Human Kidney Anatomy Quiz

Urinary System Overview

• The urinary system, also known as the renal system, includes the kidneys, ureters, bladder, and urethra.
• Its main function is eliminating metabolic waste products from the body by forming and excreting urine.
• A healthy individual typically produces between one and two liters of urine daily.

Kidneys

• The kidneys are large, reddish-brown, bean-shaped organs.
• They are located on either side of the spinal column in the retroperitoneal space of the posterior abdominal cavity.
• They extend from the 12th thoracic to the 3rd lumbar vertebrae, with the right kidney positioned slightly lower.
• Each kidney is approximately 10-12 cm long, 5-6.5 cm wide, and 3-4 cm thick.
• The adrenal gland is embedded within the renal fascia and a protective layer of perirenal adipose tissue on the upper pole of each kidney.

Kidney Structure

• The nephron is the basic structural and functional unit of the kidney.
• Urine (an unfiltered form of blood) travels via the ureters to the urinary bladder, and is discharged via the urethra.
• The kidney parenchyma is composed of numerous minute uriniferous tubules (nephrons).
• The connective tissue within the kidney is called interstitial tissue. It accounts for 7% of cortex volume and 20% of medulla volume.

Kidney Functions

• The kidneys remove metabolic wastes, drugs, and toxins from the body.
• They maintain body water balance and electrolyte balance, as well as maintain acid-base balance.
• The kidneys convert 25-hydroxyvitamin D3 to the active form 1,25-dihydroxycholecalciferol (vitamin D), and this process is affected by parathyroid hormone (PTH).
• The kidneys are also responsible for gluconeogenesis (creation of glucose) which takes place in the renal cortex, and the secretion of hormones, such as renin and erythropoietin.
• Other associated functions include the production of prostaglandins within the renal cortex.

Kidney Tubules

• The nephron has functionally distinct portions: the collecting tube and the nephron.
• The nephron collects a filtrate of the blood.
• The collecting tubule absorbs water from the filtrate to concentrate its solutes.
• A human kidney typically has approximately 1.5 million uriniferous tubules.
• Specific sections of the renal tubules include the proximal convoluted tubule, the intermediate tubule, the distal tubules, and the collecting ducts/systems.

Renal Corpuscle

• The renal corpuscle is spherical and contains the filtration apparatus of the kidney.
• It has an average diameter of 200 micrometers.
• It comprises the glomerular capillary tuft and the surrounding visceral and parietal epithelial layers of Bowman's capsule.

Filtration Apparatus

• The filtration apparatus of the kidney is enclosed in the parietal layer of Bowman's capsule.
• The components consist of the glomerular capillaries' endothelium, the glomerular basement membrane, and the visceral layer of Bowman's capsule (podocytes).

Filtration Membranes

• The glomerular filtration membrane is composed of the endothelium of the glomerular capillaries, the glomerular basement membrane, and the visceral layer of Bowman's capsule (podocytes).

Juxtaglomerular Apparatus

• The juxtaglomerular apparatus includes the macula densa, juxtaglomerular cells, and extraglomerular mesangial cells.
• This structure plays an important role in regulating blood pressure and sodium homeostasis via adjusting glomerular filtration rate. It is activated during physiological conditions such as low sodium intake, hemorrhage, and low renal perfusion.
• The juxtaglomerular cells are responsible to releasing renin.

Kidney Tubules Function

• As the filtrate travels through the uriniferous and collecting tubules of the kidney, substances are both absorbed (active and passive) and secreted from the filtrate.
• Significant substances that are filtered include water (H₂O), sodium (Na+), and bicarbonate ions. Certain substances, like glucose, are completely absorbed.
• The volume of the glomerular filtrate is reduced, making the urine more concentrated (hyperosmotic); and other substances are also eliminated.

Ureters

• The ureters are thin tubes that carry urine from the kidneys to the bladder.
• Each ureter begins as a continuation of the renal pelvis and contains smooth muscle.

Urinary Bladder

• The urinary bladder is a smooth, collapsible muscular sac that stores urine temporarily.
• Although urine is constantly produced by the kidneys, it is usually stored in the bladder until its release is convenient.

Urethra

• The urethra is a thin-walled muscular tube that drains urine from the bladder and expels it from the body.
• The urethra has two sphincters: the internal urethral sphincter (formed at the bladder-urethra junction and composed of smooth involuntary muscle) and the external urethral sphincter (formed from skeletal muscle and is voluntarily controlled.)

Homeostatic Imbalances

• Calcium, magnesium, or uric acid may crystallize and precipitate in the renal pelvis, forming renal stones.
• Kidney stones cause severe pain that radiates from the flank to the anterior abdominal wall.

Mechanisms of Urine Formation

• Each minute, the glomerulus filters 120-125 ml of fluid (glomerular filtration rate).
• The majority of the filtrate is reabsorbed into the blood in renal tubules.
• The kidneys filter approximately 180 liters of fluid daily, but only a small percentage (~1%) becomes urine.

Glomerular Filtration Rate (GFR)

• The GFR is the volume of filtrate formed per minute by the activity of all glomeruli.
• The normal GFR in adults is 120-125 ml/min.

Summary of the Urinary System

The urinary system's primary function is to filter the blood and produce urine, regulating various crucial bodily functions. This involves complex processes in the kidney, including filtration, reabsorption, secretion, and ultimately, urine excretion.

Test your knowledge on the anatomy of the human kidney with this quiz. Explore the structure of Bowman’s capsule, the glomerular filtration apparatus, and the organization of kidney lobes. Perfect for students studying human biology or anatomy.