Module 2- Membrane Physio + Osmoregulation + endocrine + renal Flashcards
phospholipids
phospholipids are amphipathic, meaning a substance with both hydrophobic and hydrophilic region
-this is a factor in membrane permeability
- hydrophobic molecules such as O2, CO2, and N2 can freely move through the phospholipid bilayer
- small uncharged polar molecules such as water and glycerol can semi move freely through
- large uncharge polar molecules such as glucose and sucrose cannot
- ions cannot move freely either
cholesterol
cholesterol can fill spaces between phospholipids and interact with them to make the membrane more viscous (thick)
changes in viscosity are used when some animals acclimate to long term temperature changes
Factors affecting membrane fluidity
- more saturated tails = less fluid
- longer tails = less fluid
- low temperature = less fluid
- cholesterol moderates the fluidity, increasing it at low temperature and decreasing it at high temperatures (generally it decreases fluidity, unless the organism lives in very cold environments)
membrane proteins
serve many different roles : transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to cytoskeleton and extracellular matrix (ECM)
passive transport
- can freely move through lipid membrane 2. passive transport down electrochemical gradient 3. carrier mediated passive transport
active transport
- primary active transport against electrochemical gradient
- secondary active transport against electrochemical gradient, driven by ion movement down its gradient
uniporter
type of facilitated transport–
symporter
type of facilitated + coupled transport–
antiporter
type of facilitated + coupled transport–
coupled transport
allows the movement of multiple solute types
conformation change
conformation change in carriers is most often caused by binding of the molecule being transported. carriers transport molecules down the concentration gradient
simple diffusion
molecules move from area of high concentration to low concentration until they reach a steady state. the rate of simple diffusion is directly correlated and driven by the concentration of the molecule at the source side of the membrane
- charged molecules are still diffusion but instead of concentrations of individual molecules in isolation, the collective charge of different areas plays a role in the movement of molecules
-while diffusion of a solute is not directly influenced by concentration of other solutes, it may be influenced by the electrical gradient
carrier mediated transport
like simple diffusion, it is directly correlated with concentration but only to a certain point. once the transport maximum (Tm) for a particular molecule is reached, the rate cannot increase any further
electrochemical gradient
this is the combined concentration and electrical gradient. while diffusion of a solute is not directly influenced by concentration of other solutes, it may be influenced by the electrical gradient.
6 Na+ and 2 Cl-
(high concentration of Na+ and net + charge)
↓ electrochemical gradient for Na+
1 Na+ and 2 Cl-
(net - charge and low concentration of Na+)
sodium-potassium-ATPase pump
- transporter binds 3 Na+ ions from cytosol
- phosphorylation by ATP favors conformational change
- Na+ is released, K+ binds
- De phosphorylation favors original conformation
- K+ is released to cytosol. cycle can repeat
Fick’s law of diffusion
rate of diffusion is determined by the concentration gradient (delta C), membrane surface area (A), the diffusion constant (D), and the membrane thickness (delta X)
diffusion constant is based on lipid solubility of the substance being transported and the molecular weight of the substances being transported
Q= (delta C * A * D)/ delta X
osmosis
diffusion of water across a selectively permeable membrane. water diffused across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides
AND from a region of lower non penetrating solute concentration to a region of higher non penetrating solute concentration
some cells have aquaporins which are water channels and allow water to move more quickly
osmotic pressure
hydrostatic pressure
fluid homeostasis
- maintenance of internal solutes
- fluid volume (plasma volume)
- removal of harmful substances
- maintenance of osmotic balance
tonicity
a measure of the ability of a solution to cause water to flow across a membrane into or out of a cell. it measures the osmotic pressure gradient across a semi permeable membrane. it is only influenced by non penetrating solutes
- hypotonic = solution has a lower osmolarity than the cell
-isotonic= solution has the same osmolarity as the cell
-hypertonic= the solution has higher osmolarity than the cell
Hypotonic
solution has lower osmolarity than the cell so water flows into the cell –> lysis, the cells can swell with water and burst
Isotonic
solution has the same osmolarity as the cell so water flows in both directions –> no net change in cell shape
Hypertonic
the solution has higher osmolarity than the cell –> crenation, cell becomes shriveled
Osmolarity
is a property of every solution; it describes the number of dissolved solute particles (OsM). this measures the concentration of both non penetrating and penetrating solutes while comparing two solutions. osmolarity alone does not inform us about the movement of water
hyposmotic, isosmotic, and hyperosmotic
hyposmotic
solution has lower osmolarity than the cell
isosmotic
solution has the same osmolarity as the cell
hyperosmotic
the solution has higher osmolarity than the cell
tonicity v osmolarity
tonicity is the property of a solution relative to a cell while osmolarity is the property of a solution and comparisons between solutions but doesn’t tell you what will happen to a cell
carrier mediated transport in the kidney
glucose reabsorption in the kidney
- under normal blood glucose levels, all glucose is reabsorbed and so not found in the urine. but when glucose levels are very high, Tm is reached and glucose can be found in the urine
mechanism of reabsorption:
- Na+ moving down its electrochemical gradient uses the SGLT protein to pull glucose into the cell against its concentration gradient
- glucose diffuses out the basolateral side of the side using the GLUT protein
-Na+ is pumped out by Na+-K+-ATPase
osmoregulation – salt reabsorption
the process of salt reabsorption cause water to move from the lumen back to the ECF (extracellular fluid)
- Nephron/ loop of Henle
endocrine signaling (glands)
a ductless gland releases hormones into the blood stream. the blood stream carries the hormone throughout the body. endocrine system regulates and coordinates distant organs through the secretion of the hormones
neuroendocrine signaling
a neuron releases neurohormones into the bloodstream. the bloodstream carries the neurohormone to its target
synaptic signaling (neurons)
a neuron releases neurotransmitter on a cell with receptors for the transmitter
hormone
hormone means “to excite”
- hormones are signaling molecules that travel to target cells via transport fluid and communicate and regulate physiological and behavioral activities
- involved in metabolism, sensory perception, stress response, growth, reproduction
- presence and absence of hormone may have impacts
- are effective at extremely low concentrations (picomolar)
- their action is often amplified in target cells due to secondary messengers
endocrine tissue
solely endocrine function: pituitary, thyroid, parathyroid, adrenal
endocrine tissues that also have non endocrine functions: pancreas, ovaries, testes
hypothalamus
has a master regulatory role with mixed nervous and endocrine functions
- is nervous tissue and functions to integrate the endocrine and nervous systems
- integrates information from other nerves and external stimuli
-makes (neuro) hormones that are stored and secreted by posterior pituitary
-secretes (neuro) hormones that regulate the anterior pituitary
peptide hormone
produced via transcription, translation, and post-translation processing
amine hormones
derived from the amino acid tyrosine
steroid hormones
produced through enzymatic reactions that modify cholesterol molecules
Receptors for steroids maybe be cytoplasmic or nuclear
- most hydrophobic steroids are bound to plasma protein carriers. only unbound hormones can diffuse into the target cell
- steroid hormone receptors are typically in the cytoplasm or nucleus
-some steroid hormones also bind to membrane receptors that use second messenger systems to create rapid cellular responses
-the receptor hormone complex binds to DNA and activates or represses one or more genes - activated genes create new mRNA that moves into the cytoplasm
- translation produces new proteins for cell processes
hormone receptor complexes
hormone-receptor complexes usually serve as transcription factors
signal transduction pathway
process by which signal received by the cell is converted into specific cellular response
- hydrophilic hormones function through STPs
-form a cascade and amplify the signal
three steps of signal transduction pathways
- reception ; different receptor types (G-protein coupled, receptor Tyrosine Kinases, Ion channels (ligand-gated))
- transduction ; uses secondary messengers and protein kinases
-second messenger: small, water-soluble molecule or ion that relays a signal as part of a STP –> common in G protein coupled receptors and often active protein kinases
- protein kinases: enzyme that activates/deactivates protein by phosphorylating them - response ; cytoplasmic or nuclear
epinephrine STP MOA
-epinephrine is both a hormone and a neurotransmitter
1. epinephrine binds to a G protein-coupled receptor
2. GTP binds to G protein to activate it
3. adenylyl converts ATP to cAMP
4. second messenger protein kinase A
5. cellular response
ligand-gates ion channel receptor
membrane receptor with region that acts as a gate for specific ions –> ligand binding to receptors controls gate that either opens or closes
Receptor tyrosine kinase
relays the message by activating protein kinases (enzymes that transfer phosphate from ATP to a particular intracellular protein)
- binding of 1 ligands can trigger multiple pathways at once
G Protein coupled receptors
these receptors are very common
-G protein: GTP-binding protein, inactivate when bound to GDP
- GPCR pathways use 1 of 2 enzymes, which “turn on” 1 of 2 secondary messengers
GPCR enzymes and 2nd messenger pairs
- Adenylyl Cyclase/ cAMP
- Phospholipase C/ IP3 and DAG
GPCR adrenaline response - Phospholipase and alpha receptor
-Phospolipase C cleaves PIP into IP3 and DAG –» Ca2+ release -» smooth muscle contraction, glycogenolysis
GPCR adrenaline response- Adenyl cyclase and alpha receptor
blocks adenyl cyclase from producing cAMP and releases calcium -» inhibition of noradrenaline release and smooth muscle contraction
GPCR adrenaline response- adenyl cyclase and beta receptor
produces cAMP -» contraction of cardiac muscle, smooth muscle relaxation, glycogenolysis
G protein couple receptors MOA
- binding of extra cellular messenger to receptor activates a G protein, the subunit of which shuttles to and activates adenylyl cyclase
- Adenylyl cyclase converts ATP to cAMP
- cAMP activates protein kinase A
- protein kinase A phosphorylates inactive designated protein, activating it
- active designated protein brings about desired response
hormone general MOA
general MOA = (1) change in membrane potential (2) alteration in the levels of intracellular “second messenger” molecules (3) activates catalytic activity (4) direct gene action
hormone general pathway
hormones…
(1) are released from an endocrine cell
(2) travel through the bloodstream
(3) enter interstitial fluid
(4) interact with specific receptors in/on a cell
(5) cause a physiological response/responses via STPs
Receptor/Ligand
the type and location of a receptor matches the chemical properties of its ligand (the hormone)
Water-soluble (hydrophilic) hormone
-peptides
-bind to receptors on cell surface
-initiates a signal transduction pathway
lipid-soluble (hydrophobic) hormone
-steriods
-bind to intracellular receptor
-signal-receptor complex often directly involved in gene regulation
amines (amino-acid derived) hormone
-hydrophilic or hydrophobic
-depends on the specific molecule
Hydrophilic hormone (water soluble) examples
all hypothalamic hormones, all pituitary hormones, epinephrine, insulin, glucagon, leptin, ghrelin, growth hormone, parathyroid hormone, insulin like growth factor, atrial natriuretic peptide
lipophilic hormone (lipid soluble) examples
adrenal cortex hormones, major gonadal hormones, estrogens (estradiol, estrone, estriol), progesterone, testosterone, aldosterone, cortisol, thyroid hormone
a single hormone can have different effects on different tissues
due to..
1. same receptors but different intracellular proteins
2. different receptors
Example of same receptors, different intracellular proteins
Epinephrine causes liver cells to break down glycogen so glucose can be released
epinephrine causes skeletal muscles in the blood vessels to cause vessel dilation
Example of different receptors
Epinephrine causes vessel dilation with beta receptors in skeletal muscle blood vessels
epinephrine causes vessel constriction with alpha receptors in intestinal blood vessels
calcium
calcium functions as an important second messenger in several tissues
-roles include altering intracellular charge, activating regulatory proteins, and triggering secretory vesicle exocytosis
cellular cytoplasmic response in STP
-regulates enzyme activity
-ex: in liver cells, epinephrine activates enzyme glycogen phosphorylase that breaks down glycogen to glucose