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.