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Pharmacology · chapter 4 · Introduction to Homeostasis

What Is Homeostasis?

The 14 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.

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Key points

  1. What homeostasis means

    Homeostasis is the ability of the body to maintain a stable and constant internal environment despite changes in the external environment (Billman, 2020).

  2. Two principles: fluid and electrolyte balance

    Disruption of homeostatic mechanisms may cause diseases and severe impacts on physiologic well-being. Two key principles govern homeostasis: fluid balance and electrolyte balance.

  3. Children dehydrate more easily

    Children are also more likely than older individuals to become dehydrated because their kidneys are less efficient at conserving water.

  4. Children lose more sodium and potassium

    Electrolyte balance in children may be more susceptible to imbalances because of their immature kidneys, resulting in higher renal losses of sodium and potassium.

  5. Pregnancy and edema

    Hormonal changes influence fluid balance, causing the client to be more susceptible to edema and electrolyte imbalances.

  6. Older adults and thirst

    Older adults often have a reduced sense of thirst and may not drink enough fluids, leading to an increased risk for dehydration.

  7. Older adults: sodium and potassium risks

    Age-related changes in the kidneys can also affect water and electrolyte regulation, resulting in a higher risk for imbalances such as hyponatremia (low sodium) and hyperkalemia (elevated potassium).

  8. Three parts of a feedback loop

    It is primarily governed by a feedback loop that involves three key components: the receptor, the control center, and the effector.

  9. The effector carries out the response

    The effector is the part of the body that carries out the response. It could be a muscle, gland, or organ that alters its activity to counteract the initial change detected by the receptor.

  10. Water is 60% of body weight

    Sixty percent of the total body weight is composed of water. The body separates this water into two main fluid compartments: one that contains intracellular fluid and one that contains extracellular fluid.

  11. Fluid loss or retention causes problems

    Disruptions in the fluid compartments, such as excessive fluid loss or retention, can lead to various health problems, including dehydration or edema.

  12. Electrolytes inside the cell

    It contains various electrolytes, such as potassium, magnesium, and phosphate ions, as well as proteins and other molecules essential for cell function.

  13. Electrolytes outside the cell

    Extracellular fluid contains various electrolytes, such as sodium, chloride, and bicarbonate, as well as proteins, hormones, and other molecules.

  14. The third space

    The transcellular compartment, also known as the third space, refers to a small volume of fluid that is contained within certain body cavities and structures, such as the pleural cavity, peritoneal cavity, and joint spaces.

Terms to know

Homeostasis
Homeostasis is the ability of the body to maintain a stable and constant internal environment despite changes in the external environment (Billman, 2020).
osmotic pressure
The concentration of ions, such as sodium, potassium, and chloride, is carefully regulated in each compartment to maintain the proper osmotic pressure, which is the pressure needed to prevent water from flowing into or out of cells.
Extracellular fluid
Extracellular fluid is the fluid that surrounds the cells of the body, including fluid in the blood vessels and the fluid in the spaces between tissues and organs.
anion
Anions An anion is a negatively charged ion, meaning it has more electrons than protons.
cation
Cations A cation is a positively charged ion, meaning it has fewer electrons than protons.
receptor
The receptor is a sensory organ that detects changes in the internal or external environment of the body.

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

  1. An 84-year-old client living alone says, "I just don't feel thirsty anymore, so I only drink with meals." What should the nurse recognise as the main risk?

    1. Hypernatremia from high salt intake
    2. Edema from hormonal changes
    3. Fluid overload
    4. Dehydration

    Answer: Dehydration

    Older adults often have a reduced sense of thirst and may not drink enough, which raises the risk for dehydration. Fluid overload and edema come from retaining fluid, not from drinking too little, and salt intake is not described.

  2. A parent asks why the pediatric nurse is so concerned about fluid intake during their toddler's vomiting illness. Which explanation is accurate?

    1. Children have a smaller proportion of body water than adults.
    2. Children's kidneys are less efficient at conserving water, so they dehydrate more easily.
    3. Children have a lower metabolic rate than adults.
    4. Children's kidneys retain too much sodium and potassium.

    Answer: Children's kidneys are less efficient at conserving water, so they dehydrate more easily.

    Children dehydrate more easily than older individuals because their kidneys are less efficient at conserving water. They have a higher, not lower, metabolic rate and proportion of body water, and their immature kidneys lose sodium and potassium rather than retain them.

  3. Which electrolytes are found mainly in the extracellular fluid, according to the section? Select all that apply.

    1. Chloride
    2. Magnesium
    3. Sodium
    4. Phosphate
    5. Bicarbonate

    Answer: Chloride, Sodium, Bicarbonate

    Extracellular fluid contains sodium, chloride and bicarbonate. Potassium, magnesium and phosphate are listed as the electrolytes of intracellular fluid.

  4. A nurse caring for a pregnant client notes new ankle swelling. Which statement from the section best explains why pregnancy makes this more likely?

    1. Pregnancy increases the sense of thirst.
    2. Pregnancy lowers progesterone levels.
    3. Pregnancy decreases blood volume.
    4. Hormonal changes make the client more susceptible to edema and electrolyte imbalances.

    Answer: Hormonal changes make the client more susceptible to edema and electrolyte imbalances.

    Pregnancy increases blood volume and fluid retention, and hormonal changes make the client more susceptible to edema and electrolyte imbalances. Blood volume rises rather than falls, and progesterone increases.

  5. A nurse is reviewing the parts of a homeostatic feedback loop. Which statements are correct? Select all that apply.

    1. The effector carries out the response.
    2. The control center is always a muscle.
    3. The effector detects the initial change and signals the brain.
    4. The control center is typically located in the brain or nervous system.
    5. The receptor detects a change in the internal or external environment.

    Answer: The effector carries out the response., The control center is typically located in the brain or nervous system., The receptor detects a change in the internal or external environment.

    The receptor detects changes, the control center (usually in the brain or nervous system) processes the signal, and the effector, such as a muscle, gland or organ, carries out the response. Detecting the change is the receptor's job, and the control center is not a muscle.

  6. An older adult's laboratory results are being reviewed. Based on age-related kidney changes, which pair of imbalances is the client at higher risk for?

    1. Hypercalcemia and hypomagnesemia
    2. Hypernatremia and hypokalemia
    3. Hyponatremia and hyperkalemia
    4. Hypophosphatemia and hyperchloremia

    Answer: Hyponatremia and hyperkalemia

    Age-related kidney changes raise the risk for hyponatremia (low sodium) and hyperkalemia (elevated potassium). The other pairs are not named in the section for older adults.

Where every quote comes from

Section 4.1 What Is 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.