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37 Cards in this Set

  • Front
  • Back
Describe the endocrine system.
Influences metabolic activity by means of HORMONES, chemical messengers that bind to cellular receptors that typically reponses after a lag or seconds or days and must more prolongued than the nervous system
What are the major processes of the endocrine system?
1 growth and development
2 mobilization of body defenses
3 maintaince of electrolyte water and nutrient balance of the blood
4 regulation of cellular metabolism and energy balance
What is endocrinology?
the study of the endocrine organs and hormones
What are the main difference between exocrine glands and endocrine glands?
Exocrine glands produce nonhormanal substances and are ductless
Endocrine glands are DUCTLESS and produce hormones, are rich vascular and lymphatic drainage tissue that recieve their hormones
How are the hormone-producing cells in the endocrine system arranged?
in cords and branching networks which maximizes contact between them and the capillaries surrounding them
Why is the hypothalamus considered a neuroendocrine organ?
it produces and releases hormones (along with its neural functions)
Which organs contain endocrine tissue and produce hormones as well as exocrine products?
Pancreas and Gonads
Besides the major endocrine organs which other tissues and organs produce hormones?
- Adipose Cells release leptin
- Walls of Sm Intestines, Stomach, kidney and heart
Are autocrines and paracrines part of the endocrine system?
NO, because they act locally
What are hormones?
they are chemical substances that are secreted by cells into the exracellular fluids, that regulates the metabolic funciton of other cells in the body
How are most of the hormones classified?
they can be classified chemically as either amino acid based or as steroids (lipid based)
A given hormone that influences the activity of only certain tissue cells is referred to as what?
Target Cells
How do hormones effect target cells?
hormones alter cell activity, they increase or decrease the rates of normal cellular processes (depending on the target cell type)
What are the typical changes that hormones produce?
1- Opens or Closes ion channels(in order to alter plasma membrane permeability or membrane potential, or both)
2- Stimulates synthesis of proteins or regulatory molecules (such as enzymes within the cell)
3- Activates or deactivates enzymes
4- Induces secretory activity
5- stimulates mitosis
What are the two main mechanisms that account for how a hormone communicates with its target cell?
depending on: chemical nature of the hormones and the cellular location of the receptor
1- WATER-SOLUBLE HORMONES(all amino acid-based except Thyroid) act on receptors in the plasma membrane coupled with the mediated response of the G proteins

2- LIPID-SOLUBLE HORMONES (steroid and thyroid) act on intercellular receptors, directly activating genes (they are inside because they can enter the cell!)
Explain Second-Messenger Systems
All amino acid based hormones (except Thyroid) exert their signaling effects through intracellular second messengers, generated when a hormone binds to a receptor on the plasma membrane

-for example, cyclic AMP, which is used by neurotranmitters and olfactory and gustatory receptors
What is the main advantage to the second-messenger system?
SIGNAL AMPLIFICATION! one hormone can cause several GTP
What are the factors that effect the reaction of cAMP?
1- type of target cell

2- the specific protein kinases it contains

3- the substrate within that cell available for phosphorylation by the protein kinase
T or F, some G proteins inhibit rather than activate adenylate cyclase, thereby reducing the cytoplasmic concentration of cAMP, so even slight changes in the level of antagonistic hormones can influence a target cells's activity
Being lipid soluble, where do steroid hormones (and thyroid hormones)bind to their target cells?
-they bind to an intercellular receptor that is activated by the coupling

-this activated hormone-receptor complex them makes its way to the nuclear chromatin, where the hormone receptor binds to a region of DNA specific for it

-this interaction "turns on" a gene to produce messenger mRNA

-the mRNA is then translated on the cytoplasmic ribosomes, producing specific protein molecules

-this promotes the synthesis of either structural proteins or proteins to be exported from the target cell
What happens to the intracellular receptors, in the absence and presence of hormones?
- the receptors are bound up in receptor-chaperonin complexes, associations that seem to keep the receptos from binding to DNA and perhaps protect them from proteolysis

-when the hormone is present, the complex dissociates, which allows it to bind to DNA and influence transcription
T or F, Hormones are molecular triggers rather than informational molecules?
What are the three factors for target cell activation by hormone-receptor interaction?
1- blood levels of the hormone
2- numbers of receptors (in or on the target cells)
3- affinity(strength) of bond between the hormone and the receptor

*note: all three factor change rapidly in response to various stimuli and changes within the body
What is up-regulation?
when target cells form more receptors in the response to rising blood levels of the specific hormones to which they respond
Can prolonged exposure to high hormones concentrations desensitize the target cells, so they respond less vigorously to hormonal stimulation?
Yes! depends on receptor and cell types

also called down-regulation
How does down-regulation work?
it involoves loss of receptors and prevents the target cells from overreacting to persistently high hormone levels
Can hormones effect the number and affinity of not only their own receptors, but also the receptors of other hormones?

-progesterone=loss of estrogen receptors in the uterus
-estrogen then causes the same cells to produce more progesterone receptors (older sister hits you, you hug her more!)
What are the two forms that hormones circulate in the blood?

-generall, steroids and thyroid (lipid-soluble) travel in the bloodstream attached to plasma proteins

-most other circulate inencumbered by carriers
What does the concentration of hormone in the blood at any time reflect?
1- its rate of release

2- the speed at ehich it is inactivated and removed from the body
How are most hormones removed from the body?
- some are rapidly degraded by enzymes in their target cells

- most are removed by the kidneys or liver (and their breakdown prodects are excreted by urine and some in feces)

-half life varies from a fraction of a minutes to a week (water-soluble having the shortest half life)
T or F, steroid hormones require hours to days before their effects are seen?
T of F, some hormones are secreted in a relatively inactive form and must be activated in the target cells?
Describe the time required for hormone effects to appear and the duration of the action of the hormone
Time required varies, some immediate and other hour to days (esp steroids)

Duration action is limited ranging from 10 seconds to several hours

Effects may dispear rapidly as blood levels drop, or may persist for hours after very low hormones levels have been reached
What are the three major types of stimuli that are used in endocrine glands to relase their hormones?
Describe Humoral Stimuli.
-simplest of endocrine control systems
-secrets hormones in direct response to changing blood levels of certain critical ions and nutrients
-examples are parathyroid (PTH in response to Ca++), pancreas (insulin), and adrenal cortex (aldosterone)
Describe Neural Stimuli.
-in a few cases, nerv fibers stimulate hormone release

-sympathetic NS stimulation of adrenal medulla to release catecholamines (NE and Epinephrine) during stress
Describe Hormonal Stimuli.
-when endocrine gland release their hormones in responce to hormones produced by other endocrine organs