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By the end of this section, you will be able to:
  • Explain how hormonal cues help the kidneys synchronize the osmotic needs of the body
  • Describe how hormones like epinephrine, norepinephrine, renin-angiotensin, aldosterone, anti-diuretic hormone, and atrial natriuretic peptide help regulate waste elimination, maintain correct osmolarity, and perform other osmoregulatory functions

While the kidneys operate to maintain osmotic balance and blood pressure in the body, they also act in concert with hormones. Hormones are small molecules that act as messengers within the body. Hormones are typically secreted from one cell and travel in the bloodstream to affect a target cell in another portion of the body. Different regions of the nephron bear specialized cells that have receptors to respond to chemical messengers and hormones. [link] summarizes the hormones that control the osmoregulatory functions.

Hormones That Affect Osmoregulation
Hormone Where produced Function
Epinephrine and Norepinephrine Adrenal medulla Can decrease kidney function temporarily by vasoconstriction
Renin Kidney nephrons Increases blood pressure by acting on angiotensinogen
Angiotensin Liver Angiotensin II affects multiple processes and increases blood pressure
Aldosterone Adrenal cortex Prevents loss of sodium and water
Anti-diuretic hormone (vasopressin) Hypothalamus (stored in the posterior pituitary) Prevents water loss
Atrial natriuretic peptide Heart atrium Decreases blood pressure by acting as a vasodilator and increasing glomerular filtration rate; decreases sodium reabsorption in kidneys

Epinephrine and norepinephrine

Epinephrine and norepinephrine are released by the adrenal medulla and nervous system respectively. They are the flight/fight hormones that are released when the body is under extreme stress. During stress, much of the body’s energy is used to combat imminent danger. Kidney function is halted temporarily by epinephrine and norepinephrine. These hormones function by acting directly on the smooth muscles of blood vessels to constrict them. Once the afferent arterioles are constricted, blood flow into the nephrons stops. These hormones go one step further and trigger the renin-angiotensin-aldosterone    system.

Renin-angiotensin-aldosterone

The renin-angiotensin-aldosterone system, illustrated in [link] proceeds through several steps to produce angiotensin II    , which acts to stabilize blood pressure and volume. Renin (secreted by a part of the juxtaglomerular complex) is produced by the granular cells of the afferent and efferent arterioles. Thus, the kidneys control blood pressure and volume directly. Renin acts on angiotensinogen, which is made in the liver and converts it to angiotensin I    . Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II. Angiotensin II raises blood pressure by constricting blood vessels. It also triggers the release of the mineralocorticoid aldosterone from the adrenal cortex, which in turn stimulates the renal tubules to reabsorb more sodium. Angiotensin II also triggers the release of anti-diuretic hormone (ADH)    from the hypothalamus, leading to water retention in the kidneys. It acts directly on the nephrons and decreases glomerular filtration rate. Medically, blood pressure can be controlled by drugs that inhibit ACE (called ACE inhibitors).

The renin-angiotensin-aldosterone pathway involves four hormones: renin, which is made in the kidney, angiotensin, which is made in the liver, aldosterone, which is made in the adrenal glands, and ADH, which is made in the hypothalamus and secreted by the posterior pituitary. The adrenal glands are located on top of the kidneys, and the hypothalamus and pituitary are in the brain. The pathway begins when renin converts angiotensin into angiotensin I. An enzyme called ACE then converts angiotensin I into angiotensin II. Angiotensin II has several direct effects. These include arterial constriction, which increases blood pressure, decreasing the glomerular filtration rate, which results in water retention, and increasing thirst. Angiotensin II also triggers the release of two other hormones, aldosterone and ADH. Aldosterone causes nephron distal tubules to reabsorb more sodium and water, which increases blood volume. ADH moderates the insertion of aquaporins into the nephridial collecting ducts. As a result, more water is reabsorbed by the blood. ADH also causes arteries to constrict. The hormone ANP is antagonistic to the angiotensin pathway. ANP decreases blood pressure and volume by increasing the glomerulus filtration rate, increasing reabsorption of sodium ions by the nephron, and by inhibiting the release of renin from the kidney and aldosterone from the adrenal gland.
The renin-angiotensin-aldosterone system increases blood pressure and volume. The hormone ANP has antagonistic effects. (credit: modification of work by Mikael Häggström)

Mineralocorticoids

Mineralocorticoids are hormones synthesized by the adrenal cortex that affect osmotic balance. Aldosterone is a mineralocorticoid that regulates sodium levels in the blood. Almost all of the sodium in the blood is reclaimed by the renal tubules under the influence of aldosterone. Because sodium is always reabsorbed by active transport and water follows sodium to maintain osmotic balance, aldosterone manages not only sodium levels but also the water levels in body fluids. In contrast, the aldosterone also stimulates potassium secretion concurrently with sodium reabsorption. In contrast, absence of aldosterone means that no sodium gets reabsorbed in the renal tubules and all of it gets excreted in the urine. In addition, the daily dietary potassium load is not secreted and the retention of K + can cause a dangerous increase in plasma K + concentration. Patients who have Addison's disease have a failing adrenal cortex and cannot produce aldosterone. They lose sodium in their urine constantly, and if the supply is not replenished, the consequences can be fatal.

Antidiurectic hormone

As previously discussed, antidiuretic hormone or ADH (also called vasopressin    ), as the name suggests, helps the body conserve water when body fluid volume, especially that of blood, is low. It is formed by the hypothalamus and is stored and released from the posterior pituitary. It acts by inserting aquaporins in the collecting ducts and promotes reabsorption of water. ADH also acts as a vasoconstrictor and increases blood pressure during hemorrhaging.

Atrial natriuretic peptide hormone

The atrial natriuretic peptide (ANP) lowers blood pressure by acting as a vasodilator    . It is released by cells in the atrium of the heart in response to high blood pressure and in patients with sleep apnea. ANP affects salt release, and because water passively follows salt to maintain osmotic balance, it also has a diuretic effect. ANP also prevents sodium reabsorption by the renal tubules, decreasing water reabsorption (thus acting as a diuretic) and lowering blood pressure. Its actions suppress the actions of aldosterone, ADH, and renin.

Section summary

Hormonal cues help the kidneys synchronize the osmotic needs of the body. Hormones like epinephrine, norepinephrine, renin-angiotensin, aldosterone, anti-diuretic hormone, and atrial natriuretic peptide help regulate the needs of the body as well as the communication between the different organ systems.

Questions & Answers

hetreothalism in fungi
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there are 3 trimester in human pregnancy
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ROHIN
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zoology, ecology
Millicent
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R0se
genetics, microbiology,botany and embryology
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cell is smallest unit of life. cells are often cell the building blocks of life...
Muhammad
the first twenty element
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R0se
growth,respiration,nutrition,sensitivity, movement,irritability, excretion,death.
Obinna
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Adeyemi
it is a natural science stadey about living things
Zamiil
Biology is the bronch of science which deals with the study of life is called biology
Aziz
what is the x in 300 stands for?
Ogbudu Reply
the properties of life
Clarinda Reply
response to the environment, reproduction, homeostasis, growth,energy processing etc.....
Pushpam
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Daniela
hi
MacPeter
Good
Thomas
what is reproduction
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a complete virus particle known as
Darlington Reply
These are formed from identical protein subunitscalled capsomeres.
Pushpam
fabace family plant name
Pushpam Reply
in eukaryotes ...protein channel name which transport protein ...
Pushpam Reply
in bacteria ...chromosomal dna duplicate structure called
Pushpam
what is a prokaryotic cell and a eukaryotic cell
Matilda Reply
There are two types of cells. Eukaryotic and Prokaryotic cells. Prokaryotic cells don't have a nucleus or membrane enclosed organelles (little organs within that cell). They do however carry genetic material but it's not maintained in the nucleus. Prokaryotic cells are also one celled.
juanita
Prokaryotic cells are one celled (single celled).
juanita
Prokaryotic cells are Bacteria and Archea
juanita
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juanita
Eukaryotic cells are more complex. They are much bigger than Prokaryotic cells.
juanita
Eukaryotic cells have a nucleus and membrane bound organelles.
juanita
Eukaryotic cells are animals cells which also includes us.
juanita
Eukaryotic cells are also multicellular.
juanita
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Amna
eukaryotic cells are individual cells .. but eukaryotes are multicellular organisms which consist of many different types of eukaryotic cells
Will
also eukaryotic cells have mitochondria. prokaryotic cells do not
Will
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John
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Pushpam
prokaryotic cell are cells dat have no true nuclei i.e no cell membrane while eukaryotic cell are cell dat have true nuclei i.e have cell membrane
Divine
grt
Thomas
we have 46 pair of somatic cell and 23 pair of chromosomes in our body, pls can someone explain it to me. pls
Matilda Reply
we have 22 pairs of somatic chromosomes and one pair of sex chromosome
Amna
thanks
Matilda
we have 23 pairs of chromosomes,22 pairs of somatic and one pair of sex chromosomes
Amna
23 chromosomes from dad & 23 chromosomes from mom 23 +23=46 total chromosomes
juanita
X & Y chromosomes are called sex cells, the very presence of a Y chromosome means the person is Male.
juanita
XX Female XY Male
juanita
If a Karyotype has more than 46 Chromosomes then nondisjunction occured. For example, having an extra chromosome 21 will cause Down Syndrome.
juanita

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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