(AnaPhy) Lesson 3: Tissues

Tissue

a group of cells with similar structure and function, plus the extracellular substance surrounding them.

Histology

the study of tissues.

Epithelial Tissues

• covers and protects surfaces, both outside and inside the body

• exocrine and endocrine glands

Epithelial Tissue Characteristics

1. Mostly composed of cells

2. Covers body surfaces

3. Has an exposed surface

4. Attaches at the basal surface

5. Specialized cell connections and matrix attachments

6. Avascular

7. Capable of regeneration

Simple epithelium

consists of a single layer of cells, with each cell extending from the basement membrane to the free surface.

Stratified epithelium

consists of more than one layer of cells, but only the basal layer attaches the deepest layer to the basement membrane.

Pseudostratified columnar epithelium

• s a special type of simple epithelium, that appears to be falsely stratified.

• It consists of one layer of cells, with all the cells attached to the basement membrane.

Squamous cells

flat or scalelike

Cuboidal cells

cube-shaped—about as wide as they are tall.

Columnar cells

tend to be taller than they are wide.

Simple Cuboidal

• 1 layer of square-shaped cells

• Secretion

• glands, ovaries, kidneys

Simple Squamous

• 1 layer of flat, tile-like cells

• good for diffusion & filtration

• blood vessels, lungs, heart, kidneys

Pseudostratified Columnar

• 1 layer of tall, narrow cells appears stratified but isn’t

• secretes mucus and propel debris out of respiratory tract (cilia)

• nasal cavity and trachea

Simple Columnar

• layer of tall, narrow cells

• secrete mucus and absorption

• stomach, intestines, resp. tract

Stratified Squamous

• many layers of flat, tile-like cells

• protect and acts as a barrier

• skin, mouth, throat, esophagus

Transitional

• special type of stratified epithelium; changes shape -stretched squamous.

• hold fluids

• urinary bladder

Keratinized Stratified Squamous Epithelium

• The outer layer of the skin

• The keratin reduces the loss of water from the body.

Nonkeratinized Stratified Squamous Epithelium

• Of the mouth is a moist nonkeratinized stratified squamous epithelium.

• Provides protection against abrasion and acts as a mechanical barrier.

Gastrulation

a critical stage in early animal development when a blastula reorganizes into a gastrula, a multi-layered embryo.

Ectoderm

• The outermost layer.

• Gives rise to:

  • Outer epithelium

  • Neural tube (spinal cord)

  • Neural crest (nervous system)

Mesoderm

• The middle layer.

• Gives rise to:

  • Notochord (bone of spine)

  • Digestive & urogenital system

Endoderm

• The innermost layer.

• Gives rise to:

  • Digestive system: Lining of the stomach, intestines, liver, pancreas.

  • Respiratory system: Lungs.

  • Endocrine glands: Thyroid, pancreas.

Tight junctions

cell connection structures that form barriers and anchor cells to each other.

Adhesion belts

• Are found just below the tight junctions, and help tight junctions anchor epithelial cells to each other.

• They prevent the passage of materials between epithelial cells because they completely surround each cell.

Endocrine glands

are ductless glands; they secrete their products (termed hormones) into the bloodstream.

Exocrine glands

glands with ducts; type of gland that release substances through ducts onto the body's surfaces.

Dense Regular Connective Tissue

• Characterized by tightly packed, parallel collagen fibers, providing high tensile strength in a single direction. (limited space / orderly)

• Found in:

  • Tendons: Connect muscles to bones.  

  • Ligaments: Connect bones to bones at joints.  

  • Aponeuroses: Sheet-like tendons that connect muscles to other muscles or bones.

Dense Irregular Connective Tissue

• Collagen fibers are interwoven in a random arrangement, providing strength and resistance to stress in multiple directions. (Scattered & random)

• Found in:

  • Dermis of the skin: Provides strength and resilience.  

  • Joint capsules: Surround and support joints.  

  • Organ capsules: Enclose organs such as the liver and kidneys.

Elastic connective tissues

• are a type of dense connective tissue that are characterized by a high proportion of elastic fibers.

• The presence of abundant elastin fibers within the extracellular matrix. Elastin is a protein that allows the tissue to stretch and recoil, returning to its original shape.

Areolar Connective Tissue

• This is the most common type.

• It has a loose arrangement of collagen, elastic, and reticular fibers. (connective tissue glue)

• Contains various cell types like fibroblasts, macrophages, and mast cells.  

• Found beneath epithelia, surrounding organs, and in the dermis of the skin.

Adipose Connective Tissue

• Primarily composed of adipocytes (fat cells).  

• Stores energy in the form of triglycerides.  

• Provides insulation and cushioning.  

• Found beneath the skin, around organs, and within bone marrow

Reticular Connective Tissue

• Contains a network of reticular fibers that form a supportive framework for cells.  

• Found in lymphoid organs like lymph nodes, spleen, and bone marrow.  

• Provides a supportive framework for immune cells.

• Forms the internal framework of stroma

   

Cartilage

• Firm but flexible.  

• Provides support, cushioning, and smooth surfaces for joints.  

• Avascular (lacks blood vessels), so nutrients diffuse through the matrix.

Bone

• Hard and mineralized (calcium and phosphorus).  

• Provides support, protection, and movement.  

• Stores minerals (calcium) and produces blood cells (in bone marrow).

Blood

• Fluid connective tissue.  

• Transports oxygen, nutrients, hormones, and waste products.

Hyaline Cartilage

• Most common type.

• Found in:

  • Ends of bones in joints (articular cartilage)

  • Nose

  • Trachea

  • Ribs

• Provides smooth surfaces for joint movement, flexibility, and support.

Elastic Cartilage

• More flexible than hyaline cartilage due to the presence of elastic fibers.

• Found in:

  • External ear

  • Epiglottis (flap of tissue that covers the windpipe)

  • Parts of the larynx (voice box)

• Provides support and maintains the shape of structures that need to bend and flex.

Fibrocartilage

• Contains a high density of collagen fibers.

• Found in:

  • Intervertebral discs (between vertebrae)

  • Menisci (cartilage pads in the knee)

  • Pubic symphysis (joint where the two pubic bones meet)

• Provides support and shock absorption in areas that experience high stress.

Osteoprogenitor

Stem cells: These are the precursor cells for all other bone cells, and can differentiate into osteoblasts.

Osteoblasts

Bone-building cells: They are responsible for synthesizing and secreting the organic matrix of bone (collagen) and initiating the process of mineralization (hardening of the bone)

Osteocytes

• Mature bone cells: These are the most abundant type of bone cell.  

• Function: They maintain the bone matrix and regulate bone turnover.

  They also play a role in sensing mechanical stress on the bone.  

Osteoclasts

• Bone-resorbing cells: They are large, multinucleated cells that break down bone tissue.  

• Function: This process is crucial for bone remodeling, repair, and calcium homeostasis/

Red Blood Cells (Erythrocytes)

Primarily responsible for transporting oxygen from the lungs to all the cells in the body and carrying carbon dioxide back to the lungs to be exhaled.

White Blood Cells (Leukocytes)

Key components of the immune system, fighting infections.

Platelets (Thrombocytes)

• Function: Essential for blood clotting.  

• Role: When a blood vessel is injured, platelets clump together to form a plug, helping to stop bleeding.  

Skeletal Muscle

• Appearance: Striated (has visible stripes)  

• Control: Voluntary

• # of Nuclei: Multinucleated

• Location of Nuclei: Peripheral

Cardiac Muscle

• Appearance: Striated  

• Control: Involuntary (you don't consciously control it)

• # of Nuclei: Mononucleated

• Location of Nuclei: Central

Smooth Muscle

• Appearance: Non-striated (no visible stripes)  

• Control: Involuntary

• # of Nuclei: Mononucleated

• Location of Nuclei: Central

Neurons

• These are the functional units of the nervous system, responsible for transmitting electrical signals (nerve impulses).  

• They have specialized structures like dendrites (receive signals), axons (transmit signals), and synapses (junctions where signals are passed between neurons).

Neuroglia

These are supporting cells that provide various functions for neurons, such as:

• Protection and defense

• Maintenance of the extracellular environment

• Support and insulation

Astrocytes

• Regulate the chemical environment: Control the levels of neurotransmitters and ions around neurons.

• Support and brace neurons: Provide a structural framework.

Oligodendrocytes

Produce myelin, a fatty substance that insulates axons and speeds up nerve impulse transmission in the central nervous system

Microglia

• Act as the immune cells of the brain.  

• Phagocytize (engulf and destroy) debris, pathogens, and damaged cells.

Ependymal Cells

• Line the cavities (ventricles) of the brain and the central canal of the spinal cord.  

• Help circulate cerebrospinal fluid (CSF).

Schwann Cells

Produce myelin, a fatty substance that insulates axons and speeds up nerve impulse transmission in the peripheral nervous system

Merocrine

secretion involves the release of secretory products by exocytosis.

Apocrine

secretion involves the release of secretory products as pinched-off fragments of the gland cells.

Holocrine

secretion involves the shedding of entire cells

Macrophages

are large cells that are capable of moving about and ingesting foreign substances, including microorganisms in the connective tissue.

Mast cells

are nonmotile cells that release chemicals, such as histamine, that promote inflammation.