The Excretory System

Excretory System Some call it the “urinary system”, but more than just urine is excreted from our bodies Excretion = removing unnecessary components from an organism Examples: Lungs excrete CO2 Skin excretes ions/salts in the form of sweat Kidneys excrete urine We are gong to focus on this part of the excretory system

Major Function Disposing of wastes and excess ions Regulation of blood volume and chemical makeup Regulation of blood pressure Manufacturing and storage of urine

Organs Kidney Ureters Urinary Bladder Urethra Form urine Tubes that connect kidney to bladder and transport urine Urinary Bladder Store urine Urethra External opening to the body where urine passes In males, the urethra does double duty and can pass semen AND urine

Kidneys Located in the upper lumbar region Protected by the 12th rib Adrenal gland sits atop the kidney When cut lengthwise, it has 3 regions

Kidney-Regions Renal cortex Renal medulla Renal pelvis Outer region Contains “medullary pyramids” Renal pelvis Connects to ureters that will send urine to the bladder

Nephrons Each kidney contains over a million nephrons Nephron = structural and functional unit of the kidney Responsible for forming urine

Nephron Each nephron consists of 2 main structures Glomerulus Knot of capillaries Renal tubule Glomerular capsule Proximal convoluted tubule Loop of Henle Ascending and descending loops Distal convoluted tubule Collecting duct

Urine Formation 3 processes Filtration Tubular reabsorption Tubular secretion Rule of thumb: whatever is not reabsorbed from the nephron will be found in the urine

Filtration The glomerulus acts as a filter and the filtrate goes into the glomerular capsule Will eventually be found in urine if not reabsorbed Filtration = nonselective passive process Only salts, glucose, urea, amino acids can pass through into the glomerular capsule Proteins and RBCs = too large

Tubular Reabsorption Begins as soon as the filtrate enters the proximal convoluted tubule and continues through all the tubes Salts, amino acids, and water are reabsorbed back into the bloodstream

Tubular Secretion Essentially reabsorption in reverse The body is trying to get rid of these substances Hydrogen, potassium, certain drugs Whatever is left in the nephron will go into the collecting duct and will eventually exit the body

What’s Next? The filtrate that passes through the collecting duct will drain into the renal pelvis It is called “urine” at this point This is connected to the ureters and will transport the urine to the urinary bladder When voided, the urine will pass through the urethra and into the outside world

Let’s Talk About Pee Every 24 hours, 1-1.8 liters are produced Urine = nitrogenous wastes and unneeded substances

Characteristics of Urine Generally clear and pale- to deep-yellow Why is urine yellow? From a pigment called urochrome that results from the body’s destruction of hemoglobin When formed, urine is sterile Means there is no bacteria Why does urine smell? The longer the urine sits, it gets exposed to bacteria and they eat the urine solutes and cause the ammonia odor

Characteristics of Urine Urine pH is slightly acidic, but this can vary based on diet Lots of protein and whole-wheat products? ACIDIC Vegetarian diet? BASIC

Characteristics of Urine Composition Sodium, potassium, urea, uric acid, creatinin, ammonia, bicarbonate ions Things that should NOT be found in urine: Glucose, blood proteins, RBCs, hemoglobin, WBCs, and bile