Download File - Ms. Richards IB Biology HL

Option D.6 Transport of
respiratory gases
Essential idea: Red blood cells are vital in the transport of respiratory
gases
D.6 Transport of respiratory gases
Nature of science: Scientists have a role in informing the public—scientific research has led to a
change in public perception of smoking. (5.1)
Understandings:
• Oxygen dissociation curves show the affinity of hemoglobin for oxygen
• Carbon dioxide is carried in solution and bound to hemoglobin in the blood
• Carbon dioxide is transformed in red blood cells into hydrogencarbonate ions
• The Bohr shift explains the increased release of oxygen by hemoglobin in respiring tissues
• Chemoreceptors are sensitive to change in blood pH
• The rate of ventilation is controlled by the respiratory control centre in the medulla oblongata
• During exercise the rate of ventilation changes in response to the amount of CO2 in the blood
• Fetal hemoglobin is different from adult hemoglobin allowing the transfer of oxygen in the
placenta onto the fetal hemoglobin
D.6 Transport of respiratory gases
Applications and Skills:
• Application: Consequences of high altitude for gas exchange
• Application: pH of blood is regulated to stay within the narrow range
of 7.35 to 7.45
• Application: Causes and treatments of emphysema
• Skill: Analysis of dissociation curves for hemoglobin and myoglobin
• Skill: Identification of pneumocytes, capillary endothelium cells, and
blood cells in light micrographs and electron micrographs of lung
tissue
Mammalian Ventilation System
• Include ribs and intercostals (muscle between the ribs) as well as
insert of alveoli
Negative Pressure: air moves from high
pressure to low pressure areas
Alveoli: SEM
D.S.6.2 Light micrograph of lung tissue: alveoli
and bronchus
Pneumocytes: Types 1 and 2
• Gas exchange occurs in alveoli
• The alveolus is composed of a single
layer of cells to facilitate oxygen and
carbon dioxide diffusion
• Alveoli are composed of specialized
cells called pneumocytes
• Type 1: very thin but has a large
membrane surface area. Ideal for
diffusion. If damaged, incapable of
mitosis for replacement
Pneumocytes: Types 1 and 2
• Type 2: cuboidal in shape (small
membrane surface area)
• Produce and secrete surfactant
which reduces surface tension of
moist inner surface of alveoli and
prevents sides from sticking to each
other
• Capable of mitosis for replacement
of both types of alveolar cells
D.S.6.2 Electron micrograph: capillary with
RBC and alveolar space
• A = alveolar epithelium
• B = basement membrane
• C = endothelium
• D = alveolar space
RBC
D
D
Control of Ventilation
Partial Pressure
• Atmospheric pressure: downward force exerted by air on the earth’s
surface.
• At sea level, this force is equivalent to the force of a column of
mercury (Hg) = 760 mm Hg
• Partial pressure of oxygen: since the atmosphere is 21% oxygen (by
volume), the partial pressure of oxygen (abbreviated PO2) is 0.21 x
760 mm = 160mm Hg
• This is the portion of atmospheric pressure contributed by oxygen
(hence partial pressure)
• The partial pressure of carbon dioxide at sea level is only 0.23 mm Hg
Dissolved Gases
• Dissolved gases are proportional to their partial pressure in the air
and their solubility in water
• Diffusion of gases: from a region of higher partial pressure to a
region of low partial pressure
• Blood arriving at the lungs has a lower PO2 and a higher PCO2 than
the air in the alveoli
• Diffusion of gases in tissues works the same way
Respiratory Gases
Oxygen Transport
• At normal body temperature and air pressure, only 4.5 mL of oxygen
can dissolve into a liter of blood.
• During exercise, a person can consume almost 2 L of oxygen per
minute leading to a need for 500 L of blood to be pumped per minute
 Unrealistic (average person has about 4.5-5.5 L of blood in whole
body)
• Most animals transport most of their oxygen bound to special
proteins called respiratory pigments instead of dissolved in solution
• Blood can carry 200 mL of oxygen per L in mammals
Oxygen Transport
• Respiratory pigment in vertebrates: hemoglobin (Hb)
• Hemoglobin consists of 4 subunits, each with a cofactor called a
heme group that has an iron atom at its center. Each hemoglobin can
carry 4 molecules of O2
• Hemoglobin must bind oxygen reversibly, loading oxygen in the lungs
and unloading it in other parts of the body
Hemoglobin
Peer Pressure among oxygen molecules
• We see subunit cooperation (cooperativity)- binding of oxygen to one
subunit induces the remaining subunits to change their shape slightly
so that their affinity for oxygen increases
• When one subunit unloads its oxygen, the other three follow quickly
because of a conformation change that lowers their affinity for
oxygen
Hemoglobin binding to oxygen
Oxygen dissociation curve
• What follows are the oxygen dissociation curves for hemoglobin
• In your text book you will see the normal dissociation curve at 37oC
and the pH of 7.4
• You will also see the effect of lowering pH to 7.2 (increase in acidity
resulting in the Bohr Effect)
• You will find more dissociation curves in the review guide and your IB
textbook
Oxygen Dissociation Curves: graphs the
affinity of hemoglobin for oxygen
Oxygen Dissociation Curves
• Show the relationship between the % saturation of hemoglobin (or
myoglobin) and the partial pressure of oxygen
• Normal conditions:
a) When pO2 is high, hemoglobin binds with large amounts of oxygen
and is almost fully saturated
b) When pO2 is low, hemoglobin is only partially saturated and
oxygen is released from hemoglobin
c) Therefore, in pulmonary capillaries, a lot of oxygen binds with Hb,
but in tissue capillaries where the pO2 is lower, Hb does not hold as
much oxygen and the oxygen is released for diffusion into tissue
cells
Oxygen Dissociation Curve
d) Note that a pO2 of 40 mm Hg, the average pO2 of tissue cells at rest,
only 25% of the available oxygen splits from Hb and is used. (Big
reserve of oxygen)
e) Several other factors influence the affinity of Hb for oxygen, the
strength of the Hb-O2 binding. Keep in mind that metabolically active
cells need oxygen and produce acids, carbon dioxide, and heat
Effect of Acidity
• In an acid environment, hemoglobin’s affinity for oxygen is lower and
oxygen splits more readily from hemoglobin
• This is referred to as the Bohr effect
• When H+ ions bind to certain amino acids in Hb, they alter its
structure and decrease its oxygen-carrying capacity
• This makes more oxygen available for tissue cells
Acidosis
• When the body’s pH is lower than 7.35
• Respiratory Acidosis is when you cannot get rid of CO2
• Asthma, injury to chest, obesity, overuse of drugs or alcohol,
muscle weakness in chest, nervous system problems
• Metabolic Acidosis is issues with the kidneys
• Diabetic, hyperchloremic (loss of sodium bicarbonate), lactic (too
much lactic acid)
Change in pH
Partial Pressure of Carbon Dioxide: Better
discussion in review guide and in Campbell
• Carbon dioxide is carried dissolved in plasma (7%), as bicarbonate
ions (70%), and as carbaminohemoglobin (20-25%)
• Carbon dioxide in blood is temporarily converted to carbonic acid.
This conversion is catalyzed by an enzyme in red blood cells called
carbonic anhydrase. This carbonic acid dissociates into H+ ions and
bicarbonate ions
• Most of the carbon dioxide (70%) is transported in blood as
bicarbonate ions. As H ions increase, pH decreases. Many of the H+
combine with Hb or other plasma protein buffers
• As bicarbonate ions accumulate inside the RBC, some of them diffuse
into the plasma, down their concentration gradient (facilitative
diffusion)
Chloride Shift
• In exchange, chloride ions (Cl-) diffuse from plasma into the RBCs.
This exchange of negative ions maintains the ionic balance between
plasma and RBCs and is known as the chloride shift
• The net effect of these reactions is that carbon dioxide is carried from
tissue cells as bicarbonate ions in plasma
• Low pH can also result from lactic acid, a by-product of anaerobic
metabolism within muscles
Summary of gas transport showing the Bohr
effect and Chloride Shift
Blood and carbon
dioxide transport
Temperature
• As temperature increases, so does the amount of oxygen released
from hemoglobin
• Temperature rises as the result of activity and infection
Oxygen dissociation curve fetal hemoglobin
Fetal Hemoglobin
• Fetal hemoglobin differs from adult hemoglobin in structure and in
affinity for oxygen
• So when pO2 is low, fetal hemoglobin can carry up to 30% more
oxygen
• As maternal blood enters the placenta, oxygen is readily transferred
to fetal blood
• This is good because oxygen saturation in maternal blood in the
placenta is low
Fetal Hemoglobin
D.A.6.1 Acute Mountain Sickness (High
altitude sickness)
• As a person ascends in altitude, the atmospheric pO2 decreases, the
alveolar pO2 decreases correspondingly, and less oxygen diffuses into
the blood
• For example, at sea level, pO2 is 160 mm Hg
• At 10,000 feet, it decreases to 110 mmHg
• At 20,000 ft to 73 mm Hg and at 50,000 ft to 18 mm Hg
Symptoms of Altitude Sickness
• Shortness of breath
• Headache
• Fatigue
• Insomnia
• Nausea
• Dizziness
• Over a period of time, the person becomes acclimatized
Acclimatization
• Red blood cell production is stimulated by the hormone,
erythropoietin from kidney
• Ventilation rate increases
• Muscles produce more myoglobin and develop a dense capillary
network
• People living permanently at high altitude have greater lung surface
area and larger lung capacity and larger tidal volume than those
living at sea level
• Might even have variant hemoglobin
• Only restrict amount of
oxygen
• Do not stimulate pressure
experienced at high altitude
• No benefits seen in studies
• According to Alex Viada, a successful hybrid-training coach and
founder of Complete Human Performance, such high-altitude devices
"simulate altitude in the same way sticking your head in a toilet
simulates swimming." Ouch.
• While some users proclaim they can breathe better after using an
altitude mask, I bet if I jammed a pillow down someone's throat and
asked him to run a mile, he'd be able to breath much better once I
took it away, too.
• http://www.bodybuilding.com/content/do-elevation-maskswork.html
• Chemosensors are sensitive to changes in pH
• The rate of ventilation is controlled by
respiratory center in the medulla oblongata
Exercise
• Leads to increased metabolic activity and therefore an increase in
carbon dioxide output which lowers blood pH
• This change in pH is detected by chemosensors in the carotid arteries
and aorta that send impulses to the breathing center of the brain=
(pons and medulla oblongata)
• Nerve impulses are then sent to the diaphragm and the intercostal
muscles to increase contraction or relaxation rates
D.S.6.1 Myoglobin vs Hemoglobin
• Oxygen dissociation curve for
myoglobin is NOT S shaped as is
hemoglobin
• Myoglobin has a different protein
structure than hemoglobin
Myoglobin
• Consists of 1 heme group attached to a globin
• Used to store oxygen in muscle
• Myoglobin has higher affinity for oxygen than hemoglobin
• At moderate pO2, hemoglobin releases oxygen and myoglobin binds
it
• Myoglobin does not release oxygen to tissue until the pO2 is very low
in tissues
• Delays the shift to anaerobic cell respiration
Myoglobin
Emphysema
• Emphysema is the replacement of alveolar tissue by thick, inelastic
connective tissue
• Also one of the diseases collectively called chronic obstructive
pulmonary disease or COPD
• Main causes are smoking tobacco, marijuana smoke, and air pollution
including fumes from manufacturing plants and coal dust
• The constant irritation from the pollutant slowly destroys the alveoli
which are replaced by thick, inelastic connective tissue
• Vilia lining airways which expel mucus are damaged and cease to
function, so mucus builds up in lungs causing infections
Emphysema: chronic, slowly progressive
disease
Emphysema
D.A.6.3 Emphysema
• Turns healthy alveoli into large, irregularly shaped structures with
gaping holes
• Inflamed and damaged cells and white blood cells release trypsin
(protease) which digests elastic fibers in lungs. Eventually causes
complete breakdown of alveolus walls
• This reduces surface area for gas exchange so less oxygen reaches the
bloodstream
• Lungs lose elasticity, making it increasingly difficult to exhale
• Mucus accumulation causes coughing and wheezing
Alveolar space increased
Decreased surface area
Normal
Emphysema
Symptoms and treatment of emphysema
• Shortness of breath, initially in response to strenuous activity
• Over time, inability to get sufficient gas exchange becomes constant
• There is no cure for emphysema once it is severe enough to be diagnosed
but progression can be slowed with the cessation of smoking or wearing of
protective mask when working around dust or chemical fumes
• Some medications can help to relieve the symptoms (dilate the bronchi)
• Supplemental oxygen from a container can be administered through small
tubes into the nostrils
• Training in breathing techniques to reduce breathlessness
• Surgery to remove damaged lung tissue and less commonly, lung
transplants
Bronchogenic Carcinoma (Lung Cancer)
• Common lung cancer starts in the walls of the bronchi
• The constant irritation by inhaled smoke and pollutants cause the
mucus producing cells of the bronchial epithelium to enlarge
• They respond by secreting excessive mucus
• The basal cells also respond to the stress by undergoing cell division
so fast that they push into the area occupied by the mucus and other
epithelial cells
• Cancerous growth takes over areas of healthy tissue that once
provided a combination of bronchioles and alveoli. Can result in
internal bleeding in the lungs
Healthy lung vs cancerous lung
Causes of Cancer
• Smoking- tobacco smoke contains mutagens/carcinogens that cause
tumors to develop. Nearly 90% of lung cancers caused by smoking
• Passive or 2nd hand smoking- smoking bans should reduce this
• Air pollution- sources include diesel exhaust fumes, nitrogen oxides
from vehicles and smoke from wood and coal fires.
• Radon gas- leaks out of rocks, especially granite.
• Asbestos and silica- dust from these cause cancer if deposited in
lungs
Consequences of Lung Cancer
• Difficulties with breathing
• Persistent coughing (so-called “dry” cough)
• Coughing up blood
• General fatigue
• Chest pain
• Loss of appetite
• Weight loss (unexplained)
Treatment
• Best treatment is achieved when the disease is diagnosed early in its
progression
• Lung cancer has a very high mortality rate
• Surgery may be used to remove the tumor along with the diseased
part of the lung
• Radiation therapy uses high-energy X-rays to kill cancer cells or keep
them from growing. It can be used before surgery to shrink the
tumor. It can be used after surgery to kill any cancer cells left in the
lungs. It can be used on metastases
Treatment
• Chemotherapy means the use of special drugs to destroy cells
throughout the body
• Targeted therapies directly address the mutations that are causing
the cancer cells to grow uncontrollably
• Cause less side effects by “targeting” the cancer cells and reducing
the damage to the healthy cells
Lung Cancer