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Title: Class 12 Biology Notes
Description: This Is A Biology Notes About Human Reproduction
Description: This Is A Biology Notes About Human Reproduction
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Class - 12 Biology
Chapter 3 - Human Reproduction
Basic Steps in Human Reproduction:
1
...
Insemination
3
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Blastocyst development
5
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Embryo development
7
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1 Male Reproductive System
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There are four main parts in the male reproductive system:
1
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Accessory ducts
3
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External Genitalia
Testes (singular Testis):
•Situated in the pelvic region outside the abdominal cavity within a pouch called a
scrotum
...
The scrotum is located behind the penis and is considered a part of the external male
genitalia
...
5◦C lower than the average human body
temperature
...
•The lower temperature in testes is required for spermatogenesis as the normal
human body temperature can lead to mutation in the sperms
...
•The testis contains about 250 compartments known as Testicular lobules
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•Seminiferous tubules are the place that forms spermatozoa by the process of
meiosis
...
e
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•These spermatogonia are diploid in nature and called the immature germ cells and
they form the sperm by the process meiosis
...
•Sertoli cells in seminiferous tubules provide nutrition to the spermatogonia
...
•leydig cells synthesize and secretes the testicular hormones called androgens
...
The male reproductive system consists of
four accessory ducts:
•Rete Testis
•Vasa efferentia
•Epididymis
•Vas deferens
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Rete testis: These are the ducts where the seminiferous tubules open into a series
of channels
...
Epididymis: It is a long, coiled tube that connects a testicle to a vas deferens
...
Vas deferens: Vas deferens is a muscular duct that ascends into the abdominal
cavity and makes a loop over the urinary bladder
...
Ejaculatory duct: This duct is situated on each side of the prostate gland
...
Urethra: Urethra is a thin muscular tube that originates from the urinary bladder
and then passes through the penis to its external opening known as the urethral
meatus
...
This secretion mixes with the sperms to nourish and protect them
...
This fluid is rich in enzymes,
proteins, vitamin C, fructose, prostaglandins, and phosphorylcholine
...
•Prostate Gland: The prostate gland is a dense structure that is placed just inferior
to the urinary bladder
...
It helps in the survival of sperms in the acidic vaginal
environment and also improves the motility of the sperms
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3
...
The
female reproductive system made up of several parts:
1
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A pair of oviducts
3
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Cervix
5
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External genitalia
7
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•They produce the female gamete generally called ovum and also produce ovarian
hormones
...
•They are connected to the pelvic wall and uterus with the help of ligaments
...
•Ovarian stroma- It is the matrix of the ovary which is divided into two regions:
➢ Peripheral cortex
➢ Inner medulla
Accessory Ducts:
The accessory ducts of the female reproductive system include the oviducts,
uterus, and vagina
...
•It covers from the periphery region of each ovary to the uterus
...
It is funnel-shaped and possesses fimbriae
...
After ovulation fallopian tube help in the collection of the ovum
...
•Isthmus: This is the last part of the oviduct that extends through the uterine walls
and opens into a narrow lumen
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•It is designed like an inverted pear and attached to the pelvic wall by ligaments
...
•It opens into the vagina via a narrow cervix
...
•Myometrium: It is the thick middle layer that is made up of smooth muscle
...
It
undergoes periodic changes during the menstrual cycle
...
•Cervical canal: The cervical canal connects the cavity of the body of the uterus
with the lumen of the vagina
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External Female Genitalia:
The main external female genitalia of the female reproductive system consist of:
mons pubis, labia majora, labia minora, hymen and clitoris
...
Labia majora: They are fleshy folds of tissue that enclose and protect the external
reproductive organs
...
Labia minora: They are the paired folds of tissue that lies just inside the labia
majora
Hymen: Hymen is a thin membrane that surrounds the opening of the vagina
...
In some women the hymen can continue even after coitus so it shows that
the presence or absence of hymen is not a reliable indication of virginity or sexual
experience
...
Mammary Glands:
All female mammals possess a pair of functional mammary glands
...
•Each mammary gland consists of 15-20 mammary lobes
...
•The secretion of milk takes place by the cells of alveoli
...
•These mammary tubules of each lobe join to form a mammary duct
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•The mammary ampulla is finally connected to a lactiferous duct that empties onto
the surface of the nipple
...
3
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Spermatogenesis: This is the process by which the immature male germ cells
also known as spermatogonia produce mature sperm cells in the testis
...
Spermatogenesis:
The spermatogenesis process starts at puberty and proceeds as follows:
-First of all, the spermatogonia multiply by mitosis to increase in number
...
Each spermatogonia is diploid in nature and contains 46
chromosomes
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These cells are called the secondary
spermatocytes
...
-The secondary spermatocytes further undergo second meiotic division and
produce four haploid spermatids that also contain 23 chromosomes
...
The heads of the sperms are embedded in the Sertoli cells
...
•Spermatogonia: They are the immature male germ cells that undergo meiotic
divisions to form sperms
...
•Primary spermatocytes: These are the spermatogonia that undergo the meiosis
process to form two equal haploid cells called secondary spermatocytes
...
•Secondary spermatocytes: They are haploid in nature and arise from the
primary spermatocytes as a result of meiosis I
...
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•Spermatids: These cells are arising from the secondary spermatocytes as a result
of meiosis II
...
•Spermiogenesis: It is the process by which spermatids mature to form
spermatozoa or sperms
...
Hormones affecting spermatogenesis:
Gonadotropin-releasing hormone (GnRH): Gonadotropin-releasing hormone
is the hypothalamic factor
...
The secretion of GnRH stimulates the release of two gonadotropins from the
anterior pituitary – Follicle Stimulating Hormone (FSH) and Luteinizing
Hormone (LH)
...
Luteinizing Hormone (LH): LH is important in regulating the function of testes
and ovaries
...
Structure of Sperm:
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•Sperm is a male reproductive cell that is made up of a head, neck, middle piece,
and tail
...
•Middle Piece: It comprises several mitochondria that provide energy for the
vigorous motility of the tail
...
•Approximately 200-300 million sperms are released during ejaculation
...
•Semen: It is a milky white organic liquid that is released by the penis at the time
of ejaculation
...
•The testicular hormones also known as androgens maintain the functions of the
male accessory ducts and glands
...
It is introduced during the embryonic development stage
...
After birth, no more oogonia are formed or added
...
•Each primary follicle is formed by primary oocytes which are surrounded by a
layer of granulosa cells
...
Therefore, there are only about 60,000-80,000 primary follicles available in the
ovary at the time of puberty
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•The tertiary follicle is formed by the secondary follicle
...
The layers of theca are arranged into two layers-inner theca interna and the outer
theca externa
...
This division is an unequal division that forms a large secondary oocyte
and a tiny first polar body
...
•The tertiary follicle finally converted into the mature Graafian follicle
...
The process of release of ovum is called ovulation
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4: Menstrual Cycle:
•Menstrual Cycle: This is the reproductive cycle that starts from one
menstruation till the next one
...
The cycle repeats at an interval of 28-35 days and
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normally releases one egg per cycle
...
•Menstruation: In this process, the blood and mucosal tissue are regularly
discharged in a periodic manner
...
This process takes place once in a month and is called periods
...
The actual age for menarche generally differs from person to person
...
•Menopause: Menopause is defined as the permanent ceasing of menstrual cycle
in females
...
menopause
...
Phases of the Menstrual Cycle:
Menstrual cycle follows four phases:
1
...
Follicular phase
3
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Luteal Phase
1
...
•The flow naturally lasts for 3-5 days
...
•This process only takes place in the condition when the ovum released by the
ovary is not fertilized
...
•Some factors like stress, poor diet, poor health, etc
...
2
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•In the ovary, the primary follicles grow to become a fully mature Graafian
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follicle
...
•These changes in endometrium and follicular regeneration are induced by
ovarian hormones- Luteinizing Hormone (LH) and the Follicle Stimulating
Hormone (FSH)
...
The secretion of oestrogens by the growing
follicles is also stimulated by this increased level of LH and FSH
...
Ovulation/Ovulatory Phase: This is the phase where the release of ovum from
ovary takes place
...
•LH surge: The rapid secretion of LH leading to maximum LH level in mid cycle
is called the LH surge
...
•Ovulation: The release of an ovum from a mature Graafian follicle is known as
ovulation
...
1
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•The ruptured parts of the Graafian follicle after ovulation form the yellow body
called corpus luteum
...
The endometrium is required for the implantation of the fertilized
ovum and other events of pregnancy
...
•In absence of fertilization, the corpus luteum degenerates
...
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3
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•The motile male gamete or sperm swims rapidly through the cervix, enters into
the uterus and finally reaches the site of fertilization which is in the ampullary
region of the fallopian tube
...
•Fertilization takes place in the fallopian tube only when the ovum and sperms are
simultaneously transferred into the site of fertilization
...
At the time of fertilization, the sperm makes
changes in the zona pellucida layer of the ovum to block the entry of other sperms
...
•The secretions of the acrosome make easy the entry of the sperm to the ovum by
the zona pellucida and the plasma membrane
...
This is
again an unequal division and forms a second polar body and a haploid ovum
...
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Hence, a zygote contains 46 chromosomes
...
As the female is XX the ovum will always carry the X chromosome
however, Males are XY and therefore, the sperm can contain either X or Y
...
•The zygote that carries a XY would develop into a male while XX would develop
into female
...
This will result in the formation of
2, 4, 8 and 16 daughter cells known as blastomeres
...
•It continues its division as it moves further along into the uterus
...
First is the outer layer called the trophoblast and the
other is inner cell mass which is attached to the trophoblast
...
•The inner cell mass differentiates to cover the blastocyst
...
This phenomenon is
called implantation which leads to pregnancy
...
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Title: Class 12 Biology Notes
Description: This Is A Biology Notes About Human Reproduction
Description: This Is A Biology Notes About Human Reproduction