Transcript Chapters 48 and 49

48 & 49
Gas Exchange and the
Circulatory System in Animals
48
Physical Processes of Respiratory Gas Exchange
• The respiratory gases are oxygen (O2) and
carbon dioxide (CO2).
• Cells require O2 from the environment to produce
ATP by cellular respiration.
• Cellular respiration produces CO2 as an end
product, which must be lost to the environment to
prevent toxic effects.
• Diffusion is the only means to exchange these
gases.
48
Gas Exchange in Human Lungs
• The air pathway in humans consists of the
following components:
 An oral or nasal cavity, followed by the
pharynx (an area for both food and air).
 The larynx (voice box), which leads to the
trachea.
 The trachea branches into two bronchi (both
of these have cartilage support).
 The bronchi branch repeatedly into
bronchioles, which terminate in the alveoli.
Figure 48.10 The Human Respiratory System (Part 1)
Figure 48.10 The Human Respiratory System (Part 2)
The alveoli are
thin-walled air
sacs and are the
sites of gas
exchange.
Figure 48.10 The Human Respiratory System (Part 3)
Capillary blood vessels
closely surround the
alveoli, resulting in a
diffusion path of less
than 2 mm, which is less
than the diameter of a
red blood cell.
48
Gas Exchange in Human Lungs
• Cells lining the airways produce a sticky mucus
that captures dirt and microbes.
• This mucus is cleared by cilia beating upward
toward the trachea and pharynx, where it is
swallowed.
• This phenomenon has been called the mucus
escalator, and it can be immobilized by smoking.
• In cystic fibrosis, a faulty chloride channel leads to
mucus that is thick and difficult to clear, resulting
in blockage and infection.
48
Gas Exchange in Human Lungs
• A surfactant is a chemical substance that
reduces the surface tension of a liquid.
• The aqueous lining of the lung has surface
tension that must be overcome to permit inflation.
• Cells in the alveoli produce surfactant molecules
when they are stretched.
• Premature babies may develop respiratory stress
syndrome if they are born before cells in the
alveoli are producing surfactant.
48
Gas Exchange in Human Lungs
• The human lungs are suspended in the thoracic
cavity in separate, closed pleural cavities.
• The thoracic cavity is bounded by the shoulder
girdle, rib cage, and the diaphragm muscle.
• With inhalation, the diaphragm muscle contracts
downward to create suction, and air flows into the
lung.
• When the diaphragm relaxes, it pushes upward,
and exhalation occurs.
• In the rib cage, intercostal muscles lift the ribs
up and down to increase thoracic cavity volume.
Figure 48.11 Into the Lungs and Out Again
48
Blood Transport of Respiratory Gases
• As O2 diffuses from the alveoli into the blood, it is swept
away and delivered to the cells and tissues of the body.
• Most O2 is carried by the oxygen-binding pigment
hemoglobin in red blood cells.
• Hemoglobin is a protein consisting of four polypeptide
subunits, each with a heme (iron-containing) group.
• Each heme group can reversibly bind a molecule of O2.
48
Blood Transport of Respiratory Gases
• Carbon monoxide (CO) binds to hemoglobin with a
much higher affinity than does O2.
• CO is a deadly poison, as it destroys the ability of
hemoglobin to transport O2.
• Myoglobin in muscle cells is an oxygen-binding
molecule that can take up one molecule of O2.
• It has a higher affinity for O2 than hemoglobin does
and provides an oxygen reserve for high metabolic
demand or when blood flow is interrupted.
48
Blood Transport of Respiratory Gases
• CO2 is highly soluble, moving easily through cell
membranes into the blood, where the partial
pressure of CO2 is lower.
• Most CO2 is transported as bicarbonate ion (HCO3–).
48
Circulatory Systems: Pumps, Vessels, and Blood
• A circulatory system is composed of a pump
(heart), fluid (blood), and conduits (blood vessels).
• This is also called a cardiovascular system.
48
The Human Heart: Two Pumps in One
• The left and right sides of the human heart may
be thought of as separate pumps.
• The left pump delivers blood to the systemic
circuit.
• The right pump delivers blood to the pulmonary
circuit.
• Atrioventricular valves between the atria and
ventricles prevent backflow into the atria when the
ventricles contract.
• The pulmonary valve and aortic valve prevent
backflow into the ventricles.
48
Figure 49.3 The Human Heart and Circulation (Part 2)
48
The Human Heart: Two Pumps in One
• The right atrium receives blood from the superior
and inferior vena cavas.
• From the right atrium, blood goes to the right
ventricle.
• The right ventricle sends blood through the
pulmonary artery to the lung.
• Pulmonary veins return oxygenated blood to the
left atrium.
• From the left atrium, blood goes to the left ventricle.
• The left ventricle sends blood through the aorta to
the body and the capillary beds.
• Blood returns to the right atrium via veins.
48
Figure 49.3 The Human Heart and Circulation (Part 1)
48
The Human Heart: Two Pumps in One
• The left ventricle is more muscular because the
resistance of the systemic circuit is much greater
than that of the pulmonary circuit.
• In the cardiac cycle, ventricle contraction is called
systole and ventricle relaxation is called diastole.
• At the end of diastole, the atria contract.
• The sounds of the cardiac cycle (the “lub-dub”) are
caused by the closure of heart valves.
• Defective valves produce heart murmurs,
whooshing sounds following the “lub.”
• The cardiac cycle can also be felt in artery pulsation,
the surge of blood during systole.
48
The Human Heart: Two Pumps in One
• Cardiac muscle cells are in electrical contact with
one another through gap junctions.
• This permits coordinated contraction for effective
blood pumping.
• The primary pacemaker of the heart is the
sinoatrial node located at the juncture of the
superior vena cava and the right atrium.
• The atrioventricular node is stimulated by
depolarization of the atria; with a slight delay it
generates action potentials that are conducted to
the ventricles via a bundle of fibers called the
bundle of His.
48
Figure 49.7 The Heartbeat
48
The Vascular System:
Arteries, Capillaries, and Veins
• Large artery walls are elastic to withstand high
pressures and to squeeze blood along their
lumens by elastic rebound.
• Smooth muscle cells in arteries and arterioles
contract and relax, varying the vessel diameters.
• As the diameter changes, resistance to flow also
changes, allowing blood to be distributed to
different tissues.
48
Figure 49.10 Anatomy of Blood Vessels (Part 1)
48
Figure 49.10 Anatomy of Blood Vessels (Part 2)
Capillary beds lie between arterioles and venules and
exchange materials between blood and tissue fluid through
their thin walls.
Blood
flows
slowly
here,
facilitating
this
exchange.
48
The Vascular System:
Arteries, Capillaries, and Veins
• Blood tends to accumulate in veins. Veins are
called capacitance vessels because of their high
capacity to store blood.
• Pressure in veins is very low, and blood
movement back to the heart relies on gravity,
vessel squeezing by skeletal muscles, breathing,
and limited smooth muscle contraction.
• Contraction of skeletal muscles pushes blood
toward the heart because one-way valves in veins
prevent backflow.
• If veins become stretched, the valves no longer
do their job and varicose veins develop.
48
Figure 49.13 One-Way Flow
48
The Vascular System:
Arteries, Capillaries, and Veins
• Heart attack or stroke is often the end
result of atherosclerosis (hardening
of arteries).
• When the smooth internal lining of
arteries becomes damaged, deposits
called plaque form at damaged sites.
• Swelling and lipid/cholesterol
deposition invite fibrous connective
tissue and calcium deposits.
• Blood platelets stick in the plaque and
form blood clots (a thrombus), further
blocking the artery.
48
The Vascular System:
Arteries, Capillaries, and Veins
• If the coronary arteries are affected, blood supply
to the heart decreases.
• A thrombus here (coronary thrombosis) can
block an artery, causing a heart attack
(myocardial infarction, or MI).
• If part of the thrombus breaks away (an
embolism), lodges in the brain, and blocks blood
flow, stroke may occur.
• The best approach to reducing heart disease is
prevention.
• Risk factors include high-fat/high-cholesterol
diets, smoking, a sedentary life style, and obesity.
48
Blood: A Fluid Tissue
• Blood is connective tissue: it consists of living
cells within an extracellular matrix.
• The fluid matrix is called plasma.
• The cellular components of blood are the red
blood cells (erythrocytes), the white blood cells
(leukocytes), and the platelets (cell fragments).
• Bone marrow makes about 2 million red blood
cells per second.
• Each red blood cell lives about 120 days and then
breaks down.
48
Blood: A Fluid Tissue
• Blood clotting involves many chemical
steps in a cascade that activates
circulating substances in the blood, many
of which come from the liver.
• Cell damage and platelet activation lead
to conversion of an inactive enzyme in
the blood, prothrombin, to its active
form, thrombin.
• Thrombin causes a plasma protein,
fibrinogen, to polymerize, forming fibrin
threads.
• These threads form a meshwork to seal
the damaged vessel and provide a base
for scar tissue.
48
Figure 49.16 Blood Clotting (Part 1)
48
Blood: A Fluid Tissue
• Plasma contains gases, ions, nutrients, proteins,
hormones, and other chemicals.
• Predominant ions are Na+ and Cl–, giving blood a
salty taste.
• Nutrient molecules in plasma include glucose,
amino acids, lipids, lactic acid, and cholesterol.
• Circulating proteins include albumin, antibodies,
hormones, and carrier molecules.
• Plasma is similar in composition to tissue fluid but
has a higher concentration of proteins.