What are Kidneys? Location of Kidneys and Constituents of Urine
Structure and Function of Kidney:
Location of kidneys is of particular importance in your body. There are two bean shaped kidneys in the human body. A normal kidney is about 2.5 cm thick, 10 cm long and 5 cm wide. They are reddish-brown in color. Each weighs around 130 gm in adults. Both kidneys receive blood from the renal artery.
In a resting adult nearly 1.2 to 1.4 liters of blood flows through both kidneys in one minute. It means every 4 to 5 minutes all the circulating blood in the body passes through the kidneys. Kidneys help remove excess salt, water and waste products from the bloodstream.
Like other endocrine organs, kidneys also secrete important hormones such as rennin and erythropoietin into the circulation. These hormones play a significant role in the production of blood cells. In addition, they also assist in the regulation of blood pressure.
It won’t be wrong to call kidney as the natural filter in your body. Its job is to purify blood and make it free from all the waste substances that it has collected from every individual cell. but how is such an important kidneys function executed? For this purpose, you need to study the kidney anatomy.
You can better understand the anatomy of kidneys from the labelled diagrams. One of these is shown here. In the kidney images, you can see that a nephron serves as the basic structural and functional unit. There are a large number of nephrons in each of these organs. They make a direct connection with a complex network of blood vessels.
From the kidneys pictures, you can easily distinguish among different parts, such as medulla, cortex and the renal pelvis. On the side of the renal hilum, you will come across renal artery and the renal vein. From the renal pelvis, there emerges a ureter which descends downward to reach bladder. It also indicates that the location of kidneys is directly above the bladder.
Location of Kidneys
Talking about the location of kidneys, each lies in the grooves or gutters alongside the upper vertebral column. You can find them on the posterior wall of the abdomen at the level of T 12 to L 3 vertebra. The right kidney is about 0.5 inches lower than the left one. This downward displacement of the right kidney is because of the large right lobe of the liver. The images and videos will make the kidneys location further clear for you.
What Do Kidneys Do?
After learning about the location of kidneys, it is important to know what do the kidneys do. A ureter of about 25 cm long descends from each kidney. It travels almost vertically downward before entering the urinary bladder. Ureter is a muscular tube that carries urine from the kidney for temporary storage in the bladder. The urine stays here till its ultimate discharge from the body.
About 1 to 1.5 liters of urine is formed by the kidneys every day. It helps in the elimination of various metabolic waste products such as urea, uric acid from the body.
Constituents of Urine
The function of kidneys is to produce urine by filtering large quantities of fluid from the blood plasma. Urine consists of approximately 95% water. Urine also contains urea, creatinine, phenols, phosphate, potassium and sulfates. There are also nitrates and a large amount of uric acid.
Urea, uric acid and creatinine are all nitrogenous waste products. Nitrogen containing compounds are among the most toxic metabolic waste substances. Your body produces them as a result of various metabolic processes.
You can express the level of nitrogenous waste products in our blood as BUN (blood urea nitrogen). In healthy adults, normal BUN level ranges from 8 mg/dL to 25 mg/dL. A high level of BUN indicates renal insufficiency, i.e. one of the kidney problems.
The volume and composition of urine that the kidneys produce and excrete every day depend crucially on various factors. These factors include fluid intake, diet, renal functions, climate, metabolic activities of cells. Meanwhile, the presence or absence of systemic diseases also has a role to play in this regard.
Dilute urine appears pale while concentrated urine has a dark yellow appearance. Yellow color of the urine is due to biological pigments, like porphyrins, urochrome and urobilin. However, its color may change in many diseases (e.g. jaundice, urinary tract infections).
Normal urine that the kidneys have just produced is slightly acidic in nature. In case of kidney problems, the urine will have some abnormal constituents. Here follows a brief description about the abnormal constituents of urine and their associations with various diseases:
Blood: If there is blood in the urine, it can be the sign of kidney stones and acute glomerulonephritis. Here glomerulonephritis is the inflammation in glomerulus. Meanwhile, the bloody urine may also serve as an indication of bacterial infections, urinary schistosomiasis and sickle cell anemia.
- Ketones: The presence of ketones in the urinary fluid is usually an outcome of starvation, and the uncontrolled diabetes mellitus. If that be the case, you should not delay in seeking medical attention.
- Proteins: Under normal conditions, there are no proteins in the urine. Therefore, their presence is indicative of some abnormality, such as renal tuberculosis, pyelonephritis, glomerulonephritis, nephritic syndrome, and urinary tract infections.
- Glucose: When the urine contains glucose, it shows that there is something rotten in the state of Denmark. So, you should go for the diagnostic tests of diabetes mellitus. Sometimes, traces can also be found in healthy individuals.
- Galactose: Galactose in urine can be a symptom of galactosemia which is a rare metabolic disorder.
- Bilirubin: You can diagnose the conditions of hepatocellular jaundice, obstructive jaundice through the presence of bilirubin in the urinary fluid.
- Urobilinogen: In case, there is urobilinogen in the liquid body waste, it can be the result of abnormal red blood cell breakdown due to other diseases.
Hormonal Control of the kidney
Aldosterone is the most physiologically active mineralocorticoid hormone. It is a secretion of the adrenal or the suprarenal glands. There are two adrenal glands on either side of the vertebral column. Each of them sits on the superior poles of each kidney.
The production of this hormone occurs in response to changes in the plasma levels of potassium and angiotensin ll of the renin-angiotensin system. Aldosterone acts on the cortical collecting ducts of the nephrons. This, in turn, increases sodium and water reabsorption by the kidneys. Aldosterone also causes an increase in the secretion of potassium and hydrogen ions by the kidneys.
Antidiuretic Hormone (ADH)
ADH or antidiuretic hormone is another name for vasopressin. This hormone originates primarily from the cells of the hypothalamus. Afterwards, it stays in the pituitary gland for further release when necessary.
Secretion of this hormone increases during dehydration when the body needs to conserve more water. Likewise, secretion of this hormone reduces after ingesting a large volume of water. Vasopressin acts on the cortical and medullary collecting ducts of the nephrons and causes greater water reabsorption by the kidneys.
As a result, small amount of concentrated urine is produced. Relative or absolute deficiency of vasopressin results in a disease “diabetes insipidus”. Patients with diabetes insipidus suffer from polyuria, dehydration, polydipsia and high metabolic rate.
Here, polyuria refers to the excretion of high volumes of urine. On the other hand, polydipsia is the condition of excessive thirst.
Angiotensin ll is an important hormone that controls the functioning of kidneys. It causes an increase in the retention of sodium and water by the kidneys.
Parathyroid Hormone (PTH)
The parathyroid glands are responsible for the synthesis and secretion of parathyroid hormone or PTH. These glands are present just behind the thyroid gland. There are usually four parathyroid glands in a normal individual.
However, the numbers of these glands may vary from two to six. PTH inhibits renal phosphate reabsorption. Therefore, it increases phosphate excretion in the urine by the kidneys. PTH also brings an increase in calcium reabsorption. It, in turn, results in a high serum calcium level in your body.
Interesting Kidneys Facts:
Below is the list of some kidney facts. Besides entertaining you, they will also add to your knowledge about the potential, working mechanism, control and location of kidneys.
- Do you know if there were no kidneys, your body would get over-flooded with water as you drank more? No matter how much water you drink, the fluid contents of your body would always remain at the normal level. It is all because of the regulatory role of the kidneys.
- Serving as natural filters, the kidneys remove all the toxins and waste products from the blood that have harmful effects. It not removed, the toxic substances will contaminate the blood to a dangerous extent.
- The kidneys not only regulate the water content; they have got another important job to keep the blood minerals in balance. They include potassium, phosphorus and sodium.
- The regulation of blood pressure also falls under the job assignments of kidneys. For this purpose, they release a hormone.
- A kidney appears no bigger than a standard mouse in its size. Find out the location of kidneys and you can observe the same over there.
- It is really surprising to note that only half of a kidney is capable of doing the whole job that is, otherwise, performed by two kidneys!
- The number of nephrons, present in each kidney, varies from one million to two millions. The nephrons are, in fact, the structural and functional units of the kidney. They are capable of filtering the blood and eliminating the waste products.
- The amount of blood flowing through the kidneys is greater than the blood flow in brain, liver and even heart!