23.2 Digestive System Processes and Regulation

what are the 6 activities in the process of digestion

ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defaction

what ingestion (1st process)

the entry of food into the alimentary canal (Gl tract or gut) through the mouth

what happens in ingestion

food is chewed and mixed with salvia containing enzymes that break down the carbohydrates in food plus some lipid digestion via lingual lipase

what does chewing do

increases the surface are of the food and allows an appropriately sized bolus to be produced

when does food leave the mouth

when the tongue and pharyngeal muscles propel it into the esophagus

what is propulsion

the movement of food through the digestive tract

what does propulsion include

the voluntary process of swallowing and the involuntary process of peristalis

what is peristalisis

sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, which act to propel food along

what role does peristalsis play in

mixing food with digestive juices

what is mechanical digestion

physical process that does not change the chemical nature of the food. Instead, it makes the food smaller to increase both surface area and mobility

what does mechanical digestion include

mastication and segmentation

what is mastication

chewing

what does the tongue do in digestion

tongue movements help break food into smaller bits and mix food with saliva

mechanical is does not only occur in the mouth, but also

after the food leaves the mouth

what is chyme

soupy liquid created when food is mixed with digestive juices

where does segmentation mainly occur

in the small intestine

what is segmentation

contraction of circular muscle in alimentary canal

what do the contractions in segmentation do

isolate small sections of the intestine, moving their contents back and forth while continuously subdividing, breaking up, and mixing the contents

what facilitates absorption

movement of back and forth in the intestinal lumen and segmentation mixing with digestive juices

where does chemical digestion start

in the mouth

what is chemical digestion

enzymatic breakdown of food

what does chemical digestion do

break down complex food molecules into their chemical building blocks; proteins into separate amino acids

where is chemical digestion completed

in the small intestine

what is the composition in chemical digestion

water, various enzymes, acids, and salts

what is absorption

takes place in small intestine where most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream through the epithelial cells that make up the mucosa

how are lipids absorbed and transported

into lacteals lacteals and are transported via the lymphatic vessels to the bloodstream (the subclavian veins near the heart)

what is the final step of digestion

defecation

what is defecation

elimination of undigested substances from the body in the form of feces

where does ingestion occur

only in the mouth

where does defecation occur

only in the anus

where can some absorption occur

in the mouth and stomach

where can some chemical digestion occur

in the mouth

How does aging affect appetite?

Taste buds become less sensitive, reducing appetite

What oral problems can make eating harder in older adults?

Tooth loss, gum disease, and reduced saliva production

Why does food move more slowly through the digestive tract with age?

Weakened muscles and reduced neurosensory feedback

What upper GI conditions are more common with age?

Hiatal hernia, gastritis, and peptic ulcers

What are common small intestine issues in older adults?

Duodenal ulcers, maldigestion, and malabsorption

What large intestine problems increase with age?

Hemorrhoids, diverticular disease, and constipation

What accessory organ conditions may develop in the elderly?

Jaundice, pancreatitis, cirrhosis, and gallstones

What is the primary goal of neural and endocrine regulatory mechanisms in the digestive system?

To maintain optimal conditions in the lumen for digestion and absorption

How do these regulatory mechanisms stimulate digestive activity?

Through mechanical and chemical activity, controlled by extrinsic and intrinsic pathways

Where are sensory receptors located that help regulate digestion?

In the walls of the alimentary canal

What types of receptors are found in the alimentary canal, and what do they detect?

mechanoreceptors, chemoreceptors, and osmoreceptors

what do mechanoreceptors detect

stretch or pressure (mechanical stimuli)

what does chemoreceptors deter

the chemical composition of contents

what do osmoreceptors detect

osmotic pressure or fluid concentration

what kinds of information can these receptors detect during digestion?

stomach expansion, food breakdown, fluid levels, and types of nutrients (lipids, carbohydrates, proteins)

What happens when these receptors are stimulated?

They trigger reflexes that further digestion by: activating glands to secrete digestive juices, stimulating muscles to perform peristalsis and segmentation

What structures in the digestive wall contain the nerve networks that control reflexes?

Nerve plexuses embedded in the walls of the entire alimentary canal

What are the two types of reflexes involved in digestive control?

extrinsic (long reflexes) and intrinsic (short reflexes)

what are extrinsic nerve plexuses

long reflexes involving the central and autonomic nervous system working to respond to stimuli outside the digestive system

what are intrinsic nerve plexuses

short reflexes within the alimentary canal wall

what is the enteric nervous system

extrinsic and intrinsic nerve plexuses

what does the intrinsic nerve plexus do

regulate activities in one area of the digestive tract and may coordinate local peristaltic movements and stimulate digestive secretions

What orchestrates long reflexes, and what do they respond to?

Extrinsic nerve plexuses, involving the central and autonomic nervous systems, and they respond to stimuli outside the digestive system

What orchestrates short reflexes, and what do they respond to?

Intrinsic nerve plexuses within the digestive wall; they respond to local stimuli such as stretching or chemical presence

What is the function of short reflexes?

They regulate local digestive activity, including peristalsis and digestive secretions in the same or nearby regions

What is an example of a long reflex?

The sight, smell, or taste of food triggers a sensory signal to the medulla oblongata, which stimulates gastric secretion in anticipation of food

What is an example of a short reflex?

Distension of the stomach by food triggers reflexes in the stomach wall that increase digestive juice secretion locally

what is the main digestive hormone of the stomach

gastrin

What role do hormones play in the digestive system?

They help regulate digestion by stimulating or inhibiting secretions and movement in the digestive tract and accessory organs

What triggers the release of gastrin?

The presence of food in the stomach

What does gastrin stimulate?

It stimulates the secretion of gastric acid by the parietal cells of the stomach lining

Where are other digestive hormones produced besides the stomach?

In the duodenum, which is the first section of the small intestine

What does the hormone secretin do?

It stimulates the pancreas to release a watery secretion of bicarbonate, which helps neutralize stomach acid

What does cholecystokinin (CCK) do?

It stimulates the pancreas to release digestive enzymes, prompts the liver to produce bile, and triggers the gallbladder to release bile

what does CCK stand for

cholecystokinin

What is the function of gastric inhibitory peptide?

It inhibits gastric secretion and slows gastric emptying and motility

What cells produce digestive hormones in the GI tract?

Specialized epithelial cells called endocrinocytes

Where are endocrinocytes located?

In the mucosal epithelium of the stomach and small intestine

How do GI hormones reach their target organs?

They are released into the bloodstream and travel to their target organs through circulation