THE RESPIRATORY SYSTEM

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THE RESPIRATORY SYSTEM

• CHAPTER 15

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Introduction

• To continue functioning, body cells must obtain
  oxygen and eliminate carbon dioxide.

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The Functions of the Respiratory System

• 1. Moving air to and from exchange surfaces
  where diffusion can occur between air and
  circulating blood

• 2. Defending the respiratory system and other
  tissues from pathogens

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• 3. Permitting vocal communication

• 4. Helping control body fluid pH.

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Organization

• The respiratory system includes the nose, nasal
  cavity, and sinuses as well as the pharynx,
  larynx, trachea, and conducting passageways
  leading to the surfaces of the lungs.

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Respiratory Tract

• The respiratory tract consists of the conducting
  passageways that carry air to and from the alveoli

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The Nose

• Air normally enters the respiratory system via
  the external nares, which open into the nasal
  cavity.
• The vestibule is guarded by hairs that screen out
  large particles.

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• The hard palate separates the oral and nasal
  cavities.
• The soft palate separates the superior
  nasopharynx from the rest of the pharynx.
• The internal nares connects the nasal cavity and
  nasophaarynx.

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• Much of the respiratory epithelium is ciliated
  and produces mucus that traps incoming particles.

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Pharynx and Larynx

• The pharynx is a chamber shared by the digestive
  and respiratory systems.
• Inhaled air passes through the glottis en route
  to the lungs.
• The larynx surrounds and protect the glottis.
• The epiglottis projects into the pharynx
• Exhaled air passing through the glottis vibrates
  the true vocal cords and produces sound.

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The Trachea

• The wall of the trachea (windpipe) contains
  C-shaped tracheal cartilages, which protect the
  airway.
• The posterior tracheal wall can distort to permit
  large masses of food to pass.

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The Bronchi

• The trachea branches within the mediastinum to
  form the right and left primary bronchi
• The primary bronchi, secondary bronchi,and their
  branches form the bronchial tree.
• As the tertiary bronchi branch within the lung,
  the amount of cartilage in their walls decreases
  and the amount of smooth muscle increases.

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The Bronchioles

• Each terminal bronchiole delivers air to a single
  pulmonary lobule.
• Within the lobule, the terminal bronchiole
  branches into respiratory bronchioles.

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The Alveolar Ducts and Alveoli

• The respiratory bronchioles open into alveolar
  ducts, which end at alveolar sacs.
• Many alveoli are interconnected at each alveolar
  sac.

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The Respiratory Membrane

• The respiratory membrane consists of
• 1. A simple squamous alveolar epithelium
• 2. A capillary endothelium
• 3. Their fused basement membranes.

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• Surfactant cells produce an oily secretion that
  keeps the alveoli from collapsing.
• Alveolar macrophages engulf foreign particles.

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The Lungs and Pleural Cavities

• The lungs are made up of five lobes three in the
  right lung and two in the left lung.
• Each lung occupies a single pleural cavity lined
  by a pleura (serous membrane)

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Respiratory Physiology

• Respiratory physiology focuses on a series of
  integrated processes
• Pulmonary ventilation or breathing.
• Gas exchange or diffusion between the alveoli and
  circulating blood and between the blood and
  interstitial fluids
• Gas transport between the blood and interstitial
  fluids.

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Pulmonary Ventilation

• A single breath, or respiratory cycle, consists
  of an inhalation (inspiration) and exhalation
  (expiration)
• The relationship between the pressure inside the
  respiratory tract and atmospheric pressure
  determines the direction of airflow.

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• The diaphragm and the external intercostal
  muscles are involved in quiet breathing, in which
  exhalation is passive.
• Accessory muscles become active during the active
  inspiratory and expiratory movement of forced
  breathing in which exhalation is active.

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• The vital capacity includes the tidal volume plus
  the expiratory reserve volume and the inspiratory
  reserve volume.
• The air left in the lungs at the end of maximum
  expiration is the residual volume.

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Gas Exchange

• Gas exchange involves external respiration,
• the diffusion of gases between the blood and
  alveolar air across the respiratory membrane,

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• Internal respiration
• The diffusion of gases between blood and
  interstitial fluid across the single endothelial
  cells of capillary walls.

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Gas Transport

• Blood entering peripheral capillaries delivers
  oxygen and absorbs carbon dioxide.
• The transport of oxygen and carbon dioxide in the
  blood involves reaction that are completely
  reversible.

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• Over the range of oxygen pressures normally
  present in the body, a small change in plasma PO2
  will mean a large change in the amount of oxygen
  bound or released by hemoglobin

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• Aerobic metabolism in peripheral tissues
  generates carbon dioxide.
• Roughly 7 percent of the CO2 transported in the
  blood is dissolved in the plasma
• 23 is bound as carbaminohemoglobin
• The rest is converted to carbonic acid which
  dissociates into a hydrogen ion and a bicarbonate
  ion.

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The Control of Respiration

• Large-scale changes in oxygen demand require the
  integration of cardiovascular and respiratory
  responses.

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Local Control of Respiration

• Arterioles leading to alveolar capillaries
  constrict when oxygen is low and bronchioles
  dilate when carbon dioxide is high

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The Respiratory Centers of the Brain

• The respiratory center include three pairs of
  nuclei in the reticular formation of the pons and
  medulla oblongata.
• These nuclei regulate the respiratory muscles and
  control the respiratory rate and the depth of
  breathing.
• The respiratory rhythmicity centers in the
  medulla oblongata set the basic pace for
  respiration.

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The Reflex Control of Respiration

• The inflation reflex prevents overexpansion of
  the lungs during forced breathing.
• The deflation reflex stimulates inspiration when
  the lungs are collapsing.
• Chemoreceptor reflexes respond to changes in the
  pH PO2 and PCO2 of blood and cerebrospinal fluid.

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Control by Higher Centers

• Conscious and unconscious thought processes can
  affect respiration by affecting the respiratory
  centers or the motor neurons controlling
  respiratory muscles.

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Respiratory Changes at Birth

• Before delivery, the fetal lungs are fluid-filled
  and collapsed.
• After the first breath, the alveoli normally
  remain inflated for the life of the individual.

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Aging and the Respiratory system

• The respiratory system is generally less
  efficient in the elderly because
• Elastic tissue deteriorates, lowering the vital
  capacity of the lungs
• Movements of the chest cage are restricted by
  arthritic changes and decreased flexibility of
  costal cartilages
• Some degree of emphysema is normal in the elderly.