Respiratory system Flashcards
Whats the conducting zone?
The conducting zone extends from the trachea to the right and left stem bronchus then to the terminal bronchioles. The conducting zone contains no alveoli and therefore no gas exchange occurs here.
Whats the respiratory zone?
The respiratory zone extends from the respiratory bronchioles down and contains the alveoli - this is where gas exchange occurs.
Describe the anatomy of the lower respiratory tract.
The walls of the trachea and bronchi contain rings of cartilage which give them there cylindrical shape and support them. The first airway branches that no longer contain cartilage are termed bronchioles which branch into smaller, terminal bronchioles. Elveoli first begin to appear attached to the walls of the respiratory bronchioles.
The bronchioles are surrounded by smooth muscle which contracts/relaxes to alter the bronchiolar radius.
What is airway resistance?
Airway resistance = 1/conduction which is proportional to 1/radius^4.
Airway resistance is conduction summative, there are huge number of respiratory bronchioles, small airways make a small contribution to total resistance. Conducting zones have the largest influence.
In what ways can airway resistance be increased?
Obstruction with mucus, inflamed/thickened airway walls, structural changes in the conducting airways like smooth muscle growth and fibrosis.
The epithelium lines the cells in the airway. What variation is there in epithelium down the airway?
Bronchi - ciliated, goblet, glandular.
Bronchioles - ciliated and non ciliated, goblet and club cells.
Alveoli - squamous, cuboidal.
Whats the cellular structure (layers) of the conducting airways?
Cartaliginous layer, lamina propria, epithelium, mucus blanket.
What does the epithelial surface of the airways contain?
The epithelial surface contains cilia which constantly beat upwards towards the pharynx.
They also contain glands and individual endothelial cells which secrete mucous and macrophages which can phagocytize inhaled pathogens.
Particulate matter sticks to the mucucs which is continuously and slowly moved by the cilia to the pharynx and then swallowed.
What can negatively effect the cilia?
The ciliary activity and number can be decreased by many noxious agents - this is why smokers often cough up mucucs that would usually have been cleared by cilia.
What helps the mucus to ride freely?
The epithelium also secretes a watery fluid upon which the mucus can ride freely (production of this is impaired in cystic fibrosis).
Describe the innervation of the conducting airways.
Sensory (afferent) nerves from the airway epithelium and smooth muscles signal to the brain.
From the CNS there are autonomic fibres to glandular epithelium and smooth muscle:
- Parasympathetic branches off the vagus nerve having both inhibitory and excitatory functions.
- Sympathetic (postganglionic) have very little innervation - B-adrenoreceptors on airway smooth muscle are stimulated by circulating adrenaline.
What are the two types of alveolar epithelial cells?
Type I pneumocytes = these have a very large surface area (only 10% of cells yet take up 95% of alveolus), are squamous and the site of gas exchange.
Type II pneumocytes = the majority of cells are type 2, they are cuboidal and secretory (surfactant) and a precursor for type 1 cells.
What is surfactant?
Surfactant is a liquid consisting of 90% lipids (mainly phospholipids) and proteins, produced by type 2 alveolar epithelial cells.
Whats the role of surfactant?
Surfactant reduces surface tension and prevents alveolar collapse (atelectasis). It also has innate immunity function.
What happens to infants with respiratory distress syndrome?
Infants don’t have enough surfactant
The infact can have surfactant instilled in them - either beractant (bovine) or pumactant (a synthetic, lipid only liquid).
When do the lungs develop?
The epithelium of the lungs develops in the third trimester of pregnancy. Maturation can be stimulated by corticosteroids in premature babies.
As a foetus, the lung is filled with fluid - how is this rapidly emptied during birth?
There is a surge in corticosteroids and catecholamines, activation of absorptive channels (epithelial sodium channels) and pressure changes as the baby is squeezed through the birth canal.
In a C section, there is reduced drive for fluid absorption.
Explain how blood gets oxygenated.
The pulmonary artery carries deoxygenated blood directly from the right ventricle of the heart - there is low pressure but high flow. Blood then enters capillaries around the alveoli, oxygenating the blood to then return to the left atrium of the heart via the pulmonary vein.
The lungs also have a bronchial circulation - what is this?
Oxygenated blood from the left ventricle of the heart (via aorta) carries high pressure blood to the conducting airways, supplying oxygen and nutrients. This is only 2% of cardiac outflow and is not involved in systemic respiration processes.
Ventilation is the movement of air from the environment into the lungs. It is automatic but also under control of the CNS.
Explain the neuronal control of breathing.
The cerebral cortex sends signals to the respiratory center in the medulla - this sends nerve impulses to the spinal cord and from the spinal cord to the respiratory muscles. This causes movement of the lungs and chest wall (mechanoreceptors feedback this to the medulla) hence causing ventilation.
Diffusion occurs accross the alveolar-capillary barrier (chemoreceptors feedback the change in oxygen and carbon dioxide concentration to the medulla).
Explain the function of somatic motor nerves in the respiratory muscles.
Motor nerves innervate skeletal muscles in the thorax:
- The phrenic nerve innervates the diaphragm - irritation causes hiccups.
- There are multiple intercostal nerves which each innervate intercostal muscles.
Explain the function of autonomic nerves in the respiratory muscles.
Autonomic nerves work in the bronchials, supplying smooth muscle and secretory cells. There are both sympathetic (from CNS) and parasympathetic (branching from vagus nerve) that meet at the pulmonary plexus.
The autonomic nerves reflex bronchospasm and mucus secretion - they are important in asthma.
What happens to the respiratory muscles during inspiration?
The diaphragm contracts and the external intercostal muscles pull the ribs up and out. Upon maximal inspiration, the sternoclastimoid and scalenes elevate the sternum whilst the pectoralis minor elevates the ribs and the diaphragm contracts more.
What happens to the respiratory muscles during expiration?
The elasticity of the lungs recoils inward, the diaphragm is relaxed and the abdominal organs recoil and press diaphragm upwards. Upon maximal expiration, the internal intercostal muscles pull the ribs down and inwards whilst the abdominal wall muscles contract and compress abdominal organs, forcing the diaphragm higher.
There are myelinated sensory afferent pathways from the lungs sending impulses via the vagus nerve to medullary centres. These can be…
Slowly adapting - pathways are stimulated by stretch receptors in airway smooth muscle, eliciting shortened inflation and the Hering-Breur reflex, this is the promotion of expiration following steady inflation, preventing over inflation of the lungs.
Rapidly adapting - stretch receptors are stimulated by sudden, sustained inflation and by ‘irritant receptors’ among the epithelium. This elicits reflexes such as cough, bronchoconstriction and mucus secretion.
There are also unmyelinated sensory afferent pathways, what are these?
The unmyelinated sensory afferent pathways are pulmonary and bronchial C fibres located close to blood vessels (J receptors). They are activated by exogenous stimuli (noxious agents in air) and endogenous stimuli (inflammatory agents generated by the body) causing the reflex of bronchoconstriction and mucus secretion.
Explain the cough reflex.
The cough reflex begins by stimulation of irritant receptors, sending a signal via a sensory nerve to the medulla. Motor nerves then relay signals to skeletal muscles. The glottis closes and abdominal and internal intercostal muscles contract rapidly. Intrapulmonary pressure then rises and the glottis opens as you cough.
Whats the pleural membrane?
There is a double membrane surrounding the lungs with a pleural space in between containing pleural fluid which acts as a lubricant.
The left and right pleura are anatomically distinct hence a collapsed lung (pneumothorax) usually only affects one lung.
Explain the mechanisms of ventilation.
The fluid in the pleural sac helps the lung wall stick to the inside of the thorax.
Contraction of the diaphragm and external intercostal muscles increases the lung volume so internal pressure falls (Boyles law) hence air is drawn in.
Exhalation is passive at rest - elastic recoil.
Whats pulmonary compliance?
A measure of the elasticity of the lung. (calculated by change in volume, divided by change in pressure)
There are two forms of pulmonary comp-liance, what are they?
Static = the compliance at zero flow (end of inspiration/exhalation) Dynamic = the compliance during active flow.
What factors affect pulmonary compliance?
Pulmonary compliance is:
- Increased by surfactant.
- Increased in emphysema (loss of elastic tissue so its easier to stretch).
- Decreased in pulmonary fibrosis (scarring makes it harder to stretch).
What are the metabolic functions of the lungs?
Club cells detoxify inhaled substances using cytochrome P450.
Vascular cells inactivate some circulating hormones like prostaglandins.
Vascular cells activate angiotensin I to angiotensin II using angiotensin converting enzyme.
Fibrinolytic function.
How is ventilation controlled?
Chemical control occurs through cental and peripheral chemoreceptors.
Neural control occurs through central rhytm generator in medulla, controlled by nociceptors and receptors in the respiratory tract causing sneezing, coughing and hypernoea.
