(AnaPhy) Digestive System — Lecture

Ingestion

The consumption of solid or liquid food.

Mastication

Chewing, which begins the mechanical breakdown of food, increasing its surface area for enzymatic action.

Propulsion

Moves food along the digestive tract via muscular contractions, primarily peristalsis (wave-like contractions)

Mixing

Involves segmental contractions that churn and mix food with digestive secretions, aiding in digestion and absorption.

Digestion

The mechanical and chemical breakdown of food.

Mechanical digestion

involves physical breakdown (e.g., chewing, churning) that increases surface area.

Chemical digestion

involves enzymatic hydrolysis of large molecules (carbohydrates, lipids, proteins, nucleic acids) into smaller, absorbable subunits.

Secretion

involves the release of enzymes, acids, buffers, and other substances by digestive glands and cells to aid in digestion.

Absorption

The transport of digested nutrients (monosaccharides, amino acids, fatty acids, glycerol, vitamins, minerals) from the digestive tract lumen across the epithelial lining into the blood or lymphatic system.

Elimination

The removal of undigested material, cellular debris, and metabolic waste products as feces through the process of defecation.

Mucosa

The innermost layer, responsible for secretion of mucus, lining the lumen.

Lamina propria

Loose connective tissue containing blood vessels, lymphatic vessels, and immune cells (mucosa-associated lymphoid tissue, or MALT).

Muscularis mucosae

A thin layer of smooth muscle responsible for local movements of the mucosa (e.g., to increase surface area).

Submucosa

• A layer of dense irregular connective tissue.

• Contains larger blood vessels, lymphatic vessels, and nerve plexuses (submucosal plexus, part of the enteric nervous system) that regulate digestive secretions and blood flow.

• May contain glands that secrete substances into the lumen.

Serosa (Visceral peritoneum)

A serous membrane covering the portions of the digestive tract within the abdominal cavity; reduces friction.

Adventitia

Dense fibrous connective tissue that binds portions of the digestive tract outside the abdominal cavity (e.g., esophagus) to surrounding tissues.

Parietal peritoneum

Lines the inner surface of the abdominal wall.

Hard palate

The anterior portion, formed by the maxillae and palatine bones; rigid structure aids in chewing.

Soft palate

The posterior portion, composed of skeletal muscle and connective tissue; closes off the nasopharynx during swallowing.

Uvula

A cone-shaped projection of the soft palate; helps to close off the nasopharynx during swallowing.

Chyme

The semifluid paste of partly digested food and digestive secretions that is formed in the stomach and passed into the small intestine.

32 Teeth

Normal adult mouth has…

Salivary amylase

Chemical in saliva that begins the digestion of carbohydrates.

Lingual lipase

Chemical in saliva that begins the digestion of lipids.

Parotid glands

Large serous glands located anterior to each ear between the masseter muscle and the skin; secrete primarily serous fluid containing amylase; mumps affects these glands.

Submandibular glands

Located along the inner surface of the mandible; produce a mixed secretion (more serous than mucous); secrete saliva into the oral cavity via ducts that open on either side of the frenulum of the tongue.

Sublingual gland

Located below the mucous membrane in the floor of the oral cavity, anterior to the submandibular glands; primarily secrete mucous secretions.

Nasopharynx

• Posterior to the nasal cavity; serves as an air passageway; contains the pharyngeal tonsils (adenoids).

• Opening to the eustachian tube

Oropharynx

Oropharynx: Posterior to the oral cavity; serves as a passageway for both food and air; contains the palatine tonsils.

Laryngopharynx

Inferior to the oropharynx, superior to the larynx; continuous with the esophagus.

Cardial (cardia) / Cardiac orifice

the opening where the esophagus connects to the stomach, specifically the cardia region. Surrounds the cardioesophageal sphincter; receives food from the esophagus.

Mucus

Secreted by mucous cells, protects the stomach lining from the acidic environment.

Hydrochloric acid (HCl)

Secreted by parietal cells, activates pepsinogen to pepsin and kills bacteria.

Pepsinogen

Inactive form of pepsin, secreted by chief cells; converted to active pepsin by HCl.

Intrinsic factor

Secreted by parietal cells, essential for the absorption of vitamin B12 in the small intestine.

Gastrin

Hormones released in the stomach, released by enteroendocrine cells

Pyloric sphincter

a muscular ring at the lower end of the stomach, acting as a valve to regulate the passage of partially digested food (chyme) from the stomach into the small intestine (duodenum).

Rugae

Large folds of the mucosa and submucosa in the stomach; allow the stomach to expand when filled with food.

Duodenum

The shortest part of the small intestine (10 inches); receives chyme from the stomach, digestive enzymes from the pancreas, and bile from the liver and gallbladder; most digestion occurs here.

Jejunum

The middle portion of the small intestine (3 feet); most nutrient absorption occurs here.

Ileum

The terminal portion (6 feet); absorbs vitamin B12 and bile salts; empties into the large intestine.

Villi

Fingerlike projections of the mucosa that extend into the intestinal lumen; increase surface area for absorption.

Microvilli

Tiny, hairlike projections of the plasma membrane of the absorptive epithelial cells; form the brush border; greatly increase surface area; contain brush border enzymes that complete the digestion of carbohydrates and proteins.

Large intestine

• Absorbs most of the remaining water, ions (e.g., sodium, chloride), and some vitamins from the undigested residue.

• Compacts and stores undigested material and waste as feces.

• Contains a large population of beneficial bacteria (gut flora) that synthesize some vitamins, ferment indigestible carbohydrates, and inhibit the growth of harmful bacteria.

Appendix

A worm-like appendage that hangs from the cecum; contains lymphoid tissue and may play a role in immunity; prone to inflammation

Cecum

The pouch-like first part of the large intestine; receives chyme from the ileum.

Rectum

Stores feces until defecation.

Pancreatic amylase

Secreted by the pancreas into the small intestine, continues the digestion of starch into disaccharides.

Trypsin

Secreted as trypsinogen (an inactive proenzyme); activated by enteropeptidase (a brush border enzyme); digests proteins into smaller peptides.

Chymotrypsin

Secreted as chymotrypsinogen (an inactive proenzyme); activated by trypsin; digests proteins into smaller peptides.

Carboxypeptidase

Removes amino acids from the carboxyl ends of peptides.

Pancreas

• Produces a wide spectrum of digestive enzymes that break down all categories of food

• Produces Insulin & Glucagon

Liver

• Largest gland in the body

• Digestive role is to produce bile

Buccal phase

• Voluntary

• Occurs in the mouth

• Food is formed into a bolus

• The bolus is forced into the pharynx by the tongue

Pharyngeal-esophageal phase

• Involuntary transport of the bolus by peristalsis

• Nasal and respiratory passageways are blocked

•  Peristalsis moves the bolus toward the stomach

• The cardioesophageal sphincter is opened when food presses against it

Type I alveolar cells

are one of the two main types of epithelial cells that line the alveoli in the lungs. They are the predominant cell type, making up about 95% of the alveolar surface area.