Lecture 15: The Respiratory System PDF

Lecture 15: The Respiratory System ================================== **Please read pages 891--932 (excluding 23.10) for this lecture.** **Learning Objectives:** - Define respiration and trace the three phases of respiration. - Identify the anatomical components of the upper and lower re...

Lecture 15: The Respiratory System ================================== **Please read pages 891--932 (excluding 23.10) for this lecture.** **Learning Objectives:** - Define respiration and trace the three phases of respiration. - Identify the anatomical components of the upper and lower respiratory systems and their relative locations. - Explain how the structures of respiratory components match the functions of those components. - List the bones (and other tissues) that form the nasal cavity. - Describe the histological changes that occur throughout the bronchial tree (e.g. epithelial lining, cartilage support, etc.) - Explain how the histology of respiratory structures is related to their physiological function. - Explain the mechanics of inhalation and exhalation. - Define lung volumes and lung capacities. - Determine the direction of gas diffusion at the different respiratory surfaces in the body. - Name and explain the factors affecting hemoglobin saturation. - Compare and contrast how oxygen and carbon dioxide are transported in the body. - Define **chloride shift** and explain its significance to respiratory homeostasis. - Explain how breathing is controlled. - Trace the negative feedback loop that is initiated by low blood pH. - Describe the effects of exercise on the respiratory system. - Explain how smoking negatively affects the function of the respiratory system. Introduction to respiration --------------------------- - **Respiration** is the acquisition of oxygen and elimination of carbon dioxide. - Three steps in the human body: - 1\. **Pulmonary \_\_\_\_\_\_\_ventilation\_\_\_\_\_\_\_\_\_\_\_\_\_** - Gas exchange between atmosphere and lung tissues - 2\. **External respiration** - Gas exchange between lung tissues and blood - 3\. **Internal respiration** - Gas exchange between blood and body's tissues - Functions of the respiratory system 1. Exchanges gases. 2. Regulates blood pH. 3. Permits **\_\_\_\_\_\_\_\_phonation\_\_\_\_\_\_\_\_** (vocal sounds) and sense of smell, filters inhaled air, and excretes wastes during exhalation. - **\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_oto(rhino)laryngology\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_** is the scientific and medical study of the respiratory system. - *Question*: *Why* do cells need oxygen? Aerobic cellular respiration Text Description automatically generated  **Above left**: There are three respiratory surfaces in the body. **Above right**: External respiration occurs at the alveoli. Anatomy of the respiratory system --------------------------------- - Structurally, the respiratory system can be further subdivided into the: - 1\. **Upper respiratory system** - Includes nose, nasal cavity, \_\_\_\_\_\_pharynx\_\_\_\_\_\_\_, and associated structures - 2\. **Lower respiratory system** - Includes \_\_\_\_\_\_larynx\_\_\_\_\_\_\_\_, trachea, bronchi, and lungs - *Functionally*, the respiratory system can be subdivided into two zones: 1. The **\_\_\_\_\_\_\_\_\_\_conducting\_\_\_\_\_\_\_\_\_\_\_\_\_ zone** - Directs air toward the respiratory zone - Filters, warms, humidifies air as it enters body 2. The **respiratory zone** - Site of gas \_\_\_\_\_\_\_\_\_\_exchange\_\_\_\_\_\_\_\_\_\_ - Includes respiratory bronchioles, alveolar ducts, alveolar sacs, ### The upper respiratory system - **The nose** - Made of bone, cartilage, other CTs - Contains the nasal cavity - Air enters body via **\_\_\_\_\_\_external\_\_\_\_\_\_ \_\_nares\_\_\_\_\_\_** or nostrils Diagram Description automatically generated  **Above left**: Label the upper and lower respiratory systems in the diagram. **Above right**: The nose is comprised of multiple tissues. - **The nasal cavity** - Interior and anterior space of the nose - Bounded inferiorly by the oral cavity and superiorly by the nasal bones - Bone and cartilage keep passages \_\_\_\_\_\_\_unobstructed\_\_\_\_\_\_\_\_\_\_\_ - Divided into left and right halves by **nasal \_\_\_\_\_septum\_\_\_\_\_\_\_\_** - Contains the **\_\_\_\_\_\_\_paranasal\_\_\_\_\_\_\_ \_\_\_\_\_\_sinus\_\_\_\_\_** - Lined with mucous membranes - Vibrates to permit singing/speech - Contains the **nasal \_\_\_\_\_conchae\_\_\_\_\_\_\_\_\_\_** - Swirls inhaled air - Contains the **\_\_\_\_\_\_olfactory\_\_\_\_\_\_\_\_ epithelium** - Ciliated with \_\_no\_\_ goblet cells - Contain sensory receptors for smells - **The pharynx** - Tube of skeletal muscle lined with mucous membrane - Starts at internal nares and continues to the **\_\_\_\_\_cricoid\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_cartilage\_\_\_\_\_\_\_\_\_** - Further subdivided into: i. **\_\_\_\_\_\_\_\_nasopharynx\_\_\_\_\_\_\_\_\_\_\_** (superior) - Lined with ciliated pseudostratified columnar epithelium - Sweeps mucus into the pharynx ii. **Oropharynx** (intermediate) - Opening from mouth into oropharynx is called the **fauces** - Common passage for air and food - Lined with non-keratinized stratified squamous epithelium - Contains the **tonsils** - **What are the functions of the tonsils?** Trap pathogens iii. **\_\_\_\_\_\_\_\_\_\_\_\_laryngopharynx\_\_\_\_\_\_\_\_\_\_\_** (inferior) - Similar structure to oropharynx but inferior Diagram Description automatically generated **Above:** Parasagittal section of the skull, showing the components of the upper respiratory system. Diagram Description automatically generated **Above left**: Sagittal view of the skull showing the bones that form the nasal cavity. **Above right**: Frontal section of the skull to show the structure of the nasal conchae. - The larynx - Tube comprising nine rings of cartilage - **\_\_\_\_\_\_\_\_thyroid\_\_\_\_\_\_\_ cartilage:** hyaline cartilage that forms anterior surface of the larynx - A.k.a. Adam's apple - Males and females have this; larger growth in males stimulated by sex hormones - **\_\_\_\_\_\_\_\_\_epiglottis\_\_\_\_\_\_\_\_\_** is a flap of elastic cartilage - During swallowing, larynx elevates and epiglottis covers entrance - **\_\_\_\_\_\_cricoid\_\_\_\_\_\_\_\_\_ cartilage:** ring of hyaline cartilage at the inferior portion of larynx - Landmark for tracheotomies Where you make an insertion if the upper respiratory tract has a blockage  Diagram Description automatically generated - **True vocal cords** or **\_\_\_vocal\_\_\_\_\_\_ folds** (inferior): - Made of non-keratinized stratified squamous epithelium - Form elastic ligaments - Stretch across the cartilages of the larynx, like strings of a guitar - Air moves through the larynx and vibrates the vocal folds, making sounds - Skeletal muscles on cartilages generate tension on ligaments to change voice \_\_\_\_pitch\_\_\_\_\_\_ - **False vocal cords** or **\_\_\_\_\_\_\_\_\_vestibular\_\_\_\_\_\_\_\_\_\_\_ folds** (superior) - Come together when you hold your breath - **The trachea** - 2.5 cm wide x 12 cm long tube - 16--20 rings of \_\_\_\_\_\_\_\_hyaline\_\_\_\_\_\_\_\_ cartilage - Rings connected by dense CT - Cartilage keeps trachea **\_\_\_\_patent\_\_\_\_\_\_\_** - Anterior to the esophagus - Lined with ciliated pseudostratified epithelium  **Above**: The vocal folds (top) and vestibular folds (bottom) in the larynx are required for phonation.  **Above left**: Components of the lower respiratory system. **Above right**: Ciliated pseudostratified epithelial lining of the trachea sweeps mucus toward the pharynx. - **The bronchi** - Trachea splits into the **right** and **left bronchi** (singular: bronchus) - **\_\_\_\_\_\_\_\_carina\_\_\_\_\_** is ridge at branchpoint - Sensitive mucous membrane; triggers cough reflex - Branch into lungs as narrowing vessels - Called the **bronchial tree** - Small tubes that end in the lung sacs called **\_\_\_\_\_\_terminal\_\_\_\_\_\_\_\_ bronchioles** - The mucous membranes of the bronchi changes throughout the bronchial tree - The supporting cartilage and proportion of smooth muscle also change throughout the bronchial tree Above: Describe the epithelial layer of the mucous membranes lining the bronchial tree by filling in the blanks in the diagram above. Graphical user interface, text, application Description automatically generated Above: Note the changes to the other tissues supporting the bronchial tree from the trachea to the terminal bronchioles. - **The lungs** - Wrapped in **\_\_\_\_\_\_pleural\_\_\_\_\_\_\_\_ membrane** - Two serous membranes - Space between = **pleural cavity** - Pleural fluid reduces friction and provides **\_\_\_\_\_\_surface\_\_\_\_\_\_\_ \_\_\_\_\_\_tension\_\_\_\_\_\_** - Lungs are separated by the mediastinum and its organs  - Extend from just superior to the clavicles to the diaphragm - Rest anteriorly and posteriorly **costal surfaces** of ribs - **Inferior** portion of the lungs is called **the \_\_\_\_\_base\_\_\_\_\_\_** - Concave shape conforms to dome-shape of diaphragm - The **superior** portion of the lungs is called **the \_\_\_\_\_apex\_\_\_\_** Diagram Description automatically generated - The **mediastinal surfaces** are the medial surfaces of the lungs, including: - The **\_\_\_\_\_\_hilum\_\_\_\_\_\_\_** - Permits passage of the bronchi, blood vessels, nerves, and lymphatic vessels - The **cardiac \_\_\_\_\_notch\_\_\_\_\_\_\_** - Provides space for the heart - Decreases size of left lung relative to right lung by 10%  - **\_\_\_\_\_\_\_fissures\_\_\_\_\_\_\_\_** divide the lung into **lobes** - **\_\_\_\_\_\_\_oblique\_\_\_\_\_\_\_ fissure** separates the **superior** and **inferior lobes** - **Horizontal fissure** borders the **middle lobe** superiorly on the *right lung only* - Lobes contain individualized bronchi - **\_\_\_\_\_\_lobar\_\_\_\_\_\_ \_\_\_\_\_bronchi\_\_\_\_\_** named after lobes they branch into: - **Superior lobar bronchus** - **Middle lobar bronchus** (right lung only) - **Inferior lobar bronchus** - The lobar bronchi branch into **segmental bronchi** - Each segmental bronchus supports one **\_\_\_\_\_\_\_\_\_\_\_\_bronchopulmonary\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_\_\_\_segment\_\_\_\_\_\_\_\_\_\_** - 13 segmental bronchi in right lung; 8 in left lung - Damaged/diseased segments can be removed surgically without perturbing surrounding tissue - Each bronchopulmonary segment is divided into **lobules** - **\_\_\_\_\_\_\_\_lobules\_\_\_\_\_\_\_\_\_\_\_\_** are smaller compartments consisting of: - A branch of a terminal bronchiole - An arteriole + venule - A lymphatic vessel... all wrapped in **\_\_\_\_\_\_\_elastic\_\_\_\_\_\_\_\_ connective tissue** - **\_\_\_\_\_\_\_\_\_\_\_\_\_respiratory\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ bronchioles** are microscopic bronchial branches - Lined with simple cuboidal epithelium - Branch into **alveolar ducts** - Lined with simple squamous epithelium - The **\_\_\_\_\_\_\_alveoli\_\_\_\_\_\_\_\_\_\_** are air sacs where pulmonary and external respiration occur - Have extensive surface area  A picture containing qr code Description automatically generated  - Alveolar ducts terminate in balloon-like sacs called **alveolar sacs** - Often likened to clusters of grapes - Each sac = **\_\_\_\_\_\_\_alveolus\_\_\_\_\_\_\_\_\_** - Alveoli are made of two types of cells: 1. **Type I alveolar cells** - Simple \_\_\_\_\_\_squamous\_\_\_\_\_\_ epithelium - Thinness facilitates gas diffusion 2. **Type II alveolar cells** - Nonciliated cuboidal epithelium at the \_\_\_\_septa\_\_\_\_ between alveoli - Secrete **\_\_\_\_\_\_surfactant\_\_\_\_\_\_\_\_\_:** phospholipids + lipoproteins - Prevents walls of alveoli from sticking to one another - Patrolled by macrophages Decrease surface tension to prevent collapse of aveolar walls A picture containing text Description automatically generated - **\_\_\_\_\_\_respiratory\_\_\_\_\_\_\_\_\_ \_\_\_\_membrane\_\_\_\_\_\_\_\_:** alveoli + associated capillaries - Very thin: 0.5 µm thick! - From superficial to deep, the layers of the respiratory membrane are: - The **alveolar wall**: type I and type II alveolar cells plus alveolar macrophages - The \_\_\_\_\_\_epithelial\_\_\_\_\_\_\_\_ basement membrane - The \_\_\_\_\_capillary\_\_\_\_\_\_\_\_\_ basement membrane - The capillary endothelium - In direct contact with blood Diagram Description automatically generated - Blood supply to the lungs - Two sets of arteries bring blood to the lungs: 1. **The \_\_\_\_\_\_\_\_pulmonary\_\_\_\_\_\_\_\_ arteries** - Bring deoxygenated blood from right ventricle to be oxygenated - *Constrict* in response to hypoxia( UNADEQUATE SUPPLE OF BLOOD TO THE BODY TISSUES) - Responsible for **ventilation-perfusion coupling** - If ventilation (ability to obtain oxygen) is *high* in that segment, perfusion will also be *high* - Ensures that only healthy lung tissues are \_\_\_\_\_\_\_maximally\_\_\_\_\_\_\_\_\_ perfused(movement of blood to the organs of body tissues) 2. **The \_\_\_\_\_\_\_bronchial\_\_\_\_\_\_\_ arteries** - Branch from the aorta - Deliver oxygenated blood to the \_\_\_\_\_muscular\_\_\_\_\_\_\_\_\_ tissue of the lungs  **Above**: Blood is brought to the lungs for oxygenation by the pulmonary arteries and returns to the heart through the pulmonary veins. - **\_\_\_\_\_\_\_patency\_\_\_\_\_\_\_\_\_\_** is the ability of a passageway to remain unobstructed (not collapsed) - If airways do not remain patent, gas exchange will *not* occur - Things that compromise patency include: - Crush injuries to the thoracic cavity - A deviated nasal septum - Inflammation of the mucous membranes - Infection or \_\_\_\_\_\_\_\_\_hypersensitivity\_\_\_\_\_ reactions Gas exchange and ventilation ---------------------------- - **Pulmonary ventilation** is inhalation and exhalation - Leads to gas exchange at the alveoli - Regulated by \_\_\_pressure\_\_\_\_\_\_\_\_ \_\_\_change\_\_\_\_\_\_\_\_ within the thoracic cavity - Requires contraction of respiratory muscles - Mechanics of inhalation - Inhalation or **\_\_\_\_\_\_\_\_\_inspiration\_\_\_\_\_\_\_\_\_\_** is the act of taking in air - Just before inhalation, pressure inside of lungs is \~equal to atmospheric pressure - Gases move from **high to low** partial pressures - For inhalation to occur, pressure in lungs must be lowered \_\_\_\_\_\_below\_\_\_\_\_\_ atmospheric pressure - How can we lower the pressure in the lungs? By increasing the volume of the lungs - Gases diffuse from high to low partial pressures - **Partial pressure** is the pressure a gas exerts on its surroundings - Gases diffuse from high to low partial pressures in a fluid - Once the thoracic cavity expands, air moves *\_\_\_\_into\_\_\_\_* the lungs - \_\_\_\_\_down\_\_\_\_\_\_\_ its partial pressure gradient - **Boyle's law** states that the pressure inside of a container is \_\_\_\_\_\_\_inversely\_\_\_\_\_\_\_\_ proportional to the volume of that container - If we want to **decrease the pressure inside of the lungs**, we need to **\_\_\_\_\_\_increase\_\_\_\_\_\_\_\_ the volume** of the lungs! Diagram Description automatically generated **Above left**: Illustration of Boyle's Law --- the pressure inside of a container is inversely proportional to the volume of that container. **Above right**: Movement of the diaphragm and external intercostal muscles changes the thoracic cavity volume during breathing. - The diaphragm contracts to increase the volume of the thoracic cavity - Starts with \_\_\_\_\_\_\_contraction\_\_\_\_\_\_\_\_ of the diaphragm - Assisted by contraction of the **intercostal muscles** - Contraction of the diaphragm \_\_\_\_\_\_\_depresses\_\_\_\_\_\_\_\_\_ it by 1 cm - Decreases pressure by 1-3 mm Hg - During **strenuous(forced)** inhalation, the diaphragm may be depressed by up to 10 cm - Decreases pressure by up to 100 mm Hg! - Depression of diaphragm responsible for 75% of inhaled air - Other 25% is from contraction of the **\_\_\_\_\_\_external\_\_\_\_\_\_\_\_ intercostal muscles** - Elevates ribs - Further increases thoracic cavity volume - Intrapleural pressure ensures lung tissue expands during inhalation - *\_\_\_\_\_negative\_\_\_\_\_\_\_\_\_\_* pressure within the pleural cavity - **\_\_\_\_\_\_lower\_\_\_\_\_\_\_\_\_** than atmospheric pressure - Keeps pleural membrane suctioned to thoracic cavity wall - When cavity wall expands, lungs do too! Diagram Description automatically generated - Mechanics of exhalation - Inhalation is an active process, but exhalation is **passive**. - When respiratory muscles relax, volume of thoracic cavity **decreases** - Stretching of elastic lung tissues results in **\_\_\_\_\_elastic\_\_\_\_\_\_ \_\_\_\_recoil\_\_\_\_\_\_** that generates pressure as well - Results in increased pressure inside of the lungs relative to outside of the lungs - Gases **diffuse** *out of* the body - The abdominal and internal intercostal muscles can assist in **active exhalation** during vigorous exercise or playing a wind instrument - Factors affecting pulmonary ventilation - **Surfactant** is essential to ventilation - Insufficient surface tension leads to difficulty breathing - **Respiratory distress syndrome** - **Pleural effusion** is an accumulation of pleural fluid in the pleural cavity - Decreases lung volume difficulty breathing  - **\_\_\_\_\_\_\_\_compliance\_\_\_\_\_\_\_\_\_** refers to the distensibility of elastic tissues - - - - - Air through respiratory system faces **\_\_\_\_\_\_\_\_resistance\_\_\_\_\_\_\_\_\_\_\_** - Product of: - **Airway diameter** - Larger diameter airways = less resistance - Contraction/relaxation of smooth muscle modulates airway resistance - Regulated by hormones and autonomic NS - **Obstruction or \_\_\_\_\_\_\_collapse\_\_\_\_\_\_\_\_** of airways increases resistance - E.g. chronic obstructive pulmonary disorder (COPD) Lung volumes and capacities --------------------------- - You are responsible for learning the lung volumes and capacities reviewed *in depth* in lab - **Lung \_\_\_\_\_\_volume\_\_\_\_\_\_\_\_\_** a specific measure of air inhaled, exhaled, or stored - Measured using a **spirometer** - Output is a **spirogram** (below) - **Lung \_\_\_\_\_\_\_capacity\_\_\_\_\_\_\_\_\_\_\_\_\_** are sums of specific lung volumes A picture containing diagram Description automatically generated Principles of Gas Exchange -------------------------- - The movement of oxygen and carbon dioxide in the body is simply **passive diffusion**. - From areas of high partial pressure to areas of low partial pressure - However, must also consider **\_\_\_\_\_\_\_solubility\_\_\_\_\_\_\_\_\_\_\_\_** of gas - Carbon dioxide is **\_\_\_\_\_\_24X\_\_\_\_** more soluble in water than oxygen - More CO~2~ in blood plasma than oxygen ### External respiration - **Recall: external respiration** is gas exchange between the **alveoli** and the blood across **pulmonary capillaries** - Here, as always, gases diffuse down their partial pressure gradients - During exercise, the partial pressure of oxygen (P~O2~) in alveoli is even **\_\_\_\_\_\_lower\_\_\_\_\_\_\_** than at rest - *Why?* - Slow movement of blood through alveolar capillaries maximizes oxygenation ### Internal respiration - **Recall**: **internal respiration** is gas exchange between the blood and the body's tissues - Again, governed by simple diffusion: - Tissue cells constantly produce CO~2~ - *Why?* - Results in constantly higher P~CO2~ outside systemic capillaries, especially at **\_\_\_\_\_\_\_venous\_\_\_\_\_\_\_\_\_** end - CO~2~ moves from tissues into the blood - Where does the oxygen go during internal respiration? - At the \_\_\_\_\_\_\_arterial\_\_\_\_\_\_ end of capillaries: - Oxygenated blood is pumped by the left ventricle to systemic capillary beds - Results in constantly \_\_\_\_\_higher\_\_\_\_\_\_\_\_ P~O2~ **inside** of blood - Oxygen moves from high partial pressure in blood to low partial pressure in the tissues  ### Factors affecting respiration - Things that affect the rate of **passive diffusion** will also affect the rate of respiration. 1. **Partial pressure \_\_\_\_\_\_\_gradient\_\_\_\_\_\_\_\_\_ of gas** - E.g. Decreased atmospheric pressure at high altitudes - Leads to a decreased \_\_\_\_\_\_\_\_difference\_\_\_\_\_\_\_\_ in partial pressure of oxygen outside and inside the body - Leads to slower rate of respiration and slower tissue oxygenation - This is **altitude sickness** 2. **\_\_\_\_\_\_\_surface\_\_\_\_\_\_\_\_ \_\_\_\_area\_\_\_\_\_ over which gases are exchanged** - More contact with gases to be exchanged = increased rates of diffusion - E.g. Total surface area of alveoli is **massive** to facilitate efficient gas exchange 3. **Diffusion \_\_\_\_\_\_\_\_distance\_\_\_\_\_\_\_\_** - Shorter distances = more efficient diffusion - E.g. Thin alveolar walls = shorter distance for gas diffusion 4. **Molecular weight and solubility of gas** - O~2~ has a smaller molecular weight than CO~2~ but CO~2~ has higher solubility in \_\_\_\_\_\_\_\_water\_\_\_\_\_\_\_\_ - Net elimination of CO~2~ is 20X faster than net O~2~ acquisition - Net effect: You will run out of O~2~ faster than you will accumulate excess CO~2~ ### Oxygen transport - 98.5% of O~2~ in blood is transported on **\_\_\_\_\_\_\_\_\_\_\_hemoglobin\_\_\_\_\_\_\_ (Hb)** in erythrocytes - Rest. Is dissolved in blood plasma - Recall: Hb consists of 4 protein subunits; 1 \_\_\_\_\_ heme\_\_\_\_\_ molecule per subunit - Oxygen binds the Fe atom of heme Diagram Description automatically generated - Hemoglobin binds oxygen reversibly - The binding and dissociation of oxygen to/from hemoglobin can be summarized as follows:  - This means: - Increased P~O2~ favours Hb-O~2~ formation - When nearly entire population of Hb is Hb-O~2~, then Hb is **\_\_\_\_\_\_\_\_\_\_\_\_\_saturated\_\_\_\_\_\_\_\_\_\_\_** - **Percent saturation** of hemoglobin is the *\_\_\_\_\_\_\_\_average\_\_\_\_\_\_\_\_\_* saturation of hemoglobin - E.g. If each Hb *on average* has two O~2~ atoms bound, then what is the % saturation of Hb? - What affects the saturation of Hb? 1. **The partial pressure of oxygen (P~O2~)** - Between 60--100 mm Hg, the saturation of Hb is almost \_\_\_100\_\_\_\_% - Average atmospheric pressure at sea level \~\_\_760\_\_\_ mm Hg - Reason that external respiration is so efficient! - In working skeletal muscle, P~O2~ is 20 mm Hg and saturation is low (35%) - In systemic capillaries at rest, P~O2~ is 40 mm Hg and saturation is high (75%) Chart Description automatically generated  **Above left**: The saturation of hemoglobin is controlled by the partial pressure of oxygen. **Above right**: The *affinity* of Hb for oxygen is affected by blood pH. 2. **Hb affinity for oxygen** - **Affinity** is the tendency for a substance to bind another. - The affinity of hemoglobin for oxygen is affected by: i. **Acidity** - Increased \[H^+^\] in blood changes Hb \_\_\_\_\_\_\_structure\_\_\_\_\_\_\_\_ - Low pH \_\_\_\_\_decrease\_\_\_\_\_\_\_\_\_\_ affinity(spontaneously) for O~2~ ii. **The partial pressure of CO~2~ (P~CO2~)** - Recall: Hb can bind CO~2~ but most is transported as \_\_\_\_\_H2CO3\_\_\_\_\_ in blood plasma - High P~CO2~ \_\_low\_\_\_ blood pH decreased affinity of Hb for oxygen A picture containing text Description automatically generated  Diagram Description automatically generated **Above left**: The affinity of Hb for oxygen is negatively affected by high partial pressures of CO~2~. **Above right**: The affinity of Hb for oxygen is negatively affected by high temperatures. iii. **Temperature** - Skeletal muscle contraction generates \_\_\_\_heat\_\_\_\_\_ - Increases temperature of blood - Favours \_\_\_\_\_release\_\_\_\_\_\_\_\_ of O~2~ to tissues iv. **The intermediate products of glycolysis** - Recall: erythrocytes have no mitochondria - Still perform **\_\_\_\_\_\_\_glycolysis\_\_\_\_\_\_\_\_\_** - One of the products of glycolysis (2,3-bisphosphoglycerate or BPG) binds Hb and changes its structure - \_\_\_\_\_\_decreases\_\_\_\_\_\_\_\_\_\_ affinity for O~2~ - Some hormones (e.g. epinephrine) increase BPG levels in cells v. **The type of hemoglobin** - During fetal development, a specific **globin** gene is expressed - Resulting **fetal Hb** (Hb-F) has a different structure and different affinity for O~2~ than adult Hb (Hb-A) - Hb-F does not bind BPG - Hb-F binds up to 30% more O~2~ than Hb-A  ### Summary - The factors that affect hemoglobin saturation: 1. P~O2~ 2. Blood acidity 3. P~CO2~ 4. Temperature 5. Intermediate products of glycolysis 6. Type of hemoglobin Carbon dioxide transport ------------------------ - Carbon dioxide is transported through the body in **three** main forms: 1. 7% is dissolved in blood plasma as CO~2~. 2. 23% binds is bound to proteins (including Hb) to form **carbamino compounds**. - Binding of Hb produces **\_\_\_\_\_\_\_\_\_\_\_carbaminohemoglobin\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_** 3. 70% is transported as **\_\_\_\_\_\_\_bicarbonate\_\_\_\_\_\_\_\_** - Product of carbonic acid dissociation A picture containing text Description automatically generated - Chloride shift ensures erythrocytes maintain electrical balance - **At the systemic capillaries**, CO~2~ is quickly converted into H~2~CO~3~ by CA and dissociates into HCO~3~^-^ - HCO~3~^-^ diffuses out of the cell from high to low concentration in blood plasma - Those **\_\_\_\_\_anions\_\_\_\_\_\_** must be replaced -- *why?* *To maintain ionic charge* - Cl^-^ ions diffuse into the red blood cell - Called **chloride \_\_\_shift\_\_\_\_** - Reverse chloride shift ensures that CO~2~ can be eliminated at the pulmonary capillaries - **At the pulmonary capillaries**, CO~2~ must be eliminated by exhalation - But only a small percentage of CO~2~ is CO~2~ in blood! - As P~CO2~ decreases in erythrocytes, HCO3^-^ recombines into H~2~CO~3~ - CA catalyzes reaction *in reverse* to produce CO~2~ - CO~2~ diffuses out of erythrocytes, out of blood, into the alveoli to be exhaled - As \[HCO~3~^-^\] decreases, Cl^-^ moves *out* of cells - This is **\_\_\_\_\_\_\_reverse\_\_\_\_\_\_\_\_ chloride shift**  Regulation of breathing ----------------------- ### The respiratory centre - The **respiratory centre** is a cluster of neurons in the brain that regulates the action of respiratory muscles - Two main centres: 1. The **\_\_\_\_\_medulla\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_oblongata\_\_\_\_\_\_\_\_\_\_** 2. The **\_\_\_\_\_pons\_\_\_\_\_** - The medullary respiratory group - Further subdivided into the: - **\_\_\_\_\_\_Dorsal\_\_\_\_\_\_\_ respiratory group** (DRG): normal breathing - **\_\_\_\_\_\_Ventral\_\_\_\_\_\_\_ respiratory group** (VRG): forceful breathing Diagram Description automatically generated  **Above left**: The respiratory centre controls breathing. **Above right**: The dorsal respiratory group (DRG) in the medullary respiratory centre controls normal breathing. Diagram Description automatically generated **Above**: The ventral respiratory group (VRG) controls forceful breathing, though the DRG is also involved. - The pontine respiratory group - Neurons in the pons affect \_\_\_\_\_\_normal\_\_\_\_\_ breathing by influencing the \_\_DRG\_\_\_\_ in the medullary group ### Cortical influences on breathing - Respiration is mostly involuntary but can control breathing when needed - Possible through the **cerebral cortex** connection to the respiratory centre - Permits us to breathe or not breathe at will - Why can't we hold our breath for *too* long? - Increased \_\_\_\_\_Pco2\_\_\_\_\_ and \_\_\_H+\_\_\_\_ in blood stimulates DRG neurons - Stimulates respiratory muscles via the **phrenic** and **intercostal nerves** - Forces normal breathing to resume ### Other influences on breathing - Chemoreceptors influence breathing - Recall: **chemoreceptors** sense changes in chemicals in the blood - **\_\_\_\_\_\_central\_\_\_\_\_\_\_ chemoreceptors** are located near the medulla oblongata - Sense changes in P~CO2~ and/or H^+^ in cerebrospinal fluid (CSF) - **\_\_\_\_\_\_\_\_\_peripheral\_\_\_\_\_\_\_\_\_\_\_ chemoreceptors** are located in aortic and carotid bodies (vessel walls)  Timeline Description automatically generated **Above left**: Chemoreceptors sense changes in blood pH. **Above right:** The response to low blood pH is regulated by a negative feedback loop. - Hyperventilation is a response to low blood pH - When blood pH is low, the P~CO2~ is likely \_\_\_\_high\_\_\_\_ - Peripheral chemoreceptors send a signal to the respiratory centre - Stimulate the DRG - DRG sends nerve impulses to respiratory muscles increased force and rate of contractions - Response: increased rate and depth of breathing or **\_\_\_\_\_\_\_\_\_\_\_hyperventilation\_\_\_\_\_\_\_\_\_\_\_\_\_\_** - Net physiological effect: increased blood pH to normal - \_\_\_\_\_\_\_\_\_\_Hypocapnia\_\_\_\_\_\_\_\_ can result from hyperventilation - When P~CO2~ in blood is *low*, the chemoreceptors do *not* send signals to stimulate the DRG - DRG is stimulated at a threshold P~CO2~ of 40 mm Hg - Can happen after hyperventilation - May cause fainting due to **\_\_\_\_\_\_hypoxia\_\_\_\_\_\_\_\_\_** - Insufficient oxygen to meet the metabolic needs of tissues - The inflation reflex - Prevents overinflation of lung tissue during rigorous exercise - **\_\_\_\_\_\_\_\_baroceptors\_\_\_\_\_\_\_\_\_\_\_\_** in the bronchi and bronchioles sense **stretching** of the lungs - Sends a signal along the **\_\_\_\_\_vagus\_\_\_\_ nerve** to the DRG - Inhibits the DRG to relax respiratory muscles **exhalation** - As exhalation proceeds, stretching relaxes and normal inhalation can resume - Many other things affect breathing! - Emotions can affect the respiratory centre via the \_\_\_\_\_limbic\_\_\_\_\_\_\_ system - Temperature (e.g. cold shock) can temporarily stop breathing - Pain can both slow or speed breathing - Irritation of the airways can increase respiration rate - Increased blood pressure \_\_\_\_\_\_\_\_\_\_decreases\_\_\_\_\_\_ respiration rate - Exercise and the respiratory system - **\_\_\_\_\_\_\_pulmonary\_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_perfusion\_\_\_\_\_\_\_\_\_\_** is the extent of blood flow to the lungs - Exercise increases pulmonary perfusion - Partly due to increased \_\_\_\_\_\_\_\_\_ventilation\_\_\_\_\_\_\_\_\_ of alveoli during exercise - Anticipation of exercise stimulates limbic system + proprioceptors stimulate DRG increased depth of breathing - During rigorous exercise, chemoreceptors sense increased \[H^+^\] - Stimulate the DRG to increase rate and depth of breathing Homeostatic imbalances of the respiratory system ------------------------------------------------ - Tobacco smoking causes: - **Chronic obstructive pulmonary disease (COPD)** - Increased goblet cell number and mucus secretion - Excess mucous impairs \_\_\_\_\_ciliary\_\_\_\_\_ function - Results in a chronic cough shortness of breath and wheezing - **\_\_\_\_\_\_\_emphysema\_\_\_\_\_\_\_\_\_\_\_\_:** immune destruction of alveolar walls - Leads to decreased alveolar surface area + decreased O~2~ acquisition Summary ------- - The respiratory system is responsible for O~2~ acquisition and CO~2~ elimination - The anatomy of the respiratory system maintains patency of airways, compliance of lung tisssue, maximal perfusion of healthy lung tissues, and high surface area over which gas exchange occurs. - Gas exchange is governed by **passive diffusion**. - Oxygen is transported bound to Hb while CO~2~ may be transported in blood plasma as bicarbonate or bound to proteins. - The respiratory centre controls breathing but is influenced by sensory inputs and other parts of the brain, including the cerebral cortex and the limbic system.