Lecture 25: Urinary System PDF May 2024

Lecture 25: urinary system Announcements - Final Exam - When: Tuesday, May 14th 2024 - Time: 3:30 PM to 5:30 PM - Where: Thompson 104 - Prep Materials - Posted on Friday, May 10th 2024 - Exam Review Session - When: Monday, May 13th 2024 - Time: 3:00 PM to 5:00 PM - Will be Echo360 Recorded - If you...

Lecture 25: urinary system Announcements - Final Exam - When: Tuesday, May 14th 2024 - Time: 3:30 PM to 5:30 PM - Where: Thompson 104 - Prep Materials - Posted on Friday, May 10th 2024 - Exam Review Session - When: Monday, May 13th 2024 - Time: 3:00 PM to 5:00 PM - Will be Echo360 Recorded - If you have 3 exams tuesday 05/14/2024 - MUST fill out an exam conflict form with the Office of Registrar in Spire - Steps: Manage Classes > Class & Final Schedule > Final Exam Conflict One Minute Essay - Proteinuria is characterized as someone having protein in the fluid excreted from their body, which is considered to be abnormal. 1) Provide detail on the mechanism that prevents protein from undergoing filtration normally a) The glomerular filtration barrier (made up of a basement membrane, podocytes, and fenestrated endothelium) in the kidneys plays a crucial role in preventing the filtration of proteins from the blood into the urine. (.5 pts) b) These components work together to selectively allow the passage of small molecules (water, ions, glucose) while restricting the movement of larger ones, such as proteins. (.5 pts) 2) Hypothesize two reasons why someone would experience protein in their urine. a) Damage to the barrier 🡪 allowing proteins to pass through. (.5 pts) b) Overload of the Filtration System 🡪 mount of protein in the blood may exceed the kidney’s ability to reabsorb the amount that enters the filtration. (.5 pts) Review - Glomerular Filtration - The first step in making urine is to separate the liquid part of your blood (plasma), which contains all the dissolved solutes, from your blood cells. - The rate at which kidneys filter blood is called the glomerular filtration rate. - The main driving force for the filtering process, or outward pressure is the blood pressure as it enters the glomerulus (60 mmHg). - This is counteracted to some extent by inward pressure due to: - the hydrostatic pressure of the fluid within the urinary space (15 mmHg) - the pressure generated by the proteins left in the capillaries (28 mmHg). Clarification - Why is urine yellow? A review of RBC recycling - What is bile exactly? Tubular Reabsorption and Secretion - In TUBULAR REABSORPTION, substances to be RETAINED in the body (i.e., Filtrate to Blood) - In TUBULAR SECRETION, substances to be REMOVED from the body (i.e., Blood to Filtrate) - Definitions - Fluid inside the nephron is known as FILTRATE - Medium inside the peritubular capillaries is BLOOD - Fluid between the two is INTERSTITIAL FLUID or PERITUBULAR FLUID - Reabsorption - Active Reabsorption - Substances are transported by mechanisms involving active transport across one membrane and passive transport across another. - Remember active transport requires ENERGY - Water Reabsorption - Based on differences in osmolarity - As solute are transported in this increases the plasma osmolarity which result in water being reabsorbed - Passive Reabsorption - Secretion - - - Solutes are exiting the peritubular capillaries and entering the renal tubules. Follows the same processes of reabsorption, just in reverse Things actively secreted: - Potassium and Hydrogen ions - Waste products - Foreign products Regional Specialization of the Renal Tubules - Properties (osmotic pressure, transport proteins, etc.) of the tubule epithelium vary from region to region - Thus, the transported items and mechanisms are different in different regions Excretion - Excretion by the kidneys entails the elimination of solute and water from the body in the form of urine. - The rate at which a substance is excreted in the urine is an important quantity because it has a direct bearing on the volume and composition of the plasma. - For any substance, the quantity that is excreted over a period of time is determined by a simple rule: - Material that enters the lumen of the renal tubules is excreted unless it is reabsorbed. Clicker questions - What is the movement of filtered solutes and water from the lumen of the tubules to the plasma fluid compartment called? - b) Reabsorption Review - Osmolarity and the Movement of Water - Osmosis - Water diffuses down the concentration gradient - Water moves from area of low solute concentration to area of high solute concentration - Therefore in the case of renal process: we can assume water reabsorption follows solute reabsorption - Why does osmolarity matter and how do we regulate it? - Under normal conditions: Osmolarity of body fluids = 300 mOsm (300 milliosmoles of solute per liter of plasma) - This is also the osmolarity of cells. - Therefore, no osmotic force for water to move between fluid compartments - If osmolarity of the extracellular fluid does change however. The kidneys can compensate by regulating water reabsorption of the filtrate. - Water Reabsorption - Proximal convoluted tubules - 70% of filtered water is reabsorbed - - Not regulated (means it happens intrinsically) Distal tubules and collecting ducts - Location where most remaining water is reabsorbed - Regulated by ADH (vasopressin) - Regulated by Aldosterone Clicker Question - Application: A student in your physiology lab is thirsty and decides to sneak a drink of deionized (hypo-osmotic) water. The student drinks a fairly large quantity of this water in a short period of time. What will happen to the student’s cells? - a) it will cause the student’s cells to swell - - - - Water reabsorption in the proximal tubule (non-regulated) - REMEMBER: WATER REABSORPTION FOLLOWS SOLUTE REABSORPTION - The primary solute to follow is…. Sodium! (Na+) - Na+ is actively transported across the basolateral membrane; establishing an osmotic gradient for water reabsorption Water reabsorption in the distal tubule and collecting duct (regulated) - Water reabsorption in the DISTAL TUBULE is simply dictated by reabsorption of Na+ which is regulated by Aldosterone 🡨 More to come. - However, In order to allow for water reabsorption to occur in the COLLECTING DUCT we must create an osmotic gradient in the Medulla. - There is where the Loop of Henle SHINES! Establishment of the medullary osmotic gradient - Osmolarity of interstitial fluid of renal medulla varies with depth - Lower osmolarity near cortex - Greater osmolarity near renal pelvis - Gradient is critical to water reabsorption - Osmotic gradient is established by the countercurrent multiplier in the Loop of Henle - Ascending limb - Impermeable to water - Active transport of Na+, Cl–, and K+ - Descending limb - Permeable to water - No transport of Na+, Cl–, or K+ Result of countercurrent multiplier - Fluid in proximal tubule = 300 mOsm - Fluid in descending limb: osmolarity increases as it descends - - Osmolarity = interstitial fluid - Osmolarity > descending limb Fluid in ascending limb: osmolarity decreases as it ascends - Osmolarity < interstitial fluid - Osmolarity < descending limb Clicker question - Which of the following accurately describes the thick ascending limb of the loop of Henle? - d) impermeable to water and contains Na+/K+/Cl- cotransports - - Role of urea in the medullary osmotic gradient - A solute is necessary to support and maintain the gradient… - Urea - Generated by liver - Nitrogen elimination - Extremely water soluble - Transport of urea through UTA from filtrate to peritubular fluid contributes approximately 40% of the osmolarity of the gradient Role of vasa recta in maintaining the medullary osmotic gradient - Anatomical arrangement of vasa recta capillaries prevents the diffusion of water and solutes from dissipating the medullary osmotic gradient - Descending limb of vasa recta (300 mOsm) - As it descends, water leaves capillaries by osmosis and solutes enter by diffusion - Ascending limb of vasa recta (325 mOsm) - Water moves into plasma and solutes move into interstitial fluid - Osmolarity is higher due to the lack of urea transporters