The Respiratory System

Respiratory System

Respiratory System

Organs of the Respiratory System

• Upper respiratory system– Nose, nasal cavity, pharynx, glottis and larynx

• Lower respiratory system– Trachea, bronchus, bronchioles, and lungs– Diaphragm-skeletal muscle; functions in ventilation

All airways that carry air to lungs:• Nose, pharynx, larynx, trachea bronchi, bronchioles, and terminal

bronchioles

Sites within lungs where gas exchange occurs• Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli

Nose

• Structure – External nares nasal cavity internal nares– Nasal septum divides nose into two sides– Nasal conchae covered by mucous membrane

• Functions– Warm, humidify, filter/trap dust and microbes

• Mucus and cilia of epithelial cells lining nose

– Detect olfactory stimuli– Modify vocal sounds

Large stiff Hairs

Nose

Sinuses

Nasal Cavity

Olfactory Receptors

Pharynx

Pharynx

• Known as the “throat”• Structure

– Funnel-shaped tube from internal nares to larynx

• Three regions (with tonsils in the upper two)– Upper: nasopharynx; posterior to nose

• Adenoids and openings of auditory (Eustachian) tubes

– Middle: oropharynx; posterior to mouth• Palatine and lingual tonsils are here

– Lower: laryngopharynx• Connects with both esophagus and larynx: food and air

larynx

• “Voice box” • Made largely of cartilage

– Thyroid cartilage: V-shaped • “Adam's apple”: projects more anteriorly in males• Vocal cords “mucoso folds

– Epiglottis: leaf-shaped piece; covers airway• During swallowing, larynx moves up so epiglottis

covers opening into trachea-glottis

– Cricoid cartilage: inferior most portion– Arytenoids (paired, small) superior to cricoid

Larynx

Vocal Cords: mucosal folds

Lower Respiratory System: Larynx

Trachea

• “Windpipe” • Location

– Anterior to esophagus and thoracic vertebrae– Extends from end of larynx to primary bronchi

• Structure– Lined with pseudostratified ciliated columnar mucous

membrane: traps and moves dust upward– C-shaped rings of cartilage support trachea, keep

lumen open during exhalation

• Tracheostomy: opening in trachea for tube

Trachea

• The methods outlined above, coughing, backblows, and abdominal thrusts (Heimlich maneuver) have a very high rate of success. In the event, however, that these methods fail to dislodge the obstructing material from the air pipe (trachea), a tracheotomy must be considered.

Larynx

tracheotomy

Cricoid Cartilage

Lungs

• Two lungs: left and right– Right lung has 3 lobes– Left lung has 2 lobes

• Lungs surrounded by pleural membrane– Parietal pleura attached to diaphragm and

lining thoracic wall– Visceral pleura attached to lungs– Pleural cavity with little fluid between pleurae

Lung Lobes

Bronchi

• Structure of bronchial tree– Bronchi contain cartilage rings– Primary bronchi enter the right and left lungs – In lungs, branching secondary bronchi

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

– Tertiary bronchi terminal bronchioles• These smaller airways

– Have less cartilage, more smooth muscle. – In asthma, these airways can close.

Bronchioles

Respiratory bronchioles– Lined with nonciliated epithelium

Alveolar ducts

Alveolar sacs

Surrounded by alveoli

Terminal Alveolar

Alveoli

• Cup-shaped

• Alveoli: composed of three types of cells– Lined with thin alveolar cells (simple squamous); sites

of gas exchange– Surfactant-secreting cells. Surfactant:

• Lowers surface tension (keeps alveoli from collapsing) • Humidifies (keeps alveoli from drying out)

– Alveolar macrophages: “cleaners”• alveoli + capillary

– Gases diffuse across these thin epithelial layers: air blood

Alveolar Sac

Surfactants

Air

• Mixture of gases (N2, O2,, CO2, H2O, and others)

• Each gas has own partial pressure, such as PO2 or PN2

• Sum of all partial pressures = atmospheric pressure

• Each gas diffuses down its partial pressure

Diffusion

• Diffusion across alveolar-capillary membrane– O2 diffuses from air (PO2 ~105 mm Hg) to pulmonary

artery (“blue”) blood (PO2 ~40 mm Hg).

(Partial pressure gradient = 65 mm Hg)

• Continues until equilibrium (PO2 ~100-105 mm Hg)

– Meanwhile “blue” blood (PCO2 ~45) diffuses to alveolar air (PCO2 ~40) (Partial pressure gradient = 5 mm Hg)

• Occurs throughout body

• O2 diffuses from blood to cells: down partial pressure gradient

• PO2 lower in cells than in blood because O2 used in cellular metabolism

• Meanwhile CO2 diffuses in opposite direction: cells blood

Internal and

External Respiration

Transport of Carbon Dioxide• CO2 diffuses from tissues into blood

• CO2 carried in blood:

– Some dissolved in plasma (7%)– Bound to proteins including hemoglobin (23%)– Mostly as part of bicarbonate ions (70%)

• CO2 + H2O H+ + HCO3-

• Process reverses in lungs as CO2 diffuses from blood into alveolar air exhaled

Transport of Oxygen and

Carbon Dioxide

External Respiration

• Bicarbonate ions

• Carbonic ahydrase

• Acidosis

• Alkalosis

• Carbaminohemoglobin

• Oxyhemoglobin

• deoxyhemoglobin

Control of Respiration• Nervous Control of Breathing is located in the

medulla oblongata of brain• Chemical control are sensory receptors in the

body that are sensitive to chemical composition of body fluids

• Two sets of chemoreceptors sensitive to pH can cause breathing to speed up.

Location: medulla oblongata and in the carotid arteries and aortic bodies .

These chemoreceptors are stimulated by the Carbon dioxide concentration.

Regulation of Respiratory Center

• Chemoreceptor input to increase ventilation– Central receptors in medulla: sensitive to H+ or

PCO2

– Peripheral receptors in arch of aorta + common carotids: respond to PO2 as well as H+ or PCO2 in blood

• Blood and brain pH can be maintained by these negative feedback mechanisms

Mechanism of Breathing

• Inspiration: rib cage moves up and out

• External intercostal muscles pull the ribs outward

• Diaphragm contracts and move down

• When pressure in lungs decreases, air comes rushing in.

Expiration

• Rib cage moves down and in

• Internal intercostal muscles pull the ribs inward during forced expiration

• Diaphragm relaxes and move up

• When pressure in lungs increases, air is pushed out