hormones

hormones

chemicals produced by cells in one part of the body that regulate the processes of cells in another part. act as messengers. produce slow and long-acting responses

endocrine system

system of glands located in various parts of the body. controlled by the nervous system.

endocrine glands

ductless organs that secrete their hormones directly into the blood of ECF, ex. pituitary gland

exocrine glands

release their secretions into ducts that lead outside the body or into body cavities ex. sweat and salivary glands

4 major points of hormones

1) only cells that contain the receptors for the hormones respond to it
2) once bound to receptors, hormones produce a response
3) hormones are effective in small concentrations
4) response to hormones differ among target organs/species

prohormones

the inactive/less-active form of hormones when they are initially secreted. prohormones are converted by target cells/enzymes into their active form.

enzymatic breakdown

the clearing of hormones from the body

2 types of hormones

protein hormones, steroid hormones

protein hormones

made of chains of amino acids. hydrophilic. act on cell membrane receptors. cannot easily cross membranes because they are water soluble. they bind to receptor molecules in the cell membrane, causing the receptor to change shape. the shape change activates a signal, passes into the cell. signal causes a series of reactions

steriod hormones

derived from cholesterol. not very soluble. easily passes through phospholipid bilayer → acts on receptors in cell. hormone-receptor complex binds to a control sequence of a gene, turning it on or off. activation/deactivation of gene changes amount of protein made → changes cellular activity

negative feedback

mechanism that hormones are regulated by