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Ch. 23 – The Respiratory System

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1 Ch. 23 – The Respiratory System
Fig. 23-7, p. 824

2 The main functions of the respiratory system
1. Provide a surface area (the alveoli of the lungs) for gas exchange between the air and blood 2. Pulmonary ventilation (breathing) = moving air in and out of the lung exchange area 3. Protection of delicate respiratory surfaces E.g. from dehydration, temperature changes, pathogens, etc. 4. Sound production for speaking, etc. 5. Provide a location for olfactory epithelium for the sensation of smell

3 The organization of the respiratory system
A. The upper respiratory system = the nose, nasal cavity, paranasal sinuses, and pharynx B. The lower respiratory system = the larynx, trachea, bronchi, bronchioles, and alveoli of the lungs Fig. 23-1, p. 815

4 The respiratory tract = passageways that carry air to and from the exchange surfaces (alveoli) of the lungs A. The conducting portion – no gas exchange occurs here = from the external nares to the terminal bronchioles Functions: Warm, filter, and humidify incoming air Cool and dehumidify outgoing air B. The respiratory portion – gas exchange occurs here = the respiratory bronchioles and alveoli Fig. 23-9a, p. 826

5 The nose = the externally visible portion of the nasal region
Is made up of bone, cartilage, skin, muscle, and mucous membranes External nares = nostrils Fig. 23-3a, p. 818

6 The nasal cavity = the internal portion of the nasal region
Opens into the nasopharynx via the internal nares Drains mucus from the paranasal sinuses and tears from the nasolacrimal ducts (the ducts are not shown here) Is divided in half midsagittally by the nasal septum (not shown here), which is made up of cartilage and bones (the perpendicular plate of the ethmoid and the vomer) Its walls have 3 pairs of nasal conchae (superior, middle, and inferior) Functions of nasal conchae: stir up inhaled air; increase surface area for functions 1-3 on the next slide Fig. 23-3c, p. 818

7 Functions of the nasal cavity
1. Warm and moisten inhaled air, because… a) It has a rich blood supply for warmth The warmth also evaporates water from mucus, adding moisture to the air b) The drainage of tears from the nasolacrimal duct provides additional moisture c) The drainage of mucus from the paranasal sinuses provides additional moisture 2. Filter inhaled air, via… a) Nose hairs b) Respiratory epithelium (see the next slide) Mucus traps particles Cilia move the mucus and particles toward the pharynx for swallowing and eventual destruction in the stomach 3. Olfaction (Ch. 17) Note: olfactory epithelium is found in the upper nasal cavity only 4. Modify speech sounds (by providing resonance and timbre)

8 Respiratory epithelium
= PCCE Is found throughout much of the conducting portion of the respiratory tract A “mucus escalator” of cilia in the lower respiratory system transports mucus up toward the pharynx for swallowing and eventual destruction in the stomach Fig. 23-2, p. 816

9 The pharynx (throat) = a common passageway for air and food
Extends from the internal nares to the junction of the esophagus and larynx Has 3 regions: 1. The nasopharynx (respiratory only) – from the internal nares to the uvula of the soft palate It’s lined with PCCE It contains the pharyngeal tonsil (adenoid) and the openings of the auditory (Eustachian) tubes 2. The oropharynx (respiratory and digestive) – from the uvula of the soft palate to the base of the tongue (or tip of the epiglottis) It’s lined with stratified squamous epithelium It contains the palatine and lingual tonsils 3. The laryngopharynx (respiratory and digestive) – from the base of the tongue (or tip of the epiglottis) to the junction of the esophagus and larynx It’s lined with stratified squamous epithelium The pharynx (throat) Fig. 23-3c, p. 818

10 The larynx (“voice box”)
Connects the laryngopharynx with the trachea Is formed by multiple pieces of cartilage and some connecting ligaments and muscles (the muscles aren’t shown here) The vocal folds and above are covered with stratified squamous epithelium Inferior to the vocal folds is covered with respiratory epithelium (PCCE) Epiglottis = an elastic cartilage plate that closes off the glottis (= the superior opening of the larynx) during swallowing Fig. 23-4, p. 820

11 The anatomy of sound production
The vestibular folds close off the glottis during breath holding, lifting heavy objects, etc. The vocal folds = the vocal cords, which… Contain elastic fibers Vibrate to produce speech sounds Are attached anteriorly to the thyroid cartilage Are attached posteriorly to the arytenoid cartilages (Note the error in this photo: the “root of tongue” is actually the epiglottis.) Fig. 23-5, p. 821

12 The physiology of sound production
Voice pitch (= the frequency of sound) – depends on the amount of tension on, length, and thickness of the vocal folds ↑ Tension on the folds = ↑ pitch Laryngeal muscles rotate the arytenoid cartilages medially or laterally to adjust the tension on the folds Shorter/thinner folds (e.g. in children and females) = ↑ pitch Loudness (= volume) – depends on the pressure/ velocity of air the rushing past the vocal folds Outgoing sound is modified by the: Movements of the tongue, face, and lips Hollow resonating chambers of the respiratory system, which include… The pharynx, mouth, nasal cavity, and paranasal sinuses

13 The trachea (“windpipe”)
= a short (4-5”) tube that carries air between the larynx and the junction of the primary bronchi Fig. 23-6, p. 823

14 Histology of the trachea
It’s lined with respiratory epithelium (PCCE) Mucous glands are found in the submucosa Tracheal cartilages = C-shaped incom- plete rings of hyaline cartilage that… Prevent collapse during inhalation Allow expansion of the esophagus during swallowing Trachealis muscle = smooth muscle that adjusts the tracheal diameter in response to airflow needs Fig. 23-6b, p. 823

15 Gross anatomy of the lungs
Note that the lungs sit on top of the diaphragm (this will be important for our discussion of pulmonary ventilation later) Fig. 23-7, p. 824

16 The lungs and the pleura
Each lung is surrounded by the pleura (= a double-layered serous membrane): 1. The parietal pleura lines the inside of the thoracic cavity 2. The visceral pleura covers the surface of the lungs The ultra-thin pleural cavity is between the two layers and contains pleural fluid, which… Reduces the friction between layers during the movements of ventilation Causes the layers to adhere to one another, so when the thoracic wall and diaphragm move, the lungs move with them Fig. 23-8, p. 825

17 The bronchial tree Each lung receives a primary bronchus
Each lobe receives a secondary (lobar) bronchus Secondary bronchi divide into tertiary (segmental) bronchi Each tertiary bronchus supplies a bronchopulmonary segment containing multiple pulmonary lobules Each lobule is supplied by a bronchiole, terminal bronchiole, and respiratory bronchiole Fig. 23-9a, p. 826

18 The structure of a pulmonary lobule
The pathway of airflow (during inhalation) within a lobule: terminal bronchiole → respiratory bronchiole → alveolar duct → alveolar sac → alveolus Fig. 23-9b, p. 826

19 Structural and functional changes along the conducting portion of the respiratory tract from the trachea to the bronchioles 1. Pseudostratified → simple columnar → simple cuboidal epithelium 2. Large, incomplete cartilage rings → cartilage plates → no cartilage 3. The relative amount of smooth muscle increases Consider asthma: the smooth muscle of small bronchi and bronchioles constricts, and there’s no cartilage to keep these airways fully open 4. The amount of mucus production decreases (due to fewer mucous cells) 5. The amount of cilia decreases (macrophages do the cleanup of particulate matter and debris instead)

20 Alveoli = the micro-scopic, thin-walled, air-filled pockets within the lungs where gas exchange between the air and blood occurs Fig ,11, p

21 The main types of alveolar cells
1. Pneumocytes type I = simple squamous epithelium Make up most of the alveolar walls Form half of the respira tory membrane (see the next slide) 2. Pneumocytes type II (septal cells) Produce surfactant (= a fluid that ↓ surface tension within alveoli) 3. Alveolar macrophages (dust cells) = wandering macrophages Remove debris and particulate matter The main types of alveolar cells Fig b, p. 828

22 The respiratory membrane
= the actual site of gas exchange Blood is on one side, and air is on the other side Is made up of 3 parts: 1. The capillary endothelial wall 2. The alveolar epithelial wall 3. The fused basement membranes of 1 and 2 Fig c, p. 828

23 An overview of respiration
Fig , p. 830

24 The main steps of respiration (Note: Martini et al
The main steps of respiration (Note: Martini et al. organize these steps somewhat differently than what you see here) 1. Pulmonary ventilation = breathing = the movement of air into and out of the lungs 2. External respiration = the exchange/diffusion of gases between the air in the alveoli of the lungs and the blood 3. Gas (O2 and CO2) transport (by the blood) 4. Internal respiration = the exchange/diffusion of gases between the blood and the tissues Note: cellular respiration is the use of O2 and substrates by individual cells to produce ATP, CO2, H2O and heat (see Ch. 25)

25 Pulmonary ventilation (breathing)
Gases (such as air) flow/move along pressure gradients (i.e., from areas of higher pressure to areas of lower pressure) Pressure is related to volume by Boyle’s law: P = 1/V I.e., pressure is inversely proportional to volume I.e., if volume goes up, pressure goes down, and vice versa So to get air to move into and out of the lungs, the volume of lungs needs to change This is accomplished by moving the diaphragm and rib cage (see the next slide) Fig , p. 831

26 Mechanisms of pulmonary ventilation
Fig , p. 832

27 Lung compliance = the expandability of the lungs; i.e., how easily they expand and contract High compliance = the lungs and thoracic cage are easily expanded Low compliance = the lungs and thoracic cage are not easily expanded Lung compliance is normally high due to: The presence of elastic fibers around the alveoli (elastic recoil aids passive exhalation) The presence of surfactant on the inner walls of the alveoli, which decreases the surface tension (≈ stickiness) of the alveolar walls and thus decreases the force necessary to inflate the lungs during inhalation Decreased compliance can be caused by: Scar tissue (e.g. tuberculosis or emphysema) Decreased surfactant (e.g. respiratory distress syndrome) Decreased ribcage mobility (e.g. arthritis in the rib joints)

28 Pressure changes during breathing
Intrapleural pressure (= the pressure within the pleural cavity)… Is due to the visceral pleura adhering to the parietal pleura Is always negative with respect to atmospheric (outside of the body) pressure and intrapulmonary (within the alveoli of the lungs) pressure Opposes the elastic recoil of the lungs Keeps the lungs attached to the thoracic wall and diaphragm, and at least partially inflated (i.e., not collapsed) at all times (even after exhalation) Fig , p. 833

29 Breathing muscles Fig , p. 835

30 Inhalation (inspiration)
During quiet breathing: The diaphragm contracts, flattens, and moves inferiorly This is specifically called diaphragmatic (deep) breathing, and it… Contributes ~ 75% to tidal volume at rest The external intercostals contract, and pull the ribs up and out This is specifically called costal (shallow) breathing, and it… Contributes ~ 25% to tidal volume at rest The thoracic cavity volume increases, so the lung volume increases Alveolar (intrapulmonary) pressure decreases below atmospheric (outside of the body) pressure Air enters the lungs (moving from higher → lower pressure) During forced inhalation: Additional muscles elevate ribs to further (and more rapidly) increase the thoracic cavity volume E.g. the scalenes, SCM, pectoralis minor, serratus anterior, etc.

31 Exhalation (expiration)
During quiet breathing: The diaphragm and external intercostals relax, recoil, and resume their resting positions There is elastic recoil of the thoracic wall and lungs The thoracic cavity and lung volumes decrease passively Alveolar (intrapulmonary) pressure increases above atmospheric (outside of the body) pressure Air leaves the lungs (moving from higher → lower pressure) During forced exhalation: The thoracic cavity volume actively decreases even more (quickly and/or powerfully) via… Contraction of the internal intercostals and other muscles that depress the ribcage Contraction of the abdominal muscles, which compress the abdomen, forcing the visceral organs (and thus the diaphragm) superiorly E.g. blowing up a balloon, shouting, coughing, sneezing, etc.

32 Respiratory volumes and capacities
Fig , p. 837

33 Respiratory volumes and capacities
1. Resting tidal volume (VT) = the volume of air moved in and out per breath during one respiratory cycle of quiet breathing (~ 500 mL) 2. Anatomic dead space (VD) = the volume of air in the conducting airways (~ 150 mL) This air does not participate in gas exchange 3. Respiratory minute volume (VE) = the total volume of air inhaled and exhaled during each minute = breaths/min x tidal volume (~ 6 L/min) 4. Inspiratory reserve volume (IRV) = the additional volume of air that can be inhaled above and beyond the resting tidal volume 5. Expiratory reserve volume (ERV) = the additional volume of air that can be exhaled above and beyond the resting tidal volume 6. Residual volume = the volume of air left in the lungs after maximal exhalation 7. Vital capacity = the maximum volume of air that can be moved in and out of the lungs during one respiratory cycle of forced breathing = IRV + VT + ERV 8. Total lung capacity = just what it says = the total volume of the lungs = vital capacity + residual volume 9. Functional residual capacity (FRC) = the volume of air in the lungs after a normal, quiet exhalation .

34 Respiratory rates and volumes
Respiratory rate (f) = the number of breaths per minute (~ for resting adults) Respiratory minute volume (VE) = the total volume of air moved in and out of the entire respiratory system per minute = respiratory rate (breaths/min) x tidal volume (volume/breath) VE = f x VT = 12 breaths/min x 500 mL = 6 L/min Alveolar ventilation rate (VA) = the volume of air actually entering the alveoli every minute = respiratory rate x (tidal volume - anatomic dead space) VA = f x (VT - VD) = 12 breaths/min x (500 mL – 150 mL) = 4.2 L/min Maximums: VT max (i.e., vital capacity) ~ 4.8 L (for a male) f max ~ breaths/min So VE max ~ 200 L/min (for a male) That’s about 50X higher than at rest! . . . . .

35 Dalton’s law (of partial pressures)
= each gas in a mixture of gases contributes its own partial pressure (P) to the total pressure of the gas mixture Total atmospheric (or barometric or air) pressure = PO2 + PCO2 + PN2 + PH2O + Pothers = 760 mm Hg Pgas = [gas] x total pressure Atmospheric air at sea level on a cool, dry day has… PO2 = 20.9% x 760 mm Hg = 159 mm Hg PCO2 = 0.04% x 760 mm Hg = 0.3 mm Hg But the air in the alveoli is saturated with water vapor, and it consists of a mix of freshly inhaled (“new”) atmospheric air (~ 13%) and “old” air that has been in the alveoli for a while (~ the other 87%), so… PO2 of air in the alveoli = 13.2% x 760 = 100 mm Hg PCO2 of air in the alveoli = 5.2% x 760 = 40 mm Hg Table 23-2, p. 839

36 Diffusion between liquids and gases
Gases dissolve in fluids (ask a fish!) Henry’s law = the amount of gas dissolved in a solution is proportional to its partial pressure (see the figure shown here)… …BUT it also depends on the solubility of that gas in that particular liquid The solubility coefficients (in water) for: CO2 = 0.57 O2 = 0.024 N2 = 0.01 The bottom line is that in the body only CO2 is trans ported in solution to any signifi cant extent Fig , p. 839

37 Factors affecting diffusion rate (flux)
FYI (this is a repeat slide from Ch. 3) Factors affecting diffusion rate (flux) In general: Distance…shorter = faster Molecule size…smaller = faster Temperature…warmer = faster Concentration (chemical) gradient size (ΔC)…larger = faster Electrical gradient forces…opposites attract, and likes repel The sum of the last two = “electrochemical gradient” For diffusion of a substance across a membrane, there are 2 more factors to consider: Surface area of the membrane through which the diffusion is occurring…larger = faster Permeability (P)…greater = faster The P of a substance is influenced by the substance’s size, electrical charge, molecular shape, lipid solubility, the presence or absence of channels or carriers for the substance, and temperature The fundamental equation: flux = P x ΔC

38 Why diffusion across the respiratory membrane is extremely efficient
1. The diffusion distance is small (~ 0.5 μm) The respiratory membrane = 2 simple squamous epithelia with their basement membranes fused together 2. Membranes are highly permeable to O2 and CO2 (which are small and lipid soluble) 3. The total surface area is enormous There are about 500 million alveoli per lung, with a total exchange area (at peak inhalation) of ~ 140 m2 (1500 ft2) 4. Bloodflow and airflow are (usually) in sync I.e., cardiac output and respiratory rate are (usually) coordinated; that’s why together it’s called the “cardiorespiratory system” 5. Partial pressure gradients are substantial (especially for O2) – see the next slide

39 Partial pressures in respiration
Note: The Ps in the green box in the figure shown here are for resting tissues; highly active tissues will have much ↓ PO2 and much ↑ PCO2 Fig , p. 842

40 Gas transport – oxygen O2 has low solubility in plasma
O2-Hb saturation (or dissociation) curve (at a body temp. of 37°C and blood pH of 7.4) O2 has low solubility in plasma So little O2 (~ 1.5% of the total amount in the blood) can be transported in solution Transport for the other 98.5% requires a carrier – hemoglobin (Hb) The temporary and reversible reaction: Hb + O2 ↔ HbO2 Hb = hemoglobin (or deoxyhemoglobin) HbO2 = oxyhemoglobin Fig , p. 843

41 Certain environmental factors can affect hemoglobin’s ability to bind O2
These factors include: Blood pH Temperature Metabolic activity within RBCs (i.e., [BPG]) These factors can cause the O2-Hb saturation curve to shift to the left or the right E.g., when the curve shifts to the right, at a given PO2, Hb will bind less O2 I.e., it’s then easier for Hb to release more O2 to the tissues To remember the factors that shift the O2-Hb saturation curve to the right, think of exercising skeletal muscle (↓ pH, ↑ temperature, and ↑ [BPG] – see the next two slides) Exercising skeletal muscle has an ↑ demand for O2, so you would want hemoglobin to release more of its O2

42 Blood pH and hemoglobin
E.g., exercising muscle is acidic (↓ pH) due to: 1. The lactic acid produced by anaerobic metabolism (glycolysis): Lactic acid ↔ lactate + H+ 2. The CO2 produced by aerobic metabolism (the citric acid cycle) Carbonic acid is produced from CO2: H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3- H+s bind to Hb, change its shape, and cause it to release more O2 to tissues at a given PO2 The “Bohr effect” Fig a, p. 844

43 Other factors that affect Hb’s ability to bind O2
Temperature – exercising muscle is hot (due to ↑ metabolic heat production) ↑ Temperature weakens the bond between Hb and O2, causing Hb to release more O2 at a given PO2 (see the graph shown here) 2,3 bisphosphoglycerate (BPG) is produced in RBCs during glycolysis, and exercise causes the release of hormones that ↑ [BPG] ↑ BPG has the same effect on Hb’s ability to bind O2 as ↑ temperature does (although it’s not shown here) Fig b, p. 844

44 What binds O2 more strongly than adult hemoglobin?
Fetal hemoglobin (see the graph shown here) So fetal blood can “steal” O2 from maternal blood at the placenta Myoglobin So muscle cells can “steal” O2 from blood and store it for future immediate use Fig , p. 845

45 Gas transport – carbon dioxide
Notes: Remember, CO2 has relatively high solubility in water (plasma) CO2 binds to exposed amino groups (--NH2) on the globin part of Hb The chloride shift maintains electrical neutrality Fig , p. 846

46 A summary of gas transport mechanisms
Lower PO2 Higher PO2 Lower PCO2 Higher PCO2 Fig , p. 847

47 Control of respiration
Local regulation: Local changes in partial pressures of O2 and CO2 affect how much O2 and CO2 is picked up and delivered by the blood (e.g. see the O2-Hb saturation curve) Blood flow to (perfusion of) the alveoli matches the airflow to (ventilation of) the alveoli The alveolar capillaries dilate if alveolar air has ↑ PO2 and constrict if alveolar air has ↓ PO2 Note: this is the opposite of the local regulation of blood flow to peripheral tissues! The bronchioles dilate if alveolar air has ↑ PCO2 and constrict if alveolar air has ↓ PCO2 The respiratory centers in the medulla oblongata and pons regulate the rate and depth of breathing (see the next slide) Respiratory reflexes – may be regulatory or protective (see the last two slides) Voluntary control – the cerebral cortex has a limited ability to consciously override the lower brain centers

48 The respiratory centers of the brain
The respiratory rhythmicity centers (in the medulla oblongata)… Stimulate the diaphragm and external intercostals, setting the basic rhythm for quiet breathing (~ 2 seconds active for inhalation, ~ 3 seconds inactive for exhalation) This basic rhythm may be adjusted in response to sensory stimuli (via respiratory reflexes) During forced breathing, they stimulate additional accessory respiratory muscles as needed The pneumotaxic and apneustic centers (in the pons)… Further adjust the output of the rhythmicity centers in response to sensory stimuli (via respiratory reflexes) or input from the higher brain The apneustic center promotes inhalation and inhibits exhalation The pneumotaxic center promotes exhalation and inhibits inhalation Fig , p. 851

49 Some respiratory reflexes
Chemoreceptor reflexes Monitor the PCO2 , PO2 , and pH in the blood (at the aortic and carotid bodies) and the CSF (at the medulla oblongata) ↑ PCO2 is a more powerful stimulus to breathe than ↓ PO2! Baroreceptor reflexes Monitor blood pressure at the aortic and carotid sinuses Hering-Breuer (stretch) reflexes Help prevent overexpansion or too much deflation of the lungs (during forced breathing only) Protective reflexes (e.g. coughing, sneezing, and laryngeal spasms) Are caused by irritants in airways such as the nasal cavity, larynx, and bronchi

50 An example of a chemo-receptor reflex: responding to changes in PCO2
Fig , p. 853

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