Animal Hormones Chemical Messaging

Hormones component of homeostatic control –slower signals (vs. nervous signals) secreted by endocrine cells diffuse to blood vessels delivered by circulatory system

hormone delivery Figure 42.1

Hormones component of homeostatic control –broadcast signals dispersed throughout the body received by target cells with receptors response is determined by target cells e.g. epinephrine (adrenaline) targets heartliver blood vesselsadipose tissues

Hormones cellular mechanisms of control –hormone release nervous system control feedback control –receptor availability genetic control feedback control

multiple receptors and transduction pathways

Hormones cellular mechanisms of control –signal transduction pathway - specificity cascade - amplification –hormone half-life

Hormones component of homeostatic control –controlled responses include developmental responses physiological responses behavioral responses

autocrine hormones bind source cells Figure 42.1

Hormones not all hormones travel far –autocrine hormones bind source cell –paracrine hormones bind nearby cells histamine released by mast cells interleukin-1 released by macrophage cells neurotransmitters

neurotransmitters are paracrine signals Figure 42.1

Hormones identical hormones are found in different animals –roles may be different stimulus may differ target cells may differ responses may differ –e.g. cAMP

Hormones endocrine cells may be single or organized into an organ (gland) different endocrine cells may be present in an endocrine gland in humans, nine endocrine glands make up the endocrine system

glands of the human endocrine system Figure 42.2

an invertebrate example insect development –larval stages - instars separated by –shedding of rigid exoskeleton - molt

an invertebrate example Rhodnius –5 molts –molts are triggered by blood meals

Rhodnius headless molting Figure 42.3

transfer from one individual to another Figure 42.3

an invertebrate example Rhodnius –two hormones trigger molting brain hormone –produced in brain –stored in corpora cardiaca –released by blood meal stimulus

an invertebrate example Rhodnius –two hormones trigger molting ecdysone –produced in prothoracic gland –released in response to brain hormone –diffuses to target tissues –stimulates molting

molting and development are not equivalent Rhodnius –proper development is controlled by another hormone –corpora allata produce juvenile hormone –if corpora allata are intact, instars molt to instars –5th instar linked to 4th instar molts to 6th instar rather than adult

brain hormone, ecdysone, juvenile hormone interaction is common among insects - complete metamorphosis Figure 42.4

human endocrine system pituitary gland - master gland –attached to hypothalamus –links nervous system with endocrine system produces & secretes hormones or secretes brain hormones –controls many endocrine glands

human endocrine system pituitary gland - master gland –two-part gland posterior pituitary –outgrowth of the hypothalamus –stores & secretes neurohormones antidiuretic hormone (ADH) oxytocin

posterior pituitary Figure 42.5

human endocrine system pituitary gland - master gland –two-part gland anterior pituitary –outgrowth of mouth cavity –produces and secretes several hormones –responds to hypothalamic control »neurohormones to portal vessels »portal vessels to ant. pit. »release or inhibit ant. pit. secretion

anterior pituitary Figure 42.7

human endocrine system pituitary gland - master gland –two-part gland anterior pituitary –four tropic hormones control endocrine glands »thyrotropin »adrenocorticotropin »luteinizing hormone »follicle-stimulating hormone

human endocrine system pituitary gland - master gland –two-part gland anterior pituitary –five non-tropic hormones or groups »growth hormone »prolactin »melanocyte-stimulating hormone »endorphins & enkephalins

global control of hormonal release hypothalamus receives information hypothalamus stimulates or inhibits pituitary pituitary secretion controls effectors directly or indirectly negative feedback loops convey internal information to hypothalamus or pituitary

negative feedback control of hormone production Figure 42.8

control of thyroxine production thyroid gland produces thyroxine (T 4 & T 3 ) thyroxine –elevates cellular metabolic rate –promotes use of carbohydrate over fat –increases basal metabolic rate in response to prolonged cold –promotes uptake of amino acids/protein synthesis during development

control of thyroxine production failure of control can produce goiter –hyperthyroidism autoimmune stimulation of thyrotropin receptor –hypothyroidism e.g. iodine deficiency loss of feedback inhibition

thyroid & parathyroid glands

control of blood calcium calcitonin –produced by thyroid gland –reduces level of circulating calcium reduces osteoclast activity stimulates osteoblast activity

control of blood calcium parathyroid hormone –produced by parathyroid glands –stimulated by low blood calcium –stimulates osteoclasts –increases calcium reabsorption by kidneys –enhances dietary uptake of calcium

control of blood calcium antagonistic activities of pairs of hormones such as calcitonin and parathyroid hormone are common among homeostatic regulatory systems

antagonistic activities of calcitonin and parathyroid hormone balance blood calcium Figure 42.9

control of blood glucose insulin –produced by islet of Langerhans cells in the pancreas –produced when blood glucose is high –stimulates target cells to take up glucose synthesize glycogen synthesize fat

control of blood glucose glucagon –produced in other islet cells –produced when blood glucose is low –stimulates liver to break down glycogen

control of blood glucose antagonistic activities of insulin and glucagon maintain glucose at set point failure of control may lead to diabetes –when insulin or its receptors are absent, cells use fat and proteins for fuel

control of blood glucose somatostatin overrides steady state control –produced in pancreas –response to rapid glucose/amino acid rise –inhibits insulin and glucagon release –reduces digestive activity of gut –increases time of absorption/use of dietary nutrients –also produced by hypothalamus to inhibit thyrotropin & growth hormone release

the adrenal glands Figure 42.10

adrenal glands located on top of kidneys two parts adrenal medulla –produces epinephrine & norepinephrine –derived from nervous tissue –under nervous system control –mediates the “fight-or-flight” response

adrenal glands located on top of kidneys two parts adrenal cortex –produces several corticosteroid hormones –under control of adrenocorticotropin –slower to respond than adrenal medulla

corticosteroids come from cholesterol Figure 42.11

adrenal cortex corticosteroids are derived from cholesterol –mineralocorticoids affect ionic balance of extracellular fluids aldosterone causes kidney to –conserve Na + –excrete K +

adrenal cortex corticosteroids are derived from cholesterol –glucocorticoids affect blood glucose fat, protein, carbohydrate metabolism cortisol –shifts non f-or-f cells to fat/protein catabolism –blocks immune system function –“slow stress response”

adrenal cortex corticosteroids are derived from cholesterol –cortisol responds to adrenocoritcotropin (ACTH) ACTH-releasing hormone produced by hypothalamus negative feedback by cortisol reduces ACTH-releasing hormone ability to recover from stress can decrease with age

adrenal cortex corticosteroids are derived from cholesterol –sex steroids affect sexual development reproductive activities

sex steroids produced predominantly in gonads –progesterone & estrogens (estradiol) female sex steroids –androgens (testosterone) male sex steroid

sex steroids mediate development of reproductive organs in fetus mediate sexual maturation & development of secondary sexual characteristics

sex steroids sex steroid control circuit –in males, LH causes androgen production in testes –in females, LH, FSH, cause female sex steroid production in ovaries

sex steroids GnRH stimulates gonadotropin production –luteinizing hormone –follicle-stimulating hormone sex steroids limit GnRH production by negative feedback sensitivity of GnRH-producing cells to sex steroids decreases to initiate puberty

Take Home hormone secretion is under multi-level control –hypothalamus collects external information –pituitary responds to hypothalamus –pituitary controls many functions directly or through other endocrine glands –many endocrine functions are controlled by feedback mechanisms –many effectors are controlled by the antagonistic activities of two or more hormones

Table 42.1