Week 5 Flashcards
Sperm
Sperm are immobile at body temperature;
therefore, the testes are external to the body so
that a correct temperature (2 C° lower than body
temp) is maintained for motility.
* Semen is a mixture of sperm (about 5% of the
total) and fluids from accessory glands that
contribute most of the semen’s volume.
* Sperm are haploid cells, consisting of a
flagellum for motility, a neck that contains the
cell’s energy-producing mitochondria, and a
head that contains the genetic material.
* This structure contains enzymes that can digest
the protective coverings that surround the egg
and allow the sperm to fuse with the egg. An
ejaculate will contain from 50–120 million
sperm per milliliter.
* Sperm form in the walls of seminiferous
tubules that are coiled inside the testes.
Scrotum and testes
- The scrotum houses the testicles and provides
passage for blood vessels, nerves, and muscles
related to testicular function. - The testes are a pair of male gonads that produce
sperm and reproductive hormones. - Each testis is divided into wedge-shaped lobes by
septa. Coiled in each wedge are seminiferous
tubules that produce sperm.
Semininferous tubules
The walls of the seminiferous tubules are
made up of the developing sperm cells,
with the least developed sperm at the
periphery of the tubule and the fully
developed sperm next to the lumen.
* The sperm cells are associated with Sertoli
cells that nourish and promote the
development of the sperm.
* Other cells present between the walls of
the tubules are the interstitial cells of
Leydig, which produce testosterone once
the male reaches adolescence.
* When the sperm have developed flagella,
they leave the seminiferous tubules and enter
the epididymis
Epididymis
The epididymis lies along the top and
posterior of the testes and is the site of
sperm maturation. The sperm leave the
epididymis and enter the vas deferens,
Vas deferens
carries the sperm behind the bladder, and
forms the ejaculatory duct with the duct from
the seminal vesicles.
* During a vasectomy, a section of the vas
deferens is removed, preventing sperm from
being passed out of the body during
ejaculation and preventing fertilization.
Spermatogenesis
- Spermatogenesis occurs in the wall of the Spermatogenesis seminiferous tubules, with the most primitive cells
at the periphery of the tube and the most mature
sperm at the lumen of the tube. - Immediately under the capsule of the tubule are
diploid, undifferentiated cells. These stem cells,
each called a spermatogonium, go through mitosis
to produce one cell that remains as a stem cell and
a second cell called a primary spermatocyte. - The diploid primary spermatocyte goes through
meiosis I to produce two haploid cells called
secondary spermatocytes. - Each secondary spermatocyte divides after meiosis
II to produce two cells called spermatids. - Spermiogenesis is the last stage wherein the
formation of spermatozoa takes place. In the last
stage, the spermatid cells see an increase in the
size of the tail and a decrease in the spermatozoa
head. - Four sperm result from each primary spermatocyte
that goes through meiosis.
FSH in males
- FSH enters the testes and stimulates the Sertoli cells
located in the walls of the seminiferous tubules to
begin promoting spermatogenesis.
LH in males
LH also enters the testes and stimulates the interstitial
cells of Leydig, located in between the walls of the
seminiferous tubules, to make and release
testosterone into the testes and the blood.
Testosterone
- Testosterone stimulates spermatogenesis. This
hormone is also responsible for the secondary sexual
characteristics that develop in the male during
adolescence. - Secondary sex characteristics in males include a
deepening of the voice, the growth of facial, axillary,
and pubic hair, an increase in muscle bulk, and the
beginnings of the sex drive.
Negative feedback system in males
- A negative feedback system occurs in the male
with rising levels of testosterone acting on the
hypothalamus and anterior pituitary to inhibit
the release of GnRH (gonadotropin-releasing
hormone), FSH, and LH. - In addition, the Sertoli cells produce the
hormone inhibin, which is released into the
blood when the sperm count is too high. - This inhibits the release of GnRH and FSH,
which will cause spermatogenesis to slow
down. If the sperm count reaches a low of 20
million/mL, the Sertoli cells cease the release
of inhibin, and the sperm count increases.
Ovary
The outermost layer of the ovary is made up of
follicles, each consisting of one or more
follicular cells that surround, nourish, and
protect a single egg.
Fallopian tubes/oviducts
- The oviducts, or fallopian tubes, extend
from the uterus in the lower abdominal
cavity to the ovaries, but they are not in
contact with the ovaries. - The lateral ends of the oviducts flare out
into a trumpet-like structure and have a
fringe of finger-like projections called
fimbrae. - When an egg is released at ovulation, the
fimbrae help the nonmotile egg enter into
the tube. - The walls of the oviducts have a ciliated
epithelium over smooth muscle. The cilia
beat, and the smooth muscle contracts,
moving the egg toward the uterus. - Fertilization usually takes place within the
oviduct and the developing embryo is
moved toward the uterus. It usually takes
the egg or embryo a week to travel through
the oviduct
Uterus
- The uterus is a structure about the size of
a woman’s fist. The uterus has a thick
muscular wall and is lined with an
endometrium rich in blood vessels and
mucus glands that develop and thicken
during the female cycle. - Thickening of the endometrium prepares
the uterus to receive the fertilized egg or
zygote, which will then implant itself in
the endometrium. The uterus supports
the developing embryo and fetus during
gestation. - The endometrium builds up again in
preparation for implantation.
Cervix
Part of the uterus, called the cervix,
protrudes into the top of the vagina.
Vagina
The vagina is a muscular tube that serves
several purposes. It allows menstrual flow
to leave the body. It is the receptacle for
the penis during intercourse and the
pathway for the delivery of offspring.
Oogenesis
- Oogenesis occurs in the outermost layers of the
ovaries. - Oogenesis starts with a germ cell. In oogenesis,
this germ cell is called an oogonium and forms
during the embryological development of the
individual. - The oogonium undergoes mitosis to produce about
one to two million oocytes by the time of birth. - The primary oocytes begin meiosis before birth.
However, the meiotic division is arrested in its
progress in the first prophase stage. - At the time of birth, all future eggs are in prophase I.
This situation is in contrast with the male reproductive
system in which sperm are produced continuously
throughout the life of the individual. - Starting at adolescence, anterior pituitary hormones
cause the development of a few follicles in an ovary
each month. This results in a primary oocyte finishing
the first meiotic division. - The cell divides unequally, with most of the cytoplasm
and organelles going to one cell, called a secondary
oocyte, and only one set of chromosomes and a small
amount of cytoplasm going to the other cell. This
second cell is called a polar body and usually dies. - Cell division is again arrested, this time at metaphase II.
- At ovulation, the secondary oocyte is released and
travels toward the uterus through the oviduct. - If the secondary oocyte is fertilized, the cell continues
through meiosis II, producing a second polar body and
haploid egg, which fuses with the haploid sperm to
form a fertilized egg (zygote) containing all 46
chromosomes.
Gonads
a specialized organ that contains germ cells which are responsible for producing
the haploid cells required for sexual reproduction.
Gonadotropim
Any hormone having a stimulating effect on the gonads.
Two such hormones are secreted by the anterior pituitary gland:
▪ Follicle-stimulating hormone (FSH)
▪ Luteinizing hormone (LH)
Yellow Body
After ovulation, the follicle in which the egg was located becomes a so-called
yellow body and begins to produce progesterone in addition to estrogen.
Endometrium
The inner mucous membrane lining of the womb (uterus) that undergoes changes
in structure and thickness at different stages of the menstrual cycle, and much of
which is shed at menstruation
Ovulation
Ovulation is the process in which a mature egg is released from the ovary
Menstural Phase
- The menstrual phase is the first stage of the menstrual
cycle when the period (bleeding) occurs - This phase starts when an egg from the previous cycle
isn’t fertilized. - Because pregnancy hasn’t taken place, levels of the
hormones estrogen and progesterone drop. - The thickened lining of the uterus, which would support
a pregnancy, is no longer needed, so it sheds through
the vagina. - During the period, a combination of blood, mucus, and
tissue from your uterus are released. - On average, women are in the menstrual phase of their
cycle for 3 to 7 days.
Follicular Phase
- Starts when the hypothalamus sends a signal
to the pituitary gland to release folliclestimulating hormone (FSH). - FSH stimulates the ovaries to produce
around 5 to 20 small sacs called follicles.
Each follicle contains an immature egg. - The follicular phase starts on the first day of
the period (so there is some overlap with
the menstrual phase) - The maturing follicle sets off a surge in
estrogen that thickens the lining of the
uterus. This creates a nutrient-rich
environment for an embryo to grow. - The average follicular phase lasts for about
16 days. - Only the healthiest egg will eventually
mature. (On rare occasions, a woman may
have two eggs mature.) - The rest of the follicles will be reabsorbed
into the body. - Follicular phase ends when ovulation
occurs.
Ovulation Phase
- Rising estrogen levels during the follicular
phase trigger the pituitary gland to release
luteinizing hormone (LH). This is what
starts the process of ovulation. - Ovulation is when your ovary releases a
mature egg. The egg travels down the
fallopian tube toward the uterus to be
fertilized by sperm. - The ovulation phase is the only time
during the menstrual cycle when a female
can get pregnant. - Symptoms of Ovulation:
oa slight rise in basal body temperature
othicker discharge that has the texture
of egg whites - Ovulation happens at around day 14 if you have a 28-day cycle — right
in the middle of your menstrual cycle. It lasts about 24 hours. After a
day, the egg will die or dissolve if it isn’t fertilized.
Luteal Phase
- After the follicle releases its egg, it changes
into the corpus luteum. - The corpus luteum releases hormones, mainly
progesterone and some estrogen. The rise in
hormones keeps the uterine lining thick and
ready for a fertilized egg to implant. - If a female gets pregnant, her body will
produce human chorionic gonadotropin
(hCG). This is the hormone pregnancy tests
detect. It helps maintain the corpus luteum
and keeps the uterine lining thick. - If pregnancy does not occur, the corpus
luteum will shrink away and be resorbed.
This leads to decreased levels of estrogen
and progesterone, which causes the onset of
the period. - The uterine lining will shed during the
period. - The luteal phase lasts for 11 to 17 days. The
average is 14 days.
