By R. Corwyn. Grand View College.

Dietary fiber is made of polysaccharides that are usually Maltotriose α-Limit dextrin Maltose poorly digested by the enzymes in the small intestine purchase 30g himcolin. They have an extremely important physiological function in that they provide the “bulk” that facilitates intestinal motility and function discount 30g himcolin amex. Many vegetables and fruits are rich in fibers, The digestion products of starch after ex- FIGURE 27. CHAPTER 27 Gastrointestinal Secretion, Digestion, and Absorption 499 fore this point. Pancreatic amylase continues the digestion of the remaining carbohydrates. However, the chyme must first be neutralized by pancreatic secretions, since pancre- atic amylase works best at neutral pH. The products of pan- creatic amylase digestion of polysaccharides are also malt- ose, maltotriose, and -limit dextrins. The digestion products of starch and glycogen, to- gether with disaccharides (sucrose and lactose), are fur- ther digested by enzymes located at the brush border membrane. Enterocytes Play an Important Role in Carbohydrate Absorption and Metabolism Monosaccharides are absorbed by enterocytes either ac- tively or by facilitated transport. Glucose and galactose are absorbed via secondary active transport by a symporter (see FIGURE 27. The movement of Na into the cell, down concentration and electrical gradients, effects the uphill movement of glucose into the cell. The low intracellular Na concentration is maintained by the The sugars absorbed by enterocytes are transported by basolateral membrane the portal blood to the liver where they are converted to Na /K -ATPase. After a meal, the level of the Na /K -ATPase activity and the K conductance of blood glucose rises rapidly, usually peaking at 30 to 60 min- the basolateral membrane. The concentration of glucose can be as high as 150 a higher concentration than in plasma and leave the cell by mg/dL.

The extrusion of the larity of the dominant follicle is twice that of the other antral oocyte-cumulus complex is aided by smooth muscle con- follicles order himcolin 30g line, permitting a more efficient delivery of cholesterol traction buy himcolin 30g without a prescription. At the time of rupture, the oocyte-cumulus complex to theca cells and better exposure to circulating go- and follicular fluid are ejected from the follicle. At this time, the main source of circulating The LH surge triggers the resumption of the first meiosis. Since estradiol is the pri- Up to this point, the primary oocyte has been protected by mary regulator of LH and FSH secretion by positive and neg- unknown factors within the follicle from premature cell divi- ative feedback, the dominant follicle ultimately determines sion. Within a couple of hours after the initiation of circulating estradiol, and it causes multiple changes in the of the LH surge, the production of progesterone, androgens, dominant follicle, which occur within a relatively short time. Progesterone, acting These include the resumption of meiosis in the oocyte (as al- through the progesterone receptor on granulosa cells, pro- ready discussed); granulosa cell differentiation and transfor- motes ovulation by releasing mediators that increase the dis- mation into luteal cells; the activation of proteolytic en- tensibility of the follicular wall and enhance the activity of zymes that degrade the follicle wall and surrounding tissues; proteolytic enzymes. As LH levels reach their peak, plasma increased production of prostaglandins, histamine, and other estradiol levels plunge because of down-regulation by LH of local factors that cause localized hyperemia; and an increase FSH receptors on granulosa cells and the inhibition of gran- in progesterone secretion. Eventually, LH receptors on luteinizing onset of the LH surge, this coordinated series of biochemical granulosa cells escape the down-regulation, and proges- and morphological events culminates in follicular rupture terone production increases. The midcycle FSH surge is not essential for ovulation because an injection of either LH or human chori- onic gonadotropin (hCG) before the endogenous go- FORMATION OF THE CORPUS LUTEUM FROM nadotropin surge can induce normal ovulation. However, THE POSTOVULATORY FOLLICLE only follicles that have been adequately primed with FSH will ovulate because they contain sufficient numbers of LH In response to the LH and FSH surges and after ovulation, receptors for ovulation and subsequent luteinization. The granulosa cells begin to cease their proliferation cycle regulator), and a transcription factor called C/EBP and begin to undergo hypertrophy and produce proges- (CCAAT/enhancer binding protein). The ruptured follicle which these proteins interact to regulate follicular rupture are develops a rich blood supply and forms a solid structure largely unknown. However, mice with specific disruption of called the corpus luteum (yellow body).

Arteries branch extensively to form a network of progres- sively smaller vessels generic 30g himcolin with visa. Conversely generic himcolin 30g with amex, microscopic-sized veins called constituting about 8% of the total body weight. Blood passes from the arterial to tion of that going to the lungs, is bright red in color because of the the venous system in capillaries, which are the thinnest and most high concentration of oxyhemoglobin (the combination of oxygen numerous blood vessels. All exchanges of fluid, nutrients, and and hemoglobin) in the erythrocytes. Venous blood is blood return- wastes between the blood and tissue cells occur across the walls ing to the heart. Except for the venous blood from the lungs, of capillaries; thus, they are considered the basic functional units it contains less oxygen and is, therefore, a darker red than the of the circulatory system. Blood has a viscosity that ranges between Fluid derived from plasma passes out of capillary walls into 4. This means that it is thicker than water, which has a the surrounding tissues, where it is called interstitial fluid or tissue viscosity of 1. Some of this fluid returns directly to capillaries and some ture within the thorax of the body of about 38° C (100. When enters into lymphatic vessels located in the connective tissues you donate blood, a “unit” (half a liter) is drained. Fluid in lymphatic vessels is called approximately a tenth of your total blood volume. This fluid is returned to the venous blood at particular Blood is composed of a cellular portion, called formed ele- sites. Lymph nodes, positioned along the way, cleanse the lymph ments, and a fluid portion, called blood plasma.

The surgery due to middle ear disease is usually com- reestablishes a more normal sound path- pletely eliminated generic 30g himcolin mastercard. Since the advent of antibiotics for treat- ment of mastoiditis purchase himcolin 30g, mastoidectomy is per- Devices and Aids for Hearing Loss formed less frequently. Mastoidectomy is a surgical procedure for removal of infect- Cochlear Implant ed mastoid air cells, which are located in the mastoid process. Because the mastoid Currently, cochlear implants are the is a portion of the acoustic system of the standard treatment for individuals with middle ear, there may be permanent severe to profound hearing loss who are hearing loss after surgery, depending on unable to have effective oral communica- the nature of the surgery. For example, tion even with the benefit of a hearing aid individuals who have had a radical mas- (Gates & Miyamoto, 2003). A cochlear toidectomy, in which other structures in implant is an auditory prosthesis. The im- addition to the mastoid cells are removed, plant is an inner ear device that helps indi- may have a greater degree of hearing loss viduals detect medium to loud environ- or permanent hearing loss. Cochlear implants trans- having a simple mastoidectomy, in late sounds into digital impulses that are which only mastoid cells are removed, fed directly to the auditory nerve, bypass- may have unaffected hearing. This elec- tronic device consists of a microphone that Tympanoplasty picks up sound; a battery-powered processor, either at ear level or typically worn on a Surgical procedures involving the mid- belt, that converts sound into digital dle ear are referred to generally as tym- impulses; and a receiver implanted into the 158 CHAPTER 5 HEARING LOSS AND DEAFNESS temporal bone that transmits digital • Severe to profound sensorineural impulses down the electrode that has been deafness surgically placed in the cochlea and that • Little or no benefit from hearing stimulates the auditory nerve directly. The processor converts able for the implant sound into digital impulses and sends it The chief predictor of success for a coch- to the receiver (the internal component, lear implant is a short duration of deafness about the size of a quarter, that is surgi- (Fischetti, 2003; Gates and Miyamoto, 2003). The receiv- though children who are prelingually deaf- er is connected to electrodes in the coch- ened may benefit from early implantation lea that receive impulses and stimulate the to facilitate speech development. Individ- auditory nerve with these digital impuls- uals receiving a cochlear implant should es, permitting perception of the digitally have realistic expectations for hearing processed information as speech.