The Urinary System - Human Anatomy & Physiology PDF

10. The Urinary System Human Anatomy & Course Physiology Status Complete Materials 10. The Urinary System - Slides Date...

10. The Urinary System Human Anatomy & Course Physiology Status Complete Materials 10. The Urinary System - Slides Date @November 14, 2024 Table of Contents Urinary System Anatomy of the Urinary System Kidney Anatomy Blood Flow in the Kidney Nephron I. Filtration II. Reabsorption Proximal Convoluted Tubule Loop of Henle and Medullary Gradient Hormonal Control of Reabsorption III. Secretion Renin-Angiotensin-Aldosterone System (RAAS) Factors Affecting GFR 10. The Urinary System 1  Urinary System Function: is to maintain internal fluid environment by regulating blood plasma 1. Regulates extracellular fluid Removes waste products (N & S compounds) and toxic substances (drugs etc.) Regulates blood volume (water balance) Regulates ions including pH 2. Is an endocrine gland (renin, EPO, calcitriol) 3. Is a site of Gluconeogenesis: glucose is formed from lactate, glycerol, glutamine Occurs in the cortex and is triggered by insulin and epinephrine Responsible for 50% of glucose formed in fasting Structure: consists of kidneys, ureter, bladder and urethra Kidneys: regulate blood plasma Ureter: passageway from kidneys to bladder Bladder: is a temporary storage for urine Urethra: passageway from bladder out Anatomy of the Urinary System 10. The Urinary System 2  System: Kidney, Ureter, Bladder, Urethra Kidney: Cortex, Medulla (pyramids & columns), calyx, pelvis Nephron: Glomerular capsule → Proximal Convoluted Tubule (PCT) → Henle’s Loop (LH) → Distal Convoluted Tubule (DCT) Collecting System: Collecting tubules or ducts (CT) → Papillae (opening to calyx) → Minor calyx → Major calyx → Pelvis → Ureter → Bladder → Urethra Kidney Anatomy Stucture: consists of three regions: cortex, medulla, pelvis 10. The Urinary System 3  Cortex: outer region Medulla: Pyramids or lobes (salt gradients) & Columns (routes for blood vessels) Pelvis: funnel-like structure, empties into ureter, consists of minor and major calyces Renal/fibrous capsule/fascia: outer covering Sinus: cavity or space containing pelvis, calyces, etc. Hilum: Indentation for vessel and nerve entry/exit 10. The Urinary System 4  Blood Flow in the Kidney Blood Flow: Renal artery → Interlobular artery → Afferent arteriole → Glomerulus → Efferent arteriole → Peritubular capillaries (vasa recta) → Interlobular veins → Renal vein Two Capillary Beds: Glomerulus: High-pressure capillary bed (55 mmHg) for filtration. Peritubular Capillary: Low- pressure capillary bed (35 mmHg) for reabsorption and secretion. 10. The Urinary System 5  Vasa Recta: Associated with the Loop of Henle in juxtamedullary nephrons Nephron 10. The Urinary System 6  Nephron: Structural and functional unit of the kidney. Location: A tubule in the cortex and medulla of the kidney Processes: 1. Filtration: forcing of fluids through a membrane Occurs in renal corpuscle (glomerular capsule + glomerulus) 10. The Urinary System 7  Passive and non-selective; plasma is filtered under pressure (55 mmHg). Produces filtrate (plasma minus proteins). 2. Reabsorption: transfer of substances from renal tubule back to plasma Occurs in PCT, LH, DCT, CT Active and passive processes 3. Secretion: Direct transfer of substances from plasma in peritubular capillaries to renal tubules Includes excess H+, K+, NH4+, creatinine, drugs. 4. Excretion: What remains in the tubules is excreted as urine. Formula: Excretion = Filtration - Reabsorption + Secretion 10. The Urinary System 8  I. Filtration Filtration: Plasma is forced through a porous membrane Is a Passive process Is non-selective (any substance below specific size limit passes through) Driving Force: Blood pressure (55 mmHg) Filtrate: is the resulting fluid in the capsule that passed through the membrane Filtrate is plasma minus proteins Includes: Water, ions, nutrients, and wastes. Excludes: Proteins and cells (RBC & WBC) Glomerular Filtration Rate (GFR): 99% of what is filtered is returned Normal value: ~120 mL/min. to the body Maintained through autoregulation mechanisms Regulated by JGA cells Filtration Membrane: is very permeable to dissolved solutes but not larger molecules 1. Capillary wall: Simple squamous epithelium with fenestrations 2. Podocyte layer: Branching phagocytes forming filtration slits, Engulf escaping proteins 3. Basement membrane: Sticky gel-like layer, negatively charged to attache 2 cell layers together & repel negatively charged proteins Autoregulation (Intrinsic) Regulation: 10. The Urinary System 9  Maintains Renal BP of 55 mmHg despite body's changing BP (60-180 mmHg) Ensures a steady flow of blood into glomerulus Secialized smooth muscle cells: are functioning as both receptor (i.e. baroreceptors) and effector Increase in BP stretch wall, walls contract = decrease in GFR Decrease in BP, walls relax or dilate = increase in GFR Net Filtration Pressure (NFP): NFP = Glomerular BP - (Colloid Osmotic Pressure + Capsular Hydrostatic Pressure) Example: 55 − (30 + 15) = 10 mmHg  10. The Urinary System 10  Juxtaglomerular apparatus (JGA): cells regulate GFR through baroreceptors and chemoreceptors Location: in the walls and at point of contact of distal portion of Henle’s loop and afferent & efferent arteriole Cells of JGA include: Smooth muscle cells of arteriole vessel wall: act as baroreceptors Juxtaglomerular (JG) cells: secrete renin when BP falls Macula Densa cells: are chemoreceptors monitoring solute concentration Large # NaCl = rate too fast, low # NaCl = slow rate Mesangial cells: change diameter of glomerulus capillaries altering GFR II. Reabsorption 10. The Urinary System 11  Reabsorption: Substances pass through wall of renal tubule into interstitial fluid of cortex then through blood capillary wall Mechanisms: Active transport: requires ATP Secondary active transport: nutrients via ion gradients formed by active transport GLUT (glucose transporter): facilitates diffusion of glucose Cotransport: water following solutes Diffusion: urea, water Osmolarity of filtrate changes as water and ions are reabsorbed: PCT = 300 osmol/L LH = 300-1200 (descending limb), 1200-100 ( ascending limb) DCT variable 10. The Urinary System 12  Proximal Convoluted Tubule Reabsorbs 65% of water, all nutrients, and most ions (65% NaCl) Selective process: facilitated diffusion and active transport Substances are moved one molecule at a time mechanisms can be regulated Passive process: Diffusion Loop of Henle and Medullary Gradient Reabsorbs aprox. 25% sodium, 25% chloride, 15% water Medullary Gradient: Salt gradient increases concentration towards the inner medulla gradient is composed of NaCl and urea is maintained by blood flow of vasa recta in opposite direction (counter current) only Loop of Henle and collecting tubules dip into this gradient Descending Limb: water reabsorption 10. The Urinary System 13  Permeable to water but not to salt. Increasing salt gradient pulls water out of tubules Water exits tubules into the medulla. Ascending Limb: NaCl reabsorption Permeable to salt but not to water. Decreasing salt gradient pulls NaCl out Salt exits (active transport in the upper portion). Hormonal Control of Reabsorption DCT & CT: Reabsorption regulated by hormones ADH (Antidiuretic Hormone): Promotes water reabsorption in the collecting ducts. Leads to more concentrated urine in its presence Via channel's found at the end of DCT and in the CT Aldosterone: Facilitates Na+ reabsorption in exchange for K+. ANP (Atrial Natriuretic Peptide): Water follows sodium, increasing blood volume. Inhibits sodium reabsorption. 10. The Urinary System 14  Found in DCT and beginning of CT III. Secretion Secretion: Failure to reabsorbed PLUS additional secretion of materials directly from peritubular capillaries Substances Secreted: Ions: Excess H+, Excess K+, NH4+ Wastes: Creatinine, Urea, Uric acid Some Hormones and Drugs Purpose: Eliminates excess ions and toxins. Regulates blood pH. Renal Tubule Segments: Most active secretion occurs in the DCT and collecting tubules. Renin-Angiotensin-Aldosterone System (RAAS) 10. The Urinary System 15  Renin Release: Triggered by low GFR or blood pressure Enzyme secreted by juxtaglomerular cells Renin-Angiotensin System: Renin → Angiotensin I → Angiotensin II Angiotensin II Effects: 1. Vasoconstriction of arterioles 2. Stimulates aldosterone and ADH release 3. Promotes thirst 4. Enhances Na+ reabsorption in PCT 5. Decrease GFR Factors Affecting GFR 1. Renal Blood Flow: Directly proportional to GFR. 2. Osmotic Pressure: 25-30 mmHg is normally a constant that opposes glomerular BP a. Dehydration: increases plasma protein concentration, reducing GFR. b. Hyperproteinemia: decrease of plasma proteins, increasing GFR 3. Sympathetic Stimulation: Constricts afferent and efferent arterioles, decreasing GFR. 10. The Urinary System 16  a. Efferent Arteriole constriction: increases GFR temporarily 4. Osmoreceptors of macula densa cells: detect NaCl in DCT a. Too much NaCl (high GFR) results in constriction of Afferent arteriole b. Too little NaCl (low GFR) results in dilation of Afferent arteriole 5. Capsular Pressure: obstruction can increase capsular pressure resulting in a decrease in GFR 6. Glomerular surface area: some renal diseases decrease surface area= decrease in GFR. a. Mesenglial cells of JGA can alter surface area. 7. Glomerular permeability i.e. integrity of filtration membrane GFR is directly proportional to permeability: (toxins, drugs, hypoxia can alter permeability) 8. Hormonal Regulation: ANP increases GFR (dilates arterioles). Angiotensin II, norepinephrine decrease GFR (constricts arterioles). 10. The Urinary System 17