Unit 1 - Homeostasis & Cell Communication Flashcards
what is the definition of physiology?
the study of the functions of living organisms and their parts
levels of organization in the body
cell –> tissue –> organ –> organ system –> organism
four classification of cells
- neurons
- muscle cells
- epithelial cells
- connective tissue cells
four major tissue types
- nerve tissue
- muscle tissue
- epithelium
- connective tissue
(correspond to cell types)
what are organ systems?
- a group of organs
- organized to perform more complex functions that any organ alone
what is homeostasis?
- the ability to maintain a relatively constant internal environment
- requires organ system integration
role of negative feedback loop in homeostasis
- negative feedback is important because it triggers changes in the regulated variable if becomes too high or too low from set point
- works to counteracts a change in the body (i.e temperature) back to its set point
what is the mechanism to maintaining homeostasis?
- sensors within in the body (aka neurons) are sensitive to a certain variable, such a temperature
- these sensors relay signals (input) to an integrating centre which compares the regulated variable to the desired set point
- an appropriate response is orchestrated within the brain or a gland
- to carry out the response, the integrating center relays signals (output) to the cells, tissues or organs that illicit the final response.
what organ system doesn’t maintain homeostasis? why?
- the reproductive system
- it functions to maintain the species (produce offspring) and not the individual
what components of the internal human environment are regulated?
- temperature (37 +/- 2)
- volume of fluids
- composition of fluids
why is homeostasis important?
- the body needs stable internal and external environments for it to operate
- if homeostasis is not restored, potentially introduces illness, disease or death
afferent
towards the CNS from PNS
efferent
away from CNS to PNS
effectors
refers to cells/tissues/organs that are effected, and receive a signal to respond to
affector
refers to a structure that affects others or sends a signal out.
structures that help maintain homeostasis
- receptors
- integrating centers
- effectors
- signals
role of receptors
- to detect physiologcial variables
- i.e heat, stretch, pressure
examples of receptors in the body
- thermoreceptors
- chemoreceptors
- baroreceptors
role of integrating centers
- orchestrates an appropriate response
- many integrating centres are found in the brain
role of effectors
- responsible for facilitation of a response in the body
- receive signals
role of signals
- allow components (receptors, effectors and centers) to communicate
what are the different signals in the body?
- input signal: receptor to an integrating center
- output signal: integrating center to an effector
2 ways cell communicate
- electrical signals
- chemical signals
what are electrical signals?
- changes in membrane potential to adjacent or long-distance cells
what are chemical signals?
- proteins secreted by cells into the ECF and go to neighboring cells
- include cytokines, hormones, neurotransmitters
what are target cells?
cells that receive messages which can illicit an appropriate response within the body
3 stages of signal transduction
- reception = key + key hole (cell affinity with a messenger)
- transduction = convert into message that can illicit a response
- response - changes within a cell
how do cells communicate locally and long distances?
local = using special junctions
long distance = combination of electrical (nerves) and chemical (blood) signals
3 main types of special junctions
- tight junctions
- desmosomes
- gap junctions
role of tight junctions
- occludins fuse adjacent cells together to form a continuous (nearly impermeable) barrier between epithelial cells
- molecules must go in/out of cell via diffusion or active transport through epithelium rather than space between plasma membrane
role of desmosomes
- to provides strength and adherence between adjacent cells so that the cells do not tear apart when the tissue is subjected to stress (i.e cardiac muscle, skin, bladder)
role of gap junctions
- membrane proteins connect adjacent cells creating channels
- allow for adjacent cells to communicate and exchange ions/molecules rapidly with each other
two types of intercellular communication
1.) direct communication between adjacent cells
2.) indirect communication using chemical messengers to act on specific receptors
what are autocrine and paracrine signals?
autocrine = a cell secretes a hormone that acts on the receptors on the same cell
paracrine = a signal secreted by one cell and act on nearby target cells (if it has the particular receptor for the chemical messenger).
role of membranes
- separate material between ICF and ECF
- allows for exchange of material between ICF and ECF
why is transport across membranes important?
- helps obtain oxygen and nutrients to processes can occur within a cell
- helps get rid of waste product (i.e CO2, H+ eliminated)
what is a selectively permeable membrane?
the membrane allows for the transport of some molecules but is restrictive to others
what molecules easily pass through a membrane?
- non polar molecules
–> includes O2, CO2, fatty acids
what molecules don’t usually pass through a membrane?
- ions and polar molecules
–> includes glucose, proteins, Na+
what factors affect transport across a mebrane?
- chemical and electrical forces (electrochemical gradient)
- depends on charges of a molecule
- depends on the polarity of a membrane
passive transport
- spontaneous, doesn’t require energy
- downhill movement i.e simple diffusion
- “high to low concentration”
active transport
- requires energy
- non-spontaneous i.e the use of pumps
- uphill movement
- “against the concentration gradient, low to high concentration”
what is a chemical driving force?
- is created by a concentration gradient across a membrane
- a force that “pushes” molecules down a concentration gradient spontaneously, from high to low concentration
what is a concentration gradient?
- the difference in particle concentration between the inside and outside of the cell
- pushes particles from high to low concentration areas
what is an electrical driving force?
- a difference in energy due to a difference of charge that acts to move ions from high energy to low energy
- an electrical gradient
what is the membrane potential?
- a force caused by unequal distribution of anions and cations across the cell membrane
- the difference in charge is a source of energy
what is a cells resting potential? why?
- approximately -70 mv
- it is due to the inside of a cell being more negatively charged than the outside
main principles of electrical driving force
- like charges repel
- opposites attract
2 factors the direction of electrical driving force depends on:
- polarity of the cell/ membrane potential (+ or -)
- charge on the particle (+ or -)
what is the electrochemical driving force?
the total force created a result of chemical and electrical driving forces together
significance of electrochemical driving force
- determines the direction the ions move
–> when ions are transported passively, they move in the direction of the electrochemical driving force
–> when ions are transported actively, they move in the direction opposite to the electrochemical force
factors influencing the direction of the electrochemical driving force on an ion
- net direction of the electrical and chemical driving forces
–> if both forces go in the same direction (Na+, Ca2+) = electrochemical driving force acts in that direction.
–> if the electrical and chemical forces go in opposite directions (K+) = electrochemical force acts in the direction of the larger force
what is equilibrium potential? what does it mean?
- a hypothetical value for the membrane potential of an ion when the electrical driving force is equal and oppositely to the chemical driving force
- results in a an electrochemical driving force of zero
- this means that an ion won’t move spontaneously in either direction because the total driving force acting on it is zero (at equilibrium)
why is equilibrium potential important?
- helps to determine whether the electrical or chemical force is larger
- determines a cells resting potential
why is cell transport important?
- key for maintaining homeostasis
- important for communication between cells
what is a selectively permeable membrane
the membrane allows some molecules to transport through but not all
types of passive transport
- simple diffusion
- facilitated diffusion
- diffusion through channels
simple diffusion
molecules/ions diffuse through the semipermeable membrane down their concentration gradient without assistance
3 factors influences the rate of passive transport
- magnitude of driving force
- amount of membrane surface area (high SA = high rate)
- membrane permeability
4 factors that influence membrane permeability
- lipid solubility of diffusing substance (non polar or polar)
- size and shape of diffusing particle (smaller = faster)
- temperature (hot = faster)
- thickness of membrane (thin = faster, thick = slower)
how does high permeability vs low permeability influence net flux?
- high permeability = faster diffusion
- low permeability = slower diffusion
what is a channel?
transmembrane protein that transports molecules via a passageway or pore
types of channels
- aquaporins
- ion channels
what is an aquaporin?
- channel that allows for the movement of water across a membrane
- without it, H2O wouldn’t be able to permeate the cell membrane because its a polar molecule
types of ion channels
- leak channels = a pore
- gated channel = ability to open and close to regulate permeability
- bidirectional = change their conformation to open or close to ECF or ICF
characteristics of ion channels
- are a transmembrane protein
- open to ECF and ICF at once
- functions like a passageway or pore for a particular ion
- substance specific
factors affecting the rate of diffusion using a channel
- individual transport rate of each channel
- number of channels in the membrane
- open or closed state of the channel
how is gating of a channel regulated?
- ligand gating = respond to binding of a chemical messenger/substrate (ligand)
- voltage gating = sensitive to changes in membrane potential
- mechanical gating = stretch and pressure change of a membrane
what are carrier proteins?
a transmembrane protein that binds to specific molecules on one side of a membrane and transports them to the other side by means of a conformational change
how do carrier proteins work?
- bind to specific substrates and carry them between intra and extracellular compartments
- carriers are only open to one side of the membrane at a time and change their conformation in order to open to ICF or ECF
membrane channels vs carrier proteins
- channel proteins transport substances only down a concentration gradient (doesn’t require energy)
- carrier proteins transport substances both down and against the concentration gradient (can do active transport)
what is facilitated diffusion
passive diffusion of molecules using carrier proteins to move molecules across a membrane
characteristics of a protein carrier
- transmembrane protein spanning from ECF to ICF
- has binding sites for specific molecules
- binding occurs one side at a time
- random conformational changes
- can transport larger molecules that channels cant
does facilitated diffusion reach saturation? why?
- yes, because the number of carrier proteins in a cell membrane is limited.
- this occurs when all the protein carriers are being used and the rate reaches a maximum, reaching a saturation point
- it cannot exceed this point because there is a fixed number of carrier proteins, and diffusion requires the use of them for transportation to occur
- increasing the amount of molecules doesn’t matter unless more carrier proteins are introduced
two forms of active transport
1.) primary active transport = requires energy and ion pumps
2.) secondary active transport = uses potential energy from another gradient, indirectly driven by primary active transport
two general factors that influence rate of active transport
- energy availability (ATP)
- concentration gradient
what is the difference between primary and secondary active transport?
- primary = use ATP
- secondary = use energy from electrochemical gradient (energy from driving ions)
cotransport
simultaneous transport of molecules across the cell membrane in the same direction
counter transport
molecules are being transported across the cell membrane at the same time but in different directions
characteristics of a pump
- a membrane protein
- functions as a transporter and an enzyme
- can harness energy
- has specific bonding sites
- demonstrates saturation
how does primary active transport work?
- energy (ATP) is used to transport molecules across a membrane against their concentration gradient (low concentration to high concentration) using a pump
steps does secondary active transport work
- the stored energy in the electrochemical gradient set up by primary active transport is able to pump ions across the membrane
- a carrier protein couples the flow of one substance so that it moves passively down its electrochemical gradient while releasing energy that is then used to drive the movement of the other substance up its electrochemical gradient
examples of secondary active transport
1.) sodium-linked glucose transport (cotransport)
–> Na+ moves down its gradient to provide energy to drive glucose against the gradient
2.) sodium-proton exchange (countertransport)
–> Na+ moves down the gradient to provide energy to drive H+ agains the gradient
examples of primary active transport
- sodium potassium pump
what is the sodium potassium pump?
the pump is a protein that uses ATP to actively transport Na+ ions out of the cell and K+ ions into the cell against their electrochemical gradients
how does the sodium potassium pump work?
- Na+ and K+ ions are actively pumped opposite directions across the plasma membrane
- For each cycle of the pump, 3 Na+ ions are transported out of the cell, and 2 K+ ions are transported into the cell.
- ATP is hydrolyzed to provide energy to move against their concentration gradients
- The pump has specific binding sites for Na+ and K+ and changes conformation to allow for transportation
- the binding site’s affinity is higher when it faces one side of the membrane and lower when it faces the opposite side so ions are transported in one direction only.
- this pump is responsible for membrane potential within cells
what is osmosis?
- the diffusion of water through a membrane
- water moves from high concentration of water (more dilute) to low concentration of water (less dilute)
characteristics of osmosis
- passive transport
- unaffected by membrane potentials
- driven by a water gradient
osmolarity
- the total solute concentration of a solution
- the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L).
iso-osmotic
- two solutions have the same osmotic pressure
hyper-osmotic
- solution with higher osmolarity
- the water concentration is lower because the solute concentration is higher
hypo-osmotic
- solution with lower osmolarity
- the water concentration is higher because the solute concentration islower.
what is osmotic pressure?
- is the minimum amount of pressure needed to prevent the flow of solvent molecules through a semipermeable membrane
what is tonicity?
- refers to the water gradient across a membrane
- it is the outside concentration (extracellular) relative to the inside (the cell’s) concentration
osmolarity vs tonicity
- osmolarity represents the total concentration of solutes
- tonicity describes how concentration of how a solution will affect cell volume and shape.
types of endocytosis
1) phagocytosis (“cell-eating”)
2) pinocytosis (“cell-drinking”)
3) receptor-mediated transport
what is exocytosis?
molecules within cells are packaged into secretory vesicles, which then fuse with the plasma membrane and release their contents into the extracellular fluid
what is endocytosis?
molecules in the ECF enter the cell through the formation of vesicles, called endosomes, that pinch off from the plasma membrane
what is transcytosis?
involves moving macromolecules across the epithelial using both endocytosis and exocytosis
what is phagocytosis?
- “cell-eating”
- the plasma membrane extends and engulfs microorganisms which pinches off to form an endosome in the cytoplasm
- degradative enzymes from within the the lysosome break down the particles and are recycled
what is pinocytosis?
- “cell-drinking”
- the plasma membrane develops an indentation to surround to fluid and dissolved solute and pinch together to form an endosome within the cytoplasm
what is receptor-mediated endocytosis?
- transmembrane proteins in the plasma membrane function as receptors that recognize and bind specific particles in the ECF
- the receptors cluster in a specific region of the plasma membrane, called coated pits
- the particles bind to the receptors and the plasma membrane forms vesicles by pinching in and surrounding it
3 functions of exocytosis
1) to add components to the plasma membrane
2) to recycle receptors removed from the plasma membrane by endocytosis
3) to secrete specific substances out of the cell and into the ECF
2 ways the epithelium transports materials
- absorption
- secretion
membranes required for epithelial transport
1) apical –> faces lumen of a body cavity
2) basolateral –> faces internal environment/ interstitial fluid
how does epithelial transport work?
to absorb or secrete materials, the cells that make up the epithelial tissue must transport substances inward across the membrane on one side of the cell and outward across the membrane on the opposite side of the cell
how is water transported across the epithelial?
- solutes are pumped into the interstitial fluid
- osmotic pressure of the interstitial fluid increases
- water is osmotically pulled across the cell
- water is transported via the lumen to the interstitial fluid
how does endocytosis/exocytosis compare to active transport?
- they are both require energy input
- active transport involves the movement of specific ions or molecules across the cell membrane with the help of protein pumps
- endocytosis and exocytosis involve the bulk transport of materials in/out of cell using vesicles
how does endocytosis/exocytosis compare to passive transport?
- endocytosis and exocytosis are active processes that require energy (move against their concentration gradient)
- passive transport doesn’t require energy (move substances along their concentration gradients)
