Glucose and amino acids

CCK is found in the digestive tract and the central and peripheral nervous systems. In the brain, CCK coexists with DA. In the peripheral nervous system, the two principal physiological actions of CCK are stimulation of gaU. bladder contraction and pancreatic enzyme secretion. CCK also stimulates glucose and amino acid transport, protein and DNA synthesis, and pancreatic hormone secretion. In the CNS, CCK induces hypothermia, analgesia, hyperglycemia, stimulation of pituitary hormone release, and a decrease in exploratory behavior. The CCK family of neuropeptides has been impHcated in anxiety and panic disorders, psychoses, satiety, and gastric acid and pancreatic enzyme secretions. 

A 0-9% salt solution is considered to be isotonic with blood. Other electrolytes present include bicarbonate ions (HCOj ) and small amounts of potassium, calcium, magnesium, phosphate, sulphate and organic acid ions. Included among the complex compounds and present in smaller amounts are phospholipids, cholesterols, natural fats, proteins, glucose and amino acids. Under normal conditions the extracellular body fluid is slightly alkaline with a pH of 7-4. ... 

Water-soluble products of digestion are transported directly to the fiver via the hepatic portal vein. The fiver regulates die blood concentrations of glucose and amino acids. 

Several types of cells are equipped with carrier proteins to transport essential nutrients such as glucose and amino acids that cannot cross the plasma membrane freely because of their hydrophilicity. Intestinal and renal epithelia have long been known to possess specialized Na+ cotransport processes for glucose [205], amino acids [206], and di- and tripeptides [207],... 

Most hydrophilic, or water-soluble, substances are repelled by this hydrophobic interior and cannot simply diffuse through the membrane. Instead, these substances must cross the membrane using specialized transport mechanisms. Examples of lipid-insoluble substances that require such mechanisms include nutrient molecules, such as glucose and amino acids, and all species of ions (Na+, Ca++, H+, Cl, and HC03). Therefore, the plasma membrane plays a very important role in determining the composition of the intracellular fluid by selectively permitting substances to move in and out of the cell. 

BRAIN GLUTAMATE IS DERIVED FROM BLOOD-BORNE GLUCOSE AND AMINO ACIDS THAT CROSS THE BLOOD-BRAIN BARRIER 269... 

The LLC-PKi (porcine kidney) cell line (Hull et al., 1976) exhibits a range of morphological and functional properties of proximal tubule epithelium. For example, Na+-dependent glucose and amino acid transport have been demonstrated in LLC-PKi cells (Rabito and Ausiello, 1980 Rabito and Karish, 1982, 1983). LLC-... 

Liver Glucose and amino acids Fatty acids... 

The major fuels of skeletal muscle are glucose and fatty acids. Because of the enormous bulk, skeletal muscle is the body s major consumer of fuel. After a meal, under the influence of insulin, skeletal muscle takes up glucose to replenish glycogen stores and amino acids that are used for protein synthesis. Both excess glucose and amino acids can also be oxidized for energy. 

The ATP generated from glycolysis will provide energy to maintain the Na ion gradient for the transport of glucose and amino acids and for the formation of chylomicrons in the enterocyte. 

Molecules such as glucose and amino acids are transported across a membrane by specific protein transporters. The... 

There is considerable discussion in the medical literature on the relative merits of enteral or parenteral feeding. For enteral feeding, the choice is between elemental (or monomeric) preparations, which contain glucose and amino acids, or polymeric preparations which contain protein and... 

Figure 7.2 Glucose regulation by insulin. Increased concentrations of glucose and amino acids in the circulation, vagus nerve stimulation and circulating hormones e.g. GLP) stimulate insulin secretion by 3-cells of the pancreatic islets. Insulin suppresses glucose production by the liver and increases glucose uptake by skeletal muscle and fat, leading to decreased circulating glucose concentrations.

The filtered substance is reabsorbed by the tubule. Some important molecules such as glucose and amino acids, and electrolytes such as sodium and chloride ions share this feature. Thus, their concentration in urine underestimates the GFR. 

Some cells couple the pure transport forms discussed on p. 218—i.e., passive transport (1) and active transport (2)—and use this mechanism to take up metabolites. In secondary active transport (3), which is used for example by epithelial cells in the small intestine and kidney to take up glucose and amino acids, there is a symport (S) located on the luminal side of the membrane, which takes up the metabolite M together with an Na" ion. An ATP-dependent Na transporter (Na /lC ATPase see p. 350) on the other side keeps the intracellular Na+ concentration low and thus indirectly drives the uptake of M. Finally, a uniport (U) releases M into the blood. 

Animal studies indicate that the primary toxic effect of uranium exposure is on the kidney, with particular damage to the proximal tubules. Functionally, this may result in increased excretion of glucose and amino acids. Structurally the necrosis of tubular epithelium leads to formation of cellular casts in the urine. If exposure is insufficient to cause death from renal failure, the mbular lesion is reversible with epithelial regeneration. Although bone is the other major site of deposition, there is no evidence of toxic or radiocarcinogenic effects to bone or bone marrow from experimental studies. ... 

Therefore, a similar pathway appears to operate in certain mammals. When S-(PCP)ThioAcetate was introduced into peanut plants, pentachlorothioanlsole was not formed. However, other metabolites were detected, possibly glucose and amino acid conjugates similar to those reported for 2,4-D (17). 

Increased blood levels of these nutrients, especially glucose and amino acids, stimulate the pancreas to release insulin and suppress glucagon release. 

The constant transport of substances among blood, CSF, and brain cells is influenced by the blood-brain barrier (BBB) (Section 3.2.1). The transport function of the BBB depends on the concentration gradient, molecular weight, ion composition, and liposolubility of compounds as well as on the presence of specific transmitters (i.e., glucose and amino acids). 

It is to be noted that similar compounds and degradation products tend to interfere with the signal of the analyzed compounds. The severest interferences were observed for catechol and resorcinol, whereas cresols and chlorophenols had only little effect. Common substrates, such as glucose and amino acids, produced only low signals. A Rhodococcus PI, which has been isolated from sediment of the river Saale, in particular had a very high sensitivity to phenol and... 

The approach described here can be applied to other cotransporters and antiporters for the development of highly sensitive and selective sensing membranes for substrates (analytes) such as sugars other than D-glucose and amino acids. 

The processes of selective reabsorption of nutrients and xenobiotics goes on within the complex tubule system. 98-99% of filtered materials (salts, water, sugars, amino acids) are eventually reabsorbed by passive or active transport. Biomolecules such as glucose and amino acids are entirely reabsorbed if their concentrations are within the normal range in the blood. However, should the concentrations be higher than normal, those molecules might not be completely reabsorbed because they have exceeded the ability of the nephron transport systems to accommodate them. This is referred to as exceeding the renal threshold. Urine is therefore a convenient body fluid to assay for the initial assessment of metabolic or excretory system malfunctions. 

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