Chap017

Digestion

The mechanical and chemical breakdown of foods into forms that cell membranes can absorb.

Mechanical digestion

Breaks down large pieces of food into smaller ones, but does not change chemical composition.

Chemical digestion

Uses enzymes to break down food particles, by changing them into simpler chemicals.

Digestive System

Organs of the digestive system carry out mechanical and chemical digestion, as well as ingestion, propulsion, absorption, and defecation.

Alimentary canal

The food passageway consisting of organs that extend from the mouth to the anus.

Accessory organs

Organs that empty secretions into the alimentary canal, such as salivary glands, liver, gallbladder, and pancreas.

Mucosa

The innermost layer of the alimentary canal wall, composed of mucous membrane that absorbs dietary nutrients, secretes mucus and enzymes.

Submucosa

The connective tissue layer of the alimentary canal wall that nourishes cells and transports absorbed food molecules.

Muscularis (externa)

The muscle tissue layer of the alimentary canal wall that moves the tube and food materials.

Serosa

The outermost layer of the alimentary canal wall that provides protection and eliminates friction with serous fluid.

Peristalsis

Ring of contraction that progresses down the tube and propels food particles down the tract in a wavelike motion.

Submucosal plexus

Controls secretions in the alimentary canal.

Myenteric plexus

Controls gastrointestinal motility in the alimentary canal.

Parasympathetic impulses

Increase activities of the digestive system (secretion and motility).

Sympathetic impulses

Inhibit digestive actions (secretion and motility).

Enteroendocrine cells

Found in the stomach and small intestine, secrete hormones to regulate GI organs and processes.

Mastication

Mechanical breakdown of solid particles in the mouth, mixing them with saliva.1. Cheeks:Form the lateral walls of the mouth, contain muscles for facial expression and chewing, have an inner lining of stratified squamous epithelium (moist)

Lips

Highly mobile structures that surround the mouth opening, sensory receptors judge temperature and texture of food, boundary between skin and mucous membrane inside mouth

Tongue

Thick, muscular organ that occupies the floor of the mouth, lingual frenulum connects tongue to floor of mouth, papillae are projections that move food and contain taste buds, lingual tonsils are lymphatic tissue masses on the root of the tongue

Palate

Forms the roof of the oral cavity, consists of an anterior portion (hard palate) and a posterior portion (soft palate), palatine tonsils are lymphatic masses on the sides of the tongue, pharyngeal tonsils (adenoids) are masses of lymphatic tissue in the posterior wall of the pharynx

Teeth

Hardest structures in the body, not part of the skeletal system, human dentition is that of an omnivore, primary (deciduous) teeth:20, secondary (permanent) teeth:32, types of teeth include central incisors, lateral incisors, canines (cuspids), first premolars (bicuspids), first molars, second molars, third molars, teeth consist of crown and root, enamel covers the crown, dentin makes up most of the tooth and surrounds the pulp cavity, periodontal ligament holds the root in place along with cementum

Dental Caries

Cavities within the enamel of a tooth, formed when sticky foods lodge between teeth or in crevices of molars, bacteria on teeth metabolize sugars, acidic by-products destroy enamel and dentin1. Salivary glands:Glands in the mouth that secrete saliva.

Saliva

Fluid secreted by the salivary glands that moistens food particles, dissolves food, and contains enzymes for digestion.

Serous cells

Cells in the salivary glands that produce a watery fluid containing salivary amylase, a digestive enzyme.

Mucous cells

Cells in the salivary glands that secrete mucus, which binds food particles and lubricates food while swallowing.

Parotid glands

The largest pair of salivary glands that secrete serous saliva with amylase.

Submandibular glands

Salivary glands located in the floor of the mouth that secrete both serous and mucous fluid.

Sublingual glands

Salivary glands located under the tongue that mainly secrete mucous fluid.

Pharynx

The cavity posterior to the mouth that extends from the nasal cavity to the esophagus.

Esophagus

The tubular organ that extends from the pharynx to the stomach and serves as a food passageway.

Swallowing

The process of moving food from the mouth to the stomach through the pharynx and esophagus.

Bolus

A mass of chewed food mixed with saliva.

Peristalsis

Waves of muscular contractions that propel food through the esophagus.

Lower esophageal (cardiac) sphincter

A muscular ring that regulates the passage of food from the esophagus into the stomach and prevents regurgitation.1. Stomach:J-shaped, pouch-like organ, about 25 to 30 centimeters long, located in the upper-left portion of the abdominal cavity.

Rugae

Folds of mucosa and submucosa in the stomach that allow for distention.

Cardia

Region near the opening to the esophagus, contains the lower esophageal sphincter.

Fundus

Rounded area that rises above the cardia, serves as temporary food storage.

Body

Main portion of the stomach, located between the fundus and pylorus.

Pylorus

Distal portion of the stomach, closest to the small intestine.

Pyloric sphincter

Circular smooth muscle that controls gastric emptying.

Gastric juice

Mixture produced by gastric glands in the stomach, contains various components.

Pepsinogen

Inactive form of pepsin, secreted by chief cells in the stomach.

Pepsin

Active enzyme that breaks down proteins into polypeptides, formed from pepsinogen in the presence of hydrochloric acid.

Gastric lipase

Fat-splitting enzyme found in small quantities in gastric juice, inhibited by low pH.

Hydrochloric acid

Produced by parietal cells in the stomach, converts pepsinogen into pepsin.

Mucus

Secreted by mucous cells in the stomach, provides lubrication and protects the stomach lining.

Intrinsic factor

Produced by parietal cells in the stomach, required for absorption of vitamin B12 in the small intestine.

Neural regulation

Sympathetic impulses decrease gastric activity, parasympathetic impulses increase gastric activity and promote release of histamine.

Hormonal regulation

Somatostatin inhibits hydrochloric acid secretion, gastrin increases gastric juice secretion, cholecystokinin (CCK) decreases gastric motility.

Cephalic phase

The sight, taste, smell, or thought of food triggers parasympathetic reflexes and secretion of gastric juice.

Gastric phase

Food in the stomach stimulates release of gastrin, which stimulates secretion of gastric juice.

Intestinal phase

Food entering the small intestine stimulates release of intestinal gastrin, which briefly promotes secretion of gastric juice.1. Gastric Absorption:The process by which the stomach absorbs certain substances such as water, salts, lipid-soluble drugs, and alcohol.

Pepsin

A gastric enzyme that breaks down proteins in the stomach.

Small Intestine

The part of the digestive system where most nutrients are absorbed.

Chyme

A semifluid paste produced by the mixing of food in the stomach with gastric juice.

Peristaltic Waves

Waves of muscular contractions that push chyme toward the pylorus of the stomach.

Pyloric Sphincter

A muscular ring that controls the flow of chyme from the stomach to the small intestine.

Vomiting

The reflex that empties the stomach in the reverse direction, often caused by certain drugs, toxins, overstretching of the stomach, or motion sickness.

Vomiting Center

The part of the brain, specifically the medulla oblongata, that controls the vomiting reflex.

Enterogastric Reflex

A reflex that slows stomach emptying and intestinal filling when the duodenum is filled with chyme.

Heartburn

A condition characterized by a burning sensation in the chest, caused by the reflux of stomach contents into the esophagus.

Pancreas

An organ that functions as both an endocrine gland, secreting insulin and glucagon, and an exocrine gland, secreting pancreatic juice for digestion.

Pancreatic Juice

A digestive fluid secreted by the pancreas that contains enzymes for digesting carbohydrates, fats, proteins, and nucleic acids.

Secretin

A hormone that stimulates the pancreas to release pancreatic juice high in bicarbonate ions.

CCK (Cholecystokinin)

A hormone that stimulates the pancreas to release pancreatic juice high in enzymes.

Regulation of Pancreatic Secretion

The control of pancreatic juice release through hormonal and nervous system regulation.1. Liver:The largest internal organ located in the upper-right abdominal quadrant, just beneath the diaphragm.

Gallbladder

A small organ located near the liver that stores and concentrates bile.

Lobes

The liver has four lobes - right lobe, left lobe, quadrate lobe, and caudate lobe.

Lobules

Functional units of the liver that contain hepatocytes (liver cells) and hepatic sinusoids (channels for blood).

Hepatic portal vein

Brings absorbed nutrients to the sinusoids of the liver.

Hepatic artery

Brings oxygen-rich blood to the liver, which mixes with oxygen-poor blood from the portal vein.

Bile

A fluid produced by the liver that aids in the digestion and absorption of fats.

Glycogen

A polysaccharide that is stored in the liver and converted into glucose when needed.

Urea

A waste product formed in the liver from the breakdown of proteins.

Plasma proteins

Proteins synthesized by the liver that play various roles in the body.

Detoxification

The process of removing toxins from the blood, which is one of the liver's major functions.

Jaundice

A condition characterized by yellowing of the skin, eye sclerae, and mucous membranes, often caused by liver diseases or blockage of bile ducts.1. Hepatitis:Inflammation of the liver

Chronic

Long-lasting or persistent

Acute

Short-term or sudden onset

Virus

Infectious agent that can cause disease

Carriers

Individuals who can transmit a disease without showing symptoms

Blood-borne

Transmitted through contact with infected blood

Feces

Waste material from the digestive system

Antibiotics

Medications used to treat bacterial infections

Hepatitis A

Type of hepatitis transmitted through contact with contaminated food or objects

Hepatitis B

Type of hepatitis transmitted through contact with body fluids

Hepatitis C

Type of hepatitis transmitted through blood contact

Gallbladder

Pear-shaped sac found on the inferior surface of the liver

Cystic duct

Duct that serves as the entry/exit point of the gallbladder

Common bile duct

Duct formed by the merger of the cystic duct and common hepatic duct

Bile

Fluid produced by the liver and stored in the gallbladder, aids in digestion

Duodenum

First part of the small intestine, receives bile from the gallbladder

Gallstones

Solid crystals formed in the gallbladder due to the precipitation of cholesterol

Cholecystokinin

Hormone that stimulates the contraction of the gallbladder and release of bile

Bile salts

Substances in bile that aid in the digestion and absorption of fats

Micelles

Structures formed by bile salts to enhance the absorption of fatty acids and cholesterol

Cholecystectomy

Surgical removal of the gallbladder

Endoscopy

Procedure to visualize and treat conditions within the body using a flexible tube with a camera

Hormones

Chemical messengers produced by various organs that regulate bodily functions

Gastrin

Hormone produced by gastric cells that increases the secretory activity of gastric glands