The "Brilliant" Kidney

TL;DR

The kidneys regulate far more than fluid balance. They control electrolytes, maintain the pH balance that lets enzymes and proteins work, help organize blood pressure, and preserve the integrity of cells. Because we have two kidneys, the body carries enormous redundancy, so a person can survive on half a kidney or even a fraction of one.

Transcript

Stanford University well good evening everyone great to see you again tonight last week uh when uh we were about to hear our presentation on the GI tra I asked how many of you had had dinner before uh the event tonight I'll be more courteous and not ask you how many have gone to the bathroom but um you will either have just beforehand or sometime a... Read More

Key Insights

• The kidneys regulate not just fluid balance but all the electrolytes in the body, which governs the integrity and configuration of cells and keeps pH carefully calibrated so enzymes and proteins work effectively.
• Redundancy is built into the kidney system because there are two kidneys, so a person can function on half a kidney, a fraction of a half, or potentially even a single nephron if successful.
• Homeostasis is the body's programmed drive to maintain neutrality and balance, and the kidneys contribute greatly to it alongside other organs.
• Electroneutrality and osmotic neutrality are the two balances the body works hard to maintain: the balance of electrical charges and the balance of dissolved substances inside and outside cells.
• Osmolytes, also called osmoles, tonales, or tonicity, are elements dissolved in the intracellular or extracellular fluid that are responsible for the composition of body fluids and hold water.
• The permeability of fluids and substances across membranes is the foundation on which cells are built, and most cellular energy is spent maintaining differences in electrolyte balance across the cell membrane.
• Extracellular fluid is compartmentalized into plasma, the fluid occupying the blood vessels, and interstitial fluid, which forms the matrix or infrastructure outside the cells.
• The stability of the internal milieu is a primary condition for the freedom and independence of living bodies, a principle the kidneys uphold by helping us survive in a desert or in water excess.

Questions & Answers

Q: What do the kidneys actually regulate in the body?

The kidneys regulate not just fluid balance but all the electrolytes in the body system, which controls the integrity and configuration of cells. They allow the pH balance in the system to be carefully calibrated so that enzymes and proteins work effectively, and they help to organize blood pressure among other functions. Because there are two kidneys, they carry enormous capacity and redundancy.

Q: How little of the kidney is needed to survive?

Because there are two kidneys, the body carries enormous capacity and redundancy. According to the lecture, a person could actually get down to about half of a kidney and still function, or even a fraction of a half, and potentially survive on as little as one nephron if they are really successful. This redundancy is one reason the kidney system is so resilient.

Q: Who is Dr. Glenn Chertow?

Dr. Glenn Chertow is the chief of the Division of Nephrology and a kidney specialist at Stanford in the Department of Medicine. He joined Stanford in 2007, recruited from UCSF. He did his undergraduate work at Penn and went to Harvard Medical School, studying nephrology and becoming an expert in kidney disease at the Brigham and Women's Hospital, while also focusing on population science and epidemiology.

Q: What is the difference between intracellular and extracellular fluid?

Intracellular fluid refers to the fluid that is within the cells, while extracellular fluid is the fluid outside the cells. The extracellular fluid is complex and compartmentalized: it can be either the plasma, which is the fluid occupying the blood vessels, or the interstitial fluid, which forms the matrix or infrastructure outside the cells. Both are visible in the body but kept in separate compartments.

Q: What is homeostasis and how do the kidneys contribute to it?

Homeostasis is balance, the body's programmed drive to maintain neutrality. The kidneys contribute greatly to homeostasis, though other organs contribute as well. Specifically, the body works hard to maintain electroneutrality, the balance of electrical charges, and osmotic neutrality, the balance of the dissolved substances inside and outside of the cells. This constant balancing is a fundamental property of how our bodies are programmed.

Q: How much blood is circulating in an average person at any one time?

For most adults, the amount of blood circulating at any one time is definitely more than two liters and certainly less than twelve. Dr. Chertow indicates that roughly three to five, or five and a half liters, would be about right for an average sized person. People often do not realize how little fluid is actually circulating around in the blood vessels compared to total body water.

Q: What are osmolytes and why do they matter?

Osmolytes, also called osmoles or, depending on who you talk to, tonales or tonicity, are elements dissolved within the fluids in either the intracellular or extracellular space. They have properties that hold water and are responsible for the composition of the body's fluids. The balance of these dissolved substances inside and outside cells is central to how the kidneys regulate fluid and electrolytes.

Q: Why is membrane permeability so important to how cells work?

The permeability of fluids across membranes, along with the permeability of some substances and the non-permeability of others, is the foundation on which cells are built. The energy that cells use to maintain differences in balance occupies most of their energy. It is these differences in electrolytes within and outside the cell that make cells work, spending energy to preserve the imbalance across the membrane.

Summary

In this video, Dr. Glenn Chertow, a kidney specialist, discusses the importance of the kidneys in maintaining fluid balance and regulating electrolytes in our body. He explains the different fluid compartments in our body and how the kidneys play a vital role in maintaining homeostasis. He also touches on the topic of water intoxication and the dangers of infusing pure water into the bloodstream. Dr. Chertow emphasizes the need for choosing the right fluids, such as normal saline, to replenish the plasma volume in cases of blood loss. He also discusses the concept of hypernatremia and the hormone antidiuretic hormone (ADH) that helps maintain fluid balance.

Questions & Answers

Q: How important are the kidneys in our overall bodily function?

The kidneys are not just responsible for maintaining fluid balance but also regulate electrolytes in our body, balance pH levels, and contribute to the functioning of enzymes and proteins. They also play a role in organizing blood pressure and have redundancy, which means we can function with even half of a kidney or a fraction of it.

Q: What is the significance of water in maintaining fluid balance?

Water is essential for maintaining fluid balance and enabling the kidneys to carry out their functions effectively. The body's fluid compartments, including intracellular and extracellular fluid, rely on water to maintain osmolality and allow electrolytes to distribute properly.

Q: What are the different fluid compartments in our body?

Our body has intracellular fluid, which refers to the fluid inside the cells, and extracellular fluid, which includes plasma (fluid within blood vessels) and interstitial fluid (fluid outside the cells). The intracellular fluid compartment is larger than the extracellular compartment.

Q: How does the composition of intracellular fluid differ from extracellular fluid?

The composition of intracellular fluid differs from extracellular fluid in terms of its electrolyte concentration. Intracellular fluid has a higher concentration of potassium and lower concentration of sodium, whereas extracellular fluid has a higher concentration of sodium and lower concentration of potassium.

Q: Why is it important to choose the right fluids for IV infusion?

Choosing the right fluids is crucial to ensure proper replenishment of the plasma volume. Infusing saline solution (normal saline) into the bloodstream is highly efficient in replenishing the vascular space, whereas infusing pure water can lead to cell swelling and burst due to its high permeability.

Q: How does hypernatremia affect fluid balance?

Hypernatremia refers to an elevated sodium concentration in the blood. It can lead to a water deficit in the body, causing dehydration. The management of hypernatremia depends on the underlying cause, such as high blood glucose levels or osmotic diuresis.

Q: What are some diseases that can cause edema?

Edema, or fluid accumulation, can be caused by various conditions. Common examples include congestive heart failure, severe chronic liver disease with cirrhosis, and kidney diseases like nephrotic syndrome.

Q: How does the body maintain electrolyte balance during periods of water scarcity or excess?

One hormone that plays a role in maintaining electrolyte balance is antidiuretic hormone (ADH), also known as vasopressin. ADH helps regulate water reabsorption in the kidneys and prevents excessive water loss in urine.

Q: What is the danger of water intoxication?

Water intoxication, also known as water poisoning, can occur when excessive amounts of pure water are consumed quickly. It can lead to cell swelling and burst, causing various complications and even death.

Q: Can you explain the concept of hypernatremia and ADH's role in maintaining fluid balance?

Hypernatremia occurs when the sodium concentration in the blood is high. In response, the body releases ADH, which helps the kidneys reabsorb water and minimize water loss in urine. ADH promotes water retention and maintains fluid balance.

Summary & Key Takeaways

• Dr. Glenn Chertow, chief of the Division of Nephrology at Stanford, argues that the kidneys are among the most brilliant organs in the body, second only to the brain. They regulate fluid balance, electrolytes, cell integrity, pH, and blood pressure, carrying enormous redundancy across two kidneys.

• The lecture frames modern physicians as surgeons of the extracellular fluid and stresses the importance of body compartments. Body water divides into intracellular fluid inside cells and extracellular fluid outside, which further splits into plasma within blood vessels and interstitial fluid forming the body's matrix.

• The body works to maintain electroneutrality and osmotic neutrality through the permeability of membranes to some substances but not others. Dissolved osmolytes hold water and determine fluid composition, while an average adult has roughly three to five and a half liters of blood circulating at any one time.