Chapter 45Chemical Signals in Animals

Hormones are chemical signals.The endocrine system consists of:Endocrine cells which are hormone-secreting cells andEndocrine glands which are hormone-secreting organs.Specific target cells respond to specific hormones.

Homeostasis Growth and Development Reproduction Energy Metabolism Behavior

blood glucose low

response

response

Tropic hormones- stimulate the production and secretion of hormones by other endocrine glands; ex. TSH

Nontropic hormones- stimulates cellular growth, metabolism, or other functions; ex. thyroxine

Invertebrate nervous systems clearly illustrate endocrine and nervous system interactionsInvertebrates have a wide variety of hormones that are involved in the regulation of homeostasis.

An example from hydra:One hormone stimulate asexual reproduction.Another hormone prevents sexual reproduction.An example from a mollusk:The hormone that regulates egg laying also inhibits feeding and locomotion.

Arthropods have extensive endocrine systems regulating molting in insects and crustaceans.The regulation of molting in insects.Ecdysone also promotes the development of adult features.Neurosecretory cells in the brain produce brain hormone (BH), which regulates the secretion of ecdysone.Juvenile hormone (JH) promotes the retention of larval characteristics.

Different signal-transduction pathways in different cells can lead to different responses to the same signal.

Secreted directly in CSF to blood

High levels at night make us sleepy; low level during day

Pineal gland is stimulated by darkness and inhibited by light

Function in regulating circadian rhythms (sleep, body temp, appetite) biological clockProduces melatonin (synthesized from seratonin, a derivative of tryptophan)

HypothalamusAnterior PituitaryPosterior Pituitary

Antidiuretic Hormone (ADH)Oxytocin (+ feedback)

HypothalamusPosterior PituitaryAnterior Pituitary

Growth Hormone (GH) Dwarfism Gigantism & Acromegaly Thyroid Stimulating Hormone (TSH) Adrenocorticotropic Hormone (ACTH) Gonadotropins (FSH, ICSH, LH) Prolactin (PRL) Melanocyte-stimulating Hormone (MSH)

Acts on the liver, stimulating it to release several polypeptide hormones.Stimulates amino acid uptake and protein synthesis in target cells.Ultimately stimulates cell growth (cell size and number), especially in muscle and bone.Also stimulates fat breakdown.

GH Levelsawakesleep

Thyroid-Stimulating Hormone (TSH)Acts on the thyroid gland, stimulating it to release T3 & T4These thyroid hormones increase glucose catabolism and body heat production.Negative feedback mechanism involved in regulating levels.

Adrenocorticotropic Hormone (ACTH)Acts on the adrenal cortex, stimulating it to secrete glucocorticoids (e.g., cortisol).Glucocorticoids promote the synthesis of glucose from noncarbohydrate sources such as amino acids, and fatty acidsNegative feedback mechanism involved in regulating levels.

thyroidtrachealarynx

Thyroxine (T4) Triiodothyronine (T3)Both control metabolic rate and cellular oxidation

Calcitonin (from parafolicular cells)- lowers blood CA ++ levels and causes CA++ reabsorption in boneThyroid gland selectively uptakes iodine to produce T3 & T4

Thyroid Hormone Regulation

Hyperthyroidism (Graves, Goiter)Hypothyroidism (Cretinism, Myxedima)Thyroid Disorders

PTH release:stimulates osteoclastsenhances reabsorption of Ca++ by kidneysincreases absorption of Ca++ by intestinal mucosal cells

Hyperparathyroidism- too much Ca++ drawn out of bone; could be due to tumor

Hypoparathyroidism- most often follow parathyroid gland trauma or after removal of thyroid--- tetany, muscle twitches, convulsions; if untreatedrespiratory paralysis and death

Regulates glucose uptake by cellsControlled via negative feedback: insulin & glucagonBlood sugar level: 90 mg/mL

Produced by the cells of the Islets of LangerhanCatalyze oxidation of glucose for ATP productionLowers blood glucose levels by promoting transport of glucose into cells. Stimulates glucose uptake by the liver and muscle cells.Stimulates glycogen synthesis in the liver and muscle cells.Also stimulates amino acid uptake and protein synthesis of muscle tissue

Produced by the cells of the Islets of Langerhans Stimulates change of glycogen to glucose in the liver. Synthesis of glucose from lactic acid and non carbohydrate molecules such as fatty acids and amino acidsCauses in blood glucose concentration hypoglycemic- low blood sugar; deficient in glucagon

Type I Diabetes hyposecretion of insulininsulin dependantjuvenile onset

Type II Diabeteslate onset (adult)insensitivity of cells to insulinmanage by exercise & diet

Adrenal Glands

Hormones of the Adrenal MedullaAdrenalin (epinephrine): converts glycogen to glucose in liverNoradrenalin (norepinephrine): increases blood pressure(sympathetic nervous system)

Corticosteroids: glucose levels)

Hormones of the Adrenal CortexGlucocorticoids- cortisolDecrease protein synthesisIncrease release and use of fatty acidsStimulates the liver to produce glucose from non carbsMineralcorticoids- aldosteroneStimulates cells in kidney to reabsorb Na+ from filtrateIncreases water reabsorption in kidneysIncreases blood pressureSex Steroids- small amts (androgens)Onset of pubertySex drive

Cushings SyndromeHypersecretion of cortisone; may be caused by an ACTH releasing tumor in pituitary

Symptoms: trunkal obesity and moon face, emotional instability

Treatment: removal of adrenal gland and hormone replacement

Addisons DiseaseHyposecretion of glucocorticoids and mineral corticoids;

Symptoms- wt loss, low levels of plasma glucose and Na+ levels, high levels of K+

Treatment- corticosteroid replacement therapy

Located anterior to the heart

Produces- thymopoetin and thymosin helps direct maturation and specialization of T-lymphocytes (immunity)Thymus

Ovaries- produce estrogen and progesteroneresponsible for maturation of the reproductive organs and 2ndary sex characteristics in girls at puberty

Gonads

Female Reproductive System

Testes- produce sperm and testosterone (initiates maturation of male repro organs and 2ndary sex characteristics in boys at puberty)Gonads

Male Reproductive System

Major Regions of the Brain