Renal I PT 1

Lecture Goals

• To understand the functions of the human kidney
• To understand the anatomy of the human kidney and the nephron
• Define filtration, reabsorption, and secretion, including how each process operates at the cellular level
• To know which substances are filtered, reabsorbed, and secreted
• To understand how filtration works and what layers a substance has to penetrate in order to be filtered into the nephron
• To understand the amount of fluid that enters the nephron that is filtered and excreted

Functions of the human kidney

• Regulation of water volume
• Regulation of electrolyte concentration
• Acid-base balance
• Elimination of metabolic wastes
• Hormone secretion includes EPO which helps with red blood cell (RBC) formation and Renin, which helps with blood pressure regulation

Kidney Anatomy

• The image lists parts of the anatomy of the human kidney
• These labels include: Hepatic veins (cut); Esophagus (cut); Inferior vena cava; Adrenal gland, Aorta, Iliac crest, Rectum (cut), Uterus (part of female reproductive system), Renal artery, Renal hilum, Renal vein, Kidney, Ureter, Calyces, Renal Pelvis, Renal Artery, Renal Vein, Medulla, Urinary bladder, Ureter, CortexUrethra

Nephron Anatomy

• The nephron is the functional unit of the kidney
• Each kidney has 1 million nephrons
• Components of the nephron include the renal corpuscle (glomerulus and glomerular capsule), proximal tubule (convoluted), nephron loop, distal tubule (convoluted), and a common collecting duct
• The glomerulus provides blood supply, and the Glomerular capsule encloses everything
• The proximal tubule is the first part of the nephron that filtrate enters
• About 6 renal corpuscles fuse and empty into the common collecting duct

Nephron Anatomy (Capillary Beds)

• Glomerulus capillaries: capillaries within the glomerular capsule
• Peritubular capillaries have two types: cortical capillaries and vasa recta
• Cortical capillaries surround the proximal and distal convoluted tubules
• Vasa recta surround the nephron loop
• Capillaries are important because this is where O2/CO2 exchange, filtration (glomerulus), and reabsorption and secretion (peritubular) takes place

3 Basic Nephron Processes

• Glomerular filtration which filters blood plasma, happens in the renal corpuscle that moves outblood to the nephron
• Reabsorption involves fluid and solutes being reabsorbed from the filtrate and returned to the blood
• Secretion involves substances being secreted from the blood into the filtrate

Renal Processes: Filtration

• Filtration is based on size and charge
• Water and small solutes filter easily
• Solutes such as glucose, amino acids, vitamins, and ions are filtered easily
• Proteins and blood cells are not filtered
• What filters out of the blood plasma moves into the nephron tubule (tubular lumen) and is called the filtrate

Glomerular Filtration

• The renal corpuscle consists of a glomerulus (capillaries) surrounded by a glomerular capsule that have pores in their capillaries
• The glomerulus is made up of fenestrated capillaries
• The visceral (inner) layer of the glomerular capsule is made of podocytes that have filtrated slits between their foot processes, where different layers act as barriers to prevent large substances from passing through

Glomerular Filtration

• Substances must pass through a 3 layered filtration membrane to get out of the blood into the filtrate

Glomerular Filtration Layers

• Fenestrations (capillary endothelium): These act as the size barrier in the blood vessel wall
• Basement membrane: This is the negative charge, charge barrier that repells -Charge
• Filtration slits (podocyte foot processes): It acts as the size barrier that prevents large things from escaping

Renal Processes: Reabsorption

• Reabsorption is the transportation of a filtrate from out of the renal lumen into to the blood
• Approximately 99% of water and 90% of solutes are reabsorbed
• Sodium (Na+) helps drive reabsorption of glucose, amino acids, vitamins, water, other ions (Cl-, K+)
• Proximal tubule accounts for 65% of reabsorption

Reabsorption at the Cellular Level

• During reabsorption at the cellular level filtrate goes into the blood & then back into blood
• Na+-K+ ATPase / pump occurs in the basolateral membrane
• Active transport of Na+ out of the tubule cell into the blood forms gradient with high to low concentrations
• Na+ passively moves down its gradient
• Sodium can cotransport other solutes, thus carrying them into proximal tubule cells, these being Glucose, Cl-, K+
• Water follows Na+ by osmosis and it subsequently moves through aquaporins into the blood

Renal Processes: Secretion

• During secretion, blood cells go into the filtrate
• Only small amount of solutes (<1%) secreted
• K+ is secreted at the distal tubule
• Water is never secreted, but always reabsorbed

Secretion at the Cellular Level

• During Secretion at the cellular level, solute moves from the blood into the filtrate
• Potassium (K+) is transported actively from the blood into the cell, the moves passively down its concentration gradient into the tubular lumen