Chemical Signals in Chemical Signals in Animals:Animals:

Endocrine System and Hormonal Control

Endocrine vs. Nervous

The nervous system brings about immediateimmediate responses, but the endocrine system is slowerslower acting and regulates processes that occur over days or even months.

Hormones

Endocrine systems exert control through the use of hormones.hormones.

HormonesHormones are chemical messengers produced by ductless glands in one part of the body which travel through the bloodstream and exert their influence in another part of the body.

Hormones

HormonesHormones are secreted into the bloodstream and regulate whole body processes like growth, reproduction, complex behaviors including courtship and migration.

HormonesHormones influence the metabolism of their target cells by binding to receptor proteins within the cell or on the surface of the cell.

Chemical CommunicationBriefly describe the two major forms of intercellular communication in animal bodies. Which organ systems are responsible for this communication?Describe the type of intercellular communication called “neuroendocrine”.What defines a “target tissue”?

Basic Mechanisms of Chemical Signaling

Exocrine vs. EndocrineExocrine vs. Endocrine

Exocrine systemsExocrine systems have ducts used for transport of substances directly into the body cavities: salivary glands

Endocrine systemsEndocrine systems are ductless and secrete hormones directly into body fluids: pituitary gland

Hormones

The endocrine and the nervous systems are related

1) structurally 2) chemically 3) functionally

simultaneously maintaining homeostasis, physiology and other body processes.

Hormones

• Neurosecretory cells: specialized nerve cells that secrete hormones located within endocrine organs and tissues.

Hormones

• Several chemicals serve as both neurotransmitters and hormones.

• Epinephrine, produced by the adrenal medulla, acts as the “fight or flight hormone” and a neurotransmitter.

Control

• Positive and Negative Feedback regulate mechanisms of both systems

• Positive feed back: output intensifies and increases the likelihood of a response

• Mammal milk production and release

Control:- Antagonistic hormones work in

opposition to one other.- Insulin and glucagon

Hormonal ControlHormonal Control

• Chemical signals operate at virtually all levels of organization:

• Local regulators– Intracellular– Cell to cell

• Tissue to tissue regulators• Organ to organ regulators• Organism to organism (pheromones)

Hormonal Control

• Local regulators affect neighboring target cells

• Histamine -- immune and regulatory responses

• Interleukins – immune response• Growth factors – peptides and proteins that

regulate the behavior of cells in growing and developing tissues

• Prostaglandins – modified fatty acids released into interstitial fluid

Hormonal Control

• Binding of a chemical signal to a specific receptor protein triggers chemical events in the target cell that result in a change in that cell.

• The response to a chemical signal depends on the number and affinity of the receptor proteins.

Chemical Signals

• Chemical signals often bind to a specific protein receptor on the plasma membrane of the target cell

• Because of their chemical nature, most signal molecules (peptides, proteins, glycoproteins) are unable to diffuse through the plasma membrane

Chemical SignalsChemical Signals

• The binding of the signal molecule to a plasma membrane receptor initiates a signal transduction pathway, a series of events that converts the signal into a specific cellular response.

Chemical Signals

• A specific example is the binding on the polypeptide hormone insulin to the insulin receptor:

• Insulin binding initiates a chain of events that accounts for the blood sugar lowering effects of insulin.

Vertebrate Endocrine SystemVertebrate Endocrine System

Coordinates:1)metabolism,2)growth,3)development, and 4)reproduction.

Major Endocrine Organs

Functions of Vertebrate Hormones

• Some hormones have a single action while other have multiple functions

• Tropic hormones act on other endocrine glands

Functions of Vertebrate Hormones:

Functions of Vertebrate Hormones:

HypothalamusHypothalamus

• Region of the lower brain • Receives information from nerves

throughout the body and brain • Initiates endocrine signals

appropriate to the environmental conditions

• Regulates the Pituitary Gland

Pituitary GlandPituitary Gland

- Located at the base of the hypothalamus

-Two lobes: anterior and posterior; numerous functions

Anterior Pituitary GlandAnterior Pituitary Gland

Anterior Pituitary GlandAnterior Pituitary Gland

Produces many different hormones Regulated by factors of the

hypothalamus Four are tropic hormones that Four are tropic hormones that

stimulate other endocrine glands stimulate other endocrine glands to synthesize and release their to synthesize and release their hormones: TSH, ACTH, FSH, LHhormones: TSH, ACTH, FSH, LH

Anterior Pituitary GlandAnterior Pituitary Gland

Luteinizing Hormone (LH) Stimulates ovulation and corpus Stimulates ovulation and corpus

luteum formation in females luteum formation in females Stimulates spermatogenesis in Stimulates spermatogenesis in

malesmales

Anterior Pituitary GlandAnterior Pituitary Gland

• Follicle-Stimulating Hormone (FSH)• Tropic hormone that affects the gonads• In males, necessary for spermatogenesis• In females, it stimulates ovarian follicle

growth

Anterior Pituitary GlandAnterior Pituitary Gland

• Growth Hormone (GH)• Promotes growth directly• Stimulates production of

growth factors

Anterior Pituitary GlandAnterior Pituitary Gland

• Thyroid-Stimulating Hormone (TSH)

• Tropic hormone that stimulates the thyroid gland to produce and secrete its own hormone

Anterior Pituitary GlandAnterior Pituitary Gland

• Adrenocorticotropin (ACTH) stimulates the adrenal cortex to produce and secrete its steroid hormones

• Melanocyte-Stimulating Hormone (MSH) regulates the activity of pigment-containing skin cells

• Endorphins inhibit pain perception

Posterior Pituitary GlandPosterior Pituitary Gland

Posterior Pituitary GlandPosterior Pituitary Gland

Synthesized in hypothalamus Secreted from posterior pituitary Oxytocin – Oxytocin – induces uterine muscle induces uterine muscle

contraction; induces lactationcontraction; induces lactation Antidiuretic Hormone Antidiuretic Hormone – acts on – acts on

kidneys to increase water retention kidneys to increase water retention thus reducing urine volumethus reducing urine volume

Pineal Gland

• Small mass near the center of the brain

• Produces melatonin – modified amino acid that modulates skin

pigmentation– secreted only at night; larger amounts

secreted in winter– Involved in regulation of biorhythms

Thyroid hormonesThyroid hormones function in:

1) development 2) bioenergetics 3) homeostasis

ThyroidThyroid is on the ventral side of

the trachea. plays a major role in vertebrate

development: participates in embryonic development

control metamorphosis in amphibians

Thyroid gland maintains

homeostasis in mammals including:

• blood pressure• heart rate • muscle tone • digestion • reproductive functions• rate of O2 consumption and

metabolism (increases)

SSerious metabolic disorders result from deficiency or excess of thyroid

hormones.

• Hyperthyroidism - high body temperature, sweating, weight loss, irritability, high blood pressure

• Hypothyroidism – can cause cretinism in infants and weight gain, lethargy, and cold-intolerance in adults

• Goiter - enlarged thyroid caused by a deficiency in iodine

TThyroid hormonehyroid hormone secretion is regulated by hypothalamus and pituitary.

• Negative Feedback System.• Hypothalamus secretes TRH • Anterior Pituitary stimulated to

produce TSH • TSH binds to receptors and T3 and T4

• High levels of T3, T4, and TSH inhibit TRH

Parathyroid hormone (PTH)Parathyroid hormone (PTH)

• balances blood calcium• needs vitamin D to function

Adrenal Glands:Adrenal Glands:

• located on top of kidneys• Adrenal medula synthesizes

catecholamines:– epinephrine – norepinephrine

• Glucose is mobilized• Heart rate is increased• Bronchioles dilate

Adrenal Glands:Adrenal Glands:

• Adrenal cortex synthesizes and secretes corticosteroids as directed by ACTH from the anterior pituitary

– Mineralocorticoids affect salt and water balance

– Aldosterone stimulates kidney cells to reabsorb sodium ions and water

– Glucocorticoids – promote glucose synthesis from noncarbohydrate substances such as proteins

Stress and The Adrenal Glands

SteroidsSteroids

• Androgens: male sex hormones• Testosterone:– Stimulate the development and

maintenance of male reproductive systems

– responsible for secondary male sex characteristics

SteroidsSteroids

• Estrogens: female sex hormones– Maintain the female reproductive system – responsible for secondary sex

characteristics

• Progestins (Progesterone)– Preparation and maintainace of uterus for

reproduction

• Gonadotropins from anterior pituitary (FSH and LH) control the synthesis of both androgens and estrogens