lecture 9 Flashcards
Features uniting bilateria
- bilateral symmetry
- cephalization
- mesodermally derived tissues (triploblastic)
bilaterally symmetrical organisms have
anterior end,
posterior end, dorsal side, ventral side, and left and
right sides
Types of sections in a bilaterally
symmetrical organism
transverse: Cross-section and x section
sagittal: longitudinal and frontal
cephalization
concentration of sense organs & nervous
system at anterior end
mesodermally derived tissues
true’ muscles derived
common features of bilaterians
- coelom
- complete through-gut with a mouth
and an anal opening - excretory organs
coelom
-a fluid transport system
-fluid-filled cavities that are fully enclosed with fluid under control of organism
2 fluid-filled systems in many bilateria
1) eucoelom
-completely lined by mesodermally derived
epithelium
2) blood-vascular system
-channels or tubes in connective tissue
why do larger body sizes and extensive
mesoderm require some kind of excretory
system
because not all cells are directly in contact
with the surrounding medium
excretion
discarding of metabolic
wastes, especially nitrogenous wastes
egestion
discarding of undigested materials
3 steps of system of excretion
1) ultrafiltration (typically across the basal lamina)
2) resorption of ions & valuable biomolecules
3) transport (to move wastes out of body)
2 forms of excretory systems
protonephridia
metanephridia
protonephridia excretory systems
-small animals lacking coelom
or blood-vascular system.
-filtration, resorption & transport
all occur in one structure
-ultrafiltration by diffusion and pressure gradients
metanephridia excretory systems
-typically in large animals with a blood-
vascular system;
-filtration occurs in a structure separate from resorption and transport
-pressure differences for ultrafiltration
