Important Diagrams Excretory Products and their Elimination - Biology Class

Human Excretory System

The human excretory system includes two kidneys, two ureters, a urinary bladder, and a urethra. Kidneys lie on the dorsal abdominal wall and remove nitrogenous wastes from blood. Ureters carry urine to the bladder, where it is stored before release through the urethra. 

Structure of Kidney

Each kidney is bean-shaped, with a central hilum from which the ureter, blood vessels, and nerves enter or leave. It has an outer cortex and an inner medulla. The medulla contains medullary pyramids, and the cortex projects inward as Columns of Bertini. The renal pelvis forms funnel-shaped calyces.

Structure of Nephron

Each kidney has about one million nephrons, the functional units. A nephron consists of a glomerulus (a capillary tuft) and a renal tubule beginning with Bowman’s capsule, followed by PCT, Henle’s loop, DCT, and ending in the collecting duct.

• Glomerulus: Capillary tuft receiving blood via the afferent arteriole and draining via the efferent arteriole.
• Bowman’s capsule: Double-walled cup enclosing the glomerulus.
• PCT: Highly coiled, located in cortex.
• Henle’s loop: Descending and ascending limbs dipping into medulla.
• DCT: Coiled region opening into collecting ducts.
• Peritubular capillaries & vasa recta: Surround the tubule for exchange.

Functions of Tubular Segments

• PCT: Major site of reabsorption; reabsorbs nutrients, water, electrolytes; helps maintain pH through selective secretion.
• Henle’s Loop: Maintains medullary osmolarity; descending limb permeable to water, ascending limb permeable to ions only.
• DCT: Conditional reabsorption of Na+ and water; pH and ionic balance through secretion. 
• Collecting Duct : Runs from cortex to inner medulla. Reabsorbs large amounts of water and small quantities of urea, maintaining medullary osmolarity. Also regulates pH and ionic composition by secreting H+ and K+.

Counter‐Current Mechanism and Concentration of Urine

Henle’s loop and vasa recta create counter-currents because filtrate and blood flow in opposite directions. This arrangement maintains a corticomedullary osmotic gradient (300 to ~1200 mOsm/L). NaCl from the ascending limb and urea from the collecting duct help sustain the gradient, enabling water reabsorption from the collecting duct to produce concentrated urine. 

Diagram Based Questions NEET PYQs

Q1. Figure shows a human urinary system with structures labelled A to D. Select option which correctly identifies them and gives their characteristics and/or functions. 

Option A: Adrenal gland-located at the anterior part of Kidney. Secrete catecholamines which stimulate glycogen breakdown 
Option B: Pelvis -broad funnel shaped space inner to hilum, directly connected to loop of Henle. 
Option C: Medulla -inner zone of kidney and contains complete nephrons. 
Option D: Cortex -outer part of kidney and do not contain any part of nephrons.
Ans: The correct option is A
A - Adrenal gland - is located at the anterior part of Kidney. Secrete catecholamines which helps regulate metabolism and helps body to respond to stress.
B - Renal pelvis - it collects urine from the calyces and funnels it into the ureter.
C - Medulla - it is the innermost part of the kidney. The renal medulla is split up into a number of sections, known as the renal pyramids.
D - Cortex - it is the outermost part of the kidney and contains the renal corpuscles and the renal tubules except for parts of the loop of Henle which descend into the renal medulla.