
...
7: Parturition and Lactation:
o
o
o
o
o
o
o
o
o
Gestation Period: The average duration of pregnancy is called as gestation period
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A fully developed foetus and placenta induces parturition
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This triggers the release of oxytocin from the mother’s pituitary
...
This leads to stronger and stronger contractions till the baby is expelled out of the uterus through the birth
canal
...
Lactation: The production of milk by the mammary glands of the females towards the end of the pregnancy
is called lactation
...
It is rich in
antibodies that provide resistance and immunity to the new-born
Title: Human Reproduction
Description: Human reproduction covers male and female reproductive system
Description: Human reproduction covers male and female reproductive system