Transcript Biology

39-3 The Reproductive System
Sexual Development
Sexual Development
In humans, the reproductive system produces,
stores, and releases specialized sex cells known
as gametes.
These cells are released to create the fusion of
sperm and egg to form a zygote, the single cell
from which all cells of the human body develop.
Sexual Development
Puberty is a period of rapid growth and sexual
maturation during which the reproductive system
becomes fully functional.
When puberty ends, reproductive organs are fully
developed.
Puberty usually begins between the ages of 9 and
15, and usually starts one year earlier in females
than in males.
Sexual Development
Puberty begins when the hypothalamus signals the
pituitary to produce increased levels of two hormones
that affect the gonads.
These hormones are follicle-stimulating hormone
(FSH) and luteinizing hormone (LH).
The Male Reproductive System
The Male Reproductive System
Release of FSH and LH stimulates cells in the
testes to produce testosterone.
FSH and testosterone stimulate the development
of sperm.
The Male Reproductive System
The main function of the male
reproductive system is to produce and
deliver sperm.
The Male Reproductive System
A sperm cell consists of:
• a head, which
Head
Nucleus
contains the nucleus
• a midpiece, which
contains energyreleasing
mitochondria
• a tail, which propels
the cell forward
Midpiece
Mitochondria
Tail
The Male Reproductive System
Male Reproductive System
Urinary bladder
Vas deferens
Pubic bone
Seminal vesicle
Urethra
Rectum
Penis
Prostate gland
Epididymis
Testis
Scrotum
Bulbourethral
gland
The Male Reproductive System
The testes are located in an external sac called the
scrotum.
The scrotum is located outside the body cavity, where
it is between 1 and 3 degrees cooler than normal
body temperature. The lower temperature helps
sperm development.
The Male Reproductive System
Within each testis are clusters of hundreds of tiny
tubules called seminiferous tubules.
The seminiferous tubules are tightly coiled and
twisted together.
Sperm are produced in the seminiferous tubules.
Sperm produced in the seminiferous tubules move
into the epididymis, where they mature and are
stored.
The Male Reproductive System
From there, sperm move into a tube called the vas
deferens, which extends up from the scrotum into the
abdominal cavity.
This merges with the urethra, the tube that leads to
the outside of the body through the penis.
The Male Reproductive System
Glands lining the reproductive tract produce seminal
fluid.
Seminal fluid nourishes sperm and protects them
from the acidity of the female reproductive tract.
The combination of sperm and seminal fluid is called
semen.
1 drop = 2, 500, 000
Ejaculation = 200 – 600 million
The Female Reproductive
System
The Female Reproductive System
The primary reproductive organs in the female are
the ovaries.
The ovaries are located in the abdominal cavity.
The Female Reproductive
System
What is the main function of the female
reproductive system?
The Female Reproductive
System
The main function of the female
reproductive system is to produce eggs. In
addition, the female reproductive system
prepares the female's body to nourish a
developing embryo.
The Female Reproductive
System
Female Reproductive System
Fallopian tube
Ovary
Uterus
Urinary bladder
Cervix
Rectum
Pubic bone
Vagina
Urethra
The Female Reproductive
System
Puberty in females starts when the hypothalamus
signals the pituitary gland to release FSH and LH.
FSH stimulates cells within the ovaries to produce
estrogen.
The Female Reproductive
System
Egg Development
Each ovary contains about 400,000 primary
follicles, which are clusters of cells surrounding a
single egg. (only about 400 are active)
The follicle helps an egg mature for release into
the reproductive tract, where it can be fertilized.
Eggs develop within their follicles.
The Female Reproductive
System
Egg Release
When a follicle has matured, its egg is released in
a process called ovulation.
The Female Reproductive
System
The follicle breaks open, and the egg
is swept from the ovary into one of
the two Fallopian tubes.
While in the Fallopian tube, an egg
can be fertilized.
After a few days, the egg passes
from the Fallopian tube into the
uterus.
If the egg is not fertilized it passes
through the cervix, and finally out of
the vagina.
The vagina leads to the outside of
the body.
The Menstrual Cycle
The Menstrual Cycle
The menstrual cycle is controlled by internal
feedback mechanisms between the reproductive
system and the endocrine system.
The cycle takes an average of 28 days.
The Menstrual Cycle
During the menstrual cycle, an egg develops and is
released from an ovary.
The uterus is prepared to receive a fertilized egg.
If the egg is fertilized, it is implanted in the uterus and
embryonic development begins.
If the egg is not fertilized, it is discharged.
The Menstrual Cycle
What are the four phases of the menstrual
cycle?
The Menstrual Cycle
The menstrual cycle has four phases:
• follicular phase
• ovulation
• luteal phase
• menstruation
The Menstrual Cycle
Menstrual Cycle
Ovulation
The Menstrual Cycle
The follicular phase begins when estrogen levels
in the blood are low.
The Menstrual Cycle
The anterior pituitary secretes FSH and LH, which
cause a follicle to develop to maturity.
As the follicle develops, cells surrounding the egg
enlarge and produce more estrogen.
Estrogen causes the lining of the uterus to
thicken.
The Menstrual Cycle
Ovulation
This phase occurs midway through the cycle and
lasts 3–4 days.
The pituitary gland produces more FSH and LH.
The release of these hormones causes the follicle
to rupture, and a mature egg is released into one
of the Fallopian tubes.
The Menstrual Cycle
Luteal Phase
The luteal phase begins after the egg is released.
As the egg moves in the Fallopian tube, the follicle
turns yellow and is called the corpus luteum.
The corpus luteum continues to release estrogen
but also begins to release progesterone.
The Menstrual Cycle
Progesterone stimulates growth and development of
the blood supply and surrounding tissue.
Within a few days of implantation, the uterus and the
growing embryo will release hormones that keep the
corpus luteum functioning for several weeks.
This allows the lining of the uterus to nourish and
protect the developing embryo.
The Menstrual Cycle
Menstruation
If fertilization does not occur, the corpus luteum will
begin to disintegrate.
The follicle breaks down and releases less
hormones, which makes the uterine lining detach.
This tissue, blood, and the unfertilized egg are
discharged through the vagina.
This phase is menstruation, and it lasts 3–7 days.
39-3
Human male and female embryos are identical
until they begin to differentiate at about
a. 7 hours of development.
b. 7 days of development.
c. 7 weeks of development.
d. 7 months of development.
39-3
The process in which a mature egg is released
from the follicle of an ovary is known as
a. fertilization.
b. ovulation.
c. menstruation.
d. meiosis.
39-3
An egg passes from a Fallopian tube into the
cavity of the
a. ovary.
b. vagina.
c. uterus.
d. cervix.
39-3
Which statement best describes male sperm
cells?
a. They are motile, produced in small numbers,
and larger than most body cells.
b. They are motile, produced in large numbers,
and smaller than most body cells.
c. They are nonmotile, produced in small
numbers, and larger than most body cells.
d. They are nonmotile, produced in large
numbers, and smaller than most body cells.
39-3
The menstrual cycle is regulated by hormones
that are controlled by
a. positive feedback mechanisms.
b. ovulation.
c. negative feedback mechanisms.
d. fertilization.
END OF SECTION