UMich NURS 210/211: Chapter 23

A long tube that open at both ends for the transit of food during processing.

Gastrointestinal Tract

Named portions of the GI tract include:

esophagus, stomach, small intestine, large intestine, rectum

Accessory structures are...

Not part of the GI tract but they do contribute to food processing.

Accessory structures include...

teeth's tongue, salivary glands, liver, gall bladder, and pancreas

What processes are involved in digestion? (6)

Ingestion, secretion, motility, digestion, absorption, defection

enteric nervous system

submucosal plexus and myenteric plexus

Autonomic nervous system

parasympathetic and sympathetic

GI reflex pathways regulate...

GI secretion and motility response to stimuli within the GI tract

What is the largest serous membrane in the body?

peritoneum

What is the "fatty apron" overlying the intestines?

Greater momentum

What is the fan-shaped fold that separates the coils of the small intestine?

Mesentery

The mouth is formed by...

Cheeks, hard and soft palates, and tongue

Salivary glands lie outside the mouth and...

Empty their contents into ducts which deliver saliva into the oral cavity.

What are the three pairs of salivary glands?

parotid, submandibular, sublingual

Salivary glands are composed of two types of secretory cells:

serous cells and mucous cells

Serous cells...

Produce watery secretion, enzymes, ions, bit of mucin.

Mucous cells...

Produce mucus.

Parotid and submandibular glands contain mostly...

Serous cells

Sublingual glands consist mostly...

Mucous cells.

What forms the floor of the oral cavity?

tongue and associated muscles

Tongue is composed of

skeletal muscle covered with mucous membrane

The tongue participates in

chewing, swallowing, speech

The upper lateral surfaces of the tongue are covered with

papillae, some of which contain taste buds

The teeth project into the mouth and are adapted for

mechanical digestion

What is mechanical digestion?

Chewing mixes food with saliva and forms a bonus which can be easily swallowed.

What is chemical digestion?

Salivary amylase converts polysaccharides to disaccharides, and Lingual lipase converts triglycerides to fatty acids and momoglycerides

The pharynx is a funnel shaped tube that

Extends from the internal nares to the esophagus posteriorly and to the larynx anteriorly

What is the pharynx composed of?

skeletal muscle lined by mucous membrane

The esophagus is a...

Collapsible, muscular tube that lies posterior to the trachea and connects the pharynx to the stomach

The tongue shapes the chewed, lubricated food and...

Moves it to the back of the mouth cavity

How does swallowing work?

The tongue rises against the palate and closes the nasopharynx. The uvula and palate seal off the nasal cavity. The epiglottis covers the larynx.

True or false? When swallowing, breathing is temporarily interrupted.

True

The stomach is a J-shaped enlargement of the...

GI tract

What are the four functions of the stomach?

1. Mixes saliva, food, and gastric juice to form chyme

2. Serves as a reservoir for food before release into the small intestine

3. Secretes gastric juice, which contains HCI, pepsin, intrinsic factor, and gastric lipase.

4. Secretes gastric into the blood.

What do the following do in gastric juice? Pepsin, HCI, Gastric Lipase, Inartistic factors

Pepsin: digestion of proteins

HCI: inactive pepsinogen to pepsin

Gastric Lipase: fat digestion

Intrinsic factor: B12 absorption

The pancreas is a gland that lies

Posterior to the stomach

The pancreas produces enzymes that

digest carbohydrates, proteins, fats, and nucleic acids

The pancreas produces sodium bicarbonate which

buffers stomach acid

The pancreas empties its contents into

duodenum

Pancreatic juices contain proteases that are secreted in a ____ form; they are _____ after they reach duodenum

Inactive; activated

What is enteropeptidase?

enzyme bound to plasma membrane of duodenal epithelial cells, activates pancreatic protease trypsinogen to trypsin

Once trypsin is activated, it then can activate:

More trypsinogen, procarboxypeptidase to active carboxypeptidase, and chymotrypsinogen to active chymotrypsin.

The liver makes

Bile

Bile is important in the

emulsification of fats

The gallbladder stores

bile until it is needed

The liver is composed of

hepatocytes, bile canaliculi, and hepatic sinusoids

What are the 7 functions of the liver and gallbladder?

1. Carbohydrate, lipid, and protein metabolism

2. Processing of drugs and hormones

3. Bilirubin excretion

4. Bile salt synthesis

5. Storage

6. Phagocytosis

7. Vitamin D activation

The majority of digestion and absorption occur in the

small intestine

The small intestine absorbs

About 90% of nutrients and water that pass through digestive system

Segemntations, found in the small intestine, mix

Chime with digestive juices and bring food into contact with mucosa for absorption.

Peristalsis propel

Chime through small intestine

The small intestine completes digestion of

Carbohydrates, proteins, lipids, and completes digestion of nuclei acids

what do circular folds do?

increase the surface area for digestion and absorption in the small intestine

Intestinal juice provides a vehicle for

absorption of substances from chyme as they come in contact with the villi

Where and what do brush border enzymes do?

found on the surfaces of the microvilli of absorptive cells, break down food products.

What are the steps in lipid digestion in the intestines?

Emulsification, digestion, Michelle formation, diffusion,chylomicron formation, chylomicron transport.

What is emulsification?

triglycerides and their breakdown products are insoluble in water. They need pre-treatment with bile salts that break down large fat globules into smaller ones.

What is digestion?

Pancreatic lipase break down fat into monoglyceride plus twos free fatty acids

What is Michelle formation?

Products from digestion become coated with bile salts

What is diffusion?

Lipid products leave Michelle's and cross epithelial membrane via diffusion

What is chylomicron formation?

lipid products are converted back into triglycerides and packaged with lecithin and lipoproteins, forming chylomicron

What is chylomicron transport?

chylomicrons are exocytosed from basolateral side and enter lymphatic lacteal. It is eventually emptied into venous blood at thoracic duct

What are the 5 functions of the colon?

1. Haustral churning, peristalsis, and mass peristalsis drive contents of colon into rectum

2. Bacteria in colon convert proteins into amino acids, break down amino acids, and produce some B vitamins

3. Absorption of some water, ions, and vitamins

4. Formation of feces

5. Defection

What is hausal churning?

Dissension reaches a certain point and the walls of the haustra contract to squeeze onward

What is peristalsis?

propulsive contractions

What is mass peristalsis?

A strong peristaltic wave that begins in the transverse colon and quickly drives the contents of the colon into the rectum.

The last stages of digestion occur through

bacterial action

What are the last stages of digestion?

Substances are further broken down by bacteria and some vitamins are synthesized by bacterial action.

What is the cephalic phase of digestion?

Stimulates gastric secretion and mobility

What is the gastric phase of digestion?

- neural and hormonal mechanisms- distension activates stretch receptors, initiating both long and short reflexes.

- Chemical stimuli, such as partially digested proteins, caffeine, and low acidity activate enteroendocrine G cells and secrete gastrin.

What is the intestinal phase of digestion?

Partially digested food enters small intestine, causing a brief release of intestinal gastrin. encourages gastric glands of stomach to continue secretory activities.