The Excretory System Chapter 36.3 Bio 392

 Excretion  the process of eliminating waste products of metabolism and other non-useful materials.  The major organs of the excretory system are the skin, the lungs, and the kidneys Bio 392

 The kidneys remove urea from the bloodstream, control the pH of the blood, and regulate the amount of water in the blood  Urea ◦ It comes from ammonia (NH 3 ) which is a very toxic compound ◦ Produced when the body breaks down proteins Bio 392

Kidney (Cross Section) Cortex Medulla Vein Artery Kidney Ureter Urinary bladder Urethra

 There are three main tubes that enter or leave the kidney ◦ Blood flows into the kidney through the renal artery ◦ Blood leaves the kidney through the renal vein ◦ The ureter carries the excess fluids (urine) to the urinary bladder Bio 392

 Inside the kidney is a very complex filtration system that is charge of cleaning the blood ◦ Removes excess salts, urea, and water ◦ Keeps vital nutrients, gasses, and cells Bio 392

 The functional part of the kidney  Tiny tubes that are surrounded by a tight ball of capillaries  Nephrons have different parts: ◦ Glomerulus ◦ Bowman’s capsule ◦ Loop of Henle ◦ Collecting duct Bio 392

Kidney Nephron Cortex Medulla Renal artery Renal vein Ureter To the bladder Bowman’s capsule Glomerulus Capillaries Collecting duct To the ureter Loop of Henle Artery Vein

 The glomerulus is a mesh-like ball of blood vessels ◦ It is here where everything leaves the blood (wastes, water, salts, nutrients,…) Bio 392

 Bowman’s capsule collects all of the materials that came out of the glomerulus ◦ It is like a cup connected to a tube  These materials are passed into the renal tubules ◦ As fluid moves through the renal tubules, nearly all the material first removed from the blood is put back into the blood by reabsorption  Reabsorption- the process of taking back useful materials that were removed during filtration Bio 392

 The loop of Henle is where the wastes are concentrated by the continued removal of water  The collecting duct is where the final result of filtration is done ◦ Carries the wastes to the ureter Bio 392

Filtration Most filtration occurs in the glomerulus. Blood pressure forces water, salt, glucose, amino acids, and urea into Bowman’s capsule. Proteins and blood cells are too large to cross the membrane; they remain in the blood. The fluid that enters the renal tubules is called the filtrate. Reabsorption As the filtrate flows through the renal tubule, most of the water and nutrients are reabsorbed into the blood. The concentrated fluid that remains is called urine.

 Ureters carry urine from the kidney to the urinary bladder  Urinary bladder – a hollow, muscular sac that stores urine  Can hold up to 0.6 L of urine  Urine exits the body through the urethra Bio 392

Kidney (Cross Section) Cortex Medulla Vein Artery Kidney Ureter Urinary bladder Urethra

 The hypothalamus monitors water content of the blood ◦ If the water amounts are low, it signal the pituitary gland to release antidiuretic hormone (ADH)  This signals the kidneys to reabsorb more water  Urine is more concentrate ◦ If water content rises in the blood, ADH is not released and more water is released through the urine  Urine is more dilute Bio 392