1. Chemical signaling within the animal body
Chapter 30

2. Hormones A hormone is a chemical signal produced in the body.
Hypothalamus
Pineal
gland
Pituitary
Thyroid
Pancreas
Testes
(in males)
Ovaries
(in females)
Adrenal
glands
Thymus
Parathyroid glands
(attached to the thyroid)
A hormone is a chemical signal produced in the body.
It typically acts at a site distant from where it was produced.
Most hormones are produced in glands that are completely enclosed in tissue.
These glands are called endocrine glands.

3. Hormones
There are three big advantages to using chemical hormones as messengers rather than speedy electrical signals (like nerve signals).
Chemical molecules can spread to all tissues via the blood.
Chemical signals can persist much longer than electrical ones.
Many different kinds of chemicals can act as hormones.

4. Hormones
The glands that produce hormones are generally controlled by the nervous system.
The endocrine system and the motor nervous system are the two main routes the CNS uses to issue commands to the organs of the body.
The two are so closely linked that they are often considered a single system—neuroendocrine system.
The hypothalamus is the main switchboard of the neuroendocrine system.

5. Hormones
The CNS regulates the body’s hormones through a chain of command.
For example, the hypothalamus controls the pituitary gland with thyrotropic-releasing hormone (TRH).
This causes the pituitary to release or thyroid-stimulating hormone (TSH).
TSH then causes the thyroid gland to release thyroid hormones.
The hypothalamus also secretes inhibiting hormones that keep the pituitary from secreting specific hormones.

6. Hormones
Hormones are effective messengers within the body because a particular hormone can influence a specific target cell.
Cells that the body has targeted to respond to a particular hormone have receptor proteins shaped to fit that hormone and no other.

7. Hormones polypeptides glycoproteins amines steroids
Hormones secreted by endocrine glands belong to four different chemical categories:
polypeptides
glycoproteins
amines
steroids

8. Hormones
The path of communication taken by a hormonal signal is a series of simple steps:
Issuing the command - the hypothalamus controls the release of many hormones.
Transporting the signal - most are transported throughout the body by the bloodstream.
Hitting the target - the hormone binds to a receptor on the target cell.
Having an effect - when the hormone binds to the receptor protein, the protein changes shape and triggers a change in cell activity.

9. Key Biological Process: Hormonal communication
Dehydration
Blood volume and
pressure drops.
Osmotic concentration
in the blood increases. 3
Osmoreceptors 1 4
Reduced urine
volume causes
increased water
retention.
Hypothalamus
ADH
Antidiuretic
hormone (ADH) 2 4
Increased
vasoconstriction
leads to higher
blood pressure.
Bloodstream 3
Posterior
pituitary 1
ADH
Generally, a part of
the neuroendocrine
system receives
sensory information
and issues a
command in the form
of a chemical
messenger (hormone). 2 3 4
The hormone
reaches the target
cells and binds to the
cell receptors.
The hormone-
recept or complex
triggers changes in the
target cells.
The hormone is
transported to target
cells via the
bloodstream.

10. How Hormones Target Cells
The steroid hormones are recognized by protein receptors located in the cytoplasm or nucleus of the target cell.
Steroids are manufactured from cholesterol.
Steroid hormones can pass across the lipid bilayer of the cell plasma membrane.

11. How Hormones Target Cells
The complex of a steroid hormone and its receptor inside the target cell bind to DNA in the nucleus.
This activates the transcription of a specific gene and a protein is subsequently synthesized.

12. How steroid hormones work
Tissue fluid
Blood plasma
Target cell E
Steroid
hormone E
Transport
protein
Plasma membrane 1
Cytoplasm 1
Estrogen (E) is a lipid soluble steroid
hormone and thus readily passes through the
plasma membrane of cells lining the uterus. E 2
Inside the cell, estrogen binds to a specific receptor
protein associated with the DNA in the nucleus. 4
Receptor
protein 3
The estrogen-receptor complex activates the
transcription of genes.
Steroid hormone-
receptor complex
Protein
synthesis 4 2
Protein synthesis is induced. In this case,
the protein produced is a receptor for
another steroid protein, progesterone. 5
Later, when progesterone enters the cell, it binds to
the receptor and stimulates the cell to produce enzymes
that help prepare the uterus to nourish an embryo in the
event of a pregnancy. 5
DNA 3
mRNA
Progesterone
receptor
Nucleus

13. How Hormones Target Cells
The receptors for peptide hormones are embedded in the plasma membrane.
The binding of the hormone to the receptor triggers changes in the cytoplasmic end of the receptor protein.
Using second messengers, this change is amplified and causes changes in the cell
Second messengers activate enzymes.
one of the most common is cyclic AMP (cAMP).

14. How peptide hormones work1
The peptide hormone
binds with its membrane
receptor. 2
The hormone-receptor
combination triggers a
series of biochemical
reactions that produces
the second messenger.
Peptide
hormone 3
The second messenger
triggers a series of
reactions that leads to
altered cell functions. P P 1
Receptor 2
Production
of second
messenger 3
Alteration of
cell activity

15. How Hormones Target Cells
A single hormone binding to a receptor in the plasma membrane can result in the formation of many second messengers in the cytoplasm.
Cyclic AMP is made from ATP by an enzyme that removes two phosphate units.
Each second messenger can activate many molecules of a certain enzyme.

16. Key Biological Process: Second messengers1
Hormone
(first messenger)
After a peptide hormone binds to its receptor, the
hormone-receptor complex activates adenylyl cyclase.
Receptor 2 1
Adenylyl cyclase converts ATP into cyclic AMP
(cAMP), and cAMP acts as a second messenger
that activates enzymes called protein kinases. 3
Protein kinases catalyze a wide variety of
actions, depending on the nature of the first
messenger. Because of the presence of a
second messenger, the effect on the cell is
greatly amplified.
Adenylyl
cyclase
(Second
messenger)
ATP
cAMP 2 3
Protein kinase
(inactive)
Protein kinase
(active)
Altered cell function(regulates enzymes,
synthesizes proteins, secretes molecules)

17. The Hypothalamus and the Pituitary
The pituitary gland is located beneath the hypothalamus and is the location where nine hormones are produced.
These hormones act principally to influence other endocrine glands.
The pituitary consists of two lobes:
Posterior pituitary regulates water conservation and, in women, milk letdown and uterine contraction.
Anterior pituitary regulates other endocrine glands.

18. The Hypothalamus and the Pituitary
The hypothalamus and the posterior pituitary are connected by a tract of neurons.
Hormones are produced by cell bodies in the hypothalamus and transported to the posterior pituitary.
Antidiuretic hormone (ADH) regulates the kidney’s retention of water.
Oxytocin initiates uterine contractions during childbirth and milk release in mothers.

19. The Hypothalamus and the Pituitary
The anterior pituitary is a complete gland that produces the hormones that it secretes.
Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to produce thyroxine, which in turn stimulates oxidative respiration.
Adrenocorticotropic hormone (ACTH) stimulates the adrenal gland to produce hormones.
Growth hormone (GH) simulates the growth of muscle and bone throughout the body.

20. The Hypothalamus and the Pituitary
Follicle-stimulating hormone (FSH)
In females, it triggers the maturation of egg cells and stimulates the release of estrogen.
In males, it regulates sperm development.
Luteinizing hormone (LH)
In females, it triggers ovulation of a mature egg.
In males, it stimulates the gonads to produce testosterone.

21. The Hypothalamus and the Pituitary
Prolactin (PRL) stimulates the breasts to produce milk.
Melanocyte-stimulating hormone (MSH) stimulates, in reptiles and amphibians, color changes in the epidermis.
Its function in humans is poorly understood.

22. Figure 30.4 The role of the pituitary
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hypothalamus
Thyroid-stimulating hormone
(TSH)
Antidiuretic
hormone
(ADH)
Thyroid gland
Posterior
pituitary
Anterior
pituitary
Adrenocorticotropic
hormone (ACTH)
Kidney
tubules
Oxytocin
Muscles of
mammary
glands and
uterus
Growth hormone (GH)
Prolactin (PRL)
Adrenal
cortex
Melanocyte-stimulating hormone (MSH)
Gonadotropic hormones:
Follicle-stimulating
hormone (FSH) and
luteinizing hormone (LH)
Mammary glands
in mammals
Bone
and muscle
Ovary
Testis

23. The Hypothalamus and the Pituitary
Cell body
Axons to
primary
capillaries
Hormones
Portal venules
Hypophyseal
portal system
Anterior
pituitary
Posterior pituitary
Pituitary stalk
Primary
The hypothalamus controls production and secretion of the anterior pituitary hormones by means of a family of special hormones.
Neurons in the hypothalamus secrete both releasing and inhibiting hormones.

24. The Hypothalamus and the Pituitary
Negative feedback (feedback inhibition) often controls the release of hormones from the hypothalamus and anterior pituitary.
When enough of the target hormone has been produced, the hormone then feeds back to the hypothalamus and anterior pituitary and inhibits the release of stimulating hormones. –
Hypothalamus
Inhibition
Releasing hormones
(TRH, CRH, GnRH)
Anterior pituitary
Target glands
Hormones
(Thyroid, adrenal cortex, gonads)
Tropic hormones
(TSH, ACTH, FSH, LH)

25. Release of stored glucose,
The Pancreas
The pancreas has both exocrine and endocrine functions.
It secretes digestive enzymes and hormones.
The hormones, produced in the islets of Langerhans, are insulin and glucagon.
Insulin promotes the uptake of glucose and the accumulation of glycogen in the liver and triglycerides in fat cells.
Glucagon causes liver cells to release stored glucose and to break down triglycerides.
Between meals
Blood glucose
Pancreas
After a meal
Pancreatic islets
Insulin secretion
Glucagon secretion
Cellular uptake
of glucose
Release of stored glucose,
break down of fat

26. The Pancreas
Diabetes mellitus is a serious disorder in which affected individuals are unable to take up glucose from the blood.
There are two kind of diabetes mellitus:
Type I is a hereditary autoimmune disease in which the islets of Langerhans are attacked, resulting in abnormally low insulin secretion.
Type II is when cells don’t respond to insulin, sometimes due to a reduction in the number of insulin receptors in the target tissue.

27. The Thyroid, Parathyroid, and Adrenal Glands
The thyroid gland makes several hormones.
Thyroxine increases metabolic rate and promotes growth.
Calcitonin inhibits the release of calcium from bones and promotes the uptake of calcium by bones.

28. The Thyroid, Parathyroid, and Adrenal Glands
The parathyroid glands are four small glands attached to the thyroid.
These glands produce parathyroid hormone (PTH), a hormone that is absolutely essential for survival because it regulates calcium levels in the blood.
Calcium ions are necessary for muscle contractions, such as those of the heart.
PTH stimulates the release of calcium from bone.
Calcitonin (released from the thyroid gland) has the opposite effect.

29. Maintenance of proper calcium levels in the blood
LOW CALCIUM LEVEL
STIMULATES PTH
SECRETION
HIGH CALCIUM LEVEL
STIMULATES CALCITONIN
SECRETION
Ca++
Inactive
osteoblast
Ca++
Ca++
Ca++
Ca++
PTH stimulates
osteoclast
(breaking down
bone matrix)
Calcitonin
stimulates
active
osteoblast
(increasing
bone
matrix)
Bone
matrix
Bone
matrix
Osteocyte
(in lacuna)
(a)
(b)

30. The Thyroid, Parathyroid, and Adrenal Glands
The adrenal glands are located just above the kidney and each is comprised of two parts.
The medulla is the inner core and produces epinephrine and norepinephrine.
The cortex is the outer region and produces the steroid hormones cortisol and aldosterone.

31. The Thyroid, Parathyroid, and Adrenal Glands
The adrenal medulla releases epinephrine (adrenaline) and norepinephrine in times of stress.
These hormones act as emergency signals that stimulate rapid deployment of body fuel.
The adrenal cortex produces
Cortisol, which acts to maintain nutritional well-being.
It is also released in times of stress but can become a chronic problem if stress continues.
Aldosterone, which affects water reabsorption in the kidney and affects both blood volume and blood pressure.