Unit 5: Tissues

Skin is a type of tissue. 

Four Types:

1.  Epithelial

2.  Connective

3.  Muscle

4.  Nervous

Tissue - a group or mass of similar cells working together to perform common functions.

Epithelial Tissue

- Covers all body surfaces both inside and out.
- Main glandular (glands) tissue.
- Attached to underlying connective tissue at the basement membrane

- Usually has no vascular tissue - no blood supply
- Cells reproduce rapidly, results in rapid healing  (and scarring)
- Cells tightly packed together

It takes about 27 days for the outer layer of skin to shed and be replaced; that works out to 1.5 pounds of skin cells per year.

Functions of Epithelial Tissue 

• Protection

• Secretion

• Absorption

• Excretion 

• Senses

Categorized based on the shape of the cells and the layers of cells.

1. Epithelial tissue:

simple = single layer

stratified = multiple layers

squamous = flat

cuboidal = square

columnar = column (rectangle)

One type of tissue can be arranged in different forms,  each form has a different function.

A. Simple Squamous:

Form:  Single layer, Flat and thin

Function: diffusion and filtration. Air sacs in lungs, capillaries

All epithelial tissue has a layer at the bottom called the:  BASEMENT MEMBRANE

B. Simple Cuboidal

Function: Secretion and absorption

Found in kidneys tubules, ducts and covering the ovaries

C. Simple Columnar

Function: Secretion and absorption

Found in digestive tract and uterus

Contains scattered goblet cells to secrete mucus

Can have microvilli to increase surface area

D. Stratified Squamous

Multi layer squamous, functions in protection

Found lining body cavities;  skin and mouth

The ink of tattoos must be injected below the  basement membrane.

E. Pseudostratified Columnar

Appear stratified, but just a single layer of cells, nuclei at different levels

Can have cilia (hair-like projections) and goblet cells, which secrete mucus

Function:  Secretion and cilia-aided movement

Location: lining air passages and tubes of the reproductive system

F. Transitional Epithelium

Stretchable

Blocks diffusion (no leaking)

Found in the urinary bladder

G. Glandular Epithelium

Cells are specialized to secrete substances 

They make up the GLANDS

exocrine and endocrine glands

Examples: salivary, sweat, hormones

What’s wrong with Rowan’s skin? 

- Mutations in the COL7A1 gene affects the protein, collagen. 

- Collagen is like the “glue” that holds tissues together.  It anchors the epidermis to the dermis.

- As the dermis pulls away from the epidermis, blisters form. Any type of pressure can cause the skin to pull away. These blisters and sores are very painful.

- Collagen and elastin are proteins found in connective tissue.

Loss of these fibers are responsible for wrinkles as we age. 

Why does a skin condition also affect nutrition? 

- Recall the epidermal tissue lines the mouth and esophagus.

- The same blistering occurs there, making it difficult to swallow.  Scar tissue can also narrow passageways for food. 

- Many  will get gastric feeding tubes (G-tube)

2. Connective Tissue

- Most abundant tissue in your body; binds structures together
- Provides support, protection, framework, fills space, stores fat, produces blood cells, fights infection

- Composed of more scattered cells within matrix
- Made up of a ground substance and fibers
- Most have a good blood supply

Three types of cells in connective tissue:

1. Mast cells (prevents clots)

2. Macrophages (consumers)

3.  Fibroblasts (produce fibers)

Main types of fibers:

Collagenous, found in bones, ligaments, tendons

Elastic, found in ears, vocal cords

A. Loose Connective Tissue or Areolar Tissue

- Binds underlying organs to skin and to each other

- Forms delicate thin membranes throughout the body

B. Adipose Tissue (fat)

• Protective cushion

• insulation to preserve body heat

• Stores energy.

C. Fibrous Connective Tissue

Tendons =  muscles to bones

Ligaments = bones to bones

D. Cartilage

Cartilage cells are called chondrocytes

Cartilage is a type of “DENSE CONNECTIVE TISSUE”

• Hyaline Cartilage: covers ends of joints, nose and respiratory passages, serves as padding

• Elastic cartilage: External Ear and Larynx

• Fibrocartilage: Tough, shock absorbing. Between vertebrae

E. Bone Tissue (Osseous)

F. Blood Tissue

Muscle Tissue:

1. Smooth muscle tissue: Involuntary control

2. Cardiac Muscle Tissue: Involuntary control

3. Skeletal Muscle Tissue: Voluntary control

Nerve Tissue:

Neurons - transmit signals( Axons & Dendrites )

Neuroglia - support cells

Skin Pigmentation:

- Melanocytes

- Keratinocytes

- MC1R gene

- Adaptation / Evolution

- Folate

- Vitamin D

How to repair skin….

Cuts on the skin may need to be stitched if they also go through the underlying tissue.

- Stitches are also called SUTURES and they hold the tissue together while the body heals.

Alternatives to sutures:

• Glue

• Medical Tape

• Staples