1 - Endocrine Physiology Flashcards
What are neurotransmitters?
released by axon terminals of neurons into the synaptic junction
act locally to control nerve cell functions
What are endocrine hormones?
released by glands or specialized cells into the circulating blood
influence the function of target cells at another location in the body
What are neuroendocrine hormones?
secreted by neurons into the circulating blood
influence the function of target cells at another location in the body
What are paracrines?
secreted by cells into the ECF to affect neighboring target cells of a different type
What are autocrines?
secreted by cells into the ECF
affect the function of the SAME CELL that produced them
What are cytokines?
peptides secreted by cells into the ECF
function as autocrines, paracrines, or endocrines
Thyroxine has what effect on most of the body’s cells?
Increased rate of chemical reactions
What are the three classes of hormones?
Proteins and polypeptides
Steroids
Amino Acid Tyrosine Derivatives
Which class of hormone doe the majority of hormones in the body belong to?
polypeptides and proteins
What’s the difference between a protein and a peptide?
Just a difference of size
Proteins are composed of 100+ amino acids
peptides are composed of < 100 amino acids
Where are protein and peptide hormones synthesized?
The rough ER, just like all other proteins
Describe the genesis of a protein hormone in the cell
- Produced in the rough ER as a larger protein that is not biologically active (preprohormone)
- In the ER it is cleaved into a prohormones
- Prohormones are transferred to the golgi for packaging into vessicles
- Enzymes in the vessicles cleave the prohormone into biologically active hormones and inactive fragments
- Vesicle is stored in the cytoplasm until stimulated for exocytosis by calcium or cAMP
Are peptide hormones water or fat soluble?
Water soluble
can easily enter the circulatory system
Steroid hormones are synthesized from ___________
cholesterol
Are steroid hormones water or lipid soluble?
lipid soluble
can simply diffuse across the cell membrane into the interstitial fluid and the plasma
How are steroids stored?
They aren’t
BUT
large stores of cholesterol esters ARE stored in the cytoplasm vacuoles and the cells can use these to rapidly synthesize steroids
Amine steroids are derived from _______
tyrosine
The two groups of amine hormones are synthesized in the:
adrenal medulla
thyroid
Epinephrine and Norepinephrine are _____ hormones and are formed in the _________
Amine
Adrenal Medulla
Which does the adrenal medulla secrete more of: epinephrine or norepinephrine?
four times more epinephrine
How are the catecholamines stored and released from the adrenal medulla?
Just like peptides: stored in vesicles and released by exocytosis
The concentrations of circulating hormones are extremely _____
low
Most hormonal regulation is controlled by ______ feedback
negative
How are peptides and catecholamines circulated in the blood?
Water soluble
dissolve in the plasma and are transported
How are steroid and thyroid hormones transported in the blood?
Lipid soluble
mainly circulate bound to plasma proteins
More than 99% of thyroxine in the blood is bound to plasma proteins!
How do protein-bound hormones diffuse?
Since they can’t easily diffuse, the large amount of hormone that is bound to proteins serves as a resevoir
when the concentration of free hormone decreases, hormone is able to detach and diffuse into the plasma to replenish the circulating concentration
The concentration of hormone in the blood is determined by:
the rate of hormone secretion into the blood
the metabolic clearance rate
How is metabolic clearance calculated?
rate of disappearance / concentration of hormone
What are the four ways hormones are cleared from the body?
- Metabolic destruction by tissues
- Binding with tissues
- Excretion by the liver into the bile
- Excretion by the kidneys into the urine
How are peptides and catecholamines cleared?
Rapidly. Short half-life.
Usually degraded by enzymes in the blood and tissue then excreted by the kidneys and liver
How are protein-bound hormones cleared?
Slowly. Several hours or even days.
Hormone receptors may be located in: (3)
the cell membrane
the cytoplasm
the nucleus
Most hormones that open or close ion channels do so by:
coupling with G protein-linked or enzyme linked receptors
not the ion channel itself
Explain the sequence of G protein activation by a hormone
- the hormone binds to the extracellular side of the receptor
- The intracellular side of the receptor phosphorylates GDP into GTP, causing the alpha unit of the G protein to dissociate from the beta and gamma subunits.
- The alpha subunit is the active portion. It goes off and interacts with the target protein as an enzyme
- When the hormone is removed, the receptor takes back its phosphate group and the two subunits reattach to the alpha subunit, inactivating it
What are enzyme-linked hormone receptors?
receptor protein that either functions as the enzyme or is directly catalytic
the receptor is doing the work the hormone triggers. It’s not just signalling to another part of the cell.
What receptor is a widely-used enzyme linked hormone receptor?
Tyrosine Kinase!
VEGF, inslin, ILGF, growth hormone and several others use these receptors
Describe the adenyl cyclase - cAMP system
- Hormone binds with G protein receptor
- A subunit binds with adenylyl cyclase
- Adenylyl cyclase converts ATP into cAMP
- cAMP activates cAMP dependent protein kinase
- Prokein kinase does the work
Catecholamine alpha receptors use the ___ second messenger system
Catecholamine Beta receptors use the ____ second messenger system
Phospholipase C
Adenylyl Cyclase - cAMP
Which second messenger system operates in response to entry of calcium into the cell?
Calcium-Calmodulin
Name one example of calcium-calmodulin action
myosin light chain kinase for muscle contraction in smooth muscle
calmodulin is very similar to ________, its skeletal muscle counterpart
troponin C
How does aldosterone cause sodium reabsorption and potassium secretion in the tubules?
It enters the cytoplasm of the tubular cells
Binds with mineralocorticoid receptor in the cytoplasm
Combined compound is transported to the nucleus
binds at specific points on the DNA and activates transcription of sodium and potassium transport proteins
What are the two unique ways thyroid hormones effect the nucleus?
- Activate genetic mechanism to synthesize multiple (100+) proteins that serves to ramp up metabolic activity in virtually all cells
- Once bound the the nucleic receptors, the thyroid hormone stays bound for days or even weeks
Low concentrations hormone increase the number of receptors per cell. This is known as:
upregulation
High concentrations of hormones decrease the number or affinity of receptors. This is called:
downregulation
Which type of hormone diffuses easily across the cell membrane: water soluble or lipid soluble?
Lipid soluble
Water soluble hormones are polarized and have a high molecular weight. Most of them require receptors.
Lipid soluble steroids diffuse freely across the membranes
What are the four second messenger systems?
- cAMP
- cGMP
- IP3 - DAG
- Tyrosine Kinase
Lipid-soluble homrones are synthesized from cholesterol. The only exception is:
thyroid hormones
If steroids can diffuse across the cell membrane freely, what keeps them from diffusing back out before causing any sort of effect?
They bind with cytosolic or nuclear receptors
What is the difference between direct and permissive effects of hormones?
Direct effects change the cell’s function from one thing to another
Permissive effects don’t change the actions of the cell, just make they cell do those actions more efficiently and at a greater rate etc.
What is the neuroendocrine system?
the integration of the neural and endocrine systems
namely, the hypothalamic pituitary axis
