WEEK 2 Flashcards
What is interstitial fluid?
It is fluid trapped amongst filaments
About 1% is water & 95-99% is gel
What are (i) crystalloids (ii) colloids?
(i) low molecular weight solutes e.g. Na+, Cl-, K+
ii) plasma proteins - exists within interstitial & capillaries but more prominent in plasma (capillaries
What are the boundaries of the anterior mediastinum?
Between the sternum & pericardium
What are the boundaries of the superior mediastinum?
Between the thoracic inlet & sternal angle at T4-5; posterior to the manubrium; anterior to T1 - T4; oblique from the manubrium upwards to T1
What is the location of the thymus?
From the jugular notch to the 4th CC (& possibly beyond). It is a bi-lobed structure in the anterior mediastinum between the manubrium, sternum & pericardium
What is the function of the thymus?
It is active throughout life, particularly in childhood & puberty, with age fibro-fatty infiltration increases. Its function is to programme T-lymphocytes; recognise “self”
What is the blood supply of the thymus?
Int thoracic & inf thyroid arteries. Venous drainage to L.brachiocephalic vein
Structures on the left of the mediastinum are related to what?
Arteries & then the LV. (Left common carotid artery, left subclavian artery, arch of aorta & thoracic aorta)
What do the vagus & phrenic nerves lie between?
The venous & arterial planes
What can the superior mediastinum be considered as?
As a series of planes moving from anterior to posterior (once the thymus has been removed)
What are the 5 bony landmarks of the venous plane?
- Internal jugular and subclavian veins join to form right and left BCVs - Posterior to the sternoclavicular joint
- Left BCV passes anterior to the arch of the aorta; posterior to the manubrium
- RBCV & LBCV join to form the SVC - posterior to the 1st R CC
- Arch of the azygous vein joins SVC - posterior to the 2nd R CC
- SVC enters the RA - posterior to the 3rd R CC
What can happen with the LBCV in children?
It receives the thyroid vein & may protrude above the manubrium where it may be at risk in tracheostomy
What does the (i) azygous (ii) subclavian (iii) internal jugular veins(s) drain?
(i) posterior chest wall (ii) upper limb (iii) head & neck
In what mediastinum does the thoracic (descending) aorta lie?
Posterior
What 2 things is the trachea “clasped” by?
the left common carotid artery & brachiocephalic trunk
At what vertebral level is the jugular notch located?
T2/3
Where is the pulmonary trunk located?
Within the pericardium to the left of the ascending aorta
At T5, what does the pulmonary trunk do?
Divides into:
the R.pulmonary artery (posterior to the asc Ao & SVC) & enters the R lung.
the L.pulmonary artery (inferior to the arch of Ao & anterior to the thoracic aorta) & enters the left lung
What is the difference between the location of the pulmonary artery & bronchus on the left & right lung roots?
On the right the artery is inferior to the bronchus whilst on the left the artery is superior to the bronchus
In what mediastinum is the ligament arteriosum located?
superior mediastinum
Where is the trachea palpable? Where does it start & end?
anteriorly in the midline of the neck. Starts at C6 & ends at T4/5 (sternal angle) at carina
What is the location & function of trachealis?
Found posteriorly, between the ends of the C-cartilages. It alters tracheal diameter
In the superior mediastinum, what is the position of the trachea, the oesophagus & the left recurrent laryngeal nerve?
the trachea is anterior to the oesophagus - with the left recurrent laryngeal nerve between
What difference(s) is there between the right & left main brochi?
the right is shorter, wider & more vertical than the left
At rest, what does smooth muscle contraction do to tracheal diameter? What does this in turn do?
It decreases tracheal (& bronchial) diameter to decrease respiratory dead space.
What effect does cigarette smoke have on cilia?
It paralyses them
What is the function of the oesophagus?
transport of food & fluid through the thorax & diaphragm to the stomach
Where is the oesophagus located?
It starts at C6, passes immediately posterior to the trachea, anterior to the vertebral column, with the arch of the arch of the aorta to its left
What is the thoracic duct a continuation of? What does it lie between & in what mediastinum?
The cisterna chyli
Lies between the aorta & azygous vein in the posterior mediastinum
Describe the route of the thoracic duct.
At T4/5 it crosses behind the oesophagus to ascend on its left side
The duct then arches over the apex of the left lung & pleura to enter the junction of the left internal jugular & the left subclavian vein
What can left lung tumours affect?
The left recurrent laryngeal nerve
Nodes in the lungs & lung hilum drain to where?
mediastinal nodes
Where are the mediastinal nodes located?
Clustered around the trachea & oesophagus in the superior mediastinum, consequently, these nodes may be involved in the spread of lung tumour
What are the mediastinal nodes called if they are (i) above (ii) below the tracheal bifurcation?
(i) Superior tracheobronchial nodes
(ii) Inferior tracheobronchial nodes
Where are the anterior mediastinal nodes found? Where do all the mediastinal nodes drain to?
Around the brachiocephalic veins
They all drain to the thoracic duct on the left OR the lymph duct on the right BUT they communicate with the deep cervical nodes
Why is the consistency of interstitial fluid more like a gel than a free flowing liquid?
Collagen fibres and proteoglycan filaments (interstitium) are dispersed in the interstitial fluid, increasing viscosity
Why do colloids (plasma proteins) not move out of the capillaries?
In a nutshell, they are too large - barred from crossing by capillary walls. A few however, may escape
What is the average hydrostatic pressure at the arterial end of circulation?
30-40mmHg
Negative hydrostatic pressure in the interstitial space leads to…?
Water drawn out of capillaries
Positive hydrostatic pressure in the interstitial space leads to…?
Water pulled into capillaries
What is the average hydrostatic pressure at the venous end of circulation?
10-15mmHg
What would be the result of having purely hydrostatic pressure pushing water out?
Oedema
Give 4 methods which increase venous pressure and hence increase venous return.
(1) Increase blood volume e.g. haemorrhage, fluid challenge
(2) Increase inspiration movements (diaphragm descends, decreased pressure in thorax => increased pressure diff btween peripheral veins & heart)
(3) Increase skeletal muscle movement (as a pump)
(4) Increase activity of sympathetic nerves to veins
Venous return is a major determinant of…
Cardiac output due to myogenic response of the ventricles
What 4 features is the lymphatic system in control of?
- Concentration of proteins in interstitial fluids 2. Volume of interstitial fluid 3. Interstitial pressure 4. Immune response
What is orthostatic (postural) hypotension?
A decrease in BP (due to decreased venous return & => decreased CO) when going from supine to upright. Reflex vasoconstriction in legs and lower abdomen (NOTE: it takes a few seconds to kick in)
Which is lower, the plasma or interstitial osmotic pressure?
Interstitial
What substances generates the Colloid Osmotic/Oncotic Pressure?
Plasma proteins (mainly albumin) This creates a difference in the abundance (and consequently pressures) between capillaries and extracellular fluid
When standing completely still, what is the mean arterial pressure at (i) the level of the heart (ii) feet?
(i) approx 100mmHg
(ii) approx 190mmHg
What is the venous system in terms of volume & pressure?
High-volume low pressure system
How can compliance of veins be adjusted?
By sympathetic innervation
In what 8 scenarios should a check x-ray be requested?
- Shortness of breath
- Acute chest pain
- Investigation for malignancy
- Following severe trauma
- Pneumonia
- Chronic lung diseases
- Pleural diseases
- Peritonitis
What is the lingula?
A combined term for the 2 lingular bronchopulmonary segments of the left UPPER lobe. Made up of: Inferior lingular segment, superior lingular segment.
What is the process for reviewing a chest XR?
- Check patient identity and date of CXR
- Heart
- Mediastinum/ airways
- Lungs + pleural reflections
- Bones
- Soft tissues
- Review areas ** -Apices -Behind the heart -Below the diaphragm
What is the carina?
The ridge of cartilage of the trachea at the bifurcation
What is possible reason for a missing rib from a CXR?
Tumour grown around the rib. If the CXR is PA then the tumour is posterior to rib
What are the review areas of the CXR?
Apices
Behind the heart
Below the diaphragm (Space between liver = gas)
What are the 4 areas of error that can occur when taking a CXR?
P-A vs A-P Film: PA preferred as the magnification of heart is reduced = film more reliable Rotation: For optimum rotation, there must be an equal distance between the medial ends of the clavicle and the spinous processes of the vertebrae Penetration: Over-penetration appears dark, Poorly penetrated appears light/fuzzy Inspiration vs Expiration: Inspiration preferred as structures more densely packing into thorax
Why are feedback systems required to control the heart & blood vessels?
Required to maintain tissue perfusion across the whole of the body
- to keep a relatively constant arterial BP
- to control distribution of the total cardiac output
If the arterial blood pressure is (i) too high (ii) too low, what happens?
(i) damage to vessels & organs
(ii) blood flow to organs would fail
Nervous control of arterial pressure is rapid, by how much (& how fast) can pressure both increase & decrease?
Can increase to 2x normal within 5-10s
Can decrease arterial pressure to 50% normal within 10-40s
What are the 6 fundamental components of a reflex control system?
- Internal variable to be maintained
- Receptors sensitive to change in the variable
- Afferent pathways from the receptors
- An integrating centre for the afferent inputs
- Efferent pathways from the integrating centre
- Target effectors that alter their activities
What are the nature and location of the baroreceptors which detect changes in blood pressure?
LOCATIONS:
(1) Walls of aorta - afferent fibres follow vagus (Xth cranial) nerve
(2) Carotid artery - afferent fibres follow (IXth cranial) glossopharyngeal nerve
NATURE:
“stretch receptors”
- their firing rate increases when BP increases & vice versa
- they are sensitive around a “set-point” which can change e.g. hypertension
What is the primary purpose of baroreceptor reflex control?
To reduce the minute-to-minute variations or arterial pulse
What is the function of cardiopulmonary baroreceptors? If their rate of firing decreases (ie signalling less blood volume) then what happens?
They sense CENTRAL blood volume - atria, ventricles, veins & pulmonary vessels
Sympathetic nerve activity to the heart & BVs increases
Parasympathetic nerve activity to the heart decreases
What is the Bainbridge Reflex?
A sympathetic-mediated reflex in response to increased blood in atria
- increases HR & contractility
- prevents damming of blood in veins etc
If aortic/carotid baroreceptors sense high pressure what can happen?
The bainbridge reflex can over-ride
What is the (i) sensory area (ii) lateral portion (iii) medial portion of the Medullary cardiovascular control “vasomotor” centre?
(i) input from baroreceptors
(ii) efferent sympathetic nerves
(iii) Efferent parasympathetic (vagal) nerves
What effect does (i) sympathetic (ii) parasympathetic system have on cardiac output?
(i) can significantly effect stroke volume & rate
(ii) predominate tone at rest
What effects does the sympathetic system have on the blood vessels?
continuous low-level tone affects total peripheral resistance => are kept partially constricted
What happens to veins when sympathetic effects are increased?
Decreased capacitance
=> Increased venous return
=> increased stoke volume
=> increased cardiac output
What happens when blood flow to the medullary CV control centre is decreased?
(1) Increase in peripheral vasoconstriction - almost completely occludes some peripheral vessels
(2) Increase sympathetic stimulation of the heart
(3) Large increase in systemic arterial pressure (as high as 250 mmHg for 10 mins)