General Zoology Lab: Circulatory and Digestive Systems

A comprehensive vocabulary review of the circulatory and digestive systems covering physiological adaptations, fluid pathways, organ evolution, and anatomical structures.

Diffusion (Transport Limitation)

A passive transport process where doubling the distance quadruples the time ($0.25\,\text{ms}$ in a single cell, $2.5\,\text{s}$ in thin tissue, $4\,\text{min}$ in a $2\,\text{mm}$ animal, $7\,\text{hours}$ in a $2\,\text{cm}$ animal, and $1\,\text{month}$ in a $20\,\text{cm}$ animal), necessitating circulatory systems for animals thicker than a fraction of a millimeter.

Circulatory System

In zoology, a broad organ system comprising the heart, blood, and blood vessels, alongside the lymphatic system, that performs transport, signaling, defense, and heat distribution.

Cardiovascular System

In human anatomy and physiology, the specific blood-transport component of the broader circulatory system.

Hemolymph

The circulatory fluid characteristic of open circulatory systems that directly bathes organs and tissues, transporting nutrients, hormones, and immune cells.

Hemocoel

The body cavity or series of open sinuses into which hemolymph is pumped directly around internal organs in open circulation.

Ostia

Valved pores in the heart of an animal with open circulation that open upon cardiac relaxation to allow hemolymph to return from the body sinuses.

Open Circulation

A circulatory arrangement found in arthropods and most mollusks where hemolymph leaves vessels to fill the hemocoel under low pressure, making up $20\,\text{--}\,40\%$ of body volume with limited flow control.

Closed Circulation

A circulatory arrangement found in annelids, cephalopods, and all vertebrates where blood stays confined to vessels under higher pressure, constituting $5\,\text{--}\,10\%$ of body volume with fine flow control via vessel diameter.

Neurogenic Heart

A heart whose rhythm originates in nerve cells via a cardiac ganglion; removing the ganglion halts heart contractions entirely (found in crustaceans like lobsters and in horseshoe crabs).

Myogenic Heart

A heart whose rhythmic contractions originate in specialized pacemaker muscle cells and propagate across muscle tissue without requiring nervous stimulation to start a beat (found in vertebrates and many mollusks).

Fish Circulatory Circuit

A single circulatory circuit driven by a two-chambered heart (one atrium and one ventricle) pushing blood through two capillary beds in series (gills then body tissues), causing blood to reach body tissues at low pressure.

Conus Arteriosus

An outflow tract of the three-chambered vertebrate heart that distributes pumped blood toward the lungs, skin, and body.

Carotid Arch

An arterial arch originating from the truncus arteriosus that delivers oxygenated blood directly to the head.

Systemic Arch

Arterial vessels supplying the trunk, internal organs, and limbs; the left and right arches unite to form the dorsal aorta.

Pulmocutaneous Arch

An arterial arch in amphibians that transports blood to the lungs and skin for external gas exchange.

Truncus Arteriosus

The major arterial trunk emerging from the ventricle that directs blood away from the three-chambered heart into branch arches.

Arteries

Thick-walled, muscular blood vessels adapted to withstand high hydrostatic pressure while conducting blood away from the heart.

Veins

Large-lumen, thinner-walled blood vessels carrying blood back toward the heart under lower hydrostatic pressure.

Venous Valves

Flap-like internal valves located in medium-sized veins—most heavily concentrated in lower limbs—that counteract gravity to prevent the backward flow of blood.

Capillaries

Microscopic blood vessels with walls only one cell layer thick, functioning as the primary exchange site for gases, nutrients, and metabolic wastes.

Intracellular Digestion

A digestive mechanism where food particles enter cells via phagocytosis into a food vacuole and are broken down by internal enzymes, as seen in protozoans and sponges.

Extracellular Digestion

A digestive process where enzymes are secreted into an internal specialized body cavity or lumen to hydrolyze larger food items prior to cell absorption.

Choanocytes

Specialized flagellated collar cells in sponges that filter and capture microscopic food particles from water canals to digest them intracellularly.

Amoebocytes (Archaeocytes)

Ameboid cells that crawl through the mesohyl of sponges to distribute absorbed nutrients, remove metabolic wastes, and differentiate into other cellular varieties.

Gastrovascular Cavity

A blind, branched internal space with a single opening that serves simultaneously as a gut for extracellular digestion and a fluid distributor in cnidarians and flatworms.

Incomplete Digestive System

A sac-like digestive layout possessing only a single opening that functions as both entrance for ingestion and exit for egestion.

Complete Digestive System

A continuous one-way alimentary canal possessing separate mouth and anal openings, first emerging in roundworms and permitting regional digestive specialization.

Crop

An expanded, thin-walled storage compartment of the digestive tract present in annelids, insects, and birds.

Gizzard

A thick, muscular chamber of the digestive system that uses ingested soil grit or swallowed stones to mechanically crush and grind food.

Typhlosole

An internal dorsal infolding of the earthworm intestinal wall that increases nutrient absorptive surface area without lengthening the body.

Foregut

The anterior segment of the insect alimentary canal primarily dedicated to food ingestion, storage, and preliminary breakdown.

Midgut

The central section of the insect digestive system where major enzymatic chemical digestion and nutrient absorption occur.

Hindgut

The posterior portion of the insect gut responsible for recovering water and preparing dry fecal pellets.

Denticles

Hard dermal scales from which vertebrate teeth evolutionarily derived, originally functioning to seize, hold, and slice prey.

Detritivore

An organism that ingests decaying organic matter and detritus, facilitating nutrient cycling within biological communities.

Accessory Digestive Organs

Glands and organs outside the gastrointestinal tube—including the liver (produces bile), gallbladder (stores bile), and pancreas (secretes digestive enzymes)—that discharge secretions into the gut.

Cloaca

A common chamber and external opening receiving the terminal outputs of the digestive, urinary, and reproductive systems in amphibians, reptiles, and birds.