D4.3 - Maintaining Excretory System

Maintaining the Excretory System

• The kidneys excrete metabolic waste.
• Antidiuretic hormone (ADH) and aldosterone are crucial for water and sodium ion reabsorption, excretion, and blood pressure regulation.

Water Balance

• Osmotic pressure is the force generated by osmosis. It affects material exchange between cells and blood while maintaining constant solute concentration in blood regardless of water consumption.
• If a person drinks too much water, the kidneys allow more water into the urine. If a person does not drink enough water, the kidneys conserve water by producing concentrated urine

Regulating ADH

• Antidiuretic hormone (ADH) increases the permeability of collecting ducts to water.
• ADH regulates water reabsorption in the nephron.
• If ADH is released, more concentrated urine is produced.
• ADH makes the upper part of the distal tubule and collecting duct permeable to water.
• Osmoreceptors are cells sensitive to osmotic pressure. They are located in the hypothalamus, part of the brain that regulates hunger, thirst, blood pressure, body temperature, fluid balance, and salt balance.

Regulating Reabsorption of Water

• If blood plasma is too concentrated, osmotic pressure increases, and osmoreceptors in the hypothalamus send impulses to the pituitary gland to release ADH.
• ADH increases the permeability of distal tubules and collecting ducts, allowing more water to be reabsorbed. This dilutes blood and lowers osmotic pressure to normal.
• If blood plasma is too dilute, osmotic pressure decreases. Osmotic receptors stop/prevent the release of ADH. The distal tubule and collecting duct become less permeable to water, allowing more water to be excreted with urine.

Diabetes

• Diabetes is a disease in which the body either can't produce insulin or can't use it properly to regulate blood glucose.
• Insulin is a hormone produced by the pancreas that regulates the amount of glucose (sugar) in the blood.
• There are 3 types of diabetes:
  • Diabetes mellitus
  • Diabetes insipidus
  • Gestational diabetes

Diabetes Mellitus

• Diabetes mellitus is caused by inadequate insulin secretion from pancreatic cells.
• This affects kidney function as insulin is needed for cells to absorb glucose from the bloodstream.
• Without insulin, higher-than-necessary blood glucose levels cause excess glucose excretion in the urine (smells sweet).
• Water is not reabsorbed into the bloodstream from the nephron due to impaired passive transport.
• As a result, individuals with this type are often thirsty due to large water loss.

Diabetes Insipidus

• Diabetes insipidus results from defects in antidiuretic hormone (ADH).
• ADH regulates water reabsorption in the nephron.
• Without ADH, the nephron becomes less permeable to water, and less water is removed from the filtrate.
• Individuals with this type produce large volumes of dilute urine.
• They will experience intense thirst because water is excreted quicker than it can be consumed.
• Treatment for this condition involves synthetic ADH to restore water and ion balance.

Diuretic

• A diuretic is a substance that increases urine volume by decreasing ADH release.
• Diuretics decrease the permeability of tubules and collecting ducts leading to water loss and dehydration.
• Examples of diuretics include alcohol, coffee, tea, and carbonated drinks.

Reabsorption of Salts

• Kidneys control salt balance in blood by controlling salt excretion and reabsorption of ions.
• When blood sodium (Na⁺) concentration decreases, aldosterone stimulates distal tubules and collecting ducts to reabsorb Na⁺, with chloride (Cl⁻) ions following due to charge attraction.
• Water follows Na⁺ by osmosis.
• Aldosterone also increases K⁺ secretion into distal tubules and collecting ducts when blood K⁺ concentration is too high.

Balance of Excretory System

• The composition of urine depends on various factors including diet, physical activity, stress, and fatigue.
• Healthcare professionals should consider multiple factors when analyzing urine for disease indicators.

Urinary Tract Infection (UTI)

• Cystitis: Bladder infection caused by bacteria or viruses.
• Urethritis: Urethra infection.
• UTIs are more common in women due to anatomical differences.
• UTIs can lead to kidney damage.
• Symptoms: Painful urination, frequent urination, bloody/brown urine, tenderness, chills, fever, nausea, vomiting.
• Treatment: Antibiotics, in severe cases, surgery.
• Prevention: Hygiene and personal behaviours.

Kidney Stones

• Kidney stones are crystalline formations due to excess calcium in urine.
• Treatment options include medication for breaking down kidney stones, ultrasound shock waves for stones smaller than 20mm, and surgery for larger stones.

Problems with Kidney Function

• Renal insufficiency: A condition where kidneys cannot regulate homeostasis, caused by damaged nephrons.
• Causes: Kidney infection, high blood pressure, trauma or injury to the kidney, poisoning, atherosclerosis blockage of kidney tubules
• Consequences: If greater than 75% of nephrons are destroyed, urine output is inadequate to maintain homeostasis.
• Treatment: Kidney transplant or artificial kidney for dialysis.

Dialysis

• Dialysis: Diffusion of dissolved substances across a semipermeable membrane to remove excess waste products from the blood.
• Dialysate: A solution that removes substances in excess in the blood.
• Types of Dialysis: Hemodialysis and peritoneal dialysis.

Hemodialysis

• Hemodialysis: Uses a machine with an artificial membrane to filter waste and excess substances from the blood.
• Blood is passed through an artificial membrane (dialyzer) to remove wastes and excess fluids.
• Dialysis treatments typically last 2-5 hours and may be repeated 3 times per week.
• Patients need a strictly regulated diet to prevent excess toxins building up in their system

Peritoneal Dialysis

• Peritoneal dialysis: Uses the lining of the abdomen (peritoneum) as the dialysis membrane.
• A special solution (dialysate) is introduced into the abdominal cavity, where it filters the blood.
• Dialysate is removed after the filtration process, removing waste products.

Kidney Transplants

• A kidney transplant is a permanent solution to replace a damaged kidney with a fully functional one.
• Often a close family member donates a kidney.
• Both the donor and recipient have one fully functional kidney.
• Patients must closely monitor their diet after the transplant.
• Kidneys can also be obtained from cadavers.

Kidney-Coronary Connection

• High blood pressure (BP) can damage blood vessels in the kidneys, impacting their ability to filter waste effectively.
• Kidney failure can result from high blood pressure.
• Symptoms of high blood pressure and kidney impairment may not appear until significant damage has already occurred.