4: Macronutrient Uptake, Absorption, and Transport
- Page ID
- 40950
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The term absorption can have a number of different meanings. Not everything that is taken up into the enterocyte from the lumen will be absorbed, so the term uptake refers to compounds being transported into the enterocyte. Absorption means that a compound is transported from the enterocyte into circulation. Under most circumstances, compounds that are taken up will then be absorbed. After this chapter, hopefully this distinction between these terms will be clear. After later micronutrient chapters, hopefully you will understand the reason for emphasizing this distinction.
- 4.1: Crypts of Lieberkuhn and Enterocyte Maturation
- This page describes the anatomy of the small intestine, focusing on the crypts of Lieberkuhn that house stem cells. These stem cells develop into enterocytes, which migrate up the villi, maturing at the tips. An enterocyte's lifespan is approximately 72 hours, after which they are either digested or excreted. The page also emphasizes that not all uptake by enterocytes results in true absorption into the body's circulation.
- 4.2: Uptake Lineup and Cell Membranes
- This page discusses the absorption of various compounds in the small intestine, including lysolecithin, fatty acids, cholesterol, small peptides, amino acids, glucose, and water. These substances must cross the plasma membrane of enterocytes, a structure composed of phospholipids, proteins, cholesterol, and carbohydrates, highlighting the importance of membrane proteins in facilitating their transport.
- 4.3: Types of Cell Uptake and Transport
- This page explains the body's mechanisms for substance uptake through passive and active transport. Passive transport, which doesn't require energy, includes diffusion, osmosis, and facilitated diffusion, moving substances along a concentration gradient. In contrast, active transport, requiring ATP, moves substances against their gradient via active carrier transport or endocytosis.
- 4.4: Carbohydrate Uptake, Absorption, Transport and Liver Uptake
- This page discusses the absorption of monosaccharides like glucose, galactose, and fructose in the enterocyte, detailing that glucose and galactose use the SGLT1 transporter while fructose utilizes GLUT5. After absorption, they are transported into the liver via the portal vein, where they undergo phosphorylation by kinases.
- 4.5: Glycemic Response, Insulin, and Glucagon
- This page outlines the body's regulation of blood glucose, focusing on insulin's role in glucose uptake and glucagon's function in glucose release. It explains diabetes types and the glycemic index/load, stressing the importance of food choices in blood sugar management. Additionally, it discusses glycemic loads based on standardized serving sizes and offers resources for estimating glycemic loads of various foods, including references to relevant literature and links.
- 4.6: Protein Uptake, Absorption, Transport and Liver Uptake
- This page explains that carbohydrate and protein absorption processes share similarities. Over 60% of amino acids are absorbed as di- and tripeptides by the PepT1 transporter in enterocytes, then cleaved into free amino acids. These amino acids are transported to the liver via the portal vein, where they are taken up using various transporters for protein synthesis or conversion into glucose.
- 4.7: Lipid Uptake, Absorption and Transport
- This page discusses lipid uptake in enterocytes, detailing how various fatty acids enter circulation and are processed into chylomicrons and subsequently into lipoproteins like VLDL and LDL. It highlights the roles of HDL and LDL in cholesterol transport, with HDL promoting reverse transport and LDL potentially leading to arterial blockages linked to heart disease.