Anatomy and Function of the Kidney: Structure, Functions, and Clinical Relations, Lecture notes of Anatomy

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Gross Anatomy

of the Renal System

Objective

• To discuss the gross anatomy of the renal system.

Functions (^) Eliminating toxic metabolites through urine, regulation of blood homeostasis and blood pressure, production of some hormones Morpho-functional characteristics Positioned retroperitoneally, consists of the cortex and medulla, empties urine into the ureter (which carries urine to the urinary bladder) Artery (^) Renal artery (branch of the abdominal aorta) Vein (^) Renal vein (drains to the inferior vena cava) Innervation (^) Renal plexus Clinical relations (^) Third kidney, horseshoe kidney, kidney agenesis, kidney stones, acute kidney failure

Main kidney functions Blood pressure regulation Regulates the amount of fluid in the body by increasing or decreasing the urine production Hormones production Calcitriol (active form of vitamin D) Erythropoietin (stimulates bone marrow to produce blood cells) Acid-base balance regulation Maintain the pH of blood at 7.4 by decreasing or increasing the excretion of hydrogen ions

• Total Body Water Water constitutes approximately 50% to 60% of total body weight.In general, the amount of blood in the body is 5 liters.
• Any excessive amount of fluid will increase the pressure on the arterial wall and cause the blood pressure to rise (hypertension).
• The kidneys also sense this increase of pressure, and in cases when this happens, they increase the filtration rate of blood and production of urine, which subsequently leads to the increase fluid excretion and decrease of blood pressure.
• If less than 5 liters of blood, blood pressure is too low (hypotension). Hypotension is a stimulus for the kidneys to increase the retention of fluid and thus increase blood pressure.

• Cells in body constantly produce hydrogen ions.
• An increased amount of hydrogen ions can acidify the blood and cause a state called acidosis.
• Kidneys have a special system for the excretion of hydrogen ions, and in that way consistently maintain the pH of blood at 7.4.
• The opposite situation is possible too, if the kidneys excrete too many hydrogen ions, the pH of blood becomes too alkaline, and leads to a state called alkalosis.

Anatomy

• The kidneys have their anterior and posterior surfaces.
• The anterior surface faces towards the anterior abdominal wall, whereas the posterior surface is facing the posterior abdominal wall.
• These surfaces are separated by the edges of the kidney, which are the major convexity laterally , and minor concavity medially.
• The center of the minor concavity is marked as the hilum of the kidney where the renal artery enters the kidney, and the renal vein and ureter leave the kidney.

External Anatomy

• The kidneys are located between the transverse processes of T12-L vertebrae , with the left kidney typically positioned slightly more superiorly than the right.
• This is because the liver and the stomach offset the symmetry of the abdomen, with the liver forcing the right kidney a bit down, and the stomach forcing the left kidney a bit up.
• The superior poles (extremities) (T12) of both kidneys are more medially pointed towards the spine than the inferior poles (extremities) (L3).
• The hilum of the kidney usually projects at the level of the L vertebra. Thus, the ureter is seen paravertebrally starting from the L and going downwards.

Borders of the kidneys.

• A bean-like structure like the kidney has two borders: medial and lateral.
• The lateral border is directed towards the periphery, while the medial border is the one directed towards the midline.
• The medial border of the kidney contains a very important landmark called the hilum of the kidney, which is the entry and exit point for the kidney vessels and ureter.

• The kidney tissue is protected by three layers that entirely surround the kidney: - The fibrous capsule (renal capsule) - The perinephric fat (perirenal fat capsule) - The renal fascia which besides the kidneys also encloses the suprarenal gland and its surrounding fat.

• Outside the fascia is the most superficial layer – a layer of fat tissue called the perinephric fat. This layer sits posteriorly and posterolaterally to each kidney and separates it from the muscles of the abdominal wall.

Right kidney relations Right suprarenal gland Superior pole Peritoneum Superior one-half of anterior surface Descending duodenum Center of the anterior surface Right colic flexure Lateral part of inferior pole Jejunum Medial part of inferior pole

• The highest portion of the superior pole is covered with the right suprarenal gland.
• The superior one-half of the anterior surface is in contact with the layer of peritoneum that separates it from the liver.
• This potential space that separates the liver from the right kidney is called the hepatorenal pouch of Morison.
• Under normal conditions, this pouch is empty, but certain pathological conditions, such as ascites or hemoperitoneum , can cause fluid to collect within the pouch.
• This can be visualized with ultrasound or CT.