Kidney Structure & Function Quiz

The kidney is a bean-shaped organ located in the lower back responsible for filtering blood and producing urine.
Its outer layer is the renal cortex containing nephrons, the functional unit of the kidney. The inner layer is the renal medulla, composed of the loop of Henle and collecting ducts.
The renal artery supplies oxygenated blood to the kidney, while the renal vein carries deoxygenated blood away.
The hilum is the point where the renal artery, vein, and ureter connect to the kidney.
The ureter is a narrow tube carrying urine from the kidney to the bladder.
The bladder stores urine temporarily.
The urethra carries urine from the bladder to the outside of the body, regulated by a sphincter muscle.

Each kidney is made up of millions of nephrons responsible for filtering blood and creating urine.
Each nephron contains a Malpighian body and a renal tubule.

Located in the renal cortex. Contains a Bowman's capsule and glomerulus.
The glomerulus (a network of capillaries) lies within the Bowman's capsule.
The Bowman’s capsule is cup-shaped, containing a specialized cell type called podocytes. Podocytes have filtration slits between them forming a filtration unit.
Glomerular filtration occurs here, forcing waste products out of the blood into the capsular space.

Blood enters the glomerulus through the afferent arteriole and exits through the efferent arteriole, which is narrower. This creates high hydrostatic pressure within the glomerulus.
This pressure forces small molecules like glucose, salts, water, amino acids, fatty acids, glycerol, and nitrogenous waste from the blood through the glomerular capillaries and podocyte slits into the Bowman's capsule.
The filtrate entering the capsular space is known as glomerular filtrate.
Glomerular filtration is non-selective, meaning both waste products and useful substances enter the filtrate.

High Blood Pressure: Blood enters through a wider afferent arteriole and exits through a narrower efferent arteriole, creating hydrostatic pressure.
Thin Membranes: Glomerular capillary membranes and the Bowman's capsule lining are both thin (single layer of squamous epithelium), minimizing distance for filtration and facilitating rapid filtration.
Large Surface Area: Cup-shaped capsule and a branched network of capillaries provide a large surface area for maximum filtration.
Porous Membranes: Glomerular capillaries contain numerous pores (microfilters), allowing only blood plasma to pass through.
Filtration Slits: Podocytes of the Bowman's capsule contain filtration slits, allowing easy passage of filtered plasma into the capsular space. They have major and minor processes creating a mesh-like structure.

Composed of the proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT).
The DCT connects to the collecting duct.
Collecting ducts join to form the duct of Bellini, which open into the calyces of the renal pelvis.
The renal tubule is lined with cuboidal epithelial cells.

As the glomerular filtrate flows through the renal tubule, essential substances like glucose, amino acids, salts, and water are reabsorbed back into the surrounding blood capillaries.
This reabsorption process occurs via both passive and active transport.

Convoluted: Increased surface area for maximum absorption and slow movement of filtrate, allowing more time for reabsorption.
Microvilli: Increase surface area of cuboidal epithelial cells for absorption.
Mitochondria: Provide energy for active transport, moving substances against their concentration gradient.
Capillary Proximity: Peritubular capillaries run close to the PCT, minimizing the distance for reabsorption of useful substances back into the blood.

Each Bowman’s capsule is supplied by an afferent arteriole, a branch of the renal artery, which forms the glomerulus.
The glomerular capillaries rejoin to form the efferent arteriole, which further forms the peritubular capillaries that run alongside the PCT, Loop of Henle, and DCT.
The peritubular capillaries connect to the renal vein.

Renal tubule cells actively excrete waste products like creatinine, drugs, ammonia, potassium, hydrogen, and bicarbonate ions from the blood back into the tubule.
This process is not universal and involves selective removal of various substances from the blood.

The kidneys maintain homeostasis by regulating the body's water content, controlling blood pH, and removing cellular waste products.

The kidneys maintain water balance by adjusting the amount of water reabsorbed into the blood.
This process is regulated by the hormone ADH (Antidiuretic Hormone).

ADH is produced by the hypothalamus and stored in the pituitary gland.
ADH increases the permeability of the DCT and collecting duct to water.
More ADH causes more water reabsorption, creating concentrated urine and reducing water loss. Less ADH leads to less water reabsorption, creating dilute urine and decreasing water loss.

High Water Levels: Increased water in blood stimulates osmoreceptors in the hypothalamus, sending signals to the pituitary gland to reduce ADH secretion. This results in less water reabsorption in the DCT and CD, leading to more dilute urine and a decrease in blood water levels.
Low Water Levels: Decreased water in blood stimulates osmoreceptors, causing the pituitary gland to secrete more ADH. Increased ADH increases water permeability in the DCT and CD, leading to more concentrated urine, more water reabsorption, and an increase in blood water levels.