Endocrine Glands

Hypothalamus

Pineal gland

Pituitary gland

Thyroid glandParathyroid glands

Adrenal glands

Pancreas

Ovary(female)

Testis(male)

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

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

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

Mechanisms of Hormone Action

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.

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

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

Mediates effects of many polypeptide & glycoprotein hormones

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

Adenylate Cyclase-cAMP

Hypothalamus

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.

Pituitary Gland

Pituitary Gland Pituitary gland is located beneath hypothalamus

Posterior Pituitary

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

Neurosecretorycells of thehypothalamus

Axon

Anteriorpituitary

Posteriorpituitary

HORMONE ADH Oxytocin

TARGET Kidney tubules Mammary glands,uterine muscles

Anterior Pituitary

Secretes 6 trophic hormones that maintain size of targets High blood levels

cause target to hypertrophy

Low levels cause atrophy

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

Anterior Pituitary

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

Luteinizing hormone (LH) causes ovulation & secretion of testosterone in testes

Prolactin (PRL) stimulates milk production by mammary glands

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

Pituitary Regulation

Release of A. Pit. hormones is controlled by 1. Hypothalamic releasing & inhibiting factors

2. Feedback from levels of target gland hormones

3. Higher brain centers (via the hypothalamus)

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

Feedback Control of Anterior Pituitary

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

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

Adrenal Gland

Adrenal Glands

Sit on top of kidneys

outer cortex inner medulla

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

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

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

Thyroid Gland

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

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

Diseases of the Thyroid

Graves’ disease

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

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

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

CalcitoninThyroid glandreleasescalcitonin.

StimulatesCa2+ depositionin bones

ReducesCa2+ uptakein kidneys

STIMULUS:Rising bloodCa2+ level

Blood Ca2+

level declinesto set point

Homeostasis:Blood Ca2+ level

(about 10 mg/100 mL)

Blood Ca2+

level risesto set point

STIMULUS:Falling bloodCa2+ level

StimulatesCa2+ releasefrom bones

Parathyroidgland

IncreasesCa2+ uptakein intestines

Activevitamin D

Stimulates Ca2+

uptake in kidneys

PTH

PancreasIslets of Langerhans

Islets of Langerhans

Are scattered clusters of endocrine cells in pancreas

Contain alpha & beta cells

Betas secrete insulin in response to low blood glucose Promotes entry of

glucose into cells & conversion of

glucose into glycogen & fat

Decreases blood glucose

Islets of Langerhans continued

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

Alphas secrete glucagon in response to low blood glucose during periods of fasting Stimulates glycogenolysis & lipolysis Increases blood glucose

Islets of Langerhans continued

Pineal Gland

Is located in basal forebrain near thalamus

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

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

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

Testosterone

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

Placenta

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

Autocrine & Paracrine Regulation

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)

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

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

Prostaglandins (PGs) continued

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

Brain

Neurosecretory cells

Corpus cardiacum

Corpus allatum

EARLYLARVA

LATERLARVA PUPA ADULT

Prothoracicgland

Ecdysone

Brainhormone (BH)

Juvenilehormone(JH)

LowJH

Neurosecretory cells in the brain produce brain hormone (BH), which is stored in the corpora cardiaca (singular, corpus cardiacum) until release.

1

BH signals its main targetorgan, the prothoracicgland, to produce thehormone ecdysone.

2

Ecdysone secretionfrom the prothoracicgland is episodic, witheach release stimulatinga molt.

3

Juvenile hormone (JH), secreted by the corpora allata,determines the result of the molt. At relatively high concen-trations of JH, ecdysone-stimulated molting producesanother 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 adultinsect emerges from the pupa.

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