Renal Physiology: Guyton Chapter 26 - 27 Flashcards
26: The Urinary System, 27: Glomerular Filtration, Renal Blood Flow and Their Control
[19-minute video]: Guyton and Hall Medical Physiology (Chapter 27) - Glomerular Filtration, Renal Blood Flow and Their Control
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Explain the role of the kidneys in vitamin D metabolism.
◾ Vitamin D obtain from the diet or synthesized in the skin (as cholecalciferol or vitamin D3) is initially inactive.
◾ It undergoes two hydroxylation reactions to become active.
◾ The first hydroxylation occurs in the liver, converting vitamin D to 25-hydroxyvitamin D (calcidiol).
◾ The second hydroxylation occurs in the kidneys, where 25-hydroxyvitamin D is converted to its active form , 1,25-dihydroxyvitamin D (calcitriol), by the enzyme 1-alpha-hydroxylase.
The smooth muscle of the bladder is called the ________ muscle.
detrusor
Micturition
What is the principal nerve supply of the bladder?
pelvic nerves which connect to the S2 and S3 segments of the spinal cord through the sacral plexus
Micturition
What do the sensory fibers in the pelvic nerves detect?
The sensory fibers detect the degree of stretch in the bladder wall and initiate reflexes that cause bladder emptying.
What type of fibers are the motor nerves transmitted in the pelvic nerves?
The motor nerves transmitted in the pelvic nerves are parasympathetic fibers.
What is the role of the pudendal nerve in bladder function?
It controls the external urethral sphincter, allowing voluntary control over urination.
Compare juxtamedullary nephrons and cortical nephrons based on the following criteria:
(a) location of glomeruli
(b) percentage of all nephrons
(a) location of glomeruli:
Glomeruli of Juxtamedullary nephrons are located deep in the renal cortex near the medulla, whereas glomeruli of cortical nephrons are located in the outer (b) percentage of all nephrons:
Juxtamedullary nephrons constitute about 20 - 30% of nephrons in the human kidney; cortical nephrons constitute 70 - 80% of nephrons.
Compare juxtamedullary nephrons and cortical nephrons based on the following criteria:
(a) loops of Henle
(b) vascular supply
(a) loops of Henle
Juxtamedullary nephrons: have long loops of Henle that dig deeply into the medulla, sometimes reaching the tips of the renal papillae.
Cortical nephrons: have short loops of Henle that penetrate only a short distance into the medulla.
(b) vascular supply
Juxtamedullary nephrons: Long efferent arterioles extend from the glomeruli into the outer medulla and divide into specialized peritubular capillaries called vasa recta, which extend downward into the medulla and return toward the cortex, emptying into Cortical nephrons: peritubular capillaries
Compare juxtamedullary nephrons and cortical nephrons in terms of function.
Juxtamedullary nephrons play an essential role in the formation of concentrated urine due to the specialized network of capillaries in the medulla; cortical nephrons are primarily involved in the filtration of blood and reabsorption of essential nutrients and water.
Briefly discuss the composition of glomerular filtrate.
💧 protein-free and devoid of cellular components
💧 The concentrations of other constituents of the glomerular filtrate, including most salts and organic molecules, are similar to the concentrations in the plasma.
What are the exceptions to the generalization that the glomerular filtrate has similar concentrations of constituents as plasma?
Exceptions include low-molecular-weight substances like calcium and fatty acids that are partially bound to plasma proteins. Almost half of the plasma calcium and most of the plasma fatty acids are bound to proteins and are not filtered through the glomerular capillaries.
What determines the rate of fluid filtration in glomerular capillaries?
The rate of fluid filtration in glomerular capillaries is determined by:
(1) the balance of hydrostatic and colloid osmotic forces acting across the capillary membrane, and
(2) the capillary filtration coefficient (Kf), which is the product of the permeability and filtering surface area of the capillaries.
Why do glomerular capillaries have a higher rate of filtration compared to most other capillaries?
Glomerular capillaries have a higher rate of filtration due to high glomerular hydrostatic pressure and a large capillary filtration coefficient (Kf).
What are the three major layers of the glomerular capillary membrane?
The three major layers are:
(1) the endothelium of the capillary,
(2) a basement membrane,
(3) a layer of epithelial cells (podocytes) surrounding the outer surface of the capillary basement membrane.
What are fenestrae in the context of the glomerular capillary membrane?
What is the role of the basement membrane in the glomerular capillary membrane?
The basement membrane consists of a meshwork of collagen and proteoglycan fibrillae with large spaces for filtering water and small solutes. It hinders the filtration of plasma proteins due to strong negative electrical charges associated with the proteoglycans.
How do podocytes contribute to the filtration process in the glomerular capillary membrane?
Podocytes line the outer surface of the glomerulus with long footlike processes (pedicels) that encircle the capillaries. The foot processes are separated by slit pores through which the glomerular filtrate moves, providing additional restriction to the filtration of plasma proteins.
Podocyte gallery: [Image 1] [Image 2] [Diagram 1] [Diagram 2] [Diagram 3]
Why are negatively charged large molecules filtered less easily than positively charged molecules of equal size in the glomerulus?
Negatively charged large molecules are filtered less easily due to electrostatic repulsion from the negative charges of the glomerular capillary wall proteoglycans. For example, albumin, with a molecular diameter of about 6 nanometers, is restricted from filtration despite the glomerular membrane pores being about 8 nanometers. [Diagram]
