12.1 Kidneys and Waste Excretion Unit D – Human Systems

Learning Objectives Covered in this Lesson Identify and describe roles of the principal structures in the excretory system. Describe the role of the kidney in excreting wastes and expelling them into the environment. Identify major structures of the nephron.

Anatomy of Urinary System renal artery carries oxygenated blood to the kidney renal veins carry deoxygenated blood from the kidney back toward the heart.

Waste material filtered from the blood by the kidney enters ureters. Ureters are tubes that carry urine from the kidney to the bladder.

urinary bladder holds urine until it fills to the point that it stretches, opening a sphincter muscle. Urine moves through sphincter into the urethra, Urethra is a tube that carries urine from the bladder to the exterior of the body.

Role of Kidneys Removing waste materials from blood (urea and uric acid) Balance blood pH Maintain water balance in blood

Eating too much protein? Modern human diet contains more protein than necessary to maintain body tissue cells. The excess protein in our diet has its Amino groups removed from its amino acids (building blocks of proteins) in the liver.

Deamination The removal of amino groups from amino acids producing ammonia gas. Ammonia is toxic and must be converted to a less toxic form, Urea.

Uric acid, another nitrogen containing waste product, produced from the breakdown of nucleic acids.

Balancing Blood pH Secrete and release H + and HCO 3 - ions in order to keep blood pH neutral.

Maintaining water balance Reabsorbs and secretes water to ensure your body has enough water.

Nephron Small “functional units” of the kidney. Approximately 1 million nephrons make up one kidney. Is a series of capillaries and tubes that filter and clean blood.

Blood Supply to the Nephron Renal arteries branch off into afferent arterioles that supply the nephrons with blood. Afferent arterioles branch into a smaller knot of capillaries called the glomerulus.

The blood leaves the nephron by way of the efferent arterioles, which are carried to the peritubular capillaries, that are wrapped around the tubes of the nephron. The peritubular capillaries connect to the renal vein and take blood back to the heart.

Parts of the Nephron Glomerulus is surrounded by a funnel called the Bowman’s capsule. This is where wastes leave the blood stream and is filtered. Bowman’s capsule is attached to the proximal tubule, which is where nutrients are reabsorbed back into the bloodstream.

The Loop of Henle connects the proximal tubule to the next section of the nephron, the distal tubule. The distal tubule is the site of secretion of waste products out of the blood, and passes urine to the collecting ducts. Many collecting ducts join together and pass urine to the ureter.

Student Tasks for Lesson Label “Urinary Structures” diagram (Pg 379). Label diagram of a Nephron, outlining the major function of each part. Complete #1-3 on page 380. Complete #1-2 on page 386.