Macroscopic and Microscopic Structure of the Mammalian Kidney

Transcription

1 Physiology 1 Redwood High School Name Class Period Background Macroscopic and Microscopic Structure of the Mammalian Kidney In vertebrate animals, the main functional organ of the urinary system is the kidney. This relatively small, yet critical, organ excretes nitrogenous wastes (ammonia, urea, and uric acid) produced by body cells during protein and nucleic acid metabolism. Additionally, the kidney excretes excess water and certain salts from the blood. These functions are important in maintaining homeostasis, the balanced internal environment of the body. The vertebrate kidney is a macroscopic structure that can be dissected and studied with the unaided eye. The function unit of the vertebrate kidney is the nephron, which is a microscopic structure. Each human kidney contains approximately one million nephrons. When stretched out, each nephron is 35 mm in length, but is less than 1 mm in diameter. However, nephrons in the kidney occupy a much smaller area, due to extensive folding and packing. The nephron is composed of small arteries that supply blood to a tuft of capillaries, the glomerulus. A spherical structure, the glomerular (Bowman's) capsule, surrounds the glomerulus and is attached to a convoluted tubule, a portion of which is the nephron loop (loop of Henle). The capillaries leaving the glomerulus are intimately associated with the tubule. The production of urine in the nephron involves three distinct processes: filtration, reabsorption and secretion. Filtration occurs is the glomerulus. Normal blood pressure forces blood plasma out of the capillaries through pores. The blood plasma is then filtered through a membrane before it enters the cavity of the glomerular capsule. This filtrate differs from blood in that it lacks blood cells and large protein molecules. Most of the useful material in this filtrate is reabsorbed as the filtrate moves through the tubule. This step is called reabsorption. The cells of the tubule pass materials out of the lumen (cavity) of the tubule by both active transport and passive diffusion. Secretion involves the movement of certain waste products from the blood directly into the collecting urine. Elimination is the last step of the process, where all materials not reabsorbed move into the collecting tubules and ultimately into the ureter, which carries the urine to the bladder. Urine, therefore, contains metabolic waste, excess salt and water. The human kidney produces approximately 150 L of filtrate each day but excretes only 1.5 L of this amount (depending on water intake, activity levels and environmental conditions). During the process the blood loses almost all of its nitrogenous wastes, the salt and water content of the body is balanced, and ph of the blood is adjusted. This complex homeostatic mechanism is largely under hormonal control. During this activity you will study the kidney at both the macroscopic and microscopic levels of organization. Focus Questions Procedure What are the important macroscopic structures of the vertebrate kidney and what are their various functions? How do the important macroscopic structures appear under microscopic examination? What are the important tissues in the vertebrate kidney and what are their functions? Part A. Macroscopic Structure of the Kidney 1. Obtain a calf kidney that has been rinsed to remove excess blood. Dry the kidney with a paper towel. 2. Using scissors and forceps, carefully remove as much of the fatty tissue surrounding the kidney as is possible. It is preferable to leave some fat and not to damage the kidney itself. 3. Observe the kidney for blood vessels and the ureter. These will be close to the medial aspect of the kidney and will, probably, be difficult to locate. 4. Make a scaled accurate, drawing of the exterior view of your kidney. Your drawing should include a scale and the following labels: adipose capsule, renal capsule, renal hilum, blood vessels, ureter. 5. Make a clean, longitudinal section through the kidney using a razor blade or scalpel. Lay the two halves of your kidney on the dissecting tray with the exterior aspect down. Each half should be very similar.

2 6. Examine the cut sides of the kidney to find the structures described below. Use available diagrams from textbooks, reference books and coloring assignments to help your identification. 7. The hilium and renal capsule can be observed from a different perspective than in the exterior view. 8. Just within the hilium are three identifiable structures: the renal sinus a fat-filled cavity; the renal pelvis a wide section of the urinary channel, distal to the ureter; and the calyces branches of the pelvis, extending into the kidney tissue proper. 9. The kidney tissue proper is divided into an outer cortex and an inner medulla, as is the tissue of many organs. The cortex usually appears as a brownish outer region, while the medulla tissue is smoother and lighter in color. Renal pyramids are cone-shaped sections of tissue lying mostly within the medulla. Each appears roughly as a triangle and is composed of collecting ducts that conduct urine toward its tip. 10. Make an accurate, scaled drawing of your longitudinal section. Your drawing should include a scale and the following labels: renal sinus, renal pelvis, renal cortex, renal medulla, renal pyramids, calyces. 11. When you are finished, put all biological waste in designated disposal container. Thoroughly wash and dry all other equipment. It is critical that you leave enough time to thoroughly complete your clean up. Part B. Microscopic Structure of the Kidney 1. Obtain a prepared slide of a mammalian kidney. The sagittal (longitudinal) section of kidney you are about to study has been made by slicing a kidney into very thin sections. Refer to diagrams in textbook and other reference sources to help you in this part of the lab. 2. Hold the slide of a kidney sagittal section up to the light and view with the unaided eye. The dark outer layer is the cortex containing the renal corpuscles; the light inner portion is the medulla containing the nephron loops. 3. Using 40X magnification of the compound microscope study this kidney section, start your observations with the cortex. Notice the large circular areas. These are the renal corpuscle and glomeruli in cross section. The smaller clear circles are the tubules. Switch to 100X magnification. The renal corpuscle appears as isolated circular areas. Identify the glomerulus, which is the capillary cluster inside the corpuscle, and the glomerular capsule, which appears as a clear area surrounding the glomerulus. Note the numerous sections of convoluted tubules between the renal corpuscles. You can distinguish between proximal convoluted tubules and distal convoluted tubules by the thickness of the tubule wall. 4. Make a scaled microscopic diagram of the cortex and medulla intersection under 40X. Your drawing should include a scale and the following labels: renal corpuscle, cortex and medulla. 5. Make a scaled microscopic diagram of a section of the cortex under 100X. Your drawing should include a scale and the following labels: renal corpuscle, glomerular capsule, glomerulus, proximal convoluted tubule, distal convoluted tubule. 5. Examine the medulla of the kidney section slide under 100X magnification. You will not find any glomeruli in this area, only portions of the collecting tubule and the nephron loop. These structures will appear in both longitudinal and cross section. 7. Make a scaled microscopic diagram of a section of the medulla. Your drawing should include a scale and the following labels: collecting tubule, nephron loop. 8. Return your slide to the slide tray and prepare your microscope for proper storage.

3 Physiology 2 Redwood High School Part A. External Anatomy Drawing. Name Class Period The Urinary System: Anatomy of a Mammalian Kidney Written Descriptions. Adipose Capsule Renal Capsule Renal Hillum Blood Vessels Ureter

4 Part A. Longitudinal Section Drawing. Written Descriptions. Renal sinus Renal pelvis Renal cortex Renal medulla Renal pyramids Calyces

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6 Name Date Period