COLLEGE OF MEDICINE AND HEALTH SCIENCES
AFE BABALOLA UNIVERSITY, ADO-EKITI
PHS 218: PHYSIOLOGY PRESENTATION
TOPIC:
THE NEPHRON – THE FUNCTIONAL AND STRUCTURAL UNIT
OF THE KIDNEY
PRESENTED BY:
AKUNA GOODLUCK TAMARALAYEFA
ABUBAKAR MUSA
OBIJIOFOR CHIJINDU
OKONKWO SUCCESS
OBASUYI DAVID
DATE:
JUNE 2, 2025
Introduction :
• .- Today, we’ll explore the nephron, the microscopic functional unit of the
kidney, critical for maintaining the body’s internal environment.
• .- Each kidney contains approximately 1–1.5 million nephrons* collectively
filtering around 180 liters of plasma daily**, yet excreting only **1–2 liters as
urine**
• -. The nephron achieves this through four key processes: **
• -glomerular filtration
• -tubular reabsorption,
• al-tubular secretion,
• - excretion.
• This presentation will cover the nephron’s anatomy, its physiological roles,
hormonal regulation, and clinical significance.
•
Anatomy of the Nephron:
1. Renal Corpuscle** (in the renal cortex):
- Glomerulus: A network of capillaries where filtration occurs.
- Bowman’s Capsule: A double-walled epithelial cup
surrounding the glomerulus, collecting the filtrate.
2. Renal Tubule (extends from cortex to medulla):
- Proximal Convoluted Tubule (PCT): Primary site for
reabsorption.
- Loop of Henle: Establishes the medullary concentration
gradient.
- Distal Convoluted Tubule (DCT): Fine-tunes electrolyte
balance.
- Collecting Duct (CD): Final site for urine concentration.
Each segment is specialized for distinct roles in processing
blood plasma into urine.
Glomerular Filtration :
The First Step
- Filtration begins in the renal corpuscle. Blood enters the glomerulus via the afferent arteriole, where high pressure (
mmHg) drives plasma filtration through a three-layered filtration membrane:
- Fenestrated endothelium of capillaries.
- Basement membrane, negatively charged to repel proteins.
- Filtration slits between podocyte foot processes.
This membrane allows small molecules like
water, sodium,
glucose,
amino acids, and
Tubular Reabsorption – Conserving Essentials :
Most of the glomerular filtrate is reabsorbed, primarily in the proximal convoluted tubule (PCT), which features
a brush border of microvilli to maximize surface area. Key reabsorption processes include:
- 100% of glucose and amino acids via sodium co-transport.
- 65–70% of sodium and water, along with chloride, bicarbonate, and potassium.
- Water follows solutes osmotically, driven by Na⁺/K⁺-ATPase pumps and secondary active transport.
• This selective reabsorption ensures the body retains essential nutrients and water while passing waste
forward.
Loop of Henle – Creating the Medullary Gradient :
The Loop of Henle establishes a concentration gradient in the renal medulla, critical for urine
concentration, via the countercurrent multiplier mechanism:
- Descending Limb : Permeable to water, impermeable to solutes. Water is reabsorbed into the
hypertonic medulla, concentrating the filtrate.
- Ascending Limb : Impermeable to water but actively reabsorbs Na⁺, K⁺, and Cl⁻, diluting the
filtrate and increasing medullary osmolarity.
• This gradient enables the kidney to produce urine ranging from dilute to highly concentrated,
depending on hydration status.
Tubular Secretion – Fine-Tuning and Detoxification :
In the distal convoluted tubule (DCT) and collecting duct, tubular secretion adds substances to the
filtrate, fine-tuning electrolyte balance and eliminating waste. Secreted substances include:
- Hydrogen ions (H⁺) for acid-base regulation.
- Potassium ions (K⁺) in exchange for Na⁺, regulated by aldosterone.
- Creatinine, urea, drugs, and organic acids/bases.
This process ensures precise control of blood pH, electrolyte levels, and clearance of toxins.
•
Collecting Duct – Final Urine Concentration :
The collecting duct integrates filtrate from multiple nephrons and determines final urine composition,
regulated by hormones:
- Antidiuretic Hormone (ADH): Inserts aquaporins into the duct, increasing water reabsorption into the
hypertonic medulla, producing concentrated urine .
- Without ADH, the duct remains impermeable, resulting in dilute urine .
The final urine drains into the renal calyces, renal pelvis, and ureters for excretion.
•
Hormonal Regulation :
• Nephrons respond dynamically to hormonal signals to maintain homeostasis
- ADH (Vasopressin) : Enhances water reabsorption in the collecting duct.
- Aldosterone : Promotes Na⁺ reabsorption and K⁺ secretion in the DCT and collecting duct.
- Renin : Released by juxtaglomerular cells, activates the renin-angiotensin-aldosterone system (RAAS),
increasing blood pressure and aldosterone release.
- Atrial Natriuretic Peptide (ANP) : Inhibits Na⁺ reabsorption, promoting water and sodium excretion to
reduce blood volume.
- Parathyroid Hormone (PTH) : Increases calcium reabsorption in the DCT.
These hormones allow the nephron to adapt to the body’s fluid and electrolyte needs.
Clinical Relevance:
Nephrons are central to renal health, and their dysfunction underlies many kidney disorders:
- Glomerulonephritis : Immune-mediated inflammation of glomeruli, impairing filtration.
- Diabetic Nephropathy : Glomerular damage from chronic hyperglycemia, leading to proteinuria.
- Acute Tubular Necrosis (ATN) : Tubular cell death, a common cause of acute kidney injury.
- Polycystic Kidney Disease (PKD) : Genetic disorder causing cystic nephron degeneration.
- Chronic Kidney Disease (CKD) : Progressive nephron loss, culminating in end-stage renal failure.
• Since nephrons cannot regenerate, preserving their function is critical for lifelong health.
Summary:
In summary, the nephron is the kidney’s functional powerhouse, performing:
- Filtration in the glomerulus.
- Reabsorption and secretion in the tubules.
- Urine concentration in the collecting duct.
• Its intricate anatomy and hormonal regulation enable precise control of fluid, electrolytes, and
waste. Understanding nephron function is essential for diagnosing and managing renal diseases.
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