A&P Quiz 8 (Ch 24 pt 3)

Stomach

enlarged segment of the digestive tract, primarily functions in storage and mixing chamber, located in left superior part of abdomen, shape and size vary from person to person and different times of day (amount of food, body posture)

4 Regions of Stomach

cardia

fundus

body

pylorus

Cardia

region of stomach where esophagus opens at the gastroesophageal opening surrounded by the lower esophageal (cardiac) sphincter

Fundus

region of stomach located to the left of the cardia and superior to the cardiac opening

Body

region of stomach, largest part that curves to the right creating the greater curvature and lesser curvature

Pylorus

region of stomach, funnel-shaped

includes pyloric antrum, pyloric canal, hypertrophic pyloric stenosis

Pyloric Antrum

wider part of the funnel opening toward the body of the stomach

Pyloric Canal

narrow part of the funnel opening the pyloric orifice (surrounded by the pyloric sphincter)

Hypertrophic Pylori Stenosis

thickening of the pyloric sphincter common in infants

Serosa of Stomach

visceral peritoneum, outermost tunic, outer layer of simple squamous epithelium, inner layer of connective tissue

Muscularis of Stomach

consists of three layers of smooth muscle, outer longitudinal layer, middle circular layer, inner oblique layer

Inner Oblique Layer of Stomach Smooth Muscle

unique to the stomach to help with mechanical breakdown of food

Submucosa & Mucosa of Stomach

large folds (rugae) when the stomach is empty

Stomach Epithelium

simple columnar epithelium, contains gastric pits, five types of cells

Gastric Pits

tubelike invaginations of the epithelium, serve as openings for gastric glands that secrete acid and other substances

5 Types of Stomach Epithelial Cells

surface mucous

mucous neck

parietal

chief

endocrine

Surface Mucous Cells

stomach epithelial cell, found on the surface around gastric pits, not part of gastric glands, protect the stomach wall from acid and digestive enzymes

Protective Functions of Surface Mucous Cells

produce alkaline mucus, tight junctions between the cells, rapidly replaced when damaged

Mucous Neck Cells

stomach epithelial cell, located near the openings of the glands, produce mucus

Parietal Cells

stomach epithelial cell, produces hydrochloric acid and intrinsic factor

Chief Cells

stomach epithelial cell, produce pepsinogen and gastric lipase

Pepsinogen

inactive enzyme that can break down proteins when activated, produced by chief cells in the stomach

Gastric Lipase

digest lipids, produced by chief cells in the stomach

Endocrine Cells

stomach epithelial cell, produce regulatory hormones and paracrine factors

3 Types of Endocrine Cells in Stomach

enterochromaffin-like

gastrin-containing

somatostatin-containing

Enterochromaffin-Like Cells

type of endocrine cell in stomach epithelium, produce histamine that stimulates parietal cells

Gastrin-Containing Cells

type of endocrine cell in stomach epithelium, secrete gastrin

Somatostatin-Containing Cells

type of endocrine cell in stomach epithelium, secrete somatostatin that inhibits gastrin and insulin secretion

Chyme

semifluid mixture of food and stomach secretions, mixed and stored in the stomach

4 Stomach Secretions

hydrochloric acid

intrinsic factor

mucus

digestive enzymes

2 Digestive Enzymes Secreted by Stomach

pepsinogen

gastric lipase

Hydrochloric Acid

stomach secretion, secreted by the parietal cells in the gastric glands of the pylorus, stomach pH is between 1-3, formed by proton pump that actively transports h+

4 Functions of HCl

kill bacteria that have been ingested

denatures many proteins

allows for activation and function of pepsin

inactivates salivary amylase stopping carbohydrate digestion

Intrinsic Factor

stomach secretion, secreted by parietal cells, glycoprotein that binds with vitamin B12 making it easier to absorb in the ileum, vitamin is needed for DNA synthesis which is important for red blood cell production

Pepsinogen

digestive enzyme secreted by stomach, secreted by chief cells, packaged in zymogen granules that are released by exocytosis, activated by hcl and previously formed pepsin molecules (conversion to pepsin) cleaves covalent bonds in proteins

Gastric Lipase

digestive enzyme secreted by stomach, secreted by chief cells, digests lipids

Mucus

stomach secretion, secreted by surface mucous cells and mucous neck cells, viscous alkaline mucus, covers the epithelial cells (1-1.5 mm thick), protects epithelial cells of the stomach from acidic chyme and pepsin, secretion increases when the wall of the stomach is irritated

Regulation of Stomach Secretion

2-3 L of gastric secretion produced daily, regulated by nervous and hormonal mechanisms

Neural Mechanisms of Stomach Secretion Regulation

reflexes regulated in the medulla oblongata, local reflexes integrated in the ens, influenced by higher brain centers

Chemical Messengers that Regulate Gastric Secretions

include hormones (gastrin, secretin, cholecystokinin)

paracrine chemical messenger (histamine)

Gastrin

gastrointestinal hormone, produced in stomach, increases gastric secretion, causes a minor increase in gastric motility

stimulated by distension, partially digested proteins, autonomic stimulation, ingestion of alcohol or caffeine

Secretin

gastrointestinal hormone, produced in duodenum, decreases gastric secretion, stimulates pancreatic and bile secretions high in hco3-, decreases gastric motility, stimulated by acidity of chyme

Cholecystokinin

gastrointestinal hormone, produced in duodenum, slightly decreases gastric secretion, stimulates pancreatic secretions high in digestive enzymes, causes contraction of the gallbladder and relaxation of the hepatopancreatic ampullar sphincter, strongly decreases gastric motility, stimulated by fatty acids and peptides

3 Phases of Stomach Secretion

cephalic phase

gastric phase

intestinal phase

Cephalic Phase of Stomach Secretion

“get start” phase, stomach secretions increase in anticipation of incoming food

Gastric Phase of Stomach Secretion

“go for it” phase, when most of the stimulation of secretion occurs

Intestinal Phase of Stomach Secretion

“slow down” phase, stomach secretion decrease

Stomach Filling

rugae flatten as stomach volume increases up to 20 fold, mediated by a reflex integrated within the medulla oblongata that inhibits muscle tone, allows stomach to accommodate large amounts of food

Stomach Mixing

mixes ingested food with secretions from stomach glands forming chyme

2 Types of Movement in Stomach Mixing

mixing waves

peristaltic waves

Mixing Waves

movement involved in stomach mixing, contractions that occur about every 20 seconds proceeding from the body of the stomach toward the pyloric sphincter, 80% of contractions

Peristaltic Waves

movement involved in stomach mixing, occur less frequently but are more powerful, 20% of contractions

Stomach Emptying

amount of time food stays in the stomach depends on type of food (liquids begin to exit within minutes and finish within 2 hours) and volume of food, typical meal takes 3-4 hours

Pyloric Sphincter Role in Stomach Emptying

usually remains closed most of the time

Pyloric Pump Role in Stomach Emptying

peristaltic contraction move a small amount of chyme into the duodenum

Hunger Pangs

increased contractions of stomach associated with low blood sugar

Stomach Emptying is Regulated by

fast emptying

slow emptying

neural mechanisms

hormonal mechanisms

Fast Emptying of Stomach

decreases efficiency of digestion and absorption, acidic gastric contents may damage the duodenum

Slow Emptying of Stomach

reduces digestion and absorption in the small intestine, stomach can be damaged by acid

Neural Mechanisms of Stomach Emptying

stimulate stomach secretions and increase stomach motility, stimulated by stretching of the stomach

Hormonal Mechanisms of Stomach Emptying

associated with stimulation of the duodenum, decrease gastric secretions and gastric motility

Small Intestine

6 m long, three segments, two major accessory glands secrete into the duodenum, greatest amount of digestion and absorption, have modifications to increase surface area around 600-fold

3 Segments of Small Intestine

duodenum

jejunum

ileum

2 Major Accessory Glands into Duodenum

liver

pancreas

Greatest Amount of Digestion and Absorption

duodenum and jejunum are major sites of nutrient absorption, water absorption occurs by osmosis in the duodenum and jejunum and 90% occurs before reaching the large intestine

Duodenum

25 cm long segment of small intestine attached to stomach, shortest part of small intestine, has nearly 180 degree arc from the stomach where the head of the pancreas sits, two small projections in the descending portion form ducts to the liver and pancreas

What are the two small projections on the descending portion of the duodenum that form ducts to the liver and pancreas?

major duodenal papilla

minor duodenal papilla

Jejunum

consists of 2/5 (2.5 m) of the small intestine, middle section

Ileum

consists of 3/5 of (3.5 m) of the small intestine, last section

3 Modifications of Small Intestine

circular folds (plicae circulares)

villi

microvilli

Circular Folds (Plicae Circulares)

folds of the mucosa and submucosa of small intestine that run perpendicular to the long axis to increase surface area

Villi

small fingerlike projections of the mucosa of the small intestine covered by simple columnar epithelium and containing blood capillaries and lacteal

Microvilli

found on the surface of the cells on the villi in small intestine to create the brush border

4 Cells of Small Intestine Submucosa

absorptive

goblet

granular (paneth)

endocrine

Absorptive Cells

cell of small intestine submucosa, cells with microvilli that produce digestive enzymes and absorb digested food

Goblet Cells

cell of small intestine submucosa, produce protective mucus

Granular (Paneth) Cells

cell of small intestine submucosa, help protect from intestinal epithelium from bacteria

Endocrine Cells

cell of small intestine submucosa, produce many regulatory hormones such as secretin and cholecystokinin

2 Glands in Small Intestine Mucosa

intestinal glands

duodenal glands

Intestinal Glands (Crypts of Lieberkuhn)

gland in small intestine mucosa, tubular invagination containing epithelial cells at the base of the villi, absorptive and goblet cells move to the top of the intestinal glands and cover the surface of the small intestine, granular and endocrine cells remain in the bottom of the glands

Duodenal (Brunner) Glands

gland in small intestine submucosa, coiled, tubular mucous glands in the submucosa of the duodenum that open at the base of the intestinal glands

Jejunum and Ileum

similar to structure to duodenum but with a gradual decrease in diameter, thickness of the wall, number of circular folds, and number of villi

Peyer Patches

lymphatic nodules in the mucosa and submucosa of the ileum

Ileocecal Junction

where the ileum meets up with the cecum of the large intestine, ileocecal sphincter is the ring of smooth muscle, ileocecal valve is a one-way valve

3 Secretions of Small Intestine

mucus

electrolytes and water

enzymes

Mucus as Small Intestine Secretion

secreted form duodenal glands, intestinal glands, and goblet cells

protects wall of intestine from acidic chyme and digestive enzymes, secretion is stimulated by vagus nerve/secretin (hormone)/or chemical and tactile irritation of the duodenal mucosa, secretions of goblet cells are stimulated by chemical and tactile stimulation

Electrolytes and Water as Small Intestine Secretion

secreted from intestinal epithelium, keeps chyme in an aqueous solution to help with digestive process

3 Enzymes Secreted by Small Intestine

brush border

disaccharidases

peptidases

Brush Border Enzymes

enzyme of small intestine, bound to membranes of the absorptive cell microvilli

Disaccharidases

enzyme of small intestine, break down disaccharides into monosaccharides

Peptidases

enzyme of small intestine, hydrolyze peptide bonds in small amino acid chains

Movement of Small Intestine

includes mixing of chyme and slow propulsion

local mechanical and chemical stimuli regulate motility of small intestine

peristaltic waves in the small intestine relax ileocecal sphincter

Mixing of Chyme and Slow Propulsion

movement of small intestine, segmental contractions to mix, peristaltic contractions in short segments of the digestive tract to propel its content at a rate of 1 cm/min which means it takes 3-5 hours to pass through the small intestine

Local Mechanical and Chemical Stimuli Regulate Motility of Small Intestine

stretching of the intestine wall, hypertonic or hypotonic solutions, solutions with low pH, certain products of digestion (amino acids, peptides)

Peristaltic Waves in Small Intestine Relax Ileocecal Sphincter

stretching of the cecum causes a local reflex that constricts the ileocecal sphincter