Ch.22 - Respiratory System (Part 1)

Respiration

refers to ventilation of the lungs (breathing)

• gas exchange

8 Functions of Respiration:

1. Gas Exchange

• O2 and CO2 are exchanged between blood and air

• gases move independently of each other

2. Communication

• involved in production of speech and sound

3. Olfaction

• sense of smell

4. Acid-Base Balance

• influences pH of bodily fluids by eliminating CO2

5. Blood Pressure Regulation

• by helping make angiotensin II (BP regulation hormone)

6. Blood and Lymph Flow

• breathing creates pressure gradients between thorax and abdomen that promote flow of lymph and blood

7. Blood Filtration

• lungs filter small clots

8. Expulsion of abdominal contents

• holding your breath helps with urination, defecation, and childbirth (called valsalva maneuver)

Principle Organs of the Respiratory System

nose, pharynx, larynx, trachea, bronchi, and lungs

• alveoli stops incoming air

Conducting Zone of the Respiratory System

zone made for moving air

• Includes those passages that serve only for airflow

• NO gas exchange in this zone

• lined with a mucous membrane,

  • filters, humidifies, and heats the air

• Goes from the nostrils through the major bronchioles

Respiratory Zone of the Respiratory System

Where we have gas exchange

• Consists of alveoli and other gas exchange regions

Upper Respiratory Tract

is in head and neck

• more specifically, it goes from the nose to the larynx

Lower Respiratory Tract

includes the organs of the thorax

• goes from trachea to lungs (neck down)

Functions of the Nose

• Warms, cleanses, and humidifies inhaled air

• Detects odors

• Serves as a resonating chamber that amplifies voice

Structure of the Nose

Nose extends from the nostrils (nares) to the posterior nasal apertures (choanae / posterior openings)

Structures include:

• Nasal Fossae

• Vesibule

• Nasal Conchae

• Meatus

• Olfactory Epithelium

• Respiratory Epithelium

• Erectile Tissue

Nasal Fossae

right and left halves of nasal cavity

• Nasal septum divides the nasal cavity into the 2 halves

• Ethmoid and sphenoid bones form the roof of the nasal cavity

• Hard palate forms the floor of the nasal cavity

  • Separates the nasal cavity from the oral cavity and allows you to breathe while you chew food

Where do the paranasal sinuses and nasolacrimal ducts drain into?

the nasal cavity

Vestibule

beginning of the nasal cavity

• small, dilated chamber/open space just inside the nostrils

• Lined with stratified squamous epithelium

• Have vibrissae

• nasal cavity gets bigger as we move posteriorly, and then gets narrow again

Vibrissae

stiff guard hairs that block insects and debris from entering nose

Nasal Conchae

3 folds of tissue that occupy the chamber behind the vestibule

• consists of the superior, middle, and inferior nasal conchae (turbinates)

• Project from lateral walls toward the septum

• Each concha has a meatus

  • a narrow air passage beneath each concha

• Narrowness and turbulence ensure that most air contacts mucous membranes

• Cleans, warms, and moistens the air

• most humidity is made with the nasal conchae

Olfactory Epithelium

detects odors

• Covers a small area of the roof of the nasal fossa and neighboring parts of the septum and superior concha

• there are immobile cilia on sensory cells that bind to odorant molecules

Respiratory Epithelium

lines the rest of nasal cavity except the vestibule

• has ciliated pseudostratified columnar epithelium with goblet cells

• Cilia are motile

• Goblet cells secrete mucus and the cilia propel the mucus back toward the pharynx

  • mucus is swallowed into the digestive tract

Erectile Tissue (Swell Body)

tissue that swells as it absorbs more blood

• In the nose, this tissue is located in the epithelium of the inferior concha

• Every 30 to 60 minutes, tissue on one side swells with blood

• This restricts airflow through that fossa, so most air is directed through the other nostril

• This allows the engorged side time to recover from drying

Pharynx

The throat

• a muscular funnel extending about 5 inches from the choanae to the larynx

• part of body that can have food and air traveling through it

• 3 regions of pharynx

  • Nasopharynx

  • Oropharynx

  • Laryngopharynx

Nasopharynx

Receives auditory tubes and contains the pharyngeal tonsil

• its 90° downward turn traps large particles

• we don’t usually get food or water in the nasopharynx

• passes only air and is lined by pseudostratified columnar epithelium

  • has mucous membrane

Oropharynx

Space between soft palate and epiglottis

• Contains palatine tonsils

• passes air, food, and drink

• is lined by stratified squamous epithelium (non-keratinized)

Laryngopharynx

space from the epiglottis to the cricoid cartilage

• Esophagus begins at that point

• passes air, food, and drink 

• lined by stratified squamous epithelium (non-keratinized)

Larynx

aka voice box

• chamber made of hyaline cartilage about 4 cm (1.5 in.) long

• Very sensitive structure

• Primary function is to keep food and drink out of the airway

  • Addition role of phonation

    • the production of sound

• 9 cartilages make up the larynx

• Ligaments suspends larynx from hyoid and hold it together

9 cartilages that make up the framework of the larynx:

3 are solitary and relatively large:

• Epiglottic cartilage

• Thyroid cartilage

• Cricoid cartilage

3 smaller, paired cartilages

• Arytenoid cartilages (2)

• Corniculate cartilages (2)

• Cuneiform cartilages (2)

Epiglottis

flap of tissue that guards the superior opening of the larynx (the glottis)

• At rest, it stands almost vertically

• During swallowing, extrinsic muscles of larynx pull the larynx upward

• Then, the tongue pushes the epiglottis down to meet the larynx

• This closes the airway and directs food to the esophagus behind it

• Vestibular folds of the larynx play a greater role in keeping food and drink out of the airway

Epiglottic Cartilage

a spoon-shaped supportive plate in the epiglottis

• most superior one

Thyroid Cartilage

is the largest cartilage of the larynx

• makes a laryngeal prominence called the Adam’s apple

  • shield-shaped

  • Testosterone stimulates its growth, so it is larger in males

Cricoid Cartilage

connects the larynx to the trachea

• ring-like

Arytenoid cartilages (2)

posterior to the thyroid cartilage

• a pair

Corniculate cartilages (2)

attached to arytenoid cartilages like a pair of little horns

• a pair

Cuneiform cartilages (2)

supports the soft tissue between the arytenoids and epiglottis

• a pair

Thyrohyoid Ligament

suspends the larynx from the hyoid

• starts at thyroid cartilage and goes to the hyoid bone

Cricotracheal Ligament

suspends trachea from larynx

• starts at cricoid cartilage and goes to the trachea

Superior Vestibular Folds

Called false vocal cords

• Close the larynx during swallowing

• Play no role in speech

• have a mucous membrane

Vocal Cords

Produce sound when air passes between them

• vocal cords vibrate when air goes out of respiratory tract

• Contain vocal ligaments

  • Covered with stratified squamous epithelium

  • Suited to endure vibration and contact

• Vocal cords produce crude sounds that are formed into words by actions of pharynx, oral cavity, tongue, and lips

Glottis

the vocal cords and the opening between them

Male Vs. Female Vocal Cords

Male vocal cords are usually:

• Longer and thicker

• Vibrate more slowly

• Produce lower-pitched sound

Loudness

Determined by the force of air passing between the vocal cords

Pitch

Higher tension results in higher pitch and lower tension in lower pitch

Trachea

the windpipe (a rigid tube)

• is a conducting zone structure (moves air, no gas exchange)

• anterior to the esophagus

• 16-20 C-Shaped hyaline cartilage rings prop trachea open and prevent collapse during inhalation

• Trachealis muscle goes across the opening in the rings

  • the gap in the rings allow room for the esophagus to expand as food passes by

  • Contracts or relaxes to adjust airflow

• Inner lining

  • has ciliated pseudostratified columnar epithelium

  • secretes a ton of mucus

  • has a mucociliary escalator

• Trachea branches off into the right and left main bronchi

Mucociliary Escalator

mechanism for debris removal in the trachea

• Mucus traps inhaled particles

• Upward beating cilia drives mucus toward the pharynx where it is swallowed

Middle Tracheal Layer

connective tissue beneath the tracheal epithelium

• Contains lymphatic nodules, mucous and serous glands, and the tracheal cartilages

Right and Left Main Bronchi

the trachea branches off at the level of sternal angle to form the main bronchi

• the ridge between the left and right bronchi forms the carina

Carina

the internal medial ridge in the lowermost tracheal cartilage

• Directs the airflow to the right and left

• has lots of pressure receptors (built in panic button)

• pressure on it causes violent coughing

• if the particles go past the carina, it is much more difficult to get out of the lungs

Tracheostomy

procedure where one makes a temporary opening in the trachea and inserts a tube to allow airflow

• Prevents asphyxiation due to upper airway obstruction

• Inhaled air bypasses the nasal cavity and is hot humidified

• If tube is left in for too long, it will dry out mucous membranes of the respiratory tract

  • membrane will become encrusted and interfere with clearance of mucus from tract, promoting infection

Anatomy of the Lung

• Base: broad concave portion resting on diaphragm

• Apex: tip that projects just above the clavicle

• Costal surface: pressed against the ribcage

• Mediastinal surface: faces medially toward the heart

  • has the hilum

Lungs are asymmetrical because of surrounding organs and major blood vessels

Hilum

slit through which the lung receives the main bronchus, blood vessels, lymphatics, and nerves

Right Lung Vs. Left Lung

Right lung

• Shorter than the left lung because liver rises higher on the right

• Has 3 lobes: superior, middle, and inferior

  • separated by horizontal and oblique fissure

Left lung

• Tall and narrow because the heart tilts toward the left and occupies more space on this side of mediastinum

• Has indentation called the cardiac impression

  • where the heart extends and presses into the left lung

• Has 2 lobes: superior and inferior

  • separated by a single oblique fissure

Bronchial Tree

a branching system of air tubes in each lung

• goes from the main bronchus to 65,000 terminal bronchioles

• 3 types of bronchi:

  • Primary Bronchi

  • Secondary Bronchi

  • Tertiary Bronchi

• All bronchi are lined with ciliated pseudostratified columnar epithelium

• Cells grow shorter and the epithelium thinner as we progress distally

• All divisions of the bronchial tree have a large amount of elastic connective tissue

  • Contributes to the recoil that expels air from lungs

• Bronchi have cartilage propping them open

Main (primary) Bronchi

the two main branches off of the trachea

• are supported by C-shaped hyaline cartilage rings

Lobar (secondary) Bronchi

branches that send air to an individual lobe of the lung

• supported by crescent-shaped cartilage plates

• One for each lobe of lung: 3 in the right lung and 2 in the left

Segmental (tertiary) Bronchi

branches within the lobe of a lung

• supported by crescent-shaped cartilage plates

• 10 on the right, 8 on the left

• tertiary bronchi supply a specific bronchopulmonary segment

  • functionally independent unit of the lung tissue

Bronchioles

smaller tubes in the lungs that move air around

• don't have or need cartilage holding them open

• 1 mm or less in diameter

• Have ciliated cuboidal epithelium

• Well-developed layer of smooth muscle

• Divides into 50 to 80 terminal bronchioles

Terminal Bronchioles

Final branches of the conducting zone

• Have no mucous glands or goblet cells

• Have cilia that move back mucus draining into them using the mucociliary escalator

• Each terminal bronchiole gives off two or more smaller respiratory bronchioles

Respiratory Bronchioles

• have gas exchange with blood stream,

• have simple squamous epithelium

• Have alveoli budding from their walls

• Considered the beginning of the respiratory zone since alveoli participate in gas exchange

• Divide into 2 to 10 alveolar ducts

• End in alveolar sacs

Alveolar Sacs

clusters of alveoli arrayed around a central space called the atrium

Alveoli

are respiratory zone structures that make up the alveolar sacs

• there are 150 million alveoli in each lung, providing lots of surface area for gas exchange

• simple squamous epithelium to maximize diffusion

• no mucus and no structures to remove the mucous

• 3 types of cells that make up the alveoli:

  • Squamous Alveolar Cells (Type 1)

  • Great Alveolar Cells (Type 2)

  • Alveolar Macrophages (Dust Cells)

• Each alveolus is surrounded by a basket of capillaries supplied by the pulmonary artery

Squamous Alveolar Cells (Type 1)

Thin, broad cells that allow for rapid gas diffusion between the alveoli and the blood

• most common 

  • covers 95% of alveoli surface area

Great Alveolar Cells (Type 2)

Round to cuboidal cells that cover the remaining 5% of alveolar surface

• Repair the alveolar epithelium when the squamous (type I) cells are damaged

• Secrete pulmonary surfactant (soap)

  • makes it easier for us to open up the airways

  • have a polar region and nonpolar region (amphipathic)

  • this allows them to H bond to water and reduce the amount of H bonds present when walls collapse

Alveolar Macrophages (Dust Cells)

Cells that wander through the lumens of alveoli and the connective tissue between them

• Keep alveoli free from debris by phagocytizing dust particles

• 100 million dust cells die each day as they ride up the mucociliary escalator to be swallowed and digested with their load of debris

Respiratory Membrane

thin barrier between the alveolar air and blood

• where gas exchange occurs

  • gases move independently

• the simple squamous alveolar cells and capillaries share a basement membrane that glues them together

• CO2 goes from blood to alveolar air

• Oxygen goes into the blood from the alveoli

How do we prevent fluid from accumulating in alveoli?

• Alveoli are kept dry by absorption of excess liquid by blood capillaries

• Lungs have more extensive lymphatic drainage than any other organ in the body

• Low capillary blood pressure also prevents the rupture of the delicate respiratory membrane

Pleural Membrane

serous membrane of the lungs (double membrane)

• Has a parietal pleura and a visceral pleura

• Has a pleural cavity in-between the two pleura

Visceral Pleura

serous membrane that covers the lungs

Parietal Pleura

attaches to the mediastinum, the inner surface of the rib cage, and the superior surface of the diaphragm

Pleural Cavity

the potential space between the pleurae

• Normally no room between the membranes, but contains a film of slippery pleural fluid

Functions of the Pleurae and Pleural Fluid

• Reduces friction

  • pleural fluid is slippery, causing less friction

• Creates a pressure gradient

  • Lower pressure than atmospheric pressure

  • assists lung inflation

  • Creates a pressure gradient to help the pleura hydrogen bond to each other

• Compartmentalization

  • Prevents spread of infection from one organ in mediastinum to others

Pulmonary Ventilation

consists of a repetitive cycle of inspiration (inhaling) and expiration (exhaling)

• Flow of air in and out of lung depends on a pressure difference between air within lungs and outside body

• Respiratory muscles change the lung volume and creates differences in pressure relative to the atmosphere

• pressure and volume are inversely proportional

Respiratory Cycle

one complete inspiration and expiration

• Quiet respiration: while at rest, effortless, and automatic

• Forced respiration: deep, rapid breathing, such as during exercise

  • happens with sympathetic activation or high metabolic needs

Diaphragm

• most important muscle for inspiration

• Prime mover of respiration

• located below the lungs

• Contraction flattens the diaphragm and pulls the abdominal organs down, making the thoracic cavity larger and pulling more air into the lungs

• Relaxation allows diaphragm to bulge upward again, compressing the lungs and expelling air

• Accounts for two-thirds of airflow

External Intercostal Muscles

used to elevate the ribs to make thoracic cavity larger

• Stiffen the thoracic cage during respiration

• Prevent it from caving inward when diaphragm descends

• Contribute to enlargement and contraction of thoracic cage

• Add about one-third of the air that ventilates the lungs

Scalenes

Synergist muscles to the diaphragm

• Fix or elevate ribs 1 and 2

Normal Quiet Expiration

An energy-saving passive process

• exhaling does not involve activation of muscles, instead we rely on elastic recoil of the lungs and thoracic cage

• allows our lungs to naturally contract on themselves for exhalation

• As muscles relax, structures recoil to the original shape and size of the thoracic cavity

  • results in airflow out of the lungs

Forced Expiration

uses muscles in addition to the elastic recoil

• uses the rectus abdominis, internal intercostals, and other lumbar, abdominal, and pelvic muscles

• the greatly increased abdominal pressure pushes the viscera up against the diaphragm, increasing thoracic pressure and forcing air out

• Important for “abdominal breathing”

Brainstem Regulatory Centers

the brain stem regulates autonomic respiration using 3 regulatory centers:

• Ventral respiratory group (VRG)

• Dorsal respiratory group (DRG)

• Pontine respiratory group (PRG)

Ventral Respiratory Group (VRG)

Primary generator of the respiratory rhythm

• Produces a respiratory rhythm of 12 breaths per minute

• located on anterior of medulla

Dorsal Respiratory Group (DRG)

Modifies the rate and depth of breathing

• Receives influences from external sources

Pontine Respiratory Group (PRG)

Modifies the respiratory rhythm by outputs to both the VRG and DRG

• modifies the respiratory rhythm in response to external stimuli

• Adapts breathing to special circumstances such as sleep, exercise, vocalization, and emotional responses

Hyperventilation

anxiety-triggered state where breathing is so rapid that it expels CO2 from the body faster than it’s produced

• As blood CO2 levels drop, the pH rises causing the cerebral arteries to constrict

  • makes blood pH more basic

• this causes there to be less blood and O2 going to the brain, which may cause dizziness or fainting

• Can be controlled by having the person rebreathe the expired CO2 from a paper bag

Voluntary Control of Breathing

• Voluntary control over breathing originates in the motor cortex

  • signals bypass brainstem to respiratory neurons

• voluntary control over breathing is temporary, the ANS will overrride

• Breaking point: when CO2 levels rise and the blood pH get too low to a point where automatic controls override one’s will