Intro to kindey

The two main functions of the kidneys are to filter blood and produce urine. They act as a crucial filter for blood, removing waste products, toxins, and excess ions while retaining essential substances. The kidneys are responsible for regulating the body's water balance, electrolyte levels, pH, and blood pressure.

The nephron is the functional unit of the kidney, responsible for filtering blood and producing urine. Each kidney contains approximately 1 million nephrons. Each nephron consists of a renal corpuscle that filters blood, and a tubule system that reabsorbs and secretes substances to form urine.

The renal corpuscle is the initial filtering unit of the nephron. It consists of the glomerulus, a network of capillaries, and Bowman's capsule, a double-walled cup-shaped structure that surrounds the glomerulus. The renal corpuscle acts as a sieve, selectively filtering blood plasma into Bowman's space.

The glomerulus is a network of capillaries within the renal corpuscle. Its structure allows for the filtration of blood plasma into Bowman's space. The glomerulus acts as a sieve, only allowing small molecules like water, glucose, and ions to pass through.

Bowman's capsule is a double-walled cup-shaped structure that surrounds the glomerulus within the renal corpuscle. It collects the fluid filtered from the glomerulus, known as the filtrate, and directs it into the proximal tubule.

Glomerular filtration rate (GFR) is the volume of fluid filtered from the glomerulus into Bowman's space per unit of time. It is a crucial indicator of kidney function. A normal GFR is approximately 90-125 ml/min.

Starling's forces are pressure gradients that determine the movement of fluid across the glomerular filtration membrane. These forces include the glomerular capillary hydrostatic pressure (PGC), Bowman's capsule hydrostatic pressure (PBS), and the osmotic pressure due to proteins (Pp).

The glomerular filtration membrane is a three-layered structure that selectively filters blood plasma into Bowman's space. The layers include the endothelial cells of the glomerular capillaries, the glomerular basement membrane (GBM), and podocytes.

Podocytes are specialized epithelial cells that wrap around the glomerular capillaries. They have foot-like processes called pedicels that interdigitate to form filtration slits, which help to regulate the passage of molecules into the filtrate.

The glomerular basement membrane (GBM) is a specialized layer of the filtration membrane. It plays a crucial role in restricting the passage of plasma proteins into Bowman's space. It is composed of collagen and other proteins.

The macula densa is a specialized region of the distal convoluted tubule (DCT) that senses the sodium chloride concentration in the filtrate. It plays a crucial role in the tubuloglomerular feedback mechanism, which regulates GFR.

The juxtaglomerular apparatus (JGA) is a specialized structure located at the point where the afferent arteriole enters the glomerulus. It comprises the macula densa, juxtaglomerular cells, and extraglomerular mesangial cells. The JGA plays a crucial role in regulating GFR and blood pressure.

The myogenic response is an intrinsic mechanism that regulates GFR in response to changes in blood pressure. When blood pressure increases, the smooth muscle cells in the afferent arteriole contract, constricting the vessel and reducing blood flow to the glomerulus. This helps to maintain a stable GFR.

Tubuloglomerular feedback is an intrinsic mechanism that regulates GFR based on the concentration of sodium chloride in the filtrate. When GFR increases, the macula densa sensors detect a higher sodium chloride concentration in the filtrate. This triggers the release of paracrine factors that constrict the afferent arteriole, reducing GFR.

Atrial natriuretic peptide (ANP) is a hormone produced in the heart that is released in response to increased blood volume. ANP has a vasodilatory effect, increasing blood flow to the kidneys and promoting sodium excretion. Its primary function is to reduce blood volume and blood pressure.

The renin-angiotensin-aldosterone system (RAAS) is a hormonal system that plays a crucial role in regulating blood pressure and fluid balance. Renin, an enzyme produced by juxtaglomerular cells, triggers a cascade that ultimately results in the release of aldosterone, a hormone that promotes sodium reabsorption in the distal convoluted tubule and collecting duct.

Creatinine clearance is a measure of the kidneys' ability to filter creatinine from the blood. It is a way to estimate GFR and assess kidney function. It is calculated by measuring the concentration of creatinine in both blood and urine and considering the volume of urine produced over a 24-hour period.

The proximal convoluted tubule (PCT) is the first section of the nephron tubule system. It plays a vital role in reabsorbing most of the filtered water, glucose, amino acids, and ions back into the bloodstream. Its epithelial cells have specialized transport mechanisms for reabsorbing various substances.

The loop of Henle is a U-shaped section of the nephron tubule that descends into the medulla and then ascends back into the cortex. It is involved in creating the osmotic gradient that helps to concentrate urine. It is composed of a descending limb, which is permeable to water, and an ascending limb, which is permeable to sodium and chloride ions.

The distal convoluted tubule (DCT) is a section of the nephron tubule that connects the loop of Henle to the collecting duct. It is involved in regulating the final composition of urine by reabsorbing or secreting various ions and water. It is also influenced by hormones, such as aldosterone, which promotes sodium reabsorption.

The collecting duct is the final portion of the nephron tubule system. It collects filtrate from multiple nephrons and transports it to the renal pelvis. The collecting duct is influenced by antidiuretic hormone (ADH), which regulates water reabsorption and urine concentration. The collecting duct's permeability to water varies depending on the level of ADH.

Antidiuretic hormone (ADH), also known as vasopressin, is a hormone that regulates water reabsorption in the collecting duct. It is released from the posterior pituitary gland in response to dehydration or a rise in blood osmolarity. ADH increases the permeability of the collecting duct to water, allowing more water to be reabsorbed and producing concentrated urine.

The renal pelvis is a funnel-shaped structure that collects urine drained from the collecting ducts of multiple nephrons. It acts as a reservoir for urine before it passes into the ureter.

The ureter is a tube that carries urine from the renal pelvis to the urinary bladder. It is lined with smooth muscle that helps to propel urine towards the bladder through peristaltic contractions.

The urinary bladder is a muscular sac that stores urine until it is eliminated from the body. It has a smooth muscle wall that can expand to hold a significant amount of urine. The bladder contracts under the control of the nervous system, expelling urine through the urethra.

The urethra is a tube that carries urine from the urinary bladder to the outside of the body. The urethra is lined with smooth muscle that helps to control the flow of urine during urination.

The kidneys play a crucial role in maintaining blood pressure. They do so by producing renin, an enzyme involved in the RAAS. Renin triggers a cascade that ultimately results in the release of aldosterone, a hormone that promotes sodium reabsorption and vasoconstriction, increasing blood pressure.

The kidneys are also an endocrine gland, producing hormones like erythropoietin (EPO), renin, and active vitamin D. EPO stimulates red blood cell production in the bone marrow. Renin, as discussed earlier, is involved in blood pressure regulation. Active vitamin D promotes calcium absorption in the gut.

The kidneys are capable of glucose production during periods of prolonged fasting or starvation. This process, known as gluconeogenesis, allows the kidneys to contribute to maintaining blood glucose levels and energy supply to other tissues.

The kidneys are responsible for maintaining the body's acid-base balance, regulating the levels of bicarbonate (HCO3-) and hydrogen ions (H+) in the blood. This helps to keep the blood pH within a narrow range, which is crucial for proper cellular function.