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Chapter 11

SCIE 22273 Chapter Notes - Chapter 11: Cyclic Adenosine Monophosphate, Follicle-Stimulating Hormone, Anterior Pituitary


Department
Faculty of Applied Health and Community Studies
Course Code
SCIE 22273
Professor
Tara Hayes
Chapter
11

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Chapter 11- Endocrine System
The nervous system and the endocrine system work together to maintain
homeostasis
The endocrine system consists of cells, tissues and organs that secrete
hormones
Hormones diffuse into the bloodstream and act on target cells
Sometimes, glands secrete substances that do not reach the bloodstream and
get broken down rapidly. These are referred to as ‘local hormones’
Local hormones include: paracrine secretions (affect only neighboring cells) and
autocrine secretions (affecting the secreting cell)
Another type: exocrine which secrete out of the internal environment
General Characteristics of the endocrine system
The endocrine system communicates with cells using hormones
Helps regulate metabolism
Specialized cells in liver, heart, gastrointestinal tract produce some hormones
Major endocrine glands are: pituitary, thyroid, parathyroid, pineal, pancreas
kidneys, thymus, reproductive organs (testes and ovaries)
Hormone Actions
There are two types:
1. Steroid hormones (synthesized from cholesterol)
2. Amines, polypeptides, proteins (synthesized from amine)
Can stimulate change in target cells even in low concentrations
Steroid hormones
Consists of complex rings of Carbon and Hydrogen with some Oxygen atoms
Differ according to types and number of atoms attached to these and way they
are joined
Insoluble in water and can cross cell membranes because lipids make up
membranes, steroid hormones are lipid soluble
When a steroid hormone enters a target cell:
1. Hormone diffuses through membrane
2. Hormones binds a specific membrane
3. Hormone-protein complex activates transcription of genes in mRNA
4. MRNA leaves nucleus, enters cytoplasm
5. Translation leads to synthesis of specific proteins
Non-steroid hormones
Usually bin receptors in target cell membrane. These receptors have a binding
site and an activity site

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Hormone that triggers this cascade of biochemical activity is called first
messenger
Biochemicals that induce change in responses are called second messengers
Entire process of cell communication is called signal transduction
Second messenger associated with one group of hormones is cyclic adenosine
monophosphate (cAMP)
This mechanism works:
1. Hormones binds to receptor
2. The complex activates G-protein
3. Adenlyate cyclase catylyzes ATP to cAMP
4. cAMP causes series of reactions
Prostogladins
Affect organs they are produced in
Variety of cells produce them, including those of the liver, kidney, heart, thymus,
lungs and reproductive organs
Not stored in cells, but synthesized just before they are released
Produce diverse and even opposite effects. For instance, some relax smooth
muscle, others contract smooth muscle
Control of Hormonal Secretions
Continually excreted in urine and broken down by various enzymes
Hormone secretion is precisely regulated
Hormone secretion is controlled in three ways, all of which include negative
feedback:
1. Release of tropic hormones from hypothalamus controls secretions of
anterior pituitary
2. Nervous system stimulates some glands directly
3. Other glands react directly to changes in fluid composition
Pituitary gland
The pituitary gland (hypophysis) is located at the base of the brain and consists
of anterior pituitary and posterior pituitary
The brain controls most of the pituitary gland’s activity
The posterior pituitary is part of the nervous system
Certain neurons whose cell bodies are in the hypothalamus have axons that
extend into the pituitary gland
Anterior pituitary contains glandular cells, but still controlled by the brain
Releasing hormones from the hypothalamus control secretions of the anterior
pituitary
Releasing hormones are carried into the bloodstream directly to the anterior
pituitary by hypohyseal portal veins
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