Circulatory Systems:
Larger animals developed circulatory systems to transport oxygen and nutrients quickly across greater distances.
Specialized Respiratory Surfaces:
Larger surface areas in organs like lungs or gills help maximize gas exchange efficiency over small distances.
Cnidarians, like the moon jelly in Figure 42.2 in your text, and
planarians do
not have a distinct circulatory system. How have
they solved the problem of exchange?
Cnidarians and planarians maximize direct diffusion by being thin or having cells close to their environment. This eliminates the need for a circulatory system.
Larger animals must have a circulatory system to move fluid between
cells and the outside
environment. What are the three basic
components of a circulatory system?
A circulatory fluid (blood or hemolymph), a set of vessels, and a pump (heart).
What is hemolymph?
Hemolymph is the fluid in animals with an open circulatory system, combining blood and interstitial fluid
Contrast open circulatory systems with closed circulatory systems.
- Open System: Fluid (hemolymph) bathes organs directly; seen in insects.
- Closed System: Blood remains in vessels; nutrient exchange occurs across vessel walls, as in vertebrates
Artery
Carries blood away from the heartThick muscular walls
Arteriole
Distributes blood to capillariesSmaller, with smooth muscle
Vein
VeinReturns blood to the heartThin walls, often with valves
Venule
Collects blood from capillariesThin-walled, leading to veins
Capillary
Site of exchangeThin-walled, single-cell thickness
Atria
Receive blood returning to the heart.
Ventricles
Pump blood out of the heart.
Single Circulation
Blood flows through the heart once per cycle, as in fish.
Double Circulation
Blood passes through the heart twice, allowing separate pulmonary and systemic circuits, as in mammals and birds.
In a circulatory system, exchange occurs in two general places. Blood
goes to a respiratory
surface (lungs, gills, skin) or to the
organs and tissues of the body (systemic circulation).
Through
which type of blood vessel does exchange actually occur?
Exchange occurs in capillaries where blood meets tissues
Fish
Two-chambered heart; single circulation; blood oxygenated in gills.
Amphibians
Three-chambered heart; partial separation in double circulation; some mixing of oxygenated and deoxygenated blood.
Mammals
Four-chambered heart; complete double circulation; full separation ensures efficient oxygen delivery
Why is a four-chambered heart a key adaptation required for endothermy?
It allows separate pulmonary and systemic circulation, supplying high oxygen levels for metabolic demands of endothermy.
Use the four-chambered heart of birds and mammals to explain the
concept of convergent
evolution
Birds and mammals independently evolved four-chambered hearts, a convergence enabling higher metabolic rates required by endothermic life.
Cardiac Cycle
Sequence of heart contraction and relaxation.
Systole
Heart chambers contract, pumping blood.
Diastole
Heart chambers relax, filling with blood.
Cardiac Output
Volume of blood pumped per minute, dependent on heart rate and stroke volume.
Atrioventricular Valves
Prevent backflow from ventricles to atria.
Semilunar Valves
Prevent backflow from arteries to ventricles.
Sinoatrial Node and Cardiac Cycle
The SA node initiates electric impulses, coordinating heart rhythm. Each blue mark in the cardiac cycle represents phases from atrial contraction to ventricular filling.
How do structure and function correlate in the capillaries?
Capillaries’ thin walls allow efficient nutrient and gas exchange between blood and tissues.
What anatomical feature of the veins maintains a unidirectional flow
of blood back toward
the heart?
- Valves in veins prevent backflow, ensuring blood returns to the heart.
As blood vessel diameter decreases, blood velocity will ____________
decreases
Why does blood slow as it moves from arteries to arterioles to
capillaries? Why is this
important?
Slowdown is crucial for efficient gas and nutrient exchange in capillaries
Explain the exchange of fluid at the two ends of a capillary by
annotating this figure. Include
these terms in your discussion:
interstitial fluid, osmotic pressure, and blood pressure.
Blood Pressure forces fluid out at the capillary’s arterial end; Osmotic Pressure draws fluid back at the venous end.
Why does the presence of blood proteins tend to pull fluid back into the capillaries?
Blood proteins increase osmotic pressure, pulling fluid back into capillaries to balance fluid exchange
The capillaries “leak” about 4 L of fluid each day. How is this returned to the blood?
- The lymphatic system collects and returns leaked fluid back to the bloodstream.
What is lymph? Is it more like blood or more like interstitial fluid?
resembles interstitial fluid, containing some white blood cells but fewer proteins than blood
We don’t have a second heart to pump lymph. What keeps lymph moving along?
- Skeletal muscle contractions and valves help move lymph through vessels.
Blood separates into two components, a liquid matrix called
________________ and the
cellular elements
Plasma is the liquid matrix in which cells are suspended
List the cellular elements of blood and give their general functions
- Red blood cells: Oxygen transport.
- White blood cells: Defense against pathogens.
- Platelets: Blood clotting.
Describe three ways in which the structure of an erythrocyte enhances
its function, which is
to transport oxygen.
Shape (biconcave) for increased surface area, no nucleus for maximum hemoglobin, and flexibility to navigate capillaries.
What is the role of hemoglobin? What mineral is required to make it?
Hemoglobin binds oxygen; iron is essential for its function
How does sickle-cell disease affect the ability of the respiratory
system to deliver oxygen and
remove waste
Abnormally shaped red cells impede oxygen transport, leading to insufficient oxygen delivery
Where are blood stem cells found?
bone marrow.
Blood Clotting Mechanism
- Prothrombin converts to thrombin, activating fibrinogen to form fibrin, creating a clot.
Plaque
from fats and cholesterol narrows arteries.
Heart Attack
Blocked coronary arteries; Stroke: Blocked brain arteries.
LDLs
transport cholesterol to cells (can lead to plaque); HDLs remove excess cholesterol.
Hypertension
damages vessels, increasing risk of heart disease.
Gas exchange with water as the respiratory medium is much more
demanding than exchange
with the air. What are three reasons for this?
Water has lower oxygen, higher density, and viscosity, making gas exchange more energy-intensive.
There are several requirements for a respiratory surface. It must be
moist, have a large
surface area, and be thin. What four
different organs satisfy these requirements?
Gills, tracheae, lungs, and skin can serve as moist respiratory surfaces
Countercurrent Exchange in Gills
Countercurrent flow maximizes oxygen absorption as water and blood flow in opposite directions across gill capillaries.
Oxygen Absorption Without Countercurrent Exchange
- Maximum absorption would be around 50%, far less efficient than countercurrent flow.
What is the most common respiratory structure among terrestrial
animals? What groups have
this system?
- Lungs are the predominant respiratory structure among terrestrial vertebrates.
Mammalian Respiratory Anatomy
The pharynx channels air to the larynx and trachea, splitting into bronchi and narrowing to bronchioles, ending in alveoli for gas exchange
explain how negative pressure breathing occurs in mammals
Diaphragm contraction expands the chest cavity, reducing pressure and drawing air into the lungs.
explain the homeostatic control of breathing
Increased CO₂, not O₂ levels, triggers the respiratory rate to prevent acidosis.
n general, what has a greater effect on the rate of
respiration,
low levels of O2 or high levels of CO2? Explain why.
High CO₂ levels primarily increase respiration to remove excess carbon dioxide and maintain pH
Oxygen and CO₂ Path from Inhalation to Exhalation
Oxygen travels from alveoli to blood, to tissues, then CO₂ moves from tissues to blood, finally exhaled through the alveoli
What is the respiratory pigment in vertebrates?
Hemoglobin
Hemoglobin is a protein with quaternary structure. How many subunits
does it have? What is
the role of iron?
Hemoglobin has four subunits, each with iron that binds oxygen.
Where does the constant production of carbon dioxide originate
and
how is it removed from the body?
Cellular respiration produces CO₂, transported in blood and removed through the lungs.