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Lipid absorption

This diagram shows how lipids are absorbed from the lumen of the intestine into the lacteals. The fatty acid micelles are shown to enter the epithelial cell and form chylomicrons inside the Golgi apparatus. Then, the chylomicrons are extruded from the epithelial cell and are taken up by the lacteals.
Unlike amino acids and simple sugars, lipids are transformed as they are absorbed through epithelial cells.

Nucleic acid absorption

The products of nucleic acid digestion—pentose sugars, nitrogenous bases, and phosphate ions—are transported by carriers across the villus epithelium via active transport. These products then enter the bloodstream.

Mineral absorption

The electrolytes absorbed by the small intestine are from both GI secretions and ingested foods. Since electrolytes dissociate into ions in water, most are absorbed via active transport throughout the entire small intestine. During absorption, co-transport mechanisms result in the accumulation of sodium ions inside the cells, whereas anti-port mechanisms reduce the potassium ion concentration inside the cells. To restore the sodium-potassium gradient across the cell membrane, a sodium-potassium pump requiring ATP pumps sodium out and potassium in.

In general, all minerals that enter the intestine are absorbed, whether you need them or not. Iron and calcium are exceptions; they are absorbed in the duodenum in amounts that meet the body’s current requirements, as follows:

Iron —The ionic iron needed for the production of hemoglobin is absorbed into mucosal cells via active transport. Once inside mucosal cells, ionic iron binds to the protein ferritin, creating iron-ferritin complexes that store iron until needed. When the body has enough iron, most of the stored iron is lost when worn-out epithelial cells slough off. When the body needs iron because, for example, it is lost during acute or chronic bleeding, there is increased uptake of iron from the intestine and accelerated release of iron into the bloodstream. Since women experience significant iron loss during menstruation, they have around four times as many iron transport proteins in their intestinal epithelial cells as do men.

Calcium —Blood levels of ionic calcium determine the absorption of dietary calcium. When blood levels of ionic calcium drop, parathyroid hormone (PTH) secreted by the parathyroid glands stimulates the release of calcium ions from bone matrices and increases the reabsorption of calcium by the kidneys. PTH also upregulates the activation of vitamin D in the kidney, which then facilitates intestinal calcium ion absorption.

Vitamin absorption

The small intestine absorbs the vitamins that occur naturally in food and supplements. Fat-soluble vitamins (A, D, E, and K) are absorbed along with dietary lipids in micelles via simple diffusion. This is why you are advised to eat some fatty foods when you take fat-soluble vitamin supplements. Most water-soluble vitamins (including most B vitamins and vitamin C) also are absorbed by simple diffusion. An exception is vitamin B 12 , which is a very large molecule. Intrinsic factor secreted in the stomach binds to vitamin B 12 , preventing its digestion and creating a complex that binds to mucosal receptors in the terminal ileum, where it is taken up by endocytosis.

Water absorption

Each day, about nine liters of fluid enter the small intestine. About 2.3 liters are ingested in foods and beverages, and the rest is from GI secretions. About 90 percent of this water is absorbed in the small intestine. Water absorption is driven by the concentration gradient of the water: The concentration of water is higher in chyme than it is in epithelial cells. Thus, water moves down its concentration gradient from the chyme into cells. As noted earlier, much of the remaining water is then absorbed in the colon.

Chapter review

The small intestine is the site of most chemical digestion and almost all absorption. Chemical digestion breaks large food molecules down into their chemical building blocks, which can then be absorbed through the intestinal wall and into the general circulation. Intestinal brush border enzymes and pancreatic enzymes are responsible for the majority of chemical digestion. The breakdown of fat also requires bile.

Most nutrients are absorbed by transport mechanisms at the apical surface of enterocytes. Exceptions include lipids, fat-soluble vitamins, and most water-soluble vitamins. With the help of bile salts and lecithin, the dietary fats are emulsified to form micelles, which can carry the fat particles to the surface of the enterocytes. There, the micelles release their fats to diffuse across the cell membrane. The fats are then reassembled into triglycerides and mixed with other lipids and proteins into chylomicrons that can pass into lacteals. Other absorbed monomers travel from blood capillaries in the villus to the hepatic portal vein and then to the liver.

Questions & Answers

sorry what are the common meaning of haemostatis
Juma Reply
what are the negatives feedback regulation of ADH
Nansi Reply
what is the the differences between DNA and RNA?
Mustapha
The major differences between the DNA and RNA are contain of double stranded and single stranded which the DNA contain duoble stranded and RNA contain single stranded.
Juma
what are the negatives feedback regulation of ADH before this we confused just verify long term of ADH firstly
Juma
How many genes consist of DNA?
Omaryare
omaryare muhyadiin when you talk about genes, is the material formed in a DNA genes have form like plasma have many genes round there
Juma
aldosterone, renin
Conan
to know the different structures of the body To know how the body works To know more about our body parts
Deitdre Reply
hi Deitdre you tock about knowledge or you ask the question
Juma
do you need any explanation when reading this book?
janet Reply
Its Good
Hashir
yes
Balogun
Yes
Mariam
yes
Sale
yes
Mustapha
if have many ability just do it!!
Juma
compare and contrast the operation of homeostasis
Dinelle Reply
what is the difference between an ionic, polar covalent and nonpolar covalent bond?
Dinelle
In summary, the bond has different in electronegativity.
Balogun
sorry help me to get the definition of hemostasis or the meaning
Juma
the definition of distal
Dinelle Reply
farthest away from the attachment point.
felix
Distal, is the farthest possition from the origin or midle point
Juma
exercise physiologist how ?
Noor Reply
hi noorr. when you talk about physiologist its a person who study physiology but exercise physiologist is what an exercise doing by physiologist in physiologican
Juma
can I get the questions of human physiology that is present in HSC 2nd semester
Rafiullah Reply
in my lerning the question com like for example ni eassy qustion must understand the the part of the body and how it work or mechanisms of each part learned
Juma
how can I memorize
mukhtaar Reply
which part of the body produces blood
aadil
give me answer
aadil
Red blood cells are formed in the red bone marrow ofbones. Stem cells in the red bone marrow called hemocytoblasts give rise to all of the formed element
mukhtaar
what is hemocytoblasts
Fatima
hemocytoblasts are stem cells in red bone marrow which give rise the all of formed elements
Khawaja
Discuss clonal theory in physiology and its application in measles infection in a 6yr child? Can anyone help me
Isaac Reply
Capillary permeability
what do you want to know about it?
Ramsin
Hello, I want to search about the topic, information and pictures
syncitium is the property of which of the following muscle
Shahab Reply
can I get the questions of human physiology that is present in HSC 2nd semester
Sai Reply
i now madam
irpa
ha can u please send me the PDF of questions
Sai
it's important to me to have that information please send as fast as u can
Sai
me too if possible?
Ramsin
of course
mukhtaar
I want too
Nazirullah
now you want to look the format of question or because i need to explain on you?
Juma
If a molecule can only pass through a membrane with the assistance of a membrane protein, but the direction of its travel is controlled only by its concentration, the process is called?
osmosis
chozen
A 52 year old woman turned her head quickly, during a tennis game and suddenly felt a sharp pain in her neck along her upper limb. Physical examination and medical imaging revealed a herniated degenerated IV disc in the cervical region of her vertebral column.
Isaac
a. What probably caused the IV disc herniation? b. What cause IV disc degeneration? c. What are the result of disc degeneration?
Isaac
b
Mirasol
Describe the neural control of erection and ejaculation.
Nana Reply
A 52 year old woman turned her head quickly, during a tennis game and suddenly felt a sharp pain in her neck along her upper limb. Physical examination and medical imaging revealed a herniated degenerated IV disc in the cervical region of her vertebral column. a)What probably caused the IV di
Isaac
a) What probably caused the IV disc herniation? b) What cause IV disc degeneration? c) What are the result of disc degeneration?
Isaac
iv disc herniation compress the nerve cause numbness tingling sensation even paralysis in severe cases...
Khawaja

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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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