A-level Biology: Homeostasis and the Kidney

Homeostasis

• Homeostasis maintains a constant internal environment despite changes in the external environment
• It involves factors such as temperature, water potential, pH, and blood glucose level
• Negative feedback counteracts changes in internal conditions to restore optimum conditions
• Elements required for negative feedback: sensory receptors, nervous or hormonal system, and effectors

Kidney Function

• The main role of the kidneys is excretion of waste products, such as urea in the form of urine
• Blood enters the kidney through the renal artery and passes through capillaries in the cortex
• Waste products are filtered out of the blood through ultrafiltration and into long tubules called nephrons
• Selective reabsorption: useful substances like amino acids, glucose, and vitamins are reabsorbed back into the blood
• The substances to be excreted pass through the tubules and ureter and reach the bladder as urine

Control of Water Potential

• In dehydration, less water is reabsorbed into the blood, leading to production of more concentrated urine
• Osmoreceptors in the hypothalamus control water potential and content
• Antidiuretic hormone (ADH) released from the posterior pituitary gland increases reabsorption of water from the tubules into the blood

Kidney Failure

• Kidney failure can be triggered by kidney infections, inflammation, and high blood pressure
• Damage causes the kidneys to perform filtration and reabsorption less efficiently
• Consequences of kidney failure: buildup of toxic waste products, fluid accumulation, and disruption of ion balance
• Kidney failure can be treated with renal dialysis, which filters the blood to remove waste products and excess water and ions
• Kidney transplant is a more convenient and long-term solution, but requires a suitable donor with the same blood type and tissue type

Kidney Function

• Substances to be excreted pass through tubules and ureter, and finally reach the bladder where they're disposed of as urine.
• Filtered blood then passes out of the kidneys through the renal vein.
• The kidneys' main role is the excretion of waste products, such as urea in the form of urine.
• Blood enters the kidney through the renal artery and passes through the capillaries in the cortex of the kidneys.
• Waste products are filtered out of the blood as it passes through the capillaries and into the long tubules called nephrons through a process known as ultrafiltration.
• Selective reabsorption is the process where useful substances such as amino acids, glucose, vitamins are reabsorbed back through the tubules in the medulla.

Control of Water Potential

• Osmoreceptors in the hypothalamus control the water potential and content.
• In the case of dehydration, not as much water is reabsorbed into the blood by osmosis from the loop of Henle, the distal convoluted tubule, and collecting duct, leading to production of more concentrated urine.
• Hormones, such as antidiuretic hormone (ADH), play an important role in controlling the reabsorption of water.
• ADH makes the walls of the DCT and collecting duct more permeable to water, increasing the reabsorption of water from the tubules into the blood.

Kidney Failure

• Kidney failure can be triggered by various kidney infections, which cause inflammation and damage to the kidneys.
• High blood pressure can also cause damage to the kidney by damaging the capillaries of glomeruli.
• Consequences of kidney failure include the buildup of toxic waste products, such as urea, which causes symptoms such as vomiting.
• In cases where excess water cannot be removed from the blood by the kidneys, fluid accumulation occurs, leading to swelling.
• Kidney failure can disrupt the balance of ions, making the bones more brittle or causing water to be retained.

Treatment of Kidney Failure

• Kidney failure can be treated with renal dialysis, which filters the blood with the help of a machine containing dialysis fluid.
• Dialysis is only a temporary solution while the patient awaits a transplant.
• Kidney transplant is required to replace the damaged kidney and to reverse kidney failure symptoms, and is believed to be a more convenient and long-term solution.
• Patients need to wait a long time for a suitable donor, which needs to be of the same blood type and tissue type to minimize the risk of rejection.