Kidney – Introduction, Structure, Anatomy, Functions

The urinary system comprises the urethra, bladder, ureters, and kidneys.

The kidneys are two bean-shaped organs lying on the posterior abdomen walls on either side of the vertebral column In the retroperitoneal space. The right kidney lies slightly lower than the left one because of the space occupies by the liver. The kidneys are vital organs in the body that are responsible for maintaining fluid balance and filtration of minerals and wastes from the blood.

Structure of Kidney:

Externally, the kidneys are encircled by three layers. The peripheral layer is an extreme connective tissue layer called the renal fascia. The subsequent layer is known as the perirenal fat capsule, which helps anchor the kidneys set up. The third and deepest layer is the renal capsule. 
Inside, the kidney has three locales, an external cortex, a medulla in the center, and the renal pelvis in the district called the hilum of the kidney. The hilum is the inward piece of the bean-shaped where veins and nerves enter and leave the kidney; it is additionally the mark of exit for the ureters.

The renal cortex is granular because of the presence of nephrons which is the functional unit of the kidney. The medulla comprises different pyramidal tissue masses, called the renal pyramids. In the middle of between the pyramids are spaces called renal sections through which the veins pass? The tips of the pyramids, called renal papillae, highlight the renal pelvis. Overall, eight renal pyramids in every kidney. The renal pyramids alongside the abutting cortical district are known as the curves of the kidney. The renal pelvis prompts the ureter outwardly of the kidney. Within the kidney, the renal pelvis branches out into a few expansions called the major calyces, which further branch into the minor calyces. The ureters are pee-bearing cylinders that leave the kidney and void into the urinary bladder.

The arteries, veins, and nerves that supply the kidney enter and exit at the renal hilum. Renal blood supply begins with the stretching of the aorta into the renal arteries and closes with the leaving of the renal veins to join the inferior vena cava. The renal conduits split into a few segmental veins after entering the kidneys. Each segmental artery parts further into a few interlobar veins and enters the renal sections, which supply the renal curves. The interlobar courses split at the intersection of the renal cortex and medulla to frame the arcuate arteries. These arcuate arteries branch into various afferent arterioles, and afterward enter the vessels providing the nephrons. Veins follow the way of the supply routes and have comparative names, besides there are no segmental veins.

The kidney is comprised of more than 1,000,000 nephrons that speck the renal cortex, giving it a granular appearance when separated sagittally. There are two sorts of nephrons:

Cortical nephrons, which are somewhere down in the renal cortex, and juxtamedullary nephrons which lie in the renal cortex near the renal medulla. A nephron comprises of three sections, a renal corpuscle, a renal tubule, and the related hair-like organization, which begins from the cortical transmit supply routes.

Anatomy of the Nephron

Nephrons are the functional units of the kidney. The structure of the nephron consists of two parts which are

1. Renal Tubule
2. Renal Corpuscle

Renal Tubule

• The renal tubule is a long and tangled structure that rises up out of the glomerulus and can be partitioned into three sections in view of capability.
• The initial segment is known as the proximal tangled tubule (PCT) because of its closeness to the glomerulus. It stays in the renal cortex.
• The subsequent part is known as the loop of Henle, or nephritic circle since it shapes a circle (with diving and climbing appendages) that goes through the renal medulla.
• The third section of the renal tubule is known as the distal tangled tubule (DCT) and this part is likewise confined to the renal cortex.
• The vessels of the glomerulus are encased by a cup-like construction called Bowman’s case. 
• This construction stretches out to shape profoundly curled tubules called PCT. PCT continues to form the circle of Henle which ascends to DCT, which opens into the collecting duct.

Proximal Convoluted Tubule (PCT)

PCT is the locale of the renal tubule where the reabsorption of fundamental substances like glucose, proteins, amino acids, a significant piece of electrolytes, and water happens. Most extreme reabsorption happens in the PCT of the nephron. The surface region for reabsorption is worked with by the coating of the straightforward cuboidal epithelium in them. PCT specifically secretes particles like hydrogen, alkali, and potassium into the filtrate and assimilates HCO₃ from it. Subsequently, PCT keeps up with the electrolyte and corrosive base equilibrium of the body liquids.

Henle’s Loop

Henle’s circle has a descending and an ascending limb. The descending limb is penetrable to water however impermeable to an electrolyte, while the ascending limb is porous to electrolytes yet impermeable to water. Since the electrolytes get reabsorbed at the climbing circle of Henle, the filtrate gets weakened as it moves towards the rising appendage. Yet, reabsorption is restricted in this portion.

Distal Convoluted Tubule (DCT)

The DCT is the last part of the nephron, associates and discharges contents into gathering channels that line the medullary pyramids. 

Like PCT, DCT additionally secretes particles like hydrogen, potassium, and NH3 into the filtrate while reabsorbing the HCO₃ from the filtrate. Restrictive reabsorption of sodium particles and water occurs in DCT. Consequently, it keeps up with the pH and sodium-potassium levels in RBC.

Collecting Duct

The collecting duct is a long, straight cylinder where H+ and K+ particles are emitted to keep up with the electrolyte equilibrium of the blood. Here the most extreme reabsorption of water occurs to create concentrated urine.

Renal Corpuscle

The renal corpuscle comprises a glomerulus encompassed by a Bowman’s container. The glomerulus emerges from an afferent arteriole and exhausts into an efferent arteriole. The more modest breadth of efferent arteriole assists with keeping up with hypertension in the glomerulus.

Disorders of Kidneys

• Polycystic Kidney Disease-Polycystic kidney sickness (PKD) is a hereditary disorder that causes cysts in the kidneys and different organs. These cysts can bring down the kidney’s capacity to filter liquid and waste from your blood.
• Lupus nephritis-It is an autoimmune disease that causes inflammation of the kidneys caused by systemic lupus erythematous. This can lead to kidney failure. The specific reason for lupus nephritis is obscure and it can’t be restored.
• IgA nephropathy-It is also known as Berger’s disease which is a kidney disease that occurs when an antibody called immunoglobulin A (IgA) builds up in the kidneys. IgA is a protein made by the immune system to protect the body from foreign substances such as bacteria or viruses.
• Glomerulonephritis-Glomerulonephritis is inflammation of the small channels in the kidneys (glomeruli). The excess liquid and waste that glomeruli eliminate from the circulation system leave the body as urine.
• Cystinosis- Caused due to the accumulation of amino acid called cystine. Excess cystine damages cells and forms crystals that can build up and cause problems in many organs and tissues.
• Diabetic nephropathy- It is a kidney disease resulting from the complications of type I and types II diabetes.

Kidney Transplant

A kidney transplant is a surgery, in which the transplantation of a healthy kidney from a living or deceased donor is done into a person whose kidneys no longer function properly. When kidneys lose the ability to filter the wastes they will accumulate in the kidneys it resulting in kidney failure. A kidney transplant is the treatment of choice for kidney failure, compared with a lifetime on dialysis. A kidney transplant can treat chronic kidney disease or end-stage renal disease.

Conceptual Question

Question 1:What are the 3 parts of the Nephron?

Answer:

• Renal Corpuscle-The renal corpuscle, situated in the renal cortex, is comprised of an organization of vessels known as the glomerulus and the container, a cup-molded chamber that encompasses it, called the glomerular or Bowman’s case.
• Renal Tubule-The renal tubule is a long and tangled structure that rises out of the glomerulus and can be separated into three sections in light of capability. The initial segment is known as the proximal convoluted tubule (PCT) because of its nearness to the glomerulus; it stays in the renal cortex. The subsequent part is known as the loop of Henle, or nephritic circle since it shapes a circle that goes through the renal medulla. The third piece of the renal tubule is known as the distal convoluted tubule (DCT) and this part is likewise limited to the renal cortex. The DCT, which is the last piece of the nephron, associates and purges contents into gathering conduits that line the medullary pyramids. The gathering pipes store up contents from various nephrons and break together as they enter the papillae of the renal medulla.
• Capillary Network inside the Nephron-The capillary organization that starts from the renal courses supplies the nephron with blood that should be separated. The branch that enters the glomerulus is known as the afferent arteriole. The branch that leaves the glomerulus is known as the efferent arteriole. Inside the glomerulus, the organization of vessels is known as the glomerular narrow bed. When the efferent arteriole leaves the glomerulus, it shapes the peritubular capillary organization, which encompasses and collaborates with parts of the renal tubule. In cortical nephrons, the peritubular capillary organization encompasses the PCT and DCT. In juxtamedullary nephrons, the peritubular capillary organization shapes an organization around the circle of Henle and is known as the vasa recta.

Question 2: What are the functions of kidneys?

Answer:

The main function of the kidney is to make urine and removes wastes that are not required from the blood. Below are the other functions of the kidneys.

• Removal of waste products like creatinine and urea which are easily measured in blood.
• Maintains homeostasis by removing excess fluid.
• Balances minerals like sodium, potassium, hydrogen, calcium, phosphorus, magnesium, and bicarbonate and maintains the normal composition of body fluid.
• Regulates blood pressure
• Plays an important role in red blood cell production.
• Maintains healthy bones by converting vitamin D into an active form.

Question 3: Enlist the kidney diseases briefly?

Answer:

• Chronic kidney disease- It is associated with gradual loss of kidney function.
• Glomerulonephritis-Glomerulonephritis is inflammation of the small channels in the kidneys (glomeruli). The excess liquid and waste that glomeruli eliminate from the circulation system leave the body as urine.
• Cystinosis– Caused due to the accumulation of amino acid called cystine. Excess cystine damages cells and forms crystals that can build up and cause problems in many organs and tissues.
• Diabetic nephropathy– It is a kidney disease resulting from the complications of type I and type II diabetes.

Question 4: What are the functional units of the kidney?

Answer:

Nephrons are the functional units of the kidney. Each nephron is composed of a renal corpuscle, a proximal tubule, an intermediate tubule (loop of Henle), a distal convoluted tubule, a connecting tubule, and cortical, outer medullary, and inner medullary collecting ducts.