Slide Set 7: Urinary System Flashcards
What is the most important function of kidneys?
homeostatic regulation of:
- water
- ion content of the blood
= electrolyte balance.
The kidneys maintain normal blood concentrations of ions and water by balancing intake of those substances with their excretion in the urine, obeying the principle of ________
mass balance
Kidney function can be divided into 6 major categories:
- Regulation of extracellular fluid volume and blood pressure.
- Regulation of osmolarity.
- Maintenance of ion balance.
- Homeostatic regulation of pH
- Excretion of wastes.
- Production of hormones
How is regulation of extracellular fluid volume and blood pressure achieved?
When extracellular fluid volume decreases, blood pressure also decreases.
If ECF volume and blood pressure fall too low, the body cannot maintain adequate blood flow to the brain and other essential organs.
The kidneys work in an integrated fashion with the cardiovascular system to ensure that blood pressure and tissue perfusion remain within an acceptable range.
How is regulation of osmolarity achieved?
The body integrates kidney function with behavioural drives, such as thirst, to maintain blood osmolarity at a value close to 290 mOsM.
How is maintenance of ion balance achieved?
The kidneys keep concentrations of key ions within a normal range by balancing dietary intake with urinary loss.
Sodium (Na+) is the major ion involved in the regulation of extracellular fluid volume and osmolarity. Potassium (K + ) and calcium (Ca2 + ) concentrations are also closely regulated.
What is the major ion involved in the regulation of extracellular volume and osmolarity?
Sodium (Na+) is the major ion involved in the regulation of extracellular fluid volume and osmolarity.
How is homeostatic regulation of pH. achieved?
The pH of plasma is normally kept within a narrow range.
If extracellular fluid becomes too acidic, the kidneys remove H+ and conserve bicarbonate ions (HCO3-), which act as a buffer. Conversely, when extracellular fluid becomes too alkaline, the kidneys remove HCO3- and conserve H+. The kidneys play a significant role in pH homeostasis, but they do not correct pH disturbances as rapidly as the lungs do.
What happens if the ECF becomes too acidic?
the kidneys remove H+ and conserve bicarbonate ions (HCO3-), which act as a buffer.
What happens if the ECF becomes too alkaline?
the kidneys remove HCO3- and conserve H+.
Which one is faster in terms of ph correction: kidneys or lungs?
lungs
How is excretion of wastes achieved?
The kidneys remove metabolic waste products and foreign substances, such as drugs and environmental toxins.
Metabolic wastes include creatinine from muscle metabolism and the nitrogenous wastes urea and uric acid.
A metabolite of hemoglobin called urobilinogen gives urine its characteristic yellow color.
Hormones are another endogenous substance the kidneys clear from the blood. Examples of foreign substances that the kidneys actively remove include the articial sweetener saccharin and the anion benzoate, part of the preservative potassium benzoate, which you ingest each time you drink a diet soda drink.
What gives the yellow color to urine?
A metabolite of hemoglobin called urobilinogen gives urine its characteristic yellow color.
How is production of hormones achieved?
Although the kidneys are not endocrine glands, they play important roles in three endocrine pathways.
Kidney cells synthesize erythropoietin, the cytokine/hormone that regulates red blood cell synthesis.
They also release renin, an enzyme that regulates the production of hormones involved in sodium balance and blood pressure homeostasis.
Renal enzymes help convert vitamin D3 into a hormone that regulates Ca2+ balance.
Give examples of kidney enzymes
erythropoietin - RBC production
renin - sodium balance and blood pressure homeostasis
renal enzymes - convert vitamin D3 into a hormone that regulates Ca2+ balance.
Explain urine production and the route it takes for excretion
- water and solutes move from plasma into the hollow tubules (nephrons) that make up the bulk of the paired kidneys.
- modify the composition of the fluid as it passes through.
- The modified fluid leaves the kidney and passes into a hollow tube called a ureter. There are two ureters, one leading from each kidney to the urinary bladder.
- The bladder expands and fills with urine until, by reflex action, it contracts and expels urine through a single tube, the urethra.
What is micturition?
is the process by which urine is excreted - urination
A cross section through a kidney shows that the interior is arranged in two layers:
an outer cortex and inner medulla
The layers of kidneys are formed by the organized arrangement of microscopic tubules called _______.
nephrons
What is the functional unit of kidneys?
The nephron is the functional unit of the kidney
Each nephron has two components:
–Vascular component
–Tubular component
From nephrons the urine travels to the ______ which can be thought of as the start of the urinary plumbing, then to the ureter
calyx
Vascular elements of kidney and the order
afferent arteriole –> glomerulus –> efferent arteriole
- -> peritubular capillaries –> vasa recta (capillaries that dip into the medulla) –> renal capillaries –> venules
- -> small veins –> renal vein
What is the function of the renal portal system?
First to filter fluid out of the blood and into the lumen of the nephron at the glomerular capillaries, then to reabsorb fluid from the tubule back into the blood at the peritubular capillaries.
Tubular elements of kidneys and the order
Nephron –> Bowman’s capsule + glomerulus –>renal corpuscle –> proximal tubule –> loop of Henle –> descending limb –> ascending limb –> distal tubule –> collecting duct —> medulla —> cortex –> renal pelvis (urine) –> ureter
The nephron begins with a hollow, ball-like structure called __________ that surrounds the glomerulus
Bowman’s capsule
The combination of glomerulus and
Bowman’s capsule is called the___________.
renal corpuscle
The loop of Henle is divided into two:
descending limb
ascending limb
a hairpin-shaped segment that dips down toward the medulla and then back up
The loop of Henle
the final part of the ascending limb of the loop of Henle passes between the afferent and efferent arterioles. is region is known as the ______
juxtaglomerular apparatus
What is a key feature to kidney autoregulation?
The proximity of the ascending limb and the arterioles allows paracrine communication between the two structures, a key feature of kidney autoregulation.
What are the 3 basic processes that take place in kidneys?
Three basic processes take place in the nephron:
filtration
reabsorption
secretion
What is filtration in kidneys?
Filtration is the movement of fluid from blood into the lumen of the nephron.
Where does filtration take place in kidneys?
Filtration takes place only in the renal corpuscle, where the walls of glomerular capillaries and Bowman’s capsule are modi ed to allow bulk flow of fluid.
What happens to the “filtrate” once it is filtrated?
passes into the lumen of the nephron, it becomes part of the body’s external environment, just as substances in the lumen of the intestinal tract are part of the external environment. For this reason, anything that filters into the nephron is destined for excretion.
After filtrate leaves Bowman’s capsule, it is modified by reabsorption and secretion.
What is excretion?
removal in the urine, unless it is reabsorbed into the body.
What is reabsorption in kidneys?
is the process of moving substances in the filtrate from the lumen of the tubule back into the blood flowing through peritubular capillaries.
What is secretion in kidneys?
Secretion removes selected molecules from the blood and adds them to the filtrate in the tubule lumen. Although secretion and glomerular filtration both move substances from blood into the tubule, secretion is a more selective process that usually uses membrane proteins to move molecules across the tubule epithelium.
Both secretion and glomerular filtration move substances from the blood into the tubule but what is the major difference?
secretion is a more selective process that usually uses membrane proteins to move molecules across the tubule epithelium
Reabsorption occurs when ___________
proximal tubule cells transport solutes out of the lumen, and water follows by osmosis.
True/False
Filtrate leaving the proximal tubule has higher osmolarity than the filtrate that entered.
FALSE!!
Filtrate leaving the proximal tubule has the same osmolarity as filtrate that entered.
What is the primary function of the proximal tubule?
the primary function of the proximal tubule is the reabsorption of isosmotic fluid.
Where is the primary site for creating dilute urine?
Filtrate leaving the proximal tubule passes into the loop of Henle, the primary site for creating dilute urine.
What happens to the filtrate as it passes through the loop?
As filtrate passes through the loop, proportionately more solute is reabsorbed than water, and the filtrate becomes hyposmotic relative to the plasma.
When does the regulation of salt and water balance take place?
From the loop of Henle, filtrate passes into the distal tubule and the collecting duct. In these two segments, the fine regulation of salt and water balance takes place under the control of several hormones.
What determines the final composition of the filtrate?
Reabsorption and (to a lesser extent) secretion determine the final composition of the filtrate.
What do the final volume and osmolarity of urine depend on?
The final volume and osmolarity of urine depend on the body’s need to conserve or excrete water and solute.
The amount of any substance excreted in the urine reflects how that substance was handled during its passage through the nephron. What is the equation that proves that?
Amount filtered - amount reabsorbed + amount secreted = amount excreted
The percentage of total plasma volume that filters into the tubule is called the ___________.
filtration fraction
Where does filtration take place?
renal corpuscle, which consists of the glomerular capillaries surrounded by Bowman’s capsule.
Substances leaving the plasma must pass through three filtration barriers before entering the tubule lumen:
- the glomerular capillary endothelium,
- a basal lamina (basement membrane)
- the epithelium of Bowman’s capsule
What is the function of pores in the glomerular capillaries
to prevent blood cells from leaving the capillary.
The negatively charged proteins on the pore surfaces also help repel negatively charged plasma proteins.
What is Glomerular filtration?
non discriminant, except blood cells and plasma proteins all constituents within the blood are filtered
What is basal lamina?
an acellular layer of extracellular matrix that separates the capillary endothelium from the epithelial lining of Bowman’s capsule
The basal lamina consists of negatively charged glycoproteins, collagen, and other proteins.
What are podocytes?
The portion of the capsule epithelium that surrounds each glomerular capillary consists of specialized cells called podocytes {podos, foot}. Podocytes have long cytoplasmic extensions called foot processes that extend from the main cell body.
What drives filtration across the walls of the glomerular capillaries?
The three pressures that influence glomerular filtration—-
- capillary blood pressure,
- capillary colloid osmotic pressure,
- capsule fluid pressure
What is hydrostatic pressure (PH)?
- The hydrostatic pressure (PH) of blood flowing through the glomerular capillaries forces fluid through the leaky endothelium.
- Capillary blood pressure averages 55 mm Hg and favors filtration into Bowman’s capsule.
- Although pressure declines along the length of the capillaries, it remains higher than the opposing pressures.
Consequently, filtration takes place along nearly the entire length of the glomerular capillaries.
What is colloid osmotic pressure (p)?
inside glomerular capillaries is higher than that of the fluid in Bowman’s capsule.
This pressure gradient is due to the presence of proteins in the plasma.
The osmotic pressure gradient averages 30 mm Hg and favours fluid movement back into the capillaries.
What is hydrostatic fluid pressure (Pfluid)?
Bowman’s capsule is an enclosed space (unlike the interstitial fluid), and so the presence of fluid in the capsule creates a hydrostatic fluid pressure (Pfluid) that opposes fluid movement into the capsule.
Fluid filtering out of the capillaries must displace the fluid already in the capsule lumen.
Hydrostatic fluid pressure in the capsule averages 15 mm Hg, opposing filtration.
What is the net driving force and is flitration achieved?
The net driving force is 10 mm Hg in the direction favouring filtration. Although this pressure may not seem very high, when combined with the very leaky nature of the fenestrated capillaries, it results in rapid fluid filtration into the tubules.
The volume of fluid that filters into Bowman’s capsule per unit time is the _______
glomerular filtration rate (GFR)
GFR is in inuenced by two factors:
the net filtration pressure just described and the filtration coefficient.
How is filtration pressure determined?
Filtration pressure is determined primarily by renal blood flow and blood pressure.
The filtration coefficient has two components:
the surface area of the glomerular capillaries available for filtration and the permeability of interface between the capillary and Bowman’s capsule.
True/False
if blood pressure increases, GFR increases, and if blood pressure falls, GFR decreases.
False
GFR is remarkably constant over a wide range of blood pressures.
How is GFR controlled?
GFR is controlled primarily by regulation of blood flow through the renal arterioles. If the overall resistance of the renal arterioles increases, renal blood flow decreases, and blood is diverted to other organs. The effect of increased resistance on GFR, however, depends on where the resistance change takes place.
If resistance increases in the ________, hydrostatic pressure decreases on the glomerular side of the constriction. This translates into a decrease in GFR.
afferent arteriole
If resistance increases in the _______, blood “dams up” in front of the constriction, and hydrostatic pressure in the glomerular capillaries increases (Fig. 19.8e). Increased glomerular pressure increases GFR.
efferent arteriole
Where does the absorption take place?
Most of this reabsorption takes place in the proximal tubule, with a smaller amount of reabsorption in the distal segments of the nephrons.