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Question 1
Correct
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To which protein is T3 mostly bound in the serum?
Your Answer: Albumin
Explanation:In normal man, approximately 0.03 per cent of the total serum T4, and 0.3 per cent of the total serum T3 are present in free or unbound form. The major serum thyroid hormone-binding proteins are: 1) thyroxine-binding globulin [TBG or thyropexin], 2) transthyretin [TTR or thyroxine-binding prealbumin (TBPA)], and 3) albumin (HAS, human serum albumin). TBG has highest affinity for T4, which is 50-fold higher than that of TTR and 7,000-fold higher that of HSA. As a result TBG binds 75% of serum T4, while TTR and HSA binds only 20% and 5%, respectively.
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This question is part of the following fields:
- Endocrinology
- Physiology
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Question 2
Incorrect
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The most resistant area in the brain to hypoxia is:
Your Answer:
Correct Answer: Brain stem
Explanation:The structures in the brainstem are more resistant to hypoxia than the cerebral cortex and the rest of the brain structures.
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 3
Incorrect
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Which of the following would be a contraindication to thrombolysis?
Your Answer:
Correct Answer: Intracranial neoplasm
Explanation:Absolute contraindications to thrombolysis include:Previous intracranial bleeding at any timeStroke in less than 6 monthsClosed head or facial trauma within 3 monthsSuspected aortic dissectionIschemic stroke within 3 months (except in ischemic stroke within 3 hours time)Active bleeding diathesisUncontrolled high blood pressure (>180 systolic or >100 diastolic)Known structural cerebral vascular lesionArterio-venous malformationsThrombocytopeniaKnown coagulation disordersAneurysmBrain tumoursPericardial effusionSeptic embolus
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 4
Incorrect
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The action potential is generated by excitable tissues, which are specialized tissues that can generate a meaningful electrical signal. Local currents transport action potentials down the axons of neurons. Which of the following claims about the action potential's conduction is correct?
Your Answer:
Correct Answer: The areas of the membrane that have recently depolarised will not depolarise again due to the refractory period
Explanation:Local currents propagate action potentials down the axons of neurons. Following depolarization, this local current flow depolarizes the next axonal membrane, and when this region crosses the threshold, more action potentials are formed, and so on. Due to the refractory period, portions of the membrane that have recently depolarized will not depolarize again, resulting in the action potential only being able to go in one direction. The square root of axonal diameter determines the velocity of the action potential; the axons with the biggest diameter have the quickest conduction velocities. When a neuron is myelinated, the speed of the action potential rises as well. The myelin sheath is an insulating coating that surrounds certain neural axons. By increasing membrane resistance and decreasing membrane capacitance, the myelin coating increases conduction. This enables faster electrical signal transmission via a neuron, making them more energy-efficient than non-myelinated neuronal axons. Nodes of Ranvier are periodic holes in a myelinate axon when there is no myelin and the axonal membrane is exposed. There are no gated ion channels in the portion of the axon covered by the myelin sheath, but there is a high density of ion channels in the Nodes of Ranvier. Action potentials can only arise at the nodes as a result of this. Electrical impulses are quickly transmitted from one node to the next, causing depolarization of the membrane above the threshold and triggering another action potential, which is then transmitted to the next node. An action potential is rapidly conducted down a neuron in this manner. Saltatory conduction is the term for this.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 5
Incorrect
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Which of the following antiarrhythmic drugs may be used in the treatment of long QT syndrome?
Your Answer:
Correct Answer: Atenolol
Explanation:Beta-blockers are the mainstay of treatment in long QT syndrome. Implantable cardioverter-defibrillators are the most effective treatment in genotypes with a high risk of recurrence.
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 6
Incorrect
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Closure of the tricuspid valve is marked by which of the following features of the jugular venous waveform?
Your Answer:
Correct Answer: c wave
Explanation:The jugular venous pressure (JVP) classically has three upward deflections and two downward deflections. The upward deflections are the a (atrial contraction), c (ventricular contraction and resulting bulging of tricuspid into the right atrium during isovolumetric systole) and v = venous filling. The downward deflections of the wave are the x (the atrium relaxes and the tricuspid valve moves downward) and the y descent (filling of ventricle after tricuspid opening).
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 7
Incorrect
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Which enzyme hydrolyses triglycerides in lipoproteins into free fatty acids for storage in fat cells?
Your Answer:
Correct Answer: Lipoprotein lipase
Explanation:Lipoprotein lipase is a water-soluble enzyme that hydrolyses triglycerides in lipoproteins, such as those found in chylomicrons and very low-density lipoproteins (VLDL), into two free fatty acids and one monoacylglycerol molecule.
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This question is part of the following fields:
- Metabolism
- Physiology
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Question 8
Incorrect
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Which of the following conditions is procoagulant?
Your Answer:
Correct Answer: Factor V Leiden
Explanation:Factor V Leiden is a variant (mutated form) of human factor V (one of several substances that helps blood clot) that causes an increase in blood clotting (hypercoagulability). With this mutation, the anticoagulant protein secreted (that stops factor V from causing inappropriate clotting) is inhibited, leading to an increased tendency to form dangerous, abnormal blood clots. Christmas disease is otherwise known as Haemophilia B. Hypothrombinaemia and afibrinogenemia both result in inadequate blood clotting.
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This question is part of the following fields:
- Haematology
- Physiology
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Question 9
Incorrect
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Which receptor type is associated with the inhibition of pancreatic endocrine secretion?
Your Answer:
Correct Answer: Α2
Explanation:The activation of alpha 2-adrenergic receptors in pancreatic beta-cells works by inhibiting the secretion of insulin.
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This question is part of the following fields:
- Neurology
- Physiology
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Question 10
Incorrect
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Which caspase is part of both the intrinsic and extrinsic apoptotic pathways?
Your Answer:
Correct Answer: Caspase-3
Explanation:Once initiator caspases are activated in both the intrinsic and extrinsic pathway, they produce a chain reaction, activating several other executioner caspases (Caspase 3, Caspase 6 and Caspase 7).
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 11
Incorrect
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Where on the surface of the chest is the normal site of auscultation for the mitral area?
Your Answer:
Correct Answer: 4th left intercostal space in the mid-clavicular line
Explanation:The mitral valve is situated in the left 4th intercostal space just beneath the sternum, in the mid clavicular line.
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 12
Incorrect
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In the olfactory pathway: Mitral cells project to five regions of the olfactory cortex. Which one of the following is not one of the five regions?
Your Answer:
Correct Answer: Posterior olfactory nucleus
Explanation:The olfactory system contains peripheral and central divisions which are connected by transduction structures. Peripheral division consists mainly of the nostrils, ethmoid bone, nasal cavity, and the olfactory epithelium. Olfactory neurons are receptor cells in the epithelium that detect odour molecules dissolved in the mucus and transmit information about the odour to the brain in a process called sensory transduction. Olfactory nerves and fibers transmit information about odours from the peripheral olfactory system to the central olfactory system of the brain. The main olfactory bulb transmits pulses to both mitral and tufted cells, which help determine odour concentration. These cells also note differences between highly similar odours and use that data to aid in later recognition. The cells are different with the mitral having low firing-rates and being easily inhibited by neighbouring cells, while tufted have high rates of firing and are more difficult to inhibit. The uncus houses the olfactory cortex which includes the piriform cortex, amygdala, olfactory tubercle, and para-hippocampal gyrus. Entorhinal cortex is an area of middle temporal lobe that has connection with the para-hippocampal gyrus.
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This question is part of the following fields:
- Neurology
- Physiology
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Question 13
Incorrect
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Tunica intima is made up of?
Your Answer:
Correct Answer: Endothelial cells
Explanation:Tunica intima is a single cell thick lining of endothelial cells that lines the inside of the blood vessels. It is the inner most layer of the blood vessel.
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 14
Incorrect
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Peristalsis is an example of:
Your Answer:
Correct Answer: Enteric nervous system
Explanation:Peristalsis is a type of contraction where radial symmetrical contraction and relaxation of muscles propagates food in a downward wave through the gut. The enteric nervous system is one of the main divisions of the nervous system and consists of a mesh-like system of neurons that controls the function of the gastrointestinal tract. It has an independent reflex activity. The neurons of this system re collected into two types of ganglia: myenteric (or Auerbach’s) and submucosal (or Meissner’s plexuses). Myenteric plexuses are located between the inner and outer layers of the muscularis externa, while submucosal plexuses are located in the submucosa.
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This question is part of the following fields:
- Gastrointestinal
- Physiology
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Question 15
Incorrect
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What is the three main structures in the portal triad ( portal space )?
Your Answer:
Correct Answer: Branch of hepatic artery, branch of portal vein, bile ductules
Explanation:A portal triad (also known as portal field, portal area, or portal tract) is a distinctive arrangement in the liver. It is a component of the hepatic lobule. It consists of the following five structures:- Proper hepatic artery- Hepatic portal vein- Common bile duct- Lymphatic vessels- Branch of the vagus nerve
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This question is part of the following fields:
- Hepatobiliary
- Physiology
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Question 16
Incorrect
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What is the most common cardiac defect seen in patients with Down’s syndrome?
Your Answer:
Correct Answer: Atrioventricular septal defect
Explanation:The rate of congenital heart disease in new-borns with Down syndrome is around 40%. Of those with heart disease, about 80% have an atrioventricular septal defect or ventricular septal defect with the former being more common. Mitral valve problems become common as people age, even in those without heart problems at birth.[3] Other problems that may occur include tetralogy of Fallot and patent ductus arteriosus.[38] People with Down syndrome have a lower risk of hardening of the arteries
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 17
Incorrect
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During anaerobic glycolysis, the net production of ATP is:
Your Answer:
Correct Answer: 2
Explanation:Anaerobic glycolysis is the transformation of glucose to lactate when limited amounts of oxygen (O2) are available. Anaerobic glycolysis is only an effective means of energy production during short, intense exercise, providing energy for a period ranging from 10 seconds to 2 minutes. It produces 2 ATP molecules per glucose molecule.
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This question is part of the following fields:
- Metabolism
- Physiology
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Question 18
Incorrect
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What is the result of maltase deficiency in the brush border of the small intestine?
Your Answer:
Correct Answer: Results in increased passage of maltose in stool
Explanation:Maltase is an enzyme produced from the surface cells of the villi, lining the small intestine and aids in hydrolysing the disaccharide maltose, which splits into two molecules of α-glucose. It is done by breaking the glycosidic bond between the ‘first’ carbon of one glucose and the ‘fourth’ carbon of the other (a 1–4 bond). Hence, a deficiency of enzyme maltase will result in the increased passage of maltose in the stool.
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This question is part of the following fields:
- Gastrointestinal
- Physiology
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Question 19
Incorrect
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Which of the following factors is most likely to lead to an increase in serum cortisol levels?
Your Answer:
Correct Answer: Severe emotional stress
Explanation:Cortisol is widely known as the stress hormone. Alterations in cortisol levels have been found in relation to mood disorders, illness, trauma, pain, fear, exertion, and anxiety, amongst other stimuli.
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This question is part of the following fields:
- Endocrinology
- Physiology
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Question 20
Incorrect
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The following cells replicate without shortening their telomeres because they express telomerase.
Your Answer:
Correct Answer: Germ cells
Explanation:Telomerase activity is seen in germ cells and is absent in somatic cells. Telomeres prevent the chromosomes from shortening and prevent the coding portion of the DNA from being lost, thus allowing the cell to replicate indefinitely. During replication telomeres may be lost resulting in cell death.
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This question is part of the following fields:
- Genetics
- Physiology
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Question 21
Incorrect
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Which of the following does not contribute to increased stroke volume during exercise?
Your Answer:
Correct Answer: Increased length of filling time during diastole
Explanation:Prolonged aerobic exercise training may also increase stroke volume, which frequently results in a lower (resting) heart rate. Reduced heart rate prolongs ventricular diastole (filling), increasing end-diastolic volume, and ultimately allowing more blood to be ejected.
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 22
Incorrect
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Which of the following tracts are involved in the control of vital functions?
Your Answer:
Correct Answer: Reticulospinal
Explanation:Reticulospinal tract pass down from the reticular formation of the mid brain, pons and medulla. It descends in the lateral white column. Both sets of fibers enter the anterior grey column and may facilitate or inhibit the gamma and alpha neurons. By this means the reticulospinal tract controls voluntary and reflex activities. It also contains the descending autonomic fiber, thus providing a pathway for the hypothalamus to control the sympathetic and parasympathetic pathways.
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This question is part of the following fields:
- Neurology
- Physiology
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Question 23
Incorrect
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Where is the aqueous humor normally reabsorbed?
Your Answer:
Correct Answer: Canal of schlemm
Explanation:Aqueous humor is a clear protein free fluid secreted by the ciliary body, it travels to the anterior chamber through the pupil and is absorbed through a network of trabeculae into the canal of schlemm
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This question is part of the following fields:
- Neurology
- Physiology
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Question 24
Incorrect
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Which statement regarding fever is correct:
Your Answer:
Correct Answer: Body temperature is regulated is by a centre in the floor of the third ventricle
Explanation:The hypothalamus is located on the floor of the third ventricle and is the centre of regulation of body temperature. It uses a set point to regulate other body systems as well. Diurnal variation of temperature is not seen in humans. the principal mediator of fever is interleukin I, although interferon alfa also plays a role. Fever can cause rhabdomyolysis or muscle breakdown
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This question is part of the following fields:
- Infectious Diseases
- Physiology
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Question 25
Incorrect
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The predominant site in the lymph node where B lymphocytes are found is:
Your Answer:
Correct Answer: Cortex
Explanation:The cortex of the lymph node consists of the lymphoid nodules and sinusoids and posses a germinal centre from which B cells proliferate. The cortex of the lymph node predominately consists of B cells.
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This question is part of the following fields:
- Immunology
- Physiology
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Question 26
Incorrect
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The lower oesophageal sphincter is under neural control. Which of the following causes contraction of the intrinsic sphincter?
Your Answer:
Correct Answer: Acetylcholine
Explanation:The lower oesophageal sphincter (LOS) is a specific region of the oesophageal circular smooth muscle. It allows the passage of a food bolus to the stomach and prevents the reflux of gastric contents into the oesophagus. The tone of the LOS is myogenic in origin and depends on smooth muscle properties that lead to the opening of Ca2+ channels but can also be modulated by enteric motor neurons, the parasympathetic and sympathetic extrinsic nervous system and several neurohumoral substances. Nitric oxide causes LOS relaxation. Acetylcholine and tachykinins are involved in the LOS contraction.
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This question is part of the following fields:
- Gastrointestinal
- Physiology
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Question 27
Incorrect
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Where is intrinsic factor secreted?
Your Answer:
Correct Answer: Gastric parietal cells
Explanation:Intrinsic factor (IF), also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 (cobalamin) later on in the small intestine.
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This question is part of the following fields:
- Haematology
- Physiology
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Question 28
Incorrect
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Near the transcription site of a gene, the site at which RNA polymerase and its cofactors bind is known as the:
Your Answer:
Correct Answer: Promotor
Explanation:Transcription will begin when the RNA polymerase II binds to the promotor. The promotor is a sequence of 25 nucleotides found upstream from the start site of transcription. This promotor sequence is known as the TATA box. Transcription factors also bond along with RNA polymerase to this site to form a complex. However some may bind to regulatory elements proximal to the promotor site.
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This question is part of the following fields:
- Genetics
- Physiology
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Question 29
Incorrect
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What is pendrin?
Your Answer:
Correct Answer: Cl-/i- antiporter
Explanation:Pendrin is an anion exchange transporter; it is a sodium-independent chloride-iodine exchanger which also accepts formate and bicarbonate. It is present in many different types of cells in the body, particularly the inner ear, thyroid, and kidney. Mutations in pendrin are associated with Pendred syndrome, which causes syndromic deafness and thyroid disease.
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This question is part of the following fields:
- Endocrinology
- Physiology
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Question 30
Incorrect
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During strenuous exercise the following arterial change can take place in a fit athlete:
Your Answer:
Correct Answer: No change takes place
Explanation:The changes which occur in arterial pH, PO2 and PCO2 values during exercise are usually small. Arterial PO2 often rises slightly because of hyperventilation although it may eventually fall at high work rates. During vigorous exercise, when sufficient oxygen for flux through the Krebs cycle is not available, the increased reliance on glycolysis results in increased accumulation of lactic acid, which initially leads to an increase in PaCO2 . However, this is counteracted by the stimulation of ventilation and as a result PaCO2 is decreased. This provides some respiratory compensation for further lactic acid production and prevents a decline in blood pH, which remains nearly constant during moderate exercise.
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This question is part of the following fields:
- Physiology
- Respiratory
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Question 31
Incorrect
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According to Poiseuille’s formula, which 1 of the following will lead to increased flow?
Your Answer:
Correct Answer: Shorter tube
Explanation:V = π p r4 / 8 η lwhere V = discharge volume flow (m3/s)p = pressure difference between the ends of the pipe (N/m2, Pa)r = internal radius of pipe (m)l = length of pipe (m)η = viscosity of fluid
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 32
Incorrect
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Which of the following is NOT a pancreatic enzyme?
Your Answer:
Correct Answer: Pepsinogen 1
Explanation:Pancreatic juice, composed of the secretions of both ductal and acinar cells, is made up of the following digestive enzymes:Trypsinogen, which is an inactive(zymogenic) protease that, once activated in the duodenum into trypsin, breaks down proteins at the basic amino acids. Trypsinogen is activated via the duodenal enzyme enterokinase into its active form trypsin.Colipase is a protein co-enzyme required for optimal enzyme activity of pancreatic lipase. It is secreted by the pancreas in an inactive form, procolipase, which is activated in the intestinal lumen by trypsin.Chymotrypsinogen, which is an inactive (zymogenic) protease that, once activated by duodenal enterokinase, breaks down proteins at their aromatic amino acids. Chymotrypsinogen can also be activated by trypsin.Carboxypeptidase, which is a protease that takes off the terminal amino acid group from a proteinSeveral elastases that degrade the protein elastin and some other proteins.Pancreatic lipase that degrades triglycerides into fatty acids and glycerol.Sterol esterasePhospholipaseSeveral nucleases that degrade nucleic acids, like DNase and RNase.Pancreatic amylase that breaks down starch and glycogen which are alpha-linked glucose polymers.
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This question is part of the following fields:
- Gastrointestinal
- Physiology
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Question 33
Incorrect
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The neurotransmitter in the synaptic cleft is either eliminated or deactivated after the postsynaptic cell responds to the neurotransmitter. Which of the following enzymes catalyses the breakdown of noradrenaline?
Your Answer:
Correct Answer: Catechol-O-methyltransferase (COMT)
Explanation:The neurotransmitter in the synaptic cleft is either eliminated or deactivated after the post-synaptic cell responds to the neurotransmitter. This can be accomplished in a variety of ways: Re-uptake Breakdown Diffusion Serotonin is an example of a neurotransmitter that is uptake. Serotonin is absorbed back into the presynaptic neuron via the serotonin transporter (SERT), which is found in the presynaptic membrane. Re-uptake neurotransmitters are either recycled by repackaging into vesicles or broken down by enzymes. Specific enzymes found in the synaptic cleft can also break down neurotransmitters. The following enzymes are examples of these enzymes: Acetylcholinesterase (AChE) catalyses the acetylcholine breakdown (ACh) The enzyme catechol-O-methyltransferase (COMT) catalyses the breakdown of catecholamines like adrenaline , dopamine and noradrenaline. The breakdown of catecholamines, as well as other monoamines like serotonin, tyramine, and tryptamine, is catalysed by monoamine oxidases (MOA). Diffusion of neurotransmitters into nearby locations can also be used to eliminate them.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 34
Incorrect
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Bone marrow barrier is important to:
Your Answer:
Correct Answer: Allow mature red blood cells to pass into circulation
Explanation:The blood vessels of the bone marrow constitute a barrier, inhibiting immature blood cells from leaving the marrow. Only mature blood cells contain the membrane proteins, such as aquaporin and glycophorin, that are required to attach to and pass the blood vessel endothelium.
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This question is part of the following fields:
- Haematology
- Physiology
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Question 35
Incorrect
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Question 36
Incorrect
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Which of the following is first to rise following myocardial infarction?
Your Answer:
Correct Answer: Myoglobin
Explanation:Myoglobin, is a sensitive indicator of muscle injury and is first to rise following MI within two hours but is nonspecific.Troponin and CK-MB both begin to rise approximately three hours after MI. The cardiac troponins T and I which are released within 4–6 hours of an attack of MI and remain elevated for up to 2 weeks, have nearly complete tissue specificity and are now the preferred markers for assessing myocardial damage.Lactate dehydrogenase (LDH) begins to rise approximately 12 hours after MI.
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 37
Incorrect
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What is the isolated effect of B2 stimulation on the coronaries.
Your Answer:
Correct Answer: Vasoconstriction
Explanation:Norepinephrine and epinephrine are agonists for all adrenergic receptor subtypes, although with varying affinities. Based on their physiology and pharmacology, adrenergic receptors have been divided into two principal types: alpha and betta. These types have been further differentiated into alpha-1, alpha-2, b1, and b2 receptors. Alpha-1 Receptors are located on postsynaptic cells in smooth muscle and elicit vasoconstriction. alpha-2 Receptors are localized on presynaptic membranes of postganglionic nerve terminals that synthesize norepinephrine. When activated by catecholamines, alpha-2 receptors act as negative feedback controllers, inhibiting further norepinephrine release. Activation of myocardial b1 receptors stimulates the rate and strength of cardiac contraction, and consequently increases cardiac output. b1 Receptor activation also stimulates renin release from the kidney. Another class of antihypertensive agents acts by inhibiting b1 receptors. Activation of b2 receptors by epinephrine relaxes vascular smooth muscle and results in vasodilation.
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This question is part of the following fields:
- Cardiovascular
- Physiology
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Question 38
Incorrect
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Inactive cellular marrow is called
Your Answer:
Correct Answer: Yellow marrow
Explanation:The two types of bone marrow are red marrow, which consists mainly of hematopoietic tissue, and yellow marrow, which is mainly made up of fat cells.
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This question is part of the following fields:
- Haematology
- Physiology
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Question 39
Incorrect
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Visual pathways - Choose the true statement:
Your Answer:
Correct Answer: The lateral geniculate nucleus, magnocellular & parvocellular pathways project to the primary visual cortex
Explanation:The optic chiasm is made by the decussation of optic fibers on the nasal side. The magnocellular pathway carries signals for detection of movement. The parvocellular pathway carries cells for detection of shape, size, colour and clarity. The lateral geniculate nucleus (LGN) is the relay centre in the thalamus for he visual pathway. It has layers of magnocellular cells and parvocellular cells that are interleaved with layers of koniocellular cells. The LGN is the main central connection for the optic nerve to the occipital lobe, particularly the primary visual cortex.
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This question is part of the following fields:
- Neurology
- Physiology
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Question 40
Incorrect
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A 60-year-old man presents with marked breathlessness. He has with a history of ischaemic heart disease. On examination, there is coarse bibasal crackles, marked peripheral oedema and chest X-ray taken is consistent with severe pulmonary oedema. RR is 28 per minute. Which receptor is responsible for detecting pulmonary oedema and the subsequent increase in respiratory rate?
Your Answer:
Correct Answer: Juxtacapillary receptors
Explanation:Pulmonary oedema causes stimulation of the Juxtacapillary receptors (J receptors) leading to a reflex increase in breathing rate. These receptors are also thought to be involved in the sensation of dyspnoea. The J receptors are sensory cells and are located within the alveolar walls in juxtaposition to the pulmonary capillaries. Aortic baroreceptor are involved in detecting blood pressure Central chemoreceptors detect changes in CO2 and hydrogen ion within the brain Atrial volume receptors regulate plasma volume
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This question is part of the following fields:
- Physiology
- Respiratory
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Question 41
Incorrect
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Cardiac muscle and skeletal muscle are alike, but there are a few key variations. Which of the following is NOT a characteristic of skeletal muscle but is a characteristic of cardiac muscle?
Your Answer:
Correct Answer: The presence of intercalated discs
Explanation:Cardiac muscle is striated, and the sarcomere is the contractile unit, similar to skeletal muscle. Contracture is mediated by the interaction of calcium, troponins, and myofilaments, much as it occurs in skeletal muscle. Cardiac muscle, on the other hand, differs from skeletal muscle in a number of ways. In contrast to skeletal muscle cells, cardiac myocytes have a nucleus in the middle of the cell and sometimes two nuclei. The cells are striated because the thick and thin filaments are arranged in an orderly fashion, although the arrangement is less well-organized than in skeletal muscle. Intercalated discs, which work similarly to the Z band in skeletal muscle in defining where one cardiac muscle cell joins the next, are a very significant component of cardiac muscle. Adherens junctions and desmosomes, which are specialized structures that hold the cardiac myocytes together, are formed by the transverse sections. The lateral sections produce gap junctions, which join the cytoplasm of two cells directly, allowing for rapid action potential conduction. These critical properties allow the heart to contract in a coordinated manner, allowing for more efficient blood pumping. Cardiac myocytes have the ability to create their own action potentials, which is referred to as myogenic’. They can depolarize spontaneously to initiate a cardiac action potential. Pacemaker cells, as well as the sino-atrial (SA) and atrioventricular (AV) nodes, control this. The Purkinje cells and the cells of the bundle of His are likewise capable of spontaneous depolarization. While the bundle of His is made up of specialized myocytes, it’s vital to remember that Purkinje cells are not myocytes and have distinct characteristics. They are larger than myocytes, with fewer filaments and more gap junctions than myocytes. They conduct action potentials more quickly, allowing the ventricles to contract synchronously. Cardiac myocytes contract by excitation-contraction coupling, just like skeletal myocytes. Heart myocytes, on the other hand, utilise a calcium-induced calcium release mechanism that is unique to cardiac muscle (CICR). The influx of calcium ions (Ca2+) into the cell causes a ‘calcium spark,’ which causes more ions to be released into the cytoplasm. An influx of sodium ions induces an initial depolarisation, much as it does in skeletal muscle; however, in cardiac muscle, the inflow of Ca2+ sustains the depolarisation, allowing it to remain longer. Due to potassium ion (K+) inflow, CICR causes a plateau phase in which the cells remain depolarized for a short time before repolarizing. Skeletal muscle, on the other hand, repolarizes almost instantly. Comparison of skeletal and cardiac muscle: Skeletal muscle Cardiac muscle Striation Striated but arrangement less organised Multiple nuclei located peripherally Usually single nucleus (but can be two), located centrally Discs None Intercalated discs No Gap junctions Gap junctions No Pacemaker Pacemaker Electrical stimulation: Nervous system (excitation) Pacemaker (excitation)
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 42
Incorrect
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Question 43
Incorrect
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An example of cholinergic autonomic neurons are:
Your Answer:
Correct Answer: Sympathetic postganglionic neurons that innervate sweat glands.
Explanation:All preganglionic neurons in both the sympathetic and parasympathetic nervous system secrete acetylcholine. The postganglionic neurotransmitter of the parasympathetic nervous system in all neurons is acetylcholine. Postganglionic fibers of the sympathetic nervous system mainly secrete Noradrenalin and Adrenalin but at sweat glands and erector pili muscles the postganglionic neurotransmitter is acetylcholine.
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This question is part of the following fields:
- Neurology
- Physiology
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Question 44
Incorrect
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With regard to the cell membrane:
Your Answer:
Correct Answer: It consists of an outer hydrophilic & an inner hydrophobic layer
Explanation:The cell membrane consists primarily of a thin layer of amphipathic phospholipids that spontaneously arrange with the hydrophobic tail regions on the inside and the hydrophilic head regions outside. Membranes typically have a large content of proteins, around 50% of membrane volume.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 45
Incorrect
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Question 46
Incorrect
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From which of the following can niacin be synthesized in humans
Your Answer:
Correct Answer: Tryptophan
Explanation:Niacin, is also known as vitamin B3. The liver can synthesize niacin from the essential amino acid tryptophan, requiring 60 mg of tryptophan to make one mg of niacin.
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This question is part of the following fields:
- Haematology
- Physiology
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Question 47
Incorrect
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Pancreatic juice is usually?
Your Answer:
Correct Answer: Alkaline
Explanation:Pancreatic juice is alkaline in nature and has a high amount of bicarbonate ions. About 1500 ml is secreted every day. It also contains a large quantity of enzymes in the inactive form.
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This question is part of the following fields:
- Gastrointestinal
- Physiology
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Question 48
Incorrect
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Which of the following with regard to autosomal dominant disorders are true:
Your Answer:
Correct Answer: The offspring of a heterozygous individual has a 50% chance of inheriting the chromosome carrying the disease allele
Explanation:50% of the children will be effected from parents who are heterozygous for an autosomal dominant disorder. An allele can be dominant or recessive. Individuals, meanwhile, can be homozygous or heterozygous: individuals who are homozygous for a certain gene carry two copies of the same allele. individuals who are heterozygous for a certain gene carry two different alleles.
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This question is part of the following fields:
- Genetics
- Physiology
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Question 49
Incorrect
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The chemosensitive area in the medulla responds to:
Your Answer:
Correct Answer: High hydrogen and high carbon dioxide
Explanation:The chemosensitive area in the medulla responds mainly to high pH levels and carbon dioxide levels. Baroreceptors in the carotid and aortic body respond mainly to oxygen and carbon dioxide partial pressure in blood.
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This question is part of the following fields:
- Physiology
- Respiratory
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Question 50
Incorrect
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Coronary flow is reduced during
Your Answer:
Correct Answer: Tachycardia
Explanation:Maximum amount of blood flow in the coronary arteries occur during diastole. When the heart rate increases which is also called tachycardia the duration of diastole decreases. Hence the amount of blood flow to the cardiac muscle also decreases.
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This question is part of the following fields:
- Cardiovascular
- Physiology
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SESSION STATS - PERFORMANCE PER SPECIALTY
