Osmoregulation
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| Homeostasis | Steady state does not equal equilibrium with environment
--- Solute concentration
--- Volume of water
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| Hyperosmotic | Dilute medium
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| Hypoosmotic | Concentrated medium
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| Regulator | Steady blood solute concentration ( horizontal line parallel with x-axis)
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| Conformer | Variable blood solute concentration and external medium solute concentration. (Isoosmotic Line)
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| Sites of H2O exchange | Gills/lungs, Digestive tract, Kidneys
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| Sites of solute exchange | Gills (not lungs), Digestive tract, Kidneys, Special glands---> Nasal glands ( desert, marine: birds, reptiles , sharks)
Sharks- Digitiform gland)
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| Renal organs (Kidneys) | Tubular, communicate with outside, regulate composition and volume of body fluids by excretion of solutes and water.
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| Why not selectively dump wastes? | Energetically expensive, toxins, set up to filter blood, plasma into tubule.
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| Kidney positioning | Paired, Retroperitoneal ( lining of cavity, sequestered behind lining from rest of organs), Adipose capsule
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| Sagittal | Divides body into left and right
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| Transverse | Divides body into top and bottom
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| Frontal | Divides body front to back
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| Kidneys Function: | 1% of body mass, receive 25% of cardiac output
Two major functions:
Filtration of blood: Removes wastes, esp. nitrogenous
Regulation: blood volume and composition, electrolytes, blood pH, Blood pressure
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| Nephron | Functional unit of the kidney
1.) Filtration
2.) reabsorption
3.)secretion
4.)concentration
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| Urine formation | Primary Urine- blood filtrate, aqeuous solution introduced into renal tubules
Definitive urine- passed from renal tubules
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| Ultrafiltration | Forms primary urine.
Bowmans capsule (Nephron): podocytes interdigitate= filtration slits
Glomerulus (blood supply): endothelial pores in capillary (extra leaky)
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| Afferent vessels | Into organ ( thicker)
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| Efferent Vessels | Out of organ ( thin)
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| Forces that influence filtration | Glomerular blood pressure ( high BP)
Opposing forces: plasma colloid osmotic pressure ( due to large proteins still in blood), Capsular hydrostatic pressure.
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| Filtrate | Resembles blood plasma, Lacks high-molceular wt. solutes (proteins)
no Platelets, RBC, WBC.
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| Glomerular Filtration Rate (GFR) | Volume of plasma filtered/unit time by all renal tubules collectively=GFR
In humans GFR= 125ml/min
180L/day
Urine Output is about 1-2L a day
*about 99% of filtrate is reasbsorbed*
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| Clearance | Volume of blood you would have to completely clear of a substance to yield the excreted quantity. C= [U]xV/P
U= Urine [ }
V= volume of urine per time (ml/min)
P= Plasma [ ]
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| GFR=Clearance assumptions | 1.) enters nephrons only via glomerulus
2.) freely filtered
3.) not secreted or reabsorbed
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| Substances used for GFR | Inulin (not insulin).
Long chain polymer of fructose
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| If clearance = 125 ml/min | Inulin is involved, free flow, no secretion or reabsoprtion
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| If clearance = 65 ml/min | reabsorption of substances is taking place
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| if clearance = 145 ml/min | Secretion is occurring.
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| Bowman's Capsule (cortex) | receives filtrate
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| proximal convoluted tubule | reabsorption of water and solutes
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| Nephron loop/ Loop of Henle (Medulla) | Descending limb, ascending limb.
Regulates concentration of urine
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| Distal convoluted tubule | Secretion (into tubule)
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| Collecting Duct | Concentration
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| Proximal Tubule function: | Reabsorption, 67% of Na+ diffuses into epithelial cells, Active transport out to interstitial fluids, Cl- follows passively to balance charges, water follows,
Other items reabsorbed: Glucose, amino acids, K+, HCO3-
secondary active transport.
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| Descending limb of LH Function: | No active Transport of solutes, Passive diffusion of water out of lumen and reabsorbed into body. ( high concentration of urea in medulla drives this)
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| Thick segment of ascending lim of LH function: | Active transport of NaCl into interstitial fluids, low permeability to water, stays in lumen.
Countercurrent multiplier (ATP)
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| Distal tubule Function: | Secretion= active transport (K+, H+, HCO3-)
Reabsorption (Na+, Cl, HCO3-)
Some water follows
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| Collecting duct Function: | Permeable to water, water flows out of lumen(reabsorbed), into interstitial space, Urea diffuse too.
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| Mechanism of kidney | Salt gradient in interstitial fluid of medulla
Differential permeability of Loop of Henle
High osmolarity of medulla due to urea this pulls water osmotically out of collecting duct
Final urine= Hyperosmotic (high solute [ ] )
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| Loop variations | Desert animals= longer loop, deeper in medulla
Cortical nephrons= shallow
juxtamedullary nephrons= deep in medulla
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| Regulation | 1.) GFR
2.) Salt absorption
3.) water absorption
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| Regulation of GFR(low) | If blood pressure is low, or sodium low or filtration low then mechanisms to regulate GFR start.
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| Juxtaglomerular apparatus (senses/regulates) | Juxtaglomerular cells in wall of afferent arteriole .
Macula densa cells in distal tubule: monitor Na+ and Cl- conc. and water, control blood flow into the glomerulus, thus controls filtration.
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| Mechanism: Renin/Angiotensin system ( if BP is low) | Renin is released ( enzyme from arteriole), renin cleaves angiotensin (from liver), Into angiotensin 1, converted in lungs to angiotensin 2.
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| Angiotensin 2 | is responsible for vasoconstriction of peripheral and efferent arterioles, raises blood pressure, increase renal blood flow in afferent arterioles, increase glomerular filtration.
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| Regulation of GFR(high) | if blood pressure high or sodium high , then renin/angiotensin inhibited, ANF (Atrialnatriuretic factor) secreted, urinate more, secrete salt
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| Regulation of Sodium | If low sodium or high potassium. 1.) aldosterone (hormone) Mineral-corticoid from adrenal cortex saves sodium secrete potassium, stimulate by angiotensin 2( helps retain water.
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| Regulation of Water | Hormone ADH( anti diuretic hormone) or vasopressin is released by posterior pituitary, increased permeability of collecting duct, osmotically sensitive neurons detect
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