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Chapter 18 The Endocrine System. Endocrine and nervous systems work together Endocrine system hormones released into the bloodstream travel throughout the body results may take hours, but last longer Nervous system certain parts release hormones into blood

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Chapter 18 the endocrine system
Chapter 18The Endocrine System

  • Endocrine and nervous systems work together

  • Endocrine system

    • hormones released into the bloodstream travel throughout the body

    • results may take hours, but last longer

  • Nervous system

    • certain parts release hormones into blood

    • rest releases neurotransmitters excite or inhibit nerve, muscle & gland cells

    • results in milliseconds, brief duration of effects


General functions of hormones
General Functions of Hormones

  • Help regulate:

    • extracellular fluid

    • metabolism

    • biological clock

    • contraction of cardiac & smooth muscle

    • glandular secretion

    • some immune functions

  • Growth & development

  • Reproduction


Endocrine glands defined
Endocrine Glands Defined

  • Exocrine glands

    • secrete products into ducts which empty into body cavities or body surface

    • sweat, oil, mucous, & digestive glands

  • Endocrine glands

    • secrete products (hormones) into bloodstream

    • pituitary, thyroid, parathyroid, adrenal, pineal

    • other organs secrete hormones as a 2nd function

      • hypothalamus, thymus, pancreas,ovaries,testes, kidneys, stomach, liver, small intestine, skin, heart & placenta


Hormone receptors
Hormone Receptors

  • Hormones only affect target cells with specific membrane proteins called receptors


Circulating local hormones
Circulating & Local Hormones

  • Circulating hormones

    • act on distant targets

    • travel in blood

  • Local hormones

    • paracrines act on neighboring cells

    • autocrines act on same cell that secreted them


Lipid soluble hormones
Lipid-soluble Hormones

  • Steroids

    • lipids derived from cholesterol on SER

    • different functional groups attached to core of structure provide uniqueness

  • Thyroid hormones

    • tyrosine ring plus attached iodines are lipid-soluble

  • Nitric oxide is gas


Water soluble hormones
Water-soluble Hormones

  • Amine, peptide and protein hormones

    • modified amino acids or amino acids put together

    • serotonin, melatonin, histamine, epinephrine

    • some glycoproteins

  • Eicosanoids

    • derived from arachidonic acid (fatty acid)

    • prostaglandins or leukotrienes


Action of lipid soluble hormones

Hormone diffuses through phospholipid bilayer & into cell

Binds to receptor turning on/off specific genes

New mRNA is formed & directs synthesis of new proteins

New protein alters cell’s activity

Action of Lipid-Soluble Hormones


Action of water soluble hormones
Action of Water-Soluble Hormones

  • Can not diffuse through plasma membrane

  • Hormone receptors are integral membrane proteins

    • act as first messenger

  • Receptor protein activates G-protein in membrane

  • G-protein activates adenylate cyclase to convert ATP to cAMP in the cytosol

  • Cyclic AMP is the 2nd messenger

  • Activates kinases in the cytosol to speed up/slow down physiological responses

  • Phosphodiesterase inactivates cAMP quickly

  • Cell response is turned off unless new hormone molecules arrive


Hormonal interactions
Hormonal Interactions

  • Synergistic effect

    • a second hormone, strengthens the effects of the first

    • two hormones acting together for greater effect

    • thyroid strengthens epinephrine’s effect upon lipolysis

  • Permissive effect

    • you need two hormone present for one hormone to work properly

    • estrogen & LH are both needed for oocyte production

  • Antagonistic effects

    • two hormones with opposite effects

    • insulin promotes glycogen formation & glucagon stimulates glycogen breakdown


Control of hormone secretion
Control of Hormone Secretion

  • Regulated by signals from nervous system, chemical changes in the blood or by other hormones

  • Negative feedback control (most common)

    • decrease/increase in blood level is reversed

  • Positive feedback control

    • the change produced by the hormone causes more hormone to be released

  • Disorders involve either hyposecretion or hypersecretion of a hormone


Hypothalamus and pituitary gland
Hypothalamus and Pituitary Gland

  • Both are master endocrine glands since their hormones control other endocrine glands

  • Hypothalamus is a section of brain above where pituitary gland is suspended from stalk

  • Hypothalamus receives input from cortex, thalamus, limbic system & internal organs

  • Hypothalamus controls pituitary gland with 9 different releasing & inhibiting hormones


Pituitary gland

Hormones:

human growth hormone- hGH

thyroid stimulating - TSH

follicle stimulating- FSH

leutinizing hormone - LH

prolactin

adrenocorticotropin - ACTH

melanocyte stimulating - MSH

Pituitary Gland

5 types of cells:

  • somatotrophs: secrete hGH/somatotropin

  • thyrotrophs: secrete TSH/thyrotropin

  • gonadotrophs: secrete FSH, LH

  • lactotrophs: secrete prolactin

  • corticotrophs: secrete ACTH/corticotropin & MSH

  • Pea-shaped, 1/2 inch gland found in sella turcica of sphenoid

  • Infundibulum attaches it to brain

  • Anterior lobe = 75% develops from roof of mouth

  • Posterior lobe = 25%

    • ends of axons of 10,000 neurons found in hypothalamus

    • neuroglial cells called pituicytes


Human growth hormone
Human Growth Hormone

  • Produced by somatotrophs

  • induces target cells to make insulin-like growth factors (IGFs) that act locally or enter bloodstream

    • common target cells of IGFs are liver, skeletal muscle, cartilage and bone

    • GH + IGFs increase cell growth & cell division by increasing their uptake of amino acids & synthesis of proteins

    • stimulate lipolysis in adipose so fatty acids used for ATP

    • retard use of glucose for ATP production by cells

    • reduces uptake of glucose by the liver and promote breakdown of liver glycogen– so blood glucose levels stay high enough to supply brain

  • Excess of growth hormone

    • raises blood glucose concentration

    • pancreas releases insulin continually

    • Leads to beta-cell burnout

  • Diabetogenic effect

    • causes diabetes mellitis if no insulin activity can occur eventually


Regulation of hgh
Regulation of hGH

  • Low blood sugar stimulates release of GNRH from hypothalamus

    • anterior pituitary releases more hGH, more glycogen broken down into glucose by liver cells

  • High blood sugar stimulates release of GHIH from hypothalamus

    • less hGH from anterior pituitary, glycogen does not breakdown into glucose


Thyroid stimulating hormone tsh
Thyroid Stimulating Hormone (TSH)

  • Hypothalamus regulates thyrotroph cells

  • Thyrotroph cells produce TSH

  • TSH stimulates the synthesis & secretion of T3 and T4

  • Metabolic rate stimulated


Thyroid gland
Thyroid Gland

  • comprised of microscopic sacs called follicles = follicular cells making up the walls, surrounds a lumen

  • synthesize T3 & T4 (thyroxin)

  • In between follicular cells cells are parafollicular cells

    • produce calcitonin

  • On each side of trachea is lobe of thyroid

  • connected by an isthmus

  • Weighs 1 oz & has rich blood supply


Formation of thyroid hormone
Formation of Thyroid Hormone

  • Iodide trapping: follicular cells actively take up iodine from blood

  • Synthesis of thyroglobulin (TGB): follicular cells make TGB - secreted into the follicle lumen as the material colloid

  • Iodination of colloid: iodine ions are oxidated (I2- -> I2) by peroxidase within the cell

    • oxidized iodine then binds onto tyrosine residues on the TGB within colloid

  • Coupling of T1 and T2: forms T3 & T4

  • Uptake of colloid by follicular cells: digestion cleaves off T3 and T4

  • Secretion of T3 & T4 into blood: T3 & T4 are transported in blood bound to thryoxine-binding globulin


Actions of thyroid hormones
Actions of Thyroid Hormones

  • T3 & T4 = increases metabolic rate

    stimulates synthesis of protein

    stimulates breakdown of fats

    stimulates cholesterol excretion

    increases use of glucose & oxygen

    (ATP production)

    increases body temperature (calorigenic effect)


Control of t3 t4 secretion
Control of T3 & T4 Secretion

  • Low blood levels of hormones stimulate hypothalamus -> TRH

  • It stimulates pituitary to release TSH

  • TSH stimulates gland to raise blood levels

  • T3 and T4 regulate themselves through a negative feedback loop


Parathyroid glands
Parathyroid Glands

  • 4 pea-sized glands found on back of thyroid gland

  • Principal cells produce parathyroid hormone (PTH)

  • Oxyphil cell function is unknown


Parathyroid hormone
Parathyroid Hormone

  • Raises blood calcium levels

    • increases activity of osteoclasts (bone degrading cells)

    • increases reabsorption of Ca+2 by kidney

    • promote formation of calcitriol (vitamin D3) by kidney which increases absorption of Ca+2 and Mg+2 by intestinal tract

  • Opposite function of calcitonin (thyroid)

  • High or low blood levels of Ca+2 stimulate the release of different hormones --- PTH or CT

    • high level of calcium in blood - release of calcitonin by parafollicular cells, promotes uptake of calcium into bone matrix, lowers blood calcium

    • low level of calcium in blood - release of PTH by parathyroid glands, promotes release of calcium from bone, raises blood calcium


Follicle stimulating hormone fsh
Follicle Stimulating Hormone (FSH)

  • Releasing hormone from hypothalamus controls gonadotrophs

  • Gonadotrophs release follicle stimulating hormone

  • FSH functions

    • initiates the formation of follicles within the ovary

    • stimulates follicle cells to secrete estrogen

    • stimulates sperm production in testes


Luteinizing hormone lh
Luteinizing Hormone (LH)

  • Releasing hormones from hypothalamus stimulate gonadotrophs

  • Gonadotrophs produce LH

  • In females, LH stimulates

    • secretion of estrogen

    • ovulation of 2nd oocyte from ovary

    • formation of corpus luteum

    • secretion of progesterone

  • In males, stimulates interstitial cells to secrete testosterone


Ovaries and testes
Ovaries and Testes

  • Ovaries

    • estrogen, progesterone, relaxin & inhibin

    • regulate reproductive cycle, maintain pregnancy & prepare mammary glands for lactation

  • Testes

    • produce testosterone

    • regulate sperm production & 2nd sexual characteristics


Prolactin prl
Prolactin (PRL)

  • Hypothalamus regulates lactotroph cells

  • Lactotrophs produce prolactin

  • Under right conditions, prolactin causes milk production

  • Suckling reduces levels of hypothalamic inhibition and prolactin levels rise along with milk production

  • Nursing ceases & milk production slows


Melanocyte stimulating hormone
Melanocyte-Stimulating Hormone

  • Secreted by corticotroph cells

  • Releasing hormone from hypothalamus increases its release from the anterior pituitary

  • Function not certain in humans (increase skin pigmentation)

  • May have a role in promoting sexual performance


Adrenocorticotrophic hormone
Adrenocorticotrophic Hormone

  • Hypothalamus releasing hormones stimulate corticotrophs

  • Corticotrophs secrete ACTH (& MSH also)

  • ACTH stimulates cells of the adrenal cortex


Adrenal glands
Adrenal Glands

  • Cortex derived from mesoderm

  • Medulla derived from ectoderm

  • One on top of each kidney

  • 3 x 3 x 1 cm in size and weighs 5 grams

  • Cortex produces 3 different types of hormones from 3 zones of cortex: mineralcorticoids (aldosterone), glucocorticoids (cortisol) & androgens

  • Medulla produces epinephrine & norepinephrine


Adrenal gland
AdrenalGland

  • Cortex

    • 3 zones

  • Medulla


Mineralocorticoids
Mineralocorticoids

  • 95% of these hormones - aldosterone

  • Functions

    • increase reabsorption of Na+ with Cl- , bicarbonate and water following it

    • promotes excretion of K+ and H+

  • dehydration, hemorrhage (decrease in blood volume) - decreases blood pressure - secretion of renin from kidneys which stimulates angiotensin II release from lungs - stimulates aldosterone release from adrenal cortex - increases water uptake from kidneys and increased excretion of K+ into urine


Glucocorticoids
Glucocorticoids

  • 95% of hormonal activity is due to cortisol

  • neurosecretory cells secrete corticotropin-releasing hormone (CRH)

  • CRH promotes the release of ACTH where it stimulates the adrenal cortex to secrete corticol

  • Functions = helps regulate metabolism

    • increases rate of protein synthesis

    • increases conversion of amino acids to glucose – energy for protein synthesis

    • stimulates lipolysis for glucose synthesis (for energy)

    • increases glucose synthesis – ATP production provides resistance to stress by making nutrients available for ATP

    • raises BP by vasoconstriction (decreases blood loss)

    • anti-inflammatory effects reduced (skin cream)

      • reduces release of histamine from mast cells

      • decreases capillary permeability

      • depresses phagocytosis


Androgens
Androgens

  • Small amount of male hormone produced by the zona reticularis

    • insignificant in males

    • may contribute to sex drive in females

    • is converted to estrogen in postmenopausal females


Adrenal medulla
Adrenal Medulla

  • hormone producing cells = Chromaffin cells receive direct innervation from sympathetic nervous system

  • Produce epinephrine & norepinephrine

  • Hormones are sympathomimetic

    • effects mimic those produced by sympathetic NS

    • cause fight-flight behavior

  • sympathetic preganglionic neurons secrete acetylcholine - which stimulates secretion by the AM


Posterior pituitary gland neurohypophysis
Posterior Pituitary Gland (Neurohypophysis)

  • Does not synthesize hormones

  • Consists of axon terminals of hypothalamic neurons

  • Neurons release two neurotransmitters that enter capillaries

    • antidiuretic hormone

    • oxytocin


Oxytocin
Oxytocin

  • Two target tissues both involved in neuroendocrine reflexes

  • During delivery

    • baby’s head stretches cervix

    • hormone release enhances uterine muscle contraction

    • baby & placenta are delivered

  • After delivery

    • suckling & hearing baby’s cry stimulates milk ejection

    • hormone causes muscle contraction & milk ejection


Antidiuretic hormone adh
Antidiuretic Hormone (ADH)

  • Known as vasopressin

  • Functions

    • decrease urine production

    • decrease sweating

    • increase BP

  • Dehydration

    • ADH released

  • Overhydration

    • ADH inhibited


Pancreas
Pancreas

  • Organ (5 inches) consists of head, body & tail

  • Cells (99%) in acini produce digestive enzymes

  • Endocrine cells in pancreatic islets produce hormones

  • Exocrine acinar cells surround a small duct = digestive enzymes


  • Endocrine cells secrete near a capillary

  • Alpha cells (20%) produce glucagon

  • Beta cells (70%) produce insulin

  • Delta cells (5%) produce somatostatin

  • F cells produce pancreatic polypeptide


Regulation of glucagon insulin secretion
Regulation of Glucagon & Insulin Secretion

  • Low blood glucose stimulates release of glucagon

  • High blood glucose stimulates secretion of insulin


Pineal gland

Pineal Gland

  • Small gland attached to 3rd ventricle of brain

  • Consists of pinealocytes & neuroglia

  • Melatonin responsible for setting of biological clock

  • Jet lag & SAD treatment is bright light

  • light strikes retina and stimulates

  • suprachiasmatic region of

  • hypothalamus

  • stimulates sympathetic ganglion

  • which then stimulates the

  • pineal gland

  • light -> NE -> no melatonin

  • dark -> lack of NE -> melatonin


Thymus gland
Thymus Gland darkness due to lack of stimulation from sympathetic ganglion

  • Important role in maturation of T cells

  • Hormones produced by gland promote the proliferation & maturation of T cells

    • thymosin

    • thymic humoral factor

    • thymic factor

    • thymopoietin


Eicosanoids
Eicosanoids darkness due to lack of stimulation from sympathetic ganglion

  • Local hormones released by all body cells normally and upon trauma

  • synthesized from arachidonic acid (fatty acid)

  • Leukotrienes influence WBCs – inflammation & allergic response

  • Prostaglandins alter

    • smooth muscle contraction, glandular secretion, blood flow, platelet function, nerve transmission, metabolism etc.

    • Ibuprofen & other nonsteroidal anti-inflammatory drugs treat pain, fever & inflammation by inhibiting prostaglandin synthesis

    • PGs are synthesized by an enzyme complex containing the enzymes COX1 and COX2

    • Aspirin and ibuprofen can inhibit activity of COX1 isoform – short term anti-inflammatory

    • Vioxx, Bextra and Celebrex inhibit activity of COX2 isoform – long term anti-inflammatory


Pituitary gland disorders
Pituitary Gland Disorders darkness due to lack of stimulation from sympathetic ganglion

  • Hyposecretion during childhood = pituitary dwarfism (proportional, childlike body)

  • Hypersecretion during childhood = giantism

    • very tall, normal proportions

  • Hypersecretion as adult = acromegaly

    • growth of hands, feet, facial features & thickening of skin

Thyroid Gland Disorders

  • Hyposecretion of TSH during infancy results in dwarfism & retardation called cretinism

  • Hypothyroidism - undersecretion of T3 and T4

    • Caused by low production of TSH

    • in adults produces sensitivity to cold, low body temp. weight gain & mental dullness

  • Hyperthyroidism – oversecretion of T3 and T4 (Grave’s disease)

    • caused by the inability of the thyroid to respond to TSH levels

    • weight loss, cardiac complications, increased fluid behind the eyes & goiter = enlarged thyroid


Cushing s syndrome
Cushing’s Syndrome darkness due to lack of stimulation from sympathetic ganglion

  • Hypersecretion of glucocorticoids

  • Redistribution of fat, spindly arms & legs due to muscle loss

  • Wound healing is poor, bruise easily

Addison’s disease

  • Hyposecretion of glucocorticoids

    • hypoglycemia, muscle weakness, low BP, dehydration due to decreased Na+ in blood

    • mimics skin darkening effects of MSH

    • potential cardiac arrest


Diabetes mellitus hyperinsulinism
Diabetes Mellitus & Hyperinsulinism darkness due to lack of stimulation from sympathetic ganglion

  • Diabetes mellitus marked by hyperglycemia

    • excessive urine production (polyuria)

    • excessive thirst (polydipsia)

    • excessive eating (polyphagia)

  • Type I----deficiency of insulin (under 20)

  • Type II---adult onset

    • drug stimulates secretion of insulin by beta cells

    • cells may be less sensitive to hormone


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