Chapter 23: The Digestive System

porta hepatis

"gateway to the liver" where the hepatic artery and hepatic portal vein enter the liver

3 phases of gastic secretion

(1) Cephalic - (aka reflex) mouth watering (2) Gastric - stomach secretes stuff in response to food (3) Intestinal - bile & pancreatic juice; slows exit of chyme from stomach; closes pyloric sphincter

Describe the three processes involved in the esophageal phase of deglutition.

(1) Peristalsis moves the bolus down the esophagus and toward the stomach. (2) Esophageal glands secrete mucus that lubricates the bolus and reduces friction. (3) When the bolus nears the stomach, the lower esophageal sphincter relaxes, allowing the bolus to pass into the stomach.

Describe three of the differences between the walls of the large and small intestines.

(1) The mucosa of the small intestine includes circular folds, villi, and microvilli. (2)The wall of the large intestine has a thick mucosal layer, and deeper and more abundant mucus-secreting glands that facilitate the smooth passage of feces. (3) There are three features that are unique to the large intestine: teniae coli, haustra, and epiploic appendages.

5 methods of transport in the body

(1) active transport (2) passive transport (3) facilitated diffusion (4) co-transport (ex: kidneys) (5) endocytosis (ex: vesicles)

cephalic phase

(also, reflex phase) initial phase of gastric secretion that occurs before food enters the stomach

3 phases of swallowing (deglutition)

1. voluntary (buccal) phase - swallowing 2. pharyngeal phase - send impulses to medulla oblongata to close off nasopharynx 3. esophageal phase - peristalis

How long is the alimentary canal?

30 feet; which is mostly small intestine

Explain the role of bile salts and lecithin in the emulsification of lipids (fats).

Bile salts and lecithin can emulsify large lipid globules because they are amphipathic; they have a nonpolar (hydrophobic) region that attaches to the large fat molecules as well as a polar (hydrophilic) region that interacts with the watery chime in the intestine.

How is vitamin B12 absorbed?

Binds with intrinsic factor and is absorbed by endocytosis

Why is it important that chyme from the stomach is delivered to the small intestine slowly and in small amounts?

If large quantities of chyme were forced into the small intestine, it would result in osmotic water loss from the blood into the intestinal lumen that could cause potentially life-threatening low blood volume and erosion of the duodenum.

Explain the mechanism responsible for gastroesophageal reflux.

If the lower esophageal sphincter does not close completely, the stomach's acidic contents can back up into the esophagus, a phenomenon known as GERD.

peristalsis

Involuntary waves of muscle contraction that keep food moving along in one direction through the digestive system.

Explain how nutrients absorbed in the small intestine pass into the general circulation.

Nutrients from the breakdown of carbohydrates and proteins are absorbed through a capillary bed in the villi of the small intestine. Lipid breakdown products are absorbed into a lacteal in the villi, and transported via the lymphatic system to the bloodstream.

What layer of the alimentary canal tissue is capable of helping to protect the body against disease, and through what mechanism?

The lamina propria of the mucosa contains lymphoid tissue that makes up the MALT and responds to pathogens encountered in the alimentary canal.

Offer a theory to explain why segmentation occurs and peristalsis slows in the small intestine.

The majority of digestion and absorption occurs in the small intestine. By slowing the transit of chyme, segmentation and a reduced rate of peristalsis allow time for these processes to occur.

Explain how the stomach is protected from self-digestion and why this is necessary.

The mucosal barrier protects the stomach from self-digestion. It includes a thick coating of bicarbonate-rich mucus; the mucus is physically protective, and bicarbonate neutralizes gastric acid. Epithelial cells meet at tight junctions, which block gastric juice from penetrating the underlying tissue layers, and stem cells quickly replace sloughed off epithelial mucosal cells.

Why does the pancreas secrete some enzymes in their inactive forms, and where are these enzymes activated?

The pancreas secretes protein-digesting enzymes in their inactive forms. If secreted in their active forms, they would self-digest the pancreas. These enzymes are activated in the duodenum.

It has been several hours since you last ate. Walking past a bakery, you catch a whiff of freshly baked bread. What type of reflex is triggered, and what is the result?

The smell of food initiates long reflexes, which result in the secretion of digestive juices.

What prevents swallowed food from entering airways?

Usually when food is swallowed, involuntary muscle contractions cause the soft palate to rise and close off the nasopharynx. The larynx also is pulled up, and the epiglottis folds over the glottis. These actions block off the air passages.

Which of the following statements about reflexes in the GI tract is FALSE? a. Short reflexes are provoked by nerves near the GI tracts. b. Short reflexes are meditated by the enteric nervous system. c. Food that distend the stomach initiates long reflexes. d. Long reflexes can be provoked by stimuli originating outside the GI tract.

a. Short reflexes are provoked by nerves near the GI tract.

Which of the following organs is supported by a layer of adventitia rather than serosa? a. esophagus b. stomach c. small intestine d. large intestine

a. esophagus

Which of these organs is not considered an accessory digestive structure? a. mouth b. salivary glands c. pancreas d. liver

a. mouth

Is intestinal juice slightly acidic or alkaline?

alkaline

segmentation

alternating contractions and relaxations of non-adjacent segments of the intestine that move food forward and backward, breaking it apart and mixing it with digestive juices

hepatic artery

artery that supplies oxygenated blood to the liver

Which of these statements about the pharynx is true? a. It extends from the nasal and oral cavities superiorly to the esophagus anteriorly. b. The oropharynx is continuous superiorly with the nasopharynx. c. The nasopharynx is involved in digestion. d. The laryngopharynx is composed partially of cartilage.

b. The oropharynx is continuous superiorly with the nasopharynx.

Which of the following stimuli activates sensors in the walls of digestive organs? a. breakdown products of digestion b. distention c. pH of chyme d. all of the above

b. distention

Which of these nutrients is absorbed mainly in the duodenum? a. glucose b. iron c. soduim d. water

b. iron

Which of these is most associated with villi? a. haustra b. lacteals c. bacterial flora d. intestinal glands

b. lacteals

Which of these processes occurs through most of the alimentary canal? a. ingestion b. propulsion c. segmentation d. absorption

b. proplusion

Which of these is involved in the chemical digestion of proteins? a. pancreatic amylase b. trypsin c. sucrase d. pancreatic nuclease

b. trypsin

hepatic sinusoid

blood capillaries between rows of hepatocytes that receive blood from the hepatic portal vein and the branches of the hepatic artery

cementum

bone-like tissue covering the root of a tooth

aminopeptidase

brush border enzyme that acts on proteins

Pancreatic juice _________.

buffers chyme

Which of these cells secrete hormones? a. parietal cells b. mucous neck cells c. enteroendocrine cells d. chief cells?

c. enteroendocrine cells

Which part of the colon attaches to the appendix?

cecum

What ingredient in saliva is responsible for activating salivary amylase?

chloride ions

acinus

cluster of glandular epithelial cells in the pancreas that secretes pancreatic juice in the pancreas

Which of these statements about bile is true? a. About 500 mL is secreted daily. b. Its main function is the denaturation of proteins. c. It is synthesized in the gallbladder. d. Bile salts are recycled.

d. Bile salts are recycled.

Which of the following membranes covers the stomach? a. falciform ligament b. mesocolon c. parietal peritoneum d. visceral peritoneum

d. visceral peritoneum

Maltose, sucrose, and lactose are examples of ____________________________.

disaccharides

cystic duct

duct through which bile drains and enters the gallbladder

What structure is located where the esophagus penetrates the diaphragm?

esophageal hiatus

Which phase of deglutition involves contraction of the longitudinal muscle layer of the muscularis?

esophageal phase

migrating motility complex (MMC)

form of peristalis in the long intestine

Where does the majority of chemical digestion in the stomach occur?

fundus and body

parietal cell

gastric gland cell that secretes hydrochloric acid and intrinsic factor

Parietal cells secrete

gastrin

motilin

hormone that initiates peristalsis in the form of migrating motility complexes

What digestion processes occur in the mouth?

ingestion, mechanical digestion, & chemical digestion

voluntary phase

initial phase of deglutition, in which the bolus moves from the mouth to the oropharynx

gastroileal reflex

long reflex that increases the strength of segmentation in the ileum

mass movement

long, slow, peristaltic wave in the large intestine

lacteal

lymphatic capillary in the villi

Where is the tongue attached?

mandible; styloid processes of the temporal and hyoid bones

labial frenulum

midline mucous membrane fold that attaches the inner surface of the lips to the gums

Glucose, fructose, and galactose are examples of __________________.

monosaccharides

Where does the chemical digestion of starch begin?

mouth

What is the bonus muscle layer in the stomach that let it digest food in a 3D way?

oblique

serosa

outermost layer of the alimentary canal wall present in regions within the abdominal cavity

Where are the most fat-digesting enzymes produced?

pancreas

oral vestibule

part of the mouth bound externally by the cheeks and lips, internally by the gums and teeth

oropharynx

part of the pharynx continuous with the oral cavity that functions in respiration and digestion

gastrin

peptide that stimulates secretion of hydrochloric acid and gut motility

gastric phase

phase of gastric secretion that begins when food enters the stomach

cecum

pouch forming at the beginning of the large intestine

What is the role of the small intestine's MALT?

preventing bacteria from entering the bloodstream

gastrocolic reflex

propulsive movement in the colon activated by the presence of food in the stomach

In what part of the alimentary canal does most digestion occur?

proximal small intestine

During gastric emptying, chyme is released into the duodenum through the ________.

pyloric sphincter

haustral contraction

slow segmentation in the large intestine

bile canaliculus

small duct between hepatocytes that collects bile

haustrum

small pouch in the colon created by tonic contractions of teniae coli

ileocecal sphincter

sphincter that connects the small and large intestine

What causes the wrinkled appearance of the colon?

teniae coli

propulsion

the action of driving or pushing forward.

deglutition

three-stage process of swallowing

micelle

tiny lipid-transport compound composed of bile salts and phospholipids with a fatty acid and monoacylglyceride core

central vein

vein that receives blood from hepatic sinusoids

hepatic portal vein

vein that supplies deoxygenated nutrient-rich blood to the liver

Valsalva's maneuver

voluntary contraction of the diaphragm and abdominal wall muscles and closing of the glottis, which increases intra-abdominal pressure and facilitates defecation occurs when you're poopin real hard