The+Kidney+HW3+MC

The Kidney 1. Describe the path of urine and the structure and function of each organ in this path. (Detail). Pp.188-189 • The kidneys are paired organs located near the small of the back, on either side of the vertebral column. They lie in depressions beneath the peritoneum, where they receive some protection from the lower rib cage. They are bean-shaped and reddish brown in color. They are covered by a tough capsule of fibrous connective tissue, called a renal capsule. Masses of adipose tissue adhere to each kidney. The concave side of a kidney has a depression, where a renal artery enters and a renal vein and a ureter exit the kidney. Kidneys produce the urine. 2. Describe the four functions of the kidney and how they contribute to homeostasis (balance) (detail) p. 189
 * Once the urine is made by the kidneys, it gets to the ureters. The ureters conduct urine from the kidneys to the bladder. They are small, muscular tubes about 25 cm long and 5 mm in diameter. The wall of the ureter has 3 layers: an inner mucosa (mucous membrane), a smooth muscle layer, and an outer fibrous coat of connective tissue. Urine enters the bladder in spurts that occur at the rate of one to five per minute.
 * The urinary bladder then stores the urine until it is expelled from the body. The bladder has 3 openings: 2 for the ureters and one for the uretha, which drains the bladder. The bladder wall is expandable because it contains a middle layer of circular fibers and two layers of longitudinal muscle. Small folds of bladder mucosa act like a valve to prevent backward flow. The internal sphincter occurs around the opening of the uretha. It’s composed of smooth muscle. The external sphincter is composed of skeletal muscle. When the urinary bladder fills about 250mL with urine, stretch receptors send sensory nerve impulses to the spinal cord. Motor nerve impulses from the spinal cord cause the urinary bladder to contract and the sphincters to relax so the urination is possible.
 * The urine from the bladder is passed to the uretha. The uretha passes the urine to the outside. It’s a small tube that extends from the urinary bladder to an external opening. It’s function is to remove urine from the body. It has a different length in females than in males. IN females it’s only 4 cm long. The short length in females makes bacteria invasion easier. As the uretha leaves the males urinary bladder, it is encircled by the prostate gland, although sometimes the flow of urine in the uretha is restricted. In females, the uretha carries urine during urination and sperm during ejaculation.
 * The kidneys excrete metabolic waste. Urea is a by-product of amino acid metabolism. The breakdown of amino acids in the liver releases ammonia, which the liver rapidly combines with carbon dioxide to produce urea. The metabolic breakdown of creatine phosphate results in creatinine. The breakdown of nucleotides produces uric acid which is insoluble. Crystals or uric acid collect in the joints and produce a painful ailment called gout.
 * Another function of the kidney is to maintain the appropriate water-salt balance of the blood. The more salts there are in the blood, the greater the blood volume and the greater the blood pressure. In this way kidneys are involved in regulating blood pressure.
 * Another function is that it regulates the acid-base balance of the blood. The kidneys monitor and help control blood pH, mainly excreting hydrogen ions and reabsorbing the bicarbonate ions as needed to keep the blood pH at 7.4.
 * Last but not least, Kidneys assist the endocrine system in hormone secretion. The kidneys release rennin, a substance that leads to the secretion of the hormone aldosterone from the adrenal glands, which lie atop the kidneys. The kidneys secrete the hormone erythropoietin, wich stimulates the red blood cell production. They also help activate vitamin D from the skin.

3.Trace the path of blood through the kidney. pp.191-192
 * Blood that leaves the glomerulus enters the efferent arteriole. The efferent arteriole takes blood to the peritubular capillary network. From there the blood goes into a venule that carries blood into the renal vein.

4. What microscopic structure is responsible for the production of urine in the kidney? p. 191
 * The nephrons produce urine and are positioned so that the urine flows into a collecting duct. Several nephrons enter the same collecting duct; the collecting ducts eventually enter the renal pelvis.

5. Describe the parts of the nephron (detail). pp.192-193 6. What are the major processes of urine formation and how does the nephron carry out each process? p. 195
 * First, the closed end of the nephron is pushed in on itself to form a cuplike structure called the glomerular capsule. The outer layer is composed of squamous epithelial cells; the inner layer is made up of podocytes that have ling cytoplasmic extensions. Next there is a proximal convoluted tubule. The cuboidal epithelial cells lining this part of the nephron have numerous microvilli that are tightly packed and form a brush border. That increases the surface area for the tubular reabsorption of filtrate components. The cells have mitochondria which supply energy for active transport of molecules from the lumen to the peritubular capillary network. Simple squamos epithelium appears as the tube narrows and makes a U-turn called the loop of the nephron. Each loop consists of a descending limb that allows water to leave and an ascending limb that extrudes salt. The cuboidal epithelial cells of the distal convoluted tubule have numerous mitochondria, but they lack micro-villi.
 * The major processes of urine formation are tubular secretion, tubular reabsorption, and glomerular filtration. In tubular reabsorption nutrient and salt molecules are actively reabsorbed from the convolted tubules into the peritubular capillary network, and water flows passively. In tubular secretion certain molecules are actively secreted from the peritubular capillary network into the convolted tubes. In glomerular filtration water, salts, nutrients molecules, and waste molecules move from the glomerulus to the inside of the glomerular capsule. These small molecules are called the glomerular filtrate.

7. Explain how an artificial kidney cleanses the blood. p. 200
 * A patients artificial blood if pumped through dialysis tubing, it is exposed to a dialysate. Wastes exit from blood into the solution because of a preestablished concentration gradient. In this way, blood is not only cleansed, but its water-salt and acid-base balances can also be adjusted.

8. How do the kidneys assist other body systems? p. 201-202
 * The kidneys assist the endocrine system and also the cardiovascular system by producing erythropoietin used to stimulate red bone marrow production in patients who are recovering from chemotherapy. The kidneys assist the skeletal, nervous, and muscular systems by helping to regulate the amount of calcium ions in the blood. The kidneys convert vitamin D to its active form needed for Ca(2+) absorption by the digestive tract, and they regulate the excretion of electrolytes, including Ca(2+). Thee kidneys also regulate the sodium and potassium content of blood. These ions, needed for nerve conduction, are necessary to the contraction of the heart and other muscles in the body.