Untitled Quiz

Respiration

• Respiration is a sequence of events resulting in the exchange of oxygen and carbon dioxide between the atmosphere and body cells.

External Respiration

• Occurs every 3 to 5 seconds
• Nerve impulses stimulate the breathing process (ventilation)
• Moves air in and out of the lungs
• Exchange of gases between the lungs and the blood

Internal Respiration

• Exchange of gases between the blood and tissue cells

Cellular Respiration

• Cells utilize oxygen for their specific activities

Sites of Gas Exchange

• External respiration:
  • CO2 diffuses from pulmonary capillaries into alveoli
  • O2 diffuses from alveoli into pulmonary capillaries
• Internal respiration:
  • O2 diffuses from systemic capillaries into cells
  • CO2 diffuses from cells into systemic capillaries

Internal Respiration: O2 and CO2 Exchange

• Partial pressures of oxygen (PO2) and carbon dioxide (PCO2) drive gas exchange.

• Gas exchange continues until equilibrium is reached

• PO2 in oxygenated blood: 100 mm Hg

• PCO2 in oxygenated blood: 40 mm Hg

• PO2 in tissue cells: 40 mm Hg

• PCO2 in tissue cells: 45 mm Hg

Overview: Respiratory System Organs

• Includes the nasal cavity, external nares (nostrils), pharynx, trachea, right primary bronchus, right lung, diaphragm, larynx, left primary bronchus, and left lung.
• Larynx contains vocal cords separating upper and lower respiratory tracts.

Air Conducting Passages

• Upper respiratory tract: nose, pharynx, larynx
• Lower respiratory tract: trachea, bronchial tree, lungs (alveoli)

Anatomic Dead Space

• Total volume of air channels that conduct inspired air to the alveoli approximately 150 ml
• Does not take part in gas exchange
• Functions as an air conduit, humidifying and warming air before reaching alveoli
• Includes structures like the mouth, nose, pharynx, trachea, and bronchi

Cleansing of the Inspired Air

• Dirt particles in the air are trapped by mucus in nasal and pharyngeal cavities, trachea, and bronchial tree.
• Particles are then phagocytosed or moved towards the pharynx by cilia of the epithelium

Bronchial Tree

• Trachea and bronchi have supporting cartilage maintaining open airways.
• Bronchiole walls contain more smooth muscle for airflow regulation.
• Airways from the nasal cavity to terminal bronchioles are the conducting zone.
• Air is moistened, warmed, and filtered flowing through these passageways.

Respiratory Zone

• Respiratory zone contains alveoli, tiny thin-walled sacs for gas exchange.
• Alveolar ducts end in clusters of alveoli called alveolar sacs.
• Respiratory bronchioles contain scattered alveoli within walls.

Resistance within the Airways

• Gas molecules encounter resistance when striking airway walls.
• Airway diameter affects resistance.
• Smooth muscle surrounding bronchioles constrict in asthma narrowing the airways

Alveoli and Pulmonary Capillaries

• Pulmonary arteries carry deoxygenated blood from the heart to the lungs.
• These blood vessels form dense networks of capillaries surrounding each alveolus.
• Oxygen and carbon dioxide exchange between air in alveoli and blood in pulmonary capillaries.
• Blood leaves via pulmonary veins carrying oxygenated blood back to the heart.

Structure of an Alveolus

• Alveolar macrophages remove debris and microbes from the alveolus' inner surface.
• Simple squamous epithelium (Type I cells) and surfactant-secreting cells (Type II cells) form the alveolus' inner walls.

Role of Surfactant

• Water in the alveolar fluid creates surface tension.
• Surfactant, a mixture of phospholipids and lipoproteins, lowers the alveolar fluid's surface tension.
• Facilitating expansion of alveoli and preventing them from collapsing during exhalation

Factors influencing External Respiration

• Depends on three main factors:
  • Surface area and structure of the respiratory membrane
  • Partial pressure gradients
  • Matching alveolar airflow to pulmonary capillary blood flow

Structure of the Respiratory Membrane

• Respiratory membrane averages 0.5 µm in width
• In many regions, there is no interstitial fluid.
• Oxygen and carbon dioxide can easily diffuse across the membrane.

External Respiration: Partial Pressures

• Partial pressures of gases in alveoli differ from the atmosphere.
• This difference is due to:
  • Humidification of inhaled air
  • Gas exchange between alveoli and pulmonary capillaries
  • Mixing of new and old air

External Respiration: Loading O2

• O2 diffuses from alveoli into the blood (high PO2 in alveoli, low PO2 in blood)

External Respiration: Unloading CO2

• CO2 diffuses from the blood into the alveoli (high PCO2 in blood, low PCO2 in alveoli)

O2 Transport

• Of the O2 that diffuses from the alveoli:
  • 98.5% combines with hemoglobin
  • 1.5% dissolves in plasma

Hemoglobin

• When 4 O2s are bound to hemoglobin, it is 100% saturated.
• Fewer O2s result in partial saturation.
• Oxygen binding occurs in response to high PO2 in the lungs.

Oxygen-Hemoglobin Dissociation Curve

• Hemoglobin saturation is determined by partial pressure of oxygen.

Factors Altering Hemoglobin Saturation

• When pH decreases, the curve shifts right (increased O2 unloading). Similar shifts occur in response to: Carbon dioxide and temperature.

Oxygen Binding and Transport in the Blood

• Oxygen binding to hemoglobin is oxygenation.
• Pressure of oxygen in arterial blood is ~95 mm Hg; in venous blood is ~40 mm Hg.
• Oxygen dissociation curve illustrates relationship between oxygen pressure in the blood and hemoglobin saturation.
• Oxygen binding capacity of hemoglobin increases with decreased temperature and increased pH e.g., in tissues

CO2 Transport

• Of the CO2 that diffuses from the tissue cells:
  • 93% diffuses into RBCs
  • 70% of CO2 is converted to bicarbonate ions
  • 23% combines with hemoglobin to form carbaminohemoglobin.
  • 7% dissolves in plasma

Carbon Dioxide Transport in the Blood

• Major part enters RBCs and is converted to bicarbonate (HCO3−).
• Carbonic anhydrase accelerates this conversion threefold.
• Pressure of carbon dioxide in arterial blood ≈ 40 mm Hg, in venous blood ≈ 46 mm Hg.

Hypoxia – Oxygen Deficit in the Tissues

• Hypoxia: oxygen deficit in tissues
  • Hypoxic hypoxia: reduced oxygen content in the air
  • Anemic hypoxia: not enough oxygen bound to blood (reduced oxygen capacity)
  • Histotoxic hypoxia: tissues cannot use oxygen
  • Ischemic hypoxia: decreased blood supply to tissues
• Brain is most sensitive organ

Cyanosis

• Dark (blue) coloration of nails, lips, ears, and thin-skinned areas.
• Occurs when deoxygenated hemoglobin in capillaries exceeds 50 g/l.

Respiratory Center

• Pons and medulla oblongata of the brain control the rate and depth of breathing.
• Inspiratory area → Phrenic nerve → Diaphragm contraction
• Normal breathing rate in adults is between 12 and 20 times per minute, higher in children (≈40/min)

Inspiratory Center

• The basic rhythm of breathing is controlled by respiratory centers in the brainstem (medulla and pons).
• Inspiratory center (dorsal respiratory group) sets the rhythm by automatically initiating inspiration.

Quiet Inspiration: Muscle Contraction

• Diaphragm and external intercostal muscles contract
• Increasing the volume decreases the pressure in the thoracic cavity.
  • Diaphragm flattens and moves inferiorly.
  • External intercostal muscles elevate the rib cage and move the sternum anteriorly.

Quiet Expiration: Muscle Relaxation

• Diaphragm and external intercostal muscles relax.
• Elastic lungs and thoracic wall recoil inward.
• This decreases the volume and increases pressure in the thoracic cavity.
  • Diaphragm moves superiorly
  • External intercostal muscles relax, rib cage, and sternum return to resting positions

Respiratory Volumes

• TV (tidal volume): air volume inspired and expired during quiet breathing (~500 ml)
• IRV (inspiratory reserve volume): additional air inspired after quiet inspiration (~2.5 L)
• ERV (expiratory reserve volume): additional air expired after quiet expiration (~1.5 L)
• VC (vital capacity): maximum air expired after maximal inspiration (TV + IRV + ERV)
• RV (residual volume): air remaining in lungs after maximal expiration (TLV - VC)
• TLV (total lung volume): TV + IRV + ERV + RV

Other Factors Influencing Ventilation

• Pain and strong emotions (through hypothalamic influence)
• Pulmonary irritants (dust, smoke, fumes, etc.) trigger coughing and sneezing reflexes.
• Voluntary control (can vary breath rate and depth)
• Lung hyperinflation is detected by stretch receptors in the visceral pleura and large airways and send inhibitory signals to inspiratory area, to protect lungs against excessive stretching (Hering-Breuer reflex).

Ventilation-Perfusion Coupling

• When airflow restricted (low PO2), local arterioles vasoconstrict.
• Blood redirected to alveoli with higher airflow and more available O2.
• In regions with high airflow (high PO2), local arterioles vasodilate; more blood delivered to alveoli to pick up available O2.