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Lecture 11 Outline I. Urinary System I Overview A. Body’s purification system B. Functions 1. Removes wastes and toxic substances 2. Conserves useful substances 3. Regulates blood volume & pressure 4. Regulates blood pH 5. Red Blood Cell Synthesis-secretes erythropoietin 1. Consists of: 2 kidneys 2 ureters 1 urinary bladder 1 urethra Kidneys Size & Shape bean-shaped organ, size of fist Length = 12 cm, Width = 6 cm, Thick = 3 cm Location Posterior abdominal wall, behind peritoneal cavity = retroperitoneal Between T12-L3 vertebrae Right kidney slightly lower than left due to liver Anatomy Kidneys are surrounded by thick layer of adipose tissue = perirenal fat Renal Capsule = fibrous connective tissue Renal cortex = outer layer Renal medulla = inner layer o Renal Pyramids Medullary Rays = collecting ducts Tip of pyramid = papillae – drains into minor calyx o Minor Calyx o Major Calyx = 2-3 per kidney o Renal Pelvis = enlarged chamber o Ureter – conveys urine away from kidney Urine Flow: Renal Pyramid → Papillae → Minor Calyx → Major Calyx → Renal Pelvis → Ureter Hilum (indentation) o Entrance for Ureter, Renal Artery, Renal Vein, and nerves Blood Flow Arterial: Abdominal Aorta → Renal Artery → Interlobar Arteries → Arcuate Arteries → Cortical Radiate Arteries → afferent arterioles → Glomerulus of nephron Venous Return: Efferent Arterioles → Peritubular Capillaries → Cortical Radiate Veins → Arcuate Veins → Interlobular veins → Renal Vein → Inferior Vena Cava Renal Arteries = receive 25% of cardiac output Interlobar arteries = pass between medullary pyramids Arcuate arteries = incomplete arches along corticomedullary boarder Cortical Radiate Arteries = radiate into cortex Afferent Arterioles – lead to nephron Nephron I. Overview a. Functional unit of kidney b. Approximately 1 million nephrons per kidney c. Consists of Renal Corpuscle + Renal Tubules II. III. IV. Renal Corpuscle a. Glomerular (Bowman’s) Capsule b. Glomerulus Renal Tubules a. Proximal Convoluted Tubule (PCT) b. Nephron Loop (Loop of Henle) – descending limb c. Nephron Loop (Loop of Henle) – ascending limb d. Distal Convoluted Tubule (DCT) Collecting Duct a. Collects filtrate from several nephrons b. Not part of any nephron c. Responsible for the striations seen in the medullary pyramids Urine Formation I. 3 Steps a. Glomerular Filtration b. Tubular Reabsorption c. Tubular Secretion II. Filtration a. 1st step in urine formation, occurs at renal corpuscle b. Glomerular Capsule – 2 layers i. Parietal Layer = outer layer of simple squamous epithelium ii. Visceral Layer = inner layer of podocytes Podocytes i. Process called Pedicles ii. Slit pores = openings between pedicles c. Glomerulus i. Capillary endothelium resting on basement membrane ii. contain openings between endothelium, called fenestrae d. Filtration Membrane = Fenestrae + Basement Membrane + Slit Pores III. IV. Glomerular Filtrate a. Formed by hydrostatic pressure of blood = Filtration Pressure b. Filtrate includes: 1. Water 2. Glucose 3. Ions (Na+, K+, Cl-, Ca2+, H+, HCO3-) 4. Amino Acids 5. Urea & Uric Acid c. Blood cells & proteins are too large to pass membrane d. Rate of filtration formation = Glomerular Filtration Rate (GFR) i. 125mL/min = 180L/day (45 gallons/day) ii. 99% of filtrate is reabsorbed, 1% passes as urine Autoregulation a. Maintaining a stable GFR with a wide range of blood pressures b. GFR is directly proportional to filtration pressure (from blood pressure) c. GFR is can be controlled by vasoconstriction/vasodilatation of both afferent arterioles & efferent arterioles Vasoconstriction of afferent arteriole (a.a.) decreases GFR Vasodilation of efferent arteriole (e.a.) also decreases GFR As blood pressure increases a.a. vasoconstrict & e.a. vasodilate to maintain a stable GFR Lecture 12 Outline Urinary System II Nephron I. Overview a. Functional unit of kidney b. Approximately 1 million nephrons per kidney c. Consists of Renal Corpuscle + Renal Tubules II. Renal Corpuscle a. Glomerular (Bowman’s) Capsule b. Glomerulus III. Renal Tubules a. Proximal Convoluted Tubule (PCT) b. Nephron Loop (Loop of Henle) – descending limb c. Nephron Loop (Loop of Henle) – ascending limb d. Distal Convoluted Tubule (DCT) IV. Collecting Duct a. Collects filtrate from several nephrons b. Not part of any nephron c. Responsible for the striations seen in the medullary pyramids V. Types of nephron a. Cortical Nephrons – 80% of nephrons located almost entirely within cortex b. Juxtamedullary Nephrons – 20% of nephrons Renal corpuscle positioned near medulla Long nephron loops dip far into the medulla Minority of nephrons, but important for concentrating urine Renal Corpuscle I. Responsible for filtration a. Filtration = first step in urine formation II. Blood Supply a. Afferent arteriole – conveys blood to glomerulus b. Glomerulus – highly permeable capillary network i. Capillaries have slits, called fenestrae c. Efferent Arterioles – conveys blood away from glomerulus III. Glomerular Capsule a. Parietal layer i. Outer layer, composed of squamous cells b. Visceral layer i. Inner layer, composed of podocytes 1. Podycytes = foot cell a. Contains process, called pedicles b. Spaces between pedicles = filtration slits. c. Filtration Membrane 1. Fenestrae of Glomerular capillaries 2. Basement membrane of capillaries 3. Filtration slits between pedicles of podoctyes IV. Blood Supply of Nephron I. Renal Portal System a. Afferent Arterioles – convey blood to glomerulus b. Glomerulus – capillary bed c. Efferent Arterioles – conveys blood away from glomerulus d. Peritubular capillaries Capillary network surrounding proximal convoluted tubule & distal convoluted tubule Drain into cortical radiate veins a. Vasa Recta Specialized capillary loop that surrounds nephron loops of juxtamedullary nephrons II. Juxtaglomerular Apparatus a. Regulates blood pressure Juxtaglomerular Cells within afferent arterioles Macula Densa within Distal Convoluted Tubule Urine Formation I. 3 Steps a. Glomerular Filtration b. Tubular Reabsorption c. Tubular Secretion II. Filtration a. 1st step in urine formation b. occurs at filtration membrane of renal corpuscle III. Glomerular Filtrate a. Formed by hydrostatic pressure of blood = Filtration Pressure b. Filtrate includes: 1. Water 2. Glucose 3. Ions (Na+, K+, Cl-, Ca2+, H+, HCO3-) 4. Amino Acids 5. Urea & Uric Acid c. Blood cells & proteins are too large to pass membrane d. Rate of filtration formation = Glomerular Filtration Rate (GFR) i. 125mL/min = 180L/day (45 gallons/day) ii. 99% of filtrate is reabsorbed, 1% passes as urine IV. Autoregulation a. Maintains a stable GFR with a wide range of blood pressures b. GFR is directly proportional to filtration pressure (from blood pressure) c. GFR is can be controlled by vasoconstriction/vasodilatation of both afferent arterioles & efferent arterioles Vasoconstriction of afferent arteriole (a.a.) decreases GFR Vasodilation of efferent arteriole (e.a.) also decreases GFR As blood pressure increases a.a. vasoconstrict & e.a. vasodilate to maintain a stable GFR Tubular Reabsorption I. Movement of filtrate from tubule into Peritubular capillaries Reclaims substances the body needs II. Proximal Convoluted Tubule H2O (65%) by osmosis Glucose Amino Acids Ions (Na+, Cl-, K+, HCO3-) III. Descending Nephron Loop Water (15%) IV. Ascending Nephron Loop Impermeable to water (0% H2O) V. Distal Convoluted Tubule & Collecting Duct H2O (19%) i. Requires Antidiuretic Hormone (ADH) ii. ADH inserts aquaporins (water channels) in collecting ducts iii. Without ADH, water passes as urine = diabetes insipidus Solutes (Na+, K+,Cl-) Reabsorption at proximal convoluted tubule (65%) I. PCT = simple cuboidal epithelium + microvilli II. Reabsorption is linked to active transport of Na+ out of the basal surface of tubule and into Peritubular capillaries Na+/K+ pumps: removes Na+ from cells, and creates a large Na+ gradient between tubular cells & filtrate Symporters link the transport of glucose, amino acids, K+, ect. to facilitated diffusion of Na+ into apical surface of cells Glucose, Na+, amino acids, K+ leave basal surface by facilitated diffusion Negatively charged ions (Cl-, HCO3-, PO42-) follows positive ions ( Na+ & K+ ) out of tubules H2O follows solutes by osmosis Concentrating Urine – Juxtamedullary Nephrons I. Countercurrent mechanism within nephron loop a. Nephron filtrate flows parallel, but opposite to vasa recta b. Ascending Nephron Loop flows adjacent to descending vasa recta Ascending Nephron Loop (NL) is impermeable to H2O As filtrate moves up ascending NL, ions such as Na+, K+, and Cl- are actively pumped out of ascending NL into descending vasa recta. Descending vasa recta becomes more and more hypertonic as it descends, finally reaching an osmolarity of 1200 at the base. c. Descending Nephron Loop flows adjacent to Ascending Vasa Recta As hypertonic blood (1200mOsm)moves up vasa recta, the high tonicity attracts water from within the descending nephron loop Water leaves descending nephron loop into the ascending vasa recta Ascending Vasa recta becomes more isotonic, while descending Nephron Loop becomes more hypertonic. i. Countercurrent multiplier creates a large osmotic gradient for water reabsorption Reabsorption in DCT & Collecting Duct (19%) Na+, K+, Cl- are actively pumped out of collecting duct & flow into descending vasa recta Water follows solutes out of filtrate and enter the hypertonic descending vasa recta o Antidiuretic Hormone (ADH) is required for water reabsorption at collecting ducts o ADH inserts water channels, called aquaporins into collecting ducts o Without ADH, water leaves as urine Diabetes Insipidus – defective ADH receptors Constant thirst, frequent urination Tubular Secretion I. Movement from Peritubular capillaries into nephron tubules II. Removes toxic substances quickly from body III. a. Secretion in Proximal Convoluted Tubule i. H+, Uric Acid, Ammonia, some drugs, Bile pigments b. Secretion in Distal Convoluted Tubule i. H+, K+ Secretion of H+ helps regulate blood pH. a. Metabolic acidosis increases H+ secretion b. Metabolic alkalosis decreases H+ secretion Juxtaglomerulus Apparatus Regulates blood pressure through renin-angiotensin-aldosterone mechanism Consists of 1. Juxtaglomerular Cells a. Within smooth muscles of afferent arterioles b. Contain renal baroreceptors – detect changes in blood pressure c. Secretes renin in response to low blood pressure, or high Na+ in filtrate 2. Macula Densa a. Within Distal Convoluted Tubule b. Detects changes in [Na+] in filtrate c. High [Na+] in filtrate stimulates secretion of renin from juxtaglomerular Cells Renin-Angiontensin-Aldosterone Pathway o Renin = converts angiontensinogen into Angiontensin I o Angiontensinogen = plasma protein produced by liver o Angiontensin Converting Enzyme (AC) = converts Angiontensin I into Angiotensin II o Angiontensin II: stimulates Aldosterone secretion from adrenal cortex & vasoconstriction o Aldosterone: increases Na+ reabsorption in distal convoluted tubule Water follows by osmosis (if ADH is present), increases blood pressure ACE inhibitors o Inhibits the actions of ACE, preventing formation of Angiontensin II o Lowers blood pressure Antidiuretic Hormone 1. Secreted by posterior pituitary gland a. Secretion stimulated by low blood pressure – baroreceptors b. High osmotic pressure “hypertonic” fluid i. Osmoreceptors in hypothalamus stimulates secretion of ADH c. Actions of ADH i. Increase blood pressure by: 1. Vasoconstriction 2. Increases water reabsorption in kidneys Urine Composition 1. 95% Water 2. Urea a. Biproduct of amino acid catabolism b. 80% of urea is recycled 3. Uric acid a. Byproduct of amino acid catabolism b. Excess uric acid in plasma is deposited as crystals in joints = gout 4. Electrolytes (K+, H+, PO42-) Ureters 25cm length Muscles of ureters contract periodically to pass urine (not constant) Urinary Bladder Hollow organ, lined with transitional epithelium that allow bladder to distend. Trigone o On floor of urinary bladder Ureters open into posterior, inferior floor of urinary bladder Urethra openining positioned on anterior, inferior floor of urinary bladder = neck Detrusor Muscle o Smooth muscle coat surrounding urinary bladder o Forms internal urethral sphincter at neck of urinary bladder o Sustained contractions prevents urination(micturation) Urethra Conveys urine from urinary bladder to exterior Opening = external urethral meatus External urethral sphincter o skeletal muscle surrounding urethra Female urethra = 4cm (1.5 inches) Male urethra = 19cm (7-8 inches) o Prostetic urethra – passes through prostate gland o Membranous urethra – passes through external urethral sphincter (urogenital diaphragm) o Penile urethra – passes through corpus spongiosum of penis