38.1. Transport in Invertebrates
A. Transport Mechanisms
1. Unicellular
protozoa make exchanges directly with environment across the plasma
membrane.
2. Some multicellular animals
lack internal transport system; they can live without it.
3. Larger invertebrates
usually have circulatory systems-either an open system
or a closed system.
B. Invertebrates With a Cavity
(Without a Circulatory System)
1. Sea
anemones and planaria are organisms with a sac body plan; a circulatory system
is unnecessary.
2. Sea anemone cells are part of
external layer or gastrovascular cavity; diffusion supplies all nutrients.
3. Planaria have a tri-lobed
gastrovascular cavity and small, flat body where diffusion meets these needs.
C. With an Open or a Closed System
1. In a circulatory
system, a pumping heart moves one of two circulatory fluids into blood
vessels.
a. Blood
is a circulatory fluid contained within blood vessels
b. Hemolymph
is a circulatory fluid which flows into the hemocoel of certain arthropods and
mollusks;
it is a mixture of blood and interstitial fluid.
2. Certain arthropods and mollusks
have an open circulatory system.
a. Hemolymph
is pumped by heart into body cavity or sinuses.
b. Hemolymph
bathes internal organs and then drains back to heart.
c. In
grasshoppers, dorsal heart pumps hemolymph into an aorta, which empties into hemocoel.
d. Hemolymph
is colorless (it lacks hemoglobin or other respiratory pigments); tracheae
provide oxygen.
3. Some invertebrates, including
earthworms and cephalopods, have a closed circulatory systemin which
blood never
leaves the heart or vessels.
a. Valves
prevent backward flow of blood as it moves through vessels.
b.
Earthworms have five pairs of anterior lateral vessels that pump blood to every
segment.
c. Blood
moves in capillaries where exchange with tissue fluid take place before
returning in veins.
d.
Earthworms' red respiratory pigment hemoglobin is dissolved in
blood, not inside blood cells.
e. With no
special cavity for gas exchange, gas must diffuse across body wall.
38.2. Transport in Vertebrates
A. Closed Circulatory System
1.
Vertebrates have a closed circulatory system in a cardiovascular
system.
2. Muscular heart
keeps blood circulating through the animal body.
a. Atrium
is chamber of the heart that receives blood.
b. Ventricles
pump blood into arteries.
3. There are three kinds of blood
vessels: arteries carry blood away from heart, capillaries
are where
exchange
with tissue fluid takes place, and veins return blood to heart.
a. Arteries:
1) have thick walls and are resilient.
2) expand to accommodate sudden increase in blood volume that results after
heart contraction.
3) divide into small arterioles.
b. Arterioles
constriction and dilation are regulated by nervous system to regulate blood
pressure.
c. Capillaries
are microscopic blood vessels with a wall formed of one layer of simple
squamous cells.
1) Capillary beds are so prevalent that, in humans, all cells are within 60-80
µm of a capillary.
2) Only 5% are open at one time; if animal eats, capillary beds of digestive
system open.
3) Capillaries are so narrow that red blood cells must pass through in single
file.
4) Gas, nutrient, and waste exchange occurs across thin walls.
d. Venules
are vessels that take blood from capillaries, and join to form a vein.
e. Veins
transport blood toward the heart.
1) Wall of a vein is much thinner than that of arteries; there is low blood
pressure.
2) One-way valves open in direction of heart; close to prevent
backflow. (Fig. 41.3d)
B. Comparison of Circulatory Pathways
1. In
vertebrates, there are three different types of circulatory pathways.
2. Fishes have a one-circuit
(single-loop circulatory) pathway.
a. Heart has
a single atrium and ventricle and pumps blood under pressure to gills.
b. Blood in
gills is oxygenated.
c. After
passing through gills, blood is under reduced pressure and flow.
3. Other vertebrates have a two-circuit
(double-loop circulatory) pathway to breathe air on land.
a. Systemic
circulation transports blood to tissues.
b. Pulmonary
circulation pumps blood to lungs.
4. In amphibians and most reptiles,
the heart has two atria but a single ventricle.
5. Hearts of some
reptiles and all birds and mammals are divided into two halves.
a. With two
atria and two ventricles, oxygenated blood is always
separate from deoxygenated blood.
b. Right
ventricle pumps blood to lungs; Left ventricle pumps
blood to rest of body.
c. This
arrangement provides adequate blood pressure for both pulmonary and systemic
circulations.
38.3. Transport in Humans
A. Heart Pumps Blood
1. Pumping of
heart keeps blood moving in arteries.
2. Skeletal muscle contraction is
responsible for blood movement in veins.
3. Heart is a
cone-shaped, muscular organ about size of a fist.
4. It is located between lungs
directly behind the sternum and is tilted so that apex is
directed to left.
5. Myocardium is major
portion of the heart consisting mostly of cardiac muscle; muscle fibers are
branched
and tightly
joined together.
6. Heart lies within a pericardium
sac that contains pericardial fluid which provides
cushioning.
7. Endocardium lines
inner surface of the heart; it consists of connective tissue and endothelial
tissue.
8. Internal wall called the septum
separates heart into right and left halves.
9. Heart has two upper, thin-walled atria
and two lower, thick-walled ventricles.
a. Atria
receive blood from venous portion of cardiovascular system.
b. Atria are
much smaller and weaker than muscular ventricles but hold the same volume of
blood.
c. Ventricles
pump blood into arterial portion of cardiovascular system.
10. Heart valves
direct flow of blood and prevent backward movement.
a. Valves
are supported by strong fibrous tendons (chordae tendineae)
attached to muscular projections
of ventricular walls; they prevent valves from inverting.
b. Atrioventricular
valves between atria and ventricles prevent back flow from ventricle to
atrium.
c. Right
atrioventricular (tricuspid) valve on right side of heart consists of
three cusps or flaps.
d. Left
atrioventricular (bicuspid or mitral) valve on left side consists of
two cusps or flaps.
e. Semilunar
valves resembling half-moons are located between a ventricle and an
artery that prevents
back flow from artery to ventricle.
1) The pulmonary semilunar valve lies between the right ventricle
and the pulmonary trunk.
2) The aortic semilunar valve lies between the left ventricle and
the aorta.
C. Path of Blood Through the Heart
1. Route
of blood through heart is as follows.
a.
Deoxygenated blood enters right atrium from both superior vena cava and
inferior vena cava.
b. Right
atrium sends blood through right atrioventricular (tricuspid) valve to right
ventricle.
c. Right
ventricle sends blood through pulmonary semilunar valve into pulmonary trunk
and arteries to lungs.
d.
Oxygenated blood returns from lungs through pulmonary veins and is delivered to
left atrium.
e. Left
atrium sends blood through left atrioventricular (bicuspid or mitral) valve to
left ventricle.
f. Left
ventricle sends blood through aortic semilunar valve into aorta and to body
proper.
2. Heart is therefore a double pump
serving the lungs and body circulations simultaneously.
3. Since the left side has the
harder job of pumping blood throughout the body, its walls are thicker.
D. The Heartbeat
1. Heart
contracts (beats) about 70 times a minute; each heartbeat lasts about
0.85 seconds.
2. Heartbeat or cardiac cycle
consists of phases: systole refers to contraction of heart
chambers
and diastole
is relaxation of heart chambers.
3. Atria contract first while
ventricles relax (0.15 sec.), then ventricles contract while atria relax (0.30
sec.),
then all
chambers rest (0.40 sec.).
4. Heart is in diastole about 50% of
the time.
5. Short systole of the atria is
needed only to send blood into ventricles.
6. When the term "systole"
is used alone, it refers to left ventricle systole.
7. When the heart beats, familiar lub-dub
sound is heard as valves of heart close.
a. Lub
is caused by vibrations of the heart when atrioventricular valves close.
b. Dub
is heard when vibrations occur due to closing of semilunar valves.
8. Pulse is a wave
effect that passes down walls of arterial blood vessels when aorta expands and
then
almost
immediately recoils following ventricle systole.
9. Since there is one arterial pulse
per ventricular systole, arterial pulse rate can be used to determine heart
rate.
10. Rhythmic contraction of heart is
due to cardiac conduction system.
a. Sinoatrial
(SA) node is "pacemaker" found in upper dorsal wall of right
atrium; it initiates heartbeat
by sending out an excitatory impulse every 0.85 seconds to cause atria to
contract.
b. Atrioventricular
(AV) node is found in base of right atrium very near septum; when
stimulated by impulses
from SA node, it sends out impulses through septum to cause ventricles to
contract.
11. Electrocardiogram (ECG or
EKG) is a graphical recording of ionic changes that occur in the heart
during a
cardiac cycle; it is used as a diagnostic tool to identify abnormal cardiac
function.
12. Normal Cardiac Cycle
a. P
wave represents excitation and occurs just before atrial contraction.
b. QRS
complex signals that ventricles are about to contract.
13. Ventricular fibrillation
is uncoordinated contraction of the ventricles; with application of a strong
electric
current, the SA node may reestablish a coordinated beat.
E. Vascular Pathways
1. Human
cardiovascular system has two major circular pathways.
2. The Pulmonary Circuit
a. Pulmonary
circuit circulates blood to lungs where blood is oxygenated.
b.
Deoxygenated blood from body collects in right ventricle, which pumps it to pulmonary
trunk.
c. Pulmonary
trunk divides into right and left pulmonary arteries to carry blood to each
lung.
d. In lungs,
carbon dioxide (CO2) is unloaded and O2 is picked up by blood.
e.
Oxygenated blood from lungs is returned through pulmonary veins
to left atrium.
3. The Systemic Circuit
a. Aorta
and vena cavae are main pathways for blood in systemic
circuit.
b. Transport
of oxygenated blood moves from left ventricle through aorta out to all tissues.
c.
Deoxygenated blood returns from all tissues via vena cava.
d. In a
systemic circuit, arteries contain bright red oxygenated blood; veins contain
dull red deoxygenated blood.
4. Coronary arteries
serve heart muscle itself.
a. Coronary
arteries originate from base of aorta just above aortic semilunar
valve.
b. Coronary
arteries lie on external surface of heart; they branch into arterioles and
capillaries.
c. Capillary
beds enter venules that join to form cardiac veins.
d. Coronary
veins collect deoxygenated blood from capillaries and empty into right
atrium.
5. Portal system is a
pathway of blood flow that begins and ends in capillaries.
a. Hepatic
portal vein transports blood from capillaries in small intestinal villi
to capillaries in liver.
b. Hepatic
vein leaves liver and enters inferior vena cava.
F. Blood Pressure
1. Systolic
pressure results from blood being forced into arteries during
ventricular systole.
2. Diastolic pressure
is pressure in arteries during ventricular diastole.
3. Human blood pressure
is measured as force pushing against wall of brachial artery of upper arm.
a. Blood
pressure is measured by a sphygmomanometer which has a pressure
cuff.
b. Clinical
blood pressure measures pressures produced by contraction and relaxation of
right ventricle.
c. It is
stated in millimeters of mercury (e.g., 120/80 mm Hg for systolic/diastolic).
4. As blood flows from aorta into
arteries and arterioles, blood pressure falls.
5. Difference in pressure between
systolic and diastolic pressures gradually diminishes.
6. Capillaries have slow, even blood
flow due to high total cross-sectional area. (Fig. 41.9)
a. Total
length of human capillaries is estimated at 60,000 miles.
b. Most of
this distance is due to quantity of capillaries.
7. Blood pressure in veins is low
and cannot move blood back to heart, especially from limbs.
8. Skeletal muscle contraction on
walls of veins with valves preventing backflow of blood is responsible
for flow of
blood in veins.
9. Varicose veins are
abnormal dilations that develop when valves become weak and ineffective.
38.4. Cardiovascular Disorders
A. Cardiovascular Disease
1.
Cardiovascular disease (CVD) is the leading cause of untimely deaths in the
2. Risk of CVD can be reduced by
following guidelines for a heart-healthy life-style.
B. Hypertension
1. An
estimated 20% of Americans suffer from hypertension or high
blood pressure.
2. Women have this condition if
their blood pressure is significantly higher than 160/95; men under age
45 if over
130/90, and beyond age 45 if above 140/95.
3. Diastolic pressure is emphasized
when medical treatment is considered.
4. Hypertension may not be detected
until a stroke or heart attack occurs.
5. Two genes are involved in
hypertension for some individuals.
a. One gene
codes for angiotensinogen, plasma protein converted to a vasoconstrictor by
product of second gene.
b. Persons
with this form of hypertension may one day be cured by gene therapy.
C. Atherosclerosis
1.
Hypertension is seen in individuals with atherosclerosis,
formerly called arteriosclerosis.
2. Soft plague masses of fatty
materials accumulate beneath inner linings of arteries.
3. As plaque accumulates, it
protrudes into a vessel, interfering with blood flow.
4. Atherosclerosis develops in early
adulthood but symptoms may not appear until age 50 or older.
5. Plaque can cause a blood clot to
form on irregular arterial walls.
6. As long as a clot remains stationary,
it is a thrombus.
7. If a clot dislodges, it is an embolus,
a blood clot that moves in the blood.
8. In some families, atherosclerosis
is inherited as familial hypercholesterolemia.
D. Stroke and Heart Attack
1. Stroke,
heart attack, and aneurysm are associated with hypertension and
atherosclerosis.
2. Strokes can result
in paralysis or death; a small arteriole bursts or is blocked by an embolus.
a. Stroke is
also called a cardiovascular accident (CVA).
b. Paralysis
or death depends on extent a portion of the brain lacks O2.
c. Warning
symptoms include: numbness in hands or face, difficulty speaking, blindness in
one eye.
3. A myocardial infarction
(MI) is also called heart attack.
a. It occurs
when a portion of heart muscle dies due to a lack of O2.
b. A
partially blocked coronary artery causes angina pectoris causing
chest pains or radiating pain in left arm.
c. Nitroglycerin
and related drugs dilate blood vessels and relieve pain.
d. One cause
of heart attacks is blockage of coronary arteries due to a thromboembolism.
38.5. Blood, a Transport Medium
A.
Blood has two
components, plasma and formed elements (cells and platelets).
1. Plasma contains water and many types of molecules, including
nutrients, wastes, salts, and proteins.
2. Salts and proteins buffer blood.
a. They
effectively keep blood pH near 7.4.
b. They maintain
blood osmotic pressure so water has a tendency to enter blood capillaries.
3. Some plasma proteins are involved
in blood clotting.
4. Some plasma proteins assist in
transporting large organic molecules in blood.
a. Lipoproteins
that transport cholesterol are globulins.
b. Albumin,
a common plasma protein, transports bilirubin, a breakdown product of
hemoglobin.
B. Formed Elements
1. Blood
cells are in three types: red blood cells (RBCs), white blood cells (WBCs), and
platelets.
2. Red Blood Cells
a. Red
blood cells (erythrocytes) are small bi-concave disks.
b. RBCs lack
a nucleus and contain hemoglobin.
c. There are
6 million RBCs per mm3 of whole blood.
d. Each RBC
contains 250 million hemoglobin molecules.
1) Hemoglobin contains four globin protein chains; each with an
iron-containing heme group.
2) Iron atom of a heme group loosely binds with an O2 molecule; thus, blood
carries oxygen.
3) Anemia is insufficient hemoglobin; an individual suffers from
a tired, run-down feeling.
e. RBCs are
manufactured in red bone marrow of skull, ribs, vertebrae, and ends of long
bones.
f. Growth
factor erythropoietin is produced when an enzyme from kidneys
acts on a precursor made by
liver and stimulates production of red blood cells; as a drug it helps people
with anemia.
g. Before
being released from bone marrow, RBCs lose their nucleus and synthesize
hemoglobin.
h. Red blood
cells have a life span of about 120 days; they are destroyed chiefly in liver
and spleen.
i. Iron is
recovered and returned to bone marrow where it is re-used.
j. Heme
portions undergo chemical degradation; excreted by liver as bile pigments, it
colors feces.
3. White Blood Cells
a. White
blood cells (leukocytes) differ from RBCs in being larger and in having
a nucleus.
b. WBCs lack
hemoglobin and appear translucent without staining.
c. Granular
leukocytes contain conspicuous granules in their cytoplasm; have a
lobed nucleus.
1) Neutrophils have granules that stain slightly pink; they are
amoeboid, spherical cells that readily
squeeze through capillary walls and phagocytize foreign material.
2) Eosinophils have granules that take up red dye eosin.
3) Basophils have granules that take up a basic dye, staining
them deep blue.
d. Newly
discovered stem cell growth factor increases production of all WBCs.
e. Agranular
leukocytes lack granules in cytoplasm and have a circular or indented
nucleus.
1) Monocytes are amoeboid and able to enter tissues where they
transform into macrophages.
2) Macrophages release white blood cell growth factors that
increase number of leukocytes.
3) Pus is a thick, yellowish fluid that contains a large
proportion of dead WBCs that have fought infection.
4) Lymphocytes play a key roles in fighting infection and include
two types.
a) T cells are lymphocytes that directly attack virus-infected
cells.
b) B cells can be stimulated to produce one type of antibody
specific for one type of antigen.
5) Antigen is any substance stimulating production of antibodies;
antigen is foreign to the body.
6) Antibodies combine with antigens to promote their being
phagocytized by a macrophage.
7) A person is actively immune when many B cells produce specific antibody for
an infection.
4. Platelets
a. Platelets
(thrombocytes) form from fragmented giant cells (megakaryocytes)
in bone marrow.
b. 200
billion platelets are produced a day; blood contains 150,000-300,000 per mm3.
c. Platelets
are involved in blood clotting or coagulation.
d. At least
12 clotting factors in blood participate in clotting.
e. Hemophilia
is an inherited disorder where liver is unable to produce one of the clotting
factors.
f. Minor
bumps can cause internal bleeding; bleeding into brain causes death in
hemophilia.
g. Vitamin K
is necessary to produce prothrombin; deficiency causes hemorrhagic disorders.
5. Blood Clotting
a. When a
blood vessel is damaged, platelets clump at site of hemorrhage and partially
seal leak.
b. Platelets
and damaged tissue cells release a clotting factor called prothrombin
activator.
c. With
calcium ions, prothrombin activator catalyzes reaction converting prothrombin
to thrombin.
d. Thrombin
acts as an enzyme to sever two amino acid chains from each fibrinogen molecule.
e. These
activated fragments join end-to-end forming long threads of fibrin.
f. Fibrin
threads wind around platelet plug and provide a framework for a clot. (Fig.
41.12b)
g. RBCs are
trapped within fibrin threads, making clot appear red.
h. When
blood vessel repair is initiated, plasmin destroys fibrin network
and restores plasma fluidity.
i. When
clotting occurs in test tube, fluid serum collects above a clot;
it has same composition as
plasma except fibrinogen.
C. Capillary Exchange
1. Two
forces control movement of fluid through capillary walls.
a. Osmotic
pressure tends to cause water to move from tissue fluid to blood.
b. Blood
pressure tends to cause water to move from blood to tissue fluid.
c. At
arterial end of a capillary, blood pressure is higher than osmotic pressure:
water exits and moves into tissues.
d. Between
ends of a capillary, O2 and nutrients diffuse out into tissue fluid, while CO2
and other metabolic
wastes diffuse into capillaries from tissue fluid.
2. Midway along a capillary, there
is no net movement of water.
3. Tissue fluid is
intercellular fluid that surrounds cells; circulatory system exchanges
materials with this fluid.
4. Exchange between blood and tissue
fluid occurs by diffusion through one-cell-thick capillary walls.
a. At venule
end, osmotic pressure is higher than blood pressure and water moves back into
blood.
b. Almost
same amount of fluid that left capillary returns to it; there is always some
excess tissue fluid
collected by lymphatic capillaries.
5. Tissue fluid within lymphatic
vessels is lymph.
6. Lymph returns to
systemic venous blood when lymphatic vessels enter subclavian veins in
shoulder.
7. Not all capillary beds open at same
time; pre-capillary sphincters shunt blood in various pathways.
8. Blood also distributes heat to
body parts and conserves heat when cold.
38.6. How Animals Exchange Gases
A. Respiration results in
gas exchange between the environment and the body's cells.
1. Breathing
includes inspiration (bringing air in) and expiration
(moving air out).
2. External respiration
involves gas exchange with external environment at a respiratory surface.
3. Internal respiration
in more complex animals involves gas exchange between blood and tissue fluid.
B. Diffusion Accompanies Gas
Exchange
1. An
effective gas exchange region must be moist, thin, and large in relation to
size of the body.
2. Some animals are small and shaped
to allow the surface to be a gas-exchange surface.
3. Complex animals have a
specialized gas-exchange surface.
4. Diffusion improves with
vascularization; delivery is promoted if blood contains hemoglobin.
C. Water Environments
1. It is more
difficult to obtain O2 from water than from air.
a. Water
fully saturated with air contains only a fraction of O2 as air.
b. Water is
more dense than air; aquatic animals use more energy to breathe.
c. Fish use
up to 25% of energy to breathe; land mammals use 1-2% of energy output to
breathe.
2. Hydras and planaria have a large
surface area in comparison to their size. (Fig. 44.1)
a. Gas
exchange occurs directly across their body surface.
b. Hydra's
outer cell layer contacts environment; inner layer exchanges gases with
gastrovascular cavity.
c. Flat body
of planaria permits ready exchange of gases with the external environment.
3. A tubular shape and parapodia
extensions (polychaete worms) provide surface areas for diffusion.
4. Often aquatic animals pass water
over gills.
a. Gills
are finely divided and vascularized outgrowths of either an outer or inner body
surface.
b. Among
clams, water drawn into mantle cavity passes over gills.
c. Decapod
gills are located in brachial chambers under exoskeleton; water circulates by
special mouthparts.
d. Fish
gills are outward extensions of the pharynx organized into arches.
e.
Ventilation is result of combined action of mouth and gill covers.
f. When
mouth is open, opercula are closed and water is drawn in; the mouth then closes
and opercula
open, drawing water from pharynx through gill slits located between gill
arches.
g. Outside
of gill arches are gill filaments folded into platelike lamellae,
each of which contains
capillaries; result is atremendous surface area for gas exchange.
1) Blood in capillaries of gill lamellae flows in a direction opposite to that
of water.
2) Countercurrent flow of water and blood increases amount of O2
and CO2 exchanged.
3) Countercurrent mechanism extracts about 80-90% of initial dissolved O2 in
water.
D. Land Environments
1. Air is a
richer source of O2 than water but dries respiratory surfaces; humans lose 350
ml of water
per day at
50% relative humidity.
2. Earthworm is an invertebrate that
uses its body surface for respiration.
a.
Earthworms expend energy to secrete mucus and release fluids from excretory
pores.
b. Earthworm
is behaviorally adapted to stay in moist soil during the day when air is
driest.
3. Terrestrial insects utilize tracheal
systems.
a. Oxygen
enters tracheal system at spiracles, valve-like openings at side
of body.
b. Tracheae
branch and rebranch to end in tiny tracheoles in direct contact
with body cells.
c. Larger
insects have air sacs located near major muscles to keep air moving in and out
of trachea.
d. Tracheae
effectively deliver oxygen to cells; circulatory system has no role in gas
transport.
4. Terrestrial vertebrates use lungs
for gas exchange.
a. Lungs
are vascularized outgrowths of lower pharyngeal region.
b. Amphibian
lungs are simple, saclike structures, that connect to external environment by
way of
two bronchi, which connect to a short trachea.
(Fig. 44.4a)
1) Amphibian gas exchange occurs through skin kept moist by mucus produced by
glands.
2) In winter, amphibians burrow in mud; gas exchange occurs across skin.
3) Frogs use positive pressure to force air in; nostrils shut and floor of
mouth forces air into lungs.
c. Reptiles,
birds, and mammals use negative pressure to move air into lungs.
1) Jointed ribs can be raised and a muscular diaphragm is flattened to expand
lungs.
2) As thoracic cavity expands, lung volume increases; air flows in due to
difference in air pressure.
3) By lowering ribs, pressure is exerted on the lungs, which forces air out.
d. Lungs of
reptiles, amphibians and mammals are not completely emptied each breathing
cycle.
1) With incomplete ventilation, entering air mixes with used air in lungs.
2) This conserves moisture but decreases gas-exchange efficiency.
e. High
oxygen requirements of flying birds requires a complete ventilation
system. (Fig. 44.5)
1) Incoming air is carried past lungs by a bronchus that takes it to set of
posterior air sacs.
2) Air then passes forward through lungs into a set of anterior air sacs and is
finally expelled.
3) One-way flow means oxygen-rich air does not mix with used air; this
maximizes gas exchange.
38.7. Human Respiratory System
A. Structure
1. Human
respiratory system includes everything that conducts air to and from
lungs; lungs lie deep
within
thoracic cavity for protection from drying out.
2. Air moves into nose,
then flows past pharynx to trachea, bronchi
and lungs.
a. This
process filters debris, warms air and adds moisture.
b. When air
reaches lungs, it is at body temperature and saturated with water.
c. Trachea
and bronchi are lined with cilia that beat upward carrying mucus,
dust and particles.
d. Hard
and soft palates separate nasal cavities from mouth.
e. Air and
food passages cross in pharynx; danger of choking is offset by providing an
alternative path
for breathing during congestion, and increasing air intake during exercise.
f. Air flows
past pharynx through glottis into larynx, which is
protected by epiglottis.
g. At edges
of glottis are vocal cords; as air passes across them, tissues
vibrate creating sounds.
h. From the
larynx, air flows down trachea to bronchi.
1) Larynx is held open by cartilage that forms Adam's apple.
2) Trachea walls are reinforced with C-shaped rings of cartilage.
3) As food is swallowed, larynx rises and glottis is closed by a flap of tissue
called epiglottis.
4) Backward movement of soft palate covers entrance to nasal passages; food is
directed down.
i. Trachea
divides into two bronchi; C-shaped rings of cartilage diminish as
bronchi branch.
j. Within
lungs, each bronchus branches into numerous bronchioles that
conduct air to alveoli.
k. Alveoli
are microscopic air sacs.
B. Breathing
1. Humans breathe
using negative pressure just as all other mammals.
2. During inhalation,
lowering diaphragm and raising ribs forms negative pressure by increasing
volume
of thoracic
cavity; air under greater outside pressure flows into lung.
3. Increases in CO2 and H+
concentrations in blood are the primary stimuli increasing breathing rate.
a. Chemical
content of blood is monitored by chemoreceptors sensitive to increases
in CO2 and H+
concentrations of blood, but minimally sensitive to decreases in O2
concentration.
1) Aortic bodies are chemoreceptors located in wall of aortic
arch.
2) Carotid bodies are chemoreceptors located in wall of carotid
arteries.
4. Information from these goes to
respiratory center in medulla oblongata increasing breathing rate
when
CO2 or H+
concentrations increase; this respiratory center is sensitive to blood reaching
brain.
C. Gas Exchange and Transport
1. Gas
exchange in lungs and tissues is primarily by diffusion.
2. Atmospheric air contains little
CO2, but blood flowing in pulmonary capillaries has a higher concentration of
CO2.
3. CO2 diffuses from higher
concentration in blood across walls of alveolar capillaries to lower
concentration
in air in
alveoli.
4. Blood coming into pulmonary
capillaries is oxygen poor and alveolar air is oxygen rich.
5. Oxygen diffuses from higher
concentration in alveoli across walls of alveolar capillaries to lower
concentration in blood.
D. Transport of O2 and CO2
1. Most O2
entering blood combines with hemoglobin (Hb) to form oxyhemoglobin
(HbO2).
Hb
+
O2 
HbO2
deoxyhemoglobin
oxygen
oxyhemoglobin
2. Hemoglobin
molecule has four polypeptide chains; each chain is folds over an
iron-containing heme.
a. Iron atom
of a heme group loosely binds with an O2 molecule.
b. Each RBC
has 250 million hemoglobin molecules; each RBC can carry a billion molecules
of O2 oxyhemoglobin.
3. Oxygen-binding ability of
hemoglobin can be graphed.
a.
Percentage of oxygen-binding sites of hemoglobin carrying O2 varies with partial
pressure of O2
(PO2) in immediate environment.
b. Partial
pressure is amount of pressure exerted by a particular gas among all
gases present.
c. At normal
partial pressures of O2 in lungs, hemoglobin becomes practically saturated with
O2.
d. But at
the O2 partial pressures in tissues, oxyhemoglobin quickly unloads much of its
O2.
HbO2 Hb
+ O2
e. Acid pH and warmer temperature of tissues promote this dissociation.
4. In tissues, some hemoglobin
combines with CO2 to form carbaminohemoglobin.
Hb
+ CO2 HbCO2
carbaminohemoglobin
5. However,
most CO2 is transported in form of bicarbonate ion (HCO3-).
a. First CO2
combines with water, forming carbonic acid (H2CO3).
b. Then this
dissociates to a H+ and a HCO3 -
CO2
+ H2O
H2CO3 H+
+ HCO3-
carbonic acid bicarbonate ion
c. Carbonic anhydrase an enzyme in red blood cells speeds this
reaction.
d. Released
H+ ions could drastically lower blood pH; however, hydrogen ions are absorbed
by
globin portions of hemoglobin and HCO3- diffuses out of RBCs into plasma.
e.
Hemoglobin combines with a H+ ions as reduced hemoglobin (HHb);
HHb plays a vital role in blood pH.
f. As blood
enters pulmonary capillaries, most CO2 is in plasma as HCO3-.
g. The
little free CO2 remaining diffuses out of blood across walls of pulmonary
capillaries into alveoli.
h. Decrease
in plasma CO2 concentration causes the following reaction also catalyzed by
carbonic anhydrase:
H+
+ HCO3
H2CO3 CO2 +
H2O
i. At same time, hemoglobin unloads H+ and HHb becomes Hb.
38.8. Respiration and Health
A. Upper Respiratory Tract
Infections (URI)
1. Entire
respiratory tract has a warm, wet, mucous membrane lining exposed to
environmental air.
2. Upper respiratory tract
consists of nose, pharynx and larynx.
3. Strept throat is a
severe infection caused by the bacteria Streptococcus pyogenes
resulting in high
fever and
difficult swallowing and it may lead to a systemic infection.
4. Sinusitis is
infection of the sinuses; 1-3% of upper respiratory infections are accompanied
by it.
5. Tonsillitis occurs
when tonsils and adenoids of pharynx are inflamed as first line of defense.
6. Laryngitis is
infection of the larynx causing hoarseness and inability to talk.
7. Persistent hoarseness
without an upper respiratory infection is one of the warning signs of cancer.
B. Lower Respiratory Tract Infections
1. Acute
bronchitis is an infection of primary and secondary bronchi usually
preceded by a viral URI.
2. Pneumonia
a. Pneumonia
is usually caused by bacterial or viral lung infection.
b. Bronchi
and alveoli fill with fluid.
c. Pneumonia
can be localized in specific lobules.
d. AIDS
patients are subject to a rare form caused by the protozoan Pneumocystis
carinii.
3. Pulmonary Tuberculosis
a.
Tuberculosis is caused by the tubercle bacillus, a type of bacterium.
b. A TB
skin test is a highly diluted extract of the bacilli injected into the
patient's skin; if a person
has been exposed, the immune response causes an area of inflammation.
c. Bacilli
that invade lung tissue are isolated by lung tissue in tiny capsules called
tubercles.
d. If the
person is resistant, the imprisoned bacteria die.
e. If the
person is not resistant, the bacteria can eventually be liberated.
f. A chest X
ray detects active tubercles.
g.
Appropriate drug therapy can ensure localization and eventual destruction of
live bacteria
h.
Resurgence has accompanied increases in AIDS, homeless, and poor; new strains
are resistant.
C. Pulmonary Disorders
1. Pulmonary
Fibrosis
a. Inhaling
particles of silica, coal dust, fiberglass and asbestos can lead to pulmonary
fibrosis.
b. These
agents result in build up of fibrous connective tissue; lungs cannot inflate
properly.
c. Asbestos
was use widely for fireproofing and widespread exposure occurred; a possible 2
million
deaths could be caused by asbestos between 1990 and 2020.
2. Chronic Bronchitis
a. Airways
are inflamed and filled with mucus; a cough brings mucus up.
b. Bronchi
degenerate, losing cilia and normal cleansing action and making infection
likely.
c. Smoking
cigarettes and cigars is most common cause but air pollution is also involved.
3. Emphysema
a. Emphysema
involves distended damaged alveoli and ballooning of lungs due to trapped air.
b. It is
often preceded by chronic bronchitis.
c. Elastic
recoil of lungs is reduced, airways are narrowed, making expiration difficult.
d. Since
surface area for gas exchange is reduced, insufficient O2 reaches the heart and
the brain.
e. This
triggers heart to work furiously to force more blood through lungs; this can
lead to a heart condition.
f. Lack of
oxygen to brain makes patient feel depressed, sluggish, and irritable.
4. Asthma
a. Asthma
is disease of bronchi and bronchioles causing wheezing, breathlessness and
cough.
b. Airways
are sensitive to specific allergens (e.g. pollen, dust, cold air, etc.)
c. Exposure
to the irritant causes smooth muscle in bronchi to spasm .
d. Bronchial
inflammation reduces diameter of airways.
e. Inhalers
can control inflammation; other inhalers can stop muscle spasms.
5. Lung Cancer
a. Formerly
more common in men, lung cancer now surpasses breast cancer as cause of death
in
women due to smoking.
b. Lung
cancer develops in lung tissue in steps:
1) First, a thickening and callusing of cells lining the bronchi appears.
2) Cilia are lost so it is impossible to prevent dust and dirt from settling in
lungs.
3) Next, cells with atypical nuclei appear in callused lining.
4) A tumor consisting of disordered cells with atypical nuclei develops as cancer
in situ.
5) When some tumor cells break free and penetrate other tissue (metastasis),
cancer spreads.
6) Tumor may grow until bronchus is blocked, cutting off air supply to lungs.
7) Entire lung collapses; trapped secretions become infected causing pneumonia
or lung abscess.
c. The only
treatment is surgery (pneumonectomy) where a lobe or whole lung is removed.