Chapter 16 Endocrine System Lecture 14 Marieb’s Human Anatomy and Physiology Marieb Hoehn.

Chapter 16Endocrine System

Lecture 14

Marieb’s HumanAnatomy and

Physiology

Marieb Hoehn

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Lecture Overview

• The Adrenal Glands

• The Pancreas

• Other Endocrine Tissues

• Stress and its effects

• Life-span changes

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Location/Blood Supply of the Adrenal

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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Adrenal Glands

Adrenal cortex and medulla are functionally distinct

Figure from: Hole’s Human A&P, 12th edition, 2010

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Hormones of the Adrenal MedullaEpinephrine (80%) and Norepinephrine (20%)

• derived from amino acid tyrosine• hormones of ‘fight or flight’ are called catecholamines

• release controlled by sympathetic nervous system (neural control of hormone release)• hormone releasing cells are considered equivalent to postganglionic sympathetic neurons

• increases heart rate and blood pressure• dilates respiratory airways• promotes glycogenolysis and gluconeogenesis• activates reticular formation• increases metabolic rates

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Adrenal Cortex and its Hormones

• Yellowish appearance of cortex is due to stored lipids, especially cholesterol and various fatty acids

• Produces more than 25 steroid hormones

• Hormones of the Adrenal Cortex are…– Called adrenocortical steroids, or corticosteroids

– Carried in blood by transcortins

– Essential to life

– Affect cellular metabolism by determining the nature and concentration of cellular enzymes

– Not stored in cell

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Adrenocortical Steroids - Aldosterone

• increases blood volume and pressure by promoting conservation of sodium ions and water (distal tubules of kidney)

• Activated by 1) the renin-angiotensin system and by 2) changing concentrations of of Na+ and K+

• Zona glomerulosaAldosterone is a mineralocorticoid

Figure from: Hole’s Human A&P, 12th edition, 2010

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Adrenocortical Steroids - GlucocorticoidsCortisol (hydrocortisone) – a glucocorticoid

• protein synthesis, protein catabolism • increases fatty acid release (glucose-sparing effect)• stimulates gluconeogenesis• controlled by CRH from hypothalamus and ACTH from anterior pituitary

Produced in the Zona Fasciculata

Blood levels peak shortly after arising in morning

Glucocorticoids have anti-inflammatory and anti-immune effects Figure from: Hole’s Human A&P, 12th edition,

2010

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Anti-Inflammatory Effects of Steroids

Eicosanoids are important paracrine factors that mediate many processes in the body, including:

- Inflammation- blood vessel constriction - blood clotting- smooth muscle contraction and relaxation

Figure from: Hole’s Human A&P, 12th edition, 2010

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Adrenocortical Steroids - Androgens

Adrenal androgens (gonadocorticoids)• supplement sex hormones from the gonads (release stimulated slightly by ACTH; inhibitory stimulus unknown). Mostly dehydroepiandrosterone (DHEA)

• may be converted to estrogen in the blood (♀)

• When secreted in normal amounts, neither adrenal androgens or estrogens affect sexual characteristics (may affect sex drive in ♀)

• Produced in the Zona Reticularis

• Tumors of this region can lead to androgenital syndrome (masculinization)

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Endocrine Pancreas

Figures from: Hole’s Human A&P, 12th edition, 2010

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Cells of the Pancreatic Islets

• Alpha cells - Glucagon

• Beta cells – Insulin, amylin

• Delta cells– Somatostatin (growth hormone-inhibiting hormone,

GH-IH)• Suppresses release of insulin and glucagon

• Slows rates of food absorption

• F cells– Pancreatic polypeptide (inhibits GB contractions –

exact physiological role is uncertain)

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Insulin

Insulin decreases blood glucose levels by allowing cells to take up glucose from the blood

Binding enhances glucose uptake

Brain, kidneys, liver, RBCs are insulin independent

Insulin release is also affected by the ANS

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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Glucagon

Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Raises blood glucose levels by: - stimulating breakdown of stored molecules- increasing release and formation of glucose

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Insulin and Glucagon

Example of a humoral stimulus (glucose) for hormone secretion

Figure from: Hole’s Human A&P, 12th edition, 2010

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Pineal Gland

Pinealocytes synthesize melatonin from serotonin

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Melatonin

• regulates circadian rhythms - daily changes in physiological processes that follow a regular pattern

Light (eyes) → retina → hypothalamus → reticular formation

melatonin pineal sympathetic fibers spinal cord

• may control onset of puberty (melatonin levels decline at puberty)

• helps regulate female reproductive cycle

• may protect CNS against free radicals (antioxidant)

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Other Endocrine GlandsReproductive Glands

• ovaries secrete estrogen and progesterone• testes secrete testosterone• placenta secretes estrogen, progesterone, and gonadotropins, e.g., hCG

Thymus Gland• secretes thymosins• promotes development of T-lymphocytes

Heart• secretes natriuretic peptides (ANP, BNP)

- Natri = sodium; uretic = in the urine- promote loss of water and Na+ at the kidney- secreted when atria/ventricles are stretched

- inhibit renin release- inhibit secretion of ADH and aldosterone

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Other Endocrine Glands• Adipose Tissue

– Leptin• After eating, adipose tissue absorbs glucose and lipids• Peptide hormone, leptin, is released• Binds to receptors in hypothalamus (esp. arcuate and paraventricular

nuclei)– Alters levels of other substances in brain– Increased sympathetic activity– Decreased insulin secretion– Permissive effect on GnRH (effects on reproductive function)– Sense of satiety and suppression of appetite

• Levels are normal in most obese individuals; receptors or cellular pathways may be defective

– Resistin• Reduces insulin sensitivity throughout body (insulin antagonist)• May be one of the ‘missing links’ between obesity and diabetes

– TNF - in obese people, inhibits glut4 protein; activates stress hormones

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Stress

Types of Stress• physical stress• psychological (emotional) stress

(Stress is any condition, physical or emotional, that threatens homeostasis)

Stress Response (General Adaptation Syndrome [GAS])

• hypothalamus triggers sympathetic impulses to various organs• epinephrine is released• cortisol is released to promote longer-term responses

Three general phases of the GAS in response to stress A R E:

• Alarm phase• Resistance phase• Exhaustion phase

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Responses to StressExhaustion - lipid reserves

- production of glucocorticoids - electrolyte imbalance - damage to vital organs

Figure from: Hole’s Human A&P, 12th edition, 2010

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GH Abnormalities

Growth Hormone Ups and Downs

• Gigantism - hypersecretion of GH in children • Acromegaly – hypersecretion of GH in adults• Dwarfism – hyposecretion of GH in children

Age 9 Age 16 Age 33 Age 52

Figure from: Hole’s Human A&P, 12th edition, 2010

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Diabetes (= Overflow)• Diabetes Mellitus (DM)

– Hyposecretion or hypoactivity of insulin– Three P’s of Diabetes Mellitus (mellitum = honey)

• Polyuria (increased urination)• Polydipsia (increased thirst)• Polyphagia (increased hunger)

– Hyperglycemia, ketonuria, glycosuria

• Renal Glycosuria– excretion of glucose in the urine in detectable amounts– normal blood glucose concentrations or absence of

hyperglycemia

• Diabetes Insipidus (insipidus = tasteless)– Hyposecretion or hypoactivity of ADH– Polyuria– Polydipsia

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Hormone Summary Table I – Pituitary HormonesTissue

Name Origin Destination Action on Target Tissue Control of Release1

FOLLICLE STIMULATING

HORMONE (FSH)

anterior pituitary

males: seminiferous tubules of testes;females: ovarian

follicle

males: sperm productionfemales: follicle/ovum maturation

Gonadotropin Releasing Hormone (GnRH)

LUETINIZING HORMONE (LH)

anterior pituitary

In males: interstitial cells in testes;

in females: mature ovarian follicle

males: testosterone secretionfemales: ovulation

Gonadotropin Releasing Hormone (GnRH)

THYROID STIMULATING

HORMONE (TSH)

anterior pituitary

thyroid secrete hormonesThyrotropin Releasing

Hormone (TRH)

GROWTH HORMONE (GH)

anterior pituitary

bone, muscle, fat growth of tissuesGrowth Hormone Rleasing

Hormone (GHRH)

ADRENOCORTICO-TROPIC HORMONE

(ACTH)

anterior pituitary

adrenal cortex secrete adrenal hormonesCorticotropin Releasing

Hormone (CRH)

PROLACTIN (PRL)anterior pituitary

mammary glands produce milkProlactin Releasing Hormone

(PRH)

ANTI-DIURETIC HORMONE (ADH)(VASOPRESSIN)

posterior pituitary

Collecting ducts of kidneys

reabsorption of water; increases blood pressure

increase in osmolarity of plasma or a decrease in blood

volume

OXYTOCIN (OT)posterior pituitary

uterine smooth muscle; breast

contraction during labor; milk letdownStretching of uterus; infant

suckling

Se(x)

T

G

A

P

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Hormone Summary Table IITissue

Name Origin Destination Action on Target Tissue Control of Release

TRIIODOTHYRONINE (T3) & THYROXINE

(T4)

Thyroid (follicular cells)

all cells increases rate of metabolism (BMR)Thyroid Stimulating Hormone

(TSH)

CALCITONIN Thyroid (C cells)Intestine, bone,

kidney

Decreases plasma [Ca2+]( intestinal absorp of Ca; action of

osteoclasts; excretion of Ca by kidney plasma [Ca2+]

PARATHYROID HORMONE (PTH)

ParathyroidsIntestine, bone,

kidney

Increases plasma [Ca2+]( intestinal absorp of Ca; action of

osteoclasts; excretion of Ca by kidney plasma [Ca2+]

EPINEPHRINE/NOREPINEPHRINE

(Catecholamines)Adrenal Medulla

cardiac muscle, arteriole and

bronchiole smooth muscle,

diaphragm, etc

increases heart rate and blood pressure...(fight or flight)

Sympathetic Nervous System

ALDOSTERONE(Mineralocorticoids)

Adrenal CortexKidneys; sweat glands; salivary glands; pancreas

reabsorption of water and Na (increases blood pressure) and excretion of K

(mineralocorticoid)

Angiotensin II plasma [Na+] plasma [K+]

CORTISOL(Glucocorticoids)

Adrenal Cortex all cellsDiabetogenic; anti-inflammatory

(glucocorticoid)ACTH

INSULINβ-cells of

Pancreatic Isletsall cells, liver and skeletal muscle

pushes glucose into cells from blood, glycogen formation (decreases blood glucose)

plasma [glucose]SNS

GLUCAGONα-cells of

pancreatic Isletsliver and skeletal

musclebreakdown of glycogen (increase in blood

glucose) plasma [glucose]

TESTOSTERONE Testessecondary sex

organsdevelopment and maintenance LH

ESTROGEN Ovariessecondary sex

organsdevelopment at puberty and maintenance

throughout lifeLH

NATRIURETIC PEPTIDES

atria and ventricles of heart

adrenal cortex, kidneys

increased excretion of sodium and water from kidneys, blood volume, blood pressure

Stretching of atria and ventricles

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Review

• Reaction to stress occurs in three stages– Short term

• Alarm or “fight or flight”• Reactions similar to sympathetic stimulation• Mediated by hormones of the adrenal medulla

– Long term• Resistance • Long-term raising of blood glucose• Mediated by hormones of the adrenal cortex

– Exhaustion• Failure of compensatory mechanisms