Endocrine Glands - PowerPoint PPT Presentation

Hypothalamus

Pineal gland

Pituitary gland

Thyroid gland

Parathyroid glands

Adrenal glands

Pancreas

Ovary

(female)

Testis

(male)

• 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

• 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

• 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

• 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.

• 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

• 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

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 is located beneath 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

• Secretes 6 trophic hormones that maintain size of targets
• High blood levels cause target to hypertrophy
• Low levels cause atrophy

• 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

• 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

• 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

• Release of A. Pit. hormones is controlled by
• Hypothalamic releasing & inhibitingfactors
• Feedback from levels of target gland hormones
• Higher brain centers (via the hypothalamus)

• 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

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

• 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

• Sit on top of kidneys
• outer cortex
• inner medulla

• 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

• 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

• 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

• 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

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

• Are 4 glands embedded in lateral lobes of thyroid gland
• Secrete Parathyroid hormone (PTH)
• Elevates blood Ca2+ levels

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

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

PancreasIslets 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

• 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

• Is located in basal forebrain near thalamus
• Secretes melatonin in response to activity of suprachiasmatic nucleus (SCN) of hypothalamus

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

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

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

• 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

• 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

Brain

Neurosecretory cells in the brain produce

brain hormone (BH), which is stored in

the corpora cardiaca (singular, corpus

cardiacum) until release.

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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.

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Ecdysone

Juvenilehormone(JH)

BH signals its main target

organ, the prothoracic

gland, to produce the

hormone ecdysone.

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EARLYLARVA

LATERLARVA

PUPA

ADULT

Ecdysone secretion

from the prothoracic

gland is episodic, with

each release stimulating

a molt.

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