Kidney Function and Nephron Structure

Kidney Function

• Kidneys filter blood, retaining beneficial substances and eliminating waste products as urine.
• Blood enters the kidney through the renal artery, passes through various vessels, and leaves through the renal vein.
• The kidney is structurally divided into the cortex and medulla.
• The medulla contains pyramids, where urine is collected in minor and major calices and drained into the pelvis, then the ureter.

The Nephron

• The nephron is the functional unit of the kidney, consisting of a filtering glomerulus and a tubule system.
• The glomerulus and tubule system are surrounded by capillaries.
• The vascular components of the nephron are the afferent arteriole, efferent arteriole, glomerulus, peritubular capillaries, and vasa recta.
• The tubular components of the nephron are the Bowman's capsule, proximal tubules, loop of Henle, distal tubules, and collecting ducts.

Types of Nephrons

• There are two types of nephrons: superficial (cortical) nephrons and juxtamedullary nephrons.
• Cortical nephrons are more numerous, accounting for about 85%, while juxtamedullary nephrons make up the remaining 15%.
• Juxtamedullary nephrons have long loops of Henle surrounded by vasa recta.
• Superficial nephrons have short loops of Henle surrounded by peritubular capillaries.
• Both types of nephrons contribute to reabsorption and secretion.
• However, juxtamedullary nephrons also contribute to the vertical osmotic gradient.

Blood Pathway through the Kidney

• The blood flow through the kidney: Heart - Aorta - Renal Artery - Segmental Artery - Lobar Artery - Arcuate Artery - Interlobular Artery - Afferent Arteriole - Glomerulus - Efferent Arteriole - Peritubular Capillaries - Interlobular Vein - Arcuate Vein - Interlobar Vein - Renal Vein - Inferior Vena Cava - Heart.

Tubular Reabsorption and Secretion

• Tubular Reabsorption: selective transfer of specific substances from the filtrate back into the blood of the peritubular capillaries.
• Tubular Secretion: selective transfer of substances from the peritubular capillary blood into the tubular lumen.

Micturition Reflex

• The micturition reflex involves temporary urine storage in the bladder and its subsequent emptying.
• It involves bladder contraction and the opening of both the internal and external urethral sphincters.
• The bladder wall is composed of detrusor smooth muscle.
• The internal sphincter is made of smooth muscle and is involuntary.
• The external sphincter is skeletal muscle and is voluntarily controlled.
• Sympathetic activity relaxes the bladder, allowing it to fill.
• Parasympathetic activity, triggered by stretch receptors, contracts the smooth muscle in the bladder and opens the internal sphincter.

Glomerulus

• Glomerular filtration rate (GFR) is determined by the balance of pressures across the glomerular capillaries.
• Hydrostatic pressure is the force exerted by the blood on the glomerular capillary wall, pushing fluid and solutes out.
• Colloid osmotic pressure is the pressure generated by proteins in the blood, pulling water back into the capillaries.

Factors Affecting GFR

• Afferent arteriole constriction: Reduces blood flow into the glomerulus, decreasing glomerular pressure, leading to decreased GFR.
• Efferent arteriole constriction: Increases resistance to blood leaving the glomerulus, raising glomerular pressure, potentially increasing GFR.
• Afferent arteriole dilation: Increases blood flow into the glomerulus, raising glomerular pressure, increasing GFR.
• Efferent arteriole dilation: Decreases resistance to blood leaving the glomerulus, lowering glomerular pressure, potentially decreasing GFR.

Net Filtration Pressure (NFP)

• NFP is the pressure driving fluid and solutes from the blood in the glomerulus into Bowman’s capsule.
• NFP is determined by the balance of:
  • Glomerular Capillary Hydrostatic Pressure (PGC)
  • Bowman's Capsule Hydrostatic Pressure (PBC)
  • Glomerular Capillary Colloid Osmotic Pressure (πGC)

GFR and NFP

• Increased NFP leads to an increase in GFR.
• Decreased NFP leads to a decrease in GFR.

Maintaining Glomerular Blood Pressure

• The kidney carefully regulates blood pressure across the glomerulus to maintain a constant GFR.

Chapter 14: Renal

• The kidneys play a crucial role in maintaining the balance of electrolytes and fluid in the body.
• They also excrete waste products and help regulate blood pressure.

This quiz covers the essential functions of the kidneys and the detailed structure of nephrons, the functional units of the kidneys. Topics include the renal artery and vein, and the types and components of nephrons, highlighting their roles in blood filtration and urine formation.