The Endocrine The Endocrine SystemSystem

Functions of the Functions of the Endocrine SystemEndocrine System Controls the processes involved Controls the processes involved

in movement and physiological in movement and physiological equilibriumequilibrium

Includes all tissues or glands Includes all tissues or glands that secrete hormones into the that secrete hormones into the bloodblood

Secretion of most hormones is Secretion of most hormones is regulated by a negative regulated by a negative feedback systemfeedback system

The number of receptors for a The number of receptors for a specific hormone can be altered specific hormone can be altered to meet the body’s demandto meet the body’s demand

Chemical Chemical Classificaton of Classificaton of

HormonesHormones

Steroid Hormones: Steroid Hormones: Lipid solubleLipid soluble Diffuse through cell membranesDiffuse through cell membranes Endocrine organsEndocrine organs

Adrenal cortexAdrenal cortex OvariesOvaries TestesTestes placentaplacenta

Chemical Chemical Classification of Classification of

HormonesHormones

Nonsteroid Hormones:Nonsteroid Hormones: Not lipid solubleNot lipid soluble Received by receptors external Received by receptors external

to the cell membraneto the cell membrane Endocrine organsEndocrine organs

Thyroid glandThyroid gland Parathyroid glandParathyroid gland Adrenal medullaAdrenal medulla Pituitary glandPituitary gland pancreaspancreas

Hormone ActionsHormone Actions

““Lock and Key” approach: Lock and Key” approach: describes the interaction describes the interaction between the hormone and its between the hormone and its specific receptor.specific receptor. Receptors for nonsteroid Receptors for nonsteroid

hormones are located on the hormones are located on the cell membranecell membrane

Receptors for steroid hormones Receptors for steroid hormones are found in the cell’s cytoplasm are found in the cell’s cytoplasm or in its nucleusor in its nucleus

Hormone ActionsHormone Actions Steroid HormonesSteroid Hormones

Pass through the cell Pass through the cell membranemembrane

Binds to specific receptorsBinds to specific receptors Then enters the nucleus to bind Then enters the nucleus to bind

with the cells DNA which then with the cells DNA which then activates certain genes (Direct activates certain genes (Direct gene activation).gene activation).

mRNA is synthesized in the mRNA is synthesized in the nucleus and enters the nucleus and enters the cytoplasm and promotes protein cytoplasm and promotes protein synthesis for:synthesis for: Enzymes as catalystsEnzymes as catalysts Tissue growth and repairTissue growth and repair Regulate enzyme functionRegulate enzyme function

Hormone ActionsHormone Actions Nonsteroid HormonesNonsteroid Hormones

React with specific receptors React with specific receptors outside the celloutside the cell

This triggers an enzyme reaction This triggers an enzyme reaction with lead to the formation of a with lead to the formation of a second messenger (cAMP).second messenger (cAMP).

cAMP can produce specific cAMP can produce specific intracellular functions:intracellular functions: Activates cell enzymesActivates cell enzymes Change in membrane permeabilityChange in membrane permeability Promote protein synthesisPromote protein synthesis Change in cell metabolismChange in cell metabolism Stimulation of cell secretionsStimulation of cell secretions

Negative FeedbackNegative Feedback

Negative feedback is the Negative feedback is the primary mechanism through primary mechanism through which your endocrine system which your endocrine system maintains homeostasismaintains homeostasis

Secretion of a specific Secretion of a specific hormone s turned on or off by hormone s turned on or off by specific physiological changes specific physiological changes (similar to a thermostat)(similar to a thermostat)

EXAMPLE: plasma glucose EXAMPLE: plasma glucose levels and insulin responselevels and insulin response

Number of Number of ReceptorsReceptors

Down-regulationDown-regulation: is the : is the decrease of hormone decrease of hormone receptors which decreases receptors which decreases the sensitivity to that hormonethe sensitivity to that hormone

Up-regulationUp-regulation: is the increase : is the increase in the number of receptors in the number of receptors which causes the cell to be which causes the cell to be more sensitive to a particular more sensitive to a particular hormonehormone

The Endocrine The Endocrine Glands and Their Glands and Their

HormonesHormones Pituitary GlandPituitary Gland

A marble-sized gland at the base of A marble-sized gland at the base of the brainthe brain

Controlled by the hypothalamus or Controlled by the hypothalamus or other neural mechanisms and other neural mechanisms and therefore the middle man.therefore the middle man. Posterior LobePosterior Lobe

Antidiuretic hormone: Antidiuretic hormone: responsible for fluid retentionresponsible for fluid retention

Oxytocin: contraction of the Oxytocin: contraction of the uterusuterus

The Endocrine The Endocrine Glands and their Glands and their

HormonesHormones Pituitary GlandPituitary Gland Exercise appears to be a Exercise appears to be a

strong stimulant to the strong stimulant to the hypothalamus for the release hypothalamus for the release of all anterior pituitary of all anterior pituitary hormones hormones Anterior LobeAnterior Lobe

AdrenocorticotropinAdrenocorticotropin Growth hormone *Growth hormone * ThyropinThyropin Follicle-stimulating hormoneFollicle-stimulating hormone Luteinizing hormone *Luteinizing hormone * ProlactinProlactin

The Endocrine The Endocrine Glands and Their Glands and Their

HormonesHormones Thyroid GlandThyroid Gland

Located along the midline of the Located along the midline of the neckneck

Secretes two nonsteroid hormonesSecretes two nonsteroid hormones Triiodothyronine (T3)Triiodothyronine (T3) Thyroxine (T4)Thyroxine (T4)

Regulates metabolismRegulates metabolism increases protein synthesisincreases protein synthesis promotes glycolysis, promotes glycolysis,

gluconeogenesis, glucose gluconeogenesis, glucose uptakeuptake

Calcitonin: calcium metabolismCalcitonin: calcium metabolism

The Endocrine The Endocrine GlandsGlands

Parathyroid GlandsParathyroid Glands Secretes parathyroid hormoneSecretes parathyroid hormone

regulates plasma calcium regulates plasma calcium (osteoclast activity) (osteoclast activity)

regulates phosphate levelsregulates phosphate levels

The Endocrine The Endocrine GlandsGlands

Adrenal MedullaAdrenal Medulla Situated directly atop each Situated directly atop each

kidney and stimulated by the kidney and stimulated by the sympathetic nervous systemsympathetic nervous system

Secretes the catecholaminesSecretes the catecholamines EpinephrineEpinephrine: elicits a fight or : elicits a fight or

flight responseflight response Increase H.R. and B.P.Increase H.R. and B.P. Increase respirationIncrease respiration Increase metabolic rateIncrease metabolic rate Increase glycogenolysisIncrease glycogenolysis VasodilationVasodilation

NorepinephrineNorepinephrine House keeping systemHouse keeping system

The Endocrine The Endocrine GlandsGlands

Adrenal CortexAdrenal Cortex Secretes over 30 different steroid Secretes over 30 different steroid

hormones (corticosteroids)hormones (corticosteroids) MineralocorticoidsMineralocorticoids

Aldosterone: maintains electrolyte Aldosterone: maintains electrolyte balancebalance

GlucocorticoidsGlucocorticoids Cortisol: Cortisol:

Stimulates gluconeogenisisStimulates gluconeogenisis Mobilization of free fatty acidsMobilization of free fatty acids Glucose sparingGlucose sparing Anti-inflammatory agentAnti-inflammatory agent

GonadocorticoidsGonadocorticoids testosterone, estrogen, progesteronetestosterone, estrogen, progesterone

The Endocrine The Endocrine GlandsGlands

Pancrease:Pancrease: Located slightly behind the Located slightly behind the

stomachstomach InsulinInsulin: reduces blood glucose: reduces blood glucose

Facilitates glucose transport into the Facilitates glucose transport into the cellscells

Promotes glycogenesisPromotes glycogenesis Inhibits gluconeogensisInhibits gluconeogensis

Glucagon: increases blood Glucagon: increases blood glucoseglucose

The Endocrine The Endocrine GlandsGlands

GonadsGonads testes (testes (testosteronetestosterone) = sex ) = sex

characteristicscharacteristics muscle development and maturitymuscle development and maturity

ovaries (estrogen) = sex ovaries (estrogen) = sex characteristicscharacteristics maturity and coordinationmaturity and coordination

Kidneys (Kidneys (erythropoietin)erythropoietin) regulates red blood cell productionregulates red blood cell production

The Endocrine The Endocrine Response to ExerciseResponse to Exercise

Table 5.3 Page 172Table 5.3 Page 172

Regulation of Regulation of Glucose Metabolism Glucose Metabolism

During ExerciseDuring Exercise Glucagon secretion increases Glucagon secretion increases

during exercise to promote liver during exercise to promote liver glycogen breakdown glycogen breakdown (glycogenolysis)(glycogenolysis)

Epinephrine and Norepinephrine Epinephrine and Norepinephrine further increase glycogenolysisfurther increase glycogenolysis

Cortisol levels also increase Cortisol levels also increase during exercise for protein during exercise for protein catabolism for later catabolism for later gluconeogenesis.gluconeogenesis.

Growth Hormone mobilizes free Growth Hormone mobilizes free fatty acidsfatty acids

Thyroxine promotes glucose Thyroxine promotes glucose catabolismcatabolism

Regulation of Regulation of Glucose Metabolism Glucose Metabolism

During ExerciseDuring Exercise

As intensity of exercise As intensity of exercise increases, so does the rate of increases, so does the rate of catecholamine release for catecholamine release for glycogenolysisglycogenolysis

During endurance events the rate During endurance events the rate of glucose release very closely of glucose release very closely matches the muscles need. matches the muscles need. (fig 5.9, pg. 174)(fig 5.9, pg. 174)

When glucose levels become When glucose levels become depleted, glucagon and cortisol depleted, glucagon and cortisol levels rise significantly to levels rise significantly to enhance gluconeogenesis.enhance gluconeogenesis.

Regulation of Regulation of Glucose Metabolism Glucose Metabolism

During ExerciseDuring Exercise Glucose must not only be Glucose must not only be

delivered to the cells, it must delivered to the cells, it must also be taken up by them. That also be taken up by them. That job relies on job relies on insulininsulin..

Exercise may enhance insulin’s Exercise may enhance insulin’s binding to receptors on the binding to receptors on the muscle fiber.muscle fiber.

Up-regulation (receptors) Up-regulation (receptors) occurs with insulin after 4 occurs with insulin after 4 weeks of exercise to increase weeks of exercise to increase its sensitivity (diabetic its sensitivity (diabetic importance). importance).

Regulation of Fat Regulation of Fat Metabolism During Metabolism During

ExerciseExercise When low plasma glucose levels When low plasma glucose levels

occur, the catecholamines are occur, the catecholamines are released to accelerate lypolysis.released to accelerate lypolysis.

Triglycerides are reduced to free Triglycerides are reduced to free fatty acids by lipase which is fatty acids by lipase which is activated by: (fig. 5.11, pg. 176)activated by: (fig. 5.11, pg. 176) CortisolCortisol EpinephrineEpinephrine NorepinephrineNorepinephrine Growth HormoneGrowth Hormone

Hormonal Effects on Hormonal Effects on Fluid and Electrolyte Fluid and Electrolyte

BalanceBalance

Reduced plasma volume leads Reduced plasma volume leads to release of to release of aldosteronealdosterone which which increases Na+ and H2O increases Na+ and H2O reabsorption by the kidneys and reabsorption by the kidneys and renal tubes.renal tubes.

Antidiuretic HormoneAntidiuretic Hormone (ADH) is (ADH) is released from the posterior released from the posterior pituitary when dehydration is pituitary when dehydration is sensed by osmoreceptors, and sensed by osmoreceptors, and water is then reabsorbed by the water is then reabsorbed by the kidneys.kidneys.