Question

Case Study: A 40-year old woman experiences pain in the right ‘flank’ region of her body. At first she thinks that the pain is a result of a ‘pulled muscle’ following a session at her local gym and tries to ignore it. However, the pain gets worse and she can no longer tolerate it so she goes to her local hospital.

A CT scan shows that she has nephrolithiasis or kidney stone formation.

Questions:

1. Describe the gross anatomy of the right kidney. [8 marks]

2. Explain the process of formation of kidney stones. [4 marks]

3. State one major cause of kidney stone formation. [1 mark]

4. Describe the anatomical location in the kidney where kidneys stones typically form. [2 marks]

5. Describe the anatomical site where the stones are most likely to cause pain, and why this is the case. [3 marks]

6. Outline the possible consequences of the stones reaching the bladder. [2 marks]

Answer 1

Gross ANATOMY
Answer 1)The kidneys are bean-shaped paired organs, each weighing about 150 gm in the adult male and about 135 gm in the adult female.
Right kidney also left kidney have upper and lower poles,medial and lateral borders,anterior and posterior surfaces .
Right kidner vertically extend from upper border of Twelfth thoracic vertebra to third Lumbar vertebrae ( T12-L3)
Right kidney is slighly lower than left .
The transpyloric plane passes through the upper part of hilum of right kidneys .
The hilum of right kidney is situated at the midpoint on the medial aspect where the artery, vein, lymphatics and ureter are located.
The kidney is surrounded by a thin fibrous capsule which is adherent at the hilum.

Cut surface of the kidney shows 3 main structures: well demarcated peripheral cortex, inner medulla and the innermost renal pelvis .

1)The renal cortex forms the outer rim of the kidney and is about 1 cm in thickness. It contains all the glomeruli and about 85% of the nephron tubules. Remaining 15% nephrons consisting of collecting tubules, collecting ducts, loops of Henle and vasa recta send their loops into the medulla, and are therefore called juxtamedullary nephrons.
This latter part of the cortex forms faint striations called medullary rays, a misnomer since thesesl structures are located in the cortex but are destined for medulla. Columns of renal cortical tissue that extend into the space between adjacent pyramids are called the renal column (septa) of Bertin; they contain the interlobar arteries.

2)The renal medulla is composed of 8-18 cone-shaped renal pyramids. The base of a renal pyramid lies adjacent to the outer cortex and forms the cortico-medullary junction, while the apex of each called the renal papilla contains the opening of each renal pyramid for passage of urine collected from collecting ducts and goes down into minor calyces.

3)Th e renal pelvis is the funnel-shaped collection area of the urine for drainage into the ureter. Th e minor calyces (8-18 in number in a normal kidney) collect urine from renal papillae and drain into major calyces (2-3 in a normal kidney).

Answer 2)
PATHOGENESIS of stone formation
There are 5 types of stones each have different mechanism for precipitation.
1.Calcium stones  
Incidence --> 75%
Causes -->Hypercalciuria with or without hypercalcaemia; idiopathic
Mechanism --->Supersaturation of ions in urine, alkaline pH of urine; low urinary volume, oxaluria and hyperuricosuria

2.Mixed (struvite) stones
Incidence is 15%
Causes -->Urinary infection with urea-splitting organisms like Proteus
Mechanism -->Alkaline urinary pH produced by ammonia from splitting of urea by bacterially produced urease

3.Uric acid stones  
Incidence-6%
Causes -->Hyperuricosuria with or without hyperuricaemia (e.g. in primary and secondary gout)
Mechanism -->Acidic urine (pH below 6) decreases the solubility of uric acid in urine and favours its precipitation

4.Cystine stones  
Incidence --2%
Cause -->Genetically-determined defect in cystine transport
Mechanism -->Cystinuria containing least soluble cystine precipitates as cystine crystals

5.Other types  
< 2%
Cause --->Inherited abnormalities of amino acid metabolism
Mechanism -->Xanthinuria

Answer 3)Calcium stone formation
Mechanism of calcium stone formation is explained on the basis of imbalance between the degree of supersaturation of the ions forming the stone and the concentration of inhibitors in the urine.A number of other predisposing factors contributing to formation of calcium stones are alkaline urinary pH, decreased urinary volume and increased excretion of
Oxalate and uric acid

Answer 4)Most likely site where the crystals of calcium oxalate and/or calcium phosphate are precipitated is the tubular lining or around some fragment of debris in the tubule acting as nidus of the stone
Stone grows bigger in size around nidus .

.Answer 5) The cause of obstruction may lie at any level of the urinary tract—
renal pelvis, ureters, urinary bladder and urethra .Stones doesnt stay in kidneys it passes from kidney to ureters .Ureters are tube which carries urine from kidneys to urinary bladder .When stones passes through urters its causes spasm and irritation in ureters and Severe excruciating pain .

Answer 6)When stone reaches the bladder it irritates the lining of bladder and may result in frequent urination which is painful.It may predispose to recurrent episodes of urinary tract infections.Also if stone get stucked at exit of urethra then sudden Anuria ( not passing urine can occur ).