Cell Structure, Function, and Tissue Types in Biology

Cell

The basic unit of life

Cell Theory

(1) All organisms are made of cells; (2) the cell is the basic unit of life in all living things; (3) all cells come from existing cells

Matthias Schleiden

German scientist who concluded that all plant parts are made of cells

Theodor Schwann

German scientist who concluded that all animal parts are made of cells; wrote the first two parts of the cell theory

Rudolf Virchow

About 20 years later, discovered that cells can't develop from anything but other cells

Prokaryotic cell

Cell lacking a membrane-bound nucleus and other membrane-bound organelles; circular DNA; bacteria

Eukaryotic cell

Cell with a membrane-bound nucleus and organelles; linear DNA; includes plants, animals, fungi, protists; more complex than bacteria; some have a cell wall and some do not

Organelles

Structures that enable the cell to live, grow, and reproduce; all cells have them but not all have membrane-covered organelles

Cell membrane

Outer layer of the cell; allows nutrients into the cell and wastes out; 'Gate into the city'

Cytoplasm

Jelly-like fluid in the cell that holds the organelles

Nucleus

Control center of the cell; contains DNA and info on how to make all the cell's proteins; 'library of the cell' / 'Mayor's Office'

Nucleolus

Part of the nucleus that stores materials used to make ribosomes

Mitochondria

Power center/power plant of the cell; makes ATP (needs oxygen) for energy to move, divide, etc.; thousands per active cell; 'Electric company of the cell'

Ribosomes

Site where proteins are made; 'Factories of the cell'

Endoplasmic reticulum (ER)

Transportation system of the cell; delivers proteins to different parts of the cell through tubular connections; 'Roadways of the cell'; like FedEx/UPS

Rough ER

ER with ribosomes attached

Smooth ER

ER with no ribosomes

Golgi complex

Packaging house of the cell; receives lipids and proteins from the ER, modifies, packages, and ships them out of the cell

Camillo Golgi

Italian scientist who first discovered the Golgi complex

Lysosomes

Special vesicles containing enzymes; digest food particles and cell parts ('Garbage men') and foreign invaders ('Police men')

Vacuole

Stores water, food, and wastes; largest organelle in plant cells; found only in plants; full of water and air to support the cell.

Turgor pressure

Pressure the water uses to keep the plant upright; when air and water are lost, the plant goes limp.

Cell wall

Found only in plants; protects and supports the cell; made of cellulose.

Cellulose

Intertwined material (like a blanket or piled hashbrowns) that makes up plant cell walls.

Chloroplasts

Found only in plant cells; contain chlorophyll (makes plants green); site of photosynthesis (uses sunlight to make sugar, which mitochondria use to make energy).

Organelles found in BOTH plant and animal cells

Nucleus, Golgi complex, mitochondrion, lysosomes, endoplasmic reticulum, cell membrane, ribosomes.

Organelles found ONLY in plant cells

Vacuoles, chloroplasts, cell wall.

4 basic tissue types

Epithelial, connective, muscular, nervous.

Two main kinds of epithelium

Covering and lining epithelium; glandular epithelium.

Covering and lining epithelium

Covers outer surfaces of the body and lines internal body passages.

Glandular epithelium

Contains cells specialized for secretion.

Functions of epithelium

Covering external surfaces, lining internal surfaces, protection, absorption, secretion, sensation, contraction.

Characteristics of epithelium

Basal lamina anchors it to connective tissue; very cohesive (intercellular junctions); varies in shape and size; avascular; shows polarity.

Basement membrane

Basal lamina + reticular lamina.

Functions of basal lamina

Structure (attaches epithelium to connective tissue); organization (arranges plasma membrane proteins); filtration (regulates movement of materials between epithelium and connective tissue).

Zonula occludens (tight junctions)

Most apical junction; bands that encircle each cell; membranes of adjacent cells fuse to seal off the intercellular space; claudins and occludins form the seal; more zonula occludens = tighter seal.

Claudins and occludins

Two families of proteins that form the seal in tight junctions.

Zonula adherens (belt desmosomes)

Bands encircling each cell; cadherin and catenin proteins provide adhesion; actin filaments insert into attachment plaques.

Macula adherens (desmosomes)

Spot adhesion between cells; cadherins in intercellular space; cytokeratin intermediate filaments insert into plaques containing desmoplakin and plakoglobin; super strong; more desmosomes = tighter attachment.

Hemidesmosomes

Attach epithelial cells to the basal lamina using integrins at the basal portion of the cell.

Junctional complex order (simple columnar of digestive tract)

ZO (zonula occludens), ZA (zonula adherens), D (desmosome).

Gap (communicating) junction / nexus

Found along lateral surfaces of epithelial cells and in other cells (e.g., cardiac muscle); connexons (protein channels with central pores) let ions and small molecules pass between adjacent cells for communication.

Connexons

Protein channels with central pores that connect plasma membranes in gap junctions.

Microvilli

Increase surface area for absorption or secretion; central core of actin microfilaments; don't wave like cilia.

Brush border (striated border)

Microvilli + cell coat (glycocalyx).

Stereocilia

Long, non-motile, branched microvilli found in parts of the male reproductive system.

Cilia

Contain microtubules in a 9 + 2 configuration called an axoneme (2 central microtubules surrounded by 9 pairs).

Squamous cell shape

Width > height (flattened).

Cuboidal cell shape

Width = height (square, round).

Columnar cell shape

Width < height (tall and slender).

Simple epithelium

Single layer of cells.

Pseudostratified epithelium

All cells contact the basal lamina but not all reach the lumen.

Stratified epithelium

Two or more layers of cells.

Transitional epithelium

Stratified epithelium that changes shape with stretching; cuboidal when relaxed, squamous when stretched.

Keratinized stratified squamous epithelium

Keratin covers areas where skin is thin but needs protection.

Non-keratinized stratified squamous epithelium

Lines areas that are always moist (e.g., esophagus); no keratin layer.

Exocrine gland

Retains connection with surface epithelium; secretes through ducts.

Endocrine gland

No connection with surface epithelium; ductless, highly vascularized; hormones secreted into the blood.

Simple exocrine gland

Unbranched duct that may be straight or coiled.

Tubular gland

Terminal secretory portion is shaped like a tube.

Unicellular gland

Consists of single cells; e.g., mucus-secreting goblet cells in intestines and respiratory passages.

Multicellular gland

Secretory portion (end-piece) plus an epithelium-lined ductal portion that delivers the secretion to the exterior.

Compound exocrine gland

Repeated branching pattern of ducts draining the secretory portion.

Acinar (alveolar) gland

Shaped like a flask.

Tubuloacinar gland

Mixture of tubular and acinar secretory portions.

Mucous glands

Produce viscous secretion that lubricates or protects the inner lining of organs.

Serous glands

Produce watery secretions rich in enzymes.

Mixed glands

Contain both mucous and serous secretory glands.

Merocrine glands

Release secretion by exocytosis without losing cellular components; most common type; e.g., mucous and serous glands.

Holocrine glands

Cells themselves become the secretory product (accumulate lipid, die, degenerate); e.g., sebaceous gland (sebum).

Apocrine glands

Intermediate type; apical portion of the cell's cytoplasm is lost during secretion; e.g., mammary gland.

Endocrine gland classes

Unicellular glands (e.g., enteroendocrine cells), separate and distinct endocrine organs, mixed glands.

Ion transporting cells

Have deep basal membrane invaginations, zonula occludens, and basal mitochondria providing energy for ion transport; e.g., proximal tubules in kidney.

Serous secretory cells

Large rounded nucleus; abundant rough ER, Golgi, and secretory granules; e.g., pancreatic acinar cells, salivary gland serous cells.

Mucous secretory cells

Abundant rough ER, Golgi, secretory granules; produce mucins (protective, lubricant glycoproteins); e.g., stomach mucous cells, goblet cells, salivary mucous cells.

Neuroendocrine cells

Dense secretory granules containing polypeptides and/or amines (e.g., epinephrine, norepinephrine); scattered throughout the body.

Myoepithelial cells

Spindle-shaped cells between basal lamina and basal cytoplasm; embrace gland acini like an 'octopus on a rock'; contain actin to contract and squeeze out secretory product.

Connective tissue

Most abundant and widely distributed primary tissue; types: embryonic, connective tissue proper, cartilage, bone, blood.

Functions of connective tissue

Binding and support, protection, insulation, transportation.

Characteristics of connective tissue

Mesenchyme as common origin; varying vascularity; nonliving extracellular matrix (ground substance + fibers).

Ground substance

Unstructured material filling space between cells; made of interstitial fluid, adhesion proteins (fibronectin and laminin), and proteoglycans (GAGs); acts as a molecular sieve.

Collagen fibers

Tough; provide high tensile strength.

Elastic fibers

Long, thin fibers that allow stretching.

Reticular fibers

Branched collagenous fibers that form delicate networks.

Fibroblast

Cell that makes connective tissue proper.

Chondroblast

Cell that makes cartilage.

Osteoblast

Cell that makes bone.

Hematopoietic stem cell

Gives rise to blood cells (WBCs, plasma cells, macrophages, mast cells).

Embryonic connective tissue

Derives from mesoderm; found mainly in the umbilical cord; stellate mesenchymal cells in jelly-like ECM; divided into mesenchyme and mucoid connective tissue.

Mesenchyme

Embryonic tissue of unspecialized stellate cells in a gelatinous ground substance; sparse collagen fibers; gives rise to all connective tissues, bone, cartilage, and circulatory and lymphatic systems.

Mucoid connective tissue (Wharton's jelly)

Gelatinous ground substance in the umbilical cord; spindle cells resemble fibroblasts; in adults found in the vitreous body of the eye and nucleus pulposus of intervertebral discs.

Connective tissue proper

All mature connective tissues besides bone, cartilage, and blood; divided into loose and dense.

Areolar connective tissue

Loose; gel-like matrix with all three fiber types; fibroblasts, macrophages, mast cells, some WBCs; wraps and cushions organs; widely distributed.

Adipose connective tissue

Loose; closely packed adipocytes; stores food, insulates against heat loss, supports and protects; under skin, around kidneys, in abdomen and breasts.

Reticular connective tissue

Loose; reticular fibers and reticular cells form a soft internal skeleton (stroma); in lymph nodes, bone marrow, spleen.

Dense regular connective tissue

Parallel collagen fibers with a few elastic fibers; fibroblasts; attaches muscle to bone/muscle and bone to bone; in tendons, ligaments, aponeuroses.

Dense irregular connective tissue

Irregularly arranged collagen fibers with some elastic fibers; withstands tension in many directions; in dermis, digestive tract submucosa, fibrous organ capsules.

Hyaline cartilage

Firm matrix with imperceptible collagen fibers; chondrocytes in lacunae; supports, reinforces, cushions, resists compression; costal cartilage, embryonic skeleton, ends of long bones, nose, trachea, larynx.

Elastic cartilage

Like hyaline but with more elastic fibers; maintains shape while allowing flexibility; external ear (pinna) and epiglottis.

Fibrocartilage

Less firm matrix with thick collagen fibers; tensile strength and absorbs compression shock; intervertebral discs, pubic symphysis, discs of the knee joint.