complete us-neha

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e r nary

System

Introduction� The urinary system consists of

± Two kidneys

± Two ureters± One urinary bladder

± One urethra

� Kidneys filter blood plasma and returnmost of the water and solutes to the

bloodstream

� The urine passes through the ureters�

Organs of the urinary

system

Transverse sections show retroperitoneal position of kidneys

Kidney Functions

1. Regulation and Maintenance

2. Production

3. Excretion

egu a on an

maintenance� Regulation of blood ionic composition: Na+, K+,

Ca2+, Cl- and HPO42-

� Regulation of blood pH: excrete H+ and conserve

� Regulation of blood volume: conserving or

eliminating water

� Regulation of blood pressure: secreting renin� Regulation of blood glucose levels: use amino

acid glutamine in synthesis of new glucose

molecules (gluconeogenesis)

� Maintenance of blood osmolarity: regulating loss

Production of hormones

� Two hormones:

±Calcitriol ± active form of vitamin D ±

regulates calcium homeostasis±Erythropoietin ± stimulates production of

foreign substrates

� By forming urine, kidney excretes waste.

� Waste maybe from 2 sources:

± Metabolic reactions in body ± examples

� Ammonia and urea ± deamination of amino acids

� Bilirubin ± catabolism of hemoglobin

� Creatinine ± breakdown of creatinphosphate in muscle fibres

� Uric acid ± catabolism of nucleic acids

± Foreign substances from diet ± drugs and

environmental toxins

Anatomy of kidneys� Reddish kidney bean-shaped organs

� Located above the waist betweenperitoneum and posterior wall of theabdomen

� Retorperitoneal ± posterior toperitoneum

� Located between the levels of the lastthoracic and third lumbar vertebrae

� Partially protected by eleventh and twelfth

pair of ribs�

x erna ana omy o

kidneys

� Typical adult kidney:

± Length ± 10-12 cm

± Width ± 5-7 cm

± Thickness ± 3 cm

± Mass ± 135-150 g

� Concave medial border ± faces vertebral

column

� Near the center of concave border ± renal

hilum ± through which ureter emerges from

kidney along with blood vessels, lymph

Locatio

Name Description Function

1 Deeplayer

RenalCapsul

Smoothtransparent sheet

of dense irregular

connective tissue.

It is continuouswith the outer coat

of ureter

1. barrier againsttrauma

2. maintain the

shape of the

kidney.

2 Middle

Adipos

Capsul

Mass of fatty

tissue surrounding

the renal capsule

1. Protects

kidney from

trauma

2. Holds it firmly

in place

3 Superfi

fascia

Thin layer of

dense irregular

1. Anchors the

kidney to the

Internal anatomy of

kidneys� Frontal section reveals two distinct

regions:

±Renal cortex ± superficiallight red area

±Renal medulla ± deep,darker reddish brown inner

region

Renal cortex

� Smooth textured area

� Extends from renal capsule to the bases of renal pyramids and into the spaces between

them� Divided into two zones:

± Cortical zone ± outer

± Juxtamedullary zone ± inner � Renal columns ± renal cortex extending

between the renal pyramids

� Renal lobe ± renal pyramids, its overlying

Renal medulla

� Renal pyramids ± cone shaped structure

� Base of each pyramid faces the renal

cortex� Apex (renal papilla) points towards renal

� Parenchyma ± renal cortex and renal

pyramids constitute the parenchyma. It is

the functional part of the kidney.

� Nephrons ± functional units of kidney.

Present in the parenchyma. About one

million in number.

� Papillary ducts ± extends through renalpapillae of pyramids. Urine formed by the

nephrons is drained into them.

� Calyces ± two types ± major (2-3) and

� Renal pelvis ± single large cavity into which

urine from major calyces in drained.

� The urine is then drained out through the

ureter to the urinary bladder.

� Renal sinus ± cavity into which the hilum

expands. It contains part of renal pelvis, the

calyces, and the branches of renal bloodvessels and nerves. These structures are

stabilised by adipose tissue in the renal

sinus.

Blood supply to the kidneys

� Abundantly supplied with blood

vessels

� They constitute less than 0.5% of total body mass but 20-25%

resting cardiac output.

� In adults, renal blood flow ± 1200

mL/min

Arteries

� S egmentals branch into

lobar arteries

� Lobars (enters

parenchyma) divides

into interlobars

� Interlobars into arcuate

in junction of medulla

and cortex

� Arcuates send

interlobular arteries into

Aorta gives off right and left renal arteriesRenal arteries divides into 5 segmental arteries as enters hilus

of kidney

� Interlobular arteries in the cortex branches

off as afferent arterioles.

� Each nephron receives one afferentarteriole

� It divides into a tangled, ball-shaped

network of capillary ± glomerulus

� Glomerular capillaries then reunite to form

the efferent arteriole

� Glomerular capillaries ± unique as they

are ositioned between two arterioles

� Efferent arterioles divide to form peritubular

capillaries which surround the tubular part of

nephron in the renal cortex� Vasa recta ± long loop-shaped capillaries

extending from some efferent arteries. They

supply to tubular portions of nephron in therenal medulla

� Peritubular capillaries reunite to form

peritubular venules

� They form interlobular veins ± receive blood

from vasa recta

� The blood drains through arcuate veins to

interlobar veins.

Vasculature of kidneys

Nerve supply to the

kidneys� Renal nerves originate in renal ganglion

� Pass through renal plexus into the kidneys

along with renal artery� They are a part of sympathetic division of

� They are mostly vasomotor nerves ±regulate the flow of blood through the

kidneys by causing vasodilation or

vasoconstriction of renal arterioles.

Uretersy

Slender tubes about 25-30 cm (10-12 ) longleaving each renal pelvis

y Diameter 1-10 mm

y One for each kidneycarrying urine from renalpelvis to the bladder

y Descend retroperitonealyand cross pelvic brim

y Enter posterolateralcorners of bladder

y Run medially withinposterior bladder wallbefore opening intointerior

y This oblique entry helps

prevent backflow of urine

� Peristaltic contractions ± push urine ± 1-5

contractions/min

� Hydrostatic pressure and gravity also aid

� As bladder if filled with urine, pressure

within it compresses the oblique openings

and prevents backflow of urine� If this physiological valve doesn¶t function

properly chances of kidney infection

Three basic layers

y Mucosa made up of transitionalepithelium stretches withunderlying lamina propria made upof areolar connective tissue withcollagen, elastic fibers andlymphatic tissue

y Mucus secreted protects cell fromurine (pH and solute conc)

y Muscularis Inner longitudinal, outer circular

layers ofsmooth muscles

Stimulated to contract whenurine in ureter: peristaltic wavesto propel urine to bladder

y Adventitia (external) areolar connective tissuecontaining blood vessels,lymphatic vessels and nerves

y Anchors the ureters in place

Urinary Bladder

y Hollow distensiblemuscular organ situatedin the pelvic cavity

y Held in place by folds of peritoneum

y Stores and expels urine

y Bladder capacity 700-800 ml

Males: anterior to rectum

Females: just anterior tothe vagina and uterus.Smaller due to uterus

The Urethra

� Male: about 20 cm (8´) long

� Female: 3-4 cm (1.5´) long± Short length is why females have more urinary tract

infections than males - ascending bacteria from stool

contamination

Urethra____

� Urethral sphincters± Internal: involuntary sphincter of smooth muscle

± External: skeletal muscle inhibits urination voluntarily

until proper time (levator anni muscle also helpsvoluntary constriction)

Males: urethra has three

regions (see right)

1. Prostatic urethra__________

2. Membranous urethra____

3. Spongy or penile urethra_____

_________trigone

female

Wi th all the labels

�M icturitionAKA:± Voiding

± Urinating

± Emptying the bladder

KNOW:Mictur ition center of

brain: pons

(but heavily inf luenced byhigher centers)

Parasympathetic: to voidSympathetic: inhibits

mictur ition

Micturition

� Act of emptying the bladder

� Exceeding 200 ml of urine, the bladder isstretched and stretch receptors are

activated� Impulses are transmitted via the pelvic

splanchnic nerves to the sacral region

� Bladder go into contractions and forceurine pass the IUS (feeling of urge to void )

� After a certain volume limit, micturition will occur whether one wills it or not

Anatomy of uriniferous tubule

± Nephron

� Renal corpuscle (in cortex)

± Glomerulus (tuft of capillaries)

± Glomerular (Bowman¶s) capsule� Tubular section

± Proximal convoluted tubule

± Loop of Henle

± Distal convoluted tubule

± Collecting duct

Nephron

Renal corpuscleTubular section

Renal corpuscle: only in

cortex

Tuft of capillaries calledglomerulus

Surrounded by cup-

shaped, hollow glomerular

(Bowman¶s) capsule

Tubular sectionProximal

convoluted tubule

Loop of Henle

Distal

convoluted tubule

Renal Corpuscle

� Blood plasma is filtered

� Lies entirely in cortex

� Two components:

± Glomerulus ± capillary network± Glomerular capsule (Bowman¶s capsule) ±

surrounds capillaries

� Visceral layer of capsule has pod ocytes

± Unusual branching epithelial cells

± Foot processes with slit processes betweenthem

Scanning EM of podocytes clinging

to capillaries (left) and filtration

membrane diagram (right)

Loop of Henle

� Descending limb ± dips into medulla

� Thin segment ± hairpin turn

� Thick ascending limb ± returns to cortex

Distal Convoluted Tubule

� Confined to the renal cortex

� Simple cuboidal epithelium

� Selective secretion and resorption of ions

� Cortical nephrons± 85% of all nephrons

± Almost entirely within cortex± Corpuscle lie in outer portion of cortex

± Have short loop of Henle which penetrate onlythe outer region of medulla

± Blood supply from peritubular capillaries only

� Juxtamedullary nephrons± Renal corpuscles near cortex-medulla junction

± Loon loop of Henle extending into deepestregions of medulla

± Blood supply ± peritubular capillaries and vasarecta

Collecting Ducts

� Each receives urine from several

nephrons

� Run straight through cortex into the deep

medulla

� At papilla of pyramid, ducts join to form

larger papillary ducts

� Empty into minor calices

� Role: conserve body fluids

Blood Vessels�Afferent and efferent arterioles

associated with glomerular

capillaries

�Allows high pressure for

forcing filtrate out of blood

�About 20% of renal plasma

flow is filtered each minute

(125 ml/min): this is the

glomerular filtration rate

(GFR), an important

clinical measure of renal

f unction

�This is about one liter

every 8 minutes (only1% ends up as urine)

�Peritubular capillaries arise from

efferent arterioles

�Absorb solutes and water

from tubule cells

Vasa RectaThe Vasa recta is a

portion of the peritubular capillary system whichenters the medulla wherethe solute concentrationin the interstitium is high.

It acts with the loop of Henle to concentrate the

urine by a complexmechanism of counter current exchange usingurea.

If the vasa recta did notexist, the highconcentration of solutesin the medullaryinterstitium would be

washed out.

Histology

Juxtaglomerular apparatus� Regulation of blood pressure

� Macula densa ± crowded columnar cells - chemoreceptors whichsecrete renin if solute concentration falls

� Granule (JG cells) ± alongside macula densa - modified muscle cellssecreting renin in response to falling blood pressure in afferent arteriole

Production of urineProduction of urine

processes1. Filtration

2. Reabsorptio

n3. Secretion

Filtration

� Filtrate formed (ultrafiltrate): blood plasma

without blood proteins

� Proteins and blood cells to large to pass

through the filtration membrane

Reabsorption

� Reclamation of useful substances from the

filtrate and returned to the blood

± Water, glucose, amino acids, ions, etc

� Begins at the PCT

� Depends mostly on active transport

� Nitrogenous waste products are poorly

reabsorbed (eg, urea, uric acid, creatinine)

Secretion

� Movement of substances from the blood or

tubule cells to be eliminated in urine

± Hydrogen ions, potassium ions, creatinine,

certain drugs

Rate of urine formation = glomerular filtration

rate + rate of secretion rate of reabsorption

Glomerular filtration

� Glomerular filtrate (GF) ± fluid entering thecapsular space

� Filtration fraction ± the fraction of blood plasma

in the afferent arterioles that becomes GF. 16-20%

� Daily volume of GF in adults:± Males ± 180 L

± Females ± 150 L

� > 99% GF returns to bloodstream via tubular reabsorption.

� Only 1-2 L excreted as urine

Filtration membrane

� Filtration membrane = endothelial cells of capillaries + podocytes encircling capillaries

� It is a sandwich like assembly ± leaky barrier

� Permits filtration of water and small solutes� Prevents filtration of most plasma proteins,

blood cells and platelets.

� 3 layers

± Glomerular endothelium

± Basal lamina

± Podocytes

Gl l d th li

Glomerular endothelium

� Large fenestrations ± 0.07-0.1 µm. Thus

leaky.� Filters all solute in blood plasma except

blood cells and platelets.

Basal lamina

� Layer of acellular material containing

collagen fibers and proteoglycans inglycoprotein matrix.

� Prevents filtration of larger plasma

proteins.

Podocytes

� Thousands of foot-like processes ±

pedicelthat wrap around capillaries.

� Spaces between pedicels ± filtration slits

� A thin slit membrane extends across each

� Permits passage of molecules having

diameter < 0.006-0.007 µm.

� Includes water, glucose, vitamins, aminoacids, very small plasma proteins,

ammonia, urea and ions

� Large volume of fluid can be filtered by

glomerular capillaries because:

1.They are long and extensive ± large surface

area for filtration.

2.Filtration membrane is thin (0.1 µm) and

porous (50 times leakier).

3.Efferent arteriole smaller than afferent

arteriole ± high resistance to outflow of blood ± Glomerular capillary blood pressure

is high

Net filtration pressure (NFP)

� 3 main pressures

1.Glomerular blood hydrostatic pressure(GBHP) ± blood pressure in capillaries (55

mmHg). Forces water and solutes inplasma through filtration membrane.

2.Capsular hydrostatic pressure (CHP) ±pressure exerted by fluid present incapillaries and tubule (15 mmHg). ³BackPressure´ opposes filtration.

3. Blood colloid osmotic pressure (BCOP) ±

pressure due to plasma proteins such as

albumin, globulins and fibrinogen (30

mmHg). Opposes filtration.

� NFP = GBHP ± CHP ± BCOP

= 55 ± 15 ± 30

= 10 mmHg

Glomerular filtration rate

� GFR ± the amount of filtrate formed in all

renal corpuscles of both kidneys each

minute.

� Adult GFR

± Males: 125 ml/min

± Females: 120 ml/min

� If GFR too high ± needed substance maynot be reabsorbed and maybe excreted.

� If GFR too low ± waste substances maybe

reabsorbed.

� GFR ± directly related to pressure

� Severe blood loss ± reduces mean arterialblood pressure ± reduces GBHP.

� Min GBHP ± 45 mmHg. After this filtrationstops.

� When systemic blood pressure rises ±

GFR increases.� GFR constants between 80-180 mmHG

mean arterial pressure

� Mechanisms regulating GFR

� Adjusting blood flow into and out of the

glomerulus� Altering the glomerular capillary surface

area available for filtration

� Mechanisms controlling GFR:

1.Renal autoregulation

2.Neural regulation3.Hormonal regulation

Renal autoregulation of GFR

� Two mechanisms:

1.Myogenic mechanism

2.Tubuloglomerular mechanism

Myogenic mechanism

Tubuloglomerular feedback

Hormonal regulation of GFR

Hormonal regulation (contd)

Tubular Reabsorption and

Tubular Secretion

Composition of Glomerular

Filtrate�� Water Water

�� Small Soluble Organic MoleculesSmall Soluble Organic Molecules

�� MineralI

onsMineralI

P i l C l t d

Proximal Convoluted

TubuleReabsorbs: water, glucose,Reabsorbs: water, glucose,

amino acids, and sodium.amino acids, and sodium.

65% of Na+

65% of H2O

90% of filtered bicarbonate (HCO3-)

50% of Cl- and K+

100% of glucose and amino acids

50% of urea

Variable amounts of H+, NH4+ and urea

Tubular Secretion

� H+

� NH4+

� Creatinine� Some drugs

� Imp ± to test athletes for performance

enhancing substances like anabolic

steroids, amphetamine etc.

Routes of reabsorption

� Substance to be reabsorbed can take

TWO routes before entering a

paratubular capillary:

1. Move between adjacent tubule cells

2. Move through a single tubule cell

� Along renal tubule there are tight

junctions joining neighboring cells.

Luminal sur f aceLuminal sur f ace

Basolateral sur f aceBasolateral sur f ace

EpithelialEpithelialtighttight

junctionsjunctions

Just thinkof it as aSix soda pack

�� The luminal cell membranes (apicalThe luminal cell membranes (apical

membrane) are those that face themembrane) are those that face the

tubular lumen (³urine´ side)tubular lumen (³urine´ side)

�� The basolateral cell membranes areThe basolateral cell membranes are

those are in contact with the lateralthose are in contact with the lateral

intercellular spaces and peritubular intercellular spaces and peritubular interstitium (³blood´ side)interstitium (³blood´ side)

�� The termThe term transcellular transcellular refers torefers to

movement of solutes and water throughmovement of solutes and water through

cellscells

�� The termThe term paracellular paracellular refers to movementrefers to movement

of solutes and water between cellsof solutes and water between cells

�� Epithelial cell junctions can be ³leaky´Epithelial cell junctions can be ³leaky´

(proximal tubule) or ³tight´ (distal(proximal tubule) or ³tight´ (distal

convoluted tubule, collecting duct)convoluted tubule, collecting duct)

Transport mechanisms

�� Passive transport (simple diffusion)Passive transport (simple diffusion)

�� Facilitated diffusionFacilitated diffusion

�� Primary active transportPrimary active transport

�� Secondary active transportSecondary active transport

�� PinocytosisPinocytosis

�� Solvent dragSolvent drag

� Reabsorption of sodium is very important

� Cells of renal tubule have very low conc of

Na+ in their cytosol due to the activity of

Na+/K+ ATPase pump ± located in

basolateral membrane

� Absence of this pump in apical membrane

ensures one way movement of Na+

� Energy obtained from hydrolysis of ATP.

� Solute reabsorption drives water

reabsorption ± due to osmosis.

� Water reabsorbed with solutes in tubular

fluid ± obligatory water reabsorption.

Occurs in PCT and descending loop of

� Reabsorption of final 10% of water ±facultative water reabsorption. Regulated

by ADH and occurs in collecting ducts

R b ti i l f H l

Reabsorption in loop of Henle

� Fluid enters the loop at the rate of 40-45

mL/min.

� 15% water

� 20-30% Na+ and K+

� 35% Cl-

� 10-20% HCO3

� Variable amounts of Ca2+ and Mg2+

� Apical cell membrane has Na+/ K+/ 2Cl-

symporter ± reclaims one Na+, one K+ and

two Cl-

from the fluid in tubular lumen� Many K+ leakage channels are there in the

apical membrane ± K+ moves back into the

tubular fluid. Thus there is reabsorption of

mainly sodium and chloride ions

� Movement of K+ into the tubular fluid leaves

the interstitial fluid and blood negatively

charged as compared to tubular fluid. Thispromotes reabsorption of Na+, K+. Mg2+ and

Ca2+ by paracellular routes

R b ti i l DCT

Reabsorption in early DCT

� Rate of fluid entry ± 25 mL/min

� 10-15% water

� 5% of Na+

� 5% of Cl-

� Variable amount of Ca2+ - due to

stimulation of parathyroid hormone

Reabsorption and secretion in late

DCT and collecting ducts

� Two types of cells ± principal cells and

intercalated cells

� Principal cells ± reabsorbs Na+ and

secretes K+

� Intercalated cells reabsorb K+ and HCO3-

and secrete H+

secretion and tubular

reabsorption� ADH

± Secreted by posterior

pituitary

± Increases water

permeability in distal

tubules and collecting

� Aldosterone

± Produced in adrenal

cortex

± Affects Na+ and Cl-

transport in nephron and

� Renin± Produced by kidneys,

causes production of angiotensin II ±enhances reabsorption

of Na+ and Cl-

� Atrial natriuretichormone± Produced by heart

when blood pressureincreases� Inhibits ADH production

� Reduces ability of kidneyt t t i

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