A&P II: THE DIGESTIVE SYSTEM PART B HOMEWORK

The presence of acidic, fatty chyme in the small intestine causes the release of secretin,

which in turn inhibits further entry of stomach contents into the intestine until the fat has been emulsified and the pH raised.

Which vessel delivers nutrient-rich blood to the liver from the digestive tract?

hepatic portal vein

What has increased rough and smooth ER, Golgi apparatus, peroxisomes, and mitochondria?

hepatocytes

What controls entry of bile and pancreatic juice into duodenum?

hepatopancreatic sphincter

What is the condition called where a proximal portion of the stomach pushes through an opening in the diaphragm, allowing stomach acid to pass into the esophagus?

hiatal hernia

Which layer of the stomach contains the gastric pits that secrete mucous, acid, and digestive enzymes?

mucosa

Pancreatic juice contains bicarbonate (as baking soda does) that can...

neutralize the pH of acidic chyme coming from the stomach.

What is a major function of pancreatic juice?

neutralizing chyme entering the small intestine from the stomach

What best describes the capillary wall structure found in the liver lobules?

the capillary walls have openings that allow large proteins and small cells to pass through

The mucosa of the stomach contains the epithelial lining and the gastric pits,

which extend down into the mucosa but do not penetrate the submucosa.

Which organ has the chief function of storing bile?

gallbladder

Gastric contractile activity:

-Contractions more vigorous/powerful near pylorus -30 ml of chyme produced is either: +delivered in approximately 3 ml spurts to duodenum or rest of 27 ml forced backward into stomach -Only liquids and small particles are allowed to pass through pyloric valve

Duodenum can prevent overfilling by controlling how much chyme enters:

-Duodenal receptors respond to stretch and chemical signals -Enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling

The pancreas:

-Exocrine function; produce pancreatic juice 1. Acne; clusters of secretory cells that produce zymogen granules containing proenzymes 2. Ducts; secrete to duodenum via main pancreatic duct; smaller duct cells produce water and bicarb -Endocrine function; secretion of insulin and glucagon by pancreatic islet cells

Gross anatomy of the liver

-Largest gland in body weighing approx. 3 lbs -4 primary lobes: right, left, caudate, and quadrate -falciform ligament; separates larger right and smaller left lobes & suspends liver from diaphragm and anterior abdominal wall -round ligament (ligamentum teres): remnant of fetal umblical vein along free edge of falciform ligament -lesser omentum anchors liver to stomach -hepatic artery and vein enter liver at porta hepatis -bile duct formed by union of common hepatic and cystic ducts

Microscopic Anatomy of Liver

-Liver lobules 1. Hexagonal structural and functional units 2. Composed of plates of hepatocytes that filter and process nutrient-rich blood 3. Central vein located in longitudinal axis -Portal triad 1. Branch of hepatic artery, which supplies oxygen 2. Branch of hepatic portal vein, which brings nutrient-rich blood from intestine 3. Bile duct, which receives bile from bile canaliculi -Liver sinusoids: leaky capillaries located between hepatic plates 1. Blood from bot hepatic portal vein and hepatic artery proper percolates from triad regions through sinusoids and empties into central vein -Stellate macrophages (hepatic) in liver sinusoids remove debris and old RBCs

Gallbladder:

1. thin-walled muscular sac on ventral surface of liver 2. functions to store and concentrate bile by absorbing water and ions 3. honeycomb folds that expand as it fills 4. cystic duct

Hepatocyte functions:

-produce approx. 900 ml bile p/day -process bloodborne nutrients such as storing glucose as glycogen and make plasma proteins -store fat-soluble vitamins -perform detoxification (converting ammonia to urea)

Bile: composition and enterohepatic circulation

-yellow-green, alkaline solution containing: 1. Bile salts; cholesterol derivatives that function in fat emulsification and absorption 2. Bilirubin; pigment formed from heme; bacteria break down in intestine to stercobilin that gives brown color of feces 3. Cholesterol, triglycerides, phospholipids, and electrolytes -Enterohepatic circulation 1. Recycling mechanism that conserves bile salts 2. Bile salts are: Reabsorbed into blood by ileum (last part of S.I.), returned to liver via hepatic portal blood, and resecreted in newly formed bile 3. About 90% of secreted bile salts are recycled, so only 5% is newly synthesized each time

Composition of pancreatic juice

1. 1200-1500 ml/day is producing containing: -watery, alkaline solution to neutralize acidic chyme coming from stomach -electrolytes, primarily HCO-3 -Digestive enzymes +proteases (proteins): secreted in inactive form to prevent self-digestion +amylase (carbs) +lipases (lipids) +nucleases (nucleic acids) 2. Proteases are secreted in an inactive form; activated after they reach duodenum -Enteropeptidase -Once trypsin activated, can also activate more typsinogen, procarboxy to active carboxy, chymotryp to active chymo

Bile secretion is increased when:

1. Enterohepatic circulation returns large bile salts 2. secretin stimulates gallbladder to release bile 3. Hepatopancreatic sphincter is closed, unless digestion is active

Peristaltic waves in the stomach:

1. Propulsion: Peristaltic waves move from the fundus toward pylorus 2. Grinding: The most vigorous peristalsis and mixing action occurs close to the pylorus. The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum. 3. Retropulsion: The peristaltic wave closes the pyloric valve, forcing most of the contents of the pylorus backward into the stomach.

Two factors cause pressure to remain constant until 1.5 L of food is ingested

1. Receptive relaxation: reflex-mediated relaxation of smooth muscle coordinated by swallowing center of brain stem. 2. Gastric accommodation: intrinsic ability of smooth muscle to exhibit stress-relaxation response, which enables hollow organs to stretch without increasing tension or contractions

Stomach empties in approx. 4 hours, but increase in fatty chyme entering duodenum can increase time to 6 hours or more.

Carbohydrate-rich chyme moves quickly through duodenum.

Enteropeptidase is a protein produced by and bound to the membranes of intestinal cells.

Contact with this protein converts trypsinogen to trypsin, the active form of the enzyme.

T/F: Chief cells secrete inactive pepsinogen in order to prevent acid erosion inside of the chief cells.

False

Where is the location of the pancreas?

mostly retroperitoneal, deep to greater curvature of stomach

The pylorus is the lowest part of the stomach.

It attaches to and empties food into the small intestine via the pyloric sphincter.

What's an enzyme secreted by the pancreas?

Procarboxypeptidase

A bile duct along with a portal venule and arteriole constitute a portal triad.

The blood vessels provide blood flow to the lobule and the bile duct drains bile.

Chief cells do secrete pepsinogen, but the result is unrelated to acidity.

When pepsinogen is activated by HCl secreted by the parietal cells, it's converted into pepsin, which is an enzyme that acts on proteins.

All areas of the alimentary canal have a circular and a longitudinal layer of muscle.

The stomach has an additional oblique layer of muscle for "wringing" itself while processing food.

What's not a characteristic of the stomach?

The stomach releases enzymes to digest carbohydrates.

Without the production of intrinsic factor, the body wouldn't be able to absorb vitamin B12 in the small intestine.

This is the only factor that would cause problem with living.

What constitutes a portal triad?

a bile duct along with a portal venule and arteriole

What role of the stomach is essential to life?

production of intrinsic factor

What's a smaller duct that empties directly into duodenum?

accessory pancreatic duct

Which of these structures is found in the stomach but nowhere else in the alimentary canal?

an oblique muscle layer

What is set by enteric pacemaker cells?

basic electrical rhythm (BER)

Which of the following is not a secretion of the pancreas?

bile

What unites in the wall of duodenum?

bile and pancreatic duct

Hormonal controls include:

cholecystokinin and secretin

Mechanical digestion occurs in the stomach by what?

churning

What increases force of contraction?

distension and contraction

Which chemical activates the transformation of trypsinogen to trypsin?

enteropeptidase

Pacemaker cells are linked by gap junctions so that...

entire muscularis contracts.

The liver produces bile,

especially when influenced hormonally by secretin.

In what phase of gastric secretion is chyme moved into the duodenum?

intestinal

The intestinal phase occurs when chyme....

is moved into the duodenum.

Bile is secreted by what?

liver

What are accessory organs associated with the small intestine?

liver, gallbladder, and pancreas

Bile is produced by what under the hormonal influence of what?

liver, secretin

Ampulla opens into duodenum via volcano-shaped

major duodenal papilla

Which of the following is the major process or function that occurs in the stomach?

mechanical digestion

Which organ supplies most of enzymes needed to digest chyme, as well as bicarbonate to neutralize stomach acid?

pancreas

What control mechanism opens the gastroesophageal sphincter?

peristalsis in the esophagus

The capillary walls in the lobules of the liver are sinusoidal and allow large proteins and even blood cells to pass,

permitting the liver to perform its functions.

The pancreas secretes what?

procarboxypeptidase

Peristaltic waves move toward ____________ at rate of 3 p/minute.

pylorus

Which area of the stomach adjoins the small intestine?

pylorus

What's not a common risk factor for acid reflux disease?

sitting upright after a meal

As the peristaltic wave triggered by deglutition reaches the stomach,

the gastroesophageal sphincter relaxes and allows food into the stomach.

All blood fro the digestive organs as well as the spleen is delivered to...

the liver in the hepatic portal vein before being returned to the general circulation.

What triggers the release of secretin from the small intestine?

the presence of acidic, fatty chyme in the small intestine