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Hypothalamus. Pineal gland. Pituitary gland. Thyroid gland. Parathyroid glands. Adrenal glands. Pancreas. Ovary (female). Testis (male). Endocrine Glands. Chemical Classification of Hormones. Amine hormones are derived from tyrosine or tryptophan

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Endocrine Glands

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Endocrine glands l.jpg

Hypothalamus

Pineal gland

Pituitary gland

Thyroid gland

Parathyroid glands

Adrenal glands

Pancreas

Ovary

(female)

Testis

(male)

Endocrine Glands


Chemical classification of hormones l.jpg

Chemical Classification of Hormones

  • Amine hormones are derived from tyrosine or tryptophan

    • Include NE, Epi, thyroxine, melatonin

  • Polypeptide/protein hormones are chains of amino acids

    • Include ADH, GH, insulin, oxytocin, glucagon, ACTH, PTH

    • Glycoproteins include LH, FSH, TSH

  • Steroids are lipids derived from cholesterol

    • Include testosterone, estrogen, progesterone & cortisol


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Water Solubility

  • Polar

    • water soluble. Cannot pass through cell membrane

    • Polypeptides, glycoproteins, most amines

  • Nonpolar (lipophilic)

    • Insoluble in water but soluble in lipid

    • Can pass through cell membrane

    • Steroids and thyroid hormone


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Common Aspects of Neural & Endocrine Regulation

  • Target cells with receptor proteins that combine with the regulatory molecule

  • The binding causes a specific sequence of changes in target cell (Signal transduction leads to response)

  • There exists mechanisms to quickly turn off the action of the regulator

    • rapid removal or chemical inactivation

    • There is an OFF switch as well as an ON switch


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Mechanisms of Hormone Action


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Lipophilic hormones

  • Pass through cell membrane

  • Bind to intracellular receptors

  • The hormone-receptor complex acts as a “Transcription factor”. It activates a gene to make an mRNA from which an enzyme protein is made. This enzyme will in some way change the metabolism of the target cell.


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Hormones That Bind to Nuclear Receptor Proteins

  • Lipid hormones travel in blood attached to carrier proteins

    • They dissociate from carriers to pass thru plasma membrane of target

      • Receptors are located in the cytoplasm or nucleus


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Polar hormones

  • Water soluble hormones use cell surface receptors because cannot pass through plasma membrane

    • Actions are mediated by 2nd messengers

    • Hormone is extracellular signal; 2nd messenger carries signal from receptor to inside of cell

  • Some second messengers include:

    • cAMP

    • Phospholipase C

    • Tyrosine kinase

    • Calcium ions


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Adenylate Cyclase-cAMP

  • Mediates effects of many polypeptide & glycoprotein hormones

  • Hormone binds to receptor causing dissociation of a G-protein subunit


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Hypothalamus


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Hypothalamus

  • Hypothalamus produces ADH and Oxytocin that are transported to the posterior pituitary for release. (more on these later)

  • Controls the pituitary gland via a variety of releasing and inhibiting factors.

    • TRH thyrotropin releasing hormone

    • GHRH growth hormone releasing hormone

    • CRH corticotropin releasing hormone

    • Prolactin inhibiting hormone

    • Etc. etc.


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Pituitary Gland


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Pituitary Gland

  • Pituitary gland is located beneath hypothalamus


Posterior pituitary l.jpg

Stores & releases 2 hormones produced in hypothalamus:

Antidiuretic hormone (ADH/vasopressin) which promotes H20 conservation by kidneys

Oxytocin which stimulates contractions of uterus during parturition & contractions of mammary gland alveoli for milk-ejection reflex

Hypothalamus

Neurosecretory

cells of the

hypothalamus

Axon

Posterior

pituitary

Anterior

pituitary

ADH

HORMONE

Oxytocin

Mammary glands,

uterine muscles

TARGET

Kidney tubules

Posterior Pituitary


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Anterior Pituitary

  • Secretes 6 trophic hormones that maintain size of targets

    • High blood levels cause target to hypertrophy

      • Low levels cause atrophy


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Anterior Pituitary

  • Growth hormone(GH) promotes growth, protein synthesis, & movement of amino acids into cells

  • Thyroid stimulating hormone (TSH) stimulates thyroid to produce & secrete T4 & T3

  • Adrenocorticotrophic hormone (ACTH) stimulates adrenal cortex to secrete cortisol, aldosterone


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Anterior Pituitary

  • Follicle stimulating hormone (FSH) stimulates growth of ovarian follicles & sperm production

  • Luteinizinghormone (LH) causes ovulation & secretion of testosterone in testes

  • Prolactin (PRL) stimulates milk production by mammary glands


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Anterior Pituitary

  • Other hormones/products of the pituitary gland include:

    • MSH - influences skin pigmentation in some vertebrates and fat metabolism in mammals

    • Endorphins - inhibit the sensation of pain


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Pituitary Regulation

  • Release of A. Pit. hormones is controlled by

    • Hypothalamic releasing & inhibitingfactors

    • Feedback from levels of target gland hormones

    • Higher brain centers (via the hypothalamus)


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Anterior Pituitary continued

  • Releasing & inhibiting hormones from hypothalamus are released from axon endings into capillary bed in median eminence

    • Carried by hypothalamo-hypophyseal portal system directly to another capillary bed in A. Pit.

      • Diffuse into A. Pit. & regulate secretion of its hormones


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Feedback Control of Anterior Pituitary

Target glands produce hormones that feedback to regulate the anterior pituitary and the hypothalamus


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Higher Brain Function & Anterior Pituitary Secretion

  • Hypothalamus receives input from higher brain centers that can affect Pituitary secretion

    • E.g. psychological stress affects circadian rhythms, menstrual cycle, & adrenal hormones


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Adrenal Gland


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Adrenal Glands

  • Sit on top of kidneys

  • outer cortex

  • inner medulla


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Adrenal Glands

  • Adrenal Cortex

    • Mineralocorticoids

      • Aldosterone which stimulate kidneys to reabsorb Na+ and secrete K

    • Glucocorticoids

      • Cortisol which inhibits glucose utilization & stimulates gluconeogenesis. Inhibits inflammation, Supresses the immune system


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Adrenal Medulla

  • Secretes Epinephrine and Norepinephrine

    • "fight or flight" response

      • causes:

        • Increased respiratory rate

        • Increased HR & cardiac output

        • General vasoconstriction which increases venous return

        • Glycogenolysis & lipolysis

        • Etc, etc, etc


Stress l.jpg

Stress


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Diseases associated with Adrenal hormone levels

  • Cushing’s disease

    • Hyperadrenocorticism

      • widened face with acne and flushing

      • fatty deposits over back of neck

      • stretch marks, easy bruising, hair overgrowth

      • diabetes mellitus

      • muscle loss and fatigue

      • depression and psychosis

      • moon-like face, 

  • Addison’s disease

    • Hypoadrenocorticism

      • Hyperpigmentation, weight loss


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Thyroid Gland


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Thyroid Gland

  • Is located just below the larynx

  • Secretes T4 & T3 which set BMR & are needed for growth, development

  • Also secretes Calcitonin which lowers blood calcium levels


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Diseases of the Thyroid

  • Hypothyroidism

    • People with inadequate T4 & T3 levels are hypothyroid

    • Have low BMR, weight gain, lethargy, cold intolerance

  • Hyperthyroidism

    • Autoimmune disease where antibodies act like TSH & stimulate thyroid gland to grow & oversecrete = hyperthyroidism

      • Characterized by exopthalmos, weight loss, heat intolerance, irritability/anxiety, high BMR, rapid heart rate


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Graves’ disease

  • Graves disease is a form of hyperthyroidism that often presents with exopthalmos


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Parathyroid Glands

  • Are 4 glands embedded in lateral lobes of thyroid gland

  • Secrete Parathyroid hormone (PTH)

    • Elevates blood Ca2+ levels


Parathyroid hormone and calcitonin control of blood calcium l.jpg

Calcitonin

Thyroid gland

releases

calcitonin.

Reduces

Ca2+ uptake

in kidneys

Stimulates

Ca2+ deposition

in bones

Blood Ca2+

level declines

to set point

STIMULUS:

Rising blood

Ca2+ level

Homeostasis:

Blood Ca2+ level

(about 10 mg/100 mL)

STIMULUS:

Falling blood

Ca2+ level

Blood Ca2+

level rises

to set point

Stimulates

Ca2+ release

from bones

Parathyroid

gland

PTH

Increases

Ca2+ uptake

in intestines

Stimulates Ca2+

uptake in kidneys

Active

vitamin D

Parathyroid Hormone and Calcitonin:Control of Blood Calcium

  • Two antagonistic hormones, parathyroid hormone (PTH) and calcitonin play the major role in calcium (Ca2+) homeostasis in mammals


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PancreasIslets of Langerhans


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Islets of Langerhans

  • Are scattered clusters of endocrine cells in pancreas

  • Contain alpha & beta cells


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Islets of Langerhans continued

  • Betas secrete insulin in response to low blood glucose

    • Promotes entry of glucose into cells

    • & conversion of glucose into glycogen & fat

    • Decreases blood glucose


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Diabetes Mellitus

  • Diabetes mellitus is the best-known endocrine disorder

    • Is caused by a deficiency of insulin or a decreased response to insulin in target tissues

    • Is marked by elevated blood glucose levels

  • Type I diabetes mellitus (insulin-dependent diabetes)

    • Is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas

  • Type II diabetes mellitus (non-insulin-dependent diabetes)

    • Is characterized either by a deficiency of insulin or, more commonly, by reduced responsiveness of target cells due to some change in insulin receptors


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Islets of Langerhans continued

  • Alphas secrete glucagon in response to low blood glucose during periods of fasting

    • Stimulates glycogenolysis & lipolysis

    • Increases blood glucose


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Pineal Gland

  • Is located in basal forebrain near thalamus

  • Secretes melatonin in response to activity of suprachiasmatic nucleus (SCN) of hypothalamus


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Pineal Gland

  • SCN is primary timing center for circadian rhythms

    • Reset by daily light/dark changes

  • Melatonin is involved in aligning physiology with sleep/wake cycle & seasons

    • Secreted at night & is inhibited by light

    • Inhibits GnRH (antigonadotropic) in many animals


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Gonads: Sex & Reproductive Hormones

  • Gonads (testes & ovaries) secrete steroid hormones

  • The testes primarily synthesize androgens, the main one being testosterone

    • Which stimulate the development and maintenance of the male reproductive system

  • Estrogens, the most important of which is estradiol

    • Are responsible for the maintenance of the female reproductive system and the development of female secondary sex characteristics

  • Progestins, which include progesterone

    • Are primarily involved in preparing and maintaining the uterus in mammals


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Testosterone

  • Testosterone causes an increase in muscle and bone mass and is often taken as a supplement to cause muscle growth


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Placenta

  • Placenta secretes estrogen, progesterone, hCG, and numerous polypeptide hormones


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Autocrine & Paracrine Regulation


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Autocrine & Paracrine Regulation

  • Autocrine regulators are produced & act within same tissue of an organ

  • Paracrine regulators are produced within one tissue & act on different tissue in same organ.

  • Examples of autocrines & paracrines include:

    • Cytokines (lymphokines, interleukins)

    • Growth factors (promote growth & cell division)

    • Prostaglandins (produced by most organs and have a wide variety of functions)


Prostaglandins pgs continued l.jpg

Prostaglandins (PGs) continued

  • Have wide variety of functions

    • Different PGs may exert antagonistic effects in tissues

      • Some promote smooth muscle contraction & some relaxation

      • Some promote clotting; some inhibit

    • Promotes inflammatory process of immune system

    • Plays role in ovulation

    • Inhibits gastric secretion in digestive system


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Prostaglandins (PGs) continued

  • Cyclooxygenase (COX) 1 & 2 are involved in PG synthesis

    • Are targets of a number of inhibitory non-steroidal anti-inflammatory drugs (NSAIDs)

      • Aspirin, indomethacin, ibuprofen inhibit both COX 1 & 2 thereby producing side effects

      • Celebrex & Vioxx only inhibit COX 2 & thus have few side effects


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Invertebrates

  • Invertebrate regulatory systems also involve endocrine and nervous system interactions

  • Example: Control of Metamorphosis in Insects

    • Brain hormone

      • Stimulates the release of ecdysone from the prothoracic glands

    • Ecdysone

      • Promotes molting and the development of adult characteristics

    • Juvenile hormone

      • Promotes the retention of larval characteristics


Control of molting and development in insects l.jpg

Brain

Neurosecretory cells in the brain produce

brain hormone (BH), which is stored in

the corpora cardiaca (singular, corpus

cardiacum) until release.

1

Neurosecretory cells

Brainhormone (BH)

Corpus cardiacum

Corpus allatum

LowJH

Prothoracicgland

Juvenile hormone (JH), secreted by the corpora allata,

determines the result of the molt. At relatively high concen-

trations of JH, ecdysone-stimulated molting produces

another larval stage. JH suppresses metamorphosis.

But when levels of JH fall below a certain concentration, a

pupa forms at the next ecdysone-induced molt. The adult

insect emerges from the pupa.

4

Ecdysone

Juvenilehormone(JH)

BH signals its main target

organ, the prothoracic

gland, to produce the

hormone ecdysone.

2

EARLYLARVA

LATERLARVA

PUPA

ADULT

Ecdysone secretion

from the prothoracic

gland is episodic, with

each release stimulating

a molt.

3

Control of molting and development in insects


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