Alveolar ventilation [PDF]

CH.13

RESPIRATORY PHYSIOLOGY

UNIT OUTLINE: I. 

INTRODUCTION i. 

II. 

Basic Functions of Respiratory System

LEVELS OF ORGANIZATION i.  ii. 

Thoracic Cavity Membranes Respiratory Tract Organization

i.  ii.  iii.  iv.  v. 

Respiration Lung Volumes & Capacities Gas Properties Breathing Transport

III.  STRUCTURE & FUNCTION

IV.  HOMEOSTASIS

i.  Hemoglobin Saturation ii.  Ventilation-Perfusion Mismatch iii.  Hyperventilation

V. 

INTEGRATION i. 

Clinical

Biol340 - Mammalian Physiology

2

Remember that these Learning Outcomes make for a great basis for your studying. (Try turning the statements into questions.)

UNIT LEARNING OUTCOMES: Student will be able to…

1.  Distinguish between the structural organization and the functional organization of the respiratory system. 2.  Trace the movement of air through the respiratory system. 3.  Describe the relationship between pressure, volume and air movement (and how muscles influence this) 4.  Explain the difference in respiratory volumes and how these are functionally relevant. 5.  Differentiate how the oxygen and carbon dioxide are carried in the blood. 6.  Explain the significance of the oxygen-hemoglobin saturation curve for both alveolar and systemic gas exchange. 7.  Compare and contrast Hb-O binding during different conditions. 8.  Explain how hyperventilation and hypoventilation influence the chemical composition of blood. 9.  List three types of cells found in alveoli and their functions. 10.  Name the two anatomic features of the respiratory membrane that contribute to the efficient alveolar gas exchange.

Biol340 - Mammalian Physiology

3

I. INTRODUCTION •  BASIC FUNCTIONS OF RESPIRATORY SYSTEM

Biol340 - Mammalian Physiology

4

I. Introduction

The main function of the respiratory system is to supply the body tissues with oxygen and dispose of carbon dioxide generated by cellular metabolism. Respiration is collectively made up of 4 processes: 1.  Pulmonary ventilation (breathing) 2.  External respiration (movement of O2 from lungs into blood; CO2 from blood to lungs) 3.  Transport of respiratory gases in the blood 4.  Internal respiration (movement of O2 from blood into tissue cells; CO2 from cells into blood)

Biol340 - Mammalian Physiology

5

I. Introduction

Cells engage in aerobic cellular respiration Aerobic cellular respiration is necessary for life •  Requires an uninterrupted supply of oxygen •  Requires removal of carbon dioxide waste

The respiratory system provides the means for gas exchange Respiration, collective process by which oxygen and carbon dioxide are continuously exchanged between the atmosphere and the body’s cells

Biol340 - Mammalian Physiology

6

I. Introduction

Air passageway •  Air is moved from the atmosphere to the alveoli as we breathe in •  Air is moved from the lungs to the atmosphere as we breathe out

Site for oxygen and carbon dioxide exchange •  Oxygen diffuses from alveoli into blood •  Carbon dioxide diffuses from blood into alveoli •  takes place between the alveoli and the pulmonary capillaries

Odor detection •  Olfactory receptors in the superior nasal cavity •  Air moving across receptors •  Sensory input relay to the brain

Sound production

•  Air moves across the vocal cords of the larynx (voice box) •  Vocal cords of the larynx vibrate, producing sound •  Sounds resonate in the upper respiratory structures

Defense/Protection

•  Defends against inhaled microbes •  Traps foreign particles (dust etc…)

Biol340 - Mammalian Physiology

7

I. Introduction

Rate and depth of breathing influences: •  blood levels of oxygen •  blood levels of carbon dioxide •  blood levels of hydrogen ion •  venous return of blood •  venous return of lymph

Biol340 - Mammalian Physiology

8

II. LEVELS OF ORGANIZATION i.  ii. 

Thoracic Cavity Membranes Respiratory Tract Organization

Biol340 - Mammalian Physiology

9

II. Levels of Organization Structural organization

Functional organization

Nose Nasal cavity

Upper respiratory tract

Pharynx Larynx Trachea

Conducting zone

Bronchus

Lower respiratory tract

Bronchiole Terminal bronchiole

Lungs

Respiratory bronchiole Alveolar duct Alveoli

Biol340 - Mammalian Physiology

Respiratory zone

10

II. Levels of Organization Larynx •  Also called the voice box •  Several major functions •  Air passageway •  Prevents ingested materials from entering the respiratory tract •  Produces sound for speech •  Assists in increasing pressure in the abdominal cavity

Esophagus

Posterior Esophagus Trachealis muscle

Larynx

Thyroid cartilage Cricoid cartilage

Biol340 - Mammalian Physiology

LM 8x

The trachea •  Flexible, slightly rigid, tubular organ •  Known as the windpipe •  Goes from the larynx to the main bronchi •  Immediately anterior to the esophagus

Lumen of trachea Mucosa Submucosa

Trachea

Tracheal cartilage

Tracheal cartilage (b)

Anterior

Anular ligament Trachea Carina (internal projection) Right main bronchus (a)

Right main bronchus

Left main bronchus

Left main bronchus (c) Carina

11

II. Levels of Organization

Main bronchi Lobar bronchi Segmental bronchi Smaller bronchi

Larynx

Trachea

Right main bronchus Right lobar bronchus Right segmental bronchus

Smaller bronchi Biol340 - Mammalian Physiology

(b)

Left main bronchus Left lobar bronchus

Tree continues to divide into smaller passageways

Left segmental bronchus

• 

Smaller bronchi

• 

• 

Leads to tubes of < 1mm, the bronchioles Leads to terminal bronchioles (last part of conducting zone) Leads to respiratory bronchioles (first part of respiratory zone)

12

II. Levels of Organization Trachea Left main bronchus

Cartilage rings

Cartilage Cartilage plates

Lobar bronchi

Segmental bronchi

Smaller bronchi Bronchiole Cross sections of bronchioles Terminal bronchiole Respiratory bronchiole

Muscularis Submucosa Mucosa

Biol340 - Mammalian Physiology

Alveoli Bronchoconstricted

Bronchodilated

No cartilage

13

II. Levels of Organization

Respiratory Zone

Branch of pulmonary artery

Composed of respiratory ducts, alveolar ducts, and alveoli •  Respiratory bronchioles subdivide to alveolar ducts •  Alveolar ducts lead to alveolar sacs, clusters of alveoli •  Alveoli = saccular outpouchings

Epithelium

Bronchiole

Terminal bronchiole

Pulmonary arteriole Pulmonary capillary beds Pulmonary venule

Branch of pulmonary vein

•  Respiratory bronchioles lined with simple cuboidal epithelium •  Alveoli and alveolar ducts lined by simple squamous •  Thinner than in the conducting portion • 

Respiratory bronchiole

Alveolar duct Alveoli Alveolar pores Interalveolar septum

facilitates gas exchange

Alveolar sac Elastic fibers

Biol340 - Mammalian Physiology

Connective tissue

14

II. Levels of Organization

Terminal bronchiole

• Alveoli

Alveoli

Respiratory bronchiole

Alveolar duct

•  contain elastic fibers: help the lungs contract and expand Biol340 - Mammalian Physiology

SEM 180x

–  Each lung containing 300-400 million –  Openings in their walls, alveolar pores –  Provide for collateral ventilation –  Surrounded by pulmonary capillaries –  Divided by interalveolar septum

(c)

© Dr. David Phillips/ Visuals Unlimited

15

II. Levels of Organization

Cell types of the alveolar wall

Erythrocyte

•  Simple squamous alveolar type I cells

Pulmonary capillaries

•  95% of alveolar surface area •  form part of the thin barrier separating air from blood •  moist environment makes prone to collapse (high surface tension)

Alveolar type I cell Alveolar type II cell

•  Alveolar type II cells (septal cells)

Alveolar macrophages

•  almost cuboidal shaped •  secrete pulmonary surfactant, an oily substance •  coats inner alveolar surface •  helps oppose the collapse of alveoli

Alveolar pores Interalveolar septum

•  Alveolar macrophage (dust cells) (a)

Biol340 - Mammalian Physiology

•  • 

leukocytes that engulf microorganisms either fixed in alveolar wall or free to migrate

16

II. Levels of Organization

Characteristics of respiratory membrane •  Thin barrier between alveoli and pulmonary capillaries •  Consists of:

Interalveolar septum

•  alveolar epithelium and its basement membrane •  capillary epithelium and its basement membrane •  two basement membranes fused

Nucleus of capillary Nucleus endothelial cell of alveolar Erythrocyte type I cell

Capillary

•  Oxygen diffuses from alveolus into capillaries •  erythrocytes become oxygenated

Diffusion of CO2

•  Carbon dioxide diffuses from blood to alveolus

Diffusion of O2

•  expired to external environment

Alveolus Respiratory membrane

Biol340 - Mammalian Physiology

(b)

Alveolar epithelium Fused basement membranes of the alveolar epithelium and the capillary endothelium Capillary endothelium

17

II. Levels of Organization

RELATION OF THE LUNGS TO THE THORACIC WALL The pleurae form a thin double-layered serosa. The parietal pleura covers the thoracic wall and superior face of the diaphragm. The visceral pleura covers the external surface of the lung. The pleura produce fluid that remains in the pleural cavity. This lubricates the lung to prevent friction while breathing.

Pleural cavity

Parietal pleura Visceral pleura

(Intrapleural Pressure)

Lung Intrapulmonary pressure Biol340 - Mammalian Physiology

18

III. STRUCTURE/FUNCTION i.  ii.  iii.  iv.  v. 

Respiration Lung Volumes & Capacities Gas Properties Breathing Transport

Biol340 - Mammalian Physiology

19

III. Structure/Function

STEPS OF RESPIRATION

Biol340 - Mammalian Physiology

20

III. Structure/Function

LUNG VOLUMES AND CAPACITIES

Biol340 - Mammalian Physiology

21

III. Structure/Function

Biol340 - Mammalian Physiology

22

III. Structure/Function

Pulmonary ventilation has two definitions: •  process of moving air into and out of the lungs •  amount of air moved between atmosphere and alveoli in one minute

Tidal volume = amount of air per breath Respiration rate = number of breaths per minute Tidal volume x respiration rate = pulmonary ventilation •  500 mL x 12 breaths/min = 6 L/ minute (typical amount)

Biol340 - Mammalian Physiology

23

III. Structure/Function

Anatomic dead space •  Space in respiratory tract in the conducting zone •  No exchange of respiratory gases here •  About 150 mL

Alveolar ventilation •  Amount of air reaching the alveoli per minute •  (Tidal volume – anatomic dead space) x respiratory rate = alveolar ventilation •  (500 mL – 150 mL) x 12 = 4.2 L/min •  Deep breathing maximizes alveolar ventilation Biol340 - Mammalian Physiology

24

III. Structure/Function

Physiologic dead space •  Normal anatomic dead space + any loss of alveoli •  Some respiratory disorders decrease number of alveoli participating in gas exchange •  due to damage to alveoli or changes in respiratory membrane (e.g., pneumonia) •  Normally physiologic dead space = normal anatomic dead space

Biol340 - Mammalian Physiology

25

III. Structure/Function

Boyle’s gas law: Relationship of Volume and Pressure •  At a constant temperature, the pressure (P) or a gas decreases if the volume (V) of the container increases, and vice versa •  P1 and V1 represent the initial conditions and P2 and V2 the changed conditions P1V1 = P2V2 •  Inverse relationship between gas pressure and volume Biol340 - Mammalian Physiology

Decreased pressure

Increased volume

Pressure decreases as volume increases (a) Boyle’s Law

Increased pressure

Decreased volume

Pressure increases as volume decreases

26

III. Structure/Function

Question

According to Boyle's law, the pressure exerted by a constant number of gas molecules in a container is inversely proportional to the volume of the container. Therefore, increasing the volume of the container will cause a decrease in its pressure. A. True B. False

Biol340 - Mammalian Physiology

27

III. Structure/Function

Area A

Area A

Area A

Airflow

Area B

Pressure A = Pressure B No net movement of air (b) Pressure gradients Biol340 - Mammalian Physiology

Decreased pressure B

Volume B

Area B Area B increases in volume and decreases in pressure. Air moves from area A into area B

Airflow Increased pressure B Area B

Volume B

Area B decreases in volume and increases in pressure. Air moves from area B into area A

Flow (F) = ΔPressure/Resistance

28

III. Structure/Function

HOW LUNGS REMAIN INFLATED

Anatomic arrangement •  Outward pull of chest and inward pull of lungs with consequent “suction” •  Pressure in the pleural cavity = intrapleural pressure •  Pressure inside the lungs = intrapulmonary pressure •  Intrapulmonary pressure > intrapleural pressure •  Difference in pressure keeps the lungs inflated •  if pressures become equal, lungs deflate

Biol340 - Mammalian Physiology

29

III. Structure/Function

IF Pip = Palv THE LUNGS WILL IMMEDIATELY COLLAPSE!

Atmosphere Atmospheric pressure (760 mm Hg)

756 mm Hg 760 mm Hg

(c) Volumes and pressures with breathing (at the end of an expiration) Biol340 - Mammalian Physiology

Intrapleural pressure (Pip) Fluctuates with breathing Is always lower than the intrapulmonary pressure to keep lungs inflated Prior to inspiration, is about 4 mm lower than intrapulmonary pressure (756 mm Hg)

Pleural cavity (intrapleural pressure) Alveolar volume of lungs (intrapulmonary pressure) Intrapulmonary pressure (Palv) Fluctuates with breathing May be higher, lower, or equal to atmospheric pressure Is equal to atmospheric pressure at end of inspiration and expiration

30

III. Structure/Function

Question

That the lung surface and the thoracic wall will move in and out together, rather than separately, during ventilation is assured by the  A. Diaphragm B. Inhalatory/inspiratory intercostal muscles C. Exhalatory/expiratory intercostal muscles D. Intrapleural fluid E. Alveoli

Biol340 - Mammalian Physiology

31

III. Structure/Function

Pressure gradient

Airflow •  Amount of air that moves into and out of the lungs with each breath •  Function of two factors: 1) the pressure gradient established between atmospheric pressure and intrapulmonary pressure 2) the resistance that occurs due to conditions within the airways, lungs, and chest wall

Biol340 - Mammalian Physiology

•  Can be changed by altering the volume of the thoracic cavity •  • 

small volume changes during quiet respiration allow 500 mL air to enter the lungs if accessory muscles of forced inspiration are used, volume increases more •  airflow increases due to greater pressure gradient

Resistance •  Includes all factors that make it more difficult to move air from the atmosphere to the alveoli •  May be altered in three ways: 1)  decrease in elasticity of the chest wall 2)  change in the bronchiole diameter or the size of the passageway through which air moves 3)  collapse of alveoli

32

III. Structure/Function

VENTILATION AND LUNG MECHANICS

Biol340 - Mammalian Physiology

33

Quiet inspiration

III. Structure/Function

1 Intrapulmonary pressure = atmospheric pressure

Quiet expiration 3

Intrapulmonary pressure = atmospheric pressure

atm = 760 mm Hg

atm = 760 mm Hg

756 mm Hg (Intrapleural pressure) 760 mm Hg (Intrapulmonary pressure)

754 mm Hg (Intrapleural pressure) Diaphragm

2 Intrapulmonary pressure becomes less than atmospheric pressure; air flows in

atm = 760 mm Hg 754 mm Hg 759 mm Hg

Biol340 - Mammalian Physiology

Air flows in (~500 mL per quiet breath) Pleural cavity volume increases Intrapleural pressure decreases Alveolar volume increases Intrapulmonary pressure decreases

760 mm Hg 4

Intrapulmonary pressure becomes greater than atmospheric pressure; air flows out

atm = 760 mm Hg 756 mm Hg 761 mm Hg

Air flows out (~500 mL per quiet breath) Pleural cavity volume decreases intrapleural pressure increases Alveolar volume decreases intrapulmonary pressure increases

34

III. Structure/Function

Inspiration

Expiration

Thoracic cavity

Thoracic cavity

Vertical changes

Diaphragm contracts; vertical dimensions of thoracic cavity increase

Diaphragm relaxes; vertical dimensions of thoracic cavity narrow

Lateral changes

Ribs are elevated and thoracic cavity widens

Ribs are depressed and thoracic cavity narrows Anteriorposterior changes

Biol340 - Mammalian Physiology

Inferior portion of sternum moves anteriorly and thoracic cavity expands

Inferior portion of sternum moves posteriorly and thoracic cavity compresses

35

III. Structure/Function

CHANGES ASSOCIATED WITH QUIET BREATHING

Biol340 - Mammalian Physiology

36

III. Structure/Function

Inspiration

Biol340 - Mammalian Physiology

Expiration

37

III. Structure/Function Sternocleidomastoid Scalenes Serratus posterior superior Pectoralis minor Erector spinae Transversus thoracis External intercostal

Skeletal Muscles of Breathing Classified into three categories: muscles of quiet breathing muscles of forced inspiration muscles of forced expiration

External intercostal

Serratus posterior inferior Internal intercostal

Diaphragm

Diaphragm

External oblique Transversus abdominis

Anterior view

Posterior view Muscles of Breathing

Muscles of quiet breathing

The diaphragm forms the rounded “floor” of the thoracic cavity and is dome-shaped when relaxed. It alternates between the relaxed domed position and the contracted flattened position and changes the vertical dimensions of the thoracic cavity. The external intercostals extend from a superior rib inferiomedially to the adjacent inferior rib. These elevate the ribs and increase the transverse dimensions of the thoracic cavity.

Muscles of forced inspiration

The sternocleidomastoid attaches to sternum and clavicle; lifts rib cage. The scalenes attach to ribs 1 and 2; elevates ribs 1 and 2. The pectoralis minor attaches to ribs 3−5; elevates ribs 3−5. The serratus posterior superior attaches to ribs 2−5 on its anterior surface; lifts ribs 2−5. The erector spinae is a group of deep muscles along the length of the vertebral column; extends the vertebral column.

Muscles of forced expiration

The internal intercostals lie deep and at right angles to the external intercostals; depress the ribs and decrease the transverse dimensions of the thoracic cavity. The abdominal muscles (primarily the external obliques and transversus abdominis) compress the abdominal contents, forcing the diaphragm into a higher domed position and the rectus abdominus pulls the sternum and rib cage inferiorly. The transversus thoracis extends across the inner surface of the thoracic cage and attaches to ribs 2−6; depresses ribs 2−6 . The serratus posterior inferior extends between the ligamentum nuchae and the lower border of ribs 9−12; depresses ribs 9−12.

Biol340 - Mammalian Physiology

38

III. Structure/Function

Question

In an average-size subject with a resting breathing rate of 10 breaths per minute at sea level, what is the approximate alveolar O2 ventilation in liters?  A. 5.0 B. 3.5 C. 1.5 D. 0.7 E. 0.2

Biol340 - Mammalian Physiology

39

III. Structure/Function

LUNG COMPLIANCE Compliance can be considered the inverse of stiffness. The greater the lung compliance, the easier it is to expand the lungs at any given change in transpulmonary pressure. There are two major determinants of lung compliance: 1.  The stretchability of the lung tissues 2.  The surface tension at the air-water interfaces within the alveoli •  Surfactant lowers surface tension

Biol340 - Mammalian Physiology

40

III. Structure/Function

Difference between Atmospheric & Alveolar: •  air from the environment mixes with the air remaining in the anatomic dead space •  oxygen diffuses out of the alveoli into the blood; carbon dioxide diffuses from the blood into the alveoli •  more water vapor is present in the alveoli

Partial pressure

The pressure exerted by each gas within a mixture of gases Measured in mm Hg Written with P followed by gas symbol (i.e., PO2 ) Each gas moving independently down its partial pressure gradient during gas exchange

Atmospheric pressure

Total pressure all gases collectively exerting in the environment Includes nitrogen, oxygen, carbon dioxide, water vapor, and minor gases 760 mm Hg at sea level

Biol340 - Mammalian Physiology

41

III. Structure/Function

Gas Solubility and Henry’s Law Henry’s law •  At a given temperature the solubility of a gas in liquid is dependent upon: •  the partial pressure of the gas in the air •  the solubility coefficient of the gas in the liquid

Partial pressure •  The driving force to move a gas into a liquid •  Determined by total pressure and percentage of gas in the mixture •  E.g., carbon dioxide in soft drinks •  CO2 forced into soda under high pressure

Solubility coefficient

•  The volume of gas that dissolves in a specified volume of liquid at a given temperature and pressure •  A constant that depends upon the interactions between molecules of both gas and liquid

Gases vary in their solubility in water •  Carbon dioxide about 24 times as soluble as oxygen •  Carbon dioxide with greater solubility coefficient •  Nitrogen about half as soluble as oxygen Biol340 - Mammalian Physiology

42

III. Structure/Function

Efficiency of Gas Exchange at the Respiratory Membrane Efficiency of diffusion dependent upon certain features: •  anatomic features of the respiratory membrane •  large surface area (70 square meters) •  minimal thickness (0.5 micrometers)

•  physiologic adjustments

•  some alveoli well ventilated at a given time, some not •  some regions of lung with ample blood, some not •  smooth muscles of bronchioles and arterioles able to contract to maximize

gas exchange

•  Ventilation-perfusion coupling • 

Ability of bronchioles to regulate airflow and arterioles to regulate blood flow

•  Ventilation •  • 

Altered by changes in bronchodilation and bronchoconstriction Dilation in response to increase in PO2 or decrease in PCO2

•  Perfusion •  • 

Altered by changes in pulmonary arteriole dilation and constriction Dilation in response to increased in PO2 or decrease in PCO2

Biol340 - Mammalian Physiology

43

III. Structure/Function

Oxygen •  Travels from the alveoli through pulmonary veins to left side of heart •  Travels to systemic circulation •  Diffuses from systemic capillaries into systemic cells

The ability to transport oxygen is dependent upon two factors: •  solubility coefficient of oxygen in blood •  presence of hemoglobin

Oxygen’s solubility coefficient is very low •  Only small amounts are dissolved in plasma

98% of oxygen in the blood is transported within erythrocytes •  Oxygen is attached to iron within hemoglobin molecules •  Oxygen bound to hemoglobin is oxyhemoglobin (HbO2) •  Hemoglobin without bound oxygen is deoxyhemoglobin (HHb)

Biol340 - Mammalian Physiology

44

III. Structure/Function Carbon dioxide

•  Travels from systemic cells within deoxygenated blood •  Travels through systemic circulation to right side of heart •  Diffuses from the pulmonary capillaries into the alveoli

Carbon dioxide has three means of transport: •  as carbon dioxide dissolved in plasma (7%) •  as carbon dioxide attached to the globin portion of hemoglobin (23%) •  as bicarbonate dissolved in plasma (70%)

Transport as bicarbonate

•  Carbon dioxide diffuses into erythrocytes and combines with water to form bicarbonate and hydrogen ion •  Bicarbonate diffuses into plasma •  Carbon dioxide is regenerated when blood moves through pulmonary capillaries and the process is reversed Biol340 - Mammalian Physiology

45

III. Structure/Function

TRANSPORT OF HYDROGEN IONS BETWEEN TISSUES AND LUNGS

Biol340 - Mammalian Physiology

46

III. Structure/Function

Question

Most of the CO2 that is transported in blood is  A. Dissolved in the plasma B. Bound to hemoglobin C. In carbonic acid D. In bicarbonate ion E. In carbonic anhydrase

Biol340 - Mammalian Physiology

47

III. Structure/Function

Hemoglobin transports: •  oxygen attached to iron (4/Hb) •  carbon dioxide bound to the globin •  hydrogen ions bound to the globin

Binding of one substance causes a change in shape of the hemoglobin molecule •  Influences the ability of hemoglobin to bind or release the other two substances Biol340 - Mammalian Physiology

48

III. Structure/Function

What is the effect of pO2 on hemoglobin saturation?

The amount of oxygen bound to a hemoglobin Expressed as the percent oxygen saturation of hemoglobin Determined by several variables PO2 the most important variable Cooperative binding effect of oxygen Saturation increases as PO2 increases loading Binding of each oxygen molecule causes a conformational changemakes it progressively easier for more oxygen to bind

Biol340 - Mammalian Physiology

Relationship between PO2 and hemoglobin saturation Graphed in the oxygen-hemoglobin saturation curve S-shaped, non linear relationship Relatively large changes initially At 60 mm Hg, oxygen 90% saturated Higher than 60 mm Hg, relatively small changes

49

III. Structure/Function

Oxygen-Hemoglobin Saturation Curve Oxygen released from hemoglobin while traveling through systemic capillaries •  75% saturation in systemic cells during rest (at sea level) •  98% saturation as it leaves the lungs (at sea level) •  Only 20-25% of oxygen transported by hemoglobin released

Oxygen reserve •  Oxygen that remains bound to hemoglobin after passing through the systemic circulation •  Provides a means for additional oxygen to be delivered under increased metabolic demands

•  Oxygen that remains bound to hemoglobin after passing through the systemic circulation •  Provides a means for additional oxygen to be delivered under increased metabolic demands

Vigorous exercise produces a significant drop in PO2 •  Produces large decrease in hemoglobin saturation •  More hemoglobin unloaded to tissues Biol340 - Mammalian Physiology

50

IV. HOMEOSTASIS i.  Hemoglobin Saturation ii.  Ventilation-Perfusion Mismatch iii.  Hyperventilation

Biol340 - Mammalian Physiology

51

IV. Homeostasis

Question

During hyperventilation, what happens to the partial pressures of oxygen and carbon dioxide in the alveoli (compared to normal ventilation)? A.  Both increase B.  Both decrease C.  Oxygen partial pressure decreases and carbon dioxide partial pressure increases D.  Oxygen partial pressure increases and carbon dioxide partial pressure decreases

Biol340 - Mammalian Physiology

52

IV. Homeostasis Temperature

EFFECTS ON HEMOGLOBIN SATURATION

Elevated temperature interferes with hemoglobin’s ability to bind and hold oxygen

Hydrogen ion binding to hemoglobin Hydrogen ion binds to hemoglobin and causes a conformational change This causes decreased affinity for O2 and oxygen release called the Bohr effect

Presence of 2,3-BPG Molecule binds to hemoglobin, causing the release of additional oxygen Glycolytic pathway produces 2,3-BPG Certain hormones stimulate production

CO2 binding to hemoglobin Binding causes release of more oxygen from hemoglobin

Biol340 - Mammalian Physiology

53

IV. Homeostasis

MATCHING OF VENTILATION AND BLOOD FLOW IN ALVEOLI

Biol340 - Mammalian Physiology

54

IV. Homeostasis

Control of ventilation by pO2, pCO2, and H+ concentration

Hyperventilation

•  Breathing rate or depth above the body’s demand •  Caused by anxiety, ascending to high altitude, or voluntarily •  pO2 levels up in the alveoli •  CO2 levels down in the alveoli

Changes affect the blood

•  Additional oxygen does not enter the blood because hemoglobin is 98% saturated •  Additional carbon dioxide leaves the blood to enter the alveoli

Blood CO2 decreases below normal levels •  Termed hypocapnia

Hyperventilation may cause: •  feeling faint or dizzy, numbness, tingling, cramps, and tetany •  if prolonged, disorientation, loss of consciousness, coma, death Biol340 - Mammalian Physiology

55

IV. Homeostasis

During exercise: •  breathing depth increases while breathing rate remains the same •  known as hyperpnea

•  blood PO2 and Blood PCO2 remain relatively the same •  increased cardiac output occurs •  the respiratory center is stimulated from one or more causes •  sensory signals relayed in response to movement •  motor output in the cerebral cortex relaying signals to the respiratory center •  conscious anticipation of participating in exercise Biol340 - Mammalian Physiology

56

V. INTEGRATION

Biol340 - Mammalian Physiology

57

IV. Homeostasis

Question

Assume a normal female with a resting tidal volume of 400 ml, respiratory rate of 13 breaths/min, and dead space of 125 ml. When she exercises, which of the following scenarios would be most efficient for increasing her oxygen delivery to the lungs? A.  Increase respiratory rate to 20 breaths/min but no change in tidal volume B.  Increase tidal volume to 550 mL but no change in respiratory rate C.  Increase tidal volume to 500 mL and respiratory rate to 15 breaths/ min

Biol340 - Mammalian Physiology

58

V. Integration

HYPOXIA •  • 

Hypoxia is an inadequate oxygen delivery to tissues. The pathophysiology of emphysema is a major cause of hypoxia. 1. 

Anemic hypoxia: poor O2 delivery because of too few RBCs or abnormal hemoglobin

2. 

Ischemic hypoxia: blood circulation is impaired

3. 

Histotoxic hypoxia: the body’s cells are unable to use O2 (cyanide causes this)

4. 

Hypoxemic hypoxia: reduced arterial O2 (can be caused by lack of oxygenated air, pulmonary problems, lack of ventilation-perfusion coupling)

Biol340 - Mammalian Physiology

59

V. Integration

CARBON MONOXIDE POISONING • 

This is a type of hypoxemic hypoxia. It is the leading cause of death from fire.

• 

CO is an odorless, colorless gas that competes with O2 for the binding sites on the hemoglobin. It has a 200-times greater affinity for hemoglobin than O2 does.

• 

The symptoms are confusion, respiratory distress, the skin becomes cherry red. NO CYANOSIS is detectable.

• 

To treat it, hyperbaric treatment or 100% oxygen is used.

Biol340 - Mammalian Physiology

60

V. Integration

Clinical Views: Pneumothorax and Atelectasis Pneumothorax = free air in the pleural cavity •  •  •  •  • 

Air introduced externally—penetrating wound to the chest Air introduced internally—rib lacerates lung or alveolus ruptures May cause intrapleural and intrapulmonary pressures to equalize Small pneumothorax resolves spontaneously Large pneumothorax is a medical emergency •  need to insert a tube into the pleural space to remove air

Atelectasis = deflated lung portion •  Occurs if intrapleural and intrapulmonary pressures equalize •  Remains collapsed until air removed from pleural space

Biol340 - Mammalian Physiology

61

V. Integration

ASTHMA Asthma is a disease characterized by intermittent episodes in which airway smooth muscle contracts strongly, markedly increasing airway resistance. The basic defect in asthma is chronic inflammation of the airways, the causes of which vary from person to person and include, among others; allergy, viral infections, and sensitivity to environmental factors. The underlying inflammation makes the airway smooth muscle hyperresponsive and causes it to contract strongly in response to such things as exercise (especially in cold, dry air), cigarette smoke, environmental pollutants, viruses, allergens, normally released bronchoconstrictor chemicals, and a variety of other potential triggers. Biol340 - Mammalian Physiology

62

V. Integration

ASTHMA The first aim of therapy for asthma is to reduce the chronic inflammation and airway hyperresponsiveness with anti-inflammatory drugs, particularly leukotriene inhibitors and inhaled glucocorticoids. The second aim is to overcome acute excessive airway smooth muscle contraction with bronchodilator drugs, which relax the airways. For example, one class of bronchodilator drugs mimics the normal action of epinephrine on beta-adrenergic (beta-2) receptors. Another class of inhaled drugs block muscarinic cholinergic receptors, which have been implicated in bronchoconstriction. Biol340 - Mammalian Physiology

63

V. Integration

CHRONIC OBSTRUCTIVE PULMONARY DISEASE The term chronic obstructive pulmonary disease refers to emphysema, chronic bronchitis, or a combination of the two. These diseases cause severe difficulties not only in ventilation, but in oxygenation of the blood. Emphysema is caused by destruction and collapse of the smaller airways. Chronic bronchitis is characterized by excessive mucus production in the bronchi and chronic inflammatory changes in the small airways. The cause of obstruction is an accumulation of mucus in the airways and thickening of the inflamed airways. Biol340 - Mammalian Physiology

64

V. Integration

Clinical View: Emphysema Emphysema causes: •  irreversible loss of pulmonary gas exchange surface area •  inflammation of air passageways distal to terminal bronchioles •  widespread destruction of pulmonary elastic connective tissue •  dilation and decreased total number of alveoli •  patient’s inability to expire effectively

Biol340 - Mammalian Physiology

65

V. Integration

Clinical View: Bronchitis Inflammation of the bronchi, caused by bacterial or viral infection or inhaled irritants Acute bronchitis •  Occurs during or after an infection •  Coughing, sneezing, pain with inhalation, fever •  Most cases resolving in 10-14 days

Chronic bronchitis •  •  •  • 

Occurs after long-term irritant exposure Large amounts of mucus, and cough > 3 months Permanent changes to bronchi occur Increases likelihood of future bacterial infections

Biol340 - Mammalian Physiology

66