Chemical Signals in Animals: Endocrine System and Hormonal Control

Endocrine vs. Nervous The nervous system brings about immediate responses, but the endocrine system is slower acting and regulates processes that occur over days or even months.

Hormones Endocrine systems exert control through the use of hormones. Hormones 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 Hormones are secreted into the bloodstream and regulate whole body processes like growth, reproduction, complex behaviors including courtship and migration. Hormones influence the metabolism of their target cells by binding to receptor proteins within the cell or on the surface of the cell.

Exocrine vs. Endocrine Exocrine systems have ducts used for transport of substances directly into the body cavities: salivary glands Endocrine 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 Control In Hydra, one hormone stimulates growth and budding while inhibiting sexual reproduction. Invertebrates exhibit a diversity of hormones which function in 1) homeostasis, 2)reproduction, 3)development, and 4)behavior.

Hormonal 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 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 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:

Hypothalamus 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 Gland - Located at the base of the hypothalamus -Two lobes: anterior and posterior; numerous functions

Anterior Pituitary Gland

Anterior Pituitary Gland Produces many different hormones Regulated by factors of the hypothalamus Four are tropic hormones that stimulate other endocrine glands to synthesize and release their hormones: TSH, ACTH, FSH, LH

Anterior Pituitary Gland Luteinizing Hormone (LH) Stimulates ovulation and corpus luteum formation in females Stimulates spermatogenesis in males

Anterior 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 Gland Growth Hormone (GH) Promotes growth directly Stimulates production of growth factors

Anterior Pituitary Gland Thyroid-Stimulating Hormone (TSH) Tropic hormone that stimulates the thyroid gland to produce and secrete its own hormone

Anterior 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 Gland

Posterior Pituitary Gland Synthesized in hypothalamus Secreted from posterior pituitary Oxytocin – induces uterine muscle contraction; induces lactation Antidiuretic Hormone – acts on kidneys to increase water retention thus 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 hormones function in:. 1) development. 2) bioenergetics Thyroid hormones function in: 1) development 2) bioenergetics 3) homeostasis

Thyroid 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)

Serious 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

Thyroid 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) balances blood calcium needs vitamin D to function

Pancreas Endocrine Tissues Islets of Langerhans: Alpha cells secrete glucagon Beta cells secrete insulin antagonistic hormones that regulate blood glucose

If glucose homeostasis is unbalanced: Type I diabetes mellitus (insulin-dependent diabetes) Type II diabetes (non-insulin-dependent diabetes) Both types untreated will result in high blood sugar: Kidneys excrete glucose More water is excreted Fat is the major source of fuel for cell respiration.

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 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

Steroids Androgens: male sex hormones Testosterone: Stimulate the development and maintenance of male reproductive systems responsible for secondary male sex characteristics

Steroids Estrogens: female sex hormones Progestins (Progesterone) 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