Hormones chemical substances produced in small quantities in one part of an organism and then transported to another part of an organism where they bring about a physiological response

Target Cells have receptors that allow them to recognize the hormone and respond

Hormone Action Depends on : –Which hormone –the effect on the target cells Can inhibit or stimulate

Site of Hormone Production In animals –usually produced in specialized tissue that serves only to produce hormones In plants –produced by tissue that is also used for some other function (in the apical meristem, in seeds, in fruits etc)

Auxin -increases the plasticity of cell walls and promotes elongation of stems -involved in the response of plants to light (phototropisms)

Figure 39.4 Early experiments of phototropism

Figure 39.5 The Went experiments

Plant Hormones Five major types: Typically work together to control various aspects of plant growth, reproduction and development

Plant Hormones Five major types: 1. Auxins –promotes growth, stem elongation, cell division –Promotes lateral bud dormancy

Plant Hormones Five major types: 2. Cytokinins –promotes cell division (with auxin) –Promotes bud formation (lateral buds when auxin not present)

Plant Hormones Five major types: 3. Gibberellins –promotes stem elongation –Speed seed germination

Plant Hormones Five major types: 4. Ethylene –controls leaf, flower and fruit abscission and fruit ripening 5. Abscisic acid –promotes leaf senescence, controls stomatal closure and seed dormancy

Hormones in Animals secreted by –specialized nerve cells called neurosecretory cells neurons that receive signals from other neurons and respond by releasing hormones –specialized cells called endocrine cells usually organized into an endocrine gland

Glands Secretory organs Endocrine glands –Produce hormones and secrete them into body fluids –Are ductless Exocrine glands –Produce variety of substance –Convey them directly to the target via ducts

15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adenohypophysis Hypothalamus Pineal gland Neurohypophysis Pituitary gland Thymus Thyroid gland Pancreas Testes (in males) Ovaries (in females) Pineal gland Parathyroid glands (behind thyroid) Adrenal glands

Vertebrate Hormone Example Islets of Langerhans in the Pancreas Control of blood glucose levels… –Alpha cells produce glucagon (raises blood glucose level) –Beta cells produce insulin (takes glucose out of the blood) Insulin and glucagon are antagonistic hormones

Figure Glucose homeostasis maintained by insulin and glucagon

Diabetes Mellitus Diabetics cannot take up glucose from blood Type I (insulin-dependent diabetes) –Individuals lack insulin-secreting  cells –Treated by daily injections of insulin Type II (noninsulin-dependent diabetes) –Most patients have this form –Very low number of insulin receptors –Treated by diet and exercise

Interaction of Nervous System and Endocrine System often cooperate and interact to maintain homeostasis of the individual some endocrine glands are controlled by the nervous system

Anterior Pituitary Gland “master gland” Controlled by hypothalamus of the brain Many tropic hormones –That stimulate growth in their target organs

Nervous System Endocrine System More structurally complex Network of neurons branching throughout the body Neurons conduct electrical signals directly to the target Very fast conduction of signal less complex organized into glands hormones released into the blood and travel throughout the body but only affect target may take minutes to hours to days for response to occur

Chemical messengers in Animals Hormones –Secreted by endocrine glands and carried by circulatory system Neurotransmitters –Secreted by neurons and affect next cell Paracrine Regulators –Secreted by cells and act within the same organ

Chemical messengers in Animals

Hormones Molecules that function as hormones must be sufficiently complex and adequately stable Peptides and proteins –ADH(9 amino acids), insulin (51 amino acids), and growth hormone (191 amino acids). Amino acid derivatives (hormones manufactured by enzymatic modification of specific amino acids) –epinephrine (adrenaline) and norepinephrine (noradrenaline), melatonin Steroids are lipids manufactured by enzymatic modifications of cholesterol. –testosterone, progesterone, aldosterone, and cortisol.

Hormones Lipophilic –Fat soluble –Easily enter cell and bind to receptors in the cytoplasm or nucleus –Steroid hormones Lipophobic (polar) or Hydrophilic –Cannot cross cell membrane –Bind to membrane receptors –Need secondary messengers

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