9.3

 Kidneys adjust the water balance in the body  Controlled by the nervous and endocrine systems  Important for maintaining blood volume and concentration of plasma solutes

 DO NOT COPY  Average adult loses 2 L of water a day  Urine  Perspiration  Exhalation  Drop in fluid intake  1%  thirst  5%  extreme pain, collapse  10%  death

 ADH  Causes kidneys to increase water reabsorption Leads to concentrated urine, and conserving body water by increasing permeability of the distal tubule  Produced in hypothalamus  Stored in pituitary  Released into blood  Alcohol and caffeine are diuretics  Increase the output of urine and decreases the release of ADH  Intensifies thirst and leads to dehydration

 Osmoreceptors  Nerves in hypothalamus (located in the brain) that detect change in osmotic pressure  High Osmotic Pressure  Water moves into blood stream  hypothalamus shrinks  signals release of ADH from pituitary  ADH causes increased reabsorption of water in kidneys, prevents osmotic pressure from increasing any further

 Sensation caused by the shrinking of the hypothalamus  Drinking water results in:  osmotic pressure decreases  Hypothalamus swells  Less ADH released  Less reabsorption of water in kidneys

 85% water reabsorbed in proximal tubule  Without ADH, 15% of water will be lost  Makes upper part of distal tubule and collecting duct permeable to water  NaCl creates osmotic pressure  draws water out of nephron

 Kidneys regulate blood pressure by adjusting for blood volumes  Aldosterone  a hormone produced in the adrenal cortex which acts on the nephrons to increase Na+ reabsorption.  As Na+ is reabsorbed, chloride ions and water follow passively  blood volume increases

 Blood pressure detected by juxtaglomerular apparatus  Specialized cells release renin which converts angiotensinogen into angiotensin  Angiotensin  Constricts blood vessels (increases blood pressure)  Initiates release of aldosterone from adrenal cortex

 Kidneys are affected when other systems break down  Kidney disorders can be detected by urinalysis  Important to remember that constituents of urine may change throughout the day due to Dietary intake Physical activity Stress Fatigue  Urine is always more concentrated first thing in the morning. (Why?)

 Bacterial or viral infection of the bladder  cystitis  Infection of the urethra  urethritis  More common in women than in men  Symptoms:  Burning sensation during urination  Frequent urination  Bloody or brown urine  Can result in permanent damage to kidneys, possible kidney failure

 Precipitation of mineral solutes from the blood  Usually due to excess calcium in urine  Alkaline or acid stones  Sharp  cause extreme pain as they move through or lodge in tissues  Depending on size of stones, treatment may involve:  Antibiotics  Ultrasound shock waves  Surgery

 Inadequate secretion of insulin from islet cells of pancreas  Proximal tubule can reabsorb 0.1% of blood sugar  More sugar remains in nephrons of people with diabetes mellitus  Osmotic gradient causes more water to be lost in urine

 Destruction of ADH-producing cells; OR  Destruction of nerve tracts between hypothalamus & pituitary  ADH levels drop, urine output increases (up to 4- 8 L per day)

 Aka: Nephritis  Describes many diseases characterized by inflammation of the nephrons  Eg.) microbes destroy blood vessels of the glomerulus  affects permeability  Proteins pass into nephron, can’t be reabsorbed  Creates osmotic gradient

 Kidneys cannot maintain homeostasis due to the damage to their nephrons  A person can survive on one-third of one kidney  any less requires medical intervention  Dialysis  Transplantation

 The diffusion of dissolved substances through a semi-permeable membrane  Hemodialysis  Uses an artificial membrane in an external device hooked up to an artery and a vein in a person’s arm  Peritoneal Dialysis  Uses the lining of the intestines (peritoneum) as the membrane  Dialysis solution (dialysate) is introduced to the abdominal cavity, where capillaries can help to filter the blood

 Individuals with 10% or less kidney function need to have a kidney transplant  Success rate is high  Better success from living donors than from cadavers  Tricky – most anti-rejection drugs cause kidney damage