Principles of Physiology II 8.16 Flashcards
Metabolic Clearance Rate
- 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.
Half Life
Half-life (t1/2) is the time it takes for half of a substance to disappear from the plasma.
Relationship between MCR and half-life
High MCR = short half-life
Factors that influence half-life
- Chemical class.
- Size
- Plasma protein binding
- Renal handling
Simple Diffusion
(Passive - downstream): Rate of movement proportional to concentration difference and permeability.
Facilitated Diffusion
(Passive - downstream): Rate of movement proportional to concentration difference and permeability.
Active Transport
“Pumps” can move substances “upstream” against a concentration gradient.
Ion Channels
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).
Sodium ATP-ase
Pump that pushes 3 Na into its high gradient (extracellular), and pushes 2 K+ into its high gradient (cellular)
Osmolarity
Total (osmotically active) solute concentration (Osm/Liter of liquid)
Osmolality
Total (osmotically active) solute concentration (Osm/Kg of water). Used in clinical context.
Oncotic Pressure
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.
Osmosis
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.
Hematocrit
Ration of RBCs over total blood volume
Cardinal rule of free molecules (oxygen) in plasma
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.)
Compliance
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”
Compliance in veins vs arteries
Veins - high
Arteries - low
Surface Tension
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
Role of surfactant in lungs
– 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.
Surfactant in premature infants
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.
Series vs. Parallel vessels
Series increases resistance
Parallel decreases resistance
(hence decrease in BP in pregnancy, parallel vessels from placenta)
Gluconeogenesis
Generation of glucose from non- carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids. Liver major site.
Glycogenolysis
is the breakdown of stored glycogen (n) to glucose-6-phosphate and glycogen (n-1).
Lypolysis
the breakdown of fats and other lipids by hydrolysis to release fatty acids
Ketogenesis
Ketone bodies produced by the breakdown of fatty acids and ketogenic amino acids.
Glycolysis
Break down of glucose to form pyruvate with the production of two molecules of ATP.
Glycogenesis
Synthesis of glycogen; glucose molecules are added to chains of glycogen for storage.
Glomerular filtration
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
Tubular secretion
Tubular secretion is the transfer of materials from peritubular capillaries to the renal tubular lumen; it is the opposite process of reabsorption.
Tubular reabsorption
Tubular reabsorption is the process by which solutes and water are removed from the tubular fluid and transported into the blood.
Role of creatinine in GFR
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).
Renal Control of Reabsorption and Secretion
- Small molecules like ions are readily filtered from the plasma in the glomerulus to the space inside Bowman’s capsule.
- 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.
- 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) - 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.)
Filtered Load
Filtered load = glomerular filtration rate times the solute’s plasma concentration (GFR x [P]).
Transport Maximum
Transport maximum (Tm or Tmax) = point at which increases in concentration of a substance in the renal tubule exceeds its capacity for reabsorption.
Spilling
If the filtered load > the Tm, the substance will “spill” into the urine.
Agonist
a substance that initiates a physiological response when combined with a receptor.
Antagonist
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.
