Fluid-Structure-Interaction: How cellular structures affect local flow in sponge canal systems

Sponges possess a highly efficient fluid transport system. As inother biological fluid transport systems the general architectureis supposed to be optimized for minimal flow resistance andconsequently requires minimum work to move the fluid. Apartfrom the general architecture, especially small sized openingsaccount for the largest contribution to flow resistance. Within thesponge canal system such structures are ostia, prosopylar andapopylar openings and the microvilli collars of choanocytes. In thedemosponge Tethya wilhelma another cellular structure with onlyminute openings is present in the canal system. These are theso called reticuloapopylocytes which span the apopylar openingwith their sieve like cell morphology. Up to now, their function isunknown. Due to their location a role in flow regulation seemslikely. In order to study their influence on local flow within the canalsystem I have developed two finite element models of a choanocytechamber connected to a canal segment with and withoutreticuloapopylocets. By comparing local hydrodynamic parametersit is possible to test for fine-tuning local flow by changes in open/close states of reticuloapopylocyte fenestra. The contribution ofreticuloapopylocytes to flow resistance could be extracted fromcomparative analysis of both models. Most prominent changesin flow occur in boundary layer thickness of the connected canalsegment. As the present analysis is limited to a local scale theexact consequences of an altered boundary layer thickness in theexcurrent canal system on transport processes on an organismicscale remain to be clarified

Forschung am Teilchenbeschleuniger – als Biologe unter Physikern an einem außeruniversitären Forschungszentrum der Helmholtz-Gemeinschaft

Dr. Jörg U. Hammel wird über seine aktuellen Tätigkeiten am Deutschen Elektronen-Synchrotron (DESY) des Helmholtz-Zentrums Geesthacht in Hamburg berichten

Moving fluids for live – a sponge perspective

Sessile filter feeding animals, including sponges (Porifera), rely on efficient fluid transport systems tokeep energy expenditure for water processing low. As a consequence of the sponge canal systemcomplexity only limited data on flow velocities and transport rates are available. This restricts ourunderstanding of this central anatomical structure and related physiological processes, functionalmorophological principles and ecology. Obtaining experimental measurements from internal parts ofthe canal system is almost impossible for most species. Therefore data are mainly based ontheoretical assumptions. This is linked to the limited availability of detailed morphometric andquantitative data on canal system architecture. Here I discuss experimental and in silico results onflow studies in marine and fresh water sponges. Canal system models based on SR-µCT data allowedfor the setup of finite element models to study flow inside the aquiferous system and the influence ofspecific canal system elements (bypasses and cellular structures). In order to calibrate the model andverify results flow velocity measurements by particle tracking velocimetry have been performed.Observed flow velocities in canal segments of diverse hierarchical orders differ from predictions basedon the classical hierarchical model of flow for sponges which reported much higher and fasterincreasing flow velocities towards the osculum. This is a consequence of the aquiferous systemarchitecture which displays a compensating increase in available canal volume. With the ability toactively change canal diameters and aperture openings in the canal system sponges are most likelyable to fine tune internal flow velocities and perfusion rates of specific areas of their body