Mod 5 Endocrine system 1 Flashcards
What is the endocrine system?
The endocrine system is one of 2 major control systems in the body, the nervous system regulates organ function via electrochemical impulses (fast), on the other hand, the endocrine system regulates organ function via hormones (slower response)
What are the endocrine organs?
- scattered
- ‘ductless’ gland with rich blood supply
- contain hormone-producing cells
What are hormones?
- chemical messengers
secreted into blood or lymph - travel throughout the body to regulate other organs
- bind to specific receptors (lock and key) to initiate the response (needs to recognize the protein)
- effects last longer than the NS
Hormones?
Long-distance chemical signals travel in the blood or lymph and exert effects throughout the body.
Autocrine?
Short distance chemical signals exert effects on the same cells that secrete them, prostaglandins released by smooth muscle cells cause those cells to contract
Paracrine?
Paracrine are short distance chemical signals that exert effects on other cells that secrete them but with the same tissue i.e. somatostatin released by a different pancreatic cell
What do hormones regulate?
- growth and development
- electrolyte, water, and nutrient homeostasis
- cellular metabolism and energy production
- body defenses
- reproduction
Cellular level?
- Plasma membrane permeability or membrane potential/both by opening/closing ion channels
- synthesis of enzymes and other proteins within the cell
- activate and deactivate enzymes
- secretory activity
- mitosis
How does the chemical structure impact its effects?
the hormone’s chemical structure determines it’s solubility in water, it affects hormones transport before degradation and receptor interactions, either amino acid-based or steroid-based
What are different processes that occur in the NS and the endocrine system (COMP)
Nervous system:
- Rapid
- short-duration response
- acts via AP and neurotransmitters
- specific locations determined by axon pathways
Endocrine:
- slow
- long-duration responses
- diffuse locations (anywhere blood reaches)
What are the amino acid-based hormones?
Most hormones are in this group, with varying molecule size, amino acid derivatives, peptides proteins are water-soluble, they can’t cross the membrane
What are the steroid-based hormones?
They are synthesised from cholesterol includes adrenocortical and gonadal hormones, lipid-soluble, and can cross the plasma membrane.
How do hormones exert their effects? 1
- must have specific receptor (target cell)
- hormones increase/decrease preprogrammed cellular processes, regulate activity and not informational molecules
Can the same hormones have different effects on different target cells?
Yes, the same hormones have different effects on different target cells
i.e. adrenaline (contracts muscle but also dilates the bronchial in the lungs)
the degree of target cell activation depends on 3 factors, what are they?
1) blood levels of the hormones
2) the number of receptors for that hormone
3) the strength (affinity) binding
Can hormones have influence over other hormone receptors?
yes, hormones have influence over other hormone receptors e.g progesterone decreases estrogen receptors in the uterus, and estrogen increases progesterone receptors
What does communication with target cells depend on?
how hormones communicate with target cells depend on the chemical structure and location of the specific receptor
How can hormones act at receptors?
1) water-soluble hormones act on plasma membrane receptors, usually couples into intracellular second messengers via regulatory molecules –> G proteins ( amino acids)
2) the lipid-soluble hormones act on intracellular receptors, directly activate genes (steroid-based and thyroid)
H20 soluble
Water-soluble hormones act via the plasma membrane receptor
i.e.
cyclic AMP 2nd messenger signaling
pip 2 ca 2+ messenger signaling
less common 2nd messenger cGMP
No 2nd messenger: insulin hormones binding to insulin receptor
What are the Interaction of three plasma membrane components?
1) hormone receptor
2) G protein (Gs or Gi)
3) Effector enzyme (adenylate cyclase) regulates intracellular levels of 2nd messenger cyclic AMP
What are the steps to cyclic AMP 2nd messenger signaling?
1) Hormones (1st messenger) bind to receptor
2) receptor activates G protein
3) G protein activates adenylate cyclase
4) adenylate cyclase converts ATP to cAMP (the 2nd messenger)
5) cAMP activates protein kinases
6) triggers responses of the target cell (activates enzymes, stimulates cellular secretion, opens ion channels)
In cyclic AMP 2nd messenger signaling, what are the different effects that may occur in different cells?
- modified heart rate
- ovaries (synthesis of female androgens)
- thyroid ( synthesis of thyroid hormone)
- kidney ( water balance
- liver breakdown stored glucose
What determines the effect of cAMP in any given cell?
- types of protein kinases
- types of substrates to be phosphorylated by protein kinases
What are the steps in lipid-soluble act via intracellular receptors?
1) the steroid hormones diffuse through the plasma membrane and binds to the intracellular receptor
2) the receptor hormone complex enters the nucleus
3) the receptor hormone complex binds to specific DNA region
4) binding initiates transcription of the gene mRNA
5) the mNRA directs protein synthesis
6) protein translation results in enzymes that promote various metabolic activities or synthesis of structural proteins or proteins to be released from target cell
what determines the effect of cAMP in any given cell?
- types of protein kinases
- types of substrates to be phosphorylated by protein kinases
Lipid soluble hormones act via intracellular receptors?
1) the steroid hormones diffuse through the plasma membrane and binds an intracellular receptor
2) the receptor hormone complex enters the nucleus
3) the receptor hormone complex binds a specific DNA region
4) binding initiates transcription of the gene to the mRNA
5) the mRNA direct protein synthesis
6) protein translation results in enzymes that promote various metabolic activities, or the synthesis of structural proteins to be released from the target cell
How are hormones released?
- negative feedback system
- internal/external stimuli
- hormone levels increase, feedback inhibits further release
How many types of stimuli trigger the endocrine glands?
3 types
What is humoral stimulus?
hormone release caused by the altered levels of certain critical ions or nutrients
stimulus: Low concentration of Ca+2 in the capillary blood
response: parathyroid glands secrete parathyroid hormone (PTH) which increases blood Ca+2
What is neural stimulus?
the hormones released caused by neural input
Stimulus: action potentials in preganglionic sympathetic fibers to the adrenal medulla
response: adrenal medulla cells secrete epinephrine norepinephrine
What is the hormonal stimulus?
the hormone release caused by other hormones (a tropic hormone)
stimulus: hormones from the hypothalamus
response: anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones
How quick and how long do hormones exert their effects?
onset: almost immediate to hours- days, some hormones are inactive when secreted and must be activated in target cells
Duration:
10 seconds - several hours (rapid and persistent)
How are hormonal blood levels controlled?
Hormonal blood levels are precisely and selectively controlled, the blood con is determined by 1) rate of release and 2) the speed of inactivation/removal
How are hormones rapidly degraded?
- some hormones rapidly degraded by the intracellular enzymes but most are removed by liver or kidneys
=> half-life varies (few seconds to a week)
What are water-soluble hormones?
water-soluble hormones are rapidly removed by kidneys and have the shortest half-lives
What are lipid-soluble hormones?
Lipid soluble hormones are metabolized by the liver and have a longer half-life
2 types of circulation?
Hormones circulate free or protein-bound, most hormones are free but lipid-soluble hormones are protein-bound
What are the three types of interaction?
multiple hormones may act on the same target cell at the same time 3 1) permissiveness 2) Synergism 3) Antagonism
What is permissiveness?
A hormone needs another hormone to exert its full effect
What is synergism?
2 hormones exert the same effect which is amplified when combined
What is antagonism?
opposing actions: Hormones that act to return body conditions to within acceptable limits from opposite extremes
