Unit 4: Human Systems BIOLOGY 20 Excretory System Unit 4: Human Systems BIOLOGY 20

10 minutes Find out all you can about the excretory system function!!

Human Excretory System Structures: Kidney Renal Artery Renal Vein Ureter Bladder Urethra Inferior Vena Cava Aorta

Urinary System Renal Arteries branch off of the aorta and carry blood to the kidneys Ureters carry the waste to the bladder The bladder stores maximum 600mL of urine; a sphincter muscle prevents the urine from entering the urethra until urination Upon urination, the urine enters the urethra and is excreted

Structure of the Kidneys There are three basic structures found within the kidneys: (1) The Cortex - Outer layer of connective tissue (2) The Medulla - Inner layer, found below the cortex (3) Renal Pelvis - Joins the kidney with the ureter (hollow)

Real Kidney

Nephrons Nephrons are the functional units of the kidneys (1 000 000 slender tubes) Nephrons are supplied with blood from the afferent arterioles (3), which branch into the capillary bed or the glomerulus (2) Filtered blood is carried away from the nephron via the efferent arterioles (4) The glomerulus is the interface between the circulatory system and the excretory system The Bowman’s capsule (1) surround each funnel like part of the nephron The Bowman’s capsule, the afferent and efferent arterioles are all found in the cortex

The Bowman’s Capsule The Bowman’s capsule is the place where waste products pass from the blood to the kidneys to form urine

Proximal and Distal Tube and Loop of Henle The Bowman’s capsule tapers into a small thin tubule, called the proximal tubule (5) The waste is then carried to the Loop of Henle (8), which descends into the medulla Urine then moves through the distal tubule (6) and then into the collecting ducts (7), which collect the urine from many nephrons, which merge in the pelvis of the kidney

Review http://www.youtube.com/watch?v=glu0dzK4dbU http://www.youtube.com/watch?v=4-15JUVxAm8

Importance of The Kidneys The cells of your body obtain energy by converting complex molecules into simpler ones Most of these molecules are toxic to your body The body must have systems which remove waste, e.g.. Liver, Large Intestine, Kidneys

Deamination Deamination is a process that occurs in the liver to help remove a toxic substance Recall protein contains a nitrogen molecule, which must be removed upon protein break down The by-product of deamination is ammonia, which is highly lethal Two molecules of ammonia and CO2 combine to form urea or uric acid, main components of urine, which is a less toxic substance to the body Urea is filtered through the glomerulus and in to the nephron

Formation of Urine Urine formation depends on three functions: (1) Filtration: Accomplished by the movement of fluids from the blood into the Bowman’s capsule (2) Reabsorption: Involves the transfer of essential solutes and water from the nephron back into the blood USEFUL SUBSTANCES THE BODY NEEDS Secretion: Involves the movement of materials from the blood back into the nephron WASTE PRODUCTS THE BODY DOES NOT NEED

Nephron Diagram and Function Draw a diagram of the nephron with the following labels AND list the function of each structure on your diagram Renal artery, renal vein Afferent arteriole, efferent arteriole Glomerulus Bowman’s Capsule Proximal and Distal tubule Loop of Henle (descending and ascending) Collecting Ducts Capillary Network

Filtration Each nephron has an independent blood supply In the glomerulus, a high pressure filter is created (8 kPa as opposed to 2 kPa) Filtration occurs when dissolved solutes pass from the walls of the glomerulus into Bowman’s capsule, moving from an area of high pressure to low pressure Dissolved solutes include water, NaCl, glucose, urea, amino acids, and hydrogen ions Not all materials in the blood will be filtered into Bowman’s capsule (i.e. blood cells, plasma proteins and platelets)

Filtration

Reabsorption Why is it important? Think about this…. 600mL fluid flows through kidneys each minute 120mL of that fluid is filtered into nephron If none of this fluid was reabsorbed, you would form 120mL of fluid every minute (remember your bladder is full at 600mL)! You would have to drink 1 L of water every 10 minutes to maintain homeostasis! AND you would have to “pee” every 5 minutes!! About 119mL of fluid and solutes is reabsorbed, the remaining 1mL forms urine

How Does Reabsorption Occur? Reabsorption occurs when solutes are pumped back into the blood from the nephron Occurs by both active and passive transport in the proximal tubule Na+ is actively pumped out of the nephron, causing Cl- , HCO3- to be drawn out of the nephron due to attractive forces Glucose and amino acids are reabsorbed Water follows (osmotic gradient) Energy for active transport is supplied via cell respiration, and is limited Thus excess salts/glucose remain in the nephron and are urinated out of the body

Filtration and Reabsorption

Secretion Secretion is the movement of wastes from the blood to the nephron Examples include nitrogen-containing wastes, histamines, excess H+ ions and other minerals Drugs, alcohol Secretion occurs using active transport

Secretion

Water Balance Urine output depends on water input and water use An increase in water intake will increase water output Exercise, or a decrease in water will cause a decrease in water output

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