Human Digestive System

Jaundice is caused by the buildup of bilirubin, a yellow pigment produced when red blood cells break down. The liver normally processes and excretes bilirubin, so liver malfunction (hepatitis, cirrhosis, etc.) leads to jaundice. The other organs (kidney, heart, stomach) are not primarily responsible for bilirubin processing.

Villi are finger-like projections in small intestine that massively increase surface area for absorption of nutrients like amino acids, monosaccharides and fatty acids. Digestion occurs primarily via enzymes in lumen; assimilation refers to cellular utilization; egestion is elimination of waste.

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.

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.

Trypsinogen is secreted by pancreas.

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.

Respiration - The process by which digested food is broken down with the help of oxygen to release energy.

The process of removal of waste products from the body is called excretion. This step not included in holozoic nutrition.

The process of digestion does not take place in this region. It simply secretes mucus, which serves as a lubricant for easy passage of the undigested matter in the form of faeces.

Expelling out the undigested food material from a cell

Amylase enzyme secreted in saliva helps break down starch.