Hormones 1 Flashcards
What are the 3 communication systems in the human body & what chemical messengers do each of them use?
- Nervous system: neurotransmitters
- Endocrine system: hormones
- Immune system: cytokines
What are the 8 glands that make up the endocrine system?
- Hypothalamus
- Pituitary gland
- Thyroid gland
- Parathyroid gland
- Adrenal glands
- Pancreas
- Pineal gland
- Reproductive glands
What are the 2 ways to classify hormones?
Chemical structure & abilty to dissolve in water
Describe the difference between endocrine, paracrine & autocrine.
- Endocrine: Hormones are substances that are synthesized in one organ & transported by the circulatory system to act on another tissue
- Paracrine: Hormones that act on adjacent cells
- Autocrine: Hormones that act on the cells where they are produced
How do hormones cause specific responses in specific tissues if they are part of the systemic circulation?
They stimulate a specific response through the receptors present on specific organs
organs, tissues, or cells lacking the specific receptor do not respond to its stimulating effects
Some horomes have several targers & some only have one
What is the name of a chemical that binds with a high degree of specificity to a receptor?
ligand
What are the types of horomones receptors & what are their binding sites?
- Plasma membrane receptors or intracellular receptors
- Generally proteins
- Binding site specific for chemical messenger
- Bindign site involved in transmitting the message
What is it called when the message from a receptor is converted to an intracellular response?
Signal transduction
Describe the intracellular cascade that results from the binding of insulin.
- Insulin binds to the receptor –> autophosphorylation of the receptor on specific Y residues
- This catalyzes the phosphorylation (on Y residues) of Insulin Receptor Substrates (IRS 1-4)
- This results in a stimulation of a nuber of different kinases that effectively perform the functions of the cell
Describe the Jak/STAT kinase cascade
- hormone binding induces dimerization of the receptor
- associated proteins (Jak) are phosphorylated & activated
- Active Jak phosphorylates the intracellular domains (Y residues) of the receptor
- STAT & other cytosolic proteins bind to the phosphorylated receptor and are phosphorylated by Jak
-
STAT-P dimerize & enter the nucleus
- activate transcription by binding to response elements
How can Jak activate proteins other than the STAT pathway?
proteins can bind to the receptor through SH2 domain to be phosphorylated & activated by Jak
What does STAT stand for?
Signal Transducers and Activators of Transcription
Describe the cascde produced by G-protein-coupled receptors.
- GDP is bound to alpha subunit of G-protein
- hormone binding displaces GDP for GTP
- The G-protein dissociates from the receptor & the alpha-GTP dissociates from the beta & gamma subunits
- the alpha-subunit of GTP auto-hydrolyzes to GDP
- The alpha, beta & gamma subunits reassemble with the receptor
What is the effect of binding Gs?
adenylyl cyclase is stimulated
What is the effect of binding Gi?
adenylyl cyclase is inhibited
What is the effect of binding Gq?
phospholipase C stimulated
Describe how cAMP acts as a second messenger for G-protein-coupled receptors.
- Adenylyl cyclase converts ATP to cAMP
- cAMP stimulates PKA by binding to regulatory subunits & releasing active catalytic subunits
- catalytic subunits PKA phosphorylate proteins
- this signal is attenuated by cAMP phosphodiesterase
What are the two forms of guanylyl cyclase?
membrane bound and soluable
How does cGMP act as a secondary messenger?
- cGMP stimulates protein kinase G (PKG)
- PKG phosphorylates a number of smooth muscle proteins
- leads to relaxation of smooth muscle & vasodilation
What molecule stimulates the soluble form of guanylyl cyclase?
NO
What molecule stimulates the membrane bound guanylyl cyclase?
Atrial natriuetic factor (ANF)
Describe the second messenger system stimulated by Gq receptor.
- hormone binds receptor, activating Gq protein
- alpha-GTP subunit stimulates membrane bound phospholipase C
- Phospholipase C cleaves phosphotidylinositol 4,5-biphosphate (PIP2) into diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3)
- IP3 interacts with receptor in ER, causing release of Ca2+, DAG or both
What are the two types of intracellular receptors?
cytosolic receptors & nuclear receptors
Describe the response of cytosolic receptors & provide an example of a hormone that uses this type of system.
Sex steroids
- Steroid hormones diffuse into the cell
- They bind to specific receptor & displace heat shock protein (HSP) attached to an allosteric site
- Hormone receptor complex enters the nucleus & binds to the specific DNA region, hormone responsive element (HRE)
- Starts transcription and translation
