By I. Yorik. Georgian Court College. 2018.
If an electronic pacemaker is attached to the right atrium and the heart rate is increased by electrical stimula- tion discount hyzaar 12.5 mg online, surprisingly little increase in cardiac output results buy hyzaar 50 mg low price. Sympathetic neural activity This is because as the heart rate increases discount hyzaar 50 mg otc, the interval be- tween beats shortens and the duration of diastole decreases order hyzaar 12.5mg with mastercard. The decrease in diastole leaves less time for ventricular fill- β β β β 1 1 1 1 ing, producing a shortened end-diastolic fiber length, which Speed of Rate of rise subsequently reduces both the force of contraction and the Force of Conduction contraction velocity contraction and of pacemaker stroke volume. The increased heart rate is, therefore, offset relaxation potential by the decrease in stroke volume. When the rate increases above 180 beats/min secondary to an abnormal pacemaker, stroke volume begins to fall as a result of poor diastolic fill- Duration of systole Heart (small effect) rate ing. Increase Events in the myocardium compensate to some degree Decrease for the decreased time available for filling. First, increases in Stroke volume heart rate reduce the duration of the action potential and, Decrease Treppe thus, the duration of systole, so the time available for dias- Increase (small effect) tolic filling decreases less than it would otherwise. Second, faster heart rates are accompanied by an increase in the Cardiac force of contraction, which tends to maintain stroke vol- output ume. The increased contractility is sometimes called treppe or the staircase phenomenon. Various effects of norepinephrine on the heart com- pensate for the decreased duration of diastole and hold stroke Effects of Increased Heart Rate as a Result of Changes in volume relatively constant, so that cardiac output increases with Autonomic Nerve Activity. The words “Increase” and “Decrease” in occurs because of decreased parasympathetic and in- small type denote quantitatively less important effects than the creased sympathetic neural activity. CHAPTER 14 The Cardiac Pump 245 3) Disease states, such as coronary artery disease, my- ocarditis (see Chapter 10), bacterial toxemia, and alter- ations in plasma electrolytes and acid-base balance 4) Intrinsic changes in contractility with changes in heart rate and/or afterload Heart rate is influenced primarily by sympathetic and parasympathetic nerves to the heart and, by a lesser extent, by circulating norepinephrine and epinephrine. The effect A of heart rate on cardiac output depends on the extent of concomitant changes ventricular filling and contractility. C Heart failure is a major problem in clinical medicine (see Clinical Focus Box 14. A V = C THE MEASUREMENT OF CARDIAC OUTPUT mg mL = The ability to measure output accurately is essential for per- mg/mL forming physiological studies involving the heart and man- FIGURE 14. Cardiac output is measured either by one of The volume (V) of liquid in the beaker equals the amount (A) of several applications of the Fick principle or by observing dye divided by the concentration (C) of the dye after it has dis- changes in the volume of the heart during the cardiac cycle. Cardiac Output Can Be Measured Using Variations of the Principle of Mass Balance A C V The use of mass balance to measure cardiac output is best Because A is known and C can be measured, V can be understood by considering the measurement of an un- calculated: known volume of liquid in a beaker (Fig. The vol- ume can be determined by dispersing a known quantity of V A/C (6) dye throughout the liquid and then measuring the con- When the principle of mass balance is applied to cardiac centration of dye in a sample of liquid. Because mass is output, the goal is to measure the volume of blood flowing conserved, the quantity of dye (A) in the liquid is equal to through the heart per unit of time. A known amount of dye the concentration of dye in the liquid (C) times the vol- or other indicator is injected and concentration of the dye ume of liquid (V): or indicator is measured over time. One possible consequence of heart failure is that pathologically dilated, hypertrophied, or stiff). The signs and symptoms typically associated with to reduce the venous fluid overload, cardiac glycosides this occurrence constitute congestive heart failure (e. This syndrome can be limited to the left ventricle terload reducing agents (e. Left heart failure Heart transplantation is becoming an increasingly vi- (which increases pulmonary venous pressure) can eventu- able option for severe, intractable, unresponsive CHF. Al- ally cause pulmonary artery pressure to rise and right though tens of thousands of patients worldwide have re- heart failure to occur. Indeed, left heart failure is the most ceived new hearts for end-stage heart failure, the supply of common reason for right heart failure. For this reason, car- The causes of CHF are numerous and include acquired diac-assist devices, artificial hearts, and genetically modi- and congenital conditions, such as valvular disease, my- fied animal hearts are undergoing intensive development ocardial infarction, assorted infiltrative processes (e. In the indicator dilution minute (rather than volume, as in equation 6).
From the splenic flexure discount hyzaar 50mg with amex, the descending colon extends feces out of the GI tract buy discount hyzaar 50 mg line. The Objective 15 Identify the regions of the large intestine and colon then angles medially from the brim of the pelvis to form an describe its gross and histological structure cheap hyzaar 50mg with mastercard. Objective 16 Describe the functions of the large intestine and explain how defecation is accomplished purchase hyzaar 12.5 mg mastercard. Digestive System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 18 Digestive System 657 Transverse colon Hepatic flexure Splenic flexure Mesocolon Ascending colon Taeniae coli Descending colon Epiploic appendage Ileum Ileocecal valve Orifice of appendix Haustrum Cecum Appendix Sigmoid colon Rectum Anal canal FIGURE 18. A third-degree hemorrhoid remains pro- and the last 2 to 3 cm of the rectum is referred to as the anal lapsed through the anal orifice. The rectum lies anterior to the sacrum, where mon medical treatment for a prolapsed hemorrhoid. The anus is the external a rubber band is tied around the hemorrhoid, constricting its blood supply, so that the tissue dries and falls off. Two sphincter muscles guard the anal ment, infrared photocoagulation, a high-energy light beam coagu- opening: the internal anal sphincter, which is composed of lates the hemorrhoid. The mucous membrane of the anal Although the large intestine consists of the same tunics as canal is arranged in highly vascular, longitudinal folds called the small intestine, there are some structural differences. A series of rhoids, in reference to the condition in which such masses occur, are also called piles. A first-degree hemorrhoid is contained within the bulges in the walls of the large intestine form sacculations, or haustra anal canal. Digestive System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 658 Unit 6 Maintenance of the Body Rectum Levator ani Hemorrhoidal muscle vessels Anal canal External anal Anal columns sphincter Internal anal sphincter Anus Loechel FIGURE 18. Submucosa Mucosa Center of Columnar lymphatic epithelium with nodule goblet cells Intestinal (a) glands Lumen Tunica muscularis Submucosa Serosa FIGURE 18. The arrow indicates the opening of a goblet cell into the intestinal lumen. Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy, © 1979 W. Digestive System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 18 Digestive System 659 TABLE 18. The parasympathetic innervation arises from peristaltic wave, involving the action of the taeniae coli, which the paired pelvic splanchnic and vagus nerves. Mass movements from the large intestine respond to bowel pressure and signal the generally occur only two or three times a day, usually during or need to defecate. This response to eating, called the gastro- branches from the superior mesenteric and inferior mesenteric colic reflex, can best be observed in infants who have a bowel arteries. Venous blood is returned through the superior and infe- movement during or shortly after feeding. It has been estimated that an average volume of 850 ml of water per day is absorbed across the mucosa of the colon. The fecal material that is left then passes to the rectum, leading to Mechanical Activities of the Large Intestine an increase in rectal pressure and the urge to defecate. If the urge to defecate is denied, feces are prevented from entering the anal canal Chyme enters the large intestine through the ileocecal valve. In this case, the feces remain in the 15 ml of pasty material enters the cecum with each rhythmic open- rectum and may even back up into the sigmoid colon. The ingestion of food intensifies peristalsis of the The defecation reflex normally occurs when the rectal ileum and increases the frequency with which the ileocecal valve pressure rises to a particular level that is determined largely by opens; this is called the gastroileal reflex. At this point, the internal anal sphincter relaxes to admit large intestine accumulates in the cecum and ascending colon. Three types of movements occur throughout the large in- During the act of defecation, the longitudinal rectal mus- testine: peristalsis, haustral churning, and mass movement. Peri- cles contract to increase rectal pressure, and the internal and ex- staltic movements of the colon are similar to those of the small ternal anal sphincter muscles relax.
Repetitive insults to the ligament allow microscopic tears that progress to significant attenuation or frank tearing within its substance (Fig purchase 50mg hyzaar with amex. A Conventional radiograph demonstrates a lytic osteochon- dral lesion in the capitellum (arrow) purchase 50 mg hyzaar amex. Coronal FSE T2-weighted image with fat suppression tensity on a T1-weighted image and has a high signal intensity rim shows a full-thickness tear of the anterior band of the ulnar collat- on a T2-weighted axial image generic hyzaar 50mg free shipping, C suggesting instability (arrow) eral ligament at the attachment to the sublime tubercle (arrow) Magnetic Resonance Imaging of the Elbow 9 visualization of the ligament complex hyzaar 12.5 mg discount, in chronic cases, the development of heterotopic calcification along the course of the ligament has been described. Varus Instability Lateral elbow instability related to isolated abnormalities of the lateral collateral ligament complex is not as well described as that on the medial side of the elbow. If it were to occur, the mechanism would be a stress or force applied to the medial side of the articulation, resulting in compression on that side, with opening of the lateral ar- ticulation and subsequent insufficiency of the radial col- lateral ligament. As the radial collateral ligament attach- es on and is intimately associated with the annular liga- ment, an abnormality discovered in one of the structures obligates careful inspection of the other. Varus stress applied to the elbow may occur as an acute injury, but rarely as a repetitive stress, as encountered on the medial side. While lateral collateral ligament injuries rarely occur as the result of an isolated varus stress, other Fig. Coronal-fat-suppressed T1-weighted image reveals full- causes can commonly lead to this injury, including dislo- thickness tears of the proximal aspects of the lateral ulnar collater- cation, subluxation and overly aggressive surgery (release al ligament and extensor tendon at the lateral epicondyle (arrow) of the common extensor tendon or radial head resection). Varus instability is also tested with the elbow in full extension and 30 degrees of flexion to unlock the olecra- non. A varus stress is applied to the elbow while palpat- bow in a semi-flexed position. Subluxation or dislocation of the elbow can be associ- The subject of elbow instability is complex and has been ated with fractures. Fracture-dislocations most common- a challenge due to the difficulty in establishing the mech- ly involve the coronoid and radial head, a constellation of anism of injury and reliable clinical tests for diagnosis. This type of instability elbow injuries to recognize is that the small flake fracture represents a spectrum of pathology consisting of three of the coronoid, commonly seen in elbow dislocations, is stages, according to the degree of soft-tissue disruption. Nothing attaches to the very tip In stage 1, there is posterolateral subluxation of the ulna of the coronoid; rather, the capsule attaches on the down- on the humerus that results in insufficiency of the lateral ward slope of the coronoid, the brachialis even more dis- ulnar collateral ligament (Fig. This fracture is a shear fracture and is likely pathog- the elbow dislocates incompletely so that the coronoid is nomonic of an episode of elbow subluxation or disloca- perched under the trochlea. A second consideration with respect to elbow dislo- lateral ligament, and anterior and posterior portions of the cation is that, as the ring of soft tissues is disrupted from capsule are disrupted, in addition to the lateral ulnar col- posterolateral to medial, the capsule is torn and insuffi- lateral ligament. In the absence of an intact capsule, joint fluid dis- fully so that the coronoid rests behind the humerus. Stage sects through the soft-tissue planes of the forearm, negat- 3 is subclassified into three further categories. In stage ing an indirect radiographic sign of trauma in the elbow, 3A, the anterior band of the medial collateral ligament is that of joint effusion. In stage 3B, the anterior band of the medial collat- eral ligament is disrupted so that the elbow is unstable Tendon Pathology with valgus stress. In stage 3C, the entire distal humerus is stripped of soft tissues, rendering the elbow grossly un- The many muscles about the elbow can be divided into stable even when a splint or cast is applied with the el- four groups: posterior, anterior, medial and lateral. Steinbach muscles of the posterior group are the triceps and an- flexor tendon. The muscles of the anterior group are the biceps tive valgus strain with pain resulting from resisting brachii and brachialis. The muscles in the medial group pronation of the forearm or flexion of the wrist. The are the pronator teres, the palmaris longus and the flex- imaging findings encountered can include tendinosis, or ors of the hand and wrist. The muscles in the lateral tendinosis with superimposed partial- or full-thickness group include the supinator, brachioradialis and extensor tear. When assessing the tendon, it is necessary to close- muscles of the hand and wrist. The vast majority of ly scrutinize the underlying ulnar collateral ligament pathology encountered in the flexor and extensor groups complex to ensure integrity. The classification of tendon injuries about the elbow This term may be somewhat inappropriate as 95% of cas- can be organized by location, acuity and degree of injury.
Describe the location of the dural sinuses and the Cerebrospinal fluid buoys the CNS and protects it from me- epidural space generic 50 mg hyzaar visa. The brain weighs about 1 buy hyzaar 12.5 mg overnight delivery,500 grams proven 12.5 mg hyzaar, but sus- pended in CSF its buoyed weight is about 50 grams generic hyzaar 50mg on-line. This means that the brain has a near neutral buoyancy; at a true neutral buoyancy, an object does not float or sink but is suspended in VENTRICLES its fluid environment. AND CEREBROSPINAL FLUID In addition to buoying the CNS, CSF reduces the damaging effect of an impact to the head by spreading the force over a larger The ventricles, central canal, and subarachnoid space contain area. Objective 23 Discuss the formation, function, and flow of cerebrospinal fluid. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 382 Unit 5 Integration and Coordination Interventricular aqueduct Lateral ventricle Interventricular foramen Third ventricle Mesencephalic Mesencephalic aqueduct aqueduct Fourth ventricle Central canal of spinal cord (a) (b) FIGURE 11. The clear, watery CSF is continuously produced by the fil- contains more sodium, chloride, magnesium and hydrogen, and tration of blood plasma through masses of specialized capillaries fewer calcium and potassium ions than does blood plasma. The ciliated ependymal cells cover the choroid although only 140–200 ml are bathing the CNS at any given plexuses, as well as line the central canal, and presumably aid the moment. A person lying in a horizontal position has a slow but movement of the CSF. The tight junctions between the ependy- continuous circulation of cerebrospinal fluid, with a fluid pres- mal cells also help to form a blood–cerebrospinal fluid barrier that sure of about 10 mmHg. An increase in amino acid glycine concentration, for which it is formed. Like blood plasma, it contains proteins, glu- example, produces hypothermia and hypotension as temperature cose, urea, and white blood cells. Comparing electrolytes, CSF and blood pressure regulatory mechanisms are disrupted. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 383 Arachnoid villi Blood-filled dural sinus Choroid plexus of third ventricle Cerebral vein Interventricular foramen Pia mater Third ventricle Subarachnoid space Mesencephalic aqueduct Arachnoid Fourth ventricle Dura mater Choroid plexus of fourth ventricle Central canal of spinal cord Pia mater Subarachnoid space Filum terminale Arachnoid Dura mater FIGURE 11. Cerebrospinal fluid is secreted by choroid plexuses in the ventricular walls. The fluid circulates through the ventricles and central canal, enters the subarachnoid space, and is reabsorbed into the blood of the dural sinuses through the arachnoid villi. Blood-Brain Barrier compounds (alcohol, for example) pass readily through the BBB. Certain inorganic ions (Ca+ and K+) pass more slowly, so that The blood-brain barrier (BBB) is a structural arrangement of the concentrations of these ions in the brain differ from those in capillaries, surrounding connective tissue, and specialized neu- the blood plasma. Other substances, such as proteins, lipids, crea- roglia called astrocytes (see figs. The BBB must be taken into account when blood to the extracellular fluid of the brain. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 384 Unit 5 Integration and Coordination Although the BBB is an important protective device, it is thoracic vertebrae. Nerves emerging from this region serve the essential that the brain be able to monitor and respond to fluctu- upper extremities. The lumbar enlargement lies between the ations in blood glucose, pH, salinity, osmolarity, and pressure. Nerves from the lumbar For this reason, the BBB is absent in limited brain areas, includ- enlargement supply the lower extremities. The embryonic spinal cord develops more slowly than the associated vertebral column; thus, in the adult, the cord does not Knowledge Check extend beyond L1. Where is cerebrospinal fluid produced and where does it level of L1 to the coccyx. The spinal cord develops as 31 segments, each of which gives rise to a pair of spinal nerves that emerge from the spinal cord through the intervertebral foramina. Two grooves, an ante- rior median fissure and a posterior median sulcus, extend the SPINAL CORD length of the spinal cord and partially divide it into right and left portions. Like the brain, the spinal cord is protected by three dis- The spinal cord consists of centrally located gray matter, involved tinct meninges and is cushioned by cerebrospinal fluid. The pia in reflexes, and peripherally located ascending and descending mater contains an extensive vascular network. The gray matter of the spinal cord is centrally located and Objective 25 Describe the structure of the spinal cord.
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