Endocrine Regulation

1
Endocrine Regulation

• Chapter 48

2
KEY CONCEPTS

• Endocrine glands and tissues secrete hormones,
  chemical messengers that bind to specific
  receptors on (or in) target cells and regulate
  physiological processes

3
Learning Objective 1

• Compare endocrine with nervous system function
• Describe how these systems work together to
  regulate body processes

4
Endocrine System

• Endocrine glands, cells, tissues that secrete
  hormones (chemical signals)
• regulate physiological processes
• Signals a wide range of target cell types
• Most endocrine responses are slow
• but long-lasting

5
Nervous System

• Helps regulate many endocrine responses
• Neurons signal other neurons, muscle cells, gland
  cells
• including endocrine cells
• Responds rapidly to stimuli
• transmits electrical and chemical signals

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KEY CONCEPTS

• The endocrine and nervous systems work closely
  together to regulate life processes and maintain
  homeostasis

7
Learning Objective 2

• How is endocrine action regulated by negative
  feedback systems?

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Negative Feedback Systems

• Regulate hormone secretion
• Hormones released in response to change in steady
  state
• trigger responses
• counteract changed conditions
• Restore homeostasis

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Negative Feedback
Fig. 48-1, p. 1030
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KEY CONCEPTS

• Most endocrine processes are regulated by
  negative feedback systems, often involving
  concentrations of specific ions or chemical
  compounds

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Learning Objective 3

• Identify four main chemical groups to which
  hormones are assigned
• Give two examples for each group

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4 Hormone Groups

• 1. Fatty acid derivatives
• prostaglandins
• juvenile hormone of insects

Juvenile hormone
A prostaglandin
(a) Hormones derived from fatty acids
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4 Hormone Groups

• 2. Steroid hormones
• secreted by adrenal cortex, ovary, testis
• molting hormone of insects

Molting hormone (ecdysone)
Cortisol
Estradiol (principal estrogen)
(b) Steroid hormones
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4 Hormone Groups
Norepinephrine

• 3. Amino acid derivatives
• thyroid hormones
• epinephrine

Epinephrine
Thyroid hormones
Thyroxine (T4)
Triiodothyronine (T3)
(c) Amino acid derivatives
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4 Hormone Groups

• 4. Peptides and proteins
• antidiuretic hormone (ADH), glucagon (peptide
  hormones)
• insulin (protein)

Oxytocin
ADH
(d) Peptide hormones
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Learning Objective 4

• Compare four types of endocrine signaling

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Classical Endocrine Signaling

• Endocrine glands (glands without ducts)
• secrete hormones into interstitial fluid
• Hormones transported by blood
• bind with receptors of specific target cells

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Neuroendocrine Signaling

• Neurons secrete neurohormones
• transported down axons and secreted
• Transported by blood

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Autocrine Signaling

• Hormone (or other signal molecule) secreted into
  interstitial fluid
• Acts on the very cell that produced it

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Paracrine Signaling

• Hormone (or other signal molecule) diffuses
  through interstitial fluid
• Acts on nearby target cells

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Types of Endocrine Signaling
Fig. 48-3, p. 1033
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Local Regulators

• Some are considered hormones
• use autocrine and paracrine signaling
• Growth factors
• peptides stimulate cell division, development
• Prostaglandins
• help regulate many metabolic processes

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Learning Objective 5

• Compare the mechanism of action of small,
  lipid-soluble hormones with that of hydrophilic
  hormones
• Include the role of second messengers, such as
  cyclic AMP

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Small, Lipid-Soluble Hormones

• Steroid hormones, thyroid hormones
• Pass through plasma membrane
• combine with receptors in target cell
• Hormonereceptor complex
• activates or represses transcription of messenger
  RNA coding for specific proteins

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Steroid and Thyroid Hormones
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Blood vessel
Target cell
Hormone molecules
Nucleus
Cells of an endocrine gland
Hormone molecules pass through plasma membrane.
1
2
Receptor
Hormone moves through cytosol.
3
Hormone passes through nuclear envelope and
binds with receptor in nucleus.
DNA
Activated receptor is transcription factor that
binds to and activates (or represses) specific
genes.
4
mRNA
Ribosome
Specific proteins are synthesized.
5
mRNA
6
Proteins alter cell activity.
Protein
Fig. 48-4, p. 1034
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Hydrophilic Hormones

• Peptide hormones
• do not enter target cells
• Combine with receptors on plasma membrane of
  target cells
• many bind to G proteinlinked receptors that act
  via signal transduction
• Receptor transduces extracellular hormone signal
  into intracellular signal

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Peptide Hormones
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Blood vessel
Extracellular fluid
Hormone
Plasma membrane of target cell
Adenylyl cyclase
G protein
Receptor
Cells of an endocrine gland
1
Peptide hormone (first messenger) binds with G
proteinlinked receptor in plasma membrane of
target cell. G protein is activated and activates
enzyme adenylyl cyclase.
Cytosol
GTP
cAMP
Second messenger
ATP
cAMP
cAMP
cAMP
2
Adenylyl cyclase converts ATP to cAMP (second
messenger).
3
cAMP relays signal activates protein kinase or
some other protein that leads to a response. Some
cell activity is altered.
Protein kinase
Protein
Protein
Affects gene activity
Alters metabolism
Opens or closes ion channels
Fig. 48-5, p. 1035
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Second Messengers 1

• First messengers (peptide hormones) carry out
  actions through second messengers
• such as cyclic AMP (cAMP)
• G proteinlinked receptor activates G protein

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Second Messengers 2

• G protein stimulates or inhibits enzyme that
  affects second messenger
• Example
• G proteins stimulate or inhibit adenylyl cyclase
  (enzyme that catalyzes conversion of ATP to cAMP)

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Second Messengers 3

• Many second messengers stimulate activity of
  protein kinases
• enzymes that phosphorylate specific proteins that
  affect cell activity

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Second Messengers 4

• Some G proteins use phospholipid derivatives as
  second messengers
• Inositol trisphosphate (IP3) and diacylglycerol
  (DAG)
• second messengers that increase calcium
  concentration, activate enzymes
• calcium ions bind with calmodulin

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Enzyme-Linked Receptors

• Receptor tyrosine kinases
• bind growth factors (including insulin and nerve
  growth factor)

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KEY CONCEPTS

• Small, lipid-soluble hormones enter target cells
  and activate genes
• Hydrophilic hormones bind to cell-surface
  receptors and initiate signal transduction,
  leading to metabolic changes in the cell

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Learning Objective 6

• Identify the classical vertebrate endocrine
  glands
• Describe the actions of their hormones

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Vertebrate Hormones

• Regulate
• growth and development
• reproduction
• salt and fluid balance
• many aspects of metabolism
• behavior

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Human Endocrine Glands
Fig. 48-7, p. 1038
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Endocrine Disorders

• Hyposecretion
• abnormally reduced output of hormones
• Hypersecretion
• abnormally increased output of hormones

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Learning Objective 7

• How do the hypothalamus and pituitary gland
  integrate regulatory functions?
• Describe the actions of the hypothalamic and
  pituitary hormones

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Integrated Regulation

• Hypothalamus
• integrates nervous and endocrine regulation
• regulates activity of pituitary gland
• produces neurohormones released by posterior lobe
  of pituitary

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Neurohormones Produced by Hypothalamus

• Oxytocin
• stimulates contraction of uterus
• stimulates ejection of milk (mammary glands)
• Antidiuretic hormone (ADH)
• stimulates reabsorption of water (kidney tubules)

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Posterior Pituitary Hormones
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Brain
Skull
Hypothalamus
Anterior lobe of pituitary gland
Posterior lobe of pituitary gland
Fig. 48-8a, p. 1039
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Neuroendocrine cells
Hypothalamus
Axons
Pituitary stalk
Posterior lobe of pituitary gland
Capillary
Vesicles containing hormones
Anterior lobe of pituitary gland
Hormones
Fig. 48-8b, p. 1039
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Antidiuretic hormone (ADH)
Oxytocin
Kidney tubules
Uterus
Mammary glands
Increases permeability
Stimulates contraction
Stimulates milk release
Increased water reabsorption
Fig. 48-8c, p. 1039
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Anterior Lobe of Pituitary

• Secretes
• prolactin
• melanocyte-stimulating hormones
• growth hormone
• several tropic hormones (stimulate other
  endocrine glands)
• TSH
• ACTH
• LH
• FSH

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Anterior Pituitary Hormones

• Melanocyte-stimulating hormones (MSH)
• suppress appetite
• help regulate energy and body weight
• skin pigmentation
• libido
• Prolactin
• stimulates mammary glands to produce milk

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Anterior Pituitary Hormones

• Growth hormone (GH)
• an anabolic hormone
• stimulates body growth (protein synthesis)
• stimulates liver to produce insulin-like growth
  factors (IGFs) (promote skeletal growth, general
  tissue growth)

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Releasing Hormones and Inhibiting Hormones

• Secreted by the hypothalamus
• Regulate hormone output of anterior lobe of
  pituitary gland

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Brain

Hypothalamus
Skull
Anterior lobe of pituitary gland
Posterior lobe of pituitary gland
Fig. 48-9a, p. 1040
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Anterior Pituitary Hormones
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Hypothalamus
Releasing hormones
Releasing hormones
Hormones
Portal vein
Posterior lobe of pituitary gland
Capillaries
Hormones
Anterior lobe of pituitary gland
Fig. 48-9b, p. 1040
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Hypothalamic releasing and release-inhibiting
factors influence the secretion of the anterior
pituitary hormones.
Melanocyte-stimulating hormones (MSH)
Thyroid stimulating hormone
Growth hormone
Gonadotropic hormones
Prolactin
ACTH
LH FSH
Mammary glands
Muscle, bone, and other tissues
Pigment cells in skin
Ovary
Thyroid gland
Adrenal cortex
Testis
Stimulate melanin production
Produce milk
Produce gametes and hormones
Increases rate of metabolism
Helps regulate fluid balance helps body cope
with stress
Promotes growth
Fig. 48-9c, p. 1040
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KEY CONCEPTS

• In vertebrates, the hypothalamus and pituitary
  gland work together to regulate growth,
  metabolism, reproduction, response to stress, and
  many other processes

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Learning Objective 8

• Describe the actions of the thyroid and
  parathyroid hormones, their regulation, and the
  effects of malfunction

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Thyroid Gland

• Secretes thyroid hormones
• thyroxine (T4 )
• triiodothyronine (T3 )
• Thyroid hormones stimulate the rate of metabolism

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Regulation of Thyroid Secretion

• Depends on a negative feedback system
• between anterior pituitary gland
• and thyroid gland

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Environmental stimuli (e.g., cold, stress)
Hypothalamus
TRH
Anterior pituitary
TSH
Thyroid gland
Thyroid hormones (T3 and T4)
Metabolism
Growth
Fig. 48-10a, p. 1041
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Thyroid Disorders 1

• Hyposecretion of thyroxine
• during childhood may lead to cretinism
• during adulthood may lead to myxedema
• Graves disease
• autoimmune disease
• most common cause of hyperthyroidism

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Thyroid Disorders 2

• Goiter
• abnormal enlargement of thyroid gland
• from either hyposecretion or hypersecretion

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Fig. 48-10b, p. 1041
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Parathyroid Glands

• Secrete parathyroid hormone (PTH)
• regulates calcium level in blood
• Parathyroid hormone increases calcium
  concentration by
• stimulating calcium release from bones
• increasing calcium reabsorption by kidney tubules
• increasing calcium reabsorption from intestine

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Calcium Homeostasis
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Decrease in Ca2 concentration in blood
Parathyroid glands
PTH
stimulates
Ca2 level increases
Osteoclasts release Ca2 from bone
Kidney tubules increase Ca2 reabsorption
Intestine increases Ca2 absorption
(a) Calcium concentration too low.
Fig. 48-11a, p. 1042
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Increase in Ca2 concentration in blood
Parathyroid glands
Thyroid gland
Calcitonin
inhibits
Ca2 level decreases
Osteoclasts decrease Ca2 release from bone
Kidney tubules decrease Ca2 reabsorption
(b) Calcium concentration too high.
Fig. 48-11b, p. 1042
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Calcitonin

• Secreted by the thyroid gland
• Acts antagonistically to parathyroid hormone

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Learning Objective 9

• Contrast the actions of insulin and glucagon
• Describe diabetes mellitus and hypoglycemia,
  including the metabolic effects of these disorders

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Insulin and Glucagon 1

• Secreted by islets of Langerhans in the pancreas
• regulated directly by glucose concentration

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Common bile duct
Pancreatic duct
Pancreas
Islet of Langerhans
Fig. 48-12, p. 1043
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Insulin and Glucagon 2

• Insulin
• stimulates cells to take up glucose from blood
• lowers blood glucose concentration
• Glucagon
• raises blood glucose concentration
• stimulates conversion of glycogen to glucose
• stimulates production of glucose from other
  nutrients

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Regulation of Glucose
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INSULIN RELEASE (a) Stimulates cells to take in
glucose (b) Stimulates muscles and liver to
store glucose as glycogen (c) Stimulates
storage of amino acids and fat
High
Stimulates beta cells
Regulation of Glucose
Stressor Eating carbohydrates
Normal range
Glucose level
HOMEOSTATIC RANGE
Stressor Fasting
Stimulates alpha cells
GLUCAGON PRODUCTION (a) Stimulates mobilization
of amino acids and fat (b) Stimulates
gluconeogenesis (c) Stimulates liver to release
stored glucose (glycogenolysis)
Low
Time
Fig. 48-13, p. 1044
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Diabetes Mellitus

• From either
• insulin deficiency
• insulin resistance
• Results in
• decreased use of glucose
• increased fat mobilization
• increased protein use
• electrolyte imbalance

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Hypoglycemia

• Impaired glucose tolerance results in
• delayed insulin response
• hypersecretion of insulin
• Glucose concentration falls
• causing drowsiness

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Learning Objective 10

• Describe the actions and regulation of the
  adrenal hormones, including their role in helping
  the body respond to stress

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Adrenal Glands

• Secrete hormones that help the body respond to
  stress

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Adrenal Glands
Adrenal cortex
Adrenal medulla
Adrenal gland
Kidney
Fig. 48-14, p. 1045
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Adrenal Medulla

• Secretes epinephrine and norepinephrine
• increase heart rate
• increase metabolic rate
• increase strength of muscle contraction
• reroute blood to organs needed for fight or
  flight
• Regulated by the nervous system

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Adrenal Cortex

• Secretes
• sex hormones
• mineralocorticoids (such as aldosterone)
• glucocorticoids (such as cortisol)
• Aldosterone increases rate of sodium reabsorption
  and potassium excretion by the kidneys

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Stress Responses 1

• Adrenal cortex
• ensures adequate fuel supplies for rapidly
  metabolizing cells
• Cortisol
• promotes glucose synthesis from other nutrients

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Stress Responses 2

• Hypothalamus
• secretes corticotropin-releasing factor (CRF)
• which stimulates anterior pituitary gland to
  secrete adrenocorticotropic hormone (ACTH)
• ACTH
• regulates aldosterone and cortisol secretion

84

STRESS
HYPOTHALAMUS
CRF
SYMPATHETIC NERVES
PITUITARY
ACTH
ADRENAL MEDULLA
ADRENAL CORTEX
Epinephrine and norepinephrine
Cortisol
Stimulate conversion of glycogen to glucose
Blood vessels
Stimulates amino acid transport into liver cells
Inhibits allergic reactions
Brain
Heart
Mobilizes fat
Lowers thresholds in RAS
Dilates blood vessels in muscles, brain
Increases cardiac output
Constricts blood vessels in skin, kidneys
Raises blood sugar level
Reduces inflammation
Provides nutrients for cellular respiration
Conversion of other nutrients to glucose
Run longer, fight harder
Raises blood sugar level
Fig. 48-15, p. 1046