Structure and Functions of Animal Cells

Hierarchy of Biological Organization

  • The structure of living organisms is often the basis for designing objects; structure is related to function.

  • In complex multicellular organisms (e.g., animals), cells vary in shape, size, and specialized function.

  • Key principle: structure determines function across biological levels.

Levels of Biological Organization (with descriptions and examples)

  • Cell

    • Description: the smallest, basic, functional unit of life formed when different atoms and molecules combine and function together

    • Examples: skin cells, blood cells, muscle cells or fibers, neurons

  • Chemical

    • Description: atoms and molecules that make up the basic unit of life

    • Examples: four biomolecule groups: carbohydrates, proteins, lipids (fats), nucleic acids

  • Organelle

    • Description: distinct and specialized subcellular structures that contribute to the cell’s maintenance and reproduction; membrane-bound in eukaryotic cells

    • Examples: mitochondria, nucleus, Golgi apparatus, endoplasmic reticulum

  • Tissue

    • Description: groups of cells that work together to perform a specialized function

    • Examples: epithelial tissue, connective tissue, muscle tissue, nervous tissue

  • Organ

    • Description: groups of tissues that work together to perform a specialized function

    • Examples: skin, lungs, heart muscle, brain

  • Organ System

    • Description: groups of organs that work together to perform a certain process in the body

    • Examples: integumentary system, respiratory system, circulatory system

  • Organism

    • Description: formed by different organ systems that create complex interactions to maintain balance/homeostasis and sustain life

    • Examples: humans, grasses, dogs, cats, mushrooms

  • Population

    • Description: organisms that belong to the same species and live in the same area

    • Examples: humans in the same house; koalas in a forest area

  • Community

    • Description: different populations living in the same area

    • Examples: humans, cats, and dogs in the same house; koalas, kangaroos, and various tree species in an area of the forest

  • Ecosystem

    • Description: all the communities interacting with one another and with their environment

    • Examples: humans, cats, dogs, and grasses obtaining resources from soil, water, and sunlight

  • Biosphere

    • Description: all the different kinds of ecosystems; the entire surface of Earth where life thrives

    • Examples: all planetary life-supporting environments on Earth

Tissues in Animals

  • Tissues are groups of cells that are similar in structure and function.

  • The four types of animal tissues differ significantly in structure and function.

Epithelial Tissue (epithelium)

  • Definition: forms the inner and outer lining of organs, coverings on surfaces, and primary glandular tissue of the body.

  • Types by arrangement and shape include:

    • Simple squamous

    • Simple cuboidal

    • Simple columnar

    • Pseudostratified columnar

    • Stratified squamous

    • Stratified cuboidal

    • Stratified columnar

  • Epithelial tissues are characterized by tightly packed cells that cover and protect body parts.

Epithelial Tissue: Simple Squamous

  • Layers/shape: One layer; flat, scale-like cells

  • Examples: air sacs or alveoli, capillary walls

  • Functions: site of diffusion or exchange of substances; secretion

Epithelial Tissue: Simple Cuboidal

  • Layers/shape: One layer; cube-shaped cells

  • Examples: glands and their ducts, ovaries, lining of kidney tubules

  • Functions: absorption and secretion

Epithelial Tissue: Simple Columnar

  • Layers/shape: One layer; elongated/column-shaped

  • Examples: walls of the gastrointestinal tract and body cavities

  • Functions: absorption and secretion

Epithelial Tissue: Pseudostratified Columnar

  • Layers/shape: One layer that appears layered (false layering)

  • Examples: lining of the respiratory tract (often ciliated)

  • Functions: absorption and secretion; typically with cilia

  • Notes: nucleus positions vary to create the false layering effect

Epithelial Tissue: Stratified Squamous

  • Layers/shape: More than one layer; flat, scale-like

  • Examples: epidermis; lining of mouth, esophagus, vagina

  • Functions: protection against abrasion or constant exposure to friction

Epithelial Tissue: Stratified Cuboidal

  • Layers/shape: More than one layer; cube-shaped

  • Examples: sweat glands, salivary glands, mammary glands

  • Functions: protection and secretion

Epithelial Tissue: Stratified Columnar

  • Layers/shape: More than one layer; elongated cells

  • Examples: ducts of some glands

  • Functions: protection and secretion

Connective Tissue

  • Connective tissues maintain the form of the body and its organs and provide support.

  • Major connective tissue groups include:

    • Bone (osseous) tissue

    • Cartilage

    • Dense connective tissue

    • Loose connective tissue

    • Blood

Cartilage (three types)

  • Hyaline cartilage

    • Locations: Between tips of ribs and bones of sternum; covering bone surfaces at synovial joints; supporting larynx (voice box), trachea, and bronchi; forming part of nasal septum

    • Functions: Provides stiff but somewhat flexible support; reduces friction between bony surfaces

    • Structure: Chondrocytes in lacunae; matrix

  • Elastic cartilage

    • Locations: Auricle of external ear; epiglottis; auditory tube; cuneiform cartilages of larynx

    • Functions: Provides support, tolerates distortion without damage and returns to original shape

  • Fibrous cartilage

    • Locations: Pads within knee joint; between pubic bones of pelvis; intervertebral discs

    • Functions: Resists compression; prevents bone-to-bone contact; limits relative movement

Hyaline/Elastic/Fibrous Cartilage visuals (illustrations included in slides)

  • Hyaline cartilage: chondrocytes in lacunae; matrix

  • Elastic cartilage: elastic fibers in matrix; chondrocytes in lacuna

  • Fibrous cartilage: dense matrix with collagen fibers; chondrocytes in lacuna

Dense connective tissue

  • Description: Matrix predominantly collagen fibers with fewer cells; fibroblasts

  • Examples: Tendons (muscles to bones); Ligaments (bones to bones at joints)

  • Function: Support

Loose connective tissue

  • Types:

    • Areolar tissue

    • Adipose tissue (fat)

    • Reticular connective tissue

  • Functions: Protection, insulation, storage, and support

  • Areolar tissue: loose, soft tissue with space between fibers; holds things together; flexibility; stores water; fights infections

  • Adipose tissue: stores fat; stores energy; insulates; cushions organs

  • Reticular tissue: mesh-like framework for immune cells; helps filter out unwanted materials

  • Locations: Under the skin; around organs; between muscles; lymphoid organs (for reticular)

Blood

  • Components: Plasma and cellular components (blood cells)

  • Special note: Fibers are visible only during clotting (soluble proteins)

  • Functions: Transport of substances; immune response; blood clotting

Muscular Tissue

  • Function: Contract to cause movement; all muscle types share this primary function

  • Types of muscle tissues:

    • Skeletal muscle

    • Cardiac muscle

    • Smooth muscle

Skeletal Muscle

  • Location: Attached to the skeleton/bones

  • Description: Long, cylindrical, striated (visible stripes), multinucleated

  • Control: Voluntary

Smooth Muscle

  • Location: Walls of hollow organs (e.g., intestines, stomach, bladder, blood vessels, uterus)

  • Description: Non-striated, uninucleated, spindle-shaped cells

  • Control: Involuntary

Cardiac Muscle

  • Location: Heart

  • Description: Uninucleated (one nucleus); striated; intercalated discs

  • Control: Involuntary

Nervous Tissue

  • Neuron: basic unit; conducts electrochemical signals

  • Supporting cells (glia) support neurons

  • Key glial components include: astrocytes, microglial cells, oligodendrocytes, satellite cells, Schwann cells

Astrocytes (CNS)

  • Location: Central Nervous System (brain and spinal cord)

  • Function: Receive information, process, and send commands; control center for movement, thought, sensation, and reaction

  • Roles: Nutrient supply to neurons; waste cleanup; repair following injury; maintenance of chemical balance

  • Metaphor: caretakers that ensure smooth operation of neural activity

Microglial cells (CNS)

  • Role: Immune cells in CNS; brain protection; cleanup of dead cells; brain repair

  • Function: Help keep the brain healthy and safe

Ependymal cells (CNS)

  • Role: Line central cavities of brain and spinal cord; produce and circulate cerebrospinal fluid (CSF)

  • Function: CSF circulation and a barrier between CSF and brain/spinal cord tissue; protective cushion for neural tissue

Oligodendrocytes (CNS)

  • Role: Speed up communication between nerve cells

  • Function: Insulate axons to enhance signal transmission in CNS

Satellite cells (PNS)

  • Role: Support cells surrounding nerve cells in ganglia (outside CNS)

  • Function: Protect and support neurons in the peripheral nervous system

Schwann cells (PNS)

  • Role: Myelinate peripheral axons; assist in nerve repair

  • Function: Speed up electrical signals; aid in nerve regeneration in the PNS

Remember: Structure and Function Relationships

  • The structure and form of animal tissues are related to their functions:

    • Epithelial tissues: tightly packed cells for covering and protection

    • Connective tissues: ground substances and fibers to support, bind, and protect organs

    • Muscular tissues: highly specialized contractile cells for movement

    • Nervous tissues: networks of nerve cells with irritability and conductivity for electrochemical signaling

Check Your Understanding (Practice prompts)

  • 1) Identify the level of biological organization described: a group of organs that coordinate to perform a specific function

    • Answer: Organ system

  • 2) Identify the level described: butterflies of the same species living in the same area

    • Answer: Population

  • 3) Identify the level described: atoms and molecules interacting with one another

    • Answer: Chemical level

Let’s Sum It Up!

  • There are several levels of biological organization, from lowest to highest: $chemical$, $organelle$, $cell$, $tissue$, $organ$, $organ system$, $organism$, $population$, $community$, $ecosystem$, and $biosphere$.

  • Animals have four types of tissue: epithelial, connective, muscle, and nervous; they differ significantly in structure and function.

  • Epithelial tissue:

    • Composed of tightly packed cells that cover, line, and protect body parts

    • Classified by arrangement: simple, stratified, pseudostratified

    • Classified by shape: squamous, cuboidal, columnar

  • Connective tissue:

    • Made up of cells and an extracellular matrix that connects, protects, and supports body parts

    • Major types: bone, cartilage, dense connective tissue, loose connective tissue, blood

  • Muscular tissue:

    • Composed of highly specialized muscle cells that contract to produce movement

    • Three types: skeletal, cardiac, smooth

  • Nervous tissue:

    • Made of neurons that receive and conduct electrochemical signals

    • Supporting cells (glial cells) provide support, protection, and insulation

  • Terminal reminders:

    • The slide also emphasizes practical examples and locations for cartilage and connective tissues, and highlights the roles of glial cells and neuron-supporting cells in the nervous system

Notation for a famous equation mentioned in the slides

  • On the slide about tendons/ligaments there is a reference to a famous equation: E=mc2E=mc^2