The Excretory System

The excretory system The excretory system includes the skin, lungs and kidneys which all release metabolic wastes from the body. The kidneys, skin and the lungs are the principle organs of excretion. These organs remove the harmful wastes of cellular respiration - CO 2 and metabolism of amino acids by the liver – Urea (nitrogenous waste product).

Organs of Excretion Kidney – main organ of excretion Lungs – removal of CO 2 from blood. Liver – breaks down excessive amino acids, and detoxifies many substances like, bacterial wastes, alcohol, drugs, etc… The Skin - Removes excess salts through sweat glands and excess heat through the water that accompanies the salt.

The kidney

The kidneys remove wastes and excess salts by filtering the blood. They produce a watery substance called urine. Within the urine can be found: urea, salts, blood cells, hormones, minerals. Kidneys control the amount of water leaving the body, in doing so they regulate your water and pH balance (homeostasis). At any given time 20% of your blood can be within your kidneys.

Kidney and bladder position

Cross section

The Kidney Outer (renal) Cortex – where blood is filtered. Renal medulla – contains the collecting ducts which carry the filtrate to the pelvis Renal Pelvis – a hallow cavity where urine accumulates and then drains into the ureter. The kidney contains approx. a million nephrons. These structures are the functional units within the kidney that remove waste while reabsorbing useful molecules and water.

X section to nephron

nephron

The Nephron

How the nephron works? Blood travels from renal artery, to capillaries, and then to the glomerulus for filtration. The pressure forces plasma and small particles out of the blood. This fluid, called the nephric filtrate, travels into the Bowman's capsule leaving large cell components in the capillaries. It next enters the proximal tubule. The fluid descends down the loop of Henle and turns back to the cortex with the distal tubule.

Blood vessels are in close contact with the tubules allowing for recovery of valuable water (osmosis) and food molecules (active transport). Tubular secretion occurs in the distal tubule where active transport pulls creatinine and other large waste molecule out of the blood and drains it into the collecting duct. The filtrate now called urine is sent to the renal pelvis.

filtration

Filtration & reabsorption

Finally- recap

Excretory System Disorders

Common Disorders UTI refers to urinary tract infection. It can occur in different places. Bladder  Cystisis Urethra  Urethritis They are more common in women because the urethral and anal openings are closer together, therefore it is easier for bacteria from the colon to enter the urethral opening causing infection.

Symptoms Painful urination (burning sensation) Frequent urination Bloody or brown urine A tender back Chills, fever, nausea If the infection reaches the kidneys it is referred to pyelonephritis. This can be caused by prostate obstruction (older men), or an infection, which traveled up from the bladder (young children). All UTIs are serious and can result in permanent damage to the kidneys, even kidney failure. Treatment is usually by antibiotics.

Kidney Stones Form when chemicals in the urine precipitate out and form crystals More common in men than in women Caused by: –UTI –Insufficient water consumption –Low activity levels –Too much vit. C and D

Symptoms include: –Severe pain in the lower back and adomen –Bloody urine –Nausea and vomiting Treatment: –Patients are asked to drink lots of water –Small stones can pass through the urinary tract on their own –Medication can help breakdown the crystals –Lithotripsy –Large stones may require surgery