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By the end of this section, you will be able to:
  • List specific transport mechanisms occurring in different parts of the nephron, including active transport, osmosis, facilitated diffusion, and passive electrochemical gradients
  • List the different membrane proteins of the nephron, including channels, transporters, and ATPase pumps
  • Compare and contrast passive and active tubular reabsorption
  • Explain why the differential permeability or impermeability of specific sections of the nephron tubules is necessary for urine formation
  • Describe how and where water, organic compounds, and ions are reabsorbed in the nephron
  • Explain the role of the loop of Henle, the vasa recta, and the countercurrent multiplication mechanisms in the concentration of urine
  • List the locations in the nephron where tubular secretion occurs

With up to 180 liters per day passing through the nephrons of the kidney, it is quite obvious that most of that fluid and its contents must be reabsorbed. That recovery occurs in the PCT, loop of Henle, DCT, and the collecting ducts ( [link] and [link] ). Various portions of the nephron differ in their capacity to reabsorb water and specific solutes. While much of the reabsorption and secretion occur passively based on concentration gradients, the amount of water that is reabsorbed or lost is tightly regulated. This control is exerted directly by ADH and aldosterone, and indirectly by renin. Most water is recovered in the PCT, loop of Henle, and DCT. About 10 percent (about 18 L) reaches the collecting ducts. The collecting ducts, under the influence of ADH, can recover almost all of the water passing through them, in cases of dehydration, or almost none of the water, in cases of over-hydration.

Locations of secretion and reabsorption in the nephron

This diagram shows the different ions and chemicals that are secreted and reabsorbed along the nephron. Arrows show the direction of the movement of the substance.
Substances Secreted or Reabsorbed in the Nephron and Their Locations
Substance PCT Loop of Henle DCT Collecting ducts
Glucose Almost 100 percent reabsorbed; secondary active transport with Na +
Oligopeptides, proteins, amino acids Almost 100 percent reabsorbed; symport with Na +
Vitamins Reabsorbed
Lactate Reabsorbed
Creatinine Secreted
Urea 50 percent reabsorbed by diffusion; also secreted Secretion, diffusion in descending limb Reabsorption in medullary collecting ducts; diffusion
Sodium 65 percent actively reabsorbed 25 percent reabsorbed in thick ascending limb; active transport 5 percent reabsorbed; active 5 percent reabsorbed, stimulated by aldosterone; active
Chloride Reabsorbed, symport with Na + , diffusion Reabsorbed in thin and thick ascending limb; diffusion in ascending limb Reabsorbed; diffusion Reabsorbed; symport
Water 67 percent reabsorbed osmotically with solutes 15 percent reabsorbed in descending limb; osmosis 8 percent reabsorbed if ADH; osmosis Variable amounts reabsorbed, controlled by ADH, osmosis
Bicarbonate 80–90 percent symport reabsorption with Na + Reabsorbed, symport with Na + and antiport with Cl ; in ascending limb Reabsorbed antiport with Cl
H + Secreted; diffusion Secreted; active Secreted; active
NH 4 + Secreted; diffusion Secreted; diffusion Secreted; diffusion
HCO 3 Reabsorbed; diffusion Reabsorbed; diffusion in ascending limb Reabsorbed; diffusion Reabsorbed; antiport with Na +
Some drugs Secreted Secreted; active Secreted; active
Potassium 65 percent reabsorbed; diffusion 20 percent reabsorbed in thick ascending limb; symport Secreted; active Secretion controlled by aldosterone; active
Calcium Reabsorbed; diffusion Reabsorbed in thick ascending limb; diffusion Reabsorbed if parathyroid hormone present; active
Magnesium Reabsorbed; diffusion Reabsorbed in thick ascending limb; diffusion Reabsorbed
Phosphate 85 percent reabsorbed, inhibited by parathyroid hormone, diffusion Reabsorbed; diffusion

Questions & Answers

what is the fuction of tostiriol glands
abdifitah Reply
It's tonsilar?
Dr.
or tostiriol
Dr.
what are some examples of muscles predominantly composed of Fast glycolytic fibers?
Rey Reply
what is cardinal signs, and pathophysiology of those cardinal signs. can anyone explain..
Richard Reply
cardinal signs of inflammation!
Madhuri
then they are rubor,tumor,calor,dolar,functio laesa
Madhuri
rubor is redness due to vasodilatation
Madhuri
tumor is swelling due exudation of plasma
Madhuri
calor is rise in temperature
Madhuri
dolar is pain due to stimulation of nerve ending
Madhuri
functio laesa is loss of function
Madhuri
correct The Question
Abdi Reply
why are tha bp
Dharm Reply
Your question is wrong
Nisha
Kya puchna chahate ho
Yamini
wrong question
Asif
blood pressure
SAJJAD
means
Dr.
means diastolic 85 up
Mohamed
whats is the cell cycle
Dharm Reply
The cell cycle is the series of events that take place in a cell leading to its division and duplication of its DNA to produce two daughter cells
Nisha
where are the rest of the chapters
Donna Reply
formation of bone in calcium
Dharm
which is the largest or smallest muscle of human body?
pankaj Reply
largest muscle is sartoreus
Asif
smallest is pyramedalis muscle
Asif
largest is Gluteus maximus
Rianicole
smallest muscle stapedius
Rianicole
smallest muscle of our body
pankaj
Stapedius muscle
PL
stapedius muscle
Dr.
describe the formation of bone
RITA Reply
in female the outer urethral opening is immediately............... to the vaginal opening
perpetual Reply
above
Madhuri
opens above
Dr.
above opening
shakra
Explain in detail anatomy of kidney with diagram
Chinna Reply
which of the main digestive organ has not got any digestive function
Awelama Reply
appendix
Rodney
appendix is a lymph node which kills bacteria
Nejat
it is also believed Appendix stores good bacteria that help us with digestion, but its function is unknown
Nejat
so the answer is appendix
Nejat
appendix
Onavwie
right answer is appendix
Asif
appendix
Himani
what is the functional units of kidney?
Subathra Reply
nephrons
Phuong
Yep Nephron,
Nejat
filter the blood
Yamini
oops sorry
Yamini
filter and refresh the blood
Sunny
nephrons
Hashini
nephrons
Himani
nephrones
Dr.
Nephrons is correct answer
Subathra
right answer is nephrons
Asif
nephrons
Himani
nephros means kidney it is tha function urin fitration and excriction
Dharm
nephrons
Hilal
Nephron
Frank
nephron
Onavwie
nephrons which collectively forms kidney
Madhuri
how many bones has the sacrum?
Kabwe Reply
5 bone in sacrum
Asif
S1 to S5
Dharm
good
Asif
very good
Kabwe
how many chromosomes has a normal human being?
Kabwe Reply
22 + XX/XY
Shiplum
22 pairs + XX/XY
Shiplum
total 46
Shiplum

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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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