Animal Cells, Tissues, and Homeostasis
Basic building block of multicellular animal is the cell
Cells organized into tissues – group of cell with same shape and function
- four (Fig 40.5)in animals
o epithelium
o connective
o muscle
o nervous
Animal tissue types
Epithelial tissue
- densely packed
- tightly connected
- cover surfaces and line hollow spaces of body
o lungs
o skin
o outsides of all organs
o blood vessels
o tend to have short lifespans
Connective tissue
- cells embedded in matrix that they secrete
- cartilage, ligaments, bone, blood
Muscle tissue
- specialized for contraction
- three different types
o skeletal
§ connected to bones (or exoskeleton)
§ Voluntary control
§ movement
o cardiac
§ only in heart
§ involuntary
o smooth
§ lines hollow spaces in body
§ involuntary
Nervous tissue
- specialized for information processing
- neurons and accessory cells
An organ is a structure that carries out a specific function in the body – composed of several different types of tissue. (Fig 40.6)
An organ system in animals is a group of organs that does a particular function. (Table 40.1)
- digestive system
- nervous system
- immune system
Body fluids
- intracellular
- extracellular
o plasma in blood
o interstitial – fluid between and around cells
- water can cross plasma membranes, so it can move in and out of cells and compartments
Surface to volume relationships
If a cell is shaped like cube, then
- surface area is l2 X 6 (because 6 sides)
- volume is l3
- so volume increases faster than surface area (s.a. increases at only 2/3 the rate of volume increase)
- so calculate surface area and volume of a cube 1mm on each side and one that is 3mm on each side
o now calculate surface area/volume ratios
o can see that volume increases faster
o who cares?
§ Cells have to exchange things across cell membrane
· Nutrients
· Wastes
· O2
§ At some size, volume is too big, it takes too long to exchange things across the cell membrane because diffusion is too slow.
§ Also works with whole animals
§ If trying to get rid of heat, very large animals simply can’t get rid of heat fast enough, so this limits size
· So basal metabolic rates (rate at which O2 is consumed at rest) (mlO2/g/hr) are lower in big animals, there simply isn’t enough surface area to exchange heat, O2, etc if BMR is too high
o Where things are being exchanged across surface (lungs/gills/leaves, blood vessels/plant vascular tissue) tends to have shape to increase surface area
§ flattened
§ folded
§ branched
Homeostasis
- maintenance of constant conditions in internal environment
o pH
o temp
- why homeostasis?
o One big reason is to keep enzymes working
o Enzymes have pH, temp, salt, etc optima and they have to be working well
- Conformers vs regulators
o Conformers conform their internal environment to the external environment
o Regulators keep internal conditions different in one or more ways from environment (like internal body temp)
§ This is energetically expensive, it takes a lot of energy to keep you warm on a cold day
o One organism can be a conformer for some thing and a regulator of others
General principles of maintaining homeostasis
sensors – monitor condition
integrator – evaluates sensory info and “decides” whether to change anything
depends on set point – desired condition (pH, temp)
effectors – cause changes in the condition when things get away from the set point
- example is temp regulation in house
o sensor – thermostat
o integrator – computer chip
§ set point – here have upper and lower set points
o effectors – furnace and air conditioner
- this works by negative feedback – feedback information causes effectors to reverse the process that is making condition get farther away from the set point.
o When gets too hot, AC comes on and reverses the rising temp