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What are the major functions of the digestive system?

Ingestion, secretion, mixing/propulsion, digestion, absorption, and defecation

. What is the gastrointestinal (GI) tract?

A continuous tube from the mouth to the anus, including the esophagus, stomach, and intestines

. What are accessory digestive organs?

Organs that aid digestion but are not part of the GI tube, such as teeth, tongue, and liver

. What is the definition of mechanical digestion?

The physical breakdown of food into smaller pieces, such as through chewing or churning

. Where does mechanical digestion primarily occur?

In the mouth (mastication) and the stomach (churning)

. What is the definition of chemical digestion?

The enzymatic breakdown of food molecules into their chemical building blocks

. Where does chemical digestion occur?

Throughout the GI tract, but primarily in the mouth, stomach, and small intestine

. What is the definition of peristalsis?

Alternating waves of contraction and relaxation of smooth muscle that move food through the GI tract

. Trace the pathway of ingested substances through the GI tract.

Mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus

. What are the four layers of the GI tract wall?

Mucosa, submucosa, muscularis, and serosa (or adventitia)

. What structures compose the mucosa layer?

(superficial) Epithelium, lamina propria, and muscularis mucosae (deep)

. What is the composition of the submucosa?

Areolar connective tissue containing blood vessels, lymphatic vessels, and the submucosal nerve plexus

. What is the composition of the muscularis (muscularis externa)?

Skeletal muscle in the upper tract and two layers of smooth muscle (circular and longitudinal) elsewhere

. What is the serosa?

The outermost layer consisting of areolar connective tissue and a simple squamous epithelium

. What is the definition of mastication?

The process of chewing food to increase its surface area for digestion

. What is the composition of saliva?

99.5% water, with solutes including ions, mucus, immunoglobulin A, lysozyme, and salivary amylase

. What are the major functions of saliva?

To moisten food, begin starch digestion, and provide antibacterial protection

. What is the general function of the esophagus?

To transport a bolus of food from the pharynx to the stomach via peristalsis

. What is the general function of the stomach?

To act as a mixing chamber and holding reservoir where mechanical and chemical digestion continue

. How many layers of muscle are in the stomach muscularis?

Three layers: outer longitudinal, middle circular, and inner oblique

. How does the stomach's inner oblique muscle layer relate to its function?

It allows the stomach to churn and vigorously mix food into chyme

. What is the function of parietal cells in the stomach?

They secrete hydrochloric acid (HCl) and intrinsic factor

. What is the function of chief cells in the stomach?

They secrete pepsinogen and gastric lipase

. What is the location and function of the inferior esophageal sphincter?

Located at the junction of the esophagus and stomach; it prevents reflux of stomach acid

. What is the location and function of the pyloric sphincter?

Located between the stomach and duodenum; it regulates the release of chyme into the small intestine

. What are the general functions of the small intestine?

Most chemical digestion and nearly all nutrient absorption occur here

. What are the three specific segments of the small intestine?

Duodenum, jejunum, and ileum

. What are circular folds (plicae circulares)?

Permanent ridges of the mucosa and submucosa that increase surface area and spiral the flow of chyme

. What are villi?

Fingerlike projections of the mucosa that increase surface area for absorption

. What are microvilli?

Microscopic projections on the apical surface of absorptive cells that form the brush border

. How do circular folds, villi, and microvilli relate to small intestine function?

They collectively increase surface area by about 600-fold to maximize absorption

. What is the function of intestinal glands (crypts of Lieberkuhn)?

They secrete intestinal juice and contain stem cells to renew the epithelium

. What is the function of lacteals?

Lymphatic capillaries in villi that absorb dietary lipids

. What are the specific segments of the large intestine?

Cecum, colon (ascending, transverse, descending, sigmoid), rectum, and anal canal

. What are the general functions of the large intestine?

Water and electrolyte absorption, vitamin production by bacteria, and formation/expulsion of feces

. List three major functions of the liver?

Bile production, nutrient metabolism, and detoxification of drugs or toxins

. What is a hepatic lobule?

The functional unit of the liver consisting of hepatocytes arranged around a central vein

. What is the function of hepatocytes?

To produce bile and perform metabolic functions

. What is the function of hepatic sinusoids?

Highly permeable blood capillaries where blood is processed by hepatocytes

. What are the two major sources of blood flow to the liver?

The hepatic artery (oxygenated) and the hepatic portal vein (nutrient-rich)

. Trace the flow of blood through the liver.

Hepatic artery/portal vein → sinusoids → central vein → hepatic veins → inferior vena cava

. What is the structure and function of the gallbladder?

A muscular sac on the ventral surface of the liver that stores and concentrates bile

. What is the structure and function of the pancreas?

A retroperitoneal gland that produces both endocrine hormones and exocrine digestive juices

. What is the function of pancreatic acini?

The exocrine portion that secretes digestive enzymes and bicarbonate-rich pancreatic juice

. What is the function of pancreatic islets (islets of Langerhans)?

The endocrine portion that secretes insulin and glucagon into the blood

. What is the function of the common hepatic duct?

To drain bile from the liver

. What is the function of the cystic duct?

To transport bile into and out of the gallbladder

. What forms the common bile duct?

The union of the common hepatic duct and the cystic duct

. What is the hepatopancreatic ampulla (ampulla of Vater)?

The site where the common bile duct and main pancreatic duct join

. What is the function of the hepatopancreatic sphincter (sphincter of Oddi)?

To regulate the entry of bile and pancreatic juice into the duodenum

. Trace the path of bile from the liver to the duodenum.

Hepatic ducts → common hepatic duct → common bile duct → hepatopancreatic ampulla → major duodenal papilla

. What is deglutition?

The act of swallowing

. How do the glottis and larynx prevent aspiration during deglutition?

The larynx moves upward and the epiglottis tips down to cover the glottis

. How does high chyme volume affect stomach motility?

It increases motility through the stretching of the stomach wall

. How does high acidity (low pH) in the duodenum affect stomach motility?

It inhibits stomach emptying (the enterogastric reflex) to allow for neutralization

. Describe the defecation reflex.

Distension of the rectum triggers parasympathetic signals that relax the internal anal sphincter and contract the rectal wall

. How does somatic innervation affect defecation?

It allows voluntary control over the external anal sphincter

. What is the source and substrate of salivary amylase?

Salivary glands; substrate is starch

. What is the source and substrate of pepsin?

Stomach (chief cells); substrate is proteins

. What is the source and substrate of pancreatic lipase?

Pancreas; substrate is triglycerides

. Where does the chemical digestion of carbohydrates begin?

In the mouth via salivary amylase

. Where does the chemical digestion of proteins begin?

In the stomach via pepsin

. Where does the chemical digestion of lipids primarily occur?

In the small intestine via pancreatic lipase and bile

. What is a zymogen?

An inactive precursor of an enzyme

. Why are zymogens important in chemical digestion?

They prevent enzymes from digesting the cells that produce them (e.g., pepsinogen prevents stomach self-digestion)

. How is hydrochloric acid (HCl) produced in the stomach?

By parietal cells using a proton pump (H+/K+ ATPase) and chloride channels

. What is the function of HCl in the stomach?

To denature proteins, kill microbes, and activate pepsinogen into pepsin

. What is emulsification?

The breakdown of large fat globules into smaller droplets by bile salts

. How do bile salts facilitate fat digestion?

They increase the surface area of lipids for lipase to act upon

. What is the role of the microbiome in digestion?

Bacteria ferment undigested carbs, produce vitamins (B and K), and inhibit pathogens

. Which structures facilitate monosaccharide (glucose, fructose, galactose, etc.) absorption?

Microvilli (brush border) of the small intestine

. What is the transport process for glucose and galactose absorption?

Secondary active transport with sodium ions (SGLT1)

. What is the transport process for amino acid absorption?

Active transport or secondary active transport with sodium

. How are fatty acids and monoglycerides absorbed?

They are packaged into micelles, diffuse into cells, and are reformed into chylomicrons

. What is bile salt recycling?

The reabsorption of bile salts in the ileum and their return to the liver via the portal vein

. Where does most water absorption occur in the GI tract?

The small intestine (about 90%)

. What is the enteric nervous system (ENS)?

The "brain of the gut," a semi-autonomous network of neurons in the GI wall

. What is the role of the parasympathetic nervous system in digestion?

It increases GI secretion and motility ("rest and digest")

. What is the role of the sympathetic nervous system in digestion?

It inhibits GI secretion and motility ("fight or flight")

. What is a short reflex in the digestive system?

A reflex mediated entirely by the enteric nervous system in response to local stimuli

. What is a long reflex in the digestive system?

A reflex involving the CNS and autonomic nerves in response to stimuli outside or inside the GI tract

. What happens during the cephalic phase of digestion?

The sight, smell, or thought of food triggers gastric secretion via the vagus nerve

. What triggers the gastric phase of digestion?

Stomach distension and the presence of proteins and high pH

. What is the effect of the intestinal phase?

It slows gastric emptying to ensure the duodenum can process the incoming chyme

. What is the source and action of gastrin?

Secreted by the enteroendocrine G-cells in stomach; it stimulates HCl secretion and gastric motility

. What is the stimulus for Cholecystokinin (CCK) release?

The presence of amino acids and fatty acids in the duodenum

. What are the actions of CCK?

Stimulates gallbladder contraction, pancreatic enzyme secretion, and inhibits gastric emptying

. What is the stimulus for secretin release?

Acidic chyme entering the duodenum

. What is the action of secretin?

Stimulates the secretion of bicarbonate-rich pancreatic juice and inhibits gastric acid secretion

. Common use for carbohydrates in the body?

Primary source of fuel for ATP production (glucose)

. Common use for fats in the body?

Energy storage, structural components of membranes, and precursor for steroid hormones

. Common use for proteins in the body?

Structural support, enzymes, hormones, and transport molecules

. What is the definition of metabolism?

The sum of all chemical reactions in the body

. What is anabolism?

Metabolic pathways that build larger molecules from smaller ones; requires energy

. What is catabolism?

Metabolic pathways that break down larger molecules into smaller ones; releases energy

. What is glycogenesis?

The synthesis of glycogen from glucose for storage in the liver and muscle

. What is glycogenolysis?

The breakdown of glycogen into glucose when blood sugar is low

. What is gluconeogenesis?

The synthesis of glucose from non-carbohydrate sources like amino acids or glycerol

. What is lipogenesis?

The synthesis of triglycerides from excess glucose or amino acids

. What is lipolysis?

The breakdown of triglycerides into glycerol and fatty acids for energy