Download Special Membranes

Biology 2121 Independent Notes – Special Tissues
I. Body Membranes
All body organs and structures are covered by membranes. These body membranes are made of (2) types of
different tissues. There are three different types of membranes that cover the body and it’s organs:
(1). Cutaneous
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Refers to your skin.
This tissue is composed of tough keratinized stratified squamous epithelium attached to dense irregular
connective tissue.
This is called a dry membrane because it is exposed to the air.
We will do an entire unit focusing on the skin.
(2). Mucous
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Also called moist membranes.
Includes hollow organs such as digestive, respiratory and urogenital tracts.
Consists of stratified squamous or simple epithelium and lies upon a layer of loose connective tissue. This loose
connective tissue is called the lamina propria.
The arrow is pointing to the lamina propria in
the esophagus. The epithelia lies on top of the
lamina propria. Both together make up the
mucosa or lining.
(3). Serous
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Also referred to as the serosa
Moist membrane found in the ventral cavity.
Composed of simple squamous epithelium (mesothelium) on top of areolar loose connective tissue.
The mesothelium cells secrete hyaluronic acid to the fluid to make serous fluid (lubricating fluid).
Fluid located between the parietal and visceral layers that surround the organs.
Named according to location
o Pleura – covers the lungs; pericardium encloses the heart
Visceral and Parietal layers – Serous
membranes surrounding the lungs (pleura).
Serous fluid is found inbetween these
layers.
II. Development of Tissues
During embryonic development cells will develop into three primary germ layers. These three layers begin to develop
into the four primary tissue types by the end of the second month. The four primary tissues are: epithelium,
connective, muscle and bone.
The three primary germ layers are:
(1). Ectoderm
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Outer most germ layers
Develop into tissue that will cover the body
Forms the epidermis of the skin and nervous system structures
(2). Mesoderm
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Middle germ layer
Develops into mesenchyme stem cells, dermis of the skin, gonads, muscles, excretory organs and the circulatory
system
(3). Endoderm
 Innermost of the three layers
 Inner lining of digestive tract, liver and pancreas, inner lining of respiratory tract