BI0005 - Lecture 13 - Respiration
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What is the pharynx?
- The pharynx is an organ found in animals, including humans.
- It is part of the digestive system and also the respiratory system.
- The pharynx is also part of the conducting zone of the respiratory system which is made up of the nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles; their function is to filter, warm, and moisten air and conduct it into the lungs.
- In humans it makes up the part of the throat situated immediately posterior to the nasal cavity, posterior to the mouth and superior to the esophagus and larynx.
What is the nasal cavity?
- The nasal cavity (or nasal fossa) is a large air filled space above and behind the nose in the middle of the face.
- Each cavity is the continuation of one of the two nostrils.
What is the larynx?
- The larynx, commonly called the voice box, is an organ in the neck of amphibians, reptiles, and mammals involved in breathing, sound production, and protecting the trachea against food aspiration.
- It manipulates pitch and volume.
- The larynx houses thevocal folds (vocal cords), which are essential for phonation.
- The vocal folds are situated just below where the tract of the pharynx splits into the trachea and the esophagus.
What is the trachea?
- In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx and larynx to the lungs, allowing the passage of air.
- It is lined withpseudostratified ciliated columnar epithelium cells with goblet cells that producemucus.
- This mucus lines the cells of the trachea to trap inhaled foreign particles that the cilia then waft upward toward the larynx and then the pharynx where it can be either swallowed into the stomach or expelled as phlegm.
What is the primary bronchus?
- A bronchus (plural bronchi, adjective bronchial), also known as a main or primary bronchus, is a passage of airway in the respiratory tract that conducts air into the lungs.
- The bronchus branches into smaller tubes, which in turn become bronchioles.
- No gas exchange takes place in the bronchi.
What are alveoli?
- An alveolus (plural: alveoli, from Latin alveolus, "little cavity") is an anatomical structure that has the form of a hollow cavity.
- Found in the lung parenchyma, the pulmonary alveoli are the terminal ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well.
- Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates.
- The alveolar membrane is the gas-exchange surface.
- Carbon dioxide rich blood is pumped from the rest of the body into the alveolar blood vessels where, through diffusion, it releases its carbon dioxide and absorbs oxygen.
What are the lungs?
- The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails.
- In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart.
- Their principal function is to transport oxygen from the atmosphere into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere.
- A large surface area is needed for this exchange of gases which is accomplished by the mosaic of specialized cells that form millions of tiny, exceptionally thin-walled air sacs called alveoli.
What is the intrapleural space?
- In human anatomy, the pleural cavity is the potential space between the two pleurae (visceral and parietal) of the lungs.
- The pleura is a serous membrane which folds back onto itself to form a two-layered membrane structure.
- The thin space between the two pleural layers is known as the pleural cavity and normally contains a small amount of pleural fluid.
- The outer pleura (parietal pleura) is attached to the chest wall.
- The inner pleura (visceral pleura) covers the lungs and adjoining structures, via blood vessels, bronchi and nerves.
What are the main functions of the respiratory system?
Provide for gas exchange: Intake of O2
for delivery to respiring cells elimination of CO2
produced by respiring cells.
- Primary role: to maintain normal levels of O2 and CO2 in the systematic arterial blood.
- - Arterial PO2 = 98mm Hg / 13kPa
- - Arterial PCO2 = 40mm Hg / 5.3.kPa
Respiration is matched to metabolism.
What are some other functions of the respiratory system?
Contributes to regulation of blood pH
Filters, warms and humidifies inpsired air
Contains receptors for the sense of smell
Metabolism of biologically-active chemicals.
What do the human airways do?
What is the pathway?
Trachae --> Bronchi --> Bronchioles --> Terminal bronchioles --> Respiratory bronchioles --> Alveolar ducts --> Alveolar sacs
For transferring of gases to/from alveoli.
Warming and humidifying inspired air.
Filtration and removal of foreign material.
Gas exchange - O2 delivery to blood, CO2 transfer from blood.
When does ventilation occur?
Ventilation occurs when active muscle force is applied to the relaxed respiratory system.
What is inspiration?
Inspiration is an active
- Volume of thorax is increased as:
- -diaphragm contracts
- -external intercostal muscles contract
- As the volume of the thorax increases:
- -intrapleural pressure falls
- -lungs expand
- -alveolar pressure < atmospheric pressure
- -air flows into lungs until alveolar pressure = atmospheric pressure
What is expiration?
Expiration is largely a passive process
Diaphragm and external intercostal muscles relax.
Elastic recoil of lungs and chest wall reduces volume of thorax (passive mechanism)
Interpleural pressure rises
Palv > Patmos
Air is expelled from lungs.
What is spirometry?
Spirometry (meaning the measuring of breath) is the most common of the pulmonary function tests (PFTs), measuring lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled.
What is a spirometer?
- A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs.
- A spirometer measures ventilation, the movement of air into and out of the lungs.
- The spirogram will identify two different types of abnormal ventilation patterns, obstructive and restrictive.
- There are various types of spirometers which use a number of different methods for measurement (pressure transducers, ultrasonic, water gauge, turbine)
How does air move passively?
Air moves passively from a region of high
- During inspiration:
- alveolar pressure < atmospheric pressure -- air moves into lungs
- During expiration:
- Alveolar pressure > atmospheric pressure -- air is expelled from lungs.
What happens during inspiration?
During inspiration, resistive forces oppose airflow:
-Airway resistance - resistance to movement of air through airways
-Pulmonary tissue resistance - friction between lungs and chest wall.
-Inertia of the air and tissues
What happens during expiration?
During respiration, resistive forces assist airflow:
-Elastic recoil of lungs and chest wall
-Surface tension in alveoli
What does gas exchange involve?
Gas exchange involves both the respiratory and cardiovascular systems
What does blood flow allow?
Blood flow through the lungs allows transfer of gases to and from the respiring tissues of the body.
What are the general paths of CO2 and O2
CO2: Cells --> Blood --> Alveoli --> Atmosphere
O2: Atmosphere --> Alveoli --> Blood --> Cells
How does blood circulation work?
Almost all of the output from the heart passes through the lungs
1. Blood returns to heart from body, enters right atrium.
2. Blood enters right ventricle.
3.Blood is pumped from right ventricle to lungs
4. Blood returns to left atrium from lungs.
5. Blood enters left ventricle
6. Blood is pumped from left ventricle to body.
In what way is pulmonary circulation specialised?
Gas composition of blood in pulmonary arteries and veins is opposite to those in systematic circulation.
Pressures in the pulmonary circulation are very low
Pulmonary arterial walls are thin and contain little smooth muscle.
Pulmonary vascular resistance is low.
Vascular resistance = (input pressure - output pressure) / blood flow
What does Alveolar and blood gas composition depend on?
Alveolar and blood gas composition depend on the balance between alveolar ventilation and metabolism.
What is the alveolar ventilation rate (VA)?
Air entering lungs ventilates both the dead space and the alveoli:
VE = VD + VA
(VA is the amount of fresh air available for gas exchange)
Alveolar ventilation rate = (tidal volume - dead space) x respiratory rate.
What is blood gas composition regulated by?
Blood gas composition is regulated by changes in alveolar ventilation rate.
Partial pressures of O2
in arterial blood are almost identical to those in alveolar gas.
- Normal values in arterial blood:
- - PaO2 = 98mm Hg (13kPa)
- - PaCO2 = 40mm Hg (5.3kPa)
What controls the generation and control of breathing?
The brainstem sets the basic rhythm and pattern of breathing.
What can ventilation be modified by?
Ventilation can be modified by:
-Feedback from the higher brain centers (cortex, hypothalmus, limbic system)
-Feedback from receptors in the lung (stretch, irritants)
-Feedback from peripheral and central chemoreceptors.
What is the ventilation response to increased CO2?
If the pressure of CO2 increases, so does the minute ventilation.
What is minute ventilation?
- Respiratory minute volume (or minute ventilation orexpired minute volume) is the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person's lungs per minute.
- It is an important parameter in respiratory medicine due to its relationship with blood carbon dioxide levels.
What part do chemoreceptors play in respiration?
Chemoreceptors are sensitive to changes in blood chemistry.
- Peripheral chemoreceptors:
- -acutely sensitive to changes in arterial PCO2
- - small increases in PCO2 causes an immediate increase in minute ventilation.
- Central chemoreceptors:
- -sensitive to longer-term changes in PCO2
Besides PCO2, what else are chemoreceptors sensitive to?
- Peripheral chemoreceptors:
- - Also sensitive to changes in arterial PO2
- - As PO2 falls below 60mm Hg, minute ventilation rises.
These ventilatory responses are more sensitive when PCO2
is elevated (Hypercapnia) AND
is reduced (hypoxia)
What is hypercapnia?
Hypercapnia or hypercapnea (from the Greek hyper = "above" or "too much" and kapnos = "smoke"), also known as hypercarbia, is a condition of abnormally elevated carbon dioxide(CO2) levels in the blood.
Hypercapnia normally triggers a reflex which increases breathing and access to oxygen, such as arousal and turning the head during sleep.
What is hypoxia?
- Hypoxia (also known as Hypoxiation or Anoxemia) is a condition in which the body or a region of the body is deprived of adequate oxygen supply.
- Hypoxia may be classified as eithergeneralized, affecting the whole body, or local, affecting a region of the body
What is hypoventilation?
- In medicine, hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (hypo meaning "below") to perform needed gas exchange.
- By definition it causes an increased concentration of carbon dioxide(hypercapnia) and respiratory acidosis.
What is hyperventilation?
- Hyperventilation occurs when the rate and quantity of alveolar ventilation of carbon dioxide exceeds body's production of carbon dioxide.
- Hyperventilation can be voluntary or involuntary.
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