243 Ch 24 Digestive System

What percent of saliva is made from each gland?

-70 percent from submandibular glands -25 percent from parotids -5 percent from sublingual glands

What is the function of bile?

-Bile salts in bile break lipid droplets apart (emulsification) in duodenum ■Creates tiny emulsion droplets coated with bile salts ■Increases surface area exposed to enzymes -Necessary because mechanical digestion in stomach creates large droplets of lipids ■Pancreatic lipase can interact only at surface -Enterohepatic circulation ■Cycling of bile salts between liver and small intestine

What do the muscles of mastication do?

-Close jaws -Slide lower jaw from side to side

What are functions of the endocrine pancreas?

-Consists of cells that form clusters known as pancreatic islets (islets of Langerhans) •Alpha (α) cells produce glucagon •Beta (β) cells produce insulin

What are functions of the exocrine pancreas?

-Consists of clusters of gland cells called pancreatic acini and their attached ducts -Takes up roughly 99 percent of pancreatic volume -Gland and duct cells secrete alkaline, enzyme-rich fluid •Passes through a network of ducts to lumen of digestive tract

What is segmentation?

-Cycles of contraction that churn and fragment the bolus ■Mixing contents with intestinal secretions -Does not follow a set pattern ■Does not push materials in any one direction

What are the functions of the tongue?

-Four primary functions ■Mechanical digestion by compression, abrasion, and distortion ■Manipulation to assist in chewing and to prepare food for swallowing ■Sensory analysis by touch, temperature, and taste receptors ■Secretion of mucins and lingual lipase

What are characteristics of the gallbladder?

-Hollow, pear-shaped muscular sac -Stores and concentrates bile prior to secretion into small intestine -Located in fossa in posterior surface of liver's right lobe

What are the integrated processes of the digestive system?

-Ingestion -Mechanical digestion and propulsion -Chemical digestion -Secretion -Absorption -Defecation

What are characteristics of the liver?

-Largest visceral organ (1.5 kg) -Lies in right hypochondriac and epigastric regions -May extend into left hypochondriac and umbilical regions -Performs essential metabolic and synthetic functions

What are characteristics of the pancreas?

-Lies posterior to stomach -Extends from duodenum toward spleen -Retroperitoneal ■Bound to posterior wall of abdominal cavity -Wrapped in thin, connective tissue capsule

What is the hepatic portal system?

-Liver lobules are hexagonal in cross section ■Each of six corners has a portal triad containing ■Interlobular vein ■Interlobular artery ■Interlobular bile duct

What is a bolus?

-Moist, rounded ball -Fairly easy to swallow

What do mass movements do?

-Movement from transverse colon through rest of large intestine -Stimulus is distension of stomach and duodenum ■Relayed over intestinal nerve plexuses -Distension of rectal wall initiates defecation reflex ■Involves two positive feedback loops ■Both triggered by stretch receptors in rectum

What is chyme?

-Partially digested food mixed with acidic secretions of stomach

What are neural mechanisms for the small intestine in the CNS?

-Prepare digestive tract for activity ■Through parasympathetic innervation -Inhibit gastrointestinal activity ■Through sympathetic innervation -Coordinate movement of materials along digestive tract ■Through reflexes -Motor neuron synapses in digestive tract release neurotransmitters

What do duodenal submucosal glands do?

-Produce copious quantities of mucus ■When chyme arrives from stomach -Mucus protects epithelium from acidity of chyme ■Contains bicarbonate ions that raise pH

What is the peritoneum?

-Serous membrane lining peritoneal cavity -Visceral peritoneum (serosa) ■Covers organs within peritoneal cavity -Parietal peritoneum ■Lines inner surfaces of body wall

What is the chemical digestion like in the stomach?

-Some digestion of carbohydrates (by salivary amylase) and lipids (by lingual lipase) -As stomach contents become more fluid, ■pH approaches 2.0 ■Preliminary digestion of proteins by pepsin increases -Nutrients are not absorbed in stomach

What is peristalsis?

-Visceral smooth muscle tissue ■Rhythmic cycles of activity ■Controlled by pacesetter cells that undergo spontaneous depolarization ■Wave of contraction spreads throughout entire muscular sheet

What are the three sections of the small intestine?

1. Duodenum 2. Jejunum 3. Ileum

What is the composition of saliva?

99.4% water, 0.6% electrolytes, glycoproteins, antibodies, enzymes, and wastes

What are local regulation factors of digestive functions?

Buffers, acids or enzymes released by stimulus

What is the gastroileal reflex?

Contents in the stomach stimulate peristalsis in the ileum and relaxation of the ileocecal sphincter, which delivers the contents to the large intestine.

What are hormonal control mechanisms in regulating digestive functions?

Enteroendocrine cells secrete hormones -> bloodstream carries to secretory cells -> cells release local factors

What does lipase break down?

Lipids

What are neural control mechanisms in regulating digestive functions?

Local factors stimulate stretch/chemoreceptors -> can stimulate CNS which will stimulate myenteric plexus (long reflex), or stimulate myenteric plexus directly (short reflex)

What are the three glands that secrete into the oral cavity?

Parotid glands, sublingual glands, submandibular glands

What happens during the gastric phase?

Pepsin is activated which breaks down proteins; gastrin causes the smooth muscle of the stomach to churn its contents (mixing waves)

What is the function of cholecystokinin (CCK)?

Production of pancreatic enzymes Contracts gall bladder Relaxes hepatopancreatic sphincter

Where are blood vessels located in the tooth?

Pulp cavity

Where is gastrin made?

Stomach, duodenum

What happens during the intestinal phase?

The enterogastric reflex allows for periodic emptying of chyme into the small intestine due to pyloric sphincter contractions; gastric put secretions are inhibited

What is the function of pepsinogen?

activated to pepsin to digest proteins

What is the function of the rugae?

allow stomach to expand

What do parotid glands secrete?

amylase

What do submandibular glands secrete?

amylase and mucous

What does amylase break down?

carbohydrates

What are the four parts of the stomach?

cardia, fundus, body, pyloric portion

What is the function of gastrin?

causes GASTRIC CONTRACTIONS and secretion by gastric glands also makes more gastric juices

What is the enterogastric reflex?

causes constriction of pyloric sphincter (small intestine has a reflex that has an opposite effect)

What are the three parts of a tooth?

crown, neck, root

What is in the gastric pit?

depressions in gastric mucosa - gastric glands

What covers the crown of a tooth?

enamel

What are liver lobules?

functional units of the liver

What are the four enzymes?

lipase, amylase, protease, pepsin

What do the gastroileal and gastroenteric reflex do in the large intestine?

move materials into cecum while you eat -Movement from cecum to transverse colon is very slow, allowing hours for water absorption -Peristaltic waves move material along length of colon -Segmentation movements (haustral churning) mix contents of adjacent haustra

What is the histology of the large intestine?

mucosa, submucosa, muscularis, serosa

What do sublingual glands secrete?

mucus

What are the cells of gastric glands?

parietal cells, G cells, chief cells

What is the function of secretin?

production of pancreatic buffer?

What is the function of enamel?

protects against abrasion and acids produced by bacteria in mouth

What do proteases break down?

proteins

What does pepsin break down?

proteins

What is the function of parietal cells?

secrete HCl and intrinsic factor

What is the function of G cells?

secrete gastrin

What is the function of chief cells?

secrete pepsinogen and gastric lipase

What is the gastroenteric reflex?

stimulates motility and secretion along the entire small intestine

What happens during the cephalic phase?

the smell, sight, thought, or initial taste of food activates neural centers in the cerebral cortex, hypothalamus, and brain stem to prepare for digestion.

What are the functions of the large intestine?

■Absorption or reabsorption of -Water -Nutrients (less than 10 percent) -Bile salts -Organic wastes -Vitamins and toxins produced by bacteria ■Compaction of intestinal contents into feces ■Storage of fecal material prior to defecation

What is the digestive system?

■Acquires nutrients from environment -Used to synthesize essential compounds (anabolism) -Broken down to provide energy to cells (catabolism)

How is the production of acid of enzymes by gastric mucosa controlled by?

■CNS ■Short reflexes of ENS ■Hormones of digestive tract

What are in the intestinal wall?

■Circular folds ■Intestinal villi ■Lacteal ■Intestinal glands (intestinal crypts) ■Duodenal submucosal glands

What are the functions of saliva?

■Cleaning oral surfaces ■Moistening and lubricating food ■Keeping pH of mouth near 7.0 ■Controlling populations of bacteria and limiting acids that they produce ■Dissolving chemicals that stimulate taste buds ■Initiating digestion of complex carbohydrates with salivary amylase

What does the lining of the digestive tract protect against?

■Corrosive effects of digestive acids and enzymes ■Mechanical stresses, such as abrasion ■Bacteria either ingested with food or that reside in digestive tract

What is mastication?

■Food is forced from oral cavity to vestibule and back across occlusal surfaces of teeth

What is the bile duct system?

■Liver secretes bile -Into a network of narrow channels (bile canaliculi) between adjacent liver cells ■Right and left hepatic ducts -Collect bile from all bile ducts of liver lobes -Unite to form common hepatic duct ■From common hepatic duct, bile enters either -Bile duct, which empties into duodenal ampulla -Cystic duct, which leads to gallbladder

What are the functions of the stomach?

■Major functions of stomach -Temporary storage of ingested food -Mechanical digestion with muscular contractions -Chemical digestion of food with acid and enzymes

What is the postabsorptive state?

■Normal blood glucose levels are maintained ■Body relies on internal energy reserves ■Most cells break down lipids or amino acids -Preserving glucose for use by nervous tissue

What is the absorptive state?

■Period following a meal when nutrient absorption is under way ■Lasts about four hours

What are physiological processes in the small intestine?

■Peristalsis and Segmentation ■Mechanical Digestion ■Chemical Digestion ■Absorption ■Secretion

What are the reflexes for the elimination of feces?

■Positive feedback loops -Intrinsic myenteric defecation reflex ■Short reflex ■Triggers peristaltic contractions in sigmoid colon and rectum -Parasympathetic defecation reflex ■Long reflex ■Coordinated by sacral parasympathetic neurons ■Stimulates mass movements ■Requires relaxation of internal and external anal sphincters -Reflexes open internal sphincter ■Somatic nervous system must be activated to consciously open external sphincter

What are the functions of the oral cavity?

■Sensory analysis -Of food before swallowing ■ Mechanical digestion -Through actions of teeth, tongue, and palatal surfaces ■ Lubrication -By mixing with mucus and saliva ■ Limited chemical digestion -Of carbohydrates and lipids