Renal System Anatomy And Physiology

Kidney Introduction

Excretion is the process by which unwanted substances and metabolic wastes are eliminated from the body.

When the food is consumed, it is digested and absorbed from the GI tract. The food particles which are absorbed from the intestine are transported to the tissue of the body through blood.

Similarly, oxygen is transported to the tissues by the blood from the lungs. By using oxygen., the cells metabolize the food particles and energy is released.

This energy is essential for growth, activity, and repair of the tissues.

During the process of metabolism, lot of waste materials and carbon dioxide are produced in the tissues.

Apart from these, the residue of undigested food, heavy metals, drugs, toxic substances, and pathogenic organisms like bacteria are also present in the body.

Read And Learn More: Medical Physiology Notes

All these substances must be removed to keep the body in a healthy condition. Various systems in the body are involved in performing the excretory function, viz.

1. The digestive system excretes food residues in the form of feces. Some bacteria and toxic substances also are excreted through feces.
2. Lungs remove carbon dioxide and water vapor
3. The skin excretes water, salts, and some wastes. It also removes heat from the body
4. The liver excretes many substances like bile pigments, heavy metals, drugs, toxins, bacteria, etc. through bile.

Although various organs are involved in the removal of wastes from the body, their excretory capacity is limited.

The renal system or urinary system is the one having maximum capacity of excretory function and so it plays a major role in homeostasis.

The renal system includes:

1. A pair of kidneys
2. Letters
3. Urinary bladder
4. Urainra.

Kidneys produce urine. Ureters transport urine to the urinary bladder. The urinary bladder stores the urine until it is voided (emptied). Urine is voided from the bladder through the urethra

 

 

Functions Of Kidney

Kidneys perform several vital functions besides the formation of urine. By excreting urine, kidneys play the principal role in the maintenance of the internal environment.

In addition, kidneys perform many other functions as described below.

1. Role In Homeostasis

• The primary function of kidneys is homeostasis. It is accomplished by the formation of urine.
• Kidneys are not only the excretory organs but are also the regulatory organs because their major role is in homeostasis.
• During the formation of urine, kidneys regulate various activities in the body, which are concerned with homeostasis.

Excretion Of Waste Products

Removal of wastes helps in homeostasis.

Kidneys excrete the unwanted waste products which are formed during metabolic activities:

1. The urea end product of amino acid metabolism:
2. Uric acid-end product of nucleic acid metabolism
3. The creatinine end product of metabolism in muscles
4. Bilirubin-end product of hemoglobin degradation
5. Products of metabolism of other substances.

Kidneys also excrete harmful foreign chemical substances like:

1. Toxins
2. Drugs
3. Heavy metals
4. Pesticides, etc.

Maintenance of Water Balance

• Kidneys maintain the water balance in the body by conserving water when it is decreased and excreting water when it is excess in the body.
• This is a very important process for homeostasis.

Maintenance of Electrolyte Balance

• Maintenance of electrolyte balance, especially sodium is in relation to water balance.
• Kidneys retain sodium if the osmolarity of body water decreases and eliminate sodium when osmolarity increases.

Maintenance of Acid-Base Balance

• The pH of the blood and body fluids should be maintained within a narrow range for healthy living.
• It is achieved by the function of the kidneys.
• The body is under constant threat to develop acidosis, because of the production of a lot of acids during metabolic activities.
• However, it is prevented by kidneys, lungs, and blood buffers, which eliminate these acids.
• Among these organs, kidneys play a major role in preventing acidosis.
• In fact, kidneys are the only organs, which are capable of eliminating certain metabolic acids like sulfuric and phosphoric acids.

2. Hemopoietic Function

• Kidneys stimulate the production of erythrocytes by secreting erythropoietin.
• Erythropoietin is an important stimulating factor for erythropoiesis. The kidney also secretes another factor called thrombopoietin, which stimulates the production of thrombocytes.

3. Endocrine Function

Kidneys secrete many hormonal substances in addition to erythropoietin and thrombopoietin.

The hormones secreted by kidneys are:

• Erythropoietin
• Thrombopoietin
• Renin
• 1,25-dihydroxycholecalciferol (calcitriol)
• Prostaglandins.

4. Regulation Of Blood Pressure

Kidneys play an important role in the regulation of arterial blood pressure.

Kidneys regulate arterial blood pressure in two ways:

1. By regulating the volume of extracellular fluid
2. Through rennin-angiotensin mechanism.

5. Regulation Of Blood Calcium Level

Kidneys play a role in the regulation of blood calcium vitamin D. Vitamin D is necessary for the absorption of levels by activating 1,25-dihydroxycholecalciferol into calcium from the intestine.

Functional Anatomy Of Kidney

The kidney is a compound tubular gland covered by a connective tissue capsule. There is a depression on the medial border of the kidney called the hilum, through which the renal artery, renal veins, nerves, and ureter pass.

Different Layers Of Kidney

The components of the kidney are arranged in three layers.

1. Outer cortex
2. Inner medulla
3. Renal sinus

1. Outer Cortex

• The cortex is dark and granular in appearance. It contains renal corpuscles and convoluted tubules.
• At intervals, cortical tissue penetrates the medulla in the form of columns, which are called renal columns or columns of Bertini.

2. Inner Medulla

• Medulla gives a radially striated appearance as it contains tubular and vascular structures arranged in parallel radial lines.
• Medullary mass is divided into 8-18 medullary or Malpighian pyramids. A broad base of each pyramid is in contact with the cortex and the apex projects into a minor calyx.

3. Renal Sinus

The renal sinus consists of the following structures:

• The upper expanded part of the ureter called the renal pelvis
• Subdivisions of the pelvis – 2 or 3 major calyces and about 8 minor calyces
• Branches of nerves and arteries and tributaries of veins
• Loose connective tissues and fat.

Parenchyma Of Kidney

• The Parenchyma of the kidney is made up of closely arranged tubular structures called uriniferous tubules.
• Blood vessels and interstitial connective tissues are interposed between these tubules.

The uriniferous tubules are of two types:

1. Terminal or secretary tubules called nephrons, which are concerned with the formation of urine
2. Collecting ducts or tubules which are concerned with the transport of urine from nephrons to the pelvis of the ureter. The collecting ducts unite to form ducts of Bellini, which open into minor calyces through the papilla.