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Human Physiology - Digestion and Absorption

Grade 11ICSEBiology

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

🔑Concepts

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Human dentition is described as Thecodont (teeth embedded in jaw sockets), Diphyodont (two sets of teeth: deciduous and permanent), and Heterodont (different types of teeth: Incisors, Canines, Premolars, and Molars).

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The wall of the alimentary canal consists of four layers from outer to inner: Serosa, Muscularis (inner circular, outer longitudinal), Sub-mucosa (contains nerves and vessels), and Mucosa (forms rugae in stomach and villi in small intestine).

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Salivary amylase (Ptyalin) initiates carbohydrate digestion in the mouth, converting approximately 30%30\% of starch into the disaccharide maltose at an optimum pHpH of 6.86.8.

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In the stomach, HClHCl provides an acidic pHpH of 1.81.8, which is optimal for the conversion of inactive Pepsinogen into active PepsinPepsin for protein digestion.

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Bile, secreted by the liver, contains bile salts (sodium glycocholate and sodium taurocholate) but no enzymes. It is essential for the emulsification of fats into small micelles.

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Pancreatic juice contains inactive enzymes: Trypsinogen, Chymotrypsinogen, Procarboxypeptidases, Amylases, Lipases, and Nucleases. Trypsinogen is activated by Enterokinase (secreted by intestinal mucosa) into TrypsinTrypsin.

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End products of digestion (glucose, amino acids) are absorbed by active transport or facilitated diffusion, while fatty acids and glycerol are first converted into ChylomicronsChylomicrons (protein-coated fat globules) before entering the lacteals.

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The Gross Calorific Value of carbohydrates, proteins, and fats are 4.1 kcal/g4.1 \text{ kcal/g}, 5.65 kcal/g5.65 \text{ kcal/g}, and 9.45 kcal/g9.45 \text{ kcal/g} respectively.

📐Formulae

Adult Human Dental Formula=21232123×2=32\text{Adult Human Dental Formula} = \frac{2123}{2123} \times 2 = 32

Milk Teeth (Child) Dental Formula=21022102×2=20\text{Milk Teeth (Child) Dental Formula} = \frac{2102}{2102} \times 2 = 20

Starch→pH6.8Salivary AmylaseMaltose\text{Starch} \xrightarrow[pH 6.8]{\text{Salivary Amylase}} \text{Maltose}

Proteins→pH1.8PepsinProteoses+Peptones\text{Proteins} \xrightarrow[pH 1.8]{\text{Pepsin}} \text{Proteoses} + \text{Peptones}

Triglycerides→BileLipasesDiglycerides→Monoglycerides\text{Triglycerides} \xrightarrow[\text{Bile}]{\text{Lipases}} \text{Diglycerides} \rightarrow \text{Monoglycerides}

Nucleic Acids→NucleasesNucleotides→Nucleosides\text{Nucleic Acids} \xrightarrow{\text{Nucleases}} \text{Nucleotides} \rightarrow \text{Nucleosides}

💡Examples

Problem 1:

Explain the role of the enzyme Enterokinase in the digestion of proteins.

Solution:

Trypsinogen→EnterokinaseTrypsin\text{Trypsinogen} \xrightarrow{\text{Enterokinase}} \text{Trypsin}

Explanation:

Enterokinase is a non-digestive enzyme secreted by the intestinal mucosa. It activates inactive pancreatic Trypsinogen into active Trypsin. Once formed, Trypsin autocatalytically activates other pancreatic enzymes like Chymotrypsinogen and Procarboxypeptidase.

Problem 2:

How is the acidic chyme neutralized in the duodenum?

Solution:

HCl+NaHCO3→NaCl+H2O+CO2HCl + NaHCO_3 \rightarrow NaCl + H_2O + CO_2

Explanation:

Bicarbonate ions (HCO3−HCO_3^-) from the pancreatic juice and mucus from Brunner's glands provide an alkaline medium (pH≈7.8pH \approx 7.8) to neutralize the HClHCl from the stomach chyme, protecting the duodenal mucosa.

Problem 3:

Calculate the total number of Molars present in a permanent human dentition.

Solution:

Total Molars=(33)×2=6 (upper)+6 (lower)=12\text{Total Molars} = \left( \frac{3}{3} \right) \times 2 = 6 \text{ (upper)} + 6 \text{ (lower)} = 12

Explanation:

According to the dental formula 2,1,2,32,1,2,3\frac{2,1,2,3}{2,1,2,3}, there are 3 molars in each quadrant of the mouth. Since there are 4 quadrants, the total is 3×4=123 \times 4 = 12.

Digestion and Absorption - Revision Notes & Key Diagrams | ICSE Class 11 Biology