A&P test 1

• exocrine: not hormones, secrete to the surface through ducts
• endocrine: lack ducts, secrete hormones into the blood, well vascularized

• The Nervous System and the Endocrine System together act to direct the maintenance of homeostasis
• – in other words, to control internal conditions.

• Control by the Nervous System is rapid, localized (via nerve impulse transmission) and
• relatively short-lived.

• Control by the Endocrine System is slower, more global (hormones distributed through
• circulatory system) and more prolonged.

long distance chemical signals, travel in blood or lymph.

• Pituitary
• Thyroid
• Parathyroids
• Adrenals
• Pineal
• Thymus

has both nervous and endocrine functions and tissues

• Chemistry: amino acid based derived from peptides proteins and amino acids steroids synthesized from cholesterol gonadal and adrenal cortical hormone 
• Solubility: 1.Water-soluble hormones (all amino acid–based hormones except thyroid hormone)
• •Act on plasma membrane receptors
• •Act via G protein second messengers
• •Cannot enter cell
• 2.  Lipid-soluble hormones (steroid and thyroid hormones)
• •Act on intracellular receptors that directly activate genes
• •Can enter cell
• Mechanism of action: •Though
• hormones circulate systemically only cells with receptors for that hormone
• affected target cells 

• –Alter plasma membrane permeability and/or membrane potential by opening or closing
• ion channels
• –Stimulate synthesis of enzymes or other proteins
• –Activate or deactivate enzymes
• –Induce secretory activity
• –Stimulate mitosis

• 1.Hormone (first messenger) binds to receptor
• 2.Receptor activates G protein
• 3.G protein activates adenylate
• cyclase
• 4.Adenylate cyclase converts ATP to cAMP
• (second messenger)
• 5.cAMP activates protein kinases that phosphorylate proteins
• –Activated kinases phosphorylate various proteins, activating some and inactivating others
• –cAMP is rapidly degraded by enzyme phosphodiesterase
• –Intracellular enzymatic cascades have huge amplification effect

• –Involves G protein and membrane-bound effector – phospholipase C
• –Phospholipase C splits PIP2 into two second messengers – diacylglycerol
• (DAG) and inositol trisphosphate (IP3)
• •DAG activates protein kinase; IP3 causes Ca2+ release
• •Calcium ions act as second messenger
• –Ca2+ alters enzyme activity and channels, or binds to regulatory protein calmodulin
• –Calcium-bound calmodulin
• activates enzymes that amplify cellular response

blood levels to hormone, number of receptors on/in target cell, affinity of binding between receptor and hormone

• permissiveness:  multiple hormones must be present to produce effect
• synergism: more than one hormone produces same effect on target cell-amplification 
• antagonism: one or more hormones oppose action of another

• pituitary (hypophysis) 
• posterior lobe (neural)
• anterior lobe (gladular)
•  -adenohypophysis

• posterior: store oxytocin and ADH(hormones made in the hypothalamus)  
• anterior: GH, TSH, ACTH, FSH, LH, and PRL

primary capillary plexus, hypophyseal portal veins, secondary capillary plexus carries releasing/inhibiting hormones to anterior pituitary to regulate hormone secretion *slide 62*

• TSH, ACTH, FSH, AND LS
• regulate secretory action of other endocrine glands

• Thyroid hormone: =>increase rate of cell metabolism = increased O2 use
• & heat production
• =>required for normal growth and development of nervous system

• Extrafollicular cells secrete hormone calcitonin
• a. Action = decrease [Ca++]blood by stimulating osteoblast activity in bone
• b. Regulation by negative feedback:
• =>high blood Calcium stimulates secretion
• =>low blood Calcium inhibits secretion

• thyroid hormone:
• a. secretion stimulated by TSH
• b. inhibited by negative feedback of ant pituitary, hypothalamus via rising levels of thyroid hormones
• c. Consequences of misregulation:
• hyposecretion in infants = cretinism
• Grave’s disease = hyperthyroidism due to autoimmune stim thyroid
• Calcitonin: 
• Regulation by negative feedback:
• =>high blood Calcium stimulates secretion
• =>low blood Calcium inhibits secretion

• •Two lateral lobes connected by median mass called isthmus
• •Composed of follicles that produce glycoprotein thyroglobulin
• •Colloid (thyroglobulin + iodine) fills lumen of follicles and is precursor of thyroid
• hormone
• •Parafollicular cells produce the hormone calcitonin

thyroid gland stores thyroid hormone extracellularly