C5 - Section 1. AN OVERVIEW OF THE ENDOCRINE SYSTEM Flashcards
Endocrinology is a field of medicine which studies hormones and their actions.
These hormones are produced from endocrine glands.
The endocrine system is a finely integrated system whereby the hypothalamus, pituitary & target glands continually communicate through feedback inhibition & stimulation, to control all aspects of metabolism, growth and reproduction (Henry) and by understanding this interplay, and carefully manipulating these systems via provocative and suppressive stimuli, it is possible to characterize an underlying abnormality and provide directed treatment
Secretory products transported in the bloodstream from their place of synthesis to a distant location where they exert their action.
These are chemical substances that have a specific regulatory effect on the activity of a certain organ or organs or cell types.
Hormones have the following important functions:
Control rates of certain chemical reactions
Transport substances across cell membranes
Help regulate water and electrolyte balance
Play a role in reproduction
Three General classes of Hormones
Steroid Hormones
Polypeptides and Proteins
Hormones derived from amino acids
generally hydrophobic
Steroid Hormones
Many circulate in plasma bound to high-affinity proteins
Steroid Hormones
Small % are free for biologic activity
Steroid Hormones
Half-life: 60 – 100 mins.
Steroid Hormones
water-soluble
Polypeptides and Proteins
Circulate unbound in plasma
Polypeptides and Proteins
Half-life: vary from 5 to 60 mins.
Polypeptides and Proteins
Initiate their response by binding to cell membrane receptor
Polypeptides and Proteins
Half-lives vary
Hormones derived from amino acids
Examples:
Thyroxine – protein-bound (Half-life: almost 1 week)
Epinephrine – not proteinbound (Half-life: <1 min.)
Hormones derived from amino acids
– protein-bound (Half-life: almost 1 week)
Thyroxine
– not proteinbound (Half-life: <1 min.)
Epinephrine
Types of Hormone Action according to Tietz
hormone synthesized in one location & released into plasma
- Endocrine
Binds to specific receptors in cells at a distant site to elicit characteristic response
- Endocrine
hormone synthesized in nerve ending & released into EC space
- Neuroendocrine
Interacts w/ receptors of cells at distant site
- Neuroendocrine
hormone synthesized in neurons & released into EC space
- Neurocrine
Binds to receptor in nearby cell & affects its function
- Neurocrine
hormone synthesized in neurons & released from nerve endings
- Neurotransmission
Crosses synapse & binds to specific receptors in another neuron
- Neurotransmission
hormone synthesized in endocrine cells & released into EC space
- Paracrine
Binds to specific receptor of nearby cell & affects its function
- Paracrine
hormone synthesized in endocrine cells & released into lumen of gut
- Exocrine
The biological response to a hormone is initiated by the binding of the hormone to target cell receptors
provide the target cell with a mechanism for recognizing & concentrating the hormone
Receptors
activates the target cell to begin the chain of events that constitutes the biological effect(s) of that hormone
hormone-receptor complex
3 ways in which control of Hormonal Secretion occurs
1.Releasing (trophic) hormones from the (?) control secretions of the anterior pituitary.
HYPOTHALAMUS
- The (?) influences certain endocrine glands directly.
NERVOUS SYSTEM
- (?): respond directly to changes in fluid composition.
FREESTANDING GLANDS
Mechanism of Hormone Secretion
An increase in one hormone would result in the increase of a second hormone
Positive Feedback Mechanism
An increase in one hormone causes a decrease in the second hormone
Negative Feedback Mechanism
