What are kidneys? structure, functions, embryonic development along disorders related to kidneys.

 KIDNEY

Introduction

Kidneys are a pair of bean-shaped organ present in all vertebrates. It is reddish brown in color, and located in the posterior abdomen. Each kidney is about 4 or 5 inches long. There is difference in the position of both the kidneys. The right kidney is slightly lower than the left kidney due to the presence of liver. They typically extend from T12 to L3. Their main function is to filter and excrete waste products from the blood. They are also responsible for water and electrolyte balance in the body. All of the blood in our body passes through them several times a day. Metabolic wastes and excess electrolytes are transported by the kidneys to form urine. Urine is transported from the kidneys to the bladder by the ureters. It leaves the body via the urethra. Each kidney has around a million tiny filters called nephrons. Nephrons are the functional unit of the kidneys. They are composed of renal tubule, proximal convoluted tubule, loop of Henle, the distal convoluted tubule, collecting tubule and the collecting ducts. The main functions of nephrons are 

• urine production 
• excretion of waste products
• regulation of electrolytes
• regulation of acid-base balance
• hormone production
• secretion
• maintenance of glucose homeostasis

Structure

The layers of the kidney are as following:

• renal cortex 
• renal medulla

cortex is the outer layer of the kidney whereas medulla is the inner layer of the kidney. Medulla are the pyramid-shaped lobes. Nephrons flow between these sections. These are the urine producing structures of the kidneys. Adrenal gland lay on top of the kidneys. The kidneys are enclosed in layers of fascia and fat are as follows:

• renal fascia 
• perirenal fat

renal fascia also called Gerota's fascia. Renal fascia is a thin sheath of connective tissue that covers the kidneys. Perirenal fat is a adipose capsule of the kidney. It is a structure between the renal fascia and renal capsule. The apex of renal pyramid is called a renal papilla. Each renal papilla is associated with structure known as minor calyx. Minor calyx collects urine from the pyramids. Minor calyxes merge to form a major calyx. Urine passes through the major calices into the renal pelvis. Real pelvis is a flattened and funnel shaped structure. Th medial margin of each kidney is marked by a deep fissure known as renal hilum. Each excretes urine through a tube called ureter that leads to bladder. Kidneys receive 20 to 25 percent of hearts output. Kidneys receive oxygenated blood from the renal artery which further divided into 

• interlobar arteries
• arcuate arteries
• interlobular arteries 

interlobular arteries pass through the cortex to form afferent arterioles and the afferent arterioles form the capillary network, the glomerulus, to form efferent arterioles. The kidneys are drained of venous blood by the left and right renal veins. They leave the renal hilum anteriorly to the renal arteries, and directly to the inferior vena cava. Lymph from the kidneys drain into the lateral aortic nodes. 

Kidneys innervate both the sympathetic and parasympathetic divisions of the nervous system. Vagus nerve are small branches which provide parasympathetic innervation to the kidney.

Embryonic Development Of Kidneys

In the embryo, development of kidneys is known by a specific term called nephrogenesis. It occurs through several stages involving classical type of interactions. Development of kidneys is form mesoderm and the several following stages are as following:

• pronephros
• mesonephros
• metanephros

Pronephros is the earliest nephric stage in humans and constitute the mature kidney. Pronephros develops in the cervical region of the embryo. Pronephros is a vestigial structure that disappears completely by the fourth week of human embryonic life. Mesonephros develops by the formation of mesonephric tubules from the intermediate mesoderm. It is the principle excretory organ by fourth to eighth week of early embryonic life. Metanephros arises caudal to the mesonephros, at five weeks of development. It is derived from the intermediate mesoderm. The ureteric bud arises as a diverticulum from the Wollfian duct, close to the entrance to the cloaca and grows towards inside and outside the metanephric mesenchyme. 

Functions Of Kidney

Kidneys perform a lot of important functions and some of the important function of the kidney in human body are as following:

• maintaining homeostasis
• waste excretion
• regulating blood pressure
• osmolality regulation 
• urine formation
• maintaining pH
• reabsorption of nutrients

Reabsorption Of Nutrients

Reabsorption is the process by which nephrons removes water and solutes from the tubular fluid and returns them to the blood. Kidneys absorb nutrients from the blood and transports them to where they would best support health. Reabsorbed products include:

• glucose 
• amino acids 
• bicarbonate
• water 
• sodium
• phosphate
• chloride ions 

Regulation Of Osmolality

Osmolality is a measure of the body's water electrolyte balance in the body. If osmolality rises in the blood plasma, the hypothalamus in the brain responds by passing a message to the pituitary gland, releases antidiuretic hormone and kidney makes a number of changes such as 

• increasing urine concentration 
• increasing water reabsorption

Diseases Related To Kidney

If there will be disturbance in any organ it will lead to abnormality. Abnormalities also arise in the kidney. Some of the common symptoms of kidney problem are as follows:

• fatigue
• feeling cold
• shortness of breath 
• feeling faint
• feeling very itchy
• swelling in hands and feet
• upset stomach 
• nausea 
• vomiting

A number of diseases can affect the kidneys. Environmental and medical factors can lead to kidney disorder, and they can cause structural and functional problems from birth in some people. Disorders related to kidney are as following:

• diabetic nephropathy
• kidney stones
• renal failure
• pyelonephritis
• nephrotic syndrome
• polycystic kidney disease
• kidney cancer
• interstitial nephritis
• kidney tumor
• glomerulonephritis
• renal cyst
• papillary necrosis
• acute renal failure 
• chronic renal failure
• nephrogenic diabetes insipidus

Pyelonephritis(kidney infection)

A kidney infection is called pyelonephritis, when bacteria and viruses cause problems in one or both of your kidneys. It is a type of urinary tract infection. Our urinary tract is made up of kidneys, ureters, bladder and urethra. If any of these parts gets germs in it, it may cause infection and its a urinary tract infection. If the bad bacteria or viruses travel up your ureters, you can get a kidney infection. Symptoms of kidney infection are as following:

• fever and chills 
• fatigue
• weakness
• pain in your lower back
• loss of appetite
• upset stomach or vomiting

to diagnose kidney infection, following tests includes:

• urine culture 
• urine analysis
• ultrasound
• digital rectal exam
• voiding cystourethrogram

Kidney Stone(nephrolithiasis)

Kidney stones are hard pebble like objects that can form inside the kidneys. They are made of minerals and salts. Kidney stones form when body has too much minerals and doesn't have enough liquid at the same time. Symptoms of kidney stones are as following:

• pain in lower abdomen
• fatigue
• nausea
• vomiting 
• less urine
• fever and chills

to diagnose kidney stones, following tests include:

• blood test 
• urine test 
• imaging test
• analysis of passed stones

Nephrogenic Diabetes Insipidus

Nephrogenic diabetes insipidus is due to problem in the kidneys. The kidneys cannot respond to a hormone that regulates fluid imbalance. Diabetes insipidus is caused by problems related to a hormone called ADH. When it's released it causes the kidneys to retain water. This results in decrease or concentration of urine. In nephrogenic diabetes insipidus enough ADH is produced. Kidneys don't absorb enough water Symptoms of nephrogenic diabetes insipidus include:

• excess thirst
• excessive urine production(polyuria)
• muscle pains
• lethargy
• irritability

treatment can reduce the nephrogenic diabetes insipidus include:

• diet
• non-steroidal anti-inflammatory drugs
• diuretics

Nephrotic Syndrome

Nephrotic syndrome is not a disease. It is a group of symptoms that can appear when body are not working properly. Small blood vessels in kidney function as a filter, cleaning out waste and extra water from blood. That waste and extra water ends up in your bladder and leaves the body as urine through the urethra. When they are damaged, too much protein slips through the filters into urine. The result is nephrotic syndrome. Symptoms of nephrotic syndrome include:

• swelling of legs 
• swelling of feet
• too much protein in urine 
• low level of albumin in blood

to diagnose nephrotic syndrome, following tests include:

• urine test
• biopsy

Kidney Cancer

Kidney cancer also called renal cancer, is a disease in which kidney cells become malignant and grow out of control, forming a tumor. All kidney cancer first appears in the lining of tiny tubules in the kidney. This type of kidney cancer is called renal cell carcinoma. Symptoms of kidney cancer includes:

• blood in your urine
• loss of appetite
• loss of weight
• anemia 
• extreme fatigue
• shortness of breadth 
• coughing up blood
• bone pain 

to make a diagnose of kidney cancer, following tests include:

• urine tests 
• blood tests
• intravenous pyelogram
• CT scan 
• ultrasound
• magnetic resonance imaging (MRI)
• renal arteriogram