PHYSIOLOGY Excretory System
Transcript of PHYSIOLOGY Excretory System
PHYSIOLOGY
Excretory System
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EXCRETORY SYSTEM
2 Kidneys
1 Bladder
2 Ureters
1 Urethra
Kidneys, Skin, Lungs, GIT, Salivary glands and Liver are the main channels through which excretion takes place
URINARY SYSTEM
comprises of:
Size of a Fist
Weight: 150 g
Anatomy:
• Has a concave medial border
• Hilum where nerves blood and lymph
vessels enter and exit & ureter exits
Histologically divided into:
o Outer cortex
o Inner medulla - consists of
▪ Medullary pyramids - Conical or pyramidal structures
▪ From the base of each medullary pyramid, parallel arrays of tubules, the medullary rays, penetrate
the cortex
▪ Urine flows from medullary pyramids – minor calyx - major calyx- ureter –bladder
KIDNEY
Location:
Retroperitoneal cavity in the upper dorsal region of the abdomen
Structure of Kidney:
• Kidneys are paired organs
• Shape: Pear shaped
• Contain approximately 1 million Nephrons
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HISTOLOGY OF EXCRETORY SYSTEM
Parts of Nephron Lining epithelium
Renal corpuscle
1. Glomerulus
2. Bowman's capsule
• Bowman’s capsule
- Simple squamous epithelium on its outer (parietal) wall
- Its glomerular (visceral) wall is composed of specialized epithelial
Podocytes.
• Podocytes give out primary foot processes - branch as secondary processes (related
to the basal lamina) tertiary processes, give rise to the terminal pedicels.
• Between two layers is urinary space, which is continuous with the proximal
convoluted tubule
Proximal convoluted
tubule
• Cuboidal, or low columnar, with microvilli which form a brush border
Loop of Henle • U-shaped structure consisting of a thick descending limb, a thin descending limb,
a thin ascending limb, and a thick ascending limb
• Thin parts lined by squamous epithelial cells, thick part same as DCT.
Distal convoluted
tubule
• Simple cuboidal epithelium with no brush border
Collecting Tubule
• Smaller collecting tubules are lined with cuboidal epithelium
• As they penetrate deeper into the medulla, their cells increase in height until they
become columnar
Nephron:
• Functional unit of Kidney
• Comprises of:
o Bowman’s capsule
o Glomerulus
o Proximal convoluted tubule
o Loop of Henle
o Distal convoluted tubule
o Collecting tubules
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JUXTA GLOMERULAR APPARATUS
URETERS
• Ureters are the ducts that carry urine from the corresponding kidneys to the urinary bladder.
• Ureter is a muscular tube made up of mainly three layers
•Modified smooth muscle cells
within afferent arteriole
•Secrete Renin which converts
Angiotensinogen to angiotensin I
•Angiotensin I is converted by
ACE (Angiotensin converting
enzyme) to Angiotensin II
Juxta glomerular cells
•Mesangeal cells/ lacis cells are
the interstitial cells of the JG
apparatus.
•They relay the signals from
macula densa to the granular
cells
Polkissen cells
•Cells of distal tubule thought to
be involved in sensing Na+
concentration- They act as
chemoreceptors
Macula Densa
Transitional epithelium, thrown onto many folds giving lumen star shape
Epithelium Lamina propria
Upper 2/3rd two layers with inner longitudinal and outer circular
Muscular layer
Connective tissue with blood vessels, lymphatic and nerves
Adventia layer
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BLADDER
The bladder itself ("musculomembranous sac") consists of 4 layers:
Mucous
•Transitional epithelium/urothelium, known for its stretchability, regaining back its original position and structure after release of force/ stretch.
•Mucosa has folds known as rugae when the bladder is empty or is only filled to a small extent
Muscular
•Detrusor muscle is the muscle of the urinary bladder wall.
•Consists of three ill defined layers of smooth (involuntary) muscle fibres:
•Internal longitudinal layer
•Middle circular layer
•External longitudinal layer
Adventitia
•Fibro elastic connective tissue with blood vessels, lymphatic and nerves
•Features observable on inside of the bladder are:
•Ureter orifices
•Trigone
•Internal orifice of the urethra
Trigone
•Synonyms:
•Trigonum vesicae or Trigone vesical
•Mucous membrane:
•Firmly bound to the muscular coat
•Always smooth
•Internal urethral sphincter :
•Sphincter (circular) muscle located at the neck of the bladder
•Control the process of Micturition
•This (involuntary) muscle is formed from a thickening of the detrusor muscle
•Closes the urethra when the bladder has emptied
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NEPHRON
NOTE: Total area of glomerular capillary membrane across which filtration occurs is about 0.8 square meters
Glomerulus
•Consists of:
•Tuft of 20-40 capillary loops
•Protruding into Bowman's capsule, which is the beginning of the renal tubule
•Capillary endothelium is fenestrated
•Incomplete basement membrane
•Together these structures provide a minimal resistance for filtration of plasma
•Show retention of plasma proteins & blood cells
Renal tubule
•Begins as Bowman's capsule, which is an expanded, invaginated bulb
surrounding the glomerulus.
•Epithelium of Bowman's capsule:
•Is an attenuated layer
•400 A in thickness
•Renal tubule consists of:
•Proximal convoluted tubule
•Loop of Henle
•Distal convoluted tubule
•Collecting duct - that carries the final urine to renal pelvis & Ureter
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Types of Nephrons
RENAL BLOOD VESSELS
Each afferent
arteriole forms
Efferent arteriole
o Tuft of capillaries
(protrude into
Bowman's
capsule)
o These capillaries
come together
and form a
second arteriole
o Which divides
shortly after to
form the
Peritubular
capillaries
o Surround various
portions of renal
tubule.
Cortical Nephrons Juxtamedullary Nephrons
85% of Nephrons in kidney 15% of Nephrons in kidney
Smaller size of glomeruli in renal cortex Larger size glomeruli at the junction of medulla and
cortex of the kidney
Short loops of henle penetrate only till outer layer
of renal medulla
Long loops of henle – penetrate deep into medulla
Descending loop of henle – thin segment
Ascending limb – thick segment
Both descending and ascending loop of henle – thin
segments
Vascular supply – peritubular capillary plexus Vascular supply – vasa recta
Rate of filtration - slow Rate of filtration - fast
Major role – excretion of waste products Major role – counter current system – kidneys
concentrate urine
NOTE: Gradual reduction in Nephrons with age after 40years. Kidney cannot regenerate new Nephrons.
Renal Arteries
• Each kidney - receives a renal artery (major branch
of aorta).
• Kidneys receive approximately 25% of the total
resting cardiac output or about 1.25 L blood/min.
• Sympathetic tone to renal vessels:
o Minimal at rest
o Increases during exercise to shunt renal blood
flow to exercising skeletal muscles
Afferent and Efferent arterioles
• Each renal artery subdivides into:
o Progressively smaller branches
o Smallest branches give off a series
of afferent arterioles
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Peritubular capillaries
Differ in organization depending on their association with different Nephrons
Efferent arterioles of Cortical Nephrons Efferent arterioles of Juxtamedullary Nephrons
o Divide into peritubular capillaries
o These connect with other Nephrons
o Forms rich meshwork of micro vessels.
o Meshwork functions to remove water &
solutes
o Also form peritubular capillaries
o Special portion of which are “Vasa recta”
o Vasa recta:
▪ Descend with the long loops of Henle into the
renal medulla
▪ Return to the area of glomerulus.
▪ Form capillary beds at different levels along the
loop of Henle.
HORMONES INFLUENCING THE RBF AND GFR
RENAL TUBULAR FUNCTION
Maintains constancy of body's internal environment
As blood passes through the kidneys, the nephrons clear the plasma of unwanted substances (e.g.,
urea) while simultaneously retaining other, essential substances (i.e., water)
Unwanted substances are removed by glomerular filtration & renal tubular secretion, further are
passed into the urine
Substances that body needs are retained by renal tubular re-absorption (e.g., Na+, HCO3-) and are
returned to the blood by re-absorptive processes
Renal Veins:
• Formed from confluence of peritubular
capillaries
• Exit the kidney at the hilus
• Pattern of the renal venous system:
o Similar to that found in the end
arterial system.
o Except for the presence of multiple
anastomoses b/w veins at all levels of
venous circulation
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Mechanism of Urine Formation
Mechanism of Filtration: Glomerular Filtrate
1. Filtering membrane:
• Filtering membrane is very thin – thus facilitates filtration
• Permeability of this membrane:
• Note: Normally albumin is not filtered (since it is negatively charged), but in certain glomerular diseases, sialic
acid molecules are damaged – negativity is lost – leading to Albuminuria
Capillary endothelium
of the glomerular
capillary
Epithelium of the visceral layer of the Bowman’s
capsule
Basement membrane present in between
these 2 layers
Filtering membrane
All particles < 4nm in diameter (molecular weight
is 5000 daltons) can pass through it
No particle > 8 nm can pass through it
Permeability of glomerular endothelial layer is 50 times more
than anywhere else
Plasma is filtered – Called ad as Ultrafiltrate
Collects in the Bowman’s capsule – called Glomerular filtrate or Capsular fluid.
Capsular fluid – enters the proximal convoluted
From now, called Tubular Fluid that proceeds onwards
Amount of glomerular filtrate is about 180 litres/day
•In Glomerulus
Tubular fluid undergoes massive re-absorption,
concentration & acidification
Some new materials are added to it
Final product formed is the Urine
•In Renal tubules
Urine enters urinary bladder via
Ureter & stored, further voided via the
urethra to the exterior -Micturition
• Final product is Urine
• Rate of Urine production is 1.5 litres/day
• Characteristics: Highly concentrated &
acidified
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2. BP in glomerular filtrate is very high, but opposed by few forces
• Starling forces regulate the distribution of fluid between any capillary and its adjacent interstitial fluid
• They also apply at the glomerular filtration barrier
3. Permeability coefficient (Kf)
4. Glomerular filtration rate (GFR)
Driving force
Glomerular capillary BP (Pc = 60 mm of Hg)
Elsewhere in the body: Capillary pressure at the arterial end is 30 mm of Hg
Opposing forces
Colloidal osmotic tension (COT) of blood plasma (πc = 30mm of Hg)
Hydrostatic pressure in bowman’s capsule (Pb = 20 mm of Hg)
Resultant force
Effective filtration pressure: Pc – (Pb + πc) = 60 – (20 + 30) = 10 mm of Hg, Facilitates filtration
Hydraulic conductivity (Volume of fluid that can transferred
across filtering membrane per unit area per unit time against
1 mm of Hg of effective filtration pressure)
* Total area of filtering membrane (Total area of Glomerular capillary bed)
GFR = Kf * Effective filtration pressure (higher Kf values,
greater is GFR & vice versa)
GFR falls in:
o Elderly
o End stage Renal disease
(ESRD), GFR = can be as low
as 10 ml/min.
o Diabetic nephropathy
o Chronic Hypertension
o Chronic renal failure
Crude index for Renal efficiency: Plasma Creatinine levels (Normal < 1.5 mg/dl)
𝑼 𝒄𝒓𝒆𝒂𝒕𝒊𝒏𝒊𝒏𝒆 𝒙 𝑽
𝑷 𝒄𝒓𝒆𝒂𝒕𝒊𝒏𝒊𝒏𝒆
Where, V = urine flow rate, U = urine, and P = plasma
Refers to the volume of glomerular filtrate formed each
minute by all of the nephrons in both kidneys
Normal healthy adult, GFR = 125 ml/minute (180 litres/day)
ACE inhibitors & ARB’s (angiotensin receptor blockers) –
chief drugs to combat
Many drugs (especially aminoglycosides) excreted through
kidneys – their doses have to be reduced in elderly
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5. Filtration fraction (FF): Fraction of plasma that is filtered.
At normal values of GFR 125 mL/min and RPF 650 mL/ min; the FF is approximately 0.2 (125/650)
20% the renal plasma flow is actually filtered per minute
Regulation of Glomerular Filtration
Renal auto
regulation
Rate of FILTRATE production must be coordinated with re-absorption rate
Myogenic
mechanism
Circular muscle around the glomerular arterioles reacts to pressure changes
- Increased blood pressure → Vasoconstriction
- Decreased blood pressure → Vasodilation
Tubuloglomerular
feedback
mechanism
Macula densa cells (Juxtaglomerular apparatus) sense the solute concentration of the
FILTRATE
- Low concentration → Vasodilation
- High concentration → Vasoconstriction
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Renin-angiotensin
mechanism
Renin (released by Juxtaglomerular cells) → Angiotensinogen → Angiotensin I →
Angiotensin II → Global vasoconstrictor (rise in blood pressure) release of
aldosterone (re-absorption of more Na+).
- Factors causing release of Renin
1. Reduced stretch of Juxtaglomerular cells
2. Stimulation by macula densa cells (as above)
3. Stimulation of Juxtaglomerular cells by Sympathetics.
Extrinsic Controls Sympathetic Innervation
- Sympathetics – cause increased release of rennin
- Epinephrine – causes increased vasoconstriction
Important values:
Resting cardiac output 5,000 ml/min 7,200 litres/day
Renal blood flow 1,200 ml/min 1,728 litres/day
Renal plasma flow 650 ml/min 936 litres/day
Glomerular filtration
rate
125 ml/min 180 litres/day
Renal Tubular Functions
Functions of Proximal tubule (PT)
Substance Plasma Concentration
(Px) (m mole/l)
Filtered load per day
(Px * GFR) (m moles)
Fractional re-
absorption (%)
Na+ 142 25000 (about 575 g) Over 99 %
K+ 4 700 (27 g) 90 %
HCO3- 24 4000 (about 240 g) 99.5 %
Glucose 5 900 (160 g) 100 %
Water 170 – 180 litres 99 %
Re-absorption Secretion Concentration Acidification
Reabsorbs 2/3rds of glomerular filtrate
•(GF = 125 ml/min, PT reabsorbs about 85 ml/min)
Absorbs organic and inorganic matters
•Glucose, aminoacids, bicarbonates – Preferentially reabsorbed
•Some are reabsorbed less avidly
•Some (Eg: Inulin) are not reabsorbed at all.
•Major inorganic matters reabsorbed: Na+, HCO3- , K+
•Organic matters reabsorbed: Glucose, aminoacids, and other
organic acids (Eg: Lactic acid, citric acid, uric acid & urea)
•Water also reabsorbed massively
GFR can be detected by:
1. Inulin clearance test
2. Creatinine clearance test
3. Urea clearance test
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Functions in PCT (Proximal Convoluted Tubule)
Na+ re-absorption in PCT
Bicarbonate Re-absorption and H+ secretion: • PT also reabsorbs HCO3- ions and secretes H+ ions
• H+ ions (proton) secretion also occurs in the distal tubule and collecting tubules
• Mechanism of secretion of H+ is not identical in PT with that of distal & collecting tubules
• Role of Peritubular capillaries: 2 Pathways of Absorption
Cotransport
•Large quantity of Na+ re-absorption occurs by Cotransport
•Cotransport operate in upper half of PCT
•Form of transport where: 1 ion of Na+ absorbed (Re-absorbed) in the PCT concomitantly 1 molecule of glucose / amino acid / lactic acid is absorbed
•Also called as Uniport – as both particles Na+ & organic compounds are transported in same direction
Antiport or Exchange
•Exchanger mechanisms operate in upper half of PCT
•1 ion of Na+ absorbed (Re-absorbed) in the PCT concomitantly 1 ion of H+ is extruded (with help of exchanger protein) from the same cell (Na+ is exchanged for H+)
•Particles Na+ & H+ are transported in opposite direction
•Inhibited by Carbonic anhydrase inhibitor
Transcellular pathway
Paracellular pathway
The proximal tubule reabsorbs:
o Approximately 67% of the filtered water, Na+, Cl−, K+ and
other solutes
o Almost all the glucose and amino acids filtered by the
glomerulus
o The proximal tubule does not reabsorb inulin, creatinine,
sucrose and mannitol
o The proximal tubule secretes H+, PAH, urate, penicillin,
sulphonamides and creatinine
• Third fraction of Na+ re-absorption occurs
in lower part of PCT
• Cl- linked Na+ re-absorption:
• Occurs in lower half of PCT
• Na+ is reabsorbed along with Cl-
Percentage reabsorption of the
filtered sodium in different
segments of the renal tubule is:
o Proximal tubule : 67%
o Loop of Henle (mainly thick :
20% ascending limb)
o Distal tubule : 7%
o Cortical collecting duct : 5%
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Glucose reabsorption
All the filtered glucose is completely reabsorbed into the proximal tubule by an active transport mechanism
Functions of loop of henle & distal nephron
Medullary gradient
Carrier mediated Na+−glucose co-transport
•The carrier protein for glucose in early proximal tubule is called
SGLT-2 and in late proximal tubule is called SGLT-1(SGLT =
sodium-dependent glucose transporter)
•Facilitated diffusion moves the glucose out of the cell through the
basolateral membrane
•The carrier for facilitated diffusion in early and late proximal tubule
is called GLUT-2 and GLUT-1, respectively (GLUT = glucose
transporter)
•Renal threshold of plasma glucose is 180–200 mg/dL
•Transport maximum (Tm) refers to the plasma concentration at
which carriers are fully saturated- for glucose= 350 mg/dL
Concentration of urineFurther absorption of Na+, Cl- & Water
Acidification of urine
Secretion of potassium, calcium, magnesium &
some drugs
Osmolality of the fluid in the medullary interstitium is as follows:
•Outer medulla – isotonic with plasma
•Mid zone of medulla – tonicity rises greatly
•Deepest zone of medulla – tonicity rises still more (about 1200 m osmols/kgH2O)
Changes in osmolality in medullary interstitium is due to:
•NaCl
•Urea
oThe urinary excretion rate increases linearly with increase in
plasma glucose concentration
oSplay refers to the region of the glucose curve between
threshold and TmG, i.e. between PG 180 and 350 mg/dL
o It represents the excretion of glucose in urine before the
TmG is fully achieved
oCauses of splay are:
▪ Heterogenicity in glomerular size
▪ Proximal tubular length
▪ Number of carrier proteins for glucose reabsorption
▪ Variability in TmG of the nephron
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Counter current system
Counter current multiplier
Thin descending limb of loop of henle
•Extremely permeable to water (due to presence of water channels called as aquaporins)
•Very slightly permeable to Na+
Thick ascending limb
•Permeable to Na+ but not Water
•Early part of distal tubule is impermeable to water but permeable to Na+
Collecting duct
•Becomes permeable only when it is subjected
to AVP (ADH, antidiuretic hormone)
•Very permeable to urea, but other parts of
distal segment is not so
In Loop of Henle
•Responsible for production of hyperosmolality & a gradient in renal
medulla
•Repetitive re-absorption of NaCl in the thick ascending loop of Henle
•Continued inflow of new NaCl from the proximal tubule into the loop of
Henle is called the Counter Current Multiplier
•The NaCl reabsorbed from the ascending loop of Henle keeps adding to
the newly arrived NaCl, thus “multiplying” its concentration in the
medullary interstitium
Descending loop
•Freely permeable to H2O
•Impermeable to solutes
•H2O leaves filtrate by osmosis
•Filtrate becomes highly concentrated to 1200 m osmols at deepest portion
of loop, concentrating segment of Nephron
Ascending Loop
•Impermeable to H2O
•Permeable to NaCl
•Most NaCl re-absorption occurs in ascending thick segment
•Filtrate becomes more dilute as it ascends (100 m osmols) diluting segment of nephron
•Interstitial fluid develops a concentration gradient that is maintained by the movement of H2O and NaCl
Refers to a system in which the inflow runs parallel to, counter to, and in close proximity
to the out flow for some distance
Counter current flow system is formed by U shaped tubules
Permeability
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NOTE: In counter current mechanism
Isotonic Bowman’s capsule
Hypotonic End of ascending loop
Hypertonic Loop of Henle
Acidification of Urine
• Metabolic processes produce phosphoric & sulphuric acids (other acids – little amounts)
• A very small amount of H+ is filtered because the plasma H+ is only 10-7.4 mol/litre (pH 7.4)
• H+ is actively secreted by the Nephron
o Mostly proximal tubule
o Approximately 10% secreted in the distal nephron especially collecting duct
Mechanism of H+ secretion & its fate
Heat exchange taking place between arteries & veins of limbs
Human intestinal villi
Brain – for regulation of brain temperature Testes – for maintaining high levels of testosterone
Other systems of counter current mechanism
Most of the H+ secreted reacts with and filtrates HCO3
-in the tubular fluid as follows:
H+ + HCO3- H2O + CO2
Approximately 9% reacts with ammonia
H+ + NH3 NH4+
Approximately 7% reacts with other urinary buffers,
mainly phosphates
H+ + HPO42- H2PO4
-
Counter current exchanger
• Occurs in vasa recta
• Responsible for maintenance of the medullary
gradient & hyperosmolality.
In Vasa Recta:
• Slow blood flow
• Freely permeable to H2O & NaCl
• As blood descends it loses H2O & gains
NaCl
• As blood ascends into cortex it gains H2O
& loses NaCl
• Protects medullary gradient by preventing
rapid removal of salt
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Buffers in the body
Whole blood Haemoglobin system
Protein system
Carbonic acid – bicarbonate system
Interstitial fluid Carbonic acid – bicarbonate system
Intracellular fluid Protein system
Phosphate system
Alterations when Acid-base balance is lost
Respiratory
acidosis
Main effect: Increase in PCO2 → Resulting in an increase in H+
Kidney compensates by:
- Increasing renal secretion of H+
- Increasing renal absorption & synthesis of HCO3-
Produced by:
- Any cause of hypoventilation
- Including: Acute respiratory failure, Cardiac arrest, Pneumonia & Opiate overdose
Respiratory
alkalosis
Problem: Decrease in body PCO2 →HCO3- falls because H+ leaves the cells & reacts with it.
Kidney compensates by:
- Decreasing H+ secretion
- Decreasing HCO3- re-absorption.
Produced by:
- Any cause of hyperventilation may produce this condition
- Including: Pulmonary embolism, Sepsis & High altitude.
Metabolic
acidosis
Primary defect is excess production or inadequate excretion of H+.
Excess H+ is buffered in part by reacting with HCO3-, which therefore decreases.
Lungs compensate by: Increasing expulsion of CO2.
Produced by:
- Diarrhoea
- Ketoacidosis
- Renal failure
Sl.no Buffers Buffering capacity
1 Bicarbonate buffer
Plasma HCO3
Erythrocyte HCO3
53%
(35% )
(18%)
2 Haemoglobin and
oxyhaemoglobin
35%
3 Plasma proteins 7%
4. Organic phosphate 3%
5. Inorganic phosphate 2%
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- Toxic ingestions
Metabolic
alkalosis
Problem is excess base or too much excretion of H+ → Rise in plasma HCO3-
Lungs compensate by: Retaining CO2.
Produced by:
- Dehydration
- Vomiting
Kidney compensates by H+ secretion & HCO3- re-absorption
Renal handling of freely filtered substances
Urea Filtered in glomerulus Reabsorbed – PCT
Deepest part of collecting duct ( when ADH is present )
Creatinine Filtered in glomerulus
Glucose Filtered in glomerulus
Reabsorbed in PCT
Amino acids Filtered in glomerulus
Reabsorbed in PCT
Sodium Passively absorbed in PCT
Reabsorbed in PCT, Ascending loop of henle, distal tubule
Collecting duct – regulated by ADH
Chloride PCT- flows passively
Potassium Passive re-absorption in PCT
Active re-absorption in ascending loop of henle, collecting duct
CHARACTERISTICS AND COMPOSITION OF URINE
Physical Characteristics
Color Clear to yellowish
Influenced by diet, drugs & health state
Odor Slightly aromatic
Influenced by diet, drugs & health state
pH (H+ conc.) Usually about 6
Changes in diet can affect the pH
Specific
gravity
Compared density to distilled water
Urine slightly heavier (with solutes)
Hypokalemia Hyperkalemia
Insulin Diabetes mellitus
Aldosterone Addison’s disease
Catecholamines Tissue damage
Alkalosis Acidosis
After heavy exercise
Increased plasma osmolality
Role of Aldosterone:
• Aldosterone – Supra renal gland
mineralocorticosteroid
• Increases:
o Na+ reabsoprtion
o K+ excretion from distal nephron
• Excess aldosterone – Na+ accumulation
& Hypokalemia
Factors causing
Chemical Composition
• 95% water
• 5% solutes - urea (breakdown of
amino acids); uric acid; creatinine
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Urine Volume
RENAL FUNCTION TESTS
KIDNEY FUNCTION TESTS
Measurement of GFR Clearance tests
Endogenous substances used for clearance test Creatinine
Exogenous substances used for clearance test Inulin
Volume, Appearance, Colour, Odour, Specific gravity Physical characteristics
Measurement of Specific gravity Urinometer
Reducing substance, Ketone bodies, Proteins, Blood, Bile salts & bile pigments Abnormal Chemical constituents
Early detection of Diabetic & Hypertensive nephropathy Microalbumin
Specific gravity, Concentration test, Urine volume, Osmolality, Dilution test,
Acidification
Renal tubular function
Hormones produced by kidney
1,25- dihydroxycholecalciferol Increase Ca2+ absorption from the intestine
Renin Angiotensinogen to Angiotensin – 1
ACE converts Angiotensin – 1 to angiotensin - 2
Polyuria Urine output > 2.5 L/day
Oliguria Urine output 300 to 500 ml/day
Anuria Urine output < 100 ml/day
Clinical Serum ADH Ser osmols/
Ser Na+
Urine
osmolality
Urine flow
rate
Free water
clearance
Primary Polydypsia Decreased Decreased Hyposmotic High Positive
Central diabetes
Insipidus (DI)
Decreased Increased Hyposmotic High Positive
Nephrogenic DI Increased Increased Hyposmotic High Positive
Water deprivation Increased High/normal Hyperosmotic Low Negative
SIADH Markedly
increased
Decreased Hyperosmotic Low Negative
Required for:
•Assessment of extent of renal damage
•Monitoring and adjusting the dose of renal toxic drugs
•Monitoring the progression of damage
Give information regarding
•Renal blood flow
•Urinary Output
•GFR (Glomerular filtration rate)
•Renal tubular function
•Renal glomerular function
•Diuretic therapy
•Diabetes Insipidus
•Diabetes mellitus
Conditions increased
•Excess sweating
•Dehydration
•Acute renal failure
Conditions decreased
Normal Range: 1000 – 1800 ml/day
PHYSIOLOGY
Excretory System
193
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Erythropoietin Hormone secreted by kidney
Needed for erythropoiesis
MICTURITION
Process of accumulation of formed urine in the urinary bladder & evacuation of the same from the bladder
from time to time, which are controlled by nervous system
Nerve Supply of Bladder & Urethra
Efferent Fibres
(Motor)
Nerve
roots
Peripheral
nerves
Structures innervated Functions
Somatic S3 & S4 Pudenal nerve External Spinchter & distal
urethra
Control Micturition
(Voluntary)
Sympathetic T11 & T12
L1 – L4
Hypogastric
nerves
Bladder & internal
Spinchter
Relax the bladder wall &
constricts the internal
sphincter
Parasympathetic S2 – S4 Nervi ergentes
(Pelvic nerves)
Muscles of the bladder
(detrusor) & internal
Spinchter
Contraction of the bladder &
relaxation of the internal
Spinchter
Mechanism of Micturition
Centres of Micturition
Central control of Micturition lies at 4 levels
Afferent (Sensory) fibers
(Concerned with Pain &
conscious awareness of
distension) from
Peripheral nerves
Bladder cavity Hypogastric nerves
Muscles of the Bladder
(Detrusor)
Pelvic nerves
Urethra Pudenal nerve
Cortical – Motor area of the cortex & upper part of postcentral gyrus
Hypothalamic
-Increased tone of detrusor muscle after electrical stimulation of anterior nuclei of hypothalamus
-Diminution of tone of detrusor muscle after electrical stimulation of posterior nuclei of hypothalamus
Brain stem – Barrington’s reflex (Refer the Table)
Spinal – 2nd, 3rd and 4th
sacral segments
Involves co-ordinated contraction of smooth muscles of:
•Bladder wall (Detrusor muscle)
•Abdominal wall
•Muscles of Pelvic floor
•Fixation of chest wall & diaphragm
•Relaxation of internal & external urethral sphincters
Involvement of autonomous and voluntary activities
PHYSIOLOGY
Excretory System
194
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