Chapter 45 ~ Chemical Signals in AnimalsEndocrine system ~Hormones

growth hormones

Regulatory systems• Hormone: chemical signal secreted into

body fluids (blood) communicating regulatory messages

• Target cells: body cells that respond to hormones

• Endocrine system/glands: hormone secreting system/glands (ductless); exocrine glands secrete chemicals (sweat, mucus, enzymes) through ducts

• Neurosecretory cells: actual cells that secrete hormones

• Feedback mechanisms : negative and positive

Local regulators: cells adjacent to or near point of secretion

• Growth factors proteins for cell proliferation• Nitric oxide (NO) neurotransmitter and a local

regulator• If oxygen in blood falls, endothelial cells in blood vessels

make and release NO• NO activates enzyme, relaxes smooth muscle cells cause

vasodilation• Viagra: prolonged activity of NO pathway

• Prostaglandins

Prostaglandins• In semen it stimulates smooth muscle in female

uterus to contract and help sperm reach egg• secreted by cells in placenta to cause

contraction in childbirth • Immune system: promote fever, inflammation,

&pain ( Ibuprofin and aspirin inhibit)• Blood: regulate aggregation of platelets

involved in blood clotting • Help protect the lining of the stomach

• Why are hormones needed?– chemical messages from one body part

to another– communication needed to coordinate

whole body– daily homeostasis & regulation of large

scale changes• solute levels in blood

– glucose, Ca++, salts, etc.• metabolism• growth• development• maturation• reproduction

Regulation

growth hormones

Regulation & Communication• Animals rely on 2 systems for regulation– endocrine system (paracrine and autocrine)• system of ductless glands

– secrete chemical signals directly into blood– chemical travels to target tissue– target cells have receptor proteins– slow, long-lasting response

– nervous system• system of neurons

– transmits “electrical” signal & release neurotransmitters to target tissue

– fast, short-lasting response

Regulation by chemical messengers

axon

endocrine gland

receptor proteins

target cell

• Neurotransmitters released by neurons• Hormones release by endocrine glands• Neurohormones specialized neuron secretory cells

receptor proteins

hormone carried by blood

neurotransmitter

Lock & Keysystem

Classes of Hormones: water or lipid soluble

• Protein-based hormones– polypeptides

• small proteins: insulin, ADH

– glycoproteins• large proteins + carbohydrate: FSH, LH

– amines• modified amino acids: epinephrine, melatoninWater solublesecreted by exocytosistravel freely in blood stream, bind to cell-surface receptors,

induce changes in cytoplasmic molecules to alter gene transcription

insulin

Classes of Hormones Cont.

• Lipid-based hormones– steroids• modified cholesterol: sex hormones, aldosterone

• Diffuse into target cells• Bind to intracellular signal receptors• Can cross the plasma membrane and nuclear

membrane• Trigger changes in gene transcription

Mode of Action: Chemical Signaling• 1- Plasma membrane reception •

signal-transduction pathways (neurotransmitters, growth factors, most hormones)

• 2- Cell nucleus reception • steroid hormones, thyroid hormones, some local regulators

nucleus

target cell

DNAmRNA

protein

blood

proteincarrier

S

S

S

S

Action of lipid (steroid) hormones

binds to receptor protein

cytoplasm

becomes transcription factor

ex: secreted protein = growth factor (hair, bone, muscle, gametes)

2

4

6

cross cell membrane

1

steroid hormone

mRNA read by ribosome5

plasma membrane

protein secreted7

3

Action of protein hormones

activatesenzyme

activatesenzyme

activates enzyme

ATP

produces an action

P1

2

3

cytoplasm

receptor protein

response

signal

secondarymessengersystem

signal-transduction pathway

acts as 2° messenger

target cell

plasma membrane

binds to receptor protein

proteinhormone

ATPactivatescytoplasmicsignal

cAMP

GTP

activatesG-protein

transduction

Benefits of a 2° messenger system

Amplification!

signal

receptor proteinActivated adenylyl cyclase

amplification

amplification

amplification

amplification

GTP G protein

product

enzyme

protein kinase

cAMP

Not yetactivated

1

2

4

35

6

7

FAST response!

amplification

Cascade multiplier!

Maintaining homeostasis

high

low

hormone 1

lowersbody condition

hormone 2

gland

specific body condition

raisesbody condition

gland

Negative FeedbackModel

Vertebrate Endocrine System• Tropic hormones : a hormone that

has another endocrine gland as a target

• Hypothalamus: pituitary• Pituitary gland• Pineal gland• Thyroid gland• Parathyroid glands• Thymus• Adrenal glands• Pancreas• Gonads (ovary, testis)

Nervous & Endocrine systems linked• Hypothalamus = “master nerve control center”– nervous system– receives information from nerves around body about

internal conditions – releasing hormones: regulates release of hormones from

pituitary

• Pituitary gland = “master gland”– endocrine system– secretes broad range

of “tropic” hormones regulating other glands in body

hypothalamus

pituitary

posterior

anterior

Thyroid gland

hypothalamus

anteriorpituitary

gonadotropic hormones:

follicle-stimulatinghormone (FSH) & luteinizing hormone (LH)

Mammaryglandsin mammals

Musclesof uterus

Kidneytubules

posteriorpituitary

thyroid-stimulating hormone(TSH)

antidiuretic hormone(ADH)

Adrenalcortex

Boneand muscle

Testes Ovaries

Melanocytein amphibian

adrenocorticotropic

hormone (ACTH)

melanocyte-stimulating hormone(M

SH)

oxytocin

prolactin (PRL

)

grow

th h

orm

one

(GH

)

tropic hormones = target endocrine glands

The hypothalamus & pituitary, I• Releasing and inhibiting hormones• Anterior pituitary:• Growth (GH):bones

√gigantism/dwarfism √acromegaly

• Prolactin (PRL):mammary glands; milk production

• Follicle-stimulating (FSH) &• Luteinizing (LH):ovaries/testes• Thyroid-stimulating (TSH): thyroid • Adrenocorticotropic (ACTH):

adrenal cortex • Melanocyte-stimulating (MSH) • Endorphins~natural ‘opiates’; brain

pain receptors

The pituitary, II

• The posterior pituitary:• Oxytocin

uterine and mammary gland cell contraction

• Antidiuretic (ADH) retention of water by kidneys

The pineal, thyroid, & parathyroid• Melatonin pineal gland;

biological rhythms

• Thyroid hormones: Calcitonin lowers blood calcium Thyroxine

metabolic processes

• Parathyroid (PTH) raises

blood calcium

Regulation of Blood Calcium

blood calcium level(10 mg/100mL)

calcitonin

parathyroid hormone (PTH)

Ca++ uptakein intestines

high

low

FeedbackEndocrine System Control

kidney reabsorption of Ca++

bones release Ca++

kidney reabsorption of Ca++

Ca++ depositedin bones

activated Vitamin D

thyroid

parathyroid

Regulating metabolism • Hypothalamus

– TRH = TSH-releasing hormone

• Anterior Pituitary– TSH = thyroid stimulating hormone

• Thyroid– produces thyroxine hormones– metabolism & development

• bone growth• mental development• metabolic use of energy• blood pressure & heart rate• muscle tone• digestion• reproduction

tyrosine+iodine

thyroxines

The pancreas• Islets of Langerhans• Alpha cells: glucagon • raises blood glucose levels by

promoting the release of glucose from the liver (glycogen)

• Beta cells: insulin • lowers blood glucose levels by

triggering uptake of glucose from blood into body cells

• Type I diabetes mellitus (insulin-dependent; autoimmune disorder)

• Type II diabetes mellitus (non-insulin-dependent; reduced responsiveness in insulin targets)

liver

pancreas

liver

Regulation of Blood Sugar

blood sugar level(90mg/100ml)

insulin

body cells takeup sugar from blood

liver storesglycogen

reducesappetite

glucagon

pancreas

liver releasesglucose

triggershunger

high

low

FeedbackEndocrine System Control

islets of Langerhans beta islet cells

islets of Langerhansalpha islet cells

The adrenal glands• Adrenal medulla (catecholamines): •epinephrine & norepinephrine~

increase basal metabolic rate (blood glucose and pressure)

• Adrenal cortex (corticosteroids): •glucocorticoids (cortisol)~ raise

blood glucose •mineralocorticoids (aldosterone)~ reabsorption of Na+ and K+

The gonads• Steroid hormones:

precursor is cholesterol

• androgens (testosterone)~ sperm formation; male secondary

sex characteristics; gonadotropin • estrogens

(estradiol)~uterine lining growth; female secondary sex characteristics; gonadotropin

• progestins (progesterone)~uterine lining growth