BIOL 252 1st Edition Lecture 23 Outline of Last Lecture I. Steps in Urine FormationII. Renal CorpuscleIII. Regulation of Glomerular FiltrationIV. Proximal Convoluted Tubule: Tubular reabsorptionOutline of Current LectureI. PCT: Tubular ReabsorptionII. Tubular SecretionIII. Loop of HenleIV. Distal Convoluted Tubule and Collecting DuctV. What about the loop?VI. Urine Storage and EliminationVII. Digestive SystemVIII. Saliva and Salivary GlandsIX. Layers of Digestive TractX. PeristalsisXI. StomachCurrent LectureI. PCT: Tubular Reabsorptiona. Why do peritubular capillaries absorb substances from ISF?i. High ISF hydrostatic pressure1. Pushing inward – because water and solutes accumulating in ISFii. Low blood hydrostatic pressure (8 mmHg)1. Volume of blood is much smaller than that going into glomerulus => pressure drops2. Because filtration removed fluid from blood iii. High osmotic pressure (high blood protein levels)1. Because filtration concentrated blood proteins II. Tubular Secretiona. Waste removal: urea, uric acid, bile acids, ammonia, catecholamines, some drugsb. Acid-base balance: H+ and HCO3-i. If pH is too low (too acidic), blood can get rid of H+ to fix the problemii. Reason urine is more acidic than blood These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.III. Loop of Henlea. Kidney has an osmolarity gradient b. Descending limb: reabsorbs water; volume of filtrate = 35%c. Ascending limb: reabsorbs NaCl; volume of filtrate = 20%d. Generates salinity gradient, enabling collecting duct to concentrate urine IV. Distal Convoluted Tubule and Collecting Ducta. Site of hormonally controlled reabsorption and secretionb. ADH stimulated by high blood osmolarity (detected by hypothalamus)i. Tells us need to conserve water c. If we leave water alone, we can have 20% leave the body as urine i. With ADH, put channels (aquaporins) for water to go back to blood ii. Why does water leave through aquaporins?1. Because of the increasing osmolarity gradient d. When sodium levels too low…i. Aldosterone => promotes Na+ reabsorption and K+ secretionii. We reabsorb more sodium e. High blood volume…i. ANP (atrial natriuretic peptide) dilates afferent arteriole, constricts efferent arteriole, inhibits ADH, renin, and aldosterone secretionii. If atrium exposed to high venous pressure, heart will release ANPiii. Increases GFR iv. Aldosterone – if reabsorb salt, water follows (must decrease)v. Must also decrease water retention w/ ADH vi. More of what’s filtered leaves as urine f. Low blood calcium…i. PTH => promotes Ca2+ reabsorption and PO4- secretion; promotes calcitriol synthesis by PCTV. What about the loop?a. Loop of Henle comprises a countercurrent multiplier i. Because fluids are flowing in opposite directionii. Multiplier part- multiplying effect on salt concentration due to actions of two sides iii. As water is reabsorbed, solute concentration in filtrate increases iv. If ascending was same as descending, would absorb water1. But made impermeable to water2. So pump more and more salt out (Na+ Cl-)3. Pump less out at the top (less to pump out)4. In ISF, more salt at the bottom (increased osmolarity) 5. So lose water and then saltv. How do we keep it extra salty at the bottom?1. At bottom of collecting duct, allow small amount of urea to escape2. Goes to tip of Loop of Henle3. Benefit: extra solutes added to medulla to maintain salty environment a. Important for water reabsorption 4. Recycling of urea: lower end of CD permeable to urea; urea contributes to osmolarity of deep medullary tissueVI. Urine Storage and Eliminationa. Whatever comes out of collecting ducts  bladderb. Micturition reflex – involuntaryi. Stretch receptors detect filling of bladderii. Signals return to bladder via parasympathetic fibersiii. Signals excite muscular contractioniv. Signals relax internal urethral sphincter v. ---Voluntary control---vi. Micturition center in pons receives signals from stretch receptorsvii. Pons enhances signals 3 and 4 ORviii. Pons signals to keep external urethral sphincter contracted; urine retained in bladderix. When it is time to urinate, signals from pons cease and external urethral sphincter relaxes; urine is voided VII. Digestive Systema. Ingestion: intake of foodb. Digestion: mechanical and chemical breakdown of foodc. Absorption: uptake of molecules through the epithelial cells of digestive tract andthen into blood or lymphd. Compaction: absorbing water and consolidating indigestibles into fecese. Defecation: elimination of feces f. *Excretion: removing a waste from inside to outside VIII. Saliva and Salivary Glandsa. First mechanical and chemical digestionb. 3 pairs of extrinsic salivary glands (not in oral cavity but secrete to oral cavity)i. Connected to oral cavity by ducts c. Parotid, sublingual, submandibulard. Saliva components: i. Mucous: helps you swallow food and liquefy food; made of water and glycoproteins ii. Bicarbonate ions: controls pH, keeps oral cavity from getting to acidic iii. Amylase: breaks up carbohydratesiv. Lipase: breaks down fatsv. Lysozyme: lyses bacteria (attacks the cell of bacterium) IX. Layers of Digestive Tracta. As propel food downward, goes through a tube w/ basic pattern b. OUTER membrane: visceral peritoneum (serosa)c. Muscularis externa: important for muscular contractions, organized into circular layer on inside – contraction of these cells contracts tube; longitudinal cells contracted – shortens the tube d. Submucosa: capillaries, lacteals, lymph vessels e. Mucosa: epithelial layer; barrier to the body X. Peristalsisa. Muscular waves of contraction that propel substances through lumen XI. Stomacha. Functions: storage, mechanical digestion, liquefies bolus producing chime, chemical digestion of protein and fatb. Delimited by pyloric sphincter and lower esophageal sphincterc. Tissuesi. Mucosa, Submucosa, Muscularis externa, serosaii. Mucosa – gastric glands1. Parietal cells: secrete HCl, secrete intrinsic factor (needed for B12 absorption) – otherwise have pernicious anemia a. Why HCl?i. Activates enzymes – pepsinogen (becomes pepsin once activated); do not want active form in your cells because it breaks down proteins ii. Denatures proteinsiii. Converts Fe3+ to Fe2+ (form we can absorb)iv. Destroys many pathogens 2. Mucous cells: secrete mucous3. Enteroendocrine cells: secrete paracrine factors and hormone