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Invertebrate Zoology
Lecture 3: Bauplans (cont.)
Lecture outline (summary)
I.
Animal Bauplans
A.
Key features of body plans (cont.)
1.
Excretion and osmoregulation
2.
Circulation and Gas Exchange
Bauplans: key features (cont.)
I.
Excretion and osmoregulation
A.
Excretion and osmoregulation: overview
1.
Excretion, defined: ridding body of metabolic wastes
a)
Carbon dioxide
b)
Water (if in excess)
c)
Nitrogenous and other wastes (=many are toxic)
2.
Excretion usually tied to osmoregulation
3.
CO2 often excreted separately
4.
Excretion ≠ removal of solid waste
B.
Nitrogenous wastes & water conservation
1.
Protein digestion  nitrogenous wastes
2.
Excess amino acids are “deaminated”
3.
Amine groups incorporated into waste molecules
a)
Discuss differences among these molecules in terms of how well each
dissolves in water, implications for aquatic vs. terrestrial existence, and
toxicity.
C.
Osmoregulation and habitat
1.
Fig. 3.21 (understand!)
a)
Note that arrows in B and C show net movement.
2.
What if osmolarity changes?
a)
Example: estuary

Osmoconformers

Osmoregulators
b)
Most osmoconformers can osmoregulate (a bit)
c)
Most osmoregulators have limits to osmoregulation
d)
Osmoregulation can occur at the cellular level

Example: Cell placed in hypotonic solution might initially swell,
and then respond by excreting salts. (Why would this help?)
D.
Specialized structures
1.
Water expulsion vesicles (as in various Protista)
a)
Accumulate water expel it to the outside
b)
Requires energy. Mechanism?
c)
Possibly in Porifera?
2.
Nephridia:
a)
Tubules acquire water/and or ions at one end and excrete wastes through
pores (usually in body wall; wastes exit body)
b)
Protonephridia: proximal end closed
c)
Metanephridia: proximal end open
II.
Circulation and gas exchange
A.
Overview
1.
Nutrients, wastes, and gases move through the body
2.
Transport systems allow for movement beyond diffusion
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3.
B.
C.
D.
E.
Origin of fluid for transport
a)
Internal body fluids; external fluids (i.e. Porifera)
b)
Movement of fluids through/within body cavity may occur instead of or in
addition to movement within a “true” circulatory system.
Circulatory systems (true)
1.
CLOSED: blood remains within vessels
a)
Associated with well-developed coelomic cavity
b)
Composition of blood vs. coelomic fluid differs
c)
Exchange of dissolved materials occurs within capillary beds (single cell
layer to promote diffusion)
2.
OPEN: vessels exist, but open into hemocoel
a)
Associated with reduced coelom,peritoneum
b)
Less efficient than closed system?

Additional functions (i.e. hydrostatic)

Secondary systems have evolved to compensate
Hearts and other pumping mechanisms
1.
Pump blood/hemolymph; maintain blood pressure
2.
Several types
a)
Contractile vessels (Annelida)
b)
Ostiate hearts (Arthropoda)

Allows entry of hemolymph back into heart from the hemocoel
c)
Chambered hearts (Mollusca)
Other key concepts (circulation)
1.
Myogenic vs. neurogenic control of contraction
2.
In general, freshly oxygenated blood/hemolymph is first circulated to the head.
3.
Vessel diameter and flow
a)
Paradox: diameter  flow rate

Problem: need low flow at capillaries (why?)

Solution:  total cross-sectional area at capillaries   flow rate!
Gas exchange and transport
1.
O2 uptake from air or water over moist membrane (body surface or specialized
structures)
a)
Why moist?
2.
O2 often diffuses into a “circulatory body fluid”, then to cells
a)
CO2 moves in opposite direction
3.
Body fluids have relatively low O2-carrying capacity
a)
Respiratory pigments increase that capacity

O2 binds to a metal, usually copper or iron
4.
CO2 primarily converted to carbonic acid and bicarbonate
a)
Requires carbonic anhydrase
b)
CO2 + H2O
H2CO3
H+ +HCO3-
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