Cumulative Physiology Exam

What is homeostasis?

The ability of the body to maintain a relatively constant internal environment.

Why is homeostasis essential for cells?

Because cells require a narrow range for regulated variables like temperature, pH, ion concentrations, and nutrient availability.

What does the body do to maintain regulated variables?

It keeps them within a desired range around a setpoint.

What type of system maintains homeostasis?

A reflex pathway (control system).

What is the first step in a reflex control pathway?

A stimulus.

What does a sensor (sensory receptor) do?

It monitors a regulated variable and detects when it deviates from normal range

What is an afferent signal?

An input signal (chemical or electrical) sent to the integrating center.

What is the integrating center?

The control center that evaluates all input and sends instructions.

What are examples of integrators?

A neuron or an endocrine cell.

What is an effector (target) in a control system?

The component that performs the physiological response — it “fixes the problem.”

What is an efferent signal?

An output signal (chemical or electrical) sent from the integrator to the effector.

What is feedforward control?

A response that occurs in anticipation of change, before feedback occurs.

What is feedback control?

A response that occurs after a change has been detected.

What is negative feedback?

A response that restores the regulated variable back to its normal value.

What is positive feedback?

A response that enhances the change in the regulated variable.

What percentage of body weight is water?

About 60%.

What are the two major fluid compartments in the body?

Intracellular fluid (ICF) and extracellular fluid (ECF).

What are the two subdivisions of ECF?

Plasma and interstitial fluid.

Where is plasma found?

Inside blood vessels.

Where is interstitial fluid found?

Between cells.

Where is most of the water in the body located?

In the ICF (inside cells).

What determines how a solute crosses the cell membrane?

Its size, charge, and concentration.

What is passive transport?

Movement down a gradient without energy input.

What is simple diffusion?

Passive movement directly through the membrane.

What is facilitated diffusion?

Passive movement through a membrane protein.

What is osmosis?

Passive movement of water across a membrane.

What is active transport?

Movement of substances against a gradient using energy.

What is primary active transport?

Direct use of ATP (e.g., Na⁺/K⁺ ATPase pump).

What is secondary active transport?

Indirect use of ATP — one substance moves down its gradient to move another against its gradient.

What is symport?

Two substances move in the same direction.

What is antiport?

Two substances move in opposite directions.

What is osmolarity?

The total concentration of solutes in a solution (mOsM).

What is tonicity?

A functional term describing how a solution affects cell volume.

What does a hypotonic solution do to a cell?

Causes the cell to swell.

What does a hypertonic solution do to a cell?

Causes the cell to shrink.

What does an isotonic solution do to a cell?

No net movement of water — cell volume stays the same.

What creates the resting membrane potential (Vm)?

Ion concentration gradients and membrane permeability.

What is the typical resting Vm in most cells?

Around -70 mV.

What ions are most important in establishing Vm?

K⁺ (most important), Na⁺, and Cl⁻.

How does K⁺ affect Vm?

K⁺ tends to leave the cell, making Vm more negative.

What maintains ion gradients across the membrane?

The Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in).

What does the Goldman equation calculate?

The resting membrane potential (Vm) based on multiple ions.

What factors does the Goldman equation consider?

• Ion concentration gradients (in vs. out)

• Membrane permeability to each ion

What makes the Goldman equation different from the Nernst equation?

It accounts for multiple ions, not just one.

What are the four basic methods of cell-to-cell communication?

• Gap junctions

• Contact-dependent signals

• Paracrine signaling

• Endocrine signaling

What are gap junctions?

Direct cytoplasmic connections between adjacent cells.

What are contact-dependent signals?

Require membrane-bound molecules on both cells to interact.

What are paracrine signals?

Local chemical messengers that act on nearby cells.

What are endocrine signals?

Hormones that travel through the blood to distant targets.

What is a signal transduction pathway?

A process where a ligand binds to a receptor and triggers a cellular response.

What are first messengers?

The extracellular signal molecules (e.g., hormones, neurotransmitters).

What are second messengers?

Intracellular signaling molecules (e.g., cAMP, Ca²⁺, IP₃).

What is amplification in signaling?

A single ligand leads to many intracellular responses.

What are the four major types of membrane receptors?

• Receptor-channel

• G-protein-coupled receptor (GPCR)

• Receptor-enzyme

• Integrin receptor

What does a receptor-channel do?

Opens or closes an ion channel.

What does a GPCR do?

Activates a G-protein, which triggers a second messenger system.

What does a receptor-enzyme do?

Acts as or activates an enzyme, often a kinase.

What does an integrin receptor do?

Alters cytoskeleton and cell adhesion.

What are the three classes of hormones?

• Peptide/protein hormones

• Steroid hormones

• Amine hormones

What are peptide hormones made of?

Chains of amino acids.

Are peptide hormones hydrophilic or hydrophobic?

Hydrophilic (lipophobic) → act on membrane receptors.

Where are steroid hormones derived from?

Cholesterol

Are steroid hormones hydrophilic or hydrophobic?

Hydrophobic → act on intracellular receptors.

What are amine hormones made from?

Tyrosine or tryptophan.

What determines hormone receptor location?

Whether the hormone is lipophilic or lipophobic.

Where do hydrophobic hormones act?

On cytoplasmic or nuclear receptors → alter gene expression.

Where do hydrophilic hormones act?

On membrane-bound receptors → trigger second messenger cascades.

What is a hormone’s half-life?

The time required to reduce the hormone concentration by 50%.

What controls endocrine reflexes?

Negative feedback loops.

What is the simplest endocrine reflex?

A hormone is released in response to a direct stimulus (e.g., blood glucose).

What is the classic endocrine pathway?

Stimulus → endocrine cell → hormone → target → response → feedback

How is hormone secretion stopped?

When the response reduces the stimulus (negative feedback).

What is the hypothalamic-pituitary axis (HPA)?

A complex endocrine pathway involving the hypothalamus, anterior pituitary, and endocrine target.

What are the three integrating centers in the HPA pathway?

• Hypothalamus

• Anterior pituitary

• Target endocrine gland

What is the typical hormone pathway of the HPA axis?

Hormone 1 (hypothalamus) → Hormone 2 (anterior pituitary) → Hormone 3 (endocrine target)

What are the three main parts of a neuron?

• Dendrites – receive incoming signals

• Cell body (soma) – integrates information

• Axon – conducts electrical signal to target

What is the axon hillock?

The site where action potentials are initiated.

What are axon terminals?

The output regions that release neurotransmitters onto target cells.

What is myelin and what does it do?

Insulating sheath that speeds conduction of action potentials.

What is a graded potential?

A small, local change in membrane potential — varies in size.

What is an action potential?

A large, rapid, all-or-none electrical signal along the axon.

What triggers an action potential?

When depolarization reaches threshold at the axon hillock.

What ion is responsible for depolarization?

Na⁺ influx through voltage-gated channels.

What ion is responsible for repolarization?

K⁺ efflux.

Are action potentials graded or all-or-none?

All-or-none — they either happen fully or not at all.

What happens during the absolute refractory period?

A second action potential cannot be initiated — Na⁺ channels are inactivated.

What happens during the relative refractory period?

A stronger-than-normal stimulus can trigger an action potential.

What ensures one-way propagation of the AP?

The refractory periods.

What does myelination allow?

Saltatory conduction — the AP jumps from node to node.

What triggers neurotransmitter release?

Ca²⁺ influx at the axon terminal.

How does Ca²⁺ enter the axon terminal?

Through voltage-gated calcium channels.

What do neurotransmitters do once released?

They bind to receptors on the postsynaptic membrane.

How is the neurotransmitter signal stopped?

By diffusion, enzyme breakdown, or reuptake into the presynaptic cell.

What are ionotropic receptors?

Ligand-gated ion channels that cause fast, short responses.

What are metabotropic receptors?

GPCRs that cause slower, longer-lasting effects via second messengers.

What is an EPSP (excitatory postsynaptic potential)?

A depolarizing graded potential that brings the membrane closer to threshold.

What is an IPSP (inhibitory postsynaptic potential)?

A hyperpolarizing graded potential that moves the membrane away from threshold.

What is spatial summation?

Multiple presynaptic neurons release neurotransmitter at the same time to influence the postsynaptic neuron.

What is temporal summation?

A single presynaptic neuron releases neurotransmitter repeatedly in quick succession.

What happens if EPSPs and IPSPs arrive at the same time?

They cancel each other out, depending on strength.