Tissues and histology

Endoderm

inner germ layer that forms the lining and main organs of the digestive and respiratory systems

Mesoderm

Middle layer. Forms tissues such as muscle, bone, blood vessels

Ectoderm

Outer layer. Forms the skin

Functions of epithelia

1. Protecting underlying structures

2. Acting as a barrier

3. Permitting the passage of substances

4. Secreting substances

5. Absorbing substances

Simple

Allows diffusion of gases, filtration of blood, secretion, absorption

Stratified

Protection, particularly against abrasion

Squamous

Allow diffusion or acts as filters

Cuboidal and columnar

Secretion or absorption

Simple squamous epithelium

Single layer of flat cells. Diffusion, filtration, some protection against friction, secretion, absorption

Simple cuboidal epithelium

Single layer of cube-shaped cells. Secretion and absorption in the kidney. Secretion in glands. Movement of mucus out

Simple columnar epithelium

Single layer of tall, narrow cells. Movement of particles out. Aids in the movement of eggs through uterine tubes

Stratified squamous epithelium

Protection against abrasion, caustic chemicals, water loss and infection

Stratified cuboidal epithelium

Multiple layers of somewhat cube-shaped cells. Secretion, absorption and protection against infections

Stratified columnar epithelium

Multiple layers of cells with tall thin cells. Protection and secretion

Pseudostratified columnar epithelium

Appears stratified but is not. Synthesize and secrete mucus, move mucus that contains foreign particles over the free surface and from passages

Transitional epithelium

Cells change shape depending upon amount of distention of the organ. Accommodates fluctuations in the volume of fluid in an organ or tube

Types of ducts

1. Simple

2. Compound

Simple duct

Duct with few branches

Compound duct

Ducts with many branches

Merocrine

No loss of cytoplasm. Secretion leaves by either active transport or exocytosis

Apocrine

Part of the cell secretes. Fragments of the gland go off into secretion. Mammary glands

Holocrine

Whole cell becomes part of secretion. Secretion accumulates in cell, cell ruptures and dies

Function of connective tissue

1. Enclose organs

2. Connect tissues to one another

3. Support and movement

4. Storage

5. Cushion and insulate

6. Transport blood

7. Protect

Collagen

Most common protein in body. Strong, flexible, inelastic

Reticular

Fill spaces between tissues and organs

Elastic

Returns to its original shape after distension or compression

Loose (areolar) connective tissue

Packing material to most organs and tissues

Dense regular elastic C.T.

Allows tissues to stretch and return to their original shape

Dense irregular collagenous C.T.

Protects and supports structures by resisting tearing and stretching from different angles

Dense irregular elastic C.T.

Provides structural strength

Adipose C.T.

Stores fat, cushions organs, insulates body

Reticular C.T.

Supportive framework. Helps filter and support blood

Types of cartilage

1. Hyaline

2. Fibrocartilage

3. Elastic

Hyaline cartilage

Absorbs shock, supports and strengthens structures, provides smooth surfaces to reduce friction

Fibrocartilage

Prevents bones from grinding together, controls pressure

Elastic cartilage

Provides support while being flexible. Allows structures to bend and spring back to their original shape

Hemopoietic tissue

Forms blood. Produces red and white blood cells

Types of muscle tissue

1. Skeletal

2. Cardiac

3. Smooth

Skeletal muscle

Voluntary movement

Cardiac muscle

Involuntary movement

Smooth

Nonstriated and involuntary

Epidermis

Protection, prevents water loss, sensation, immune defense, vitamin D production