Stokes flowStokes flow (named after George Gabriel Stokes), also named creeping flow or creeping motion, is a type of fluid flow where advective inertial forces are small compared with viscous forces. The Reynolds number is low, i.e. . This is a typical situation in flows where the fluid velocities are very slow, the viscosities are very large, or the length-scales of the flow are very small. Creeping flow was first studied to understand lubrication. In nature, this type of flow occurs in the swimming of microorganisms and sperm.
BrachiopodBrachiopods (ˈbrækioʊˌpɒd), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major categories are traditionally recognized, articulate and inarticulate brachiopods. The word "articulate" is used to describe the tooth-and-groove structures of the valve-hinge which is present in the articulate group, and absent from the inarticulate group.
NephridiumThe nephridium (plural nephridia) is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body. Nephridia come in two basic categories: metanephridia and protonephridia. All nephridia- and kidney- having animals belong to the clade Nephrozoa. A metanephridium (meta = "after") is a type of excretory gland found in many types of invertebrates such as annelids, arthropods and mollusca.
PhototaxisPhototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis. Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite. Two types of positive phototaxis are observed in prokaryotes.
FlatwormThe flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning "worm") are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Unlike other bilaterians, they are acoelomates (having no body cavity), and have no specialised circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion.
Animal testing on invertebratesMost animal testing involves invertebrates, especially Drosophila melanogaster, a fruit fly, and Caenorhabditis elegans, a nematode. These animals offer scientists many advantages over vertebrates, including their short life cycle, simple anatomy and the ease with which large numbers of individuals may be studied. Invertebrates are often cost-effective, as thousands of flies or nematodes can be housed in a single room.
Esophageal motility disorderAn esophageal motility disorder (EMD) is any medical disorder causing difficulty in swallowing, regurgitation of food and a spasm-type pain which can be brought on by an allergic reaction to certain foods. The most prominent one is dysphagia. Esophageal motility disorder may be a result of CREST syndrome, referring to the five main features: calcinosis, Raynaud syndrome, esophageal dysmotility, sclerodactyly and telangiectasia. Symptoms of EMD can include chest pain, and intermittent dysphagia for solids, liquids, or both, and regurgitation.
Esophageal motility studyAn esophageal motility study (EMS) or esophageal manometry is a test to assess motor function of the upper esophageal sphincter (UES), esophageal body and lower esophageal sphincter (LES). An EMS is typically done to evaluate suspected disorders of motility or peristalsis of the esophagus. These include achalasia, diffuse esophageal spasm, nutcracker esophagus and hypertensive lower esophageal sphincter. These disorders typically present with dysphagia, or difficulty swallowing, usually to both solids and liquids even initially.
