2 - Homeostasis Flashcards
Homeostasis concept
Homeostasis is the maintenance of a stable internal environment within tolerable limits, despite external changes
Essential for physiological functions such as temperature regulation, pH balance, and ion concentrations
Regulated variable
directly controlled or regulated and for which there are specific sensors that monitor any changes
(eg. Body temperature which is specifically monitored by peripheral and central temperature receptors)
Unregulated variables
contribute to control of process but don’t have specific sensors
Negative feedback
system that detects deviations from a set point and initiates corrective actions (eg. Body temperature regulation)
Positive feedback
amplifies changes until a specific endpoint is reached (eg. Childbirth contractions) / there must be an end point at which the systems switched off and homeostasis
Factors influeincing homeostasis
Genetics / nutrition / physical activity / mental health / environmental exposure
Physically activity - effects gas usage and production —> CO2 production will affect pH and ATP use
Failure of homeostasis
Deficiency - lack of essential elements impairs biological processes
Toxicity - excess elements can disrupt cellular function
Components of cell membrane
Phospholipids bilayer
Proteins
Cholesterol
Carbohydrates
CM structure - phospholipids bilayer
hydrophilic heads face outward; hydrophobic tails face inward
CM structure - proteins
embedded in the membrane for transport, signalling, and structural support
CM structure - cholesterol
Provides membrane fluidity and stability
CM function
Controls the movement of substances in and out of the cell
Maintains homeostasis by regulating internal conditions
CM - Protein pores
Beta pleated sheets
Form a pore through the membrane (can be selective or non-selective)
Can also be known as leakage channels
Passive transport
No ATP required
Simple diffusion
movement of molecules (e.g., O₂, CO₂) from high to low concentration
Facilitated diffusion
movement via protein channels or carrier proteins (e.g., glucose transport)
Osmosis
diffusion of water through a semi-permeable membrane driven by solute concentration
RBC - why cant they withstand pressure increase
bursts due to lack of cell wall
(cant withstand the pressure increase when water moves in from hypotonic solution)
Isotonic
Equal concentration inside and outside
Hypertonic solution
Water moves out of the- shrivelled
Hypotonic solution
Water moves in - burst or swell
What’s transpiration controlled by
Concentration of a sciatic acid
Living in saline water - impermeable membranes
Prevents excess water loss
Marine organisms tend to be…
Isotonic
How do marine mammals have efficient kidneys
gain NaCl from breathing and drinking (pump excess Cl- out)
How are sharks different
Accumulate urea so hyperosmotic
Living in fresh water - hypertonic
Face constant influx of water (or loss of ions)
Living in fresh water - impermeable surface
Prevent excess water coming in
Water permeability is permitted to only a limited number of specilised cells (all other cells are maintenance in isotonic solution)
Living in freshwater - how to maintain osmotic balance
Use ATP driven Cl- pumps into the cell
Primary active transport
direct use of ATP (eg. Sodium-potassium pump moves Na+ out and K+ in)
Secondary active transport
uses energy from ion gradients (eg. Na+ glucose symporter)
Transporters - uniporters
move a single molecule (eg. Glucose transporter)
Transporters - symporters
move 2 molecules in the same direction (eg. Na+ and glucose) (co-transport)
Transporters - antiporters
move 2 molecules in opposite directions (eg. Na+ Ca2+ exchanger)
Factors influencing diffusion rate (5)
Concentration gradient
Temperature
Surface area
Membrane permeability
Molecule size
Concentration gradient
Greater difference = faster diffusion
Temperature
higher temperature = increased kinetic energy = faster diffusion
Surface area
Larger area = more diffusion
Membrane permeability
lipid-soluble molecules diffuse more easily
Molecule size
smaller molecules diffuse faster
Active transport mechanisms
Definition: Movement of molecules against the concentration gradient using energy (ATP)
Sodium-Potassium Pump (Na⁺/K⁺ ATPase)
Active transport - where is it useful
Maintains resting membrane potential in nerve cells
Calcium Pump: Regulates Ca²⁺ levels in muscle cells
Vesicle transporters (packages)
Lipid bilayers / allow separation from the cytosol
Involved in metabolism / transport / enzyme storage / buoyancy control
Eg. Vacuoles (plant cells) / lysosomes / transport vesicles / secretory vesicles / gas vesicles (bacteria, planktonic)
Macromolecular Transport Mechanisms (4)
Endocytosis
Phagocytosis
Pinocytosis
Receptor-Mediated Endocytosis
Endocytosis
Cell engulfing substances
Phagocytosis
engulfing large particles (e.g., immune cells ingesting bacteria)
Pinicytosis
uptake of fluids and dissolved substances
Receptor-Mediated Endocytosis
selective uptake via receptors (e.g., LDL cholesterol intake)
Exocytosis definition
Releasing substances outside of the cell
Exocytosis (2)
Constitutive exocytosis
Regulated exocytosis
Constitutive exocytosis
Continuous vesicle fusion for membrane protein delivery
Regulated exocytosis
Triggered by signals (eg. Neurotransmitter release from neurones)
Lysosomes Function
Waste disposal system (acid hydrolyse enzymes)
Endocytosis (endosomes - pH 6.2-6.3 / recycling of receptor)
