Tutor profile: Euan R.
Describe the phases of the cardiac cycle, starting at the end of ventricular diastole.
1. Late Diastole - Both sets of chambers are relaxed and the ventricles are passively filling with blood via the open atrioventricular valves (tricuspid and mitral). 2. Atrial systole - Atrial contraction forces a small amount of additional blood into the ventricle (the active filling phase). 3. Isovolumic ventricular contraction - The first phase of ventricular contraction creates enough pressure to push the atrioventricular valves closed, but does not create enough pressure to open the semilunar valves (aortic and pulmonary). The closed of the AV valves gives S1, the first heart sound ("Lub") 4. Ventricular Ejection phase - As ventricular pressure rises and exceeds the pressure in the arteries. the semilunar valves open and blood is ejected. 5. Isovolumic ventricular relaxation - As ventricles relax, pressure in ventricles falls, and blood flows back into the cusps of the semilunar valves, snapping them closed. This gives S2, the second heart sound ("Dub")
Subject: Biomedical Science
Describe the process of synaptic transmission at the neuromuscular junction.
1. Synthesis and packaging of neurotransmitter (usually) in presynaptic terminals 2. Na+ action potential invades terminal 3. Activates voltage gated Ca2+-channels 4. Triggers Ca2+-dependent exocytosis of pre-packaged vesicles of transmitter 5. Transmitter diffuses across cleft and binds to ionotropic and/or metabotropic receptors to evoke postsynaptic response 6. Presynaptic autoreceptors inhibit further transmitter release 7. Transmitter is (usually) inactivated by uptake into glia or neurones 8. Transmitter is metabolised within cells
There are three major hiatuses of the thoracic diaphragm. Describe the vertebral level at which each occurs, and the structures that pass through them.
The three thoracic diaphragmatic hiatuses are the caval opening, which occurs at T8, the oesophageal hiatus, which occurs at T10 and the aortic hiatus which occurs at T12. The inferior vena cava and branches of the right phrenic nerve pass through the caval opening. The oesophagus and the anterior and posterior vagal trunks of the Vagus Nerve (Cranial nerve X) pass through the oesophageal hiatus. Finally, the descending thoracic aorta, the azygos vein and the thoracic duct pass through the aortic hiatus. At this juncture, the descending aorta becomes known as the abdominal aorta. Remember the mnemonic "I ate 10 eggs at 12" -> I (Inferior vena cava) ate (T8 vertebral level) 10 (T10 vertebral level) eggs (oesophagus + vagus) at (Aorta, azygos vein and thoracic duct) 12 (T12 vertebral level). I hope this helps to simplify the thoracic diaphragmnatic hiatuses and their contents.
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