Anatomy

Body Tissues and Membranes

The human body starts out as a single cell, the fertilized egg, which divides almost endlessly. The millions of cells that result become specialized for particular functions. Some become muscle cells, some become cells of the bones, others become skin cells, and so on as cells become specialized for specific functions in the body. Thus, there is a division of labor in the body, with groups of highly specialized cells performing functions that benefit you as whole and contribute to homeostasis, allowing our bodies to function to their highest potential. Body membranes cover surfaces, line body cavities, and form protective sheets around organs. Body membranes fall into one of two categories; epithelial membranes or connective tissue membranes. There are three types of epithelial membranes, one being cutaneous membranes. Cutaneous membranes form the skin, also known as the integumentary system. The skin serves to protect underlying organs and tissues in the body. The skin also forms vitamin D which allows for absorption of calcium, important for making the bones of your body hard.

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Connective Tissue- Binds structures together, provides support and protection, fills spaces, stores fat.

Cartilage- Cells are separated by a solid yet flexible matrix. Three types of cartilage get based on fiber type:

Hyaline Cartilage

Found in: nose, ends of bone, rings of trachea, fetal skeleton

Elastic Cartilage

Found in: outer ear, and other places

Fibro cartilage

Absorbs shock

Reduces friction between joints

Bone: Most rigid of the connective tissue, calcium salts deposits around protein fiber. Calcium provides the rigidity. Proteins then provide the elasticity and strength.

Bones are classified into three types

Long bones - structure and support

Short bones - facilitate movement

Flat bones - protection

For anatomical purposes:

Compact bone

The canals supply blood to the cells

Spongy bone

Exists on the ends of bone

Composed of bars and plates for reinforcement

Not as dense as compact, but stronger

Blood

Also a connective tissue

It is separated by plasma

Blood cells are of two types

Red Blood Cells (erythrocytes)

Contain the oxygen

White Blood Cells (leukocytes)

Fight infection

Plasma and Platelets

Fragments of large bone marrow cells

Important in blood clotting

Muscular Tissue

Composed of fiber that contain "actin" and "myosin" microfilaments

Movement (muscular contraction) occurs when these two interact

Three types of muscular tissue exist:

Skeletal, Smooth, and Cardiac

Skeletal (striated)

Attaches to the bones

Its function is to move the skeleton

Its fibers are cylindrical

Run the length of the muscle

Have concentric bands that give striated appearance

Is under voluntary control (our voluntary system controls it)

Is the fastest of all muscular contractions?

Smooth

Lacks dark bands, no striations

Is an involuntary muscle (not under voluntary control, for most - biofeedback)

Found in the intestines, stomach, arteries

Muscles contract more slowly

Remain contracted for a longer period of time

Cardiac

Appears to combine both smooth and striated features

Fibers appear branched, so that the contractions occur in many directions

It present in the heart, responsible for the heartbeat

It’s a voluntary muscle

Nervous Tissue: Found in the brain and spinal cord, composed of Neurons and neuroglial cells

Neurons are composed of:

Dendrite - conducts impulse

Cell body - contains nucleus

Axon - conducts impulse away from the body

Glial Cells support and protect the neurons

Those that encircle the fibers are called "Schwann" cells

Outer layer called "neurilemma"

Promotes growth in damaged cells

Inner fatty layer called "myelin"

There are "gaps" between these cells

Gaps are called nodes of Ranvier

The nodes pass on the nervous impulse