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Mechanisms of recovery

Mechanisms by which substances move across membranes for reabsorption or secretion include active transport, diffusion, facilitated diffusion, secondary active transport, and osmosis. These were discussed in an earlier chapter, and you may wish to review them.

Active transport utilizes energy, usually the energy found in a phosphate bond of ATP, to move a substance across a membrane from a low to a high concentration. It is very specific and must have an appropriately shaped receptor for the substance to be transported. An example would be the active transport of Na + out of a cell and K + into a cell by the Na + /K + pump. Both ions are moved in opposite directions from a lower to a higher concentration.

Simple diffusion moves a substance from a higher to a lower concentration down its concentration gradient. It requires no energy and only needs to be soluble.

Facilitated diffusion is similar to diffusion in that it moves a substance down its concentration gradient. The difference is that it requires specific membrane receptors or channel proteins for movement. The movement of glucose and, in certain situations, Na + ions, is an example of facilitated diffusion. In some cases of facilitated diffusion, two different substances share the same channel protein port; these mechanisms are described by the terms symport and antiport.

Symport mechanisms move two or more substances in the same direction at the same time, whereas antiport mechanisms move two or more substances in opposite directions across the cell membrane. Both mechanisms may utilize concentration gradients maintained by ATP pumps. This is a mechanism described by the term “secondary active transport.” For example, a Na + ATPase pump on the basilar membrane of a cell may constantly pump Na + out of a cell, maintaining a strong electrochemical gradient. On the opposite (apical) surface, a Na + /glucose symport protein channel assists both Na + and glucose into the cell as Na + moves down the concentration gradient created by the basilar Na + ATPase pumps. The glucose molecule then diffuses across the basal membrane by facilitated diffusion into the interstitial space and from there into peritubular capillaries.

Most of the Ca ++ , Na + , glucose, and amino acids must be reabsorbed by the nephron to maintain homeostatic plasma concentrations. Other substances, such as urea, K + , ammonia (NH 3) , creatinine, and some drugs are secreted into the filtrate as waste products. Acid–base balance is maintained through actions of the lungs and kidneys: The lungs rid the body of H + , whereas the kidneys secrete or reabsorb H + and HCO 3 ( [link] ). In the case of urea, about 50 percent is passively reabsorbed by the PCT. More is recovered by in the collecting ducts as needed. ADH induces the insertion of urea transporters and aquaporin channel proteins.

Substances Filtered and Reabsorbed by the Kidney per 24 Hours
Substance Amount filtered (grams) Amount reabsorbed (grams) Amount in urine (grams)
Water 180 L 179 L 1 L
Proteins 10–20 10–20 0
Chlorine 630 625 5
Sodium 540 537 3
Bicarbonate 300 299.7 0.3
Glucose 180 180 0
Urea 53 28 25
Potassium 28 24 4
Uric acid 8.5 7.7 0.8
Creatinine 1.4 0 1.4

Questions & Answers

what is hypoxia
Akas Reply
I guess it's low supply the oxygen to the tissues
A condition in which tissues (especially the blood) are deprived of an adequate supply of oxygen
hanifa pia uko hapa
where is present Glenoid Cavity ?
A- Reply
what is the muscular tissue
Md Reply
muscular tissue is a type of tissue that provide to help in cotraction to aur body.
What's the difference in epithelial, connective, muscular and muscle tissue
and it's similarities
what is limb bone
Akshu Reply
this are bone attaching or joining to the axial bone.axial bone including skull,vertebrate and ribcage
how many bones make up the skull?
22 bones
where is present Glenoid cavity ?
how many bone in skull
Explain the stages of mitosis and cell division
Bella Reply
systems of human body
Udezue Reply
define lymphatic system And give the composition of lymphatic fluid
sakshi Reply
the network of vessels through which lymphatic drains From the tissue into blood.lymph contain variety of substance like salts, glucose, proteins and fatsand water, white blood cells
what is lymphatic system
Adie Reply
the network of vessels through which lymph drains from tissue into the blood
to describe the boundaries of four cavity
Pius Reply
homeostatic variables such as body temperature fluctuates within a normal range around the set point, or ideal, for a given homeostatic condition. for example, 98.6°F is a set point for body temperature. The response of the effector determines whether or not the homeostatic variable remains in the n
Chidinma Reply
why rbc is biconcave?
Sudhakar Reply
to carry oxygen easily
What part of the brain controls the body temp
what are epithelial tissues
Sachibu Reply
epithelial tissue that cover overall parts of the body and it's free from blood and nerves
Epithelial tissues are composed of cells laid out in sheets with strong cell-to-cell attachments.
Epithelial tissues perform a variety of functions that include; protection, secretion, filtration, diffusion, absorption, etc.
what control the flow of the blood ?
Donkor Reply
the pumping action of the heart
what is bony promises on the human body
Kelly Reply
what is the bony promises on human body
what are bony prominences on human body
support of the body
what are the characteristics of blood
yeboah Reply
they are red in colour
why blood is red in color?
blood is red because it contains hemoglobin

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