1. Describe the process of water, nutrient and electrolyte reabsorption in the nephron of the kidney. In your answer, make sure to address the following questions:
a) What is the order of structures that the renal filtrate will pass through as it moves through a nephron?
A person has more than one million nephrons that are stacked in the renal cortex. Basically the nephron can be said to be composed of tubes and the glomerulus. In which the filtrate passes through. The filtrate therefore passes from the glomerulus through the tubes to the nephrons (Levey et al., 2015). The glomerulus contains a mass of capillaries which are joined together. The glomerulus is enclosed in the Bowman’s capsule which is cup shaped. The space found between the glomerulus and the Bowman’s capsule is called a bowman’s space. The fluid substance which is filtered through the capillaries gets the filtrate collected in the Bowman’s capsule by use of the glomerular filtration membrane. The filtrate moves through the tubes with addition of substances from blood (secretion) or removal of substances (reabsorption).
Thus the filtrate passes through the following structure in their order: proximal convoluted tubules-they perform the nutrient reabsorption, loop of henle-controls urine concentration, distal convoluted tubules- regulation of sodium, pH and potassium and finally collecting gland- regulation of water and sodium.
b) What molecules are reabsorbed in each tubular element of the nephron?
Proximal convoluted tubule- sodium chloride, glucose- Potassium, amino acids, water and bicarbonate ions.
Distal convoluted tubules- sodium chloride, hydrogen and potassium ions, and water bicarbonates (Malnic et al., 2017)
Loop of henle- sodium chloride and water
Collecting duct- sodium chloride and water
c) Describe the structure & function of the countercurrent multiplier (exchange) system.
Countercurrent multiplier is the use of energy in order to come up with an osmotic gradient which enhances the reabsorption of water from the tubular fluids and form urine which is highly concentration. This process helps an individual from producing liters of water when urinating on a daily basis. Moreover it helps an individual to avoid drinking water continuously (Hofmeister et al., 2015). This process occurs in the loop of henle fluid leaves the ascending limb and moves to the distal convoluted tubule. Here the concentration becomes higher and finally it drains into the collecting tubules. The tubules then empty into the collecting ducts which in turn descend back to the medulla and finally connect to the ureter. Finally the urine is transported to the bladder.
d) What property of the peritubular capillaries facilitates the absorption of materials from the interstitial fluid of the kidneys?
The peritubular capillaries travel along the kidney nephrons to enhance the secretion and reabsorption of fluid. These structures are porous and have low pressure which adapts them for reabsorption functions (Levey et al., 2015). They originate from the arterioles and empty into the renal veins.
Define the term saturation as it relates to the reabsorption of nutrients from the nephron. How does this process affect glucose reabsorption during diabetes mellitus?
Saturation is the maximum rate at which transport occurs when the carriers are all occupied with the substrate.
In diabetes mellitus, since there is no insulin produced by the pancreatic cells, glucose in blood becomes high. Thus the filtered glucose exceeds the capacity of the kidneys because all the glucose transport proteins are saturated. Thus glucose is released in urine.
2.Describe the hormonal regulation of water and electrolyte reabsorption in the kidneys. In your answer, make sure to address the following questions:
a) Where is antidiuretic hormone (ADH) synthesized and where is it secreted? What is the primary stimulus for the secretion of ADH? Where does this hormone act? What effect does ADH have on the osmolarity of the renal filtrate? What is the specific mechanism responsible for producing this effect (Be specific)?
ADH is synthesized in the hypothalamus and secreted in the posterior pituitary gland why it is released slowly in blood. The stimulus for ADH is the high osmolarity in the plasma. In other cases, ethanol is reported to cause release of ADH by reducing the calcium dependent release of AVP which blocks the calcium channels.
This hormone acts in the kidneys and to a lesser extent to the brain. In the kidney nephrons, ADH increases the permeability of water in the distal convoluted tubes enhancing reabsorption and release of urine (Bowman and Foulkes, 2016). In this process, this hormone facilitates the insertion of aquaporin 2 a water channel. Another function of ADH is that it increases the permeability of medulla to urea through the regulation of urea transporters on the cell surface of the medulla. To the brain, ADH is involved in regulation of social and sexual behaviors.
Describe the renin-angiotensin-aldosterone system (RAAS). What is the primary stimulus for the production of rennin and where is rennin secreted from? What are the specific steps involved in the RAAS pathway? Make sure to include the names of all of the enzymes and hormones involved, as well as their specific actions. Where does aldosterone act and what effect does it have?
The rennin-aldosterone angiotensin refers to a hormone system which regulates the sodium concentration and pressure in the arteries. When the concentration of sodium in the plasma is low, the juxtaglomerular cells of the nephron converts the pro-rennin to rennin. Rennin is then released into the blood circulation and in turn chops off a portion of amino acid in the angiotensinogen to form the active angiotensin 1 (Fu et al., 2014). The angiotensin 1 then forms angiotensin 11 by the enzyme angiotensin converting enzyme which is a vasoactive and causes the constriction of arteries and hence high blood pressure. Rennin is produced from the kidneys and is released directly to the blood stream.
Where is atrial natriuretic peptide (ANP) produced in the body? What stimulates the production of this hormone? What effect does it have on the kidneys?
This is a protein vasodilator which is released by the muscles of the heart. The production and release of atrial natriuretic peptide is as a result of increased volume of blood (Nojiri et al., 2015) Therefore when it is produced, it reduces the volume of water, concentration of sodium and adipose thereby lowering blood pressure. The atrial natriuretic peptide has effects in the kidneys because once it is produced; the kidneys are stimulated to reduce the rates of water reasbsorption. Thus much release of water in the urine leads to blood volume and pressure.
Bowman, F. J., & Foulkes, E. C. (2016). Antidiuretic hormone and urea permeability of collecting ducts. American Journal of Physiology--Legacy Content, 218(1), 231-233.
Fu, Z., Zhao, L., Aylor, K. W., Carey, R. M., Barrett, E. J., & Liu, Z. (2014). Renin-Angiotensin-Aldosterone System. Hypertension, 63, 1219-1227.
Hofmeister, L. H., Perisic, S., & Titze, J. (2015). Tissue sodium storage: evidence for kidney-like extrarenal countercurrent systems?. Pflügers Archiv-European Journal of Physiology, 467(3), 551-558.
Levey, A. S., Becker, C., & Inker, L. A. (2015). Glomerular filtration rate and albuminuria for detection and staging of acute and chronic kidney disease in adults: a systematic review. Jama, 313(8), 837-846.
Malnic, G., Aires, M. M., & Vieira, F. L. (2017). Chloride excretion in nephrons of rat kidney during alterations of acid-base equilibrium. American Journal of Physiology--Legacy Content, 218(1), 20-26.
Nojiri, T., Hosoda, H., Kimura, T., Miura, K., Ishikane, S., Tokudome, T., & Kangawa, K. (2015). Atrial natriuretic peptide protects against cisplatin-induced acute kidney injury. Cancer chemotherapy and pharmacology, 75(1), 123-129.