# 25.6 Tubular reabsorption  (Page 4/18)

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Reabsorption of Major Solutes by the PCT
Basal membrane Apical membrane
Active transport Symport with Na +
Na + (exchange for K + ) K +
Facilitated diffusion Cl
K + Ca ++
Cl Mg ++
Ca ++ HCO 3
HCO 3 ${\text{PO}}_{4}^{3-}$
${\text{PO}}_{4}^{3-}$ Amino acids
Amino acids Glucose
Glucose Fructose
Fructose Galactose
Galactose Lactate
Lactate Succinate
Succinate Citrate
Citrate Diffusion between nephron cells
K +
Ca ++
Mg ++

About 67 percent of the water, Na + , and K + entering the nephron is reabsorbed in the PCT and returned to the circulation. Almost 100 percent of glucose, amino acids, and other organic substances such as vitamins are normally recovered here. Some glucose may appear in the urine if circulating glucose levels are high enough that all the glucose transporters in the PCT are saturated, so that their capacity to move glucose is exceeded (transport maximum, or T m ). In men, the maximum amount of glucose that can be recovered is about 375 mg/min, whereas in women, it is about 300 mg/min. This recovery rate translates to an arterial concentration of about 200 mg/dL. Though an exceptionally high sugar intake might cause sugar to appear briefly in the urine, the appearance of glycosuria    usually points to type I or II diabetes mellitus. The transport of glucose from the lumen of the PCT to the interstitial space is similar to the way it is absorbed by the small intestine. Both glucose and Na + bind simultaneously to the same symport proteins on the apical surface of the cell to be transported in the same direction, toward the interstitial space. Sodium moves down its electrochemical and concentration gradient into the cell and takes glucose with it. Na + is then actively pumped out of the cell at the basal surface of the cell into the interstitial space. Glucose leaves the cell to enter the interstitial space by facilitated diffusion. The energy to move glucose comes from the Na + /K + ATPase that pumps Na + out of the cell on the basal surface. Fifty percent of Cl and variable quantities of Ca ++ , Mg ++ , and ${\text{HPO}}_{4}^{2-}$ are also recovered in the PCT.

Recovery of bicarbonate (HCO 3 ) is vital to the maintenance of acid–base balance, since it is a very powerful and fast-acting buffer. An important enzyme is used to catalyze this mechanism: carbonic anhydrase (CA). This same enzyme and reaction is used in red blood cells in the transportation of CO 2 , in the stomach to produce hydrochloric acid, and in the pancreas to produce HCO 3 to buffer acidic chyme from the stomach. In the kidney, most of the CA is located within the cell, but a small amount is bound to the brush border of the membrane on the apical surface of the cell. In the lumen of the PCT, HCO 3 combines with hydrogen ions to form carbonic acid (H 2 CO 3 ). This is enzymatically catalyzed into CO 2 and water, which diffuse across the apical membrane into the cell. Water can move osmotically across the lipid bilayer membrane due to the presence of aquaporin water channels. Inside the cell, the reverse reaction occurs to produce bicarbonate ions (HCO 3 ). These bicarbonate ions are cotransported with Na + across the basal membrane to the interstitial space around the PCT ( [link] ). At the same time this is occurring, a Na + /H + antiporter excretes H + into the lumen, while it recovers Na + . Note how the hydrogen ion is recycled so that bicarbonate can be recovered. Also, note that a Na + gradient is created by the Na + /K + pump.

Differentiate between pharmacist and apothecary
What is metatarsal
bone of the foot is known as metatarsal
Patrick
yes 👆 right
Sneha
metatarsal (foot bone).....👍
Rishi
what is the meaning for cadavers
Malar
yes metatarsal are foot bone
Rakiya
the term "mental" pertain to which of the following a. chin b.navel c. ear d. nose e. skull
a
Lina
chin
Sneha
hi
Mohamed
skull
Monica
skull
Peter
chin
Kelly
skull
Juma
skull
Gul
skull
Laraib
skull
anwaar
skull
Nirmala
skull
Tessmol
chin
Derrick
mental chin nerve
Katarzyna
e. skull
Jennifer
skull
prince
e. skull
Natasha
It's not skull but chin
mwango
the skull
Rakiya
what are the three many components of the lymphatic system?
those are...... organ, tissue and blood capillary or vessals
Juma
anatomical terms and use them appropriatly in the language of anatomy of anterior body landmarks
what is human anatomy?
Sa
what is the study of how the body functions?
Bright
What is human anatomy
Sherifat
human antomy is the body of structure
Malar
is the study of human body
Rakiya
what is abdomipelvic cavity?
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Maureen
where can we find the short bones
Carpal bones are examples of short bones
Dara
what is blood supply
Chidi
on upper limb and lower limb
Juma
carpal bones
Priya
during pregnancy which would more increase size the mothers abdominal or pelvic cavity?
pelvic cavity I think
Priya
What is anatomical position
Nwoye
pelvic
Maureen
@ Nwoye... when standing erect, feet parallel, arms hanging at the sides with palms facing forward
Maureen
The pelvic cavity
Rakiya
pelvic
Malar
define the main directional terms of the body
during physical exercise respiratory rate increace two student are discussing the mechanisms involved. student A claim they are positive feedback and student B claim negative feedback do you agree with student A or B and why
cris
what is the physiology of circulation
Chidi
please I mean the physiology of criculation
Chidi
blood flow refers to the movement of blood through the vessels from arteries to the capillaries and then to the veins
Laraib
the heart&the lungs
Rakiya
during pregnancy, which would more size the mother's abdominal or pelvic cavity? explain
list and define the three plane of devision of the body
cris
complete the following statements using correct directional terms for human being. 1. the navel is________to the nose 2. the heart is______to the breastbone(sternum) 3 the ankle is______to the knee 4 the ear is______to the eyes.
cris
1. superior 2. posterior 3. superior 4. lateral
Mnm
anterior fuerior
Chidi
inferior medial posterior lateral we
Susan
name the system of the body and its function
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Vineeta
during pregnancy, which would more size the mother's abdominal or pelvic cavity? explain
cris
how the body maintain hormeostasis in terms of bloodglucose level
It releases hormones from the pancreas insulin and glucagon
TONY
why human blood pressure high
fear, anxiety, sickness
Inemesit
why in mothers womb the foetus head is in anus direction?
Kick
As it seems the position downside n if we did such position thn soon we got vomiting then how foetus stay in downward position long time?
Kick
What is red blood cell
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Noor
red blood cell are the most numerous blood cells.they comprise about 99% of all blood cells red blood cells are non nucleated it has red colour due to present to hemoglobin.
Vineeta
HANNAH