Chapter 45—Chemical Signals In Animals

Chapter 45—Chemical Signals in Animals I. Regulatory Systems maintain homeostasis

A. Nervous system sends high speed signals along neurons B. Endocrine system produces chemical messengers travel more slowly regulate biological processes

C. Several chemicals are used by both systems (overlap) D. control: 1. reproduction 2. development 3. behavior

II. Modes of action A. local regulators—affect nearby target cells 1. neurotransmitters-s end message from nerve to nearby cell 2. histamines —inflammatory response—released by mast cells and basophils 3. interleukins —T cells 4. Growth factors 5. Prostaglandins —modified fatty acids that are released from most cells and have a wide range of effects on nearby cells

B. Hormones—act on more distant cells 1. usually bind to plasma membrane proteins (hormones are protein)

2. initiate signal transduction pathways reception transduction—pathway of several steps response—action of cell

3. Some diffuse through the membrane and initiate transcription (hormones are steroids)

III. Vertebrate Endocrine System Hypothalamus and pituitary integrate many functions of the vertebrate endocrine system 1. hypothalamus a. in lower brain

b. integrates endocrine and nervous system c. releases hormones in response to nervous impulses d. hormones stored in pituitary at the base of the hypothalamus

2. pituitary—divided into two parts a. posterior pituitary (neurohypophysis)—stores and secretes two hormones that are produced by the hypothalamus

oxytocin —produces uterine contractions during birth and milk “let down” during nursing antidiuretic hormone (ADH )—osmoregulation (water retention by kidneys)

b. anterior pituitary (aka: adenohypophysis) regulated by releasing and inhibiting hormones

Growth hormone —affects many tissues promoting growth directly and stimulating the release of growth factors Prolactin —milk production in mammals ( delay of metamorphosis in amphibians)

Tropic hormones—target other endocrine glands (2 step process) Thyroid stimulating hormone —release of thyroid hormones Follicle stimulating hormone — gonadotropin Luteininzing hormone— gonadotropin

Adrenocorticotrophic hormone (ACTH)— stimulates adrenal cortex to produce and release steroid hormones

Endorphins —inhibit pain perception (morphine and other opiates are endorphins)

3. Pineal gland a. center of mammalian brain b. secretes melatonin—biological clock

4. Thyroid gland a. produces two hormones involved in development and maturation and calcitonin, involved in lowering calcium levels in the blood triiodothyroxine (T 3 ) thyroxine (T 4 ) Maintain normal blood pressure Heart rate Muscle tone Digestion Increase cellular metabolism

b. excess results in hyperthyroidism —weight loss and irritability c. hypothyroidism (low thyroid activity) can result in weight gain and lethargy

e. negative feedback loop: TSH—releasing hormone (TRH) is released by hypothalamus and stimulates anterior pituitary to release TSH. TSH binds to receptors in thyroid gland triggering the synthesis and release of thyroid hormones. High levels of T 3 and T 4 inhibit the secretion of TRH

5. Parathyroid glands (4) a. secrete parathyroid hormone (PTH) which stimulates uptake of Ca 2 + in small intestine Re-absorption of Ca 2 + in kidney b. vitamin D is needed for proper function of PTH

6. Pancreas —produces insulin and glucagon which are “antagonistic” a. insulin produced by beta cells in the islets of Langerhans within Pancreas lowers blood sugar by promoting movement of glucose into body cells from the blood and by slowing breakdown of glycogen in the liver

b. glucagon produced by alpha cells in the islets of Langerhans raises glucose concentration by stimulating liver to breakdown glycogen and convert fatty acids and amino acids to sugars

Diabetes Type I—an autoimmune disorder in which pancreatic cells are destroyed— injections of insulin are required Diabetes Type II—insulin deficiency or reduced responsiveness of target cells—sometimes controlled by diet and exercise

7. Adrenal Glands Epinephrine (adrenaline)—produced in adrenal medulla in response to neurotransmitters; produced in response to stress—prepares the body for “fight or flight”

Increases BMR Bioenergetic boost Produces glycogen breakdown Increases blood glucose levels Increases heart rate and stroke volume Dilates bronchioles Positive over the short run

Norepinephrine (noradrenaline)—produced in adrenal medulla; produces same effects as adrenaline Glucocorticoids —produced by adrenal cortex; increases blood glucose in response to hormones (ACTH) to long term stress Mineralcorticoid s —produced by adrenal cortex; increases reabsorption og Na+ and K+ in the kidneys; reduces blood glucose

8.Gonads a. testes—produce androgens such as testosterone —supports sperm development; development and maintenance of secondary sexual characteristics

b. Ovaries estrogen—stimulates uterine lining growth; development and maintenance of secondary sexual characteristics progesterone—promotes growth of uterine lining

Chapter 45—Chemical Signals In Animals

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Chapter 45—Chemical Signals In Animals