THe Urinary System
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What does the Urinary System consist of?
1 urinary bladder
What is the major function of the urinary system
Excretion of Organic Wastes
Other Functions of the Urinary System?
- 1) Regulation of plasma concentrations of important ions
- (Na, K, Cl, Ca, Mg, PO4)
2) Regulation of blood volume and thus blood pressure
3) pH regulation in blood
4) Conserve nutrients and H20
5) Assists liver in detoxifying
6) Activation of Vitamin D
7) Aid in RBC production
How does the urinary system regulate blood volume and blood pressure?
1) Adjusting the volume of H2O lost in the urine (ADH & Aldosterone)
2) Release of EPO
3) Release Renin--> angiotensin I ---> angiotensin II ----> ALDOSTERONE -----> and increases thirst
The Kidney are protected by 3 layers of the concentric connective tissue. What are they?
1) Renal Capsule- collagen covers the entire surface of the kidney
2) Adipose Capsule- Surrounds the renal capsule, may be quite thick
3) Renal Fascia- Collagen fibers, fibers extending outward from the renal capsule through the apidose to anchor kidneys into the abdominal wall
Where is the Urine made?
How many nephrons are in a kidney?
Where are most nephrons located?
Adrenal Cortex (80-85%)
WHat are the 3 Processes in making the urine?
1) FIltration (renal corpuscle)
2) Absorption (prox. tubule, loop of henle, distal tube and collecting duct)
3) Secretion (distal tubule, and other areas of the nephron)
What is Filtration based on?
Large proteins dont get filtered, but smaller molecules like amino acids, glucose, vitamins, and h2o are filtered across the kidney tubule
IMPORTANT NUTRIENTS (AA'S, GLUCOSE, VIT'S) ARE REABSORBED BACK INTO THE BLOOD!!!!
HOW MUCH OF THE H2O WILL BE REABSORBED IN THE NEPHRON?
Substances like H+ and morphine or penicillin will be actively secreted into the tubule and exit the body in the urine
WHat is the Glomerulus and what is its function?
Filtrates 180L of filtrate enter the nephron each day!!!!
Capillary network across which filtration occurs.
force of the BP forces the H2o and other small molecules out (10 mmHG)
How does the Blood FLow through the glomerulus?
Blood Enters through the afferent arteriole
Blood EXITS through the EFFERENT arteriole
(Blood in the efferent arteriole travels through the peritubular capillaries and enters the venous system through the interlobular vein)
Function of Bowman's Capsule?
Filtrate enters here
has a visceral and parietal layer
- CONTAINS PODOCYTES!!!!!!!!!
- ------>>>>>> FILTERING CELLS!!!!!
Function of the Proximal Convoluted Tubule??
Much reclaiming of H2O and nutrients occur here
60% of H2O and 65% Nutrients are REABSORBED HERE!!!!!
Contains many microvilli
What is the function of the Loop of Henle
20% of H2O entering the nephron is reclaimed in the Henle's Loop
Na+ and H2O are regulated here
Ascending Loop- Na+ is Actively pumped out
Descending Loop - moves H2O out by osmosis
What is the Countercurrent Mechanism?
Where Na+ is actively pumped out (countercurrent multiplier) This Mechanism allows for a high [Na] to "pull" H2O out of the descending tubule from whence in enters the peritubular capillaries
WHat occurs at the Distal Tubule and Collecting Duct?
1) Aldosterone is used to promote Na+ retention in the kidney
2) H2O is only absorbed if ADH IS PRESENT
****without ADH, this part of the nephron is impermeable to H2O and water cannot move out of the tubule and is lost as urine
HOWEVER- WITH ADH:
The tubule is permeable to H2O and so Water is Drawn out into the salty interstitial fluid by osmosis
3) Secretion of molecules (H ions for pH levels, K for neural and cardiac system- controlled by aldosterone)
Diabetics who do not have ADH present
Can void up to 20L a day
Will dehydrate the diabetic if treatment is not given
What is the function of Aldosterone?
Promotes Na+ retention in the kidney.
Acts on Na+ pumps in the distule tubule and collecting duct.
Pumps out more Na+ into the interstitial fluid, thus H2O follows, conversing H2O in the body----> K is pumped into the tube as Na+ is reabsorbed in a countertransport mechanism
ALDOSTERONE REGULATES BOTH THE RETENTION OF NA+ AND THE EXCRETION OF K+
How is Aldosterone turned on?
High Potassium promotes the release of aldosterone from the zona glomerulosa of the adrenal cortex
How is Secretion Importatant? Which part of the nephron is this mostly found in?
Secretion occurs in the distal tubule and collecting duct
Secretion is important for pH REGULATION
---->>>>>>When the blood pH is too acidic, the kidney secretes H+ into the lumen of the tubule to leave in the urine
What is the juxtaglomerular apparatus?
1) Macula Densa- special cells on distal convoluted tubule
2) Juxtaglomerular cells- on the walls of teh afferent arteriole
What is the function of the Juxtaglomerular Apparatus?
Function of the Juxtaglomerular Apparatus:
1) Secrete EPO
2) Secrete Renin
How does the Renal arteries supply blood in the urinary system?
Branches from the abdominal aorta to deliver blood to the kidney
How do Segmental arteries supply the kidney with blood?
They branch from the renal artery
How do Interlobar arteries supply blood to the kidney?
Branch from the renal artery and run between the renal pyramids
Where are the Arcuate arteries located?
Arc across the renal pyramids, located at the boundary between the medulla and cortex
Where are the interlobular arteries located?
branch from arcuate arteries
connects to many glomeruli
then enters to the afferent arteriole
Order of Blood flow through the kidneys
1) Renal Artery
2) Segmental Artery
3) Interlobar Artery
4) Arcuate Artery
5) Interlobular Artery
6) Afferent Artery (many glomeruli branch from 1 interlobular artery)
7-8) Afferent Artery enters the glomerulus, while Efferent Artery exits and goes to the peritubular capillaries
9) From the peritubular capillaries, goes down to the Vasa recta
10) Out through the Interlobular Vein
11) Arcuate veins
12) Interlobar veins
13) Renal vein
14) INferior Vena Cava
15) Back to the Heart
What is the Vasa Recta?
Portion of the peritubular capillaries that cover/line Henle's Loop
WHat is Renal Fraction?
How much of the blood supply got into the kidney. Amount of % of cardiac output that goes through renal corpuscle in one minute
Where does the FIltrate occur?
After the Bowman's Capsule!
What is a FIltration Fraction?
it's what you have filled. (% of the plasma- liquid part) that got filtrated
Functions of the Innervations of the Nephron
Functions of the sympathetic innervation include:
1 ) Regulation of glomerular blood flow and pressure via efferent and afferent arterioles
- 2) Sympathetic CONSTRICTS the small arteries and afferent arteries
- ------>>>>>> THis decreases renal blood flow and decreases filtrate formation.
During intense/ extreme sym. inervation- decreases rate of filtrate formation to 2-3 mls (normal is 125/mls)
Processes of Tubular Function
- 1) Filtration- hydrostatic pressure (blood pressure)
- forces blood out of glomerus
- H2O- passive through osmosis
- Nutrients- active transport, carrier proteins employed
- Ions- active or passive (diffusion)
3) Secretion- active and passive processes used. Carrier proteins maybe used
What are characteristics of Carrier Mediated Transport
1) Specificity- carriers are specific for their substances
2) Carries go in 1 direction
3) May vary from 1 are of a cell to another
4) Cell membranes my carry > 1 type of carrier
5) Carrier proteins (enzymes) have saturation enzymes
What is the Tm Value, Tubular Transport Maxim?
The concentration of the substrate at saturation (can only go soo fast ie. I Love Lucy)
What is Renal Threshold?
The [ ] of substrate which exceeds the Tm value, at which point the substances begin to appear in the urine
Normal Renal Threshold for glucose is 180 mg/dl
- Normal Renal Threshold for Amino Acids is 65 mg/dl
- ---> Thus, after high protein meals, protein is found in urine bc of low renal threshold
What is the Glomerular Filtration Rate, GFR
GFR is the amount of filtrate formed a minute
= 125 ml/ min
GFR IS DIRECTLY DEPENDENT ON FILTRATION OF THE GOLMERULAR CAPILLARIES
decrease in renal pressure= decrease in GFR
- (if renal blood pressure decreases too much, no filtration occurs)
What is Autoregulation?
Local control over the GFR
Carried out by the Macula Densa cells of the distal tubule
THROUGH AUTOREGULATION, GFR IS KEPT AT A CONSTANT RATE
What happens if the GFR is too Low?
NOT ENOUGH FILTRATION WILL OCCUR!!!!
(GFR= AMOUNT OF FILTRATE MADE PER MINUTE)
THE AFFERENT ARTERIOLE IS DILATED AND THE EFFERENT ARTERIOLE IS CONSTRICTED---->>>>>
THIS SPEEDS UP THE GFR AND RAISES HYDROSTATIC PRESSURE IN TEH GLOMERULUS
WHAT HAPPENS WHEN GFR IS TOO HIGH??
CONVERSELY, AFFERENT ARTERIOLE IS CONSTRICTED AND EFFERENT ARTERIOLE IS DILATED.
THIS SLOWS DOWN THE GFR AND LOWERS FILTRATION PRESSURE
What is Osmotic Concentration of the Filtrate
The number of particles of solutes/ L
1 mole of solute/L = 1 osmole or 1000 milliosmoles
**** body fluids are 300 mOsm
- (sea water= 1000 mOsm)
- (fresh water= 5 mOsm)
How is the filtrate concentrated?
Filtrate starts out at 300 mOsm---> then becomes more concentrated as it descends
Becomes more concentrated as it descends Henle's Loop because of the loss of H2O
MOST CONCENTRATED AT TEH END OF THE LOOP WITH 1200 mOsm
How is the Filtrate more Dilute?
As the filtrate ascends, it becomes more dilute
Becomes more dilute because of the loss of Na+
THEN, in distal tubule becomes more concentrated with ADH and ALDOSTERONE
What is most important for determining concentration and volume of the urine?
WHAT ACTS TO INHIBIT ADH AND ALDOSTERONE?
ANP (Atrialnuretic peptide)
Which term describes the reabsorption of H2O in the proximal tube?
Obligatory water reabsorption
"Obligatory" because proximal tube is water permeable and this CANOT be altered
Which term describes the reabsorption of H2O in the Distal tube & Collecting Duct?
Facultative water reabsorption
"Facultative" because reabsorption is regulated in this part of the tubule
What is a calculated value representing The VOLUME of plasma that is cleared of a specific substance each minute?
- (quality of urine) ml/min X [substrate] in urine [substances] in the plasma
What is the Tubular Load
THe total amount of a substance that passes through the filtration membrane into the nephron each minute
(ie) WHen the tubular load of glucose exeeds the Tm, glucose is found in the urine
(Tm is the [ ] of substrate at saturation and the tubular transport maximum)
Tubular Load _____ 1) calculated value representing volume of plasma that is cleared of a specific substance each minute
Tubular Maximum value ____ 2) Amount of filtrate formed per minute
Glomerular Filtration Rate ____ 3) [ ] of substrate at saturation
Osmotic Concentration of Filtrate ____ 4) Number of Particles of solutes/ Liters
Plasma Clearance ___ 5) Total number of substances that passes through the filtration membrane into the nephron each minute
Renal Threshold ___6) the [ ] of the substrate which exceeds the Tm value atwhich point the substrate shows in the urine
Tubular Load _5_ 1) calculated value representing volume of plasma that is cleared of a specific substance each minute
Tubular Maximum value _3_ 2) Amount of filtrate formed per minute
Glomerular Filtration Rate _2_ 3) [ ] of substrate at saturation
Osmotic Concentration of Filtrate __4__ 4) Number of Particles of solutes/ Liters
Plasma Clearance 1_ 5) Total number of substances that passes through the filtration membrane into the nephron each minute
Renal Threshold _6_6) the [ ] of the substrate which exceeds the Tm value atwhich point the substrate shows in the urine
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