Dr. Michael P. Gillespie
Mediator Molecules in Nervous & Endocrine SystemsThe nervous system utilizes
neurotransmitters to control body functions.The endocrine system utilizes hormones to
control body functions.
Site Of Mediator Action In Nervous & Endocrine SystemsThe neurotransmitters perform their action
close to the site of release.The hormones usually perform their action
far from their site of release.
Types Of Target Cells In Nervous & Endocrine SystemsThe nervous system acts upon muscle cells
(smooth, cardiac, and skeletal), glands, and other neurons.
The endocrine system acts upon virtually all cells of the body.
Time To Onset Of Action In Nervous & Endocrine SystemsIn the nervous system, action typically occurs
within milliseconds of neurotransmitter release.
In the endocrine system, action can take seconds to days to occur after release of the hormone.
Duration Of Action In Nervous & Endocrine SystemsThe actions tend to be briefer in duration in
the nervous system and longer in duration in the endocrine system.
Comparison of Nervous and Endocrine System ControlCharacteristic Nervous System Endocrine System
Mediator Molecules Neurotransmitters – released locally
Hormones – delivered throughout the body by the blood
Site of Mediator Action
Close to site of release
Usually far from site of release
Types of target cells Muscle (smooth, cardiac, and skeletal) cells, gland cells, other neurons
Cells throughout the body
Time to onset of action
Within milliseconds Seconds – hours - days
Duration of Action Typically briefer (milliseconds)
Generally longer (seconds to days)
HormonesA hormone is a mediator molecule that is
released in one part of the body but regulates activity of cells in other parts of the body.
Most hormones enter the interstitial fluid and then the bloodstream.
Hormones travel through the bloodstream to cells throughout the body.
Several neurotransmitters are also hormones (i.e. norepinephrine).
Functions Of HormonesHelp regulate:
Chemical composition and volume of the internal environment (interstitial fluid).
Metabolism and energy balance.Contraction of smooth and cardiac muscle
fibers.Glandular secretions.Some immune system activities.
Functions Of HormonesControl growth and development.Regulate operation of reproductive systems.Help establish circadian rhythms.
“Supersystem”The nervous and endocrine systems function
together.Parts of the nervous system stimulate or
inhibit the release of hormones.Hormones can promote or inhibit the release
of nerve impulses.
Exocrine Glands Versus Endocrine GlandsExocrine glands (Exo = outside) – secrete
their products into ducts that carry secretions into body cavities, into the lumen of an organ, or to the outer surface of the body.
Endocrine glands – secrete their hormones into the interstitial fluid surrounding the secretory cells.
Exocrine Glands Versus Endocrine GlandsExocrine glands.
Sudoriferous (sweat).Sebaceous (oil).Mucous.Digestive.
Exocrine Glands Versus Endocrine GlandsEndocrine glands.
Pituitary.Thyroid.Parathyroid.Adrenal.Pineal.Other organs that secrete hormones:
Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, SI, skin, heart, adipose tissue, & placenta.
Endocrine SystemAll endocrine glands and hormone secreting
cells comprise the endocrine system.Endocrinology (-logy = study of) is the study
of the science of endocrine glands, function of endocrine glands, diagnosis of endocrine disorders and treatment of endocrine disorders.
Hormone ReceptorsHormones bind with specific receptors.Only target cells for a given hormone have
specific receptors that bind and recognize that hormone.
A target cell can have anywhere between 2000 and 100,000 receptors for a particular hormone.
Receptors are constantly being synthesized and broken down to meet the needs of the body.
Down-regulationIf a hormone is present in excess, the number
of target cell receptors may decrease.Down-regulation decreases the
responsiveness of the target cell to the hormone.
Up-regulationWhen a hormone (or neurotransmitter) is
deficient, the number of receptors may increase.
Up-regulation makes a target cell more receptive to a specific hormone.
Synthetic HormonesSynthetic hormones in the form of drugs can
block the receptors from naturally occurring hormones.
Circulating & Local HormonesCirculating hormones – pass from secretory
cells that make them into the interstitial fluid and then into the blood.Most hormones are of this type.
Local hormones – act locally on neighboring cells or on the same cells that secreted them without first entering the bloodstream.
Local HormonesParacrines – (para = beside or near) act on
neighboring cells.Autocrines – (auto – self) act on the same cell
that secreted them.
Local Hormones
Example Of A Local HormoneInterleukin 2 (IL-2) is an example of a local
hormone.It is released by helper T cells during immune
responses.It acts on nearby immune cells (paracrine) and
on itself (autocrine).This generates more helper T cells and boosts
the immune response.
Duration of Local Versus Circulating HormonesLocal hormones usually are inactivated
quickly.Circulating hormones linger longer.The liver eventually deactivates circulating
hormones and the kidneys excrete them.
Chemical Classes Of HormonesLipid-soluble hormones.
Steroid hormones.Thyroid hormones.Nitric oxide (NO).
Chemical Classes Of HormonesWater-soluble hormones.
Amine hormones.Peptide hormones and protein hormones.Eicosanoid hormones.
Prostaglandins. Leukotrienes.
Hormone Transport In BloodMost water-soluble hormones are transported
in their “free” form (not attached to plasma proteins).
Most lipid-soluble hormones are bound to transport proteins.
Hormone ReceptorsLipid-soluble hormones – the receptors are
located inside the target cells.Water-soluble hormones – the receptors are
located within the plasma membrane of the target cells.
Action Of Lipid-soluble HormonesLipid soluble hormones turn specific genes of
the nuclear DNA on or off.This directs the synthesis of a new protein
(often an enzyme).These new proteins alter the cells activity.
Action Of Water-soluble HormonesWater soluble hormones are the first
messenger. They activate the second messenger i.e. cyclic AMP (cAMP).
This initiates a cascade of events within the cell that produces millions of enzymes to catalyze reactions.
Phosphodiesterase inactivates cAMP.
Lipid Soluble Hormones
Water Soluble Hormones
Summary of Hormones By ClassRefer to Table 18.2
Responsiveness Of The Target CellThe responsiveness of the target cell depends
upon the following:The hormone’s concentration.The number of the hormone receptors on the
target cell.Influences exerted by other hormones.
Influences Of Other HormonesPermissive effect – the action of a 2nd
hormone is required for the 1st hormone to take effect.Thyroid hormones (2nd) allow epinephrine to
stimulate lipolysis.
Influences Of Other HormonesSynergistic effect – the sum of the actions
of the 2 hormones is greater than either hormone individually.Estrogens and FSH promote development of
oocytes.
Antagonistic effect – one hormone opposes the actions of another.Insulin promotes synthesis of glycogen and
glucagon stimulates breakdown of glycogen.
Control Of Hormonal SecretionHormone secretion is regulated by:
Signals from the nervous system.Chemical changes in the blood.Other hormones.
HypothalamusServes as a major integrating link between
the nervous system and the endocrine system.
Painful, stressful, and emotional experiences cause changes in hypothalamic activity.
Synthesizes at least 9 different hormones.Regulates the pituitary gland.
Pituitary Gland (hypophysis)Synthesizes at least 7 different hormones.Release of anterior pituitary hormones is
stimulated by releasing hormones and suppressed by inhibiting hormones from the hypothalamus.
Attaches to the hypothalamus by a stalk, the infundibulum (= a funnel).
Types Of Anterior Pituitary Cells & Their HormonesSomatotrophs – secretes human growth
hormone (hGH) or somatotropin, which stimulates tissues to secrete insulinlike growth factors (IGFs).
Thyrotrophs – secrete thyroid-stimulating hormone (TSH) or thyroptropin.
Types Of Anterior Pituitary Cells & Their HormonesGonadotrophs – secrete follicle-stimulating
hormone (FSH) and luteinizing hormone (LH) which act on the gonads.They stimulate the secretion of estrogen and
progesterone and the maturation of oocytes in the ovaries.
They stimulate the secretion of testosterone and sperm production in the testes.
Types Of Anterior Pituitary Cells & Their HormonesLactotrophs – secrete prolactin (PRL), which
initiates milk production.Corticotrophs – secrete adrenocorticotropic
hormone (ACTH) or corticotropin, which stimulates the adrenal cortex to secrete glucocorticoids.
Tropic Hormones (tropins)Hormones that influence another gland are
called tropic hormones or tropins.
Control Of Secretion By The Anterior Pituitary (adenohypophysis)The hypothalamus secretes five releasing
hormones and two inhibiting hormones.Negative feedback loops from hormones
released from target glands decrease the release from the anterior pituitary gland.
Human Growth Hormone & Insulinlike Growth FactorsThe main function of hGH is to promote
synthesis of IGFs.IGFs cause cells to grow and multiply.They help to maintain the mass of muscles
and bones.They promote healing of injuries and
tissue repair.They enhance lypolysis in adipose tissue.
Release Of hGHTwo hypothalamic hormones control the
release of hGH:Growth hormone releasing hormone (GHRH).
Stimulated by hypoglycemia. Inhibited by hyperglycemia.
Growth hormone inhibiting hormone (GHIH). Stimulated by hyperglycemia. Inhibited by hypoglycemia.
Thyroid-stimulating HormoneThyroid-stimulating hormone (TSH)
stimulates the synthesis and secretion of two thyroid hormones:Triiodothyronine (T3).
Thyroxine (T4).
Thyrotropin-releasing hormone (TRH) from the hypothalamus controls TSH secretion.
Negative feedback from T3 and T4 inhibits the release of TRH.
Follicle-stimulating HormoneFSH initiates the development of ovarian
follicles and stimulates follicular cells to secrete estrogens in females.
FSH stimulates sperm production in the testes in males.
Follicle-stimulating HormoneGonadotropin-releasing hormone (GnRH)
from the hypothalamus stimulates FSH release.
Estrogens in females and testosterone in males suppresses release of GnRH and FSH through negative feedback systems.
Luteinizing Hormone (LH)In females LH triggers ovulation.FSH and LH work together to stimulate the
release of estrogen.In males, LH stimulates the release of
testosterone from the testes.
Prolactin (PRL)Initiates and maintains secretion of milk by
the mammary glands.By itself, prolactin has only a weak effect.
Prolactin (PRL)Only with the effects of estrogens,
progesterone, glucocorticoids, hGH, thyroxine and insulin does PRL bring about milk.
The hypothalamus secretes both inhibitory and excitatory hormones that regulate PRL secretion:Prolactin-inhibiting hormone (PIH).Prolactin-releasing hormone (PRH).
Hypersecretion Of ProlactinIn males – erectile dysfunction.In females – galactorrhea (inappropriate
lactation) and amenorrhea (absence of menstrual cycles).
Adrenocorticotropic Hormone (ACTH)ACTH controls secretion of cortisol and
other glucocorticoids by the cortex of the adrenal gland.
Corticotropin-releasing hormone (CRH) from the hypothalamus stimulates secretion of ACTH.
Glucocorticoids cause inhibition of CRH and ACTH through negative feedback systems.
Principle Actions Of Anterior Pituitary HormonesTable 18.4 page 655.
Posterior Pituitary (neurohypophysis)The posteror pituitary does not synthesize
any hormones; however, it does store and release two hormones from the hypothalamus:Oxytocin (OT).Antidiuretic hormone (ADH) a.k.a. vasopressin.
OxytocinDuring delivery, oxytocin enhances
contraction of smooth muscle cells in the wall of the uterus.
After delivery, oxytocin stimulates milk ejection (“letdown”) from the mammary glands in response to the suckling infant.
Antidiuretic Hormone (ADH)ADH is a substance that decreases urine
production.ADH causes the kidneys to return more water
to the blood.
Summary Of Posterior Pituitary HormonesTable 18.5 page 658.
Thyroid GlandLocated inferior to the larynx (voice box).Right and left lateral lobes connected by
an isthmus.Anterior to the trachea.Highly vascular.Consists of thyroid follicles (spherical
sacs).The walls of each follicle contain follicular
cells, which extend into the lumen of the follicle.
Follicular CellsProduce two thyroid hormones (both are lipid
soluble).Thyroxine (tetraiodothyronine or T4).Triiodothyrronine (T3).
Parafollicular CellsAlso known as C cells.Produce the hormone calcitonin (CT).
Regulates calcium homeostasis.CT inhibits the action of osteoclasts.CT accelerates the uptake of calcium and
phosphates into the bone matrix.
Actions Of Thyroid HormonesIncrease basal metabolic rate (BMR).Stimulates synthesis of Na+ / K+ ATPaseCalorigenic effect.
Helps to regulate body temperature.Regulate metabolism.
Protein synthesis.Increase the use of glucose and fatty acids for
ATP.Increase lypolysis.
Actions Of Thyroid HormonesAccelerate body growth, especially of the
nervous system.Enhances actions of the catecholamines
(norepinephrine and epinephrine). In hyperthyroidism there is an increased heart rate, more forceful heartbeats, and increased blood pressure.
Parathyroid GlandsEmbedded into the posterior surface of the
lateral lobes of the thyroid gland.Superior and inferior parathyroid glands.Two kinds of epithelial cells.
Chief (principal) cells – produce parathyroid hormone (PTH) or parathormone.
Oxyphil cell – function unknown.
Parathyroid HormoneRegulates levels of calcium, magnesium, and
phosphate ions in the blood.PTH increases the activity and # of
osteoclasts.PTH stimulates the kidneys to synthesize
calcitrol (active form of vitamin D).Calcitrol stimulates increased absorption of
Ca2+ from the GI tract.
Adrenal GlandsThe paired adrenal (suprarenal) glands lie
superior to each kidney.Consists of the adrenal cortex (80-90% of the
gland) and the adrenal medulla.Highly vascularized.
Adrenal Gland HormonesAdrenal Cortex – steroid hormones.Adrenal Medulla – 3 catecholamine
hormones.Norepinephrine.Epinephrine.Dopamine.
Aldosterone (Cortex)Regulates homeostasis of sodium ions and
postassium ions.Promotes the secretion of H+ in the urine to
regulate acid-base balance. Prevents acidosis (pH below 7.35).
Renin-angiotensin-aldosterone (RAA) pathway controls the secretion of aldosterone (Controls blood pressure).
Glucocorticoids (Cortex)Regulate metabolism and resistance to
stress.Cortisol (hydrocortisone).Corticostrerone.Cortisone.
Low levels of glucocorticoids, mainly cortisol, stimulate the hypothalamus to secrete corticotropin-releasing hormone (CRH), which promotes the release of ACTH from the anterior pituitary, which in turn stimulates glucocorticoid secretion.
Effects Of GlucocorticoidsIncrease the rate of protein breakdown.Stimulates glucose formation by breaking
down glycogen stores and through gluconeogenesis.
Stimulates lypolysis.
Effects Of GlucocorticoidsResistance to stress by supplying ATP and
raising BP in cases of severe blood loss.Anti-inflammatory effects – inhibit WBCs
(also slows wound healing).Depression of immune responses (utilized
with organ transplant recipients).
Androgens (Cortex)The adrenal cortex secretes small
amounts of androgens (primarily dehydroepiandrosterone DHEA).
Assists in early growth of axillary and pubic hair in both sexes.
Contributes to libido and provides a source of estrogens after menopause in females.
ACTH stimulates its secretion.
Adrenal Medulla HormonesEpinephrine (adrenaline).Norepinephrine (noradrenaline).These two hormones augment the fight or
flight response.Increase the heart rate and force of
contraction.Dilates the airways in the lungs.Shunts blood to heart, liver, skeletal muscles,
and adipose tissue.Increases blood levels of glucose and fatty
acids.
Pancreatic IsletsBoth and endocrine and exocrine gland.Pancreatic islets (a.k.a. islets of Langerhans).4 major cell types:
Alpha (A) cells – secrete glucagon.Beta (B) cells – secrete insulin.Delta (D) cells – secretes somatostatin
(identical to growth hormone inhibiting hormone).
F cells – secrete pancreatic polypeptide.
Pancreatic HormonesGlucagon raises blood glucose levels.Insulin lowers blood glucose levels.Somatostatin inhibits both glocagon and
insulin release.Pancreatic polypeptide inhibits
somatostatin secretion, gallbladder contraction and secretion of digestive enzymes by the pancreas.
Regulation Of Glucagon & Insulin SecretionHypoglycemia stimulates release of glucagon.Glucagon causes hepatocytes to convert
glycogen to glucose (glycogenolysis).Hyperglycemia inhibit release of glucagon.
Regulation Of Glucagon & Insulin SecretionInsulin allows glucose to diffuse into cells,
increases amino acid uptake by cells, and increaes fatty acid uptake by cells.
This facilitates glucose conversion into glycogen (glycogenesis), synthesis of proteins, and synthesis of fatty acids (lipogenesis).
GonadsOvaries (female gonads).
Produce steroid hormones. Estrogens. Progesterone.
Produce inhibin.Produce relaxin.
Testes (male gonads).Produce testosterone (an androgen).Produce inhibin.
Females Sex HormonesEstrogen and progesterone along with FSH
and LH (from the anterior pituitary), regulate the menstrual cycle, maintain pregnancy, and prepare the mammary glands for lactation.
Maintain the feminine secondary sex characteristics (larger breasts and hips).
Inhibin & RelaxinInhibin inhibits secretion of FSH.Relaxin increases the flexibility of the pubic
symphisis during pregnancy and helps dilate the cervix during labor and delivery.
Male Sex Hormones (Androgens)Testosterone regulates the production of
sperm.Stimulates the production of male secondary
sex characteristics (beard growth and deepening of the voice).
Pineal GlandA small endocrine gland attached to the roof
of the third ventrical of the brain.Secretes melatonin.More melatonin is released in darkness.Melatonin contributes to the body’s biological
clock.
Seasonal Affective Disorder (SAD)Thought to be due to overproduction of
melatonin during the winter months.Full spectrum bright-light therapy can assist
with SAD and jet lag.
ThymusLocated behind the sternum between the
lungs.Hormones produced – thymosin, thymic
humoral factor (THF), thymic factor (TF), amd thymopoeietin.
Promotes the maturation of T cells and may retard the aging process.