Lecture Objectives

Endocrine System

Discuss the differences between neural and endocrine mechanisms of control of body functioning.

Neural mechanisms can have a response up to milliseconds Endocrine mechanisms have a lag time up to days

Differentiate exocrine and endocrine glands. Exocrine glands – digestive system, sweat glands, saliva glands, excretes into a

duct (non-hormonal) Endocrine glands – secrete hormones; secretes into the fluids around the cells

(extracellular fluids); no ducts

Identify the neuroendocrine link, and discuss its functioning. The neuroendocrine link is the hypothalamus; it integrates neural signals; the

hypothalamus can also secrete hormones Nervous system can activate endocrine glands through electrical impulses

List and differentiate the types of chemical messengers. Hormone is a chemical that is produced within one part of the body, but has an

effect on another part of the body – long distance chemical messenger Autocrine affects the cells that produce it Paracrine – a chemical that is secreted by the cell that affects neighboring cells,

not itself Pheromones – chemicals that are produced by one individual that affect another

individual (usually of the same species); evidence that humans also produce pheromones; most likely in sweat

Identify the cells at which hormones exert their effects, and discuss the generalized effects hormones can produce.

Hormones exert their efforts on target cells; some cells have multiple receptors for different hormones; hormones alter the way target cell acts:

o Stimulates protein synthesis – enzyme synthesiso Open or close ion channelso Activate or deactivate enzymeso Promote secretion – opening/closing ion channelso Promote mitosis – stimulates # of target cells

Describe the chemical classifications of hormones. Amino acid based – water soluble; polar; can’t diffuse across a membrane

passively (EX. Insulin) Steroid – derived from cholesterol; gonadal and adrenocortical (adrenal cortex)

hormones are steroids; produced by gonads and adrenal cortex; can diffuse across a membrane passively

Eicosanoid – a biologically active lipid that is more technically a paracrine secretion (effects neighboring cells).

Describe the two major mechanisms by which these two classes of hormones bring about their effects.

Amino acid-based:o Hormones bind to receptors on the plasma membraneo Involves G proteins and secondary messengers

Steroid:o Since steroids are lipid soluble, they can pass through the membrane

passivelyo Steroids then bind to receptor hormone complex; this entire complex

moves into the nucleus to directly to a specific DNA sequenceo This produces mRNA to be translated on the cytoplasmic ribosomes o These proteins promote synthesis of either structural proteins or proteins

to be exported from the target cell

Discuss the two models of amino acid-based action. Cyclic AMP mechanism

o Hormone binds to receptor on plasma membrane causing the receptor to change shape

o Modified receptor binds with G protein.o G protein activates when the GDP is displaced by the GTP (off and on

switch)o G protein activates the adenylate cyclase (eventually, the GTP is

hydrolyzed to GDP again)o Adenylate cyclase converts ATP to cyclic AMP (cAMP)o cAMP stimulates protein kinase reactions to start a chain of chemical

reactionso This reaction is called phosphorylation (adding a phosphate group) and

phosphorylation activates some proteins while inhibiting others meaning a variety of processes can be affected by one target cell.

o Phosphodiestrerase degrades cAMP

PIP2- Calcium Mechanismo Hormone binds to receptor on plasma membrane causing the receptor to

change shapeo Modified receptor binds with G proteino G protein activates when the GDP is displaced by the GTPo G protein activates phospholipaseo Phospholipase splits PIP2 into DAG and IP3

o DAG activates protein kinases near membraneo IP3 triggers calcium release through the endoplasmic reticulum (ER)o Calcium acts as additional second messenger; can also affect enzyme

activity or opening/closing of channels

Identify the factors that control hormone action. Hormone level in bloodstream

o High hormone level means more activity Number of receptors in/on target cell

o More receptors on target cell means more activity Receptor affinity

o Some cells just have higher affinity which increases the amount of activity Up regulation – activity of hormones causes increase in number of receptors

which increases activity Down regulation – decrease in number of receptors due to activity of hormone

List three kinds of interaction that different hormones acting on the same target cell can have.

Permissiveness – activity of one hormone requires a second hormone to exert its full effects (EX. Thyroid hormone and reproductive development)

Synergism – more than one hormone produces the same effects, and therefore the effects are amplified (EX. Glucagon and epinephrine both increase blood glucose)

Antagonism – hormones have opposite effects (EX. Insulin)

Explain how hormone release is regulated.

List the major endocrine organs, and describe their body locations.

Discuss the structure of the neurohypophysis, and describe the effects of its two hormones.

Sac like structure underneath the hypothalamus connected by the hypothalamic-hypophyseal tract

o Oxytocin stimulates smooth muscle contraction Child birth and milk ejection Functions in sexual arousal and sexual satisfaction Functions through positive feedback

o Antidiuretic hormone (ADH) regulates water balance Prevents urine formation Seeks to maintain proper blood concentration

List and describe the adenohypophyseal hormones and their effects. Growth hormone stimulates cell growth and division, protein synthesis, fat

metabolism, and glucose conservation o Too much: Acromegaly in adults; Gigantism in childreno Too little: No effect in adults; pituitary dwarfism in children

Direct Actions of Growth Hormone:o Increase blood levels of fatty acidso Decreases glucose uptake and metabolismo Encourages breakdown and release of glucose from glycogen in liver

(diabetogenic effect) Thyroid stimulating hormone (thyrotropin) stimulates development of and

secretion from thyroid gland Adrenicirtucitropic hormone (ACTH) stimulates the adrenal cortex to release

corticosteroids; especially glucocorticoidso Helps the body resist stress

Gonadotropins regulate functions of gonads which includes FSH and LH.o FSH stimulates gamete production (egg or sperm)o LH promotes hormone secretion

Male Female

FSH Stimulates sperm production Stimulates ova production and maturation of follicle

LH Stimulates interstitial cells of testes to produce testosterone

Triggers ovulation, promotes synthesis of ovarian hormones, and maturation of follice

Prolactin stimulates milk production by breasts (works with oxytocin) and may enhance testosterone production in males