Excretory Products and Their Elimination - Notes | Class 11 | Part 2: Human Excretory System

Human Excretory System

It includes kidneys, ureters, urinary bladder & urethra.

Structure of Kidney

• Reddish brown, bean-shaped structures situated between the levels of last thoracic & 3rd lumbar vertebra.
• Length: 10-12 cm, width: 5-7 cm, thickness: 2-3 cm. Average weight: 120-170 gm.
• It is enclosed in a tough, 3-layered fibrous renal capsule.
• On the concave side of kidney, there is an opening (hilum or hilus) through which blood vessels, nerves, lymphatic ducts and ureter enter the kidney.
• Hilum leads to funnel shaped cavity called renal pelvis with projections called calyces.
• A kidney has outer cortex & inner medulla.

• Medulla has few conical projections called medullary pyramids (renal pyramids) projecting into the calyces.
• Cortex extends in between the medullary pyramids as renal columns (Columns of Bertini).
• Each kidney has nearly one million tubular nephrons.

Nephron

• Nephrons are the structural & functional units of kidney.
• Each nephron has 2 parts: Glomerulus & Renal tubule.
• Glomerulus: A tuft of capillaries formed by afferent arteriole (a fine branch of renal artery). Blood from glomerulus is carried away by efferent arteriole.
• Renal tubule: It begins with a double walled cup-like Bowman’s capsule, which encloses the glomerulus.

Glomerulus + Bowman’s capsule = Malpighian body

• The tubule continues with proximal convoluted tubule (PCT), Henle’s loop & distal convoluted tubule (DCT).
• Henle’s loop is hairpin-shaped. It has descending and ascending limbs.
• The DCTs of many nephrons open into a collecting duct. Collecting duct extends from cortex to inner parts of medulla. They converge and open into the renal pelvis through medullary pyramids in the calyces.
lip>Malpighian body (Renal corpuscle), PCT and DCT are situated in renal cortex. Loop of Henle dips into medulla.
• The efferent arteriole forms a fine capillary network (peritubular capillaries) around the renal tubule. A minute vessel of this network runs parallel to Henle’s loop forming a ‘U’ shaped vasa recta.

Types of nephrons

1. Cortical nephrons (85%): In this, the Henle’s loop is short and extends only very little into the medulla. Vasa recta is absent or highly reduced.
2. Juxtamedullary nephrons (15%): In this, Henle’s loop is long and runs deep into medulla. Vasa recta present.

Select a Topic 👇

1. Types of Excretion and Excretory Organs 2. Human Excretory System 3. Urine Formation, Micturition 4. Regulation of Kidney Function 5. Disorders of Excretory System

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