Biology 2201 11.3 The Excretory System EXCRETORY SYSTEM 1
Excretory System How does the excretory system maintain homeostasis? It regulates heat, water, salt, acid base concentrations and metabolite concentrations ORGANS OF EXCRETION Skin and associated glands: Removes heat and salts Lungs: Removes carbon dioxide 2
Organs of Excretion Kidneys (part of the Urinary system): MAJOR excretory organs that excrete metabolic wastes, regulate water salt balance and acid base balance. Liver: Removes metabolic wastes Urinary System 3
PARTS OF THE URINARY SYSTEM (pg. 374) Kidneys: filter blood to produce urine. Ureters: carry urine from the kidneys to the urinary bladder PARTS OF THE URINARY SYSTEM (pg. 374) Urinary Bladder: stores urine. Urethra: carries urine from the bladder to the outside of the body. 4
IMPORTANT BLOOD VESSELS Renal Artery: carries contaminated blood into the kidney. Renal Vein: carries purified blood from the kidney and returns it back into circulation by way of the inferior vena cava. The Kidney 5
KIDNEY PARTS (pg. 375) Cortex: the outer part of the kidney, where the glomerulus, Bowman s capsule, proximal tubule and distal tubule of nephrons are located. Medulla: the inner part of the kidney, where the loop of Henle and the collecting ducts of nephrons are located Pelvis: part of the kidney where urine accumulates before it enters the ureters MAJOR FUNCTIONS OF KIDNEYS 1. Filters blood of: Urea formed in the liver from the breakdown of ammonia. When proteins are broken down in humans, a compound called ammonia (NH3) is formed. Ammonia is highly toxic, so it is converted into urea by the liver, and this urea is the primary nitrogenous waste found in urine. Creatinine formed in the muscles Uric Acid formed as a result of the breakdown of nucleic acids (DNA and RNA) 6
MAJOR FUNCTIONS OF KIDNEYS 2. Controls the balance of water in our bodies 3. Regulates ph of the blood 4. Regulates the concentration of dissolved ions in the blood MAJOR FUNCTIONS OF KIDNEYS 5. Secretes a hormone that causes a production of red blood cells 6. Activates Vitamin D production in the skin 7
NEPHRONS (pg. 375) Tiny filtering units called nephrons fill the cortex and medulla of the kidney. Each kidney contains 1 to 1.25 million nephrons. Each nephron is composed of 6 main parts: glomerulus,bowman s capsule, proximal tubule, loop of Henle, distal tubule & collecting duct 8
Parts of a nephron: 1. glomerulus the blood vessel inside the Bowman s capsule from which water, salts, nutrient molecules, and waste molecules leave the blood to be filtered by the kidney 2. Bowman s capsule the receiving end of a renal (kidney) tubule at which water and small solutes from the blood enter the proximal tubule from the glomerulus 3. proximal tubule the tube between the Bowman s capsule and the loop of Henle. Reabsorption of important nutrients like water, glucose, and amino acids begins here. Parts of a nephron: 4. loop of Henle the long loop of the nephron that extends into the medulla of the kidney between the proximal tubule and the distal tubule. The main function of the loop of Henle is to remove water from the filtrate. 5. distal tubule the tube that connects the loop of Henle to the collecting duct. The main job of the distal tubule is to secrete material like hydrogen ions, creatinine, and drugs out of the blood into the filtrate. 6. collecting ducts carries urine to renal pelvis 9
1. Filtration: Blood travels from the renal artery, to an arteriole and then into the glomerulus, a mass of capillaries surrounded by the Bowman s capsule. Blood pressure forces some plasma of the blood, containing both waste and useful material, into the Bowman s capsule. This material is called the nephric filtrate. 10
The filtrate contains such things as: water, urea, uric acid, salt, glucose, amino acids, ions and vitamins. 2. Re absorption: From the Bowman s capsule the filtrate is pushed into the proximal tubule. The process of re absorption, of useful materials within the filtrate, into the capillary network that surrounds the nephron than begins. 11
Reabsorption occurs by osmosis, diffusion, and active transport Reabsorbed materials include water, glucose, amino acids, ions and vitamins When the filtrate reaches the end of the distal tubule the solution is isotonic (the filtrate and the surrounding cells have the same concentration of water and solutes). 12
The filtrate then moves down the descending loop of Henle; as the loop descends further into the inner medulla, sodium concentrations in the surrounding tissue increase which draws water out of the filtrate (by osmosis). At the bottom of the loop sodium ions in the filtrate are at high concentration and therefore diffuse out of the tubule. 13
Positive sodium ions are followed by negative chloride ions Water cannot reenter the ascending loop because this loop is impermeable to water 3. Secretion: Occurs in the distal tubule Involves active transport of substances from the capillaries into the tubule Substances include hydrogen ions, creatinine and drugs 14
4. Elimination: The fluid than enters the collecting duct as urine. It passes through the pelvis into the ureter. Most of the water, ions and useful nutrients (glucose, amino acids) have been reabsorbed. Path of filtrate through nephron: Bowman s capsule proximal tubule loop of Henle distal tubule collecting duct 15
Control of Water Balance When water levels are too low: The hypothalamus stimulates the pituitary gland to secrete a hormone called anti diuretic hormone (ADH). ADH travels through blood to kidneys. Control of Water Balance 2) ADH increases the permeability of the tubules and collecting ducts 3) More water is reabsorbed into the blood so the urine is more concentrated 16
Control of Water Balance When water levels are too high: Hypothalamus doesn t stimulate ADH secretion Little water is reabsorbed into the blood so the urine is more dilute. Disorders of the Urinary System 1. Urinary tract infections - if bladder is infected, the infection is termed cystitis. If only the urethra is infected, the term is urethritis. - urinary tract infections are more common in women than men - symptoms include painful urination, a need to constantly urinate, brown or bloody urine, fever, nausea, etc. 17
Disorders of the Urinary System 2. Kidney stones - chemicals in urine precipitate and form crystals, mostly calcium oxalate - more common in men than women - factors that cause stones include urinary tract infections, insufficient water intake, low activity level, and/or too much vitamin C or D - symptoms include severe pain, blood in the urine, nausea - small stones can pass in urine, but larger ones need to be broken down (either by chemicals or sound) before they can pass. In extreme cases, they have to be removed by surgery Disorders of the Urinary System 3. Renal failure - renal failure the condition in which an individual s kidneys no longer function and waste accumulates in the blood - if waste levels get too high, a person can suffer loss of consciousness and finally heart failure - hemodialysis medical treatment of kidney failure; the process of removing blood from an artery, purifying it, adding vital substances and returning it to a vein 18