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Biochemistry Key Answers Paper IV April 2001 Sub code: 4003 I) 1. Arrangements of tracts in internal capsule: - Internal capsule is a mass of white fibers lying between the basal ganglia and thalamus. - Laterally by lenticular nucleus - Medically by caudate nucleus and thalamus. Pyramidal tract in internal capsule: - in horizontal section the internal capsule is ‗V‘ looking medical (a) the pyramidal tracts lie in the Genu, and anterior 2/ 3rd of posterior limb (b) other tracts present in the internal capsule are a. corticonuclear b. frontopontine c. lateral fifth of the temperopontine fibers (c) Posterior limb of internal capsule where superior colliculi is present contains the tract of optic and olfactory pathway. 2. a) Cyanosis: Cyanosis is defined as bluish discolouration of skin and mucous membrane due to increased amount of reduced haemoglobin above 5 mg / dl. Types of cyanosis: (a) Central cyanosis: a. Respiratory causes i. Decreased oxygenation ii. Impaired diffusion across resp membrane Eg. COPD b. Cardio vascular causes i. A-V admixture ii. Congenital anomalies Eg. ASD, Tetrology of fallot etc. (b) Peripheral cycnosis: a. Stagnant hypoxia b. Obstruction to vessels at peripheries c. Fracture Sites: ear lobes, fingers etc. b) Near response : - Also called accomadation reflex - It is a three part response when n individual looks at a near object o Contraction of ciliary muscles o Contraction of pupil o Convergence of visual axis Accomadation pathway: Retina Optic nerve (visual pathway) Primary visual area 17 Frontal eye field area 8 III nerve Edinger – Wesphal nucleus Ciliary muscles; spinchter pupillae & Medial rectus c. Otolith organ: - two sac swellings o saccule o utricle - Utricle communicates with saccules by means of ductus endolymphaticus - Utricle and saccule contain a projecting ridge, the macula - Covering the projecting ridge is 30 – 150 long stiff hair – cupla terminalis - One end long non-motile hair is kinocillium - Progressive increase in height is stereocilia Functioning; - Saccule and utricle provide information about linear acceleration and change in head position - Saccules are affected by a lateral tilt of head - Utricle are affected by nodding the head up and down. d. Jugular pulse; - there is no valve at the junction of superior vena cava and right atrium - so the right atrial pressure changes are transmitted to jugular vein in neck - they produce 3 positive waves and 3 negative waves - Positive waves are a,c,v and negative waves are x, x1 and y ‗a‘ wave – due to atrial systole ‗c‘ wave – bulging of tricuspic valve into right atrium during isovolumetric contraction phase ‗v‘ wave – due to rise in atrial pressure before the tricuspid valve opens during diastole. e. P –R interval - interval from the beginning of ‗p‘ wave the beginning of Q or R wave - it represents atrial depolarization plus conduction time to bundle of His - Normal duration 0.12 sec to 0.16 sec - If duration is more than 0.2 sec indicates delayed conduction o Eg. Incomplete heart block - Duration less than 012 sec indicate impulses arised from AV node. f. Chyne – stokes breathing: - it is a type of periodic breathing - in this phase of hyperventilation is followed by apnea - waxing and wanning of waves occurs alternatetively - it is of gradual onset - Causes o Physiological . Voluntary hyperventilation . High altitude o Pathological . Brain damage . Uremia g. Buffer nerves The nerves innervating the baroreceptors aortic and carotid sinus are buffer nerves BP raises Baroreceptor discharge increases Inhibition of VMC Stimulation of CVC Fall in sypmpathtetic activity & raise in vagal activity Prevent rise in BP Hence, hering‘s nerve (branch of glossopharyngeal nerve ) and vagus nerve are known as Buffer nerves. h. Dyspnoeic index - Maximum amount of air that can be breathed in and out above normal ventilation. - MVV – PV - It is usually expressed in percentage as (MVV – PV) / MVV x 100 - normal range >= 60 – 70 % (usually 90 %) - < 60 % represents dyspnoea i. Nystagmus When a subjects ‗s gaze is fixed at a stationary object, the eye balls are not still (without motion), there are continuous jerky movements (nystagmus) - Types o Physiological / occulovestibular nystagmus o Pathological nystagmus Eg. Cerebellar lesions j. Cushing’s reflex; Increase in intracranial tension above 33 mmHg Decreases blood supply to medulla & hypercapnea Stimulates VMC Restores BP by increased Sympathetic activity HR decreases Paper IV April 2001 Sub code: 4054 1. Hypoxia and its types: Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole (generalized hypoxia) or a region of the body (tissue hypoxia) is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise. A mismatch between oxygen supply and its demand at the cellular level may result in a hypoxic condition. Hypoxia in which there is complete deprivation of oxygen supply is referred to as anoxia. Hypoxic hypoxia is a generalized hypoxia, an inadequate supply of oxygen to the body as a whole. The term "hypoxic hypoxia" specifies hypoxia caused by low partial pressure of oxygen in arterial blood. In the other causes of hypoxia that follow, the partial pressure of oxygen in arterial blood is normal. Hypoxic hypoxia may be due to: o Low partial pressure of atmospheric oxygen such as found at high altitude or by replacement of oxygen in the breathing mix either accidentally as in the modified atmosphere of a sewer or intentionally as in the recreational use of nitrous oxide. o Low partial pressure of oxygen in the lungs when switching from inhaled anaesthesia to atmospheric air, due to the Fink effect, or diffusion hypoxia. o A decrease in oxygen saturation of the blood caused by sleep apnea or hypopnea o Inadequate pulmonary ventilation (e.g., in chronic obstructive pulmonary disease or respiratory arrest). o Shunts in the pulmonary circulation or a right-to-left shunt in the heart. Shunts can be caused by collapsed alveoli that are still perfused or a block in ventilation to an area of the lung. Whatever the mechanism, blood meant for the pulmonary system is not ventilated and so no gas exchange occurs (the ventilation/perfusion ratio is zero). Normal anatomical shunt occurs in everyone, because of the Thebesian vessels which empty into the left ventricle and the bronchial circulation which supplies the bronchi with oxygen. o hypemic hypoxia in which arterial oxygen pressure is normal, but total oxygen content of the blood is reduced. o Hypoxia when the blood fails to deliver oxygen to target tissues. Carbon monoxide poisoning which inhibits the ability of hemoglobin to release the oxygen bound to it. Methaemoglobinaemia in which an abnormal version of hemoglobin accumulates in the blood . Histotoxic hypoxia in which quantity of oxygen reaching the cells is normal, but the cells are unable to effectively use the oxygen due to disabled oxidative phosphorylation enzymes. The effects of drinking alcoholic beverages is a common example. Ischemic, or stagnant hypoxia in which there is a local restriction in the flow of otherwise well-oxygenated blood. The oxygen supplied to the region of the body is then insufficient for its needs. Examples are cerebral ischemia, ischemic heart disease and Intrauterine hypoxia, which is an unchallenged cause of perinatal death. Acclimatization to Low PO2 A person remaining at high altitudes for days, weeks, or years becomes more and more acclimatized to the low Po2, so that it causes fewer deleterious effects on the body. And it becomes possible for the person to work harder without hypoxic effects or to ascend to still higher altitudes. The principal means by which acclimatization comes about are (1) a great increase in pulmonary ventilation, (2) increased numbers of red blood cells, (3)increased diffusing capacity of the lungs, (4) increased vascularity of the peripheral tissues, and (5) increased ability of the tissue cells to use oxygen despite low Po2 2. a) Cardiac Catherization Cardiac catheterization (heart cath) is the insertion of a catheter into a chamber or vessel of the heart. This is done for both investigational and interventional purposes. Subsets of this technique are mainly coronary catheterization, involving the catheterization of the coronary arteries, and catheterization of cardiac chambers and valves. Indications for investigational use This technique has several goals: confirm the presence of a suspected heart ailment quantify the severity of the disease and its effect on the heart seek out the cause of a symptom such as shortness of breath or signs of cardiac insufficiency make a patient assessment prior to heart surgery Investigative techniques used with coronary catheterization to measure intracardiac and intravascular blood pressures to take tissue samples for biopsy to inject various agents for measuring blood flow in the heart; also to detect and quantify the presence of an intracardiac shunt to inject contrast agents in order to study the shape of the heart vessels and chambers and how they change as the heart beats b) P- R Interval Repeated : March 02, Sept 02 C) Periodic Breathing Repeated : Aug 04, 08 d) Oxygen dissociation curve: Repeated : Feb 2005 3. Thalamus – nucleus, connections and functions. The thalamus is a midline symmetrical structure within the brains of vertebrates including humans, situated between the cerebral cortex and midbrain. Its function includes relaying sensory and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep, and alertness. The thalamus surrounds the third ventricle. It is the main product of the embryonic diencephalon. Thalamic nuclei Nuclei of the thalamus The thalamus is part of a nuclear complex structured of four parts, the hypothalamus, epithalamus, ventral thalamus, and dorsal thalamus. Derivatives of the diencephalon also include the dorsally-located epithalamus (essentially the habenula and annexes) and the perithalamus (prethalamus formerly described as ventral thalamus) containing the zona incerta and the "reticulate nucleus" (not the reticular, term of confusion).
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