Excretory System (sometimes called Urinary System) Function and Parts http://www.youtube.com/watch?v=chhNaLi9P3E

Body Water Balance Drinking & eating provides water Kidney conserves water so output = intake

Why is excretion necessary? In order for cells to stay alive, they must continually intake water and other molecules. The cells would continue to get bigger and bigger if they only took in molecules They must also export molecules These molecules may be important signaling molecules such as hormones, or they may be molecules of glucose on their way to other cells, or they may be waste products of cellular metabolism that cells need to dispose.

Waste Products Carbon dioxide – a waste product of cellular respiration is dumped into the blood stream and eventually removed by the lungs Ammonia (NH3) is removed through water This waste comes from the cell’s breakdown of old proteins In these high physiological concentrations, it is poisonous to the cells and must be removed

Removal of Ammonia Once excreted into the blood stream by cells, it is carried to the liver where it is converted from ammonia into urea which is much less toxic It is then carried from the liver to the kidneys where it is removed

The Job of the Kidneys They are responsible for cleaning the blood by removing metabolic wastes, excess solutes, and excess water and excreting them as urine Besides removing urea, it also removes excess salts or glucose, the remnants of drugs (rationale for urine tests), and excess water.

Regulation of Water Levels If the blood becomes too dilute or too concentrated with solutes, then it can interfere with normal cellular activity. The kidneys are able to regulate water concentration in the blood by removing excess water if the blood is too dilute, or conserving water in the blood if it is not dilute enough

Regulation of Water Levels If the blood becomes too dilute or too concentrated with solutes, then it can interfere with normal cellular activity. The kidneys are able to regulate water concentration in the blood by removing excess water if the blood is too dilute, or conserving water in the blood if it is not dilute enough

Kidney Functions Filter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine Regulate volume and chemical makeup of the blood Maintain the proper balance between water, electrolyte salts, and acids and bases

Other kidney functions Gluconeogenesis during prolonged fasting Production of rennin to help regulate blood pressure and erythropoietin to stimulate RBC production Activation of vitamin D

The Hard-working Kidneys The two kidneys in the body receive between 180 – 220 liters of blood per day – about the volume of a car! Because the body has only about 5.6 liters of blood, your blood runs through the kidneys to be cleaned about once every four minutes. http://youtube.com/watch?v=wdBsm8E1wuM&feature=related

Kidney Location and External Anatomy

The Kidney http://youtube.com/watch?v=glu0dzK4dbU&feature=related

The Kidney

The Kidney http://www.youtube.com/watch?v=vEXx5YLcGmQ&feature=related

The nephron The nephron is the functional unit of the kidney Each region is composed of cells suited to perform specific transport functions Distal convoluted tubule Proximal convoluted tubule Collecting duct Ascending thin limb of loop of Henlé Ascending thick limb of loop of Henlé

The Kidney

Structure of the Bowman’s (glomerular) capsule Parietal layer of glomerular capsule Afferent arteriole Juxtaglomerular cell Capsule space Efferent arteriole Proximal convoluted tubule Endothelium of glomerulus Podocyte Pedicel http://www.youtube.com/watch?v=_XL_uxFseYQ&feature=related

Formation of Urine The kidneys filter the body’s entire plasma volume 60 times each day The filtrate: Contains all plasma components except protein Loses water, nutrients, and essential ions to become urine The urine contains metabolic wastes and unneeded substances

Formation of Urine If there is too much water in the blood, then it is removed and put in urine. If there is not enough water in the blood, the kidneys will not remove any. If there is too much urea or other solutes in the blood, the kidneys will remove these excess solutes. By regulating solute numbers and water volume, the kidneys normally maintain homeostasis in blood solute concentration.

Mechanisms of Urine Formation Urine formation and adjustment of blood composition involves three major processes Glomerular filtration Tubular reabsorption Secretion

Nephron Recycling: Overview

Water Reabsorption in Descending Loop of Henle Countercurrent multiplier exchange Medullary osmotic gradient H2OECFvasa recta vessels

Factors that affect kidney function Antidiuretic hormone (ADH) – prevents excess water loss from kidneys Alcohol – inhibits secretion of ADH = more urine volume, leading to dehydration Aldosterone – prevents excess loss of sodium and water from kidneys Caffeine – increases rate of salt and water loss from kidneys Increased blood pressure – increase rate of water loss from kidneys.

Normal kidneys Kidneys beyond help! Chronic kidney disease Normal kidneys Kidneys beyond help! L RAS End-stage kidneys

The Urinary System Part B 25 The Urinary System Part B

Tubular Reabsorption All organic nutrients are reabsorbed Water and ion reabsorption is hormonally controlled Reabsorption may be an active (requiring ATP) or passive process

Sodium Reabsorption: Primary Active Transport Sodium reabsorption is almost always by active transport Na+ enters the tubule cells at the luminal membrane Is actively transported out of the tubules by a Na+-K+ ATPase pump

Sodium Reabsorption: Primary Active Transport From there it moves to peritubular capillaries due to: Low hydrostatic pressure High osmotic pressure of the blood Na+ reabsorption provides the energy and the means for reabsorbing most other solutes

Routes of Water and Solute Reabsorption Figure 25.11

Osmotic Gradient in the Renal Medulla

Loop of Henle: Countercurrent Multiplier The descending loop of Henle: Is relatively impermeable to solutes Is permeable to water The ascending loop of Henle: Is permeable to solutes Is impermeable to water Collecting ducts in the deep medullary regions are permeable to urea

Loop of Henle: Countercurrent Exchanger The vasa recta is a countercurrent exchanger that: Maintains the osmotic gradient Delivers blood to the cells in the area

Loop of Henle: Countercurrent Mechanism Figure 25.14

Formation of Dilute and Concentrated Urine Figure 25.15a, b

Diuretics Chemicals that enhance the urinary output include: Any substance not reabsorbed Substances that exceed the ability of the renal tubules to reabsorb it Substances that inhibit Na+ reabsorption

Diuretics Osmotic diuretics include: High glucose levels – carries water out with the glucose Alcohol – inhibits the release of ADH Caffeine and most diuretic drugs – inhibit sodium ion reabsorption Lasix and Diuril – inhibit Na+-associated symporters

Renal Clearance The volume of plasma that is cleared of a particular substance in a given time Renal clearance tests are used to: Determine the GFR Detect glomerular damage Follow the progress of diagnosed renal disease

Renal Clearance RC = UV/P RC = renal clearance rate U = concentration (mg/ml) of the substance in urine V = flow rate of urine formation (ml/min) P = concentration of the same substance in plasma

Chemical Composition of Urine Urine is 95% water and 5% solutes Nitrogenous wastes include urea, uric acid, and creatinine Other normal solutes include: Sodium, potassium, phosphate, and sulfate ions Calcium, magnesium, and bicarbonate ions Abnormally high concentrations of any urinary constituents may indicate pathology

Micturition (Voiding or Urination) The act of emptying the bladder Distension of bladder walls initiates spinal reflexes that: Stimulate contraction of the external urethral sphincter Inhibit the detrusor muscle and internal sphincter (temporarily) Voiding reflexes: Stimulate the detrusor muscle to contract Inhibit the internal and external sphincters

Kidney dissection http://www.youtube.com/watch?v=JBsUUYZKAlU&feature=related http://www.youtube.com/watch?v=YnU6REgJU74&feature=related http://www.youtube.com/watch?v=AU-CGGzcSRg&feature=related