PowerPoint Lectures for Biology, Seventh Edition

Lectures by Ching-wei Luo

Chapter 45Chapter 45

Hormones and theEndocrine System

Overview: The Bodys Long-Distance Regulators

Hormone definition:

Hormones may reach all parts of the body

But only certain types of cells (target cells) are equipped to respond

Hormone (from the Greek Hormone (from the Greek hormanhorman, to excite), to excite)

a chemical signal secreted into the circulatory system and communicates regulatory messages within the body

Q

Endocrine systemConstituted by hormonesecreting cells and glands

Secretes hormones that coordinate slower but longer-acting responses to stimuli

ductless

Two systems act individually and together in regulating an animals physiology

Nervous systemConveys high-speed electrical signals along specialized cells called neurons

rapid messages control the movement of body parts

Two systems act individually and together in regulating an animals physiology

vesicle

Endocrine cell NeuronSecrete signal molecules

neurosecretory cells: release neurohormones into the bloodPathway Example

Stimulus Low bloodglucose

Receptorprotein

Pancreassecretesglucagon ( )

Endocrinecell

Bloodv essel

Liv erTarget

effectors

Response

Pathway Example

Stimulus Suckling

Sensoryneuron

Hypothalamus /posterior pituitar y

Neurosecretorycell

Bloodv essel

Posterior pituitarysecretes oxytocin( )

Targeteffectors

Smooth musclein breast

Response Milk release

Pathway Example

Stimulus Hy pothalamicneurohormonereleased inresponse toneural andhormonalsignals

Sensoryneuron

Hy pothalamussecretes prolactin-releasinghormone ( )

Neurosecretorycell

Bloodv essel

Anteriorpituitarysecretesprolactin ( )

Endocrinecell

Bloodv essel

Targeteffectors

Response

Mammary glands

Milk production

(c) Simple neuroendocrine pathway

(b) Simple neurohormone pathway

(a) Simple endocrine pathway

Hypothalamus

Glycogenbreakdown,glucose releaseinto blood

negativepositive

FeedbackHomeostasis

Three major classes of molecules function as hormones in vertebrates

Hormone composition

Receptionsignal transductionresponse

Signaling by any of these molecules involves three key events

Proteins and peptides (soluble)Amines derived from amino acids (soluble)Steroids (insoluble)

Water-soluble hormones act on cell-surface receptorsSECRETORYCELL

Hormonemolecule

VIABLOODSignal receptor

TARGETCELLSignal

transductionpathway

Cytoplasmicresponse

Nuclearresponse NUCLEUS

DNA

OR

(a) Receptor in plasma membrane

Receptor embedded in the plasma membrane

Signal transductionconverts an extracellular chemicalsignal to a intracellular response

Cytoplasmic response

Nuclear response

eg: Glucagon (an 8-aa peptide)Camouflage mechanism

Response

Steroids (estrogens, progesterone), thyroid hormones, and the hormonal form of vitamin D

Intracellular Receptors for Lipid-Soluble Hormones

SECRETORYCELL

Hormonemolecule

VIABLOOD

TARGETCELL

Signalreceptor

Signaltransductionand response

DNA

mRNA

NUCLEUS

Synthesis ofspecific proteins

(b) Receptor in cell nucleus

Receptor: located in the nucleus or trapped in

the cytoplasm

Signal transductionusually perform the entire task of transducing signals within a target cell.

Hormones: mostly nonpolar (lipidsoluble)

diffusible

The same hormone may have different effects on target cells that have

eg. Epinephrine () : fightorflight hormone

A B

Response A Response B

Different receptors for the hormone

Different proteins for carrying out the response

Different receptors different cell responses

Epinephrine

receptor

Epinephrine

receptor

Epinephrine

receptor

Vesselconstricts

Vesseldilates Glycogen

breaks downand glucose is releasedfrom cell

(a) skin, Intestinal blood vessel

(b) Skeletal muscleblood vessel

(c) Liver cell

Different intracellular proteins different cell responses

Glycogendeposits

Figure 45.4ac

EpinephrineResponds to short-term stress Resulting in decreased blood flow to the digestive tract and increased delivery of glucose to major skeletal muscles.

Paracrine Signaling by Local RegulatorsVarious types of chemical signals elicit responses in nearby target cells

More quickly than hormones can

Examples:Neurotransmitters

Cytokines/ growth factors : play a role in immune responses

nitric oxide (NO) : free radical, easy to breakdown (1998 Nobel)secreted by endothelial cellsactivates an enzyme that relaxes the neighboring smooth muscle cells dilates the vessels and improves blood flow

Viagra (sildenafil citrate)

Prostaglandins (PGs) (1982, Nobel Prize)

First discovered in prostategland secretions-stimulate smooth muscles of the females uterus to contract

Secreted by placenta cells during childbirth-induce labor

In the immune system

In the reproductive system

-induce fever and inflammation; intensify the sensation of pain The antiinflammatory drugs: aspirin and ibuprofen

-regulate the aggregation of platelets In the circulation system

Figure 45.5 platelets (pink and purple) develop a sticky outer surface and adhere to each other

In the respiratory system

Prostaglandin E signals the muscle cells to relax

Prostaglandin F signals the muscle cells to contract

E F

The major human endocrine glands

( )

Major human endocrine glands and their hormones

Major human endocrine glands and their hormones

The pineal gland-Melatonin

The pineal gland, located within the brain

Secretes melatonin

melatoninhttp://en.wikipedia.org/wiki

Contains lightsensitive cells

The primary functions of melatonin ()

Affects skin pigmentation in many vertebrates

Appear to be related to biological rhythms associated with reproduction

Release of melatonin

Is controlled by light/dark cycles

main target cells are in the part of the brain called the suprachiasmaticnucleus (SCN)

Relation Between the Hypothalamus and Pituitary Gland The hypothalamus, a region of the lower brain

Contains different sets of neurosecretory cells

hypothalamus

pituitary

Relationship Between the Hypothalamus and Pituitary Gland

Figure 45.7

Hypothalamus

Neurosecretorycells of thehypothalamus

Axon

Anteriorpituitary

Posteriorpituitary

HORMONE ADH Oxytocin

TARGET Kidney tubulesMammary glands,uterine muscles

The pituitary gland: a lima beansized organ located at the base of the hypothalamus

The posterior pituitary( neurohypophysis): -an extension of the hypothalamus-stores and secretes two hormonesfrom hypothalamus

Posterior Pituitary HormonesThe two hormones released from the posterior pituitary

Act directly on nonendocrine tissues

Antidiuretic hormone (ADH)

Oxytocin

acts on the kidneys, increasing water retention and thus decreasing urine volume.

acts on uterine muscles to contract during childbirth

causes the mammary glands to eject milk during nursing

The anterior pituitary

A true-endocrine gland, controlled by the neurohormones from hypothalamus

Synthesize and secrete at least eight different hormonesdirectly into the blood.

Tropic Effects OnlyFSH, follicle-stimulating hormoneLH, luteinizing hormoneTSH, thyroid-stimulating hormoneACTH, adrenocorticotropic hormone

Nontropic Effects OnlyProlactinMSH, melanocyte-stimulating hormoneEndorphin

Nontropic and Tropic EffectsGrowth hormone

Neurosecretory cellsof the hypothalamus

Portal vessels

Endocrine cells of theanterior pituitary

HORMONE FSH and LH TSH ACTH Prolactin MSH Endorphin Growth hormone

TARGET Testes orovaries

Thyroid Adrenalcortex

Mammaryglands

Melanocytes Pain receptorsin the brain

Liver Bones

Pituitary hormones(blue dots)

Tropic hormones:

Hormones that regulate the function of endocrine organs

Tropic H Hx response

Anterior Pituitary Hormones

Follicle-stimulating hormone (FSH)

Luteinizing hormone (LH)

Thyroid-stimulating hormone (TSH)

Adrenocorticotropic hormone (ACTH)

The four strictly tropic hormones areThe four strictly tropic hormones are

GlycoproteinHormone(~25kDa)

Gonadotropins: stimulate the activities of the male and female gonads

Peptide; stimulates the production and secretion of steroid hormones by the adrenal cortex.

ACTH ()

The nontropic hormones include

Prolactin (PRL)

Anterior Pituitary HormonesAnterior Pituitary Hormones

Stimulates mammary gland growth and lactation in mammalsRegulates fat metabolism and reproduction in birds

Melanocyte-stimulating hormone (MSH)

-endorphin

Regulates the activity of pigmentcontaining cells in the skin of some fishes, amphibians, and reptiles. Act on neurons in the brain, inhibiting hunger in mammals

Bind to brain receptors and inhibit the sensation of pain Runners high effects

The hormones play both tropic and nontropic effects Anterior Pituitary Hormones

Growth hormone (GH)

Tropic action: signal the liver to release insulinlike growth factors (IGFs), which circulate stimulate bone/cartilage growth.

Non-tropic action: exerts diverse metabolic effects that tend to raise blood glucose

Hyposecretion of GH in childhood

~about 4 feet (1.2 m) Dwarfism

Hypersecretion of GH during childhood

Gigantismas tall as 8 feet (2.4 m) http://www.mm52.com

Acromegaly

Excessive production of GH in adulthood

(tyrosine)http://www.answers.com/topic/thyroid-hormone

The thyroid gland

Consists of two lobes located on the ventral surface of the trachea

Produces two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4)

T4 is converted to T3 by deiodinases

Hypothalamus

Anteriorpituitary

TSH

Thyroid

T3 T4+ Figure 45.9

Secretion of thyroid hormones is regulated by hypothalamus and anterior pituitary hormones

two negative feedback loops

TRHTSHreleasing hormone

thyroidstimulating hormone

Functions in mammals Thyroid hormones help maintain normal blood pressure, heart rate, muscle tone, digestion, and reproductive functions.

Important in bioenergetics, generally increasing the rate of oxygen consumption and cellular metabolism

Hyperthyroidism

lead to high body temperature, profuse sweating, weight loss, irritability, and high blood pressure.Graves disease

Fig 45.10

Tissue behind the eyes can become swollen and fibrous

HypothyroidismCan produce symptoms such as weight gain, lethargy, and intolerance to cold in adults.

GoiterA deficiency of iodine in the diet

TSH enlarging the thyroid

Hypothalamus

Anteriorpituitary

TSH

Thyroid

T3 T4+

TRH

Cretinism Inherited condition of thyroid deficiency or lacked of thyroid hormones in childhoods

endemic cretinism in the Democratic Republic of Congo : Four inhabitants aged 15-20 years : a normal male and three females with severe longstanding hypothyroidism with dwarfism, retarded sexual development, puffy features, dry skin and hair and severe mental retardation. From Delange (229).

Calcitonin (; from thyroid gland)a 32-aa peptide

parathyroid glands

four small structures embedded in the surface of the thyroid

Parathyroid Hormone; PTH (from parathyroid glands)

- Blood calcium homeostasis

CalcitoninThyroid glandreleasescalcitonin.

StimulatesCa2+ depositionin bones

ReducesCa2+ uptakein kidneys

STIMULUS:Rising bloodCa2+ level

Blood Ca2+level declinesto set point

Homeostasis:Blood Ca2+ level

(about 10 mg/100 mL)

Blood Ca2+level risesto set point

STIMULUS:Falling bloodCa2+ level

StimulatesCa2+ releasefrom bones

Parathyroidgland

IncreasesCa2+ uptakein intestines Active

vitamin DStimulates Ca2+ uptake in kidneys

PTH

Fig 45.11

Calcitonin and Parathyroid Hormone

Osteoclasts (direct)

Ca2+ reabsorption (direct)

Conversion of vitamin D

In kidney

In bone

(indirect)

Osteoblasts In bone

Ca2+ reabsorptionIn kidney

Hormones in the pancreas

Insulin

Glucagon (peptide, 11 aa)Somatostatin (peptide, 14 aa)

islets of Langerhans

hormonesecreting cells make up only 12% of its weight

first discovered in hypothalamic extracts

identified as a hormone that inhibited secretion of growth hormone.

a paracrine manner to inhibit the secretion of both glucagon and insulin.

Somatostatin (endocrine and paracrine functions)

suppress pancreatic exocrine secretions

tropic

endocrine

paracrine

non-tropic

;

antagonistic hormones that regulate the glucose concentrationin the blood

Insulin and Glucagon

Beta cells ofpancreas are stimulatedto release insulininto the blood.

Insulin Body cellstake up moreglucose.

Blood glucose lev eldeclines to set point;stimulus for insulinrelease diminishes.

STIMULUS:Rising blood glucoselev el (f or instance, aftereating a carbohy drate-

rich meal)

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

Blood glucose lev elrises to set point;

stimulus for glucagonrelease diminishes.

STIMULUS:Dropping blood glucose

lev el (f or instance, afterskipping a meal)

Alpha cells of pancreasare stimulated to releaseglucagon into the blood.

GlucagonFigure 45.12

Promoting the cellular uptake of glucose (except brain cells)Slowing glycogen breakdown in the liverPromoting fat storageInhibit the conversion to glucose

Stimulating the conversion of glycogen to glucose in the liver

Stimulating the breakdown of fat and protein into glucose

Diabetes Mellitus (~6.5% of US population) - the best-known endocrine disorder

- marked by high blood glucose.

Diabetes ( diabainein): to pass through, refers to this copious urinationMellitus (meli): honey, refers to the presence of sugar in urine

Fat becomes the main substrate for cellular respirationthreatening life by lowering blood pH.

Type I diabetes mellitus (insulin-dependent diabetes)Is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas

Type II diabetes mellitus (non-insulin-dependent diabetes)

reduced responsiveness of target cells due to some change in insulin receptors

usually appears during childhood

heredity; excess body weight and lack of exercise

90% of people with diabetes have type II

Diabetes Mellitus

Adrenal Hormones: Response to Stress

Are adjacent to the kidneys

Are actually made up of two glands: the adrenal medulla and the adrenal cortex

The adrenal glands

Stress and the adrenal gland

Spinal cord(cross section)

Nervesignals

Nervecell

Releasinghormone

Stress

Hypothalamus

Anterior pituitary

Blood vessel

ACTHAdrenalgland

Kidney

Adrenal medullaAdrenal cortex

Effects of epinephrine and norepinephrine:1. Glycogen broken dow n to glucose;

increased blood glucose2. Increased blood pressure3. Increased breathing rate4. Increased metabolic rate5. Change in blood f low patterns, leading to

increased alertness and decreased digestiveand kidney activity

Effects ofmineralocorticoids:

1. Retention of sodiumions and w ater bykidneys

2. Increased bloodvolume and bloodpressure

Effects ofglucocorticoids:

1. Proteins and fatsbroken dow n andconverted to glucose,leading to increasedblood glucose

2. Immune system maybe suppressed

(b) Long-term stress response(a) Short-term stress response

Nerve cell

Figure 45.13a,b

(negative/positive)

neuronblood

Hormones from the Adrenal Medulla Hormones from the Adrenal Medulla ((Short-term response)

Epinephrine

(Tyrosine)

Norepinephrine

members of catecholamines, derived from tyrosine

(adrenaline)

(noradrenaline)

epinephrine and norepinephrine mediate Short-term response

Main: give the body a rapid bioenergetic boost

increase the rate of glycogen breakdown in the liver and skeletal muscles, promote glucose release

stimulate the release of fatty acids from fat cells

shunting blood away from the skin, digestive organs, and kidneys

cause blood vessels in smooth muscles to contract and vessels in skeletal muscles to relax

Profound effects on cardiovascular/respiratory systems increase the heartbeat and dilate the bronchioles in the lungs (prescriptions for heart stimulant or asthma)

Corticosteroids ( ) from the Adrenal Cortex

Glucocorticoids (), such as cortisol

Augmenting glucagon from the pancreas

Causing the breakdown of fat and muscle proteinshelping withstand longterm environmental challenge.

Suppress certain components of the bodys immune system

Mineralocorticoids () , such as aldosteronePrincipally on salt and water balance

Act on kidneys to reabsorb sodium ions and water from filtrate, raising blood pressure and volume

Sex hormones, mainly male hormones (androgens)

Long-term response

Steroidogenesis

Glucocorticoids

Mineralocorticoids

CYP19

CYP19

cholesterol