anatomy

2. 39-1 The Endocrine System

3. 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.
The chemicals released by the endocrine
system can affect almost every cell in the
body.

4. Hormones
Hormones 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.

5. Hormones bind to specific chemical receptors on
cells.
Cells that have receptors for a particular hormone
are called target cells.
If a cell does not have receptors or the receptors
do not respond to a hormone, that hormone has
no effect on it.

6. A gland is an organ that produces and
releases a secretion. There are two kinds
of glands:
Exocrine glands release
secretions through ducts directly
to the organs that use them.
Endocrine glands release their
secretions directly into the
bloodstream.

7. Hypothalamus
The hypothalamus makes
hormones that control
the pituitary gland. In
addition, the
hypothalamus makes
hormones that are stored
in the pituitary gland.

8. Pituitary gland
The pituitary gland
produces hormones
that regulate many of
the other endocrine
glands.

9. Parathyroid glands
The parathyroid glands
release parathyroid
hormone, which regulates
the level of calcium in the
blood.

10. Thymus
During childhood, the
thymus releases
thymosin, which
stimulates T cell
development and proper
immune response.

11. Adrenal glands
The adrenal glands
release epinephrine and
norepinephrine, which
help the body respond
to stress.

12. Testis
The testes produce
testosterone, which is
responsible for sperm
production and the
development of male
secondary sex
characteristics.

13. Ovary
Ovaries produce
estrogen and
progesterone. Estrogen
is required for the
development of female
secondary sex
characteristics and for
the development of
eggs. Progesterone
prepares the uterus for
a fertilized egg.

14. Pancreas
The pancreas produces
insulin and glucagon,
which regulate the level
of glucose in the blood.

15. Thyroid
The thyroid produces
thyroxine, which
regulates metabolism
throughout the body.

16. Pineal gland
The pineal gland releases
melatonin, which is
involved in rhythmic
activities, such as daily
sleep-wake cycles.

17. Hormone Action
Hormones are classified as
either steroids or nonsteroids.
Steroid hormones are produced
from a lipid called cholesterol.
Nonsteroid hormones include proteins,
small peptides, and modified amino
acids.

18. Steroid Hormones
Steroid hormones can cross cell
membranes easily.

19. Steroid Hormone Action
Hormone-receptor
complex
NucleusNucleus
DNADNA
mRNAmRNA
Protein
synthesis
Altered cellular
function
Receptor
Steroid hormone

20. A steroid
hormone enters a
cell directly
across its
membrane.
It binds to a
receptor to form
a hormone-
receptor
complex.
Steroid hormone
ReceptorHormone-receptor
complex

21. The hormone-
receptor complex
enters the nucleus,
where it binds to a
DNA control
sequence.
Binding initiates
transcription of
genes to mRNA.
NucleusNucleus
DNADNA
mRNAmRNA

22. mRNA moves into the cytoplasm to direct
protein synthesis.
Protein
synthesis
Altered cellular
function

23. Hormone-receptor complexes regulate gene
expression.
Because steroid hormones affect
gene expression directly, they can
produce dramatic changes in cell
and organism activity.

24. Nonsteroid Hormones
Nonsteroid hormones cannot
pass through the cell membrane.

25. A nonsteroid
hormone binds
to receptors on
the cell
membrane.
This activates an
enzyme on the
inside of the
membrane.
Nonsteroid hormone
(first messenger)

26. This enzyme
activates
secondary
messengers that
carry the
message of the
hormone inside
the cell.
These
messengers
activate and
inhibit many cell
activities.
ATP cAMP
(second messenger)
Enzyme
activities
Altered
cellular
function

27. Prostaglandins
All cells (except red blood cells) produce
small amounts of hormonelike
substances called prostaglandins.
Prostaglandins are modified fatty acids.
They affect nearby cells and tissues, and
are known as “local hormones.”

28. The endocrine system is regulated by
feedback mechanisms that function to
maintain homeostasis.
Feedback inhibition = too
much of a substance signals
to stop producing the
substance.

29. Example: Controlling Metabolism
Thyroxine, a hormone of the thyroid
gland, affects the activity of cells
throughout the body, increasing their rate
of metabolism.
A drop in thyroxine decreases the
metabolic activity of cells.

30. If thyroxine is low, the hypothalamus secretes
thyrotropin-releasing hormone (TRH), which
stimulates the anterior pituitary to secrete
thyroid-stimulating hormone (TSH).
TSH stimulates the release of thyroxine.
High levels of thyroxine in the blood inhibit
secretion of TRH and TSH, which stops the
release of additional thyroxine.

31. Controlling
Metabolism

32. The hypothalamus is also sensitive to
temperature.
If body temperature drops, it produces extra TRH.
TSH is released, which causes the release of
more thyroxine.
Thyroxine increases oxygen consumption and
cellular metabolism.
Increased metabolic activity maintains a core
temperature.

33. Complementary Hormone Action
Sometimes two hormones with
opposite effects act to regulate
part of the body’s internal
environment.
Such a complementary system regulates
the level of calcium ions in the
bloodstream.

34. Two hormones that regulate calcium
concentration are calcitonin and parathyroid
hormone (PTH).
Calcitonin decreases the level of calcium in the
blood, while PTH increases it.

35. If calcium levels are too high, the thyroid secretes
calcitonin.
Calcitonin signals the kidneys to reabsorb less
calcium.
Calcitonin also reduces the amount of calcium
absorbed in the intestines and stimulates calcium
deposition in the bones.

36. If calcium levels drop too low, PTH is released by
the parathyroids.
PTH, with vitamin D, stimulates the intestine to
absorb more calcium from food.
PTH also causes the kidneys to retain calcium,
and it stimulates bone cells to release calcium
stored in bone tissue into the bloodstream.

37. 39-2 Human Endocrine Glands

38. 39-2 Human Endocrine Glands
The endocrine glands are scattered throughout
the body.
The human endocrine system regulates a variety
of activities.
Any improper functioning of an endocrine gland
may result in a disease or a disorder.

39. The major glands of the endocrine
system include:
• the pituitary gland
• the hypothalamus
• the thyroid gland
• the parathyroid glands
• the adrenal glands
• the pancreas
• the reproductive glands

40. The pituitary gland secretes nine
hormones that directly regulate
many body functions and controls
the actions of several other
endocrine glands.

41. •The pituitary gland is a structure at the
base of the skull.
•The gland is divided into two parts: the
anterior pituitary and the posterior
pituitary.

42. The Pituitary Gland
Hypothalamus
Pituitary
gland
Posterior
pituitary
Anterior
pituitary

46. The hypothalamus is the part of the brain
attached to the posterior pituitary.
The hypothalamus controls the secretions
of the pituitary gland.

47. Hypothalamus
Pituitary gland

48. The hypothalamus is influenced by hormone
levels in the blood and by sensory information.
Interactions between the nervous system and the
endocrine system take place at the
hypothalamus.
The close connection between the hypothalamus
and the pituitary gland means that the
nervous and endocrine systems
act together to coordinate body
activities.

49. 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.

50. The thyroid produces thyroxine.
Thyroxine regulates the metabolic rate of cells.

51. Thyroid Gland
Larynx
Thyroid gland
Esophagus
Trachea

52. Thyroid Disorders
Hyperthyroidism: the body produces too much
thyroxine. It is characterized by elevated
temperature and metabolic rate, increased blood
pressure, and weight loss.
Hypothyroidism: the body produces too little
thyroxine. It is characterized by lower
temperature and metabolic rate, lack of energy,
and weight gain.
Goiter: enlargement of thyroid gland. Caused by
an iodine deficiency.

53. The four parathyroid glands are found on
the back surface of the thyroid gland.
Hormones from the parathyroid
glands act to maintain
homeostasis of calcium levels in
the blood.

54. Parathyroid glands secrete parathyroid hormone
(PTH).
PTH regulates calcium levels in the blood by
increasing reabsorption of calcium in the kidneys
and by increasing uptake of calcium from the
digestive system.
PTH affects other organ systems, promoting
proper nerve and muscle function and bone
structure.

55. Parathyroid Glands
Thyroid gland
Parathyroid glands

56. The 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.

57. Adrenal Glands
Adrenal gland
Kidney

58. An adrenal gland has
an outer part called
the adrenal cortex
and an inner part
called the adrenal
medulla.
Adrenal
cortex
Adrenal
medulla

59. Adrenal Cortex
•The adrenal cortex produces over 24
steroid hormones.
•The hormone aldosterone regulates
reabsorption of sodium ions and the
excretion of potassium ions by the
kidneys.
•The hormone cortisol controls the rate
of metabolism of carbohydrates, fats,
and proteins.

60. Adrenal Medulla
•The release of hormones from the
adrenal medulla prepares the body for
energy-intense activities.
•The two hormones released by the
adrenal medulla are epinephrine and
norepinephrine.

61. Epinephrine and norepinephrine:
•increase heart rate, blood pressure, and
blood flow to the muscles.
•cause air passageways to open wider,
allowing for an increased intake of
oxygen.
•stimulate the release of extra glucose
into the blood to help produce a sudden
burst of energy.

62. The pancreas has both exocrine
and endocrine functions.
•It is a digestive gland whose
secretions break down food.
•It produces insulin and
glucagon.

63. Insulin and glucagon
(produced by pancreas) help
to keep the level of glucose
in the blood stable.
QuickTimeª and a
decompressor
are needed to see this picture.

64. Insulin stimulates cells in the liver and muscles to
remove sugar from the blood and store it as
glycogen or fat.
Glucagon stimulates the liver to break down
glycogen and release glucose back into the
blood.

65. Maintaining Blood Sugar Levels
•When glucose levels rise, the pancreas
releases insulin.
•Insulin stimulates cells to take glucose
out of the bloodstream.

66. Glucose taken out of circulation is stored
as glycogen in the liver and skeletal
muscles.
In fat tissue, glucose is converted to lipids.
When blood glucose level drops, glucagon
is released from the pancreas.

67. Glucagon stimulates liver cells and skeletal
muscles to break down glycogen and increase
glucose levels.
It causes fat cells to break down fats for
production of carbohydrates.
This makes more chemical energy available and
helps raise the blood glucose level back to
normal.

68. Diabetes Mellitus
•When the pancreas fails to
produce or properly use insulin,
diabetes mellitus occurs.
Blood sugar videoBlood sugar video

69. The gonads are the body’s reproductive
glands.
The gonads serve two
important functions: the
production of gametes, and the
secretion of sex hormones.

70. The female gonads—the ovaries—
produce eggs.
The male gonads—the testes—
produce sperm.
The gonads also produce sex
hormones.

71. The ovaries produce the female sex hormones
estrogen and progesterone.
Progesterone prepares the uterus for the arrival
of a developing embryo.
Estrogen is needed for the development of eggs
and for the formation of physical characteristics
of the female body.

72. The testes produce testosterone, which is needed
for normal sperm production and development of
male physical characteristics.

73. 39-3 The Reproductive System

74. Sexual Development
•In humans, the reproductive system
produces, stores, and releases specialized
sex cells known as gametes.
•Sperm + egg = zygote, the single
cell from which all cells of the
human body develop.

75. •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.

76. 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).

77. 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.

78. The main function of the male
reproductive system is to produce and
deliver sperm.

79. A sperm cell consists
of:
• a head, which
contains the
nucleus
• a midpiece,
which contains
energy-releasing
mitochondria
• a tail, which
propels the cell
forward
Head
Nucleus
Midpiece
Mitochondria
Tail

80. Male Reproductive System
Urinary bladder
Vas deferens
Pubic bone
Urethra
Penis
Seminal vesicle
Rectum
Prostate gland
Bulbourethral
gland
Scrotum
Testis
Epididymis

81. 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.

82. 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.

83. From there, sperm move into a tube called the vas
deferens, which extends up from the scrotum into
the abdominal cavity.
The vas deferens merges with the
urethra, the tube that leads to the
outside of the body through the
penis.

84. 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.

85. Male reproductive diagram
Seminiferous tubules- In testes,
where sperm are made (meiosis)
Epididymis- where sperm matures &
waits
Vas deferens- tube from testes
Urethra- where sperm
& urine exit

86. The Female Reproductive System
•The primary reproductive organs in the
female are the ovaries.
•The ovaries are located in the
abdominal cavity.

87. 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.

88. Fallopian tube
Ovary
Uterus
Urinary bladder
Pubic bone
Urethra
Vagina
Rectum
Cervix
Female Reproductive System

89. 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.
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decompressor
are needed to see this picture.

90. Egg Development
•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.
•Eggs develop
within their follicles. QuickTimeª and a
decompressor
are needed to see this picture.

91. Egg Release
•When a follicle has matured, its
egg is released from the ovary in
a process called ovulation.
•The follicle breaks open,
and the egg is swept
from the ovary into one
of the two Fallopian
tubes.
QuickTimeª and a
decompressor
are needed to see this picture.

92. •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.

93. The Menstrual Cycle
•The menstrual cycle is controlled by
internal feedback mechanisms between
the reproductive system and the
endocrine system.
•The menstrual cycle takes an
average of 28 days.

94. 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.

95. The menstrual cycle has four phases:
•follicular phase
•ovulation
•luteal phase
•menstruation

96. The Menstrual
Cycle
Menstrual Cycle
Ovulation

97. •The follicular phase begins when
estrogen levels in the blood are low.

98. •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.

99. 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.
QuickTimeª and a
decompressor
are needed to see this picture.

100. 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.

101. 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.

102. 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.

103. Sexually Transmitted Diseases
•Diseases that spread from one person
to another during sexual contact are
called sexually transmitted diseases
(STDs).
•STDs are a serious problem in the U.S.,
infecting millions of people each year
and accounting for thousands of deaths.

104. STDs caused by bacteria include chlamydia,
syphilis, and gonorrhea.
STDs caused by viruses include hepatitis B,
genital herpes, genital warts, and HIV/AIDS.

105. Female reproductive diagram
Ovary- egg develops & is released
Fallopian tube- Fertilization
usually happens here
Uterus- Where baby develops
Vagina- birth canal
QuickTimeª and a
decompressor
are needed to see this picture.

106. 39–4 Fertilization
and Development

107. When an egg is fertilized, human development
begins.
In this process, a single cell undergoes a series
of cell divisions that results in the formation of a
new human being.

108. Fertilization
•During sexual intercourse, sperm are
released when semen is ejaculated
through the penis into the vagina.
•Sperm swim through the uterus into the
Fallopian tubes.
•if an egg is present in one of the
Fallopian tubes, its chances of being
fertilized are good.

109. 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, its head
releases 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.

110. The process of a sperm joining an egg is
called fertilization.

111. Fertilization
After the two haploid (N) nuclei fuse,
a single diploid (2N) nucleus is
formed.
A diploid cell has a set of
chromosomes from each parent cell.
The fertilized egg is called a zygote.

112. Early Development
•While still in the Fallopian tube, the
zygote begins to undergo mitosis.
•Four days after fertilization, the embryo
is a solid ball of about 64 cells called a
morula.

113. The stages of early development
include implantation, gastrulation,
and neurulation.

114. Implantation
•As the morula grows, it becomes a
hollow structure with an inner cavity
called a blastocyst.
•6–7 days after fertilization, the
blastocyst attaches to the uterine wall.
•The embryo secretes enzymes that
digest a path into it.
•This process is known as implantation.

115. Fertilization
Fertilization and Implantation

116. Blastocyst cells specialize due to the activation
of genes.
This process, called differentiation, is responsible
for the development of the various types of tissue
in the body.

117. A cluster of cells, known as the inner cell mass,
develops within the inner cavity of the blastocyst.
The embryo will develop from these cells, while
the other cells will differentiate into tissues that
surround the embryo.

118. Gastrulation
•The inner cell mass of the blastocyst
gradually sorts itself into two layers,
which then give rise to a third layer.

119. Mesoderm
Amniotic cavity
Primitive
streak
Ectoderm
Endoderm
Early Development
The third layer is produced by a process of cell
migration known as gastrulation.

120. The result of gastrulation is the
formation of three cell layers—the
ectoderm, the mesoderm, and the
endoderm.
Amniotic cavity
Primitive
streak
Ectoderm
Endoderm
Mesoderm

121. The ectoderm develops into the skin and nervous
system.
The endoderm forms the digestive lining and
organs.
Mesoderm cells differentiate into internal tissues
and organs.

122. Neurulation
•Gastrulation is followed by neurulation.
•Neurulation is the development
of the nervous system.

123. Shortly after gastrulation is complete, a block of
mesodermal tissue begins to differentiate into the
notochord.

124. Neural crest Neural fold
Notochord
•As the notochord develops, the neural
groove changes shape, producing neural
folds.

125. Neural crest Neural tube
Ectoderm
Notochord
•Gradually, these folds move together to
create a neural tube from which the
spinal cord and the nervous system
develop.

126. Extraembryonic Membranes
•As the embryo develops, membranes
form to protect and nourish the embryo.
•Two of these membranes are the
amnion and the chorion.

127. •The amnion
develops into a
fluid-filled
amniotic sac.
•The amniotic
sac cushions
and protects
the
developing
embryo.
Uterus
Amnion
Fetus
Amniotic sac
Placenta
Umbilical cord

128. Fingerlike projections called chorionic villi form
on the outer surface of the chorion and extend
into the uterine lining.
Fetal portion
of placenta
Maternal portion
of placenta
Maternal
artery
Maternal
vein
Umbilical
vein
Umbilical
arteries
Umbilical cord
Amnion
Chorionic villus
Mom & Mom &
baby baby
blood do blood do
NOT NOT
mix!!mix!!

129. The chorionic villi and uterine lining form the
placenta.
The placenta
•Lies between the
uterus and the
developing embryo
•provides nutrients
to the fetus.

130. The placenta is the embryo's organ of
respiration, nourishment, and excretion.

131. The placenta acts as a barrier to some harmful or
disease-causing agents.
Some disease causing agents, such as German
measles and HIV can cross the placenta.
Some drugs, including alcohol and medications
also can penetrate the placenta and affect
development.

132. After eight weeks, the embryo is called a
fetus.
After three months, most major organs and
tissues are formed. During this time, the
umbilical cord also forms.
The umbilical cord connects
the fetus to the placenta.

133. Control of Development
•The fates of many cells in the early
embryo are not fixed.
•The inner cell mass contains embryonic
stem cells, unspecialized cells that can
differentiate into nearly any specialized
cell type.
•Researchers are still learning the
mechanisms that control stem cell
differentiation.

134. Later Development
•4–6 months after fertilization:
•The heart can be heard with a
stethoscope.
Bone replaces cartilage that forms
the early skeleton.
A layer of soft hair grows over the
fetus’s skin.
The fetus grows and the mother can
feel it moving.

135. During the last three months, the organ systems
mature.
•The fetus doubles in mass.
•It can now regulate its body
temperature.
•The central nervous system and lungs
completely develop.

136. Childbirth
•About nine months after fertilization, the
fetus is ready for birth.
•A complex set of factors affects the
onset of childbirth.

137. The mother’s posterior pituitary gland releases
the hormone oxytocin, which affects involuntary
muscles in the uterine wall.
These muscles begin rhythmic contractions
known as labor.
The contractions become more frequent and
more powerful.

138. The opening of the cervix expands until it is large
enough for the head of the baby to pass through
it.
At some point, the amniotic sac breaks, and the
fluid it contains rushes out of the vagina.
Contractions force the baby out through the
vagina.

139. The baby now begins an independent existence.
Its systems quickly adapt to life outside the
uterus, supplying its own oxygen, excreting
waste on its own, and maintaining its own body
temperature.

140. Multiple Births
Multiple Births
•If two eggs are released during the
same cycle and fertilized by two different
sperm, fraternal twins result.
•A single zygote may split apart to
produce two embryos, which are called
identical twins.

141. Early Years
•The first two years of life are called
infancy. It is a period of rapid growth and
development.
•Childhood lasts from infancy until
puberty.
•Adolescence begins with puberty and
ends with adulthood.
•Puberty produces a growth spurt that
will conclude in mid-adolescence.

142. Adulthood
•Development continues during
adulthood.
•Adults reach their highest levels of
physical strength and development
between the ages of 25 and 35.
•Most people begin to show signs of
aging in their 30s.
•Around age 65, most body systems
become less efficient, making
homeostasis more difficult to maintain.

143. 39-1
Cells that have receptors for a
particular hormone are called
a. nerve cells.
b. target cells.
c. exocrine cells.
d. endocrine cells.

144. 39-1
Chemicals that travel through the
bloodstream and affect the activities of
other cells are known as
a. hormones.
b. receptors.
c. enzymes.
d. messengers.

145. 39-1
Which group of hormones act on target
cells by binding directly to DNA in the
nucleus?
a. steroids
b. nonsteroids
c. proteins
d. second messengers

146. 39-2
Diabetes mellitus is a disease that
results when the pancreas fails to
produce or properly use
a. glucose.
b. insulin.
c. glucagon.
d. carbohydrate.

147. 39-2
Metabolism is regulated by
a. thyroxine.
b. parathyroid hormone.
c. epinephrine.
d. estrogen.

148. 39-2
The gonads are the body's
a. target cells.
b. exocrine glands.
c. reproductive glands.
d. reproductive cells.

149. 39-2
The endocrine glands responsible for
maintaining homeostasis of calcium in
the blood are the
a. thyroid and parathyroid glands.
b. adrenal and pituitary glands.
c. hypothalamus and thyroid glands.
d. gonads.

150. 39-2
Epinephrine is a hormone produced by
the adrenal medulla and is responsible
for
a. the “fight or flight” response to
stress.
b. controlling the level of insulin in the
blood.
c. maintaining proper levels of sodium
and potassium in the blood.
d. regulating the water content of the
body.

151. 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.

152. 39-3
An egg passes from a Fallopian tube
into the cavity of the
a. ovary.
b. vagina.
c. uterus.
d. cervix.

153. 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.

154. 39–4
Fertilization takes place in the
a. ovary.
b. Fallopian tube.
c. cavity of the uterus.
d. cervix.

155. 39–4
The process in which a blastocyst
attaches to the wall of the uterus is
called
a. fertilization.
b. implantation.
c. gastrulation.
d. neurulation.

156. 39–4
The central nervous system develops
during which phase of early
development?
a. gastrulation
b. neurulation
c. implantation
d. fertilization

157. 39–4
The placenta is a structure that
a. belongs entirely to the mother.
b. belongs entirely to the fetus.
c. brings blood from the mother and
fetus close together.
d. provides an impermeable barrier
between the mother and the fetus.

158. 39–4
Which of the following is not a primary
germ layer?
a. neural tube
b. endoderm
c. ectoderm
d. mesoderm