Lecture 1 (Resp)

Respiratory physiology

study of how oxygen is brought into the lungs and then delivered to the tissue and how carbon dioxide is eliminated from the tissue and from the system

Respiratory System Functions (6)

1. Provides oxygen (O2 ) and eliminates carbon dioxide (CO2 ) (Homeostatic regulation of blood gases)

2. Protects against microbial infection (Filtering action)

3. Regulates blood pH (In coordination with the kidneys)

4. Contributes to phonation

5. Contributes to olfaction

6. Is a reservoir for blood

Lungs

have a very ramified, branched airway system

Fundamental unit of the respiratory system

alveoli

alveoli

embedded in a dense network and tissue characterized by the presence of smooth muscle tissue, smooth muscle cells and connective tissue

amount of capillaries in lungs

Large number of capillaries

Components of Resp system

1. upper airways

2. trachea

3. lungs

4. muscles of respiration

5. rib cage & pleura

6. CNS part that regulates respiration

Upper Airways

- Pharynx: composed of the nasopharynx and the laryngopharynx

- Larynx: contains the vocal cords

- Trachea

How does air travel through upper airways?

- Air enters through the nasal cavity and oral cavity in the upper airway

Air passage

larynx → trachea → two primary bronchi → lungs

Trachea and primary bronchi

- C-shape cartilage (Anteriorly)

‒ Smooth muscle (Posteriorly)

- This provides protection for the airway and gives elasticity

Bronchi

-Plates of cartilage & smooth muscle

- C-shaped rings of cartilage replaced by plates of cartilage and smooth muscle

Bronchioles

Structure is provided by smooth muscle only

What is at each branch?

a reduction in the bronchiole size

airways beyond the larynx that are divided into 2 zones:

conducting zone and respiratory zone

Conducting zone

- contains trachea, primary bronchi, bronchioles & terminal bronchioles - no alveoli --> no gas exchange

- anatomical dead space b/c it is not available for gas exchange

Respiratory zone

- further down in branching of airways & contains the alveoli that become more and more numerous with ramification/branching

- Contains respiratory bronchioles, alveolar ducts and alveolar sacs

- Where gas is exchanged

- Air that enters the respiratory zone is available for gas exchange

Terminal bronchioles

smallest airways without alveoli

Respiratory bronchioles

have occasional alveoli

alveoli sacs

contain a large number of alveoli

Tracheobronchial tree

- Begin at generation 0 at trachea and arrive at generation 23 at alveolar sacs

- diameter and length of the airways at each generation decrease

- number of branches at each specific generation level tends to increase

- Airways are smaller but more numerous towards the alveolar sacs

- Total surface area increases towards the alveolar sacs

generation

What each branching is called

Alveoli structure

- Tiny sacs with a very thin wall

- Highly vascularised → many capillaries that contact the alveolar surface

Amount of blood in capillaries

is variable and changes with metabolic demand

Type I alveolar cells

- flat epithelial cells

- internal surface of alveoli is lined with liquid that contains a surfactant

- Do not divide; susceptible to inhaled or aspirated toxins

Type II alveolar cells

- Not found frequently in alveoli (7 % of alveolar surface)

Functions of Type II alveolar cells

1. Produce the surfactant - important for respiratory function

2. act as progenitor cells - When there is injury to Type I cells, Type II cells can multiply and eventually differentiate into Type I cells

alveolar walls

contain a dense network of capillaries and a small interstitial space (Connective tissue and interstitial fluids)

alveoli capillaries

-Capillaries are very small (allow only a single RBC at a time)

- Estimated that in less than 1 second a RBC passes through the pulmonary capillary system. This is sufficient time for oxygen and carbon dioxide diffusion between the alveoli and the capillary cells

O2 and CO2 Transfer between Alveolar Air and Blood

- Oxygen and carbon dioxide diffuse through the respiratory membrane

- Oxygen diffuses from the alveoli to the blood stream and carbon dioxide diffuses from the blood stream to the alveoli

Respiratory membrane

respiratory surface made of the alveolar epithelial cell (Type I alveolar cells) and the pulmonary capillary endothelial cell

-Very thin, easily damaged

Pneumocyte

one of the cells lining the alveoli of lung (type I and type II alveolar cells)

Steps of Respiration (5)

1. Ventilation: Exchange of air between atmosphere and alveoli by bulk flow

2. Exchange of O2 and CO2 between alveolar air and blood in lung capillaries by diffusion

3. Transport of O2 and CO2 through pulmonary and systemic circulation by bulk flow

4. Exchange of O2 and CO2 between blood in tissue capillaries and cells in tissues by diffusion

5. Cellular utilization of O2 5 and production of CO2

What is ventilation independent of (step 1)?

gas composition (the movement is generated due to changes in V & P that will push movement from areas of high P to low P

Where does exchange of O2 and CO2 between alveolar air and blood in lung capillaries by diffusion? (Step 3)

at the level of the respiratory membrane due to changes in pressure of oxygen and carbon dioxide between the alveoli and the blood

How is Respiratory Airflow (Ventilation) Produced? (4)

1. . CNS sends rhythmic excitatory (Respiratory) drive to respiratory muscles

2. Respiratory muscles contract rhythmically and in a very organized pattern

3. Changes in volume and pressures at the level of the chest and lung occur

4. Air flows in and out

3 categories of muscles involved in respiration

pump muscles, airway muscles and accessory muscles

Pump muscles

- make changes in P & V at level of the lungs

- 2 classes which allow air to come in and out: inspiratory & Expiratory

Inspiratory

- active throughout inspiration

- Main muscle: diaphragm

Expiratory

active throughout expiration

Airways muscles

- located at level of the airways and have an important role in keeping the upper airways open

- Mostly inspiratory but there are some that are active in expiration

accessory muscles

- facilitate respiration during (eg) exercising, when there is an increased metabolic drive

What coordinates the activity of various muscle groups for breathing?

Brain

Muscles of Inspiration

- Sternocleidomastoid Scalenes

- External intercostals

- Parasternal intercostals

- Diaphragm

Muscles of Expiration

- Internal intercostals & Abdominals

Most important muscle for respiration

diaphragm

Diaphragm

- dome-shaped muscle which flattens during contraction (INS), abdominal contents are forced down and forward and rib cage is widened

- Increase in volume of the thorax

- separates lungs from abdominal content

External intercostals

- contract and pull ribs upward increasing the lateral volume of the thorax

- Bucket handle motion

Parasternal intercostal muscles

- contract and pull sternum forward, increasing anterior posterior dimension of the rib cage

‒ Pump handle motion

Inspiratory pump muscles

active all the time during inspiration (during inspiration at rest or during exercise)

Expiratory pump muscles

- Do not contract during expiration at rest and passive during inspiration

- Active during the expiratory phase when you are making an effort to breathe in and out (ie. During stress, exercise, coughing)

What must happen during exercise?

Deeper, faster breathing requires active contraction of abdominal & internal intercostal muscles to return the lung to its resting position

Internal intercostals

- Relaxed at rest

- During exercise, internal intercostal muscles pull rib cage down, reducing thoracic volume

Accessory Inspiratory Muscle

Not commonly active during resting breathing

- active during exercise and forced respiration

Quiet inspiration (Inspiration at Rest)

diaphragm (contracts, pushing the abdominal content down and expanding the thorax as air comes in) and the external intercostals and parasternal intercostals

Inspiration at Forced Respiration (During exercising or deep breathing)

stronger contraction of the diaphragm and recruitment of the accessory muscles, further expanding the thoracic cavity

Quiet Expiration (At Rest)

- abdominal and intercostal muscles are not active

- no muscles are recruited (no active contraction of the respiratory muscles)

-inspiratory muscles relax and air moves out of the lungs because of the recoil of the lungs

Forced Expiration

- abdominal muscles contract intensely, causing abdominal content to be pushed upward so the diaphragm is moved even higher than its resting level and more air is expelled

- Internal intercostal muscles contract and push the rib cage down

Upper Airway Muscles

- majority are inspiratory; only a few are also expiratory

- usually active during inspiration

- Main function is to keep the upper airways open to maintain the airway and allow for gas exchange

State-dependent & upper airway muscles

when you sleep, the activity of these muscles tends to be depressed

Upper airway muscles in Healthy patient

Air passes through the nasal and oral cavities and the tone of the tongue is maintained

Obstructive sleep apnea

- Reduction in upper airway patency during sleep

- Reduction in muscle tone

‒ Anatomical defects

- Tone of the upper respiratory muscles is depressed and they become a floppy muscle

- Air cannot go in and out, especially during sleep, resulting in snoring and large drops in oxygen saturation in the blood

Regions involved in the filtering action

Conducting zone and at the level of the alveoli

muco-ciliary escalator

The filtering action in the conducting zone

Two types of cells line the surface of the trachea

goblet cells & ciliated cells

Goblet cells

sparse; produce mucus; no cilia

Ciliated cells

layer of cells with cilia on the apical surface *

Goblet & ciliated cells

function in a coordinated manner to entrap inhaled biological and inert particulates and remove them from the airways

What does the effective clearance of deposited particles in the tracheobronchial tree require?

both ciliary activity and respiratory tract fluids

Ciliated cells & Removal Of Deposited Particles In the Tracheobronchial Tree

- Produce periciliary fluid that has a very low density and sits on top of the ciliated cells and is called the SOL layer

- low density of the fluid allows the cilia to move freely in this fluid

Goblet cells & Removal Of Deposited Particles In the Tracheobronchial Tree

- Produce mucus called the thick gel layer

- Has a high viscosity and high elastic properties to trap particulates that enter the respiratory system during inhalation

How do we eliminate this mucus rich in particulates?

- through the cilia movements; the cilia move in the SOL layer and the tip of the cilia touches the mucus and pushes it continuously in one direction

- Cilia movement is downward in the nasopharynx and upward at the level of the trachea to eliminate mucus through the esophagus

What affects muco-ciliary escalator?

changes in the composition or in the thickness of the sol layer and the gel layer will affect the

Affect of smoking on cilia and goblet cells

Smoking reduces the activity of the cilia and increases the number of mucusproducing goblet cells

filtering Action in respiratory system

mediated by Macrophages in Alveoli

Macrophages in Alveoli

- Last defense to inhaled particles

- Rapidly phagocytize foreign particles and substances as well as cellular debris

What occurs when you inhale silica dust and asbestos?

the development of pulmonary fibrosis

- Lungs that are not able to expand lose their elastic properties