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At the transition from the DCT to the collecting duct, about 20 percent of the original water is still present and about 10 percent of the sodium. If no other mechanism for water reabsorption existed, about 20–25 liters of urine would be produced. Now consider what is happening in the adjacent capillaries, the vasa recta. They are recovering both solutes and water at a rate that preserves the countercurrent multiplier system. In general, blood flows slowly in capillaries to allow time for exchange of nutrients and wastes. In the vasa recta particularly, this rate of flow is important for two additional reasons. The flow must be slow to allow blood cells to lose and regain water without either crenating or bursting. Second, a rapid flow would remove too much Na + and urea, destroying the osmolar gradient that is necessary for the recovery of solutes and water. Thus, by flowing slowly to preserve the countercurrent mechanism, as the vasa recta descend, Na + and urea are freely able to enter the capillary, while water freely leaves; as they ascend, Na + and urea are secreted into the surrounding medulla, while water reenters and is removed.

Watch this video to learn about the countercurrent multiplier system.

Reabsorption and secretion in the distal convoluted tubule

Approximately 80 percent of filtered water has been recovered by the time the dilute forming urine enters the DCT. The DCT will recover another 10–15 percent before the forming urine enters the collecting ducts. Aldosterone increases the amount of Na + /K + ATPase in the basal membrane of the DCT and collecting duct. The movement of Na + out of the lumen of the collecting duct creates a negative charge that promotes the movement of Cl out of the lumen into the interstitial space by a paracellular route across tight junctions. Peritubular capillaries receive the solutes and water, returning them to the circulation.

Cells of the DCT also recover Ca ++ from the filtrate. Receptors for parathyroid hormone (PTH) are found in DCT cells and when bound to PTH, induce the insertion of calcium channels on their luminal surface. The channels enhance Ca ++ recovery from the forming urine. In addition, as Na + is pumped out of the cell, the resulting electrochemical gradient attracts Ca ++ into the cell. Finally, calcitriol (1,25 dihydroxyvitamin D, the active form of vitamin D) is very important for calcium recovery. It induces the production of calcium-binding proteins that transport Ca ++ into the cell. These binding proteins are also important for the movement of calcium inside the cell and aid in exocytosis of calcium across the basolateral membrane. Any Ca ++ not reabsorbed at this point is lost in the urine.

Collecting ducts and recovery of water

Solutes move across the membranes of the collecting ducts, which contain two distinct cell types, principal cells and intercalated cells. A principal cell    possesses channels for the recovery or loss of sodium and potassium. An intercalated cell    secretes or absorbs acid or bicarbonate. As in other portions of the nephron, there is an array of micromachines (pumps and channels) on display in the membranes of these cells.

Questions & Answers

briefly explain the similarities between transcription and DNA replication
Emmanuel Reply
transcription copies DNA into RNA while replication makes another copy of DNA
Goode
A general explanation: Replication occurs when a copy of DNA is made. Transcription is the first step in the process of protein synthesis. Messenger RNA is made using a portion of the DNA molecule as a template.
Lessa
please what group is this?
Winifred
hello guys
PRINCE
Relationship between essential amino acids and immune response
Eunice
transcription from DNA to rna involves the matching of the nucleotides represented by c,g, t and A, but where there is a t, it is replaced by a u- uracil
Patrick
what is the main function of the pcn?
DAVID Reply
career in the health professions, respond appropriately to signs of illness, help you in your roles as a parent, spouse
Coach Reply
student would have an appreciation of the heart anatomy to give understanding of anatomy while opening ideas of function and physiology
Coach
study of the parts of the body
Coach
macro anatomy, study of big structures of the body that can be viewed with the naked eye
Coach
that is called gross anatomy
Patrick
what is integumentry
Amiebo Reply
chemical level cell level tissue level organs level organ system organism
sam Reply
when you sitting close to a campfire your sense smell adapts the smell but when the trace of smoke is introduced into your environments it becomes unsual for you
sam
I need to know mechanism of body fluid
johnson
OK but I need to know where are you coming from
johnson
ask how
Amiebo
oh ft, help out with integumentary system now
Amiebo
Pls give me a brief description of vetebra
Deborah Reply
7 cervical (c1 atlas and c2 axis help the neck rotate) 12 thoracic 5 lumbar 1 sacral and 2 coccyx
Anna
breakfast at 7, lunch at 12, and dinner at 5. sacrum holds 5, coccyx holds 4
Patrick
really there's just one coccyx and sacrum
Patrick
atlas like the Greek God holds the weight of the world on top of him
Patrick
elasticity of the vagina
Mariam Reply
The vagina is an elastic muscular wall
antouman
*organ
antouman
It has I think squamous cuboidal or maybe columnar epithelium designed for secretion, expansion and friction.
Patrick
how can you remember the integumentary system
Naomi Reply
integumentary system is the skin the skin is protection all the body and contain deid cells
Drs
how can you remember the formation of bone?
Maame
the largest organ of the body
Toni
skin is largest organ
Zara
what is the best way to remember the cranial bones or any other bones ?
Savannah
skeletal system?
Savannah
look at the diagram structure and then remember it considering it your own body i memorise like that
Zara
hi guys! do you have to remember ALL the structures of the bones- I mean every single hole, depression or tuberosity?
Kristina
tuborisity
Zara
hey guz i hv to remember Immune antibodies and antigens how? i found it difficult
Zara
well, they are all grouped, aren't they? I mean they all come in series like H1, H2A, H2B and so on. In this case I learn the common part first and then that what's different
Kristina
nd what about IgG , IgE etc.
Zara
the majors
Toni
the thin skin does not have stratum lucidium I believe
Patrick
acronyms
Patrick
if u know the bones, the muscle has part of the name of the bone in it
Patrick
epidermis, I believe epi means on top. dermis in the middle and hypodermis, hypo meaning below. the hypodermis is actually considered not part of the skin or int system
Patrick
big sweet guys love candy = basale, spinosum, granulosum, lucidum ( only in thick skin), corneum
Anna
I love it ☝🏾
Savannah
thank you Zara !
Savannah
can anyone send diet plan for asthma patients
waseem
is
Drs
hey
Daud
jam how are you
Daud
Hey guys l am Matrin
Matrin
blood is a connective tissue which transport oxygen and other nutrients to body
Zara Reply
which type of protein is blood?
Zara
what is blood?
Masthan Reply
blood is a connective tissue which transport oxygen and nutrients to body
Zara
which type of protein is blood?
Zara
haemoglobin
Rashid
and what about its structure i think its Quartenary structure 🤔💭
Zara
yes it is
Rashid
it is globular
Rashid
a vascular structure compose of vessels.
Toni
what is the functions of lymph
moula Reply
what is plasma
Chukwu Reply
A plasma is a hot ionized gas consisting of approximately af a equal number of positive ly charged ionized and negative ly charged electron is called plasma.
Muhammad
what is an atomical position?
Madinatu
military position, body erect where by the body will be up straight..the cephalic and thoracic are straight
Mwita
functions of plasma membrane
Dinyando Reply
what is heparin
Lawrence Reply
why is it anatomy
Tenacious Reply
hello
ASIMENU
hi
asare
hws life
Tenacious
anatomy is the scientific study of the body's structure
Lawrence
great
Lawrence
good night
Kaaya
anatomy is the study of form, physiology is the study of function
Patrick
anatomy is the study of the structure of the body and the physical relationship between it constituent part
Florence
what is heparin
Lawrence
what is the trunk
Tenacious
trunk is define as a person's or animal's body apart from the limp and head
Lawrence
The trunk is part of the axial skeleton
Patrick
hellow friends
mickson
hi friends
mickson
Hi
REEMA
hii
sampath
hi
Inayat
am fine
Ematai

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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