Introduction
Macula densa are the cells that maintain body fluids and homeostasis and regulate blood pressure. These are the chief cells present in the kidneys. They are the specialized cells responsible for important renal processes like glomerular filtrate rate (GFR), renal blood flow, and renin release. They are located in the juxtaglomerular apparatus. The macula densa cells are an integral part of the distal convoluted tubule. The apex of the cell is open towards the tubular fluid, and the base is in contact with the mesangium cells and the afferent arterioles. Even though they are an important part of the renal system, they are few, with around 20 cells per nephron. The research and studies about these cells are uncertain and not descriptive, as they are not easily accessible. Only a few common functions of the cells are known, and research on them is restricted due to accessibility. They play sensory and regulatory functions in the kidney. The juxtaglomerular apparatus is a very important part of the kidneys, and macula densa cells are part of it.
What Exactly Is a Renal System?
The renal system is a vital part of the human body. The system consists of two bean-shaped, structured organs known as kidneys. Kidneys help regulate electrolyte homeostasis and blood pressure and eliminate toxins and waste. The kidneys produce the type of excrement known as urine. The urine is transported to the urinary bladder with the help of two hollow, elastic, tube-like structures known as ureters. The urinary bladder is a pouch-like structure that holds urine until it is eliminated through the urethra. The urethra forms a way for the urine to exit. The juxtaglomerular apparatus is a part of the kidneys, and the macula densa is a part of the juxtaglomerular apparatus.
What Role Do Kidneys Play in the Renal System?
They are an integral part of the renal system. Kidneys are two in number, about the size of fists, and are bean-shaped concave structures. They are located below the rib cage and are present on each side of the abdomen. They balance the blood's minerals like sodium, potassium, calcium, and phosphorus. Without this balance, the body may not function properly.
What Is a Nephron and Its Significance in the Renal System?
A nephron is defined as the structural and functional unit of the kidney. "Nephros" is a word in Greek from which the word "nephron" is derived. Each kidney has about 1 million nephrons. It contains the glomerulus and its associated tubules, via which the glomerular filtrate passes before it takes the form of urine. Structurally, it is a tube-like structure with varying lengths. At one point, this tube-like, double-walled structure encloses a pouch-like structure known as the Bowman's capsule renal corpuscle capsule, in which the cluster of vessels called the glomerulus is found. The Bowman's capsule and the glomerulus form the renal corpuscle.
What Is a Juxtaglomerular Apparatus and What Is Its Significance?
The juxtaglomerular apparatus is a part of the nephron of the kidney. It is a complex structure and is also known as the juxtaglomerular complex. It comprises the glomerulus, distal tubules, and afferent and efferent arterioles. The juxtaglomerular apparatus is located at the junction of the afferent arteriole and the distal convoluted tubule. Juxtaglomerular or granular cells are present in the juxtaglomerular apparatus. The juxtaglomerular or granular cells produce an important enzyme called renin. When the body signals low blood pressure, the cells release renin to regulate the blood pressure. They also control sodium and potassium levels. Renin is an integral part of the renin-angiotensin-aldosterone system (RAAS). The juxtaglomerular apparatus’s main function is to regulate blood pressure, maintain glomerular filtrate rate (GFR), and preserve sodium and potassium levels.
What Is Renin?
Renin sometimes acts as a hormone and sometimes as an enzyme. It is produced by the specialized cells of the juxtaglomerular apparatus known as granular cells of juxtaglomerular cells. The main function of renin is to maintain blood pressure. It is an important part of the renin-angiotensin-aldosterone system (RAAS).
What Are the Functions of Macula Densa?
The macula densa cells work along with the juxtaglomerular cells. The macula densa cells sense sodium chloride levels in the lumen and signal the juxtaglomerular cells to release renin into the blood. Renin release stimulates the renin-angiotensin-aldosterone system (RAAS), which helps regulate blood. Renin is in charge of converting angiotensinogen into angiotensin I.The angiotensin-converting enzyme converts angiotensin I into angiotensin II. Then angiotensin II stimulates the adrenal glands to produce and release aldosterone. Aldosterone then helps regulate the sodium-water reabsorption back into the blood.
What Is the Morphology of the Macula Densa Cells?
The macula densa cells comprise epithelial cells at the distal end of the TAL, i.e., the thick ascending limb. There is a high nucleus-to-cytoplasm ratio, which gives the cells their dense appearance. The dense appearance of the cells distinguishes them from other cells. The mitochondria of the macula densa are not in contact with the basal membrane. They are generally found scattered in the cytoplasm of the cell. These cells do not have sharp infoldings. The macula densa cells of the distal convoluted tubule are generally small compared to the tubule's cuboidal cells and almost adhere to each other. They are detected by the unique feature where the cells are tightly packed and have a dark-staining nucleus. These cells are different morphologically from the proximal cuboidal cells. Between the nuclei and the base membrane, there lies the golgi apparatus. Macula densa cells are sensitive to sodium concentration, and as the level of sodium concentration increases, the amount of renin released decreases. Renin is produced by extraglomerular mesangial cells and juxtaglomerular cells.
Conclusion
As mentioned in the article, the macula densa is an important renal system factor. The cells are responsible for the proper functioning of the body, as they regulate blood pressure, and many other vital functions of the body are interrelated with the macula densa cells. For example, they release renin, which has numerous essential functions. Thus, the macula densa is the primary cell of the juxtaglomerular apparatus.
