Respiratory SystemRespiratory SystemChapter 15Chapter 15

Respiratory SystemRespiratory SystemChapter 15Chapter 15

The main function of the respiratory system is to supply oxygen to, & eliminate carbon dioxide from the body

In order to accomplish this task, the respiratory system must work in conjunction with the cardiovascular system

“Respiration” refers to the overall exchange of gases between the atmosphere, blood & cells

Respiration involves 3 processes

Pulmonary ventilation

Gas exchange (gas diffusion)

External respiration

Internal respiration

Gas transport

Anatomy OverviewNasal cavity

Pharynx

Larynx

Trachea

Bronchi

RightLung

Left Lung

Bronchioles

Respiratory bronchioles

Alveolar duct

Alveoli

The respiratory tract includes: Nose (nasal cavity) Pharynx (nasopharynx, oropharynx, laryngopharynx) Larynx Trachea Bronchi (primary, secondary (lobar), tertiary (segmental) Bronchioles Terminal bronchioles Alveolar ducts Alveoli

Histology

Respiratory Epithelium = Pseudostratified Ciliated Columnar (PSCC)

Nose (nasal cavity)Air normally enters through external nares through nasal vestibule into nasal cavity.

Functions of nasal cavity include: warming, moistening & filtering air; olfaction

PharynxAir passes from nasal cavity into nasopharynx, past oropharynx & through laryngopharynx to larynx

Nasopharynx lined with PSCC epithelium, but oro & laryngopharynx lined with stratified squamous epithelium

LarynxAir passageway made of 9 pieces of cartilage – (1) Thyroid cartilage, (1) Epiglottis, (1) Cricoid cartilage, (2) Arytenoid, (2) Corniculate, (2) Cuneiform

A.K.A your “voicebox” because it contains the vocal cords

Thyroid cartilage – protects anterior & lateral walls of airway

Epiglottis – leaf-shaped cartilage that protects opening (“glottis”) of airway when swallowing

Cricoid cartilage – complete ring of cartilage; protects posterior wall of airway; attaches to trachea

Arytenoid, corniculate & cuneiform cartilages – attach to upper (false) vocal folds & lower (true) vocal cords

Trachea

Tough but flexible “windpipe”, anterior to esophagus

attached to cricoid cartilage (at about C6 vertebral level) & ends within mediastinum by branching into left & right primary bronchi (at T5 vertebral level)

End of trachea known as Carina

Carina

Trachea Lined with respiratory epithelium

“C”-shaped pieces of hyaline cartilage protecting airway while allowing for swallowing

Trachealis muscle (smooth muscle) runs across posterior wall of trachea connecting ends of tracheal cartilage

Bronchi

Carina

Trachea splits into a left & right primary bronchus which enters into the hilus (hilum) of each lung

Within the lung, the primary bronchi branch into secondary (lobar) bronchi (3 in right lung/2 in left lung)

Secondary bronchi then branch into 10 tertiary (segmental) bronchi

Tertiary bronchi then continue to branch into smaller & smaller bronchi & then into very narrow bronchiolesThis branching patterns

creates the “bronchial tree”

Changes In AirwayAs you go further down into the bronchial tree of each lung, changes in the airway occur: increased number of airways (1 primary; 2 or 3 secondary; 10 tertiary bronchi; 6000 terminal bronchioles; millions of alveolar ducts) decreased diameter of each airway decreased amount of cartilage in the airways (no cartilage at all by terminal bronchioles) increased amount of smooth muscle (relative to diameter) lining epithelium changes from PSCC simple squamous epithelium (in alveoli)

Lungs Located within the thoracic cavity, surrounded by the double-layered pleural membrane –

parietal pleura – lines cavity wall

visceral pleura – covers the lungs

Lungs- Anatomical Features

Apex – extends 1” above clavicle

Base – rests on diaphragm

Right lung Left

lung

Superior lobe

Middle lobe

Inferior lobe

Horizontal fissure

Oblique fissure

Superior lobe

Inferior lobe

Oblique fissure

Cardiac notch

Hilum – at medial surface; where primary bronchus, pulmonary artery & veins enter/exit lung

Each lung has a primary bronchus entering at the hilum

Each lobe of a lung has a secondary (a.k.a. lobar) bronchus

Lobes are functionally divided into bronchopulmonary segments & each segment has a tertiary (segmental) bronchus

Segments are functionally divided by elastic CT partitions into many lobules & each lobule receives a terminal bronchiole

Airways within Lungs

Relationship of Airways & Pulmonary Vessels

As airways branch within lungs, they are accompanied by branches of the pulmonary artery (carrying de-oxygenated blood into the lungs), & branches of the pulmonary veins (carrying oxygenated blood out of the lungs)

As the alveolar ducts expand to form alveoli, pulmonary arterioles will branch to form a network of pulmonary capillaries, surrounding the alveoli

Alveoli Alveoli are expanded chambers of epithelial tissue that are the exchange surfaces of the lungs

There are about 150 million alveoli in each lung

Multiple alveoli usually share a common alveolar duct, creating “alveolar sacs”

Alveoli

There are three types of cells found within alveoli:

Alveolar Squamous epithelial (aka “type I”) cells – primary cells making up the wall of the alveoli

Septal (aka “type II”) cells – sectrete “surfactant” to reduce surface tension which prevents alveoli from sticking together & allows for easier gas exchange

Alveolar macrophages (aka “dust cells”) – phagocytic cells that remove dust, debris & pathogens

Gas “exchange” (external respiration) occurs across the Respiratory membrane – the fused membranes of the alveolar epithelium & the pulmonary capillary endothelium

“Respiration” refers to the overall exchange of gases between the atmosphere, blood & cells

Respiration involves 3 processes

Pulmonary ventilation

Gas exchange

External respiration

Internal respiration

Gas transport

Physiology of Respiration

Physiology of Respiration

Two phases of ventilation:

Inspiration

active process involving contraction of diaphragm & external intercostal muscles

Expiration

normally passive due to relaxation of above muscles

can be made active (forced expiration) due to contraction of abdominals & internal intercostal muscles

Pulmonary Ventilation – “exchange” (movement) of gases between the atmosphere & lungs; movement of gases occurs because of pressure differences between the atmosphere (atmospheric pressure (Po)) & lungs (intrapulmonic pressure (Pi))

Pulmonary Ventilation

Lung Volumes & Capacities Respiratory frequency (f) – number of ventilations (inspiration+expiration) per minute

Tidal volume (TV) - amount of air moved in or out of the lungs during a normal breath

Minute ventilation (VE=TV x f)- amount of air inhaled or exhaled in one minute

Lung Volumes & Capacities (cont.) Inspiratory reserve volume (IRV) – amount of air that can be inhaled after a normal inspiration (above the resting TV)

Inspiratory capacity (IC = TV+IRV) – amount of air inhaled after a normal expiration

Expiratory reserve volume (ERV) – amount of air that can be exhaled after a normal expiration

Residual volume (RV) – amount of air remaining in lungs even after maximal expiration

Lung Volumes & Capacities (cont.) Vital capacity (VC=TV+IRV+ERV) – maximum amount of air you can exhale, following a maximal inhalation

Total lung capacity (TLC=TV+IRV+ERV+RV) – maximum amount of air in your lungs, following a maximal inhalation

Gas Exchange (gas diffusion) External respiration - the diffusion of O2 & CO2 between the alveoli & blood across the respiratory membrane

occurs because of pressure differences of each gas within alveolar air & pulmonary (deoxygenated) blood

results in creation of oxygenated blood

Gas Exchange Internal respiration – the diffusion of O2 & CO2 between the blood & interstitial fluid across the endothelium of systemic capillaries

occurs because of pressure differences of each gas between systemic (oxygenated) blood & interstitial fluid

results in creation of deoxygenated blood

Gas Transport - O2

During external respiration O2 diffuses across respiratory membrane into blood plasma

The majority of O2 (98.5%) then immediately diffuses into RBCs & binds (loosely) to the iron (Fe+3) in hemoglobin for transport

only 1.5% is transported freely dissolved within plasma

Gas Transport – CO2 During internal respiration CO2 diffuses from interstitial fluid into plasma

Only 7% of CO2 remains in plasma for transport, the rest diffuses into RBCs

Within RBCs 23% binds to the globin proteins of hemoglobin (Hb) (“carbaminohemoglobin”)

Most (70%) of CO2 gets converted within RBCs to bicarbonate ions (HCO3

-) – CO2 + H2O H2CO3 (carbonic acid) HCO3- + H+

HCO3- diffuses out to plasma (as Cl- diffuses in); the H+ attach to

Hb to maintain normal plasma pH (so plasma does not become too acidic)

Control of RespirationUnconscious control of breathing occurs through the activity of the respiratory centers of the brain

Medulla oblongata – “Rhythmicity center” controls basic pattern of breathing; inhale 2 seconds, exhale 3 seconds

Pons – has 2 centers (apneustic & pneumotaxic centers) that can unconsciously modify the rate & depth of respiration

Respiratory centers can be influenced by mechanoreceptors (i.e. stretch receptors in lungs) & chemoreceptors (sensitive to CO2 levels, arterial pH, & O2 levels) in the body, as well as by higher brain centers