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CHAPTER 25
Hormones
PowerPoint® Lectures for
Essential Biology, Third Edition
– Neil Campbell, Jane Reece, and Eric Simon
Essential Biology with Physiology, Second Edition
– Neil Campbell, Jane Reece, and Eric Simon
Lectures by Chris C. Romero
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Biology And Society:
Of Hunger and Hormones
• What causes hunger?
• In 1999, scientists discovered the hormone ghrelin,
– Which may induce hunger and stimulate eating.
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• The amount of ghrelin in the blood
– Tends to fluctuate during different times in a day.
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Figure 25.1
Hormones: An Overview
• The endocrine system
– Is the body’s main system for internal chemical
regulation.
• Hormones
– Are regulatory chemicals that affect specific sites
in the body.
– Are made by endocrine glands.
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• Hormone secretion from an endocrine cell
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Figure 25.2
• There are two general mechanisms by which
hormones trigger changes in target cells.
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• In the first mechanism,
– Hormones bring about changes without ever
entering their target cells.
Water-Soluble Hormone
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Figure 25.3
• In the second mechanism,
– Hormones trigger changes by binding to receptors
inside the cell.
Lipid-Soluble Hormone
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Figure 25.4
The Human Endocrine System
• The human endocrine system consists of about a
dozen major glands.
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• The major endocrine glands in humans
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Figure 25.5
• The actions of the major human endocrine
hormones
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Table 25.1
Table 25.1 (continued)
The Hypothalamus and Pituitary Gland
• The hypothalamus
– Is the main control center of the endocrine
system.
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• As part of the brain, the hypothalamus receives
information from the nervous system and sends out
appropriate responses.
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Figure 25.6
• The pituitary gland
– Receives signals directly from the hypothalamus.
– Consists of two parts, a posterior lobe and an
anterior lobe.
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• The posterior lobe of the pituitary
– Stores and secretes hormones made in the
hypothalamus.
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• The anterior lobe of the pituitary
– Synthesizes its own hormones, such as FSH, LH,
and PRL, and secretes them directly into the
blood.
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• The hypothalamus
– Operates through the posterior pituitary to direct
the activity of the kidneys.
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Figure 25.7
• The anterior lobe of the pituitary also secretes
growth hormone, which can have a broad effect on
the body.
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Figure 25.8
The Thyroid and Parathyroid Glands
• The thyroid gland
– Is located in the neck just under the larynx.
– Produces several hormones involved in
controlling oxygen consumption, metabolism, and
development.
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• Hypothyroidism
– Is a condition in which there is too little thyroid
hormone in the blood.
– Can result from dietary deficiencies of iodine or
from a defective thyroid gland.
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Figure 25.9
• Hyperthyroidism
– Is a condition in which there is too much thyroid
hormone in the blood.
– Causes Graves’ Disease, an autoimmune disease.
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• The parathyroid glands
– Are four disk-shaped glands embedded within the
thyroid.
– Produce hormones that control calcium
homeostasis.
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• Calcitonin and parathyroid hormone (PTH)
– Have opposite effects that control calcium levels
in the blood.
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Figure 25.10
The Pancreas
• The pancreas
– Produces two hormones that play important roles
in managing the body’s energy supplies.
• Insulin and glucagon
– Help maintain a homeostatic balance of blood
glucose and stored glucose.
– Are antagonists.
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• Control of blood glucose and stored glucose is
carried out by negative feedback.
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Figure 25.11
• Diabetes mellitus
– Is a hormonal disease in which body cells are
unable to absorb glucose.
– Includes type 1, or insulin-dependent diabetes,
and type 2, or non-insulin-dependent diabetes.
– Can be treated.
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The Adrenal Glands
• The human body has two adrenal glands.
• Each adrenal gland is two glands in one:
– The adrenal medulla
– The adrenal cortex
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• The hormones produced by the adrenal glands
– Enable the body to respond to stress.
– Are epinephrine (adrenaline) and norepinephrine
(noradrenaline).
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• Stressful stimuli, whether negative or positive,
activate nerve cells in the hypothalamus that send
signals to stimulate the adrenal medulla.
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• Epinephrine and norepinephrine
– Are the “fight-or-flight” hormones that the
adrenal medulla secretes.
– Ensure a rapid, short-term response to stress.
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• The adrenal cortex
– Is also stimulated by the hypothalamus.
– Secretes hormones that provide a slower, longerlasting response to stress.
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• The short-term and long-term responses to stress
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Figure 25.12 part 1
Figure 25.12 part 2
The Gonads
• The gonads secrete sex hormones that
– Affect growth and development.
– Regulate reproductive cycles and sexual behavior.
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• The three categories of sex hormones are
– Androgens.
– Estrogens.
– Progestins.
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• Estrogens
– Maintain the female reproductive system.
– Promote the development of specific female
features.
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• Progestins
– Are primarily involved in preparing the uterus to
support a developing embryo.
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• Androgens
– Stimulate the development and maintenance of
the male reproductive system.
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• Hormone production by the gonads is regulated by
the hypothalamus and pituitary gland.
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Evolution Connection:
The Changing Roles of Hormones
• Hormones play important roles in all vertebrates.
– The same hormone can have different actions in
different animals.
– Hormonal regulation was an early evolutionary
adaptation.
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• The hormone prolactin (PRL) is a good example.
– It performs a variety of functions in nonmammals.
– It stimulates mammary glands to grow and
produce milk in mammals.
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Figure 25.13