Lecture 1 - Intro to Human Physiology

What surrounds each cell to separate it from its environment?

A phospholipid bilayer surrounds each cell.

What are the chemical properties of phospholipid heads?

Phospholipid heads are hydrophilic.

Where does one layer of phospholipid heads face?

One layer faces the extracellular environment.

Where does the other layer of phospholipid heads face?

The other layer faces the intracellular environment.

What are the chemical properties of phospholipid tails?

Phospholipid tails are hydrophobic.

Where do phospholipid tails project within the membrane?

They project toward the center of the cell membrane.

What are phospholipid tails made of?

Fatty acid chains.

Where is cholesterol located in the cell membrane?

Within the central portion of the membrane among phospholipid tails.

How does increased cholesterol affect membrane hydrophobicity?

It increases hydrophobicity.

What role does cholesterol play in membrane fluidity?

It stabilizes membrane fluidity.

How does cholesterol affect membrane fluidity at high temperatures?

It reduces fluidity.

How does cholesterol affect membrane fluidity at low temperatures?

It increases fluidity.

What is the glycocalyx?

A coating on the extracellular side of the cell membrane.

What is the glycocalyx made of?

Glycoproteins and glycolipids (carbohydrates).

What are the functions of the glycocalyx?

Cell communication, protection, and adhesion.

Where can membrane proteins be located?

Either embedded in part of the membrane or spanning the entire membrane.

What are examples of membrane protein types?

Membrane channels, membrane receptors, and adhesion molecules.

Why are phospholipid bilayers described as selectively permeable?

Only certain molecules can pass directly through the membrane.

What types of molecules can pass directly through the membrane?

Small, nonpolar, uncharged molecules.

What causes gradients across cell membranes?

Unequal distribution of ions, water, solutes, and molecules.

Why are gradients important for cellular physiology?

They drive movement across membranes and cellular metabolism.

What types of gradients exist across cell membranes?

Concentration, electrical, electrochemical, and osmotic pressure gradients.

What is passive transport?

Movement of substances along a concentration gradient from higher to lower concentration.

Does passive transport require energy?

No.

What is simple diffusion?

Movement of substances directly through the cell membrane.

What is facilitated diffusion?

Movement of substances across the membrane with assistance from membrane proteins.

What are channel proteins?

Membrane proteins that create tunnels linking intracellular and extracellular spaces.

What types of channel proteins exist?

Voltage-gated, chemical-gated, ligand-gated, and non-gated.

What are aquaporins?

Water channels found in the lens, cornea, and retina.

What are carrier proteins?

Membrane proteins that change shape to move substrates across the membrane.

What characteristics define carrier proteins?

Require binding sites, slower, more selective, can carry larger molecules.

What is active transport?

Movement of substances against a concentration gradient from lower to higher concentration.

Does active transport require energy?

Yes.

How do carrier proteins function in active transport?

They change shape to move ions across the membrane.

What are transporters?

Proteins that use ATP to transport molecules against gradients.

What is an example of a transporter?

Sodium-potassium pump (Na+/K+ ATPase).

What are co-transporters?

Proteins that transport two molecules simultaneously, one with its gradient and one against it.

Ex: Na+/glucose co-transporter.

What are tight junctions?

Fused connections between membranes and cytoskeletons of adjacent cells.

How do substances pass when tight junctions are present?

They must be transported through the cell itself.

Where are tight junctions commonly found?

Epithelium and ocular barrier areas.

What is the zonula occludens?

A tight junction that encircles the entire cell.

What is the macula occludens?

A localized tight junction.

What are anchoring junctions?

Attachments between cells or between cells and the basal lamina to increase stability.

What is the zonula adherens?

An anchoring junction that encircles the entire cell.

What is the macula adherens?

A localized anchoring junction.

What is a desmosome?

A junction connecting cell to cell with filaments extending into the cytoplasm.

What is a hemidesmosome?

A junction connecting a cell to the basement membrane.

Where do hemidesmosome filaments extend?

Into the cytoplasm and underlying connective tissue.

Where are hemidesmosomes clinically relevant?

Corneal basal epithelium; corneal abrasions sometimes involve displacement of hemidesmosomes

What are gap junctions?

Junctions formed by connexin proteins joining between adjacent cells.

What channel is formed by gap junctions?

A connexon channel.

What is the function of gap junctions?

Rapid communication for ions and small molecules.

What factors can affect intercellular junctions?

Pressure, biochemical factors, and pharmaceutical factors.

How do cells respond to junctional changes?

Through intracellular processes to maintain homeostasis and function.

What does cellular metabolism refer to?

All chemical reactions occurring in the cell.

What are major metabolic energy sources?

Nucleotides, carbohydrates, amino acids, and lipids.

What are examples of metabolic energy molecules?

ATP, NADPH, glucose.

What pathways make up aerobic cellular respiration?

Glycolysis, TCA cycle, and ETC.

Does aerobic respiration require oxygen?

Yes.

What occurs during glycolysis?

Glucose is broken down into pyruvate, producing 2 ATP and NADH.

What occurs during the TCA cycle?

Pyruvate is broken down, producing NADH, FADH2, 2 ATP, and excess CO2.

What occurs during the ETC?

Bulk ATP production and regeneration of NAD+ and FAD.

Produces ~30-32 ATP.

What harmful byproduct is generated by the ETC?

Free radicals.

What makes up anaerobic cellular respiration?

Glycolysis and fermentation.

Does anaerobic respiration use oxygen?

No.

How efficient is anaerobic respiration compared to aerobic?

Much less efficient, produces much less ATP.

What occurs during fermentation?

Pyruvate is converted to lactic acid, producing NAD+

(The NAD+ allows glycolysis to continue, producing minor amounts of ATP)

What is the polyol (sorbitol) pathway?

A pathway that converts glucose to sorbitol and fructose using NADPH.

What conditions is the polyol pathway associated with?

Diabetes and cataract formation.

What is the mechanism behind sorbitol-related swelling?

Excess glucose leads to sorbitol overproduction, causing osmotic swelling.

What is the ideal pH for most biological processes?

Around 7.40.

Why is pH balance important?

Necessary for oxygen transport, protein structure, and biochemical reactions.

What is the bicarbonate buffer system?

A major buffer system that neutralizes excess acids or bases.

CO2 + H2O ⇆ H2CO3 ⇆ HCO3 + H+.

What metabolic byproduct does the bicarbonate system utilize?

Excess CO2 from the TCA cycle.

What enzyme is involved in the bicarbonate buffer system?

Carbonic anhydrase.

What creates membrane potentials in cells?

Electrochemical gradients across the cell membrane.

What are the ion characteristics of the extracellular space?

Positively charged, high Na+, low K+.

What are the ion characteristics of the intracellular space?

Negatively charged, high K+, low Na+.

What is a resting membrane potential?

The baseline electrical potential present in all cells.

What triggers depolarization?

When Na+ enters the cell, causing membrane voltage to become more positive than -70 mV.

What is hyperpolarization?

When membrane voltage becomes more negative than -70 mV to to K+ leaving the cell.

What causes hyperpolarization?

K+ leaving the cell or Cl- entering the cell.

What role does the Na+/K+ ATPase play in membrane potential?

Maintains ion gradients by causing a buildup of K+ inside the cell and Na+ outside the cell.

How many ions does the Na+/K+ pump move?

3 Na+ out and 2 K+ into the cell.

What are K+ leak channels?

Channels that allow K+ to exit the cell down its gradient.

What are graded potentials?

Electrical signals with variable amplitude.

Where do graded potentials occur?

They occur across short distances and localized areas.

What can initiate graded potentials?

Depolarization or hyperpolarization.

Can graded potentials summate?

Yes.

Do graded potentials require a threshold?

No.

What channels are involved in graded potentials?

Ligand-gated channels or sensory stimuli.

What are action potentials?

Electrical signals with fixed amplitude.

Where do action potentials occur?

Over long distances.

What initiates an action potential?

Depolarization.

Can action potentials summate?

No.

Do action potentials require a threshold?

Yes.

What channels are involved in action potentials?

Voltage-gated channels.

What happens during action potential depolarization?

Neurotransmitters open Na+ channels causing Na+ influx.

At what voltage does action potential threshold usually occur?

Around -55 mV.

What happens during repolarization?

Na+ channels close and K+ channels open, leaking out positive ions (+30 mV)