Animal Structure and Homeostasis

Vocabulary flashcards covering animal structural levels, basic tissue types, cellular junctions, fluid compartments, and mechanisms of homeostasis.

Levels of Organization

The structural hierarchy of animals progressing from cells to tissues, organs, organ systems, and the overall organism.

Tissue

A group of similar cells doing the same job.

Organ

Two or more different tissues working together.

Organ system

Several organs cooperating on one big task.

Anchoring junctions

Cell junctions that act like buttons or rivets holding cells together, which are well-suited for tissues that get stretched such as skin and heart muscle.

Tight junctions

Cell junctions that fuse neighboring cells so nothing can leak between them, such as in the bladder lining or the blood-brain barrier.

Gap junctions

Cell junctions that open tiny tunnels between cells so signals or molecules pass directly cell-to-cell.

Epithelial Tissue

Sheets of cells packed tightly together with almost no extracellular matrix between them that cover outside surfaces and line internal cavities or tubes.

Apical surface

The exposed side of an epithelium facing air, gut contents, blood, or other non-tissue spaces.

Basal surface

The anchored side of an epithelium glued down by the basal lamina to the underlying tissue.

Cilia

Tiny hair-like oars on epithelial cells that beat to move fluid along.

Microvilli

Tiny finger-like bumps on epithelial cells that increase surface area for absorption.

Keratin

A tough protein made by some epithelial cells that forms hair, nails, claws, hooves, and feathers.

Exocrine glands

Epithelial glands that have a duct (tube) to release their products out of the body or into a cavity.

Endocrine glands

Ductless epithelial glands that release hormones directly into the surrounding fluid to travel via blood.

Connective Tissue

Tissue composed mostly of extracellular matrix with cells scattered inside it, which functions to connect, support, protect, store fat, make blood cells, fight infection, and repair damage.

Fibroblast

A star-shaped cell in connective tissue that builds the fibers of the extracellular matrix.

Collagen fibers

Connective tissue fibers made of collagen protein in thick bundles that are very strong and resist stretching.

Reticular fibers

Thin, crosslinked collagen fibers that form a supportive mesh or net in organs like the liver.

Elastic fibers

Connective tissue fibers made of elastin protein that are stretchy and spring back to shape.

Muscle Tissue

Tissue made of cells that can contract (shorten), powered by the proteins actin and myosin.

Skeletal muscle

A muscle tissue type responsible for voluntary movement of limbs and the body.

Cardiac muscle

A muscle tissue type that functions to pump the heart.

Smooth muscle

An involuntary muscle tissue type that squeezes organs such as the intestine and uterus.

Nervous Tissue

Tissue composed of neurons that carry electrical signals and glial cells that support, feed, insulate, and clean up debris.

Dendrites

Branch-like extensions of a neuron that receive signals from other cells.

Axon

A long, usually unbranched extension of a neuron that sends signals away from the cell body.

ICF (Intracellular Fluid)

Fluid located inside cells, consisting of cytoplasm fluid.

ECF (Extracellular Fluid)

Fluid located outside cells, comprised of plasma and interstitial fluid.

Interstitial fluid

The component of extracellular fluid that surrounds cells.

Homeostasis

The maintenance of a stable internal environment.

Regulators

Organisms that keep an internal factor constant regardless of environmental changes.

Conformers

Organisms whose internal environment matches external environmental conditions.

Local control

A homeostatic mechanism that fixes a problem directly where it occurs at the local site.

Systemic control

A homeostatic mechanism where the nervous system or endocrine system sends distant signals to coordinate multiple organs simultaneously.

Negative Feedback

A homeostatic mechanism where a detected change triggers a body response in the opposite direction to cancel out the change and return to normal.

Integrator

A feedback component that compares a detected signal to a set point (such as the hypothalamus at approximately $37\,^\circ\text{C}$) and determines the corrective response.

Positive Feedback

A control loop that amplifies a change instead of opposing it, creating a snowball effect until a triggering event is finished.

Circadian rhythm

A predictable, cyclic change in a biological set point that operates on a roughly $24\text{-hour}$ cycle.

Acclimatization

A temporary shift in a set point occurring naturally in response to real-world environmental changes.

Acclimation

A temporary shift in a set point induced artificially in a laboratory setting.

Evolutionary adaptation

A permanent, inherited genetic change occurring over many generations across a population.