Download Regulation of Glomerular Filtration Rate and Urine Production - Prof. Douglas N. Ishii and more Study notes Biology in PDF only on Docsity! 30 April Regulation of GFR (Continuation) The amount of metabolites, ions, and water that is excreted is dependent in part on the rate of GFR) Blood pressure at the glomerulus determines GFR rate Constriction/dilation of afferent and efferent arterioles GFR increases → flow through tubule increases → flow past macula densa increases → paracrine diffuses from macula densa to afferent arteriole → afferent arteriole constricts → resistance in afferent arteriole increases → hydrostatic pressure in glomerulus decreases → GFR decreases Macula densa cells sense distal tubular flow and release paracrines Bladder at rest External sphincter (skeletal muscle) stays contracted Internal sphincter (smooth muscle) passively contracted Micturition Stretch receptors fire Parasympathetic neurons fire. Motor neurons stop firing Smooth muscle contracts. Internal sphincter passively pulled open. External sphincter relaxes Urinary Incontinence Urinary incontinence is inability to voluntarily control urination (micturition). Females > males Urethral external sphincter muscle pressure is normally > bladder detrusor muscle pressure Stress incontinence: Sneeze, cough, or exercise can cause detrusor pressure > sphincter pressure. Often due to reduced strength of supportive pelvic floor muscles Urge incontinence: Idiopathic increased desire to urinate Incontinence in diabetes: Diabetic autonomic neuropathy; atonic bladder; incomplete voiding Functional incontinence: Functional disturbance prevents getting to bathroom in time. Dementia, mobility impairment, inebriation, Alzheimer’s disease Water/NaCl Intake and Output Normally is Balanced Table 14 – 3 Table 14 – 4 Regulating input/output of NaCl and water to maintain a steady-state is important for maintaining blood volume and pressure Renal Tubules and Reabsorption Bowman’s capsule: Filtrate 180 L/day (300 mOsm) Proximal tubules: (Reabsorbs most of metabolites and water). Na+ pumped out by Na+/K+ ATPase. Solutes from filtrate follow Na+ by co-transport. H+ secreted into tubule by counter- transport. Water follows solute down its concentration gradient. Remaining filtrate 54 L/day is isosmotic Loop of Henle: Makes dilute filtrate Reabsorbs much of ions (mostly Na+) more than water Filtrate 18 L/day is hypoosmotic (about 100 mOsm) Distal tubules: (Hormones fine tune reabsorption output) Filtrate 1.5 L/day; osmolarity variable, depending on need to secrete or excrete water and solutes in response to hormones such as aldosterone Figure 14 – 10 The luminal section of the plasma membrane of the tubule cells faces the filtrate, whereas the basolateral section is in close proximity to the peritubular capillary The tubular epithelial cells have transporters to regulate the reabsorption of water and solutes
