BI 210 - Digestive Systems

1. Tract - hollow, connected set of structures that food passes through & continuous w/ outside world

2. Accessory structures — Solid organs making digestive secretions through exocrine glands

Difference between gastrointestinal tract & accessory digestive organs

1. Digestive — mouth, esophagus, stomach, small intestine, colon, rectum, anus

2. Accessory — liver, gallbladder, pancreas, salivary glands

Name the organs of the digestive tract vs. accessory structure

1. Break down foods you eat, release nutrients, & absorb nutrients into body

2. Generate, store, and excrete some wastes

What are the major functions of digestive system? (2)

enzymes + acids to break up food molecules

Chemical Digestion

physically breaking up food molecules through chewing & grinding

Mechanical Digestion

Teeth

Muscularis layer through GI tract

esophagus (peristalsis

Locations of mechanical digestion

Mouth, stomach, small intestine

Locations of chemical digestion

sequential, alternating waves of contraction + relaxation of 2 muscularis layers that propels food along tract + mixes food w/ digestive juices

What is peristalsis?

1. Mouth

2. Pharynx (Nasopharynx, oropharynx, larnygophayrnx)

3. Esophagus 

4. Stomach

5. Small Intestine (duodenum, jejunum, Ileum)

6. Large Intestine (transverse colon, ascending colon, descending colon)

7. Rectum 

8. Anus

Trace the pathway of ingested substances through the gastrointestinal (GI) tract (8)

1. Mucosa

   1. Epithelium

   2. Lamina Propia

   3. Muscularis Mucosae

2. Submucosa

3. Muscularis Externa

4. Serosa/Adventitia

Describe the entire layer structure of gastrointestinal tracts

Epithelium w/ mucus 

Mucosa

simple columnar (stomach, intestines)

stratified squamous (mouth, pharynx, esophagus

What epithelium is found in mucosa

numerous blood & lymphatic vessels/lymphocytes that transport nutrients across wall of GI tract

What is present in lamina propia?

thin layer of smooth muscle in contant state of tension

What is muscularis mucosae?

Dense CT rich w/ lymphatic vessels + glands 

What is submucosa?

double smooth muscle layer

Circular, longitudinal, oblique

contract layers that propel food along tract

What is muscularis externa? what are the 2/3 layers? What is its responsibility?

CT that holds bigger arteries, veins, nerves to GI tract wall

Adventitia — mouth, pharynx, esophagus

What is serosa/adventitia?

1. Parietal Peritoneum

2. Peritoneal Cavity w/ serous fluid

3. Visceral peritoneum

Structure of peritoneums

Parietal — lining abdominal wall

Visceral — abdominal organs

What does the parietal vs. visceral peritoneum hug?

suspend each fold from posterior abdominal wall & hold abdominal organs in place

What are mesenteries?

Liver w/ stomach

What does lesser omentum tie together?

curtain on intestine

Serve as policemen w/ immune cells during sites of inflammation

Where does greater omentum hang? What other purpose do they have?

Lying within peritoneal cavity

Stomach, small intestine

Intraperitoneal Organs & examples

Posterior to peritoneum

Kidneys, duodenum, portions of colon, rectum

Retroperitoneal Organs & examples

1. Parotid - between skin + masseter muscles

2. Submandibular - floor of mouth

3. Sublingual - below tongue

3 major salivary glands and locations

Solubilizes taste molecules

How does saliva go into taste pores?

1. Histostatin — wound healing molecule

2. Lysozyme — bacterial fighting molecule

3. Basic compound that neutrlizes acidic foods + beverages

What does saliva contain? (3)

Forces food down throat as bolus and initiating periastalsis

Swallowing

What is pharynx’s role in relation to food?

muscular tube that connects pharynx to stomach & triggers pharynx and allows bolus to move

What is the esophagus’s role in digestion?

 ring of smooth or skeletal muscle that can close completely, creating doorway between one space in body & another 

What are sphincters?

Prevents acid from traveling up esophagus (acid reflux, heart burn)

What’s the purpose of esophageal sphincters?

1. Cardia

2. Fundus

3. Body

4. Pylorus

What are the 4 main regions of the stomach in order?

release of stomach contents from stomach into small intestine

What does the pyloric sphincter control?

1. Mechanical digestion - muscle layers

2. Chemical digestion - protein from acids

3. Holding tanks so we can slowly digest things

4. Protect itself from itself

Describe the 4 general functions of the stomach and its specialization

Long tunnels leading to gastric glands secreting juice with cells that aid in process of digestion

What are gastric pits and their purpose?

Acid (HCl)

What does parietal cells secrete?

Pepsinogen (becomes pepsin + breaks peptide bonds — inactive to active)

What do chief cells secrete?

Digestive hormones

What do enteroendocrine cells secrete?

Prevents acidic stomach contents from entering esophagus

What is the purpose of lower esophageal sphincter?

Each fold in internal lining of empty stomach

What are rugae?

breakdown/digestion + absorption

What is the small intestine most responsible for in digestion?

1. Ileum

2. Jejunum

3. Duodenum

Name the segments of small intestine in terms of longest to shortest

Deep ridge of mucosa + submucosa that expands surface area + increases amount of nutrient absorption

Purpose of circular folds?

fingerlike projections that increase surface area for secretion + absorption

Purpose of villi and microvilli

unique to duodenum, secrete alkaline mucus to protect duodenum from acidic chyme

What are duodenal glands?

tubular depression between villi of small intestine secreting intestinal juices (watery fluid that services as transport medium for absorbing nutrients)

What are intestinal glands?

1. Haustra

2. Cecum

3. Appendix

4. Ascending colon

5. Descending colon

6. Sigmoid colon

7. Rectum

8. anal canal

9. Anal aphincter

What are all the parts of the large intestine? (9)

packed w/ bacteria; bacterial reservoir + small cohort of every bacterial population in colon present (microbiome)

What is appendix purpose?

storage tank for feces

What is the rectum?

passage way for feces

What is the anal canal?

1. Detoxifies ingested substances via hepatic portal system

2. Makes plasma proteins

3. Recycles RBCs

4. Generates bile

5. Adjusts nutrient concentrations in blood

What are the general functions of the liver? (5)

fundamental units of liver made of hepatocytes

What are hexagonal lobules?

stores + concentrates bile & secretes it into the common bile duct via cystic duct into duodenum

What is the gallbladder?

posterior to the stomach, exocrine portion secretes pancreatic juice + endocrine portion secretes insulin + glucagon

What is the pancreas?

small opening that enters into duodenum

What is the ampulla of the pancreas?

largest duct in the pancreas fusing w/ common bile duct

What is the main pancreatic duct?

small islands of endocrine cells producing hormones involved in metabolism + nutrient homeostasis

What are islet cells?