Bio 182- Ecology Unit Outline 1

Bio 182- Ecology Unit Outline 1 Excretory System Introduction 1. Terrestrial organisms must deal with the problems of: a. obtaining and conserving water b. Removing excess salts c. Eliminating products of protein catabolism such as: urea, ammonia d. These are primary functions of the excretory system 2. Excretion-elimination of waste products of metabolism and the removal of surplus substances from the body 3. Organs of excretion: a. Skin-eliminates urea, ammonia, salts, & water b. Lungs-eliminates CO2 and H2O c. Intestines-eliminates Fe++ and Ca++ d. Liver-eliminates bilirubin & cholesterol via intestines; also forms urea e. Urinary system: kidneys, ureters, Urinary bladder, & urethra 4. Kidney functions: a. Maintains homeostasis b. Regulates blood volume & chemical composition c. Regulates ph d. Eliminates foreign substances such as drugs & toxins e. Endocrine functions: 1) Renin-regulates BP & electrolytes 2) Erythropoietin-regulates RBC counts d. Metabolizes Vitamin D to active form 5. Kidney macrostructure: a. Bean-shaped and resides in retroperitoneal cavity of superior lumbar region 1) R kidney lower than L 2) 150 g; 12 X 6 X 3 cm 3) Lateral surface convex; medial surface concave 4) Hilus is entry/exit point for blood vessels, ureter, & nerves 5) Adrenal gland above kidney b. External supportive connective tissues: 1) Outer layer of CT over kidney is renal capsule 2) Outside renal capsule is a thick layer of adipose tissue called the adipose capsule a) During starvation, kidneys may drop in position kinking ureters and impeding urine exit, a condition called ptosis 3) A layer of dense fibrous CT encloses kidney & adrenal gland; anchors these organs to surrounding structures-called renal fascia c. Internal macrostructures: 1) Outer cortex and inner medulla

Bio 182- Ecology Unit Outline 2 2) Cortex houses structures called renal corpuscles 3) Medulla: a) Renal pyramids-cone-shaped masses of microscopic tubules b) Renal papilla-tip of pyramid facing renal pelvis c) Renal columns-ct and cortical tissues that separate pyramids 4) Calyxces a) Renal papillae empty into minor calyces, channels that conduct urine into still larger channels called major calyces b) Major calyces empty into renal pelvis, an expanded collecting area inside kidney 5) Renal pelvis is drained by the ureter 6. Kidney circulation a. Renal artery branches from descending abdominal aorta and enters at hilum of kidney b. Renal artery divides into interlobar arteries; these enter each renal column c. Each interlobar artery makes a sharp turn, or arc, between cortex and medulla regions to form the arcuate arteries d. Each arcuate artery gives off several interlobular arteries entering cortex region e. Afferent arterioles branch off interlobular arteries and form a capillary bed called the glomerulus f. Glomerulus is surrounded by Bowman s capsule of nephron 1) Capillaries here are heavily fenestrated 2) Fluid from blood is filtered, now called filtrate, and enters nephron, a tubular structure that forms urine g. Exiting glomerulus is efferent arteriole h. Efferent arteriole breaks up into a second capillary bed called the peritubular capillary bed 1) Much of this bed stays in cortex region, but some capillaries enter medulla; those that enter medulla are called the vasa recta i. Peritubular capillaries reunite into interlobular vein j. Interlobular vein-à arcuate vein-à interlobar vein-à renal vein-à IVC 7. Nephron a. Functional unit of kidney 1) Over 1 million/kidney 2) About 3 cm total length 3) Components: BC, PCT, LH, DCT 4) CD-collecting duct usually not considered part of nephron since many DCT s enter one CD b. Bowman s capsule (BC) 1) Cup-like structure that surrounds glomerulus, a ball-like tuft of capillaries formed from afferent arteriole

Bio 182- Ecology Unit Outline 3 a) BC + glomerulus = Renal corpuscle 2) BC has 2 layers: a) Parietal layer-simple squamous epithelium; structural function only b) Visceral layer-clings to surface of glomerular capillaries by cells called podocytes i. Podocytes are highly branched epithelial cells with footlike extensions called pedicels ii. Pedicels touch basement membrane of endothelium iii. Between pedicels are openings called slit pores iv. Fluids are pushed out of fenestrations through slit pores into BC v. When fluids enter BC & PCT, they are called filtrate c. Proximal convoluted tubule (PCT) 1) Coiled tubule leading from BC 2) Mostly in cortex 3) Walls are simple cuboidal epithelium with dense microvilli a) Microvilli are important in absorption/reabsorption d. Loop of Henle (Nephron loop) 1) Descending limb (= thin segment)-initially similar to PCT, but changes into simple squamous epithelium; freely permeable to water 2) Ascending limb (=thick segment)-becomes cuboidal or slightly columnar epithelium; impermeable to water e. Distal convoluted tubule (DCT) 1) Coiled tubule leading from LH into cortex region 2) Walls are simple cuboidal epithelium with few microvilli 3) Secretion is more important function here 4) Juxtaglomerular apparatus (JGA)-site where coiled DCT contacts afferent arteriole a) Arteriole wall has enlarged smooth muscle cells, called JG cells, containing granules of renin; also has mechanoreceptors for monitoring BP b) DCT has cluster of columnarly-shaped cells, called macula densa, in contact with JG cells; densa cells house osmoreceptors for monitoring solute conc in filtrate f. Collecting duct (CD) 1) Not part of nephron 2) Larger lumen tubule that receives DCT s from many nephrons 3) Simple cuboidal epithelium 4) Gives striped appearance to renal pyramids 5) Fuse to form papillary ducts g. Papillary ducts (in renal papillae)-à minor calyx-à major calyx-à renal pelvis-à ureter--à urinary bladder-à urethra-à outside h. Kinds:

Bio 182- Ecology Unit Outline 4 1) Cortical nephrons (85%) a) Short nephron loops b) Peritubular capillaries branch off efferent arterioles 2) Juxtamedullary nephrons a) Very long nephron loops b) Maintain salt gradient and conserve water c) Efferent arterioles branch off vasa recta-blood supply to medulla 8. Nephron Physiology a. Statistics: 1) 180 L/day filtered or 60X plasma volume each day 2) 1% body weight, but requires 20-25% oxygen demands 3) 1.5 L/day as urine (180L 1.5L = 178.5L reabsorbed as mostly water, but many critical electrolytes, nutrients, vitamins, etc) b. Major processes: 1) Filtration-separation of substance based on size and under pressure 2) Reabsorption-return of substances from kidney tubules to blood 3) Secretion-movement of substances in blood back into kidney tubules c. Filtration 1) Occurs at glomerulus and BC 2) Glomerular filtration rate (GFR)-amt of filtrate produced by the nephrons of each kidney per minute; ~ 125 ml/min a) Usually measured with creatine or inulin b) Creatine clearance test: i. Most creatine comes from creatine phosphate in muscle metabolism and is not reabsorbed by kidneys ii. Compare amt going into kidney to amt found in urine to estimate GFR rate c) Renal clearance: volume of blood plasma cleared of a waste in 1 min i. Determined GFR: inulin is neither reabsorbed or secreted so for this solute GFR = renal clearance 3) Filtration occurs because of hydrostatic pressure in capillary (HPc) a) Normal HPc at arterial end of capillary = ~ 26mmHg b) HPc in glomerular capillaries is 55 mmhg! c) HPc is higher because of slightly constricted efferent arteriole d) Combined with fenestrations, this makes glomerular capillaries 1000X more permeable than typical continuous capillaries e) 180L/day of filtrate in glomerular capillaries compared to about 3 L/day in continuous capillaries

Bio 182- Ecology Unit Outline 5 4) Filtration membrane a) Fenestrated capillary endothelium b) Visceral membrane of BC with podocytes c) Basement membrane d) These membranes filter most substances smaller than plasma proteins: 3nm or less i. glucose, water, aa, urea ii. 3-9 nm pass through, but not easily iii. Anything larger than 8-9 nm is excluded completely in healthy kidney e) Fenestrated endothelium: 70-90nm pores exclude blood cells f) Basement membrane is a proteoglycan gel with negative charge that excludes molecules > 8 nm i. Blood plasma 7% protein; glomerular filtrate is 0.03% protein g) Filtration slits created by podocyte arms with pedicels; negatively charged filtration slits allow particles < 3 nm to pass 5) Factors that affect GFR a) Afferent arteriole diameter: decrease diameter (or vasoconstrict), decreases GFR-slows blood entry into glomerulus b) Arterial BP: Increased BP, increases GFR because of high HPc in glomerulus c) Efferent arteriole diameter: Decrease diameter, increases GFR because exit of blood in glomerulus is slowed allowing pressure to build 6) Renal autoregulation of GFR a) Adjustments to GFR w/o nervous or hormonal controls b) Afferent mechanism: increase BP and therefore blood flow in afferent arteriole increases stretch of smooth muscle-à smooth muscle constricts afferent arteriole (efferent dilates) -à decreases GFR i. If BP drops then there is decreased stretch of smooth muscle, smooth muscle relaxes (dilates) allowing more blood to enter afferent arteriole and increase GFR ii. Stable for BP range of 80-170 mmhg (systolic values) iii. Cannot compensate for extreme BP c) Tubuloglomerular feedback mechanism; a form of negative feedback (see flow chart) i. High GFR -à rapid flow of filtrate in renal tubules -à sensed by macula densa-à releases paracrine H -à causes constriction of afferent arteriole-à reduces GFR d) Renin-angiotensin feedback mechanism i. via JG cells in JGA

Bio 182- Ecology Unit Outline 6 ii. Decreased GFR caused by drop in BP causes increased release of H (EZ) renin iii. Renin causes formation of angiotensin II; angiotensin II causes widespread vasoconstriction to increase BP iv. In kidney, efferent arteriole vasoconstricts, increasing GFR, but also increasing reabsorption-à more water returned to main circulation-à more water in blood-à increased blood volume-à increased BP e) Thirst centers activated; aldosterone released 7) Sympathetic (neural) controls a) E/NE cause vasoconstriction of afferent arterioles b) Insures sufficient blood flow to skeletal muscles, brain, & heart in times of stress or exercise d. Tubular reabsorption 1) Filtrate initially contains everything that blood plasma does except large proteins 2) Begins in PCT 3) Tubule cells united by tight jcts; therefore solutes & water move through, not between tubule cells 4) 3 membranes involved in return of substances to blood: a) Luminal membrane of tubule cell b) Basolateral membrane of tubule cell c) Endothelial membrane of peritubular capillary 5) 100% of glucose & aa reabsorbed in healthy kidney 6) Ions & water reabsorbed, but regulated hormonally 7) Active tubular reabsorption a) Often a cotransport with Na+ b) Substances actively transported: glucose, aa, lactate, vitamins, most ions, & plasma proteins (by pinocytosis) i. Proteins degraded to aa inside tubule cell; some used, but rest returned to blood 8) Passive forms of reabsorption: diffusion, facilitated diffusion, & osmosis 9) Gradients that allow passive forms to work are often created by active transport with strategic placement of pumps a) If pump is placed in basolateral edge of tubule cell then b) Solute is pumped out of tubule cell into interstitial fluid c) This keeps solute conc low in tubule cell relative to lumen; therefore solute can diffuse from lumen into tubule cell d) High conc in interstitial fluid allows diffusion to move solute into capillary e) Genetic defects occur in protein pumps creating many kidney disorders

Bio 182- Ecology Unit Outline 7 10) With gradients created by active transport several forms of passive transport occur: a) Electrochemical attractions: Na+ is the most important as its movement creates an electrical gradient which draws negatively charged Cl- and HCO3- with it b) Obligatory water reabsorption: Pumping Na+ to one side of a membrane creates hypertonic environment on the side receiving Na+ (or any pumped solute); water moves by osmosis from hypotonic to hypertonic solutions c) Solvent drag: if water leaves an area, the area it came from becomes more hypertonic in various solutes; these solutes (e.g. urea, fatty acids, Cl-), now in higher concentration than before, can now diffuse out 11) In all these passive processes, solute size, charge, & solubility are keys to how much will move 12) Substances not reabsorbed: Urea only about 40-50% reabsorbed allowing build up in interstitial fluid a) Creatinine and uric acid are too large 13) Reabsorption by tubule region: a) PCT: 100% nutrients (glucose, aa, vitamins, small proteins); 60-70% Na+ and water; some anions (Cl- & HCO3-), and even urea (a waste) b) DLH: 25% water c) ALH: 2-25% Na+ and/or Cl-/K+ by active transport d) DCT: Na+ by active transport influenced by aldosterone; water (5%) by osmosis; anions by diffusion e) CD: Na+, H+, K+, HCO3-, Cl-, water, & urea by diffusion f) Papillary ducts: most urea in interstitial fluid comes from here g) 3 H s directly or indirectly affect water reabsorption: i. ADH-makes DCT & CD permeable to water allowing water to return to blood ii. Aldosterone-causes Na+ to be reabsorbed in DCT; water follows & is returned to blood iii. Atrial natriuretic peptide-causes secretion of Na+; water follows Na+ into urine e. Secretion 1) Substances such as: H+, K+, creatinine, ammonia, drugs, toxins, & organic acids move from blood into tubule cells to filtrate 2) Functions: a) Helps regulate ph i. If blood ph too low, then secrete H+ ii. If blood ph too high, then secrete HCO3- b) Eliminates toxins, wastes, & drugs c) Gets rid of excess K+

Bio 182- Ecology Unit Outline 8 9. ph balance a. Normal blood ph: 7.45 b. ph range for human life: 7.0-7.8 c. Acidosis (7.35 to 7.0)-CNS so depressed that a person enters a coma & dies d. Alkalosis (7.45-7.8)-over excitation of NS causing tetany, extreme nervousness, convulsions, & death e. Several ways of controlling ph: 1) Buffer systems: Bicarbonate, protein, & phosphate 2) Respiratory centers 3) Kidney f. Bicarbonate buffer system 1) Uses carbonic acid (H2CO3) and sodium bicarbonate (NaHCO3) 2) In presence of strong acid such as HCl: a) HCl + NaHCO3 --à H2CO3 + NaCl b) Turns a strong acid into a weak acid and salt 3) In presence of strong base such as NaOH: a) NaOH + H2CO3 ---à NaHCO3 + H2O b) Turns a strong base into weak base and water 4) Bicarbonate ion is closely regulated by the kidney g. Protein buffers 1) Most plentiful and strongest 2) Amino acid structure: H / NH2 ------ C --- COOH / R 3) Amine group picks up H+ when too acid 4) Carboxyl group releases H+ when too basic h. Phosphate buffers 1) As in other buffer systems: In presence of strong acid, turns it into a weak acid; strong base turned into weak base i. Respiratory control of ph 1) Neutralizes 2-3 times as much acid as chemical buffers 2) Collaborates with bicarbonate system: a) CO2 + H2O -à H2CO3 -à HCO3- + H+ i. Lowers ph by releasing H+ b) CO2 (expired) + H2O <--- H2CO3 ß - HCO3- + H+ i. Raises ph by binding H+ 3) Increase CO2 and decrease ph stimulate pulmonary ventilation while an increase ph inhibits pulmonary ventilation j. Kidney controls 1) ph decrease: secretion of H+ into tubules: HCO3- reabsorbed

Bio 182- Ecology Unit Outline 9 2) ph increase: reabsorption of H+ into blood; HCO3- (&Cl-) secreted into tubules 3) Most important organ in long term; lungs important short term k. ph disorders 1) Acidosis-failure of respiratory system to eliminate CO2 from the blood; a) ph decreases and pco2 increases, a condition called respiratory acidosis b) Too much H+ formed due to increased metabolism is called metabolic acidosis i. Alcohol, diarrhea (loss of HCO3-) diabetes (ketone bodies), excessive exercise due to build up of lactic acid 2) Alkalosis-Too much CO2 eliminated by hyperventilation-called respiratory alkalosis and is rarely pathological a) Metabolic alkalosis is rare than metabolic acidosis; caused by excessive vomiting (loss of HCl) or too many antacids 10. Countercurrent multiplier a. Units & terms of measurement: 1) Osmolarity- # of solute particles dissolved in one L of water; reflects a solution s ability to cause osmosis 2) Osmol-unit of measure for osmolarity = 1 mole of a nonionizing solute in water 3) milliosmol )mosm)-equals 0.001 osmol; unit small enough to describe body fluids b. Kidney keeps body fluids at ~ 300 mosm c. Theory to explain how it does this is called Countercurrent Multiplier system 1) Countercurrent-something (filtrate & blood) flow in opposite directions 2) Multiplier-kidney has ability to concentrate urine 4X (1200 mosm) compared to blood 3) Countercurrent exchanges are common and can allow efficient exchanges of heat, solutes, or water 4) Urine conc ranges from 65 to 1200 mosm 5) Juxtamedullary nephrons & vasa recta are key structures to explain high conc d. Steps: 1) Cortex-renal corpuscle-pct a) Plasma & filtrate = 300 mosm b) Filtrate reduced by ~80% in PCT, but still isotonic (isosmotic) to interstitial fluid 2) Medulla: LH & CD

Bio 182- Ecology Unit Outline 10 a) Interstitial fluid becomes more & more hypertonic as you move away from cortex (upper medulla) toward renal pelvis (lower/deep medulla) b) Filtrate (in LH) & blood (in vasa recta) descends & ascends through this gradient c) DLH i. Relatively impermeable to solutes & freely permeable to water ii. Therefore, water is pulled out of DLH as it proceeds deeper into medulla iii. Since water is leaving, filtrate becomes more & more hypertonic iv. By the time filtrate reaches lower/deep medulla, it can be as much as 1200 mosm d) ALH i. Impermeable to water ii. Na+ (Cl- & K+) actively pumped out of tubule into interstitial fluid iii. Active transport (AT) of salt from filtrate contributes to high osmolarity of interstitial fluid iv. Since ALH is impermeable to water, water stays in filtrate v. Since solutes (ions) are pumped out, filtrate becomes more & more hypotonic as it goes into upper medulla and cortex e) What happens if you get dehydrated? Your kidney should reabsorb as much water as possible. i. If dehydrated, you have a hypertonic solute content in your blood and also filtrate (comes in high to BC) ii. As filtrate passes down DLH, water is drawn out by osmosis iii. As hypertonic filtrate swings up into ALH, a lot of salt is available for pumps to transport out into interstitial fluid iv. With more salt, more salt is pumped out and the more hypertonic the interstitial fluid becomes v. The more hypertonic interstitial fluid, the more water is pulled out in the DLH vi. The more water that is pulled out in the DLH, the more hypertonic the interstitial fluid becomes vii. Cycle is repeated allowing more water to be drawn from DLH-This is a positive feedback loop viii. Water enters the vasa recta

Bio 182- Ecology Unit Outline 11 ix. Water does not destroy interstitial gradient because vasa recta runs countercurrent x. Also conditions favor water to move into vasa recta because vasa recta has a high OPc and a low HPc; (also high HPif) f) DCT i. With solutes leaving, filtrate becomes hypotonic relative to interstitial fluid ii. Can reach 200 mosm less than interstitial fluid in cortex region iii. Solutes can be added back by secretion g) CD i. Descends back through increasingly hypertonic gradient of interstitial fluid ii. How much water exits depends on ADH; this H causes synthesis of aquaporins that are gates for water to exit and return to blood via vasa recta (also going countercurrent) iii. Lower part of CD is permeable to urea; urea leaks out and contributes to high osmorality of deep/lower medulla iv. Osmolarity 4X as high in deep medulla v. Medullary portion of CD is permeable to water, but not NaCl e. Importance of vasa recta 1) Acts as countercurrent exchanger 2) Delivers nutrients/oxygen to tubule cells 3) Blood flow is very slow; prevents destruction of gradient 4) Freely permeable to water & salts 5) By going in opposite direction to tubules, or countercurrent, the vasa recta removes water that would destroy gradient 6) NaCl not taken in as quickly as water; therefore a lot stays to support gradient f. Forming concentrated urine 1) ADH released by neurohypophysis 2) Causes formation of aquaporins in CD and DCT 3) Water is drawn out by gradient in interstitial fluid 4) Urine becomes more hypertonic as it travels into deep medulla 5) As high as 1200 mosm g. Forming dilute urine 1) Absence of ADH allows water to stay in tubule as part of filtrate 2) DCT & CD impermeable to water 3) Also AT of ions from DCT males filtrate/urine dilute (hypotonic) 11. Diuretics a. Any chemical that increases urine output

Bio 182- Ecology Unit Outline 12 b. High blood glucose in diabetics (some glucose escapes reabsorption & acts as an osmotic draw to keep water in tubules) c. High protein meals; more urea formed d. Caffiene increase renal vasodilation; increases GFR e. Alcohol inhibits ADH 12. Urine characteristics a. Color-clear to deep yellow (from urochrome -à Hb breakdown) 1) Pink-brown-blood present or certain foods (beets) 2) Cloudy-urinary tract infection b. Odor-slightly aromatic, but altered by diet & bacterial action that forms ammonia c. ph-slightly acidic-6 1) Protein rich diets-more acidic because of aa 2) Vegetarian diets-more alkaline d. Specific gravity: 1.001 to 1.035 e. Composition: 1) Water 95% 2) Solutes 5% a) Urea b) Sodium c) K+ d) Phosphate e) Sulfate f) Uric acid g) Creatinine h) Ca++, Mg++, HCO3- i) Urochrome 13. Nitrogenous wastes a. Urea-from protein catabolism-à aa -à NH2 removed-à forms NH3 -à liver takes 1 CO2 and 2 NH3 s and makes urea b. Uric acid from nucleic acid catabolism c. Creatinine-creatinine phosphate breakdown d. Azotemia-N wastes in blood e. Uremia-toxic effects of N wastes 14. Factors that affect urine production a. BP-increase BP, increases GFR b. Hormones: 1) Aldosterone: helps retain Na+ -à increases water reabsorption-à decreases urine volume 2) ADH: helps reabsorb water -à decreases urine volume 3) NE/E: vasoconstriction of afferent arteriole -à decreases GFR -à decreases urine volume c. Temperature: Increased temperature -à increased water loss at skin -à decreased water loss at kidney

Bio 182- Ecology Unit Outline 13 d. Diuretics e. Emotions: generally increases urine volume 15. Ureters a. Slender tube, 25-30 cm long, that drains urine from kidneys to urinary bladder b. Retroperitoneal c. Trilayered: 1) Inner T. mucosa of transitional epithelium 2) Middle T. muscularis-2 sheets of smooth muscle for peristalsis 3) Outer adventitia 16. Urinary Bladder a. Smooth, collapsible, muscular sac that holds urine b. Location: 1) Males-anterior to rectum; neck is surrounded by prostate gland 2) Females-anterior to vagina & uterus c. Trigone area-where 2 ureters enter & urethra exits d. Histology 1) T. mucosa-transitional epithelium; little overlap of epithelial cells when empty and thrown into folds (rugae) when empty 2) T. muscularis-3 layers of smooth muscle a) Inner & outer longitudinal b) Middle circular c) All 3 collectively called detrusor muscle because fibers are mixed 3) T. adventitia 17. Urethra a. Tube that leads out from U. bladder to outside 1) External urethral orifice in females 2) Penis in males b. Epithelium-transitional -à pseudostratified or stratified columnar-à stratified squamous c. Female 1) 3-4 cm long 2) External urethral orifice found between vaginal orifice and clitoris 3) Internal urethral sphincter has detrusor muscle thickened; smooth muscle and under involuntary control 4) External urethral sphincter is skeletal muacle and has voluntary (learned) control d. Male 1) 18 cm long 2) Internal urethral sphincter at base of U. bladder 3) External urethral sphincter at base of penis 4) 3 regions: a) Prostatic urethra-receives semen during orgasm

Bio 182- Ecology Unit Outline 14 b) Membranous urethra-passes through pelvic cavity c) Penile urethra-enclosed by penis 18. Micturition or urination a. Volumes: ~ 500 ml, but can hold more b. Volumes of 200 ml activate stretch receptors-ap s reach brain 1) If not emptied, stretch-relaxation response initiated c. Micturition reflex 1) Stretch receptors -à sensory neuron-à brain à PS motor neurons -à detrusor muscle & sphincters 2) Internal & external sphincters relax; detrusor muscle contracts 19. Kidney stones or renal calculi a. Composed of Calcium oxalates, uric acid, calcium phosphates b. Causes: Excessive Ca++ intake; low water intake; overactive parathyroid c. Treatment: shock-wave lithotripsy 1) High E shock waves disintegrate stones 2) 30-60 min of 1000+ waves 3) Stones pass out with urine