06Human PhysEndocrine

5/20/2018 06Human PhysEndocrine

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Human PhysiologyEndocrine System

Control pathways May be

Local pathways

Paracrine and autocrine responsesIn or in the vicinity of the cells or tissues

Long-Distance pathways

Response loops Stimulus


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Negative feedback loops Stabilizing a function and maintain it withing a

normal range

Response is in opposition to stimuli Homeostatic control

Positive feedback loops

Response reinforces the stimulus


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Negative feedback

Controlled

system

Sensor

Output

Set-point

adjuster

Inverting

amplifierError

signal

Disturbance

_


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Control systems vary in their speed &specificity

Specificity

Nervous control very specificHormonal control more general

Nature of signal

Nervous system uses both electrical and chemical

Endocrine system uses only chemicals


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It brings about changes via chemical messengers,

hormones, released into the blood stream and carriedto target organs.

Endocrinology- the study of hormones and the

endocrine organs.

Endocrine system- all of the glands that secrete

hormones

Endocrine and exocrine glands

Exocrine glands - have ducts through which their

nonhormonal products travel to the membrane surfaceand to the exterior e ithelial surface


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Endocrine glands - release their substances into thesurrounding fluid (ductless glands). They include the

pituitary, thyroid, parathyroid, adrenal, pineal, and the

thymus glands. Also included are thepancreasand

gonads. The hypothalamusis called a neuroendocrineorgan.

Know Fig 7.2


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Human PhysiologyEndocrine System, Hormones

Hormones - chemical messengers carried bythe blood from endocrine glands to the cell upon

which they act.

Are chemical messengers

Secreted into the blood by endocrine cells or

neurons

Affect distal targets


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Classification Peptide hormones - 3 or more amino acids

Steroid hormones - derived from cholesterol

Amine hormones - single amino acids Know Table 7-1


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Human Physiology

Endocrine System, Hormones

Classification, Peptide hormone - eg: Insulin Synthesis - RER, preprohormone

Packaged in vescicles

In Golgi apparatus, pre to pro hormone then to hormone

and fragments

Released into ECF when cell is signaled to do so

Transported in blood, half-life - minutes

Mechanism of action - bind to cell surface receptors.Many use cAMP and some use tyrosine kinase

Action - open or close membrane channels or modulate

metabolic enzymatic activity or transport proteins

Fig 7.3 - 7.5


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Human PhysiologyEndocrine System, Classification

Peptide hormone synthesis, packaging, andrelease

Figure 7-3


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Classification, Steroid hormones, eg: estradiol Synthesis - SER, lipophilic, sythesized as needed

Found bound (inactive) to protein carriers in blood

Half-life - hours

Mechanism - diffuses across cell membrane to

cytoplasmic and nuclear receptors. Interact with DNA

Slow response by cells - hours

Fi 7.7


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Action of Steroid Hormones


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Classification, Amine hormonesNitrogen-containing

Most derived from tryptophan or tyrosine

They behave like peptide hormones

(catecholamines) or like steroid hormones (thyroid

hormones)

Thyroid hormones: produced by thyroid gland found

in the lower part of the neck. It secretes 3 hormones:


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Amine hormone, Adrenal medullary hormones The adrenal gland consists of a medullary and

cortical section. The cortex secretes steroid hormones.

The adrenal medulla secretes two hormonesEpinephrine (E) and

Norepinephrine (NE)

These are also called catecholamines


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Second messenger mechanisms of amino acid-based hormones


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Human PhysiologyQuiz (1 of 2)

It takes much longer for sex hormones andother steriods to produce their effects than it

takes nonsteroid hormones. Why?

A. Steroids are bigger, slower molecules B. Steroids usually must be carried longer distances

in the blood

C. Steroids cause target cells to make new proteins,

which takes time


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Human PhysiologyQuiz (2 of 2)

List the hormones produced by the adrenalgland.


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Peptide hormone production


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Steroid hormones Produced by the adrenal cortex, the gonads, and the

placenta

Precursor is cholesterol Synthesis of steroid hormones


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Cholesterol

PregnenoloneDihydroepi-

andrsterone

Progesterone 17-Hydroxyprogesterone Androstenedione

TestosteroneCortisolCorticosterone

Aldosterone

(Mineralocorticoid)

(Glucorticoids)

Testes

Estradiol

Ovaries

(Androgens)


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Direct gene activation mechanism of steroidhormones


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Hormonal Specificity All major hormones circulate to virtually all tissues

(target cells), but for these cells to respond to a

hormone, they must have a specific protein receptor

on their plasma membrane or in their interior.

Hormone-target interaction depends on:

Blood levels of the hormone

The relative number of receptors for that hormone


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Onset, Duration, and Half-life Onset varies greatly, from almost immediately to

hours or days

Duration can range from several minutes to severalhours

Half-life is the length of time the hormone

concentration takes to drop by half

From a fraction of a minute to several hours


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Human PhysiologyEndocrine System, Control of Hormone Release

Endocrine glands are stimulated by humoral,neural and hormonalmeans.

Humoralstimuli - changing levels of blood ions and

nutrients. Example:-calcium parathyroidhormone

Neuralstimuli - nerve fiber stimulates hormonal

release. Example:-nervous input to adrenal medulla

release of catecholamines


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Human PhysiologyEndocrine System, Neurohormones

Hypothalamic-pituitary system Pituitary gland- lies just below hypothalamus, in

pocket of bone at base of brain. Consists of two

adjacent lobes - the anterior pituitary and the posterior

piruitary

Posterior pituitary hormones

Oxytocinand vasopressinare released

Made in hypothalamus, move down the neural axons and


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Hypothalamus and Anterior Pituitary The hypothalamus also secretes hormones that

control the secretion of ALL the anterior pituitary

hormones. The basic pattern is as follows:

Secretion of a hypothalamic hormone, which controlssecretion of

An anterior pitiutary hormone, which controls the secretionof

A hormone from some other endocrine organ/gland


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Stimulus

Hypothalamus

Hormone 1 Secretion

Third Endocrine Gland

Hormone 3 Secretion

Plasma Hormone 1

Anterior Pituitary

Hormone 2 Secretion

Plasma Hormone 2

Target Cells

Plasma Hormone 3


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Hypothalamic Releasing Hormones Corticotropin Releasing Hormone (CRH)

Thyrotropin Releasing Hormone (TRH)

Growth Hormone Releasing Hormone (GHRH)

Somatostatin (SS) also called Growth hormone

releasing Inhibitin Hormone (GIH)

Gonadotropin Releasing Hormone (GnRH)

Prolactin Releasin Hormone PRH


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Anterior Pituitary Hormones Gonadotropic Hormones

Follicle-Stimulating Hormone (FSH)

Luteinizing Hormone (LH)

Growth Hormone (GH)

Thyroid-stimulating Hormone (TSH)

Prolactin

AdrenoCorticoTro ic Hormone ACTH


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Human Physiology

FSH

and

LH

GHRH CRHPRHTRH PIHSS

Anterior

PituitaryGROWTH

HORMONE

TSH PROLACTIN ACTH

Hypothalamus

GnRH

Hormones-estrogen,

progesterone and

testosterone

Other

organs

IGF-1

Gonads Adrena

l

cortex

Liver Thyroid Breasts

Growth

Metabolism

Germ cell

developmentDevelopment

Milk

Cortiso

l

Thyroxine

T3

Summary of Hypothalamic-anterior-pituitary system


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H Ph i l


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Human Physiology

Endocrine System

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06Human PhysEndocrine