physiology excretory system

PHYSIOLOGY

Excretory System

175

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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

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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

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physiology excretory system

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