BPK 105 Study Guide - Midterm Guide: Lipid Bilayer, Half-Life

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Module 6 - Objectives - Part 2
Differentiate between protein and lipid derived hormones and provide two
detailed examples of each.
- Hormones fit into one of two chemical categories: lipid-soluble hormones and
water-soluble hormones, a distinction based on their chemical composition, which
influences their chemical behavior.
- plasma membrane is a selectively permeable phospholipid bilayer that excludes most
water-soluble molecules but allows lipid-soluble molecules to pass through.
- the entire basis of a hormone’s metabolism—its transport in the blood, its interaction with
its target, and its removal from the body—is dependent on the hormone’s chemical
nature.
- Within the two chemical categories, hormones can be subdivided into groups based on
their chemical structures. Steroid hormones are those derived from cholesterol, thyroid
hormones are derived from the amino acid tyrosine, and other hormones are categorized
as amino acid derivatives, peptides, or proteins.
Lipid-Soluble Hormones
- nonpolar, and include steroid hormones, thyroid hormones, and fatty acid derivative
hormones, such as certain eicosanoids.
Transport of Lipid-Soluble Hormones
- Because of their small size and low solubility in aqueous fluids, lipid-soluble hormones
travel in the bloodstream attached to binding proteins, proteins that transport the
hormones.
- As a result, the rate at which lipid-soluble hormones are degraded or eliminated from the
circulation is greatly reduced and their lifespans range from a few days to as long as
several weeks.
- Without the binding proteins, the lipid-soluble hormones would quickly diffuse out of
capillaries and be degraded by enzymes of the liver and lungs or be removed from the
body by the kidneys.
- Circulating hydrolytic enzymes can also metabolize free lipid-soluble hormones. The
breakdown products are then excreted in the urine or the bile.
Water-Soluble Hormones
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