Homeostasis and Control Systems
What type of feedback loop acts to oppose or counteract a stimulus to maintain physiological stability around a set point?
Negative feedback
Total body water is divided into two major fluid compartments. Which compartment accounts for roughly two-thirds of total body water volume?
Intracellular fluid (ICF)
Which form of passive membrane transport requires helper proteins (such as carriers or channels) to move polar molecules down their concentration gradient without consuming ATP?
Facilitated diffusion
What type of local cell-to-cell communication allows direct electrical and chemical passage between adjacent cells through protein bridges composed of connexons?
Gap junctions
In the reflex arc scenario analysis, which component of the pathway carries the incoming signal from the sensory receptor to the integrating center?
The afferent pathway (or sensory neuron)
According to the Law of Mass Balance, if the total amount of a substance in the body is to remain constant, any gain must be offset by an equal loss. What are the two primary pathways by which the body eliminates or clears a substance?
Excretion and metabolism (or clearance)
Extracellular fluid (ECF) is further subdivided into two main sub-compartments. Name both of these sub-compartments.
Blood plasma and interstitial fluid
According to Fick’s Law of Diffusion, name two factors that are directly proportional to the rate of simple diffusion across a membrane.
Surface area, concentration gradient, or membrane permeability (lipid solubility). (Any two)
Differentiate between autocrine signals and paracrine signals based on their target location.
Autocrine signals act on the same cell that secreted them, whereas paracrine signals diffuse to adjacent/neighboring cells
When red blood cells were placed in a 280 mM solution of urea or glycerine in lab, why did the cells rapidly swell and hemolyze/burst even though the solution was initially isosmotic (280 mOsm)?
Because urea and glycerine are penetrating solutes that diffuse into the cell, creating an osmotic gradient that causes water to follow by osmosis (making the solution hypotonic)
Unlike negative feedback, feedforward control does not wait for a change in a regulated variable to occur. How does a feedforward control system operate?
By anticipating a change and initiating a response before the stimulus/change actually occurs (e.g., salivation before eating)
A solution has a concentration of 400 mOsm/L. Compared to a standard intracellular fluid concentration of 300 mOsm/L, what is the correct osmolarity term for this solution?
Hyperosmotic
What is the fundamental energy source difference between primary active transport and secondary active transport?
Primary active transport directly hydrolyzes ATP, whereas secondary active transport utilizes potential energy stored in an existing electrochemical gradient (established by primary active transport)
In receptor pharmacodynamics, what is the key functional difference between a receptor agonist and a receptor antagonist?
An agonist binds to a receptor and activates it (mimicking the endogenous ligand), whereas an antagonist binds to a receptor and blocks signal activation
During the cellular respiration yeast lab, why did yeast under aerobic conditions produce significantly more CO2 per glucose molecule than under anaerobic fermentation conditions?
Because aerobic respiration completely oxidizes glucose to CO2 and H2O via the Krebs cycle, whereas anaerobic fermentation produces ethanol along with far less CO2 and lower ATP yield
While both represent a state of constancy, how does a physiological "steady state" fundamentally differ from chemical or physical "equilibrium"?
Steady state requires a continuous input of energy to maintain constant conditions, whereas equilibrium requires no energy input
While osmolarity measures total solute concentration, tonicity describes how a solution affects cell volume at equilibrium. Which specific class of solutes determines the tonicity of a solution?
Non-penetrating solutes
Mediated transport exhibits saturation kinetics. What specific term describes the maximum transport rate achieved when all available transport proteins are bound to substrate?
Transport maximum
What physiological regulation model is demonstrated when a single signal/neurotransmitter can either constrict or dilate blood vessels depending entirely on the specific receptor subtype present on the target tissue?
Receptor specificity / tissue-specific response (or target-receptor modulation)
In the taste perception lab, swishing Gymnema sylvestre tea specifically eliminated the ability to taste sweet foods. What mechanism explains why it blocks the sweet sensation without affecting salty or sour tastants?
Gymnemic acid molecules act as competitive antagonists by binding to and blocking the sweet G-protein coupled receptors on taste buds, whereas salt Na+ and sour H+ pass through ion channels
Why is a positive feedback loop inherently incapable of maintaining homeostasis on its own, and what structural component is required to stop it?
It amplifies/reinforces the original stimulus rather than opposing it, and it requires an external event or factor outside the loop to terminate it
A red blood cell (300 mOsm/L of non-penetrating solutes) is placed in a solution containing 200 mM NaCl (non-penetrating) and 150 mM urea (penetrating). At equilibrium, will the cell swell, shrink, or remain unchanged?
Shrink. (Explanation: NaCl dissociates into 400 mOsm/L of non-penetrating solute in ECF vs. 300 mOsm/L non-penetrating in ICF; water moves out of the cell).
The resting membrane potential is largely maintained by Na+/K+-ATPase pumps. In what direction do each of these ions move and at what mV charge is the typical resting membrane potential maintained?
Na+ ions pumped OUT of the cell and K+ ions pumped INTO the cell, with a -70mV charge maintained inside the cell
How does tonic control differ from antagonistic control in the autonomic regulation of an organ system?
Tonic control uses a single input signal that continuously varies in frequency (up or down regulation), whereas antagonistic control uses two distinct inputs with opposing effects (e.g., sympathetic vs. parasympathetic)
Why can't human physiological ATP production be accurately estimated using CO2 output as a direct proxy measurement in the same simple way it was measured for yeast in lab?
Because humans use multiple metabolic pathways and substrates (fats, proteins, carbohydrates), and CO2 produced in tissues is buffered in the blood as bicarbonate HCO3 rather than being directly released as a proportional gas volume