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The Endocrine System. Part A. Endocrine System: Overview. Endocrine system – the body’s second great controlling system which influences metabolic activities of cells by means of hormones Endocrine glands – pituitary, thyroid, parathyroid, adrenal, pineal, and thymus

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Endocrine system overview
Endocrine System: Overview

  • Endocrine system – the body’s second great controlling system which influences metabolic activities of cells by means of hormones

  • Endocrine glands – pituitary, thyroid, parathyroid, adrenal, pineal, and thymus

  • The pancreas and gonads produce both hormones and exocrine products


Endocrine system overview1
Endocrine System: Overview

  • 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



Intercellular communication
Intercellular communication

  • Direct communication

    • Through gap junctions

    • Ions, small solutes, etc

    • Limited to adjacent cells of the same type

  • Synaptic communication

    • Neurotransmitters

    • Used in crises management


Intercellular communication1
Intercellular communication

  • Autocrine

    • chemicals that exert effects on the same cells that secrete them

  • Paracrine

    • locally acting chemicals that affect cells other than those that secrete them

      • Cytokines or local hormones

      • These are not considered hormones since hormones are long-distance chemical signals


Intercellular communication2
Intercellular communication

  • Endocrine

    • Hormones – chemical substances secreted by cells into the extracellular fluids

      • Regulate the metabolic function of other cells

      • Have lag times ranging from seconds to hours

      • Tend to have prolonged effects


Types of hormones
Types of Hormones

  • Amino acid based

    • Amines,

    • Thyroxine,

    • ADH

    • Oxytocin

    • GH

    • Prolactin


Types of hormones1
Types of Hormones

  • Lipid derivatives

    • Steroids – gonadal and adrenocortical hormones

    • Eicosanoids – leukotrienes and prostaglandins

      • Function as paracrine and autocrine factors

      • Function as hormones


Hormone action
Hormone Action

  • Hormones that bind to receptors in the cell membrane:

    • First and second messengers

    • Regulatory G proteins

    • Water-soluble hormones

  • Hormones that bind to intracellular receptors

    • Direct gene activation

    • Steroid and thyroid hormones

  • The precise response depends on the type of the target cell


Mechanism of hormone action
Mechanism of Hormone Action

  • Hormones produce one or more of the following cellular changes in target cells

    • Alter plasma membrane permeability

    • Stimulate protein synthesis

    • Activate or deactivate enzyme systems

    • Induce secretory activity

    • Stimulate mitosis


Hormones that bind to receptors in the cell membrane camp mechanism
Hormones that bind to receptors in the cell membrane: cAMP mechanism

  • Hormone (first messenger) binds to its receptor, which then binds to a G protein

  • The G protein is then activated as it binds GTP, displacing GDP

  • Activated G protein activates the enzyme adenylate cyclase

  • Adenylate cyclase generates cAMP (second messenger) from ATP

  • cAMP activates protein kinases, which then cause cellular effects


Hormones that bind to receptors in the cell membrane camp mechanism1
Hormones that bind to receptors in the cell membrane : cAMP mechanism

Extracellular fluid

Hormone A

Adenylate cyclase

Hormone B

1

1

2

3

3

2

GTP

GTP

GTP

GTP

4

Receptor

Receptor

Gs

Gi

GDP

GDP

GTP

GTP

ATP

cAMP

Catecholamines

ACTH

FSH

LH

Glucagon

PTH

TSH

Calcitonin

5

Triggers responses of target

cell (activates enzymes,

stimulates cellular

secretion, opens ion

channels, etc.)

Inactive

protein

kinase A

Active

protein

kinase A

Cytoplasm


Hormones that bind to receptors in the cell membrane pip calcium mechanism
Hormones that bind to receptors in the cell membrane: PIP-Calcium mechanism

  • Hormone binds to the receptor and activates G protein

  • G protein binds and activates phospholipase

  • Phospholipase splits the phospholipid PIP2 into diacylglycerol (DAG) and IP3 (both act as second messengers)

  • DAG activates protein kinases; IP3 triggers release of Ca2+ stores

  • Ca2+ (second messenger) alters cellular responses


Hormones that bind to receptors in the cell membrane pip calcium mechanism1
Hormones that bind to receptors in the cell membrane: PIP-Calcium mechanism

Extracellular fluid

Hormone

DAG

1

4

5

Active

protein

kinase C

2

3

PIP2

GTP

GTP

Receptor

Gq

Inactive

protein

kinase C

GDP

GTP

IP3

Phospholipase C

Catecholamines

TRH

ADH

GnRH

Oxytocin

Catecholamines (α1 receptors)

TRH

ADH

GnRH

Oxytocin

Triggers responses

of target cell

5

Endoplasmic

reticulum

6

Cytoplasm

Ca2+

Ca2+- calmodulin


Hormones that bind to intracellular receptors
Hormones that bind to intracellular receptors PIP-Calcium mechanism

  • Steroid Hormones

    • This interaction prompts DNA transcription to produce mRNA

    • The mRNA is translated into proteins, which bring about a cellular effect


Steroid PIP-Calcium mechanism

hormone

Cytoplasm

Steroid

hormone

Receptor-

chaperonin

complex

Receptor-hormone

complex

Molecular

chaperones

Hormone

response

elements

Binding

Chromatin

Transcription

mRNA

mRNA

Nucleus

Ribosome

New protein

Translation


Target cell specificity
Target Cell Specificity PIP-Calcium mechanism

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

  • Target cells must have specific receptors to which the hormone binds

  • These receptors may be intracellular or located on the plasma membrane


Target cell specificity1
Target Cell Specificity PIP-Calcium mechanism

  • Examples of hormone activity

    • ACTH receptors are only found on certain cells of the adrenal cortex

    • Thyroxin receptors are found on nearly all cells of the body


Target cell activation
Target Cell Activation PIP-Calcium mechanism

  • Target cell activation depends on three factors

    • Blood levels of the hormone

    • Relative number of receptors on the target cell

    • The affinity of those receptors for the hormone


Target cell activation1
Target Cell Activation PIP-Calcium mechanism

  • Up-regulation – target cells form more receptors in response to the hormone

  • Down-regulation – target cells lose receptors in response to the hormone


Hormone concentrations in the blood
Hormone Concentrations in the Blood PIP-Calcium mechanism

  • Hormones circulate in the blood in two forms: free or bound.

    • Bound:

      • Attached to plasma proteins

      • Bound to their own carriers


Hormone concentrations in the blood1
Hormone Concentrations in the Blood PIP-Calcium mechanism

  • Concentrations of circulating hormone reflect:

    • Rate of release

    • Speed of inactivation and removal from the body

  • Hormones are removed from the blood by:

    • Degrading enzymes

    • The kidneys

    • Liver enzyme systems


Interaction of hormones at target cells
Interaction of Hormones at Target Cells PIP-Calcium mechanism

Permissiveness – one hormone cannot exert its effects without another hormone being present.

  • Estrogen and thyroid hormone

  • Synergism – more than one hormone produces the same effects on a target cell

    • Glucagon and epinephrine

  • Antagonism – one or more hormones opposes the action of another hormone.

    • Glucagon and insulin


  • Control of hormone release
    Control of Hormone Release PIP-Calcium mechanism

    • Blood levels of hormones:

      • Are controlled by negative feedback systems

      • Vary only within a narrow desirable range

    • Hormones are synthesized and released by glands in response to:

      • Humoral stimuli

      • Neural stimuli

      • Hormonal stimuli


    Humoral stimuli
    Humoral Stimuli PIP-Calcium mechanism

    • Humoral stimuli – secretion of hormones in direct response to changing blood levels of ions and nutrients

    • Example: concentration of calcium ions in the blood

      • Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid hormone)

      • PTH causes Ca2+ concentrations to rise and the stimulus is removed


    Humoral stimuli1
    Humoral PIP-Calcium mechanismStimuli


    Neural stimuli
    Neural Stimuli PIP-Calcium mechanism

    • Neural stimuli – nerve fibers stimulate hormone release

      • Preganglionic sympathetic nervous system (SNS) fibers stimulate the adrenal medulla to secrete catecholamines


    Hormonal stimuli
    Hormonal Stimuli PIP-Calcium mechanism

    • 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


    Hormonal stimuli1
    Hormonal PIP-Calcium mechanismStimuli


    Nervous system modulation
    Nervous System Modulation PIP-Calcium mechanism

    • The nervous system modifies the stimulation of endocrine glands and their negative feedback mechanisms


    Nervous system modulation1
    Nervous System Modulation PIP-Calcium mechanism

    • The nervous system can override normal endocrine controls

      • For example, control of blood glucose levels

        • Normally the endocrine system maintains blood glucose

        • Under stress, the body needs more glucose

        • The hypothalamus and the sympathetic nervous system are activated to supply ample glucose


    Major endocrine organs pituitary hypophysis
    Major Endocrine Organs: Pituitary (Hypophysis) PIP-Calcium mechanism

    • 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 hormones


    Pituitary hypophysis
    Pituitary (Hypophysis) PIP-Calcium mechanism


    Pituitary hypothalamic relationships posterior lobe
    Pituitary-Hypothalamic Relationships: PIP-Calcium mechanismPosterior Lobe

    • The posterior lobe is a downgrowth of hypothalamic neural tissue

    • Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract)

    • Nuclei of the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH)

    • These hormones are transported to the posterior pituitary


    Pituitary hypothalamic relationships anterior lobe
    Pituitary-Hypothalamic Relationships: PIP-Calcium mechanismAnterior Lobe

    • The anterior lobe of the pituitary is an outpocketing of the oral mucosa

    • There is no direct neural contact with the hypothalamus


    Pituitary hypothalamic relationships anterior lobe1
    Pituitary-Hypothalamic Relationships: PIP-Calcium mechanismAnterior Lobe

    • There is a vascular connection, the hypophyseal portal system, consisting of:

      • The primary capillary plexus

      • The hypophyseal portal veins

      • The secondary capillary plexus


    Pituitary hypothalamic relationships anterior lobe2
    Pituitary-Hypothalamic Relationships: PIP-Calcium mechanismAnterior Lobe


    Adenophypophyseal hormones
    Adenophypophyseal Hormones PIP-Calcium mechanism

    • The six hormones of the adenohypophysis:

      • Abbreviated as GH, TSH, ACTH, FSH, LH, and PRL

      • Regulate the activity of other endocrine glands

    • In addition, pro-opiomelanocortin (POMC):

      • Has been isolated from the pituitary

      • Is split into ACTH, opiates, and MSH


    Activity of the adenophypophysis
    Activity of the Adenophypophysis PIP-Calcium mechanism

    • The hypothalamus sends a chemical stimulus to the anterior pituitary

      • Releasing hormones stimulate the synthesis and release of hormones

      • Inhibiting hormones shut off the synthesis and release of hormones


    Activity of the adenophypophysis1
    Activity of the Adenophypophysis PIP-Calcium mechanism

    • The tropic hormones that are released are:

      • Thyroid-stimulating hormone (TSH)

      • Adrenocorticotropic hormone (ACTH)

      • Follicle-stimulating hormone (FSH)

      • Luteinizing hormone (LH)


    Thyroid stimulating hormone thyrotropin
    Thyroid Stimulating Hormone (Thyrotropin) PIP-Calcium mechanism

    • Stimulates the normal development and secretory activity of the thyroid

    • Triggered by hypothalamic peptide thyrotropin-releasing hormone (TRH)

    • Rising blood levels of thyroid hormones act on the pituitary and hypothalamus to block the release of TSH


    Adrenocorticotropic hormone corticotropin
    Adrenocorticotropic Hormone (Corticotropin) PIP-Calcium mechanism

    • Stimulates the adrenal cortex to release corticosteroids

    • Triggered by hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm

    • Internal and external factors such as fever, hypoglycemia, and stressors can trigger the release of CRH


    Gonadotropins
    Gonadotropins PIP-Calcium mechanism

    • Gonadotropins – follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

      • Regulate the function of the ovaries and testes

      • FSH stimulates gamete (egg or sperm) production

      • Absent from the blood in prepubertal boys and girls

      • Triggered by the hypothalamic gonadotropin-releasing hormone (GnRH) during and after puberty


    Functions of gonadotropins
    Functions of Gonadotropins PIP-Calcium mechanism

    • In females

      • LH works with FSH to cause maturation of the ovarian follicle

      • LH works alone to trigger ovulation (expulsion of the egg from the follicle)

      • LH promotes synthesis and release of estrogens and progesterone


    Functions of gonadotropins1
    Functions of Gonadotropins PIP-Calcium mechanism

    • In males

      • LH stimulates interstitial cells of the testes to produce testosterone

      • LH is also referred to as interstitial cell-stimulating hormone (ICSH)


    Growth hormone gh
    Growth Hormone (GH) PIP-Calcium mechanism

    • Produced by anterior pituitary gland and:

      • Stimulate most cells, but target bone and skeletal muscle

      • Promote protein synthesis and encourage the use of fats for fuel

    • Most effects are mediated indirectly by somatomedins or IGFs


    Growth hormone gh1
    Growth Hormone (GH) PIP-Calcium mechanism

    • Antagonistic hypothalamic hormones regulate GH

      • Growth hormone–releasing hormone (GHRH) stimulates GH release

      • Growth hormone–inhibiting hormone (GHIH) or somatostatin inhibits GH release


    Metabolic action of growth hormone
    Metabolic Action of Growth Hormone PIP-Calcium mechanism

    • GH stimulates liver, skeletal muscle, bone, and cartilage to produce insulin-like growth factors (IGFs)

    • Direct action promotes lipolysis and inhibits glucose uptake



    Prolactin prl
    Prolactin (PRL) PIP-Calcium mechanism

    • In females, stimulates milk production by the breasts

    • Triggered by the hypothalamic prolactin-releasing hormone (PRH)

    • Inhibited by prolactin-inhibiting hormone (PIH)

    • Blood levels rise toward the end of pregnancy

    • Suckling stimulates PRH release and encourages continued milk production


    The posterior pituitary and hypothalamic hormones
    The Posterior Pituitary and Hypothalamic Hormones PIP-Calcium mechanism

    • Posterior pituitary – made of axons of hypothalamic neurons, stores antidiuretic hormone (ADH) and oxytocin

    • ADH and oxytocin are synthesized in the hypothalamus

    • ADH decreases urine formation

    • Oxytocin stimulates smooth muscle contraction in breasts and uterus

    • Both use PIP-calcium second-messenger mechanism


    The endocrine system1

    The Endocrine System PIP-Calcium mechanism

    P A R T B


    Oxytocin
    Oxytocin PIP-Calcium mechanism

    • Oxytocin is a strong stimulant of uterine contraction

    • Regulated by a positive feedback mechanism to oxytocin in the blood

    • This leads to increased intensity of uterine contractions, ending in birth

    • Oxytocin triggers milk ejection (“letdown” reflex) in women producing milk


    Oxytocin1
    Oxytocin PIP-Calcium mechanism

    • Synthetic and natural oxytocic drugs are used to induce or hasten labor

    • Plays a role in sexual arousal and satisfaction in males and nonlactating females


    Antidiuretic hormone adh
    Antidiuretic Hormone (ADH) PIP-Calcium mechanism

    • ADH helps to avoid dehydration or water overload

      • Prevents urine formation

    • Osmoreceptors monitor the solute 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 PIP-Calcium mechanism

    • 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 hormone

    • Other endocrine cells, the parafollicular cells, produce the hormone calcitonin


    Thyroid gland1
    Thyroid Gland PIP-Calcium mechanism


    Thyroid hormone
    Thyroid Hormone PIP-Calcium mechanism

    • Thyroid hormone – major metabolic hormone

    • Consists of two related iodine-containing compounds

      • T4 – thyroxine; has two tyrosine molecules plus four bound iodine atoms

      • T3 – triiodothyronine; has two tyrosines with three bound iodine atoms


    Effects of thyroid hormone
    Effects of Thyroid Hormone PIP-Calcium mechanism

    • TH is concerned with:

      • Glucose oxidation

      • Increasing metabolic rate

      • Heat production

    • TH plays a role in:

      • Maintaining blood pressure

      • Regulating tissue growth

      • Developing skeletal and nervous systems

      • Maturation and reproductive capabilities


    Synthesis of thyroid hormone
    Synthesis of Thyroid Hormone PIP-Calcium mechanism

    • Thyroglobulin is synthesized and discharged into the lumen

    • Iodides (I–) are actively taken into the cell, oxidized to iodine (I2), and released into the lumen

    • Iodine attaches to tyrosine, forming T1 (monoiodotyrosine, or MIT), and T2 (diiodotyrosine, or DIT)


    Synthesis of thyroid hormone1
    Synthesis of Thyroid Hormone PIP-Calcium mechanism

    • Iodinated tyrosines link together to form T3 and T4

    • Colloid is then endocytosed and combined with a lysosome, where T3 and T4 are cleaved and diffuse into the bloodstream


    Thyroid PIP-Calcium mechanism

    follicle cell

    Capillary

    1

    Thyroglobulin is synthesized

    and discharged into the follicle lumen

    Colloid

    Colloid in lumen of follicle

    Golgi

    apparatus

    Iodine is attached

    to tyrosine in colloid,

    forming DIT and MIT

    3b

    Rough ER

    Iodine

    Thyroglobulin

    colloid

    2

    Iodide (I–)

    is trapped

    (actively transported in)

    Iodide is

    oxidized

    to iodine

    3a

    Iodide

    (I–)

    DIT (T2)

    MIT (T1)

    T4

    Iodinated tyrosines are

    linked together to form

    T3 and T4

    4

    T3

    T4

    Lysosome

    T3

    T3

    T4

    T3

    Thyroglobulin colloid

    is endocytosed and

    combined with a

    lysosome

    5

    T4

    Lysosomal enzymes cleave

    T4 and T3 from thyroglobulin

    colloid and hormones diffuse

    from follicle cell into bloodstream

    6

    T4

    T3

    To peripheral

    tissues


    Transport and regulation of th
    Transport and Regulation of TH PIP-Calcium mechanism

    • T4 and T3 bind to thyroxine-binding globulins (TBGs) produced by the liver

    • Both bind to target receptors, but T3 is ten times more active than T4

    • Peripheral tissues convert T4 to T3

    • Mechanisms of activity are similar to steroids

    • Regulation is by negative feedback

    • Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback


    Calcitonin
    Calcitonin PIP-Calcium mechanism

    • A peptide hormone produced by the parafollicular, or C cells

    • Lowers blood calcium levels in children

    • Antagonist to parathyroid hormone (PTH)


    Calcitonin1
    Calcitonin PIP-Calcium mechanism

    • Calcitonin targets the skeleton, where it:

      • Inhibits osteoclast activity (and thus bone resorption) and release of calcium from the bone matrix

      • Stimulates calcium uptake and incorporation into the bone matrix

    • Regulated by a humoral (calcium ion concentration in the blood) negative feedback mechanism


    Parathyroid glands
    Parathyroid Glands PIP-Calcium mechanism

    • 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


    Parathyroid glands1
    Parathyroid Glands PIP-Calcium mechanism


    Effects of parathyroid hormone
    Effects of Parathyroid Hormone PIP-Calcium mechanism

    • PTH release increases Ca2+ in the blood as it:

      • 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 mucosal

    • Rising Ca2+ in the blood inhibits PTH release


    Effects of parathyroid hormone1
    Effects of Parathyroid Hormone PIP-Calcium mechanism


    Adrenal suprarenal glands
    Adrenal (Suprarenal) Glands PIP-Calcium mechanism

    • Adrenal glands – paired, pyramid-shaped organs atop the kidneys

    • Structurally and functionally, they are two glands in one

      • Adrenal medulla – neural tissue that acts as part of the SNS

      • Adrenal cortex – glandular tissue derived from embryonic mesoderm


    Adrenal cortex
    Adrenal Cortex PIP-Calcium mechanism

    • Synthesizes and releases steroid hormones called corticosteroids

    • Different corticosteroids are produced in each of the three layers

      • Zona glomerulosa – mineralocorticoids (chiefly aldosterone)

      • Zona fasciculata – glucocorticoids (chiefly cortisol)

      • Zona reticularis – gonadocorticoids (chiefly androgens)


    Adrenal cortex1
    Adrenal Cortex PIP-Calcium mechanism


    Mineralocorticoids
    Mineralocorticoids PIP-Calcium mechanism

    • Regulate electrolytes in extracellular fluids

    • Aldosterone – most important mineralocorticoid

      • Maintains Na+ balance by reducing excretion of sodium from the body

      • Stimulates reabsorption of Na+ and secretion of K+ by the kidneys


    Mineralocorticoids1
    Mineralocorticoids PIP-Calcium mechanism

    • Aldosterone secretion is stimulated by:

      • Rising blood levels of K+

      • Low blood Na+

      • Decreasing blood volume or pressure


    The four mechanisms of aldosterone secretion
    The Four Mechanisms of Aldosterone Secretion PIP-Calcium mechanism

    • Renin-angiotensin mechanism – kidneys release renin, which is converted into angiotensin II that in turn stimulates aldosterone release

    • 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



    Glucocorticoids cortisol
    Glucocorticoids (Cortisol) PIP-Calcium mechanism

    • Help the body resist stress by:

      • Keeping blood sugar levels relatively constant

      • Maintaining blood volume and preventing water shift into tissue

    • Cortisol provokes:

      • Gluconeogenesis (formation of glucose from noncarbohydrates)

      • Rises in blood glucose, fatty acids, and amino acids


    Excessive levels of glucocorticoids
    Excessive Levels of Glucocorticoids PIP-Calcium mechanism

    • Excessive levels of glucocorticoids:

      • Depress cartilage and bone formation

      • Inhibit inflammation

      • Depress the immune system

      • Promote changes in cardiovascular, neural, and gastrointestinal function


    Gonadocorticoids sex hormones
    Gonadocorticoids (Sex Hormones) PIP-Calcium mechanism

    • Zona Reticularis produces mainly androgens that are converted to testosterone in the testes

    • Androgens contribute to:

      • The onset of puberty

      • The appearance of secondary sex characteristics

      • Sex drive in females

    • Androgens can be converted into estrogens after menopause


    Adrenal medulla
    Adrenal Medulla PIP-Calcium mechanism

    • Made up of cells that secrete epinephrine and norepinephrine

    • Secretion of these hormones causes:

      • Blood glucose levels to rise

      • Blood vessels to constrict

      • The heart to beat faster

      • Blood to be diverted to the brain, heart, and skeletal muscle


    Adrenal medulla1
    Adrenal Medulla PIP-Calcium mechanism

    • Epinephrine is the more potent stimulator of the heart and metabolic activities

    • Norepinephrine is more influential on peripheral vasoconstriction and blood pressure


    Stress and the adrenal gland
    Stress and the Adrenal Gland PIP-Calcium mechanism


    Pancreas
    Pancreas PIP-Calcium mechanism

    • A triangular gland, which has both exocrine and endocrine cells, located behind the stomach

    • 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 () cells that produce glucagon

      • Beta () cells that produce insulin


    Pancreas1
    Pancreas PIP-Calcium mechanism


    Glucagon
    Glucagon PIP-Calcium mechanism

    • 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 cells


    Insulin
    Insulin PIP-Calcium mechanism

    • Synthesized as part of proinsulin and then excised by enzymes, releasing functional insulin

    • Insulin:

      • Lowers blood glucose levels

      • Enhances transport of glucose into body cells

      • Counters metabolic activity that would enhance blood glucose levels


    Effects of insulin binding
    Effects of Insulin Binding PIP-Calcium mechanism

    • The insulin receptor is a tyrosine kinase enzyme

    • After glucose enters a cell, insulin binding triggers enzymatic activity that:

      • Catalyzes the oxidation of glucose for ATP production

      • Polymerizes glucose to form glycogen

      • Converts glucose to fat (particularly in adipose tissue)


    Regulation of blood glucose levels
    Regulation of Blood Glucose Levels PIP-Calcium mechanism

    • The hyperglycemic effects of glucagon and the hypoglycemic effects of insulin


    Diabetes mellitus dm
    Diabetes Mellitus (DM) PIP-Calcium mechanism

    • Results from hyposecretion or hypoactivity of insulin

    • The three cardinal signs of DM are:

      • Polyuria – huge urine output

      • Polydipsia – excessive thirst

      • Polyphagia – excessive hunger and food consumption

    • Hyperinsulinism – excessive insulin secretion, resulting in hypoglycemia


    Diabetes mellitus dm1
    Diabetes Mellitus (DM) PIP-Calcium mechanism


    Gonads female
    Gonads: Female PIP-Calcium mechanism

    • Paired ovaries in the abdominopelvic cavity produce estrogens and progesterone

    • They are responsible for:

      • Maturation of the reproductive organs

      • Appearance of secondary sexual characteristics

      • Breast development and cyclic changes in the uterine mucosa


    Gonads male
    Gonads: Male PIP-Calcium mechanism

    • Testes located in an extra-abdominal sac (scrotum) produce testosterone

    • Testosterone:

      • Initiates maturation of male reproductive organs

      • Causes appearance of secondary sexual characteristics and sex drive

      • Is necessary for sperm production

      • Maintains sex organs in their functional state


    Pineal gland
    Pineal Gland PIP-Calcium mechanism

    • Small gland hanging from the roof of the third ventricle of the brain

    • Secretory product is melatonin

    • Melatonin is involved with:

      • Day/night cycles

      • Physiological processes that show rhythmic variations (body temperature, sleep, appetite)


    Thymus
    Thymus PIP-Calcium mechanism

    • Lobulated gland located deep to the sternum

    • Major hormonal products are thymopoietins and thymosins

    • These hormones are essential for the development of the T lymphocytes (T cells) of the immune system


    Other hormone producing structures
    Other Hormone-Producing Structures PIP-Calcium mechanism

    • Heart – produces atrial natriuretic peptide (ANP), which reduces blood pressure, blood volume, and blood sodium concentration

    • Gastrointestinal tract – enteroendocrine cells release local-acting digestive hormones

    • Placenta – releases hormones that influence the course of pregnancy


    Other hormone producing structures1
    Other Hormone-Producing Structures PIP-Calcium mechanism

    • Kidneys – secrete erythropoietin, which signals the production of red blood cells

    • Skin – produces cholecalciferol, the precursor of vitamin D

    • Adipose tissue – releases leptin, which is involved in the sensation of satiety, and stimulates increased energy expenditure


    Developmental aspects
    Developmental Aspects PIP-Calcium mechanism

    • Exposure to pesticides, industrial chemicals, arsenic, dioxin, and soil and water pollutants disrupts hormone function

    • Sex hormones, thyroid hormone, and glucocorticoids are vulnerable to the effects of pollutants

    • Interference with glucocorticoids may help explain high cancer rates in certain areas


    Developmental aspects1
    Developmental Aspects PIP-Calcium mechanism

    • Ovaries undergo significant changes with age and become unresponsive to gonadotropins

    • Female hormone production declines, the ability to bear children ends, and problems associated with estrogen deficiency (e.g., osteoporosis) begin to occur

    • Testosterone also diminishes with age, but effect is not usually seen until very old age


    Developmental aspects2
    Developmental Aspects PIP-Calcium mechanism

    • 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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