Animal Form, Function, Digestion, and Circulatory Systems

Flashcards covering animal form and function, surface area to volume constraints, digestion steps and structures, and taxa circulatory system variations.

Square-Cube Law

A physical principle stating that as an object increases in size, its volume grows faster than its surface area (e.g., doubling dimensions quadruples surface area $2^2 = 4$ and octuples volume $2^3 = 8$).

Homeostasis

The steady-state physiological condition of the internal environment maintained by organisms despite external change.

Essential Nutrients

Substances required by an organism that cannot be assembled from simple organic molecules and must be obtained directly from the diet.

Ingestion

The first stage of food processing, defined as the act of eating or taking in food.

Digestion

The second stage of food processing, involving the physical and chemical breakdown of food into molecules small enough for body absorption.

Absorption

The third stage of food processing, in which animal cells take up small molecules such as amino acids and simple sugars.

Elimination

The final stage of food processing, in which undigested or unabsorbed material exits the digestive system.

Filter Feeding

A feeding mechanism in which an animal sifts or strain small food particles from the surrounding water (e.g., baleen whales).

Substrate Feeding

A feeding mechanism where an animal lives in or on its food source and eats its way through it (e.g., a caterpillar on a leaf).

Fluid Feeding

A feeding mechanism in which an organism sucks nutrient-rich fluid from a living host (e.g., a mosquito or cicada).

Bulk Feeding

A feeding mechanism where an animal consumes relatively large pieces of food (e.g., a python swallowing prey).

Chemical Digestion

The enzymatic breakdown of macromolecules into smaller subunits through hydrolysis reactions using water and enzymes.

Intracellular Digestion

The cellular breakdown of food inside specialized organelles called food vacuoles that fuse with lysosomes.

Extracellular Digestion

The enzymatic breakdown of food within compartments that are continuous with the outside of an animal's body.

Gastrovascular Cavity

A digestive compartment with a single opening that functions in both extracellular digestion and the distribution of nutrients.

Alimentary Canal

A complete digestive tract consisting of a tube running between a mouth and an anus with specialized compartments.

Oral Cavity

The mouth chamber where initial mechanical breakdown (chewing) and chemical digestion (e.g., salivary amylase) begin.

Esophagus

A muscular tube that connects the pharynx to the stomach, conducting food via rhythmic contractions.

Peristalsis

Alternating waves of smooth muscle contraction and relaxation that move food along the digestive tract.

Gastric Juice

A digestive fluid produced by the stomach lining containing enzymes and acid that processes food into chyme.

Chyme

An acidic liquid suspension of partially digested food and digestive enzymes produced in the stomach.

Small Intestine

The organ where most enzymatic hydrolysis and nutrient absorption occur, measuring approximately $20\,\text{feet}$ in humans.

Villi

Finger-like projections on the inner wall of the small intestine that increase surface area for nutrient absorption.

Microvilli

Microscopic projections on the apical membrane of intestinal epithelial cells, forming a brush border to maximize surface area.

Hepatic Portal Vein

A blood vessel that transports nutrient-rich blood from the gastrointestinal tract directly to the liver for regulation and detoxification.

Large Intestine

The digestive tract segment consisting of the colon, cecum, and rectum, measuring around $5\,\text{feet}$ long in humans and lacking villi.

Colon

The main region of the large intestine responsible for recovering water and completing the formation of feces.

Gradient

A physical difference in concentration, pressure, or electrical charge across a distance that drives net particle movement.

Diffusion

The net passive movement of molecules down a concentration gradient from higher to lower concentration over small distances.

Interstitial Fluid

The fluid filling the spaces around cells that acts as an exchange medium between body tissue cells and the circulatory system.

Open Circulatory System

A system where hemolymph acts as both blood and interstitial fluid, directly bathing body tissues inside sinuses.

Closed Circulatory System

A system in which blood is completely confined to blood vessels and kept distinct from interstitial fluid.

Arteries

Thick, muscular blood vessels that carry high-pressure blood away from the heart toward capillaries.

Capillaries

Microscopic blood vessels with thin walls through which gas, nutrient, and waste exchange occurs via diffusion.

Veins

Thin-walled, low-pressure vessels equipped with internal valves that carry blood back toward the heart.

Single Circulation

A circulatory pathway found in fish where blood passes through two capillary beds and one two-chambered heart per circuit.

Pulmocutaneous Circuit

A double-circulation loop in amphibians that pumps oxygen-poor blood to gas exchange organs in both the lungs and skin.

Pulmonary Circuit

The double-circulation loop in mammals that routes oxygen-poor blood from the right side of the heart to capillary beds in the lungs.

Systemic Circuit

The pathway in double circulation that delivers oxygen-rich blood from the left side of the heart to capillary beds in rest of the body tissue.

Atrium

A heart chamber that receives returning blood from veins and pumps it into a ventricle.