*Physiology 1 (lectures 1, 2 + 3) Flashcards
Tissue?
Group of cells with similar structure and specialise function
Organs?
2 or more types of primary tissues that function together to perform a particular function(s)
Body systems?
groups of organs that perform related functions and work together to achieve a common goal(s)
Homeostasis
Stable internal environment (maintenance of steady states within our bodies by co-ordinated physiological mechanisms)
In order to maintain homeostasis, what just a control system do?
Sense deviations from normal
Integrate this info. with other relevant info.
Make appropriate adjustments in order to restore a controlled variable to its desired value
2 classes of control systems and explanation
Intrinsic control (local controls that are inherent in an organ) Extrinsic controls (regulatory mechanism initiated outside an organ - this is accomplished by nervous and endocrine systems)
Feedforward?
Feedback?
Feedforward - responses made in anticipation of a change - usually act in combination with negative feedback)
Feedback - response made after a change has been detected
Negative feedback?
Positive feedback?
Negative - opposes initial change
Positive - amplifies initial change
Components of a negative feedback system
Sensor, control centre (compared sensor’s input with a set point), effectors
Example of positive feedback
Uterine contractions during labour become increasingly stronger until birth of baby
What are the major components of a cell membrane? (3)
Mostly lipids (phospholipids and cholesterol) and proteins (plus small amounts of carbohydrates)
How do you describe the appearance of the plasma membrane through an electron microscope?
Trilaminar
What are the 2 main parts of a phospholipid? Charged? hydrophilic or hydrophobic?
Head (negatively charged, polar, hydrophilic)
Tail (uncharged, nonpolar, hydrophobic)
What makes up the lipid bilayer of the cell membrane?
Phospholipids
The lipid bilayer is rigid. True or false?
False - it is fluid
What is the purpose of having cholesterol interspersed in the phospholipid bilayer?
To prevent the phospholipids sticking together (contributes to the fluidity and stability of the membrane)
What word describes proteins embedded in the lipid e.g. receptors?
Integral proteins
What word described proteins that extend through the membrane e.g. transporters, channels?
Transmembrane proteins
What word describes proteins that do not penetrate the membrane (most commonly intracellular) e.g. receptor-associated enzymes?
Peripheral proteins
What are short carbohydrate chains found on the membrane often bound to?
What is the name for the layer formed by the membrane carbohydrates which coat the surface of the cell (“the sugar coating”)?
Usually membrane proteins (glycoproteins) and to a lesser extent lipids (glycolipids)
Glycocalyx
What are the 3 important functions of the lipid bilayer?
It forms the basic structure of the membrane
Its hydrophobic interior serves as a barrier
It is responsible for the fluidity of the membrane (enables the cell to change shape)
What type of membrane proteins are located on the inner membrane surface and interact with secretariat vesicles leading to exocytosis of the vesicle contents?
Docking-marker acceptors
What is an example of a cell adhesion molecule that helps hold cells within tissue together?
Cadherins
What do the short carbohydrate chains on the outer surface act as?
Self-identity markers that enable cells to identify and interact with one another
Role of carbohydrate chains on cell surface in tissue growth?
Makes sure cells do not overgrow their own territory
What are the 3 types of specialised cell junctions?
Desmosomes
Tight junctions
Gap junctions
What are desmosomes?
Adhering junctions that anchor cells together, especially in tissues subject to stretching e.g. skin
What are tight junctions?
Join the lateral edges of epithelial cells near their lumens (apical) membranes (tight or leaky)
What are gap junctions?
Communicating junctions that allow the movement of charge carrying ions and small molecules between 2 adjacent cells
Is the plasma membrane permeable?
Selectively permeable
What 2 properties influence whether a particles can permeate the plasma membrane without assistance?
Solubility of the particle in lipid
Size of the particle
What 2 driving forces can cause something to move across a membrane?
Passive
Active (requires ATP)
What 2 forces drive molecules and ions that can diffuse across the membrane?
Diffusion down a concentration gradient, and/or
Movement along an electrical gradient
What is Fick’s law of diffusion?
In addition to concentration gradient, the following factors influence rate of net diffusion:
The magnitude of the concentration gradient
The surface area of the membrane across which diffusion is taking place
The lipid solubility of the substance
The molecular weight of the substance
The distance through which diffusion must take place
In addition to concentration gradient, what is ion movement also affected by?
Electrical charge e.g. cations tend to move towards more negatively charged areas
What is osmosis?
The net diffusion of water down its own concentration gradient
Why can water molecules pass through/ permeate the plasma membrane more readily than would be expected from solubility in lipid?
Due to aquaporins (water channels)
What is osmolarity?
the concentration of osmotically active particles present in a solution
What are the units of osmolarity?
Osmoles/ litre (Osm)
What is the approximate osmolarity of body fluids?
Approx. 300 mOsm
What is tonicity?
The effect a solution has on cell volume
What are the units of tonicity?
No units
Isotonic?
Doesn’t change cell volume
Hypotonic?
Increase in cell volume
Hypertonic?
Decrease in cell volume
What happens in substance mediated transport?
Substance binds onto a specific carrier which undergoes a conformational change which transports the substance
What important characteristics determine the kind and amount of material transferred across the membrane?
Specificity - each carrier is specialised to transport a specific substance or a few closely related chemical compounds
Saturation (transport maximum, Tm)
Competition
What are the 2 forms of carrier-mediated transport?
Facilitated diffusion (Not requiring energy) - transfer downhill Active transport (requiring energy)- transfer uphill
What are the 2 forms of active transport?
Primary active transport
Secondary active transport
What is primary active transport?
Energy is directly required to move a substance across its concentration gradient
What is secondary active transport?
The transfer of a solute across the membrane is always coupled with the transfer of the ion that supplies the driving force (typically Na+) - energy source comes from another reaction
Is the Na+K+ATPase involved in primary or secondary active transport?
Primary
What does the Na+K+ATPase do?
Transports 3 X Na+ out of the cell for every 2 X K+ in
What are the 3 important roles of the Na+K+ pump?
Helps establish Na+ and K+ concentration gradients across the plasma membrane of all cells
Helps regulate cell volume by controlling concentration of solutes inside the cell
The energy used to drive the pump indirectly serves as the energy source for secondary active transport
What are the mechanisms by which secondary active transport can occur?
Symport (co-transport)
Antiport (exchange or countertransport)
What is symport (co-transport)?
The solute and Na+ move in the same direction e.g. glucose absorption at the apical membrane of enterocytes
What is antiport?
The solute and Na+ move in opposite directions (Na+ into, solute out of the cell)
Is vesicular tranport passive or active?
Always active as requires energy for vesicle formation and movement within the cell
