Chapter 4- Histology

Tissue

collection of specialized cells that perform a specific function

Histology

study of tissue

4 basic tissue types

1. Epithelial

2. Connective

3. Muscle

4. Nervous

What makes up the extracellular matrix (ECM)?

1. Ground substance

2. Protein fibers

3 types of protein fibers

1. Collagen

2. Elastic

3. Reticular

3 cell junctions

1. Tight

2. Desmosomes

3. Gap

Tight Junctions

-”zippers”

-hold cell tightly together

-sealed space: macromolecules cannot pass between cells

Example of tight junctions

-blood vessels—> prevent blood from leaving

-digestive tract: lines stomach—> stomach acid stopped from getting to underneath tissue layer

Desmosomes

-”buttons”

-very strongly hold onto cells, lots of mechanical stress

Example of desmosomes

-skin: epidermis (skin comes off in one sheaf not cell by cell)

Gap Junctions

-channels

-allow substances to pass between two cells quickly

Example of gap junctions

Cardiac muscle cells: communicate with electrical signals

• ions need to pass in between the muscle cells to keep the heart beating

Where is epithelial tissue found?

on every internal and external body surface

• acts as barriers

Functions of epithelial tissue

1. Protect- shield underlying tissue from mechanical and thermal injury

2. Immune Defense- prevent invasion of microorganisms

3. Secretion- form glands, produce hormones and oils

4. Transport- allow substances to cross barriers by passive or active transport

5. Sensation- detect changes in internal and external enviornments

Example of transportation in epithelial tissue

in the small intestine, nutrients must cross the intestinal epithelium to enter the blood

Characteristics of epithelia

1. Cellularity

2. Avascular

3. Basement membrane

4. Polarity

Cellularity

cells are closely packed together making it more resistant to stresses and mechanical injury

Avascular

lacks blood vessels

Basement membrane

a. ECM is located beneath the cells in a structure

b. anchors epithelial tissue to underlying connective tissue

c. Two layers

What are the two layers of the basement membrane?

1. Basal lamina (epithelial)

2. Reticular lamina (connective)

Polarity

cells have one side in contact with extracellular space

Apical Surface

“free edge” that comes in contact with ECM

-(seen)

Basal Surface

“anchored” portion

-(unseen)

Endocrine Glands

-secrete hormones

-goes directly into blood stream (lacks ducts)

• ex) insulin secreted by the pancreas

Exocrine Glands

-secretions go to apical surface

• ex) saliva-secreted by salutatory glands into mouth

• sweat-secreted by sweat glands onto skin surface

3 types of secretion

1. Merocrine

2. Holocrine

3. Apocrine

Merocrine Secretion

-released via exocytosis

• ex) salivary and sweat glands

Holocrine Secretion

-product accumulates in cytosol and isn’t released until the cell ruptures and dies

• ex) sebaceous oil gland (sebum)

Apocrine Secretion

-cytoplasm are pinched off with the product being secreted

• ex) lactating mamatory glands

Functions of connective tissue

1. Connecting and binding- bind other tissue layers together

2. Support- bones and cartilage support weight of the body

3. Protect- bone tissue protect internal organs

4. Transport- blood is the main transport medium in the body

Muscle Tissue

1. Specialized for contraction

2. Excitable

Excitable

can respond to electrical and chemical stimulation

• ex) muscle tissue

3 types of muscle tissue

1. Skeletal

2. Cardiac

3. Smooth

Skeletal muscle tissue

produces body movement

• voluntary

Cardiac muscle tissue

found only in heart

• involuntary

Smooth muscle tissue

in the wall of every hollow organ

• involuntary

• ex) blood vessels, eyes, skin, gland, ducts

Nervous tissue

specialized for conduction of electrical impluses

What does nervous tissue make up?

majority of the brain, spinal cord, and nerves

Two types of nervous tissue cells

1. Neurons

2. Neuroglia

Neurons

send and receive messages

Neuroglia

performs various supportive functions

Membranes

thin sheet of one or more tissue that lines a body surface or cavity

4 functions of membranes

1. Anchors organs

2. Serves as barriers

3. Function in immunity

4. Secretion

4 types of membranes

1. Mucous

2. Serous

3. Cutaneous

4. Synovial

Mucous Membrane

-lines passageways and chambers that communicate with the exterior of the body

-epithelial surfaces are lubricated by mucus to protect underlying tissue

-made up of layer of epithelium and lamina propid(loose connective tissue)

Example of mucous membrane

respiratory tract- mucus traps inhaled debris so ciliated epithelium can sweep it out

• mouth, nasal cavity, digestive tract, reproductive systems

Serous Membrane

-lines the pleural pericardial and perineal body cavities

-consists of mesothelium 

-parietal and visceral layers

Parietal layer 

outer layer that comes in contact with the body wall

Visceral layer

inner layer that covers the organs within a cavity

What is between the parietal and visceral layer?

serous fluid is between to provide lubrication

Cutaneous Membrane

covers the surface of the body

• skin, consists of epidermis and dermis

Epidermis

outer layer of epithelium

Dermis

deep to the epidermis, connective tissue

Synovial Membrane

-lines freely movable joint cavities

-made up of two connective tissue layers

• secrete synovial fluid that lubricates the joints

Example of synovial membrane

hip, knee, elbow, shoulder