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The Nephron
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Water Filtration and Reabsorption
The majority of the human body is composed of water. Regulating the volume of water in each of the fluid compartments of the body is key for a variety of reasons, including the regulation of blood pressure, cardiac output and ion transport. In addition to this, it plays a vital role in maintaining electrolyte balance […]
Sodium Regulation
Sodium (Na) is the most abundant cation in the extracellular fluid (ECF) compartment. The normal plasma sodium concentration is 135-145 mmol/L, while the intracellular fluid (ICF) concentration is approximately 10-12 mmol/L. Maintaining this transmembrane concentration gradient is necessary for generating the resting membrane potential and for action potential propagation. Sodium is also the main osmotic […]
Diffusion
Cell membranes are selectively permeable. This means that they allow the movement of some molecules freely across them, but do not allow the free passage of others. In broad terms, there are three ways in which molecules move across membranes. These processes are diffusion, osmosis and active transport. In this article, we will describe the process of diffusion, discuss […]
Active Transport
Cell membranes are selectively permeable. This means that they allow the movement of some molecules freely across them, but do not allow the free passage of others. In broad terms, there are three ways in which molecules move across membranes. These are the processes of diffusion, osmosis and active transport. In this article, we will discuss active transport, and […]
Urinary Regulation of Acid-Base Balance
The acid-base balance is vital for normal bodily functions. When this equilibrium is disrupted, it can lead to severe symptoms such as arrhythmias and seizures. Therefore, this acid-base balance is tightly regulated. In this article, we will look at the buffering system, urinary acid-base regulation and relevant clinical conditions. Information on the buffering system of […]
Renin-Angiotensin-Aldosterone System
The Renin-Angiotensin-Aldosterone System (RAAS) is a hormone system within the body that is essential for the regulation of blood pressure and fluid balance. The system is mainly comprised of the three hormones renin, angiotensin II, and aldosterone. Primarily it is regulated by the rate of renal blood flow. This article will describe the system, discuss […]
Distal Convoluted Tubule and Collecting Duct
The distal convoluted tubule (DCT) and collecting duct (CD) are the final two segments of the nephron. They have an important role in the absorption of many ions and in water reabsorption. The distal convoluted tubule can be subdivided into early and late sections, each with its own functions. This article will consider the functions […]
Antidiuretic Hormone
Antidiuretic hormone (ADH), also known as vasopressin, is a small peptide hormone which regulates the body’s retention of water. It is one of only two hormones secreted by the posterior pituitary gland. In this article, we will discuss the synthesis, storage, release and action of ADH, and consider its clinical relevance. Synthesis and Storage of […]
External Balance of Potassium
External balance of potassium is achieved through balancing dietary intake, intracellular and extracellular potassium levels and excretion by kidneys. Extracellular potassium concentration is usually maintained within 3.5-5 mmol/L. This narrow window of control is critically important as the difference between the intracellular and extracellular potassium affects electrically excitable muscle and nerve cells due to its […]