Basic Concepts in Physiology 1 – Homeostasis and Body Fluids

Question-and-Answer flashcards covering definitions, mechanisms, examples, and numerical values for homeostasis, feedback loops, fluid balance, and body fluid composition.

What is the definition of homeostasis?

A condition of dynamic equilibrium in the body’s internal environment maintained by many regulatory processes.

Which two body systems primarily maintain homeostasis?

The nervous system (rapid responses) and the endocrine system (slower, hormone-mediated responses).

What are the three basic components of any feedback system?

Receptor, control center, and effector.

How does a negative feedback loop affect a change in a controlled condition?

It reverses the change, returning the variable toward its set point.

How does a positive feedback loop affect a change in a controlled condition?

It strengthens or amplifies the change until an outside event stops the loop.

Give three common physiological examples of negative feedback.

Thermoregulation, regulation of blood pressure/volume, and blood glucose control.

Name two normal physiological examples of positive feedback.

Childbirth (uterine contractions) and blood clotting.

What dangerous situation can arise from a positive feedback loop gone out of control?

Runaway fever with body temperature above 40 °C.

During thermoregulation, which center in the brain acts as the control center?

The hypothalamus.

List four effectors activated when body temperature rises.

Dilation of skin blood vessels, activation of sweat glands, relaxation of arrector pili muscles, and behavioral changes (e.g., removing clothing).

List four effectors activated when body temperature falls.

Constriction of skin blood vessels, inhibition of sweat glands, shivering by skeletal muscles, and secretion of adrenaline and thyroxine.

What is the typical set-point range for normal body temperature?

Approximately 36.5–37.5 °C.

What is the normal fasting blood glucose set point?

About 70–110 mg / 100 mL of blood.

Define dynamic equilibrium.

Internal conditions fluctuate within a limited range around a set point rather than remaining absolutely constant.

Which ion is the principal cation of extracellular fluid (ECF)?

Sodium (Na⁺).

Which ion is the principal cation of intracellular fluid (ICF)?

Potassium (K⁺).

Which anion is most abundant in ECF?

Chloride (Cl⁻).

Which intracellular anion is especially abundant in ICF?

Phosphate ions (HPO₄²⁻/Pi).

How does the sodium–potassium pump (Na⁺/K⁺-ATPase) maintain ion gradients?

It actively transports Na⁺ out of cells and K⁺ into cells, preserving high extracellular Na⁺ and high intracellular K⁺ levels.

State the total body water (TBW) of an average 70-kg adult male.

About 42 L.

What are the volumes of ICF and ECF in a 70-kg male?

ICF ≈ 28 L; ECF ≈ 14 L.

Break down the ECF volume into interstitial fluid and plasma.

Interstitial fluid ≈ 11 L; plasma ≈ 3 L.

Name the two physical barriers that separate major fluid compartments.

Plasma membranes (ICF vs. interstitial fluid) and blood vessel walls (plasma vs. interstitial fluid).

List four specialized subcompartments of ECF.

Cerebrospinal fluid, synovial fluid, aqueous/vitreous humor, and pleural/pericardial/peritoneal fluids.

What is the approximate osmolarity of plasma, interstitial fluid, and ICF?

Each is about 300 mOsm/L.

Why do plasma and interstitial fluid differ in protein content?

Capillary walls have low permeability to plasma proteins, so proteins remain mainly in plasma.

How much water is typically ingested or produced metabolically each day?

About 2100 mL from food/drink plus ≈ 200 mL produced by metabolism.

Identify four daily routes of water loss.

Insensible loss (skin & lungs), sweat, feces, and urine (kidney excretion).

Which organ adjusts water and electrolyte excretion to match intake?

The kidneys.

Describe the direction of water movement when ECF osmolarity increases.

Water moves from ICF to ECF by osmosis.

Describe the direction of water movement when ECF osmolarity decreases.

Water moves from ECF to ICF by osmosis.

How quickly is osmotic equilibrium between ICF and ECF usually restored after a disturbance?

Within seconds to minutes, and body-wide equilibrium is reached about 30 minutes after drinking water.

What small solutes primarily determine water distribution between ICF and ECF?

Electrolytes such as Na⁺, Cl⁻, and other small ions.

Explain capillary filtration in fluid movement.

Water moves from blood plasma to tissue (interstitial) fluid through capillary walls driven by hydrostatic pressure.

How is water absorbed back into the bloodstream from tissues?

By capillary osmotic reabsorption or via the lymphatic system returning fluid to blood.

In childbirth, identify the receptor, control center, output, and effector in the positive feedback loop.

Receptor: stretch-sensitive cervical nerves; control center: brain; output: oxytocin release; effector: uterine muscle contraction.

Why is the endocrine response generally slower than the nervous response in homeostatic regulation?

Because hormones must be synthesized, released into the bloodstream, and transported to target tissues, which takes more time than neural impulses.

Which subdiscipline of physiology studies hormone control of body functions?

Endocrinology.

Which subdiscipline examines functional properties of nerve cells?

Neurophysiology.