Study Guide - Lecture Exam 3 PDF

**Chapter 23: The Digestive System** **2. List and define the major digestive processes.** **(1) Ingestion: Taking food into digestive tract. (2) Propulsion: Move food through digestive tract. Includes *swallowing*, and *peristalsis*. (3) Mechanical breakdown: Include *chewing*, mixing food with s...

**Chapter 23: The Digestive System** **2. List and define the major digestive processes.** **(1) Ingestion: Taking food into digestive tract. (2) Propulsion: Move food through digestive tract. Includes *swallowing*, and *peristalsis*. (3) Mechanical breakdown: Include *chewing*, mixing food with saliva by tongue, *churning* food in stomach and *segmentation*. (4) Digestion: Catabolic steps in which enzymes secreted into the lumen of GIT break down complex food molecules to their chemical building blocks. (5) Absorption: Passage of digested food from the lumen of GIT through mucosal cells by active or passive transport into blood or lymph. (6) Defecation: Elimination of indigestible substance from the body via anus in the form of feces.** **3. Explain chemical digestion of carbohydrate, protein and fat.** **1) Carbohydrates: Digestion of polysaccharides (starch) begins in the mouth; *Salivary amylase* in saliva splits starch into oligosaccharides. *Pancreatic amylase* in intestinal lumen breaks down starch and glycogen into oligosaccharides and disaccharides. *Brush border enzymes* break oligo- and disaccharides into monosaccharides. Monosaccharides are transported by *secondary active transport* into the epithelial cells; Monosaccharides then exit the basolateral membrane by *facilitated diffusion* and pass into the capillaries.** **2) Proteins: Protein digestion begins in the stomach when pepsinogen secreted by the chief cells is activated to *pepsin* which breaks proteins into polypeptide chains. Pancreatic proteases (trypsin, chymotrypsin, carboxypeptidase) break them into smaller polypeptide chains. *Brush border enzymes (peptidases)* break them into amino acids; Amino acids are transported by *secondary active transport* across the apical membrane of absorptive epithelial cell. Amino acids then exit the basolateral membrane by *facilitated diffusion* and pass into the capillaries via intercellular clefts.** **3) Lipids: Triglycerides are the most abundant fats in the diet. The small intestine is the primary site of lipid digestion because the pancreas is the major source of lipases (fat-digesting enzymes). The steps of lipid digestion and absorption: (1) Emulsification: Because triglycerides are insoluble in water, they aggregate to form large fat globules, and only the molecules at the surface are accessible to lipase enzymes. Bile salts in the duodenum break large fat globules into smaller fat droplets, increasing the surface area available to lipase enzymes. Bile salts cling to the fat molecules: repel each other. (2) Digestion: Pancreatic lipase hydrolyze triglycerides, yielding monoglycerides and free fatty acids. (3) Micelle formation: products of fat digestion (monoglycerides and fatty acids) become associated with bile salts to form micelles. These tiny micelles ferry their contents to the apical border of epithelial cells. (4) Diffusion: Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. (5) Chylomicron formation: In the epithelial cells, the fatty acids and monoglycerides are recombined and packaged with other fatty substances and proteins to form droplets called chylomicrons. (6) Chylomicron transport: The milky white chylomicrons are extruded from the epithelial cells by exocytosis and enter the permeable lacteals and are carried away from the intestine in lymph. Eventually the chylomicrons are emptied into the venous blood via the thoracic duct.** **4/6. Describe peritoneum and controls of digestive activity.** **(1) Peritoneum: serous membrane of abdominal cavity. (i)** **Visceral peritoneum on external surface of most digestive organs. (ii) Parietal peritoneum lines body wall. (iii) Peritoneal cavity: Between two layers; Fluid lubricates mobile organs** **(2) Mesentery: Double layer of peritoneum; Routes for blood vessels, lymphatics, and nerves; Holds organs in place; stores fat.** **Retroperitoneal organs: posterior to peritoneum** **Intraperitoneal organs: surrounded by peritoneum** **\[I\] Intrinsic nerve supply (Short reflexes): Enteric Nervous System (i) Submucosal nerve plexus (ii) Myenteric nerve plexus: \[II\] Extrinsic nerve supply: Enteric Nervous System is linked to CNS via: Afferent visceral fibers; Sympathetic and parasympathetic branches of the ANS (Sympathetic impulses inhibit digestive activities; Parasympathetic impulses stimulate digestive activities); Enteric nerve plexuses (gut brain) respond to stimuli in GI tract; Long reflexes respond to stimuli inside or outside GI tract; involve CNS centers and autonomic nerves** **Digestive activity is provoked by a range of mechanical and chemical stimuli: Receptors located in wall of tract respond to several stimuli (stretch of organ by food, changes in solute concentration and pH of the contents, presence of substrates and end products). External stimuli include sight, smell, taste, and thought of food. Effectors of digestive tract are smooth muscle and glands: activate or inhibit digestive glands; stimulate smooth muscle to mix and move lumen contents. \[III\] Hormones from cells in stomach and small intestine stimulate target cells in same or different organs to secrete or contract.** **8/10. Describe functions of saliva, chewing and swallowing.** **Functions of saliva: (i) Cleanses mouth. (ii) Dissolves food chemicals for taste. (iii) Moistens food; compacts into bolus. (iv) Begins breakdown of starch with enzymes** **Composition of Saliva: 97--99.5% *water*; contains e*lectrolytes*, d*igestive enzymes*: Salivary amylase *Proteins* (Mucin, Lysozyme IgA); *Metabolic wastes*: urea and uric acid.** **Chewing (mastication): Cheeks and closed lips hold food between teeth; Tongue mixes food with saliva; compacts food into bolus; Teeth cut and grind; Deglutition (swallowing): (1) Buccal phase: Occurs in mouth and is voluntary. (2) Pharyngeal-esophageal phase: is involuntary and controlled by swallowing center in brain stem.** **(i) During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. (ii) The pharyngeal-esophageal phase begins as the uvula and soft palate rise, closing off the nasopharynx. The tongue blocks off the mouth. The larynx rises so that epiglottis blocks the trachea. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. (iii) The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper\ esophageal sphincter contracts (closes) after food enters.** **(iv) Peristalsis moves food through the esophagus to the stomach. (v) The gastroesophageal sphincter surrounding the cardial orifice opens, and food enters the stomach.** **11/12. Gastric gland and regulation of gastric secretions.** **Mucosal Barrier: Harsh digestive conditions in stomach (1) Has mucosal barrier to protect: Thick layer of bicarbonate-rich mucus (2) Tight junctions between epithelial cells: Prevent juice seeping underneath tissue (3) Damaged epithelial cells quickly replaced by division of stem cells.** **Gastric gland cells: (1) Parietal cells: secrete (a) *Hydrochloric acid* (HCl): pH 1.5--3.5; denatures protein, activates pepsin, breaks down plant cell walls, kills many bacteria. (b) *Intrinsic factor:* Glycoprotein required for absorption of vitamin B~12~ in small intestine; B~12~ needed to produce mature red blood cells** **Lack of intrinsic factor results in *pernicious anemia;* (2) Chief cells: secrete *Pepsinogen* - inactive form of enzyme pepsin; Activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism); (3) Enteroendocrine cells: secrete Gastrin: regulate stomach secretion and motility; Stomach Delivers chyme to small intestine; Three phases of regulation of gastric secretion: (1) Cephalic Phase: occurs *before* food enters stomach; Stimulatory events: Sight, thought, smell and taste of food through vagus nerve. (2) Gastric phase: once food *reaches* the stomach. (i) Stomach distension activates stretch receptors that stimulate vagus nerve; (ii) Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors stimulate release of gastrin. Inhibitory event: (3) Intestinal Phase: Distension, of duodenum; presence of fatty, acidic, or hypertonic chyme by: (i) Entero-gastric reflex: (involves both short and long reflexes). (ii) Release of enterogastrones (secretin, cholecystokinin)** **13. Modifications of small intestine that enhance absorption.** **(1) Circular folds (plicae circulares): Permanent folds of mucosa and submucosa that force chyme to slowly spiral through lumen, slowing its movement and allowing time for full nutrient absorption. (2) Villi: Finger like projections of mucosa with capillary bed and lacteal for absorption. (3) Microvilli: Microvilli (brush border) of the absorptive cells of mucosa contain enzymes for carbohydrate and protein digestion.** **Hepatic Portal Vein: travel route of nutrients absorbed form the small intestines to the liver; Intestinal Juice: Slightly alkaline; Largely water; enzyme-poor; contains mucus; Facilitates transport and absorption of nutrients.** **14-16. Describe role of liver and pancreatic juice in digestion.** **Liver histology: Portal triad at each corner of lobule; Branch of *hepatic artery* supplies oxygen; Branch of *hepatic portal vein* brings nutrient-rich blood; *Bile duct* receives bile from bile canaliculi; Blood from both the hepatic portal vein and the hepatic artery percolated from triad regions through the sinusoids and empty into the central vein.; Hepatocyte functions: (i) Process bloodborne nutrients (ii) Store fat-soluble vitamins (iii) Perform detoxification (iv) Produce bile.** **Pancreas: (1) Endocrine function: *Pancreatic islets* secrete insulin and glucagon; (2) Exocrine function: *Acini* secrete pancreatic juice: To duodenum via main pancreatic duct.** **Pancreatic Juice: Watery alkaline solution; neutralizes chyme;** **(i) Electrolytes (primarily HCO~3~^--^); (ii) Enzymes include: \[*Proteases* (proteins); *Amylase* (starch); *Lipases* (fats); *Nucleases* (nucleic acid)\]; Proteases are secreted in inactive form and are activated in the duodenum:** **Regulation of pancreatic juice and bile secretion:** **(1) Chyme entering duodenum causes duodenal entero-endocrine cells to release cholecystokinin (CCK) and secretin. CCK and secretin enter the bloodstream. (3) CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO~3~^−^ -rich pancreatic juice. (4) Secretin transported via bloodstream stimulate Liver to produce bile and CCK (via blood stream) causes gallbladder to contract and bile Enters duodenum.** **19. List the major functions of the large intestine.** **Bacterial Flora: (1) Our gut bacteria help us by recovering energy (by fermentation) from otherwise indigestible foods (such as cellulose). (2) Vitamin synthesis: B complex vitamins and vitamin K are synthesized by bacterial flora.** **Major function of large intestine: propulsion of feces to anus; defecation; Defecation reflex: (1) Feces move into and distend the rectum, stimulating stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons. (2) A spinal reflex is initiated in which parasympathetic motor fibers stimulate contraction of the rectum and sigmoid colon, and relaxation of the internal anal sphincter. (3) If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so feces may pass.** **Chapter 24: Metabolism** **1. Indicate sources/uses of carbohydrates, lipids and proteins.** **Carbohydrates: Dietary sources: starch (grains and vegetables); sugars (fruits); cellulose (insoluble fiber; provide roughage)\]** **Uses in Body: fuel used by cells to make ATP; Lipids: Dietary sources: Triglycerides (neutral fats): (i) Saturated fats: Animal source; (ii) Unsaturated fats: Most vegetable oils; Uses in Body: Used as fuel; Stored as adipose tissue; Proteins: Dietary sources: Eggs, milk, fish, most meats, soybeans contain complete proteins (contain all essential amino acids); Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids); Uses in Body: *Structural* materials: Keratin; collagen and elastin; muscle proteins; *Functional* molecules: Enzymes, hormones, antibodies; *Fuel*** **2. State the main substrates/products of cell respiration.** **Carbohydrate Metabolism: Complete glucose catabolism requires three pathways: 1. Glycolysis (sugar splitting): *Location:* An anaerobic process that occurs in the cytosol; *Substrate:* Glucose; *Product:* 2 pyruvic acid molecules, *2 ATP molecules*, high energy electrons; 2. Krebs cycle (Citric acid cycle): *Location:* the mitochondria; *Substrate:* mostly uses pyruvic acid that was generated during glycolysis (can also use fatty acids); *Products:* 6CO~2~, *2ATP molecules*, high energy electrons; 3. Electron transport chain and oxidative phosphorylation: *Location:* mitochondria; *Substrate:* Energy-rich electrons picked up by coenzymes are transferred to the electron transport chain. The electron transport chain carries out oxidative phosphorylation; *Product: 28 ATP molecules*** **3. Define terms associated with carbohydrate metabolism.** **Glycolysis: In response to low levels of ATP, glucose is converted to pyruvic acid. Glycogenesis: However, rising intracellular ATP concentration inhibit glucose catabolism and cause glucose molecules to combine in long chains to form glycogen (storage form of carbohydrates in animals). Glycogenolysis: When blood glucose levels drop, glycogen lysis occurs. Gluconeogenesis: When too little glucose is available, glycerol and amino acids are converted to glucose. This process of forming new *(neo)* glucose from non-carbohydrate molecules is called gluconeogenesis.** **4/5. Describe lipid and protein metabolism.** **Lipogenesis: Lipogenesis occurs when cellular ATP and glucose levels are high; Acetyl CoA is converted to Fatty acids, and glycerol; Lipogenesis is a process in which fatty acids and glycerol join together to form triglycerides. Lipolysis: Lipolysis occurs when carbohydrate intake low; The breakdown of stored fats into glycerol and fatty acids is called lipolysis.** **Glycerol and Fatty acid: converted t Acetyl CoA; Ketogenesis is a process by which the liver converts acetyl CoA molecules to ketone bodies (ketones).** **Protein Metabolism: The goal of amino acid degradation is to (i) produce molecules that can be oxidized for energy in the Kreb's cycle or (ii) converted to glucose (gluconeogenesis).** **6. Summarize events of absorptive and post-absorptive states.** **I\] Absorptive state: (controlled by insulin); *Carbohydrates: (i)* Glucose is the major energy fuel. Glucose is converted to glycogen and fat in liver. (ii) Glycogen is stored in liver and (iii) fat is picked up by adipose tissue for storage. (iv) Glycogen is also stored in skeletal muscle; *Triglycerides: (i)* Adipose, skeletal, cardiac, and liver cells use triglyceride as energy source, but when dietary carbohydrates are limited, other body cells also begin to oxidize more fat for energy. (ii) Most fatty acids and glycerol enter adipose tissue to be converted to triglyceride and stored; *Amino Acids:* (i) enter the citric acid cycle to be used for ATP synthesis. (ii) synthesize structural and functional proteins** **II\] Postabsorptive state: (regulated by glucagon and other hormones). In fasting state, the body reserves are catabolized to supply energy. (1) Glycogenolysis in liver; (2) Glycogenolysis in skeletal muscle; (3) Lipolysis in adipose tissues and the liver: Liver converts glycerol to glucose (gluconeogenesis); (4) protein converted to glucose (gluconeogenesis)** **Chapter 25: The Urinary System** **1. List functions of the kidney.** **(i) Regulating total water volume and total solute concentration in water (ii) Ensuring long-term acid-base balance (iii) Removal of metabolic wastes, toxins, drugs (iv) Endocrine functions (Renin - regulation of blood pressure; Erythropoietin - regulation of RBC production). (v) vitamin D to its active form** **4 / 5. Describe the structure and function of the nephron.** **Nephron: Structural and functional units of kidney that form urine: Two main parts: I\] Renal corpuscle: it has two parts: (1) Glomerulus: Consists tuft of capillaries; endothelium of capillaries is fenestrated that makes it highly porous and allows large amounts of solute rich (but protein free) fluid (called filtrate) to pass from blood into the glomerular space. (2) Glomerular capsule (Bowman\'s capsule): Cup-shaped, hollow structure surrounding glomerulus (two layers); *Parietal layer* : is simple squamous epithelium; *Visceral layer* : clings to the glomerular capillaries, consists of modified branching epithelial cells called *podocytes; Filtration slits* (openings) between foot processes allow filtrate to pass into *capsular space* inside the glomerular capsule; II\] Renal Tubule and Collecting Duct: (both contain simple cuboidal epithelium);regions: (1 Proximal convoluted tubule (PCT): It leaves the renal capsule as a coiled tubule; it is composed of cuboidal epithelial cells with dense microvilli (brush border) that increases surface area that functions in reabsorption of water and solutes from the filtrate and secretion of substances into it. (2) Nephron loop: The U-shaped nephron loop has descending and ascending limbs. (3) Distal convoluted tubule (DCT): The nephron loop is winds and twists again as the distal convoluted tubule. (4) Collecting Ducts: DCT empty into the collecting duct. Each collecting duct receive filtrate from many nephrons; Run through medullary pyramids giving them striped appearance;** **Cortical nephrons: (i) Account for 85% of nephrons of the kidney. (ii) Short nephron loops (iii) Glomerulus further from cortex-medulla junction. Located almost entirely in cortex; small parts of nephron loops dip into medulla (iv) Efferent arterioles supplies peritubular capillaries** **Juxtamedullary nephrons: (i) Fewer (ii) Long nephron loops deeply invade medulla (iii) Glomerulus closer to cortex-medulla junction (iv) Efferent arteriole supplies vasa recta; Important in production of concentrated urine** **6. Identify different capillary beds associated with nephrons.** **(1) Glomerulus: Is specialized for filtration; It is different from other capillary beds in that it is both fed and drained by an arteriole (Afferent arteriole, Efferent arteriole). This arrangement maintains high blood pressure that is needed for filtration; Afferent arteriole arise from cortical radiate arteries and Efferent arteriole feed either the peritubular capillaries or the vasa recta: (2) Peritubular capillaries: Cling to adjacent renal tubules in cortex and empty into venules. Adapted for absorption of water and solutes from tubule cells. (2) Vasa recta: The efferent arterioles serving the Juxtamedullary nephron form bundles of long straight vessels called vasa recta. These play an important role in formation of concentrated urine.** **7. Describe components of the juxtaglomerular complex (JGC).** **(1) Macula densa: is a group of tall, closely packed cells in the ascending limb. These cells are chemoreceptors; that monitor the NaCl content of filtrate entering the distal convoluted tubule. (2) Granular cells (juxtaglomerular, or JG cells): are enlarged, smooth muscle cells of arteriole wall. These cells contain secretory granules contain enzyme renin. These cells act as mechanoreceptors; sense blood pressure in afferent arteriole** **8. List and define the three major renal processes.** **Urine formation and adjustment of blood composition involve three processes: (1) Glomerular filtration: takes place in the renal corpuscle and produces cell- and protein-free filtrate.** **(2) Tubular reabsorption: selectively returns substances from filtrate to blood. It takes place in renal tubules and collecting ducts. It reclaims all of the glucose, amino acids and some 99% of water, salt, and other components. Anything that is not reabsorbed becomes urine. (3) Tubular secretion: selectively moves substances from blood to filtrate in renal tubules and collecting ducts; Filtrate: produced by glomerular filtration. It includes blood plasma (no blood cells) minus proteins; Urine: Contains metabolic wastes and unneeded substances.** **9/10. Describe structure/pressures of the filtration membrane.** **Glomerular Filtration: is passive process in which hydrostatic pressure forces fluids and solutes through filtration membrane** **The Filtration Membrane: (1) Fenestrated endothelium: These capillary pores allow all blood components except blood cells to pass through. (2) Basement membrane: (fused basal laminae of two other layers) (3) Foot processes of podocytes: The visceral layer of glomerular capsule is made of podocytes that have *filtration slits* between their foot processes.** **I\] Outward pressures: (1) Hydrostatic pressure in glomerular capillaries (HP~gc~): (55 mm Hg); (2) Capsular space colloid osmotic pressure (Op~cs~): (0 mm of Hg); virtually no proteins enter the capsule; II\] Inward forces: (1) Hydrostatic pressure in capsular space (HP~cs~): (15 mm Hg): Pressure exerted by filtrate in the glomerular capsule. (2) Colloid osmotic pressure in capillaries (OP~gc~): (30 mm Hg): is exerted by the \"Pull\" of proteins in blood; Net filtration pressure (NFP): Pressure responsible for filtrate formation (10 mm Hg).** **11. Compare the intrinsic and extrinsic controls of GFR.** **Glomerular Filtration Rate (GFR): is the volume of filtrate formed per minute by both kidneys (normal = 125 ml/min). Regulation of GFR: \[I\] Intrinsic controls (renal autoregulation): act locally within kidney to maintain GFR** **(1) Myogenic mechanism: The smooth muscle afferent arteriole contracts (constricts) when stretched and relaxes (dilates) when not stretched. Declining systemic blood pressure, causes dilation of afferent arterioles, that increases blood flow into the glomerulus, and raises the glomerular hydrostatic pressure, that increases the GFR.** **(2) Tubuloglomerular feedback mechanism: is controlled by the macula densa cells. When GFR is low, the low levels of NaCl (due to decreased filtrate flow) inhibits the macula densa cells from releasing vasoconstrictor chemicals, causing the afferent arteriole vasodilation. This allows more blood to flow to the glomerulus, thus increasing the GFR.** **\[II\]. Extrinsic controls: Control by nervous and endocrine mechanisms (goal is to maintain systemic blood pressure regardless of kidneys): (1) Renin-angiotensin aldosterone mechanism: Drop in blood pressure causes release of renin from granular cells of the JGC. Cascade leads to activation of angiotensin II; Constriction of arterioles (increase systemic blood pressure); Triggers aldosterone release from adrenal cortex. Sodium and water reabsorbed into blood (increase systemic blood pressure)** **(2) Sympathetic nervous system: Drop in systemic blood pressure stimulates sympathetic nervous system, that causes systemic vasoconstriction, which in turn increases systemic blood pressure.** **12/13. Describe tubular reabsorption/secretion processes.** **I\] Tubular Reabsorption: (1) Proximal convoluted tube: PCT *reabsorbs all of the glucose and amino acids* in the filtrate, and *65% of Na+ and water*. The *bulk of electrolytes* are also reabsorbed here. (2) Loop of Henle: *Water can leave (osmosis) in the descending limb* of the nephron loop but not the ascending limb. Opposite is true for solutes; (3) Distal Convoluted tubule and Collecting ducts: (i) Antidiuretic hormone: Released by posterior pituitary gland in response to dehydration; causes *collecting ducts* to become more permeable to water reabsorption; *(ii)* Aldosterone: Secreted by adrenal cortex in response to decreased blood volume, or blood pressure; *Reabsorption of Na^+^* (therefore *water*); Targets *collecting ducts* and *distal DCT*; *(iii) PTH:* Parathyroid hormone acts on *DCT* to *increase Ca^2+^ reabsorption.*** ***II\] Tubular secretion* is an important way to *clear plasma of unwanted substances. (1) Disposes of substances (e.g., drugs and metabolites*); (2) *Eliminates undesirable substances* that were reabsorbed earlier (e.g., nitrogenous wastes such as *urea and uric acid*). (3) *Rids body of excess K^+^* (aldosterone driven active tubular secretion into DCT and collecting duct). (4) *Controls blood pH* by altering amounts of H^+^ or HCO~3~^--^ in urine** **14/15. Describe concentrated urine formation.** **One main function of kidneys is to make any adjustment needed to maintain body fluid osmotic concentration at around 300 mOsm; Kidneys produce only small amounts of urine if the body is dehydrated, or dilute urine if overhydrated; Accomplish this by using *countercurrent* mechanism; 1. Countercurrent multiplier; 2. Countercurrent exchanger; These mechanisms work together to: Establish and maintain medullary osmotic gradient from renal cortex through medulla (Gradient runs from 300 mOsm in cortex to 1200 mOsm at bottom of medulla); i. Countercurrent multiplier *creates* gradient; ii. Countercurrent exchanger *preserves* gradient; iii. Collecting ducts can then *use* gradient to vary urine concentration;** **Countercurrent Multiplier: Countercurrent multiplier involves the nephron loop and depends on: i. Filtrate flow in opposite directions (descending/ascending); ii. Difference in permeability between descending nephron loop and ascending loop; iii. Active transport of solutes out of ascending limb;** **Countercurrent Exchanger: Countercurrent exchanger utilizes vasa recta; Vasa recta is able to reabsorb water and solutes without undoing osmotic gradient created by countercurrent multiplier; Countercurrent exchanger preserves medullary gradient by 1. Preventing rapid removal of salt from interstitial space; 2. Removing reabsorbed water;** **Formation of Dilute or Concentrated Urine: Established medullary osmotic gradient can now be used to form dilute or concentrated urine; Without gradient, would not be able to raise urine concentration \> 300 mOsm**[ ]{.math.inline}**to conserve water; This allow kidneys to vary urine concentration; (1) If we were so overhydrated we had no ADH: Decreased ADH \>Decreased permeability of collecting duct to H~2~O \> Decreased H~2~O reabsorption from collecting duct \> Large volume of dilute urine; (2) If we were so dehydrated we had maximal ADH: Increased ADH \> Increased permeability of collecting duct to H~2~O \> Increased H~2~O reabsorption from collecting duct \> Small volume of concentrated urine; Diuretics: Chemicals that enhance urinary output: 1. ADH inhibitors, such as alcohol** **2. Na^+^**[ ]{.math.inline}**reabsorption inhibitors (and resultant H~2~O reabsorption), such as caffeine or drugs for hypertension or edema** **3. Loop diuretics inhibit medullary gradient formation** ***4. Osmotic diuretics*: substance not reabsorbed, so water remains in urine; for example, in diabetic patient, high glucose concentration pulls water from body** **15/16.Describe renal clearance and the physical/chemical properties of urine.** **Renal Clearance: Volume of plasma from which the kidneys clear of particular substance in given time (usually 1 minute).** **There are three possibilities: (1) If C = 125 ml/min \[inulin\]: Freely filtered, no net reabsorption or secretion; This means that the kidneys have cleared all the inulin present in 125ml of plasma. (2) If C \< 125 ml/min, (e.g. urea has a C=70ml/min); means that 125ml of glomerular filtrate formed each minute, 70 ml is completely cleared, while 55 ml is returned to plasma.** **If C = 0, substance completely reabsorbed, or not filtered (e.g. glucose); (3) If C \> 125 ml/min, substance secreted (most drug metabolites, creatinine); Creatinine, is freely filtered and secreted.** **\[I\] Physical Characteristics of Urine** **(1) Color and transparency: Freshly voided urine is *clear* and *pale to deep (concentrated) yellow* in color. Yellow color is due to *urochrome* (a pigment that results when the body destroys hemoglobin). \[II\] Chemical Characteristics of Urine: Normal components: Nitrogenous wastes (Urea, Uric acid, Creatinine, electrolytes); Abnormal components: *Glucose* (diabetes mellitus); *Albumin* (hypertension); *Ketone bodies* (diabetes mellitus); *Red blood cells - hematuria* (infection, tumor); *White blood cells -- pyuria* (urinary tract infection)** **17. Describe function of the ureters, urinary bladder, urethra.** **Ureters: are tubes that begin as a *continuation of renal pelvis*, and that *convey urine from kidneys to bladder*** **Urinary Bladder: smooth, collapsible, *muscular sac* for temporary *storage of urine*; The interior of bladder has openings for ureters and urethra; The smooth triangular area outlined by these three openings is the trigone; The bladder collapses when empty and the wall is thrown into folds (*rugae*).** **Histology of ureter and bladder: three layers from inside out:** ***(1) Mucosa: contains* transitional epithelium (2) *Muscularis*: smooth muscle sheets; Contracts in response to stretch; Bladder has (thick detrusor muscle) - three layers of smooth muscle. (3) *Adventitia*: outer fibrous connective tissue** **Urethra: thin walled muscular tube draining urinary bladder to the exterior of body via *external urethral orifice*** **Sphincters: (i) Internal urethral sphincter: *smooth muscle* at the bladder urethra junction; *Involuntary,* controlled by the ANS, keeps urethra closed when urine is not being passed. (ii) External urethral sphincter: *Voluntary, (skeletal) muscle* surrounding urethra as it passes through pelvic floor (urogenital diaphragm); Female urethra (shorter): carries urine. Male urethra (longer): carries semen and urine. Three regions: Prostatic urethra, *Membranous urethra*: and Spongy urethra** **18. Define micturition and describe its neural control.** **Micturition/urination, is the act of emptying the urinary bladder.** **(1) Reflexive urination (urination in infants): Distension of bladder with urine activates stretch receptors in its walls; Impulses from receptors travel via visceral afferent to reflex center in sacral region of spinal cord; Stimulation of parasympathetic neurons; Contraction of detrusor muscle and opening of internal sphincter; allowing its relaxation (opening) so urine can flow.** **(2) Pontine control centers (mature between ages 2 and 3)** **Descending circuits from the brain have matured enough to begin to override reflexive urination. When a person chooses not to void, reflex bladder contractions subside. The pons has two centers that control micturition: (i) Pontine storage center inhibits micturition by acting on all three spinal efferents \[Excites sympathetic and somatic efferent pathways; inhibits parasympathetic pathway\]** **(ii) Pontine micturition center promotes micturition by acting on all three spinal efferents \[Excites parasympathetic pathways; inhibits sympathetic and somatic efferent pathways\]**