1 2 3 4 5 6 7 8

Bio 220 Lecture 10 Notes: Homeostasis Read Ch. 40 now as an introduction to the basic structures of animals and to the concepts of metabolic rate and homeostasis. Pay particular attention to pages 784-790. I. Basic organization of animals

A. Cells

1. Extracellular matrix

7.29

Animal cells are surrounded by an extracellular matrixmade up of proteins and proteoglycans (proteins coupled to carbohydrates). The ECM holds tissues together.

2. Intercellular junctions

7.30

Like plant cells, animal cells are connected by intercellular junctions.

a. Tight junctions

Tight junctionsbring the plasma membranes of 2 cells very close together. They form a ring around the cell, preventing molecules from moving between cells, creating a barrier. In addition, tight junctions restrict the movementof membrane proteins; this allows the plasma membrane of the cell to be separated into 2 separate domains.

b. Desmosomes

Desmosomesand adhering junctions provide strong mechanical connections that hold cells together. They can be located in discrete patches or as narrow bands around cells.