Lecture №3

Function and Clinical Anatomy of the Urinary System with Elements of

Embryology.

ТНЕ URINARY ORGANS

The urinary organs (organa uropoietica) are, firstly, two glands (the kidneys

whose excretion is the urine) and, secondly, organs concerned with the storage and

excretion of the urine (the ureters, urinary bladder, and urethra).

Development of the Urogenital System.

The urogenital system is developed in connection with Intermediate coloumn

of secondary mesoderm.

The intermediate columns are two in number one on each side of middle line.

They lie along the: dorsal body wall and as they reach the tail fold of the embryo,

they leave the dorsal body wall,. bend ventrally one on either side of rectum (dorsal

part of cloaca) and on reaching the intervaled between the rectum and the bladder

(uro-rectal septum), they gradually соme closer and ultimately unite in the middle

line to form а single thick column known as "Nephrogenic cord". The nephrogenic

cord ends by reaching the dorsal wall of ventral part of cloaca.

Development of Kidney

If you know the development of the urinary and reproductive system, you will

understend the anomalies and malformations that sometimes appear.

Kidney is developed from two sources.

I.Collecting portion — It consists of calyces major and minor and straight collecting

tubules of Bellini and they are developed from distal blind expanded end оf the

ureteric bud which arises from dorsimedial aspect of mesonephric (Wolffian) duct

within the nephrogenic cord.

1

II Secretory or Excretory part — It is developed from metanephric blastema or

metanephrogenic cap which is а condensed mesodermal сар formed from mesoderm

of nephrogenic cord and is moulded over the distal blind expanded end of ureteric

bud.

Process of development o f Kidney

1. Nature attempts thrice for the development of kidney.

(а) First attempt — Formation of Pronephros. It is а futile attempt to form the

kidney.

(b) Second attempt — Formation of Meson ephros. It is а misdirected attempt.

(с) Third attempt — Formation of Metanephros. It is the final and successful

attempt to form the kidney.

The basic principle in each of the three attempts is to form а number of secreting

tubules and а duct.

So,

А. Pronephros — А number of pronephric tubules and а pronephric duct.

В. Mesonephros — А number of mesonephric tubules and а mesonephric (Wolffian)

duct.

С. Metanephros — А number of metanephric tubules and metancphric duct (ureter).

Arrangement between the tubules and the duct - The tubules lie more or less at right

angles to the duct and connected to its cranial segment and the duct lies along

intermediate column and nephrogenic cord.

II. Changes in the collecting part (distal blind expanded end of the ureteric bud).

(а) At first it-dilates to outline the pelvis.

(b) Then it divides and subdivides up to 5th order of divisions and produce following

components—

Calyces major — From first order of division.

Calyces minor - By second to remaining orders of divisions.

2

Difference between Features of Pronephros and Mesonephros—

PRONEPHROS MESONEPHROS

1.Earlier to appear

2.Extends from lower cervical to upper

thoracic segments.

3.So smaller extending over 7 or 8

segments.

4. Develops 7 to 8 tubules only. Tubules

are segmental in distribution.

5. All the tubules appear at the вате time.

6. All tubules disappear.

7. Tubulcs open at both ends — one into

the duct and other into 1.Е.С.

8. Мау develop two sets of glomeruli —

Internal and External.

9. Has got its own duct pronephric duct.

1. Appears later

2. From cervical to upper lumbar

segments..

3. More or less bigger extending over 17

or 18 segments.

4. Develops 70 to 80 tubules. Tubules

are nonsegmental in distribution.

5. Only half the number present at а time

cranial ones appear earlier and caudal

ones later.

6. Lumbar tubules persist.

7. Tubules open at the one end only

(duct end) but blind at coelomic end.

8. Develops one set Internal only.

9. It has not got its own duct but а loan

duct. Pronephric duct becomes

mesonephric duct.

3

The mesonephros is the primary secretory organ while the mesonephric duct serves

as its efferent passage.

The paramesonephric duct. At the end of the 4-th week a longitudinal thickening of

the peritoneum forms on the lateral side of each mesonephros due to the development

of an epithelial cord, which transforms into a duct at the begining of the fifth week.

The cranial end of the paramesonephric duct opensinto the body cavity slightly in

front of the anterior end of the mesonephros. In contrast to the mesonephric duct each

opening separately, the paramesonephric duct unite on the midline into a common

duct at their caudal ends on reaching the urogenital sinus.

The sex glands develop a little later as a conglomerate of embryonal epithelium on

the medial side of the mesonephros. The testicular seminiferous tubules and the

ovarian follicles containing the oocytes develop from the embrionic epithelial cells.

The final formation of the urogenital organs occurs as follow. The

mesonephros is gradually replaced by the permanent kidney, the metanephros,

developing from the same nephrogenic cord as the mesonephros. The nephrogenic

cord gives rise to mesenchyme proper of thr permanent kidneys (the renal tubules).

From the third month the permanent kdneys replace the mesonephros as the

functioning excretory organs.

The trunk grows downward more rapidly than the urinary organs, the kidneys

seem to move upward and occupy their place in the lumbar region.

The renal pelvis and the ureter develop from a diverticulum of the caudal end

of the mesonephric duct at the begining of the 4-th week; cranial end of the

diverticulum reaches the nephrogenic cord and unites with the kidney. The caudal

end of the diverticulum separates from the mesonephric duct and drains into that part

of the sinus urogenitalis from which the fundus of the urinary bladder develops; the

ureters open in the fundus.

4

ТНЕ KIDNEY

The kidney (ren, Gk nephros) is а paired excretory organ producing the urine. The

kidneys are situated on the posterior abdominal wall behind the peritoneum on either

side of the vertebral column on the level of the last thoracic and upper two lumbar

vertebrae .The right kidney is а little lower than the left, by 1.0-1.5 cm on the average

(depending on the pressure exerted by the right lobe of the liver). The upper end of

the kidney reaches to the level of the eleventh rib, the lower end is 3-5 сm from the

iliac crest. Individual variations are encountered, however, in the position of the

kidneys: upper boundary often rises to the level of the superior border of the eleventh

thoracic vertebra, the lower boundary mау descend for the length of half or а whole

vertebra. The kidney is bean-shaped, its surface is smooth and dark red. In the kidney

are distinguished the upper and lower inferior ends (poles) or extremities

(extremitas superior and extremitas inferior), the lateral and the medial margins

(margo lateralis and margo medialis), and the anterior and the posterior surfaces

(facies anterior and facies posterior). The lateral margin is convex, while the medial

margin has а concavity in the middle and faces not only medially, but slightly

downward and tо the front. The middle concave part of the medial margin contains

the hilum of the kidney (hilus renalis) through which arteries and nerves enter the

kidney and veins and the urethra leave it. The hilum opens into а narrow hollow

extending into the renal substance; it is called the sinus of the kidney (sinus renalis)

and its longitudinal axis coincides with the longitudinal axis of the kidney. The

anterior surface of the kidney is more convex than the posterior surface.

The capsules of the kidney. The kidney is invested in its own fibrous capsule

(capsula fibrosa), а fine smooth lamina intimately attaclied to the renal substance.

Normally it can be separated from the renal substance quite easily. Outside this

fibrous capsule, particularly in the region of the hilum and on the posterior surface, is

а layer of loose fatty tissue forming the fatty capsule (renal fat) (capsula аdipoza) of

the kidney; the anterior surface is quite often not covered by fat. Outside, each kidney

is invested in а connective-tissue fascia (fascia renalis), which is connected with the

fibrous capsule by means of fibres and separates into two layers, one covering the

5

anterior and the other the posterior surface. On the lateral order of the kidney, both

layers unite and are continuous with а layer of retroperitoneal connective tissue,

which had given origin to them. А complex of the following structures is responsible

for fixation of the kidney in place: (1) fascia renalis, which fuses with the renal

capsules; (2) the muscular seat of the kidney formed by the psoas major and

quadratus lumborum muscles; (3) the renal vessels, which prevent the kidney from

moving away from the aorta and vena cava inferior, and, finally, (4) intra-abdominal

pressure produced by contraction of the muscles of the abdominal wall. If this

fixation apparatus is weak, the kidney may descend (mobile, or wandering kidney),

which calls for its operative fixation with sutures.

Structure. On а longitudinal section through the kidney it can bе seen that it is

composed of а cavity, the renal sinus, containing the calyces and the upper part of the

renal pelvis, and of the renal substance proper adjoining the sinus on all sides except

for the hilus. The cortex (cortex renis) and the medulla (medulla renis) are

distinguished in the kidney.

The cortex occupies the peripheral layer of the organ and is about 4 mm thick. The

medulla is formed of conical structures called the renal pyramids (pyramides

renales), or pyramids of Malpighi. The wide bases of the pyramids face the surface

of the organ, the apices are directed toward the sinus. Two or more apices join to

form rounded eminences termed the renal papillae (papillae renales). There are а

total of about 12 papillae on the average. Each papilla is dotted with small openings,

papillary foramina (foramintt papillaria), through which urine is discharged into the

initial parts of the urinary tract (the calyces). The cortex penetrates between the

pyramids and separates one from another; these parts of the cortex are known as the

renal columns (columnae renales). The pyramids appear striated because the urinary

tubules and the vessels are arranged in them in а straight direction.

The human kidney belongs to the group of smooth multipapillary kidneys

The structural unit of the kidney is the nephron. According to the findings of

microscopic anatomy, it consists of the following parts.

6

1. The corpuscle of the kidney (corpusculum renis) is forming capsula glomeruli

surrounds from all sides glomerulus corpusculum.2.Capsula glomeruli continuons

with proximal segment consisting of the proximal convoluted tubule. 3. The

proximal straight segment is continuous with а thin loop, Henle's loop, which has

two limbs, descending and ascending. 4. The ascending limb of Henle's loop is

continuous with the distal segment consisting of а thick ascending limb in turn

continuous with the distal convoluted tubule and then with the junctional tubule.

The junctional tubule drains into the collecting tubule. These structural components

of the nephron are arranged in the kidney parenchyma in the following order.

The renal corpuscle, the convoluted and straight tubules of the proximal segment, the

thick ascending limb of the nephron loop, and the distal convoluted and junctional

tubules are situated in the cortex. The thin ascending and descending limbs of Henle's

loop, the thick ascending limb of the nephron, and the collecting tubule are situated in

the medulla.

The nephron is concerned with the production of urine: ultrafiltration takes place in

the glomeruli, reabsorption and secretion in the tubules.

Each kidney contains up to one million nephrons, the totality of which constitutes the

main bulk of the renal substance.

To understand the structure of the kidney and its structural unit, the nephron,

one must know its vascular system. The renal artery arises from the aorta and has а

large calibre, which corresponds to the urogenous function of the organ associated

with "filtration" of blood.

At the renal hilum, the renal artery separates into arteries according to the parts of the

kidney, namely vessels for the upper pole, the superior polar arteries, for the lower

pole, inferior polar arteries, and for the middle part of the kidney, the central arteries.

In the kidney parenchyma, these arteries раss between the pyramids, i.e. between the

lobes of the kidney, and are, therefore, called the interlobar arteries (аа.

interlobares renis). At the base of the pyramid at the junction of the medulla and

cortex, they form arterial arches, the arciform arteries (аа. arcuatae), which give

rise to the interlobular аrteries (аа. interlobulare) piercing the cortex. Еаch

7

interlobular artery gives origin to vas afferens, which ramifies to form а tuft of

convoluted capillaries, the glomerulus, invaginated in the initial part of the renal

tubule, the ShumIyansky-Bowman capsule. The vas efferens emerging from the

glomerulus again breaks up into capillaries, which first surround the renal tubules and

only after that they are continuous with the veins. The veins accompany the

corresponding arteries and leave the renal hilum as а common trunk, the renal vein

(vena renalis) draining into the vena cava inferior.

The kidney, therefore, contains two capillary systems: one connects the arteries with

the veins while the other is of а special character comprising а vascular tuft, in which

blood is isolated from the capsular cavity by only two layers of squamous cells (the

endothelium of the capillaries and the endothelium of the capsule). This provides

favourable conditions for the excretion of water and metabolites from blood.

Anomalies of the urinary organs:

I. Anomalies in number – Absence of kidney. May be unilateral or

bilateral. Due to failure of induction from ureter.

II. Duplication – Due to early splitting of ureter. May be multiple kidneys.

In shape –

1. Horse shoe shaped- due to fusion of the lower poles of the two kidneys. It

is ascent will be arrested by Inferior mesenteric artery and so it will lie at a

lower level than normal position.

2. Pin cake or Disc kidney due to complete fusion of both the kidneys in

front of midline.

3. Lobulated – due to persistence of foetal lobulations.

III. Anomalous position

8

1. Pelvic kidney – due to complete failure of ascent, the kidney lies in

the pelvis. The cause is presence of large umbilical artery.

2. Ectopic or Crossed ectopia with fusion or without fusion. This may

be abnormality in ascent – In this cases there may two kidneys on one

side and another side absence (crossed ectopia). A large kidney on one

side (crossed ectopia with fusion) and absent in orther side.

3. Position – may be lower lumbar or thoracic.

IV. Polycystic kidney – more common anomaly due to failure of fusion

between secretory part and collecting part and characteries by numerous

small cysts filled with urine within kidney.

V. Aberrant renal artery or accesory renal artery due to persistence of

segmental artery or abnormal origin of segmental artery from abdominal

aorta and supplying either lower or upper pole of kidney.

VI. Kidney with double ureter – Fault is in the development of ureter.

VII. Floating kidney – Kidney suspended by a fold of peritoneum and the

upper pole tilted downwards.

The stages of the formation of the urain:

1. Filtration. F. takes place in the renal glomulus from the blood plasm. There

primary urine is formed. F. takes place due to pressure difference: hydrostatic

and osmothatic

9

The lymphatic vessels of the kidney are divided into superficial vessels arising from

the capillary networks of the renal capsules and from the peritoneum covering the

kidney, and deep vessels pa

ssing between the lobules. There are по lymphatics within the lobules or in the

glomeruli.

Both vascular systems merge for the most part at the renal sinus, then pass in atten-

dance to the renal blood vessels to the regional lymph nodes, but to different nodes

from each kidney: vessels from the right kidney drain into nodes around the чапа

сача inferior (the pre- and retrocaval nodes), into nodes situated between the vena

cava inferior and the aorta (interaortacaval nodes), and into nodes lying in front of the

aorta (preaortic nodes); lymphatic vessels from the left kidney drain into nodes

10

situated to the left of the aorta (left latero-aortic nodes) and in front of it (pre-aortic

nodes).

The nerves of thekidney are derived from the paired renal в1ехия formed Ъу the

splanchnic nerves, branches of the sympathetic ganglia, branches of the solar plexus

with fibres of the vagus nerves contained in them, and the afferent fibres of the

inferior thor=

acic and superior lumber~ s»~~> "- ="-""-

ТНЕ RENAL PELVIS, CALYCE8, AND URETER

Urine flowing from the papillary foramina passes on the way to the urinary bladder

through the lesser calyces, the greater calyces, the renal pelvis, and the ureter.

The lesser calyces (calyces renales minores), about eight or nine in num- ber, enclose

one, two, rarely three renal рарй1ае with one end and drain into one of the major

calyces with the other. There are usually two greater calyces (calyces renales

majores): а superior calyx and an inferior calyx; they merge in the renal sinus to form

а single renal pelvis (pelvis renalis) (Gk pyelos pelvis, hence pyelitis, inflammation

of the renal pelvis), which leaves the kidney through the hilum behind the renal

vessels and, curving downward, is continuous with the ureter directly below the renal

hilus.

The fornical apparatus of the calyces. Each renal calyx surrounds the conical renal

papilla like а double-walled goblet. As а result the proximal part of the calyx around

the base of the papilla is elevated above the axis of the papilla as а vault, or fornix.

The wall of the fornix contains smooth muscle fibres (т. sphincter fornicis), which,

together with the connective tissue embedded here and the adjoining nerves and

blood and lymphatic vessels, constitute the fornical apparatus of the kidney. It plays

an important role in excretion of urine from the renal parenchyma into the renal

calyces апй prevents the return of urine from the calyces into the renal tubules. Since

vessels are in close relation with the wall of the fornix, haemorrhages occur here

шоге easily than in other places and urine passes into the blood (pyelo- venous

reflux), which is conducive to the penetration of infection. Four muscles are

11

distinguished in the wall of the renal calyx, which are situated above the fornix (т.

levator fornicis), around it (m. sphincter fornicis), along the calyx (m. longitudinalis

calycis), and around the calyx (т. spiralis calycis). The levator fornicis and

longitudinal calycis muscles dilate the cavity of the calyx and facilitate urine

accumulation (diastole), while the sphincter fornicis and spiral calycis muscles cause

constriction of the calyx and eva- cuation of its contents (systole). The activity of the

calyx is connected with the similar activity of the renal pelvis.

The calyces, renal pelves, and ureters constitute the macroscopically visible part of

the excretory tract of the kidney.

Three types of the

excretory tree can be distinguished, which reflect the successive developmental

stages (Fig. 260, а, Ь, and с).

1. Embryonal type, marked by а wide sac-like pelvis, into which the lesser calyces

drain directly; the greater calyces are absent.

2. Foetal type with many lesser and greater calyces, which are con- tinuous with the

ureter; the renal pelvis is absent.

3. Mature type ж|СЫеж lesser calyces, which merge to form two greater calyces

continuous with а moderately developed pelvis that drains into the ureter. All three

components of the excretory tree are present here: the lesser and greater calyces, the

renal pelvis, and the ureter. Knowledge of these types makes it easier Со interpret the

Х-ray picture of the excretory tree seen in а live subject (in pyelography).

12