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Human Anatomy, Second Edition

McKinley & O'Loughlin

Chapter 20 Lecture Outline: Endocrine System

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Endocrine System Endocrine system and the nervous

system often work together to bring about homeostasis.

Both use specific communication methods and affect specific target organs.

Their methods and effects differ.

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Differences Communication Method

NS: Nerve impulses and neurotransmitters ES: Hormones

Target of Stimulation NS: Other neurons, muscles cells, and gland cells ES: Any cells with receptors for hormone

Effect of Stimulation NS: Stimulates or inhibits muscle contraction +/- gland secretion ES: Changes in metabolic activities

Response time NS: Quick action: msec or minutes (sometimes minutes) ES: Slower response: sec to hours to days

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Differences Range of Effect

NS: Localized ES: Widespread

Duration of Response NS: Short term effects generally ES: Long-term effects generally

Recovery Time NS: rapid ES: Slow

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Similarities Release chemicals that bind to receptors Many of the same chemical messengers Regulated mainly by negative feedback Common goal: coordinate and regulate Interlocking systems: neuroendocrine

system

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Endocrine Glands & Hormones Exocrine glands

secretions released into ducts opening onto an epithelial surface

Endocrine glands ductless organs that secrete their

molecules directly into the bloodstream

All endocrine cells are located within highly vascularized areas to ensure that their products enter the bloodstream immediately.

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Overview of Hormones Molecules that have an effect on specific organs. Only cells with specific receptors respond to

that hormone. Receptors are large proteins or glycoproteins About 2000-100,000 receptors/target cell Combination of hormone and receptor activates

a chain of events in the target cell leading to physiological effects

Increasing the hormone levels leads to a decrease in the number of receptors

Amount of hormone released regulated by need

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Overview of Hormones Cell with receptors are called target cells,

and the organs that contain them are called target organs. The response to a hormone depends on

both the hormone and the target cell Various target cells respond differently

to the same hormone Organs, tissues, or cells lacking the

specific receptor do not respond to its stimulating effects.

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Blocking Hormone Receptors RU-486 blocks the receptor for

progesterone and, thereby, blocks the effects of progesterone in maintaining the uterine lining and abortion of the embryo

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Classification of Hormones Peptide hormones (water soluble)

formed from chains of amino acids most of our body’s hormones are peptide hormones longer chains are called protein hormones Examples: all hormones of the hypothalamus and the

anterior pituitary Biogenic amines (water soluble)

small molecules produced by altering the structure of a specific amino acid

Examples: thyroid hormone, catecholamines Steroid hormones (lipid soluble)

derived from cholesterol Examples: hormones of the reproductive organs and

adrenal cortex

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Classification of Hormones Circulating hormones

Act on distant target cells Inactivated by liver in time Most common

Local hormones Act on nearby target cells or same

cell Inactivated quickly

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Negative Feedback Loop A stimulus starts a process, and

eventually either the hormone that is secreted or a product of its effects causes the process to slow down or turn off.

Many hormonal systems work by negative feedback mechanisms.

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Positive Feedback Loop Accelerates the original process, either

to ensure that the pathway continues to run or to speed up its activities.

Only a few positive feedback loops occur in the human endocrine system. one example is the process of milk

release from the mammary glands

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Control of Hormone Secretions Most hormones released in short

bursts When endocrine gland stimulated,

then more frequent bursts Three regulatory mechanisms

Humoral (ex., blood levels of a nutrient)

Neural Hormonal

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Hypothalamic Control of the Endocrine System The hypothalamus is the master control center of

the endocrine system and oversees most endocrine activity.

the hypothalamus secretes regulatory hormones that regulate the secretion of most of the anterior pituitary hormones

The hypothalamus has indirect control over these endocrine organs.

It is the major integrating link between the nervous and endocrine systems

The hypothalamus and pituitary gland have important roles in all aspects of growth, development, metabolism, and homeostasis

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Hypothalamic Control of the Endocrine System Hypothalamus produces two hormones that are

transported to and stored in the posterior pituitary.

oxytocin antidiuretic hormone (ADH) or vasopressin

Hypothalamus directly oversees the stimulation and hormone secretion of the adrenal medulla.

An endocrine structure that secretes its hormones in response to stimulation by the sympathetic nervous system.

Some endocrine cells are not under direct control of hypothalamus.

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Pituitary Gland (Hypophysis) Called the “master gland” but it is controlled

in two ways by the hypothalamus Partitioned both structurally and functionally

into an anterior pituitary and a posterior pituitary. Anterior pituitary (adenohypophysis)

is glandular tissue that produces hormones

Posterior pituitary (neurohypophysis) is neural tissue

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Control of Anterior Pituitary Gland Secretions Anterior pituitary gland is controlled by

regulatory hormones secreted by the hypothalamus. Releasing hormones Inhibiting hormones

Hormones reach the anterior pituitary via hypothalamo- hypophyseal portal system. a “shunt” that takes venous blood carrying

regulatory hormones from the hypothalamus directly to the anterior pituitary before the blood returns to the heart

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Tropic Hormones Most hormones from the anterior

pituitary are tropic hormones or tropins and activate other endocrine glands

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Anterior Pituitary Hormones TSH - thyroid stimulating hormone PRL - prolactin develops the breast and milk

production in pregnant women ACTH - adrenocorticotropic hormone Gonadotropins: FSH and LH - regulate hormone

synthesis by gonads and production and maturation of gametes

MSH - melanocyte stimulating hormone has little effect on humans and production ceases prior to adulthood except in specific diseases

GH - growth hormone (somatotropin) stimulates growth of the entire body by increasing protein production and growth of the epiphyseal plates

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Disorders of Growth Hormone Secretion Pituitary dwarfism

Lack of GH in a child Very short and often have periodic low blood sugar Injections of GH helps

Pituitary gigantism Excess GH in a child Very tall and leads to increased levels of blood sugar

(untreated can lead to diabetes and heart failure) and large internal organs

Acromegaly Excess GH in an adult Bones of hands, feet and face increase in size Diabetes and large internal organs Cause: lack of feedback or pituitary tumor

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Hypophysectomy Historically, used to treat

advanced breast and prostate cancer to remove the hormone stimulation for their growth. Medications used now.

Currently, used to treat pituitary tumors. Radiation may also be used.

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Posterior Pituitary Hormones Made by the hypothalamus, stored in the

posterior pituitary Oxytocin (OT)

stimulates contraction of smooth muscle of the uterus and ejection of milk in females

leads to prostate gland secretion in males regulated by positive feedback! makes us want to cuddle, groom, and pair bond

Antidiuretic hormone (ADH) or vasopressin stimulates water reabsorption by the kidneys and arteriole

constriction secretion inhibited by alcohol Lack: diabetes insipidus (normal urine output of 1-2

liters/day increases to about 20 liters/day)

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Thyroid Gland Inferior to the thyroid cartilage of the larynx and

anterior to the trachea. “Butterfly” shape due to its left and right lobes

connected by a narrow isthmus. The thyroid gland is highly vascularized, giving it

an intense reddish coloration. Regulation of thyroid hormone secretion depends

upon a complex thyroid gland–pituitary gland negative feedback process.

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Thyroid Gland Hormones Follicular cells produce thyroxine (T4) and

triiodothyronine (T3) Regulate the rate of metabolism Most cells are targets Needed for normal growth and development

(including the brain) Iodide is oxidized to iodine and then combines

with tyrosine to produce these hormones - occurs within a large glycoprotein molecule, thyroglobulin, which is secreted into follicle

Scalloping of edges of thyroglobulin indicates active secretion

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Thyroid Gland Hormones Parafollicular cells (Clear or C cells)

produce calcitonin which reduces blood calcium levels in children and deposits calcium in the bones. Opposes actions of parathyroid hormone.

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Disorders of Thyroid Gland Secretion Hyperthyroidism

Increased metabolic rate, weight loss, hyperactivity and heat intolerance

Causes: ingestion of T4, excessive stimulation by the pituitary, loss of feedback control by the thyroid (Graves disease)

Graves disease Autoimmune Exophthalmos Goiter

Treatment: removal or radioactive iodine

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Disorders of Thyroid Gland Secretion Hypothyroidism

Lack of thyroid hormone Low metabolic rate, lethargy, feel cold, weight gain some

times, photophobia Causes: decreased iodine intake, loss of pituitary

stimulation, post-therapeutic hypothyroidism, autoimmune Treatment: oral replacement Cretinism - severe form Myxedema - adult form

Goiter Enlargement of the thyroid Endemic from lack of iodine Surgical removal to decrease size may be required

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Parathyroid Glands Small, brownish-red glands on the posterior

surface of the thyroid gland. Usually four small nodules, but some may have as few

as two or as many as six. The chief cells are the source of parathyroid

hormone (PTH). stimulates osteoclasts to resorb bone and release

calcium ions from bone matrix into the bloodstream stimulates calcitriol hormone synthesis in the kidney promotes calcium absorption in the small intestine prevents the loss of calcium ions during the

formation of urine The function of oxyphil cells is not known.

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Disorders of Parathyroid Gland Secretion Hyperparathyroidism is most common

Bones depleted of calcium (fractures) Extra urinary calcium leads to kidney stones High blood calcium leads to decreased GI

motility and constipation High blood calcium leads to psychological changes

Hypoparathyroidism is rare Most of the symptoms are neuromuscular and in

severe cases, convulsions may occur Due to accidental removal or damage during thyroid

surgery usually or, less common, autoimmune disorder

Therapy is dietary vitamin D/calcium supplementation

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Adrenal Glands (suprarenal) Paired, pyramid-shaped endocrine glands

anchored on the superior surface of each kidney.

Retroperitoneal and embedded in fat and fascia to minimize their movement.

Outer adrenal cortex and an inner adrenal medulla secrete different types of hormones

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Adrenal Cortex Yellow color due to stored lipids in its cell. Synthesize more than 25 different steroid

hormones, the corticosteroids. corticosteroid synthesis is stimulated by the ACTH

produced by the anterior pituitary corticosteroids are vital to our survival; trauma to

or removal of the adrenal glands requires corticosteroid supplementation

Divided into the zona glomerulosa, the zona fasciculata, and the zona reticularis.

Different functional categories of steroid hormones are synthesized and secreted in the separate zones.

Regulates salt, sugar, and sex!

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• Mnemonic device for adrenal cortical hormones:

•Salt

•Sugar

•Sex

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Zona glomerulosa (salt) Mineralocorticoids (ex., aldosterone) Increase Na+ (and water) reabsorption

and K+ loss from kidneys Control salt/water balance (and,

therefore, blood pressure) Lack: Addison disease Excess: hypertension, edema, loss of K+

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Zona fasciculata (sugar) Glucocorticoids (ex., cortisone) Acts on most cells Help regulate blood nutrient levels (energy

sources) Increase blood sugar by increasing liver

glucose and glycogen formation Anti-inflammatory Helps resist long-term stress Lack: Addison disease Excess: Cushing syndrome

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Zona reticularis (sex) Gonadocorticoids or sex

hormones Most androgens from testes in

adult males

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Disorders in Adrenal Cortex Hormone Secretion Cushing syndrome

Excessive glucocorticoids (usually from taking corticosteroids but may be from too much production)

Immunosuppressant, but have side effects: osteoporosis, muscle weakness, redistribution of body fat and salt retention

Symptoms: body obesity (“moon face” and “buffalo hump”), hypertension, excess hair growth, kidney stones, and menstrual irregularities

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Disorders in Adrenal Cortex Hormone Secretion Addison disease

Chronic shortage of glucocorticoids and sometimes mineralocorticoids

Symptoms: weight loss, general weakening, hypotension (can be deadly), and darkening (“bronzing”) of the skin

Treat with oral corticosteroids President Kennedy had it

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Disorders in Adrenal Cortex Hormone Secretion Adrenogenital syndrome (androgen insensitivity

syndrome or congenital adrenal hyperplasia) Starts in embryo and fetus Inability to synthesize corticosteroids so body

releases massive amounts of ACTH Results in hyperplasia of the adrenal cortex and

causes release of intermediary hormones that have a testosterone-like effect, virilization in newborn girls and enlarged penis and premature puberty in males. Most have salt-losing problem.

Treat with oral corticosteroids to inhibit release of ACTH

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Adrenal Medulla Red-brown color due to its extensive vascularization. Primarily clusters of large, spherical cells called

chromaffin cells. When innervated by the sympathetic division

of the ANS, one population of cells secretes the hormone epinephrine and the other population secretes the hormone norepinephrine.

Hormones work with the sympathetic nervous system to prepare the body for an emergency or fight-or-flight situation.

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Disorder in Adrenal Medulla Hormone Secretion Pheochromocytoma

Benign tumor of chromaffin cells Episodic secretion of large amounts of

epinephrine and norepinephrine Marked swings in blood pressure Prolonged fight or flight symptoms Metabolic problems: hyperglycemia and

glycosuria Untreated: fatal brain hemorrhage or heart failure Treatment: surgery to remove tumor

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Pancreas Elongated, spongy, nodular organ between

the duodenum of the small intestine and the spleen and posterior to the stomach.

Both exocrine and endocrine activities. Mostly composed of cells called pancreatic

acini that produce an alkaline pancreatic juice that aids in digestion

Scattered among the acini are small clusters of endocrine cells called pancreatic islets (islets of Langerhans) composed of four types of cells

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Pancreas Alpha cells secrete glucagon when blood glucose

levels drop. Beta cells secrete insulin when blood glucose

levels are elevated. Delta cells are stimulated by high levels of nutrients in the

bloodstream. synthesize somatostatin, also described as growth

hormone-inhibiting hormone, or GHIH, which slows the release of insulin and glucagon and slows the rate of nutrient entry into the bloodstream

F cells are stimulated by protein digestion. secrete pancreatic polypeptide to suppress and regulate

somatostatin secretion from delta cells Pancreatic hormones provide for orderly uptake and

processing of nutrients.

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Diabetes Mellitus (“sweet urine”) General

Inadequate uptake of glucose from blood Glucose spills over into the urine “Starving in the midst of plenty” Chronically high blood glucose damages blood

vessels especially smaller arterioles Retinal blindness Kidney failure Leg amputations

Increases incidence of heart disease and stroke

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Diabetes Mellitus (“sweet urine”) Type 1 diabetes

Insulin-dependent DM Usually in children and young individuals -

not related to obesity Autoimmune - trigger event may be viral Beta cells are destroyed New monitoring instruments and automated

delivery of insulin have helped treatment and lifestyle

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Diabetes Mellitus (“sweet urine”) Type 2 diabetes

Insulin-independent DM Decreased insulin release or decreased insulin

effectiveness at peripheral tissues Formerly, adult-onset DM but it is being seen in

the young increasingly Obesity plays a major role in its development Treatment: For most, diet, exercise, and

medications that enhance insulin release or increase its sensitivity at the tissue level. More severe cases, insulin injections.

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Diabetes Mellitus (“sweet urine”) Gestational diabetes

Occurs in some pregnant women esp. towards end of pregnancy

Untreated: risk to fetus and increases complications of delivery

Risk: overweight, African American, Native American, or Hispanic, or those with a family history

Usually resolves after birth, but 20-50% chance of type 2 DM within 10 years

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Pancreas transplants have many risks Islet cell transplants less invasive but still

many complications

New Treatments for Severe DM

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May result from too much insulin Quickly leads to insulin shock If not sure if diabetic coma or insulin

shock, treat for insulin shock

Hypoglycemia Danger

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Metabolic Syndrome According to the American Heart

Association, almost 25% of Americans have metabolic syndrome.

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Metabolic Syndrome Metabolic syndrome increases the

risk of: Coronary artery disease Stroke Diabetes

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Metabolic Syndrome Risk factors (must have 3)

Obesity (waist greater than 35 in. for women and 40 in. for men)

High blood pressure (greater than 130/85 mm Hg)

High blood glucose (110 mg/dL or greater) Abnormal cholesterol profile (dyslipidemia)

Triglycerides (greater than 150 mg/dL) HDL (less than 50 mg/dL for women and less than 40

mg/dL for men)

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Metabolic Syndrome Treatment requires long-term

management of the risk factors Lose weight Exercise Eat a heart healthy diet

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Pineal Gland (body) A small, cone-shaped structure attached to the

posterior region of the epithalamus. Secretes melatonin.

helps regulate a circadian rhythm (24-hour body clock)

also appears to affect the synthesis of the hypothalamic regulatory hormone responsible for FSH and LH synthesis

role in sexual maturation is not well understood

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Thymus Bilobed - within the mediastinum superior to the

heart and posterior to the sternum. Size varies

always relatively large in infants and children as with the pineal gland, the thymus decreases in

size and activity with age, especially after puberty Functions principally in association with the

lymphatic system to regulate and maintain body immunity.

Produces complementary hormones thymopoietin and thymosins. act by stimulating and promoting the

differentiation, growth, and maturation of T-lymphocytes (thymus-derived lymphocytes)

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Endocrine Functions of the Kidneys, Heart, GI Tract, and Gonads Organs of the urinary, cardiovascular,

digestive, and reproductive systems contain their own endocrine cells, which secrete their own hormones. help regulate electrolyte levels in the

blood red blood cell production, blood volume,

and blood pressure digestive system activities sexual maturation and activity

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Aging and the Endocrine System Secretory activity of endocrine glands

decreases, especially secretion of growth hormone and sex hormones.

Reduction in GH levels leads to loss of weight and body mass.

Testosterone or estrogen levels decline