Comparative Anatomy

Comparative Anatomy

Chapters 27, 32, 34, 36, 39, 41, &

42

What IS an animal?

• All animals are:

▫ Members of Kingdom Animalia

▫ Multicellular

▫ Heterotrophs

▫ Organisms that move about during part or all of their life cycles

• Most animals are invertebrates

Variation in Animal Body Plans

• Organization

▫ All animals are multi-celled

▫ The most ancient animal linages are just aggregates of cells (Phylum Poriferia)

▫ All animals show “division of labor” in their cells

 This leads to tissue formation


• Organization

▫ Tissue formation begins in the embryo

 In early evolutions (jellyfish and flatworms), there are two tissue layers (ectoderm and endoderm)

 Later a third layer developed (mesoderm)

 Allowed increased complexity

 Most animals have organs derived from mesoderm


• Body Symmetry

▫ Simplest animals are asymmetrical

▫ Jelly fish and hydras have radial symmetry

▫ Most animals have bilateral symmetry

 Most bilateral animals have also undergone

cephalization (process in which nerve cells become concentrated at the head end)


• Gut and Body Cavity

▫ Most animals have an incomplete digestive

system (gut)

 The sac-like gut opens at the end

 Cannot perform all the tasks of digestion simultaneously


• Gut and Body Cavity

▫ The two lineages of bilateral animals differ in how their digestive system and coelom (body cavity lined by mesoderm) form

 Protostomes: Animals in which the first opening that appears in the embryo becomes the mouth and the second becomes the anus

 Deuterostomes: Animals in which the first opening that appears in the embryo becomes the anus and the second becomes the mouth


• Circulation

▫ In small animals, nutrients diffuse through the body (ex. Flatworms, jellyfish)

 Flatworms MUST stay flat so that nutrients can diffuse in


• Circulation

▫ Diffusion doesn’t supply nutrients fast enough for large organisms

▫ These animals have either an open or closed circulatory system

 Open: Blood diffuses directly with tissues

 Closed: Blood travels around in veins and arteries, diffusing to tissues through the vessel walls

 Much faster; allows for larger organisms


• Segmentation

▫ Many bilateral organisms are segmented (similar units are repeated along the length of the body)

▫ Leads to specialization

Reflect…

• What is an animal?

• Pretend you are taking a quiz with the following essay question:

▫ Explain how animal body plans vary, giving an example of each variation. (10 pts.)

▫ What would you write?

Now…

• Work on one of the following:

▫ Worksheet packet

▫ Article response

▫ Re-writing and highlighting your notes

▫ Flashcards

Comparison of Major Systems

• It is important to understand how different organ systems function in different organisms

• Important organ systems that we will study:

▫ Gas exchange (respiratory)

▫ Removes waste (excretory)

▫ Transmit information (nervous)

▫ Reproductive system

Gas Exchange

• All animals move about at some point in their life cycle

• Movement takes energy (in the form of a molecule called ATP)

• The fastest and easiest way to get ATP is through aerobic respiration

▫ This requires oxygen and gives off carbon dioxide

▫ Animals must supply cells with oxygen and give off carbon dioxide waste

Gas Exchange

• Respiration: Physiological process by which an animal exchanges oxygen and carbon dioxide with its environment

▫ Depends on O2 and CO2’s tendency to diffuse down its concentration gradient

Gas Exchange

• Gases enter and leave an animal’s internal environment at a respiratory surface (moist, thin layer)

▫ Why is it moist?

▫ Why is it thin?

Gas Exchange

• Factors affecting diffusion rates:

▫ Surface-to-volume ratio

▫ Ventilation

▫ Respiratory proteins

Gas Exchange in Invertebrates

• Some don’t have respiratory organs

▫ Integumentary exchange: Diffusion of gases across their outer body surface (integument)

▫ Ex. Sponges, cnidarians, flatworms, and earthworms

▫ Live in aquatic or damp environments (why?)

▫ Tend to be flat and small or have thin layers

▫ Assists in vertebrates with gills as well


• Invertebrate gills

▫ Gills: Filamentous respiratory organs that increase the surface area available for gas exchange

▫ Ex. Aquatic mollusks, some sea slugs, aquatic arthropods

▫ Water flows into the body cavity and passes over gills where gas exchange occurs


• Snails that spend their lives on land have a lung instead of (or in addition to) gills

▫ Lung: Sac-like respiratory organ

▫ Branching tubes deliver air to a respiratory surface with many blood vessels

▫ A pore allows air to enter and can be closed to conserve water


• Tracheal tubes and book lungs

▫ Insects and arachnids have hard exoskeletons that provide protection but prevent gas exchange

▫ Have a tracheal system (repeatedly branching, air-filled tubes reinforced with chitin)

▫ Start with spiracles (small openings across the integument) that can be opened and closed to regulate air flow

▫ Some pesticides clog spiracles



▫ Tracheal tubes end near body cells, where respiration takes place

▫ Some organisms can force air in and out of the tracheal tubes (ex. Grasshoppers)



▫ Some spiders have book lungs (air and blood exchange gases across thin sheets of tissue)

▫ Hemocyanin picks up oxygen and transports it to body tissues

Reflect…

• Create a chart comparing and contrasting the forms of invertebrate respiration.

Gas Exchange in Vertebrates

• Fish gills

▫ All fishes have gill slits that open across their

pharynx (throat region)

 In jawless fishes the gills are visible from the outside

 In bony fishes the gills are covered by gill slits

▫ In all fishes, respiration occurs when water flows into the mouth, into the pharynx, and over the gills


• Fish gills

▫ Jawless fishes actively suck water into their mouths and over their pharynx and force water out by contracting muscles that make the opening smaller


• Fish gills

▫ Bony fishes have gill filaments with capillary beds

▫ Blood in the capillary and water flow in opposite directions so the oxygen levels can never equalize

(counter current exchange)

 Why would this be important?


• Paired lungs evolved from outpouchings of the gut wall in some bony fishes

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• Gills would be useless on land

▫ Without water, they would dry out and collapse

▫ Lungs became more and more necessary as organisms spend more time outside of water


• Amphibians

▫ Larvae have external gills

▫ Gills disappear as they develop and are replaced with internal lungs

▫ Integumentary exchange accounts for nearly all carbon dioxide leaving the body

▫ Frogs draw air in by lowering the bottom of their mouth and push air out by raising it


• Amniotes (Reptiles, birds, mammals)

▫ Have waterproof skin and no gills as adults

▫ Have two well-developed lungs

▫ Contraction of chest muscles pulls air into the lungs


• Reptiles and mammals

▫ Respiration occurs in sacs at the ends of the smallest airways


• Birds

▫ Have small inelastic lungs that don’t expand

▫ Air sacs attached to lungs inflate and deflate

▫ It takes TWO breaths to move air through the system

 Air flows through tubes during inhalation AND exhalation

 Tubes are covered in respiratory surfaces

Reflect…

• Create a Venn Diagram comparing and contrasting vertebrate and invertebrate gas exchange.

• Add vertebrate gas exchange to the comparison chart you made of invertebrate gas exchange

Fluid Regulation and Waste Removal

• Vertebrates have a urinary system

▫ Filters water and solutes from blood

▫ Reclaims or excretes water and solutes as needed to maintain the volume and composition of the extracellular fluid

• Kidneys filter blood


• Invertebrates

▫ Marine invertebrates the same fluid concentration as seawater (why would this be important?)

▫ Sharks also have isotonic fluids with sea water


• Fishes

▫ Bony fishes have body fluids that are less salty than saltwater and more salty than freshwater

▫ Marine fishes lose water across their bodies and their gills

 To replace water, they gulp seawater and pump salt out through the gills

 Produce small amount of concentrated urine


• Fishes

▫ Freshwater fishes continually gain water

 Don’t drink water

 Produce large volume of dilute urine

 Loss of solutes is offset by solutes absorbed from the gut and pumped across the gills

Think about it…

• What is the MAIN problem for fluid regulation in marine fishes and salt water fishes?


• Amphibians

▫ In water, amphibians have the same problems as freshwater bony fish

 Gain water across their skin

 Keep body fluids from becoming too dilute by pumping in ions across their skin


• Amphibians

▫ On land, amphibians lose water

 Evaporates across their skin

 Most excrete either ammonia or urea as adults

 Some that spend most time in dry habitats excrete uric acid

 Costs extra energy but reduces water loss


• Reptiles, birds, and mammals have adaptations to life on land

▫ Waterproof skin

▫ Highly efficient kidneys

▫ Why are these adaptations necessary for life on land?


• Reptiles and birds convert ammonia to uric acid, whereas mammals convert it to urea

▫ Takes 20-30x more water to excrete urea than uric acid

▫ Thus, mammals require more water than a bird or reptile of similar size

▫ Mammals have adaptations that allow them to get along with very little water


• Ex. Kangaroo rat


• Ex. Whales and dolphins

Nervous System

• Of all multicelled organisms, animals respond the fastest to external stimuli

▫ Neurons are the key to this fast response

▫ Neuron: Cell that can relay chemical signals along its plasma membrane and can communicate with other cells by way of specific chemical messages

Nervous System

• There are three main types of neurons

▫ Sensory: Detect internal or external stimuli and signal interneurons or motor neurons

▫ Interneurons: Process information from other neurons and send it to other interneurons or motor neurons

▫ Motor: Signal and control muscles and glands

Nervous System

• Cnidarian nerve net

▫ Cnidarians are the simplest animals with neurons

 First step in the evolution of the mammalian nervous system

▫ Nerve net allows them to respond to food or danger arriving from all directions

▫ Nerve net: Mesh of interconnected neurons

▫ Have no centralized controlling organ; impulses flow from any direction at any time

Nervous System

• Bilateral, cephalized nervous system

▫ Evolution of bilateral body plans was accompanied by cephalization

▫ Flatworms are the simplest bilateral cephalized animals

 Head has pair of ganglia

 Ganglia receive signals from eye spots and chemicaldetecting cells

 Connect to two nerve cords that run the length of the body

 Crisscross, forming a ladder of neurons that coordinate the two sides of the body

Nervous System


▫ Annelids and arthropods

 Have paired nerve cords that connect to a simple brain

 Pair of ganglia in each body segment provides control over that segment

Nervous System


▫ Chordates

 Single, dorsal nerve cord

 In vertebrates, the anterior region of the nerve cord evolved into a brain

 Bigger brains give organisms competitive edge in finding resources and reacting to danger

 As organisms moved onto land, brains adapted to specific environmental challenges

Nervous System

• Vertebrate nervous system

▫ Has two functional divisions

 Central nervous system: brain and spinal cord

 Most interneurons are located in the CNS

 Peripheral nervous system: nerves that extend through the rest of the body

 Further classified as somatic or autonomic

Nervous System

Nervous System

• Vertebrate nervous system

▫ Vertebrate nervous system is vastly complex

▫ Scientists are STILL researching how the brain works!

Modes of Reproduction

• There are two main types of reproduction

▫ Asexual: Single individual makes offspring that are genetically identical to it

▫ Sexual: Two parents make gametes that combine at fertilization to produce offspring with gene combinations unlike either parent


• Asexual reproduction

▫ Can be advantageous in stable environments

 Why would this be a good thing in stable environments specifically?

 When could this be a bad thing?



▫ Many invertebrates reproduce asexually

 Fragmentation: Piece of the parent breaks off and grows into a new individual (ex. Hydras)

 Parthenogenesis: Producing offspring from unfertilized eggs (ex. Insects and rotifers)



▫ Some fishes, amphibians, and lizards can form offspring from unfertilized eggs

▫ No known mammals reproduce asexually


• Sexual reproduction

▫ Has higher genetic and energetic costs than asexual reproduction

 Producing gametes

 Finding and courting a mate

 What benefits offset these costs?



▫ Hermaphrodites: Produce both eggs and sperm

 Simultaneous hermaphrodites: Produce both at the same time (ex. Tape worms)

 Sequential hermaphrodites: Switch from one sex to the other through the course of a lifetime (ex.

Fishes)

 What benefits do hermaphrodites have?



▫ External fertilization: Organisms release gametes into water where they combine

 Most aquatic invertebrates, fishes, and amphibians use this form of fertilization

 Produce lots and lots of gametes in hopes that some will be fertilized and survive

 Don’t typically care for young



▫ Internal fertilization: Egg and sperm meet inside the female’s body after the sperm is delivered by a specialized organ (penis)

 Eggs may be laid outside the body and abandoned

(snails) or be protected and cared for (birds)

 Eggs may develop inside the mother’s body


• Many female animals make yolk

▫ Yolk nourishes the developing individual

▫ Some produce very little yolk

 Ex. Sea urchins

 Offspring develop and become self-feeders very quickly

▫ Some produce large amounts of yolk

 Ex. Birds

 Yolk is the only nourishment inside the egg shell


• Many female animals make yolk

▫ Humans produce very little yolk in eggs

 Nutrients in the mother’s blood diffuse into an offspring’s blood and support its development

Gamete

Formation

Fertilization

Cleavage

Gastrulation

Organ

Formation

Growth, Tissue

Specialization

See pg. 760-761 for more information

Stages of Reproduction

• Gamete formation: Eggs or sperm arise from germ cells in the parental body

▫ Each gamete has ½ of the genetic information necessary to produce viable offspring

▫ Gametes form through a cell division process called meiosis


• Fertilization: Joining of the two gametes

▫ Incredibly complex process!

▫ Forms the first cell of the new individual (zygote)

▫ Occurs when sperm penetrates the egg


• Cleavage: Carves up the zygote by repeated mitotic cell divisions

▫ Number of cells increases, but size does not

▫ Forms a blastula (ball of cells that enclose a cavity of its own secretions)

 Blastocoel: The aforementioned cavity

▫ Cells of the blastula are called blastomeres


• Gastrulation: Cells self-organize as an early embryo with two or three primary tissue layers

▫ Gastrula: Name for the early embryo in this stage

▫ These tissue layers are the forerunners of the adult animal’s tissues and organs (germ layers)


• Organ formation (organogenesis): Tissues arrange into organs

▫ Organs incorporate tissues derived from more than one germ layer


• Growth/tissue specialization: Tissues and organs continue to grow and slowly take on final sizes, shapes, proportions, and functions

▫ Continues into adulthood

Comparative Anatomy

Comparative Anatomy

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Comparative Anatomy

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