chapter 12
Which physiological parameters affect the GFR?
Determined by the net filtration pressure (NFP), permeability of the corpuscular membranes, surface area available for filtration, and blood pressure/blood flow to the glomerular capillaries. (at any given net filtration pressure, the GFR will be directly proportional to the membrane permeability and the surface area)
how can the processes of tubular reabsorption and secretion can be modulated by upregulation and downregulation of membrane channels
Regulation of reabsorption and/or secretion of many substances is achieved by regulating the activity or concentrations of the appropriate transport proteins in response to homrones and paracrine/autocrine factors.
Explain how the pressure in glomerular capillaries can be regulated.
Regulation of the pressure in glomerular capillaries can be done as vasodilation and vasoconstriction of the afferent and efferent arterioles alter the blood flow through the glomerular capillaries and thus alter the glomerular filtration rate.
Provide an example of how the tubules can be involved in metabolic processes.
Renal tubule cells can synthesize glucose during fasting and add it to the blood. They can also catabolize many organic compounds.
Define the main characteristics of the process of tubular secretion.
Tubular secretion: substances such as hydrogen ions, potassium, and organic anions move from the peritubular capillaries into the tubular lumen
Explain how we can determine this parameter quantitatively and how does it reflect the renal function.
We use inulin to determine RC because it is a freely filtered and neither absorbed nor secreted. Creatine can be used but its less accurate because it is freely filtered but secreted in small amounts.
main functional characteristics of the process of glomerular filtration
passive process in which hydrostatic pressures force the fluids and solute through the glomerular filter (membrane like structure). These filters are very efficient because they have a large surface area that is permeable to water and solutes AND the pressure is very high in the glomerulus.
the definition of the glomerular filtration rate (GFR).
volume of fluid filtered from the glomeruli into Bowman's space per unit of time (volume of filtrate formed each minute).
Define the determinants of filtration efficiency
• Surface area of filtration membrane • permeability • hydrostatic pressure
Describe the structure and function of the renal corpuscles, glomeruli and Bowman's capsules
-Renal Corpuscle: it is the filtration unit and made up of capillaries, the glomerulus, and Bowman's (double walled epithelial capsule). The internal layer envelops the capillaries of the glomerulus and the external layer forms the outer limit of the renal corpuscle and called the parietal layer of Bownman's capsule. -Glomerulus: supplied with blood from the afferent arterioles, capillaries are fenestrated, which allows large amounts of solute rich fluid to pass (doesn't usually have proteins because proteins are too large to pass)
Explain which cells serve as mechanoreceptors sensing the blood pressure, chemoreceptors sensing ion concentration, and which cells produce renin.
1. Macula densa: sensory function (patch of cells on ascending limb of loop of henle). These are chemoreceptors that sense changes in the NaCl content of the filtrate 2. Justaglomerular cells: produce renin. These cells are mechanoreceptors sense BP in the afferent arteriole.
Name the cell types forming the renal corpuscles.
1. Parietal layer: squamous epithelium forming the walls of the Bowman's capsule. 2. Podocytes: within visceral layer located on surface of the basal lamina of glomerular capillaries formed fenestrated endothelial cells 3. Capsular space (bowman's capsule): between parietal and visceral layers
Provide the definition of diuretics.
Diuretics: substances that promote the loss of Na and water
the main structural and functional components of nephrons
Each nephron has a renal corpuscle which contains the glomerulus (tuft of capillaries) and a renal tubule. The tubule forms a cup shape around the glomerulus called the glomerular capsule (Bowman's capsule).
Describe the functional difference between the glomerular and peritubular capillaries, and their functional role.
Glomerular capillaries-used for filtration and they are the only capillaries in the body that are fed and drained by an arteriole (afferent and efferent) Most of the filtrate is reabsorbed in the renal tubule cells and returns to the blood through the peritubular capillaries.
Explain the location, the main structural characteristics and the functional role of podocytes in the process of glomerular filtration
Inner layer (visceral) of the glomerular capsule contains highly modified branching epithelial cells called podocytes. Podocytes end in the foot processes which surround the basement membrane of the glomerulus. The clefts between the foot processes are called filtration slits (where filtrate enters the capsular space).
Define the physiological role of the juxtaglomerular apparatus.
Juxtaglomerular apparatus: made up of juxtaglomerular granular cells, macula densa, and extraglomerular mesangial cells AND it lies between the afferent and efferent arterioles.
difference between juxtamedullary and cortical nephrons
Juxtamedullary nephron: • Long loop of henle • Involved in the concentration of urine • Found at the border between the cortex and medulla • 15% of nephrons Cortical Nephrons: • most nephrons • short loop of henle (very short thin descending limbs and no thin ascending limbs) • located in kidney cortex
The rate of filtration of blood plasma in the kidneys and the volume of urine excreted daily in humans
The blood flow in the two kidneys of an adult amounts to 1.2-1.3 L of blood per minute. This means that all the circulating blood in the body passes through the kidney every 4-5 minutes. The urinary system excretes about 1-1. L of urine per day.
explain the force driving the process of glomerular filtration and the origin of this force
The driving force in the process of glomerular filtration is the hydrostatic pressure in capillaries which favors filtration. This force is opposed by both the hydrostatic pressure in Bowman's space and osmotic force due to proteins in plasma
explain the basic mechanism of sodium, potassium, and water reabsorption.
a. Sodium reabsorption i. Active process occurring in all tubular segments except descending limb and medullary conducting duct ii. Active pumping of Na (via the Na/K ATpase) generates an electrochemical gradient that couples to passive entrance of other substances (glucose) via cotransporters...known as secondary active tranport b. Water reabsorption i. By diffusion and is dependent on sodium reabsorption ii. Water moves through aquaporin channels. Highly expressed in the proximal nephron and absent in collect duct unless ADH is active c. Potassium reabsorption i. Most of K is reabsorbed in the proximal tubule and loop of Henle ii. Cortical collecting ducts can secrete K
main physiological process that occurs in the vascular component of the nephron
afferent arteriole: carries blood to the glomerulus glomerulus: tuft of capillaries that filters a protein-free plasma into the tubular component efferent arteriole: carries blood from the glomerulus peritubular capillaries: supply the renal tissue and is involved in exchanges with thte fluid in the tubular lumen
main physiological process that occurs in the tubular component of the nephron
bowman's capsule: colelcts the glomerular filtrate proximal tubule: uncontrolled reabsorption and secretion of selected substances occur here loop of henle: establishes an osmotic gradient in the renal medulla that is important in the kidney's ability to produce urine of varying concentrations distal tubule and collecting duct: variable, controlled reabsorption of sodium and water and secretion of potassium and hydrogen occur here. fluid leaving the collecting duct is urine, which enter the renal pelvis.
Describe the blood vessels associated with nephrons
glomerular and peritubular
Explain the structure and function of the glomerular filtration barrier (the glomerular filter) and explain how does it work.
has a fenestrated capillary endothelium, glomerular basement membrane (blocks larger proteins), and filtration slits diaphragms between pedicels (blocks many small proteins)
Explain the role of aldosterone in the process of reabsorption.
hormone controlling sodium reabsorption i. Released by the adrenal cortex ii. Acts on both the distal tubule and the cortical collecting duct iii. Inhibited by high salt consumption iv. Stimulated by low salt diets v. Stimulate K excretion by the renal tubule
main physiological process that occurs in both the tubular and vascular component of the nephron
juxtaglomerular appartatus: produces substances involved in the control of the kidney function
Provide the definition of renal clearance and the units of renal clearance.
measure of renal function and is basically the volume of plasma that is cleared of a substance per unit of time. Every substance has its own unit of clearance but the units are always in volume of plasma per unit of time. i. RC=UV/P ii. U=concentration of the substance in urine (mg/mL) iii. P=concentration of substance in plasma (mg/mL) iv. V=flow rate of urine formation (mL/min)
