Digestive System and Nutrition

Crypts of Lieberkuhn are intestinal glands located between the villi that secrete succus entericus (intestinal juice). This juice contains enzymes like maltase, lipase, and peptidases that complete digestion in the small intestine.

Villi are finger-like projections that massively increase the surface area of the small intestine for absorption. The stomach lacks villi, having instead gastric folds (rugae). This structural difference is key to their different functions.

Below freezing point, enzymes become inactivated (option A) because molecular motion virtually stops. They are not destroyed - enzyme activity returns when temperature rises above freezing. The 'activated' option incorrectly suggests cold enhances enzyme function.

The human body cannot store excess amino acids. Unlike fats and glucose, there's no amino acid storage depot. Excess amino acids are deaminated (nitrogen removed) and the carbon skeletons are used for energy or converted to fat, while nitrogen is excreted as urea.

Fats are broken down by lipase enzymes into fatty acids and glycerol. Fatty acids are the primary end products of fat digestion, along with glycerol. Amino acids come from proteins, starch is a carbohydrate, and glucose is a simple sugar.

Lactose is the disaccharide sugar found in milk, composed of glucose and galactose. Fructose is fruit sugar, galactose is a component of lactose (not free in milk), and glucose is a monosaccharide. Mammalian milk is characterized by its lactose content.

Trypsinogen is secreted by pancreas.

Glucose is the primary fuel for cellular respiration, producing ATP through glycolysis and oxidative phosphorylation. While fats can provide energy, they require breakdown first. Proteins are primarily for building structures, and fructose must be converted to glucose for cellular use.

Fatty acids and glycerol are absorbed through lacteals, which are lymphatic vessels located within the intestinal villi. They enter the lymphatic system first before reaching bloodstream. Blood capillaries absorb water-soluble nutrients like amino acids and sugars, not fats.

Secretin is a hormone produced by the small intestine in response to acidic chyme. It stimulates the pancreas to release bicarbonate-rich secretions to neutralize stomach acid. While it aids digestion, it is not an enzyme itself - enzymes are biological catalysts, whereas hormones are signaling molecules.

Bile salts emulsify fats, breaking large fat globules into smaller droplets, which increases surface area for lipase enzymes to work. This emulsification is essential for proper fat digestion and absorption. Glycerol is a fat component, lipase is the enzyme, and bile pigments are waste products.

Amino acids are water-soluble molecules absorbed directly into blood capillaries within the intestinal villi. Lacteals are specialized lymphatic vessels that absorb fats, not amino acids. The rectum is the final portion of the colon for waste storage, not absorption.

Rhodopsin is a visual pigment in rod cells that requires vitamin A (retinal) for its formation. Carrots are rich in beta-carotene, which the body converts to vitamin A. While tomatoes, radish, guavas, and bananas are nutritious, they are not significant sources of vitamin A precursors.

Satiety” and “thirst” centres are located in the hypothalamus.

Sulfur is an essential mineral contained in amino acids cysteine and methionine, which are necessary for protein synthesis. While sodium, iron, and potassium are important minerals, they are not specifically required for protein structure formation. Proteins contain sulfur but not the other listed elements as structural components.

Vitamin A deficiency causes xerophthalmia (dry eyes, corneal damage) in children and night blindness (nyctalopia) in adults because retinal (derived from vitamin A) is essential for rhodopsin formation in rod cells for low-light vision.

Vitamin B12 (cobalamin) is essential for DNA synthesis and red blood cell formation in bone marrow. Deficiency causes megaloblastic anemia due to impaired erythropoiesis, not effects on fat absorption, liver stimulation, or RBC lifespan.

Vitamin C is a water-soluble vitamin that is readily excreted in urine when consumed in excess, unlike fat-soluble vitamins (A, D, E, K) which are stored in body tissues and liver.

Calciferol is the chemical name for Vitamin D, which is essential for calcium absorption and bone health. It exists in two forms: D2 (ergocalciferol) and D3 (cholecalciferol).

Vitamin C is ascorbic acid, a water-soluble vitamin essential for collagen synthesis, wound healing, and antioxidant function. Nicotinic acid (niacin) is Vitamin B3, lipoic acid is a cofactor, and aspartic acid is an amino acid.