Download Lecture 14a – Introduction to Animal Function

Biology 240 – General Zoology
Lecture 14a – Introduction to Animal Function
I. Requirements for Life
Water (H2O)
Energy: glucose, fatty acids
+ O2 → CO2 + H2O
→ ATP formation
Organic monomers: sugars, lipids, amino acids
Inorganic ions:
K+, Na+, Cl–, Ca2+, PO43(micronutrients: vitamins, Fe, Cu, Mn, Mg, Zn, etc.)
Waste elimination: N waste, organic waste
Processes
Ingestion, osmosis, metabolism, excretion
Ingestion, digestion, absorption, metabolism
Gas exchange
Metabolism (cellular respiration)
Ingestion, digestion, absorption, metabolism
Transport, excitation, regulation
Metabolism, transport
Excretion
Tolerance Limits
Temperature
Water availability/hydration
Salinity/osmolarity
pH
O2 concentration or partial pressure (PO2)
II. Physiological Principles
A. Exchange Processes
1. Organisms are open systems that continually exchange materials and energy between the body
and environment.
unicellular organisms - exchange across the cell membrane
most animals - exchange across epithelial tissues (epithelium)
- epithelial tissue forms a dynamic boundary between internal and external environments
Epithelium
ICF
Internal
Environment
ECF
ICF
ICF
ICF
ICF
ICF
External
Environment
Cells
- internal environment consists of extracellular fluid (ECF) that surrounds cells
- ECF serves as a buffer between cells and the external environment
- ECF composition is regulated, different from intracellular fluid (ICF = cytosol)
- external environment includes the lumen of hollow organs that open to the outside
(e.g., GI tract, lungs)
2. Exchange occurs across surfaces by diffusion or active transport;
rate of exchange is dependent on surface area.
Fick’s Law:
Rate of Diffusion = (Diffusion Constant) x (Surface Area) x (Concentration Difference)
(Diffusion Distance)
Biology 240 – General Zoology
- surface area to volume ratio (SA/V) decreases with increasing body size;
exchange across body surface is effective only in very small organisms
- specialized exchange organs have epithelia with very large surface areas:
small intestine - long length, circular folds, villi, and microvilli
lungs - alveoli ~ 400 million in human lungs
kidneys - nephrons > 1 million in human kidneys
3. Circulatory systems transport materials by bulk flow between exchange surfaces and body cells.
- exchange by diffusion is only effective over very short distances
- larger vessels (arteries and veins) carry blood over longer distances;
smallest vessels (capillaries) function for exchange; located very close to body cells
B. Homeostasis - maintenance of relatively constant internal conditions in the body
- homeostasis is a steady state process: input = output; not equilibrium
- different animals maintain homeostasis to different degrees
- maintaining homeostasis increases range of environmental tolerance but requires energy
Examples:
endotherms (mammals and birds) - maintain high, constant body temperature (37-41°C);
can live and function effectively in cold environments but at a high energy cost
freshwater and marine bony fishes maintain internal ion (Na+ and Cl–) concentrations by
active transport of ions across gill epithelium
lined shore crab partially regulates internal ion concentrations; can tolerate wide salinity range
Negative feedback control maintains homeostasis
Variable
negative
feedback
Sensors
input
(afferent
pathway)
Integrating Center
↑
[set point]
output
(efferent
pathway)
Effectors
Response
- variables are regulated in relation to a set point
- corrective change is in the opposite direction of deviation from the set point
Example - thermoregulation in humans
Heat balance - to maintain constant body temperature (Tb):
heat gain (metabolism + input from environment) = heat loss (to environment)
If heat gain > heat loss → Tb ↑; If heat loss > heat gain → Tb ↓
Negative feedback control:
set point: 37ºC
sensors: peripheral (skin), central (hypothalamus)
integrating center: hypothalamus
hot (↑ Tb > 37ºC)
cold (↓Tb < 37ºC)
sweat glands: sweat
skeletal muscles: shivering
skin blood vessels: vasodilation skin blood vessels: vasoconstriction
(skin, arrector pili: piloerection)
corrective change:
↓ Tb
↑ Tb
deviation:
effectors:
& response