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Endocrine System

System in charge of regulating mood, growth, and development, tissue function, metabolism, and sexual function and reproductive processes


Transfer information and instructions from one set of cells to another. Each type is designed to affect only certain cells


Group of cells that produce and secrete, or give off, chemicals

Endocrine Glands

Release more than 20 major hormones directly into the bloodstream where they can be transported to cells in other parts of the body

Direct Communication

Specialized case where cellular activities are coordinated by the exchange of ions and molecules between adjacent cells across gap junctions. Occurs between two cells of the same type

Paracrine Communication

The use of chemical messengers to transfer information from cell to cell within a single tissue

Target Cells

Specific cells that possess the receptors needed to bind and "read" the hormonal message when it arrives

Synaptic Communication

Across synaptic clefts through neurotransmitters

Endocrine Communication

Through the circulatory system--The activity of hormones in coordinating cellular activities in tissues and distant protions of the body

Three groups of hormones

Amino acid derivates, peptide hormones, lipid derivatives


Inactive molecules tjat are converted to active hormones either beofre or after they are secreted (peptide hormones in general are)


Small molecules witha five-carbon ring at one end. Important paracrine factors that coordinate cellular activities and affect enzymatic factors that coordinate celluar activities and affect enzymatic processes (such as blood clotting) in extracellular fluids


Eicosanoids released by activated white blood cells, or leukocytes


A second group of eicosanoids, are produced in most tissues of the body. Involved primarily in coordinating local cellular activities

Prostaglandins are sometimes convered to:

Thromboxanes and prostacyclins which also have strong paracrine effects

Steroid hormones

Lipids structurally similar to cholesterol. Released by male and female reproductive organs

First messenger

Does something that leads to the appearance of a second messenger in the cytoplasm

Second messenger

May act as an enzyme activator, inhibitor, or cofactor, but the net results is a change in the rates of various metabolic reactions


A process in which the presence of a hormone triggers a decrease in the numebr of hormone receptors. When levels of a particular hormone are high, cells become less sensitive to it


A process in which the absence of a hormone triggers an increase in the number of hormone receptors. When levels of a particular hormone are low, cells become more sensitive to it

G protein

An enzyme complex coupled to a membrane receptor. The link between the first and second messenger usually involves this.

Endocrine Reflexes

Functional counterparts of neural reflexes

Humoral stimuli

Changes in the composition of the extracellular fluid

Hormonal stimuli

The arrival or removal of a specific hormone

Neural stimuli

The arrival of neurotransmitters at neuroglandular junctions

Three things that can trigger endocrine reflexes:

Humoral stimuli, hormonal stimuli, and neural stimuli

Regulatory Hormones

Special hormones that control endocrine cells in the pituitary gland

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