BIO 132 – Anatomy and
Physiology II
Study Outline
21.1. General Principles:
a. Of the various portions of the nephron, the bulk of reabsorption takes place in the ________________________________.
b. A substance that is reabsorbed from tubular fluid takes one of two possible routes called ______________________ or ___________________________.
c. ____________________________ involves the movement of water or solutes between cells whereas __________________________________ involves the transfer of materials across the tubular epithelial cells.
d. In paracellular reabsorption, solute movement is _______________________, in which these substances move down their ___________________________ gradients. When the substance is water, this movement is referred to as _______________________________________.
e. An example of primary active transport is the movement of Na+ via the _________________________________________________ located in the _______________________________________ membrane. This transporter moves Na+ _____________________________ its concentration gradient.
f. An example of secondary active transport is the movement of a solute against its electrochemical gradient by coupling it with _______________________ transport. The membrane protein that moves the solute in the same direction as Na+ is called a ___________________________ whereas when the direction is opposite to Na+, it is called a _____________________________.
g. Glucose appears in urine when the _________________________________ is exceeded meaning that all the glucose-Na+ symporters are saturated. The condition in which glucose appears in urine is called ____________________.
h. In passive transport the movement of the substance is ___________________ the concentration gradient and thus does not require any _________________. Examples of passive transport include _______________________________, __________________________, and ________________________________.
i. Water reabsorption is always _______________________________ and takes place via the process of __________________________________. When the process is non-regulated and is subject to osmotic pressure, this type of water reabsorption is called ______________________________ whereas when the process is subject to regulation it is called ____________________________.
21.2. Reabsorption and Secretion along the Proximal Tubule:
a. It is in this segment where approximately ___________________ % of Na+ is reabsorbed along with _______________________% of water. Normally all ____________________________, _____________________________, and ____________________ are reabsorbed here.
b. The Na+-glucose symporter transfers ____________________ molecule(s) of glucose per every ___________________________ Na+ ions across the apical membrane. In turn the glucose crosses the basolateral membrane via the process of __________________________________ and Na+ crosses via the ____________________________________.
c. In the proximal tubule Na+ coupled symporters exist for _______________________________, _____________________________, and ____________________________.
d. The Na+/H+ antiporter allows one Na+ to enter the cell in exchange for _____________________________ H+ which leaves the cell across the apical membrane. The H+ are created within the cell through the action of the enzyme ___________________________. This enzyme is also present in the apical membrane (brush border) allowing for bicarbonate in the tubular fluid to combine with H+ to produce carbonic acid which then dissociates into CO2 and H2O. In this way, both ____________________ and ________________ are reabsorbed using this cycle.
e. As Na+, bicarbonate, other solutes, and water are reabsorbed, the remaining solutes become concentrated creating electrochemical gradients favoring their passive reabsorption in a process called _____________________________.
f. Two examples of waste products that are secreted into tubular fluid in the proximal tubule are ____________________ and ______________________.
21.3. Reabsorption in the Loop of Henle and Distal Tubule:
a. While the _______________________ limb of the loop of Henle is permeable to water, the _______________________ is not.
b. Within the thick ascending limb is the Na+-K+-2Cl- symporter which moves _____________________ Na+, _______________________ K+, and _________________________ Cl- ions into the cell.
c. Tubular fluid entering the loop of Henle has an osmolarity that is ____________________ to plasma. Tubular fluid that is in the ascending limb has an osmolarity that is ____________________________ than plasma.
d. In the distal tubule water permeability is _____________________________, so that the osmolarity of the tubular fluid continues to ___________________ relative to plasma.
e. In the distal tubule the main solute reabsorption is via a _______________________________________.
21.4. Reabsorption along the Collecting Ducts:
a. The cells responsible for Na+ reabsorption and K+ secretion in the collecting ducts are the ____________________ cells whereas those responsible for H+ secretion are the ____________________ cells.
b. In principal cells, Na+ ____________________________ the cell at the apical membrane and K+ ____________________________, both ions moving down their concentration gradients.
c. Principal cells vary K+ secretion according to body conditions: when plasma K+ is high (due to dietary excess), K+ secretion _______________________; but when plasma K+ is low, K+ secretion ____________________________. Both K+ secretion and Na+ reabsorption are increased in the presence of _______________________________.
d. In intercalated cells, H+ is secreted into the tubular fluid through the action of a ____________________________. The H+ is derived through the action of the enzyme _____________________________, and the resulting bicarbonate is transferred across the basolateral membrane via ________________________.
21.5. Hormonal Regulation of Tubular Reabsorption and Secretion:
a. Regulation is accomplished through the actions of four hormones named _____________________________, ________________________________, _____________________________, and _____________________________.
b. Angiotensin II stimulates the Na+/H+ antiporters in the proximal tubule and thus increases _______________________, __________________________, and ________________________________ reabsorption. Angiotensin II also stimulates the adrenal cortex to secrete ______________________________.
c. Aldosterone stimulates __________________________________ cells of the collecting ducts to increase Na+ reabsorption and _____________________.
d. ADH stimualates principal cells of the collecting ducts to _______________ their water permeability through the insertion of special _________________ channels in their apical membrane. In the absence of ADH, water permeability is ________________________.
e. _______________________________ is released from the atria of the heart in response to ____________________ in blood volume. ANP causes Na+ and water reabsorption to _________________________________, along with the secretion of aldosterone and ADH to ________________________________. As a result of ANP, Na+ excretion in urine ___________________________ as does the volume of urine.
21.6. Production of Dilute and Concentrated Urine:
a. The glomerular filtrate has about the ________________________ osmolarity as plasma, and this condition is maintained through the _________________________ because of the high water permeability.
b. In the descending limb of the loop of Henle, the osmolarity of the tubular fluid _______________________________________ because the osmolarity of the interstitial fluid of the renal medulla increases with distance. As a result water ________________________________ tubular fluid in this segment.
c. In the ascending limb of the loop of Henle, the osmolarity of the tubular fluid _______________________________ because now the water permeability is ___________________________ and Na+, K+ and Cl- reabsorption continue. By the distal tubule the osmolarity of the tubular fluid is ________________ compared to plasma.
d. In the absence of ADH, the urine leaves the kidney with a _______________ osmolarity. In the presence of ADH however, the urine leaves the kidney with a ___________________ osmolarity.
e. The ability of ADH to produce concentrated urine depends on the presence of a _____________________________ gradient within the renal medulla. Two factors contribute to this gradient: ___________________________________ and __________________________________.
f. The osmotic gradient is the result of the action of the ___________________ in the thick ascending limb of the loop of Henle which add _______________ to the interstitium and the collecting ducts which add ___________________.
g. The countercurrent mechanism of the vasa recta allow __________________ to be brought to the medulla without the _________________________ being carried away.
h. A substance that enhances urinary outflow is called a ___________________. Different examples of diuretics work in different ways. Alcohol acts as a diuretic by decreasing water reabsorption through inhibiting ______________ secretion. Caffeine and most diuretic drugs act by inhibiting _____________ reabsorption thus decreasing water reabsorption. For example, furosemide inhibits the _______________________ in the thick ascending limb whereas ______________________ inhibit Na+Cl- symporters in the distal tuble.
21.7. Evaluation of Kidney Function:
a. __________________________ involves the determination of a number of characteristics of urine.
b. The ___________________________ is defined as the volume of blood that is cleared of some substance per unit time. The clearance of glucose is usually ___________________ because all filtered glucose is normally returned to blood and so no blood is cleared of glucose.
c. The renal clearance of substance S is equal to the product of _________________________ and _________________________ divided by _____________________________.
d. A substance that is filtered but neither reabsorbed or secreted will have a clearance equal to _______________________. An example of such a substance is ________________________ which is used to estimate GFR.
e. A substance that has a clearance less than inulin is at least partially _______________________; whereas one whose clearance is greater than inulin is __________________________.