Human Digestion and Nutrition

Flashcards covering human digestion, nutrition, anatomy of the gastrointestinal tract, enzymes, accessory organs, absorption, and related homeostasis disorders.

What is nutrition?

The process by which organisms obtain and utilize their food.

What are the four parts of the nutrition process in humans?

1. Ingestion (taking food into the system to be digested), 2. Digestion (mechanical and chemical breakdown of food), 3. Absorption (diffusion of soluble food particles into the bloodstream), 4. Assimilation (incorporation and utilization of food substances by the body).

What is the distinction between micronutrients and macronutrients?

Micronutrients include vitamins and minerals, whereas macronutrients include proteins, lipids, and carbohydrates.

What enzyme is present in saliva, and what chemical reaction does it catalyze?

Salivary amylase, which digests starch into maltose.

What are the functions of mucin in saliva?

Mucin is a slippery protein (mucus) that protects the soft lining of the digestive system and lubricates food for easier swallowing.

What role do buffers and anti-bacterial chemicals play in saliva?

Buffers neutralize acid to prevent tooth decay, while anti-bacterial chemicals kill bacteria entering the mouth with food.

What is the function of the epiglottis during swallowing?

The epiglottis is a flap of cartilage that covers and blocks the trachea to prevent choking while swallowing.

What is peristalsis?

A series of involuntary, wave-like muscle contractions that move food along the digestive tract.

What is the approximate length of the pharynx?

Approximately $15\,cm$.

What sphincter muscle prevents backflow out of the stomach?

The pyloric sphincter muscles.

What are the main functions of the stomach?

Temporary food storage (can stretch to fit ~$2\,L$ of food for 2-5 hours), disinfecting food with hydrochloric acid ($\text{HCl}$ at pH 1.5-2.5), chemical digestion of proteins via pepsin, and mechanical digestion by churning food into chyme.

What enzyme in the stomach breaks down proteins, and what are the resulting products?

Pepsin, which breaks down proteins into polypeptides and amino acids.

What protects the stomach lining from self-digestion by stomach acid and enzymes?

Mucus secreted by stomach cells protects the stomach lining.

How does bile assist in fat digestion?

Bile emulsifies lipids by physically breaking fats apart into tiny droplets, which are later broken down by lipase in the small intestine.

Which digestive enzymes are secreted in pancreatic juice, and what do they digest?

Lipase breaks down emulsified fat into fatty acids and glycerol; Trypsin breaks down protein and polypeptides into amino acids; Amylase breaks down starch into maltose.

Why does pancreatic juice contain sodium bicarbonate ($\text{NaHCO}_3$)?

Sodium bicarbonate acts as a buffer to neutralize acid coming from the stomach.

What metabolic processes regarding proteins and carbohydrates take place in the liver?

Carbohydrates: Excess glucose is converted to glycogen (and excess carbohydrates are stored as fats). Proteins: Excess amino acids are converted to ammonia and then to urea, which is sent to the kidneys.

What are the three sections of the small intestine, and what are their primary functions?

1. Duodenum (site of most digestion, mixing with pancreatic juice and bile), 2. Jejunum (absorption of nutrients and water), 3. Ileum (absorption of nutrients and water).

What are the structural adaptations of the small intestine for absorption?

It is over $6\,m$ long with a surface area of ~$300\,m^2$; its lining features villi (one cell thick) with microvilli; villi contain lacteals for fat absorption and a capillary network for absorbing simple sugars, amino acids, vitamins, and minerals.

Which membrane-bound enzymes covering the villi complete digestion in the small intestine?

Maltase (maltose to glucose), Sucrase (sucrose to glucose + fructose), Lactase (lactose to glucose + galactose), and Peptidase (polypeptides to amino acids).

Through which vessel are absorbed nutrients transported from the small intestine to the liver?

The hepatic portal vein.

What is the primary function of the large intestine (colon)?

To re-absorb water (re-absorbing >90% of the ~$9\,L$ used daily in digestive juices) and re-absorb vitamins K and B.

What helpful bacteria reside in the large intestine, and what do they produce?

Escherichia coli (E. coli), which produce vitamin K and B vitamins, as well as gases such as methane and hydrogen sulfide.

What bacterium is the primary cause of peptic ulcers?

Helicobacter pylori, an acid-tolerant bacterium.

What causes heartburn?

Stomach acid backing up into the esophagus when the bottom ring of esophageal muscles does not keep the lower esophagus tightly closed.

What anatomical structures of the biliary and pancreatic duct system are shown in this diagram?

The gallbladder, cystic duct, hepatic ducts, common hepatic duct, common bile duct, pancreatic duct, pancreas, and the hepatopancreatic duct (ampulla) entering the duodenum.

What structural components of a villus are depicted in this diagram?

A single layer epithelium with microvilli, a rich capillary network, a central lacteal, and an intestinal crypt.