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The high blood flow to the cortex rapidly 400 400 200 NaCl NaCl Urea carries away this water purchase 100mg januvia with amex, so there is no detectable dilution of Urea cortical tissue osmolality buy generic januvia 100 mg line. Before the tubular fluid reenters 600 600 400 600 Inner the medulla cheap 100mg januvia, it is isosmotic and reduced to about 5% of the medulla H2O original filtered volume discount januvia 100 mg line. The reabsorption of water in the NaCl NaCl cortical collecting ducts is important for the overall opera- Urea Urea 800 tion of the urinary concentrating mechanism. If this water 800 800 600 were not reabsorbed in the cortex, an excessive amount H2O H2O NaCl would enter the medulla. It would tend to wash out the gra- 1,000 1,000 1,000 800 NaCl Urea H2O 1,200 1,200 1,200 1,200 1 Vasa Loop of Collecting recta Henle duct Osmolality Osmotically concentrated urine. Numbers in boxes represent relative amounts of water present at each level of the nephron. Solid ar- rows indicate active transport; dashed arrows indicate passive transport. The heavy outlining along the ascending limb of the Outer loop of Henle indicates relative water-impermeability. As discussed earlier, proximal Inner reabsorption of water is essentially an isosmotic process, so medulla fluid entering the loop is isosmotic. As the fluid moves along the descending limb of the loop Henle in the medulla, it be- comes increasingly concentrated. This rise in osmolality, in principle, could be due to one of two processes: 1) The movement of water out of the descending limb because of the hyperosmolality of the medullary in- terstitial fluid. The relative importance of these processes may depend on the species of animal. For most efficient operation of the Osmolality concentrating mechanism, water removal should be pre- 1,200 mOsm/kg H2O dominant, so only this process is depicted in Figure 23. Flow The removal of water along the descending limb leads to a 1 mL H2O/min rise in [NaCl] in the loop fluid to a value higher than in the FIGURE 23. In the steady state, the When the fluid enters the ascending limb, it enters wa- inputs of water and solutes must equal their respective outputs. NaCl is transported out of the Water input into the medulla from the cortex (100 36 6 ascending limb and deposited in the medullary interstitial 142 mL/min) equals water output from the medulla (117 24 fluid. CHAPTER 23 Kidney Function 399 dient in the medulla, leading to an impaired ability to con- 50 centrate the urine maximally. All nephrons drain into collecting ducts that pass 30 through the medulla. In the presence of AVP, the medullary 100 50 100 collecting ducts are permeable to water. Water moves out of the collecting ducts into the more concentrated interstitial fluid. In high levels of AVP, the fluid equilibrates with the Cortex interstitial fluid, and the final urine becomes as concentrated as the tissue fluid at the tip of the papilla. Outer Many different models for the countercurrent mechanism medulla have been proposed; each must take into account the princi- ple of conservation of matter (mass balance). In the steady state, the inputs of water and every nonmetabolized solute must equal their respective outputs. It provides some additional insight Inner into the countercurrent mechanism. Notice that fluids enter- medulla ing the medulla (from the proximal tubule, descending vasa recta, and cortical collecting ducts) are isosmotic; they all have an osmolality of about 285 mOsm/kg H2O. It follows from mass balance considerations that somewhere a hypoosmotic 50 fluid has to leave the medulla; this occurs in the ascending limb of the loop of Henle. Because water is added to the medulla along the de- 30 scending limbs of the loops of Henle and the collecting ducts, this water must be removed at an equal rate. The cending limbs of the loops of Henle cannot remove the numbers indicate relative amounts (100 fil- added water, since they are water-impermeable. The heavy outline from the thick is removed by the vasa recta; this is why ascending exceeds ascending limb to the outer medullary collecting duct indicates descending vasa recta blood flow (see Fig. Urea is added to the inner blood leaving the medulla is hyperosmotic because it drains medulla by its collecting ducts; most of this urea reenters the loop a region of high osmolality and does not instantaneously of Henle, and some is removed by the vasa recta.
This causes a deviation of one eye januvia 100 mg free shipping, so that there is not a concurrent con- vergence of both eyeballs cheap januvia 100 mg overnight delivery. With this condition buy 100 mg januvia with amex, two images are re- ceived by the optic portion of the cerebral cortex—one of which is FIGURE 15 purchase 100mg januvia with mastercard. A person who has amblyopia will experience dimness of vi- The optic disc is frequently called the blind spot because it is devoid sion and partial loss of sight. Light rays refracted The eyes transduce the energy of the electromagnetic spectrum from the periphery would not be brought into focus on the retina (fig. Electromagnetic energy with pupil and accommodation of the lens occur simultaneously. Light of longer wavelengths, which are in the infrared re- Convergence of the Eyeballs gions of the spectrum, does not have sufficient energy to excite Convergence refers to the medial rotation of the eyeballs when photoreceptors but is perceived as heat. In fact,focusing on an object close to shorter wavelengths and more energy than visible light, is filtered the tip of the nose causes a person to appear cross-eyed. Certain insects, such as balls must converge when viewing close objects because only honeybees, and people who have had their lenses removed and not then can the light rays focus on the same portions in both retinas. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 512 Unit 5 Integration and Coordination Smooth muscle tissue of iris Smooth muscle tissue of ciliary body FIGURE 15. It is secreted into the posterior chamber, flows through the pupil into the anterior chamber, and drains from the eyeball through the scleral venous sinus. Lens Cornea Fovea centralis Pupil Optic nerve Anterior chamber Anterior cavity Posterior chamber (contains aqueous humor) Conjunctiva Optic disc Creek Posterior cavity (contains vitreous humor) FIGURE 15. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Chapter 15 Sensory Organs 513 FIGURE 15. The visible spectrum (bottom) constitutes only a small range of this spectrum and is shown in nanometer units (1 nm = 10–9 meter). Three distinct and specialized types of cone cells within the retina to the opposite side. Different photosensitive pigments from the lateral (temporal) half of the retina do not cross, how- enable each type to absorb light rays primarily in the blue, green, or red portion of the color spectrum. The optic tract is a continuation of optic nerve fibers from lengths between 400 and 550 nm; green cone cells are stimulated by the optic chiasma. It is composed of fibers arising from the reti- wavelengths between 450 and 550 nm; and red cone cells are stimu- nas of both eyeballs. Color blindness is the As the optic tracts enter the brain, some of the fibers in inability to distinguish colors, particularly reds and greens. Color blindness for the majority of fibers and the motor pathways they activate constitute the tectal these people is a misnomer, however, because in nearly all cases there system, which is responsible for body-eye coordination. Here the fibers synapse with neurons whose axons type—is able to distinguish traffic signals without difficulty be- cause yellow has been added to the red light, and blue has been constitute a pathway called the optic radiation. This arrangement of visual fibers, known as the geniculostriate system, is responsible for perception of the Neural Pathways for Vision, visual field. Eye Movements, and Processing The nerve fibers that cross at the optic chiasma arise from the retinas in the medial portions of both eyes. The photoreceptors Visual Information of these fibers are stimulated by light entering the eyeball from the periphery. If the optic chiasma is cut longitudinally, peripheral vision The photoreceptor neurons, rod and cone cells, are the func- will be lost, leaving only “tunnel vision. Nerve impulses from the rod and cone cells eye, and the medial field of vision lost for the other. The optic nerve consists of axons of aggregated gan- Superior Colliculi and Eye Movements glion neurons that emerge through the posterior aspect of the eyeball. At this point, all of the spinal cord help mediate the startle response to the sight,for the fibers arising from the medial (nasal) half of each retina cross example,of an unexpected intruder. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 514 Unit 5 Integration and Coordination pathetic neurons by fibers from the superior colliculi. Postganglionic Monocular field neurons in the ciliary ganglia behind the eyes, in turn, stimulate Binocular field constrictor fibers in the iris.
The blistering and erythema characteristic of second-degree burns is a During the aging of the skin discount januvia 100 mg without a prescription, the number of active hair fol- manifestation of intact and functioning blood vessels 100 mg januvia fast delivery, which exist in licles buy januvia 100mg low price, sweat glands purchase januvia 100mg online, and sebaceous glands also declines. In third-degree burns, the entire quently, there is a marked thinning of scalp hair and hair on the dermis and its vasculature are destroyed, thus explaining the absence of extremities, reduced sweating, and decreased sebum production. In addition, nerve endings and other nerve end organs Because elderly people cannot perspire as freely as they once did, that reside in the dermis are destroyed in third-degree burns, resulting they are more likely to complain of heat and are at greater risk in a desensitized area. By contrast, significant numbers of these struc- tures are spared and functional in second-degree burns, thus preserving for heat exhaustion. The third-degree burn areas will all require because of the loss of insulating adipose tissue and diminished skin grafting in order to prevent infection, one of the skin’s most vital circulation. In second-degree burns, the spared dermis serves somewhat of skin to dry and crack frequently. Consequently, skin grafting is usually unnecessary, The integument of an elderly person is not as well pro- especially if sufficient numbers of skin adnexa (hair follicles, sweat tected from the sun because of thinning, and melanocytes that glands, and so forth), which generally lie deep within the dermis, are produce melanin gradually atrophy. These structures serve as starting points for regeneration of sur- face epithelium and skin organs. Integumentary System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 128 Unit 4 Support and Movement CLINICAL PRACTICUM 5. Important Clinical Terminology acne An inflammatory condition of sebaceous glands. Acne is effected by gonadal hormones, and is therefore common during puberty and adolescence. Pimples and blackheads on the face, chest, and back are expressions of this condition. Abnormal dandruff may inflammatory condition of the skin carbuncle A bacterial infection similar to a be caused by certain skin diseases, such as producing itchy, red vesicular lesions that boil, except that a carbuncle infects the seborrhea or psoriasis. It may be localized epithelial debris in the hair follicle and scrubbing. It may be dandruff Common dandruff is the continual relationship of cutaneous lesions to systemic caused by drugs, food, insect bites, inhalants, shedding of epidermal cells of the scalp; it disease. Hair is characteristic of all mammals, but consists of several kinds of tissues. The appearance of the skin is clinically (a) Keratin and acidic oily secretions on texture varies across mammalian species. The skin regulates body fluids and (c) Lanugo, vellus, and terminal are the the epidermis is composed of five temperatures. The skin permits the absorption of UV (a) Each nail consists of a body, free the blood of the dermis and light, respiratory gases, steroids, fat- border, and hidden border. Integumentary glands are exocrine, creases and flexion lines are has a role in the synthesis of vitamin D, because they either secrete or excrete acquired. Sensory reception in the skin is provided (a) Sebaceous glands secrete sebum onto of fibrous connective tissue interlaced through cutaneous receptors throughout the shaft of the hair. Cutaneous (b) The two types of sudoriferous (sweat) dermis are the papillary layer and the receptors respond to precise sensory glands are eccrine and apocrine. Hair, nails, integumentary glands, and the dietary deficiency of thin skin of the face is the stratum epidermis of the skin are derived from (a) zinc. Integumentary System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 130 Unit 4 Support and Movement 4. Explain the similarities and differences (a) dermal papillae associated hair, glands, and nails. What between the growth of hair and the (b) melanin role do the ectoderm and mesoderm play growth of nails. Which of the following is not true of the occur(s) passively as a result of the structure epidermis?