D4.3 - Maintaining the Excretory System

Maintaining the Excretory System

• The amount of water reabsorbed from the filtrate affects blood volume and plasma solute concentration.
• The excretory system is crucial for homeostasis.
• Disorders in the excretory system can impact other body systems.

Water Balance

• Osmotic pressure is the force generated by osmosis and affects the exchange of materials between blood and cells.
• Solute concentration in blood usually remains constant despite variations in water intake.
• If a person drinks a lot of water, kidneys allow more water into urine.
• If water is scarce, kidneys conserve water by producing concentrated urine.

Regulating ADH

• Antidiuretic hormone (ADH) regulates osmotic pressure in kidneys to enhance water absorption.
• Release of ADH leads to more concentrated urine.
• ADH makes the upper part of the distal tubule and collecting duct permeable to water.
• Osmoreceptors are cells sensitive to osmotic pressure located in the hypothalamus.
• The hypothalamus regulates hunger, thirst, blood pressure, body temperature, fluid balance, and salt balance.

Regulating Reabsorption of Water

• High blood plasma concentration (increased osmotic pressure) triggers the release of ADH from the pituitary gland.
• ADH increases the permeability of the distal tubules and collecting ducts, allowing more water to be reabsorbed and lowering the osmotic pressure.
• Low blood plasma concentration (decreased osmotic pressure) stops ADH release, reducing water reabsorption, and increasing urination.

Regulating Reabsorption of Water (continued)

• If blood plasma is too dilute, osmotic pressure decreases.
• Osmoreceptors stop/prevent the release of ADH which makes the distal tubule and collecting duct less permeable to water.
• More water is excreted in the urine.

Diabetes Insipidus

• Diabetes insipidus happens when ADH activity is insufficient, causing excessive urination.
• This leads to intense thirst, dehydration, and ion imbalances.
• Treatment includes synthetic ADH to restore water and ion balance.

Diuretic

• A diuretic increases urine volume by reducing ADH release.
• This causes decreased permeability of the tubules and collecting ducts.
• Diuretics, such as alcohol, coffee, tea, or carbonated drinks, increase water loss and can lead to dehydration.

Reabsorption of Salts

• Kidneys control salt balance by regulating the excretion and reabsorption of ions.
• Aldosterone is a hormone that stimulates the reabsorption of Na+ when blood Na+ concentration drops.
• Chloride (Cl-) ions follow Na+ due to charge attraction.
• Water follows by osmosis.
• Excess K+ in the blood signals aldosterone to increase excretion of K+ in the distal tubules and collecting ducts.

Maintaining Blood pH

• Body fluids maintain a pH of 7.4.
• Acid-base buffer systems in the blood adjust H+ ion concentrations.
• If the blood becomes too acidic, H+ ions are excreted, and bicarbonate ions are reabsorbed.
• If the blood is too basic, H+ ions aren't excreted, and bicarbonate ions aren't reabsorbed.
• The bicarbonate buffer system, which combines carbon dioxide, water, and carbonic acid, regulates the pH.

Balance of Excretory System

• The balance of substances in urine depends on several factors, including diet, physical activity, stress, and fatigue.
• Healthcare professionals consider many factors when analyzing urine to detect diseases like diabetes.

Urinary Tract Infection (UTI)

• Cystitis is a bladder infection caused by bacteria or viruses.
• Urethritis is a urethra infection.
• UTIs are more common in women than men due to anatomical differences.
• UTIs can cause permanent kidney damage.

UTI Symptoms

• UTI symptoms include painful urination, frequent urination, even when no urine is produced, bloody or brown urine, and tenderness, chills, fever, nausea, and vomiting.

UTI Treatment

• UTI treatment primarily involves antibiotics.
• In severe cases, surgery might be necessary.

Kidney Stones

• Kidney stones are crystalline formations caused by excess calcium in urine.
• Treatment options include medications to dissolve the stones, ultrasound shock waves for smaller stones, or surgery for larger stones.

Problems with Kidney Function

• Renal insufficiency is when kidneys can't maintain homeostasis.
• Nephrons can be damaged due to high blood pressure, kidney infections, trauma, poisoning, and atherosclerosis.
• Complete nephron destruction (greater than 75%) leads to inadequate urine output to maintain homeostasis.
• Kidney transplants and artificial kidneys (performing dialysis) are possible solutions.

Dialysis

• Dialysis uses a semipermeable membrane to remove waste products from the blood.
• Involves diffusion of substances across the membrane, from high to low concentration.
• Dialysate (a solution similar to clean blood plasma) is on the other side of the membrane.
• Two main types of dialysis are hemodialysis and peritoneal dialysis.

Hemodialysis

• Uses an artificial membrane (machine) to filter waste products from blood.
• Filtered blood (dialysate) is returned to the patient.
• Typically takes 2-5 hours, 3x per week.
• Patients need a regulated diet to avoid toxin buildup.

Peritoneal Dialysis

• Uses the lining of the abdomen (peritoneum) to filter waste products.
• Dialysis solution is introduced into the abdominal cavity.
• The solution contains capillaries that slowly filter the blood.

Kidney Transplants

• Kidney transplants replace damaged kidneys with healthy ones, often from a living donor.
• Recipients must maintain a healthy diet and lifestyle to care for the transplanted kidney.
• Kidneys can also be obtained from deceased donors who have completed the necessary paperwork.

Kidney-Coronary Connection

• High blood pressure can damage blood vessels in the kidneys.
• This can lead to kidney failure.
• Damage from high blood pressure might go unnoticed initially.