DIgestive system lecture exam

What is the alimentary canal?

continuous muscular tube that food passes through; includes mouth → pharynx → esophagus → stomach → small intestine → large intestine → anus.

Function of the mouth?

Ingestion, mastication, begins carbohydrate digestion, forms bolus.

Function of the pharynx?

Passageway for food from the mouth to esophagus ; involved in swallowing (deglutition).

Function of the esophagus?

Moves bolus to stomach via peristalsis.

Function of the stomach?

Mechanical mixing + chemical digestion of proteins; converts bolus → chyme.

Function of the small intestine?

Main site of digestion AND absorption.

Function of the large intestine?

Absorbs water/electrolytes, forms feces.

What are accessory digestive organs?

Organs that assist digestion but food does not pass through them.

list of accessory digestive organs

includes the liver, pancreas, and gallbladder.

Salivary glands function?

Produce saliva (amylase for carbs, mucus for lubrication).

Liver function?

Produces bile for fat emulsification

Gallbladder function?

Stores and concentrates bile.

Pancreas function?

Produces digestive enzymes + bicarbonate.

what is bicarbonate

A chemical compound that acts as a buffer to neutralize stomach acid in the small intestine, aiding digestion.

Ingestion

Taking in food (mouth)

Propulsion

Movement of food (swallowing + peristalsis)

Deglutition

The process of swallowing, which involves the voluntary and involuntary movements that transport food from the mouth to the esophagus.

Mechanical digestion

Physical breakdown (chewing, churning)

Chemical digestion

Enzymatic breakdown of food

Absorption

Nutrients enter blood/lymph (small intestine)

Defecation

Elimination of waste (anus)

digestive process in order'

ingestion > mechanical digestion > chemical digestion > absorption > defecation.

Peristalsis

Wave-like contractions that move food forward

Segmentation

Back-and-forth mixing movement (mainly small intestine)

Visceral peritoneum

Covers organs

Parietal peritoneum

Lines the abdominal wall

Peritoneal cavity

Space with serous fluid

Mesentery

double layer of peritoneum that anchors the abdominal organs to the body wall and also carries blood vessels, nerves, and lymphatics to those organs

Intraperitoneal organs

organs that are fully covered by peritoneum- serous membrane-(e.g., stomach)

Retroperitoneal organs

Behind peritoneum (e.g., pancreas)

mastication

The process of chewing food to break it down into smaller pieces, which aids in digestion.

Mucosa

Epithelium + lamina propria + muscularis mucosae ; The innermost layer of the gastrointestinal tract that secretes mucus, enzymes, and some hormones, facilitating digestion and absorption.

lamina propria

A layer of connective tissue found beneath the epithelium in mucosal membranes, providing support and housing blood vessels, nerves, and immune cells.

muscularis mucosae

A thin layer of muscle located within the mucosa of the gastrointestinal tract, involved in the local movement of the mucosal layer for better digestion and absorption.

Submucosa

connective tissue located beneath the mucosa in the gastrointestinal tract, containing blood vessels, lymphatics, and nerve plexuses, and providing structural support to the gut wall.

Muscularis externa

smooth muscle in the gastrointestinal tract responsible for peristalsis and segmentation. It consists of inner circular and outer longitudinal muscle layers, facilitating food movement through the digestive system.

Serosa

The outermost layer of the gastrointestinal tract, composed of connective tissue and epithelium, providing protection and support while anchoring the digestive organs in the abdominal cavity.

What digestion occurs in the mouth?

Mechanical + chemical digestion of carbohydrates

Which nutrient starts digestion in mouth?

Carbohydrates (via salivary amylase)

Three major salivary glands?

Parotid, submandibular, sublingual

parotid salivary gland

located near the ear, responsible for producing saliva that contains enzymes to initiate digestion.

submandibular salivary gland

located beneath the jaw, it produces saliva that aids in digestion and lubricates food.

sublingual salivary gland

located under the tongue, it secretes saliva that helps with digestion and maintains oral moisture.

how many teeth do adults have

32

how many teeth do babes have

20

Incisors

are the front teeth primarily used for cutting food. Adults typically have eight

Canines

are pointed teeth located next to the incisors, primarily used for tearing food. Adults typically have four

Premolars

are flat-topped teeth located behind the canines, used for crushing and grinding food. Adults typically have eight

Molars

are large, flat teeth located at the back of the mouth, used for grinding and chewing food. Adults typically have twelve, including wisdom teeth.

Enamel

is the hard, outer layer of a tooth that protects it from decay and damage. It is composed mostly of minerals, primarily hydroxyapatite.

Dentin

is the dense, inner layer of a tooth located beneath the enamel and cementum. It contains microscopic tubules and provides structural support, sensitivity, and strength.

pulp

is the soft tissue inside a tooth that contains nerves and blood vessels. It plays a crucial role in the tooth's vitality and nourishment.

Unique stomach features?

3 muscle layers

Gastric pits/glands

Rugae (folds)

Pylorus

Region connecting stomach to small intestine that regulates passage of food and digestive secretions.

Pyloric sphincter

Controls chyme release into duodenum and prevents backflow into the stomach.

Chief cells

Specialized cells in the gastric glands of the stomach that secrete pepsinogen

pepsinogen

Inactive precursor of pepsin, activated by stomach acid.

Parietal cells

Specialized cells in the gastric mucosa that secrete hydrochloric acid and intrinsic factor, essential for vitamin B12 absorption.

what is HCI and intrinsic factor

a strong acid produced in the stomach that aids in digestion and creates an acidic environment ; is a glycoprotein secreted by parietal cells that is crucial for the absorption of vitamin B12 in the intestines.

Mucous cells

Specialized cells in the gastric epithelium that secrete mucus, which protects the stomach lining from acid and digestive enzymes.

Why Stomach Doesn’t Digest Itself

Mucus barrier + tight junctions + rapid cell turnover prevent gastric acid from harming tissues.

Cephalic phase

Sight/smell → brain stimulates stomach to prepare for digestion by increasing gastric juice production and gastric motility.

Gastric phase

Food in stomach → stretch + chemicals stimulate gastric secretions, enhancing digestion.

Intestinal phase

Small intestine slows stomach emptying and further regulates gastric secretions as nutrients are absorbed.

Alkaline tide

Increase in blood pH after eating due to HCl production by the stomach, leading to bicarbonate release into the bloodstream.

Small Intestine Divisions

Duodenum, jejunum, ileum

Duodenum

The first section of the small intestine where most chemical digestion occurs and nutrients begin to be absorbed.

jejunum

The middle section of the small intestine where the majority of nutrient absorption takes place, following the duodenum.

ileum

The final section of the small intestine where absorption of nutrients and bile salts occurs before the contents pass into the large intestine.

Circular folds

Folds of mucosa in the small intestine that increase surface area for absorption and slow down the passage of food.

Villi

Small, finger-like projections on the circular folds of the small intestine that significantly enhance nutrient absorption by increasing the surface area.

Microvilli

Tiny projections on the surface of villi in the small intestine that further increase the surface area for absorption, aiding in the efficient uptake of nutrients.

Hepatic Portal Vein

Carries nutrient-rich blood from GI tract → liver for processing and detoxification.

Liver Unit

the functional structure of the liver, consisting of hepatocytes arranged in plates around a central vein. It plays a crucial role in metabolic processes, detoxification, and synthesis of essential proteins.

Lobule

the structural and functional unit of the liver, comprising a collection of hepatocytes, sinusoids, and bile ducts organized around a central vein.

Portal triad components?

Hepatic artery, hepatic portal vein, bile duct

What is bile?

Fluid that emulsifies fats and aids in digestion. It is produced by the liver and stored in the gallbladder.

Gallbladder

A small organ that stores bile produced by the liver, releasing it into the small intestine to aid in fat digestion.

Pancreas

A gland located behind the stomach that produces digestive enzymes and hormones, including insulin and glucagon, essential for regulating blood sugar levels.

Pancreatic juice contents?

Amylase, lipase, proteases, nucleases

Large Intestine Five subdivisions?

Cecum, colon, rectum, anal canal, appendix

Colon regions?

Ascending, transverse, descending, sigmoid

Bacterial Flora function

Produce vitamins (K, B), ferment waste and help maintain gut health.

Enzymatic Hydrolysis

Breaking bonds using water + enzymes

Carbs broken down into

Monosaccharides such as glucose, fructose, and galactose.

Proteins broken down into

amino acids such as leucine, alanine, and valine.

Lipids broken down into

fatty acids and glycerol.

Nucleic acids broken down into what nitrogenous bases

Nucleotides such as adenine, guanine, cytosine, and thymine.

Carbs absorption

Active transport → broken down into simple sugars > absorbed into blood and transported to the liver.

Proteins absorption

Active transport →broken down into amino acids > processed into blood and transported to the liver.

Lipids absorption as fatty acids and monoglycerides.

Passive diffusion → blood and transported to the liver. Enter lacteals → lymph

Nucleic acids absorption

Active transport → blood and transported to the liver. Absorbed as bases/sugars

Cecum

First part of the large intestine, where fermentation of indigestible food occurs. It's a pouch-like structure that connects the ileum to the colon.

colon

The final part of the large intestine where water is reabsorbed and solid waste is formed.

rectum

The last section of the large intestine that stores feces before it is expelled from the body.

anal canal

The short tube that connects the rectum to the anus, allowing for the passage of feces out of the body.

appendix

A small, tube-like structure attached to the cecum of the large intestine, often thought to play a role in immune function.

Ascending colon

The portion of the large intestine that extends upward from the cecum to the transverse colon, absorbing water and salts from the material that has not yet been digested.

transverse colon

The section of the large intestine that crosses the abdomen from the ascending colon to the descending colon, playing a key role in the absorption of water and electrolytes.