Kidney - SS3 Biology Lesson Note

KIDNEYS

Homeostasis in the human kidney plays a crucial role in maintaining the balance of various substances and fluids in the body. The kidney is responsible for filtering waste products, regulating water and electrolyte balance, and controlling blood pressure. The key mechanisms involved in kidney homeostasis include filtration, reabsorption, and secretion.

1.    Filtration: The first step in kidney homeostasis is glomerular filtration, which occurs in the glomerulus. Blood enters the glomerulus, and under pressure, water, ions, nutrients, and waste products are filtered into the renal tubules while larger molecules and blood cells are retained in the bloodstream.

2.    Reabsorption: Following filtration, the renal tubules reabsorb essential substances such as water, glucose, amino acids, and ions back into the bloodstream. This reabsorption process ensures that vital substances are conserved and returned to the body, preventing excessive loss.

3.    Secretion: The renal tubules also actively secrete certain substances, such as hydrogen ions, potassium ions, and drugs, into the tubular fluid. Secretion helps regulate the pH of body fluids, maintain electrolyte balance, and eliminate potentially harmful substances.

4.    Regulation of Water and Electrolyte Balance: The kidney plays a crucial role in maintaining proper water and electrolyte balance in the body. Through the reabsorption and secretion processes, the kidney regulates the concentrations of ions, such as sodium, potassium, calcium, and phosphate, in the blood. It adjusts the reabsorption of water in response to hormonal signals, primarily from the hormone antidiuretic hormone (ADH), to control urine concentration and maintain proper fluid balance.

5.    Blood Pressure Regulation: The kidney also participates in regulating blood pressure through the renin-angiotensin-aldosterone system (RAAS). When blood pressure drops, specialized cells in the kidney release the enzyme renin, which triggers a series of reactions leading to the production of angiotensin II. Angiotensin II constricts blood vessels, stimulates the release of aldosterone, and promotes reabsorption of sodium and water, ultimately increasing blood volume and restoring blood pressure.

 

Overall, homeostasis in the human kidney ensures the proper filtration, reabsorption, and secretion of substances to maintain fluid balance, electrolyte concentrations, pH levels, and blood pressure within narrow ranges. These processes are vital for the overall stability and optimal functioning of the body's internal environment.