Gas Exchange and Circulatory Systems

Functions of respiratory systems?

• gas exchange

• to supply the body with oxygen for cellular metabolism and to remove metabolic waste gas, carbon dioxide

Gas exchange is always by ____

Passive diffusion

Earthworms have ____ _____

Cutaneous respiration

Simple gills

(extension of tissue out into water)

• gills enclosed in chambers

• allows pumping of water across surface

_____ _____ in terrestrial arthropods

tracheal system

• branched tubes lined with cuticle

• spiracles open to outside

Vertebrates (have different structures for different lifestyles)

• gills for water

• lungs for air

• cutaneous respiration in amphibians, aquatic retiles

Vertebrate Gills

• external gills

  • not enclosed

  • fish and amphibian larvae, some adult amphibians

Internal gills in bony fish

• oral valve and operculum pump water past gills

• ram ventilation —> swimming with mouth open

• Countercurrent exchange

• maintains oxygen gradient along entire pathway

• highly efficient

Countercurrent exchange

blood and water move in opposite directions

Evolution of the lung

• Primitive fish had sac attached to pharynx

• Two different evolution paths: Swim bladder & lungs

• Lungs have two-way flow (less efficient)

Swim bladder

• lost connection to gut

Lungs in tetrapods

• still attached to digestive tract

• increased surface area

Why don’t gills work in a terrestrial environment?

• they require water

• desiccation

Vertebrate Lungs: Amphibians

• Simple lungs, not much surface area

• Positive pressure breath

Positive pressure breathing

pushing air into by contracting oral cavity

Amniotes

• negative pressure breathing

Negative pressure breathing and how

(suck air into lungs by muscular expansion of rib cage)

• inhalation: Diaphragm contracts (moves down)

• Exhalation: Diaphragm relaxes (moves up)

Reptile lungs

• slightly larger internal surface area

Mammals lungs

• extensive internal surface area

• Still two-way flow

• Bronchi branch into many bronchioles

• Alveoli

Alveoli

(Sacs where gas exchange with blood occurs)

• thin epithelium

• net of capillaries

• moist surface

Birds lung

• one-way path through lungs, much more efficient

• respiration in two cycles

• cross-current exchange

Cross-current exchange

blood runs 90 degrees to air flow

Respiratory pigments

(Bind oxygen for transport)

• hemoglobin

• none in insects

hemoglobin

(binds oxygen to iron)

• maintains oxygen reserve in blood

Functions of circulatory systems?

homeostasis, thermoregulation, transport of materials (blood/hemolymph, hormones, ions, water, nutrients, waste), reduce diffusion distance, clotting

- immune system: white blood cells, clotting

Major components of the Circulatory System?

• muscular heart

• fluid hemolymph (open circulatory system) & blood (closed circulatory system),

What does not need a circulatory system?

• Sponges or flatworms do not require a circulatory system because of their high surface to volume ratio

• Pseudocoelomates do not need one because of their small and long worm like body which allows for simple diffusion

• Cnidarians do not need a circulatory system because they are diploblastic that allowing the materials to move by diffusion.

Sponges

• no internal tissues

• Circulate water through body

• diffusion assisted by amoebocytes

Cnidarians

• diploblastic

• Gastrovascular cavity with circulating water

• Body movements help move water

Flatworms

• flattened body

• branching gastrovascular cavity

• Body movements

Pseudocoelomates

• small or long or thin

• Circulate fluids in body cavity

• body movements

Open circulatory system

fluid directly contacts body tissues

• heart pumps hemolymph into vessels

• vessels open to hemocoel

• drains back into heart

• body movements assist

arthropods

• no respiratory function by circulatory system in insects

closed circulatory system

fluid always enclosed in blood vessels

Annelids

• heart —> dorsal blood vessel and 5 arteries

• ventral blood vessel carries blood backwards

• smaller vessels in each segment

Heart with chamber

• atrium

• ventricle

Atrium

receives blood

Ventricle

pumps blood onward

3 types of blood vessels

• arteries

• veins

• capillaries

Arteries

out of heart

Veins

back to heart

capillaries

narrowing branching

Fish

• 2 chamber heart

  • single atrium

  • single ventricle

• Gill capillaries oxygenate blood

• cost: low blood pressure to tissues after gills

Terrestrial vertebrates:

Lungs & double circulation

• Pulmonary circulation

• Systemic circulation

Pulmonary Circulation

between heart and lungs

Systemic circulation

Between heart and rest of body

Amphibians

• 3 chamber heart

  • atrium divided into right and left

  • single ventricle

• some separation of oxygenated and deoxygenated blood, but incomplete

Reptiles (except crocodilians)

• 3 chamber heart

  • right and left atria

  • Single ventricle, but partially divided by septum

• Some mixing, but more efficient

• Con sometimes push blood back to body or lungs

Birds, crocodilians and mammals

• 4 chamber heart

  • Right and left atria

  • Right and left ventricles

• Completely separate pulmonary and systemic circulation

Movement of blood out of heart

• Large muscular arteries

• branch into arterioles

• thin-walled capillaries —> exchange

• from capillaries into venules

• converge into veins, surrounded by skeleton muscle

• valves prevent backward flow

Lymphatic system

• water and solutes in blood filter out capillaries into interstitial fluid

• Drains into lymphatic system

• eventually re-enters veins

• Major role in the immune system

Why do larger animals need respiratory and circulatory systems?

because they have a small surface area-to-volume ratio, making simple diffusion too slow and inefficient to supply oxygen and nutrients directly to deep internal cells. The respiratory system (like lungs or gills) provides a large surface area to quickly take in oxygen and remove carbon dioxide from the environment, while the circulatory system (heart and blood vessels) acts as a pump and network to rapidly transport those gases and nutrients across the long distances inside a big body.

In what ways do respiratory systems maximize the rate of gas diffusion?

providing a very large surface area through millions of tiny air sacs (alveoli), keeping the diffusion barrier extremely thin (just one cell thick), maintaining a constant concentration gradient via continuous blood flow and breathing, and keeping the respiratory surface moist so gases dissolve easily

How do most invertebrate phyla accomplish gas exchange?

through diffusion across moist, thin membrane surfaces directly into their cells or circulatory systems. Because they lack complex lungs, simpler invertebrates like sponges, cnidarians, and flatworms rely entirely on direct cutaneous respiration through their outer body surfaces. Larger or more complex invertebrates utilize specialized, highly folded structures to maximize surface area while maintaining moisture: aquatic phyla (like mollusks and crustaceans) use gills to extract dissolved oxygen from water, whereas terrestrial arthropods (like insects) rely on a tracheal system of internal air tubes that deliver gases directly to tissues.

Explain how bony fishes keep water moving over their gills.

move water over their gills using a synchronized two-pump system involving their mouth (buccal cavity) and a protective bony flap called the operculum. First, the fish opens its mouth and lowers the floor of the buccal cavity to draw water in, while keeping the operculum closed. Next, the fish closes its mouth and raises the floor of the buccal cavity to push the water backward across the gill filaments. Finally, the operculum opens to let the water exit, keeping a steady, one-way flow of oxygen-rich water passing over the respiratory surfaces

What is countercurrent gas exchange? Why is it especially efficient?

where blood and a medium like water flow in opposite directions past one another.

It is especially efficient because this opposite flow maintains a concentration gradient across the entire length of the exchange surface. As oxygen-poor blood moves through, it always encounters water that has slightly more oxygen, allowing oxygen to continuously diffuse into the blood the whole way. In contrast, if they flowed in the same direction (concurrent flow), the two fluids would quickly reach an equal balance (equilibrium) and stop absorbing oxygen long before the blood was fully loaded. This design allows fish to absorb up to 80% of the oxygen available in the water.

Why do endothermic animals need more efficient respiratory and circulatory systems?

Endothermic animals require highly efficient respiratory and circulatory systems to maintain a constant, warm body temperature, which demands a massive amount of metabolic energy. To generate internal heat, their cells must continuously break down nutrients through cellular respiration at a much higher rate than ectothermic (cold-blooded) animals. To sustain this intense metabolism, the respiratory system must rapidly absorb large amounts of oxygen and expel carbon dioxide, while the circulatory system must quickly deliver that oxygen and nutrients to tissues throughout the body. Without these high-performance systems, endotherms could not supply their cells with the fuel needed to keep their internal furnaces running.

What limitations does diffusion impose on the organism?

Size restrictions include smaller single celled organisms relying solely on diffusion for gas exchange while larger animals that are more active wont allow for diffusion to supply enough oxygen so they need to find a more efficient and effective way to bring oxygen into the body and carbon dioxide out of the body.

Animals that are aquatic or terrestrial

They have to be small thin long or flat, diploblastic is also beneficial in you lack a respiratory system.

Animals with a low metabolic rate or are ectothermic often lack a respiratory system, being sessile is also a way for diffusion to be simpler.

What are the advantages of a closed circulatory system? Any disadvantages?

• higher metabolic rates

• delivers more specifically and quickly

• high blood pressure is maintained