Chapter 22: The Respiratory System

Question 1

Respiration and the 4 Processes That Supply the Body with O2 and Dispose of CO2:

Answer 1

o Involves both the respiratory and the circulatory systems.
o 1) Pulmonary ventilation (breathing): movement of air into and out of the lungs (Respiratory System).
o 2) External respiration: O2 and CO2 exchange between the lungs and the blood (Respiratory System).
o 3) Transport: O2 and CO2 in the blood (Circulatory System).
o 4) Internal respiration: O2 and CO2 exchange between systemic blood vessels and tissues (Circulatory System).
o Major Organs of Respiratory System: Nose, Nasal Cavity, Paranasal Sinuses, Pharynx, Larynx, Trachea, Bronchi, Bronchi Branches, Lungs, and Aveoli.

Question 2

Functions of the Nose:

Answer 2

o	Provides an airway for respiration.
o	Moistens and warms the entering air.
o	Filters and cleans inspired air.
o	Serves as a resonating chamber for speech.
o	Houses olfactory receptors.

Question 3

Nasal Cavity:

Answer 3

o Nasal cavity: in and posterior to the external nose
o Divided by a midline nasal septum
o Posterior nasal apertures (choanae) open into the nasal pharynx.
o Roof: ethmoid and sphenoid bones
o Floor: hard and soft palates
o Olfactory mucosa: Lines the superior nasal cavity. Contains smell receptors.
o Respiratory mucosa:
o Pseudostratified ciliated columnar epithelium.
o Mucous and serous secretions contain lysozymes and defensins.
o Cilia move contaminated mucus posteriorly to throat.
o Inspired air is warmed by plexuses of capillaries and veins.
o Sensory nerve endings triggers sneezing.
o Superior, middle, and inferior nasal conchae: Protrude from the lateral walls. Increase mucosal area.
o Enhance air turbulence
o Olfaction, Meatus.

Question 4

Functions of the Nasal Mucosa and Conchae:

Answer 4

o During inhalation, the conchae and nasal mucosa = Filter, heat, and moisten air.
o During exhalation these structures = Reclaim heat and moisture.

Question 5

Paranasal Sinuses:

Answer 5

o In frontal, sphenoid, ethmoid, and maxillary bones: Lighten the skull and help to warm and moisten the air.

Question 6

Pharynx:

Answer 6

o A muscular tube that connects to the:
o Nasal cavity and mouth superiorly.
o Larynx and esophagus inferiorly.
o Has openings for Eustachian tube which equalizes air pressure between middle ear cavity and the nasopharynx.
o Tonsils present: pharyngeal, palatine, lingual (tongue).
o The pharnyx extends from the base of the skull to the level of the sixth cervical vertebra.

Question 7

Larynx:

Answer 7

o 1.5” passageway connecting larynogpharynx to trachea.
o Continuous with the trachea.
o Functions:
o Primary function = Provides a patent airway by keeping food and airways separate.
o Voice production = SOUND.
o 9 separate pieces of cartilage
o Hyaline cartilage except for the epiglottis
o Thyroid cartilage with laryngeal prominence (Adam’s apple)
o Ring-shaped cricoid cartilage

Question 8

Epiglottis of Larynx:

Answer 8

o Elastic cartilage; covers the laryngeal inlet during swallowing.

Question 9

Glottis of Larynx:

Answer 9

o False vocal cords (or vestibular folds) are superior and not part of sound production.
o True vocal folds are inferior where sound is produced.
o Rima glottidis (glottis) = the space between the vocal folds, this window closes when we swallow, false vocal cords help with this.
o True Vocal Folds (or vocal cords) vibrate to produce sound as air rushes up from the lungs.

Question 10

Voice Production:

Answer 10

o Speech: intermittent release of expired air while opening and closing the glottis.
o Pitch is determined by the length and tension of the vocal cords.
o Loudness depends upon the force of air.
o Chambers of pharynx, oral, nasal, and sinus cavities amplify and enhance sound quality.
o Sound is “shaped” into language by muscles of the pharynx, tongue, soft palate, and lips.

Question 11

The 4 Lower Respiratory System Components:

Answer 11

o 1) Trachea.
o 2) Bronchi.
o 3) Bronchioles.
o 4) Lungs = alveolar ducts, alveolar sacs, alveoli.

Question 12

Trachea:

Answer 12

o Windpipe: from the larynx into the mediastinum (superior border of T5).
o Trachea is 4 to 5”.
o Wall composed of three soft tissue layers:
o Mucosa: ciliated pseudostratified columnar epithelium with goblet cells (produce mucin à mucous).
o Submucosa: connective tissue with seromucous glands.
o Adventitia: outermost layer made of connective tissue that encases C-shaped rings of hyaline cartilage.
o Trachealis muscle:
o Connects posterior parts of cartilage rings.
o Strongly contracts during coughing to expel mucus.
o Carina:
o Last tracheal cartilage.
o Point where trachea branches into two bronchi.
o Generates a very strong cough reflex.

Question 13

Bronchi and Subdivisions:

Answer 13

o Air passages undergo 23 orders of branching.

o Branching pattern called the bronchial (respiratory) tree.

Question 14

Conducting Zone Structures:

Answer 14

o Trachea: right and left main primary bronchi.
o Each main bronchus enters the hilum of one lung.
o Right main bronchus is wider, shorter, and more vertical than the left.
o Each main bronchus branches into lobar (secondary) bronchi (three right, two left).
o Each lobar bronchus supplies one lobe.
o Each lobar bronchus branches into segmental (tertiary) bronchi.
o Tertiary or Segmental bronchi divide and branch repeatedly.
o Bronchioles are less than 1 mm in diameter.
o Terminal bronchioles are the smallest, less than 0.5 mm diameter.
o From bronchi through bronchioles, structural changes occur:
o Decreasing amounts of cartilage = cartilage is absent from bronchioles.
o Epithelium changes from pseudostratified columnar to cuboidal; cilia and goblet cells become sparse.
o Relative amount of smooth muscle and elastic tissue increases.

Question 15

Bronchioles:

Answer 15

o “Bronchial tree” = 20 to 25 orders of branching….blood supply from bronchial arteries come off the thoracic aorta.
o Once the bronchioles get less that 1mm in diameter, there is no cartilage.
o BRONCHCONSTRICTION = smooth muscle contraction with narrowing of the airways.
o BRONCHODILATION = smooth muscle relaxation with lumen of airways increasing in size, sympathetic nervous system stimulated.

Question 16

Terminal Bronchioles:

Answer 16

o Less that 0.5 mm in diameter.
o Over 65,000 terminal bronchioles between the two lungs (one bronchiole may divide into 50 to 80 terminal bronchioles!!).
o No mucous glands, no goblet cells, very few cilia which means a great need for macrophages.
o Each terminal bronchiole divides into two or more respiratory bronchioles.

Question 17

Respiratory Zone (Respiratory Bronchioles):

Answer 17

o Beginning of the Respiratory Zone (vs. the “conducting zone”)….this is where gas exchange can begin.
o Respiratory bronchioles divide into 2 to 10 alveolar ducts
o Alveolar ducts end in alveolar sacs.
o Alveolar sacs are clusters of individual alveoli (one is called an alveolus, several are called alveoli.

Question 18

Alveolus:

Answer 18

o Air pouch 0.2 to 0.5 mm in diameter may contain alveolar pores (equalize air pressure and allow air to pass between alveoli).
o Specialized cells:
o Squamous alveolar cells (Type I) = simple squamous epithelial cells for gas exchange.
o Great (Type II) alveolar cells = also called septal cells (secrete surfactant = lipoprotein that reduces alveolar surface tension).
o Alveolar macrophages = dust cells.
o Outer surface = network of blood capillaries branching off the pulmonary blood vessels.
o Fibroblasts produce reticular and elastic fibers that surround alveoli.

Question 19

Respiratory Membrane:

Answer 19

o Consists of 4 layers of tissue = 0.5 microns thick (1/16th the diameter of an RBC)
o Alveolar wall with 3 cell types
o Basement membrane underlying the alveolar wall
o Capillary basement membrane
o Capillary wall = simple squamous = endothelium
o Estimated that the two lungs contain 300 million alveoli with a combined surface area of 750 square feet = the size of a racquetball court!!

Question 20

Ventilation-Perfusion Coupling:

Answer 20

o Pulmonary blood vessels constrict (smooth muscle) in the response to localized hypoxia (remember that most blood vessels would conversely vasodialate with hypoxia).
o This diverts pulmonary blood from poorly ventilated areas to better ventilated regions of the lungs!!

Question 21

Lungs:

Answer 21

o Located on either side of the mediastinum.
o Right lung is broader but shorter (has 3 lobes).
o Left lung is 10% smaller (2 lobes only).
o Apex of lungs is just superior to clavicles.
o Base of lungs sits on top of the diaphragm.
o Phrenic nerve (from the cervical plexus) innervates the diaphragm.
o Lungs are surrounded by the pleura.

Question 22

Pleuritis:

Answer 22

o Inflammation of the pleura.
o Not enough pleural fluid = pleural friction rub.
o Too much fluid = pleural effusion.

Question 23

Thoracentesis:

Answer 23

Removal of excess fluid in the pleural cavity.

Question 24

Atelectasis:

Answer 24

Collapse of a portion/all of lung.

Question 25

Pneumothorax:

Answer 25

Air in the pleural space.

Question 26

RDS:

Answer 26

Respiratory Distress Syndrome usually caused by deficiency of surfactant in infants.

Question 27

Physiology of Breathing:

Answer 27

o Pulmonary ventilation = physical “breathing” (atmospheric air enter/leaves alveoli).
o Alveolar gas exchange = gas exchange at the respiratory membrane (=external respiration).
o Transport of gases in the blood.
o Systemic gas exchange = gas exchange between the systemic capillaries, interstitial fluid, cells (= internal respiration).

Question 28

Blood Supply to the Lungs:

Answer 28

o Pulmonary circulation is characterized as low pressure but high volume.
o Pulmonary arteries (deoxy blood) deliver systemic venous blood from right ventricle.
o Branch profusely, along with bronchi and Feed into the pulmonary capillary networks.
o Pulmonary veins (oxy blood) carry oxygenated blood from respiratory zones to the left atria of the heart.
o Lungs have their very own blood supply to nourish its’ tissue cells:
o Bronchial arteries provide oxygenated blood to lung tissue.
• Arise from the thoracic aorta and enter the lungs at the hilum.
• Supply all lung tissue except the alveoli.
o Bronchial veins join with pulmonary veins.
o Pulmonary veins carry most venous blood back to the heart to right atrium via the superior vena cava.

Question 29

Pleurae:

Answer 29

o Thin, double-layered serosa.
o Parietal pleura on thoracic wall and superior face of diaphragm.
o Visceral pleura on external lung surface.
o Pleural fluid fills the slit-like pleural cavity.
o Provides lubrication and surface tension.

Question 30

Two Phases of Pulmonary Ventilation:

Answer 30

o Inspiration: Gases flow into the lungs.

o Expiration: Gases exit the lungs.

Question 31

Pressure Relationships in the Thoracic Cavity:

Answer 31

o Atmospheric pressure (Patm)
o Pressure exerted by the air surrounding the body
o It is 760 mm Hg at sea level
o Respiratory pressures are described relative to Patm
o Negative respiratory pressure is less than Patm
o Positive respiratory pressure is greater than Patm
o Zero respiratory pressure = Patm

Question 32

Intrapulmonary (Intra-Alveolar) Pressure (Ppul):

Answer 32

o Pressure in the alveoli.
o Fluctuates with breathing.
o Always eventually equalizes with Patm.

Question 33

Intrapleural Pressure (Pip):

Answer 33

o Pressure in the pleural cavity.
o Fluctuates with breathing.
o Always a negative pressure (

Question 34

Homeostatic Imbalance of the Lungs:

Answer 34

o	Atelectasis (lung collapse) is due to
o	Plugged bronchioles: collapse of alveoli could lead to intrapulmonary pressure in lung becoming less than 760 mm Hg).
o	Not enough surfactant.
o	A wound that admits air into pleural cavity = pneumothorax.

Question 35

Pulmonary Ventilation:

Answer 35

o Inspiration and expiration.
o Pulmonary ventilation is a mechanical process that depends on volume changes in the thoracic cavity.
o Volume changes lead to pressure changes.
o Pressure changes gases flow to equalize pressure.
o Like blood it flows from high pressure to low pressure.

Question 36

Boyle’s Law:

Answer 36

o The relationship between the pressure and volume of a gas
o Pressure (P) varies inversely with volume (V):
o The greater the volume, the lower the pressure of gas present.
o The less the volume, the greater the pressure of gas present.

Question 37

Inspiration:

Answer 37

o Inspiration is an active process.
o Inspiratory muscles contract.
o Thoracic volume increases.
o Lungs are stretched and intrapulmonary volume increases.
o Intrapulmonary pressure drops (by −1 mm Hg) according to Boyle’s Law.
o So, air flows into the lungs, down its pressure gradient, until Ppul = Patm or 760 mmHg.

Question 38

Sequence of Events for Inspiration:

Answer 38

o 1) Inspiratory muscles contract (diaphragm descends, rib cage rises).
o 2) Thoracic cavity volume increases.
o 3) Lungs are stretched; intrapulmonary volume increases.
o 4) Intrapulmonary pressure drops.
o 5) Air flows into lungs down its pressure gradient until intrapulmonary pressure is 0.

Question 39

Expiration:

Answer 39

o Quiet expiration (not forced) is normally a passive process
o Inspiratory muscles relax.
o Thoracic cavity volume decreases.
o Elastic lungs recoil and intrapulmonary volume decreases (smaller volume).
o Ppul rises (by +1 mm Hg or 761 mmHg).
o Air flows out of the lungs down its pressure gradient until Ppul = 0 or 760 mmHg.

Question 40

Sequence of Events for Expiration:

Answer 40

o 1) Inspiratory Muscles relax (diaphragm rises, rib cage descends due to recoil of costal cartilages).
o 2) Thoracic cavity volume decreases.
o 3) Elastic lungs recoil passively; intrapulmonary volume decreases.
o 4) Intrapulmonary pressure rises.
o 5) Air flows out of lungs down its pressure gradient until intrapulmonary pressure is 0.

Question 41

Physical Factors Influencing Pulmonary Ventilation:

Answer 41

o Inspiratory muscles consume energy to overcome three factors that hinder air passage and pulmonary ventilation = ATP.
o 1) Airway resistance.
o 2) Alveolar surface tension.
o 3) Lung compliance.

Question 42

Airway Resistance:

Answer 42

o Diameter of the Bronchioles = as the lungs expand, the bronchioles ALSO expand becauses their walls are pulled outward in every direction.
o The smaller the airway, the greater the resistance.
o Smooth muscle in the bronchiole walls contain sympathetic receptors (dialation) and parasympathetic receptors (constriction), also histamines, cold air, anaphylaxis, asthma causes constriction.
o Resistance disappears at the terminal bronchioles where diffusion drives gas movement.

Question 43

Pulmonary Compliance:

Answer 43

o Refers to how much effort is required to STRETCH the lungs and chest wall.
o High compliance = lungs and chest wall expand easily.
o Low Compliance = lungs and chest wall resist expansion.
o Normally, healthy lungs have HIGH COMPLIANCE because elastic fibers are easily stretched (and easily recoil) and surfactant reduces the surface tension of the alveoli.

Question 44

Factors Affection Pulmonary Compliance:

Answer 44

o 1) Surface tension of the alveoli: If the surface tension in the alveoli is too high (walls of the alveolus are TOO attracted to each other because there is not enough surfactant):
o The lung tissue will not want to expand = lower lung compliance RESPIRATORY DISTRESS SYNDROME (RDS) in premature babies because not enough surfactant has been produced yet.
o 2) Impairment of elasticity related to lung scarring = fibrosis or impediment of external intercostal muscles or diaphragm.
o 3) Pulmonary edema (hard for alveoli to expand if increased IFHP from edema). ALSO, fluid flows into alveoli all caused by congestive heart failure.

Question 45

Respiratory Volumes:

Answer 45

o TIDAL VOLUME = amt. of air normally exchanged in a single breath during normal quiet breathing = about 500 mL of air into and out of lungs with each breath (about 2 cups).
o About 350 mL (70%) of this actually gets to lungs, sometimes called the FUNCTIONAL VOLUME.
o About 150 mL (30%) constitutes ANATOMICAL DEAD SPACE = air found in the conducting division.
o INSPIRATORY RESERVE VOLUME = the amt. of air that can be taken in forcibly OVER the tidal volume inspiration, about 3000 mL in addition to the 500 mL of tidal volume
o EXPIRATORY RESERVE VOLUME = the amt. of air that can be forcibly exhaled OVER the tidal volume exhalation, about 1200 mL after the tidal volume is expelled.
o RESIDUAL VOLUME = air that remains in the lungs that can NOT be voluntarily expelled even with most strenuous exhalation, this is important because it allows gas exchange to go on continuously, even between breaths, and helps to keep the alveoli inflated/open, about 1300 mL.

Question 46

Respiratory Capacities:

Answer 46

o Inspiratory capacity (IC):
o Tidal volume (TV) + Inspiratory Reserve Volume (IRV)
o Maximum amount of air that can be inspired after a normal expiration (3600 ml).
o Functional residual capacity (FRC):
o Expiratory reserve volume (ERV) + residual volume (RV).
o Total Volume of air remaining in the lungs after a normal tidal volume expiration (2400 ml).
o Vital capacity (VC):
o Tidal volume (TV) + Inspiratory Reserve Volume (IRV) + Expiratory Reserve Volume (ERV).
o Maximum amount of air that can be expired after maximum inspiratory effort (4800 ml).
o Total lung capacity (TLC) =
o Tidal Volume (TV) + Inspiratory Reserve Volume (IRV) + Expiratory Reserve Volume (ERV) + Residual Volume (RV).
o Maximum amount of air contained in the lungs (6000 ml).

Question 47

Pulmonary Function Tests:

Answer 47

o Minute ventilation: total amount of gas flow into or out of the respiratory tract in one minute.
o Forced vital capacity (FVC): gas forcibly expelled after taking a deep breath.
o Forced expiratory volume (FEV): the amount vital capacity that can be expelled after maximum inhalation during specific time interval, healthy person will exhale 80% in one minute after max. inhalation, person with emphysema or an obstructive pulmonary disorder may only exhale 50%.

Question 48

Alveolar Ventilation:

Answer 48

o	Alveolar ventilation rate (AVR): flow of gases into and out of the alveoli during a particular time…e.g. = MV (minute ventilation).
o	AVR (ml/min)= frequency (breaths/min.) x Tidal Volume (ml/breath)
o	Rapid, shallow breathing decreases AVR.

Question 49

Nonrespiratory Air Movements:

Answer 49

o Most result from reflex action.

o Examples include: cough, sneeze, crying, laughing, hiccups, and yawns.

Question 50

Gas Exchanges Between Blood, Lungs, and Tissues:

Answer 50

o External respiration (O2 and CO2 between blood and lungs).

o Internal respiration (O2 and CO2 between blood and tissues).

Question 51

Dalton’s Law of Partial Pressure:

Answer 51

o Total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas.
o The partial pressure of each gas is directly proportional to its percentage in the mixture.

Question 52

Henry’s Law:

Answer 52

o When a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure.
o The amount of gas that will dissolve in a liquid also depends upon its solubility.
o CO2 is 20 times more soluble in water than O2.
o Very little N2 dissolves in water.

Question 53

Composition of Alveolar Gas:

Answer 53

o The Atmosphere contains mostly oxygen and nitrogen
o Alveoli contain more CO2 (40 mmHg) than CO2 in atmospheric air (0.3 mm Hg), due to:
o Gas exchanges in the lungs (oxygen diffuses into blood, CO2 diffuses into alveoli).
o Humidification of air by respiratory passages.
o Carbon dioxide solubility (CO2 has high solubility, so more CO2 dissolves into fluid walls of the respiratory membrane).

Question 54

External Respiration:

Answer 54

o External Respiration is the exchange of O2 and CO2 across the respiratory membrane.
o Influenced by:
o Partial pressure gradients and gas solubilities.
o Structural characteristics of the respiratory membrane.

Question 55

Partial Pressure Gradients of Gas Solubilities:

Answer 55

o Partial pressure gradient for O2 in the lungs is steep
o Deoxygenated capillary blood entering the lungs = Po2 = 40 mm Hg
o Alveolar Po2 = 104 mm Hg (partial pressure)
o The basic law of diffusion is flow from a high pressure gradient to low pressure and vice-versa which drives the mechanism.
o Due to such a large pressure gradient, oxygen diffuses rapidly across the respiratory membrane into blood capillaries.
o O2 partial pressure in blood reachs equilibrium of 100 mmHg (less than atmospheric PO2 due to less solubility) in ~0.25 seconds across the respiratory membrane.
o Partial pressure gradient for CO2 in the lungs is less steep:
o Deoxygenated capillary blood from pulmonary arteries Pco2 = 45 mm Hg
o Alveolus Pco2 = 40 mm Hgo
CO2 is 20 times more soluble in plasma and alveolar fluid than oxygen so, even though the pressure gradient is only 5 mm Hg difference, CO2 ends up diffusing readily due to its’ high solubility

Question 56

Final Result of External Respiration:

Answer 56

o After alveolar gas exchange has occurred (gas exchange between the alveolus and capillaries), blood in systemic arteries, will have a pO2 of app. 95-100 mm Hg and pCO2 of 40 mm Hg after external respiration.
o This is the composition that heads to the cells where internal respiration occurs.

Question 57

Ventilation-Perfusion Coupling:

Answer 57

o Ventilation: amount of gas reaching the alveoli through bronchioles.
o Perfusion: blood flow reaching the alveoli through alveolar capillaries.
o Ventilation and perfusion must be matched (coupled) for efficient gas exchange.
o Changes in Po2 in the alveoli cause changes in the diameters of the arterioles of the alveolar capillaries.
o Where alveolar O2 is high, arterioles dialate for to take advantage of maximum uptake of oxygen.
o Where alveolar O2 is low, arterioles constrict and blood is shunted to areas where O2 is higher.
o Changes in Pco2 in the alveoli cause changes in the diameters of the bronchioles:
o Where alveolar CO2 is high, bronchioles dilate to get rid of CO2 (acid-base).
o Where alveolar CO2 is low, bronchioles constrict to keep CO2 (acid-base).

Question 58

External Respiration Related to Thickness and Surface Area of Respiratory Membrane:

Answer 58

o Respiratory membranes
o 0.5 to 1 μm (1 millionth meter) thick.
o Large total surface area (40 times that of one’s skin) or size of a racquet ball court.
o Respiratory membrane thickens if lungs become waterlogged and edematous (pulmonary edema), and gas exchange becomes inadequate.
o Reduction in surface area with emphysema, when walls of adjacent alveoli break down.

Question 59

Internal Respiration:

Answer 59

o Internal Respiration is the capillary gas exchange in body tissues / cells
o Partial pressures and diffusion gradients are reversed compared to external respiration.
o Po2 in the tissue cells (40 mmHg) is always lower than in systemic arterial blood (100 mm Hg).
o Pco2 in the tissue cells is (45 mmHg) is always higher than the systemic arterial blood (40 mmHg).

Question 60

O2 Transport by Blood:

Answer 60

o Molecular O2 is also carried in the blood besides hemoglobin.
o 1.5% dissolved in plasma (very little solubility in water).
o 98.5% of oxygen is loosely bound to each Fe of hemoglobin (Hb) in RBCs.
o 4 O2 per Hb.

Question 61

O2 and Hemoglobin:

Answer 61

o Oxyhemoglobin (HbO2) = hemoglobin-O2 combination.
o Reduced or deoxyhemoglobin (HHb) = hemoglobin that has released O2.
o HHb + O2 Hb-O2 + H, or:
o Deoxyhemoglobin + Oxygen ->Oxyhemoglobin + H.
o Loading and unloading of O2 is facilitated by change in shape of Hb:
o As O2 binds, Hb attraction for O2 increases.
o As O2 is released, Hb affinity for O2 decreases.
o Fully (100%) saturated if all four heme groups carry O2.
o Partially saturated when one to three hemes carry O2 .
o Rate of loading and unloading of O2 regulated by: PO2, Temperature, Blood pH, PCO2, and Concentration of BPG.

Question 62

Influence of PO2 on Hemoglobin Saturation:

Answer 62

o Oxygen-hemoglobin dissociation curve.
o Hemoglobin saturation is plotted against Po2 and is not linear.
o S-shaped curve.
o Shows how binding and release of O2 is influenced by the Po2:
o The higher the partial pressure of O2, the tighter the O2 is bound to to Hb, the lower the partial pressure of O2, the less tightly O2 is bound and O2 is more readily released.
o In arterial blood:
o Po2 = 100 mm Hg.
o Hb is 98% saturated.
o Further increases in Po2 (e.g., breathing deeply) produce minimal increases in O2 binding.
o Tissue cells:
o Po2 = 40 mm Hg or less in tissue cells.
o Hb is still 75% saturated after releasing O2 to the resting tissues = app. 25% has been released to the tissues.
o Hemoglobin is almost completely saturated at a Po2 of 70 mm Hg
o Further increases in Po2 produce only small increases in O2 binding
o O2 loading and delivery to tissues is adequate when Po2 is below normal levels
o Only 20–25% of bound O2 is unloaded during one systemic circulation
o If O2 levels in tissues drop:
o More oxygen dissociates from hemoglobin and is used by cells.
o Respiratory rate or cardiac output need not increase.

Question 63

Other Factors Influencing Hemoglobin Saturation:

Answer 63

o Increases in temperature, H+, Pco2, and BPG = bisphosphoglycerate (is produced by red blood cells from anaerobic glycolysis and binds to globin parts of hemoglobin)
o They all modify the structure of hemoglobin and decreases its affinity for O2 (or O2 is less tightly bound to Hb).
o Occurs in systemic capillaries.
o Enhances O2 unloading.
o The net result is that these factors shift the O2-hemoglobin dissociation curve to the right.
o Decreases in these factors shift the curve to the left.

Question 64

Factors that Increase Release of O2 by Hemoglobin (in tissues) :

Answer 64

o As cells metabolize glucose:
o Pco2 and H+ increases in concentration in capillary blood with formation of carbonic acid (H2CO3) and lactic acid from metabolically active tissues (remember CO2 is released in cellular respiration).
o Declining pH (higher acidity) weakens the hemoglobin-O2 bond (Bohr effect)
o When heat production (muscles) increases:
o Increasing temperature directly and indirectly decreases Hb affinity for O2.

Question 65

CO2 Transport in the Blood:

Answer 65

o CO2 is transported in the blood in three forms:
o 7 to 10% in dissolved in plasma.
o 20% is bound to globin of hemoglobin (carbaminohemoglobin).
o 70% transported as bicarbonate ions (HCO3–) in plasma.

Question 66

Transport and Exchange of CO2 in the Blood:

Answer 66

o CO2 combines with water to form carbonic acid (H2CO3) which is unstable and quickly dissociates:
o Occurs in both blood plasma and in the RBCs.
o Most of the above occurs in RBCs, where carbonic anhydrase reversibly and rapidly catalyzes the reaction.
o In systemic capillaries = internal respiration
o As bicarbonate ions (HCO3– ) increases in the RBCs, it quickly diffuses from RBCs into the plasma (due to the concentration gradient)
o The chloride shift occurs: outrush of HCO3– from the RBCs is balanced as Cl– moves in from the plasma into the RBCs. This happens to keep the electrochemical balance in the RBC.

Question 67

Transport and Exchange of CO2 in Pulmonary Capillaries (External Respiration):

Answer 67

o HCO3– moves into the RBCs and binds with H+ to form H2CO3.
o H2CO3 is split by carbonic anhydrase in the RBC into CO2 and water.
o CO2 diffuses into the alveoli.

Question 68

Haldane Effect:

Answer 68

o The amount of CO2 transported is affected by the Po2.
o The lower the Po2 and hemoglobin saturation with O2, the more CO2 can be carried by blood hemoglobin.
o At the tissues, as more carbon dioxide enters the blood:
o More oxygen dissociates from hemoglobin due H+ combining with hemoglobin which causes increased acidity = the Bohr effect.
o Hb-O2 à Hb + O2 .
o Hb + H = HHb .
o As HbO2 releases O2, it more readily forms bonds with CO2 to form carbaminohemoglobin.

Question 69

Influence of CO2 on Blood pH:

Answer 69

o HCO3– in plasma is the alkaline reserve of the carbonic acid–bicarbonate buffer system.
o If H+ concentration in blood rises (increased acidity), excess H+ is removed by combining with HCO3– to form a weak acid = carbonic acid .
o If H+ concentration begins to drop (increased alkalinity), H2CO3 dissociates, releasing H+.

Question 70

Control of Respiration:

Answer 70

o Breathing is controlled by two centers of the brain:
o Conscious control = voluntary. For example, being able to hold your breath, singing, talking, swallowing = initiated in the primary motor cortex (pre-central gyrus).
o Unconscious control: centers in our brain stem automatically adjust the rate and depth of breathing = the brain stem receives information from both and Central and Peripheral chemoreceptors + other receptors, then adjusts pulmonary ventilation accordingly.

Question 71

Respiratory Centers in the Brain:

Answer 71

o 1) Medullary Rhythmicity Areas:
o Separate groupings of neurons that stimulate skeletal muscles for inspiration as well as causing relaxation of muscles of inspiration as well as stimulating the muscles of forced expiration
o The Medulla oblongata runs the show!!
o 2) Pontine Respiratory Centers
o Located in the superior pons.
o Helps coordinate between inhalation and exhalation.
o Rate and depth of respiration.

Question 72

Central and Peripheral Input into Respiratory Centers:

Answer 72

o 1) Higher Brain Centers send impulses to the medulla and pons:
o Cerebral Cortex.
o Limbic System.
o Hypothalamus.
o 2) These centers allow voluntary alteration of breathing:
o For singing
o Holding breath (if too long, respiratory center takes over)
o Laughing, crying, gasping (limbic system)
o Increases rate and depth of respiration related to temperature increase (hypothalamus).

Question 73

Central Chemoreceptors:

Answer 73

o Chemoreceptors measure chemical concentrations of gases in blood and sensitive in changes in pO2, [H+], pCO2 .
o Central chemoreceptors are found in the Medulla:
o Medulla is strongly stimulated by changes in H+ concentration (pH)
o Hypercapnia = excess CO2 which causes acidosis = CO2 + H2O ßà H2CO3 ßà H+ and HCO3-

Question 74

Peripheral Chemoreceptors:

Answer 74

o 1) Aortic bodies: clusters of chemoreceptors in the wall of the aortic arch (sensory info carried back to medulla via the vagus nerve).
o 2) Carotid bodies: located in the wall of the carotid arteries near the bifurcation (sensory info carried back to the medulla via the glossopharyngeal nerves).
o These peripheral receptors are sensitive to changes in:
o pO2 = if pO2 drops below 60 mm Hg, increase in rate/depth of breathing.
o [H+] = if respiratory acidosis, then increase respiration ; if alkalosis, the decrease in the rate and depth of breathing.
o pCO2 = if increased, then increased respiration & vice-versa.
o If pCO2 40 mmHg =hypercapnia
o This causes a stronger respiratory rate than pO2 falling below normal. So, levels of CO2 determine rate and depth of respiration, not O2
o Inspiratory neurons of the medulla area are strongly stimulated.
o Causes an increased rate and depth of breathing = (Hypernea) until excess CO2 is blown off.

Question 75

Other Peripheral Receptors (Not chemoreceptors):

Answer 75

o	3) Proprioceptors = monitor joints, and when movement occurs impulses are send to the medulla (DRG area)
o	So, there is an increase in rate and depth of breathing as soon as we begin exercising before any changes in pCO2, pO2, [H+]
o	4) Stretch Receptors = located in smooth muscle of bronchi and bronchioles and in the visceral pleura of the lung
o	Medulla (DRG = dorsal respiratory group) area sends signals to the lungs via the vagus nerve in case of excessive stretch of the lungs (inhibitory neurons stop inspiration)
o	5) Irritant Receptors = in the epithelial cells of respiratory airways (bronchi, bronchioles, alveolar ducts, etc.) = initiates a variety of reflexes