Epithelial Tissue

• Animal tissues are divided into 4 main types: epithelial, connective, muscle, and nervous.

Epithelial Tissue

• Epithelial tissue is found as the inner and outer layers of organs with main functions including protection, absorption, and secretion.
• Can be classified by cell shape and arrangement.
• Cell shapes: squamous (flat), cuboidal (cube-shaped), columnar (tall).
• Arrangements: simple (one layer), stratified (multiple layers), pseudostratified (single layer, varying size and shape).
• Has polarity: apical (top side, faces lumen) and basal (bottom side).
• The basement membrane is a thin protein sheet attaching the basal surface to other tissues.
• Cilia are hair-like projections that move substances past cells.
• Microvilli are tiny extensions that increase surface area for absorption or adhesion.
• Simple squamous epithelium is mainly used for protection and is found in the lung cavity, heart, and abdominal cavity.
• Simple cuboidal epithelium specializes in secretion and is found in glands like the thyroid, salivary glands, and pancreas.
• Simple columnar epithelium has a nucleus closer to the basal surface and is capable of secretion and absorption.
• Simple columnar ciliated epithelium is found in the respiratory tract (for removing foreign particles), uterus, and oviducts (for moving eggs), with a primary protective function.
• Stratified squamous epithelium is found in areas with common abrasion, like skin, cheek, gums, cornea, and vagina.
• Pseudostratified ciliated columnar epithelium appears layered but is a single layer, primarily found in the respiratory tract for protection.
• Goblet cells are specialized mucus-secreting cells.
• Goblet cells + ciliated columnar cells = pseudostratified ciliated columnar epithelium.

Connective Tissue

• Connects and supports body structures.
• Consists of extracellular matrix (solid, liquid, or gelatinous) and fibers.
• Fibers include collagenous (strength and flexibility), elastic (elasticity), and reticular (holding tissues and organs together).
• Fibroblasts produce all fibers in connective tissue.
• Immune defense cells include macrophages (engulf and digest foreign particles) and mast cells (release histamine for inflammation).
• Chondrocytes are cells of cartilage, and osteocytes are cells of bone.
• Loose connective tissue is found around organs and attached to epithelium, with loosely scattered fibers and fibroblasts.
• Collagenous fibers are long, thick, and stretchy.
• Elastic fibers are thin.
• Fibroblasts are dark purple circles (usually the nucleus).
• Mast cells are grainy.
• Extracellular matrix is everything that isn't cells.
• Dense irregular connective tissue is found in the dermis of the skin and submucosa of the digestive tract, composed of tightly packed interwoven collagenous fibers and fibroblasts
• Regular connective tissue has densely packed collagenous fibers arranged in an orderly manner with fibroblasts.
• Elastic connective tissue is composed of a mix of collagenous and elastic fibers, densely packed.
• Reticular connective tissue is branching tissue that holds organs together.
• Adipose tissue stores lipid for energy reserves, insulation, and cushioning.
• Hyaline cartilage has a solid matrix, is smooth and semitransparent and supports the body.
• Lacunae are areas not filled with solid matrix, where cells are located.
• Chondrocytes are cartilage cells that build and maintain the solid cellular matrix.
• Elastic cartilage, similar to hyaline cartilage, has elastic fibers and is more stretchy.
• Bone's functional unit is the osteon (Haversian system), with a central canal surrounded by concentric rings of lacunae.
• Lamellae: layers of solid matrix between lacunae.
• Canaliculi are tiny channels delivering oxygen and nutrients to osteocytes.
• Blood has a liquid matrix (plasma) containing erythrocytes (oxygen carriers), platelets (clotting), and leukocytes.

Muscle Tissue

• Muscle is contractile, enabling movement.
• Cells tend to be large, and some are multinucleated.
• Muscle fiber is a single muscle cell composed of myofibrils, which are composed of myofilaments.
• Sarcolemma is the muscle cell's plasma membrane.
• Sarcoplasm is the muscle cell's cytoplasm.
• Three major types are striated (skeletal), smooth, and cardiac.
• Striated muscle (skeletal) is striped, attaches to bones, and is usually associated with voluntary movements.
• Smooth muscle is found within organs, and its movement is usually not under conscious control.
• Cardiac muscle is found only in the heart.
• Striated muscle (longitudinal section): A bands (thicker myofilaments, darker bands) and I bands (thinner myofilaments, lighter bands).
• A and I bands are not visible on cross sections
• Smooth muscle (longitudinal): less regularly arranged than skeletal muscle (no striations), single nucleus, smaller cells.
• Smooth muscle (cross-section): smaller in diameter than striated muscle; each cell has one nucleus.
• Cardiac muscle: interwoven fibers, one or more nuclei, striations, shorter cells than striated muscle.
• Intercalated discs are bold lines representing tight connections between neighboring cardiac muscle cells for coordinated timing.

Nervous Tissue

• Functions to send electrical signals throughout the body.
• Found in the central and peripheral nervous system.
• Two major categories of cells: neurons (carry signals) and glial cells (support neurons/neuroglia).
• Perikaryon (cell body) contains the nucleus and other major organelles.
• Neuron processes include dendrites (carry signals toward the perikaryon) and axons (carry signals away from the perikaryon).
• Nerves (l.s.) are bundles of neuron processes carrying nerve signals
• Schwann cells are specialized glial cells that insulate and speed up conduction of the never signal
• Contain myelin, a lipid that functions to insulate the nerve signal
• Myelin sheath is multiple Schwann cells wrapped in a series around the neuron process
• Nodes of Ranvier are tiny gaps between Schwann cells.
• The spinal cord is divided into grey matter (neuron perikaryon and glial cells) and white matter (neuron processes covered with myelin sheath).
• Oligodendrocytes are the cells around the neuron process.
• The central canal is a hollow area in the middle of the spinal cord.

Animal Diversity

• Animals belong to the domain Eukarya and kingdom Animalia.
• There are 7-8 million extant species, with only about 1 million formally named and described.
• Distinguished from other multicellular eukaryotes by the inability to perform photosynthesis.
• Linnaean classification: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
• Clades are monophyletic and do not have an agreed-upon rank.

Phylum Porifera

• Commonly known as sponges.
• Composed of about 5,500 species of marine and freshwater animals.
• Simplest animals, asymmetrical, and lack true tissues.
• Sessile (non-mobile) with sac-like bodies.
• Filter feeders use intracellular digestion.
• Sponges pull water through pores into the spongocoel (central chamber).
• Choanocytes lining the spongocoel engulf and digest food particles.
• Amoebocytes transport nutrients and produce spicules.
• Water exits through the osculum ("little mouth").
• Food must be small enough to be engulfed and broken down inside a cell.
• Spongin fibers are composed of protein spongin.
• Spicules are composed of calcium carbonate or silica.
• Connected to the environment by the basal disc.

Class Calcarea, Order Leucosolenida, Family Grandtiidae, Genus Grantia

• Genus of sponge with a folded body wall that creates water circulation and increases surface area.
• The body plan is a tall tube.

Phylum Ctenophora

• Commonly known as comb jellies.
• Composed of about 100 extant marine animals.
• Move with eight rows of cilia.
• Radially symmetrical.
• Generally considered to have two simple tissues
• Comb rows: rows of fused cilia that beat synchronously to propel animal.
• Many members have two long tentacles for capturing prey with sticky cells called colloblasts.
• Cannot sting.

Phylum Cnidaria

• Commonly known as stinging nettles.
• Composed of about 10,000 mostly marine animals.
• Split into subphylum Medusozoa and subphylum Anthozoa
• Radially symmetrical.
• Have two simple tissues: epidermis (external) and gastrodermis (internal).
• Named after cnidocytes (stinging cells).
• Release nematocysts containing poison and barbed threads.
• Digestion uses extracellular digestion.
• The gastrovascular cavity is where food is broken down and absorbed.
• Incomplete gut: food and waste enter and exit through the same opening.
• Body plans: polyp (sessile, upward-pointed mouth) and medusa (free-floating, downward-pointing mouth).
• Some cnidarians have only one form, while others have both stages.

Subphylum Medusozoa

• Cnidarians that (usually) have a medusa stage form monophyletic group, now known as Medusozoa.
• Includes jellies, box jellies, and hydrozoans.

Subphylum Anthozoa

• Sea anemones are soft, fairly large, polyps.
• Corals: lack a medusa stage.
• Coral colonies are made of small anthozoan polyps that construct and live in a coral skeleton.
• Have a symbiotic relationship with zooxanthellae algae that perform photosynthesis and give them their color.
• Bleached coral lacks algae.

Class Hydrozoa, Order Leptothecata, Family Campanulariidae, Genus Obelia

• Has both polyp and medusa stages.
• Polyps live in colonies with some specialized for food capture and some for asexual reproduction.
• Reproductive polyps reproduce tiny medusae via budding.

Superphylum Lophotrochozoa

• Have bilateral symmetry and true tissues.
• Some members have a lophophore (crown of tentacles for suspension feeding).
• Other members have trochophore larva (specialized ciliated larva).
• Superphylum due to shared sequenced DNA.

Phylum Platyhelminthes

• Contains about 20,000 species of flatworms.
• Bilateral symmetry, simple flattened bodies.
• Flat bodies allow for easy exchange with the environment by diffusion.
• Most have an incomplete gut with a gastrovascular cavity.
• Lack a coelom (body cavity) and circulatory system.

Phylum Platyhelminthes Class Cestoda

• Tape worms (cestode worms).
• Lack gastrovascular cavity, absorb nutrients through body wall.
• Have scolex (anterior structure), hooks, suckers, and proglottids (repeated segments).
• Reproduce by filling posterior proglottids with eggs and detaching them.

Phylum Platyhelminthes Class Trematoda

• Flukes (trematodes).
• Obligate parasites with complex lifecycles involving multiple hosts.

Phylum Platyhelminthes Class Turbellaria

• Small freshwater flatworms (planarians).
• Free-living (non-parasitic).
• Can regenerate.
• Notable structures: eyespots (detect light), auricles (touch and chemical sensation), pharynx (connects to mouth), and gastrovascular cavity (diffuses nutrients).

Phylum Syndermata

• Contains about 1,800 species of rotifers and 1,100 species of acanthocephalans.

Rotifers

• Named for the crown of cilia around their mouth (draws in water and food).
• Notable structures: alimentary canal (one-way digestive system) and pseudocoelom (false cavity).
• Many rotifers are entirely female, reproducing asexually via parthenogenesis.

Brachiopoda

• Consists of a few hundred living species.
• Commonly known as lamp shells.
• Resemble clams but are not closely related.
• Shells are dorsal and ventral.
• Notable structures: lophophore (feeding), true coelom, and pedicel (attaches to substrate).

Phylum Annelida

• Composed of about 17,000 species of segmented worms.
• Perfect example of metamerism (repeated body segments).
• Septa are thin walls internally separating segments.
• Found in virtually every habit (fresh, salt, and land).
• Bilaterally symmetrical with true tissues, complete gut, and coelom.
• Setae are bristle-like body projections that help propel the animal

Phylum Mollusca

• Mollusks, composed of 100,000 known species.
• Bilaterally symmetrical with true tissues, complete gut, and coelom.
• Most have a shell composed of calcium carbonate.
• Common parts: foot (muscle for movement), mantle (creates the shell), and radula (feeding structure).

Phylum Mollusca Class Polyplacophora

• Chitons have multiple valves on their dorsal surface.
• Commonly found in intertidal zones, clinging tightly to rocks.
• Use their radula to scrape off and feed on algae.

Phylum Mollusca Class Bivalvia

• Includes clams, oysters, mussels, and scallops.
• Named for the two shells.
• Tend to be filter feeders.
• Can use their muscular foot to dig into sand.
• Scallops have sensory tentacles on the outside rim of their shells.

Phylum Mollusca Class Gastropoda

• Includes snails and slugs.
• Found in a wide variety of environments.
• Undergo torsion: asymmetrical due to coiled shells.
• They have two pairs of tentacles.

Phylum Mollusca Class Cephalopoda

• Includes squids, octopods, cuttlefish, and nautiloids.
• Fast and mobile, great swimmers, have excellent vision.
• Most extant species have a reduced internal shell.
• Most have 8 arms, while squids and cuttlefish also have 2 tentacles.
• Arms have suckers along most of their length.
• Use jet propulsion for mobility.

Superphylum Ecdysozoa

• Encompasses 8 phyla.
• Animals have a cuticle (hard external coating) that grows with the animal and is periodically shed.
• Ecdysis is the process of growing and shedding cuticles.

Phylum Nematoda

• Comprise about 25,000 species.
• Includes nematodes (roundworms that are unsegmented).
• Live in aquatic and moist terrestrial environments.
• Have a tough cuticle, alimentary canal, and pseudocoelom.
• All of their body wall muscles are longitudinal, leading to a "thrashing" motion.

Phylum Tardigrada

• Composed of about 800 species, including water bears.
• Live in water, but known for surviving extreme conditions by going into a state of dormancy.

Phylum Arthropoda

• Composed of over 1 million extant species.
• Appendages in serial pairs: jointed, sensory, and feeding.
• Segmented bodies and rigid exoskeleton made of chitin.
• Alimentary canal and coelem.
• An open circulatory system circulatory fluid is only partially enclosed in vessels.
• Adult arthropods' coelom is replaced by a hemocoel.
• Hemolymph is the circulatory fluid of an open circulatory system found in arthropods.

Subphylum Chelicerata

• Includes spiders, ticks, mites, scorpions, and horseshoe crabs.
• Six pairs of appendages: chelicerae (feeding), pedipalps (sensory), and four walking legs.
• Lack antennae.
• Body is divided into cephalothorax (anterior) and abdomen (posterior).
• Only spiders have spinnerets, usually located by the bootyhole, to extrude silk threads.

Subphylum Myriapoda

• Includes centipedes and millipedes.
• One pair of antennae and three pairs of appendages are modified as mouthparts.
• Millipedes are herbivores and have two pairs of legs per body segment.
• Centipedes are carnivores and have one pair of legs per body segment.

Subphylum Pancrustacea

• Includes crustaceans (crabs, lobsters, shrimps, and relatives) and insects.
• Crustaceans have two pairs of antennae and gills for gas exchange.

Subphylum Pancrustacea Class Insecta

• More named species than all other forms of life combined.
• One pair of antennae and a tracheal system.
• Three body segments: head, thorax, and abdomen.
• Three pairs of legs.
• Many insects have wings.

Superphylum Deuterostomia

• United by a developmental pattern in which the anus forms before the mouth, it's confirmed by DNA analysis
• Includes Echinodermata and Chordata (us!).

Phylum Echinodermata

• Includes sea stars, brittle stars, sea urchins, sea cucumbers, and crinoids.
• Are bilaterally symmetrical, ancestrally
• Water vascular system hydraulic system of water pressure that terminates in tube feet.
• Tube feet help animals move and feed.
• The Madreporite opening regulates water entrance.
• Endoskeleton made of calcium carbonate and spines.
• Gills aid in gas exchange.
• Pathway of water: madreporite → stone canal → ring canal → radial canal → ampulla → podium.
• Body plans include oral and aboral surfaces.

Phylum Chordata

• Includes ~57,000 species: mammals, birbs, reptiles, amphibians, fishies and relatives
• Named for the notochord which is an internal stiff, slightly flexible rod of connective tissue that supports the body and provides muscle attachment sites
• Many extant species have vertebrae that replaced the notochord during development
• -United by: notochord; pharyngeal gill slits (gas exchange and feeding), a muscular post-anal tail; and a dorsal hollow nerve cord.

Subphylum Cephalochordata

• Commonly called the lancelets, they are suspension feeders that use cirri around the mouth.
• Use their muscular post-anal tail to burrow.

Subphylum Urochordata

• Commonly called tunicates.
• Larvae are free-swimming chordates.
• Adults are sessile filter feeders with a thick tunic.
• Most commonality is pharyngeal slits.

Subphylum Vertebrata

• Have bony structures supporting the dorsal midline of the body.
• Usually endoskeleton (inside) composed of bone (rarely cartilage).