Lecture 8b Nephron Physiology and Urination Chptr 26 PDF

Urinary (AKA Renal) System Nephron Physiology and Urination Chapter 26  Nephron locations of Water and Ion Reabsorption into the Cortex and Medullar Basic Concepts: Co...

Urinary (AKA Renal) System Nephron Physiology and Urination Chapter 26  Nephron locations of Water and Ion Reabsorption into the Cortex and Medullar Basic Concepts: Cortex *The Ion Conc. Through the Entire Cortex is consistent and 300 4 LOWEST ~300 mol/L – The PCT 1 and DCT are in the Cortex *There is an Ion Conc gradient in 400 the Medulla with the Far End Medulla 5 Being High Conc. (1200 mol/L and the Top part Being Low Con. (400 mol/L) 2 3 * The gradient has to be actively maintained (via activity at 3) to maximize the water reabsorbed at 2 (descending limb) and 5 (collection duct). Both the ascending (2) and descending 1200 limb (3) of the loop of Henley AND the Collecting Duct (5) are © 2018 Pearson Education, Inc. in the Medullary Gradient Nephron locations of Water and Ion Reabsorption into the Cortex and Medullar 1) The is an Osmotic Balance are Salt and Water in the Cortex. Salt, water and Glucose passively reasorbed by cortex at PCT. 60 – 80% of water and ions reabsorbed 2) Maximize passive water reabsorption into Medulla, only 4 permeable to water. Medullary Ion 1 Gradient draws water out of the tubule for reabsorption 5 3) Active Medullary reabsorption of Ions, only permeable to Ions. Ions largely used to Maintain Medullary 2 Ion gradient to draw water out for reabsorption (2). Active Ion Transport 3 against gradient in salty medulla 4) Variable passive reabsorption of water and ions into cortex. Site of Blood Pressure Control (aldosterone) 5) Variable passive reabsorption of water and ions into Medulla. Site of variable H+ and Bicarbonate reabsorption to buffer pH of Blood.  Medullary Osmotic Gradient Maximizes the amount of water the kidneys reabsorb – Important to survive drought states – **This Kidney Physiology is further maximized in desert animals Basic Concepts: The Medulla is very salty (maximize PASSIVE absorption of water). There is a Gradient of salt with the Lower part of the Medulla being much more concentrated then the upper part. Only the Descending limb is permeable to water and only the ascending limb is permeable to Ions. The Medullar osmotic Gradient has to be activity MAINTAINED or else it will diffuse out © 2018 Pearson Education, Inc.  The Ascending and Descending limbs of the nephron create an osmotic concentration gradient in the renal medulla via Counter Current Multiplication to Maximize Countercurrent multiplication in Medulla (Ion Gradient and Maximize Water Reabsorption in Medulla)  Result of the descending limb and ascending limb of Henley Located proximal to each other Separated by peritubular fluid (fluid that has be reabsorbed from the Nephron) which has a concentration gradient Reabsorption activity between these adjacent limbs is called countercurrent multiplication – Countercurrent—Tubular fluid moves in opposite directions (Down or Descending part of the Loop of Henley and UP or Ascending part of the Loop of Henley – Multiplication—effect increases with fluid movement Responsible for creating conc. gradient in the renal medulla Produces highly conc. Urine (most water reabsorbed) © 2018 Pearson Education, Inc.  Variable Reabsorption from the loop of Henley – Countercurrent Multiplier Active Ion Medullary Ion Passive Gradient Needs to Water Be Maintain so Na+ / Cl- is continuously pumped out (active transport in Ascending Limb) © 2018 Pearson Education, Inc.  Nephron loop – Descending vs Ascending Limb – Maintaining Medullary Concentration Gradient The Medullary conc. gradient of peritubular fluid is increased from activity of the thick ascending limb On the other side the Thin descending limb is…  Permeable to water & Impermeable to solutes  Water moves from tubular fluid into the peritubular fluid by osmosis Thick ascending limb  Actively transports Na+ and Cl– out of the tubular fluid against the gradient into the Peritubular fluid of the Medullar  Impermeable to water © 2018 Pearson Education, Inc.  Putting it All Together – Counter Current Multiplier – Medullary Ion Gradient – Maximal Water Resorption https://www.khanacademy.org/science/health-and-medicine/human-anatomy-and-p hysiology/introduction-to-the-kidneys/v/countercurrent-multiplication-in-the-kidney © 2018 Pearson Education, Inc.  Nephron loop – Concentrates Urine and Maximizes Water Reabsorption Concentration of urine  Water is variably reabsorbed along the DCT and collecting duct (blood pressure management)  The papillary region of the Collecting duct system also helps maintain the Medullar Ion Gradient by reabsorption of urea in the Medullary Peritubular Fluid  Tubular fluid within the Collecting duct that reaches the papillary duct has a typical urea concentration of ~450 mols/L  Urine volume and concentration can be hormonally regulated to manage blood pressure Obligatory water reabsorption  Occurs in locations where water movements cannot be prevented PCT and descending limb of nephron loop  Rate cannot be adjusted  Recovers up to 85 percent of filtrate © 2018 Pearson Education, Inc.  Urine volume and concentration can be hormonally regulated to manage blood pressure Facultative water reabsorption  Occurs in the DCT and collecting tubule  Allows precise control of water reabsorption  Adjusts urine volume by reabsorbing a portion (or all) of the remaining 15 percent of filtrate volume © 2018 Pearson Education, Inc.  Urine volume and concentration can be hormonally regulated to manage blood pressure Urine volume without ADH (antidiuretic hormone)  No water is reabsorbed in DCT and collecting tubule No facultative water reabsorption © 2018 Pearson Education, Inc.  Urine volume and concentration can be hormonally regulated to manage blood pressure Urine volume with ADH  ADH allows water channels to form Aquaporins appear in the apical plasma membranes of the DCT and collecting tubule cells  Water permeability of the last tubular segments increases, increasing water reabsorption © 2018 Pearson Education, Inc.  Normal Urine volume and concentration Normal urine  Normal volume is about 1200 mL/day with an osmotic concentration of 1000 mOsm/L  Values differ from person to person and from day to day Kidneys alter their function to maintain homeostasis © 2018 Pearson Education, Inc.  Renal function is an integrative process involving filtration, reabsorption, and secretion Renal corpuscle  Filtrate has the same osmotic composition as plasma (~300 mOsm/L)  Same composition as plasma except for plasma proteins © 2018 Pearson Education, Inc.  Renal function is an integrative process involving all Segment of the Nephron Proximal convoluted tubules (PCT)  Ions and organic nutrients reabsorbed from tubular fluid  Water follows by osmosis  Reduces tubular fluid volume but keeps tubular fluid and peritubular fluid isotonic PCT and descending limb of nephron loop  Obligatory water reabsorption concentrates the tubular fluid (future urine) within the Nephron © 2018 Pearson Education, Inc.  Reabsorption – Integrative Process of All Segments Efferent Most Water and Solutes Reabsorbed Arterioles from the PCT segment of the Nephron within the Cortex are Redistributed back into circulation at the Efferent Arterioles… Few enter back into the circulation via the Vasa Recta of the Peritubular Capillaries The Water resorbed in the Medullar via the Thin potion of Descending Limb is Redistributed back into circulation at the Vasa Recta of the Peritubular Capillaries. Tubular Fluid Vasa Recta of is Concentrated because water is the Peritubular removed (Urine Gets Conc.) Capillaries © 2018 Pearson Education, Inc.  Renal function as an integrative process Ascending limb of nephron loop  Actively transports Na+ and Cl– out of tubule (impermeable to water)  Lowers the osmotic concentration of tubular fluid (Urine gets Diluted) because ions are removed  Ions Used to Maintain the Medullary Ion Gradient DCT and collecting system make adjustments  Reabsorption and secretion of solutes is variable (Facultative)  Hormonally controlled water reabsorption **More water is removed from Collecting duct then Solutes SO Urine is Concentrated to its final conc. in the Collecting Duct © 2018 Pearson Education, Inc.  Renal function as an integrative process Vasa recta  Absorbs solutes and water in the Medullary region from the tubules into the systemic circuit  Maintains concentration gradient of medulla © 2018 Pearson Education, Inc.  Production of urine © 2018 Pearson Education, Inc.  Clinical Module: Renal failure is a life- threatening condition Occurs when the kidneys cannot filter wastes from blood and can no longer maintain homeostasis Impairs all systems in the body, resulting in:  Decrease in urine production  Rise in blood pressure  Anemia from decline in erythropoietin production  Central nervous system problems (sleeplessness, seizures, delirium, and coma) © 2018 Pearson Education, Inc.  Renal failure Chronic renal failure  Kidney function deteriorates gradually  Progression can be slowed, but the condition is not reversible  Management involves restricted water, salt, and protein intake – Minimizing volume of urine produced – Minimizes the amount of nitrogenous waste generated  Acidosis (Blood pH is too acidic which is a common problem with renal failure) can be countered by ingesting bicarbonate ions since the kidney is no longer reabsorbed the bicarbonate due to failure Acute renal failure  Kidney function deteriorates rapidly in just a few days May be impaired for weeks  Sudden slowing or stopping of filtration caused by: Exposure to toxic drugs, Infection, renal ischemia (blockage in blood circulation), urinary obstruction, or trauma, Allergies to antibiotics or anesthetics in sensitized individuals  Recovery of partial or complete function is possible if patients survive the initial incident Survival rate ~50 percent with supportive treatment © 2018 Pearson Education, Inc.  Renal failure – Chronic Treatment Dialysis  Process of passive diffusion across a selectively permeable membrane – Supplements the activity of the Nephron  Hemodialysis Uses an artificial membrane as an alternative to the kidney’s normal membrane around the glomerulus and Nephron Regulates the composition of blood using a dialysis machine Membrane pores allow diffusion of ions, nutrients, and organic wastes, but not plasma proteins Dialysis fluid containing specific concentrations of solutes is run on the other side of the membrane Shunts (silicone rubber tubes) connect blood vessels with the dialysis machine © 2018 Pearson Education, Inc.  Renal failure Dialysis Machine © 2018 Pearson Education, Inc.  Renal failure - Transplant Renal failure treatment  Dialysis relieves renal failure symptoms, but is not a cure  Kidney transplant is the only real cure for severe renal failure Patient survival is more than 90 percent at 2 years after the transplant Close relative donor increases success rate Immunosuppressive drugs are necessary to reduce rejection of transplant © 2018 Pearson Education, Inc.  The urinary tract transports, stores, and eliminates urine Urinary tract (Post Kidney Functions)  Transports, stores, and eliminates urine  Includes the ureters, urinary bladder, and urethra  Can be visualized using a pyelogram X-ray image of the urinary tract taken after a radiopaque dye is administered intravenously © 2018 Pearson Education, Inc.  The urinary tract Anatomy  Ureters Paired muscular tubes extending from the kidney to the urinary bladder (about 30 cm) Retroperitoneal and attached to the posterior abdominal wall  Urinary bladder Hollow, muscular organ holding up to a liter of urine  Urethra © 2018 Pearson Education, Inc.  The urinary tract Anatomy Urethra  Extends from the neck of the urinary bladder to the exterior of the body  Different lengths and functions in males versus females Male urethra is longer and transports semen as well as urine © 2018 Pearson Education, Inc.  The ureters, urinary bladder, and urethra are specialized to conduct (release) urine - Bladder  Filled by the ureters and drained by the urethra  Dimensions vary with state of distension  Largley Located in the Abdominal Cavity but can extend inferiorly into the Pelvic cavity especially when full (distended) Anchored to pelvic & pubic bones by supporting ligaments Lateral umbilical ligaments – Vestiges of the umbilical arteries Middle umbilical ligament  Rugae Bladder lining Folds that disappear with distension as the bladder fills  Ureteric orifices Slitlike shape helps prevent backflow of urine into ureters due to increased with bladder contraction during Urination © 2018 Pearson Education, Inc. Conduction & storage of urine – Urinary Bladder  Ureters penetrate posterior bladder wall at an oblique angle  Trigone Triangular area bounded by the ureteral openings and the entrance to the urethra  Neck of the urinary bladder Surrounds the urethral opening and contains a muscular internal urethral sphincter (involuntary smooth muscle) – Autonomic closure when bladder is filling / full (no leakage)  External urethral sphincter Located where the urethra passes through the urogenital diaphragm Under voluntary control to permit conscious urination  Conduction and storage of urine Wall of the urinary bladder  Contains mucosa, submucosa, and muscularis layers (smooth muscle)  Muscularis layer has three layers Inner longitudinal layer Circular layer Outer longitudinal layer  Collectively, the layers form the detrusor muscle © 2018 Pearson Education, Inc.  Conduction and storage of urine Wall of the urethra (continued)  Thick, elastic lamina propria  Longitudinal folds in the mucous membrane Mucin-secreting cells in the epithelial pockets  Lined with stratified epithelium that varies by location Transitional Epithelium at the neck (stretchy) Stratified columnar at midpoint Stratified squamous near the external urethral orifice © 2018 Pearson Education, Inc.  Urinary reflexes coordinate Urine storage & Urination Micturation reflexes **Coordinates Storage (spinal Reflex) and Urination (voiding) **Involves afferent sensory and subsequent Efferent Motor Response Two anatomical Regions for Reflexes For Storage - The Spinal Reflex Constricts Sphincter to Hold Urine in Bladder Stretch receptors of urinary bladder wall distort as it fills **Afferent impulses stimulate sympathetic stimulation to detrusor muscle of the bladder via a spinal reflex and stimulates contraction which closes internal urethral sphincter to prevent leakage  Pontine storage center (voluntary control) (voids the Spinal Reflex to release bladder) (Voluntary Urination) – Located in Pons of the Brain - increases somatic motor nerve activity which results in Relaxation of sphincter muscles and Urination Occurs © 2018 Pearson Education, Inc.  Urinary reflexes coordinate Urine storage & Urination Micturation reflex (continued)  Urine voiding reflex through pontine micturition center This blocks (voids) the activity of the spinal reflex Interneuron relays sensation of bladder fullness to the thalamus Projection fibers relay the information to the cerebral cortex Voluntary relaxation of the external urethral sphincter –Causes relaxation of the internal urethral sphincter Since pressure is already increased in the bladder, relaxing the sphincters leads to urination © 2018 Pearson Education, Inc.  Urinary reflexes – Spinal Reflex and Voiding (Via Pons) © 2018 Pearson Education, Inc.  Clinical Module: Urinary disorders can be detected by physical exams and laboratory tests Uranalysis: signs of urinary disorders  Change in volume and appearance of urine Polyuria – Excessive urine production – Results from hormonal or metabolic problems o Possibly diabetes or glomerulonephritis Oliguria – Reduced urine production (50–500 mL/day) Anuria – Severely reduced urine production (0–50 mL/day) Oliguria and anuria indicate serious kidney problems and potential renal failure  Change in chemical composition Change in pH too ; Change in Glucose levels etc.  Presence of foreign or unwanted Biological Material Red Blood cells ; Bacteria © 2018 Pearson Education, Inc.  Clinical Module: Urinalysis © 2018 Pearson Education, Inc.  Other signs of Urinary disorders Primary signs of urinary disorders  Change in frequency Increased urgency or frequency – Can be from irritation of the lining of the ureters or urinary bladder Incontinence – Inability to control urination voluntarily – May involve periodic involuntary leakage (stress incontinence), inability to delay urination (urge incontinence), or continual trickle of urine from full bladder (overflow incontinence) Urinary retention – Urination does not occur – In males, commonly results from enlarged prostate gland and compression of prostatic urethra © 2018 Pearson Education, Inc.  Other Signs of Urinary disorders Primary signs of urinary disorders  Pain Pain in the superior pubic region – Associated with urinary bladder disorders Pain in the superior lumbar region or in the flank that radiates to the right or left upper quadrants – Associated with kidney infections (pyelonephritis) – Also associated with kidney stones (renal calculi) Dysuria – Painful or difficult urination – Can occur with cystitis or urethritis or urinary obstructions (possibly enlarged prostate in males) © 2018 Pearson Education, Inc.