Pharmacology · chapter 4 · Introduction to Homeostasis
Maintaining Homeostasis
The 13 things this section of the textbook says that you are most likely to be asked about — quoted word for word, not retold. Then 6 practice questions with the reasoning.
Key points
Disease as a homeostasis breakdown
Most medical conditions can be attributed to a breakdown in the homeostatic control system, whether it is due to an inability to detect external changes, failure to initiate a feedback loop, inability to respond to or return to the set point, or failure in the set point itself.
The goal of care
The primary objective of health care providers is to restore the body’s homeostasis to prevent cellular death and irreversible organ damage.
Balance within a narrow range
Even when the external environment fluctuates, the body strives to keep this balance within a narrow range. However, a temporary transient change can occur before the body returns to a steady state.
Why the narrow range matters
Changes in the extracellular or intracellular fluid compartments can occur due to internal or external factors and are crucial for maintaining a narrow range to prevent cell death, tissue damage, and organ dysfunction (Libretti Puckett, 2023).
Physiologic disturbances affect homeostasis
Factors Impacting Homeostasis Disturbances in physiologic factors can have a significant impact on the body’s ability to maintain homeostasis.
When osmotic equilibrium is achieved
It is achieved when the osmotic pressure of a solution is equal to the hydrostatic pressure on the solution.
Osmotic pressure pulls fluid back in
Unlike hydrostatic pressure, which pushes fluid out of the capillaries, osmotic pressure pulls fluid back into them.
What the balance protects
This balance ensures that the optimal concentrations of electrolytes and nonelectrolytes are maintained in cells, body tissues, and interstitial fluid.
Transient changes shift water and solutes
Transient changes in the body, such as changes in temperature or pH, can disrupt the osmotic equilibrium, leading to a shift of water and solutes between intracellular and extracellular fluid compartments in an attempt to restore balance.
The sodium-potassium pump
The Na + K + ATPase pump (also referred to as the sodium-potassium-ATPase pump) is an essential component in maintaining osmotic equilibrium (Pirahanchi et al., 2023).
Which way the pump moves ions
This pump moves sodium ions out of the cell and potassium ions into the cell, against their concentration gradients.
The pump needs energy from ATP
This active transport process requires energy from adenosine 5-triphosphate (ATP), an energy molecule (Hoorm et al., 2020).
Why osmotic equilibrium matters
Osmotic equilibrium is essential for maintaining proper functioning of cells and body tissues.
Terms to know
- Osmotic equilibrium
- Osmotic Equilibrium Osmotic equilibrium occurs when the concentration of solutes on either side of a semipermeable membrane is equalized.
- oncotic pressure
- The force that causes the reabsorption of fluid from the interstitial fluid into the capillaries is known as osmotic pressure or oncotic pressure.
- homeostasis
- Maintaining Homeostasis The human body maintains a state of internal balance, called homeostasis, that is regulated at the cellular level.
Practice questions
Stuck on select-all-that-apply? How to take them one option at a time.
The graded version needs JavaScript. Every question is below anyway, with the answer and why.
Every question here, with the answer
A nursing student asks which force pulls fluid from the interstitial space back into the capillaries. What is the nurse's best answer?
- Active transport by the sodium-potassium pump
- Hydrostatic pressure
- Osmotic (oncotic) pressure
- Gravity
Answer: Osmotic (oncotic) pressure
Osmotic, or oncotic, pressure reabsorbs fluid from the interstitial fluid into the capillaries. Hydrostatic pressure does the opposite and pushes fluid out, and the sodium-potassium pump moves ions across cell membranes.
Which statement about the Na+ K+ ATPase pump is correct?
- It works without energy because ions follow their concentration gradients.
- It moves only water, not ions.
- It moves sodium out of the cell and potassium into the cell, using energy from ATP.
- It moves sodium into the cell and potassium out of the cell.
Answer: It moves sodium out of the cell and potassium into the cell, using energy from ATP.
The pump moves sodium out of and potassium into the cell against their concentration gradients, which is active transport requiring ATP. Because it works against the gradients, it cannot work without energy.
A nurse is reviewing disturbances that can impair the body's ability to maintain homeostasis. Which are included? Select all that apply.
- Disturbances in sodium, potassium and calcium levels
- Dysregulation of pH and cortisol
- A change in the client's hair colour
- Fluctuations in glucose levels
- Wearing glasses
Answer: Disturbances in sodium, potassium and calcium levels, Dysregulation of pH and cortisol, Fluctuations in glucose levels
The section lists disruptions in energy and nutrient balance such as glucose fluctuations, dysregulation of immune response modulators such as pH and cortisol, and disturbances in fluid and electrolyte levels. Hair colour and glasses are not physiologic disturbances of homeostasis.
A client has a high fever. The nurse knows this transient change can affect fluid balance. What happens as a result?
- The sodium-potassium pump stops permanently.
- Nothing, because temperature does not affect fluid balance.
- Hydrostatic pressure disappears from the capillaries.
- Osmotic equilibrium is disrupted and water and solutes shift between compartments.
Answer: Osmotic equilibrium is disrupted and water and solutes shift between compartments.
Transient changes such as changes in temperature or pH can disrupt osmotic equilibrium, shifting water and solutes between the intracellular and extracellular compartments to restore balance. The other options are not described in the section.
Which statements describe how a breakdown in the homeostatic control system can lead to disease? Select all that apply.
- Inability to detect external changes
- An increase in the number of feedback loops
- Inability to return to the set point
- Failure to initiate a feedback loop
- Failure in the set point itself
Answer: Inability to detect external changes, Inability to return to the set point, Failure to initiate a feedback loop, Failure in the set point itself
Most medical conditions come from an inability to detect changes, failure to start a feedback loop, inability to respond or return to the set point, or failure in the set point itself. An increased number of feedback loops is not named as a cause.
What is the primary objective of health care providers when a client's homeostasis is disrupted?
- To raise the osmotic pressure above the hydrostatic pressure
- To stop the sodium-potassium pump
- To remove all transient changes permanently
- To restore homeostasis and prevent cellular death and irreversible organ damage
Answer: To restore homeostasis and prevent cellular death and irreversible organ damage
The primary objective is to restore homeostasis to prevent cellular death and irreversible organ damage. Transient changes are a normal part of returning to a steady state, and the other options would disrupt balance.
Where every quote comes from
Section 4.3 Maintaining Homeostasis of Pharmacology for Nurses by Tina Barbour-Taylor, Leah Mueller (Sabato), Donna Paris, Dorie Weaver, OpenStax, 2024. Read the whole section free at openstax.org.
The textbook is licensed under CC BY-NC-SA 4.0. This page quotes it word for word and adds the headings, the order and the practice questions; references to the book's figures and stray spaces left by its formatting are removed. The page is shared under the same licence. Nothing here is sold.