# 25.9 Regulation of fluid volume and composition  (Page 3/9)

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## Regulation of cl –

Chloride is important in acid–base balance in the extracellular space and has other functions, such as in the stomach, where it combines with hydrogen ions in the stomach lumen to form hydrochloric acid, aiding digestion. Its close association with Na + in the extracellular environment makes it the dominant anion of this compartment, and its regulation closely mirrors that of Na + .

## Regulation of ca ++ And phosphate

The parathyroid glands monitor and respond to circulating levels of Ca ++ in the blood. When levels drop too low, PTH is released to stimulate the DCT to reabsorb Ca ++ from the forming urine. When levels are adequate or high, less PTH is released and more Ca ++ remains in the forming urine to be lost. Phosphate levels move in the opposite direction. When Ca ++ levels are low, PTH inhibits reabsorption of ${\text{HPO}}_{4}^{2-}$ so that its blood level drops, allowing Ca ++ levels to rise. PTH also stimulates the renal conversion of calcidiol into calcitriol, the active form of vitamin D. Calcitriol then stimulates the intestines to absorb more Ca ++ from the diet.

## Regulation of h + , bicarbonate, and ph

The acid–base homeostasis of the body is a function of chemical buffers and physiologic buffering provided by the lungs and kidneys. Buffers, especially proteins, ${\text{HCO}}_{3}^{2-}$ , and ammonia have a very large capacity to absorb or release H + as needed to resist a change in pH. They can act within fractions of a second. The lungs can rid the body of excess acid very rapidly (seconds to minutes) through the conversion of HCO 3 into CO 2 , which is then exhaled. It is rapid but has limited capacity in the face of a significant acid challenge. The kidneys can rid the body of both acid and base. The renal capacity is large but slow (minutes to hours). The cells of the PCT actively secrete H + into the forming urine as Na + is reabsorbed. The body rids itself of excess H + and raises blood pH. In the collecting ducts, the apical surfaces of intercalated cells have proton pumps that actively secrete H + into the luminal, forming urine to remove it from the body.

As hydrogen ions are pumped into the forming urine, it is buffered by bicarbonate (HCO 3 ), H 2 PO 4 (dihydrogen phosphate ion), or ammonia (forming NH 4 + , ammonium ion). Urine pH typically varies in a normal range from 4.5 to 8.0.

## Regulation of nitrogen wastes

Nitrogen wastes are produced by the breakdown of proteins during normal metabolism. Proteins are broken down into amino acids, which in turn are deaminated by having their nitrogen groups removed. Deamination converts the amino (NH 2 ) groups into ammonia (NH 3 ), ammonium ion (NH 4 + ), urea, or uric acid ( [link] ). Ammonia is extremely toxic, so most of it is very rapidly converted into urea in the liver. Human urinary wastes typically contain primarily urea with small amounts of ammonium and very little uric acid.

## Elimination of drugs and hormones

Water-soluble drugs may be excreted in the urine and are influenced by one or all of the following processes: glomerular filtration, tubular secretion, or tubular reabsorption. Drugs that are structurally small can be filtered by the glomerulus with the filtrate. Large drug molecules such as heparin or those that are bound to plasma proteins cannot be filtered and are not readily eliminated. Some drugs can be eliminated by carrier proteins that enable secretion of the drug into the tubule lumen. There are specific carriers that eliminate basic (such as dopamine or histamine) or acidic drugs (such as penicillin or indomethacin). As is the case with other substances, drugs may be both filtered and reabsorbed passively along a concentration gradient.

## Chapter review

The major hormones regulating body fluids are ADH, aldosterone and ANH. Progesterone is similar in structure to aldosterone and can bind to and weakly stimulate aldosterone receptors, providing a similar but diminished response. Blood pressure is a reflection of blood volume and is monitored by baroreceptors in the aortic arch and carotid sinuses. When blood pressure increases, more action potentials are sent to the central nervous system, resulting in greater vasodilation, greater GFR, and more water lost in the urine. ANH is released by the cardiomyocytes when blood pressure increases, causing Na + and water loss. ADH at high levels causes vasoconstriction in addition to its action on the collecting ducts to recover more water. Diuretics increase urine volume. Mechanisms for controlling Na + concentration in the blood include the renin–angiotensin–aldosterone system and ADH. When Na + is retained, K + is excreted; when Na + is lost, K + is retained. When circulating Ca ++ decreases, PTH stimulates the reabsorption of Ca ++ and inhibits reabsorption of ${\text{HPO}}_{4}^{2-}$ . pH is regulated through buffers, expiration of CO 2 , and excretion of acid or base by the kidneys. The breakdown of amino acids produces ammonia. Most ammonia is converted into less-toxic urea in the liver and excreted in the urine. Regulation of drugs is by glomerular filtration, tubular secretion, and tubular reabsorption.

There was this time when the teacher is explaining about something that involves calculating.When the teacher calculate that (2×4)-(1×-3)=11.I was confused and think that the answer is wrong, so I asked the teacher.Then,I realized I calculate wrongly and then my head feels hot. Why?
I mean... (2 x 4)- (1 x -3) = 11
Dicky
But since I don't really care about it. My head slowly goes back to normal.
Dicky
blood is unique it is the only flueid tissue in the body
yeh
Ayoub
this is fascinating
mery
for real
Musa
what is blood
lol. the red substance in your body. that circulates food nutrients and oxygen
Nii
Blood is composed of plasma and formed elements. The plasma is about 55% of blood and is about 80-90% water usually. The other 20-10% accounts for solutes such as ions, nutrients, gases, and hormones.
Carmelo
Blood is a fluid type of connective tissue and it's formed elements (cells) include RBC, WBC, and plalets.
Carmelo
what is sasamoid bone?
how many types of bone on the base of shape
hafeez
5
Husna
i want join the conversation
Alright
Haya
feel free to do so
Vida
where are you from ?
Haya
hi what's up
Mar
well hello
Im from kashmir,but I'm studying in punjab
Aabid
Hello
Aabid
I'm studying pharmacy at JUST University in jordan
shereen
afg
Ayoub
I am Javed Ali
Javedali
hello i am hafeez from gilgit
hafeez
explain the mechanism(release and control) of hormonal interplay for fluid and electrolyte.
There are three main ways in which hormones may be released. Humoral stimulus - occurs when their is an inbalance in electrolytes in the body. Neural stimulus - occurs when autonomic nerve fibers stimulate glands to release hormones.
Carmelo
Hormonal stimulus - occurs when a hormone causes another hormone to be released from another gland.
Carmelo
what are the main pumps found in the cell membrane
calcium
Schmidt
sodium potassium pump
Husna
Differences between ligaments and catilage
differences between catilage and ligaments
joy
Both are different types of connective tissues. Second difference is that cartilage contains chondroblasts rather than fibroblasts. Their is also slight differences on their extracrullar matrix. For ex, cartilages tend to contain more collagen than tendons and ligaments.
Carmelo
Both types of connective tissue also function differently. Ligaments connect bone to bone, while cartilage have a variety of function like cushioning bones and giving structural support like on the nose and ears.
Carmelo
explain the causes of the refractory period of a nerve fiber
Refractory period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation. Brief pause in stimulus or excitation.
Nii
To add on, the brief pause is produced because of the event of establishing a resting membrane potential that needs to be produced before depolarization (another action potential) can occur again.
Carmelo
The refractory period also gives a chance for neurotransmitters to be replenished on the axon terminal.
Carmelo
what is hypoxia
I guess it's low supply the oxygen to the tissues
famuyiwa
yup
Natalie
A condition in which tissues (especially the blood) are deprived of an adequate supply of oxygen
Panthera
hanifa pia uko hapa
Panthera
Hypoxia is the lack of oxygen concentration in the blood. Therefore, tissues will receive a low concentration of oxygen. Usually our bodies respond to Hypoxia by stimulating erythropoiesis in red bone marrow.
Carmelo
hypoxia is the lack of oxygen in blood absolutely.
hafeez
hypoxia: is a condition in wich the concentration of oxygen goes down in tissue or all over the body but the low concentration of oxygen in blood is called hypoxiemia.
Ayoub
where is present Glenoid Cavity ?
what is the muscular tissue
muscular tissue is a type of tissue that provide to help in cotraction to aur body.
A-
What's the difference in epithelial, connective, muscular and muscle tissue
and it's similarities
what is limb bone
this are bone attaching or joining to the axial bone.axial bone including skull,vertebrate and ribcage
Eliasi
how many bones make up the skull?
Matthew
22 bones
Husna
22bones
Bhanu
where is present Glenoid cavity ?
A-
how many bone in skull
Md
almost there are 8 bones in skull
hafeez
Explain the stages of mitosis and cell division
Bella, this is a very long process to detail by text. However, to keep it brief, mitosis has four phases in order: prophase, metaphase, anaphase, and telophase which sometimes followed by cytokinesis. Note that some cells do not always do the cytokinesis phase.
Carmelo
As a result, some of the cells in the body are multinuclear (osteoclasts for ex).
Carmelo
explain further
Nana
difference between mitosis and meosis
Nana
In mitosis, two genetically exact daughter cells (somatic cells) are produced and they are diploid. In meiosis, four genetically unique cells (gametes) are produced and they are haploid.
Carmelo
Meiosis only occurs in reproductive organs. Mitosis is a type of asexual reproduction and is involved in tissue growth and regeneration(repair).
Carmelo
mitosis > Diploid to Diploid meiosis > Diploid to Haploid
Carmelo
systems of human body