RAT #2 Flashcards
Define receptor and ligand
Receptors are proteins that are embedded in the plasma membrane or inside the cell (cytosol or nucleus)
A ligand is a signal molecule that binds to the receptors on/in the cell which creates a change in the cells activity.
Changes may include:
- activation of an enzyme
- Opening/closing of an ion channel
- Changing gene expression
Autocrine signal & example
Local communication
Chemical signal that acts on the cell that created it
“auto” = self
Ex: Growth - it may be noted that some hypothesis’ about cancer growth is due to an autocrine signal that won’t stop
Explain how one signal can cause different effects in a target cell
The signal molecule (ligand) binds to a protein receptor. Then ligand-receptor binding activates the receptor. The receptor then initiates one or more intracellular molecules. Finally the last signal molecule creates a response by changing existing proteins or beginning the synthesis of new proteins.
Define antagonistic control and explain how heart rate is controlled this way
When chemical signals have opposing effects they are said to be antagonistic. Ex: insulin decreases glucose in the blood but glucagon increase glucose in the blood. (therefore they are antagonistic)
Chemical signals from the sympathetic nervous system (EPI/NE) increase heart rate by chemical signals from the parasympathetic nervous system (Ach) decrease heart rate.
Explain the relationship between the hypothalamus, the anterior pituitary and the posterior pituitary
x
Explain what is meant by a tripartite axis for hormone control and release
Example - the stress axis. Tripartite means that the signaling pathway involved 3 different endocrine glands: the hypothalamus, the anterior pituitary gland, and the adrenal corte
Paracrine signal & example
Signal binds with receptor on nearby cell - passes only through ISF
“para” - beside
Example: histamine, or neurotransmitters (Ach) at a synapse
Endocrine signal & example
Hormones - chemicals that are secreted into the blood and distributed all over the body. However, only cells with the right receptors will respond to the signal.
ex: insulin, testosterone, estrogen
Steroid hormone
-Fat soluble
-Need a protein carrier (in the blood) because they aren’t water soluble (steroid-binding globulins)
-Receptor located in cytosol or nucleus
-Steroids enter the cell by simple diffusion
-Steroids activate gene expression
-Once inside the cell, if not already in the nucleus the signal moves there and then binds with DNA to begin transcription which then ends in protein synthesis
-Response tends to be slow and enduring
Examples - estradiol, testosterone, progesterone, cortisol
Non-steroid hormones
-Water soluble
-Travel dissolved in blood; may need a carrier protein to protect from enzymes
-Receptors located on plasma membrane; hormone does NOT enter the cell
-Transduction mechanisms:
1. Changes in ion permeability
2. Change in concentration of 2nd messengers inside the cell
3. Change in the amount of enzyme activity inside a cell
-Response tends to be fast (brief and enduring)
Examples - epinephrine, insulin, antidiuretic, oxytocin
G-couped receptors
Large membrane spanning proteins. The types of ligands that bind to G-protein coupled receptors include: hormones, growth factors, olfactory molecules, visual pigments, and neurotransmitters.
When G-proteins are activated they:
-open an ion channel in the membrane or alter enzyme activity on the cytoplasmic side of the membrane
Enzyme - coupled receptors
Ligand binding to a receptor-enzyme complex activates an intracellular enzyme.
Ion-channel coupled receptors
Ligand binding open or closes the channel and alters the ion flow across the membrane.
Agonist
A competing ligand that binds to a receptor and elicits a response.
Antagonist
Competing ligands that bind to a receptor and DONT elicit a response. (blocking the primary ligand).
Examples and chemical nature of steroids
- Lipophilic (hydrophobic) “water hating, lipid loving)
- derived from cholesterol
- Glucocorticoids (cortisol)
- Testosterone
- Progesterone
- Estradiol
Examples and chemical nature of non steroids
- Lipophobic “water loving, lipid hating”
- Proteins - insulin, oxytocin, ADH (antidiuretic hormone)
Steroid transport in the blood
Steroids are not soluble in the blood, which means that they have to be transported via a protein created by the liver
Steroid transport in the blood
Steroids are not soluble in the blood, which means that they have to be transported via a carrier protein created by the liver
Non steroid transport
These signals dissolve in the plasma of the blood for transport. However some require a carrier protein in order to be protected from enzymatic degradation
Location of steroid receptor
Steroid receptors are inside the cell cytosol or the nucleus.
Hormones cross the plasma membrane by simple diffusion
Location of non steroid receptor
Non steroid receptors are located on the cells membrane. These hormones DO NOT enter the cell.
Transduction mechanism of steroids
The hormone-receptor complex moves into the nucleus (if it was not there already) and binds with DNA to activate transcription.
Transduction mechanisms of non steroids
- A change in the permeability of the membrane to ions
- A change in the concentration of 2nd messengers inside the cell ex cAMP
- A change in the amount of enzyme activity inside the cell
Temporal patterns of response steroids
Slow and enduring - it can take up to 90 mins to activate gene expression but the effect can last up to several days
Temporal patterns of response non steroids
Brief and dramatic (ex the adrenaline surge of a panic attack)
These signals need to be constantly secreted because their half lives are very short
ADH source
Posterior pituitary gland
Oxytocin source
Posterior pituitary gland
Stimulus for secretion of ADH
- decreased blood pressure
- increased osmolarity (“saltiness”) of the cerebrospinal fluid
Stimulus for secretion of oxytocin
-neural reflex initiated by mechanical stimulation of the nipples
Target of hormone (location of receptors) ADH
Kidney - water conservation
Peripheral vascular circular smooth muscle - causes blood vessels to squeeze blood from the periphery into the heart brain loop
Target of hormone (location of receptors) oxytocin
Increased contraction of myoepithelial cells in the mammary glands
(Prolactin from the APG is responsible for milk production)
Transduction mechanism of ADH
ADH-receptor on the surface of the target cell; ADH is a protein (can’t diffuse across the membrane)
Transduction mechanism of Oxytocin
Oxytocin - receptors on the surface of the target cells
Functional response of tissues ADH
Increased blood pressure and less urine formed
Functional response of tissues oxytocin
Milk “let down” reflex
Tonic control
Control that blood vessels are under. There are not two different signals to cause contraction/relaxation.
When EPI/NE binds with the alpha adrenergic receptor the blood vessel contracts. For the vessel to relax, stimulation by EPI/NE has to be reduced.
The stress axis
Stress causes the hypothalamus to release CRH (corticotropin releasing hormone) which travels to receptors in the anterior pituitary gland which causes it to release ACTH (adreno-corticotropic hormone) which travels to receptors in the adrenal cortex which stimulates it to release cortisol, which then affects the immune system cells, liver cells, muscles, and adipose tissue.
*Cortisol causes catabolism of stored fuel molecules
How is the stress axis an example of negative feedback?
Because cortisol binds with receptors in the hypothalamus and anterior pituitary gland to suppress release of CRH and ACTH
Posterior pituitary hormones
Antidiuretic hormone (vasopressin) and oxytocin
