Slide set 3- Endocrine system Flashcards
What is the difference between electrical and chemical signal?
Electrical: involve change in membrane potential (typical nervous system)
Chemical: are molecules secreted into extracellular fluid, responsible for most communication within the body (typical in endocrine)
Describe the 4 basic methods for cell-to-cell communication.
- GAP JUNCTIONS: allows direct cytoplasmic transfer of electrical and chemical signals between adjacent cells
- CONTACT-DEPENDENT SIGNAL: occurs when surface molecules of one cell bind to surface molecules of other cell
- CHEMICALS THAT DIFFUSE: through the extracellular fluid to act on cell close by
- LONG-DISTANCE COMMUNICATION: uses a combination of chemical signals transported by the blood
What are the characteristics of gap junctions? (5)
- Simplest form of cell-to-cell communication
- Direct transfer of electrical and chemical signals
- Creates cytoplasmic bridges between adjacent cells
- Forms from the union of membrane-spanning proteins called CONNEXINS
- The ONLY means by which electrical signals can pass directly from cell to cell
What are characteristics of contact dependant signals? (3)
- Requires that surface molecules on one cell membrane bind to a membrane protein of another
- Occurs in immune system and during growth and development
- Includes CELL-ADHESION MOLECULES (CAMs)
What is the difference between paracrine and autocrine signals?
PARACRINE signals: secreted by one cell and diffuse to ADJACENT cells
AUTOCRINE signals: act on the SAME CELL that secreted them
What are characteristics of long-distance communication?
- Hormones are secreted by endocrine glands or cells into the blood. Only target cells with receptors for the hormone will respond to the signal.
- Use also of NEUROTRANSMITTERS
What are neurotransmitters?
- Neurotransmitters are chemicals secreted by neurons that diffuse across a small gap to the target cell. Neurons use ELECTRICAL SIGNAL as well.
- Neurotransmitters have a RAPID EFFECT
What are neurohormones?
- Chemicals released by neurons into the blood for action at distant targets.
- Hormones produced by brain structures that act at distant targets
What are cytokines?
- Are synthesized and secreted by all nucleated cells (not produced by specialized cells)
- May act as both local and long-distance signals => act on on a BROADER SPECTRUM ot target cells than hormones
- Control CELL DEVELOPMENT, DIFFERENTIATION, and IMMUNE RESPONSES
- Made on demand (are not stored)
- ex: cytokines are especially used in tissue healing. Cytokines will be released to attract the right cells to the area in order to repair it.
What are the 4 features shared by all signal pathways? (4)
- The signal molecule (ligand, can be cytokine, hormone, para or autocrine signal) brings info to the target cell.
- Ligand-receptor binding activates the receptor
- The receptor activates one or more intracellular signal molecules
- The last signal molecule initiates SYNTHESIS of target PROTS or MODIFIES existing proteins to CREATE A RESPONSE
True or false
Receptor prots are only located on the cell membrane
FALSE
Receptor prots are located inside the cell or on the cell membrane.
On what does the location of ligand/receptor binding depend?
On whether the signal molecule is lipophilic or hydrophilic
Where will a LIPOPHILIC signal molecule bind, and what will happen?
Since it is lipophilic, it can diffuse through the phospholipid bilayer, and bind to CYTOPLASMIC or NUCLEAR RECEPTORS.
- This kind of receptor activation often turns on or off a gene
- RELATIVELY SLOW
Where will a LIPOPHOBIC signal molecule bind, and what will happen?
- Lipophobic signal molecules cannot diffuse through plasma membrane
- Will bind to EXTRACELLULAR receptors (on plasma membrane)
- Causes cascade of event to occur
- VERY RAPID
If the response of a chemical signal is related to change in gene activity, it will than be ______ (slower, faster)
Slower.
True or false, some lipophobic signal molecules also bind to cell membrane receptors in addition to intracellular receptors.
TRUE
Which ligand/receptor binding will create a faster response ? (membrane receptor binding or cytoplasmic/nuclear receptor binding)
Membrane receptor binding will create a faster response.
What is a biological signal transduction?
Converts CEHMICAL SIGNAL into CELLULAR RESPONSES
What can a second messenger do? (3)
- Alter the gating of ion channels
- INCREASE intracellular CALCIUM ( which bind to prots to change their function)
- Change ENZYME ACTIVITY, especially prot KINASES and PROTEIN PHOSPHATASES
Go see signal pathway of tyrosine kinase (slide 20)
go
What are characteristics of GPCR?
- GPCR are large complex family of membrane-spanning prots that CROSS the phospholipid bilayer 7 TIMES
- Cytoplasmic tail linked to G protein, a three-part transducer molecule
What happens when a G protein is activated?
When they are activated, G prots can:
- Open ion channels in the membrane
- Alter enzyme activity on the cytoplasmic side of the membrane
What are the steps in GPCR signaling? (5)
- Signal molecule binds to G prot-linked receptor, which activates G prot
- G protein turns on adenylyl cyclase, an amplifier enzyme
- Adenylyl cyclase converts ATP to cyclic AMP
- cAMP activates protein kinase A
- Protein kinase A phosphorylates other proteins, leading ultimately to cellular response
Go check phospholipase C and Receptor channel on slide 23-24
Go
What is the difference between agonist and antagonist ligand/receptor binding?
- Agonist will also activate the receptor on which a reference ligand can bind
- Antagonist will block receptor activity
What are some differences between nervous and endocrine system?
NERVOUS SYSTEM:
- Each nerve cell terminates on a specific target cell -> wired specific transmission to a target
- Neurotransmitters are RAPID and SHORT LIVED
- Neurons can ONLY STIMULATE MUSCLES and GLANDS across a synapse
ENDOCRINE SYSTEM:
- Wireless
- Glands are not linked with target cells
- Endocrine chemical messengers are secreted into the blood and delivered to distant target sites => ACCESS MOST TISSUES AND CELLS
- Effect of hormones is SLOWER and LONGER lasting
What is the difference in specificity between neural and endocrine communication?
- Specificity of neural communication depends on ANATOMICAL RELATIONSHIP between nerve cell and target cells
- Unlike the endocrine system, specificity is not totally reliant on the MESSAGE and cell having CORRECT RECEPTOR
- Which muscle moves depends on WHICH NEURON RELEASES OF Ach, as all motor neurons have Ach receptors
What is the main differences between endocrine and exocrine?
ENDOCRINE:
- “Ductless glands”
- Made of glandular epithelium whose cells MANUFACTURE and SECRETE hormones
- Secrete HORMONES
EXOCRINE:
- Product is excreted OUTSIDE
- Often has a DUCT
- Secrete products
True or false,
A few endocrine glands are mande of neurosecretory tissue
TRUE
Modified neurons that secrete CHEMICAL MESSENGER that diffuse into BLOOD STREAM rather than across a synapse
ex: Adrenal gland
What gland is the master gland in endocrine system? What is the role of this gland?
Hypothalamus
- Receives input and acts accordingly
- Controls release of anterior pituitary hormones through releasing and inhibiting factors
What happens if we don’t have any iodine in our diet?
No thyroid hormone. Iodine is a major component of thyroid hormone (thyroxine hormone =>T4).
What happens if iodine deficiency ? (childhood, adulthood…)
Child: Children will have PHYSICAL GROWTH and development problems, and brain development can also be severely impaired => CRETINISM
Adult: Thyroid gland can be considerably enlarged=> goitre
What is Grave’s disease?
- Most common form of hyperthyroidism
- An immune system protein mimics TSH (autoimmune)
- Also treated with radioactive iodine to destroy thyroid cells
What are the 2 hormone classifications based on structure?
Whether a hormone is HYDROPHILIC or LIPOPHILIC.
HYDROPHILIC hormones : most are PEPTIDE or PROTS hormone => Insulin, or catecholamines (adrenal hormrones -> epinephrine)
LIPOPHILIC hormones: include THYROID HORMONES AND STEROIDS
- All steroids are derived from cholesterol (CORTISOL and SEX HORMONES)
- Thyroid hormone is an exception as it is an IODINATED TYROSINE (aa) DERIVATE
What are the 3 hormone classifications based on function?
TROPIC HORMONES: target other endocrine glands and stimulate their growth abd secretion of other hormones (ACTH targets the adrenal cortex)
SEX HORMONES: target REPRODUCTIVE TISSUES
ANABOLIC HORMONES: stimulates anabolism (to build) in taret cells ( Testosterone stimulates protein synthesis and build up of cellular tissue, especially in muscle)
- Insulin is considered anabolic hormone
What do the hormone solubility properties determine?
- The way the hormone is TRANSPORTED in the blood
- The mechanism by which the hormone exerts its EFFECT-SIGNALING
- The means by which the hormone is processed by the endocrine cell
How are hydrophilic vs lipophilic hormones transported?
Hydrophilic: dissolved in the plasma
Lipophilic: Bound reversibly to plasma proteins