Integration and Control: THE ENDOCRINE SYSTEM Campbell & Reece Chapter 45 1.

Integration and Control:

THE ENDOCRINE SYSTEM

Campbell & Reece Chapter 45

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Endocrine

• Hormones: substances produced by particular tissues of the body carried by the bloodstream to "target cells," upon which they exert special effects

• *Hormones are secreted by glands, made mostly of epithelial tissue

• Exocrine glands: secrete into ducts (sweat glands, digestive glands)

• Endocrine glands: secrete hormones (into bloodstream) "ductless glands"

• Endocrine Gland--->hormone--> Bloodstream------> target organ/tissue

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• Hormones may be: – Steroids – Peptides/proteins; – Amino acids

• Active in very small quantities • Controlled by:

– Negative Feedback

• Rapid degradation by the body

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Hormonal communication http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter20/animation__hormonal_communication.html

• Positive & Negative feedback• http://highered.mcgraw-hill.com/sites/00724

95855/student_view0/chapter20/animation__positive_and_negative_feedback__quiz_1_.html

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Mechanisms of Action of Hormones:2 Main ways that Hormones Effect Target Cells:

Intracellular receptor molecules- steroids, thyroid hormonesMembrane receptor molecules- amino, peptide, protein

hormonesA. Intracellular Receptors

• Steroid hormones and thyroid hormones are soluble in lipids and pass freely through cell membranes; must contact receptor site with in a cell

• This changes a cell’s actions (protein synthesis, etc.)

B. Membrane Receptors • Combine with receptors on or in the membrane target cells • Once combined, send a second messenger inside ? to the nucleus (cyclic AMP)• May simply increase/decrease a cell’s permeability to substances

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Action of Steroid Hormones http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120109/bio46.swf::Mechanism%20of%20Steroid%20Hormone%20Action

The Hypothalamus-Pituitary Axis: • Pituitary was once

considered the "master gland" until it was learned that it was under control of the hypothalamus (brain region)

• The hypothalamus makes several hormones which travel to and are released by the pituitary lobes.

• Target tissues are stimulated by (or inhibited by) release of these hormones into the bloodstream.

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Hormone Major Target Organ(s) Effects

AnteriorPituitary

Growth hormone (GH) Liver, adipose tissue

Promotes growth (indirectly), control of protein, lipid and carbohydrate metabolism

Thyroid-stimulating hormone (TSH) Thyroid gland Stimulates secretion of

thyroid hormones

Adrenocorticotropic hormone (ACTH) Adrenal gland (cortex) Stimulates secretion of

glucocorticoids

Prolactin (PRL) Mammary gland Milk production

Luteinizing hormone (LH) Ovary and testis Control of reproductive

function

Follicle-stimulating hormone (FSH) Ovary and testis Control of reproductive

function

PosteriorPituitary

Antidiuretic hormone (ADH) Kidney Conservation of body

water

Oxytocin Ovary and testisStimulates milk ejection and uterine contractions 7

The Hypothalamus-Pituitary Axis:

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PITUITARY: •About the size of a kidney bean•Divided into three lobes: Anterior, posterior, intermediate

Anterior PituitarySomatotropin = growth hormone (GH), stimulates protein

synthesis, growth of muscle and bone• Deficit: midget • Excess: giantism (acromegaly) • Affects glucose metabolism; inhibits uptake and oxidation of

glucose by cells, stimulates breakdown of fatty acid for energy (conserves glucose)

Prolaction (PRL) –stimulates the secretion of milk in mammals• controlled by inhibiting hormone in hypothalamus • continued by nerve impulses from suckling; hypothalamus

(supply upon demand)

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Intermediate Pituitary Lobe

• Melanocyte- stimulating Hormone (MSH) • (Wikipedia) ...stimulate the production and

release of melanin (melanogenesis) by melanocytes in skin and hair.

• MSH is also produced by a subpopulation of neurons in the hypothalamus.

• MSH released into the brain by these neurons has effects on appetite and sexual arousal.

• More important for color change in reptiles, etc.

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Posterior Pituitary Lobe

• Hypothalamus releases Oxytocin and antidiuretic hormone (ADH) and stores it here, released by posterior pituitary

• Oxytocin- "milk let down" hormone, stimulates uterine contractions, smooth muscle contraction (BP regulation)

• Antidiuretic Hormone (ADH)- a.k.a. vasopression (increase BP) decreases excretion of water by kidneys. Increases permeability of water in nephrons

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Regulation of The Other Glands:• Regulation: negative feedback system involving a gonadotropic (gonad-

stimulating) hormone

LH (luteinizing hormone): produced by ant. pituitary • In males:

– LH is carried by blood to stimulate testes – as blood level of testosterone increases, LH production decreases

• In females:– rise in LH stimulates ovulation

FSH (follicle-stimulating hormone): • In males: acts upon the sertoli cells of the testes, important for

spermatogenesis• In females:  stimulates maturation of germ cells, sets mentrual cycle• High concentrations of LH cause germ cells to produce an inhibitor, "inhibin",

which will then lower LH levels

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The Endocrine Glands

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Testes• Androgens- the "male sex hormones"• Testosterone (steroid) is one type. Produced

in the testes necessary for sperm production and secondary sex characteristics: • genitals • larnyx (voice change) • skeletal enlargement • muscle tissue • acne

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The Ovaries• Estrogens- the "female sex hormones"

• Different kinds of estrogen hormones: estriol, estrone, and estradiol (most important)

• Produced by ovaries by stimulation of FSH from pituitary • Stimulate development of secondary sex characteristics

(breast development, genital development, distribution of body fat)

• Progesterone- maintenance of pregnancy, uterus• (estrogen, progesterone interaction= menstrual cycle)• estrus cycle diagram, showing hormone fluctuations in the

mare http://www.equine-reproduction.com/articles/estrous.htm

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Prostaglandins• Hormone-like chemicals differ from other hormones:• Fatty acids (formed by oxygenation of Arachidonic Acid) • Produced by cell membranes of most organs (as opposed

to specific glands) • Often exert effects on the tissues that produce them • The target tissue may be that of another person (e.g. in

semen, for fertilization) • More patent than hormones (needed in smaller amounts) • Effects- stimulation of smooth muscle (uterus-

menstruation labor); blood vessel dilation/constriction (BP down, up); inflammatory response by T-cells

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Adrenal Glands• Adrenal Cortex- outer layer of adrenal glands;

major source of steroid hormones • Adrenal glands lie on top of kidneys ("ad-

renal") • Humans: two major groups of adrenocortical

steroids • Glucocorticoids • Mineralocorticoids

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Adrenal Cortex: Glucocorticoids

• Glucocorticoids- used to suppress inflammation (medical)

• Cortisol- (most important) mainly the formation of glucose from fats and proteins. Inhibit up take of glucose by most cells (except brain and heart). Release increases during excitement etc.; work with sympathetic nervous system.

• Secreted in response to Adrenocorticotropic Hormone (ACTH), secreted by Ant. Pituitary ("master gland") which is stimulated by hormone released from Hypothalamus

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Adrenal Cortex: Mineralocorticoids

• Affect the ion concentration in the blood; water loss/retention.

Aldosterone- (example) regulation of ions (K+, Na+)• Affect the transport of ions across membranes of

the NEPHRONS• Deficiency leads to Na+ ion loss (via urine) = loss

of water = lowers blood pressure• Since adrenal cortex is source of androgens (male

and female) sex hormones, a tumor can increases male secondary sex characteristics (e.g. bearded ladies)

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Adrenal MedullaAdrenal Medulla

• Central portion of adrenal made up of neurosecretory cells (rather than epithelial)

• Adrenaline and Noradrenalin- increase rate and strength of heartbeat; raise BP; dilate resp. passages (act as enforcer of sympathetic N.S.)

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Pancreatic Hormones: "Islets of Langerhans"

• Insulin: secreted in response to rise in blood sugar or AA concentration. It lowers blood sugar by stimulating up take of glucose (conversion of glucose to glycogen by liver)

• Glucagon: increases blood sugar by breakdown of glycogen glucose in liver and breakdown of fats/proteins

• Somatostatin: synthesis of insulin• Five different sugar-regulating hormones (growth

hormone, cortisol, insulin, adrenalin, glucagon)• Diabetes- insulin too low• Hypoglycemia- insulin too high

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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter20/animation__blood_sugar_regulation_in_diabetics.html

Thyroid Gland:

• Located on top of Larynx • Controlled by "hypothalamus- pituitary axis" - TSH (thyroid-

stimulating hormones a.k.a. "thyrotropin" • A. Thyroxine • Accelerates rate of cellular respiration (metabolism) • differs from androgens, estrogens, corticosteroids because it is an

amino acid with 4 iodine atoms (T4), also T3

• B. Calcitonin: inhibits release of calcium ions [Ca2+ ions] from bones. Secretion is controlled by Ca ion conc. in fluid around thyroid cells.

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Thyroid diseases

• Goiter is a swelling of the thyroid gland, results from low iodine in diet

• Hyperthyroidism: (overproduction) weight loss, nervousness, fatigue. Most common cause in Grave's Disease.

• Hypothyroidism: (underproduction) dwarfism in infants (Cretinism) low energy, low brain cell development, can be caused by insufficient iodine in diet

• autoimmune disease of thyroid : Hashimoto's thyroiditis 23

Parathyroid Glands:

• Located below thyroid, pea- size, smallest endocrine gland

• Parathormone: essential in mineral metabolism, regulation of Calcium and Phosphate ions in blood

• stimulates release of Ca?? ions from bones; secreted in response to low blood [Ca2+]

• (Calcium = blood coagulation, muscle contraction, nerve function)

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The Pineal Gland • Small lobe in forebrain, near center • Involved in "photoperiodism"- seasonal

enlargement of ovaries etc. • Secretes hormone: Melatonin (up/down,

day/night) • Melatonin: causes pigment cells to

open/close "biological clock"

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