Digestive System (BIO201)

2 Types of Digestive System organs

1. Alimentary canal (GI tract) — mouth → pharynx → esophagus → stomach → small intestine → large intestine → anal canal.

2. Accessory organs — teeth, tongue, salivary glands, liver, gallbladder, pancreas. — teeth, tongue, salivary glands, liver, gallbladder, pancreas.

Name the 6 basic digestive processes.

• Ingestion

• Secretion (mucus, enzymes, acid, hormones)

• Propulsion (peristalsis)

• Digestion (mechanical + chemical)

• Absorption

• Defecation

Mechanical v.s. Chemical Digestion

• Mechanical: Physical breakdown (chewing, churning).

• Chemical: Enzymatic hydrolysis breaking chemical bonds.

How is digestive motility regulated?

• ANS long reflexes:

  • Sympathetic → inhibits digestion

  • Parasympathetic → stimulates digestion

• ENS short reflexes: Local control of secretion & motility (“second brain”).

Name & briefly describe the 4 tunics of the alimentary canal.

1. Mucosa — epithelium, lamina propria, muscularis mucosae

2. Submucosa — dense irregular CT, vessels, glands

3. Muscularis externa — inner circular + outer longitudinal

4. Serosa/Adventitia — outer CT layer

Saliva

• What

• Functions

What:

Functions

• Moistens, lubricates, cleans oral mucosa

• Contains lysozyme + antibodies

• Begins carbohydrate digestion via salivary amylase (“first digestive enzyme that ingested food encounters” )

• Dissolves food molecules for taste

• Helps form bolus

The 3 Phases of Swallowing

1. Voluntary phase — tongue pushes bolus

2. Pharyngeal phase — soft palate + epiglottis close pathways

3. Esophageal phase — peristaltic waves move bolus to stomach

Name the 5 anatomical regions of the stomach.

• Cardia — receives bolus

• Fundus — dome-shaped, stores food & gases

• Body — gastric glands

• Pyloric antrum — mixes food, releases hormones

• Pylorus — connects to duodenum; pyloric sphincter

What structural features increase absorption in the small intestine?

• Circular folds

• Villi

• Microvilli (brush border)

Pancreas - Location

• LUQ

• Retroperitoneal

• Extends from duodenum → spleen

What does the pancreas secrete and why?

• Digestive enzymes → break down lipids, carbs, proteins, nucleic acids

• Bicarbonate ions → neutralize acidic chyme

Pancreas — Hormonal Regulation

CCK

• Trigger → Stimulated by lipids & partially digested proteins in duodenum

• Effect → Stimulates acinar cells which ↑ digestive enzyme secretion

Secretin

• Trigger → Stimulated by acidic chyme (lipid composiiton) in duodenum

• Effect → Stimulates duct cells to ↑ bicarbonate secretion

Liver - Major Functions

1. Endocrine & exocrine secretion

2. Nutrient metabolism (carbs, proteins, lipids) (“glucose → glycogen” )

3. Detoxification - converts harmful chemicals into nontoxic substances

4. Bile production

Gallbladder — Function

• Stores, concentrates, and releases bile.

Name the 4 types of motility in digestive system

• Swallowing

• Churning

• Peristalsis (“rhythmic contractions of smooth muscle” )

• Defecation

How does the ANS regulate digestion?

• ANS (long reflexes):

  • Sympathetic → inhibits digestive processes

  • Parasympathetic → stimulates digestion

How does the ENS regulate digestion?

• Local, self‑contained “second brain”

• Controls secretion & motility independently of CNS

Describe the 3 components of mucosa.

• Epithelium (“simple columnar epithelium with copious goblet cells” )

• Lamina propria — vessels, glands, MALT

• Muscularis mucosae — smooth muscle that increases contact with lumen

Peritoneal Membrane

Which arteries supply the digestive organs?

• Celiac trunk

• Superior mesenteric artery (SMA)

  • Inferior mesenteric artery (IMA)
    Organs drain into hepatic portal vein → liver → hepatic veins → IVC

What are the three salivary glands and their secretion types?

• Parotid (25–30%) — serous

• Submandibular (65–70%) — serous + mucus

• Sublingual (5%) — mostly mucus

Parotid Gland — Location

Submandibular Gland — Location

Sublingual Gland — Location

What are the four major gastric cell types and their functions?

• Mucous neck cells — acidic mucus

• Parietal cells — HCl + intrinsic factor (“responsible for acidic pH of gastric juice” )

• Chief cells — pepsinogen → pepsin

• Enteroendocrine cells — hormones (e.g., gastrin)

What increases surface area in the small intestine?

• Circular folds

• Villi

• Microvilli (brush border)

What are the three types of teeth and their functions?

• Incisors — cutting

• Canines — ripping/tearing

• Molars — grinding

Deciduous Teeth

• What

• How many do we have?

Permanent Teeth

• What

• How many do we have?

Tongue — Structure

Tongue — Functions

• Mechanical digestion

• Propulsion (swallowing)

• Taste

Large Intestine — Structural Features

• Terminal portion of alimentary canal

• Simple columnar epithelium

• Muscularis arranged into ribbon‑like taeniae coli

• Contains abundant bacterial flora

Large Intestine — Functions

• Absorption of water, electrolytes, vitamins

• Propulsion

• Limited secretion

• Defecation

Small Intestine — Structural Features

• Long tube from stomach → large intestine

• Simple columnar epithelium

• Three fold types: circular folds → villi → microvilli

Small Intestine — Functions

• Chemical digestion

• Mechanical digestion

• Absorption

• Secretion

• Propulsion

Goblet Cells

• Location

• What do they secrete and why?

L:

F: Secretes alkaline mucus

• Protect epithelium from acidic chyme & digestive chemicals

What is the submucosa composed of and what does it contain?

• Dense irregular connective tissue

• Houses submucosal plexus (Meissner’s)

• Contains vessels, glands

Myenteric Plexus

• Other name

• Location

• Function

• Other name: Auerbach’s plexus

• L: Muscularis externa

• F:

Serosa v.s. Adventitia

Serosa = Visceral Peritoneum

• Simple squamous epithlium

• Loose CT

• L: inside peritoneal cavity

Adventitia

• Dense irregular CT

• L: outside peritoneal cavity

Which digestive organs are retroperitoneal?

• Pancreas

• Duodenum (parts)

• Rectum (parts)

Trace venous drainage of digestive organs.

Digestive organs → hepatic portal vein → liver → hepatic veins → IVC

What is the vagus nerve’s role in digestion?

• Major parasympathetic nerve

• Stimulates secretion & motility throughout GI tract

For each of the swallowing phases, state the part of nervous system its regulated by.

• Voluntary phase: cerebral cortex

• Pharyngeal phase: medulla oblongata

• Esophageal phase: ENS

What are the two stomach curvatures?

• Greater curvature — convex left

• Lesser curvature — concave right

Rugae

• What?

• Function?

• Folds in stomach mucosa

• Allow expansion when stomach fills

Where are gastric glands located?

Fundus of stomach

Body of stomach

T or F: "Fundus” is another name for the body of the stomach.

False.

• Fundus → most superior part of kidneys

• Body →

Pyloric Sphincer — Function

Controls emptying of chyme into duodenum

Stomach — Functions

• Stores food

• Begins protein digestion

• Mixes food with gastric secretions → chyme

• Regulates emptying into duodenum

What is chyme?

Substance produced by stomach turn chewed food into:

thick semi-liquid mixture of partially digested food + gastric secretions

Swallowed food travelling from esophagus to stomach is called a _____.

Swallowed food travelling from esophagus to stomach is called a bolus.

The 4 Gastric Gland Cell Types

• Mucous neck cells — acidic mucus

• Parietal cells — HCl + intrinsic factor

• Chief cells — pepsinogen → pepsin

• Enteroendocrine cells — hormones (gastrin)

Describe the 3 regions of the small intestine. (ask chatgpt)

Small Intestine — Location

Stomach — Location

Name the 3 anatomical features of small intestine that increase absorption