Objectives 30.4 The Excretory System -Describe the structures of the excretory system and their functions. -Explain how the kidneys clean blood. -Describe how the kidneys maintain homeostasis.

What is Excretion? Excretion is the process by which metabolic wastes are eliminated.

Structures of the Excretory System The excretory system includes the skin, lungs, liver and kidneys.  

The Skin The skin excretes excess water, salts and a small amount of urea in sweat.  

The Lungs The blood transports carbon dioxide, a waste product of cell respiration, from the cells to the lungs.   When you exhale, your lungs excrete the carbon dioxide.

The Liver One of the liver’s functions is to convert ammonia, a byproduct of protein breakdown, into less toxic urea.   Urea is then transported through the blood to the kidneys for elimination from the body.

The Kidneys The kidneys remove excess water, urea and metabolic wastes from the blood in urine.

Path of waste from the kidneys… Urine travels from the kidneys to the ureters, into the bladder and out of the body via the urethra.

Excretion and the Kidneys The blood is filtered at the nephron. The nephron consists of a small, dense network of capillaries known as the glomerulus. This structure is known collectively known as Bowman’s capsule.  

Control of Kidney Function Hormones influence kidney function.   If you have not consumed enough fluids, your pituitary gland releases antidiuretic hormone (ADH) into your blood causing the kidneys to reabsorb more water. If the blood contains excess water, ADH secretion stops and more water is excreted.

Kidney Disorders Kidney Stones occur when substances such as calcium, magnesium, or salts in the urine can crystallize and form kidney stones. Kidney Failure occurs when the kidneys can no longer cleanse the blood and maintain homeostasis. urinary track infections: An infection of the kidney, ureter, bladder, or urethra. Proteinuria: the presence of abnormal quantities of protein in the urine, which may indicate damage to the kidneys Gout: a metabolic disease marked by a painful inflammation of the joints, deposits of urates in and around the joints, and usually an excessive amount of uric acid in the blood. Major nitrogenous end product of protein breakdown. Small quantities are normally found in human blood; in gout, levels are abnormally high.

Treatments: Dialysis: a procedure that is a substitute for many of the normal duties of the kidneys. Urinalysis: Urine is evaluated by its physical appearance (color, cloudiness, odor, clarity), Or its chemical and molecular properties or microscopic assessment.