The Endocrine System and Hormone Function--An Overview Define hormone and target organ.Describe how hormones bring about their effects in the body.Explain how various endocrine glands are stimulated to release their hormonal products.Define negative feedback and describe its role in regulating blood levels of the various hormones.

The Major Endocrine Organs Describe the difference between endocrine and exocrine glands.On an appropriate diagram, identify the major endocrine glands and tissues.List hormones produced by the endocrine glands and discuss their general functions.Discuss ways in which hormones promote body homeostasis by giving examples of hormonal actions.Describe the functional relationship between the hypothalamus and the pituitary gland.Describe major pathological consequences of hypersecretion and hyposecretion of the hormones considered in this chapter.

Other Hormone-Producing Tissues and Organs Indicate the endocrine role of the kidneys, the stomach and intestine, the heart, and the placenta.

Define hormone and target organ

• Hormone: A chemical substance produced in the body that controls and regulates the activity of certain cells or organs.

• Target organ: A tissue or organ upon which a hormone exerts its action; generally, a tissue or organ with appropriate receptors for a hormone.

Describe how hormones bring about their effects in the body.• Changes in plasma membrane permeability or electrical

state

• Synthesis of proteins, such as enzymes

• Activation or inactivation of enzymes

• Stimulation of mitosis

• Promotion of secretory activity

The Chemistry of Hormones

• Hormones are classified chemically as1. Amino acid–based, which includes

• Proteins, Peptides, Amines

2. Steroids—made from cholesterol; sex hormones made by gonads & hormones of adrenal cortex

Local Hormones:– Prostaglandins—made from highly active lipids

released by nearly all cell membranes

Direct Gene Activation (Steroid Hormone Action)

1. Diffuse through the plasma membrane of target cells

2. Enter the nucleus

3. Bind to a specific protein within the nucleus

4. Bind to specific sites on the cell’s DNA

5. Activate genes that result in synthesis of new proteins

Second-Messenger System (Nonsteroid Hormone Action)

1. Hormone binds to a membrane receptor

2. Hormone does not enter the cell

3. Sets off a series of reactions that activates an enzyme

4. Catalyzes a reaction that produces a second-messenger molecule

5. Oversees additional intracellular changes to promote a specific response

Explain how various endocrine glands are stimulated to release their hormonal products

1. Hormonal Stimuli- Endocrine glands are activated by other hormones

2. Humoral Stimuli-Changing blood levels of certain ions stimulate hormone release

3. Neural Stimuli-Nerve impulses stimulate hormone release; Most are under the control of the sympathetic nervous system

Hormonal Stimuli of Endocrine Glands

Figure 9.2a

• Most common stimuli• Endocrine glands are

activated by other hormones

• Examples:– Anterior pituitary

hormones

Humoral Stimuli of Endocrine Glands

Figure 9.2b

• Changing blood levels of certain ions stimulate hormone release

• Humoral indicates various body fluids such as blood and bile

• Examples:– Parathyroid hormone– Calcitonin– Insulin

Figure 9.2c

Neural Stimuli of Endocrine Glands• Nerve impulses stimulate

hormone release• Most are under the

control of the sympathetic nervous system

• Examples include: the release of norepinephrine and epinephrine by the adrenal medulla

Define negative feedback and describe its role in regulating blood levels of the various hormones.

• Negative feedback– Includes most homeostatic control mechanisms– Shuts off the original stimulus, or reduces its

intensity• Hormone secretion is triggered by a stimulus or low

hormone levels in the blood triggers the release of more hormone

• Hormone release stops once an appropriate level in the blood is reached

Describe the difference between endocrine and exocrine glands.

• Two major gland types– Endocrine gland

• Ductless since secretions diffuse into blood vessels• All secretions are hormones

– Exocrine gland• Secretions empty through ducts to the epithelial

surface• Include sweat and oil glands

On an appropriate diagram, identify the major endocrine glands and tissues.

List hormones produced by the endocrine glands and discuss their general functions.

1. Pituitary gland2. Thyroid gland3. Parathyroid glands4. Adrenal glands5. Pineal gland6. Thymus gland7. Pancreas8. Gonads (Ovaries

and Testes)9. Hypothalamus

Hormones of the Anterior Pituitary

Figure 9.4

Hormones of the Posterior Pituitary

Figure 9.6

Thyroid Gland

Figure 9.7a

• Thyroid hormone– Major metabolic hormone– Composed of two active

iodine-containing hormones

• Thyroxine (T4)—secreted by thyroid follicles

• Triiodothyronine (T3)—conversion of T4 at target tissues

• Calcitonin– Decreases blood calcium

levels by causing its deposition on bone

– Antagonistic to parathyroid hormone

– Produced by parafollicular cells

– Parafollicular cells are found between the follicles

Hormones of the Adrenal Cortex

Figure 9.11

Hormones of the Adrenal Cortex

• Mineralocorticoids (mainly aldosterone)• Glucocorticoids (cortisone and cortisol) • Sex hormones(Mostly androgens (male sex hormones)

some estrogens (female sex hormones)

Hormones of the Adrenal MedullaTwo similar hormones (catecholamines)

Epinephrine (adrenaline)Norepinephrine (noradrenaline)

Hormones of the Adrenal Cortex

Figure 9.12

• Mineralocorticoids (mainly aldosterone)– Produced in outer adrenal cortex– Regulate mineral content in blood– Regulate water and electrolyte

balance– Target organ is the kidney– Production stimulated by renin

and aldosterone– Production inhibited by atrial

natriuretic peptide (ANP)

Hormones of the Adrenal Cortex

• Glucocorticoids (including cortisone and cortisol)– Produced in the middle layer of the adrenal cortex– Promote normal cell metabolism– Help resist long-term stressors– Released in response to increased blood levels of

ACTH

Hormones of the Adrenal Cortex

• Sex hormones– Produced in the inner layer of the adrenal cortex– Small amounts are made throughout life– Mostly androgens (male sex hormones) are made

but some estrogens (female sex hormones) are also formed

Hormones of the Adrenal Medulla

• Produces two similar hormones (catecholamines)– Epinephrine (adrenaline)– Norepinephrine (noradrenaline)

• These hormones prepare the body to deal with short-term stress (“fight or flight”) by– Increasing heart rate, blood pressure, blood

glucose levels– Dilating small passageways of lungs

Roles of the Hypothalamus and Adrenal Glands in the Stress Response

Figure 9.13

Short term More prolongedStress

Hypothalamus

Nerve impulses

Adrenalcortex

Releasing hormone

Corticotropic cells ofanterior pituitary

ACTH

Mineralocorticoids Glucocorticoids

1. Retention of sodiumand water by kidneys

2. Increased bloodvolume and bloodpressure

1. Proteins and fatsconverted to glucoseor broken down forenergy

2. Increased bloodsugar

3. Suppression ofimmune system

Long-term stress responseShort-termstress response

Spinal cord

Adrenalmedulla

Preganglionicsympatheticfibers

Catecholamines(epinephrine andnorepinephrine)

1. Increased heart rate2. Increased blood pressure3. Liver converts glycogen to

glucose and releases glucoseto blood

4. Dilation of bronchioles5. Changes in blood flow

patterns, leading to increasedalertness and decreaseddigestive and kidney activity

6. Increased metabolic rate

Pineal Gland

• Found on the third ventricle of the brain

• Secretes melatonin– Helps establish the body’s wake and

sleep cycles– Believed to coordinate the hormones

of fertility in humans

Thymus Gland

• Located posterior to the sternum

• Largest in infants and children

• Produces thymosin– Matures some types of

white blood cells– Important in developing

the immune system

Pancreatic Islets• The pancreas is a mixed gland and has both

endocrine and exocrine functions• The pancreatic islets produce hormones

– Insulin—allows glucose to cross plasma membranes into cells from beta cells

– Glucagon—allows glucose to enter the blood from alpha cells

– These hormones are antagonists that maintain blood sugar homeostasis

Gonads

• Ovaries– Produce eggs– Produce two groups of

steroid hormone• Estrogens• Progesterone

• Testes– Produce sperm– Produce androgens,

such as testosterone

Hormones of the Ovaries• Estrogens

– Stimulate the development of secondary female characteristics – Mature female reproductive organs

• With progesterone, estrogens also– Promote breast development– Regulate menstrual cycle

• Progesterone– Acts with estrogen to bring about the menstrual cycle– Helps in the implantation of an embryo in the uterus– Helps prepare breasts for lactation

Hormones of the Testes

• Produce several androgens• Testosterone is the most important androgen

– Responsible for adult male secondary sex characteristics

– Promotes growth and maturation of male reproductive system

– Required for sperm cell production

Discuss ways in which hormones promote body homeostasis by giving examples of hormonal actions.

• Homeostasis—maintenance of a stable internal environment

Hormonal Regulation of Calcium in Blood

Figure 9.10

Calcium homeostasis of blood9–11 mg/100 ml

RisingbloodCa2+

levels

Thyroid glandreleasescalcitonin

Osteoclastsdegrade bonematrix and releaseCa2+ into blood

PTH

Calcitonin Calcitoninstimulatescalcium saltdepositin bone

Parathyroidglands releaseparathyroidhormone (PTH)

Thyroidgland

Thyroidgland

Parathyroidglands

FallingbloodCa2+

levels

Imbalance

Imbalance

Hormonal Regulation of Blood Glucose

Describe the functional relationship between the hypothalamus and the pituitary gland.

• Hormonal release by pituitary is regulated by releasing and inhibiting hormones produced by the hypothalamus

• Hypothalamus produces two hormones• These hormones are transported to neurosecretory

cells of the posterior pituitary– Oxytocin– Antidiuretic hormone

• The posterior pituitary is not strictly an endocrine gland, but does release hormones

Describe major pathological consequences of hypersecretion and hyposecretion of the hormones considered in this chapter.• Growth hormone (GH) disorders

– Pituitary dwarfism results from hyposecretion of GH during childhood– Gigantism results from hypersecretion of GH during childhood– Acromegaly results from hypersecretion of GH during adulthood

• Thyroid Gland• Goiters

– Thyroid gland enlarges due to lack of iodine– Salt is iodized to prevent goiters

• Cretinism– Caused by hyposecretion of thyroxine– Results in dwarfism during childhood

• Myxedema– Caused by hypothyroidism in adults– Results in physical and mental slugishness

• Graves’ disease– Caused by hyperthyroidism– Results in increased metabolism, heat intolerance, rapid heartbeat, weight loss, and

exophthalmos

• Adrenal Glands• Adrenal cortex disorders• Addison’s disease

– Results from hyposecretion of all adrenal cortex hormones– Bronze skin tone, muscles are weak, burnout, susceptibility to

infection• Hyperaldosteronism

– May result from an ACTH-releasing tumor– Excess water and sodium are retained leading to high blood pressure

and edema• Cushing’s syndrome

– Results from a tumor in the middle cortical area of the adrenal cortex– “Moon face,” “buffalo hump” on the upper back, high blood

pressure, hyperglycemia, weakening of bones, depression

Indicate the endocrine role of the kidneys, the stomach and intestine, the heart, and the placenta.

Table 9.2 (2 of 2)