Lecture 1: Fluid Compartments, Homeostasis, and Feedback Systems

These flashcards cover key concepts related to fluid compartments, homeostasis, feedback systems, and the electrical properties of neurons highlighted in Lecture 1.

Homeostasis

The physiological variables in a state of dynamic constancy, it is NOT a static process

Feedback Systems

Mechanisms that help regulate homeostasis by responding to changes in the body, including negative and positive feedback.

Ionic Basis of Action Potentials

The movement of ions across the neuronal membrane that creates an action potential.

Fluid Compartments

The various areas in the body where fluids are contained, such as intracellular fluid and extracellular fluid.

Negative Feedback

A feedback system where the response moves in the opposite direction of the stimulus, helping to stabilize physiological changes.

Positive Feedback

A feedback system that enhances or accelerates the original stimulus until a specific event is completed.

Resting Membrane Potential

The voltage difference across a membrane at rest, typically around -70mV in neurons.

Graded Potential

A potential change of variable amplitude and duration that is conducted decrementally, having no threshold or refractory period.

Action Potential

A brief all-or-none depolarization of the membrane, which reverses polarity in neurons and has a threshold and refractory period.

Electrolyte Balance

The distribution and concentration of ions in the body fluids, crucial for maintaining membrane potentials and cellular functions.

Intracellular Fluid

Fluid contained within cells, making up about two-thirds of total body water.

Extracellular Fluid

Fluid outside cells, including interstitial fluid and plasma, contributing to one-third of total body water.

Depolarization

A decrease in the membrane potential, making it more positive and closer to the threshold for triggering an action potential.

Hyperkalemia

A condition characterized by elevated levels of potassium in the blood, which can affect resting membrane potential and excitability of cells.

Threshold Potential

The membrane potential at which an action potential is initiated, typically around -55mV for neurons.

Membrane Permeability

The ability of ions to pass through the cell membrane, which influences resting and action potentials.

What is physiology

Study of FUNCTION

Function and INTEGRATION

Why is it important that there are different concentrations of sodium ions in and outside of cells

More Na+ OUTSIDE than inside

Makes inside more Negatively charged

Allows for action potential/nerve impulses → contractions

Regulated cell volume/prevent bursting

Secondary active transport for glucose, amino acids, calcium

Blood is part of which fluid compartment?

Plasma

Interstitial fluid and plasma are both considered extracellular

fluid and thus have similar ionic components.

True

Circulatory system

Circulatory System

Major organs/tissues: Heart, blood vessels, blood

Primary functions: Transport of blood throughout the body

Digestive System

Major organs/tissues: Mouth, salivary glands, pharynx, esophagus, stomach, small & large intestines, anus, pancreas, liver, gallbladder

Primary functions: Digestion and absorption of nutrients and water; elimination of wastes

Endocrine System

Major organs/tissues: Pituitary, thyroid, parathyroid, adrenals, pancreas, ovaries/testes, hypothalamus, pineal gland

Primary functions: Regulation and coordination of body activities (growth, metabolism, reproduction, blood pressure, electrolytes)

Musculoskeletal System

Major organs/tissues: Bones, cartilage, ligaments, tendons, joints, skeletal muscle

Primary functions: Support, protection, movement; blood cell production

Nervous System

Major organs/tissues: Brain, spinal cord, peripheral nerves, ganglia, sense organs

Primary functions: Rapid regulation and coordination; sensation, response to stimuli, consciousness, learning, memory

Reproductive System

Male organs/tissues: Testes, penis, ducts, glands

Female organs/tissues: Ovaries, fallopian tubes, uterus, vagina, mammary glands

Primary functions:

Male: Production and transfer of sperm

Female: Production of eggs; support and nourishment of embryo/fetus and infant

Respiratory System

Respiratory System

Major organs/tissues: Nose, pharynx, larynx, trachea, bronchi, lungs

Primary functions: Gas exchange (O₂ and CO₂); regulation of blood pH

Urinary System

Urinary System

Major organs/tissues: Kidneys, ureters, bladder, urethra

Primary functions: Regulation of plasma composition; excretion of water, ions, and wastes

Fluid Compartments in the Body

7% Plasma

26% Interstitial Fluid

67% Intracellular Fluid

intracellular

Fluid within cells (e.g., cytoplasm); makes up about 2/3 of total body water.

Extracellular

Fluid outside cells; includes interstitial fluid and plasma, which have similar composition; makes up about 1/3 of total body water.

Fluid Compartments in the Body: Why do we care?

Cells only work if their fluid environment is stable.

It explains what happens when patients get IV fluids

Edema, dehydration, and shock all come down to fluid shifts

Drugs and electrolytes depend on compartments

negative feedback

Why:
The drop in body temperature triggers responses (vasoconstriction, curling up, shivering) that oppose the initial change by:

• decreasing heat loss

• increasing heat production

These responses return body temperature toward its original value, which is the defining feature of negative feedback.

👉 Key rule to remember:

• Negative feedback = reverses the change

• Positive feedback = amplifies the change

If the amount of sodium in the blood decreases, what would a negative feedback control mechanism be expected to do?

A) Increase the amount of sodium in the blood

Negative Feedback Systems

increase or decrease in variable → response moves it in opposite direction

Positive Feedback Systems

accelerated process, explosive system, ends when stimulus is gone

Negative feedback loop Ex. blood sugar DESCRIBE

Positive feedback loop: labor & delivery DESCRIBE

Which of the following is an example of homeostasis?

none of the above