Which substance directly controls the reabsorption of water from the collecting ducts quizlet?

Filtration

Filtration is the mass movement of water and solutes from plasma to the renal tubule that occurs in the renal corpuscle. About 20% of the plasma volume passing through the glomerulus at any given time is filtered. This means that about 180 liters of fluid are filtered by the kidneys every day. Thus, the entire plasma volume (about 3 liters) is filtered 60 times a day! Filtration is primarily driven by hydraulic pressure (blood pressure) in the capillaries of the glomerulus.

Note that the kidneys filter much more fluid than the amount of urine that is actually excreted (about 1.5 liters per day). This is essential for the kidneys to rapidly remove waste and toxins from the plasma efficiently.

Reabsorption

Reabsorption is the movement of water and solutes from the tubule back into the plasma. Reabsorption of water and specific solutes occurs to varying degrees over the entire length of the renal tubule. Bulk reabsorption, which is not under hormonal control, occurs largely in the proximal tubule. Over 70% the filtrate is reabsorbed here. In addition, many important solutes (glucose, amino acids, bicarbonate) are actively transported out of the proximal tubule such that their concentrations are normally extremely low in the remaining fluid. Further bulk reabsorption of sodium occurs in the loop of Henle.

Regulated reabsorption, in which hormones control the rate of transport of sodium and water depending on systemic conditions, takes place in the distal tubule and collecting duct.

Secretion

Even after filtration has occured, the tubules continue to secrete additional substances into the tubular fluid. This enhances the kidney's ability to eliminate certain wastes and toxins. It is also essential to regulation of plasma potassium concentrations and pH. (See Fluid and electrolyte balance).

Excretion

Excretion is what goes into the urine, the end result of the above three processes. Although the original concentration of a substance in the tubule fluid may initially be close to that of plasma, subsequent reabsorption and/or secretion can dramatically alter the final concentration in the urine.

The amount of a particular substance that is excreted is determined by the formula:

amount excreted = amount filtered - amount reabsorbed + amount secreted

What is aldosterone?

Aldosterone is a steroid hormone produced in the outer section (cortex) of the adrenal glands, which sit above the kidneys. It plays a central role in the regulation of blood pressure mainly by acting on organs such as the kidney and the colon to increase the amount of salt (sodium) reabsorbed into the bloodstream and to increase the amount of potassium excreted in the urine. Aldosterone also causes water to be reabsorbed along with sodium; this increases blood volume and therefore blood pressure.

How is aldosterone controlled?

Aldosterone is part of a group of linked hormones, which form the renin–angiotensin–aldosterone system. Activation of this system occurs when there is decrease in blood flow to the kidneys following loss of blood volume or a drop in blood pressure (e.g. due to a haemorrhage). Renin is an enzyme that leads to a series of chemical reactions resulting in the production of angiotensin II, which in turn stimulate aldosterone release. Aldosterone causes an increase in salt and water reabsorption into the bloodstream from the kidney thereby increasing the blood volume, restoring salt levels and blood pressure.

What happens if I have too much aldosterone?

The most common cause of high aldosterone levels is excess production, frequently from a small benign adrenal tumour (primary hyperaldosteronism). The symptoms include high blood pressure, low blood levels of potassium and an abnormal increase in blood volume.

What happens if I have too little aldosterone?

Low aldosterone levels are found in a rare condition called Addison's disease. In Addison's disease, there is a general loss of adrenal function resulting in low blood pressure, lethargy and an increase in potassium levels in the blood (see the article on Addison's disease for further information).

Last reviewed: Jul 2022

Adrenocorticotropic hormone

Understanding:

•  The loop of Henle maintains hypertonic conditions in the medulla

    
Osmoregulation is the third of three processes by which blood is filtered and urine is formed

• Osmoregulation is the control of the water balance of the blood, tissue or cytoplasm of a living organism

Osmoregulation occurs in the medulla of the kidney and involves two key events:

• The loop of Henle establishes a salt gradient (hypertonicity) in the medulla
• Anti-diuretic hormone (ADH) regulates the level of water reabsorption in the collecting duct

Establishing a Salt Gradient

• The function of the loop of Henle is to create a high solute (hypertonic) concentration in the tissue fluid of the medulla
• The descending limb of the loop of Henle is permeable to water but not salts
• The ascending limb of the loop of Henle is permeable to salts but not water
• This means that as the loop descends into the medulla, the interstitial fluid becomes more salty and hypertonic
• Additionally, the vasa recta blood network that surrounds the loop of Henle flows in the opposite direction (counter-current)
• This means that salts released from the ascending limb are drawn down into the medulla, further establishing a salt gradient

Creating Hypertonicity in the Medulla

Understanding:

•  ADH controls reabsorption of water in the collecting duct

    
Water Reabsorption

• As the collecting duct passes through the medulla, the hypertonic conditions of the medulla will draw water out by osmosis
• The amount of water released from the collecting ducts to be retained by the body is controlled by anti-diuretic hormone (ADH)
• ADH is released from the posterior pituitary in response to dehydration (detected by osmoreceptors in the hypothalamus)
• ADH increases the permeability of the collecting duct to water, by upregulating production of aquaporins (water channels)
• This means less water remains in the filtrate, urine becomes concentrated and the individual urinates less (i.e. anti-diuresis)
• When an individual is suitably hydrated, ADH levels decrease and less water is reabsorbed (resulting in more dilute urine)
  • Remember:  ADH is produced when you Are DeHydrated

Role of ADH in Water Reabsorption

Which substance directly controls the reabsorption of water from the collecting ducts group of answer choices?

Where do the collecting ducts meet quizlet?

What substances that are eliminated by the kidneys quizlet?

Which of the following results from decreasing the blood flow to the kidneys?