Chapter 42 - Circulation & Gas Exchange

Question 1

Explain why we eat & breathe.

Answer 1

All animals need to exchange substances, nutrients and oxygen, with their enviornment.

Question 2

Describe two forms of circulatory systems and their features.

Answer 2

• Gastrovascular cavity
  
  • “Incomplete” system good for thin, small, moist organism.
  • Uses diffusion to transport nutrients
• “True” circulatory system
  
  • Features pump, tubes, fluid
  • Open circulation vs. closed circulation
    
    • Open systems have vessels which are “open ended” like a straw, and do not have blood but instead have hemolymph (blood & interstitial fluid mixed)
    • Closed systems have vessels which do not open up into body cavities, and all vessels are connected back (a “closed circuit”)

Question 3

Describe vertebrate circulatory systems. Explain the evolutionary trends from fish up to mammals.

Answer 3

• Fish
  
  • Single circulation: blood passes through heart once in each complete circuit
  • Heart with two chambers: an atrium and a ventricle
• Amphibians
  
  • Double circulation evolves: system with two circuits: one pump (right side of heart) delivers O2 poor blood to lungs (pulmonary circuit), then enters other pump (left side) to be delivered to organs & tissues (systemic circuit)
  • Heart with three chambers: two atria and one ventricle
  • Ridge devides ventricle, but some mixing occurs (10%) of oxygen rich and oxygen poor blood
  • O2 & CO2 exchanged in pulmocutaneous circuit (skin or lungs)
• Reptiles (Except Birds)
  
  • Continued double circulation.
  • Three chambered heart: two atria and one ventricle with partial septum.
    
    • Septum partially divides ventricle into left & right chambers.
  • Aorta is introducted: two aorta in reptiles which allow shunting of bloodflow away from lungs when submerged under water.
• Mammals and Birds
  
  • Continued double circulation.
  • Four chambered heart: two atria and two completely divided ventricles.
  • Complete division of ventricle allows for pumping of 100% oxygenated or unoxygenated blood.
  • Endotherms require this extra efficiency due to high energetic demands to maintain temperature.

Question 4

Describe pulmonary and systemic circuits.

Answer 4

• Pulmonary
  
  • The branch of the circulatory system that supplies the lungs
• Systemic
  
  • The branch of the circulatory system that supplies oxygenated blood to and carries deoxygenated blood away from organs and tissues throughout the body.

Question 5

Describe heart structure and function.

Answer 5

Heart is composed of four sections:

1. Right atrium
2. Right ventricle
3. Left atrium
4. Left ventricle

Function is as follows:

1. Right ventricle contracts to pump blood to lungs via pulmonary arteries…
2. Blood moves through capillary beds in lungs loading O2 and unloading CO2 and returns from lungs via pulmonary veins…
3. Blood moves into left atrium of the heart where it enters the left ventricle…
4. Left ventricle pumps blood out to body tissues through systemic circuit via aorta which descended to arteries throughout body…
5. Coronary arteries supply blood to the heart itself…
6. Then branches to arteries to feed superior, the posterior body sections.
7. Within the capilaries a net diffusion of O2 from the blood to the tissues and exchange of CO2 occurs.
8. Oxygen poor blood from head, neck, forelimbs channeled into a large vein called the superior vena cava.
9. Oxygen poor blood from trunk and hind limps is drained via the inferior vena cava.
10. The two venae cavae empty their blood into right atrium, which delivers blood into right ventricle.

Question 6

Describe blood vessel structure and function.

Answer 6

• Capillaries have narrow diameters and thin walls facilitiating exchange.
• Arteries contain thick elastic walls that maintain blood pressure.
  
  • Sizes decrease as moves away from heart and is then called arterioles.
• Veins contain one-way valves that contribute to the return of blood to the heart.

Question 7

Describe process of fluid return by the lymphatic system.

Answer 7

• Due to the high pressure of the circulatory system fluid is squeezed out of the capillaries into lymphatic vessels.
• Lymph is similar to interstitial fluid, and composition varies depending on where fluid is being lost in the body.
• The lymph is returned via the subclavian veins which dumps into superior vena cava, a point of very low pressure in the circulatory system which allows for reentry.
• Lymph travels the lymphatic vessels via valves, automatic function of smooth muscle, and manual function (squeezing, movement) of skeletal muscle.

Question 8

Describe blood composition and function.

Answer 8

Blood is composed of:

• Plasma:
  
  • “liquid matrix” of blood in which the blood cells are suspended
• Cells:
  
  • RBCs (erythrocytes)
  • WBCs (leukocytes)
  • Platelets (thrombocytes)
    
    • fragments of cytoplasm released from bonemarrow cells
    • function is to stop bleeding

Question 9

Describe types of respiratory systems.

Answer 9

• Gills
  
  • Outfoldings of the body surface on which ventilation occurs
  • Uses countercurrent heat exchange:
    Blood flows in the opposite direction of the water passing over the gills, at each point in its travel the blood is less saturated with O₂ than the water it meets favoring the diffusion of O₂ along the entire gill structure.
• Tracheal Systems in Insects
  
  • System of air-filled tubes that extend throughout body and carries oxygen directly to cells.
• Lungs
  
  • Localized respiratory organs

Question 10

Describe the mammalian respiratory system structure & function.

Answer 10

From the nasal caivty and pharynx, inhaled air passes through the larynx, trachea, and bronchi to the bronchioles, which end in microscopic alveoli lined by a thin, moist epithelium. Branches of the pulmonary arteries convey oxygen-poor blood to the alveoli; branches of the pulmonary veins transport oxygen-rich blood from the alveoli back to the heart.

Question 11

Describe breathing in animals.

Answer 11

• Amphibians
  
  • Ventilates lungs by “swallowing air” using positive pressure breathing.
    
    • A system in which air is forced into the lungs.
• Birds
  
  • Use one-way flow (more efficient) & negative pressure
  • Uses posterior and anterior air sacs on either side of lungs
    
    • First inhale: air fills posterior air sacs.
    • First exhale: posterior air sacs contract, pushing air into lungs
    • Second inhale: air passes through lungs and fills anterior air sacs.
    • Second exhale: anterior air sacs contract, air that entered body at first inhale is pushed out.
• Mammals
  
  • Suck air in with diaphragm using negative pressure.
  • Vital capacity describes the maximum amount of air that can be inhaled and exhaled with each breath
  • Residual volume is the amount of air that remains in lungs after forceful exhalation.
    
    • This increases with age & disease… decreases vital capacity

Question 12

Describe respiratory pigments and O₂ and CO₂ transport.

Answer 12

Respiratory pigments are proteins that transport oxygen in blood or hemoplymph:

• Hemocyanin
  
  • Used by arthropods and molluscs to transport O₂
• Hemoglobin
  
  • Used by vertebrates and wide variety of invertebrates
  • Single molecule can carry 4 O₂ molecules
  • Also helps transport CO₂ and buffers blood.

CO₂ is also transported in plasma in dissolved form or as bicarbonate (HCO₃^-)