Cell Membranes, Transport, Anatomy Orientation, and Histology

These flashcards cover cell membrane structure, transport mechanisms, osmotic concepts, body orientation, basic histology of epithelia and connective tissues, and glandular classifications.

What are the two major structural components of a phospholipid that give the cell membrane its amphipathic nature?

A hydrophilic (polar) head and a hydrophobic (non-polar) tail.

Which membrane component modulates fluidity and forms ‘rafts’ that organize proteins?

Cholesterol.

What does the term selective permeability mean when applied to the cell membrane?

The membrane allows some substances to cross freely while restricting others.

Name the two broad categories of transport mechanisms that move solutes across cell membranes.

Diffusion (passive) and active transport.

Does diffusion require cellular energy (ATP)?

No; it is a passive process.

In which direction does simple diffusion move molecules with respect to their concentration gradient?

From high concentration to low concentration (down the gradient).

Give an example of a substance that crosses membranes by simple diffusion.

Oxygen, carbon dioxide, or steroid hormones (any lipid-soluble molecule).

Why do water-soluble (lipophobic) molecules need facilitated diffusion?

Because the hydrophobic core of the membrane blocks their passage, so they require protein channels or carriers.

How does a channel protein differ from a carrier protein?

Channels form aqueous pores accessible from both sides when open; carriers bind solute and change shape, exposing binding sites to one side at a time.

Which transport proteins can reach a maximum rate based on their number—channels or carriers?

Carrier proteins.

What energy source powers the sodium–potassium pump (Na⁺/K⁺-ATPase)?

Hydrolysis of ATP.

How many Na⁺ and K⁺ ions are moved and in which directions during one pump cycle of Na⁺/K⁺-ATPase?

3 Na⁺ are pumped out of the cell and 2 K⁺ are pumped into the cell.

Define osmosis.

The movement of water across a semipermeable membrane from a region of lower solute osmolarity (higher water concentration) to a region of higher solute osmolarity (lower water concentration).

What term describes solutes that cannot cross the membrane and therefore drive osmosis?

Non-penetrating solutes.

What is osmolarity measured in?

Milliosmoles per litre (mOsm/L).

Water moves toward which side of an osmotic gradient?

Toward the side with higher solute osmolarity.

Define isotonic solution.

Two solutions with equal concentrations of non-penetrating solutes.

What happens to red blood cells in a hypotonic solution and why?

They swell (and may burst) because water enters the cell to dilute the higher intracellular solute concentration.

Describe the appearance of red blood cells placed in a hypertonic solution.

They shrivel (crenate) into a spiky shape as water leaves the cell.

Name the three major body cavities in mammals.

Thoracic cavity, abdominal cavity, and pelvic cavity.

What separates the thoracic and abdominal cavities in mammals?

The diaphragm.

What is the single body cavity in birds and reptiles called?

The coelomic cavity (coelom).

Define the anatomical directional term ‘dorsal’.

Toward the back (upper surface).

Define the term ‘ventral’.

Toward the belly (underside).

What does the directional term ‘proximal’ mean on a limb?

Closer to the trunk or main body mass.

Which directional term describes the surface of the hindlimb below the tarsus that contacts the ground?

Plantar.

Which anatomical plane divides the body into right and left halves?

Median (midsagittal) plane.

What plane is perpendicular to the long axis of the body?

Transverse plane.

List the four primary tissue types.

Epithelial, connective, muscle, and nervous tissue.

What thin layer of specialised extracellular matrix underlies all epithelia?

The basement membrane.

Do epithelia contain blood vessels?

No; they are avascular and receive nutrients by diffusion across the basement membrane.

How is epithelium classified?

By number of cell layers (simple vs. stratified) and cell shape (squamous, cuboidal, columnar).

Where would you most likely find simple squamous epithelium in the body?

In areas where diffusion is important, e.g., alveoli of lungs or capillary endothelium.

Which epithelium provides physical protection in high-stress areas such as skin or oesophagus?

Stratified squamous epithelium.

What is transitional epithelium and where is it found?

A stratified cuboidal-like epithelium that stretches and is located in the urinary bladder and ureters.

What surface modification increases absorptive surface area on intestinal epithelial cells?

Microvilli.

What motile projections on respiratory epithelium move mucus toward the pharynx?

Cilia.

Name the intercellular junction that forms a seal preventing paracellular passage of substances.

Tight junction.

Which intercellular junction acts like rivets to resist mechanical stress?

Desmosomes.

What type of junction allows ions to pass directly from one cell to another for communication?

Gap junction.

Differentiate between exocrine and endocrine glands.

Exocrine glands have ducts that carry secretions to a surface; endocrine glands are ductless and release hormones into the bloodstream.

What is the secretory unit of an exocrine gland called?

An acinus.

Connective tissue is composed of cells and what two extracellular components?

Fibres and ground substance (forming the extracellular matrix).

Name the three fibre types found in connective tissue.

Collagen, elastic, and reticular fibres.

What is the primary function of collagen fibres?

To provide tensile strength and resist stretching.

Which connective tissue fibre type can stretch and recoil like a rubber band?

Elastic fibres.

What is the functional difference between a fibroblast and a fibrocyte?

A fibroblast actively produces fibres, whereas a fibrocyte is a quiescent cell that maintains existing fibres.

Describe loose (areolar) connective tissue.

It has a loose arrangement of fibres, abundant ground substance, and various cell types; found beneath epithelia and around vessels.

Where would you expect to find dense regular connective tissue?

In tendons and ligaments where collagen fibres are aligned parallel to resist unidirectional tension.

Which dense connective tissue type forms the dermis and organ capsules?

Dense irregular connective tissue.

List the three types of cartilage.

Hyaline cartilage, fibrocartilage, and elastic cartilage.

Which cartilage type forms articular surfaces on bones and has fine collagen fibres?

Hyaline cartilage.

Which cartilage type contains thick bundles of collagen making it very tough, as in intervertebral discs?

Fibrocartilage.

What gives elastic cartilage (e.g., ear pinna) its flexibility?

A high content of elastin fibres.

Bone extracellular matrix becomes hard due to deposition of what mineral salts?

Calcium salts (hydroxyapatite).

What name is given to the liquid extracellular matrix of blood?

Plasma.

What protein precursor in plasma polymerises to form fibres during blood clotting?

Fibrinogen (converts to fibrin).

Identify the transport method: glucose moves into a cell via a carrier that does not use ATP.

Facilitated diffusion.

Identify the transport method: Ca²⁺ is pumped from cytosol into the sarcoplasmic reticulum against its gradient using ATP.

Active transport (Ca²⁺-ATPase pump).

What property of carrier-mediated transport limits the rate of facilitated diffusion?

Saturation—the finite number of carriers can become fully occupied.

Give the equation for osmotic pressure (Π) according to van ’t Hoff’s law (conceptual level).

Π ≈ iCRT (where i = number of particles, C = molar concentration, R = gas constant, T = temperature).

Explain why non-penetrating solutes are crucial in determining cell volume.

Because they cannot cross the membrane, they create osmotic gradients that drive water movement, altering cell volume.

What happens to a cell placed in an isotonic extracellular solution?

No net water movement; cell volume remains unchanged.

Which anatomical term means ‘toward the nose’ on the head?

Rostral.

What term describes a structure farther from the midline of the body?

Lateral.

Name the limb surface terms for the front limb below the carpus.

Dorsal (front surface) and palmar (rear/ground-contact surface).

Which epithelial junction primarily allows coordinated beating of cilia by sharing ions and small molecules?

Gap junction.

What are the three general functions of epithelia?

Barrier/protection, absorption, and secretion.

Which epithelial cell type typically lines kidney tubules and ducts of glands to perform secretion and absorption?

Simple cuboidal epithelium.

What does ‘pseudostratified’ mean in pseudostratified columnar epithelium?

Cells vary in height so nuclei appear at different levels giving a false impression of multiple layers, but every cell contacts the basement membrane.

Which resident connective tissue cell type stores triglycerides and cushions organs?

Adipocyte.

Which connective tissue cell releases histamine in response to allergens?

Mast cell.

Define a hormone.

A chemical messenger secreted by endocrine cells into the bloodstream to regulate distant target tissues.

What mechanical advantage does dense irregular connective tissue provide over loose connective tissue?

Greater resistance to multidirectional tension because of densely packed, interwoven fibres.

Why is hyaline cartilage shiny and glassy on histological slides?

Its fine collagen fibres are too thin to be resolved easily and are embedded in a gelatinous ground substance.

Name the specialised connective tissue that stores calcium and provides rigid support for the body.

Bone tissue.

Which transport term describes substances moving ‘uphill’ from low to high concentration with energy input?

Active transport.

True or False: Active transport depends on an existing concentration gradient for the solute.

False; it can move solutes against (regardless of) the gradient.

When a membrane channel is open, is it simultaneously accessible from both sides of the membrane?

Yes.

State one reason why carrier-mediated diffusion is slower than channel-mediated diffusion.

Carriers require a conformational change for each transport cycle, whereas channels provide a continuous pore.