Four primary tissue types

What forms the four primary tissue types

• Cell differentiation from stem cells

• Creates collections of similar specialised cells

• Stem cells → specialised cells → four tissue types → tissues combine to form organs.

What are the four primary tissue types

• Epithelial tissue

• Connective tissue

• Muscle tissue

• Nervous tissue

What do organs consist of

• Combinations of all four tissue types

Nervous tissue main function

• Internal communication

Nervous tissue locations

• Brain

• Spinal cord

• Nerves

Muscle tissue main function

• Contracts to cause movement

Muscle tissue locations

• Skeletal muscles (attached to bones)

• Cardiac muscle (heart)

• Smooth muscle (walls of hollow organs)

Epithelial tissue main function

• Forms boundaries

• Protects

• Secretes

• Absorbs

• Filters

Epithelial tissue locations

• Skin surface (epidermis)

• Lining of GI tract and other hollow organs

Connective tissue main function

• Supports

• Protects

• Binds other tissues together

Connective tissue locations

• Bones

• Tendons

• Fat and soft padding tissues

What is nervous tissue the main component of

• Brain

• Spinal cord

• Nerves

What is nervous tissue composed of

• Neurons

• Supporting cells

What is the function of nervous tissue

• Communication

• Transmits electrical signals

• Regulates and controls body functions

What is muscle tissue composed of

• Muscle cells containing contractile microfilament

What is muscle tissue specialised for

• Contraction to allow movement

Three types of muscle tissue

• Skeletal muscle

• Cardiac muscle

• Smooth muscle

Skeletal muscle - describe

• Voluntary

• Produces skeletal movement

Cardiac muscle - describe

• Involuntary

• Found in the heart

Smooth muscle - describe

• Involuntary

• Found in blood vessels, gut, bladder, uterus

What is epithelium

• A sheet of cells that covers the body, lines cavities and organs, and forms glands

What is epithelial tissue composed of

• Epithelial cells forming continuous sheets

Does epithelial tissue have blood vessels

• No — it is avascular

• Oxygen and nutrients diffuse from underlying connective tissue

Does epithelial tissue contain nerves

• Yes — it is innervated

Epithelial Tissue Functions

• Protection

• Absorption

• Excretion

• Filtration

• Secretion

• Transport of mucus

• Sensory function

Epithelial Tissue Functions - Protection

• Forms a barrier to protect underlying tissues from injury, pathogens, and dehydration

Epithelial Tissue Functions - Absorption

• Takes in substances such as nutrients (e.g., in the intestines)

Epithelial Tissue Functions - Excretion

• Removes waste products from the body or from cells (e.g., sweat, urine components)

Epithelial Tissue Functions - Filtration

• Allows selective movement of substances, especially in structures like the kidneys

Epithelial Tissue Functions - Secretion

• Produces and releases substances such as mucus, enzymes, and hormones

Epithelial Tissue Functions - Transport of mucus

• Ciliated epithelial cells move mucus along surfaces (e.g., respiratory tract)

Epithelial Tissue Functions - Sensory function

• Contains sensory receptors that detect stimuli (e.g., touch, pressure)

What is connective tissue

• The connecting tissue of the body

• Most abundant and widely distributed tissue type

What are the three basic components of connective tissue

• Specialised cells

• Ground substance

• Protein fibres

What is the extracellular matrix (ECM) in connective tissue

• A combination of ground substance + fibres

• Makes up most of the tissue

• Cells are few and widely separated

Connective Tissue — Cell Types

Fibroblasts

• Produce fibres and ground substance

Macrophages

• Engulf and digest pathogens and debris

Lymphocytes

• Immune defence cells

Mast cells

• Release histamine during inflammation

Neutrophils

• Short‑lived immune cells that attack bacteria

Fat cells (adipocytes)

• Store energy as fat

Connective Tissue — Classifications (branch one)

• Connective tissue proper → loose/dense

• Cartilage

• Blood

• Bone

Connective Tissue Proper — Loose CT

• Areolar

• Reticular

• Adipose

Connective Tissue Proper — Dense CT

• Dense regular

• Dense irregular

• Elastic

Cartilage Types

• Hyaline

• Elastic

• Fibrocartilage

Bone Types

• Compact bone

• Spongy bone

Blood

• A fluid connective tissue

Which tissue type is the most diverse

• Connective tissue

Why is connective tissue the most diverse

• It includes many different subtypes with very different structures and functions

• e.g., areolar, adipose, dense CT, cartilage, bone, blood

Why is epithelial tissue more susceptible to damage

• It is exposed to the external environment, so it experiences friction, pathogens, chemicals, and physical stress.

How does epithelial tissue cope with this

• It has a high rate of cell division and regeneration, allowing rapid repair and replacement of damaged cells.

What is the ECM

• A non‑living substance surrounding the cells

• Composed of ground substance and protein fibre

What is ground substance

• Unstructured material filling the space between cells

• Contains protein fibre

What does ground substance do

• Holds a large volume of water (interstitial fluid)

• Can range from liquid → gel → solid

Types of protein fibres

• Collagen fibres

• Elastic fibres

• Reticular fibres

Collagen fibres - describe

• Tough

• High tensile strength

• Resist twisting and pulling forces

Elastic fibres - describe

• Long, thin fibres

• Allow stretch and recoil

Reticular fibres - describe

• Short fibres

• Continuous with collagen fibres

• Form delicate supporting networks

Why can connective tissue bear weight and withstand tension

• Because of its ECM, especially strong collagen fibres and water‑rich ground substanc

What do all classes of CT have

• A resident cell type in both immature and mature forms

What suffix do immature CT cells have

• “‑blast”

What do “blast” cells do

• Secrete ground substance and fibres

• Build the extracellular matrix

• Example: fibroblasts

What suffix do mature CT cells have

• “‑cyte”

What do “cyte” cells do

• Maintain the matrix

• Example: fibrocytes

What do Adipocytes do

• Store fat

What do Macrophages do

• Engulf pathogens and debris

What do Mast cells do

• Release histamine during inflammatio

Connective Tissue Proper - immature, mature

• Fibroblasts (immature)

• Fibrocytes (mature)

Cartilage - immature, mature

• Chondroblasts

• Chondrocytes

Bone - immature, mature

• Osteoblasts

• Osteocytes

Blood - immature, mature

• Haematopoietic stem cells (“blast” form)

• Erythrocytes (RBCs)

• Leukocytes (WBCs)

What is connective tissue proper

• A major category of CT with 6 subclasses (loose + dense) — you do not need to know the 6

What specialised cells does CT proper contain

• Fibroblasts (immature)

• Fibrocytes (mature)

What other tissue does CT proper include

• Adipose tissue, which contains adipocytes

Functions of CT proper

• Support

• Binding

• Storage

• Insulation

What are the 3 types of cartilage

• Hyaline

• Elastic

• Fibrocartilage

What is cartilage structurally like

• Has qualities between dense CT and bone

What is the ECM of cartilage like

• Up to 80% water

• Contains collagen and some elastic fibres

• Allows cartilage to withstand tension and compression

What specialised cells does cartilage contain

• Chondroblasts (immature)

• Chondrocytes (mature)

Does cartilage have nerves or blood vessels

• No — it is avascular and lacks nerve fibre

Functions of cartilage

• Support

• Absorb compression

What is bone made of

• Abundant collagen fibres

• A hard matrix due to calcium phosphate crystals

Which cells does bone contain

• Osteoblasts — produce the organic portion of the matrix

• Osteocytes — resorb bone when needed

Does bone have blood vessels and nerves

• Yes, bone contains both

Functions of bone

• Support

• Protection

• Storage

What is blood

• A fluid within blood vessels

• Blood cells surrounded by a liquid matrix called plasma

What cells does blood contain

• Erythrocytes (RBCs)

• Leukocytes (WBCs)

• Platelets

Function of blood

• Transport substances throughout the body

Where does all connective tissue come from

• Mesenchyme (an embryonic tissue)

What is loose connective tissue

• CT with a loose arrangement of fibres

• Contains lots of ground substance

What does this structure allow

• Flexibility

• Space for diffusion, nutrients, and immune cell

What is dense connective tissue

• CT with closely packed bundles of fibres

• Contains very little ground substance

What does this structure allow

• High tensile strength

• Ability to resist pulling forces