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Human Physiology - Digestion and Absorption

Grade 11IBBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The human digestive system follows a specific sequence: ingestion, digestion, absorption, and egestion. Mechanical digestion involves teeth and stomach churning, while chemical digestion involves enzymes like amylaseamylase, lipaselipase, and endopeptidaseendopeptidase.

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Peristalsis is the contraction of circular and longitudinal muscles in the wall of the gut which moves food along the alimentary canal and mixes it with enzymes.

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The pancreas secretes enzymes into the lumen of the small intestine. These include pancreatic amylasepancreatic \ amylase for starch, lipaselipase for triglycerides, and endopeptidaseendopeptidase for proteins.

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Villi increase the surface area of the epitheliumepithelium over which absorption is carried out. They absorb monomers formed by digestion as well as mineral ions and vitamins.

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Different methods of membrane transport are required to absorb different nutrients: glucoseglucose and amino acidsamino \ acids use active transport or co-transport with Na+Na^+, while fatty acidsfatty \ acids are absorbed via simple diffusion.

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Starch digestion involves two types of molecules: amyloseamylose (unbranched α−1,4\alpha-1,4 bonds) and amylopectinamylopectin (branched with α−1,6\alpha-1,6 bonds). Specific enzymes like maltasemaltase, glucosidaseglucosidase, and dextrinasedextrinase are required for complete breakdown into glucoseglucose.

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Dialysis tubing can be used as a model for the small intestine, demonstrating the semi−permeabilitysemi-permeability of the membrane and the role of concentration gradientsconcentration \ gradients in passive transport.

📐Formulae

Actual Size=Image SizeMagnificationActual \ Size = \frac{Image \ Size}{Magnification}

Starch+nH2O→AmylaseMaltoseStarch + nH_2O \xrightarrow{Amylase} Maltose

Triglyceride+3H2O→LipaseGlycerol+3 Fatty AcidsTriglyceride + 3H_2O \xrightarrow{Lipase} Glycerol + 3 \ Fatty \ Acids

Peptide+H2O→ExopeptidaseDipeptides/Amino AcidsPeptide + H_2O \xrightarrow{Exopeptidase} Dipeptides/Amino \ Acids

💡Examples

Problem 1:

Explain how glucoseglucose is absorbed from the lumen of the small intestine into the capillaries, mentioning the specific ion involvement.

Solution:

  1. Na+Na^+ ions are actively pumped out of the epithelial cells into the interstitial space by the Na+/K+Na^+/K^+ pump. 2. This creates a low concentration of Na+Na^+ inside the cell. 3. GlucoseGlucose is then moved into the cell against its concentration gradient via a sodium−glucose co−transportersodium-glucose \ co-transporter protein. 4. GlucoseGlucose moves from the cell into the blood capillary via facilitated diffusion.

Explanation:

This is an example of secondary active transport where the electrochemical gradientelectrochemical \ gradient of Na+Na^+ provides the energy for glucoseglucose transport.

Problem 2:

Calculate the magnification of a micrograph of a villus if the actual length of the villus is 0.5 mm0.5 \ mm and the image length is 5 cm5 \ cm.

Solution:

Convert 5 cm5 \ cm to mmmm: 5 cm=50 mm5 \ cm = 50 \ mm. Use the formula M=IAM = \frac{I}{A}. M=50 mm0.5 mm=100M = \frac{50 \ mm}{0.5 \ mm} = 100.

Explanation:

The magnification is ×100\times 100. Always ensure units for Image sizeImage \ size and Actual sizeActual \ size are the same before dividing.

Problem 3:

Why can amylopectinamylopectin not be fully digested by amylaseamylase alone?

Solution:

AmylaseAmylase specifically breaks α−1,4\alpha-1,4 glycosidic bonds. AmylopectinAmylopectin contains α−1,6\alpha-1,6 glycosidic bonds at its branching points, which amylaseamylase cannot hydrolyze.

Explanation:

Specific enzymes like isomaltaseisomaltase or dextrinasedextrinase are required to break the α−1,6\alpha-1,6 linkages found in dextrinsdextrins resulting from partial starch digestion.