Biology: Digestion

Question 1

Heterotrophic

Answer 1

Unable to synthesize your own nutrients. Animals.

Question 2

Digestion In Humans

Answer 2

Tract begins with the oral cavity and continues with the pharynx, the esophagus, the stomach, the small intestine, and the anus. Accessory organs, such as salivary glands, the pancreas, the liver, and the gall bladder, also play essential roles in digestion.

Question 3

Oral Cavity

Answer 3

The mouth. It’s where mechanical and chemical digestion of food begins.

Mechanical digestion is the breakdown of large food particles into smaller particles through the biting and chewing action of teeth (mastication).

Chemical digestion refers to the enzymatic breakdown of macromolecules into smaller molecules and begins in the mouth when the salivary glands secrete saliva.

Question 4

Saliva

Answer 4

Saliva lubricates food to facilitate swallowing and provides a solvent for food particles. Saliva is secreted in response to a nervous reflex triggered by the presence of food in the oral cavity. Saliva contains the enzyme salivary amylase (ptyalin), which hydrolyzes starch to maltose (a disaccharide).

Question 5

Esophagus

Answer 5

The muscular tube leading from mouth to stomach.

The body of the esophagus lies within the thoracic cavity, which is negatively pressured on inhalation. The abdominal cavity has a positive pressure gradient. Therefore, without normal defense mechanisms, the pressure gradients favor a continual reflux of gastric materials into the esophagus.

Question 6

Peristalsis

Answer 6

Food is moved down esophagus by rhythmic waves of involuntary muscular contractions called peristalsis.

Question 7

Gastroesophageal Reflux Disease (GERD)

Answer 7

There is a pathological condition known as gastroesophageal reflux disease (GERD). The primary mechanisms by which gastroesophageal reflux may occur are as follows:

• Reflux can occur after spontaneous transient lower esophageal sphincter relaxations not associated with swallowing.
• Resting pressures of the lower esophageal sphincter normally range from 15-35 mmHg above gastric baseline pressure.
• Patients with GERD usually have a decreased lower esophageal reflux pressure (5-10 mmHg above gastric baseline pressure), leading to an increased passage of stomach contents into the esophagus.
• A decreased lower esophageal sphincter pressure is not always associated with the development of GERD; however, the majority of patients with GERD are noted to have a decreased lower esophageal sphincter pressure.

Question 8

Stomach

Answer 8

A large, muscular organ located in the upper abdomen, stores and partially digests good.

Question 9

Gastric Mucosa

Answer 9

The walls of the stomach are lined by the gastric mucosa, which contains the glands.

These glands secrete mucus, which protects the stomach lining from the harshly acidic juices (pH = 2) present in the stomach. They also secrete pepsin, protein-hydrolyzing enzyme, and hydrochloric acid (HCl), which kills bacteria, dissolves the intercellular “glue” holding food tissues together, and activates certain proteins.

Chief cells synthesize pepsinogen, which is converted to pepsin. Parietal cells synthesize and release HCl and intrinsic factor.

Question 10

Chyme

Answer 10

The churning of the stomach produces an acidic semifluid mixture of partially digested food known as chyme. The chyme passes into the first segment of the small intestine, the duodenum, through the pyloric sphicter.

Question 11

Small Intestine

Answer 11

Chemical digestion is completed in the small intestine. It’s divided into the duodenum, jejunum, and ileum. It is highly adapted to absorption.

To maximize the surface area available for digestion and absorption, the intestine is extremely long (over 6 meters) and highly coiled.

In addition, numerous finger-like projections called villi extend out of the intestinal wall. Villi contain capillaries and lacteals (vessels of the lymphatic system). Amino acids and monosaccharides pass through the villi walls into the capillary system.

Question 12

Most digestion in the small intestine occurs in…

Answer 12

…the duodenum, where the secretions of the intestinal glands, pancreas, liver, and gallbladder mix together with the acidic chyme entering from the stomach.

Question 13

Intestinal Mucosa

Answer 13

The intestinal mucosa secretes lipases (for fat digestion), aminopeptidases (for polypeptide digestion), and disaccharidases (digestion of maltose, lactose, sucrose).

The disaccharidase lactase breaks down lactose (milk sugar). This enzyme is present in infants, but many adults lack the enzyme and are lactose-intolerant. In these people, lactose in the small intestine cannot be digested and is metabolized by bacteria, producing intestinal discomfort.

Question 14

Parietal Cell of Stomach

Answer 14

The parietal cell of the stomach secretes two substances: intrinsic factor and HCl.

Question 15

Gastrin

Answer 15

Gastrin, produced by the G cells of the duodenum, primarily functions to stimulate HCl, histamine, and pepsinogen secretion as well as increase gastric blood flow.

Gastrin stimulates the parietal cells to produce a substance (HCl) that denatures proteins and activates digestive enzymes.

Question 16

Intrinsic Factor

Answer 16

Intrinsic Factor is a secretion of the parietal cells that facilitates the absorption of vitamin B₁₂ across the intestinal lining.

Question 17

Cholecystokinin

Answer 17

Cholecystokinin is produced and stored in the I cells of the duodenal and jejunal mucosa. It is involved in stimulation of pancreatic enzymes and somatostatin secretion as well as gallbladder contraction.

Question 18

Secretin

Answer 18

Secretin is synthesized and stored in the S cells of the upper intestine. It stimulates the secretion of bicarbonate-containing substances from the pancreas and inhibits gastric emptying and gastric acid production.

Question 19

Liver: Bile

Answer 19

Produces bile that is stored in the gallbladder before release into the small intestine.

Bile contains no enzymes; it emulsifies fats, breaking down large globules into small droplets. Emulsification of fats exposes a greater surface area of the fat to the action of pancreatic lipase.

In the absence of bile, fats cannot be digested.

Question 20

Liver’s Functions

Answer 20

The liver’s functions also include storage of glycogen, conversion of ammonia to urea, protein synthesis, detoxification, and cholesterol metabolism.

Question 21

Pancreas

Answer 21

Produces enzymes such as amylase for carbohydrate digestion, trypsin for protein digestion, and lipase for fat digestion.

The pancreas secretes a bicarbonate-rich juice that neutralizes the acidic chyme arriving from the stomach. The pancreatic enzymes operate optimally at this higher pH.

Question 22

Large Intestine

Answer 22

Approximately 1.5m long and functions in the absorption of salts and water not already absorbed by small intestine.

The rectum provides for transient storage of feces before elimination through the anus.