Kidney Structure and Nephron Histology

Kidney Structure

• The kidney is composed of two main regions: the cortex and the medulla.
• The cortex contains glomeruli, Bowman's capsules, and convoluted tubules, which are involved in filtering and processing blood.
• The medulla contains collecting ducts and loops of Henle, which are important for concentrating urine.
• Renal pyramids, triangular structures, are formed within the medulla by collecting ducts, and these drain into the minor calyces.
• Renal columns are extensions of cortical tissue separating the pyramids.
• The nephron is the functional unit of the kidney, consisting of a glomerulus, Bowman's capsule, proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

Nephron Histology

• The glomerulus is a tuft of capillaries surrounded by Bowman's capsule, allowing for filtration of blood.
• Bowman's capsule, a double-walled cup-shaped structure, surrounds the glomerulus and collects the filtrate.
• The proximal convoluted tubule (PCT) is highly convoluted and lined with simple cuboidal epithelium possessing prominent brush border which are microvilli increasing surface area for reabsorption.
• The loop of Henle, a hairpin-shaped loop, is responsible for concentrating urine by creating a concentration gradient. Descending loop is permeable to water and ascending loop to sodium.
• The distal convoluted tubule (DCT) is involved in fine-tuning electrolyte balance and is lined with simple cuboidal epithelium with few microvilli.

Glomerulus

• The glomerulus is a specialized capillary network enabling filtration.
• It's composed of fenestrated capillaries which have small openings in their endothelium.
• The basement membrane is a specialized filter structure that restricts the passage of large molecules.
• Podocytes are specialized epithelial cells that form the outer layer of Bowman's capsule and help filter the glomerulus.

Collecting Ducts

• Collecting ducts are the last part of the nephron tubule system.
• They converge to form larger ducts as they move to the renal pelvis.
• Collecting ducts are lined by simple cuboidal epithelium and play a crucial role in water reabsorption and urine concentration, regulated by hormones like antidiuretic hormone (ADH).

Juxtaglomerular Apparatus

• The juxtaglomerular apparatus (JGA) is a complex structure containing specialized cells regulating blood pressure and filtration rate.
• Juxtaglomerular cells of the afferent arteriole wall which also act as mechanoreceptors that detect blood pressure changes.
• Macula densa cells are specialized cells in the distal convoluted tubule that sense the concentration of sodium chloride in the filtrate.

Urinary Bladder

• The urinary bladder is a hollow, muscular organ that temporarily stores urine.
• It's lined with transitional epithelium, which allows it to stretch and expand during filling; the transitional epithelium is stratified.
• The bladder wall consists of three layers of smooth muscle which contract to expel urine during micturition.

Urethra

• The urethra is a tube that carries urine from the bladder to the outside of the body.
• The epithelium changes along the urethra, from transitional in the proximal part to stratified squamous in the distal part.
• The urethra is thicker in men than women and contains sphincters to control urination.

Histology of Other Urinary Structures

• The ureters are lined with transitional epithelium, allowing for distension, resembling the bladder's structure to avoid damage.
• The ureters have a muscular layer that contracts to move urine.
• The kidneys also contain interstitial cells and adipocytes.

This quiz covers the essential structures of the kidney, including the cortex and medulla, along with their functional units, the nephrons. It delves into the histology of the glomerulus, Bowman's capsule, and proximal convoluted tubule, essential for understanding kidney function and urine concentration.