Renal Anatomy

Renal Anatomy and Physiology By: Wong Ann Cheng MD (UKM) MRCPCH (UK)

Renal Anatomy and Physiology 

Macroscopic anatomy    

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Embrology Gross Procedures Investigations

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Physiology 

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Microscopic anatomy  

Excretory function

Homeostatic function 

Glomerular Tubular

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Nitrogenous metabolic waste: urea, uric acid, creat

Water and salt regulation Renin angiotensin mechanism Acid/ base balance

Endocrine function 

Erythropoeitin

Embrology ◆Early

development and evolution ◆Pronephros ◆Mesonephros ◆Metanephros ◆Ascent

and abnormalities

Metanephros – definitive kidney  The metanephros or

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definitive kidney of higher vertebrates, begins when the metanephric ducts (ureteric buds) sprout from the distal end of the mesonephric duct at about 5 weeks. The ureteric buds induce intermediate mesoderm in the sacral region to form a metanephric blastema which forms the

Evolution of the Kidneys: Metanephros The ureteric buds bifurcate again 

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and again to form the calyces and collecting duct system of the definitive kidney. The kidneys begin producing urine by week 12, and it adds to the volume of the amniotic fluid. The fetus drinks this fluid in utero. The fetal kidneys are not responsible for excretion as the placenta serves this function

Ascent of the Kidneys 

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In the 6th week the kidneys begin to ascend from the sacral region to their position in the upper abdomen. The metanephric ducts elongate and become the ureters. As the kidney ascends it receives new segmental arteries from the aorta and loses those vessels below (“climbing a ladder”). Thus sometimes there is more than one renal artery. Sometimes one kidney fails to ascend => pelvic

Position of kidneys

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Kidneys lie on the psoas muscle beside the vertebral bodies. The diaphragm and 11th and 12th ribs lie behind the upper half of each kidney. Therefore they move with breathing Left is higher than right (liver) Upper poles T12 Hilum is at L1/2 Lower poles at L3 Upper poles are more medial (psoas). In the hilum:

It crosses the aorta Is crossed by the SMA Receives left gonadal vein

Anterior relations 

Right Adrenal  Liver 

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bare area Hepatorenal pouch

Duodenu m  Pancreas  Right colic flexure 

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◆Left ◆Adrenal ◆Stomach ◆Spleen ◆Pancreas ◆Descending

Colon ◆Jenunum

Macroscopic anatomy

Nephrology / Urology

Renal

Upper urinary tract

Lower urinary tract

Perirenal Fat

A layer of adipose tissue (fat) partially surrounds the kidney. It is usually a radilogy finding but occassional a tumor can arise from it.

Renal Capsule

The thin but tough covering of the kidney. It helps protect the kidney. During a kidney biopsy, may feel a "pop" as the needle goes through the renal capsule

Renal Cortex

The outer shell of the kidney between the renal capsule and the renal medulla. The renal cortex contains the renal corpuscles (particularly the glomeruli) and most of the renal tubules (except for the loop of Henle). It is about 1 centimeter thick and also goes down between the renal pyramids. Many kidney diseases affect the glomeruli so the goal of a kidney biopsy is to sample this area.

Renal Medulla

The innermost area of the kidney. It is separated into 8 to 18 cone-shaped sections called the medullary pyramids. If the biopsy needle goes in too far, you may only get medulla and the biopsy will likely have to be repeated.

Medullary Pyramid

An important part of the inner kidney. It consists primarily of collecting tubules as well as loops of Henle. The base of the medullary pyramid is next to the cortex and it tapers to form the renal papillae. There are between 8 to 18 medulla pyramids in each kidney.

Calyx

An extension of the renal pelvis that surrounds the renal papillae. It collects urine from the papillary ducts. Several minor calyces drain into a major calyx and then onto the renal pelvis.

Renal Pelvis

The area where the urine collects before entering the ureters. Two or three major calices come together to enter the renal pelvis. Cancers and kidney stones can form in renal pelvis and cause blood to be lost in the urine.

Renal Sinus

A cavity in the kidney that contains the calices and the renal pelvis. It also contains the blood vessels, nerves, and fat.

Physiologic anatomy Retroperitoneal organ Weight: 150gm each Size: ~clenched fist size Location Right: hilum at L1-2 Left: hilum at L1 Divided into cortex and medulla Each ~1million unit nephrons and kidney cannot regenerate new nephrons.

paired organs. (1 in 1,000) only one kidney develops called congenital agenesis. Shaped Like Beans: The kidneys are bean shaped. (1 in 400), the two kidneys fuse into a single horseshoe kidney Located in Your Lower Back: The kidneys lie in the retroperitoneum on either side of the spine. Some people are born with ectopic kidney, not proper location. Roughly the Size of Your Fist: On the average, the kidneys are about 11-12 cm in length, 7-8 cm wide, 2-3 cm thick and weigh about 1/4 to 1/3 pound each.

Microscopic anatomy

Renal blood supply Total blood flow ~25% cardiac output.(1.2L/min) Renal arterysegmentalinterlobararcuate interlobularafferent Glomerulusefferentperitubular (vasa recta) veins 2 capillary beds High presure system hydrostatic pressure 60mmHg minus (32mmHg oncotic pressure + 18 mmHg bowman hydrostatic pressure) Renal cortex receives the most of the blood flow. Renal medulla only receives 1-2% total blood flow

Substance

Mol wt

Filterability

H2O

18

1.0

Na

23

1.0

Glu

180

1.0

Inulin

5 500

1.0

Myoglobin

17 000

0.75

Albumin

69 000

0.005

GFR depends on Starling force net pressure 1= capillary hydrostatic pressure. 2= bowman capsule hydrostatic pressure 3= capillary oncotic pressure

GFR depends on 1.

Glomerular permeability -capillary and bowman capsule endothelium, glomerular basement mambrane.

2.

Number of functioning glomeruli and total capillary surface area

3.

Glomerular capillary plasma flow  ultrafiltrate: plasma minus protein/fat

Use of clearance method to quantify kidney function 

The rates at which different substance are cleared from plasma provide a useful way of quantifying the effectiveness of which the kidney excrete various substances

Renal clearance of a substance 

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Volume of plasma completely cleared of the substance by the kidney per unit time Provides a useful way to quantify the excretory function of the kidneys Can be used to quantify the rate at which blood flow through the kidneys as well as the basic function of the kidney, glomerular filtration rate, tubular reabsorption and tubular

Cs x Ps = Us x Vs  

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Cs = clearance rate of a substance s Ps = plasma concentration of the substance V = urine flow rate Us = urine concentration of the substance

Cs = Us x V / Ps 

Renal clearance of a substance is calculated from the urinary excretion rate (Us x V) of the substance divided by its plasma concentration

Inulin clearance  

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Can be used to estimate GFR Substance existed that was freely filtered, not absorped or secreted by the renal tubules, then the rate at which the substance was excreted in the urine (Us x V) is equal the rate at which the substance was filtered by the kidneys (GFR x Ps) GFR x Ps = Us x V

GFR = US x V / Ps = Cs 

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Inulin – polysaccharide molecule which molecular rate of 5200 Not produced in the body Found in the roots of certain plants. Must be administered IV to a patient to measure GFR

Other substances used to estimate GFR  

Radioactive iothalamate Creatinine By product of skeletal muscle metabolism  Present in plasma at relatively constant concentration  Does not require IV infusion 

Creatinine clearance 

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Most widely used method for estimating GFR clinically Creatinine not a perfest marker for GFR  

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A small amount is excreted by the tubules The amount of creatinine excreted in the urine slightly exceeds the amount filtered Overestimation of the plasma concentration

The creatinine clearance provides a reasonable estimate of the GFR

Formula GFR (total plasma volume/min from capillary to bowman capsule) 

38× Ht( cm )/ plasma Creatinine (mcmol/L) Normal adult- 120ml/min/1.73m2

Creat. clearance (plasma volume removed /min by kidney) 

Urine creatinine (mmol/L) × Urine volume (ml/min)/ plasma creatinine(mmol/L)

Normal: ♂ 90-140ml/min ♀ 80-125ml/min

Creatinine clearance

Physiologic control of GFR and Renal blood flow 1.

2.

Sympathetic NS activation: all blood vessels are richly innervated. Most important during severe acute disturbances

Hormone or autocoid

Effect on GFR

Norepinephrine

↓

Epinephrine

↓

Endothelin

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Hormonal (see table)

Angiotensin II

↔ (prevents ↓)

Endothelial derived NO

↑

Prostaglandin

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Autoregulation of GFR & Renal blood flow

Renin Angiotensin Aldosterone System 

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Powerful mechanism for controlling pressure Renin: small protein released by kidneys when arterial pressure falls too low Synthesized and stored in an inactive form called prorenin in the JG cells of the kidneys  JG cells are modified smooth muscle cells located in the walls of the afferent arterioles immediately proximal to the 

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Two principal effects of Angiotensin II that can elevate AP 

Vasoconstriction – occurs rapidly 

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Intense in the arterioles and less extent in veins Constriction in arterioles increases peripheral resistance, raising AP Mild constriction in veins promotes increase venous return to the heart,

Decreased excretion of both salt and water – slowly increases the ECF volume, increases AP over period of hours and days 

Even more powerful than acute vasoconstrictor mechanism in eventually returning AP back to normal

Two ways by which Angiotensin causes salt and water retention

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Angiotensin acts directly on the kidneys to cause salt and water retention Angiotensin causes the adrenal glands to secrete aldosterone, and the aldosterone in turn increases salt and water reabsorption by the kidneys tubules

Procedure anatomy

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Orientation and surroundings The medial border of each kidney is anterior to

the lateral border (psoas). Thus the coronal plane of the kidney is at 30 degrees to the coronal plane of the body. ◆Layers surrounding the kidney ◆Outside

the renal capsule is perirenal fat ◆Then

is the renal fascia which also surrounds the adrenals ◆This

is embedded in extraperitoneal fat (pararenal fat)

RENAL BIOPSY

Normal anatomy

The kidneys are paired organs that lie posterior to the abdomen, in the area of the lower back. The kidneys make urine, which is transported from the kidneys to the bladder by the ureters, long muscular tubes which connect the kidneys with the bladder.

Kidney transplant may be recommended for patients with kidney failure caused by: severe, uncontrollable high blood pressure (hypertension) infections diabetes mellitus congenital abnormalities of the kidneys other diseases which cause renal failure, such as autoimmune disease Donor kidneys

Incision

While the patient is deep asleep and painfree (general anesthesia), an incision is made in the lower right quadrant of the abdomen. The donor kidney is transplanted into the right lower pelvis of the recipient.

Procedure The new kidney is sutured into place. The vessels of the new kidney are connected to the vessels leading to the right leg (the iliac vessels), and the ureter is sutured to the bladder.

Aftercare In most cases, the recipient's native kidneys are left in place, and the transplanted kidney performs all the functions that both kidneys perform in healthy people. Kidney transplant recipients are required to take immunosuppressive medications for the rest of the lives, to prevent immune rejection of the transplanted organ.

RENAL ULTRASOUND Kidney Structure •Number of Kidneys: agenesis •Shape of the Kidneys: horseshoe kidney •Location of the Kidneys: ectopic kidney. Finding Kidney Stones, Cysts, and Masses •Kidney Stones: The kidney ultrasound is a useful screening test for kidney stones. Not all kidney stones can be seen on ultrasound, but many can be. If a stone is causing ureter obstruction, there may be hydronephrosis. •Ureter Obstruction: A kidney ultrasound is routinely ordered to rule out obstruction in kidney failure. Impeding the flow of urine can cause it to back up and dilate the ureters and kidneys. It should be noted that finding hydronephrosis doesn’t necessarily mean there is an obstruction. •Kidney Cysts: The kidney ultrasound is very good at discovering kidney cysts, most of which are uncomplicated and incidental findings. Some cysts look complicated or complex and may represent infection, bleeding or cancer. People with polycystic kidney disease have multiple large cysts that replace normal tissue and destroys the kidneys. •Kidney Masses: The ability of kidney ultrasound to detect a kidney mass depends on its size. It is very good for large masses (> 3 cm) but not so good for small tumors. Signs of Kidney Chronic Disease •Kidney Size: On the average, the kidneys are about 11-12 cm in length, 7-8 cm wide, and 2-3 cm in thickness. If they are very small, it suggests significant scarring and irreversible damage. •Thickness of the Cortex: The cortex is the outer shell of the kidney (about 1 cm in thickness) and contains all the glomeruli. If it particularly thin, it suggests chronic kidney disease and may make it hard to biopsy. If it is thick, it may mean inflammation and congestion. •Echogenicity of the Cortex: Echogenicity refers to how the sound waves look when they bounce off something. It is often said that it is not normal if there is a lot of echogenicity (compared to the liver). In reality, it is not a very reliable indicator of kidney disease.

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