Week 1 Flashcards
1
Q
What are true ribs?
A
Ribs whose costal cartilages articulate with the sternum directly. e.g. ribs 1-7
2
Q
What are false ribs?
A
Ribs whose costal cartilages articular with the costal cartilage above forming the costal margin e.g ribs 8-10
3
Q
What are floating ribs?
A
Ribs that are short e.g. ribs 11, 12
4
Q
What structures are contained within the vertebral canal? (5)
A
Spinal cord Cerebrospinal fluid Spinal blood vessels Meninges Fat
5
Q
What structure pass through the intervertebral foramina?
A
Thoracic spinal nerves
Arteries
Veins
6
Q
What type of joint is between the ribs and costal cartilages anteriorly?
A
Primary cartilaginous joint
7
Q
What is the point of greatest weakness of the rib?
A
The angle of the rib, where a short distance beyond the tubercle the shaft swings forward
8
Q
What is the scalene tubercle?
A
Attachment point found on the first rib for the scalenus anterior muscle
9
Q
The roughened area on the superior surface of the 2nd rib provides attachment for which muscle?
A
Seratus anterior muscle
10
Q
What are the 3 superior and 2 lateral notches of the manubrium?
A
Superior:
- Single
- Central suprasternal
- jugular
Lateral:
- 2x clavicular
11
Q
What is the Sternal Angle/Angle of Louis and what type of joint is it?
A
Articulation of the manubrium and the sternum
Secondary cartilaginous joint
12
Q
What are the 3 beauchamp & childress principles of medical ethics?
A
Respect for patient autonomy
Beneficence
Non-maleficence
Justice (ie equality for all patients)
13
Q
What are the 4 quadrants of ethics used to approach a case?
A
Medical indications: Considering the treatment options for each condition
Patient preferences
Quality of life
Contextual features: Surrounding aspect that could influence decision or be affected by the decision
14
Q
In the neck which fascia surrounds the following columns:
- Neuro-musculo-skeleton
- Visceral
- Carotid neurovascular bundle
- Investing fascia
A
- Neuro-musculo-skeleton = Prevertebral fascia
- Visceral = Pretracheal and buccopharyngeal
- Carotid neurovascular bundle = Carotid sheath
- Investing fascia = Everything surround by this collar-like layer
15
Q
What muscles are enclosed by investing layer?
A
Trapezius
Sternocleidomastoid
16
Q
What fascial layers are separated by the retropharyngeal space?
A
The buccopharyngeal and prevertebral fascia
17
Q
Where do these fascial columns start and finish:
1. Pretracheal
2. Prevertebral
3.
A
- Pretracheal: Hyoid to pericardium
2. Prevertebral: Base of skull to T3:
18
Q
Where do these spaces start and finish:
- Pretracheal
- Retropharyngeal
A
- Neck to superior mediastinum
2. Base of skull to diaphragm
19
Q
What are the borders of the posterior triangle of the neck?
A
Anterior: Posterior border of the SCM.
•Posterior: Anterior border of the trapezius muscle.
•Inferior: Middle 1/3 of the clavicle.
20
Q
What are the borders of the anterior triangle of the neck?
A
Superiorly – Inferior border of the mandible (jawbone)
•Laterally – Medial border of the sternocleidomastoid
•Medially – Imaginary sagittal line down midline of body
21
Q
What passes through the stylomastoid foramen?
A
The Facial Nerve
22
Q
What are the two cartilages of the larynx?
A
Thyroid and cricoid
23
Q
Trapezius:
Attachment?
Innervation?
Action?
A
Attachment- From the base of the skull, ligamentum nuchae and the spinous processes of T7-12. Attaches to the spine of scapula, the clavicle and acromion
Innervation- Accessory nerve
Action- Elevates, rotates and pulls the scapula inferior
24
Q
Sternocleidomastoid:
Attachment?
Innervation?
Action?
A
Attachment- It originates on the anterior surface of the manubrium, and the superior border and anterior surface of the medial third of the clavicle. Attaches on the lateral surface of the mastoid process and the nuchal line of the occipital bone.
Innervation- Accessory nerve
Action- Rotates head to opposite side and tilts ear to same shoulder
25
What gland overlies the transverse process of the atlas?
The parotid gland
26
What are the two main veins of the head and neck?
Internal jugular vein
| External jugular vein
27
Where exactly is the carotid pulse found in relation to the vessels of the head/neck?
At the bifurcation of the common carotid artery into the internal and external carotid artery)
This is at level C3/4
28
What are the two pulses that can be felt as branches of the external carotid artery?
Superficial temportal
| Facial
29
Which lies more posterior, the IJV or IJA?
IJV
| [Although the IJV is anterior to the artery at it's termination]
30
What emerges posterior o the sternocleidomastoid and passes adjacent to the external jugular vein?
The cutaneous cervical plexus
31
What the 8 lymphatic nodes in the head and neck?
1. Submental node
2. Submandibular node
3. Occipital node
4. Mastoid nodes
5. Jugulodigastric node
6. Superficial cervical nodes
7. Deep cervical nodes
8. Jugulo-omohyoid node
32
Describe the structure of a thoracic vertebrae
The vertebral canal contains the spinal cord, its coverings, meninges and cerebrospinal fluid, spinal blood vessels and fat.
The vertebral body is small and heart shaped.
There are 2 pairs of demifacets on each side of the body. These are surfaces for articulation with the heads of 2 pairs of ribs. The superior demifacets articulate with the heads of its own numbered pair of ribs and the inferior demifacets articulate with the heads of the pair of ribs below (vertebra T4 articulates with the fourth and fifth pairs of ribs).
There are articular facets are on the tips of the transverse processes for articulation with the tubercles of the ribs (the transverse processes of vertebra T4 articulate with the fourth pair of ribs).
33
What are the costal cartilages made up of?
Hyaline cartilage
34
Identify the 5 notches on the manubrium?
Superiorly there are 3 notches, a single, central suprasternal or jugular notch which is easily palpable.
2 clavicular notches for the medial ends of the clavicles.
35
What are the 4 factors contributing the conduction of cardiac muscle?
Functional syncytium
Conduction network (ie not all muscle cells contract)
"Pacemaker" activity
Autonomic innervation
36
What does the term functional syncytium mean in terms cardiac conduction?
Cells of atrial myocardium are all electrically connected.
They depolarize and contract synchronously
Ventricles are similar but have a separate functional unit
37
What is the intrinsic pacemaker of the cardiac muscle?
Sinoatrial Node
38
What is the effect of sympathetic and parasympathetic nerves on the rate of SAN depolarization?
Sympathetic nerves increase the rate of SAN depolarization
| Parasympathetic nerves decrease the rate of SAN depolarization
39
What are the 5 phases of atrial/ventricular depolarization?
```
PHASE 0
Rapid depolarization due to increase in Na perm
PHASE 1
Start of repolarisation as fast
Na+ channels close
PHASE 2
Effect of Ca2+ entry via L-type, causes a plateau.
channels
PHASE 3
Rapid repolarisation as ↑
[Ca2+]i stimulates K+ channels to open and gK+↑
Ca2+ L-type channels close
PHASE4
Stable resting membrane
potential where gK+ exceeds
gNa+ by 50:1
```
40
What are the 3 phases of SAN depolarization?
PHASE 1
• Gradual drift ↑ in resting membrane potential due to ↑ gNa+ as “funny” F-type Na+ channels open and ↓ gK+ as K+ channels slowly close
• “Pacemaker potential”
• Transient (T) Ca2+ channels help with
the “final push”
PHASE 2
• Moderately rapid depolarisation due to Ca2+ entry via slow (L) channels
PHASE 3
• Rapid repolarisation as elevated internal Ca2+ stimulates opening of
K+ channels and an ↑ in gK+
41
What are F-type Na+ channels?
A mixed sodium/potassium current that activates upon hyperpolarisation
42
What nerves innervate the SAN and AVN?
The vagus nerve
43
How does sympathetic ANS stimulate the pacemaker activity?
| What is chronotropic effect on the pacemaker activity?
SYMPATHETIC STIMULATION: Noradrenaline acts on B1 receptors to increase cAMP production
Increases rate of SAN phase 1 depolarization. By increasing the conductance of Ca and Na.
Sympathetic stimulation shows positive chronotropic effect
44
How does parasympathetic ANS stimulate the pacemaker activity?
What is chronotropic effect on the pacemaker activity?
Acetylcholine acts on M2 receptors to decrease cAMP production
This reduces the rate of phase 1 depolarization
Hyperpolarises membrane potential to lower starting level
Parasympathetic stimulation shows negative chronotropic effect
45
```
Order the following in order of rate of depolarization:
SAN
Bindle of His
Purkinje Fibers
AV Node
Ventricles
```
1. SAN 90/min
2. AV Node 60/min
3. Bundle of His 50/min
4. Purkinje fibers 40/min
5. Ventricles 30/min
46
Why is the SAN the intrinsic pacemaker? And if conduction is blocked, what happens?
The SAN has the fastest rate hence it is the intrinsic factor
If conduction is blocked, downstream tissue assume their intrinsic rate
47
How many electrodes does an ECG use?
10 (4 on the limbs, 6 across the chest)
| Arranged in Einthoven's triangle
48
What do the limb leads of an ECG measure?
The sum of electrical activity of the heart and the direction that electrical activity is moving in
49
Observed signal=
E x Cosx
E= Electrical event
x= Angle between event and ECG lead
50
In an ECG what do the following waves represent:
P wave?
QRS wave?
T wave?
P wave: Atrial depolarization
QRS wave: Ventricular depolarization
T wave: Ventricular repolarization
51
What are the time intervals for the following:
P-R interval?
QRS complex width?
Q-T interval?
– P-R interval (0.15-0.2s)
– QRS complex width (0.08-0.12s)
– Q-T interval (0.25-0.35s)
52
At the resting heart rate, why can't the maximal contractile force be generated?
The increase in [Ca] (via influx and sarcoplasmic release) isn't sufficient.
53
How can a greater contractility be generated?
The main aim is to increase the Ca release by the SR. Hence during relaxation if more Ca is returned to the SR instead of being exchanged for extracellular Na at the cell membrane.
54
How does the release of Noradrenaline on B1 receptors alter contractility?
Leads to an increase in cAMP with enhances Ca influx. This promotes storage and release of Ca from the SR.
- -> increase contractility
- -> increase speed of relaxation
55
Difference between inotropic and chronotropic?
Inotropic: The affect on the strength of contraction of heart muscle
Chronotropic: Effect on the heart rate and rhythm
56
Inotropic effect of:
Sympathetic innervation?
Parasympathetic innervation?
Sympathetic innervation: Positive inotropic effect
| Parasympathetic innervation: Indirect negative inotropic effect
57
What is the difference between the locations of innervation of the heart between sympathetic and parasympathetic innervation?
Sympathetic innervates entire heart
| Parasympathetic innervates mainly the SAN but also the atria
58
What causes the refractory period in cardiac muscle cells?
| Can cardiac muscle cells significantly summate contractions?
Inactivation of Na channels.
| Cannot significantly summate contractions
59
What does the term relative refractory period represent (RRP)?
The period when a stronger than normal stimulus is needed to elicit neuronal excitation.
60
What does the term absolute refractory period mean (ARP)?
The period immediately following the firing of a nerve fiber when it cannot be stimulated no matter how great a stimulus is applied
61
What does the term "Period of supranormal excitability" mean? (SNP)
A period at the end of phase 3 of the action potential during which activation can be initiated with a milder stimulus than is required at maximal repolarization
62
In a cardiac cell action potential, put these periods in order:
ARP, SNP, RRP
ARP --> RRP --> SNP
63
What happens if during the RRP a sufficient stimulus elicits an excitation and why?
An early premature contraction forms which doesn't reach the maximal force of contraction as the Ca levels weren't completely restored.
64
Why are atria described as primer pumps?
As 80% of ventricular filling is passing due to normal blood flow so atrial contraction ‘tops up’ remaining ~20% volume
65
What is the End Systolic volume? (ESV)
Volume in ventricle at the end of systole (ie when the mitral valve opens)
66
When is the End Diastolic Volume? (EDV)
Volume in the ventricle at the end of diastole (ie when the mitral valve closes)
67
How do you calculate stroke volume?
EDV-ESV = Stroke volume = Quantity of blood expellec per beat in LITRES
68
Cardiac output =
SV x HR = CO = Volume of blood pumped by the heart (L/min)
69
What is the intrinsic mechanism for controlling the stroke volume?
The Frank-starling mechanism ie by increase the End Diastolic Volume which increases the force of contraction (as the ventricle walls are stretched full
70
What is preload?
The end-diastolic-ventricular pressure
71
What is afterload?
The pressure in the wall of the left ventricle during ejection. (ie the end load against which the heart contracts to eject blood.)
Afterload is readily broken into components: one factor is the aortic pressure the left ventricular muscle must overcome to eject blood.
72
What is the extrinsic mechanism for controlling stroke volume?
Sympathetic nervous control
73
Increases in which two factors increases the stroke volume and HR?
Sympathetic nerve activity and adrenaline
74
What limits how fast blood can escape into the arterial system?
The systemic vascular resistance (SVR)
During SYSTOLE the arterial system expands to accommodate full ventricular stroke volume
During DIASTOLE the energy stored in arterial walls during systole drives blood forward during diastole
75
What is compliance?
When the change in volume is greater than the change in pressure (i.e. tubes that have elastic walls)
76
What happens to compliance of blood vessels as age increases?
Compliances decreases hence internal pressurs rise
77
How do you calculate pulse pressure?
Systolic pressure - diastolic pressure
78
How do you calculate Mean Arterial Blood Pressure (MABP)?
MABP= Diastolic pressure + 1/3Pulse Pressure
79
How do you calculate arterial pressure?
Arterial pressure = Cardiac Output x Total peripheral resistance
80
What is the Poiseuille Equation?
Flow = (difference in pressure)/(resistance)
81
What are the 3 factors which determine the magnitude of pulse pressure?
Stroke volume: intrinsic/extrinsic factors, afterload, preload, sympathetic innervation
Speed of ejection of stroke volume
Arterial compliance
82
What are 3 grooves/sulci of the heart?
1. Coronary sulcus/ atrioventricular groove
2. Anterior interventricular groove
3. Posterior interventricular groove
83
What are the only 2 branches of the ascending aorta?
The left and right coronary arteries
84
What does the left coronary artery divide into?
1. Anterior interventricular/ Left Anterior Descending (LAD)
| 2. Circumflex branches
85
Describe the journey of the right coronary artery in supplying the heart?
1. Arises from the right aortic sinus
2. Passes between R auricle and pulmonary trunk
3. Enters the coronary sulcus and gives an SA nodal branch
4. Gives a right Marginal branch (which supplies inferior surface)
5. Gives of the Posterior interventricular branch
6. Anastomoses with branches of the Left Coronary Apex in the coronary sulcus and at the apex
86
Where does the right coronary artery and its branches usually supply?
- Walls of RA and RV
- Sinu-atrial and AV nodes
- Posterior part of interventricular septum (incl. Bundle of His)
- Small areas of the walls of the LA and LV
87
Which is usually dominant, the RCA or LCA?
RCA
88
Describe the course of the left coronary artery?
1. Arises from the left aortic sinus between the left auricle and the pulmonary trunk
2. Enters the coronary sulcus
3. Divides into: Circumflex branch, Anterior interventicular branch (/LAD)
4. Anastomoses with branches of the RCA in the coronary sulcus posteriorly and at the apex
89
What are obstructions of the following vessels usually referred to as:
- Right coronary artery?
- Left anterior descending artery?
- Left circumflex branch?
RCA obstruction= Inferior infarct
LAD obstruction= Anterior infarct
Circumflex obstruction= Lateral infarct
90
Where does the left coronary artery and it's branches usually supply?
- Walls of the LA and LV
| - Most of the interventricular septum (incl. part of the AV node)
91
What does CABG stand for?
Coronary Artery Bypass Grafting
92
What is a minimally invasive way to treat a coronary obstruction?
Percutaneous Transluminal Coronary Angioplasty (PTCA)
| A catheter is passed into the femoral artery and guided up into the coronary artery to insert a Thrombokinase stent)
93
What is a sinus?
A channel permitting the passage of blood or lymph fluid that is not a blood or lymphatic vessel
94
What are the 3 main coronary veins and what arteries do they lie alongside?
Great cardiac veins (with LAD)
Middle cardiac vein (with Post. Interventricular Artery)
Small cardiac vein (with marginal artery)
MOST DRAIN TO THE CORONARY SINUS
95
Where does the coronary sinus lie and drain into?
Lies between the posterior LA and LV and empties into the RA
96
What are the 5 key components of the conducting system of the heart?
```
SAN (In RA)
AV Node (In RA)
Bundle of His
Right Bundle Branch
Left Bundle Branch
```
97
What is the only conductive route through the fibrous skeleton?
The atrioventricular bundle of His
98
What does the bundle of His divide to form?
1. Right bundle branch
2. Left bundle branch
3. Purkinje fibres (spreads conduction to ventricles)
99
What is the route of parasympathetic and sympathetic innervation of the heart?
Sympathetic cardiac nerves from both sympathetic trunks
| Parasympathetic cardiac branches from both left and right vagus nerves
100
Where are the two common sites of cardiac referred oain?
Anterior chest wall and medial aspect of left arm
101
How is laminar blood flow in vessels encouraged?
Vessels are lined with endothelial cells
Fluid molecules making contact with the vessel wall, move slower. So in the centre of the lumen the flow is smooth and fast
102
What is Reynold's number? (Re)
A value used to indicate whether flow is laminar or turbulent.
For a given system, there will be a "critical value" for Re, above which turbulence is highly likely
103
What is the equation for Reynold's number?
Re = (velocity)(radius)/(viscosity)
104
What 4 factors would promote turbulence in a vessel?
High velocity flow
Large diameter vessels
Low blood viscosity
Abnormal vessel wall
105
What is thixotropy? Example?
Thixotropy is when certain fluids that are thick/viscous under static conditions will flow (become thin, less viscous) over time when shaken, agitated, or otherwise stressed.
Blood is thixotropic
106
What is LaPlace's law?
```
Distending pressure (P) produces an opposing force/tension (T) in the vessel wall, which is proportional to the radius of the vessel
Tension = Pressure x Radius
T=PR
```
107
What are the 3 benefits of Laplace's law? (CCA)
Control of blood flow: Low tensions in vessels walls permit blood pressures in arterioles. Precapillary sphincters regulate tissue blood flow.
Capillaries: The thin walls essential for exchange can still withstand pressure
Aneurysm: A weakness in the wall can be counteracted by the tension from the muscle in the vessel wall
108
Name 4 mechanisms in vessels that alter tissue blood flow?
- Active and reaction hyperemia
- Flow autoregulation
- Vasomotion
- Response to injury: via release of endothelin-1
109
What is flow autoregulation?
Changes in arterial pressure causes the arterioles to constrict or dilate. If the pressure is too high, the arterioles constrict to reduce flow
Also myogenic response is when the smooth muscle in arterioles are stretched, the calcium release channels open which cause vessel to constrict
110
What is vasomotion?
Spontaneous oscillating contraction of blood vessels
111
What is the difference between active and reaction hyperaemia?
Active hyperaemia: Result of increased demand e.g. in skeletal muscle
Reactive hyperaemia: Result of occluded blood vessels
112
What is mechanism by which endothelial cells regulate vascular tone?
The endothelial cells produce eNOS (endothelial Nitric Oxide Synthase). This convents arginine to NO which then promotes dilation of the underlying smooth muscle
113
Name the substances/structures involved in the vasoconstriction via the following mechanisms:
- Neural?
- Hormonal?
- Local?
Neural: Sympathetic nerves
Hormonal: Adrenaline, Angiotensin II, Vasopressin
Local: Myogenic response, endothelin-1
114
Name the substances/structures involved in the vasodilation via the following mechanisms:
- Neural?
- Hormonal?
- Local?
Neural: NO-releasing nerves
Hormonal: Adrenaline, Atrial-natriuretic peptide
Local: Decrease O2, NO, bradykinin, K, CO2, H, Adenosine
115
What are viruses?
Small infective agents consisting essentially of nucleic acid (RNA/DNA) enclosed in a protein coat.
They are obligate intracellular parasites
116
What are the main stages in viral replication?
The binding sites on the virus (ie polypeptides on the envelope or capsid) attach to the receptors on the host cell.
The receptor-virus complex enters the cell by receptor-mediated endocytosis during which the virus coat may be removed
Once in the host cell, the nucleic acid of the virus then uses the cell's machinery for synthesizing new virus particles
117
Name 7 classes of antiviral drugs?
1. Entry inhibitors
2. Viral uncoating
3. Reverse transcriptase (RT) Inhibitors:
- Nucleoside anologue e.g. Aciclovir, NRTIs (nucleoside reverse transcriptase inhibitors, prevents viral replication).
- NNRTIs (Non-nucleoside reverse transcriptase inhibitor)
4. Protease inhibitors: Chops up nucleic acid
5. Integrase inhibitors: Integrates host nucleic acid with viral nucleic acid
6. Virus release inhibitors
7. Immunomodulator PEG-IFN
118
What are the 9 stages of the virus life cycle?
1. Recognition
2. Attachment
3. Penetration/Fusion
4. Uncoating
5. Transcription
6. Protein synthesis
7. Replication
8. Assembly /Envelopment
9. Lysis + release / Budding + release
119
Name 4 drugs for the treatment of HCV?
Ribavirin
Peginterferon alpha
Simeprevir, Ledipasvir and sofobuvir
Protease inhibitors: Telaprevir, Boceprevir, Paritaprevir
120
Name 2 DNA viruses? and the drug that treats them?
Herpes Simplex Virus (HSV)
Human Papilloma Virus (HPV)
Treatment: Aciclovir
121
Name 2 of the main RNA viruses?
Influenza (Flu)
| Hepatitis C Virus (HCV)
122
What is the difference between positive and negative sense viral RNA?
Positive-sense viral RNA= Similar to mRNA and can be immediately translated by the host cell
Negative-sense viral RNA= Complementary to mRNA and must be converted to positive-sense by an RNA polymerase before translation
123
Name 2 of the main retroviruses?
HIV, Human T Cell Leukemia Virus (HTLV)
124
What is the mechanism of a retrovirus?
The virus contains reverse transcriptase (RT) an RNA-dependent DNA polymerase, which makes a DNA copy of the viral RNA
This DNA copy is integrated into the genome of the host cell, making a provirus.
This provirus is transcribed into genomic RNA and mRNA for translation into viral proteins.
125
How do the mechanisms of NRTIs and NNRTIs differ?
NRTI: Inhibit viral DNA synthesis by acting as a chain terminator
NNRTI: Binding induces conformational changes that inhibit the catalytic activity of RT
126
Name 6 examples of NRTIs
```
Zidovudine
Abacavir
Lamivudine
Didanosine
Zalcitabine
Stavudine
```
All analogues of bases that act as chain terminators by not offered the 3' hydroxyl function
127
What is the mechanism for protease inhibitors as anti-viral drugs?
In HIV the mRNA is translated into biochemically inert proetins. A virus specific protease then converts them into various functional proteins.
Protease inhibitors are effective as the protease does not occur in the host so it is a good selective-toxicity target.
128
What two reactions does integrase mediate?
1. 3' end processing of the double-stranded viral DNA ends
| 2. Strand transfer which joins the viral DNA to the host chromosomal DNA = Functionally integrated provirus
129
What is the mechanism of the entry of HIV into a new cell?
The process of mediates by the envelope glycoproteins spike (which is a trimer of gp120 and gp41).
On the new cell, the recetopr CD4 plus one of two co-receptors CCR5 CXCR4
```
CD4= Glycoproteins found on the surface of immune cells
CCR5= C-C chemokine receptor type 5 on WBC surface
CXCR4= C-X-C chemokine receptor type 4
```
130
Name 2 fusion/entry inhibitors and how they work?
Maraviroc: Binds to CCR5, preventing an interaction with gp120
Enfuvirtide: Binds to gp41 and interferes with its ability to approximate with two membranes
131
What does HAART stand for?
Highly Active Antiretroviral Therapy
132
How do Amantadine and Rimantadine function as antiviral drugs?
By blocking the ion channel, M2, which is essential for two stages of viral replication(in the fusion and release stages)
133
Name 2 influenza inhibitors and their mechanism?
Examples of neuraminidase (NA) Inhibitors: Tamiflu and Relenza
NA inhibitors mimic the sialic acid natural substrate by binding to the NA active site which halts virus replication
134
What is the role of Neuraminidase in influenza infection?
Cleaves sialic acid from the cell surface so that newly made viruses are released and able to spread to uninfected cells
135
As pregnancy progresses the placenta becomes...
Thinner
136
Describe the structure and interactions present at the membrane between the maternal and foetal circulations?
Endothelium of the foetal capillaries is covered only by syncytiotrophoblast which presents a huge surface area of microvilli.
Maternal capillaries break down and maternal blood baths the foetal microvilli direction.
Low pressure system
There is no mixing of maternal and foetal blood
137
What are the 3 placental vessels?
1 x Umbilical vein: Which carries oxygenated blood from placenta
2 x Umbilical arteries: Which carries deoxygenated to placenta via the umbilical cord
138
How does foetal circulation differ from post-natal circulation? (5)
1. No requirement for a pulmonary circulation
2. The foetal has a restricted hepatic circulation
3. Foetal circulation has 3 shunts to avoid the lungs and liver (only). These must be obliterated at birth
4. Each circuit of the body involves ONE passage through the heart
5. Oxygenated and deoxy blood are not completely separated
139
What stunt is used to by-pass the pulmonary circulation from the IVC in foetal circulation and what is the route of the blood?
The foramen ovale
| IVC-->RA --> (foramen ovale) --> LA --> LV --> Aorta --> Systemic circulation
140
What forces the foramen ovale to close?
At birth thef rist breath pulls blood into the pulmonary circulation. When blood is then returned to the LA the pressure rises, closing the foramen ovale
141
What stunt is used to by-pass the pulmonary circulation from the SVC in foetal circulation and what is the route of the blood?
The ductus arteriosus
| SVC --> RA --> RV--> PT --> (Ductus arteries) --> Aorta
142
What is the position of the ductus arteriosus?
Connected the pulmonary trunk to the inferior aspect of the arch of the aorta
143
What is the distribution of blood from the RV in foetal circulation?
90% passes via ductus arteriosus into aorta
| 10% of RV passes to pulmonary circulation to supply developing lungs
144
Patency of the ductus arteriosus is dependent upon...
Prostaglandins
145
Which stunt is used to by pass the liver in foetal circulation?
Ductus venosus
146
What is the consequence of non-closure of the foramen ovale?
Patent foramen ovale (PFO)
147
What major events happen to the circulation at birth?
1. Pulmonary circulation is established immediately
| 2. Obliteration of ductus arteriosus
148
What are the two phases of ductus arteriosus obliteration?
1. Initial phase during the first hour due to smooth muscle constriction.
- Oxygen is potent DA constrictor, levels increase after first breath
- Prostaglandin levels fall as placenta no longer producing them
- Prostaglandin receptors and bp fall in the DA
2. Anatomic closure results from thickening of the tunica intima. Occurs over period of 1-3 months
149
What is left behind after ductus arteriosus obliteration?
Ligamentum arteriosum
150
What is the risk of a patent ductus arteriosus forming?
Aortic pressure > PT pressure
| Hence blood will flow back into the pulmonary circulation causing PULMONARY HYPERTENSION and CONGESTIVE CARDIAC FAILURE
151
How and when does the formation of the heart tube begin?
In the mesoderm from angiogenetic clusters, as a horseshoe at the cephalic end of the trialminar disc. Due to folding the two limbs of the horseshoe fuse to form one heart tube in the thorax.
By day 18 there is the beginning of heart development
152
Order the following events in the development of the heart:
- Folding and looping of the heart tube
- Formation of the primitive heart tube (in mesoderm)
- Formation of the 3 germ layers (trilaminar disc: Ectoderm, endoderm, mesoderm)
- Septum formation in the common atrium
- Septum formation in the ventricles
- Endocardial cushions and AV canal
- Valve formation
- Growth of atria and ventricles
- Septum formation in the ventricles
1. Formation of the 3 germ layers
2. Formation of the primitive heart tube in mesoderm
3. Folding and looping of the heart tube
4. Septum formation in the common atrium
5. Endocardial cushions and the AV canal
6. Septum formation in the ventricles
7. Septum formation in the truncus arteriosus
8. Growth of atria and ventricles
9. Valve formation
153
What is the difference between the epicardium, myocardium and endocardium?
Epicardium: Visceral pericardium
Myocardium: Cardiac muscle
Endocardium: Endothelial lining
154
How does the heart tube loop and fold?
The 2 "ends" fold towards each other and to the right.
| This pushes the "apex" of the loop to the left, which rotates the heart tube so that the right side is more anterior.
155
What is dextrocardia?
When the "ends" of the heart tube fold to the left, which then pushes the developing heart to the RIGHT
156
The venous end of the developing heart receives blood from which vessels?
Cardinal vein
Umbilical vein
Vitelline vein
157
The bulbus cordis will develop to forms different parts of the heart. What will develop from the proximal, middle and distal part?
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Proximal= RV
Middle= Outflow of the ventricles
Distal= PT and Aorta
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158
What is responsible for augmenting the developing heart tube?
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Endocardial cushion growth
There are 3:
- Ventral endocardial cushion tissue
- Dorsal endocardial cushion tissue
- Conotruncal endocardial cushion tissue
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159
What 4 structures are formed during to the enlargement of the endocardial cushions?
1. Interatrial septum
2. Membranous part of the interventricular septum
3. AV valves
4. PT and aorta form the truncus arteriosus
160
How are left and right AV channels formed from a common AV channel?
The tissue in the narrowing between atrium and ventricle swells to form endocardial cushions which then grow to divide the AV canal
161
Name the 5 stages in interatrial septum formation?
1. Weeks 5/6
2. Septum primum grows down towards the endocardial, atrioventricular cushions. Blood passed from RA to LA via the foramen primum
3. Prior to foramen primum closing perforations appear in upper part of the septum primum. These develop into foramen secundum
4. Septum secundum grows down not fully to endocardial cushion and forms foramen ovale
5. Blood passes from RA to LA through two openings: foramen ovale and foramen secundum
162
What are the 4 elements involved in formation of the interventicular septum?
[complete by the end of the 7th week]
1. Endocardial cushions form left and right ridges int he conus
2. An extension of the inf. antriventricular cushion will contribute to the membranous portion of the interventricular septum
3. Proliferation of interventicular septum forms muscular portion
4. The left and right truncal ridges spiral and fuse to form the conotruncal septum with
The interventricular foramen is closed when the membranous part of IVS (on truncal ridges) meet the inferior AV cushion.
163
What is the difference between ASD (Atrial Septal Defect) and VSD (ventriculo-septal defect)?
ASD: Can be a defect in foramen secundum/foramen primum. Ie a large opening between RA and LA
VSD: e.g. no truncal ridges, no spiral to the ridges, truncal septum deviates right and doesn't meet IVS (ie Fallot's tetralogy)
164
What are the features of atrial growth?
Atria enlarge
Atria incorporate adjacent veins to make them smooth. E.g. In RA the crista terminalis defines the change between the original atrium with its musculi pectinate, whilst the part of the atrium derived from foetal vein (sinus venosus) is smooth.
165
How does the formation of the mitral/tricuspid and pulmonary/aortic valve differ?
Mitral/tricuspid: Endocardial cushion growth and cavitation to from papillary muscles and chordae tendineae
Pulmonary/aortic: Hollowing of endocardial tubercles
166
Name the vessels which is formed from the following pharyngeal arches:
- 1st left arch
- 3rd left arch
- 4th left arch
- 4th right arch
- 6th left arch
- 6th right arch
Hint: Superior to inferior vessels
- 1st left arch: Maxillary arteries
- 3rd left arch: Common carotid arteries
- 4th left arch: Aortic arch
- 4th right arch: Right subclavian artery
- 6th left arch: Pulmonary trunk and ductus arteriosus
- 6th right arch: Contributes to pulmonary trunk
167
What is coartaction of the aorta and how is it clinically recognized?
Aortic narrowing after the original of the left subclavian artery
Clinical sign: Femoral pulse weak
168
What is the difference in position of the left and right recurrent laryngeal nerves?
Right: Tucked behind right subclavian artery
Left: Tucked behind ductus arteriosus
So the left is carried into the thorax, the right is not. Refer to slide 35 of thorax 6 for diagram
