A single celled organism, such as the amoeba has a sufficient
membrane surface area in contact with its environments to
carry out all necessary exchange
A multicellular organization works only if every cell has access
to suitable aqueous environment, either inside or outside the
animals body. Many animals with a simple internal
organization have body plans that enable direct exchange
between almost all their cells and the external environment
Interstitial fluid
The spaces between cells that are filled with fluid in the body of many animals
Exchanges between the interstitial fluid and the circulatory fluid (such as blood) Enables cells
throughout the body to obtain nutrients and get rid of wastes
Cells are organized in tissues
tissues are groups of cells with similar appearance and a common function
Different types of tissues are further organized into functional units called organs
Groups of organs that work together providing an additional level of organization and coordination
make up an organ system
,
,There are four main types of animal tissues
1. Epithelial
2. Connective
3. Muscle
4. Nervous
Epithelial tissues occur as sheets of cells, they cover the outside of the body. Because they are closely
packed, they function as barrier against mechanical injury pathogens and fluid loss.
All epithelia have 2 different side
The apical surface faces the lumen or outside of the organ and is therefore exposed to fluid or air.
Microvilli projections Increase the surface area available for absorbing nutrients.
The opposite side of each epithelium is the basal surface
, Connective tissue
Consisting of a sparse population of cells scattered through an extracellular matrix holds many tissues
and organs together in place
Within the matrix are cells called
• Fibroblasts → secrete fiber proteins
• Macrophages → Engulf foreign particles and any cell debris by phagocytosis
Connective tissue fibers are of 3 kinds
1. Collagenous fibers
Provide strength and flexibility
2. Reticular fibers
Join connective tissues to adjacent tissues
3. Elastic fiber
Makes tissues elastic
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