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