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									                                                 Endocrine System: Overview

                                                  Endocrine system – the body’s second great
                                                  controlling system which influences metabolic
              The Endocrine System                activities of cells by means of hormones
                                                  Endocrine glands – pituitary, thyroid,
                                                  parathyroid, adrenal, pineal, and thymus
                               Part A             The pancreas and gonads produce both
                                                  hormones and exocrine products

Endocrine System: Overview                       Major Endocrine Organs

 The hypothalamus has both neural functions
 and releases hormones
 Other tissues and organs that produce
 hormones – adipose cells, pockets of cells in
 the walls of the small intestine, stomach,
 kidneys, and heart

                                                                                           Figure 16.1

Intercellular communication                      Intercellular communication
 Direct communication                               chemicals that exert effects on the same
   Through gap junctions                            cells that secrete them
   Ions, small solutes, etc                       Paracrine
   Limited to adjacent cells of the same type        locally acting chemicals that affect cells
                                                    other than those that secrete them
 Synaptic communication
                                                       Cytokines or local hormones
   Neurotransmitters                                   These are not considered hormones since
   Used in crises management                           hormones are long-distance chemical

Intercellular communication                     Types of Hormones
 Endocrine                                       Amino acid based
   Hormones – chemical substances secreted         Amines, thyroxine, peptide, and protein
   by cells into the extracellular fluids
     Regulate the metabolic function of other
     cells                                       Peptides hormones
     Have lag times ranging from seconds to        Short peptides
     hours                                           ADH, oxytocin
     Tend to have prolonged effects                Small proteins
                                                     GH, prolactin

Types of Hormones                               Hormone Action
                                                 Hormones that bind to receptors in the cell
 Lipid derivatives                               membrane:
   Steroids – gonadal and adrenocortical            First and second messengers
                                                    Regulatory G proteins
   Eicosanoids – leukotrienes and
   prostaglandins                                   Water-soluble hormones
      Function as paracrine and autocrine         Hormones that bind to intracellular receptors
      factors                                       Direct gene activation
      Function as hormones                          Steroid and thyroid hormones
                                                 The precise response depends on the type of the
                                                 target cell

                                                Hormones that bind to receptors in the cell
Mechanism of Hormone Action                     membrane: cAMP mechanism

 Hormones produce one or more of the             Hormone (first messenger) binds to its
                                                 receptor, which then binds to a G protein
 following cellular changes in target cells
                                                 The G protein is then activated as it binds
    Alter plasma membrane permeability           GTP, displacing GDP
    Stimulate protein synthesis                  Activated G protein activates the effector
    Activate or deactivate enzyme systems        enzyme adenylate cyclase
    Induce secretory activity                    Adenylate cyclase generates cAMP (second
    Stimulate mitosis                            messenger) from ATP
                                                 cAMP activates protein kinases, which then
                                                 cause cellular effects

   Hormones that bind to receptors in the cell                                                                                                   Hormones that bind to receptors in the cell
       membrane : cAMP mechanism                                                                                                                 membrane: PIP-Calcium mechanism
Extracellular fluid

        Hormone A                                                             Adenylate cyclase                           Hormone B
               1                                                                                                             1
                                                                                                                                                  Hormone binds to the receptor and activates
                                                                                                                                                  G protein
Receptor Gs
                             2    GTP        3    GTP
                                                                         GTP     3         GTP       2
                                                                                                                                 Gi   Receptor
                                                                                                                                                  G protein binds and activates phospholipase
                      GTP   GDP                                                                    GDP        GTP

                                                                      cAMP                                                                        Phospholipase splits the phospholipid PIP2 into
  ACTH                                                                    5
                                                                                                                Triggers responses of target
                                                                                                                cell (activates enzymes,
                                                                                                                                                  diacylglycerol (DAG) and IP3 (both act as
  Glucagon                                                                                                      stimulates cellular
  TSH                                                                 Inactive              Active
                                                                                                                secretion, opens ion
                                                                                                                channels, etc.)
                                                                                                                                                  second messengers)
  Calcitonin                                                          protein               protein
                                                                      kinase A              kinase A                                              DAG activates protein kinases; IP3 triggers
                                                                                                                                                  release of Ca2+ stores
                                                                                                                                                  Ca2+ (third messenger) alters cellular responses

   Hormones that bind to receptors in the cell
     membrane: PIP-Calcium mechanism                                                                                                             Hormones that bind to intracellular
Extracellular fluid

                                                                                                                                                  Steroid Hormones
                                                                                                                                                    This interaction prompts DNA transcription
                              2      GTP          3         GTP           PIP2
                                                                                       4         5                                Active
                                                                                                                                                    to produce mRNA
Receptor Gq                                                                                                                       kinase C
                      GTP   GDP
                                                                                      IP3                protein
                                                                                                         kinase C
                                                                                                                                                    The mRNA is translated into proteins, which
  Catecholamines                                 Phospholipase C
  ADH                                                                                      5
                                                                                                                     Triggers responses
                                                                                                                     of target cell
                                                                                                                                                    bring about a cellular effect
                                  Endoplasmic                                                                         6

Cytoplasm                                                                                                     Ca2+    Ca2+- calmodulin


                                                                                                                                                 Target Cell Specificity

                                                                                                                                                  Hormones circulate to all tissues but only
                                                                                                                                                  activate cells referred to as target cells

                                                          Binding                 Hormone
                                                                                                                                                  Target cells must have specific receptors to
                                                                                                                                                  which the hormone binds
                                                                                                                                                  These receptors may be intracellular or
                                                                                                                                                  located on the plasma membrane

                                                                                     New protein

Target Cell Specificity                           Target Cell Activation
                                                   Target cell activation depends on three factors
 Examples of hormone activity                        Blood levels of the hormone
   ACTH receptors are only found on certain          Relative number of receptors on the target
   cells of the adrenal cortex                       cell
   Thyroxin receptors are found on nearly all        The affinity of those receptors for the
   cells of the body                                 hormone

Target Cell Activation                            Hormone Concentrations in the Blood

 Up-regulation – target cells form more            Hormones circulate in the blood in two forms:
 receptors in response to the hormone              free or bound
 Down-regulation – target cells lose receptors        Steroids and thyroid hormone are attached
 in response to the hormone                           to plasma proteins
                                                      Bound to their own carriers

Hormone Concentrations in the Blood               Interaction of Hormones at Target Cells
                                                  Permissiveness – one hormone cannot exert
 Concentrations of circulating hormone reflect:   its effects without another hormone being
   Rate of release                                present. Estrogen and thyroid hormone
   Speed of inactivation and removal from the     Synergism – more than one hormone
   body                                           produces the same effects on a target cell
 Hormones are removed from the blood by:             Glucagon and epinephrine
   Degrading enzymes                              Antagonism – one or more hormones
                                                  opposes the action of another hormone.
   The kidneys
                                                  Glucagon and insulin
   Liver enzyme systems

Control of Hormone Release                         Humoral Stimuli

 Blood levels of hormones:                          Humoral stimuli – secretion of hormones in
   Are controlled by negative feedback systems      direct response to changing blood levels of
   Vary only within a narrow desirable range        ions and nutrients
 Hormones are synthesized and released in           Example: concentration of calcium ions in the
 response to:                                       blood
   Humoral stimuli                                     Declining blood Ca2+ concentration
                                                       stimulates the parathyroid glands to secrete
   Neural stimuli                                      PTH (parathyroid hormone)
   Hormonal stimuli                                    PTH causes Ca2+ concentrations to rise and
                                                       the stimulus is removed

                                                   Neural Stimuli
                                                    Neural stimuli – nerve
                                                    fibers stimulate
                                                    hormone release
                                                       nervous system
                                                       (SNS) fibers
                                                       stimulate the
                                                       adrenal medulla to

Hormonal Stimuli                                   Stimuli
 Hormonal stimuli – release of hormones in
 response to hormones produced by other
 endocrine organs
   The hypothalamic hormones stimulate the
   anterior pituitary
   In turn, pituitary hormones stimulate targets
   to secrete still more hormones

Nervous System Modulation                     Nervous System Modulation
                                               The nervous system can override normal
The nervous system modifies the stimulation    endocrine controls
of endocrine glands and their negative
                                                 For example, control of blood glucose levels
feedback mechanisms
                                                   Normally the endocrine system maintains
                                                   blood glucose
                                                   Under stress, the body needs more
                                                   The hypothalamus and the sympathetic
                                                   nervous system are activated to supply
                                                   ample glucose

Major Endocrine Organs: Pituitary             Pituitary (Hypophysis)
Pituitary gland – two-lobed organ that
secretes nine major hormones
Neurohypophysis – posterior lobe (neural
tissue) and the infundibulum
   Receives, stores, and releases hormones
   from the hypothalamus
Adenohypophysis – anterior lobe, made up of
glandular tissue
   Synthesizes and secretes a number of

Pituitary-Hypothalamic Relationships:         Pituitary-Hypothalamic Relationships:
Posterior Lobe                                Anterior Lobe
The posterior lobe is a downgrowth of
hypothalamic neural tissue                    The anterior lobe of the pituitary is an
Has a neural connection with the              outpocketing of the oral mucosa
hypothalamus (hypothalamic-hypophyseal        There is no direct neural contact with the
tract)                                        hypothalamus
Nuclei of the hypothalamus synthesize
oxytocin and antidiuretic hormone (ADH)
These hormones are transported to the
posterior pituitary

Pituitary-Hypothalamic Relationships:          Pituitary-Hypothalamic Relationships:
Anterior Lobe                                  Anterior Lobe

 There is a vascular connection, the
 hypophyseal portal system, consisting of:
   The primary capillary plexus
   The hypophyseal portal veins
   The secondary capillary plexus

Adenophypophyseal Hormones                     Activity of the Adenophypophysis

 The six hormones of the adenohypophysis:       The hypothalamus sends a chemical stimulus
    Abbreviated as GH, TSH, ACTH, FSH, LH,      to the anterior pituitary
    and PRL                                        Releasing hormones stimulate the synthesis
    Regulate the activity of other endocrine       and release of hormones
    glands                                         Inhibiting hormones shut off the synthesis
 In addition, pro-opiomelanocortin (POMC):         and release of hormones
    Has been isolated from the pituitary
    Is split into ACTH, opiates, and MSH

                                               Thyroid Stimulating Hormone
Activity of the Adenophypophysis
 The tropic hormones that are released are:     Stimulates the normal development and
   Thyroid-stimulating hormone (TSH)            secretory activity of the thyroid
   Adrenocorticotropic hormone (ACTH)           Triggered by hypothalamic peptide
   Follicle-stimulating hormone (FSH)           thyrotropin-releasing hormone (TRH)
   Luteinizing hormone (LH)                     Rising blood levels of thyroid hormones act
                                                on the pituitary and hypothalamus to block
                                                the release of TSH

Adrenocorticotropic Hormone
                                                 Gonadotropins – follicle-stimulating hormone
 Stimulates the adrenal cortex to release        (FSH) and luteinizing hormone (LH)
 corticosteroids                                   Regulate the function of the ovaries and
 Triggered by hypothalamic corticotropin-          testes
 releasing hormone (CRH) in a daily rhythm         FSH stimulates gamete (egg or sperm)
 Internal and external factors such as fever,      production
 hypoglycemia, and stressors can trigger the       Absent from the blood in prepubertal boys
                                                   and girls
 release of CRH
                                                   Triggered by the hypothalamic
                                                   gonadotropin-releasing hormone (GnRH)
                                                   during and after puberty

Functions of Gonadotropins                      Functions of Gonadotropins

 In females                                      In males
    LH works with FSH to cause maturation of        LH stimulates interstitial cells of the testes to
    the ovarian follicle                            produce testosterone
    LH works alone to trigger ovulation             LH is also referred to as interstitial cell-
    (expulsion of the egg from the follicle)        stimulating hormone (ICSH)
    LH promotes synthesis and release of
    estrogens and progesterone

Growth Hormone (GH)                             Growth Hormone (GH)

 Produced by somatotropic cells of the           Antagonistic hypothalamic hormones regulate
 anterior lobe that:                             GH
   Stimulate most cells, but target bone and       Growth hormone–releasing hormone
   skeletal muscle                                 (GHRH) stimulates GH release
   Promote protein synthesis and encourage         Growth hormone–inhibiting hormone (GHIH)
   the use of fats for fuel                        inhibits GH release
 Most effects are mediated indirectly by

                                                 Metabolic Action of Growth Hormone
Metabolic Action of Growth Hormone               (GH)
 GH stimulates liver, skeletal muscle, bone,
 and cartilage to produce insulin-like growth
 Direct action promotes lipolysis and inhibits
 glucose uptake

                                                 The Posterior Pituitary and
Prolactin (PRL)
                                                 Hypothalamic Hormones
                                                 Posterior pituitary – made of axons of
 In females, stimulates milk production by the   hypothalamic neurons, stores antidiuretic
 breasts                                         hormone (ADH) and oxytocin
 Triggered by the hypothalamic prolactin-        ADH and oxytocin are synthesized in the
 releasing hormone (PRH)                         hypothalamus
 Inhibited by prolactin-inhibiting hormone       ADH influences water balance
 (PIH)                                           Oxytocin stimulates smooth muscle
 Blood levels rise toward the end of pregnancy   contraction in breasts and uterus
                                                 Both use PIP-calcium second-messenger
 Suckling stimulates PRH release and
 encourages continued milk production


                                                  Oxytocin is a strong stimulant of uterine
              The Endocrine System
                                                  Regulated by a positive feedback mechanism
                                                  to oxytocin in the blood
                                                  This leads to increased intensity of uterine
              PART B                              contractions, ending in birth
                                                  Oxytocin triggers milk ejection (“letdown”
                                                  reflex) in women producing milk

Oxytocin                                           Antidiuretic Hormone (ADH)
                                                   ADH helps to avoid dehydration or water
 Synthetic and natural oxytocic drugs are used     overload
 to induce or hasten labor                           Prevents urine formation
 Plays a role in sexual arousal and satisfaction   Osmoreceptors monitor the solute
 in males and nonlactating females                 concentration of the blood
                                                   With high solutes, ADH preserves water
                                                   With low solutes, ADH is not released, thus
                                                   causing water loss
                                                   Alcohol inhibits ADH release and causes
                                                   copious urine output

                                                   Thyroid Gland
Thyroid Gland
The largest endocrine gland, located in the
anterior neck, consists of two lateral lobes
connected by a median tissue mass called
the isthmus
Composed of follicles that produce the
glycoprotein thyroglobulin
Colloid (thyroglobulin + iodine) fills the lumen
of the follicles and is the precursor of thyroid
Other endocrine cells, the parafollicular cells,
produce the hormone calcitonin

Thyroid Hormone
                                                   Effects of Thyroid Hormone
                                                   TH is concerned with:
 Thyroid hormone – major metabolic hormone           Glucose oxidation
 Consists of two related iodine-containing           Increasing metabolic rate
 compounds                                           Heat production
   T4 – thyroxine; has two tyrosine molecules      TH plays a role in:
   plus four bound iodine atoms                      Maintaining blood pressure
   T3 – triiodothyronine; has two tyrosines with     Regulating tissue growth
   three bound iodine atoms                          Developing skeletal and nervous systems
                                                     Maturation and reproductive capabilities

     Synthesis of Thyroid Hormone                                                                                                          Synthesis of Thyroid Hormone
      Thyroglobulin is synthesized and discharged
      into the lumen                                                                                                                        Iodinated tyrosines link together to form T3
      Iodides (I–) are actively taken into the cell,                                                                                        and T4
      oxidized to iodine (I2), and released into the                                                                                        Colloid is then endocytosed and combined
      lumen                                                                                                                                 with a lysosome, where T3 and T4 are
      Iodine attaches to tyrosine, mediated by                                                                                              cleaved and diffuse into the bloodstream
      peroxidase enzymes, forming T1
      (monoiodotyrosine, or MIT), and T2
      (diiodotyrosine, or DIT)

                                                                              follicle cell

Capillary             1 Thyroglobulin is synthesized
                        and discharged into the follicle lumen                                                            Colloid
                                                                                                                                           Transport and Regulation of TH

                                                               Golgi                               Colloid in lumen of follicle
                                                                                                   3b Iodine is attached                    T4 and T3 bind to thyroxine-binding globulins (TBGs)
                                                               Rough ER                                  to tyrosine in colloid,
                                                                                                         forming DIT and MIT                produced by the liver
                                                                                                                                            Both bind to target receptors, but T3 is ten times
                 2 Iodide (I–)
                      is trapped
                                                               3a Iodide is
                                                                                                                           colloid          more active than T4
 (I–)                 (actively transported in)                   to iodine                        DIT (T2)    MIT (T1)

                                                                                                                                            Peripheral tissues convert T4 to T3
                                 T3    T4                                                           4 Iodinated tyrosines are
T3                        T4
                                                                                                         linked together to form
                                                                                                         T3 and T4                          Mechanisms of activity are similar to steroids
                                                                                                                                            Regulation is by negative feedback
                                                                               5 Thyroglobulin colloid
                                                                                  is endocytosed and                                        Hypothalamic thyrotropin-releasing hormone (TRH)
                      6 Lysosomal enzymes cleave                                  combined with a
                         T4 and T3 from thyroglobulin
                                                           T4 T3                  lysosome                                                  can overcome the negative feedback
To peripheral            colloid and hormones diffuse
tissues                  from follicle cell into bloodstream

     Calcitonin                                                                                                                            Calcitonin

            A peptide hormone produced by the                                                                                               Calcitonin targets the skeleton, where it:
            parafollicular, or C, cells                                                                                                       Inhibits osteoclast activity (and thus bone
            Lowers blood calcium levels in children                                                                                           resorption) and release of calcium from the
            Antagonist to parathyroid hormone (PTH)                                                                                           bone matrix
                                                                                                                                              Stimulates calcium uptake and incorporation
                                                                                                                                              into the bone matrix
                                                                                                                                            Regulated by a humoral (calcium ion
                                                                                                                                            concentration in the blood) negative feedback

Parathyroid Glands                                  Parathyroid Glands

 Tiny glands embedded in the posterior aspect
 of the thyroid
 Cells are arranged in cords containing oxyphil
 and chief cells
 Chief (principal) cells secrete PTH
 PTH (parathormone) regulates calcium
 balance in the blood

Effects of Parathyroid Hormone                      Effects of Parathyroid Hormone

 PTH release increases Ca2+ in the blood as
     Stimulates osteoclasts to digest bone matrix
     Enhances the reabsorption of Ca2+ and the
     secretion of phosphate by the kidneys
     Increases absorption of Ca2+ by intestinal
 Rising Ca2+ in the blood inhibits PTH release

Adrenal (Suprarenal) Glands
                                                    Adrenal Cortex
                                                    Synthesizes and releases steroid hormones
 Adrenal glands – paired, pyramid-shaped            called corticosteroids
 organs atop the kidneys                            Different corticosteroids are produced in each
                                                    of the three layers
 Structurally and functionally, they are two
                                                       Zona glomerulosa – mineralocorticoids
 glands in one
                                                       (chiefly aldosterone)
   Adrenal medulla – neural tissue that acts as        Zona fasciculata – glucocorticoids
   part of the SNS                                     (chiefly cortisol)
   Adrenal cortex – glandular tissue derived           Zona reticularis – gonadocorticoids
   from embryonic mesoderm                             (chiefly androgens)

Adrenal Cortex                             Mineralocorticoids

                                            Regulate electrolytes in extracellular fluids
                                            Aldosterone – most important
                                              Maintains Na+ balance by reducing excretion
                                              of sodium from the body
                                              Stimulates reabsorption of Na+ and secretion
                                              of K+ by the kidneys

Mineralocorticoids                         The Four Mechanisms of Aldosterone
 Aldosterone secretion is stimulated by:   Renin-angiotensin mechanism – kidneys
   Rising blood levels of K+               release renin, which is converted into
                                           angiotensin II that in turn stimulates
   Low blood Na+                           aldosterone release
   Decreasing blood volume or pressure     Plasma concentration of sodium and potassium
                                           – directly influences the zona glomerulosa cells
                                           ACTH – causes small increases of aldosterone
                                           during stress
                                           Atrial natriuretic peptide (ANP) – inhibits
                                           activity of the zona glomerulosa

Major Mechanisms of Aldosterone
Secretion                                  Glucocorticoids (Cortisol)
                                            Help the body resist stress by:
                                              Keeping blood sugar levels relatively
                                              Maintaining blood volume and preventing
                                              water shift into tissue
                                            Cortisol provokes:
                                              Gluconeogenesis (formation of glucose from
                                              Rises in blood glucose, fatty acids, and
                                              amino acids

Excessive Levels of Glucocorticoids                Gonadocorticoids (Sex Hormones)

 Excessive levels of glucocorticoids:               Most gonadocorticoids secreted are
   Depress cartilage and bone formation             androgens (male sex hormones), and the
                                                    most important one is testosterone
   Inhibit inflammation
                                                    Androgens contribute to:
   Depress the immune system                           The onset of puberty
   Promote changes in cardiovascular, neural,          The appearance of secondary sex
   and gastrointestinal function                       characteristics
                                                       Sex drive in females
                                                    Androgens can be converted into estrogens
                                                    after menopause

Adrenal Medulla                                    Adrenal Medulla

 Made up of chromaffin cells that secrete           Epinephrine is the more potent stimulator of
 epinephrine and norepinephrine                     the heart and metabolic activities
 Secretion of these hormones causes:                Norepinephrine is more influential on
   Blood glucose levels to rise                     peripheral vasoconstriction and blood
   Blood vessels to constrict                       pressure
   The heart to beat faster
   Blood to be diverted to the brain, heart, and
   skeletal muscle

Stress and the Adrenal Gland                       Pancreas
                                                   A triangular gland, which has both exocrine
                                                   and endocrine cells, located behind the
                                                   Acinar cells produce an enzyme-rich juice
                                                   used for digestion (exocrine product)
                                                   Pancreatic islets (islets of Langerhans)
                                                   produce hormones (endocrine products)
                                                   The islets contain two major cell types:
                                                     Alpha (α) cells that produce glucagon
                                                     Beta (β) cells that produce insulin


                                                A 29-amino-acid polypeptide hormone that is
                                                a potent hyperglycemic agent
                                                Its major target is the liver, where it promotes:
                                                   Glycogenolysis – the breakdown of
                                                   glycogen to glucose
                                                   Gluconeogenesis – synthesis of glucose
                                                   from lactic acid and noncarbohydrates
                                                   Release of glucose to the blood from liver

Insulin                                        Effects of Insulin Binding
 A 51-amino-acid protein consisting of two
 amino acid chains linked by disulfide bonds    The insulin receptor is a tyrosine kinase
 Synthesized as part of proinsulin and then     enzyme
 excised by enzymes, releasing functional
 insulin                                        After glucose enters a cell, insulin binding
                                                triggers enzymatic activity that:
    Lowers blood glucose levels                    Catalyzes the oxidation of glucose for ATP
    Enhances transport of glucose into body
    cells                                          Polymerizes glucose to form glycogen
    Counters metabolic activity that would         Converts glucose to fat (particularly in
    enhance blood glucose levels                   adipose tissue)

                                               Diabetes Mellitus (DM)
Regulation of Blood Glucose Levels

 The hyperglycemic                              Results from hyposecretion or hypoactivity of
 effects of glucagon                            insulin
 and the                                        The three cardinal signs of DM are:
 hypoglycemic                                      Polyuria – huge urine output
 effects of insulin                                Polydipsia – excessive thirst
                                                   Polyphagia – excessive hunger and food
                                                Hyperinsulinism – excessive insulin
                                                secretion, resulting in hypoglycemia

Diabetes Mellitus (DM)                              Gonads: Female

                                                     Paired ovaries in the abdominopelvic cavity
                                                     produce estrogens and progesterone
                                                     They are responsible for:
                                                       Maturation of the reproductive organs
                                                       Appearance of secondary sexual
                                                       Breast development and cyclic changes in
                                                       the uterine mucosa

Gonads: Male                                        Pineal Gland

 Testes located in an extra-abdominal sac            Small gland hanging from the roof of the third
 (scrotum) produce testosterone                      ventricle of the brain
 Testosterone:                                       Secretory product is melatonin
   Initiates maturation of male reproductive         Melatonin is involved with:
   organs                                              Day/night cycles
   Causes appearance of secondary sexual               Physiological processes that show rhythmic
   characteristics and sex drive                       variations (body temperature, sleep,
   Is necessary for sperm production                   appetite)
   Maintains sex organs in their functional state

                                                    Other Hormone-Producing Structures

 Lobulated gland located deep to the sternum         Heart – produces atrial natriuretic peptide
 Major hormonal products are thymopoietins           (ANP), which reduces blood pressure, blood
 and thymosins                                       volume, and blood sodium concentration
 These hormones are essential for the                Gastrointestinal tract – enteroendocrine cells
 development of the T lymphocytes (T cells) of       release local-acting digestive hormones
 the immune system                                   Placenta – releases hormones that influence
                                                     the course of pregnancy

Other Hormone-Producing Structures
                                                  Developmental Aspects

 Kidneys – secrete erythropoietin, which           Hormone-producing glands arise from all
 signals the production of red blood cells         three germ layers
 Skin – produces cholecalciferol, the precursor    Endocrine glands derived from mesoderm
 of vitamin D                                      produce steroid hormones
 Adipose tissue – releases leptin, which is        Endocrine organs operate smoothly
 involved in the sensation of satiety, and         throughout life
 stimulates increased energy expenditure           Most endocrine glands show structural
                                                   changes with age, but hormone production
                                                   may or may not be affected

Developmental Aspects                             Developmental Aspects

 Exposure to pesticides, industrial chemicals,     Ovaries undergo significant changes with age
 arsenic, dioxin, and soil and water pollutants    and become unresponsive to gonadotropins
 disrupts hormone function                         Female hormone production declines, the
 Sex hormones, thyroid hormone, and                ability to bear children ends, and problems
 glucocorticoids are vulnerable to the effects     associated with estrogen deficiency (e.g.,
 of pollutants                                     osteoporosis) begin to occur
 Interference with glucocorticoids may help        Testosterone also diminishes with age, but
 explain high cancer rates in certain areas        effect is not usually seen until very old age

Developmental Aspects

 GH levels decline with age and this accounts
 for muscle atrophy with age
 Supplemental GH may spur muscle growth,
 reduce body fat, and help physique
 TH declines with age, causing lower basal
 metabolic rates
 PTH levels remain fairly constant with age,
 and lack of estrogen in women makes them
 more vulnerable to bone-demineralizing
 effects of PTH


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