Animal Architecture and Embryology

5 levels of organization

1. Cytoplasmic

2. Cellular

3. Cell-Tissue

4. Tissue-Organ

5. Organ-System

Organization: Cytoplasmic level

• unicellular organisms

  • single celled so all life functions occur within the single cell

  • Conducted by cell organelles

• Example: Ameoba, paramecium, Stentor

Organization: Cellular level

• Multicellular or colonial

  • Multicellular organisms have cells that have differentiated to serve different purposes

  • Colonies have undifferentiated cells

  • Cells communicate with other cells

• Example: Sponges

• Aggregations of cells

Organization: Cell-Tissue

• Cells with similar purposes are grouped together to form highly coordinated units like ctenophores and cnidarians

  • Distinct layers of cells

  • Have ECM

• Example: Sea jellies (Cnidarians)

• Aggregations of cells that form tissues

Organization: Tissue-Organ

• Different types of tissues grouped together based on similar functions, to form an organ

  • Parenchyma - functional tissue

  • Stroma - supporting tissues

• Example: Platyhelminthes

• Aggregations of tissues that form organs

Organization: Organ-System

• Multiple organs with different functions work together to achieve bodily functions

  • Humans, frogs, arthropods, Nemertean worms, etc.

• Aggregations of organs that form systems

Body Size and Complexity

Complex organization needed in large animals because of increased need for oxygen

• Large animals: Low SA vs High body volume

  • Increased need of oxygen, nutrient transport, removal of waste becomes difficult

• To combat this: circulatory system and alteration to body shape

  • Increased folds and flattened shape

Animal Symmetry Definition and Types

Consistency in shape and size of body on the opposite sides of a median plan

1. Asymmetry

2. Spherical symmetry

3. Radial symmetry

4. Bilateral symmetry

Asymmetry

• No median plane to divide the animal into two identical halves

  • Example: Sponges, snails, wrybill

Spherical symmetry

• Any plane passing through the center of the body divides the body into two identical halves

  • Example: Volvox

Radial symmetry

• Any plane, 2 or more, passing through longitudinal axis divides the body evenly

  • Example: Cnidarians

Bilateral symmetry

• Division through the sagittal plane of the animals would result in right and left halves

  • Example: Cephalization

Animal development steps

1. Fertilization of ovum by sperm → zygote

2. Zygote → cleavage -? divide into blastomeres

3. Fate of a cell

   1. Cytoplasmic specification: factors excreted into the cytoplasm of the cell during cleavage

   2. Conditional specification: Interaction with other cells

      • Inducers vs responders

   3. Syncytial specification: morphogen

      • Example: sonic hedgehog, retinoic acid

Radial Cleavage

• Produces layers of cell son top of one another in the early embryonic stages

  • Blastomeres separated from others and can still form a complete embryo - regulative development

  • Example: Echinoderms: sea urchins, sea cucumber, starfish

Spiral Cleavage

• Cells tightly packed in furrows b/w cells

  • Cells cannot be separated from each other to form complete embryo - mosaic development

  • Example: Molluscs, annelids, etc.

Germ layers: Ectoderm

• forms nervous system and epidermis

Germ layers: Endoderm

• forms primitive git, epithelial lining of gastrointestinal tract

  • Forms openings - mouth and anus

Germ layers: Mesoderm

• organs NOT formed by ectoderm and endoderm

  • Example: kidneys, vessels, skeletal muscles, bones

Gut: Internal body cavity

• Has at least one opening for the nutrients to enter/waste removal

• Most animals have 2 openings where nutrients enter through one and leaves through another

• In some animals, gut is surrounded by a coelom (hollow fluid filled cavity)

  • Coelom facilitates movement and space for organs and provides flexibility

    • Peristalsis, locomotion in some animals

Coelom

• In some animals, gut is surrounded by a coelom (hollow fluid filled cavity)

  • Coelom facilitates movement and space for organs and provides flexibility

    • Peristalsis, locomotion in some animals

Coelomates

• Animals that have a coelom with complete body lining - peritoneum

Peritoneum

• Derived from mesoderm

• Covers inner and outer edges of cavity

• Most bilaterally symmetrical animals and coelomates

Acoelomates

• Lack fluid filled cavity between body wall and digestive tract

• Mesoderm completely fills area b/w endoderm and ectoderm

Pseudocoelomates

• Mesoderm lines ectoderm but not the endoderm - so body cavity is not derived from mesoderm

  • No peritoneum

  • “False coelomates“

Development of zygote to form coelomates, acoelomates, and pseudocoelomates

Triploblastic Bilateria

Most animal phyla are bilaterally symmetrical and develop from 3 germ layers

Deuterostomes

• Development starts with radial regulative cleavage

• Blastopore becomes anus

• Second opening becomes the mouth

• Has coelom

• Includes 3 phyla: Echinodermata, Hemichordata, and Chordata

Protostomes

• Development begins with spiral mosaic cleavage

• Blastopore forms the mouth

• Anus forms secondarily

• Includes acoelomates, pseudocoelomates, or even coelomates (depending on the group or species)

  • Example: Flatworms, earthworms, insects, etc.

Epithelial Tissue

• Covers the internal and external surface of organs, body cavities, ducts and other passages through which material passes, more often a mucus lining

  • Functions: Separates one body region from another

  • Supported by a basement membrane, mostly made up of collagen - ECM

Types of epithelial tissue

1. Single squamous epthelium

2. Simple cuboidal epithelium

3. Single columnar epithelium

Connective tissue

• Supportive tissues spread in different types throughout the body to support, protect, aid in transport, storage amongst other functions

• Has few cells but many extracurricular fibers (collagen) and ground substance

• Types:

  • Connective tissue proper: loose areolar connective tissue vs. dense connective tissue

  • Cartilage

  • Bone

  • Blood

Muscle

• Made up of muscle fibers for contraction

  • Facilitates movement

Smooth muscle

Involuntary movement like digestive system

Striated muscle

Voluntary movement like in skeletal muscle and involuntary like cardiac muscle

Nervous

Regulation and control of various bodily functions: impulses sent from one part of teh body to another

Neuron

transmits electrical signals

• Can perceive and respond to various stimuli

Neuroglia

• Supportive cell for neurons for nourishment and protection