Transcript chorion - SCIS Teachers

HUMAN REPRODUCTIVE
SYSTEM
HL
TOPIC 11.4
11.4 Reproduction
• Annotate a light micrograph of testis tissue to show the
location and function of interstitial cells (Leydig cells),
germinal epithelium cells, developing spermatozoa and
Sertoli cells.
• Outline the processes involved in spermatogenesis
within the testis, including mitosis, cell growth, the two
divisions of meiosis and cell differentiation.
• State the role of LH, testosterone and FSH in
spermatogenesis.
• Annotate a diagram of the ovary to show the location
and function of germinal epithelium, primary follicles,
mature follicle and secondary oocyte.
• Outline the processes involved in oogenesis within the
ovary, including mitosis, cell growth, the two divisions of
meiosis, the unequal division of cytoplasm and the
degeneration of polar body.
• Draw and label a diagram of a mature sperm and egg.
• Outline the role of the epididymis, seminal vesicle and
prostate gland in the production of semen.
• Compare the processes of spermatogenesis and
oogenesis, including the number of gametes and the
timing of the formation and release of gametes.
• Describe the process of fertilization, including the
acrosome reaction, penetration of the egg membrane by
a sperm and the cortical reaction
• Outline the role of HCG in early pregnancy
• Outline early embryo development up to the implantation
of the blastocyst.
• Explain how the structure and functions of the placenta,
including its hormonal role in secretion of estrogen and
progesterone, maintain pregnancy.
• State that the fetus is supported and protected by the
amniotic sac and amniotic fluid.
• State that materials are exchanged between the
maternal and fetal blood in the placenta.
• Outline the process of birth and its hormonal control,
including the changes in progesterone and oxytocin
levels and positive feedback
GAMETOGENESIS: gamete formation
SPERMATOGENESIS: production of sperms by meiotic
division.
OOGENESIS: production of egg cells by meiotic
division.
ROLES OF HORMONES
• FSH: stimulates testes to produce sperm
• LH: stimulates testes to produce testosterone
• Testosterone:
a. stimulates testes cells (leydig cells) for sperm
production (meiosis)
b. provides secondary sexual characteristics
c. stimulates hypothalamus for the regulation of FSH and
LH secretion and for reproductive behaviors.
HORMONAL
CONTROL OF
MALE
REPRODUCTIVE
SYSTEM
FERTILIZATION
• It takes place in the upper part of the oviduct.
• Uterus muscle contraction helps in drawing semen from
cervix to oviduct.
• When sperms reach to oocyte, they have to pass
glycoprotein layer (zona pellucidia) by using their
hydrolytic enzymes which are stored in their acrosome.
• When a sperm cell contacts with the membrane of an
egg cell sudden block reaction (electric charge changes
on the membrane) takes place to prevent binding of
other sperms.
• Egg cell secretes chemicals (cortical granules) to provide
slow block reaction to prevent binding of other sperms.
• Sperm nucleus is injected into the egg cell and meiotic
division of egg is cell is completed.
STRUCTURE OF A SPERM
CELL
Figure 27.15A–B
Cleavage starts
Fertilization
of mature
egg
Blastocyst
Trophoblast
Uterine
cavity
Cavity
Oviduct
Ovary
Inner cell mass
Blastocyst
(implanted)
Secondary
oocyte
Ovulation
Endometrium
Uterus
Uterine
cavity
Early developmentt of an embryo
Early development: Cleavage
-After fertilization, zygote starts mitotic division.
-Total size of the embryo does not change, the
number of daughter cells increase.
-Embryo reaches to 100 cells in 7 days and it
starts to become embedded into the endometrium.
-Inner cells become fetus.
• Pregnancy, or gestation, is the carrying of
developing young within the female
reproductive tract.
• Human pregnancy
– averages 266 days (38 weeks) from fertilization
or
– 40 weeks (9 months) from the start of the last
menstrual period.
Human development begins with fertilization in the
oviduct.
© 2012 Pearson Education, Inc.
Figure 27.15C
Endometrium
Uterine cavity
Multiplying
cells of
trophoblast
(contribute to
future placenta) Trophoblast
Embryo
Future
yolk sac
Blood vessel
(maternal)
• Four extra embryonic membranes develop.
1. The amnion
• surrounds the embryo and
• forms a fluid-filled amniotic cavity that protects the embryo.
2. The yolk sac,
• in reptiles, stores yolk, in humans, does not store yolk but is a
source of the first germ cells and blood cells.
3. The allantois
• contributes to the umbilical cord,
• forms part of the urinary bladder, and
• in reptiles, stores embryonic waste.
4. The chorion
• contributes to the placenta and
• secretes human chorionic gonadotropin (HCG), which
prevents menstruation in mammals.
© 2012 Pearson Education, Inc.
Figure 27.15D
Yolk sac
Chorion
Amnion
Amniotic
cavity
Mesoderm
cells
Figure 27.15E
Embryo:
Endoderm
Mesoderm
Ectoderm
Chorionic
villi
Chorion
Amnion
Allantois
Yolk
sac
Figure 27.15F
Placenta
Amnion
Amniotic
cavity
Embryo
Mother’s
blood Allantois
vessels
Yolk
sac
Chorion
Chorionic
villi
• The placenta is a
– close association of
• embryonic chorion and
• mother’s blood vessels, and
– site of
• gas exchange—from mother to embryo,
• nutrient exchange—from mother to embryo,
• waste exchange—from embryo to mother
• Antibody exchange- from mother to embryo (passive
immunity)
– Secretion of HCG hormone
• HCG maintains corpus luteum as an endocrine gland,
so secretion of estrogen and progesterone continue in
16 weeks.
• After 16 weeks, placenta secretes estrogen and
progesterone
© 2012 Pearson Education, Inc.
Figure 27.16A–C
January
0
Conception
February
35 days
March
April
63 days
98 days
Figure 27.16C
14 weeks (98 days)
Figure 27.16D–E
May
June
July
August
September
October
280 days
140 days
Figure 27.16D
20 weeks (140 days)
Figure 27.16E
At birth (280 days)
Childbirth is induced by hormones and other
chemical signals
• Hormonal changes induce birth.
– Estrogen makes the uterus more sensitive to
oxytocin.
– Oxytocin acts with prostaglandins to initiate
labor.
– The cervix dilates to about 10 cm.
– The baby is expelled by strong uterine
contractions.
– The placenta dislodges and is expelled after the
baby.
© 2012 Pearson Education, Inc.
Figure 27.17A
Estrogen
from
ovaries
Oxytocin
from fetus and
mother’s pituitary
Induces oxytocin
receptors on uterus
Stimulates
placenta to make
Prostaglandins
Stimulate more
contractions
of uterus
Positive feedback
Stimulates uterus
to contract
Figure 27.17B
Placenta
Umbilical
cord
Uterus
Cervix
1 Dilation of the cervix
2 Expulsion: delivery of the infant
Uterus
Placenta
(detaching)
Umbilical
cord
3 Delivery of the placenta
THE PROCESS OF BIRTH
1- Contractions of uterus muscles pushes the baby
to cervix.
2- Stretching of the cervix
3- stimulation of stretch –sensitive receptors in the
cervix
4- Brain- control centre
5-pituitary gland secretes oxytocin
6-Uterus muscles contract more forcefully
7-further stretching of cervix
8-Birth
9-Decrease in the stretching of cervix breaks the
positive feedback
10. Oxytocin secretion stops.