CHAP 23 DIGESTION

Triglycerides are the most abundant fats in the diet (p. 45). The small intestine is the primary site of lipid digestion because the pancreas is the major source of fat-digesting enzymes, or lipases (see Figure 23.36).

fat organs involved and enzymes

Hormone secreted in the stomach; regulates gastric juice secretion by stimulating HCl production.

gastrin production site, stimulus, target site and activity

A chemical messenger (neurotransmitter or paracrine); causes vasodilation and increased capillary permeability; in stomach causes acid secretion.

histamine production site, stimulus, target site and activity

Bile is the major vehicle for excreting cholesterol from the body, and bile salts keep the cholesterol dissolved within bile.

What is the composition and role of bile?

mainly of water, and contains enzymes and electrolytes (primarily bicarbonate ions)

What is the composition of pancreatic juice?

The buccal phase occurs in the mouth and is voluntary. It ends when a food bolus or a "bit of saliva" leaves the mouth and stimulates tactile receptors in the posterior pharynx, initiating the next phase. The pharyngeal-esophageal phase is involuntary and is controlled by the swallowing center in the brain stem (medulla and lower pons). Various cranial nerves, most importantly the vagus nerves, transmit motor impulses from the swallowing center to the muscles of the pharynx and esophagus. Once food enters the pharynx, respiration is momentarily inhibited and all routes except the desired one into the digestive tract are blocked off. Solid foods pass from the oropharynx to the stomach in about 8 seconds, and fluids, aided by gravity, pass in 1 to 2 seconds.

Describe 5 phases of swallowing.

The esophageal mucosa contains a nonkeratinized stratified squamous epithelium. At the esophagus-stomach junction, that abrasion-resistant epithelium changes abruptly to the simple columnar epithelium of the stomach, which is specialized for secretion (Figure 23.13b). The submucosa contains mucus-secreting esophageal glands. As a bolus moves through the esophagus, it compresses these glands, causing them to secrete mucus that "greases" the esophageal walls and aids food passage. The muscularis externa is skeletal muscle in its superior third, a mixture of skeletal and smooth muscle in its middle third, and entirely smooth muscle in its inferior third. Instead of a serosa, the esophagus has a fibrous adventitia composed entirely of connective tissue, which blends with surrounding structures along its route.

Describe 5 special features of the esophagus wall.

Mucous cells: secrete an alkaline mucus that protects the epithelium against shear stress and acid Parietal cells: secrete hydrochloric acid Chief cells: secrete pepsin, a proteolytic enzyme G cells: secrete the hormone gastrin

Describe the 4 types of secretory cells.

The enteric nervous system (enter = gut) is the in-house nerve supply of the alimentary canal. It is staffed by enteric neurons that communicate widely with one another to regulate digestive system activity. These semiautonomous enteric neurons constitute the bulk of the two major intrinsic nerve plexuses (ganglia interconnected by unmyelinated fiber tracts) found in the walls of the alimentary canal: the submucosal and myenteric nerve plexuses These plexuses interconnect like chicken wire all along the GI tract and regulate digestive activity throughout its length.

Describe the enteric nervous system.

Most saliva is produced by the major or extrinsic salivary glands that lie outside the oral cavity and empty their secretions into it. Minor or intrinsic salivary glands (buccal glands and others) scattered throughout the oral cavity mucosa augment the output slightly. Contains amylase to breakdown food. Mostly water.

Describe the glands, composition and control of saliva and salivation.

Cephalic Phase. Controlled by brain: sight ,smell, taste of food relays nerve impulses to brainstem to signal stomach to secrete gastric juice and gastrin. Gastric Phase. Begins when food enters stomach: stretching of stomach increases secretion of gastric juice and gastrin. Intestinal Phase.

Describe the three phases of gastric secretion.

Once carbohydrates are broken down into their simplest forms, they are quickly absorbed along the upper and lower parts of the small intestine. Small, finger-like projections, called villi, absorb the carbohydrates, then they are transferred to the blood stream and carried to muscles and the liver.

How are carbs absorbed?

from the colon

How are electrolytes absorbed?

Lipids, or fat, go undigested in your digestive tract until they reach your small intestine, where they meet bile. Bile contains bile salts, which act as an emulsifier of lipids. This breaks the large fat droplets into smaller droplets that are then easier for the fat-digesting enzyme pancreatic lipase to digest.

How are fats absorbed?

Iron enters the stomach where it is exposed to stomach acid and changed into a form that allows it to be absorbed. The portion of the small intestine called the duodenum is the chief area where iron absorption takes place. ... Once iron is absorbed it is carried (transported) by a protein called transferrin.

How are irons absorbed?

Amino acids are readily absorbed and then transported to the liver. ... Nucleic Acid Digestion: Put simply, a group of enzymes called nucleases break down nucleic acids such as RNA (ribonucleic acid) and DNA (deoxyribonucleic acid) into nucleotide chains.

How are nucleic acids absorbed?

Pepsin is an enzyme in the stomach that breaks down the peptide bonds in protein. ... Enzymes continue to break down polypeptides and peptides into amino acids. Because amino acids are very small, they are able to be absorbed through the small intestine lining and into your bloodstream.

How are proteins absorbed?

Cirrhosis (sĭr-ro′sis; "orange colored") is the last stage of progressive chronic inflammation of the liver. It typically results from severe chronic hepatitis due to chronic alcoholism, NAFLD, or viral hepatitis. While damaged hepatocytes can regenerate, the liver's connective (scar) tissue regenerates faster. Liver activity is depressed and the liver becomes fibrous with scar tissue. The scar tissue obstructs blood flow throughout the hepatic portal system, causing portal hypertension.

How does cirrhosis occur and what are common causes?

Calcium dissolves in the stomach and is absorbed through the lining of the small intestine into the blood stream. Once in the blood stream, calcium builds bone, regulates the expansion and contraction of the blood vessels, and performs other important functions.

How is calcium absorbed?

A majority of water's absorption into the bloodstream occurs after water passes through the stomach and on to the small intestine. The small intestine, at around 20 feet long, efficiently absorbs water into the cell membrane and bloodstream. ... Once absorbed into the body, water aids a number of vital functions.

How is water absorbed?

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STUDY VOCAB

digestion, immunity, neural synthesis

What are 3 functions of intestinal flora?

metaolism, storage, biotransformation

What are 3 roles of hepatocytes?

Long length Villi and microvilli smooth muscle Digestive Enzymes

What are 4 modifications for absorption in the small intestine?

A,E, D, K

What are the four fat-soluble vitamins?

The ascending colon including the cecum and appendix The transverse colon including the colic flexures and transverse mesocolon The descending colon The sigmoid colon - the s-shaped region of the large intestine The rectum

What are the six components of the large intestine?

chronic hepatitis, liver cirrhosis, and cancer.

What are the three main viral causes of hepatitis? Which is most concerning?

alcohol, mushrooms, drugs

What are three addition non-viral causes of hepatitis?

A compact epithelial cell lining. Cells in the epithelium of the stomach are bound by tight junctions that repel harsh fluids that may injure the stomach lining. A special mucus covering, derived from mucus secreted by surface epithelial cells and Foveolar cells. This insoluble mucus forms a protective gel-like coating over the entire surface of the gastric mucosa. The mucus protects the gastric mucosa from autodigestion by e.g. pepsin and from erosion by acids and other caustic materials that are ingested. Bicarbonate ions, secreted by the surface epithelial cells. The bicarbonate ions act to neutralize harsh acids.

What are three components of the stomach mucosal barrier?

bacteria and use of nonsteroidal anti-inflammatory drugs

What is the cause of gastric ulcers?

r, the presence of bilious emesis in the neonate is known to be suggestive of acute surgical conditions such as midgut volvulus, intestinal atresia, or other forms of intestinal obstruction. Similar concern should be maintained for infants with bilious vomiting, although the condition may be related to a nonobstructive condition such as acute gastroenteritis. The following case illustrates that bilious vomiting in infants may be a sign of potentially serious pathology, and highlights the subtleness with which intussusception may present.

What is the concern with bilious vomiting in a one-month old infant? What is the treatment?

The gallbladder is chiefly a storage organ for bile.

What is the role of the gallbladder?

The pancreas supplies most of the enzymes that digest chyme as well as bicarbonate that neutralizes stomach acid.

What is the role of the pancreas?

the proper hepatic artery, hepatic portal vein and bile ducts, as well as other structures.

What makes up the portal triad?

1 Pancreatic amylase breaks down starch and glycogen into oligosaccharides and disaccharides. 2 Brush border enzymes break oligo- and disaccharides into monosaccharides. 3 Monosaccharides are cotransported across the apical membrane of the enterocyte. 4 Monosaccharides exit across the basolateral membrane by facilitated diffusion.

carb organs and enzymes

An intestinal hormone that stimulates gallbladder contraction and pancreatic juice release.

cholectystokinin production site, stimulus, target site and activity

1.Ingestion 2.Propulsion 3.Mechanical breakdown 4.Digestion 5.Absorption 6.Defecation

digestive processes

reabsorption of water and mineral ions such as sodium and chloride formation and temporary storage of faeces maintaining a resident population of over 500 species of bacteria bacterial fermentation of indigestible materials.

large intestine function

True peristalsis occurs only after most nutrients have been absorbed. At this point, segmenting movements wane and the duodenal mucosa begins to release the hormone motilin.

motilin production site, stimulus, target site and activity

the tongue and teeth help to get the process started by chewing and chopping the food so it's small enough to be swallowed. Salivary glands secrete saliva, releasing an enzyme that changes some starches into simple sugars and softens the food for swallowing.

mouth function

The nuclei of the cells of ingested foods contain DNA and RNA. Pancreatic nucleases in pancreatic juice hydrolyze the nucleic acids to their nucleotide monomers. Intestinal brush border enzymes (nucleosidases and phosphatases) then break the nucleotides apart to release their nitrogenous bases, pentose sugars, and phosphate ions (see Figure 23.36). Special carriers in the epithelium of the villi actively transport the breakdown products of nucleic acid digestion across the epithelium. These then enter the blood.

nucleic acid organs involved and enzymes

The pharynx is a passageway connected to esophagus and trachea. Its only function is to move food mechanically along its length. The esophagus is a muscular tube (about 25 cm long or 10 inches) that delivers food from the pharynx to the stomach.

pharynx and esophagus function

Dietary proteins (typically about 125 g per day) Enzyme proteins secreted into the GI tract by its various glands (15-25 g) Protein derived from sloughed and disintegrating mucosal cells

protein organs involved and enzymes

a hormone released into the bloodstream by the duodenum (especially in response to acidity) to stimulate secretion by the liver and pancreas.

secretin production site, stimulus, target site and activity

As a neurotransmitter, serotonin helps to relay messages from one area of the brain to another. ... This includes brain cells related to mood, sexual desire and function, appetite, sleep, memory and learning, temperature regulation, and some social behavior.

serotonin production site, stimulus, target site and activity

The primary function of the small intestine is the absorption of nutrients and minerals from food, using small finger-like protrusions called villi.

small intestine function

Somatostatin release is stimulated by increased plasma amino acids, fatty acids, and glucose. Somatostatin release is also stimulated by GI hormones. Somatostatin inhibits the release of both insulin and glucagon, and it decreases activity and secretion by the GI tract.

somatosatin production site, stimulus, target site and activity

digestion of food. secretion of gastric juices as well as mucus which helps to coat its lining, preventing erosion by gastric juices. secretion of gastric hormones. regulation of the rate at which partially digested food is delivered to the small intestine.

stomach function