Medessentials for the usmle step 1 pdf free download

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Moreover Doctorsbooks. If you feel that we have violated your copyrights, then please contact us immediately. Extraembryonic visceral mesoderm covers the yolk sac. Embryology Hypoblast The connecting stalk suspends the conceptus within the chorionic cavity.

The wall of the chorionic cavity is called the chorion, consisting of extraembryonic somatic mesoderm, the cytotrophoblast, and the syncytiotrophoblast. Week 2 Human chorionic gonadotropin hCG is a glycoprotein produced by the syncytiotrophoblast. It stimulates progesterone production by the corpus luteum. Low hCG levels may predict a spontaneous abortion or ectopic pregnancy. High hCG levels may predict a multiple pregnancy, hydatidiform mole, or gestational trophoblastic disease.

By the end of this period, the embryo begins to look human. Week 3 Clinical Correlation Sacrococcygeal teratoma: a tumor that arises from remnants of the primitive streak; often contains various types of tissue bone, nerve, hair, etc.

Chordoma: a tumor that arises from remnants of the notochord, found either intracranially or in the sacral region Caudal dysplasia sirenomelia : a constellation of syndromes ranging from minor lesions of the lower vertebrae to complete fusion of lower limbs.

Occurs as a result of abnormal gastrulation, in which migration of mesoderm is disturbed. In a partial mole, there is a haploid set of maternal chromosomes and usually two sets of paternal chromosomes so that the typical karyotype is 69,XXY.

Embryology The placenta permits exchange of nutrients and waste products between maternal and fetal circulations. If the twinning occurs very early on before the chorion forms , two separate chorions will form dichorionic. All other possible types of twins are monochorionic because the chorion has already formed. Fraternal twins are dizygotic and identical twins are monozygotic. Multiple abnormalities, e.

Diffusion Kinetics. Fluid Volume Compartments and Distribution. Membrane Potentials. Action Potential. Steady state Steady state is a condition in which a variable is maintained within narrow limits by regulating an opposing activity.

This process requires energy. Negative feedback This is a common system that acts to oppose changes in the internal environment.

Negative feedback systems promote stability and act to restore steady-state function after a perturbation. Positive feedback This is a less common system also called a vicious cycle that acts to magnify a change in the internal environment; the initial change in a system is increased as a result of feedback activity.

In a viable organism, any positive feedback system is ultimately overridden by one or more negative feedback systems. Negative Feedback Example Positive Feedback Example Follicular Phase Pre-ovulatory Phase Gonadotropin-releasing hormone Gonadotropin-releasing hormone Luteinizing hormone Luteinizing hormone Estradiol Estradiol The figures above show the negative feedback relationship between estrogens and the gonadotropins that dominates during the follicular phase, which transforms into a positive feedback relationship, producing the LH surge prior to ovulation.

Solid arrows show direct relationships stimulation and dashed arrows show inverse relationships inhibition. Active transport can produce a concentration gradient, and passive processes will lead to an equilibrium state right. Intracellular volume changes only when extracellular osmolarity changes. All substances enter or leave the body by passing through the extracellular compartment. Definition of abbreviation: RISA, radio-iodinated serum albumin. The Darrow-Yannet diagram right represents this information.

The y-axis is solute concentration or osmolarity. The solid line represents the control state, and the dashed line represents changes in volume or osmolarity. Proteins anions in cells that do not diffuse help establish the electrical potential across the membrane. The greater the conductance, the closer the membrane will approach the equilibrium potential of that ion. Hyperpolarization occurs when the membrane potential becomes more negative.

Depolarization occurs when the membrane potential becomes less negative or even positive. Definition of abbreviation: EC, extracellular. Physiology Absolute refractory period Relative refractory period Sodium equilibrium potential 60 mV Action potential 0 mV Sodium conductance Potassium conductance — 70 mV Resting equilibrium potential — 90 mV Potassium equilibrium potential Time The action potentials AP of excitable cells involve the opening and closing of voltage-gated channels for sodium, potassium, and in some cells, calcium.

The figure above shows a neuronal AP. The opening of a channel increases conductance. Steps are shown below. These channels can be blocked by tetrodotoxin.

Clinical Correlations Calcium has a low resting conductance and does not contribute to the resting potential. It has a very positive equilibrium potential, so when conductance increases e. Calcium concentration affects the action potentials and force of contraction of cardiac and smooth muscle.

Hypercalcemia stabilizes excitable membranes, leading to flaccid paralysis of skeletal muscle. Hypocalcemia destabilizes membranes, leading to spontaneous action potentials and spasms. Abnormal increases and decreases of extracellular potassium have severe consequences for cardiac conduction and rhythm. Renal and gastrointestinal disorders are likely to cause abnormalities of electrolytes and alteration of resting potentials and action potentials. As the Degree of Cellular Injury Worsens Irreversible Injury and Cell Death.

Wound Healing. Connective Tissue Components. Connective Tissue Diseases. The cellular response to injury depends on the type, duration, and severity of injury, the type of cell injured, metabolic state, and ability to adapt. Cells shrink; lipofuscin granules can be seen microscopically. May coexist with hyperplasia. Pathology Wound healing involves regeneration of cells in a damaged tissue, along with repair of the connective tissue matrix.

Different types of collagen are found in different body sites. Thus, an early symptom is bleeding gums. There are many types. Amyloidosis An accumulation of various insoluble fibrillar in various tissues. It stains with Congo red and shows apple-green birefringence with polarized light. Pathology Carcinogenesis is a multistep process involving multiple genetic changes from inherited germ-line mutations or acquired mutations, leading to monoclonal expansion of a mutated cell.

Pathology There are many proposed mechanisms of carcinogenesis. The most important mutations involve growth-promoting genes proto-oncogenes , growth-inhibiting tumor suppressor genes, and genes regulating apoptosis.

Clinically Important Oncogenes Proto-oncogenes are normal cellular genes involved with growth and cellular differentiation. Pathology Tumor suppressor genes encode proteins that regulate and suppress cell proliferation by inhibiting progression through the cell cycle.

Pathology These are usually normal cellular components that are increased in neoplasms but may also be elevated in non-neoplastic conditions.

Can be used for screening, monitoring of treatment efficacy, and detecting recurrence. Low stage means a localized tumor. Stage rises as tumors spread locally then metastasize. It represents the ratio of drug elimination to its plasma concentration.

For a drug with first-order elimination, clearance is constant. Rate of drug elimination Plasma drug concentration Elimination is synonymous with termination of drug action. The two primary mechanisms are hepatic metabolism to inactive metabolites or renal excretion. First-Order Elimination A constant fraction of drug is eliminated with time.

Units of Drug Most drugs have first-order elimination. It is constant for drugs eliminated by firstorder kinetics. Half-life is not applicable. For some drugs, their rapid hepatic metabolism decreases bioavailability. This can be avoided by giving the drug by an alternate route e. It is equal to the rate of elimination. F If therapeutic plasma concentrations are needed quickly and the Vd is large, a loading dose may be given to produce the desired drug levels fill up the Vd without the typical delay of 4 to 5 half-lives.

There are two main types of metabolic reactions: phase I and phase II. Phase I The parent drug becomes more water-soluble by oxidation, reduction, or hydrolysis by cytochrome P isozymes also called mixed function oxidases located in smooth endoplasmic reticulum in liver, and in the GI, lungs, and kidney to a lesser extent.

Often the drug is converted to compounds with little or no pharmacologic activity; in other instances, the metabolites retain pharmacologic activity. Examples include glucuronidation, acetylation, sulfation, glutathione conjugation, and methylation. Phase II reactions lead to inactive molecules, which are polar and usually renally excreted. All phase II reactions use enzymes called transferases.

It will elicit a partial response when administered alone. When administered with a full agonist, it acts as an antagonist because it displaces the full agonist from the receptor. It can be overcome by increasing the agonist dose. A noncompetitive antagonist binds to the receptor without activating the effector system. It cannot be overcome by increasing the agonist dose. Log Dose of Drug Kd Potency: the measure of how much drug is required to produce a given effect. Efficacy: the maximal effect a drug can produce.

It is also known as maximal efficacy. A partial agonist has a lower efficacy than a full agonist. It can be less potent C or more potent A than a full agonist B. See figure to left. Figure I It is the percent of population responding versus log dose. Intracellular receptors Lipid-soluble agents diffuse across the plasma membrane to bind intracellular receptors e.

This permits receptor binding to nuclear DNA sequences that modify gene expression. Ligand binding causes dimerization and activates the enzyme activity often a tyrosine kinase. Examples: insulin and growth factor receptors. Transmembrane receptors that activate a separate tyrosine kinase These also form dimers when activated, then activate a separate cytoplasmic tyrosine kinase Janus kinases; JAKs.

The kinase phosphorylates STAT factors signal transducers and activators of transcription. STAT dimers then regulate transcription. Examples: cytokine and growth hormone receptors. The autacoids include histamine, serotonin, vasoactive peptides, and prostaglandins see page Although the mechanism of action varies, each agent hinders cell replication in some way.

Specificity relies on differential effect between neoplastic cells and normal tissue. The mechanism of action may be cell-cycle specific affecting cells in all stages except G0 or cell-cycle nonspecific. Inhibit synthesis of nucleic acids and thus protein synthesis.

This class of agents causes alkylation of DNA, leading to cross-linking, abnormal base pairing, or DNA strand breakage. Mechanisms of action vary. Doxorubicin Intercalates DNA, creating breaks. Hinders DNA replication and transcription. Prevents estrogen from binding estrogen receptor— positive breast CA cells, leading to involution of estrogen-dependent tumors. Cell-cycle specific drugs. Most prevent the assembly of microtubules and the formation of the mitotic spindle.

However, many of your patients may be taking herbal medicines such as these, and familiarity with these agents is useful. Anatomy of the Eye and Glaucoma. Pharmacology of the Eye. Drugs Used to Treat Glaucoma. Pupillary Light Reflex Pathway. Descending Pathways. Commonly Tested Muscle Stretch Reflexes. Ascending Pathways. Dorsal Column-Medial Lemniscus. Anterolateral Spinothalamic. Classic Spinal Cord Lesions. Accommodation-Convergence Reaction. Clinical Correlations. Eye Movement Control Systems.

Alzheimer Disease. Creutzfeldt-Jakob Disease. Pick Disease Lobar Atrophy. CNS Trauma. Cerebral Herniations. Neuromuscular junction Note: Arrows indicate lesion sites that result in Horner syndrome. Submandibular VI ganglion Submandibular gland Sublingual gland 3.

Otic ganglion C1 Terminal ganglia Viscera of the thorax and abdomen foregut and midgut XI Descending hypothalamic fibers drive all preganglionic sympathetic neurons Internal carotid a.

External carotid a. Blood vessels are solely innervated by SANS nerve fibers. The uptake of choline into the nerve terminal is the ratelimiting step of ACh synthesis and can be blocked by hemicholinium. Note: The numbers in the figure correspond to the numbers in the table below. Mechanism of Action Agent Clinical Uses Other Notes and Toxicity Muscarinic antagonists Atropine Counteracts cholinergic toxicity Antidiarrheal Mydriatic agent for eye exams Reversal of sinus bradycardia and heart block Mydriasis and cycloplegia blind as a bat Decreased secretions dry as a bone Vasodilation red as a beet Delirium and hallucinations mad as a hatter Hyperthermia Tachycardia Urinary retention and constipation Sedation, amnesia Homatropine Cyclopentolate Tropicamide Ophthalmology topical , for mydriasis — Ipratropium Asthma and COPD Localized effect because is a quaternary amine; few antimuscarinic side effects Scopolamine Motion-sickness Antiemetic See side effects for atropine.

The effect of the blockade will be the opposite of what the predominant tone causes. In general, the predominant tone to blood vessels and sweat glands is sympathetic, and most everything else is parasympathetic.

The first step of the synthetic pathway is carried out by tyrosine hydroxylase; it is also the rate-limiting step. NE levels inside the presynaptic terminal may also be regulated by metabolism by monoamine oxidase MAO. Once released, NE binds to various adrenergic receptors to transmit its signal. Reuptake especially uptake-1 and diffusion are most important in the termination of action of NE and DA.

Metabolites such as metanephrine, normetanephrine, vanillylmandelic acid VMA can be measured in the urine and are used in the diagnosis of diseases such as pheochromocytoma.

Note: The numbers in the figure correspond to the numbers in the following table. Meningeal spaces are spaces or potential spaces adjacent to the meninges. There are two main classes: amides and esters. Side Effects 1. The Nervous System General Anesthetics The ideal general anesthetic produces unconsciousness, analgesia, skeletal muscle relaxation, loss of reflexes, and amnesia.

There are two broad classes of general anesthetics: inhalational and intravenous. Treat with dantrolene. The primitive heart tube undergoes dextral looping bends to the right and forms five dilatations.

Four of the five dilatations become subdivided by a septum. Most of the common congenital cardiac anomalies result from defects in the formation of these septa. This results in an opening between the right and left atria.

If the ASD is small, clinical symptoms may be delayed as late as age This is the most clinically significant ASD. The foramen ovale FO is the fetal communication between the right and left atria. Premature closure of the FO is the closure of the FO during prenatal life. This results in hypertrophy of the right side of the heart and underdevelopment of the left side. Patients with left-to-right shunting complain of excessive fatigue upon exertion.

Left-to-right shunting of blood is not cyanotic but causes increased blood flow and pressure to the lungs pulmonary hypertension. Pulmonary hypertension causes marked proliferation of the tunica intima and media of pulmonary muscular arteries and arterioles. At this stage, the condition is called Eisenmenger complex. VSD is the most common congenital cardiac anomaly. Figure legend: a, right bulbar ridge; b, left bulbar ridge; c, AV cushions.

The AP septum divides the truncus arteriosus into the aorta dark gray and pulmonary trunk light gray. Transposition of the Great Vessels Occurs when the AP septum fails to develop in a spiral fashion and results in the aorta opening into the right ventricle and the pulmonary trunk opening into the left ventricle.

This causes right-to-left shunting of blood with resultant cyanosis. Infants born alive with this defect must have other defects like a PDA or VSD that allow mixing of oxygenated and deoxygenated blood.

Tetralogy of Fallot Occurs when the AP septum fails to align properly and results in 1 pulmonary stenosis, 2 overriding aorta, 3 interventricular septal defect, and 4 right ventricular hypertrophy. Tetralogy of Fallot is the most common congenital cyanotic cardiac anomaly. This results in a condition in which only one large vessel leaves the heart and receives blood from both the right and left ventricles. This defect is always accompanied by membranous ventricular septal defect.

Definition of abbreviation: PDA, patent ductus arteriosus. Patent ductus arteriosus PDA occurs when the ductus arteriosus connection between the pulmonary trunk and aorta fails to close after birth.

PDA is common in premature infants and cases of maternal rubella infection. It causes a leftto-right shunting of blood. Note: During fetal development, the ductus arteriosus is a right-toleft shunt. Right and left umbilical arteries In the fetal circulation, the ductus venosus allows fetal blood to bypass the liver, and the foramen ovale and the ductus arteriosus allow fetal blood to bypass the lungs.

Note the sites where the oxygen saturation level of fetal blood is the highest umbilical vein and the lowest ductus arteriosus. The superior mediastinum contains the thymic remnants, superior vena cava and its brachiocephalic tributaries, aortic arch and its branches, trachea, esophagus, thoracic duct, and the vagus and phrenic nerves.

The anterior mediastinum is anterior to the heart and contains remnants of the thymus. The middle mediastinum contains the heart and great vessels, and the posterior mediastinum contains the thoracic aorta, esophagus, thoracic duct, azygos veins, and the vagus nerves. The inferior vena cava passes through the diaphragm at the caval hiatus at the level of the eighth thoracic vertebra; the esophagus through the esophageal hiatus at the tenth thoracic vertebra; and the aorta courses through the aortic hiatus at the level of the twelfth thoracic vertebra.

The right coronary artery supplies the right atrium, the right ventricle, the sinoatrial and atrioventricular nodes, and parts of the left atrium and left ventricle. The left coronary artery supplies most of the left ventricle, the left atrium, and the anterior part of the interventricular septum.

The two main branches of the left coronary artery are the anterior interventricular artery LAD and the circumflex artery. The auricle is derived from the fetal atrium; it has rough myocardium known as pectinate muscles. The sinus venarum is the smooth-walled portion of the atrium, which receives blood from the superior and inferior venae cavae. The crista terminalis is the vertical ridge that separates the smooth from the rough portion of the right atrium; it extends longitudinally from the superior vena cava to the inferior vena cava.

The SA node is in the upper part of the crista terminalis. The right AV tricuspid valve communicates with the right ventricle. Right Ventricle The right ventricle receives blood from the right atrium via the tricuspid valve; outflow is to the pulmonary trunk via the pulmonary semilunar valve.

The trabeculae carneae are the ridges of myocardium in the ventricular wall. The papillary muscles project into the cavity of the ventricle and attach to cusps of the AV valve by the strands of the chordae tendineae. Papillary muscles contract during ventricular contraction to keep the cusps of the AV valves closed. The chordae tendineae control closure of the valve during contraction of the ventricle. The infundibulum is the smooth area of the right ventricle leading to the pulmonary valve.

Left Atrium The left atrium receives oxygenated blood from the lungs via the pulmonary veins. There are four openings: the upper right and left and the lower right and left pulmonary veins. The left AV orifice is guarded by the mitral bicuspid valve; it allows oxygenated blood to pass from the left atrium into the left ventricle. Left Ventricle Blood enters from the left atrium through the mitral valve and is pumped out to the aorta through the aortic valve. Trabeculae carneae, the ridges of myocardium in the ventricular wall, are normally three times thicker than those of the right ventricle.

Papillary muscles usually two large ones are attached by the chordae tendineae to the cusps of the bicuspid valve. The aortic vestibule leads to the aortic semilunar valve and ascending aorta; the right and left coronary arteries originate from the right and left aortic sinuses at the root of the ascending aorta.

Clinical Correlation Murmurs Murmurs in valvular heart disease result when there is valvular insufficiency or a stenotic valve. The posterior surface is formed mainly by the left atrium.

A diaphragmatic surface is formed primarily by the left ventricle. All rights reserved. The atrioventricular node receives the impulse from the sinoatrial node and transmits that impulse to the ventricles through the bundle of His.

The bundle divides into the right and left bundle branches and Purkinje fibers to the two ventricles. Sympathetic innervation from the T1 to T5 spinal cord segments increases the heart rate, while the parasympathetics by way of the vagus nerves slow the heart rate. Surgical neck fracture of humerus Superior thoracic artery Thoracoacromial artery Teres major Midshaft fracture of humerus Supra-condylar fracture of humerus Aortic arch Pectoralis minor Lacerates profunda brachii artery may lesion radial n.

Lateral circumflex artery Medial circumflex artery Major source of blood supply to head of femur Deep femoral artery Supplies anterior and posterior thigh and shaft of femur Lateral thoracic artery Lacerates brachial artery may lesion median n. Medial epicondyle fracture Radial collateral artery Superior ulnar collateral artery may lesion ulnar n. Subscapular artery anastomoses with suprascapular artery to provide collateral circulation around the axillary artery Popliteal artery Popliteal artery Anterior tibial artery Inferior ulnar collateral artery Radial artery Common interosseus artery Ulnar artery Posterior tibial artery Compressed with tibial nerve in posterior compartment syndrome Anterior tibial artery Compressed with deep fibular nerve in anterior compartment syndrome Peroneal artery Deep palmar arch Superficial palmar arch Medial plantar artery Dorsalis pedis artery Lateral plantar artery Plantar arch artery Anterior Posterior Figure III In fact, the abnormal shape of action potentials initiated during the relative refractory period reduces calcium influx and thus contractile force, as shown.

A depolarizing wave moving away from the positive toward the negative terminals produces a negative deflection. A wave of depolarization moving at right angles to the axis of the electrode terminals produces no deflection. Upon repolarization, the reverse occurs. Intersection of the CFC and VFC is the stable operating point; if contractility or blood volume changes, the system will operate at the intersection of the two new curves.

Point A: venous pressure is increased from 3 to 6 mm Hg because of sudden removal of blood from arterial system and injection into venous system. This causes CO to increase to point B. Increased blood volume e. Increased CO follows. Decreased blood volume e. Decreased CO follows. Increases and decreases in preload produce increases and decreases in CO by the Frank-Starling mechanism.

The initial large increase in CO point B returns to point D on the VFC as blood is transferred from the venous system to the arterial system. Within hours to days, blood volume increases, shifting VFC upward, and point C becomes the equilibrium point.

With progressive failure, blood volume cannot increase enough to maintain CO at a normal level. Blood volume continues to increase, which overstretches the heart point E. Ejection Isovol. During ejection, aortic pressure is slightly below ventricular pressure.

Minimum is diastolic pressure. Pressure falls during diastole as blood flows from aorta into capillaries and then veins. Left atrial pressure Systole; isolated from ventricular pressure because mitral valve is closed Diastole, blood flows from atrium into ventricle because mitral valve is open.

Note mitral closed during isovolumic relaxation. Aortic flow measured at root Systolic ejection begins when ventricular pressure exceeds aortic diastolic and aortic valve opens. Ejection ends when rapidly falling ventricular pressure causes aortic valve to close. Ventricular volume Maximum at end of diastole; does not change during isovolumic contraction because mitral and aortic valves are closed. Minimum at end of ejection phase; does not change during isovolumic relaxation both valves closed.

Decreased afterload produces the opposite changes as increased afterload. Normal left ventricular function. Immediate effec of reduced contractility, no compensation. Compensated LV failure: SV is partially restored because of moderately increased preload. A: Decompensated failure: despite extreme increases Normal of preload, SV of remains low, and in fact the heart is B: Acutethe loss contractility without beingcompensation overly stretched, so additional "compensation" is actually harmful.

Pressure drop increases along circuit with constant flow, and flow decreases with constant input pressure P1. RAP is assumed to be 0 mm Hg, unless specified. Other causes included lymphatic obstruction, sodium retention. As the heart fails, stroke volume decreases, with compensatory increases in heart rate and systemic vascular resistance. Massive peripheral vasodilation with a decrease in systemic vascular resistance. There is peripheral pooling of blood decreased effective circulatory volume.

The heart compensates with an increase in heart rate. The effective circulatory volume decreases through actual loss. The heart is able to attempt to compensate with an increase in heart rate. Class I drugs are subdivided into three groups based on their effect on AP duration. Classically, this symptom is described as a crushing, pressure-like pain that occurs during periods of exertion. Inadequate cardiac output secondary to decreased contractility leads to decreased exercise tolerance and muscle fatigue.

Neurohumoral responses to this physiologic shortcoming play an integral role in the pathogenesis of heart failure; thus, drugs used to treat this condition may be aimed at these responses. Physiologically, these drugs may reduce afterload, reduce preload, or increase contractility. The Larynx. Intrinsic Muscles of the Larynx. Pleura and Pleural Cavities. Elastic Properties of the Lung. Elastic Properties of the Lung and Chest Wall.

Surface Tension. Airway Resistance. The Breathing Cycle. Pulmonary Disease. Summary of Classic Lung Diseases. CO2 Transport. Pulmonary Blood Flow. Ventilation-Perfusion Relationships. Control of Ventilation. Response to High Altitude.

The lung bud forms at the distal end of the diverticulum and divides into two bronchial buds. These branch into the main bronchi, lobar bronchi, and segmental bronchi. The right bud divides into three main bronchi, and the left divides into two. The tracheoesophageal septum divides the foregut into the esophagus and trachea. Clinical Correlate A tracheoesophageal fistula is an abnormal communication between the trachea and esophagus caused by a malformation of the tracheoesophageal septum.

It is generally associated with esophageal atresia and polyhydramnios. Symptoms include gagging and cyanosis after feeding and the reflux of gastric contents into the lungs, causing pneumonitis. It is composed of the trachea, bronchi, bronchioles, and terminal bronchioles. The trachea and bronchi contain pseudostratified ciliated columnar cells and goblet cells secrete mucous. Bronchioles and terminal bronchioles contain ciliated epithelial cells and Clara cells which secrete a surfactant-like substance, aid in detoxification, and are stem cells for the ciliated cells.

The respiratory zone carries out gas exchange and consists of respiratory bronchioles, alveolar ducts, and alveoli. Type II cells Capillary Endothelial cell Red blood cell Alveolus Type I cell Basal lamina Endothelial cell Capillary Terminal bronchioles divide into respiratory bronchioles, which contain alveoli and branch to form alveolar ducts.

The ducts terminate in alveolar sacs and are lined by squamous alveolar epithelium. Alveoli are thin-walled sacs responsible for gas exchange. There are approximately million alveoli in each lung. It has lateral, posterior, and medial walls throughout but is open anteriorly in its upper regions nasopharynx, oropharynx , communicating with the nasal cavity and the oral cavity. The nasopharynx is the region of the pharynx located directly posterior to the nasal cavity.

It communicates with the nasal cavity through the choanae i. The oropharynx is the region of the pharynx located directly posterior to the oral cavity. It communicates with the oral cavity through a space called the fauces. The fauces are bounded by two folds, consisting of mucosa and muscle, known as the anterior and posterior pillars.

The laryngopharynx is the region of the pharynx that surrounds the larynx. It extends from the tip of the epiglottis to the cricoid cartilage. Its lateral extensions are known as the piriform recesses. It also maintains a patent airway and acts as a sphincter during lifting and pushing. The free, upper border of the latter is specialized to form the vocal ligament on either side. All other intrinsic laryngeal muscles are supplied by the recurrent laryngeal branch of the vagus nerve.

Inflammation of the central part of the diaphragmatic pleura may produce pain referred to the shoulder phrenic nerve; C3, C4, and C5. This space is occupied by the lingula of the left lung during inspiration. The lingula of the upper lobe corresponds to the middle lobe of the right lung. There are 10 on the right and eight on the left.

The pulmonary arteries deliver deoxygenated blood to the lungs from the right side of the heart. They are usually branches of the thoracic aorta. They share drainage from the bronchi with the pulmonary veins.

Spirometry can only measure changes in volume. It is the effective part of ventilation. Therefore, the fraction shows the dilution of CO2 by the dead space. In lung disease, this number can increase. It is inversely related to elasticity tendency of a material to recoil when stretched. This high-yield reference guide is ideal for first- and second-year medical students, both to prep for Step 1 and to supplement med school curricula.

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