Physiology

Question 1

Homeostasis

Answer 1

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

Question 2

Physiological steady state

Answer 2

A steady internal, physical, and chemical balance within the different cellular components of the body

Question 3

Thermoregulation

Answer 3

The homeostatic process by which our body regulates its core temperature

Question 4

Negative feedback

Answer 4

When some variable triggers a counteracting response in order to come back to some set point (to achieve homeostasis)

Question 5

Positive feedback

Answer 5

When instead of getting a counteracting response to some variable you instead intensify the variable

Question 6

Osmosis

Answer 6

The process by which water flows across a semi-permeable membrane down its concentration gradient

Question 7

Hypertonic

Answer 7

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

Question 8

Hypotonic

Answer 8

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

Question 9

Isotonic Solution

Answer 9

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

Question 10

Water Potential ψ

Answer 10

The measurement of potential energy and water, considering both solute potential and pressure potential

Question 11

Water Potential formula

Answer 11

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

Question 12

Tonicity

Answer 12

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)

Question 13

Total body water

Answer 13

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)

Question 14

Extracellular fluid volume

Answer 14

Fluid outside of cells which comprises about 1/3 of the body’s total body fluid

Question 15

Intracellular fluid volume

Answer 15

Fluid found inside cells which comprises about 2/3 of the body’s total body fluid

Question 16

Plasma volume

Answer 16

Fluid in circulation which comprises about 20% of the ECF volume

Question 17

Interstitial fluid volume

Answer 17

The fluid between cells which comprises about 80% of the total ECF volume

Question 18

Concentrations of the main electrolytes within extracellular spaces

Answer 18

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

Question 19

Sodium potassium pumps

Answer 19

Transports three sodium molecules out of the intracellular space and in exchange, moves to potassium molecules into the intracellular space

Requires ATP

Question 20

Main electrolyte concentrations within intracellular fluid

Answer 20

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)

Question 21

Electrolyte concentration comparison between ECF and ICF

Answer 21

ECF/ICF (mmol/L)

Na+ 145/12

K+ 4/155

Ca²+ 2.5/<0.5

Cl- 115/4

Question 22

Interstitial space

Answer 22

The fluid that bathes the outside of the cells, and through which substances pass when traveling from plasma to intracellular spaces and vice versa

Question 23

Hypovolemic hypernatremia

Answer 23

Decreased plasma volume and increased plasma sodium concentration which is caused by fluid loss

Question 24

Ouabain

Answer 24

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)

Question 25

Normal saline

Answer 25

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.

Question 26

Normal NaCl concentration in humans

Answer 26

285-290 mOsm/L

Question 27

5% Dextrose in water (D5W)

Answer 27

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)]

Question 28

What does the infusion of D5W do to the total body water concentration?

Answer 28

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

Question 29

Mannitol

Answer 29

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

Question 30

Water ingestion above required daily amount

Answer 30

Will result in decreased plasma osmolality, and thus decreases antidiuretic hormone (ADH) release from the pituitary leading to increased diuresis

Question 31

Where are changes in plasma osmolality detected?

Answer 31

Receptors within the hypothalamus, which induce the need to drink (thirst) when osmolar concentrations too high

Question 32

Capillary filtration

Answer 32

Fluid moves out of the capillary

Question 33

Capillary reabsorption

Answer 33

Fluid moves back into the capillary

Question 34

Hydrostatic pressure

Answer 34

The driving force exerted by fluid, and the main determinant of capillary filtration

Question 35

Osmotic pressure

Answer 35

Determined by osmotic concentration gradients, i.e. The difference in the solute to water concentrations in the blood and tissue fluid

Drives capillary reabsorption

Question 36

Starling equation

Answer 36

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

Question 37

Permeability coefficient

Answer 37

(Kf in the Starling equation)

Membranes permeability to water per surface area

Question 38

Albumin

Answer 38

The most abundant protein in plasma

Question 39

Colloid reflection coefficient

Answer 39

(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)

Question 40

Capillary hydrostatic pressure

Answer 40

(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

Question 41

Donnan effect

Answer 41

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

Question 42

Interstitial gel matrix (IGM)

Answer 42

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