Urinary System-Human Physiology
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- Function of urinary system
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To maintain proper chemical composition of blood.
Kidneys remove things that are too high in concentration - What maintains pH of blood
- Kidney's and lungs
- Components of urine production (4)
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1) Maintain proper ionic concentrations in plasma
2) Maintain proper pH of blood
3) Eliminate toxins
4) Maintain proper water in plasma (add/remove water) to control blood pressure - Nephrons are?
- Functional unit that make up kidneys
- Vasculature of Nephron
- Renal Artery-->Afferent Arteriole-->Glomerulus--> Efferent Arteriole--> Peritubular Capillary--> Venule--> Renal Vein (leaves kidney)
- Glomerulus
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Where filtration occurs
Knot of a capillary
"fenestrated capillary" endothelial pores allow filtration of blood plasma.
Proteins do not filter
Plasma and dissolved particles filter through glomerulus - Tubules of Nephron
- Bowman's capsule-->Proximal Convoluted Tubule--> Loop of Henle--> Distal Convoluted Tubule-->Collecting Duct
- Reabsorption
- Things sucked out of tube, back to bloodstream
- Secretion
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Out of blood stream into tube. Seen with toxins.
Utilizes active transport. - Urine=
- Filtered-Reabsorbed + Secreted
- P(gr)
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Pressure of glomerular capillary
Pressure driving blood out of glomerulus
55mmHg - P(t)
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Tubular (capsular) pressure
15mmHg - P(co)
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Colloid osmotic pressure
30mmHg - P(f)
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Effective Filtration Pressure
10mmHg - What happens in nephron
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-20% of plasma is filtered at glomerulus
-99% of filtrate, reaborbed
-1% of that which is filtered becomes urine - Glomerular Filtration Rate
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1) P(f) Effective Filtration Rate
2) Filtration Coefficient - Filtration Coefficient
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Under normal conditions =12.5ml/min/1mmHg P(f)
GFR= 125 ml/min- Amount of plasma squeezed out/min - Ideal substance to monitor for GFR measurement
- Creatinine
- "Plasma Clearance Test"
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How much of substance is being filtered
Collect urine over 24 hours and blood test to see how much creatinine in blood - Ucr
- [Cr] in Urine--> 30mg/ml
- Pcr
- [Cr] in plasma--> 0.3 mg/ml
- Uvol
- Urine Volume--> 1800ml
- T
- Time (minute)-->1440 minutes
- Plasma Clearance Test Equation
- (Ucr/Pcr)x(Uvol/T)=125ml/min
- Results of Clearance Test leads to medicine?
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High-->Filtered/Secreted
Low-->Filtered/Reabsorbed...administer in higher does to keep in body - Autoregulation of GFR
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Myogenic Reflex
-In afferent arteriole
-Smooth muscles within arterioles act to a stretch, by constricting - GFR and Blood Pressure
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-BP(UP)-->Arterioles Stretch-->Vasoconstriction--> Blood Flow Stabilized
-BP(Down)--> Arteriole Strength (Down)--> Vasodilation--> Blood Flow Stabilized
-BP (DOWN,DOWN)-->Filtration (DOWN)
-Kidneys stop using glomerulus - Reabsorption is Variable
- Differential factor composing blood composition
- Volume of Blood Filtered and Reabsorbed
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Filtered=125ml/min
Reabsorption=124ml/min
Urine is 1ml/min - Components that are reabsorbed
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Water-99%
Sodium-99.5%
Glucose-100%(normal)
Amino Acids-100%
If glucose/AA seen then they are in excess or there is kidney damage - Passive Reabsorption
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-Via specific channels
-Concentration gradients and electrical gradients are created by active transport - What is passively absorbed?
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Water
Urea
Chloride - Why is water highly reabsorbed?
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-Most complex because it is last mechanism under control of a hormone
-Reabsorption is increased if ADH is not available - ADH?
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Anti-Diuretic Hormone
-vasopressin
When ADH is high in blood, don't make as much urine.
Alcohol supresses ADH--> Urinate more - Active Reabsorption
- Pumping components back into blood so that little of it is in urine
- Sodium Reabsorption
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80% of ATP Generation
Unique and complex process - Where sodium reabsorption occurs
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1) Proximal Convoluted Tubule
2) Loop of Henle
3) Distal Convoluted Tubule & Collecting Duct - Sodium Reabsorption in Proximal Tubule
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Sets up passive reabsorption of Chloride, Water, and Urea
-Chloride-electrical gradient
-Water and Urea-Concentration Gradient - Sodium Reabsorption in Loop of Henle
- In ascending limb water will follow sodium resulting in concentrated urine production
- Sodium Reabsorption in Distal Tubule & Collecting Duct
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Depends on Aldosterone
Presence of aldosterone causes sodium to be reabsorbed
No Aldosterone= No Absorption= No water absorption= More urine produced - Secretion in Urine Production
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Get things out of blood stream
Essentially is active transport backwards
Uses sodium linked pumps (antiport pumps) - Antiport pumps in secretion
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Na/K Pump
Na/H Pump
Na/NH3 Pump
Various other pumps - Na/K Pump in secretion
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Na out/K in
Eliminates K+ - Na/H Pump
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Secretes H+
Maintains Blood pH - Na/NH3 Pump
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Ammonia (nitrogenous) is toxic to tissues
Pumped out of blood and in to tubules - Drug Tests
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Use Plasma Clearance Test
Normal GFR=125ml/min
If urinated amount is greater than 125ml/min then drug is secreted
-Antibiotics are secreted (penicillin in wartime) - Urine Composition
- -99% water
- Kidney Regulation
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1) Blood Osmolarity (water/electrolyte balance)
2) Blood Pressure
(by regulating blood volume)
Incredible water osmolarity gradient set up in loop of henle - Actions in Descending Loop
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Impermeable to sodium
water channels-aquaporins
Becomes more concentrated as it loses water and becomes incredibly salty
Losing water generates higher osmolarity to pump sodium out of ascending limb - Actions in Ascending Loop
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Sodium Pumps
Impermeable to Water
Change of 200mOsM of sodium concentration
Pumps out sodium, potassium, and chloride and filtrate becomes hyposmotic - "Renal Counter Multiplier"
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Makes region extremely concentrated in sodium
Reason: Since final collecting duct passes through region and water can be sucked out to concentrate urine - Vasa Recta
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Loop of blood vessel traveling down with loop of henle
Collects water from loop so water does not dilute sodium - Characteristics of Animal Urinary Tract
- Animals who must store water to survive have extremely long loops of henle and produce very concentrated urine
- ADH (part 2)
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Target cells that make up collecting duct
Collecting duct cells--> synthesis of aquaporins
-ADH produced by pituitary gland
-Essentially hypothalamus controls production of urine - Hypothalamus Responds To (3)
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Blood Osmoreceptors
Baroreceptors
Angiotensin II - Hypothalamus Response: Blood Osmoreceptors
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Responds to osmolarity of blood and CSF (within Hypothalamus)
Trigger Hypothalamus to allow more/less urine production - Osmolarity Up/Down
- Up: hypothalamus-->pituitary--> ADH (UP)--> Water reabsorbed
- Osmolarity (Down)
- Hypothalamus-->Pituitary-->ADH (DOWN)-->No (less) water reabsorbed
- Baroreceptors: Hypothalamus Response
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Located in Aorta, Int. Carotid
Monitor BP
No effect when BP in normal range with regards to ADH - -Blood Pressure (Way Up)
- --> ADH (Down)--> Water Reabsorption (Down)--> Urine (UP)
- -Water intake (UP)
- -->Blood osmolarity (Down)-->ADH (Down)--> Water Reabsorption (Down)-->Urine Volume (UP)
- -Sodium Intake (UP)
- Blood Osmolarity (UP)-->ADH (UP)--> Water reabsorption (DOWN)-->Urine Volume (Up)
- Angiotensin II: Hypothalamus Response
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Hormone
Certain levels cause hypothalamus to produce ADH - After a lot of salt intake, control for Sodium is?
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Aldosterone
-Controls sodium reabsorption - Cells for sodium regulation
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Juxtaglomerular Cells (JG)
-Located in wall of afferent arteriole
-Sensitive to changes in blood pressure
-Secrete Renin - JG Cells respond to?
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1)Blood Pressure Directly
2)Sympathetic Nervous System - JG response to blood pressure
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BP (DOWN)-->JG Cells-->Renin
BP (DOWN)-->Hypothalamus--> Increase sympathetic tone--> Heart rate increases--> NorE--> JG Cells-->Renin - Angiotensinogen
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-always in blood; inactive
Angiotensinogen--renin-->Angiotensin I (still inactive)--ACE-->Angiotensin II (active hormone) - ACE?
- Angiotensin Converting Enzyme
- Angiotensin II Effects?
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1) Adrenal Gland--> Aldosterone
-Increase activity on sodium pumps
-Increase sodium reabsorption
-More sodium in blood, water reabosrbed, BP up
2) Vasoconstrictor (most powerful), BP up
3) Hypothalamus--> Pituitary Gland-->ADH (UP)-->BP (UP) - Normally seen in urine?
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Water
Electrolytes
Nitrogen-Base Metabolic Bi-Products
-filtered and actively secreted - Not normally seen in urine?
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Protein
Amino Acids
Glucose - How protein can be found in urine?
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Too big to be filtered
Only seen in urine if:
-Incredibly high blood pressure
-Renal pathology causing inflammation of glomerulus: pores open wider - Why amino acids/glucose not seen in urine?
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- All are Actively Absorbed
-Secondary Active Transport
--Use [Na] gradients to carry glucose/amino acids into blood stream (synport) - How amino acids/glucose can be seen in urine?
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Limited in rate they can work
-if synports are saturated, not all glucose/amino acids can be reabosrbed -
Max Reabsorption Rate of Glucose
Max Plasma Glucose -
375mg/min
>375mg/min, saturated with glucose
Max Plasma Glucose=300mg/dl, more than 300, glucose seen in blood. - Average Glucose in blood
- 100mg/100ml, in blood 100mg/dl
- How much glucose is filtered?
- 125ml/min...so all glucose can be filtered at normal level
- Diabetes Mellitis (Honey)
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Cells cannot take up glucose
Glucose found in urine
Produce large volume of urine
Water not reabosrbed since water follows concentraton gradient. Concentration is high in urine, no osmosis - Diabetes Insipidus (No Taste)
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Urine Production (UP)
Pituitary gland insufficient in ADH production
Water not reabsorbed
Urinate often - Hypertension Medication
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1) ADH Inhibitors
2) Inhibit Production of Aldosterone. ACE Inhibitors
-Angiotensin Converting Enzymes
-Bind ACE
-Allow Vasodilation