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4 main types of tissue in the human body

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1. Epithelial tissue: covers internal and external surfaces of the body. lines body cavities.

2. Connective tissue: supports, protects, and gives structure to tissues and organs

3. Muscle tissue: tissue movement by creating force, heat production

4. Nervous tissue: detects changes and transmits signals between different body parts (action potentials)

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Connects/separates and supports other tissue types.

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All connective tissue develops from mesenchyme (collection of undifferentiated cells).

1. Mesenchyme develops into immature cells (-blast: fibroblast, chondroblast, osteoblast)

2. Immature cells divide and make up the extracellular matrix (protein fibre + ground substance)

3. Immature cells differentiate into mature cells (-cyte: fibrocyte, chondrocyte, osteocyte)

4. Mature cells regulate and maintain the extracellular matrix. They have reduced capacity for cell division.

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Fibroblasts: Most common tissue cells. Secrete extracellular matrix

Macrophages: Develop from monocytes. Engulf cellular waste and bacteria via phagocytosis.

Plasma cells: Antibodies that attack foreign substances (B-lymphocyte)

Mast cells: Inflammatory response (produce histamine --> dilates blood vessels)

Adipocytes: fat storage cells (store triglycerides)

Leukocytes: White blood cells. Part of the immune response (allergies/infections)

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Collagen fibres (bone, cartilage, tendons, ligaments): Large and strong. Provide tensile strength (thick, parallel bundles).

Elastic fibres (skin, blood vessels, lung tissue): Smaller in diameter. Thin branching fibres allow stretch (up to 150%) and recoil.

Reticular fibres (spleen, lymph nodes, liver): Fine/thin branching fibres. Make up supporting structure.

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Found between cells and fibres

Consistency depends on tissue type

Support of cells

Storage of water

Site of exchange (between blood and cells)

Can be fluid, semi-fluid, gelatinous or hard

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Areolar, adipose, and reticular connective tissue, respectively.

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1. Areolar: Random arrangement of fibres in semifluid ground substance. Connects and surrounds structures like skin, organs, and vessels.

2. Adipose: contains adipocytes (fat cells).

White adipose tissue: energy reserve, insulates and protects organs.

Brown adipose tissue: generates heat (has lots of mitochondria and blood vessels)

3. Reticular: Fine interlaced network of reticular fibres and cells. Supporting framework for organs like the liver, spleen, and lymph nodes

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Contains more fibres, less ground substance in-between

1. Regular (tendons, ligaments): Collagen fibres arranged in parallel. Resists pulling forces from one direction (muscle-muscle, muscle-bone)

2. Irregular (deep layers of skin, pericardium, GI tract): Collagen fibres arranged irregularly. Resists forces from different directions. Provide strength to tissue.

3. Elastic (lung tissue, blood vessels): Made of elastic fibres. Ability to stretch and recoil.

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Very low blood supply, therefore harder to heal if damaged

Can endure more stress due to gel-like consistency

1. Hyaline (embryonic skeleton, external part of nose): The most abundant but weakest type. Gel-like ground substance surrounded by thin collagen fibres and chondrocytes. Reduces friction at the end of long bones and supports structure.

2. Fibrocartilage (intervertebral discs, menisci, pubic symphysis): Dense bundles of collagen fibres. Resists weight-bearing and compression forces.

3. Elastic (external ear, auditory canal, epiglottis): Elastic fibres surrounding chondrocytes. Provides support and elasticity in non-weight-bearing structures.

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Osteocytes inside hard extracellular matrix of calcium and phosphorous.

Supports soft tissue.

Protects delicate structures.

Promotes muscle movement.

1. Compact: Repeating unit- osteon. Strong, and provides protection and support. Bears stress of growing.

2. Spongy: Deliberately located where stresses are from different directions. Supports red bone marrow.

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Only connective tissue type that does not contain fibres (ground substance and cells only)

A special type of liquid connective tissue

Made of blood plasma

Elements: red blood cells, white blood cells, platelets