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Transplant Surgery
Renal Transplant Focus Note
Renal (Kidney) Basics
URINARY SYSTEM
The human urinary system consists of two kidneys, two ureters, one
urinary bladder and one urethra. The system has two basic functions,
both of which occur in the kidneys. They are:
1) Removal of nitrogenous wastes (creatine, urea, uric acid) from the
body;
2) Maintain the electrolyte, acid-base, and fluid balances of the
blood.
Urine, one product of these functions, contains water, urea, sodium,
potassium, sulfate ions, creatine, uric acid, calcium, magnesium, and
bicarbonate ions.
KIDNEYS
Fig. 1: Site of right kidney (on left)
and left kidney (on right)
with neighboring organs,
and vessels.
The kidneys are a pair of reddish-brown, bean-shaped organs the
size of a fist that lie behind the peritoneum (retroperitoneal) on
the posterior abdominal wall (Figs. 1). In the adult human, the
kidneys weigh between 115 to 170 grams each, about 0.5% of
total body weight. They lie on either side of the vertebral column
between the first and third lumbar vertebra. The right kidney lies
behind the duodenum and head of the pancreas. The left kidney
lies behind the tail of the pancreas, stomach and spleen. The right
kidney lies somewhat lower (caudal) than the left kidney due to the
large size and position of the right lobe of the liver. The kidneys
are surrounded by a cushioning layer of fat and are enclosed in an
envelop of connective tissue (Gerota’s Fascia).
GROSS ANATOMY
Each kidney is enclosed in a smooth semi-transparent membranous
renal capsule that adheres tightly to the outer surface of the kidney.
Each kidney has a (Fig. 2):
1) RENAL CORTEX just under the fibrous capsule.
2) RENAL MEDULLA that extends all the way to the renal pelvis which
is formed from three major calyces (ducts) that merge together.
3) RENAL PELVIS which becomes the ureter that descends in the
retroperitoneum along the spine to the bladder where urine is
stored.
RenalBasics(Tx-20-fn)RevC2014USltr.
Fig. 2: Kidney Components:
a) Renal Vein
b) Renal Artery
c) Ureter
d) Renal Medulla
e) Pelvis
F) Renal Cortex
Transplant Surgery
Renal (Kidney) Basics cont.
NEPHRON - BASIC UNIT OF THE KIDNEY
(Fig. 3).
Within the renal cortex and medulla of each kidney are one million (1,000,000)
tiny tubular nephrons consisting of:
1. BOWMAN’S CAPSULE: closed end at the beginning of the nephron; located
within the renal cortex. Site of the glomerulus, a coiled bundle of capillaries.
2. PROXIMAL TUBULE: first twisted tubular region near Bowman’s capsule;
located in the cortex.
3. LOOP OF HENLE: long, hairpin loop extending from the proximal tubule down
into the medulla and back to the cortex; surrounded by capillaries.
4. DISTAL TUBULE: second twisted tubular region after the Loop of Henle;
located in the cortex.
5. PERITUBULAR CAPILLARIES: second network of capillaries surrounding the
tubules and loop of Henle.
6. COLLECTING DUCT: long straight duct after the distal tubule that is the open
end of the nephron. It extends from the cortex down through the medulla.
RENAL BLOOD FLOW
Each kidney is perfused by a single main renal artery which lies behind the
renal veins.1 The right renal artery passes behind the inferior vena cava. The left
renal vein usually passes over the aorta and beneath the superior mesenteric
artery. The renal arteries branch at the hilum of the kidney into three to four
segmental branches. These segmental branches give rise to interlobar vessels
which run between the lobes of the kidney to the junction of the cortex and
medulla. There, they give rise to perpendicular branches, the arcuate arteries
(Fig. 4).
Every nephron has a unique blood supply which includes:
• AFFERENT ARTERIOLES connecting the renal artery with the glomerular
capillaries.
• COILED GLOMERULAR CAPILLARIES inside Bowman’s capsule.
• EFFERENT ARTERIOLES - connect the glomerular capillaries with the
peritubular capillaries.
• PERITUBULAR CAPILLARIES - surround the proximal tubule, loop of Henle, and
distal tubule.
• INTERLOBULAR VEINS that drain the peritubular capillaries into the renal
vein. The kidney is the only organ of the body which has two capillary beds
in series, (the glomerular and peritubular capillaries) connecting the arteries
with veins within the nephron. This arrangement is important for maintaining
a constant blood flow through and around the nephron despite fluctuations
in systemic blood pressure.
Fig.3: Nephron
1. Glomerulus
2. Tubule, prox.
3. Capillaries
4. Henle’s Loop,
descending
5. Henle’s Loop,
ascending
6. Tubule, distal
In about 10% of cases, one kidney has two renal arteries. In about
15% of cases, there will be multiple renal arteries.
1
REFERENCES
http://.science/howstuffworks.com/kidney2
Fig. 4: Renal arterial
vasculature.
Renal (Kidney) Basics cont.
WHY IS THE KIDNEY IMPORTANT?
The kidney maintains blood in its proper composition by removing nitrogenous waste products or unwanted substances to form urine by the interaction of three processes:
1. FILTRATION: In the nephron, blood gets filtered (similar to a coffee filter) through the walls of the glomerular
capillaries and Bowman’s capsule. The filtrate is composed of water, ions (e.g. sodium, potassium, chloride),
glucose and small proteins. The rate of filtration (Glomerular Filtration Rate) (GFR) is approximately 125 ml/min, or
45 gallons (180 liters) each day. This represents 20 to 25 times the body’s entire blood volume each day. Once the
filtrate has entered the Bowman’s capsule, it flows through the lumen of the nephron into the proximal tubule
where the next process, reabsorption, begins.
Note: All kidney functions, including endocrine functions, are related to GRF. The GRF is
the best index of kidney function.
2. REABSORPTION: Ninety-eight to ninety-nine percent of the filtrate is reabsorbed.
Specialized transporter proteins located on the cell membranes of tubular cells grab small
molecules such as ions, glucose and amino acids from the filtrate as it flows by. Some
transporters require energy (ATP, adenosine triphosphate) for active transport. Others
such as water are reabsorbed passively. Water is reabsorbed by osmosis in response to
the buildup of reabsorbed sodium (Na) in spaces between the nephron’s cell walls. Other
molecules are reabsorbed passively when they are swept along in the flow of water
(solvent drag). The reabsorption of sodium (Na) is critical to the reabsorption of other
substances.
3. SECRETION: The kidney then secretes unwanted waste products of the blood into
the lumen of the nephron. Anything (fluid, ions, small molecules) that has not been
reabsorbed from the lumen create urine, which ultimately leaves the body via the ureter,
bladder and urethra.
GRF — Glomerular
Filtration rate
The amount of water
filtered out of the
plasma through
glomerular capillary
walls into Bowman’s
capsule per unit
time. Measures
kidney functions and
determines the stage of
kidney disease.
In normal clinical
practice cretinine
clearance is used to
determine GFR.
Normal range: males
97-137 ml/min; females
88-128 ml/min.
In addition to playing a major role in controlling the water and electrolyte balance within the body and
regulating the acid-base balance of blood, the kidneys are also endrocrine organs that produce and secrete
hormones such as renin to activate the renin-angiotensin aldosterone system; erythropoietin that stimulates the
formation of red blood cells in bone marrow and calcitriol, a metabolite of vitamin D.
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