TEST BANK for Human Biology, 17th Edition ISBN10: 1260710823, ISBN13: 9781260710823 By
Sylvia Mader and Michael Windelspecht
TEST BANK for Human Biology, 17th
Edition ISBN10: 1260710823, ISBN13:
9781260710823 By Sylvia Mader and
Michael Windelspecht Study Notes
,TEST BANK for Human Biology, 17th Edition ISBN10: 1260710823, ISBN13: 9781260710823 By
Sylvia Mader and Michael Windelspecht
Human Biology
Endocrine system/Hormones
Introduction
- Cells, tissues, organs and systems work together in a coordinated
manner.
- This coordination is achieved through the activities of the nervous
and endocrine systems
- Nervous system exerts control by the transmission of nerve
impulses to and from various tissues
- Endocrine system influenced the activity of cells by the release of
chemical messengers known as hormones
- Homeostasis is the maintenance of a constant internal environment
Endocrine System
There are two types of glands:
Exocrine Glands: secrete into a duct that carries the secretion to the body
surface or to one of the body cavities e.g. sweat glands, salivary glands
and mucous
Endocrine Glands: secrete into extracellular fluid that surrounds the cells
that make up the gland.
Hormones
- Hormones are a secretion of an endocrine glands
- Classified as either proteins and amines (water based) or steroid
(lipid based)
- Transported through the body in the bloodstream
- May affect all the cells in the body or only one particular group of
,TEST BANK for Human Biology, 17th Edition ISBN10: 1260710823, ISBN13: 9781260710823 By
Sylvia Mader and Michael Windelspecht
cells, target cells or particular organs, target organs
- Paracrine’s are substances secreted by cells that diffuse to and
effect adjacent cells
- Hormones are secreted by specialised cells and are transported by
the bloodstream
- Hormone receptors are specific meaning they are only able to
influence cells in the same tissue by secreting chemicals that diffuse
to adjacent cells
- Saturation can occur which means once all the receptor molecules
are occupied by hormone molecules the addition of more hormones
does not produce any greater effect
- The mode of action of protein and amine hormones and steroid
hormones is dependent on their ability to cross the cell membrane
Mode of action of hormones
Protein and amine hormones (water based)
- Bind to the receptor on the surface of cell membrane
- Hormone receptor complex forms on cell membrane surface
- This produces a molecule that acts as a secondary messenger which
diffuses through the cell and is activated within the cytoplasm,
activating particular enzymes.
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, TEST BANK for Human Biology, 17th Edition ISBN10: 1260710823, ISBN13: 9781260710823 By
Sylvia Mader and Michael Windelspecht
Steroid hormone (lipid based)
- Binds to receptor inside cytoplasm
- Hormone receptor complex forms
- Hormone receptor complex enters the nucleus and binds to the DNA
- This interferes with the cells ability to read some genes, either
switch on or switch off protein synthesis or particular genes
Effects of hormones
- Hormones change the functioning of cells by changing the type,
activities or quantities of proteins produced
- Hormones are not enzymes, however, they can change the activity
of enzymes or change the concentration of enzymes
- Enzyme amplification is the process whereby one hormone molecule
activates thousands of enzyme molecules
- The hormone triggers a cascading effect in which the number of
reacting molecules involved is increased hundred’s or thousands of
times for each step along the metabolic pathway
- A very small stimulus can produce a very large effect
- Once the hormone has achieved its required effect, it needs to be
turned off. This occurs by breaking down the hormone molecule in
Test Bank Page 4
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