8.2 Nephron structure and function
4 min read•august 14, 2024
The , the kidney's functional unit, is a marvel of biological engineering. It filters blood, reabsorbs nutrients, and excretes waste through a series of specialized structures. From the renal corpuscle to the , each part plays a crucial role in urine formation.
Understanding nephron structure and function is key to grasping how our bodies maintain fluid balance and remove waste. This process involves complex mechanisms like , , and the in the .
Nephron Structure and Function
Nephron Components and Their Roles
Top images from around the web for Nephron Components and Their Roles
Nephron - Wikipedia View original
Is this image relevant?
Kidney Function and Physiology | Biology for Majors II View original
Is this image relevant?
16.4 Kidneys – Human Biology View original
Is this image relevant?
Nephron - Wikipedia View original
Is this image relevant?
Kidney Function and Physiology | Biology for Majors II View original
Is this image relevant?
1 of 3
Top images from around the web for Nephron Components and Their Roles
Nephron - Wikipedia View original
Is this image relevant?
Kidney Function and Physiology | Biology for Majors II View original
Is this image relevant?
16.4 Kidneys – Human Biology View original
Is this image relevant?
Nephron - Wikipedia View original
Is this image relevant?
Kidney Function and Physiology | Biology for Majors II View original
Is this image relevant?
1 of 3
- The nephron is the functional unit of the kidney responsible for filtering blood, reabsorbing essential nutrients, and excreting waste products
- Each nephron consists of a renal corpuscle ( and ) and a renal tubule (, loop of Henle, , and collecting duct)
- The renal corpuscle filters blood
- The renal tubule modifies the filtrate by reabsorbing essential nutrients (glucose, amino acids) and secreting waste products (urea, creatinine)
- The collecting duct system collects the final urine from multiple nephrons and transports it to the renal pelvis
Urine Formation and Transport
- Urine formation begins with the filtration of blood in the glomerulus, followed by the modification of the filtrate as it passes through the renal tubule
- The final urine is collected by the collecting duct system and transported to the renal pelvis
- From the renal pelvis, urine flows through the ureters to the bladder for storage and eventual elimination through the urethra
Glomerular Filtration
Glomerular Structure and Filtration Barrier
- The glomerulus is a network of capillaries surrounded by Bowman's capsule, forming the renal corpuscle
- Blood enters the glomerulus through the afferent arteriole and exits through the
- The glomerular capillary walls, along with the inner layer of Bowman's capsule (), form a
- The filtration barrier allows the passage of water, small solutes, and waste products while retaining larger molecules like proteins (albumin)
- The filtration barrier consists of the of the capillaries, the , and the filtration slits between the podocytes
Starling Forces and Glomerular Filtration Rate (GFR)
- The filtration process is driven by , which include the and the across the glomerular capillary wall
- The hydrostatic pressure in the glomerular capillaries favors filtration, while the oncotic pressure of the blood opposes filtration
- The (GFR) is the volume of fluid filtered from the glomerular capillaries into Bowman's capsule per unit time
- GFR is an important indicator of kidney function and is typically around 125 mL/min in a healthy adult
- Factors that affect GFR include blood pressure, afferent and efferent arteriolar tone, and plasma oncotic pressure
Proximal vs Distal Tubules
Proximal Convoluted Tubule (PCT) Functions
- The proximal convoluted tubule (PCT) is the initial segment of the renal tubule, located immediately after Bowman's capsule
- The PCT is responsible for the bulk reabsorption of essential nutrients, such as glucose, amino acids, and electrolytes (sodium, potassium, chloride)
- The PCT also secretes organic acids (uric acid) and bases into the tubular lumen
- The PCT has a brush border of microvilli on the apical surface of its cells, increasing the surface area for reabsorption and secretion
Distal Convoluted Tubule (DCT) Functions
- The distal convoluted tubule (DCT) is the segment of the renal tubule located after the loop of Henle and before the collecting duct
- The DCT fine-tunes the composition of the filtrate by selectively reabsorbing or secreting specific ions
- Sodium and in the DCT is regulated by
- Calcium reabsorption in the DCT is regulated by
- in the DCT is regulated by aldosterone and the electrochemical gradient
- The DCT plays a role in regulating blood pressure through the (RAAS)
Concentration Gradient in Loop of Henle
Loop of Henle Structure and Function
- The loop of Henle is a U-shaped segment of the renal tubule, consisting of the descending and ascending limbs, that connects the proximal and distal tubules
- The loop of Henle is responsible for creating a in the medulla of the kidney, which is essential for the production of concentrated urine
- The descending limb is permeable to water but not to solutes, allowing water to move out of the tubule and into the of the medulla
- The ascending limb is impermeable to water but actively transports sodium, potassium, and chloride out of the tubule, further increasing the osmolarity of the interstitium
Countercurrent Multiplier System
- The countercurrent multiplier system, created by the opposing flows in the descending and ascending limbs, amplifies the concentration gradient in the medulla
- The of solutes out of the ascending limb creates a hypertonic interstitium
- The of water from the descending limb further concentrates the interstitium
- This process is repeated along the length of the loop of Henle, multiplying the concentration gradient
- The concentration gradient established by the loop of Henle enables the collecting duct to reabsorb water and produce concentrated urine when necessary, such as during dehydration
- (ADH) increases the permeability of the collecting duct to water, allowing for greater water reabsorption and the production of concentrated urine (up to 1200 mOsm/L)
Key Terms to Review (33)
Active transport: Active transport is a cellular process that moves molecules across a membrane against their concentration gradient, utilizing energy, usually in the form of ATP. This mechanism is crucial for maintaining cellular homeostasis and allows for the selective uptake of essential substances, such as ions and nutrients, while removing waste products. Active transport plays an important role in various physiological functions, including those in the kidneys and cellular membranes.
Affluent arteriole: The affluent arteriole is a blood vessel that carries oxygenated blood to the glomerulus in the nephron, playing a crucial role in the filtration process of the kidneys. This structure connects the renal artery to the glomerulus and is responsible for regulating blood flow and pressure within the nephron, which is essential for maintaining proper kidney function and homeostasis.
Aldosterone: Aldosterone is a steroid hormone produced by the adrenal glands that plays a key role in regulating sodium and potassium balance, as well as blood pressure. It primarily acts on the kidneys to promote sodium reabsorption and potassium excretion, which helps maintain fluid balance and electrolyte homeostasis in the body.
Antidiuretic hormone: Antidiuretic hormone (ADH), also known as vasopressin, is a peptide hormone produced in the hypothalamus and released by the posterior pituitary gland that plays a critical role in regulating water balance in the body. By promoting water reabsorption in the kidneys, it helps maintain blood pressure and fluid homeostasis, making it essential for overall fluid regulation and electrolyte balance.
Basement membrane: The basement membrane is a thin, fibrous extracellular matrix that separates epithelial cells from the underlying connective tissue. It plays a critical role in providing structural support, regulating cell behavior, and influencing the filtration process in organs such as the kidneys.
Bowman's capsule: Bowman's capsule is a cup-like structure in the nephron of the kidney that encases the glomerulus, which is a network of tiny blood vessels. It plays a critical role in the initial filtration of blood, allowing water, ions, and small molecules to pass into the renal tubule while preventing larger molecules and blood cells from entering. This structure is vital for the kidney's ability to filter waste and regulate fluid balance in the body.
Chloride reabsorption: Chloride reabsorption is the process by which chloride ions (Cl-) are reclaimed from the renal tubular fluid back into the bloodstream during urine formation. This process is crucial for maintaining electrolyte balance, fluid homeostasis, and acid-base balance in the body, particularly within the nephron, the functional unit of the kidney.
Collecting duct: The collecting duct is a crucial structure in the nephron, responsible for the final concentration of urine as it transports filtrate from the nephron's distal convoluted tubule to the renal pelvis. It plays a key role in regulating water and electrolyte balance through its permeability to water, which is controlled by hormones such as antidiuretic hormone (ADH). The collecting duct also integrates signals from various parts of the nephron and contributes to the overall homeostasis of the body's fluid balance.
Concentration gradient: A concentration gradient refers to the difference in the concentration of a substance between two areas. This difference drives the movement of substances, allowing them to flow from regions of higher concentration to regions of lower concentration, a process that is crucial for various physiological functions. Understanding concentration gradients helps in grasping how materials are exchanged across cell membranes and how substances are filtered and reabsorbed in renal structures.
Countercurrent multiplier system: The countercurrent multiplier system is a mechanism in the kidney that creates a concentration gradient in the renal medulla, allowing for efficient reabsorption of water and solutes. This system relies on the flow of fluid in opposite directions in the nephron's loops of Henle and the blood vessels surrounding them, maximizing the concentration of urine. The result is a highly concentrated urine, which plays a critical role in maintaining the body's fluid balance and electrolyte levels.
Diabetes Insipidus: Diabetes insipidus is a medical condition characterized by excessive thirst and the excretion of large volumes of dilute urine due to a deficiency in the secretion or action of the antidiuretic hormone (ADH), also known as vasopressin. This condition disrupts the body’s ability to regulate fluid balance, connecting it directly to the functions of the hypothalamus and pituitary gland, the nephron's structure and function, as well as urine formation and concentration processes in the kidneys.
Distal convoluted tubule: The distal convoluted tubule (DCT) is a segment of the nephron in the kidney that follows the loop of Henle and precedes the collecting duct. It plays a crucial role in the regulation of electrolyte balance, acid-base homeostasis, and water reabsorption, which are essential for maintaining overall fluid balance and blood pressure in the body. The DCT is where selective reabsorption occurs, particularly for sodium and calcium ions, influenced by hormones like aldosterone and parathyroid hormone.
Efferent arteriole: The efferent arteriole is a small blood vessel that carries blood away from the glomerulus in the kidney. It plays a crucial role in regulating blood flow and pressure within the nephron, affecting the filtration process and the overall function of the renal system.
Fenestrated endothelium: Fenestrated endothelium refers to a specialized type of endothelial lining that contains small pores, or fenestrae, which facilitate the rapid exchange of substances between the blood and surrounding tissues. This feature is particularly important in organs where filtration and absorption occur, such as the kidneys, allowing for efficient movement of molecules while maintaining some level of selectivity.
Filtration barrier: The filtration barrier is a specialized structure in the kidneys that selectively allows certain substances to pass from the blood into the urinary space while preventing the passage of larger molecules and blood cells. This barrier consists of three main components: the glomerular endothelium, the glomerular basement membrane, and the podocytes, each playing a crucial role in maintaining the kidney's filtering capacity and ensuring proper fluid balance in the body.
Glomerular filtration: Glomerular filtration is the process by which blood is filtered in the kidneys to form urine. During this process, water and small solutes are separated from blood plasma as it passes through the glomeruli, which are tiny networks of capillaries in the nephron. This initial step is crucial as it sets the stage for further processing of filtrate into urine and helps maintain fluid and electrolyte balance in the body.
Glomerular filtration rate: Glomerular filtration rate (GFR) is a measure of how well the kidneys are filtering blood, specifically the volume of fluid that passes from the blood into the glomerular capsules per minute. GFR is crucial for understanding kidney function, as it indicates how effectively the kidneys remove waste and excess substances from the bloodstream. The value of GFR can be influenced by various factors including age, sex, body size, and overall health status.
Glomerulus: The glomerulus is a network of tiny blood vessels, or capillaries, located within the nephron of the kidney that plays a crucial role in the filtration of blood. It is surrounded by a structure called Bowman's capsule, and together they form the renal corpuscle, where the initial stages of urine formation begin. The glomerulus filters out waste, excess substances, and fluids from the blood while retaining larger molecules like proteins and blood cells.
Hydrostatic pressure gradient: The hydrostatic pressure gradient refers to the change in pressure exerted by a fluid at rest due to the force of gravity, typically increasing with depth. This concept is crucial in understanding how fluids move within biological systems, particularly in relation to kidney function and the filtration process occurring in nephrons.
Hypertonic interstitium: A hypertonic interstitium refers to the extracellular fluid surrounding cells that has a higher concentration of solutes compared to the intracellular fluid of the cells. This condition is crucial for the function of the nephron, particularly in the loop of Henle, as it facilitates water reabsorption and helps maintain osmotic balance within the renal system. The presence of a hypertonic environment influences how kidneys concentrate urine and regulate fluid balance in the body.
Loop of Henle: The Loop of Henle is a U-shaped segment of the nephron in the kidney that plays a crucial role in concentrating urine and conserving water. It consists of a descending limb that allows water to be reabsorbed and an ascending limb that actively transports sodium and chloride out of the filtrate, contributing to the generation of an osmotic gradient essential for water reabsorption in the kidneys.
Nephritis: Nephritis is an inflammation of the kidneys that can affect their ability to filter waste from the blood effectively. This condition can arise from various causes, including infections, autoimmune diseases, and exposure to toxins, leading to significant alterations in kidney function. Understanding nephritis is crucial because it directly impacts the functioning of nephrons, which are the basic structural and functional units of the kidneys responsible for urine formation and regulation of bodily fluids.
Nephron: A nephron is the basic structural and functional unit of the kidney, responsible for filtering blood and producing urine. Each kidney contains about a million nephrons, which work together to regulate water, electrolyte balance, and waste removal, maintaining overall homeostasis in the body.
Oncotic pressure gradient: The oncotic pressure gradient refers to the osmotic pressure exerted by proteins, particularly albumin, in a solution that helps to draw water into the circulatory system or other compartments. This pressure is crucial in maintaining fluid balance between blood vessels and surrounding tissues, which is essential for proper kidney function and fluid regulation.
Parathyroid Hormone: Parathyroid hormone (PTH) is a key hormone produced by the parathyroid glands that regulates calcium levels in the blood. It plays a crucial role in maintaining calcium homeostasis by increasing blood calcium levels through its actions on bones, kidneys, and the intestines. By influencing these systems, PTH ensures that the body has adequate calcium for vital physiological processes, including muscle contraction and nerve transmission.
Passive reabsorption: Passive reabsorption is the process by which certain substances are reabsorbed from the renal tubules back into the bloodstream without the use of energy. This mechanism relies on concentration gradients, allowing solutes and water to move from areas of higher concentration to lower concentration, thus playing a crucial role in maintaining fluid and electrolyte balance in the body.
Podocytes: Podocytes are specialized epithelial cells that line the Bowman's capsule in the nephron of the kidney. They play a critical role in the filtration barrier, allowing for selective filtration of blood while preventing the loss of larger molecules like proteins. Their unique structure, characterized by foot-like extensions called processes, enables them to form filtration slits that are essential for maintaining kidney function.
Potassium secretion: Potassium secretion is the process by which the kidneys excrete excess potassium ions (K+) from the bloodstream into the urine. This process is crucial for maintaining normal potassium levels in the body, which is vital for proper muscle function, nerve signaling, and overall cellular homeostasis. Potassium secretion primarily occurs in the distal convoluted tubule and the collecting duct of the nephron, where hormones like aldosterone play a significant role in regulating this activity.
Proximal convoluted tubule: The proximal convoluted tubule (PCT) is a highly coiled segment of the nephron located in the kidney that plays a vital role in the reabsorption of essential nutrients, water, and electrolytes from the filtrate back into the bloodstream. It connects the Bowman's capsule to the loop of Henle and is characterized by its brush border microvilli that increase surface area for absorption. The PCT is responsible for reclaiming about 65-70% of the filtered water and a significant amount of solutes, including glucose, amino acids, and bicarbonate.
Renin-angiotensin-aldosterone system: The renin-angiotensin-aldosterone system (RAAS) is a hormone system that regulates blood pressure and fluid balance in the body. It begins when the kidneys release renin in response to low blood pressure or low sodium levels, which activates angiotensinogen into angiotensin I. Angiotensin I is then converted to angiotensin II, a potent vasoconstrictor that stimulates aldosterone secretion from the adrenal glands, promoting sodium and water reabsorption in the kidneys, thereby increasing blood volume and blood pressure.
Sodium reabsorption: Sodium reabsorption is the process by which the kidneys reclaim sodium ions from the filtrate back into the bloodstream. This crucial function occurs mainly in the nephron, particularly in structures like the proximal convoluted tubule and the loop of Henle, where sodium transport mechanisms are vital for maintaining electrolyte balance, fluid homeostasis, and overall blood pressure regulation.
Starling Forces: Starling forces refer to the physical forces that govern the movement of fluid across capillary membranes, specifically the balance between hydrostatic pressure and oncotic pressure. These forces play a critical role in fluid exchange between blood vessels and surrounding tissues, influencing the function of the kidneys, particularly within the nephron's glomerulus where filtration occurs.
Tubular reabsorption: Tubular reabsorption is the process in the kidneys where valuable substances are reclaimed from the filtrate back into the bloodstream after the initial filtration. This crucial function occurs primarily in the nephron, specifically in the proximal convoluted tubule, loop of Henle, and distal convoluted tubule, helping to maintain homeostasis by regulating water, electrolytes, and other essential nutrients.