NEPHROLOGY Demo Course: RENAL ANATOMY

Nephrology

RENAL ANATOMY AND PHYSIOLOGY OF DIFFERENT SEGMENTS OF NEPHRON

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The nephron is the basic functional unit of the kidney responsible for filtering blood, reabsorbing essential substances, secreting waste products, and maintaining fluid and electrolyte balance. Each nephron is composed of different segments, each with unique anatomical features and physiological functions.

Overview of the Nephron Segments

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Glomerulus and Bowman's Capsule
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Proximal Convoluted Tubule (PCT)
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Loop of Henle (Thin Descending, Thin Ascending, Thick Ascending)

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Distal Convoluted Tubule (DCT)
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Collecting Duct
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Table: Anatomy and Physiology of Nephron Segments

Segment	Location	Anatomy	Functions
Glomerulus	Renal cortex	Network of capillaries	Filtration of plasma; forms ultrafiltrate
Bowman's Capsule	Surrounds glomerulus	Double-layered capsule	Receives filtered fluid from glomerulus
Proximal Convoluted Tubule (PCT)	Renal cortex	Highly convoluted tube with brush border (microvilli)	Reabsorption of Na+, Cl-, K+, glucose, amino acids, bicarbonate, water; secretion of H+, organic acids, drugs
Loop of Henle	Renal medulla	U-shaped loop with descending and ascending limbs	Water reabsorption (descending limb), Na+ and Cl- reabsorption (thick ascending limb); generates medullary osmotic gradient
Distal Convoluted Tubule (DCT)	Renal cortex	Convoluted tubule with fewer microvilli	Reabsorption of Na+ and Ca2+ (regulated by aldosterone and PTH); secretion of H+ and K+
Collecting Duct	Extends from cortex to medulla	Straight tubule composed of principal and intercalated cells	Water reabsorption (regulated by ADH); Na+ reabsorption, K+ and H+ secretion

Detailed Physiology of Nephron Segments

Glomerulus and Bowman's Capsule

Glomerulus: Capillary bed where blood filtration occurs under pressure. Fenestrated endothelium allows water, ions, and small molecules to pass through while retaining larger molecules like proteins.

Bowman's Capsule: Captures the filtrate from the glomerulus and channels it to the PCT.

Proximal Convoluted Tubule (PCT)

Reabsorption: Approximately 65-70% of filtered water and electrolytes are reabsorbed here. The brush border significantly increases surface area for reabsorption.

Mechanisms: Active transport of sodium, facilitated transport of glucose and amino acids, and passive reabsorption of water via osmotic gradient.

Secretion: Secretes hydrogen ions, organic acids, and drugs into the lumen.

Loop of Henle

Thin Descending Limb:

Permeable to water but not to Na+ and Cl-.

Water leaves by osmosis, concentrating the filtrate.

Thin Ascending Limb:

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Impermeable to water.
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Passive reabsorption of Na+ and Cl-.
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Thick Ascending Limb:

Active reabsorption of Na+, K+, and Cl- via the Na-K-2Cl symporter.

Contributes to the creation of the medullary osmotic gradient, crucial for urine concentration.

Distal Convoluted Tubule (DCT)

Reabsorption: Active transport of sodium and chloride, and regulated calcium reabsorption under the influence of parathyroid hormone (PTH).

Secretion: Hydrogen and potassium ions are actively secreted into the tubular fluid.

Hormonal Regulation: Aldosterone promotes sodium reabsorption and potassium secretion.

Collecting Duct

Composed of principal cells (involved in Na+ reabsorption and K+ secretion) and intercalated cells (involved in acid-base balance).

Reabsorption:

Water reabsorption is regulated by antidiuretic hormone (ADH).

Sodium reabsorption is influenced by aldosterone.

Secretion: Potassium and hydrogen ions are secreted.

Summary of Functions by Nephron Segment

Segment	Major Functions
Glomerulus	Filtration of blood, formation of glomerular filtrate
Bowman's Capsule	Collection of filtrate
PCT	Reabsorption of majority of water, electrolytes, glucose, amino acids; secretion of H+ and organic compounds
Loop of Henle	Establishes osmotic gradient; reabsorbs water (descending) and electrolytes (ascending)
DCT	Fine-tuning of Na+, K+, Ca2+ reabsorption and H+ secretion; aldosterone and PTH influence
Collecting Duct	Final water reabsorption (under ADH control); Na+ reabsorption and acid-base regulation

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