AP II: Unit 3

What is the definition of digestion?

The breakdown of large food particles into small nutrients that can be absorbed and used for energy.

List in order from mouth to anus the path of food.

Mouth, Pharynx, Esophagus, Stomach, Small intestine, Large intestine, Anus

When does it become a bolus?

Formed in the mouth (chewing + saliva)

When does it become a Chyme?

Formed in stomach (acidic slurry)

When does it become Feces?

Formed in the large intestines.

What are the organs of the alimentary canal?

Mouth, Pharynx, Esophagus, Stomach, Small intestine, Large intestine, Anus

What are the accessory organs of the digestive system?

Salivary glands, Liver, Gallbladder, Pancreas, Teeth and tongue.

What is the difference between the alimentary organs and accessory organs?

Alimentary organs HOLD food; Accessory organs assist in digestion but do NOT hold food.

Define Ingestion and describe where it occurs.

Ingestion is the taking in of food, and it occurs in the mouth.

Define Mechanical digestion and describe where it occurs.

Mechanical digestion is the physical breakdown of food (chewing, churning, segmentation). Occurs in the mouth, stomach, and small intestine.

Define Propulsion and describe where it occurs.

Propulsion is the movement of food (swallowing + peristalsis). Occurs in the entire GI tract.

Define Digestion and describe where it occurs.

Digestion is the chemical breakdown of nutrients. Occurs in the mouth, stomach, and intestines.

Define Absorption and describe where it occurs.

Absorption is the bringing of nutrients into blood/lymph. Occurs in stomach and intestines.

Define Defecation and describe where it occurs.

Defecation is the elimination of waste. Occurs in the large intestine.

Define mechanical digestion.

Physical breakdown of food; chewing, churning, segmentation. (ex. mouth)

Define chemical digestion.

Enzymes breaking down food particles (ex. stomach acid)

What is peristalsis? Where does it occur?

Peristalsis describes wave-like contractions that move food forward. Caused by muscularis externa (smooth muscle).

What layer of the alimentary canal is responsible for peristalsis?

The muscularis externa

What are sphincters?

Circular muscle valves that control movement in peristalsis.

What is segmentation?

Segmentation describes the back-and-forth mixing movement that breaks down chyme mechanically.

What is the peritoneum?

Serous membrane around digestive organs; fluid reduces friction.

Which layers of the peritoneum lines the organs / body wall?

Visceral peritoneum: covers organs.

Parietal peritoneum: lines body wall.

How is the peritoneum related to the serosa layer of the Alimentary canal?

The serosa The serosa layer of the alimentary canal is the visceral layer of the peritoneum.

What is peritonitis and how does a burst appendix cause it?

The inflammation of the peritoneum; burst appendix releases bacteria into the peritoneal cavity, leading to infection and inflammation.

What are the mesenteries, and what are their main functions? (Specific Examples)

Extensions of the peritoneum that anchor digestive organs to the body wall; serve as pathway for blood vessels, nerves, and lymphatics.

Dorsal mesentery (posterior) & Ventral mesentery (anterior).

Define splanchnic circulation.

The blood flow to digestive organs, including the hepatic portal system which carries nutrient-rich blood to the liver.

What is the hepatic portal cirrculation.

The system that carries nutrient-rich blood from the digestive organs to the liver for processing.

From where does the hepatic portal circulation drain blood? To where does it drain?

Drains blood from digestive organs; delivers it to the liver for processing before returning to the heart.

What is special about the blood in the veins of the hepatic portal circulation?

It is nutrient-rich; nutrients absorbed from digestive organs.

What are the four layers of the alimentary canal?

Mucosa, submucosa, muscularis externa, serosa.

What cells does the Mucosa layer of the alimentary canal contain?

Epithelial cells; connective tissue cells (lamina propria); smooth muscle cells (muscularis mucosae).

What cells does the Submucosa layer of the alimentary canal contain?

Areolar connective tissue cells; cells associated with blood vessels, glands, nerves, and lymphoid tissue.

What cells does the Muscularis externa layer of the alimentary canal contain?

Smooth muscle cells

What cells does the serosa layer of the alimentary canal contain?

Simple squamous epithelial cells and areolar connective tissue cells

What is the alimentary canal?

A tube that goes from the mouth to the anus

How do the layers of the alimentary canal change in the esophagus? What difference does this reflect.

Stratified squamous; features protective lining. Designed to withstand abrasion from swallowed food particles.

How do the layers of the alimentary canal change in the stomach? What difference does this reflect?

Simple columnar; features gastric pits and extra muscle layer. Designed for churning (extra muscle layer) and chemical digestion (cells secrete mucus and gastric juices).

How do the layers of the alimentary canal change in the small intestine? What difference does this reflect?

Simple columnar epithelium; features villi and microvilli. Designed for digestion and absorption, microvilli increase surface area to maximize.

How do the layers of the alimentary canal change in the large intestine? What difference does this reflect?

Simple columnar (mostly); stratified squamous (anal canal). Features goblet cells; designed for water absorption and waste movement.

In which layers if mucosa-associated lymphatic tissue (MALT) found?

In the lamina propria of the mucosa layer.

What is the function of the mucosa layer of the alimentary canal?

To secrete mucus, enzymes, and hormones; absorbs nutrients; protects against pathogens.

What is the function of the submucosa layer of the alimentary canal?

Supports the mucosa and provides blood vessels, lymphatics, glands, and nerves.

What is the function of the muscularis externa layer of the alimentary canal?

Moves food through the tract via peristalsis and mixes it through segmentation.

What is the function of the serosa layer of the alimentary canal?

Reduces friction and allows organs to move smoothly with the abdominal cavity.

Name 3 chemical and 1 mechanical stimuli that provide intrinsic control of the GI tract

pH, nutrients, and solutes; stretch

Name 3 hormones that regulate GI tract activity.

Gastrin, cholecystokinin (CCK), and secretin.

Where is Gastrin secreted? How does it act?

Stomach; stimulates acid (HCL) secretion in the stomach, increases contraction of small intestine, and promotes defecation in the large intestine.

Where is cholecystokinin (CCK) secreted? How does it act?

Duodenum (small intestine); inhibits stomach secretion and stimulates the liver, pancreas, and gallbladder to release digestive (especially for fat digestion).

Where is secretin secreted? How does it act?

Duodenum (small intestine); inhibits stomach secretion and stimulates the pancreas and liver to release alkaline fluids to neutralize acidic chyme.

Which branch of the ANS stimulates digestion and which inhibits digestive activities?

Parasympathetic stimulates digestion; sympathetic inhibits digestive activities.

Compare short reflexes of the enteric nervous system to long reflexes

Short: controlled within the ENS; triggered by local GI stimuli; immediate responses.

Long: CNS and ENS; triggered by external stimuli; sends signals back to regulate digestion.

What is the enteric nervous system?

The network or nerves embedded in the walls of the GI tract that control digestion.

Which subdivisions of the nervous system provide inputs for long reflexes?

The autonomic nervous system; sympathetic and parasympathetic divisions.

What digestive processes occur in the mouth and which accessory organs are necessary for these processes?

Ingestion, mechanical breakdown (chewing), propulsion (swallowing), and the start of chemical digestion (carbs and fat); teeth, tongue, and salivary glands.

What is the lingual frenulum?

A fold of tissues that anchors the tongue to the floor of the oral cavity.

Which epithelial tissue type lines the mouth?

The mouth is lined with stratified squamous epithelium.

List the three salivary glands.

Parotid, submandibular, and sublingual glands.

What is the function of saliva?

Dissolves food for taste, moistens and compacts food into a bolus, and begins chemical digestion (especially of starch).

What are the components of saliva? pH?

Water (97-99.5%), electrolytes, enzymes, mucin, metabolic wastes, and antimicrobial substances; slightly acidic.

How many baby teeth are there?

There are 20 baby (deciduous) teeth.

What is heartburn?

Burning sensation caused by stomach acid flowing back into the esophagus when the cardiac sphincter fails to close properly.

What epithelial tissue type lines the pharynx and esophagus?

stratified squamous

what is the structure of a tooth?

Crown: visible part above gum, covered by enamel; neck: region between crown and root at the gum line; root: embedded in jawbone.

what are the internal structures of a tooth?

Enamel: hard outer covering; dentin: bone-like layer beneath enamel; pulp cavity: contains blood vessels and nerves; root canal: extension of pulp into the root.

What anchors a tooth into its socket?

Periodontal ligament.

What is the function of each type of tooth?

Incisors: cut or snip; canines: tear or pierce; premolars: grind and crush; molars: grind food most thoruoghly.

What are wisdom teeth?

The third molars; erupt between ages 17-25, not in all individuals.

What is chyme?

An acidic, semi-liquid mixture of partially digested food formed in the stomach.

What does the pyloric valve do? (stomach)

Controls the release of chyme from the stomach into the small intestine; prevents backflow.

What digestive actions occur in the stomach? Can anything be absorbed here?

Mechanical breakdown (churning), chemical digestion (pepsin and gastric lipase), Propulsion (chyme into small intestine); limited absorption; mainly alcohol and aspirin to blood.

What are the components of gastric juice? pH?

HCL, pepsinogen, gastric lipase, mucus, and intrinsic factor; highly acidic (around 1-2).

What are the cell types found in gastric pits?

Lined with mucous, parietal, chief, and enteroendocrine cells.

What is secreted by mucous cells in gastric pits?

Cloudy, alkaline mucus to protect surface epithelium.

What is secreted by parietal cells in gastric pits?

HCL and intrinsic factor (required for B12 absorption).

What is secreted by chief cells in gastric pits?

Pepsinogen (immature form of pepsin) and lipases.

What is secreted by enteroendocrine cells in gastric pits?

paracrines, hormones, and gastrin (stimulates HCl secretion)