What is the functional unit of the kidney?
Nephron
How many nephrons does each kidney have approximately?
Each kidney has approximately 1.2 million nephrons.
What are the types of nephrons?
- Superficial cortical nephrons (85%): Extend partially into the medulla.
- Midcortical nephrons: Short or long loops.
- Juxtamedullary nephrons (12%): Close to and extend deep into the medulla; most important for the concentration of urine.
What are the components of the renal corpuscle?
- Glomerulus
- Bowman’s capsule
- Mesangial cells
What is the glomerular filtration membrane?
Filters blood components and separates blood of the glomerular capillaries from fluid in the Bowman’s space.
What are the three layers of the glomerular filtration membrane?
- Inner Capillary Endothelium: Cells in continuous contact with the basement membrane, contains pores.
- Middle Basement Membrane: Selectively permeable network of glycoproteins and mucopolysaccharides.
- Outer Layer of Capillary (Visceral) Epithelium: Podocytes with pedicles that form filtration slits.
What does the glomerular filtration membrane allow to be filtered?
Allows all components of the blood to be filtered, except blood cells and plasma proteins with a molecular weight greater than 70,000.
What is the juxtaglomerular apparatus?
Contains juxtaglomerular cells (renin-releasing cells) and macula densa (sodium-sensing cells) that control renal blood flow, glomerular filtration, and renin secretion.
What is the glomerular filtration rate (GFR)?
Filtration of plasma per unit of time.
What regulates renal blood flow (RBF) and GFR?
- Intrinsic autoregulatory mechanisms
- Neural control
- Hormonal regulation
What happens to RBF and urinary output if mean arterial pressure decreases?
If mean arterial pressure decreases or vascular resistance increases, RBF decreases and urinary output decreases.
What is the normal urinary output in adults?
30 mL/hour minimum or 0.5 to 1.0 mL/kg/hr.
What are the two mechanisms that maintain autoregulation of intrarenal blood flow?
- Intrinsic Autoregulatory Myogenic Mechanism
- Tubuloglomerular Feedback
What occurs during the myogenic mechanism?
If BP increases in the afferent arteriole, the arteriole will contract and resistance increases.
What is tubuloglomerular feedback?
Macula densa cells sense sodium levels and adjust afferent arteriolar constriction to regulate GFR.
How does neural regulation affect renal blood flow?
Sympathetic nerve fibers innervate kidney blood vessels, and increased renal sympathetic nerve activity decreases RBF and GFR.
What is the role of the Renin-Angiotensin-Aldosterone System (RAAS)?
Regulates blood pressure and fluid balance through renin release and subsequent angiotensin II generation.
What triggers the release of renin?
- Decreased BP in afferent arterioles
- Decreased sodium chloride concentration in distal tubule
- Sympathetic nerve stimulation of β-adrenergic receptors
What are natriuretic peptides?
Hormones synthesized and released from the heart that act as natural antagonists to the RAAS.
What is the effect of ADH?
Increases water permeability of the distal tubule and collecting duct, leading to concentrated urine.
What does aldosterone do?
Stimulates sodium reabsorption in the distal convoluted tubule and collecting duct, promoting water reabsorption.
What triggers the release of ADH?
A decrease in BP that accompanies loss of fluid from the internal environment.
What are the parts of the kidney?
- Renal Capsule: Perirenal fat.
- Renal Fascia: Fibrous protective layer.
- Cortex: Outer layer.
- Medulla: Inner region.
- Hilum: Entry/exit for nerves, vessels, ureter.
- Minor + Major Calyces: Chambers receiving urine.
What are the major functions of nephron segments?
- Glomerulus: Filtration.
- Proximal Tubule: Reabsorption of Na+, glucose, K+, amino acids, HCO3−, urea, H2O.
- Loop of Henle: Concentration of urine.
- Distal Tubule: Reabsorption of Na+, H2O, HCO3−.
- Collecting Duct: Reabsorption of H2O, urea, Na+, K+.
