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Explain how the structure of the epithelial cells of the proximal convoluted tubule and the location of the Na+/K+ pump therein contribute to the ability of the tubule to reabsorb salt and water.
Transcellular transports salt and water into the cell. The structure of the epithelial cells determines whether salt and water move into and out of the epithelial cells and whether some move through the junctions (paracellular pathway) of the cells.
Especially by which transport is sodium, water, glucose, protein, and urea moved in or out of the urine?
ransepithelial transport-transports these things from tubular lumen into the tubular epithelial cells, interstitial, peritubular capillaries
Specifically, what is the mechanism of sodium reabsorption? How is the reabsorption of other solutes coupled to it?
The active transport of Na+ is the primary driving source for most renal absorption. Secondary active transport in the nephron is responsible for the reabsorption of many substances including glucose, amino acids, ions, and various organic metabolites.
Which hormone controls the rate of sodium reabsorption
The more Aldosterone, the more sodium absorbed.
What is the mechanism of water reabsorption and how is coupled with sodium reabsorption
*The process involves adding or removing water pores in the apical membrane under the direction of an antidiuretic hormone.
Which of these transports are active which are passive?
Water reabsorption is passive and sodium reabsorption is active transport.
Generally, what is the function of the Henle loop of the nephron?
- making of urine of variable H2O content (dilution/concentration)
How does the descending and ascending branch of the Henle loop differ in their function? Describe the characteristics of the two limbs of the with regard to their transport of Na+, Cl- and H2O.
- Descending: Only water is reabsorbed in this tube, isometric fluid leaving the proximal tubule becomes progressively more concentrated.
- Ascending: Ions are reabsorbed but no water; removal of solute in the thick ascending limb creates hyposmotic fluid.
What is meant by the counter current mechanisms within the Henle loop?
The thick ascending limb of the loop of henle transport salt to create dilute urine.
What are the sources of gain or loss of water in the body?
- Intake must equal output, adults ingest a little more than 2 liters of water in food and drink in a day, normal metabolism adds about 0.3 liters of water
- Most water is lost from the body from urine which has a daily volume of about 1.5 liters. Some water is lost in the feces. Water also loses water through insensible water loss. Only water loss in the urine can be regulated.
How is the osmotic gradient in the medulla of the kidney established?
This countercurrent multiplication between the ascending and descending limbs of the loop of Henle helps to create the osmotic gradient in the medulla. Urea diffusing out of the terminal segments of the collecting duct makes a significant contribution to the osmolarity of the deeper portions of the medulla. The vasa recta assists in the maintenance of the osmotic gradient by opposing the diffusion of solutes out of the medulla and by removing water and solutes retrieved from the filtrate.
What is the function of the osmotic gradient?
The loop of henle creates a very strong sodium gradient via Na pumps. When it pumps all the sodium out of the loop, water is absorbed. This is how you manage to absorb so much of the filtrate back into your system instead of urinating it all out. The glomerulus in the kidney creates about 180 liters of filtrate per day, and only get rid of about 1.8 liters of actual waste. You absorb over 99% of what is filtered, and much of it is due to the osmotic gradient in the loop of henle.
What is the condition of the urine when reaches the end of the Henle loop?
The urine is hyposmotic, created when cells in the thick portion of the ascending limb of the loop transport Na+, K+, and Cl- out of the tubule lumen.
What is the function of the peritubular capillary system in the kidney?
- In the renal system, peritubular capillaries are tiny blood vessels that travel alongside nephrons allowing reabsorption and secretion between blood and the inner lumen of the nephron. Ions and minerals that need to be saved in the body are reabsorbed into the peritubular capillaries through active transport, secondary active transport, or transcytosis.
What is the function of the collecting ducts of the nephron?
- The collecting duct system of the kidney consists of a series of tubules and ducts that connect the nephrons to the ureter.
Describe function and control of ADH. Where is the hormone produced?
Posterior pituitary hormone that regulates water reabsorption in the kidney.
ADH acts on which part of the nephron?
Collecting ducts and late distal tubule. But mostly on collecting ducts.
In which way is ADH related to blood pressure?
When the blood volume decreases the receptors in the heart atrium send impulses up the brain to cause a release of ADH from the pituatary gland that signals to the kidneys to release adh to work on the collecting ducts of the nephrons within the kidneys to make them less permeable to water. Thus, saving the release of fluid and causing an increase in fluid and increase in blood volume
What are the major functions of aldosterone? Where is it produced?
It’s a steroid hormone that stimulates Na+ reabsorption and K+ secretion. Controls sodium balance. It is produces in the adrenal cortex of the brain.
What are the major controls of aldosterone secretion
The primary sight of aldosterone action is the last third of the distal tubule and the cortical collecting duct.
What are the stimuli for renin release?
Peptide secreted by juxtaglomerular cells that convert angiotensinogen into angiotensin I. When blood pressure is decreased renin is released.
What happens to the urinary bicarbonate (HCO3-) excretion when a person hyperventilates? How might
his response be helpful?
If a person hyperventilates blowing off CO2 which decreases pCO2 hydrogen combines with HCO3 and becomes carbonic acid. Thereby decreasing H+ concentration and raising pH. It helps to maintain the pH balance.
By which mechanisms do the kidneys regulate the pH of the blood?
- Directly: excreting or reabsorbing H+ =(Acidosis)
- Indirectly: changing the rate at which HCO3 buffer is reabsorbed or excreted =(Alkalosis)
How does hydrogen ion secretion influence the contribution of bicarbonate to the blood?
- H+ binds with bicarbonate to create CO2
What is the function of the carbonic anhydrase in reabsorption of bicarbonate?
- It facilitates the H+ that combines with filtered HCO3 to form CO2 in the lumen.
The concentration of glucose in the blood plasma is 100mg/100mL and the GFR is 125 mL/min. How much glucose is filtered per min.
Filtered load of X= (X)plasma x GFR …….(100/100)x 125= 125 mgglucose/min
Which are the respiratory and metabolic processes that tend to increase the acidity (acidoses) as well as those that tend to increase the alkalinity (alkalosis)?
- Respiratory: hyperventilation and hypoventilation
- -Acidosis- Hypoventilation
- -Alkalosis- Hyperventilation
- Metabolic: If the pH problem arises from acids or bases of non-CO2 origin
- -Acidosis- is a disturbance of mass balance that occurs when the dietary and metabolism input of H+ exceeds H+ excretion
- -Alkalosis- excessive vomiting and excessive ingestion of bicarbonate containing antacids.
Where are the sensors that measure the pH of the blood (central / peripheral)?
- Peripheral Chemoreceptors- Carotid and aortic arteries
- Central Chemoreceptors- in the brain on the ventral surface of the medulla
How does the body rid itself of excess alkalinity or acidity? (lungs, kidney
- Buffers-include proteins, phosphate ions, HCO3,
- Ventilation- changes in ventilation can correct disturbances in acid balance.
- Renal regulation of H+ and HCO3-
How is bicarbonate eliminated as well as absorbed by the kidneys?
- The proximal tubule reabsorbs most filtered bicarbonate into the tubule cell
- Bicarbonate is eliminated through alkalosis when H+ concentration of the body is too low
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