Principles of Physiology II 8.16

Question 1

Metabolic Clearance Rate

Answer 1

• Substances (like hormones) are “cleared” (metabolized) from the blood.
  – Rate at which this occurs is called the metabolic clearance rate (MCR).
  – The higher the MCR, the faster the material is removed from the blood.

Question 2

Half Life

Answer 2

Half-life (t1/2) is the time it takes for half of a substance to disappear from the plasma.

Question 3

Relationship between MCR and half-life

Answer 3

High MCR = short half-life

Question 4

Factors that influence half-life

Answer 4

1. Chemical class.
2. Size
3. Plasma protein binding
4. Renal handling

Question 5

Simple Diffusion

Answer 5

(Passive - downstream): Rate of movement proportional to concentration difference and permeability.

Question 6

Facilitated Diffusion

Answer 6

(Passive - downstream): Rate of movement proportional to concentration difference and permeability.

Question 7

Active Transport

Answer 7

“Pumps” can move substances “upstream” against a concentration gradient.

Question 8

Ion Channels

Answer 8

Ions are molecules or atoms that are positively or negatively charged. Ion channels create tiny openings in the membrane. They only allow specific ions to pass through (selectivity).

Question 9

Sodium ATP-ase

Answer 9

Pump that pushes 3 Na into its high gradient (extracellular), and pushes 2 K+ into its high gradient (cellular)

Question 10

Osmolarity

Answer 10

Total (osmotically active) solute concentration (Osm/Liter of liquid)

Question 11

Osmolality

Answer 11

Total (osmotically active) solute concentration (Osm/Kg of water). Used in clinical context.

Question 12

Oncotic Pressure

Answer 12

Form of osmotic pressure exerted by proteins, notably albumin, in a blood vessel’s plasma (blood/liquid) that usually tends to pull water into the circulatory system.

Question 13

Osmosis

Answer 13

a process by which molecules of a solvent (typically water) tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane.

Question 14

Hematocrit

Answer 14

Ration of RBCs over total blood volume

Question 15

Cardinal rule of free molecules (oxygen) in plasma

Answer 15

It is the “free” oxygen that can diffuse into the tissues and exert a biological effect in the cells. O2 must dissociate from Hb in the tissues.
IT IS THE FREE (biologically-active) OXYGEN THAT IS HIGHLY REGULATED BY HOMEOSTASIS. (The Hb concentration is also regulated but much more slowly.)

Question 16

Compliance

Answer 16

Compliance is the total volume that can be stored in a container for each unit of pressure.
• Change in volume divided by a change in pressure.
• Gives an idea of the “stiffness” or “distensibility” of a compartment
High compliance is “floppy”
Low compliance is “stiff”

Question 17

Compliance in veins vs arteries

Answer 17

Veins - high

Arteries - low

Question 18

Surface Tension

Answer 18

The intermolecular attraction at the surface of a liquid in contact with air…..tending to pull the molecules of the liquid inward from the surface

Question 19

Role of surfactant in lungs

Answer 19

– Lowers surface tension of air water interface
overall (like a detergent)
– Other unique properties that stabilize alveolar volume that you will learn later in the course.

Question 20

Surfactant in premature infants

Answer 20

Babies born prematurely have inadequate surfactant in their lungs.
– Their lung surface tension is very high.
– The lungs easily collapse as a result and take
an enormous amount of energy to fill with air.

Question 21

Series vs. Parallel vessels

Answer 21

Series increases resistance
Parallel decreases resistance
(hence decrease in BP in pregnancy, parallel vessels from placenta)

Question 22

Gluconeogenesis

Answer 22

Generation of glucose from non- carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids. Liver major site.

Question 23

Glycogenolysis

Answer 23

is the breakdown of stored glycogen (n) to glucose-6-phosphate and glycogen (n-1).

Question 24

Lypolysis

Answer 24

the breakdown of fats and other lipids by hydrolysis to release fatty acids

Question 25

Ketogenesis

Answer 25

Ketone bodies produced by the breakdown of fatty acids and ketogenic amino acids.

Question 26

Glycolysis

Answer 26

Break down of glucose to form pyruvate with the production of two molecules of ATP.

Question 27

Glycogenesis

Answer 27

Synthesis of glycogen; glucose molecules are added to chains of glycogen for storage.

Question 28

Glomerular filtration

Answer 28

Glomerular filtration is the process by which the kidneys filter the blood, removing excess wastes and fluids. Glomerular filtration rate (GFR) is a calculation that determines how well the blood is filtered by the kidneys, which is one way to measure overall kidney function

Question 29

Tubular secretion

Answer 29

Tubular secretion is the transfer of materials from peritubular capillaries to the renal tubular lumen; it is the opposite process of reabsorption.

Question 30

Tubular reabsorption

Answer 30

Tubular reabsorption is the process by which solutes and water are removed from the tubular fluid and transported into the blood.

Question 31

Role of creatinine in GFR

Answer 31

Creatinine is produced by metabolism of creatine and is excreted in the urine.
With some exceptions, creatinine is:
a. Produced at a fairly constant rate in the body.
b. Filtered in the kidney
c. Not reabsorbed and only a small amount is secreted
in the kidney (GFR slightly overestimated).

Question 32

Renal Control of Reabsorption and Secretion

Answer 32

1. Small molecules like ions are readily filtered from the plasma in the glomerulus to the space inside Bowman’s capsule.
2. Most small molecules are primarily reabsorbed into the blood in the early part of the kidney (proximal tubules). This is typically not controlled by hormones.
3. The distal tubule is the site of most fine tuning of the amounts of these substances in the body. Therefore, it is the site of the control of the reabsorption and/or secretion of many substances. For example:
   a. Sodium (controlled by the adrenal hormone aldosterone)
   b. Potassium (controlled by the adrenal hormone aldosterone) c. Calcium (controlled by parathyroid hormone)
4. A major exception is the control of phosphate excretion. Its reabsorption is controlled primarily in the proximal tubule by parathyroid hormone. (PTH actually inhibits phosphate reabsorption in the proximal tubules and leads to an increase in excretion of phosphate.)

Question 33

Filtered Load

Answer 33

Filtered load = glomerular filtration rate times the solute’s plasma concentration (GFR x [P]).

Question 34

Transport Maximum

Answer 34

Transport maximum (Tm or Tmax) = point at which increases in concentration of a substance in the renal tubule exceeds its capacity for reabsorption.

Question 35

Spilling

Answer 35

If the filtered load > the Tm, the substance will “spill” into the urine.

Question 36

Agonist

Answer 36

a substance that initiates a physiological response when combined with a receptor.

Question 37

Antagonist

Answer 37

a substance that interferes with or inhibits the physiological action of another. Typically, an antagonist “blocks” the action of the endogenous agonist at a receptor and makes the body “think” the hormone is low or absent.