Chapter 28, Problem 1O

Summary Introduction

To describe:

The normal anatomy and physiology of the renal system.

Introduction:

Metabolism of the human body inevitably produces a variety of unwanted or waste products. This waste product is not simply needed by the body. If it is allowed to accumulate in the body, it may produce harmful effects. These wastes are completely excreted from our body through digestive tracts, respiratory tracts, and by sweat glands. The principal system that is involved in the excretion of waste is the urinary system. From the blood, the metabolic waste is removed by the kidney. The rest of the urinary system involves in the elimination of urine, storage, and for transport. The kidney plays an important role in controlling the blood pressure and blood volume.  Kidney physiology is administrated by certain principles. This includes osmotic pressure, down pressure, and electrochemical gradients. The stages of urine production and the role of the kidney (regulating urine concentration and fluid balance) mainly depend on concepts such as osmolarity, tonicity, and osmosis.

Explanation of Solution

Pictorial representation:

The normal anatomy and physiology of the renal system are described below:

The principal system that is involved in the excretion of waste is the urinary system. From the blood, the metabolic waste is removed by the kidney. The kidney plays an important role in regulating blood pressure and blood volume. The back of the abdominal cavity is the place where the kidney (bean shaped) is located. Vertebrae T12 to L3 is the level where the kidney lies. The left kidney is located slightly higher than the right kidney (lower). This is due to the large right lobe of the liver that occupies the space above the right kidney. The middle part of the left kidney is nearly crossed by Rib 12. The kidneys are retroperitoneal, along with the renal artery, vein, ureters, adrenal glands, and the urinary bladder.

The structural unit of the kidney is referred to as nephron. One million nephrons are present in each kidney. The filtering process takes in the glomerulus. The glomerulus is a bunch of capillaries that is encapsulated by the glomerular capsule. The time taken for filtering the blood is called as glomerular filtration rate (GFR).

The glomerular filtration rate is controlled by the afferent arterioles (approaching the glomerulus) and the efferent arterioles (exiting the glomerulus). The proximal tubule or proximal convoluted tubule plays an important role in returning 60% - 70% of water and sodium from the filtered fluid into the blood. The nephron is surrounded by the blood vessels that permit the reabsorbed substances directly to reach the blood stream.  This process (one of the active transport) needs the adenosine triphosphate molecule as an energy source. The active transportation of potassium and sodium ions returns back into the bloodstream, which is known as passive reabsorption (water and chloride). The water and chloride ions follow (passively) the potassium and sodium ions by means of osmosis. The loop of Henle (ascending) is the area where  20% - 25% of sodium ion is reabsorbed back into the blood. In the loop of Henle, sodium is passively reabsorbed, and chloride is actively reabsorbed.

In the distal convoluted tubule or distal tubule, the remaining (5%-10%) sodium is reabsorbed. The sodium ion is actively filtered in the distal tubule. This process is controlled by aldosterone. The final pathway (common) for the remains that begin in the glomerulus is called as collecting duct. The antidiuretic hormone plays an important role to raise water absorption (into the blood). Hence, excess water is prevented from being excreted in the urine.

Conclusion

The glomerular filtration rate’s measurement is used in the detection of some kidney diseases. Yet, the quantity of NaCl could not be assumed by the glomerular filtration rate; there are two causes to explain this reason. (1) The glomerulus is not able to filter the NaCl in urine that is produced by the renal tubule. (2) The tubule reabsorbs all the NaCl that the glomerulus has filtered.