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Filtration of blood and production of urine
Transportation of urine
Urinary Bladder function?
Storage of urine
Excretion of urine
- Stretch receptors signal spinal cord and brain
- When VL exceeds 200-400ml
Micturition center in sacral spinal cord triggers what reflex?
- Parasympathtic fibers cause detrusor muscle to contract - squeezes urine out
- external & internal sphincter muscles to relax and allow flow
Desire to urinate before reflex occurs..
- Conscious control of external sphincter
- Cerebral cortex can initate micturition or delay it for a period of time.
Kidneys: Renal corpuscle function?
filtration ofblood plasma
Capillary with blood in Renal Corpuscle
Collects filtrate from blood in Renal Corpuscle
- Proximal convoluted tubule
- Descending & Ascending loop of Henle
- Distal convoluted tubule
- Collecting duct
- Papillary duct
- Minor & Major Calyx
- Renal Pelvis
- Ureter > Urinary bladder > Urethra
- Water & small soultes in blood plasma move across the wall of the glomerular capillaries into glomerular corpuscle and then renal tubule.
- PCT > loop of henle > DCT > collecting duct
As filtrate moves along tubule water and many useful solutes reabsorbed = returned to blood
filtrate moves along tubule other molecules are secreted into fluid (wastes, drus & excess ions)
What drives filtration?
- Blood Pressure
- 20% of plasma becomes filtrate
Filtration Membrane: What is filtered?
- Water, ions, small molecules & small proteins move through membrane :lucose, amino acids,
- Becomes filtrate
Fenestration of glomerular endothelial cell
Prevents filtration of blood cells but allows all components of blood plasma to pass through
Basal lamina of glomerulus
Prevents filtration of larger proteins -Albumins
Slit membrane between pedicels
Prevents filtration of medium sized proteins
Glomerular Blood Hydrostatic Pressure (GBHP)
Capsular Hydrostatic Pressure (CHP)
Blood Colloid Osmotic Pressure (BCOP)
Net Filtration Pressure (NFP)
GHBP - CHP - BCOP = 55mmhg - 15mmhg - 30 mmhg = 10mmhg
Functions of Kidneys
- Regulates ions in blood
- - blood pH
- - Blood Volume and Blood Pressure
- - Blood Glucose levels
- Maintains Blood Osmolarity
- Produces Hormones
- Excretion of wastes
Regulation of pH in Kidneys
- Removes H+ from blood
- Maintains bicarbonate ions (HCO3-) in blood
Regulation of Blood Volume and BP
- Retention of water = increases BP
- Elimination of water = decreases BP
Production of Hormones in Kidneys
- Calcitrol - Form of Vita. D (Active)
- ---Calcium homeostasis
- Erthropoietin (EPO) - RBC production
Regulation of Blood Glucose levels in kidneys
Can synthesize glucose from glutamine
Excretion of wastes in Kidneys
- Ammonia & Urea
- Uric Acid (purine metabolism - A's & G's of DNA)
- Drugs and Toxins
Arthritis - Excess uric acid
Production of Urine
- 1. Glomerular Filtration
- 2. Tubular reabsorption
- 3. Tubular secretion
GFR -too high =
useful substances are lost Urine
GFR- too low =
Not enough Waste products removed from body
Mechanisms that maintain a constant GFR
- Renal Autoregulation
- - 1. Myogenic Mechanism
- - 2. Tubuloglomerular feedback
2 ways kidneys help maintain a constant renal blood flow
- - Evalated BP cause Stretching of the afferent arteriole
- - Smooth muscle contraction constricts afferent arteriole returning GFR to its previous level.
Tubuloglomerular feedback :
- Elevated BP raises the GFR so that fluid flows too rapidly through the renal tubule
- - macula Densa Cells detect that filtrate is moving too fast.
- - Inhibits the release of Nitric Oxide (NO)- a vasodilator
- - Afferent arterioles constrict & reduce GFR
- Sympathetic neurons cause vasocontriction of afferent arterioles
- - Decreases GFR = lowers urine output and permits blood flow to other tissues
- -At rest, renal Blood vessels are maximally dilated because sympathetic activity is minimal. (Parasympathetic is maximal)
- - Angiotensin II = decrease GFR
- -low blood VL & low BP stimulates productoin of Angiotensin II
- - Potent vasoconstrictor that narrows bothafferent & efferent arterioles reducing GFR
- - atrial natriuretic peptide (ANP)
- -strecthing of the atria due to an increase in blood volume causes release of ANP
- - increases capillary suface area by relaxation of mesangial cells
- - Increases GFR
Glomerular Filtration Rate must remain
Constant - homeostasis requires GFR to remain constant
- -low blood volume and low BP stimulates production of Angiotensin II
- -Potent Vasoconstrictor that narrows both afferent & efferent arterioles reducing GFR
Atrial Natriuretic Peptide (ANP)
due to an increase in blood VL causes release of ANP
- increase in capillary surface area by relaxation of mesangial cells
What is the Renal Hilum? 5 specific structures?
- 1. lymphatics
- 2. nerves
- 3. ureters
- 4. renal vein
- 5. renal artery
What are renal Columns?
columns of tissue that are identical to the tissue found in the renal cortex but located in the medulla between renal pyramids.
What are renal pyramids?
Cone-shaped arrangement of tubules in renal medulla
Who has a loner urethra males or females?
Internal urethral sphincter is voluntary or involuntary?
external urethral sphincter is voluntary or involuntary?
Tubular Reabsorption along the Nephron
- 180L of filtrate produced
- 99% must be reabsorped by Nephron
- Water + Solutes move tubules to Peritubular Capillaries
Peritubular Capillaries (PCT)
65% of water follows by osmosis
- Has Microvilli- does the reabsorption
- Solutes are reabsorbed by Active Transport and Passive Diffusion - GLucose, amino acids, urea, and ions
Reabsorption in the PCT
100% of: Glucose, amino acids, lactic acid, water soluble vitamins and other nutrients are Completely areaborped in the 1st half of the PCT
Reabsorption of NA+ in PCT produces what?
Produces electrical gradient that caused Cl- to follow by passive transport
What helps "pull" water out of the tubule in PCT?
Accumulation of NaCl outside tubule produces an osmotic gradient?
Reaborption at the descending Loop of Henle
- 15% of filtered water ir reabsorbed
- High solute content of medulla "pulls" water out -By Osmotic gradient
- Impermeable to solutes = Little reabsorption of more solutes
Reaborption at the Ascending Loop of Henle
- Variety of transporters reclaim more ions by diffusion
- Impermeable to water = little reabsorption of water
Reabsorption at the Distal Convoluted Tubule
- Reabsorption of Na+ and Cl- continues
- 10-15% of water reabsorption by Osmosis
- Serves as the major site where Parathyroid hormone stimulates reaborption of Ca+2
What Serves as the major site where Parathyroid hormone stimulates reaborption of Ca+2?
The Distal Convoluted Tubule
Collecting Ducts cells
- 95% of solutes & water have been reabsorbed by the end of DCT
- Principal Cells & Intercalated cells make the final adjustments
- Target 2 hormones that promote reabsorption of more water and Ions
- 1.ADH-anti-dieuretic, Targets principal cells in collecting duct
- ----Increases water reabsorption
- 2. Aldosterone- increases reabsorption of Na+ and Cl- (water's reabsorbed)
- ----Secretion of a varible amount of K+
What does ADH do in the collecting duct?
-anti-dieuretic, Targets principal cells in collecting duct----Increases water reabsorption
What does Aldosterone do in the collecting duct?
- - increases reabsorption of Na+ and Cl- (water's reabsorbed)
- -Secretion of a varible amount of K+
- Help regulate pH of body fluids
- Proton pumps (H+ATPases) secrete H+ into tubule (prevents accumulation of blood)
- Reabsorption of bicarbonate ions (buffers blood pH)
What do proton pumps do in Intercalated cells? What does this prevent?
- Proton pumps (H+ATPases) secrete H+ into tubule
- Prevents accumulation of blood
What is the function of bicarbonate ions in Intercalated cells?
- When reabsorbed they buffer blood pH
- (so you dont urinate acid)
ADH Feedback System
- -Simulus: High osmolarity of body fluids (low water, dehydration)
- -Receptor: Osmoreceptors of hypothalamus
- -Control: Hypothalamus/Post. Pituitary release ADH
- -Effectors: Principal cells of collecting ducts
- 1. insertion of aquaporin-2 channels into the tubule
- 2. h20 molecules move out of collectging duct and into bloodstream
- 3. Conservation of water results in concentrated urine (yellow urine)
ADH Feedback: Stimulus
-Simulus: High osmolarity of body fluids (low water, dehydration)
ADH Feedback: Receptors
-Receptor: Osmoreceptors of hypothalamus
ADH Feedback: Control Center
-Control: Hypothalamus/Post. Pituitary release ADH
ADH Feedback: Effectors
Effectors: Principal cells of collecting ducts
ADH Feedback: Responses (3)
- 1. insertion of aquaporin2 channels into the tubule
- 2. h20 molecules move out of collecting duct and into bloodstream
- 3. Conservation of water results in concentrated urine (yellow urine)
- 1.Low BV/BP causes Renin to be release from kidneys
- 2.Renin stimulates release of angiotensinogen converts to angiotensin 1
- 3. Angiotensin 1 converts ACE into Angiotensin 2
- 4. Angiotensin 2 causes aldosterone to retain Na+ & water and vasoconstriction of Afferent arterioles which lowers GFR. (Both raise BV then BP), and vasoconstriction of arterioles which raise BP
Atrial Natriuretic peptide does what?
- 1.Inhibits secretion of aldosterone & ADH
- 2.Suppresses reabsroption of Na+ which increases urine output and decreases blood volume
- 3.increases GFR by increasing permeability of glomerulus
Angiotensin 2 stimuli & effects
- Stimuli: low BV/BP
- Effects: Increases reaborption of Na+ & other solutes, Increases BV
Aldosterone stimuli & effects
Effects: Increases secretion of K+ and reabsorption of Na+, Cl-; increases reabsorption of water = Increase in BV
ADH stimuli, mechanism & effects
- Stimuli: increased osmolarity, decreased BV, released from post. pituitary gland
- Mechanism: insertion of aquaporin 2 channels.
- Effects: Increases facultative reaborption of water
Atrial Natriuretic Peptide (ANP) effects
- Natriuresis- increased excretion of Na+ in urine
- Diuresis- Increased urine output
- Decreases BV
- Gets rid of water
What is Natriuresis?
Natriuresis- increased excretion of Na+ in urine
What is Diuresis?
Increased urine output
Parathyroid Hormone site of action & effects
- Site of action: Distal tubule cells
- Effects: Increases reabsorption of Ca2+
What hormones Increase BV?
Angiotensin 2, Aldosterone
Tubular Secretion does what?
Transfers materials from blood into filtrate/urine
Tubular Secretion is located where?
At various locations along tubules
Tubular Secretion eliminates what?
excess K+, ammonia, urea, creatinine - depends on diet
Tubular Secretion & Penicillin
Penicillin gets metabolized by liver or kidneys secrete it
Where does H20 get reabsorbed?
- 65% Proximal convoluted tubule (osmosis)
- 15% Loop of Henle (osmosis in descending limb)
- 10-15% Early Distal Convoluted Tubule
- 5-9% Late DCT & collecting duct (insertion of h20 channels stimulated by ADH)
Where does glucose get reabsorbed?
100% Proximal convoluted tubule
Where do amino acids get reabsorbed?
100% proximal convoluted tubule (symporters and facilitated diffusion)
- Promote diuresis
- -Most potent- loop diuretics- inhibits transporters (Na-K-Cl symporter) in the ascending loop of henle
- Drug: LASIX - congestivie heart failure, edema, hypertension
What are some substances that slow the renal absorption of h20 and cause diuresis?
- Caffeine - inhibits Na+ reabsorption
- Alcohol- inhibits ADH secretion
- Prescription meds- can act on the PCT, loop of henle or DCT
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