Human Physiology unit 1 flashcards

What is homeostasis and why is it important?

Keeping internal conditions stable so cells and organs can function properly.

How does negative feedback maintain homeostasis?

It detects a change and reverses it, bringing the body toward its set point.

What are the main parts of a feedback loop?

Receptor senses → control center decides → effector acts.

Give an example of negative feedback.

BP drops → baroreceptors alert brain → heart rate rises → BP is restored.

How does positive feedback differ from negative feedback?

Positive increases the change; negative reverses the change toward normal.

What are helpful examples of positive feedback?

Childbirth, blood clotting, protein digestion, and nerve signals.

What is a harmful example of positive feedback?

Runaway fever: the change keeps worsening instead of returning toward normal.

What is a gradient?

A difference in concentration, charge, temperature, or pressure between areas.

What does moving DOWN a gradient mean?

Moving from high → low.

What does moving UP a gradient mean?

Moving low → high; this usually requires energy.

What are the main physiological gradients and how they apply to different areas of human physiology?

Pressure gradient → moves fluids, like blood or air
Concentration gradient → moves substances from high → low concentration
Electrical gradient → moves charged particles based on charge
Electrochemical gradient → combines concentration + electrical gradients
Thermal gradient → heat moves from warmer → cooler areas

How are phospholipids arranged in the plasma membrane?

A bilayer: hydrophilic heads face water; hydrophobic tails face inward.

What do phospholipids do in the membrane?

Form the bilayer and move laterally, helping keep the membrane fluid.

What does cholesterol do in the membrane?

Holds phospholipids more still and can stiffen the membrane.

What do glycolipids do?

Help form the glycocalyx, the carbohydrate coating on the cell surface.

What jobs do the proteins in the cell membrane do?

• Receptors → receive chemical signals.

• Enzymes → help chemical reactions happen.

• Channels/carriers → help substances cross the membrane.

• Gated channels → channels that open only when triggered.

• Pumps → use energy to move substances across the membrane.

• Cell-ID markers → identify the cell.

• CAMs → attach cells to other cells or surrounding material.

What is the glycocalyx and what does it do?

Fuzzy outer cell layer that protects cells and acts as an ID tag and helps recognize self vs. foreign.

What does selectively permeable mean?

The membrane allows some substances through but blocks others.

What is passive transport?

Movement that requires NO ATP.

What are the types of passive transport?

Filtration, simple diffusion, facilitated diffusion, and osmosis.

How do the passive transport mechanisms compare?

Filtration → pressure pushes particles through a membrane.

Simple diffusion → particles move high concentration → low concentration on their own. No carrier protein is needed.

Facilitated diffusion → solutes move high → low using a carrier

Osmosis → specifically the movement of water. Water moves high water concentration → low water concentration, toward the side with more solute.

All require no ATP.

What is filtration?

Pressure pushes water and small particles through a membrane; no ATP needed.

What is simple diffusion?

Particles move high → low concentration without ATP or a carrier.

What increases or decreases the rate of simple diffusion?

faster diffusion→ Higher temperature, steeper concentration gradient, larger surface area, and greater permeability

slower diffusion→ Higher molecular weight

What is facilitated diffusion?

A carrier moves a solute high → low concentration; no ATP is needed.

Which transport methods are carrier-mediated?

Facilitated diffusion, primary active transport, and secondary active transport.

What does specificity of a carrier mean?

A carrier only binds certain solutes; like a glucose carrier binding glucose.

What does saturation of carriers mean?

All carriers are occupied, so transport cannot get faster.

What is a uniport?

A carrier that moves one type of solute.

What is a symport?

Moves two or more solutes together in the same direction; cotransport.

What is an antiport?

Moves two or more solutes in opposite directions; countertransport.

What is primary active transport?

A carrier directly uses ATP to move a solute from low → high concentration.

What is an example of primary active transport?

The Na⁺/K⁺ pump moves three Na⁺ out and two K⁺ in using ATP.

What is secondary active transport?

It uses ATP indirectly. Another pump creates a gradient that provides the energy for transport.

How do active and passive transport differ?

Passive does not require ATP. Active requires ATP directly or indirectly.

What is vesicular transport?

ATP-powered transport that uses vesicles to move material into or out of a cell.

Which transport methods require vesicles?

Endocytosis and exocytosis.

What is endocytosis vs. exocytosis?

Endocytosis brings material into the cell. Exocytosis sends material out of the cell.

What are the types of endocytosis?

Phagocytosis, pinocytosis, and receptor-mediated endocytosis.

What are phagocytosis and pinocytosis?

Phagocytosis = cell eating. Pinocytosis = cell drinking.

What is osmosis?

Water moves across a selectively permeable membrane from high → low water concentration, which is the same as low → high solute concentration. No energy is required.

How can cells increase the rate of osmosis?

By using aquaporins, which are special channels that allow water to cross faster.

What is osmolarity?

The amount of nonpermeating solutes per liter of solution. It is a number.

What is tonicity?

How a surrounding solution affects a cell's volume and pressure.

What happens to a cell in a hypotonic solution?

Water enters → cell swells and may burst (lyse).

What happens to a cell in an isotonic solution?

There is no net change in cell volume because the concentrations are equal.

What happens to a cell in a hypertonic solution?

Water leaves → cell shrivels (crenates).

What is the structure and function of DNA?

DNA is a double helix located in the nucleus. It carries genes with instructions for making proteins.

What sugar and bases does DNA contain?

Sugar = deoxyribose. Bases = adenine, guanine, cytosine, and thymine.

How is DNA organized into chromosomes?

DNA wraps around histones → forms chromatin → chromatin packs into chromosomes.

What is the structure and function of RNA?

RNA is a single nucleotide chain mainly found in the cytoplasm. It uses DNA's instructions to help make proteins.

How do DNA and RNA compare?

DNA = double helix, deoxyribose, thymine, mainly nucleus, stores protein instructions. RNA = single chain, ribose, uracil, mainly cytoplasm, helps use DNA's instructions.

What sugar and bases does RNA contain?

Sugar = ribose. Bases = adenine, guanine, cytosine, and uracil.

What are the 5 universal properties of muscle?

• Excitability (responsiveness) → muscle can respond to a stimulus, like a nerve signal.

• Conductivity → muscle can spread that electrical signal along the muscle cell.

• Contractility → muscle can shorten and create force.

• Extensibility → muscle can stretch without being damaged.

• Elasticity → muscle can return to its original shape/length after being stretched.

What are the main characteristics of skeletal muscle?

Voluntary, striated, usually attached to bones, and multinucleated.

How is skeletal muscle organized from largest → smallest?

Muscle → fascicle → muscle fiber/cell → myofibril → myofilament.

What are the types of myofilaments?

Thick, thin, and elastic.

What protein makes up thick filaments?

Myosin. Its heads bind to actin and pull during contraction.

What proteins make up thin filaments?

Actin, tropomyosin, and troponin.

What does actin do?

It contains active sites where myosin heads can bind.

What do tropomyosin and troponin do?

Tropomyosin blocks the binding sites on actin. Ca²⁺ binds to troponin, causing tropomyosin to move.

What protein makes up elastic filaments?

Titin → stabilizes thick filaments, prevents overstretching, and helps the muscle recoil.

What is a sarcomere?

The functional contractile unit of a muscle fiber. It extends from one Z disc → the next Z disc.

What is the A band?

The dark band containing thick filaments and areas where thick and thin filaments overlap.

What is the I band?

The light band containing thin filaments only.

What is the H zone/band?

The middle of the A band containing thick filaments only.

What are the M line and Z disc?

M line = center of the H band. Z disc = anchors thin and elastic filaments.

What happens to sarcomeres during contraction?

Z discs move closer together as thin filaments slide over thick filaments. The filaments themselves do not shorten.

What is the nerve-muscle relationship?

Skeletal muscle needs nerve stimulation to contract. Each muscle fiber is supplied by one motor neuron.

What is the neuromuscular junction (NMJ)?

The synapse where a motor neuron communicates with a skeletal muscle fiber.

What structures are found at the neuromuscular junction?

Axon terminal, ACh vesicles, synaptic cleft, sarcolemma, ACh receptors, and ion channels.

How are muscle cells electrically excitable?

Ions moving in or out of the muscle cell change its electrical charge. If the change is big enough, it starts an action potential (electrical signal).

What are the phases of muscle contraction?

Excitation → excitation-contraction coupling → contraction → relaxation.

What are the 5 steps of excitation at the NMJ?

• Nerve signal arrives → Ca²⁺ channels open and Ca²⁺ enters

• Ca²⁺ causes ACh release

• ACh binds receptors

• Na⁺ enters → end-plate potential

• Voltage-gated Na⁺ channels open → muscle action potential.

What are the steps of excitation-contraction coupling?

Action potential travels down T-tubules → SR releases Ca²⁺ → Ca²⁺ binds to troponin → tropomyosin moves and exposes the binding sites on actin.

What is the sarcoplasmic reticulum (SR)?

A network around the myofibrils that stores and releases Ca²⁺.

Why is Ca²⁺ essential for skeletal muscle contraction?

Ca²⁺ binds to troponin, causing tropomyosin to move so myosin can bind to actin.

What is the sliding filament theory?

Thin filaments slide over thick filaments, shortening the sarcomere. The filaments themselves do not shorten.

What are the steps of cross-bridge cycling?

ATP is broken down and cocks the myosin head →

myosin binds to actin, forming a cross-bridge →

myosin pulls actin during the power stroke →

new ATP binds to myosin, causing it to release actin and repeat the cycle.

What is a cross-bridge?

The connection formed when a myosin head binds to an exposed active site on actin.

What are the steps of muscle relaxation?

Nerve signals stop →

ACh is removed/broken down →

Ca²⁺ is pumped back into the SR →

Ca²⁺ leaves troponin →

tropomyosin covers the actin binding sites again.

What does acetylcholinesterase (AChE) do?

It breaks down ACh so ACh can no longer stimulate the muscle.

What is the length-tension relationship?

The amount of force a muscle produces depends on how stretched or shortened it was before stimulation.

When can skeletal muscle produce the greatest tension?

When it is at its optimal, partially stretched resting length. Too stretched or too shortened = weaker contraction.

What is a muscle twitch?

A quick cycle of muscle contraction and relaxation after stimulation.

What are the phases of a muscle twitch?

Latent period → contraction phase → relaxation phase.

What does threshold mean for a muscle twitch?

The minimum stimulus voltage needed to cause a muscle twitch/contraction.

What can change muscle twitch strength?

Starting muscle length, muscle fiber type, fatigue, temperature, hydration, and stimulus frequency.

What is a motor unit?

One motor neuron and all the muscle fibers it controls.

What is the difference between small and large motor units?

Small motor units = fine control. Large motor units = greater strength and power.

How does a muscle increase contraction strength?

By increasing nerve stimulus voltage and frequency. Higher voltage recruits more motor units; higher frequency can cause temporal summation.

What is multiple motor unit (MMU) summation?

Recruiting more motor units to create a stronger contraction.

What is the size principle?

Small motor units are recruited first. Larger motor units are recruited when more force is needed.

What is wave/temporal summation?

High-frequency stimulation causes twitches to overlap, creating a stronger contraction.

What is the difference between incomplete and complete tetanus?

Incomplete tetanus = some relaxation occurs between contractions.

Complete tetanus = contractions fuse with no relaxation.

What is an isometric contraction?

The muscle develops tension but stays the same length.

What is an isotonic contraction?

The muscle changes length while tension stays constant.

What is the difference between concentric and eccentric contraction?

Concentric = muscle shortens.

Eccentric = muscle lengthens while maintaining tension.

Which type of muscle contraction is most prone to injury?

Eccentric contraction.

What are slow-twitch (Type I) muscle fibers like?

Fatigue resistant, good for endurance, use aerobic respiration, and have lots of mitochondria and myoglobin.