Urinary system

Department of Histology, Cytology and EmbryologyTatiana Globa

Urinary SystemUrinary System

State University of Medicine and Pharmacy “Nicolae Testemitanu”

Urinary System FunctionsUrinary System Functions Clear the blood of nitrogenous and other waste metabolic

products (urea, uric acid, toxic stuff, drugs) by filtration and excretion

Regulation of – blood volume – concentration of blood solutes– pH of extracellular fluid

Endocrine function: synthesis of erythropoietin, renin, prostaglandins

Makes calcitrol (from Vit D3: stim Ca2+ absorption by intestinal epithelium)

Recovers by reabsorbtion small molecules (amino acids, glucose, and peptides), ions (Na, Cl, Ca, PO), and water, in order to maintain blood homeostasis.

Assists liver in detoxification of poisons

Urinary SystemUrinary System

Consists: Kidneys Ureters Urinary bladder

(storage) Urethra

KidneysKidneysKidney are paired, bean-shaped organs, enveloped by

a thin capsule of connective tissueRenal hilum is the concavity on the medial border of

the kidney where there are:– Renal artery, vein; nerves, lymphatic vessels and

ureterSizes:10 cm X 5.5 cm X 3 cmEach kidney is divided into an outer cortex and an

inner medullaEach kidney contains about 2 million nephrons –

morpho-functional units

Kidney consists ofKidney consists of Cortex, which is divided into inner and outer regions.

– Renal corpuscles and convoluted tubules Medulla, which is formed by conical masses, the

medullary pyramids, with their bases located at the cortico-medullary border.– 10-18 renal pyramids– Each renal pyramid opens into the renal papilla– A medullary pyramids, together with the associated

covering cortical region, constitutes a renal lobe Minor calyx Major calyx Renal pelvis (connected to ureter)

MedullaMedulla

Medulla dividedinto pyramids

Tip of pyramidlike top ofsalt shaker

MedullaMedulla

pyramid

….….

….Minor calyx

urine

Parts of the KidneyParts of the KidneyWithin the kidney, utilize the diagram on the right to identify the

capsule, cortex, renal corpuscles, and medulla, which has no renal corpuscles. The slide on the left is a representative section from this part

of the kidney.

Slide B93 Monkey Kidney H&E X20

medullamedulla

cortexcortex

Parts of the KidneyParts of the KidneyOn the left, locate an area in the cortex where tubules run parallel to one another and are cut longitudinally. This is a pars radiata or medullary ray. On either side is a pars convoluta, which contains renal corpuscles

and coiled tubules.

B93 Monkey Kidney H&E X20

Medullary R

ay

Pars Convoluta

medullamedulla

cortexcortex

Kidney: Kidney: CortexCortex versus versus MedullaMedullaWith the same image, note the medullary rays are composed of

collecting tubules. On either side is a pars convoluta, which contains renal corpuscles and coiled tubules.

Medullary Ray

Pars Convoluta

medullamedulla

cortexcortexP

ars Rad

iata

Pars Convoluta

Kidney Blood SupplyKidney Blood Supply The main function of the kidney is to filter the blood

The kidneys receive 20-25% of the total cardiac output per minute and filter about 1.25 L of blood per minute. All the blood of the body passes through the kidneys every 5 minutes

About 90% of the cardiac output goes to the renal cortex; 10% of the blood goes to the medulla

Approximately 125 ml of filtrate are produced per minute, but 124 ml of this amount are reabsorbed

About 180 L of fluid ultrafiltrate are produced in 24 hours and transported through the uriniferous tubules. Of this amount, 178.5 L are recovered by the tubular cells and returned to the blood circulation, whereas only 1.5 L are excreted as URINE

Kidney Blood SupplyKidney Blood Supply

Renal artery– Branches until afferent arterioles to nephrons– GLOMERULI capillaries– Efferent arterioles– Secondary capillary network, surrounding the cortical segments of the

superficial uriniferous tubules Venules renal vein

Nephron-Nephron- morphofunctional unit morphofunctional unitConsists of 2 components:

1. Renal corpuscle– Bowman’s capsule and

glomerulus

2. Renal tubule Proximal thick segment

– Proximal convoluted tubule and proximal straight tubule

Thin segment– descending and ascending

limbs of loop of Henle Distal thick segment

– Distal convoluted tubule and distal straight tubule

Proximal straight tubule

Distal straight tubule

GlomerulusGlomerulus

Types of NephronsTypes of NephronsDepending on the distribution

nephrons can be: Cortical (85%)

– Is located in the outer region of the cortex

– Its loop of Henle is short and does not enter the medulla

– Most of reabsorption and secretion

Juxtamedullary (15%)– Is located in the cortex

region adjacent to the medulla

– Its loop of Henle is longer and extends deep into the medulla

– Create conditions for making concentrated urine

TermsTerms

Blood filtration and formation of the primary urine:

Cause: high pressure in glomeruli, glomeruli caps more permeable than others in body

ReabsorptionSecretion

Peritubular caps/vasa recta

Formation of the secondary urine

Renal Corpuscle - Renal Corpuscle - site of filtrationsite of filtration Consists of :1) Glomerulus2) Bowman’s capsule Glomerulus

– tufts of fenestrated capillaries; fed by afferent arteriole and drains to efferent arteriole

Mesangial cells– Support capillaries– Phagosytose– Contraction and regulation of blood flow– Secretion of amorphous extracellular matrix

Bowman’s capsule – double-walled (visceral and parietal) epithelial capsule– Visceral layer: is attached to the capillary glomerulus, is lined by podocytes

– modified simple squamous epithelium; – Parietal layer: is lined by simple squamous epithelium– Bowman space (containing primary urine)– Vascular pole: site of afferent (incoming) and efferent (outgoing) arterioles

supplying glomerulus– Urinary pole: leads to proximal convoluted tubule; route of filtrate

Renal CorpuscleRenal CorpuscleBowman’s Capsule

Kidney: Kidney: Renal CorpuscleRenal Corpuscle

Slide B92 Human Kidney PAS X200

Note the schematic of the renal corpuscle (glomerulus) on the right and how it is suspended in the urinary (Bowman’s) space. The afferent and efferent arterioles enter and leave the glomerulus at the vascular pole.

DCTDCT

Renal filtration barrierRenal filtration barrierCapillary fenestrated endotheliumBasement Membrane

– Much thicker than typical basement membrane Lamina rara externa – an electron-lucent zone Lamina densa – an electron dense intermediate zone Lamina rara interna – an electron-lucent zone

Bowman’s Capsule Visceral Epithelium– Podocytes – have long and branching cell processes that

completely encicle the surface of the glomerular capillary. The endings of the cell processes, the pedicels, from the same podocyte or adjacent podocytes, interdigitate to cover the basal lamina and are separated by gaps, the filtration slits (are bridged by a membranous material, the filtration slit diaphragm).

Podocytes

Capillary Endothelium

Basement Membrane

Podocyte

Composition of the primary urine

WaterIons (K, Ca, Mg, bicarbonate, phosphate,

sulfate ions)GlucoseSmall-weight proteins (less than 69,000

DaltonsAmino acidsUrea

Renal tubule – Renal tubule – site of selective re-absorption / site of selective re-absorption /

secretion of solutessecretion of solutes Proximal convoluted tubule Proximal convoluted tubule

Functions: receives filtrate from urinary space  site of selective re-absorption of most solutes

–  all glucose and amino acids  60 - 80% of NaCl (active) and water (passive) proteins absorbed by pinocytosis followed by lysosomal

degradation and release of amino acids re-absorbed materials released to peritubular capillary

network site of pH balance site of creatinine secretion

Proximal Convoluted TubuleProximal Convoluted TubuleSTRUCTURESTRUCTURE tubules formed by simple cuboidal / columnar epithelia apical surface covered with microvilli creating LM brush

border – increase surface area for ion absorption

cells tightly bound to one another to seal off intercellular space from lumen – tight junctions and zonula adherens apically; interdigitating plicae (folds)

laterally

interdigitating basal processes contain numerous mitochondria; creates LM basal striations; associated with ion transport

Histological appearance most abundant tubule in cortex eosinophilic cytoplasm with basal nucleus (polarized)

– brush border rarely preserved producing occluded lumen– Indistinct cell margins due to basal and lateral border interdigitations

Proximal Proximal SStraight traight TTubuleubule

located within or near medulla, depending upon type of nephron

lower cuboidal epithelium – microvilli and basal and lateral interdigitations

simplified

Loop of Henle: Thin SegmentLoop of Henle: Thin Segment

Descending thin tubule located within medulla low cuboidal to squamous epithelium microvilli and basal and lateral interdigitations

poorly developed creating leaky cell site of passive transport of ions (inward) and

water (outward) between lumen and interstitium

Ascending thin tubules located within medulla similar in appearance to descending thin tubules water impermeable; passive transport of

NaCl into interstitium

Distal Convoluted & Straight TubulesDistal Convoluted & Straight Tubules

Distal straight tubuleDistal straight tubule located within medulla and cortex simple cuboidal epithelium with sparse microvilli and lacking

lateral interdigitations– apical nucleus– basal interdigitations present  with abundant mitochondria

function:  water impermeable; site of ion transport from lumen to interstitum which establishes ion gradient of medulla

Distal convoluted tubuleDistal convoluted tubule located within cortex approximately 1/3 as long as proximal contacts renal corpuscle at macula densa to form

juxtaglomerular apparatus (below) morphology similar to straight portion function:  ion exchange

Kidney: Convoluted TubulesKidney: Convoluted TubulesWithin the pars convoluta, identify proximal convoluted tubules (PCT)

and distal convoluted tubules (DCT). The PCT is more than twice as long as the DCT, so the majority of tubules are PCT.

Slide B92 Human Kidney PAS X200

DCTDCT

DCTDCT

DCTDCT

DCTDCT

DCTDCT

DCTDCT

PCTPCT

PCTPCT

PCTPCT

PCTPCT

PCTPCTPCTPCT

PCTPCT

PCTPCT

PCTPCTDISTINGUISHING

CHARACTERISTICS

PCT star-shaped lumen

glycocalyx debris in lumen

highly eosinophilic tall cuboidal cell

DCT more cells per lumen

clear lumen (no debris) no or minimal

brush border less eosinophilic cells normal cuboidal

epithelium

Kidney: Kidney: PCTPCT versus versus DCTDCTThe diameter of the distal convoluted tubules (DCT) is much smaller

than the proximal convoluted tubules (PCT), although the luminal diameter of the two tubules are approximately the same.

DISTINGUISHING CHARACTERISTICS

PCT star-shaped lumen is due to the autolysis of the brush border. Fewer nuclei appear in cross-section and cell boundaries are

indistinct. Basal infoldings due

to mitochondria

DCT no precipitate in lumen

more nuclei with distinct cell boundaries

paler cytoplasmSlide B90 Human Kidney H&E X400

DCTDCT

DCTDCT

PCTPCT

PCTPCTrenal renal

corpusclecorpuscle

renal renal corpusclecorpuscle

Collecting Tubules & DuctsCollecting Tubules & Ducts

Start in cortex and descend through medulla

Is lined by a cuboidal epithelium composed of two cell types:– Principal cells – resorb Na

and water and secrete K in a Na, K ATPase pump-depending manner

– Intercalated cells – have abundant mitochondria and secrete either H and HCO3. they are important regulators of acid-base balance

Kidney: Kidney: Collecting DuctsCollecting DuctsPhoto of renal papilla projecting into renal calyx. The apex of the papilla contains openings, the collecting ducts (of Bellini). These ducts deliver

urine from the renal pyramid to the minor calyx.

Collecting tubulesCollecting tubules, , widen to form widen to form

collecting ductscollecting ducts (columnar (columnar

epithelium). The epithelium). The outer portion of the outer portion of the minor calyxminor calyx is lined is lined

with transitional with transitional epithelium.epithelium.

renal papillarenal papilla

renal (minor) calyxrenal (minor) calyx

renal calyxrenal calyx

Collecting Collecting tubulestubules

collecting ductscollecting ducts ((of Belliniof Bellini).).

Kidney: Kidney: Renal PapillaRenal PapillaHigher magnification photo of renal papilla projecting into renal calyx.

The openings seen within the papilla are the collecting ducts (of Bellini).

Note the Note the transitional transitional

epitheliumepithelium lining lining the outer surface the outer surface

of the minor calyx.of the minor calyx.

The renal papilla The renal papilla has a has a simple simple

columnar columnar epitheliumepithelium renal papillarenal papilla

renal renal (minor) (minor) calyxcalyx

renal renal calyxcalyx

*

**

*

*

Juxtaglomerular Apparatus - Juxtaglomerular Apparatus - site of blood site of blood

pressure regulation via renin-angiopressure regulation via renin-angiottensin-aldosterone systemensin-aldosterone system Macula densa: specialized cells in distal convoluted

tubule adjacent to renal corpuscle – these cells have receptors for Na. If it is necessary

they stimulate production of aldosterone Juxtaglomerular cells: modified smooth muscle cells of

afferent and efferent arterioles– produce renin. Renin provides the transformation

of angiotensinogen into angiotensin I, which transforms into angiotensin II (in lungs) that elevates the blood pressure

Juxtavascular cells: extraglomerular mesangial cells – their function is not well known. Probably they are

involved in the renin and erythropoietin secretion and blood pressure regulation

Juxtaglomerular ApparatusJuxtaglomerular Apparatus

MMechanismechanism

macula densa cells monitor NaCl levels in afferent arteriole renin secretion juxtaglomerular cells is stimulated by

paracrine activity from the macula densa renin is a protease that cleaves plasma angiotensinogen into

angiotensin I angiotensin I converted to angiotensin II in the lung (by

enzyme in capillaries) angiotensin II promotes vascular smooth muscle contraction

and release of aldosterone from the adrenal cortex aldosterone stimulates absorption of NaCl and water in the

distal convoluted tubule thus increasing blood volume net result is to increase blood pressure

Kidney: Kidney: Vascular PoleVascular Pole

Wheater’s Fig.16.18bSlide B94 Rabbit Kidney PAS X200

Search for an area within the renal corpuscle where a distal convoluted tubule makes contact with the vascular pole of the renal corpuscle. Note the macula densa and juxtaglomerular cells

DCTDCTDCTDCT

Kidney: Kidney: Vascular PoleVascular PoleThe macula densa of the distal convoluted tubule and the juxtaglomerular (JG) cells constitute a juxtaglomerular apparatus (JGA). The JG cells secrete renin and erythropoietin.

PCT

PCT

Ureters and Urinary BladderUreters and Urinary Bladder

UreterUreter Drains urine from kidney to

urinary bladderStructure mucosa – lined by transitional

epithelium over connect tissue lamina propria

– transitional epithelium – impermeable to water and salts; distendable

– lamina propria - loose connective tissue

muscularis externa – smooth muscle layer

– bi-laminar:  inner longitudinal and outer circular; produce peristalsis

adventitia / serosa – connective tissue coat with or without mesothelial covering

UreterUreter

Urinary BladderUrinary Bladder

Hollow muscular organ: distensible reservoir Full: ~1 liter receives bilateral ureters and empties via midline urethra smooth muscle forms detrussor muscle; specialized distally as

internal urethral sphincter

Urinary BladderUrinary BladderThe gross regions of the urinary bladder are

Fundus Body Neck

The histology of the urinary bladder is as follows: Mucosa - transitional epithelium and lamina

propria Submucosa - connective tissue with blood supply Muscularis externa - 3 layers of smooth muscle

termed the detrusor muscle

Serosa/Adventitia

MUCOSA

SUBMUCOSA

MUSCULARIS EXTERNA

Urethra

urethraurethra

UrethraUrethra Neck of bladder to exterior Female:

– Short: 1-1.5 in UTI (bacteria or fungus)

– External urethral orifice: very close to vaginal orifice

Male: – Long: 7-8 in– terminal duct for both urinary and genital

systems – Prosthatic, membranous, penile

Urogenital diaphragm: external urethral sphincter (skeletal muscle)– resting to urinate

Urinary SystemUrinary System

Internal urethral sphincterExternal Urethral Sphincter

Male Sphincters Female Sphincters