Ch.16 Digestive System

Human Physiology

The primary function of the digestive system is to transfer nutrients, water, and electrolytes from ingested food into the body’s internal environment.

electrolytes

This system has 4 processes: motility, secretion, digestion, and absorption. (p.589-590)

4

___ is the muscular contractions that mix and move the contents forward of the digestive tract.

motility

___ is the transfer of digestive juices by exocrine glands into the digestive tract

secretion

___ is the chemical change (catabolism by hydrolysis) of large molecules (e.g., carbohydrates, proteins, and fats) into their smaller subunits (e.g., starch into glucose, proteins into amino acids, etc).

digestion

___ is the passage of the products of digestion (e.g., glucose), along with water, vitamins, and electrolytes, into the blood and lymph.

absorption

The smooth muscle in the walls of the digestive tract maintains a low level of contraction called ___.

tone

There are two types of digestive motility: propulsive movements and mixing movements. ___ push the contents forward through the tract

propulsive movements

Digestive secretions consist of water, electrolytes, and organic constituents such as enzymes, bile, salts, and mucus. They are released by ___ or neural stimulation

hormonal

___ (e.g., starch and glycogen) are chemically changed into disaccharides, which are reduced into monosaccharides. Proteins are chemically changed into polypeptides, which are changed into amino acids. The end products of fat digestion are monoglycerides and free fatty acids

polysaccharides

Most absorption occurs in the ___ intestine where it is completed

small

Motility associated with the pharynx and ___ is swallowing. (p.598-)

esophagus

___ is of chewed or liquid food

bolus

Swallowing is initiated when a food bolus contacts receptors in the ___. Afferent impulses are sent to the swallowing center in the medulla. This triggers various swallowing responses

pharynx

Food is prevented from entering the wrong passageways during the oropharyngeal stage. Responses include the closing of the ___ (laryngeal hole) by the tilting of the epiglottis, preventing food from entering the respiratory tract

glottis

The ___ sphincter prevents air from entering the digestive tract during breathing. The ___ sphincter keeps the esophagus closed, preventing eructation (burping). It is circular skeletal muscle

pharyngoesophageal

___ refers to ringlike contractions of the circular smooth muscle that move progressively forward, pushing the bolus into a relaxed area ahead of the contraction

peristalsis

Peristalsis waves push food through the ___.

esophagus

The ___ initiates a primary peristaltic wave.

swallowing center

___ is smooth muscle, in contrast to the upper esophageal sphincter. The ___ sphincter prevents reflux of gastric contents

gastroesophageal

Draw peristalsis in the esophagus graphic

Draw peristalsis in the esophagus graphic

The ___ stores food and begins protein digestion.

stomach

The most important function of the stomach is to store food. Most of this occurs in the ___ of the stomach

body

The stomach also secretes ___ to begin protein digestion

HCl

___ is a thick liquid mixture formed through the stomach’s mixing movements. The ingested food is pulverized and mixed with gastric secretion to produce it.

chyme

The stomach accommodates a twenty-fold increase in volume by ___.

receptive relaxation

Gastric emptying is largely controlled by factors in the ___ (fat, acid, hypertonicity, and distension) (p.602-603)

duodenum

___ - to swell, stretch, or expand out of shape

distend

___ - too much chyme in the duodenum inhibits the emptying of even more gastric contents, giving the distended duodenum time to cope with the excess volume of chyme it already contains before it gets any more

distension

Peristaltic action in the stomach drives chyme from the stomach into the small intestine. Distension of the stomach increases gastric motility. Signaling by the vagus nerve and the hormone ___ increases motility.

gastrin

Factors in the duodenum that prevent gastric emptying include undigested fat, unneutralized acid, an increase in ___, and distension

osmolarity

___ are any hormone secreted by the intestinal mucosa (specifically the duodenum) that slows down digestion

enterogastrones

Gastric emptying is inhibited by the neural response and hormonal responses. Secretin and ___ are enterogastrones that inhibit this process.

cholecystokinin (CCK)

___ is secreted by glands located at the base of gastric pits

gastric digestive juice

Mucous cells secrete a thin, watery mucus. Parietal cells secrete HCl and the intrinsic factor. This factor is essential for the absorption of vitamin B12. The exocrine secretions of these cells are released into the ___.

gastric lumen

Other secretory cells of the gastric mucosa release endocrine and ___ regulatory factors.

paracrine

The low pH in the stomach converts ___ into the active form, pepsin

pepsinogen

Functions of hydrochloric acid in the stomach include ___ formation, the breakdown of connective tissue and muscle fibers, the denaturation of proteins, and the killing of most microorganisms

pepsin

A mucus lining on the surface of the ___ is protective.

gastric mucosa

Draw Mechanisms of HCI secretion (s & p.607)

Draw Mechanisms of HCI secretion (s & p.607)

Draw Pepsinogen activation in the stomach lumen diagram (s & p.608)

Draw Pepsinogen activation in the stomach lumen diagram (s & p.608)

Gastric secretion gradually ___ as food empties from the stomach into the intestine. The presence of protein is withdrawn from the stomach as the meal enters the small intestine.

decreases

The stomach lining is protected from gastric secretions by the ___. The mucosal membrane is almost impermeable to hydrogen ions

gastric mucosal barrier

Carbohydrate digestion continues in the body of the stomach. Protein digestion begins in the ___. Salivary amylase continues to work in the internal mass of food. Food is not mixed with gastric secretions in the body of the stomach

antrum

The stomach absorbs alcohol and aspirin, but does not absorb ___.

food

Draw HCI tight junction mucus coating graphic (s & p.611)

Draw HCI tight junction mucus coating graphic (s & p.611)

___ is an elongated gland that lies behind and below the stomach, above the first loop of the duodenum. Contains both exocrine and endocrine tissue

pancreas

___ contained within the endocrine part of the pancreas. Consist of isolated islands of endocrine tissues. Secrete hormones

islets of Langerhans

The exocrine pancreas secretes digestive enzymes and an aqueous ___. The ___ has sodium carbonate.

alkaline fluid

The enzymes are proteolytic enzymes, pancreatic amylase, and pancreatic lipase.

enzymes

Trypsin, formed from trypsinogen, is a ___. Chymotrypsin and carboxypeptidase are other proteolytic enzymes

proteolytic enzyme

___ converts starch to disaccharides

pancreatic amylase

___ hydrolyzes dietary lipids.

pancreatic lipase

Pancreatic exocrine secretion is regulated by ___ and cholecystokinin (CCK), enzymes secreted by the small intestine. ___ signals the secretion of sodium bicarbonate from the pancreas. Cholecystokinin (CCK) regulates the secretion of pancreas digestive enzymes.

secretin

Draw membrane-bound enterokinase Diagram (slides)

Draw membrane-bound enterokinase Diagram (slides)

The ___ carries out numerous functions. One is bile production. It carries out the metabolic processing of nutrients. It detoxifies or degrades body wastes. It synthesizes plasma proteins. It stores substances such as glycogen and fats. It activates vitamin D. It removes bacteria and worn-out RBCs. It excretes cholesterol and bilirubin

liver

Blood enters the liver from the digestive tract by the hepatic portal system. The ___ of this system breaks into a capillary network, the liver sinusoids

portal vein

___ are the functional units of the liver. Are hexagonal arrangements of tissue surrounding a central vein. (p.617 for visual)

lobules

The liver lobules are delineated by vascular and bile channels. ___ continuously secrete bile into these channels

hepatocytes

Bile ducts from the lobules in the liver converge to form the common bile duct. This duct transports bile from the liver to the ___.

duodenum

___ is stored in the gallbladder between meals. After a meal the liver and gallbladder secrete ___ into the small intestine for fat digestion

bile

Bile salts aid fat digestion and absorption. (p.618-620)

fat

The detergent action of bile emulsifies fats. Fat globules are broken into smaller droplets, increasing surface area to facilitate enzymatic attack (pancreatic lipase). Pancreatic lipase is anchored to a fat droplet by the ___. Bile salts adsorb on the surface of small fat droplets, preventing the droplets for recoalescing. This also helps enzymatic attack

polypeptide colipase

___ is a waste product excreted in the bile

bilirubin

___ are the most potent stimulus for increased bile secretion. Its secretion occurs by a chemical mechanism, hormonal mechanism, and a neural mechanism

bile salts

Draw and read micelle graphic (s & p.620)

Draw and read micelle graphic (s & p.620)

The small intestine is where most digestion and absorption occur. Its three segments are the duodenum, jejunum, and ___

ileum

___ is the small intestines' primary method of motility during digestion of a meal. Both mix (with secretions) and slowly propel the chyme. Consists of oscillating, ringlike contractions of the circular smooth muscle along the small intestines' length; between the contracted segments are relaxed areas containing a small bolus of chyme

segmentation

The circular smooth muscle responsiveness is influenced by the distension of the intestine, ___, and extrinsic nerve activity

gastrin

The ___ is an internal housekeeper. It sweeps the intestine clean between meals.

migrating motility complex

The ___, between the small and large intestine, prevents contamination of the small intestine by colonic bacteria

ileocecal juncture

The small intestine does not secrete digestive enzymes. The ___ secretes enzymes into the tract

pancreas

The small intestine enzymes complete digestion intracellularly. These include the ___ and aminopeptidases

disaccharidases

A lactose intolerance is due to a deficiency of ___.

lactase

The small intestine has adaptations to maximize absorption. The ___ has a large surface area due to its circular folds and fingerlike projections called villi (singular - villus). The epithelial cells also have microvilli

mucosal lining

A villus has a cover of epithelial cells, a connective tissue core, a capillary network, and the ___.

terminal lymphatic vessel

During ___, molecules produced by digestion enter the capillary or lymphatic vessel.

absorption

___ are the shallow invaginations between the villi

crypts of Lieberkuhn

The mucosal lining has a rapid turnover. The crypts of Lieberkuhn have stem cells for cell ___.

regeneration

Draw villi diagrams (s & p.625)

Draw villi diagrams (s & p.625)

___-The enzymatic breakdown of food molecules, as there is the addition of water in breaking the molecular bonds. Carbohydrates, Proteins,  Fats (lipids), Nucleic Acids

hydrolysis

___ are absorbed in the form of monosaccharides. Begins with salivary amylase, continues with pancreatic amylase. Specific enzymes for sugars, ending with –ase ending: Lactose = Lactase, Maltose = Maltase

carbohydrates

Review monosaccharides graphic (slides)

Review monosaccharides graphic (slides)

___ are absorbed as amino acid monomers. Begins with conversion of pepsinogen to pepsin in stomach. Carboxypeptidase splits carboxyl group. Aminopeptidase splits amino group

proteins

Review amino acid graphics (slides)

Review amino acid graphics (slides)

Draw Flowchart of chemical digestion of carbohydrates and proteins (slides)

Draw Flowchart of chemical digestion of carbohydrates and proteins (slides)

___ is a digestive enzyme primarily produced by the pancreas that catalyzes the breakdown of dietary fats (triglycerides) into fatty acids and glycerol

lipase

___ are absorbed as monoglycerides. Lipases break triglycerides from glycerol backbone for absorption

lipids

Review lipids graphic

Review lipids graphic

___ are hydrolyzed into nucleotide monomers by pancreatic nucleases | Nucleosidases | Phosphatases | Release free bases, pentose sugars and phosphate ions

nucleic acids

Review nucleic acids graphic

Review nucleic acids graphic

Draw flowchart of chemical digestion of lipids and nucleic acids

Draw flowchart of chemical digestion of lipids and nucleic acids

Absorption - occurs through Active Transport across the epithelial surface (requires ATP). This is termed ___, as the nutrients must pass through cells

transepithelial transport

Transport of ___: Facilitated diffusion, coupled with sodium

carbohydrates

Glucose and ___ are moved by secondary active transport. They are cotransported with sodium

galactose

___ is absorbed by passive facilitated diffusion

fructose

Draw carbohydrate transportation diagram (slides)

Draw carbohydrate transportation diagram (slides)

Transport of proteins: amino acid monomers by diffusion or facilitated diffusion coupled to ___

sodium

Draw protein transportation diagram (slides)

Draw protein transportation diagram (slides)

Transport of Lipids: Couple with Bile Salts (lecithin) to form micelles (phospholipid bilayer). Enter the ___ of the lymphatic system to enter the blood

lacteals