Renal System Structure and Function

Paired organs located in the retroperitoneal space, between the twelfth thoracic and third lumbar vertebrae.

The functional unit of the kidney, responsible for filtering blood and producing urine.

The filtration membrane in the nephron consists of three layers: the endothelium, basement membrane, and epithelium. The epithelium has podocytes, which have filtration slits.

Specialized cells in the distal convoluted tubule that sense sodium levels and communicate with juxtaglomerular cells to regulate renin release.

The proximal tubule is lined with microvilli, which increase its surface area and enhance reabsorption of essential substances.

The loops of Henle create a concentration gradient in the medulla of the kidney, which is important for the concentration of urine.

The collecting ducts adjust acid-base balance by secreting hydrogen or bicarbonate ions and potassium.

The ureters transport urine from the kidneys to the bladder using peristaltic contractions.

The bladder is a muscular organ that stores urine before it is expelled from the body. It's composed of two main muscles: the detrusor and the trigone. Nerves control its functions, including contraction (parasympathetic) and relaxation (sympathetic) of the bladder and urethra.

When urine volume reaches 250-300mL, stretch receptors in the bladder wall send signals to the brain, triggering the urge to urinate. This is the micturition reflex.

Renal blood flow is the volume of blood passing through the kidneys per minute. It's crucial for filtering waste and maintaining blood pressure.

The kidneys can adjust blood flow to maintain a stable filtration rate, even when blood pressure fluctuates. This is known as autoregulation.

The glomerular filtration rate (GFR) measures how much fluid is filtered from the blood by the kidneys per minute. It's a key indicator of kidney function.

The sympathetic nervous system can constrict blood vessels in the kidneys, reducing blood flow and GFR.

Renin-angiotensin-aldosterone system (RAAS) is a complex hormonal pathway that regulates blood pressure and blood volume by controlling sodium and water reabsorption. It's initiated by the release of renin from the kidneys.

Natriuretic peptides (NPs) are hormones that counteract the RAAS by promoting sodium and water excretion. This helps lower blood pressure and volume.

The distal tubules actively reabsorb sodium and water, while secreting potassium and hydrogen ions to maintain fluid, electrolyte, and acid-base balance in the body.

ADH (antidiuretic hormone) regulates water reabsorption in the distal tubules and collecting ducts, influencing the concentration of final urine. The countercurrent exchange system in the loop of Henle creates a concentration gradient in the renal medulla, facilitating further water reabsorption in the collecting duct.

The distal nephron plays a crucial role in acid-base balance by excreting hydrogen ions and generating new bicarbonate, neutralizing excess acid in the blood.

Plasma creatinine concentration, cystatin C plasma concentration, and BUN levels are used to assess glomerular function. Creatinine clearance, calculated from plasma and urine creatinine levels, is a common clinical indicator of GFR (glomerular filtration rate).

PAH (para-aminohippuric acid) clearance is used to determine renal plasma flow and blood flow, providing insights into the overall kidney function and blood delivery rate.

Urinalysis involves examining the color, turbidity, protein content, pH, specific gravity, sediment, and supernatant of urine. Abnormal components in the sediment, such as bacteria, red blood cells, white blood cells, casts, or crystals, may indicate a renal disorder.

With aging, the number and size of nephrons decrease, leading to reduced renal blood flow and glomerular filtration rate. Tubular transport and reabsorption decrease, potentially causing delayed responses to acid-base changes and glucose reabsorption.

Neurogenic and myogenic changes in the bladder can occur with age, potentially leading to symptoms of urgency, frequency, or urine retention.