A&P2 Ch 29 Digestive System

coordination of the different functions of the digestive system

Regulation

some compounds of food resist digestion and are eliminated as feces

Residues of digestion

Mucus lubricates food and, with water, facilitates mixing

Saliva

Sodium bicarbonate increases the pH for optimum amylase function

Saliva

secreted by salivary glands

Saliva

digestive enzyme secretion facilitates chemical digestion

Secretion

mouth to oropharynx

Oral stage

-voluntarily controlled - food bolus in middle of the tongue -tongue press bolus against palate and food is moved to the oropharynx

Oral stage (3)

is the main fat-digesting enzyme

Pancreatic lipase

(secreted as inactive pepsinogen by chief cells)—a protease that begins the digestion of proteins

Pepsin

oropharynx to esophagus

Pharyngeal stage

A small amount of salivary lipase is released; function uncertain

Saliva

Chemical digestion: Chemical changes result from hydrolysis-

process in which compound unites with water and breaks down further

-involuntary movement -contractions and gravity move bolus through esophagus to stomach

(2)Esophageal stage

-wavelike ripple of the muscle layer of a hollow organ -progress motility that produces forward movement of matter along the GI tract

(2)Peristalsis

-2 main types of motility produced by the smooth muscle of the GI tract -can occur together in an alternating fashion

(2)Peristalsis and Segmentation

-mixing movement -digestive reflexes cause a forward-and-backward movement with a single segment of the GI tract -helps break down food particles -mixes food and digestive juices, and brings digested food to intestinal mucosa to absorption

(4)Segmentation

movement of nutrients through the GI mucosa into the internal environment

Absorption

an enzyme that begins digestion of starches

Amylase (Saliva)

all changes in chemical composition of food as it travels thru the digestive tract

Chemical digestion

breakdown of complex nutrients into simple nutrients

Digestion

food is taken in

Ingestion

Reduces size of food particles

Mastication

is functionally an extension of the external

digestive tract

-involuntary movement -propel bolus from the pharynx to the esophagus -the mouth -nasopharynx -larynx must be blocked -combination of contractions and move bolus into esophagus

(6)Pharyngeal stage

Properties of digestive enzymes (5)

-Specific in their action -Function optimally at a specific pH -Most enzymes catalyze a chemical reaction in both directions -Enzymes are continually being destroyed or eliminated from the body and must continually be synthesized -Most digestive enzymes are synthesized as inactive proenzymes

Food in the stomach is churned (propulsion and retropulsion) and mixed with gastric juices to form chyme

Gastric motility

process of swallowing; complex process requiring coordinated and rapid movements

Deglutition

Operate in lumen of digestive tract, outside of any body cells

Digestive enzymes

extracellular, organic (protein) catalysts

Digestive enzymes

excretion of material that is not absorbed

Elimination

esophagus to stomach

Esophageal stage

controlled by hormonal and nervous mechanisms

Gastric emptying

secreted by gastric glands

Gastric juice

-Chyme is ejected every 20 seconds into the duodenum -takes 2 to 6 hours to empty the stomach

Gastric motility

-fats in duodenum stimulate and release of gastric inhibitory peptide, which decreases peristalsis of gastric muscle and slows passage of chyme into duodenum

Hormonal mechanism

(7)Mechanisms used use for the primary function of the digestive system

Ingestion, Digestion, Motility of GI wall, Secretion, Absorption, Elimination, and Regulation

After leaving stomach, pass of chyme to the small intestine take about 5 hours

Intestinal motility

Peristalsis rate picks up as chyme approaches end of jejunum, moving it through small intestine into the large intestine

Intestinal motility

Segmentation in duodenum and upper jejunum mixes chyme with digestive juices from the pancreas, liver, and intestinal mucosa

Intestinal motility

includes peristalsis and segmentation

Intestinal motility

Mixes food with saliva in preparing for swallowing

Mastication

chewing movements

Mastication

Change ingested food from large particles into minute particles, facilitating chemical digestion

Mechanical digestion

Churn contents of the GI lumen to mix with digestive juices and contact w/ the surface of intestinal mucosa, facilitating absorption

Mechanical digestion

Propel food along the alimentary tract, eliminating digestive waste from the body

Mechanical digestion

movements of the digestive tract

Mechanical digestion

physically breaks down large chunks of food materials and moves food along the tract

Motility of the GI wall

-enterogastric reflex -receptors in the duodenal mucosa are sensitive to presence of acid and to distention -impulses over sensory and motor fibers in the vagus nerve cause a reflex inhibition of gastric peristalsis

Nervous mechanism

are hydrolyzed by amylases to form disaccharides

Polysaccharides

Fats must be emulsified by:

bile in small intestine before being digested

material does not truly enter the body until it is absorbed into the internal environment

digestive tract

Main proteases:

pepsin in gastric juice, trypsin in pancreatic juice, peptidases in intestinal brush border

regulated by intrinsic stretch reflexes; stimulated by cholecystokinin (CCK)

peristalsis

Proteases catalyze hydrolysis of:

proteins into intermediate compounds and, finally, into amino acids

Carbohydrates are:

saccharide compounds

Final steps of carbohydrate digestion are catalyzed by:

sucrase, lactase, and maltase, found in the cell membrane of epithelial cells covering the villi that line the intestinal lumen

Primary function of the digestive system:

to bring nutrients into the internal environment so they are available to each cell of the body

Protein compounds are made up of:

twisted chains of amino acids