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Protein absorption

Active transport mechanisms, primarily in the duodenum and jejunum, absorb most proteins as their breakdown products, amino acids. Almost all (95 to 98 percent) protein is digested and absorbed in the small intestine. The type of carrier that transports an amino acid varies. Most carriers are linked to the active transport of sodium. Short chains of two amino acids (dipeptides) or three amino acids (tripeptides) are also transported actively. However, after they enter the absorptive epithelial cells, they are broken down into their amino acids before leaving the cell and entering the capillary blood via diffusion.

Lipid absorption

About 95 percent of lipids are absorbed in the small intestine. Bile salts not only speed up lipid digestion, they are also essential to the absorption of the end products of lipid digestion. Short-chain fatty acids are relatively water soluble and can enter the absorptive cells (enterocytes) directly. Despite being hydrophobic, the small size of short-chain fatty acids enables them to be absorbed by enterocytes via simple diffusion, and then take the same path as monosaccharides and amino acids into the blood capillary of a villus.

The large and hydrophobic long-chain fatty acids and monoacylglycerides are not so easily suspended in the watery intestinal chyme. However, bile salts and lecithin resolve this issue by enclosing them in a micelle    , which is a tiny sphere with polar (hydrophilic) ends facing the watery environment and hydrophobic tails turned to the interior, creating a receptive environment for the long-chain fatty acids. The core also includes cholesterol and fat-soluble vitamins. Without micelles, lipids would sit on the surface of chyme and never come in contact with the absorptive surfaces of the epithelial cells. Micelles can easily squeeze between microvilli and get very near the luminal cell surface. At this point, lipid substances exit the micelle and are absorbed via simple diffusion.

The free fatty acids and monoacylglycerides that enter the epithelial cells are reincorporated into triglycerides. The triglycerides are mixed with phospholipids and cholesterol, and surrounded with a protein coat. This new complex, called a chylomicron    , is a water-soluble lipoprotein. After being processed by the Golgi apparatus, chylomicrons are released from the cell ( [link] ). Too big to pass through the basement membranes of blood capillaries, chylomicrons instead enter the large pores of lacteals. The lacteals come together to form the lymphatic vessels. The chylomicrons are transported in the lymphatic vessels and empty through the thoracic duct into the subclavian vein of the circulatory system. Once in the bloodstream, the enzyme lipoprotein lipase    breaks down the triglycerides of the chylomicrons into free fatty acids and glycerol. These breakdown products then pass through capillary walls to be used for energy by cells or stored in adipose tissue as fat. Liver cells combine the remaining chylomicron remnants with proteins, forming lipoproteins that transport cholesterol in the blood.

Questions & Answers

list types epithelial tissue
Sangu Reply
explain how hormonal control aids in homeostasis regarding fluids and electrolytes, internal organs, clinical application, edema electrolyte imbalance?
Hensheal Reply
someone to help me explain those
Hensheal
parathyroid hormone : Calcium uptake, H+ and PO-4 wasting thyroid hormone, cortisol for temperature regulation by acting on B.V
Kartik
also renin
Kartik
thanks
Hensheal
why retro abdominal region called flank?
Huma
it is just Anatomical terminology
Kartik
meaning side of body b/w rib cage and hip bone
Kartik
r
Sangu
list down all the hormones secreted by adrenal gland
Odong Reply
adrenaline hormones
Sangu
The amount of blood pumped by the left ventricle of the heart in one contraction.
Javid Reply
how we can calculate the cardiac output
khater
and how do we calculate the strock valume
khater
stroke volume is not all the blood contained in the left ventricle; normally, only about two-thirds of the blood in the ventricle is expelled with each beat.
Javid
Cardiac output 5.5 l S. V 68.75 ml H. R 80bpm
Javid
If we consider SV 70, end systolic vol is about 15% of total(approx always) out of a total of 80-85 ml only 70ml is pumped per systole
Kartik
what is macrophages?and its function
Sajjad Reply
macrophages they are white blood cells that engulf dead cells in the body
patience
what is power stroke?
muravha
no idea
patience
what is the stroke volume of heart?
up
If an autoimmune disorder targets the alpha cells, production of which hormone would be directly affected?
Samantha Reply
what is a muscle?
Gideon Reply
A band or bundle of fibrous tissue in a human or animal body that has the ability to contract, producing movement in or maintaining the position of parts of the body
Mody
ok
Gideon
what's endolphthamities and panophthalmities?
Gideon
fluid around the brain
louise Reply
what ?
Asif
cerebro spinal fluid
Bhupender
The brain and spinal cord are surrounded by a clear fluid called cerebrospinal fluid (CSF). This fluid is produced and stored in cavities in the brain called ventricles. It circulatesaround the brain, moving from ventricle to ventricle. ... Hydrocephalus is a condition in which there is too much CSF
Archie
what is hydrocphalus
aminul Reply
Google krlena na madarchod yha maa chudwa rha ha sabko notification bhjke
Bhupender
when cerebrospinal fluid produce în the brain, i.e. brain ventricles, is to abundent in the brain and is not trăind out of the brain. as a consequence this lichid pute mechanical pressure oñ the brain and it pushes the cerebrum tissue. as a consequence this pressure on the neuronscan cause neurologi
Centerkinet
cal disfunctions, for example clinical headache
Centerkinet
. It is posible to drainout the fluid through a device dalles shunt,as i remember.
Centerkinet
but where are also home medicinsfor decreasing the production of cerebrospin.fluid etc
Centerkinet
there are some medicines that can decrease the production of csf
Centerkinet
a neurologist advice is needed
Centerkinet
i wrote some medicines NOT home medicines. it is a serious condition and specialized medical advice is needed. of course also general medical knowledge may be helpful, but not enough, a specialist is neede
Centerkinet
if anyone help me in physiology
Radika Reply
i am BSN student of first year which book is best for physiology
Radika
i am BSN student of first year which book is best for physiology
Radika
ross and wilson anotomy and physiology
Sajjad
it's 1 book for anotomy and physiology it's best for bs nursing
Sajjad
yes Ross and wilson physiology is better for study
Nasir
I'm also the student of bs nursing
Sajjad
I study guiton and hall &ganong
Gentle
I'm also midwif help me be the best book for midwif
nimco
what ia the function of indocrine system
sheraz
salam all friend
sheraz
help me with this question; explain at least five emergency acute pain found in fundamental emergency medicine
Christon
Fascial compartment of forearm
Hidayatullah
what's a tissue?
Mwape Reply
a group of cells with the same function
Dee
tissue is a group of cells that perform the same functions.
Rashid
explain a bit about a tissue
Mwape
A tissue is made up of cells that are similar in shape and perform the same function, for instance brain cells form up a brain tissue. Whereas a group of tissues that perform the same function form an organ... so in this case the brain which is the organ is formed as a result of brain tissues.
Isaac
what is gross anatomy
Joseph
the branch of anatomy that deals with the structure of organs and tissues that are visible to the naked eye.
Archie
1.To know how the structures functions. 2.To easily identify the micro structures and the macro structures. 3.To be able to explain that anatomy is the study of the structures and physiology is the study of how the structures functions
Abban Reply
Describe the two classes of hormones (3 with subclasses) and how they affect their target cells.
Shalaeha Reply
what is control centre
Gohil Reply
Angie The larger air passage of the lung is
Angie Reply

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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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