homeostasis and response

• The main job of the kidneys is to filter the blood and remove waste products like urea, which is made in the liver during deamination
• The kidneys also regulate the levels of ions like sodium and potassium, as well as water in the body
• Water regulation is crucial because cells can lose or gain water through osmosis, affecting their size and function
• Inside each kidney are around a million structures called nephrons, which are responsible for filtering blood
• Kidney tubules absorb small molecules like water, glucose, amino acids, and urea during the filtration process
• Selective reabsorption occurs in the kidney tubules, where only the substances that the body needs are reabsorbed back into the bloodstream
• The hypothalamus in the brain detects water concentration in the bloodstream and signals the release of ADH (antidiuretic hormone) from the pituitary gland if water levels are too low
• ADH travels to the kidneys and instructs the tubules to reabsorb more water into the blood, reducing urine production
• This process of water regulation is an example of a negative feedback loop, where the body constantly monitors and adjusts water levels to maintain balance
• The three main roles of the kidneys are to:

  • Remove waste products like urea from the blood
  • Regulate the levels of ions in the blood
  • Regulate the amount of water in the blood
• Blood cycles through the kidneys, passing in through the renal arteries and out through the renal veins
• The kidneys produce urine from the blood, which passes down the ureters and is stored in the bladder until it is urinated out through the urethra
• In a cross-section of a kidney, there are tiny structures called nephrons
• Nephrons consist of:

  • Tubule (yellow part) that carries the filtered fluid that will become urine
  • Blood vessels (red parts)
• The process starts with filtration, where liquid from the blood is forced from the glomerulus into the Bowman's capsule
• Only small substances like water, amino acids, urea, glucose, and ions can be filtered through to the Bowman's capsule
• About 20% of the plasma in the blood is filtered through to the Bowman's capsule
• The kidneys reabsorb substances like glucose and amino acids back into the blood vessels, while selectively reabsorbing water and ions, and not reabsorbing urea
• Selective reabsorption happens throughout the entire region as fluid moves through the tubule
• Parts of the nephron include:

  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct, which also receives fluid from other nephrons
• Fluid that passes out of the collecting duct is classified as urine, which then passes down the ureter to the bladder and can be released as waste
• Main consequences of kidney failure:

  • Waste substances build up in the bloodstream
  • Inability to regulate water and ion levels
  • Person quickly becomes sick and could die if not treated
• Mild kidney disease can be treated with medication, but kidney failure requires dialysis or kidney transplant
• Dialysis:

  • Dialysis machines act as artificial kidneys to filter a patient's blood
  • Blood passes into the machine through a circuit and back out into the patient
  • Blood comes into contact with dialysis fluid separated by a partially permeable membrane
  • Dialysis fluid contains the same concentrations of water and molecules as healthy blood
  • Small molecules like water and ions can diffuse across the membrane, while bigger molecules cannot
  • Dialysis fluid is constantly replaced to maintain a concentration gradient and remove unwanted substances from the blood
• Issues with dialysis:

  • Time-consuming, requiring hospital visits 3-4 days a week for 3-4 hours each time
  • Unpleasant experience with potential complications like blood clots or infections
  • Expensive and lifelong treatment
• Kidney transplant:

  • Surgical procedure transferring a healthy kidney from a donor to a patient
  • Donor kidneys can come from deceased or living donors
  • Risk of rejection where the patient's immune system attacks the transplanted organ
  • Medication is given to suppress the immune system, but rejection can still occur
• Transplants tend to be better and cheaper than dialysis, but there is a shortage of available organs

  • Many people still rely on dialysis due to the limited availability of organs
• The brain is made up of billions of interconnected nerve cells and holds all of our thoughts and memories
• The brain is responsible for all of our complex behaviors, from choosing clothes to running or reading
• The brain is made up of different regions, each with different functions
• Cerebral cortex or cerebrum:

  • Responsible for consciousness, intelligence, memory, language, vision, and hearing
  • Split into two hemispheres, with the left hemisphere controlling the right side of the body and vice versa
• Cerebellum:

  • Responsible for controlling balance and muscle coordination
• Hypothalamus:

  • Involved in regulating body temperature and sending signals to the pituitary gland
• Brain stem:

  • Connects the brain to the spinal cord
  • Contains the medulla, which controls unconscious activities like breathing and heartbeats
• Scientists study the brain by observing people with brain damage
• Studying people with brain damage helps identify which brain regions are responsible for specific functions
• Another technique is electrically stimulating different parts of the brain to observe the resulting effects
• The most common technique used today is scanning the brain, which includes CT scans, PET scans, and MRI scans
• CT scans are used to see which areas of the brain are damaged

  • PET and MRI scans are better at measuring the underlying activity of the brain
• Treating the brain is difficult due to various factors