Human Excretory System   I.         The human excretory system has two major excretory functions: A.    Remove cellular wastes B.     Maintain homeostasis -keep a stable internal environment

There are four types of waste products: A.    CO2 B.     H2O C.    Urea (nitrogenous waste) D.    Mineral salts There are four organs of excretion: A.   Liver B.    Kidneys C.    Lungs D.    Skin

Liver A.    The liver is a large, brown gland located underneath the diaphragm. B.    The liver has three jobs: 1.      Detoxification - The liver detoxifies blood that flows through it. Harmful substances such as bacteria, drugs, alcohol, and hormones (steroids) are changed into inactive or less poisonous forms. These less toxic forms are returned to the blood and eventually excreted by the kidney.

The liver is responsible for the breakdown of worn-out red blood cells. In the liver excess amino acids are broken down into urea. Urea will enter the blood to be taken to the kidney from which it is excreted. It is important to remember that the liver makes urea not the kidney. The kidney will filter urea out as waste.  

Kidney – Components of the Urinary System A.    The kidneys are paired, bean-shaped organs approximately 10 cm in length. The kidneys lie in a relatively unprotected spot against back muscles on either side of the vertebral column. B.     The bladder stores urine. It is a single, midline, muscular organ which lies in the lower abdomen above the pubic bone. C.    The tube that carries urine from the kidney to the bladder is the ureter. The tube that carries urine from the bladder to the outside world is the urethra. It is found in both male and females. In males, however, it also carries semen.

Anatomy of the urinary system:   Kidney (makes urine) Ureter (transports urine from kidney to bladder) Bladder (stores urine) Urethra (tube for exit)

Anatomy of the Kidney – The kidney has three parts Anatomy of the Kidney – The kidney has three parts. In a length-wise section of the kidney you can see the cortex, medulla, and pelvis. Cortex (blood filtered here) Pelvis (urine collects here) Medulla (collecting ducts) Ureter

http://www.youtube.com/watch?v=WtrYotjYvtU VII. Functions of the Kidney A.     The kidney removes wastes (urea) from blood. B.     The kidney controls the concentration of most of the constituents of body fluid. C.     Higher magnification of the kidney reveals that the kidney is made up of millions of small units called nephrons. Nephrons are responsible for filtering of the blood. Nephrons are considered the functional units of the kidney. D.     A nephron is composed of a series of tubules which filter blood.

Nephron: Glomerulus Bowman’s capsule Renal artery Renal vein Loop of Henle Capillaries – takes out “good stuff” water, glucose, amino acids) Collecting duct (to renal pelvis and ureter) – carries salts and urea

Bowman’s Capsule and Glomerulus:   Bowman’s capsule Glomerulus H2O, Glucose, Amino acids, Urea, Salts

START At one end of the nephron is Bowman’s capsule, which leads into a system of tubules which eventually empty filtrate into the Collecting duct.   In the nephron, blood from an arteriole off of the renal artery enters the Bowman’s capsule and forms a tuft (ball) of capillaries called a glomerulus. Another arteriole exits Bowman’s capsule and forms a capillary network over a nephron’s tubules. The capillaries eventually unite to form a venule which contains filtered blood exiting the nephron. Venules will return filtered blood to the systemic circulation via the renal vein. END

How is blood filtered? In the Bowman’s capsule, filtrate from blood (liquid part of the blood minus the large proteins and cells) passes from capillaries to space in Bowman’s capsule. The filtrate travels through the tubules of the nephron. As it does, H2O, glucose, and amino acids are reabsorbed back into the capillary network around the tubules and returned to the bloodstream. Wastes, such as urea, H2O, and mineral salts, stay in the tubule and are deposited as urine in the collecting duct. From the collecting duct urine is deposited in the pelvis. The ureter takes the urine from the pelvis to the bladder. On occasion, the urine exits the body from the bladder through the urethra.

Lungs A.     CO2 and H2O which are waste products of respiration diffuse from the blood into the alveoli. These gases are removed from the body when you exhale.  

Skin A.     The skin secretes sweat. Sweat is composed of 98% H2O and 2% salts and urea. B.     The skin is divided into two layers: epidermis and dermis. C.     There are four functions of the skin: 1.      Excretes sweat (urea) 2.      Protection 3.      Prevents dehydration 4.      Temperature regulation - evaporation of water on body cools off body

Skin: