Comparative Anatomy

DigestionChapter 41

Digestion Compared• Sponges: digestion occurs within individual cells• Gastrovascular cavity: functions in both digestion

and distribution of nutrients• Cnidarians & platyhelmintes• Partial digestion occurs in cavity, completed in cells

• Complete digestive tract: a digestive tube extending between two openings – a mouth and an anus.

• Food moves along the tube in one direction• No mixing of nutrients and waste leads to more

efficient energy release.

Circulation and RespirationChapter 42

Circulation� Diffusion alone is not sufficient for

transporting substances to all cells of a multicellular organism

� Circulatory systems deliver materials close enough to cells that diffusion may occur.

� Materials to be carried include nutrients, oxygen, carbon dioxide, hormones, etc.

Circulation Compared� Sponges - diffusion only� Gastrovascular cavities: function in

transport in animals that have thick body layers

� Circulatory systems: all have three basic components

� Circulatory fluid – blood� Set of tubes – blood vessels� Muscular pump - heart

Circulation (continued)• Open circulatory system:

• Insects, other arthropods, most mollusks• No distinction between blood and interstitial fluid

(fluid between cells) therefore the fluid is called hemolymph

• One or more hearts pump fluid into a system of sinuses = spaces around organs

• Closed circulatory system:• Earthworms, octopi, all vertebrates• Blood is confined to vessels and is separate from

interstitial fluid• One or more hearts pump blood through vessels• Diffusion from blood into interstitial fluid into cells• More efficient transport allows animals to meet

higher metabolic demands

Hearts! <3 <3 <3� Fish: 2 chambers� Amphibians: 3 chambers� Reptiles: 3 chambers and septum� Mammals and Birds: 4 chambers

Gas Exchange (respiration)� Uptake of O2 for cellular respiration and

release of CO2.

� Respiratory surface = part of the animal�s body where gases are exchanged with the environment.

� Large surface area allows for rapid diffusion of gases

� Respiratory surfaces of both terrestrial and aquatic organisms must remain moist

Respiratory surfaces• Skin: some animals use entire skin for gas

exchange.• Gills in aquatic animals: designed to obtain

oxygen from water• Ventilation of gills enhances gas exchange

• Tracheal systems in insects: made up of air tubes that branch throughout the body

• Tubes branch throughout the entire body• Lungs in spiders, snails, vertebrates: lung are

restricted to one location

Lungs� Respiratory surface is not in contact with

all cells – circulatory system transports gases between lungs and cells

� In general, the size and complexity of the lungs are correlated with an animal�s metabolic rate.

Excretion• Form that the nitrogen containing waste

takes is dependent on evolutionary history and habitat.

• When proteins and nucleic acids are broken down NH3 (ammonia) is released.

• Some animals excrete ammonia directly» Toxic ammonia cannot be stored in the body

• Many species first convert ammonia to other compounds that are less toxic and then temporarily store and/or excrete the material

Forms of nitrogenous wastes• Ammonia:

• Aquatic animals• Ammonia diffuses directly into surrounding water

• Urea:• Mammals, most amphibians, sharks, some bony fishes• Ammonia is converted to urea in the liver and

transported by the circulatory system to the kidneys• Urea is less toxic, required less water to dilute than

ammonia• Production of urea requires energy from the organism

• Uric acid: • Insects, many reptiles, including birds• Relatively non-toxic• Insoluble in water and is excreted as a semi-solid past

with little water loss.• Significant energy investment required to convert to

uric acid.

Osmoregulation in Fish p.924

Comparative Anatomy� Contractile Vacuole

(protists)� Metanephridia

(annelids)excretion from every segment

� Malpighian Tubules (arthopods)branch from digestive tract, waste excreted through anus

� Kidney (vertebrates) millions of tubes, filter and produce urine which is stored in bladder before excretion

Nervous system organization� Cnidarians have nerve nets � With cephalization come more complex

nervous systems.� In simple cephalized animals such as the

planarian, a small brain and longitudinal nerve cords form a simple central nervous system (CNS).

� annelids and arthropods have more complicated brains and ventral nerve cords containing clusters of neurons called ganglia.

� Nerves that connect the CNS with the rest of the animal�s body make up the peripheral nervous system (PNS).