 The Endocrine system and the Nervous system.  Local Regulators  The Hypothalamus and Pituitary  Nonpituitary hormones  Invertebrate Regulatory Systems

 The nervous system conveys high-speed electrical signals along specialized cells called neurons.  These rapid messages control the movement of the body parts in response to sudden environmental changes.  Jerk your hand away from a hot pan  Pupils dilate when you enter a dark room

 Collectively, all of an animal’s hormone secreting cells constitute its endocrine system.  Hormone-secreting organs, called endocrine glands, are referred to as ductless glands because they secrete their chemical messengers directly into extracellular fluid.

 Certain specialized nerve cells known as neurosecretory cells release hormones into the blood via the extracellular fluid.  These hormones are called neurohormones to avoid confusion with normal hormones.  A few chemicals serve both as hormones in the endocrine system and as chemical signals in the nervous system.  Epinephrine, functions as the “fight or flight” hormone and as a neurotransmitter.

 In addition, the nervous system plays a role in certain sustained responses— for example, controlling day/night cycles and reproductive cycles in many animals— often by increasing or decreasing secretion from endocrine glands.

 A biologist was interested in studying how far bullfrogs can jump. He brought a bullfrog into his laboratory, set it down, and commanded, "Jump, frog, jump!" The frog jumped across the room. The biologist measured the distance, then noted in his journal, "Frog with four legs jumped eight feet."Then he cut the frog's front legs off. Again he ordered, "Jump, frog, jump!" The frog struggled a moment, then jumped a few feet. After measuring the distance, the biologist noted in his journal, "Frog with two legs jumped four feet."  Next, the biologist cut off the frog's back legs. Once more, he shouted, "Jump, frog, jump!" The frog just lay there. "Jump, frog, jump!" the biologist repeated. Nothing. The biologist noted in his journal, "Frog with no legs goes deaf."

 Receptor, sensor— detects a stimulus  a change in blood calcium level  … send information to the control center  … after, the control center sends out an effecter to respond 

 In contrast to long-distance endocrine signaling by hormones, local regulators convey messages between neighboring cells— a process referred to as paracrine signaling.  Once secreted by the cells that make them, local regulators act on nearby target cells within seconds or even milliseconds, eliciting cell responses more quickly than hormones can  Some local regulators have cell-surface receptors; others have intracellular receptors.

 Cytokines - play a role in immune responses  Growth factors – stimulate cell proliferation and differentiation  Nitric oxide (NO) – improves blood flow to tissues when blood oxygen level falls; nitric oxide also plays a role in male sexual function  Prostaglandins (PGs) – modified fatty acids, often derived from lipids in the plasma membrane

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Major Human Endocrine Glands

 The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system  The hypothalamus plays an important role in integrating the vertebrate endocrine and nervous systems  Receives information from nerves throughout the body  Initiates endocrine signals appropriate to environmental conditions  E.g.: Seasonal changes triggering release of reproductive hormones required for breeding.

 The hypothalamus contains two sets of neurosecretory cells whose hormonal secretions are stored in or regulate the activity of the pituitary gland, a lima bean-sized organ located at the base of the hypothalamus.  Posterior Pituitary (neurohypophysis): extension of the hypothalamus that grows downward toward the mouth during embryonic development.  Anterior Pituitary (adenohypophysis): develops from a fold of tissue at the roof of the embryonic mouth; this tissue grows up toward the brain and eventually loses its connection to the mouth.

 In humans and other mammals, the thyroid gland consists of two lobes located on the ventral surface of the trachea.  Produces triiodothyronine (T 3 ) and thyroxine (T 4 )  Secretion controlled by hypothalamus and pituitary  Plays a crucial role in vertebrate development and maturation  E.g.: Metamorphosis of frog (tissue reorganization)

 When blood Ca 2+ levels fall below a set point, parathyroid hormone (PTH) is released.  PTH is produced by the parathyroid glands, embedded on the surface of the thyroid.  The dual functioning pancreas functions in both the endocrine and digestive systems.  Produces glucagon and insulin  Produces bicarbonate and digestive enzymes  Reactions to danger are part of the fight-or-flight response stimulated by hormones of the adrenal glands.  The adrenal medulla of the adrenal glands releases these hormones  Adrenaline and non Adrenaline

 Involve endocrine and nervous system reactions  Function in reproduction and development  In insect hormonal regulation, three hormones play major roles in molting and metamorphosis into the adult form.  Brain hormone: produced by neurosecretory cells; stimulates release of ecdysone  Ecdysone: Promotes molting and development of adult characteristics  Juvenile hormone: secreted by glands behind the brain; promotes retention of larva characteristics