Lecture 2 Flashcards
What advantage does being multicellular give over unicellular in regards to environment? Why? What is this process called.
Unicellular organisms are limited in regards to what environments they can survive in. This is because they depend on the immediate external environment to provide conditions which allow them to survive such as: nutrients, solute concentration, temperature, pH, lack of toxins (including their own waste) and lack of predators.
Multicellular organisms have specialised tissues, organs and organ systems made up of specialised cells which can provide a stable environment inside the body instead of relying on the external environment. Maintaining this is known as homeostasis.
Why must the parameters of the internal environment be kept constant? What is this internal environment known as?
It is important to keep the internal environment of our body constant in order to ensure all cells are supplied the correct nutrients and allow organs and organ systems to work correctly. The internal environment in our bodies is the extracellular fluid (ECF) and it surround individual cells.
What do multicellular organisms still get from the external environment?
Nutrient sources, waste disposal, pathogens, can also be used sometime to help maintain the internal environment (e.g sitting on a hot rock when you are cold). The extracellular fluid provides a pathway for many of these.
How is water in our body divided?
1/3 of total body water in extracellular fluid(ECF), 2/3rds in intracellular fluid (ICF).
Define homeostasis.
Homeostasis is the maintenance of relatively constant conditions in the internal environment despite external or internal changes.
What are some important concentrations in the extracellular fluid and why?
Na+: acts as the main extracellular cation for maintaining membrane potentials and triggering action potentials. Heavily determines the extracellular fluid volume (influences blood pressure) and normal concentration is about 135-145 mmol/L.
Ca2+: important structural component of bone and teeth, involved in neurotransmission and muscle contraction, essential for coagulation, regulates enzyme function and normal concentration in ECF is about 2.2-2.6 mmol/L
Glucose: used by cells (especially neurons, which can’t use many other sources) to produce ATP, high blood glucose causes problems. Has two normal ranges
FASTING: 3.5-6 mmol/L
NON FASTING: 3.5-8.0 mmol/L.
Potassium: The main intracellular cation, main determinant of resting membrane potential and as such must have low extracellular fluid levels, normal concentration of 3.5-5 mmol/L.
What is the normal ECF pH? What occurs if it isn’t at this level?
Normal pH is 7.35-7.45, acidosis (too low pH) decreases neuronal function and can lose to loss of consciousness, alkalosis (to high pH) causes over excitability of nerves and muscle, leading to ‘pins and needles’, muscle spasms and convulsions.
What is the normal core body temperature? Why is this important and is the temperature the same throughout?
Normal core body temperature is from 36-37.5 degrees celsius. This allows for optimal metabolic and physiological functioning. At higher levels proteins denature, at lower levels chemical reactions slow down, preventing normal cells function (nerve cells are particularly vulnerable to this). Peripheral temperature is more variable (as a rule the further away from core areas the lower the temperature).
What is diffusion? Why is it so rapid for cells?
Diffusion is the spreading out of molecules due to random movement of individual molecules due to thermal energy, this leads to high concentration molecules flowing down into low concentration areas. This process is rapid in cells due to the short distances within cells and between the cells and capillaries.
What is passive diffusion?
Diffusion down the concentration gradient, as this is the path the molecules would typically diffuse no energy input is needed.
What molecules can diffuse through the lipid bilayer? What allow molecules which can’t do this to get past (what is waters called)
Lipid soluble (non polar) substances can cross the lipid bilayer without help. water soluble (polar) molecules require channels to allow them in e.g ion channels or in the case of water aquaporins.
What three channel types are there? What other option can be used to passively transport molecules?
Leak channels: open and close spontaneously
Ligand gated: open and close based on stimuli
Voltage gated: open and close based on changes in membrane potential.
Carrier mediated passive transport (facilitated transport) involves the substance binding to a carrier protein, this changes the shape of the carrier protein and allows the substance through.
What is primary active transport? What kind of processes do this? What can they help with?
Active transport uses energy from the hydrolysis of ATP into ADP and inorganic phosphate to move substances against their concentration gradient.
Examples of this are ion pumps (like Na+/K+ ATPase which moves 3 Na+ out for 2 K+ ions in). This can help maintain ionic gradients and regulate cell volume.
Endocytosis (transporting substances into the cell via membranous vesicles, e.g secretion of insulin) and exocytosis (moving substances out of the cell via membranous vesicles e.g phagocytosis).
What is osmosis?
the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration. Water moves across a semi permeable membrane down its own concentration gradient.
What is osmolarity, osmolality and tonicity? How are they related?
Osmolarity is a measure of total number of solute particles per litre (given as osmol/L or mosmol/L), normally about 275-300 mosmol/L in ECF AND ICF.
Osmolality: a measure of total solute numbers per kilogram of solute
Tonicity refers to the effect a solution has on cell volume
Hyper tonic solutions cause shrinkage of cells and typically have high osmolarity, hypotonic solutions cause cells to swell and typically have low osmolarity, isotonic solutions cause no change in cell volume and typically have 275-300 mosmol/L.
A solution doesn’t necessarily have to have high osmolarity to be hypertonic and vice versa.
