Cell Communication Flashcards
Function of gap junctions:
- for adjacent cells
- direct cytoplasmic transfer of chemical and electrical signals
Gap junctions have two components:
- connexons
- connexins
Connexons:
- protein channel (open/close) formed by united connexins
- connects pre and post synaptic cells
Connexins:
membrane proteins
Contact dependent signals:
- needs cell adhesion molecules (CAM) for cell-cell signaling
- has to bind to receptor on post synaptic cell
Chemicals that diffuse into ISF:
- histamine
- cytokine
- eicosanoids
Histamines are produced by…
basophils and mast cells
- help vasodilate things
Cytokines are produced by…
lymphocytes and helper T cells
Cytokines:
regulatory peptides for local and long distance communication
Examples of cytokines:
- interleukins
- CSF
- GF
- lymphokines
Eicosanoids are produced by…
oxidation of phospholipids
- lipid derivative of arachidonic acid
- uses phospholipase A2
2 major groups of eicosanoids:
- leukotrienes: produced by lipoxygenase
- prostanoids: produced by cyclooxygenase (COX)
Function of leukotrienes:
helps with asthma and anaphylaxis
Examples of prostanoids:
- prostaglandins: vasodilators
- thromboxanes: vasoconstrictors and platelet aggregation
Methods of cell communication:
- local
- long distance
Local communication:
- gap junctions
- autocrine: acts on same cell that secreted it
- paracrine: secreted by one cell and diffuses to adjacent cells
T/F: local communication is not contact dependent
F, is contact dependent
Long distance communication is used by…
- hormones
- neurocrines
- neurotransmitters
- uses neuromodulators
Examples of neuromodulators:
- carbon monoxide
- nitric oxide
- H sulfide
- all are vasodilators
Carbon monoxide and nitric oxide both diffuse into….
smooth muscle cells to activate guanylyl cyclase forming cGMP
Nitric oxide is catalyzed by…
NO synthase
A good source of H sulfide is…
garlic
Components of signal pathways:
- ligand (primary messenger) that binds to receptors
- receptors: proteins that are on membrane
- membrane signaling pathway: starts at membrane
Transduction pathway tells target cells…
what to do and create response
Extracellular signal molecules are…
primary messenger that activates membrane receptor
How do intracellular signal molecules create response?
it’s a secondary messenger that gets altered to send signal
Endocrine system regulates:
- metabolic rate
- H2O and electrolyte balance
- cell proliferation
- reproductive organs
How does endocrine system help the body cope with stress?
controls adaptive change
Hormones:
- secreted in very small amounts by specialized cells
- responds to specific change in environment
- act on receptors of target cells to alter function
Endocrine hormones:
- made by classical endocrine cells
- travel via blood to target tissue
- ex: LH and FSH, growth hormone, thyroid stimulating hormone
Neurocrine hormones:
- released by axonal ends of neurons into blood
- ex: oxytocin, antidiruetic hormone
Paracrine hormones:
- diffuses to different local cell types via ISF/gap junctions
- activates neighboring cells
- ex: hormones from ovaries/testes (ovaries/testosterone)
Autocrine hormones:
- acts back on itself / other identical cells via gap junctions
- ex: cytokine interleukin-1
Pituitary gland and target glands has ______ feedback
negative feedback
Neural control:
- ANS alters hormone secretion that responds to change detected by nervous receptors
Example of input for neural control:
- visual
- auditory
- olfactory
- gustatory
- tactile
- pressure
- limbic
Chronotropic control of hormones:
- released in distinct phases based on rhythms that are genetically encoded or acquired
Examples of chronotropic control:
- circadian: 24 hr
- dirunal: day/night
- ultradian: multiple times w/in a day
- circadian clock in: suprachiasmatic nucleus
- seasonal variation: dependent on light cycle
Function of pineal gland:
regulates circadian rhythm via release of melatonin
Steroids:
- derived from cholesterol
- lipid soluble: diffuse from cell when formed
1/2 life of hormone:
- time required for [ ] to drop 1/2 of initial [ ]
- transportation form affects 1/2 life
Free hormones:
- fast acting
- short 1/2 life
- susceptible to enzymatic degradation
Prohormone:
- circulates as inactive precursor of H2O soluble hormones until cleaved
- prolongs 1/2 life
Hormone bound to carrier:
- longest 1/2 life time
- slowest response time
- bind to specific globulins synthesized by liver
- carriers protect enzyme degradation b/c hormone is inactive when bound
What form of hormone removal from plasma is irreversible?
- target cell uptake
- metabolic degradation
- urinary and biliary excretion
Metabolic clearance rate (MCR):
- sum of removal processes
- volume of plasma cleared per unit of time (mL/min)
What are the two major sites of hormone extraction/degradation?
- kidney and liver
- renal clearance is reduced by carriers
Radioimmunoassay (RIA):
- helps measure [hormone] in blood
Enzyme linked immunosorbent assay (ELISA):
- helps measure [hormone] in blood
- enzyme converts product into different color
Mechanism of hormone action:
- hormone must be recognized and bound by specific cell receptor
- hormone receptor complex gets coupled to signal-generating mechanism/act on itself
- generated signal changes intracellular processes
How does generated signal change intracellular processes?
- enzyme activity/ [ ]
- functional proteins
- structural proteins
What are the two receptor systems based on solubility?
- membrane
- intracellular
Plasma membrane receptors (Rm):
- response is sec/min and target proteins are activated/inactivated
- are large glycoproteins w/ specific extracellular binding sites
- is within plasma membrane of target cell
Plasma membrane is activated by…
non-lipid soluble (NLS) hormones
T/F: hormone occupancy changes receptor conformation
T
Receptor capacity:
- increased binding affinity leads to more binding of hormone, which leads to decrease of [free hormone]
- occupancy of 5-10% of total available Rm means max biological action
Up-regulation:
- increase # of Rm
- results from intermittent exposure to submaximal [hormone]
- hormones can recruit own receptor and enhance sensitivity of cell
Down-regulation:
- decrease # of Rm
- results when excess hormones is sustained for awhile
- lessens effect of chronic exposure to excessive hormones
Phosphorylation and dephosphorylation of Rm:
- alters K: affinity of receptor for hormone
- can also be affected by: pH, osmolarity, [ion], substrate levels
Non-G protein signaling mechanism:
Rm with single transmembrane portion
Mitogen-activated protein kinases (MAPK):
promotes growth
Tyrosin kinases:
- binding of hormone to receptor induces autophosphorylation of intracellular portion of receptor
- strong modulators of gene transcription
Intracellular receptor system:
- used by lipid soluble hormones
- Rc: cortisol
- Rn: reproductive hormones
- hormones diffuse through membrane and enters cell to attach to receptor, which is usually in the nucleus
Receptor hormone complex in intracellular receptor system:
interacts w/ DNA in nucleus
How does [hormone] affect responsiveness of target cells to hormones?
- impacts # of receptors on cell
- target cell upregulate # of receptors if [ ] decreases
How does # of receptors affect responsiveness of target cells to hormones?
can cause upregulation or downregulation
How does chronotropic factor affect responsiveness of target cells to hormones?
affects how quickly receptors and hormones bind
How do intracellular conditions affect responsiveness of target cells to hormones?
w/ rate limiting enzymes, co-factors, and substrates
How do other hormones affect responsiveness of target cells to hormones?
- concurrent effects of antagonistic/synergistic hormones
- permissive action: one hormone increases the responsiveness of a target tissue to another hormone
How do the number of target cells affect responsiveness of target cells to hormones?
- decreased # of target cells = lower response
- # of receptors can be increased by hormone that stimulates movement through key points in mitotic cycle or by inhibiting apoptosis
Receptor saturation, specificity, and competition on single receptor is impacted by:
- agonists: promote binding/activation of signaling pathway
- antagonists: blocks receptors
Termination of signal pathways occur with…
degradative enzymes
