Reproductive System Flashcards
gonads
Both sexes in humans have
a set of gonads where gametes are produced,
ducts for gamete transport, and
structures for copulation.
Ovaries
Ovaries contain follicles that
develop eggs and
produce sex hormones.
ovulation
An immature egg is ejected from the follicle in a process called ovulation.
Oviducts
Oviducts (Fallopian tubes) convey eggs to the uterus where a fertilized egg develops.
uterus
The uterus opens into the vagina through the cervix.
The vagina
The vagina
receives the penis during sexual intercourse and
forms the birth canal.
Testes
Testes (singular, testis) produce
sperm and
male hormones.
epididymis
The epididymis stores sperm as they develop further.
Several glands contribute to semen. These are the
seminal vesicles,
prostate gland, and
bulbourethral glands.
During ejaculation
sperm is expelled from the epididymis,
seminal vesicles, prostate, and bulbourethral glands secrete into the urethra
semen is formed and expelled from the penis.
Sperm production
is regulated by a negative feedback system of hormones and
involves the
hypothalamus,
hormones of the anterior pituitary (LH and FSH), and
testes (Leydig cells and Seminiferous tubules, respectively).
Spermatogenesis
occurs in seminiferous tubules.
Primary spermatocytes
are formed by mitosis and
divide by meiosis I to produce secondary spermatocytes.
Secondary spermatocytes
divide by meiosis II to produce round spermatids,
spermatids differentiate into elongate sperm, and
mature sperm are released into seminiferous tubules.
Oogenesis
begins when a diploid cell in a developing follicle begins meiosis.
Each month about one primary oocyte resumes meiosis.
A secondary oocyte arrested at metaphase of meiosis II is ovulated.
Meiosis of the ovum is completed after fertilization.
Oogenesis and spermatogenesis are
alike in that both produce haploid gametes but
different in that
oogenesis produces only one mature egg and two polar bodies that degenerate and……..
spermatogenesis produces four mature gametes.
About every 28 days
the hypothalamus signals the anterior pituitary to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH),
which trigger the growth of a follicle and ovulation, the release of an egg.
FSH
FSH targets the follicles, drives growth of the follicle and production on estrogen and an oocyte.
LSH
targets the corpus luteum and drives production of progesterone.
After ovulation,
the ruptured ovarian follicle heals over as the corpus luteum.
The corpus luteum
mostly secretes progesterone, which
stimulates the endometrium to thicken,
prepares the uterus for implantation of the embryo, and
inhibits the hypothalamus, reducing LH secretion.
If the egg is fertilized
the embryo releases hormones that maintain the uterine lining and
menstruation does not occur.
If the egg is not fertilized
the drop in LH shuts down the corpus luteum and its hormones,
menstruation is triggered, and
the hypothalamus and pituitary stimulate development of a new follicle.
Embryonic development
begins with fertilization,
the union of sperm and egg,
to form a diploid zygote.
Sperm are adapted to reach and fertilize an egg
Sperm have
a flagellum comprised of microtubules,
many mitochondria in the midpiece, which provide ATP for tail movements, and
a head that contains a haploid nucleus and is tipped with an acrosome containing enzymes that help it penetrate the egg.
During fertilization,
sperm squeeze past follicle cells,
acrosomal enzymes digest the egg’s jelly coat,
a sperm binds to egg receptors,
sperm and egg plasma membranes fuse,
the sperm nucleus enters the egg cytoplasm,
The vitelline layer separates and becomes impenetrable, and
the egg and sperm nuclei fuse.
Cleavage
is a rapid series of cell divisions that produces
more cells,
smaller cells, and
a fluid-filled embryo called a blastula.
gastrulation
During gastrulation
cells migrate to new locations,
a rudimentary digestive cavity forms, and
the basic body plan of three layers is established with
ectoderm outside—becomes skin and nervous systems,
endoderm inside—becomes digestive tract,
mesoderm in the middle—becomes muscle and bone.
Organs develop
from the three embryonic layers.
notochord
The stiff notochord forms the main axis of the body and is later replaced by the vertebral column in most chordates.
neural tube
The neural tube develops above the notochord and will become the
brain and
spinal cord.
As the embryo elongates, paired somites
form along the sides of the notochord,
hollow out to form a coelom (body cavity located between the intestinal canal and the body wall), and
eventually contribute to muscles, bone, and other connective tissues.
Other systems develop at the same time.
Tissues and organs develop by
changes in cell shape,
cell migration, and
programmed cell death (also called apoptosis).
Pattern formation,
the emergence of the parts of a structure in their correct relative positions,
involves the response of genes to spatial variations of chemicals in the embryo, and
results in tissues and organs developing in their proper positions at the correct times.
gestation
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 (fallopian tubes).
blastocyst
Cleavage produces a blastocyst whose inner cell mass becomes the embryo and the trophoblast, the outer cell layer, which attaches to the uterine wall and forms part of the placenta.
Gastrulation
occurs and organs develop from the three embryonic layers.
4 extraembryonic membranes develop
The amnion
The yolk sac,
The allantois
The chorion
The amnion
surrounds the embryo and
forms a fluid-filled amniotic cavity that protects the embryo.
The yolk sac,
in humans, does not store yolk but is a source of the first blood cells.
The allantois
contributes to the umbilical cord,
forms part of the urinary bladder, and
The chorion
contributes to the placenta and
secretes human chorionic gonadotropin (HCG), which prevents menstruation in mammals.
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, and waste exchange—from embryo to mother.
The first trimester
is the period of greatest change.
The embryo forms, looking like other vertebrate embryos.
Extraembryonic membranes form.
All major organ systems are established.
After 9 weeks from fertilization, the embryo is called a fetus and
can move its arms and legs and
starts to look distinctly human.
During the second trimester,
there is a great increase in the size of the fetus, and
human features are refined.
At 20 weeks (140 days), the fetus - is about 7.6 inches….and
- weighs about 1 lb.
The 3rd trimester is a time of rapid growth
The circulatory and respiratory systems mature.
Muscles thicken and the skeleton hardens.
The third trimester ends with birth.
Babies born as early as 24 weeks may survive only with extensive medical care.
Hormonal changes induce birth.
Estrogen makes the uterus more sensitive to oxytocin and growing fetus stretches uterus.
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.
