Chapter 42: Gas Exchange and Circulation

42.1 The Respiratory and Circulatory Systems

• Ventilation, the movement of air or water through a specialized gas exchange organ, such as a lung or gill.
• Diffusion αt the respiratory surface, where 02 moves from 1e air or water into the blood and C02 moves from 1e blood into 1e air or water, along their concentration gradients.
• Circultion, the transport of dissolved 02 and C02 throughout the body-along with nutrients, wastes, and other types of molecules-via the circulatory system.
• Diffusion in the tissues, where 02 moves from the blood into the tissues and C02 moves from the tissues into the blood, along their concentration gradients.
• Cellulαr respirαtion, the cell’s use of 02 and production of C02.
  • ==In tissues, where cellular respiration has led to low 02 levels and high C02 levels, gas exchange occurs between blood and cells.== 

42.2 Air and Water as Respiratory Media

• Partial pressure is the press of a particular gas in a mixture of gases.

42.3 Organs of Gas Exchange

•  Fick’s law of diffusion, states that the rate of diffusion of a gas depends on five parameters:
  • Solubility of the gas in the aqueous film lining the gas exchange surface
  • Temperature 
  • Surface area available for diffusion 
  • The difference in partial pressures of the gas across the gas exchange surface
  • The thickness of the gas-exchange surface
• A tube known as the trachea (not to be confused with the tracheae of insects) carries the inhaled air to narrower tubes called bronchi.
• The bronchi branch off into yet narrower tubes，the bronchioles. 
• Lungs are internal organs that are used for gas exchange.
• The lungs of mammals, in contrast, are finely divided into tiny sacs called alveoli.
•  One mechanism for pumping air is positive pressure ventilation, used by frogs and some other amphibians. 
• The change in volume is caused by a downward motion of the thin muscular sheet called the diaphragm and an expansion of the rib cage.
• The formed elements in the blood include platelets, several types of white blood cells, and red blood cells.
  • Platelets are cell fragments that act to minimize blood loss from ruptured blood vessels.
  •  ==They do so by releasing material that helps form the blockages known as clots.==
  • White blood cells ( also called leukocytes) are part of the immune system.
  • ==They fight infections==.
  • Red blood cells transport oxygen from the lungs to tissues throughout the body. 
  • ==They also play a role in transporting carbon dioxide from tissues to the lungs.== 

42.5 Circulation

• In an open circulatory system, a fluid connective tissue called hemolymph is actively pumped throughout the body in a limited system of vessels.

• ==In a closed circulatory system, blood flows in a continuous circuit through a series of vessels in the body, under pressure generated by a heart.== 

• Blood vessels are classified as follows:

  • Arteries are tough, thick-walled vessels that take blood away from the heart. 
  • Small arteries are called arterioles.
  • Capillaries are vessels whose walls are just one cell thick, allowing an exchange of gases and other molecules between blood and tissues.
  •  Networks of capillaries are called capillary beds.
  • Veins are thin-walled vessels that return blood to the heart. 
  • Small veins are called venules.

• Larger veins also contain one-way valves, which are thin flaps of tissue at prevent any backflow of blood.

•  In fact, the fluid is collected in the lymphatic system: a collection of thin-walled, branching tubules called lymphatic vessels that permeate all tissues.

  • An interstitial fluid that enters the lymphatic ducts is called lymph.

• This blood is low in oxygen, and it arrives via two large veins called the inferior (lower) and superior (upper) venae cavae. 

• If heart valves are damaged or defective, the resulting backflow can be heard through a stethoscope and is called a heart murmur.

• The cells that initiate contraction in the vertebrate heart are known as pacemaker cells.

  • They are located in a region of the right atrium called the sinoatrial (SA) node.

•  Blood pressure measured in the systemic arterial circulation at the peak of ventricular ejection into the aorta is called systolic blood pressure. 

  • Blood pressure measured just before ventricular ejection is called diastolic blood pressure. 

• The body has specialized pressure-sensing receptors called baroreceptors that detect changes in blood pressure. 

• As people age, their blood vessels harden and lose elasticity-a condition called arteriosclerosis.

• If the arteries that deliver blood to the heart muscle become completely blocked, a myocardial infarction, or heart attack, can occur.

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