Physiology Flashcards
Which cells secrete surfactant?
Type 2 alveolar pneumocytes
Tell me about fetal haemoglobin and shift of O2 dissociation curve
2 alpha and 2 gamma subunits.
Present to about 6 months of life.
Fetal haemoglobin has higher affinity for O2 so curve is shifted to the left.
How is airflow obstruction categorised?
According to the latest NICE guidelines (2010) airflow obstruction is defined as follows:
Mild airflow obstruction = an FEV1 of >80% in the presence of symptoms
Moderate airflow obstruction = FEV1 of 50-79%
Severe airflow obstruction = FEV1 of 30-49%
Very severe airflow obstruction = FEV1 <30%.
What are J receptors, where are they located, and what nerve innervates them?
Juxtacapillary receptors (J receptors) are sensory cells that are located within the alveolar walls in juxtaposition to the pulmonary capillaries of the lung.
The J receptors are innervated by the vagus nerve and are activated by physical engorgement of the pulmonary capillaries or increased pulmonary interstitial volume, for example in the presence of pulmonary oedema, pulmonary embolus, pneumonia and barotraumas. They may also be stimulated by hyperinflation of the lung.
Stimulation of the J receptors causes a reflex increase in breathing rate, and is also thought to be involved in the sensation of dyspnoea. The reflex response that is produced is apnoea, followed by rapid breathing, bradycardia, and hypotension.
Respiratory tract is lined with what kind of epithelium.
Which parts are not?
Ciliated pseudostratified columnar - not in oropharynx, larynx and laryngopharynx.
4 cell types - ciliated cells, goblet cells, club cells, airway basal cells.
What are the 3 main types of alveolar cell?
Type I pneumocytes – the abundant simple squamous epithelium that forms the gas exchange surface with the capillary endothelium
Type II pneumocytes – which secrete pulmonary surfactant, which reduces the surface tension at the air-water interface in the lung
Alveolar macrophages – which ingest foreign materials and destroy bacteria.
Tell me about carbon monoxide effect on oxygen transport.
240 times the affinity for Hb as O2
Shifts oxygen dissociation curve to left
pO2 of blood can be normal
What is static and dynamic lung compliance?
Compliance = change in volume / change in pressure
Static compliance is during periods without gas flow, eg. during an inspiratory pause.
= TV / ( Pplat - PEEP )
Dynamic compliance is during periods of gas flow, eg. during inspiration.
= TV / ( PIP - PEEP )
Dynamic is always lower than or equal to static compliance.
What is the main lipid component of surfactant?
dipalmitoylphosphatidylcholine (DPPC)
Tell me about QT interval?
Normally less than 440 ms. Inversely proportional to heart rate. From start of QRS to end of T wave. Represents ventricular depolarisation and repolarisation. Tends to be longer in women.
Prolonged QT:
hypokalaemia, hypocalcaemia and hypomagnesaemia), hypothermia, drugs, congenital syndromes and myocardial ischaemia. The QT interval tends to lengthen during sleep and shorten when awake.
Drugs that can cause a prolonged QT interval include: Quinidine Amiodarone Methadone Procainamide Haloperidol Tricyclic antidepressants Erythromycin
Digoxin causes shortened QT
What are the 3 salivary glands and their innervation?
Parotid gland - glossopharyngeal nerve via otic ganglion.
Submandibular and sublingual glands - facial nerve via submandibular ganglion.
What is the primary muscle of the upper oesophageal sphincter?
Cricopharyngeus portion of inferior pharyngeal constrictor
Describe transition in mucosa between lower oesophagus and stomach
From non-keratinised stratified squamous to simple columnar
Name some things absorbed in the stomach
Ethyl alcohol
Aspirin
Name 3 conditions associated with a split S1?
RBBB
LV pacing
Ebstein anomaly - malformation of tricuspid valve and right ventricle enlargement
What ECG changes are seen in RBBB?
What is the difference between primary and secondary T wave changes?
As the left ventricle is activated normally the early part of the QRS complex remains unchanged. The delayed activation of the right ventricle, however, produces a secondary R wave (R’) in the right praecordial leads, and a wide, slurred S wave in the lateral leads. It also causes secondary repolarisation abnormalities, with T wave inversion and ST depression being seen in the right praecordial leads.
Broad QRS complex (> 120 ms)
RSR’ pattern in leads V1-V3 (‘M’ shaped QRS complex)
Wide, slurred S wave in the lateral leads – I, AVL, V5 and V6 (‘W’ shaped QRS complex)
Secondary T wave changes are a normal finding in RBBB. T wave changes are classed as secondary if the T wave is upright when the terminal portion of the QRS complex is negative and the T wave is inverted when the terminal portion of the QRS complex is positive. Primary T wave changes occur when these rules are violated and are consistent with myocardial ischaemia.
List causes of RBBB?
Can be normal finding in young healthy people.
Ischaemic heart disease Rheumatic heart disease Right ventricular hypertrophy (cor pulmonale) Pulmonary embolus Cardiomyopathy Myocarditis Congenital heart disease (e.g. ASD) Degenerative disease of the conduction system
In a split S2 which valve normally closes first?
What conditions are associated with a widely split S2?
What conditions are associated with a reversed split S2?
Aortic valve normally closes before pulmonary.
Splitting during inspiration is a normal finding.
Widely split S2:
Deep inspiration
Right bundle branch block
Prolonged right ventricular systole (e.g. pulmonary stenosis, P.E.)
Severe mitral regurgitation
Atrial septal defect (fixed splitting, doesn’t vary with respiration)
Reversed split S2: Deep expiration Left bundle branch block Prolonged left ventricular systole (e.g. severe aortic stenosis, hypertropic cardiomyopathy) Severe aortic stenosis Right ventricular pacing Wolff-Parkinson-White (type B)
What 2 equations describe blood flow to the brain?
What are the 2 mechanisms of autoregulation of cerebral blood flow?
How does hypothermia affect cerebral blood flow?
Cerebral perfusion pressure = MAP - ICP
Cerebral blood flow = CPP / CVR
myogenic reflexes - at higher pressures the myogenic stretch reflex causes vasoconstriction which increases CVR and reduces CBF.
metabolic feedback - at lower pressures decreased blood flow allows vasoactive metabolites to accumulate (primarily CO2 and K+) that cause vasodilation and reduce CVR and increase CBF.
Outside of the CPP range 60-160mmHg, or in trauma or cerebral disease, auto-regulation is lost and CBF is dependant on MAP in a linear relationship.
Hypothermia reduces CBF by 5% per degree fall in temperature.
At what stage of inspiration, and in what position should the patient be, when measuring CVP?
CVP should be measured with the patient lying flat at the end of expiration.
CVP is a useful indicator of right ventricular preload. A volume challenge of 250-500 ml crystalloid causing an increase in CVP that is not sustained for more than 10 minutes suggests hypovolaemia.
What is the cause of Wolf-Parkinson-White (WPW) syndrome?
What are 3 typical ECG features?
What are the 2 types of WPW?
Presence of an abnormal electrical conducting pathway in heart - bundle of Kent, acts as pre-excitation pathway.
This results in the generation of a type of supraventricular tachycardia referred to as an atrioventricular re-entrant tachycardia (AVRT).
The typical ECG features of WPW in sinus rhythm are:
Shortened PR (< 120 ms)
Delta wave (slurring of the initial rise in the QRS complex)
Widening of the QRS complex (> 110 ms)
Type A – the delta waves and QRS complexes are predominantly positive in the praecordial leads with a dominant R wave in V1. The dominant R wave in V1 can be mistaken for RBBB
Type B – The delta wave and QRS complex are predominantly negative in leads V1 and V2 and positive in the other praecordial leads, resembling LBBB
Describe ECG changes seen in LBBB?
Normally the septum is activated from left to right, which produces small Q waves in the lateral leads. In the presence of LBBB, however, this septal activation is reversed, which eliminates these normal septal Q waves.
The right to left depolarization of produces deep S waves in the right praecordial leads (V1-V3) and tall R waves in the lateral leads (I, V5 and V6).
It also usually causes left axis deviation.
As the ventricles are activated sequentially from right to left, rather than simultaneously, the R wave in the lateral leads is broad and notched (‘M’ shaped).
Secondary T wave changes are a normal finding in LBBB.
The diagnostic criteria for LBBB are:
Broad QRS complex (> 120 ms)
Dominant S wave in lead V1
Broad, monophasic R wave in lateral leads (I, AVL, V5 and V6)
Prolonged R wave peak time > 60 ms in left praecordial leads (V5-V6)
Absence of Q waves in lateral leads (I, V5 and V6)
List causes of LBBB?
Ischaemic heart disease Anterior myocardial infarction Hypertension Aortic stenosis Dilated cardiomyopathy Primary fibrosis of the conducting system (Lenegre disease) Hyperkalaemia Digoxin toxicity
What does the QT interval represent?
Where does it start and end on the ECG?
List causes of prolonged QT interval?
It represents the duration of time taken for the ventricles to depolarize and repolarize.
From start of QRS to end of T wave.
The normal QT interval is less than 440 ms under normal circumstances and tends to be longer in women.
Should be less than half the preceding RR interval.
electrolyte disturbance (hypokalaemia, hypocalcaemia and hypomagnesaemia) hypothermia drugs congenital syndromes myocardial ischaemia
An abnormally prolonged QT interval is associated with an increased risk of Torsades de Pointes.
What are the 5 points on a CVP waveform?
a wave - end diastole, atrial contraction
c wave - early systole, closing and bulging of the tricuspid valve
x descent - mid systole, atrial relaxation
v wave - late systole, systolic filling of atria
y descent - early diastole, early ventricular filling
What is Wenckebach block otherwise known as?
Mobitz type 1 AV block
Mobitz type 1 AV block is generally considered to be a benign rhythm that infrequently causes haemodynamic disturbance and has a low risk of progression to complete heart block. Asymptomatic patients require no treatment and those that are symptomatic usually respond to the administration of atropine. Permanent pacing is rarely required.
What is the usual paper speed of an ECG?
25 mm/sec
What is considered normal MAP?
65 to 110 mmHg
Needs to be a minimum of 65 mmHg for adequate organ perfusion to occur
