ENDOCRINE SYSTEM

Endocrine - General

Major Control System of HomeostasisNegative FeedbackDuctless Glands; Produce HormonesDiffuse into BloodSlow Initial Effects, but Effects Persist

much longerHormones act on specific Targets

Classification of Glands

Endocrine – ductless glands that secrete hormones into the blood stream

Exocrine – ducted glands that secrete their products onto a surface

Hormones – Definition

Definitions- Literal: To spur on, to set in motion- Physiological: A chemical

messenger that affects another tissue or organ (the target)

Hormones - General Function

Modify activity of target cells

Targets have specific receptors for the particular hormone

Distributed by blood

Location of Receptors

Cell Surface

- cell membraneIntracellular

- Cytoplasm

- Nucleus

Mechanisms of Hormone Action

Steroids (Synthesized from Cholesterol)- Hormone enters cell- Hormone forms complex with receptor- Hormone/receptor complex enters nucleus- Complex binds to DNA- Protein synthesis occurs- Protein alters cell function (i.e. produces the

effect)- E.g. Testosterone

Mechanisms of Hormone Action continued

Non-Steroids (Proteins/Peptides/Amine) Hormones- Hormone does not enter cell- Hormone is 1st messenger- Hormone binds to receptor on cell

membrane- Triggers formation of 2nd messenger (cyclic

AMP)- 2nd messenger alters cellular activities (i.e.

produce the effect)- E.g. Pituitary hormones

Regulation by Receptors

Changeable Number of receptors on target- Up Regulation

* Low hormone levels* Number of receptors increases* Target’s responsiveness increases

- Down Regulation* Excess hormone levels* Number of receptors decreases* Target’s responsiveness decreases

Secretion Stimuli

Hormonal- Tropic hormones regulate activity of

other endocrine glands - Most common

Humoral- Changing levels of ion or nutrients

trigger release of hormonesNeural

- Stimulated by nerve fibers

Hormonal Stimuli Hormonal Stimuli of Endocrine of Endocrine GlandsGlands

Slide 9.11Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Endocrine glands are activated by other hormones

Figure 9.2a

Humoral Stimuli of Humoral Stimuli of Endocrine GlandsEndocrine Glands

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Figure 9.2b

Changing blood levels of certain ions or nutrients stimulate hormone release

Neural Stimuli of Neural Stimuli of Endocrine GlandsEndocrine Glands

Slide 9.13Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Nerve impulses stimulate hormone release

Most are under control of the sympathetic nervous system

Figure 9.2c

Endocrine Organs

HypothalamusPituitary

- Anterior

- PosteriorThyroid GlandParathyroid

Glands

Adrenal Glands

- Cortex

- MedullaPancreasPineal GlandThymusGonads

Hypothalamus

Integrates Nervous System & EndocrinePortal Circulation carries hormones to

Anterior PituitaryReleasing Factors (hormones) stimulate

secretion by Anterior PituitaryInhibiting Factors (hormones) are

antagonistic to ReleasingNervous tissue carries hormones to

Posterior Pituitary

Pituitary Gland

Attached to Hypothalamus via infundibulum

Protected by sella turcica of sphenoidDivided into 2 lobes:

- Anterior (glandular)

- Posterior (neuroendocrine)

Anterior Pituitary (Adenohypophysis)

“Master Gland” (makes & secretes various tropic hormones)

Tropic Hormones- Act on other Endocrine Glands- Serve as Hormonal Stimuli- Stimulate release of another hormone

Anterior Pituitary (Adenohypophysis)

- Human Growth Hormone (GH):

*Target: All/Most Body Cells (esp. Bone & Muscle)

*Action: Promotes Growth & Repair,

*Increases Blood Glucose

- Prolactin (PRL):

*Target: Mammary Tissue*Action: Promotes milk secretion

Anterior Pituitary continued

Thyroid Stimulating Hormone (TSH)

- Target: Thyroid Gland

- Action: Stimulates production of Thyroxine

Anterior Pituitary continued

Adrenocorticotropic Hormones (ACTH)- Target: Adrenal Cortex- Action: Controls production/secretion adrenal

cortex hormonesGonadotropic Hormones

- Follicle Stimulating Hormone (FSH)* Target: Gonads (Ovaries/Testes)* Action: Production of gametes & sex

hormones

Anterior Pituitary continued

- Luteinizing Hormone (LH/ICSH)

*Target: Gonads

*Functions: Production of sex hormonesPrepare uterus for implantationDevelop corpus luteum

Hormones of the Anterior PituitaryHormones of the Anterior Pituitary

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Figure 9.4

Posterior Pituitary (Neurohypophysis)

Does NOT synthesize HormonesNeural rather than glandularStores & Releases two hormones produced

by hypothalamus

- Oxytocin

*Target: Uterus & Mammary Glands

*Action: Stimulates Contractions to eject fetus & milk

Posterior Pituitary continued

- Antidiuretic Hormone (ADH) also called vasopressin

*Target: Kidneys

*Action: Conserve Water (decrease urine

volume)Increase BP

Hormones of the Posterior PituitaryHormones of the Posterior Pituitary

Slide 9.22b

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 9.5

Thyroid Gland

Thyroid Hormone- T3 (Triiodothyronine), T4 (Thyroxine)- Target: Most body cells- Action: Increase metabolic rate, regulate

body temperatureCalcitonin

- Target: Bone/Osteoclast Inhibition- Action: Decrease blood Ca2+

(Hypocalcemia if excessive)

Parathyroid Glands

Parathyroid Hormone

- Target: Bone/Stimulation of Osteoclasts

- Action: Increase blood Ca2+

(Hypercalcemia if excessive)

Parathyroid GlandsParathyroid GlandsSlide 9.26

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Tiny masses on the posterior of the thyroid

Secrete parathyroid hormone (PTH)

Adrenal Glands

Adrenal Cortex (outer/glandular)- Cortisol

* Target: Many tissues* Action: make glucose, decrease

inflammation- Aldosterone

* Target: Kidneys* Action: Maintain Na+/K+ blood levels

Adrenal Glands continued

Adrenal Medulla (inner/nervous)

- Epinephrine/Adrenalin (Fear/Flight)

- Norepinephrine/Noradrenalin (Anger/Fight)

- Targets:Heart, Liver, Muscles, Blood Vessels, etc.

- Functions: Prepare for sudden threat

Pancreas

Endocrine (Islets of Langerhans) & Exocrine

Glucagon (from Alpha Cells)- Target: Liver- Action: Release glucose from glycogen

(increases blood glucose)Insulin (from Beta Cells)

- Target: Most/All Cells- Action: Promotes glucose transport into

cells (decreases blood glucose)

Pineal & Thymus Glands

Pineal Gland (Endocrine & CNS)- Melatonin

* Target: Hypothalamus* Action: Sets Diurnal Clock/Circadian rhythm

& promotes sleepThymus (atrophies at puberty)

- Thymosins* Target: T cells of immune system* Action: T cell maturation

(immunocompetence)

Gonads

Ovaries- Estrogen

* Target: Uterus, Ovaries, other* Action: prepare for fetus, secondary sexual

characteristics - Progesterone

* Target: Uterus* Action: maintains pregnancy, prevents

uterine contractions

Gonads continued

Testes

- Testosterone

*Target: Various body parts

*Action: Secondary sexual characteristics