Download chapter 39 * endocrine and reproductive systems - McGann

CHAPTER 39 – ENDOCRINE AND
REPRODUCTIVE SYSTEMS
39-1 – The Endocrine System
The endocrine system is made up of glands that release their products
into the bloodstream. These products deliver messages throughout
the body.
Hormones
• Hormones – the chemicals that send messages from the endocrine
system. They are chemicals released in one part of the body that
travel through the bloodstream and affect the activities of cells in
other parts of the body. Hormones bind to specific chemical
receptors on those cells.
• Target cells – cells that have receptors for a particular hormone
If a cell does not have receptors or the receptors do not respond to a
particular hormone, the hormone has no effect on it.
Glands
• A gland is an organ that produces and releases a substance, or
secretion.
• Exocrine glands – release their secretions through ducts directly to
the organs that use them (sweat, tears, digestive juices)
• Endocrine glands – release their hormones directly into the
bloodstream.
The major endocrine glands in the human body:
Hormone Action
• There are two groups of hormones: steroid hormones and
nonsteroid hormones.
• Steroid hormones are lipids and can cross cell membranes easily,
passing directly into the cytoplasm and into the nuclei of target cells.
Steroid hormones affect gene expression directly and can produce
dramatic changes in cell and organism activity.
• Nonsteroid hormones cannot pass through the cell membrane of
their target cells.
Prostaglandins
• Prostaglandins – modified fatty acids that are produced by a wide
range of cells. They generally affect only nearby cells and tissues, and
are known as “local hormones”
• Some prostaglandins cause smooth muscles, such as those in the
uterus, bronchioles, and blood vessels, to contract. Another group
causes the sensation of pain in most headaches. Aspirin inhibits the
synthesis of these prostaglandins.
Control of Endocrine System
• The endocrine system is regulated by feedback mechanisms that
function to maintain homeostasis.
• For example, the thyroid gland releases a hormone called thyroxine
which controls the rate of metabolism. A drop in thyroxine decreases
the metabolic activity of cells. The activity of the thyroid gland is
controlled by the hypothalamus and the anterior pituitary gland. The
thyroid does not work alone.
Complementary Hormone Action
• Sometimes two hormones with opposite effects act to regulate part
of the body’s internal environment. Many endocrine functions
depend on the complementary effects of two opposing hormones.
39-2 Human Endocrine Glands
• Endocrine glands are scattered throughout the body
• The human endocrine system regulates a wide variety of activities.
Any endocrine not functioning properly could result in a disease or a
disorder.
• The major glands of the endocrine system are the pituitary gland, the
hypothalamus, the thyroid gland, the parathyroid glands, the adrenal
glands, the pancreas, and the reproductive glands.
Pituitary Gland
• Pituitary gland – a bean-sized structure that dangles on a slender
stalk of tissue at the base of the skull. It is divided into two parts: the
anterior pituitary and the posterior pituitary
• The pituitary gland secretes nine hormones that directly regulate
many body functions and controls the actions of several other
endocrine glands.
Hypothalamus
• The hypothalamus controls the secretions of the pituitary gland.
• The thyroid gland is located at the base of the neck and wraps around
the upper part of the trachea.
• The thyroid gland has the major role in regulating the body’s
metabolism.
• Hyperthyroidism is when the thyroid produces too much thyroxine. It
can result in nervousness, elevated body temperature, increased
metabolic rate, increased blood pressure, and weight loss.
• Hypothyroidism is when too little thyroxine is produced. This can
result in lower metabolic rates and body temperature, lack of energy,
and weight gain.
Parathyroid Glands
• The four parathyroid glands are found on the back surface of the
thyroid gland.
• Hormones from the thyroid gland and the parathyroid glands act to
maintain homeostasis of calcium levels in the blood.
Adrenal Glands
• Adrenal glands are two pyramid-shaped structures that sit on top of
the kidneys, one gland on each kidney.
• The adrenal glands release hormones that help the body prepare for
and deal with stress.
• About 80% of an adrenal gland is its adrenal cortex. The adrenal
cortex produces more than two dozen steroid hormones called
cortiscosteroids. One of these hormones, called cortisol, helps
control the rate of metabolism of carbohydrates, fats, and proteins.
• The adrena medulla produces the “fight or flight” response to stress.
This is the feeling you get when you’re excited or scared.
Pancreas
• The pancreas produces enzymes that help breakdown food. The
pancreas also produces hormones called insulin and glucagon.
• Insulin and glucagon help to keep the level of glucose in the blood
stable. When blood glucose levels rise after eating, the pancreas
releases insulin, which takes glucose out of the bloodstream.
When the pancreas fails to produce or properly use insulin, a condition
call diabetes mellitus occurs. In diabetes, the amount of glucose in the
blood may rise so high that the kidneys actually excrete glucose in the
urine. Very high blood glucose levels can damage almost every cell in
the body, including the coronary artery.
There are two types of diabetes: Type I and Type II
• Type I diabetes is an autoimmune disorder that usually develops in
people before they turn 15. They’re bodies make little to no insulin.
They must follow a strict diet and get daily injections of insulin to
keep their blood glucose levels under control.
• Type II diabetes commonly develops in people after the age of 40.
They produce low to normal amounts of insulin, however, their cells
are unable to properly respond to the hormone because the
interaction of the insulin receptors and the insulin is inefficient. In
the beginning, it can be controlled with diet and exercise. Eventually,
they may also need daily shots of insulin.
Reproductive Glands
• The gonads are the body’s reproductive glands. The gonads serve
two important functions: the production of gametes and the
secretion of sex hormones.
• The female gonads are the ovaries. They produce eggs (ova).
• The male gonads are the testes. They produce sperm.
The gonads also produce sex hormones. The ovaries produce estrogen
and progesterone. Estrogen is needed for the development of eggs and
for the formation of the physical characteristics associated with the
female body, like the development of the female reproductive system,
widening of the hips, and development of the breasts. Progesterone
prepares the uterus for the arrival of a developing embryo.
The testes produce testosterone, which is needed for normal sperm
production and the development of physical characteristics associated
with the male body, like facial hair, increase in body size, and
deepening of the voice.
39-3 The Reproductive System
Sexual Development
• For the first six weeks of development, human male and female
embryos are identical in appearance. During the seventh week, major
changes occur. The primary reproductive organs, testes or ovaries,
begin to develop.
• The testes produce testosterone, which is a male sex hormone
needed for sperm production and the development of male physical
characteristics.
• The ovaries produce the female sex hormones estrogen and
progesterone. Estrogen is needed for the development of eggs and
for the formation of female physical characteristics. Progesterone
prepares the uterus for the arrival of a developing embryo.
• Neither the testes nor the ovaries are capable of producing active
reproductive cells until puberty.
• Puberty – a period of rapid growth and sexual maturation during
which the reproductive system becomes fully functional.
• By the end of puberty, the male and female reproductive organs are
fully developed. When puberty begins is different for everyone but
may occur any time between the ages of 9 and 15 and on average
begins a year earlier in females than males.
The Male Reproductive System
• The release of hormones FSH and LH stimulates cells in the testes to
make testosterone. Testosterone produces a number of secondary
sex characteristics that appear in males at puberty such as facial and
body hair, increase in body size, and deepening of the voice.
• The main structures of the male reproductive system are the testes,
the epididymis, the vas deferens, the urethra, and the penis. These
structures work together to produce and deliver sperm.
• Scrotum – an external sac that contains the testes
• Seminiferous tubules – tiny tubules in the testes that are tightly
coiled and twisted together.
Sperm is produced in them.
A sperm cell is made up of a head, which contains the nucleus, a
midpiece, and a tail (flagellum) which propels the cell forward.
• Epididymis – place where sperm fully mature and are stored.
• From the epididymis, some sperm move into a tube called the vas
deferens. The vas deferens merges with the urethra, which is the
tube that leads to the outside of the body through the penis.
• Sperm mixes with a nutrient-rich fluid called seminal fluid. This
combination is called semen. Between 50 and 130 million sperm are
present in 1 milliliter of semen.
The Female Reproductive System
• The main structures of the female reproductive system are the
ovaries, the Fallopian tubes, the uterus, and the vagina. In addition to
producing eggs, the female reproductive system prepares the
female’s body to nourish a developing embryo.
• The ovaries usually produce only one mature ovum each month.
Each ovary contains about 400,000 primary follicles, which are
clusters of cells surrounding a single egg. The follicle helps an egg
mature for release into the reproductive tract where it can be
fertilized.
• An egg is released about every 28 days. This is called ovulation. The
egg is swept into the opening of one of the two Fallopian tubes.
While an egg is in the Fallopian tube, it can be fertilized. Then the egg
goes into the uterus. The lining of the uterus is ready to receive a
fertilized egg.
The Menstrual Cycle
• The menstrual cycle takes on average 28 days. It begins at puberty
and continues until a female is in her mid-forties. The production of
estrogen decreases and menstruation ends permanently at about 51,
but can occur anytime from the late 30s to late 50s.
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 the embryo develops. If the
egg is not fertilized, it is discharged with the lining of the uterus.
• The menstrual cycle has four phases: follicular phase, ovulation,
luteal phase, and menstruation
• The follicular phase begins when the level of estrogen in the blood is
low. Hormones released cause a follicle to mature. The follicle
produces estrogen. The estrogen causes the lining of the uterus to
thicken in preparation of receiving a fertilized egg. The development
of an egg in this stage takes about 10 days.
• Ovulation is the shortest phase in the cycle. It occurs midway through
the cycle and lasts three to four days. Hormones cause the follicle to
rupture and a mature egg is released into one of the Fallopian tubes.
• The luteal phase begins after the egg is released. The egg moves
through the Fallopian tube. The follicle turns yellow and is now called
the corpus luteum. The corpus luteum releases estrogen and
progesterone.
During the first two days of the luteal phase, the chances that an egg
will be fertilized are the greatest. If an egg is fertilized by a sperm, it
will start to divide by the process of cell division known as mitosis.
After several divisions, a ball of cells forms and implants itself in the
lining of the uterus.
If fertilization does not occur, within two to three days of ovulation, the
egg will pass through the uterus without implantation. The corpus
luteum begins to disintegrate. Less estrogen and progesterone is
released. When the level of estrogen falls below a certain point, the
lining of the uterus begins to detach from the uterine wall. This tissue,
along with blood and the unfertilized egg, are discharged through the
vagina. This is called menstruation. After a few days, the cycle begins
all over again.
39-4 Fertilization and Development
• An egg is usually fertilized in a Fallopian tube. During
sexual intercourse, sperm are released when semen is
ejaculated through the penis into the vagina.
• The egg is surrounded by a protective layer that
contains binding sites to which sperm can attach.
When a sperm attaches to a binding site, a sac in the
sperm head releases powerful enzymes that break
down the protective layer of the egg. The sperm
nucleus enters the egg and chromosomes from the
sperm and egg are brought together.
•The process of a sperm joining an egg is
called fertilization.
•The fertilized egg is call a zygote.
Early Development
• While still in the Fallopian tube, the zygote begins to
undergo mitosis.
• About six days after fertilization, the ball of cells,
called a blastocyst, attaches to the wall of the uterus.
This is called implantation.
• During gastrulation, three layers are formed called the
ectoderm, mesoderm, and endoderm. All organs and
tissues will be formed from these layers.
•Placenta – the mother and developing
embryo and supplies the developing
embryo with nutrients and oxygen. It also
eliminates carbon dioxide and metabolic
wastes.
•The placenta is the embryo’s organ of
respiration, nourishment, and excretion.
• At 7 weeks, most of the organs have begun to
form. The heart is beating. By 14 weeks, the
hands, feet, and legs have reached their birth
proportions. Eyes, ears, and nose are well
developed. At full term, the fetus is fully
developed and capable of living on its own.
• About nine months after fertilization, the fetus is
ready for birth. Contractions of the uterus force
the baby out through the vagina. (Sometimes a
caesarean section is needed).