Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

www.cengage.com/biology/starr

Chapter 31Endocrine Control

(Sections 31.1 - 31.5)

31.1 Hormones in the Balance

• Some synthetic chemicals, such as DDT (pesticide), PCBs (used in electronic products, caulking, and solvents), and Atrazine (herbicide) are endocrine disrupters that harm the environment and threaten human health

• endocrine disrupter • Synthetic chemical that adversely affects hormone

production or function

Costs of Herbicide Applications• Atrazine keep cornfields nearly weed-free – it also interferes

with sexual development in amphibians

31.2 Vertebrate Endocrine System

• Animal cells communicate with adjacent cells by way of gap junctions, neurotransmitters, and local signaling molecules

• Animal hormones travel through the blood and can carry signals between cells in distant parts of the body

• All hormone-secreting glands and cells in a body constitute the animal’s endocrine system

Mechanisms of Intercellular Signaling

• Signaling molecules exert effects only when they bind to a matching receptor on or inside a “target” cell

• Local signaling molecules diffuse a short distance through interstitial fluid and bind to nearby cells• Example: Prostaglandins released by injured cells activate

pain receptors and increase local blood flow

• Animal hormones circulate through the bloodstream, and exert their effects on a greater number of cells

Key Terms

• local signaling molecule• Chemical signal, such as a prostaglandin, that is secreted

by one cell and affects neighboring cells in an animal body

• animal hormone • Intercellular signaling molecule secreted by an endocrine

gland or cell

Discovery of Hormones

• Physiologist E. Starling coined the term “hormone” to describe his discovery of secretin (the hormone that stimulates the pancreas to secrete bicarbonate)

• Endocrine glands and other structures that secrete hormones are collectively referred to as an animal’s endocrine system

• endocrine system • Hormone-producing glands and secretory cells of a

vertebrate body

The Endocrine System

Fig. 31.2, p. 505

Testes (one pair of male gonads) Make and secrete testosterone and other androgens (affect primary sex organs and influence secondary sexual traits).

Ovaries (one pair of female gonads) Make and secrete progesterone and estrogens (affect primary sex organs and influence secondary sexual traits).

Adrenal glands (one pair) Adrenal cortex makes and secretes cortisol (affects metabolism, immune response), aldosterone (acts in kidneys), small amount of sex hormones. Adrenal medulla makes and secretes norepinephrine and epinephrine, which prepare body for exciting or dangerous situations.

Pituitary glandAnterior lobe makes and secretesACTH, TSH, LH, FSH (stimulate secretion by other endocrine glands), prolactin (acts on mammary glands) and growth hormone (affects overall growth). Posterior lobe secretes antidiuretic hormone (acts on kidneys) and oxytocin (acts on uterus and mammary glands). Both are made in the hypothalamus.

Hypothalamus Makes and secretes releasers and inhibitors, hormones that act in the anterior lobe of the pituitary. Also makes antidiuretic hormone and oxytocin, which are stored in and released from the posterior lobe of the pituitary.

closer view of the hypothalamus and pituitary gland

pituitary gland

hypothalamus

Pancreas Makes and secretes insulin (lowers blood glucose level) and glucagon (raises blood glucose level).

Thymus gland Makes and secretes thymosins (act in maturation of T cells, a type of white blood cell).

Parathyroid glands (four) Make and secrete parathyroid hormone (raises blood calcium level).

Thyroid glandMakes and secretes thyroid hormone (metabolic and developmental effects) and calcitonin (lowers blood calcium).

Pineal gland Makes and secretes melatonin (affects sleep/wake cycles, onset of puberty).

The Endocrine System

ANIMATION: Major human endocrine glands

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Neuroendocrine Interactions

• The endocrine system and nervous system are closely linked• Hormones affect nervous processes such as sleep/wake

cycles, emotion, mood, and memory• The nervous system affects hormone secretion

• Both respond to signals from the hypothalamus, and both affect the activity of the same organs

Key Concepts

• The Vertebrate Endocrine System • Hormones and other signaling molecules regulate the

pathways that control metabolism, growth, development, and reproduction

• Nearly all vertebrates have an endocrine system composed of the same hormone-producing structures

31.3 The Nature of Hormone Action

• For a hormone to have an effect, it must bind to receptors on or inside a target cell

• Hormones initiate responses in different ways, but in all cases, binding to a receptor is reversible and the response declines over time

Reception, Transduction, Response

• Signal processing is a three-step process:

Signal Reception

Signal Transduction

Cellular Response

• A chemical signal binds to a receptor on a target cell, the signal is transduced (converted to a form that acts in the receiving cell), and the target cell makes a response

Types of Hormones

• Animal hormones are chemical signals derived from either cholesterol or amino acids

• Steroid hormones are lipid soluble and derived from cholesterol; they enter cells and bind to receptors inside them

• steroid hormone • Hormone such as testosterone that is derived from

cholesterol

Types of Hormones (cont.)

• Peptide and protein hormones are derived from amino acids

• They bind to receptors in the cell membrane

• Binding often triggers formation of a second messenger, a molecule that elicits changes inside the cell

Categories of Hormones

Intracellular Receptors

• Steroid hormones form a hormone-receptor complex by binding to a receptor in the cytoplasm or nucleus

• The hormone-receptor complex binds to a promoter near a hormonally regulated gene

• Transcription and translation result in a protein product, such as an enzyme, that carries out the target cell’s response to the signal

Steroid Hormone Action

Fig. 31.3a, p. 507

A Example of steroid hormone action inside a target cell.

The hormone– receptor complex triggers transcrip-tion of a specific gene.

hormone– receptor complex

The resulting mRNA moves into the cytoplasm and is transcribed into a protein.

gene product

receptor

The hormone diffuses through the

cytoplasm and nuclear envelope. It binds with

its receptor in the nucleus.

Being lipid soluble, the hormone easily diffuses across the cell’s plasma membrane.

A steroid hormone molecule is moved from blood into interstitial fluid bathing a target cell.

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Steroid Hormone Action

ANIMATION: Hormones and target cell receptors

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Receptors at the Plasma Membrane

• Peptide and protein hormones bind to receptor proteins in a target cell’s plasma membrane

• Binding causes a second messenger to form, which causes more cellular changes

• second messenger • Molecule that forms inside a cell when a hormone binds at

the cell surface• Sets in motion reactions that alter activity inside the cell

Peptide Hormone Action

Fig. 31.3b, p. 507

The enzyme activated by cyclic AMP also inhibits

glycogen synthesis.

The enzyme activated by cyclic AMP activates another enzyme, which in turn activates another kind that catalyzes the breakdown of glycogen to its glucose monomers.

Cyclic AMP activates another enzyme in the cell.

Glucagon binds with a receptor. Binding activates an enzyme that catalyzes the formation of cyclic AMP from ATP inside the cell.

ATPcyclic AMP

unoccupied glucagon receptor at target cell’s plasma membrane

A peptide hormone molecule, glucagon,

diffuses from blood into interstitial fluid bathing the plasma membrane

of a liver cell.

+ Pi

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B Example of peptide hormone action inside a target cell.

Peptide Hormone Action

Steroid Hormone Receptors

• Some cells have receptors for steroid hormones at the plasma membrane

• Binding a steroid hormone triggers a fast response by way of a second messenger, or by altering a property of the membrane

• Example: When aldosterone binds to target cells in kidneys, target cells quickly become more permeable to sodium ions

Receptor Function and Diversity

• Hormone receptors are proteins

• Mutations can result in receptors with a lowered capacity for binding hormone, or none at all

• Variations in receptor structure also affect responses to hormones; different tissues often have receptor proteins that respond in different ways to binding of the same hormone

Example: ADH Receptor Diversity

• ADH (antidiuretic hormone) binds to kidney cells and helps maintain solute concentrations in the internal environment

• ADH also binds to receptors in blood vessels and helps maintain blood pressure by causing vessels to narrow

• ADH also binds to brain cells and influences sexual and social behavior

Key Concepts

• Signaling Mechanisms • A hormone travels through the blood and acts on any cell

that has receptors for it• Receptor activation leads to transduction of the signal and

a response in the targeted cell• Hormones are derived from either cholesterol or amino

acids

31.4 The Hypothalamus and Pituitary Gland

• The hypothalamus and pituitary gland deep inside the brain control the activities of many other endocrine glands

• hypothalamus • Forebrain region that controls processes related to

homeostasis and has endocrine functions

• pituitary gland • Pea-sized endocrine gland in the forebrain that interacts

closely with the adjacent hypothalamus

Hypothalamus and Pituitary Gland• The hypothalamus connects structurally and functionally with

the two lobes of the pituitary gland

p. 508

anterior lobe of pituitary

posterior lobe of pituitary

hypothalamus

Hypothalamus and Pituitary Gland

Functions of the Hypothalamus

• The hypothalamus is the main center for control of the internal environment

• Axons of neurons in the hypothalamus extend into the posterior pituitary, where they release oxytocin and antidiuretic hormone

• Releasing hormones and inhibiting hormones secreted by the hypothalamus control the secretion of hormones made by the anterior lobe of the pituitary

Key Terms

• releasing hormone • Hormone that is secreted by one endocrine gland and

stimulates secretion by another

• inhibiting hormone • Hormone that is secreted by one endocrine gland and

discourages secretion by another

Posterior Pituitary Hormones

• The posterior pituitary secretes hormones synthesized in the hypothalamus: • Oxytocin targets smooth muscle in mammary glands

during nursing and the uterus during birth• Antidiuretic hormone concentrates the urine by increasing

reabsorption of water in kidney tubules

Posterior Pituitary Function

1. Cell bodies of secretory neurons in hypothalamus synthesize ADH or oxytocin

2. ADH or oxytocin moves downward inside axons of secretory neurons and accumulates in the axon terminals

3. Action potentials trigger release of hormones, which enter blood capillaries in the posterior lobe of the pituitary

4. Blood vessels carry hormones to the general circulation

Posterior Pituitary Function

Fig. 31.4, p. 509

Action potentials trigger the release of these hormones, which enter blood capillaries in the posterior lobe of the pituitary.

Blood vessels carry hormones to the general circulation.

The ADH or oxytocin moves downward inside the axons of the secretory neurons and accumulates in the axon terminals.

Cell bodies of secretory neurons in hypothalamus synthesize ADH or oxytocin.

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Posterior Pituitary Function

Anterior Pituitary Hormones

• The anterior pituitary makes hormones and secretes them in response to hormones from the hypothalamus

• Four anterior pituitary hormones (ACTH, TSH, FSH, LH) hormones target other glands

• Prolactin encourages milk production

• Growth hormone (GH) secreted by the anterior pituitary acts throughout the body

Growth Hormone Disorders

• Pituitary gigantism and dwarfism result from mutations that affect GH secretion or GH receptors

• Over-secretion of growth hormone in children leads to pituitary gigantism

• Low GH secretion in childhood causes pituitary dwarfism

Pituitary Gigantism

• One of the world’s tallest men, Bao Xishun stands 2.36 meters (7 feet 9 inches) tall

Anterior Pituitary Function

1. Neurons in the hypothalamus secrete inhibitors or releasers into the stalk that connects to the pituitary

2. Blood carries inhibitors or releasers to the anterior pituitary

3. Inhibitors or releasers diffuse out of capillaries in the anterior pituitary and bind to target cells

4. Encouraged by a releaser, anterior pituitary cells secrete a hormone that enters the general blood circulation

Anterior Pituitary Function

Fig. 31.5, p. 509

Cell bodies of secretory neurons in hypothalamus synthesize inhibitors or releasers that are secreted into the stalk that connects to the pituitary.

The inhibitors or releasers picked up by capillaries in the stalk get carried in blood to the anterior pituitary. When encouraged

by a releaser, anterior pituitary cells secrete hormone that enters blood vessels that lead into the general circulation.

The inhibitors or releasers diffuse out of capillaries in the anterior pituitary and bind to their target cells.

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Anterior Pituitary Function

ANIMATION: Posterior pituitary function

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ANIMATION: Anterior pituitary function

Hormones Secreted by the Pituitary Gland

Key Concepts

• A Master Integrating Center • In vertebrates, the hypothalamus and pituitary gland deep

inside the brain are connected structurally and functionally• Together, they coordinate activities of many other glands

Animation: Hypothalamus and Pituitary

31.5 Sources and Effects of Other Vertebrate Hormones

• In addition to major endocrine glands, the human body has hormone-secreting cells in many organs:• Parts of the gut secrete secretin and other hormones that

affect appetite and digestion• Adipose (fat) tissue makes leptin, a hormone that acts in

the brain and suppresses appetite• Kidneys secrete erythropoietin, a hormone that stimulates

maturation and production of red blood cells• The heart makes atrial natriuretic peptide, that stimulates

the kidneys to excrete water and salt

Sources and Actions of Vertebrate Hormones

BBC Video: Adrenalin and the Body