Git renal physiology

Kidneys: Paired organs located on the posterior abdominal wall, measuring approximately 150 grams in weight. Each kidney is about 12 cm long and less than 8 cm wide, encased in a tough protective capsule. The renal artery, vein, lymphatics, nerve supply, and ureter enter the kidney at the hilum.
Structural Division: The kidney is composed of an outer cortex and an inner medulla consisting of renal pyramids that taper into renal papillae, projecting into the renal pelvis.
Nephrons: The functional unit of the kidney, comprising approximately 1.3 million nephrons per kidney. Each nephron includes a renal glomerulus and renal tubule (composed of the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting ducts).

Homeostasis: The kidneys maintain a constant internal environment through regulation of water, electrolyte balance, blood pressure, and acid-base balance.
- Regulation through the Renin-Angiotensin-Aldosterone System (RAAS) ensures sodium and water excretion matches intake, contributing to blood pressure stability.
- Acid-Base Balance: Kidneys regulate buffer stores and excrete metabolic acids, impacting systemic pH levels.
Excretion: The kidneys filter metabolic waste products like urea, uric acid, and creatinine, and foreign chemicals (drugs, food additives), ensuring they are effectively cleared from the bloodstream.
Endocrine Functions: The kidneys secrete a variety of hormones critical to maintaining homeostasis:
- Erythropoietin stimulates red blood cell production in response to anemia (treatable with EPO injections).
- Renin regulates blood pressure via the RAAS.
- Prostaglandins and other local hormones regulate renal blood flow.
- Active Vitamin D regulates calcium and phosphate metabolism, essential for maintaining bone health.
Gluconeogenesis: During fasting, the kidneys synthesize glucose from amino acids, thus maintaining blood glucose levels.

Erythropoietin (EPO) Deficiency: Leads to normocytic normochromic anemia primarily due to impaired erythropoiesis.
Uremia: Damages red blood cells and inhibits their production, shortening their lifespan.
Nutritional Deficiencies: Patients may suffer from deficiencies in folate and vitamin B12 largely due to dietary restrictions and dialysis. Iron deficiency can result from chronic blood loss or impaired absorption.

Atherosclerosis, bilateral renal artery stenosis, and diabetes mellitus influence renal blood flow, potentially leading to hypertension. Management focuses on inhibiting angiotensin II and blocking its receptors.

The nephron consists of the glomerulus (capillary tuft for filtration) and tubules (for reabsorption and secretion). The loop of Henle further facilitates urine concentration.
Various types of cells within the nephron are responsible for specific functions such as sodium reabsorption, water regulation (controlled by ADH), and acid-base balance (via intercalated cells).

Normal GFR: Approximately 125 ml/min, dependent on hydrostatic pressures and osmotic gradients. Conditions affecting GFR include aging and renal disease.
GFR is critical to assessing overall kidney function, where lower rates indicate impairment.

Mechanisms: Urine formation involves glomerular filtration (separating blood and filtrate), tubular reabsorption (solutes and water back into blood), and tubular secretion (substances from blood into filtrate).
The nephron's structure allows selective reabsorption of water and solutes, and hormonal regulation plays a significant role in adjusting these processes.

The kidneys play a vital role in acid-base homeostasis by secreting hydrogen ions and reabsorbing bicarbonate. Changes in acid secretion and buffer levels directly influence systemic pH.

Disturbances in pH can arise from metabolic and respiratory processes, with corresponding physiological responses aimed at maintaining homeostasis.

Understanding kidney function and anatomy is pivotal for diagnosis and treatment related to renal pathophysiology. Regular monitoring of kidney biomarkers and hormones is essential for assessing renal health.