Osmoregulation and Excretion The Kidney Osmoregulation and Excretion Crash course video link below: https://www.youtube.com/watch?v=WtrYotjYvtU

IB Learning Objectives Define excretion.

Overview: A Balancing Act Physiological systems of animals operate in a fluid environment Relative concentrations of water and solutes must be maintained within fairly narrow limits

Excretion definition – Chemical reactions of metabolism produce byproducts (waste). These byproduct can be toxic if the accumulate Excretion is the removal from the body the waste products of metabolism.

Osmoregulation, Homeostasis and Excretion Excretion plays an important role in maintaining homeostasis. Associated with both homeostasis and excretion is the process of osmoregulation.

IB Learning Objective Define osmoregulation

Osmoregulation and Excretion Osmoregulation regulates solute concentrations and balances the gain and loss of water Excretion gets rid of metabolic wastes

Osmosis Cells require a balance between osmotic gain and loss of water

Water balance in a kangaroo rat (2 mL/day) Water balance in a human LE 44-5 Water balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day) Ingested in food (750 mL) Ingested in food (0.2 mL) Ingested in liquid (1,500 mL) Water gain Derived from metabolism (1.8 mL) Derived from metabolism (250 mL) Feces (0.09 mL) Feces (100 mL) Urine (1,500 mL) Urine (0.45 mL) Water loss Evaporation (1.46 mL) Evaporation (900 mL)

4 3 (L/100 kg body mass) Water lost per day 2 1 Control group LE 44-6 4 3 (L/100 kg body mass) Water lost per day 2 1 Control group (Unclipped fur) Experimental group (Clipped fur)

An animal’s nitrogenous wastes reflect its phylogeny and habitat The type and quantity of an animal’s waste products may greatly affect its water balance Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids

Forms of Nitrogenous Wastes Different animals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acid

LE 44-8 Proteins Nucleic acids Amino acids Nitrogenous bases —NH2 Amino groups Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Ammonia Urea Uric acid

Urea The liver of mammals and most adult amphibians converts ammonia to less toxic urea The circulatory system carries urea to the kidneys, where it is excreted

IB Learning Objective Draw and label a diagram of the kidney. Include the cortex, medulla, pelvis, ureter and renal blood vessels.

Excretory Processes Most excretory systems produce urine by refining a filtrate derived from body fluids Key functions of most excretory systems: Filtration: pressure-filtering of body fluids Reabsorption: reclaiming valuable solutes Secretion: adding toxins and other solutes from the body fluids to the filtrate Excretion: removing the filtrate from the system

LE 44-9 Capillary Filtration Excretory tubule Reabsorption Secretion Filtrate Reabsorption Secretion Urine Excretion

The Kidney The kidneys regulate the amount of water, salts and other substances in the blood. The kidneys are fist-sized, bean shaped structures that remove nitrogenous wastes (urine) and excess salts from the blood Because the kidney regulates both salt and water concentration in the blood it is the central organ that controls osmoregulation.

The Kidney

The urinary system: The pathway of Urine to the outside the body. The ureters are tubes that carry urine from the pelvis of the kidneys to the urinary bladder. The urinary bladder temporarily stores urine until it is released from the body. The urethra is the tube that carries urine from the urinary bladder to the outside of the body. The outer end of the urethra is controlled by a circular muscle called a sphincter. These parts work together and are part of the urinary system.

Blood vessels of the mammalian kidney Each kidney is supplied with blood by a renal artery and drained by a renal vein Animation: Nephron Introduction

The Kidney

The kidney structure Each kidney is composed of three sections: The cortex is where the blood is filtered. The medulla contains the collecting ducts which carry filtrate (filtered substances) to the pelvis. The pelvis is a hollow cavity where urine accumulates and drains into the ureter.

The Kidneys Cortex Renal artery Medulla Renal vein Ureter To the bladder

The medulla and cortex The outer cortex and inner medulla are made up of a million or more tiny tubules called nephrons. Part of a nephron is in the medulla the other part is in the cortex. Nephrons is a thin walled tubules about (3 cm) long.

LE 44-13 Posterior vena cava Renal artery and vein Kidney Renal medulla Aorta Renal cortex Ureter Renal pelvis Urinary bladder Urethra Excretory organs and major associated blood vessels Ureter Kidney structure Section of kidney from a rat Juxta- medullary nephron Cortical nephron Afferent arteriole from renal artery Glomerulus Bowman’s capsule Proximal tubule Renal cortex Peritubular capillaries Collecting duct SEM 20 µm Efferent arteriole from glomerulus Renal medulla Distal tubule To renal pelvis Branch of renal vein Collecting duct Descending limb Loop of Henle Nephron Ascending limb Vasa recta Filtrate and blood flow

The Kidneys Structure of the Kidneys Kidney Nephron Kidneys are made up of nephrons. Blood enters the nephron, where impurities are filtered out and emptied into the collecting duct. The purified blood leaves the nephron through the renal vein.

IB Learning Objective Annotate a diagram of a glomerulus and associated nephron to show the function of each part.

Parts of the Nephron Each nephron consists of the following parts: 1) glomerulus ; 2) Bowman’s capsule ; 3) proximal tubule ; 4) loop of Henle ; 5) distal (convoluted) tubule ; 6) collecting duct.

Capillaries Bowman’s capsule Glomerulus Collecting duct Vein Artery Loop of Henle Bowman’s capsule Glomerulus Capillaries Collecting duct To the ureter Kidneys are made up of nephrons. Blood enters the nephron, where impurities are filtered out and emptied into the collecting duct. The purified blood leaves the nephron through the renal vein.

Functions of the parts of the Kidney The glomerulus is a mass of thin-walled capillaries. The Bowman’s capsule is a double-walled, cup-shaped structure. The proximal tubule leads from the Bowman’s capsule to the Loop of Henle. The loop of Henle is a long loop which extends into the medulla. The distal tubule connects the loop of Henle to the collecting duct.

IB LEARNING OBJECTIVE Explain the process of ultrafiltration, including blood pressure, fenestrated blood capillaries and basement membrane

Five Steps in the Formation of Urine Ultrafiltration in the renal capsule Selective reabsorption in the proximal convoluted tubules Water conservation in the loop of henle (osmoregulation) Blood pH and ion concentration regulation in the distal convoluted tubule (osmoregulation) Water reabsorption in the collecting ducts. (osmoregulation)

Step 1: Ultrafiltration in the renul capsule. Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule This process is called Ultrafiltration because it is powered by pressure of the blood. The entire content of the blood is not forced out. The basement membrane of the of the capsule does not allow blood cells and proteins to enter the filtrate.

IB Learning Objective Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis and active transport.

Step 2 : Selective reabsorption in the proximal convoluted tubules The convoluted proximal tubules is the longest section of the nephron. The walls are one cell thick and they are packed with mitochondria. The cell membrane in contact with the filtrate is packed with microvilli to increase surface area for absorption.

Step 2 : Selective reabsorption in the proximal convoluted tubules (see figure 12.22 page 373) The proximal convoluted tubules absorb filtrate through the following mechanisms: Movement of water via osmosis Active transport of glucose and amino acids across membranes Movement of some minerals and ions via a combination of active transport, facilitated diffusion and some gas exchange of ions Diffusion of urea Movement of protein via pinocytosis (endocytosis)

Step 3 Water conservation in the loop of henle Urea is excreted from the body in solution, thus water loss is inevitable Water loss is minimized by having the solutes concentration in urine higher than the blood. The role of the loop of Henle is to maintain a high concentration of solutes in the medulla of the kidney The loop of henle has a descending and ascending limbs that parallels the blood supply.

LE 44-14 Proximal tubule Distal tubule NaCl Nutrients H2O HCO3– H2O K+ NH3 K+ H+ CORTEX Descending limb of loop of Henle Thick segment of ascending limb Filtrate H2O Salts (NaCl and others) HCO3– H+ Urea Glucose; amino acids Some drugs NaCl H2O OUTER MEDULLA NaCl Thin segment of ascending limb Collecting duct Key Urea Active transport Passive transport NaCl H2O INNER MEDULLA

IB LEARNING OBJECTIVE Explain the roles of the loop of Henle, medulla, collecting duct and ADH (vasopressin) in maintaining the water balance of the blood.

Step 3 Water conservation in the loop of henle figure 12.23 page 374 The descending limb is permeable so salt diffuses into the loop of Henle and water diffuses out into the medulla tissue. At the hairpin zone (base of the loop) water and salt diffuse into the medulla tissue. In the ascending limb of the loop of Henle, salt diffuses from the permeable loop tubule into the interstitial fluid of the medulla, but water is retained

Step 4: Blood pH and ion concentration regulation in the distal convoluted tubule The distal tubule cells are the same as in the proximal tubule (one cell thick, microvilli and lots of Mitochondria) The role of the distal tubule cells is to adjust the composition of the blood, in particular pH. Blood pH is initially buffered by blood proteins, but if it deviates from a pH of 7.4 the concentrations of Hydrogen ion (H+) and hydroxide (OH-) are adjusted Blood pH does not vary outside the range of pH 7.35 to 7.45, but urine pH ranges from 4.5 to 8.2.

Step 5: Water reabsorption in the collecting ducts. The collecting ducts are where the water content is regulated. When the water content of the blood is low the antidiuretic hormone (ADH) is secreted from the posterior pituitary gland. When the water is the blood is high, NO ADH is released.

Step 5: Water reabsorption in the collecting ducts. The permeability of the walls of the collecting ducts are variable. If ADH is present the walls of the collecting tubules become fully permeable. This allows water to be withdrawn from the filtrate of the tubule in the medulla. The water will be taken up and redistributed throughout the body. ADH is remove from the body by the kidney When no ADH is present the walls of the collecting duct become less permeable.

Kidney Animations/ tutorials http://www.biologymad.com/resources/kidney.swf http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter26/ http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter26/animation__micturition_reflex.html http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter27/ http://www.sumanasinc.com/webcontent/animations/content/kidney.html http://www.zerobio.com/target_practice_quiz/target_practice_quiz_kidney.swf Hormonal Control Animation http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter20/animation__hormonal_communication.html http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter20/animation__blood_sugar_regulation_in_diabetics.html

hypothalamus detect an increase in the osmolarity LE 44-16a Osmoreceptors in hypothalamus Thirst Hypothalamus Drinking reduces blood osmolarity to set point ADH Increased permeability Pituitary gland Distal tubule H2O reab- sorption helps prevent further osmolarity increase STIMULUS The release of ADH is triggered when osmo- receptor cells in the hypothalamus detect an increase in the osmolarity of the blood Collecting duct Homeostasis: Blood osmolarity

IB Learning Objective Explain the differences in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine.

Differences in the composition of blood plasma, glomerular filtrate and urine The composition excrete from urine is variable. Greatly influenced by six factors Diet (salt intake, protein consumed) Physical Activity Water intake Amount of sweating Environmental condition State of health (i.e. Diabetics)

Differences in the composition of blood plasma, glomerular filtrate and urine The composition of blood is constant Constancy is due to the efficiency of our homeostatic mechanisms

Differences in the composition of blood plasma, glomerular filtrate and urine The composition of glomerular filtrate (ultrafiltration of the glomerus) is constant Constancy is due to the ultrafiltration, the pressure of the blood, and the size of blood proteins that are too large to filter.

IB Learning Objectives Explain the presence of glucose in the urine of untreated diabetic patients.

The composition of the urine of a diabetic patient The disease known as diabetes – blood glucose levels are erratic and frequently above normal. A consequence to this elevated blood glucose level is the failure of the kidney tubules to reabsorb all the glucose forced out of the blood. Thus the urine of a diabetic generally contains a lot of glucose. Raise glucose level in the urine is a symptom of a patient being a diabetic.

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