Endocrine System: all an animals hormone secreting cells

Chemical Signals Categories of Signals Chemical signals that are secreted into the circulatory system and communicate regulatory messages to the body: between individuals between body parts between cells

Chemical Signals (Between Individuals Pheromones are environmental signals that act at a distance between individual organisms. Ants lay down a pheromone trail for other members to find food. Female silkworm moth releases pheromone to lure a male moth from miles away. Dog urine serves as a territorial marker.

Chemical Signals Between Body Parts Endocrine secretions or hormones are environmental signals that act at a distance between body parts. A hormone is an organic chemical produced by one set of cells that affects a different set. A hormone travels through the circulatory system to its target organ. Cells respond to a hormone depending on their receptors; lock-and-key manner This also includes the secretions of neurosecretory cells (specialized nerve cells)

Chemical Signals Between Cells Environmental signals can act locally between adjacent cells. Neurotransmitters released by neurons belong to this category. Prostaglandins and growth factors are also called local hormones. Tumor angiogenesis factor promotes formation of capillaries; antagonists can stop this growth.

The Action of Hormones The Action of Hormones (between body parts) A hormone does not seek out a target organ; the organ is awaiting the arrival of the hormone. Different cells/organs have specialized receptors that recognize specific hormones Steroid hormones Peptide hormones

Target Cell Concept

Action of Hormones Chemical signals produced by one cell that regulate the metabolism of other cells Steroid Hormones -Can cross cell membranes Peptide Hormones Most bind to receptor in plasma membrane First Messenger Causes internal release of cAMP Second Messenger

Review of Cell Signaling 1.Reception: target cell detection 2.Transduction: single-step or series of changes 3.Response: triggering of a specific cellular response

Steroid hormones are lipids and cross cell membranes freely Hormone- receptor complex binds to DNA resulting in activation of genes that produce enzymes

Peptide hormones never enter a cell so they bind to a receptor protein in plasma membrane.

Examples of Hormone Activity

Different activity for same hormone Many times hormones can elicit a myriad of responses. The same hormone can activate different receptors on different cell types to elicit several responses In each case, there is some sort of signal transduction pathway, but with a different effect Example: Release of epinephrine in the “fight or flight” response

The Action of Hormones The Action of Hormones (between cells) Paracrine signaling is the term given to hormone signaling, locally, between cells Release of a hormone can activate neighboring cells in seconds (much quicker response than body to organ – long distance signaling) Examples: Cytokines (remember immune system) Growth factors (stimulate cell growth and differentiation – after a cut or broken bone) Nitric Oxide (improves blood flow by vasodilation when low O 2 levels are sensed) Prostaglandins (general group of modified fatty acids that modify neighboring cells depending on cell type)

Homeostasis Endocrine system is especially involved with homeostasis. Effect of hormones is controlled in 3 ways: Negative Feedback Stops release of hormone Postivie Feedback Enhances hormone release Antagonistic hormones Hormones have opposing (or opposite) effect

Homeostasis Negative feedback (ex.) Pancreas produces insulin when blood glucose rises; this causes liver to store glucose. When glucose is stored, level goes down and pancreas stops insulin production. Positive feedback (ex.) Oxytocin stimulates uterine muscle contractions during birth As more contractions occur, more oxytocin is released Antagonistic hormones (ex.) Effect of insulin is offset by glucagon Thyroid lowers blood calcium level; parathyroids raise blood calcium level.

Negative Feedback All body cells utilize glucose; therefore, its level must be closely regulated. Beta cells secrete Insulin Secreted when blood glucose level is high after eating Alpha cells secrete Glucagon secreted between meals in response to low blood glucose level.

pancreas & insulin.ram

Positive Feedback Oxytocin is also made in hypothalamus & stored in posterior pituitary. Oxytocin stimulates uterine muscle contraction stimulates release of milk from mammary glands This positive feedback increases intensity; positive feedback does not maintain homeostasis.

Antagonistic hormones Thyroid hormones increase metabolic rate; there is no one target organ, all organs respond Thyroid gland also produces calcitonin Calcitonin lowers calcium level in blood and increases deposit in bone by reducing osteoclasts. Low calcium levels stimulate release of parathyroid hormone (PTH) from the parathyroid gland The two hormones (calcitonin and parathyroid hormone) counteract the effects of the other

What type of regulation? Antidiuretic hormone (ADH) promotes reabsorption of water from collecting ducts in kidneys. Nerve cells in the hypothalamus determine when blood is too concentrated; ADH is released and kidneys respond by reabsorbing water. As blood becomes dilute, ADH is no longer released What type of feedback is this?

NEGATIVE FEEDBACK

Example: Hormone Disease Diabetes mellitus is a common disease where body cells do not take up or metabolize sugar. Liver is not storing glucose as glycogen & cells are not utilizing glucose for energy. Type I (insulin-dependent) diabetes - pancreas does not produce insulin (autoimmune disease: immune system destroys insulin producing beta- cells in the pancreas a.k.a. islet cells) type II (noninsulin-dependent) diabetes - usually occurs in obese & inactive individuals of any age. Cells do not respond to insulin