types of reproduction

1. ANIMAL REPRODUCTION
Mammalian Reproduction
1. Human reproduction involves intricate anatomy and complex behavior
2. Spermatogenesis and oogenesis both involve meiosis but differ in three
significant ways

2. Human reproduction involves intricate anatomy
and complex behavior
 Reproductive Anatomy of the Human Male.
The mammalian male reproductive system includes the
external genitalia and the internal reproductive organs
 The scrotum and the penis are the external components of the
reproductive system.
 The internal reproductive organs consist of
 the gonads (testes) that produce gametes (sperm cells) and
hormones
accessory sex glands that secrete products essential to sperm
movement
A set of ducts that carry the sperm and glandular secretion.
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3. Reproductive Anatomy of the Human Male
Fig. 46.8

4. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 46.8

5. The scrotum is a fold of the body wall which aids the reproductive
process in different ways:
Testes develop in the abdomen and descend into the scrotum
just before birth. This is important since sperms can not develop
at normal body temperature.
By having the testes hanging outside the abdominal cavity in
the scrotum, the temperature is 2° C lower and sperm production
can occur
In many rodents, the testes are drawn back into the abdominal
cavity, and sperm maturation is interrupted between breeding
seasons.
Some mammals whose body temperature is low enough to
allow sperm maturation, such as monotremes, whales and
elephants retain the testes within the abdominal cavity
permanently.

6. Internal male reproductive organs are:
 The gonads or Testes (singular testis) are the male gonads.
 highly coiled tubules surrounded by layers of connective tissue.
These tubules are the seminiferous tubules.
Sperm form in seminiferous tubules.
Leydig cells, scattered between seminiferous tubules produce
testesterone and other androgens (male sex hormones).
 Sperm pass from the seminiferous
tubules into the tubules of the
epididymis.
 It takes 20 days for sperms to pass
through the 6-m long tubules of each
epididymis of a human male
 During this passage the sperm
become motile and gain the ability
to fertilize.

7. Fig. 46.11
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8.  At ejaculation, sperm are forced from the epididymis, through the vas
deference which is a muscular duct running from epididymis and out of
the scrotum around and behind the urinary bladder to the ejaculatory
duct.
 Each ejaculatory duct forms by the joining of the vas deferens duct
with the duct from the seminal vesicle.
 The two ejaculatory
ducts opens into the
urethra.
The urethra is the
tube that:
Drains both the
excretory and
reproductive systems
Runs through the penis and opens to the outside at the tip of the penis.

9. There are three sets of accessory glands associated with the male
system. These glands add their secretions to the semen (the fluid that
is ejaculated):
(1) A pair of seminal vesicle is located below and behind the bladder
and empty into the ejaculatory duct
Their secretion is thick, yellow and
alkaline
 They secrete a fluid containing
mucous, a coagulating enzyme
(causes semen to coagulate after
deposited in female), fructose
(provides energy for sperm) and
prostaglandins (stimulates female
uterine contractions to help move
semen to the uterus
Seminal vesicle secretion make up
about 60% of the total semen
volume.

10. (2) The prostate gland is the largest of the semen-secreting glands:
Surrounds the upper portion of the urethra and empties directly into it.
It secretes a thin, milky fluid that contains anticoagulating enzymes,
citrate (a sperm nutrient) and is slightly acidic.
Benign (noncancerous)
enlargement of the prostate
occurs in more than half of all
men over the age of 40 and in
virtually all men over 70.
Prostate cancer is one of the
most common cancer in men, it
is treated surgically or with
drugs that inhibit gonado-tropins,
resulting in reduced
prostate activity and size.

11. (3) The bulbourethral glands are a pair of small glands below the
prostate that empty into the urethra at the base of the penis:
 It secretes a clear mucous before ejaculation
 The fluid neutralizes any acidic urine remaining in the urethra.
• A man usually ejaculates about 2 – 5
ml of semen containing about 50–130
million sperm/ml.
•Once in the female reproductive tract,
prostaglandins in the semen stimulate
contractions of the uterine muscles,
which help move the sperm up the
uterus.
•The semen is slightly alkaline
and this neutralizes the acidic
environment of the vagina, protecting
the sperm and increasing their motility.
•When first ejaculated the semen coagulates, making it easier for uterine contractions
to move it along; then anticoagulants liquefy the semen and the sperm begins
swimming through the female tract.

12. The human penis is composed of three layers of spongy erectile
tissue.
 During sexual arousal the erectile tissue fills with blood from
arteries.
 The penis of some mammals (rodents, raccoons walruses )
possesses a baculum, a bone that helps stiffen the penis.
 Temporary impotence, a reversible inability to achieve an
erection can result from the consumption of alcohol and certain
drugs, and emotional problems:
 Several drugs (e.g.Viagra® ) and penile implant devices are
available for men with nonreversible impotence due to
nervous system, or circulatory problems.
 External structure of the penis is covered by a thick skin:
 The head of the penis,the glans penis is covered by thinner
skin. The glans is covered by the prepuce which may be
removed by circumcision.

14.  Reproductive Anatomy of the Human Female.
 External reproductive structures consists of two sets of
labia surrounding the clitoris and vaginal opening.
 Internal reproductive organs consist of a pair of gonads
(ovaries) and a system of ducts and chambers.
 The role of the ducts and chambers are involved with gamete
movement and embryo development .
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15. Fig. 46.9
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16. Fig. 46.9
 Ovaries are the female gonads.
 Located in the abdominal cavity and enclosed in a tough
protective capsule..
 Attached by mesentery to, the uterus.
 Each ovary contains follicles.

17.  Each follicle consists of one egg cell
surrounded by one or more layers of
follicle cells.
 Follicles produce the primary female
sex hormones: estrogens.
 Follicle cells nourish and protect the
developing egg cell.
 A woman is born with about 400,000
follicles.
 Only several hundred of which
will release eggs during a
female’s reproductive years.
 Starting at puberty and continuing to menopause, one follicle
matures and releases its egg cell during each menstrual cycle.
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18.  During ovulation, the egg is expelled from the follicle.
 After ovulation the remaining follicular tissue
develops into the corpus luteum.
Secretes estrogens and progesterone.
Maintain the uterine
lining during pregnancy.
If the egg is not fertilized
(pregnancy does not
occur) the corpus luteum
degenerates and a new
follicle matures during
the next cycle.
Fig. 46.10
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20.  At ovulation the egg is expelled into the abdominal
cavity near the funnel-shaped opening of the
oviduct or fallopian tube.
The cilia-lining the oviduct draws in the egg.
Cilia convey the egg through the oviduct to the uterus.
 The uterus (or Womb) is a thick muscular
organ that can expend during pregnancy to
accommodate a 4 kg fetus.
 The inner uterine lining , the Endometrium is
richly supplied with blood vessels

21. The remaining female
reproductive structures
are:
 Cervix: neck of the
uterus, the opens into
the vagina.
Vagina: thin-walled
chamber that forms the
birth canal and is the
repository for sperm
during copulation.

22. Hymen: A vascularized membrane, usually covers the vaginal
opening from birth until ruptured by vigorous physical activity
or sexual intercourse.
 Vestibule: Chamber-like area bordered by the 2 pairs of skin
folds covering vaginal opening and the separate urethral
opening.
 Labia minora: The slender skin folds bordering the vestibule.
 Labia majora: A pair of thick , fatty ridges enclosing and
protecting the labia minora and vestibule.
 Clitoris: bulb of erectile tissue found at the front edge of the
vestibule. It is covered by a prepuce. It is richly supplied with
nerve endings and is one of the most sensitive points of sexual
stimulation.
 Bartholin’s glands are small glands located near the vaginal
opening that secrete mucous into the vestibule during sexual
arousal.
 The mucous facilitates intercourse by lubricating the vagina

23. Mammary glands.
 Are present in both males and females but
normally function only in women.
 They are important to mammalian reproduction,
although not actually a part of the reproductive
system.
 Consist of small sacs of epithelial tissue that secrete milk.
 Milk drains into a series of ducts opening at the nipple.
 In nonlactating female mammal, the mammary glands are
composed primarily of fatty (adipose) tissue.
 In males, the low level of estrogen prevents the
development of both the secretory apparatus and the fat
deposits, so male breasts remain small, and nipples are not
connected to ducts.
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24. Spermatogenesis and oogenesis both involve
meiosis but differ in three significant ways
 Spermatogenesis is the production of mature sperm
cells in adult males.
 A continuous and process in the adult male.
 Each ejaculation contains 100 – 650 million sperm.
 Occurs in seminiferous tubules.
 Begins with the differentiation of primordial germ cells into
spermatogonia in embryonic testes. Both types of cells are diploid.
 The spermatogonia are located near the outer wall of the seminiferous
tubules. They increase in number through repeated mitosis throughout
development and early life.
 When the male matures, spermatogonia begin to differentiate into
primary spermatocyte which are diploid.
 Primary spermatocyte will pass through several stages before giving rise
to mature spermatozoa:
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25. Fig. 46.11

26.  Each primary spermatocyte undergoes meiosis I to
produce two haploid secondary spermatocytes.
Each secondary spermatocyte undergoes meiosis II to form
two spermatids.
Thus, each primary spermatocyte forms four haploid
spermatids through meiotic division.
 Each spermatid becomes associated with a large Sertoli cell
from which it receives nutrients.
 All spermatids differentiate into mature spermatozoa.
 During spermatogenesis, the developing sperm are gradually
pushed toward the center of the seminiferous tubule and make
their way to epididymis, where they acquire motility.
 The process, from spermatogonia to motile sperm, takes 65 to
75 days in the human male.

27. Spermatozoon (Sperm) structure:
 The thick head contains the haploid nucleus is tipped
with an acrosome which contains enzymes to aid in
egg penetration.
Behind the head the sperm contains many mitochondria that
provide ATP for movement of the tail (flagellum).
 Mammalian sperm shape varies from
species to species.
Fig. 46.12

28. Oogenesis is the development of ova (mature, unfertilized egg cell).
 Begins in the embryo when primordial
germ cells undergo mitotic divisions to
produce diploid oogonia.
 Each oogonium will develop into primary
oocyte by the time of birth of the female,
resulting in all potential ova being present
in the ovaries at birth.
 Between birth and puberty, primary
oocytes enlarge and their surrounding
follicles grow: They replicate their DNA
and enter Prophase and remain there until
activated by hormones (Puberty)
 After puberty during each ovarian cycle,
FSH stimulates a follicle to enlarge and the
primary oocyte completes meiosis I.

29. Meiosis in oogenesis involves
unequal cytokinesis
Meiosis I produces a haploid
secondary oocyte (large) and the
first polar body (much smaller)
Meiosis then stops again
LH triggers ovulation and the
secondary oocyte is released from
the follicle.
If the sperm cell penetrates the
secondary oocytes membrane,
meiosis II will occur and the small
secondary polar body will separate
from the ovum, this completes
oogenesis.

30. The three important differences between spermatogeneis
and oogenesis.
(1) In oogenesis the unequal cytokinesis during meiosis results in
most of the cytoplasm being in one daughter cell which will form
the single ovum the other cells (polar bodies) will degenerate. In
spermatogeneis all four products of meiosis I and II become mature
spermatozoa.
(2) Spermatogenesis is a continuous process throughout the
reproductive life of the male as spermatogonia continue to divide
by mitosis. At the time of the female’s birth an ovary contains all
of the primary oocytes it will ever have.
(3) Spermatogenesis occurs as an uninterrupted sequence; in
oogenesis long “resting” periods occur between the formation of
the initial steps and final production of the ovum.
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31. Fig. 46.13
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