Physiology Flashcards
Homeostasis
The state of physiological equilibrium and the processes involved maintain it
It involves control pathways that integrate sensory (input) and effector (output) information in order to respond to a challenge or to remain in a physiological steady state
Physiological steady state
A steady internal, physical, and chemical balance within the different cellular components of the body
Thermoregulation
The homeostatic process by which our body regulates its core temperature
Negative feedback
When some variable triggers a counteracting response in order to come back to some set point (to achieve homeostasis)
Positive feedback
When instead of getting a counteracting response to some variable you instead intensify the variable
Osmosis
The process by which water flows across a semi-permeable membrane down its concentration gradient
Hypertonic
A solution with a higher concentration of solutes than the cell it is being compared to; causes water to flow out of the cell and the cell shrinks
E.g. saltwater
Hypotonic
A solution with a lower concentration of solutes than the cell. It is being compared to; causes water to move into the cell which swells and possibly bursts
E.g. distilled water
Isotonic Solution
When the solution has the same concentration of solutes as the cells it is being compared to; results in no net movement of water across the cell membrane
E.g. normal saline
Water Potential ψ
The measurement of potential energy and water, considering both solute potential and pressure potential
Water Potential formula
Ψ = Ψp + Ψs
Water potential = pressure potential (lowering pressure lowers pressure potential) + solute potential (adding solute lowers solution potential)
Water travels to the lower water potential
Tonicity
The effective osmolarity and is equal to the sum of the concentrations of the solutes which have the capacity to exert an osmotic force across the membrane (i.e. it depends on the concentration of impermeant solutes)
Total body water
The total amount of fluid or water within one body; correlates inversely with body fat
60% for men on average
55% for women on average (usually due to a higher percentage of adipose tissue)
Extracellular fluid volume
Fluid outside of cells which comprises about 1/3 of the body’s total body fluid
Intracellular fluid volume
Fluid found inside cells which comprises about 2/3 of the body’s total body fluid
Plasma volume
Fluid in circulation which comprises about 20% of the ECF volume
Interstitial fluid volume
The fluid between cells which comprises about 80% of the total ECF volume
Concentrations of the main electrolytes within extracellular spaces
Sodium 145 mmol/L (main ECF cation) Potassium 4 mmol/L Calcium 2.5 mmol/L Chloride 115 mmol/L (main ECF anion) Bicarbonate 28 mmol/L
Sodium potassium pumps
Transports three sodium molecules out of the intracellular space and in exchange, moves to potassium molecules into the intracellular space
Requires ATP
Main electrolyte concentrations within intracellular fluid
Sodium 12 mmol/L Potassium 155 mmol/L (main ICF cation) Calcium <0.5 mmol/L Chloride 4 mmol/L Phosphorus 105 mmol/L (main ICF anion)
Electrolyte concentration comparison between ECF and ICF
ECF/ICF (mmol/L)
Na+ 145/12
K+ 4/155
Ca²+ 2.5/<0.5
Cl- 115/4
Interstitial space
The fluid that bathes the outside of the cells, and through which substances pass when traveling from plasma to intracellular spaces and vice versa
Hypovolemic hypernatremia
Decreased plasma volume and increased plasma sodium concentration which is caused by fluid loss
Ouabain
A drug that blocks the NA+/K+ ATPase pump.
This causes cells to swell due to the larger hydration shell for sodium (6-8 water molecules/Na molecules than for potassium (3-5)
Normal saline
Made by adding 9 g of NaCl to a liter (1 kg) of water, resulting in a 0.154 M solution. When the NaCl totally dissociates in the body, the final concentration will be approx. 308 mOsm/L (higher than human baseline of 285-290)
The solution is both isomatic and isotonic. When administered intravenously, it does not change the concentration of the ECF compartment.
Normal NaCl concentration in humans
285-290 mOsm/L
5% Dextrose in water (D5W)
An intravenous solution made by adding 5 g of dextrose (r-glucose) to 100 mL of water or 50 g per liter
Dextrous has a MW of 180 g/mole, so D5W is 277 mM [(50 g/L)/(180g/mol)]
What does the infusion of D5W do to the total body water concentration?
While D5W is considered to be isotonic with plasma, shortly after it is administered, the glucose will be metabolized to CO2 and water (in the abscene of diabetes). This results in a rapid decrease in plasma concentration, so water will move from ECF to ICF
The most effective way to decrease intracellular osmolarity and increase intracellular volume.
Provides free water for the kidneys, aiding renal extraction of solutes and may be used to treat hypernatremia
Mannitol
Mannitol is an isomer of sorbitol (a sugar alcohol) and a hyper osmolar agent that is easily filtered by the glomerulus of the kidney. Does not enter the intracellular compartment
Increases urinary output since it is not reabsorbed by the renal tubules, thus promoting water and salt excretion (osmotic diuretic effect)
Can be used as an osbianic agent to lower intracranial pressure in the context of acute brain injury to prevent cerebral edema. It increases extracellular osmolality by raising plasma colloid osmotic pressure to help remove water from the brain
Water ingestion above required daily amount
Will result in decreased plasma osmolality, and thus decreases antidiuretic hormone (ADH) release from the pituitary leading to increased diuresis
Where are changes in plasma osmolality detected?
Receptors within the hypothalamus, which induce the need to drink (thirst) when osmolar concentrations too high
Capillary filtration
Fluid moves out of the capillary
Capillary reabsorption
Fluid moves back into the capillary
Hydrostatic pressure
The driving force exerted by fluid, and the main determinant of capillary filtration
Osmotic pressure
Determined by osmotic concentration gradients, i.e. The difference in the solute to water concentrations in the blood and tissue fluid
Drives capillary reabsorption
Starling equation
Q = Kf * [(Pc - Pi) - σ(πc - πi )]
Q = rate of fluid movement Kf = permeability coefficient Pc = hydrostatic pressure in the capillary Pi = hydrostatic pressure in the interstitial space σ = colloid reflection coefficient πc = colloid osmotic pressure in the capillary πi = colloid osmotic pressure in the interstitial space
Permeability coefficient
(Kf in the Starling equation)
Membranes permeability to water per surface area
Albumin
The most abundant protein in plasma
Colloid reflection coefficient
(σ in the Starling equation)
Just takes into account the ease with which large particles can cross the membrane
A high reflection coefficient (~1) represents very minimal or no crossing of proteins from the blood into the interstitium (e.g. glomerular capillaries in the kidneys, which prevent protein loss in the urine)
A low reflection coefficient (~0) represents increased permeability to proteins (e.g. capillaries in the liver - hepatic sinusoids - to allow free protein movement across the capillary bed)
Capillary hydrostatic pressure
(Pc in the Starling equation)
Drops from around 30 mmHG to 10 mmHG during capillary exchange. This is mainly due to the large cross-sectional area of the capillaries
Donnan effect
The force exerted by the negative charge of proteins favoring fluid retention within the capillary by attracting and concentrating osmotically active cations such as sodium and potassium
Interstitial gel matrix (IGM)
A network of fine proteoglycan filaments that form a gel-like amorphous structure within the interstitium.
Fluid diffuses slowly through the gel, except for when the gel matrix is compressed, like during muscle contractions, and water moves freely again
