The Endocrine System

Chapter 9

Intro to Endocrine System

Endocrine works with nervous system to control body (homeostasis).

Endocrine acts slower than nervous though.

Endocrine system uses hormones – chemical messengers (transported through bloodstream).

Endocrine System &

Hormone Function

Endocrine organs are very small compared to other organs in the body.

THE CHEMISTRY OF HORMONES:

Hormones are chemical substances that regulate the metabolic activity of other cells in the body.

Amino Acid-based hormones vs. Steroids

AA-based: proteins, peptides, and amines

Steroids: cholesterol; sex hormones (gonads) & hormones in adrenal cortex

Prostaglandins: lipids in cell membrane

Endocrine System &

Hormone Function

MECHANISMS OF HORMONE ACTION:

Target cells/organs – responds to hormones

Must have specific protein receptors on cell membrane where hormone can attach

Hormones act to increase or decrease the rate of normal metabolic activities within the cell.

Endocrine System &

Hormone Function

MECHANISMS OF HORMONE ACTION:

What happens when the hormone binds to the cell membrane? 1. Changes in plasma membrane permeability

or electrical state.

2. Synthesis of proteins or certain regulatory molecules (enzymes) in the cell.

3. Activation or inactivation of enzymes.

4. Stimulation of mitosis (cell division).

Endocrine System &

Hormone Function

2 Main Mechanisms for Hormone Action:

Steroid Hormone Action

1. Steroid hormones diffuse across plasma membrane (lipid-soluble).

2. Steroid hormones enter nucleus.

3. Steroid hormones bind to specific receptor protein.

4. Hormone-receptor complex binds to DNA.

5. Activates transcription & translation (makes protein).

Endocrine System &

Hormone Function

Nonsteroid Hormone Action:

1. Hormone binds to membrane receptor (cannot go through membrane on its own).

2. Starts a series of reactions that activate enzyme.

3. Enzyme catalyzes rxn to make a 2nd messenger molecule.

4. 2nd messenger molecule oversees other intracellular changes.

Endocrine System &

Hormone Function

CONTROL OF HORMONE RELEASE:

Negative Feedback Mechanisms – hormone secretion is triggered by some stimulus, and when hormone levels reach a certain level, hormone release is inhibited.

Endocrine System &

Hormone Function 3 Categories for

Endocrine Gland Stimuli:

1) HORMONAL – most common; Hypothalamus secretes hormones that stimulate the anterior pituitary gland to secrete hormones that stimulate other endocrine glands to secrete hormones.

Hierarchal control system with the hypothalamus in control

Endocrine System &

Hormone Function

3 Categories for Endocrine Gland Stimuli:

2) HUMORAL – monitoring levels of various substances in body fluids such as blood

Changing blood level concentrations release hormone

Ex. Decrease blood Ca release of PTH to increase Ca

Increase Ca release of calcitonin to decrease Ca

Endocrine System &

Hormone Function

3 Categories for Endocrine Gland Stimuli:

3) NEURAL – Nerve fibers stimulate hormone secretion

Ex. Sympathetic NS stimulates adrenal medulla cells to secrete catecholamines (epinephrine and norepinephrine) during times of stress

Major Endocrine Organs - 10

Organs can be endocrine only (anterior pituitary, thyroid, adrenals, & parathyroids) OR

Endocrine & Exocrine (pancreas & gonads)

Endocrine glands are ductless (hormones release into blood or lymph)

Exocrine glands have ducts to release to body surface or cavities – Ex sweat glands

Major Endocrine Organs

Hypothalamus

Pituitary gland

Thyroid gland

Parathyroid glands

Adrenal gland

Pineal gland

Thymus gland

Pancreas

Gonads – Ovaries and Testes

Pituitary Gland

About the size of a grape

Hangs from inferior surface of hypothalamus

Surrounded by “turk’s saddle” of sphenoid bone

2 Lobes: Anterior pituitary (glandular tissue) & Posterior pituitary (nervous tissue)

Tropic hormones – stimulate target organs, which are also endocrine glands, to secrete their hormones (HORMONAL)

Pituitary Gland Hormones ANTERIOR PITUITARY:

All are proteins, act through 2nd messenger system, and regulated by hormonal stimuli

Growth Hormone (GH) - stimulates growth of bones and muscles; metabolism; regulated by hypothalamus releasing and inhibiting hormones

Prolactin (PRL) – stimulates milk production

targets human breasts; regulated by hypothalamic hormones

Follicle-stimulating hormone (FSH) – stimulates production of ova & sperm; regulated by hypothalamic hormones

Pituitary Gland Hormones ANTERIOR PITUITARY:

Luteinizing hormone (LH) – stimulates ovulation of egg and causes ruptured follicle to become corpus luteum

produce progesterone and some estrogen; in men (also interstitial cell-stimulating hormone (ICSH)) stimulates interstitial cells of testes to produce testosterone; regulated by hypothalamic hormones

Thyrotropic hormone (TSH) – Thyroid-stimulating hormone – stimulates thyroid; regulated by thyroxine in blood and hypothalamic hormones

Adrenocorticotropic hormone (ACTH) – stimulates adrenal cortex to secrete glucocorticoids; regulated by glucocorticoids and hypothalamic hormones

Pituitary Gland Hormones

POSTERIOR PITUITARY:

Storage area

Oxytocin – made by hypothalamus; released during childbirth to increase contractions, released during sex, released when breast-feeding; oxytocin drugs are used to induce labor; oxytocics are used to stop postpartum bleeding and stimulate milk ejection reflex

Pituitary Gland Hormones

POSTERIOR PITUITARY:

Antidiuretic hormone (ADH) – produced by hypothalamus; inhibits urine production causes kidneys to reabsorb more water

urine volume decreases & blood volume increases; can increase blood pressure (vasopressin)

Drinking alcohol and caffeine inhibits ADH urinate more

Homeostatic

Imbalance Too much or too little

GROWTH HORMONE:

Hyposecretion

pituitary dwarfism

Hypersecretion

pituitary gigantism

If hypersecretion after long-bone growth has ended acromegaly

(malformed facial features)

READ pg. 286 Closer Look box

Homeostatic Imbalance

Too little (hyposecretion) of FSH or LH

sterility in males & females

Drugs that promote fertility stimulate gonadotropic hormones (multiple births may occur)

Hyposecretion of ADH excessive urine

(DIABETES INSIPIDUS)

Pituitary-Hypothalamus

Relationship

Anterior pituitary gland is sometimes called the “master endocrine gland”

However the hypothalamus produces releasing & inhibiting hormones (sent into the portal circulation)

Hypothalamus makes OXYTOCIN & ANTIDIURETIC HORMONE (sent to posterior pituitary for storage by the axons of neurosecretory cells)

Thyroid Gland

Located at base of throat, inferior to Adam’s apple

2 lobes joined by a central mass called the isthmus

Follicles inside thyroid gland store colloidal material hormones

Thyroid hormone – major metabolic hormone; made in follicles; Thyroxine (T4) and Triiodothyroxine (T3)

Thyroid Gland

T4 is major hormone secreted by thyroid follicles

T3 is formed at target tissues by converting T4

Thyroid hormone – controls rate of glucose burning into energy; every cell is targeted; controls growth and development in reproductive & nervous systems; regulated by TSH

Thyroid Gland

Calcitonin – decreases blood calcium levels calcium is deposited into bones; it does

opposite of parathyroid hormone; made by C cells in connective tissue between follicles; released when blood calcium is too high; calcitonin production decreases in elderly; regulated by calcium in blood

Homeostatic Imbalance

Goiters – enlargement of thyroid gland caused by deficient amount of iodine in diet; TSH keeps calling for thyroxine and thyroid gland tries to put it out (enlarges); not common in US (salt has iodine in it)

Cretinism – occurs in early childhood as a result of hyposecretion of thyroxine lack of TH stimulation (dwarfism)

Myxedema – hypothyroidism in adults; physical and mental sluggishness, puffiness in face, fatigue, poor muscle tone, low body temp. Treat with oral thyroxine

Parathyroid Glands

Found on posterior surface of thyroid gland

Normally 2 glands per lobe = 4 (but 8 have been reported before)

Parathyroid hormone (PTH) – regulates blood calcium levels; low blood Ca2+ release PTH

stimulates osteoclasts to break down bone and release calcium; regulated by calcium in blood

**PTH is hypercalcemic hormone & Calcitonin is hypocalcemic hormone

Homeostatic Imbalance

Hypoparathyroidsim: Blood calcium is too low neurons become overactive

TETANY (uncontrollable spasms)

Severe hyperparathyroidism massive bone destruction bones are fragile

Adrenal Glands

2 bean-shaped glands that curve over kidneys

Parts are medulla region & adrenal cortex

Adrenal Cortex Hormones

Produces corticosteroids mineralcorticoids,

glucocorticoids, and sex hormones

MINERALCORTICOIDS:

Aldosterone – regulate mineral content of blood; mainly Na & K; Blood levels of aldosterone rises

kidney tubules keep Na and allow K to leave in the urine keeps water in body; regulated by changes

in bv or bp & K/Na levels in blood

RENIN – enzyme that kidneys release when bp drops that causes aldosterone to be released retains Na in blood retains water bv increases bp

increases

Adrenal Cortex Hormones

GLUCOCORTICOIDS:

Cortisone & Cortisol – promote normal cell metabolism; help resist long-term stressors (increase blood glucose); Glucocorticoids are high in blood fats & proteins broken down

for glucose (hyperglycemic hormones); they also decrease edema (inflammation) and inhibit prostoglandins (cause pain)

Given to patients to suppress inflammation

Regulated by blood levels of ACTH (released when ACTH is high)

Adrenal Cortex Hormones

SEX HORMONES:

Produced in small amounts

Androgens – male hormone; support sperm formation and development of male characteristics; regulated by FSH and LH

Estrogens – female hormone; stimulate uterine lining growth and help with development of female characteristics; regulated by FSH and LH

Homeostatic Imbalances

Addison’s disease – caused by hyposecretion of all adrenal cortex hormones; bronze tone of skin; sodium and water are lost from body (water and electrolyte imbalance); muscles weaken and shock may occur

Homeostatic Imbalance

Cushing’s syndrome – tumor in middle of cortex area in adrenal gland; too much of the glucocorticoids are released moon

face & buffalo hump on back

High blood pressure

Possible diabetes

Weakened bones

Homeostatic Imbalances

Masculinization – caused by oversecretion of sex hormones

Dramatic in women

beard, body hair, voice

Hormones of the Adrenal Medulla

Developed from nervous tissue – stimulated by sympathetic nervous tissue

Epinephrine (adrenaline) & Norepinephrine (noradrenaline) = Catecholamines

Released for “fight or flight” response

Increase HR, BP, and blood glucose levels, and dilate small passageways of lungs

Catecholamines are for short-term stressors, whereas Glucocorticoids are for prolonged stressors.

Hormones of the Adrenal Medulla

HOMEOSTATIC IMBALANCE:

Hypersecretion of catecholamines leads to excessive sympathetic nervous system activity.

Corrected by surgically removing catecholamine-secreting cells.

Pancreatic Islets

Pancreas = mixed gland

Called islets of Langerhans

Exocrine parts act in digestive system

Insulin – released from beta cells in response to high blood glucose; increases ability of body cells to transport glucose across their membranes glucose oxidized for energy or

stored as glycogen (hypoglycemic – acts to lower glucose in blood)

Homeostatic Imbalance Diabetes mellitus – no insulin causes blood

glucose to rise over normal (80-120 mg / 100 mL blood) Glucose flows out through urine and takes water with

it = dehydration Fats & Proteins are broken down for energy

weaker, harder to fight infection Large amounts of fats used for energy blood

becomes acidic (acidosis) ketones are in blood (can cause coma or death)

Signs: 1) polyuria (excessive urination) 2) polydipsia (excessive thirst) 3) polyphagia (hunger)

Treat with diet, insulin injections, and oral medications.

Type I: juvenile (serious) and Type II: adult

Pancreatic Islets

Glucagon – antagonist of insulin; released by alpha cells in response to low blood glucose; (hyperglycemic = acts to increase blood glucose); targets the liver to break down stored glycogen

Pineal Gland

Also called Pineal Body; found in 3rd ventricle of brain

Melatonin – levels change for day and night; peak levels at night make you

drowsy; lowest at noon; establishes day-night cycle; helps coordinate hormones of fertility and inhibits reproductive system

Thymus

In upper thorax, posterior to sternum

Large in infants and decreases in size throughout adulthood

Thymosin – programs “T cells”

Incubator for maturation of white blood cells = T lymphocytes

Hormones of the Ovaries

Ovaries produce eggs and 2 steroid hormones

Anterior pituitary gonadotropic hormones stimulate puberty

Estrogens – estrone and estradiol are produced by Graafian follicles = stimulate development of secondary sex characteristics

Work with progesterone to prepare uterus (menstrual cycle)

Help maintain pregnancy and prepare breasts

Hormones of the Ovaries

Progesterone – helps with menstrual cycle; helps to relax muscles of uterus when pregnant; produced by corpus luteum

Both hormones are released in a cycle by the anterior pituitary gonadotropic hormones

Hyposecretion of either hormone can inhibit the ability to get pregnant

Hormones of the Testes

Testes are suspended in scrotum (sac) outside pelvic cavity

Testes produces sperm and androgens

Androgens Testosterone – made by

interstitial cells and causes development of adult male characteristics; needed for continuous production of sperm

Hyposecretion sterile

Testosterone production is stimulated by LH

Other Hormone-Producing Tissues

& Organs

Hormone-producing cells are found in walls of small intestine, stomach, kidneys and heart.

Placenta – temporary organ during pregnancy produces estrogen & progesterone

Cancer cells – make excessive and uncontrollable amounts of normal hormones

Placenta

Formed in uterus of pregnant women

Respiratory, Excretory, and Nutrition-delivery for fetus

Human chorionic gonadotropin (hCG) – produced by conceptus and then by fetal part of placenta; similar to LH stimulates corpus luteum of ovary to produce progesterone and estrogen (keep uterus wall in tact)

Home pregnancy tests mainly for hCG in woman’s urine

Placenta

3rd month: ovaries become inactive, so placenta must make progesterone and estrogen (to maintain lining of uterus & prepare breasts)

Human placental lactogen (hPL) – works with estrogen and progesterone to prepare breasts for lactation

Relaxin – causes mother’s pelvic ligaments and pubic symphysis to relax and become flexible for birth

Developmental Aspects

Menopause – woman’s reproductive organs begin atrophy estrogen deficiency arteriosclerosis, osteoporosis, decreased skin elasticity, sympathetic nervous system (hot flashes), fatigue, nervousness, mood changes

Anterior pituitary declines in old age muscle atrophy & target organs become less productive

Older people have decline in insulin production diabetes