Transcript Chapter 5 Gases - Colorado Mountain College

Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 31
Endocrine Control
(Sections 31.6 - 31.11)
Albia Dugger • Miami Dade College
31.6 Thyroid
and Parathyroid Glands
• The thyroid gland regulates metabolic rate, and the adjacent
parathyroids regulate calcium levels
• thyroid gland
• Endocrine gland at the base of the neck
• Produces thyroid hormone, which increases metabolism
• parathyroid glands
• Four small endocrine glands whose hormone product
increases the level of calcium in blood
Thyroid Function
• The thyroid secretes thyroid hormone (two iodine-containing
molecules: triiodothyronine and thyroxine) which increases
metabolic activity of tissues throughout the body
• The thyroid gland also secretes calcitonin, a hormone that
causes deposition of calcium in bones of growing children
• The anterior pituitary gland and hypothalamus regulate
thyroid hormone secretion by a negative feedback loop
Feedback Control
of Thyroid Function
1. A low level of thyroid hormone causes the hypothalamus to
secrete thyroid-releasing hormone (TRH)
2. TRH causes the anterior pituitary to secrete thyroidstimulating hormone (TSH)
3. TSH stimulates the secretion of thyroid hormone
4. When the blood level of thyroid hormone rises, secretion of
TRH and TSH declines
Negative Feedback Loop
Negative Feedback Loop
STIMULUS
Blood level of
thyroid hormone falls
below a set point.
RESPONSE
Hypothalamus
1
TRH
4
Anterior Pituitary
2
TSH
Rise of thyroid
hormone level
in blood inhibits
the secretion of
TRH and TSH.
Thyroid Gland
3
Thyroid hormone is secreted.
Fig. 31.7, p. 511
RESPONSE
STIMULUS
Blood level of
thyroid hormone falls
below a set point.
+
Hypothalamus
TRH
Anterior Pituitary
TSH
Rise of thyroid
hormone level
in blood inhibits
the secretion of
TRH and TSH.
Thyroid Gland
Negative Feedback Loop
Thyroid hormone is secreted.
Stepped Art
Fig. 31.7, p. 511
Hypothyroidism
• A diet deficient in iodine can cause thyroid hormone
deficiency (hypothyroidism)
• Hypothyroidism can also arise when the body’s immune
system mistakenly attacks the thyroid
• In either case, ongoing stimulation of the thyroid can lead to
thyroid enlargement, or goiter
Goiter
• Enlarged thyroid (goiter)
caused by a dietary
iodine deficiency
Parathyroid Glands
and Calcium Levels
• Four parathyroid glands located at the rear of the thyroid
gland are the main regulators of calcium levels in the blood
• When blood calcium level declines, the glands release
parathyroid hormone (PTH), which increases breakdown of
bone – blood calcium level rises
• PTH also encourages calcium reabsorption by kidneys and
activation of vitamin D, which helps the intestine take up
calcium from food
Rickets
• Rickets caused by a
lack of vitamin D
• Parathyroid hormone
softens the bones,
causing bowed legs
ANIMATION: Parathyroid hormone action
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31.7 The Adrenal Glands
• There are two adrenal glands, one above each kidney
• An adrenal gland has two functional zones, controlled by
different mechanisms:
• The outer cortex secretes steroid hormones
• The inner medulla releases molecules that function as
neurotransmitters
Key Terms
• adrenal gland
• Endocrine gland that is located atop the kidney
• adrenal cortex
• Outer portion of adrenal gland
• Secretes aldosterone and cortisol
• adrenal medulla
• Inner portion of adrenal gland
• Secretes epinephrine and norepinephrine
The Adrenal Cortex
• The adrenal cortex secretes two steroid hormones:
• Aldosterone controls sodium and water reabsorption in the
kidneys
• Cortisol helps maintain blood glucose available to the brain by
inducing the liver to break down glycogen, adipose cells to
degrade fats, and skeletal muscles to degrade proteins
Negative Feedback and Cortisol
• Cortisol secretion is governed by a negative feedback loop to
the anterior pituitary gland and hypothalamus
• In times of stress, the central nervous system overrides the
feedback controls so that cortisol levels rise
• Over the long term, excess cortisol has negative impacts on
health
Negative Feedback Mechanism
1. A decrease in cortisol triggers secretion of CRH (corticotropinreleasing hormone) by the hypothalamus
2. CRH stimulates secretion of ACTH by the anterior pituitary
3. ACTH causes release of cortisol from the adrenal cortex
4. Cortisol level increases, causing hypothalamus and anterior
pituitary to secrete less CRH and ACTH, and cortisol
secretion slows
Negative Feedback Mechanism
Negative Feedback
Mechanism Blood level of
STIMULUS
RESPONSE
Hypothalamus
cortisol declines.
1
CRH
4
Anterior Pituitary
adrenal
cortex
2
ACTH
adrenal
medulla
Rise of cortisol level
in the blood inhibits
the secretion of CRH
and ACTH.
Adrenal Cortex
3
Cortisol secretion increases
and has the following effects:
Cellular uptake of glucose from blood slows in many tissues,
especially muscles (but not in the brain). Protein breakdown
accelerates, especially in muscles.
Some of the amino acids freed by this process get converted
to glucose.
kidney
Fats in adipose tissue are degraded to fatty acids and enter
blood as an alternative energy source, indirectly adrenal cortex
adrenal medulla kidney conserving glucose for the brain.Fig. 31.9, p. 512
STIMULUS
A Blood level
of cortisol falls
below a set point.
adrenal
cortex
adrenal
medulla
+
RESPONSE
Hypothalamus
Negative
Feedback
Mechanism
B CRH
Anterior Pituitary
ACTH
Adrenal Cortex
D Hypothalamus and
pituitary detect rise
in blood level of
cortisol and slow its
secretion.
C Cortisol is secreted
and has the following
effects:
Cellular uptake of glucose from blood slows in many tissues, especially
muscles (but not in the brain).
Protein breakdown accelerates, especially in muscles. Some of the amino
acids freed by this process get converted to glucose.
Fats in adipose tissue are degraded to fatty acids and enter blood as an
alternative energy source, indirectly conserving glucose for the brain.
Stepped Art
Fig. 31.9, p. 512
The Adrenal Medulla
• The adrenal medulla contains specialized neurons of the
sympathetic division that release norepinephrine and
epinephrine that enter the blood and function as hormones
• Like sympathetic stimulation, norepinephrine and epinephrine
cause a fight-flight response: they dilate the pupils, increase
breathing, and make the heart beat faster
Stress, Elevated Cortisol,
and Health
• When an animal is frightened or under physical stress,
commands from the nervous system trigger increased
secretion of cortisol, epinephrine, and norepinephrine
• Physiological responses to chronic stress interfere with
growth, the immune system, sexual function, and
cardiovascular function
• Chronically high cortisol levels harm cells in the hippocampus,
a brain region central to memory and learning
Elevated Cortisol: Cushing Syndrome
• Before and after removal of a adrenal gland tumor
Hypocortisolism: Addison’s Disease
• Tuberculosis and other
infectious diseases can
damage adrenal glands,
resulting in adrenal
insufficiency
• President John F.
Kennedy had an
autoimmune form of
Addison’s Disease
31.8 Pancreatic Hormones
• The pancreas has both exocrine and endocrine functions:
• Exocrine cells secrete digestive enzymes into a duct to the
small intestine
• Endocrine cells are grouped in pancreatic islets; each islet
contains three types of hormone-secreting cells
• pancreas
• Organ that secretes digestive enzymes into the small
intestine and hormones into the blood
The Pancreas and Digestion
• Delta cells in
pancreatic islets
secrete somatostatin
• Somatostatin helps
control digestion and
nutrient absorption
The Pancreas and Digestion
Fig. 31.12a, p. 514
The Pancreas and Digestion
stomach
pancreas
small
intestine
Fig. 31.12a, p. 514
The Pancreas and Blood Sugar
• Two pancreatic hormones with opposing effects work together
to regulate the level of sugar in the blood
• Insulin (secreted by beta cells) stimulates glucose uptake by
muscle and liver cells and thus lowers the blood glucose
• Glucagon (secreted by alpha cells) stimulates the release of
glucose, which increases blood levels
Regulating High Blood Sugar
1.
2.
3.
4.
5.
Blood glucose rises
Glucagon is blocked
Insulin is secreted
Glucose is taken up
Blood glucose level
decreases
Regulating
High Blood
Sugar
1 Stimulus
Increase in blood glucose
PANCREAS
2
glucagon
LIVER
3
insulin
MUSCLE FAT CELLS
4 Body cells, especially in muscle
and adipose tissue, take up and use
more glucose.
Cells in skeletal muscle and liver
store glucose in the form of glycogen.
5 Response
Decrease in blood glucose
Fig. 31.12b, p. 514
Regulating Low Blood Sugar
6.
7.
8.
9.
Low blood glucose
Glucagon is secreted
Insulin is blocked
Liver breaks down
glycogen into glucose
10.Blood glucose
increases
Regulating
Low Blood
Sugar
6 Stimulus
Decrease in blood glucose
7
8
glucagon
insulin
9 Cells in liver break
down glycogen faster.
The released glucose
monomers enter
blood.
10 Response
Increase in blood glucose
Fig. 31.12c, p. 514
ANIMATION: Hormones and glucose
metabolism
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31.9 Diabetes
• Diabetes mellitus is a disorder in which the body does not
make or does not respond to insulin
• When cells do not take up and store glucose as they should,
high blood sugar (hyperglycemia) disrupts normal metabolism
• Cells have to use proteins and fats for energy – breakdown of
these substances yields harmful waste products
Some Complications of Diabetes
Type 1 Diabetes
• Type 1diabetes develops after white blood cells wrongly
identify insulin-secreting beta cells as foreign (nonself) and
destroy them (autoimmune response)
• All affected individuals require injections of insulin, and must
monitor their blood sugar level carefully
• When fats and proteins are used as energy sources, ketones
accumulate in the blood and urine (ketosis)
Insulin Pump
• An insulin pump
helps smooth out
fluctuations in blood
sugar, lowering risk
of complications
Type 2 Diabetes
• In type 2 diabetes insulin levels are normal or even high
• However, target cells do not respond to the hormone as they
should, and blood sugar levels remain elevated
• Western diets and sedentary life-styles are contributing
factors in type 2 diabetes – diet, exercise, and oral
medications can control most cases
31.10 Gonads,
Pineal Gland, and Thymus
• Outputs from gonads, pineal gland, and thymus all change as
an individual enters puberty
• gonads
• Primary reproductive organs (ovaries or testes) that
produce gametes and sex hormones
• pineal gland
• Endocrine gland deep inside the brain that secretes
melatonin when the retina is not stimulated by light
•
thymus
• Endocrine gland beneath the breastbone; secretes
hormones that encourage maturation of T lymphocytes
The Gonads
• Gonads are primary reproductive organs, which produce
gametes (eggs or sperm)
• Gonads produce steroid sex hormones with roles in
reproduction and development of secondary sexual traits
• Male gonads (testes) secrete mainly testosterone
• Female gonads (ovaries) secrete mainly estrogens and
progesterone
Location of Human Gonads
Location of Human Gonads
testis
(where sperm
originate)
Fig. 31.14a, p. 516
Location of Human Gonads
ovary
(where eggs
develop)
Fig. 31.14b, p. 516
Control of Sex Hormone Secretion
• The hypothalamus and
anterior pituitary control
secretion of sex
hormones
The Pineal Gland
• The pineal gland lies deep within the vertebrate brain
• Melatonin secreted by the pineal gland affects the daily
sleep/wake cycle and the onset of puberty
• Melatonin also protects against some cancers
• Melatonin secretion declines when the retina detects light and
sends action potentials along the optic nerve to the brain
The Thymus
• The thymus lies beneath the breastbone
• It secretes thymosins that encourage maturation of infectionfighting white blood cells (T lymphocytes, or T cells)
• At puberty, the surge of sex hormones causes the thymus to
shrink, and its secretions decline – this can be a problem for
people with HIV infection, because AIDS kills T cells
Key Concepts
• Other Hormone Sources
• Endocrine glands throughout the body respond to signals
from the hypothalamus and the pituitary
• Others secrete hormones in response to internal changes
such as a shift in blood glucose level
• Poor diet, immune problems, and genetic factors can
cause hormone disorders
31.11 Invertebrate Hormones
• Vertebrate hormone receptor proteins often resemble similar
receptor proteins in invertebrates and probably evolved from
them
• Invertebrates also have hormones with no vertebrate
counterpart, such as the steroid hormone ecdysone, which
regulates molting in arthropods such as crabs and insects
Evolution of Receptor Diversity
• Genetic analysis has revealed the invertebrate ancestry of
some vertebrate hormone receptors
• Sea anemones have receptors that are structurally similar to
vertebrate receptors for TSH, LH, FSH, and other signaling
molecules
• Genes that encode these receptors have similar nucleotide
sequences in vertebrates and invertebrates, and have the
same number and type of introns in similar regions
Control of Molting
• In arthropods, hormones regulate the periodic molting of the
cuticle that allows the animal to grow
• Details vary, but in all cases, molting is largely controlled by
ecdysone, a steroid hormone unique to invertebrates
• A molting gland produces and stores ecdysone and releases
it at molting time
Molting in Crustaceans
Molting in Crustaceans
Absence of
suitable stimuli
Presence of
suitable stimuli
X organ releases
molt-inhibiting
hormone (MIH)
Signals from
brain inhibit
release of MIH
MIH prevents
Y organ from
making ecdysone
Y organ makes
and releases
ecdysone
No
molting
Molting
Fig. 31.16, p. 517
Molting in
Crustaceans
Fig. 31.16c, p. 517
Key Concepts
• Invertebrate Hormones
• Hormones control molting and other events in invertebrate
life cycles
• Vertebrate hormones and receptors for them first evolved
in ancestral lineages of invertebrates
Hormones in the Balance (revisited)
• The photo shows breast
development in a girl
less than two years old
• Exposure to high levels
of synthetic chemicals
(phthalates) may cause
such premature breast
enlargement