Chapter 23 Study Guide

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o   What is the definition of digestion?

Digestion is the process by which food is broken down into smaller components that can be absorbed into the bloodstream for use by the body.

o   List in order from mouth to anus the path of food. When does it become a bolus? When does it become chyme? When does it become feces?

1. Mouth - Food is chewed and mixed with saliva, forming a bolus.

2. Esophagus - The bolus travels down the esophagus through peristalsis.

3. Stomach - The bolus is mixed with gastric juices and becomes chyme.

4. Small intestine - Chyme is further digested and nutrients are absorbed into the bloodstream.

5. Large intestine - Remaining waste is formed into feces.

6. Anus - Feces are expelled from the body.

o   What digestive activities (ingestion, mechanical breakdown, propulsion, digestion, absorption, defecation) are happening at each point as the food makes its way to that section of the GI tract?

At the mouth: ingestion, mechanical breakdown (chewing), propulsion (swallowing), and digestion

At the stomach: mechanical breakdown (churning), digestion, and absorption

At the small intestine: mechanical breakdown (segmentation). digestion, and absorption

At the large intestine: digestion, absorption, and defecation

o   Define mechanical digestion.  Define chemical digestion.  What are some of the examples given in class?

• Mechanical Digestion: The physical process of breaking down food into smaller pieces without altering its chemical structure. Examples include chewing and churning in the stomach.

• Chemical Digestion: The enzymatic breakdown of food into smaller molecules that can be absorbed. Examples include the breakdown of carbohydrates by amylase and proteins by pepsin.

o   What is peristalsis. Where does it occur? What layer of the alimentary canal is responsible for this action? What are sphincters?

Peristalsis is the main method of propulsion. Adjacent segments of the GI tract alternately contract and relax. (smooth muscle). Food moves along the tract. Sphincters are a ring-shaped muscle that relaxes or tightens to open or close a passage or opening in the body.

o   What is segmentation?

segments of GI tract contract and relax (smooth muscle. Food moves forward and then backward. Mixes and breaks down food.

o   What is the peritoneum? Which layer lines the organs? The body wall?

peritoneum is a serous membrane that surrounds most abdominopelvic organs. The parietal peritoneum lines the body wall. the visceral peritoneum lines the external surface of most digestive organs.

o   How does the peritoneum relate to the serosa layer of the Alimentary canal?

The serosa layer of the Alimentary canal is essentially the visceral peritoneum that directly covers the organs, providing a protective layer and reducing friction as digestive organs expand and contract during digestion.

o   What is peritonitis and how does a burst appendix cause it?

peritonitis is inflammation of the peritoneum. A burst appendix can spill infectious materials into the abdominal cavity, leading to a bacterial infection that irritates and inflames the peritoneum.

o   What are the mesenteries, and what are their main functions? Provide specific examples from lecture.

Mesenteries are folds of the peritoneum that suspend and support the abdominal organs, ensuring they maintain their proper position in the abdominal cavity. Their main functions include providing a pathway for blood vessels, nerves, and lymphatics to reach the organs, as well as storing fat. For example, the mesentery of the small intestine helps to anchor the small bowel while allowing for the necessary mobility during digestion.

o   What is the hepatic portal circulation?

Hepatic portal circulation refers to the system of veins that carry blood from the digestive organs to the liver. This process allows the liver to process nutrients and detoxify harmful substances before the blood is circulated to the rest of the body.

o   From where does the hepatic portal circulation drain blood? To where does it drain?

drains from nutrient rich blood + drains to the liver

o   What is special about the blood in the veins of the hepatic portal circulation?

The blood in the veins of the hepatic portal circulation is unique because it is rich in nutrients absorbed from the digestive tract, which the liver then processes for distribution and detoxification.

o   What are the four layers of the alimentary canal?

The four layers of the alimentary canal are:

• Mucosa: The innermost layer, responsible for secretion and absorption.

• Submucosa: A layer of connective tissue that contains blood vessels, nerves, and glands.

• Muscularis: Composed of smooth muscle, it facilitates movement and digestion through contractions.

• Serosa: The outermost layer, providing protection and support.

o   What cell types does each layer contain?

• Submucosa: Contains fibroblasts, immune cells, and endothelial cells.

• Muscularis: Comprises smooth muscle cells and interstitial cells of Cajal (pacemaker cells).

• Serosa: Made up of mesothelial cells and connective tissue.

o   How do the layers change from esophagus to stomach to small and large intestine? How does this reflect the difference in function at each point? What is the epithelial cell lining in each spot?

• Esophagus: The mucosa features stratified squamous epithelium for protection against abrasion, while the muscularis includes both skeletal and smooth muscle to facilitate swallowing.

• Stomach: The mucosa transitions to simple columnar epithelium, with specialized cells for secretion of gastric juices. The muscularis thickens to include three layers (oblique, circular, and longitudinal) to aid in churning and mixing food.

• Small Intestine: The mucosa remains simple columnar epithelium but includes villi and microvilli for increased surface area and absorption. The muscularis is adapted for peristalsis to move chyme along.

• Large Intestine: The mucosa retains simple columnar epithelium with numerous goblet cells to facilitate lubrication and absorption of water. The muscularis has fewer layers of smooth muscle, reflecting a main function of water reabsorption and feces formation.

o   In which layer is mucosa-associated lymphatic tissue (MALT) found?

The mucosa-associated lymphatic tissue (MALT) is found in the mucosal layer, providing an essential role in immune function within the gastrointestinal tract.

o   Name 3 chemical and 1 mechanical stimuli that provide intrinsic control of the GI tract.

• Chemical Stimuli:

• Presence of food in the stomach triggers gastric secretions

• Hormonal signals such as gastrin influencing digestive processes

• Changes in pH levels in the intestinal lumen affecting enzyme activity

• Mechanical Stimulus:

• Stretch receptors activated by the distension of the stomach or intestines during digestion.

o   Name 3 hormones that regulation GI tract activity. Where is each hormone secreted? Where does each hormone act?

• Gastrin: Secreted by G cells in the stomach, acts on the gastric glands to stimulate secretion of gastric acid.

• Secretin: Secreted by S cells in the duodenum, acts on the pancreas to stimulate the secretion of bicarbonate.

• Cholecystokinin (CCK): Secreted by I cells in the duodenum, acts on the gallbladder to stimulate bile release and the pancreas to promote enzyme secretion.

o   Which branch of the ANS stimulates digestion and which inhibits digestive activities?

• The parasympathetic branch of the autonomic nervous system (ANS) stimulates digestion, enhancing digestive activities through increased blood flow to the digestive tract and promoting peristalsis.

• Conversely, the sympathetic branch of the ANS inhibits digestive activities, often during stress, by diverting blood flow away from the gastrointestinal tract and slowing down digestive processes.

o   Compare short reflexes of the enteric nervous system to long reflexes.

Short reflexes: intrinsic stimuli act within the GI wall (stretch or changes in pH, nutrients, or solutes)

Long reflexes: extrinsic stimuli act through the CNS

o   Which subdivisions of the nervous system provide inputs for long reflexes?

Long reflexes are influenced by both the autonomic nervous system, which includes the sympathetic and parasympathetic divisions, and higher centers in the brain that can modulate digestive functions.

o   What digestive processes occur in the mouth and which accessory organs are necessary for these processes?

In the mouth, mechanical digestion begins with chewing, while chemical digestion starts with enzymes in saliva. The accessory organs necessary for these processes include the salivary glands, which produce saliva containing enzymes like amylase, and teeth for breaking down food.

o   What is the lingual frenulum?

The lingual frenulum is a thin band of tissue that connects the underside of the tongue to the floor of the mouth, helping to stabilize the tongue's position and aiding in movement during speech and swallowing.

o   Which epithelial tissue type lines the mouth?

The mouth is lined with non-keratinized stratified squamous epithelium, which provides protection against abrasion and allows for the passage of food.

o   List the three salivary glands.

• parotid gland

• submandibular gland

• sublingual gland

o   What is the function of saliva?

• dissolves food & chemicals for taste

• moistens & compacts food into a bolus

• begins the breakdown of starch with enzymes

o   What are the components of saliva? pH?

• Components of saliva include water, electrolytes (like sodium, potassium, calcium), mucus, antibacterial compounds (such as lysozyme), and enzymes (like amylase and lipase).

• The pH of saliva typically ranges from 6.2 to 7.6, making it slightly acidic to neutral.

o   How many baby teeth are there?

There are 20 baby teeth, also known as primary teeth, which typically begin to emerge around six months of age and are fully developed by the age of three.

o   Know the structure of the teeth.

• incisors

• canines

• premolars

• molars

crown: part above the gum

root: jawbone

neck: connects crown to root

o   What is the function of each type of tooth?

incisors- shear and cut

canines- tear or pierce

premolars- grind and crush

molars- best gringers

peridontal ligament- anchors tooth in socket

enamel- hardest substance in body

dentin- bonelike material under enamel

root canal- contains blood vessels and nerves

o   What are wisdom teeth?

Wisdom teeth are the third set of molars that typically emerge in late adolescence or early adulthood, often requiring removal due to impaction or overcrowding.

·      23.5.1 Describe the anatomy and basic functions of the pharynx and esophagus.

pharynx: The pharynx is a muscular tube that connects the nasal cavity and mouth to the esophagus, playing a crucial role in both the respiratory and digestive systems by facilitating the passage of air and food.

esophagus: The esophagus is a muscular tube connecting the pharynx to the stomach, responsible for transporting food and liquids through peristaltic movements.

o   What is heartburn?

Heartburn is a burning sensation in the chest caused by the reflux of stomach acid into the esophagus

o   Which epithelial tissue type lines the pharynx and esophagus?

stratified squamous epithelium lines the pharynx and esophagus

·      23.6.1 Describe stomach structure and indicate changes in the basic alimentary canal structure that aid its digestive function.

cardia, fundus, body, pylorus

o   What is chyme? 

chyme is an acidic slurry of ingested food formed in the stomach

o   What is does the pyloric valve do?

the pyloric valve regulates the passage of chyme from the stomach into the small intestine, controlling the release of partially digested food and ensuring proper digestion.

o   What digestive actions occur in the stomach? Can anything be absorbed here?

The stomach primarily serves to mechanically and chemically break down food using gastric juices, which include hydrochloric acid and enzymes such as pepsin. Additionally, while the stomach is not a major site for absorption, it can absorb small amounts of certain substances like alcohol and some medications.

o   What are the components of gastric juice? pH?

Gastric juice is composed of hydrochloric acid, pepsinogen, intrinsic factor, and mucin, with a pH typically ranging from 1.5 to 3.5, which creates an acidic environment essential for digestion.

o   What are the cell types found in gastric pits and their secretions?

mucous cells: secrete alkaline mucus to protect surface epithelium

parietal cells: secrete HCI and secrete intrinsic factor

chief cells: secrete pepsinogen (immature form of pepsin) and secretes lipases

enteroendocrine cells: secrete paracrine and hormones also secretes gastrin

§  How do the mucous cells protect the stomach from being digested by the enzymes it secretes?

it uses alkaline mucus to protect the surface epithelium

§  What do chief cells secrete?

secrete: pepsinogen and lipases

§  What do parietal cells secrete and how does this activate what chief cells secrete?

Parietal cells secrete hydrochloric acid (HCl) and intrinsic factor; the HCl activates pepsinogen into pepsin, which is crucial for protein digestion.

o   What is the function of gastrin?  Which cells secrete it? In which organ are those cells located?

Gastrin functions to stimulate the secretion of gastric acid by parietal cells; it is secreted by G cells, which are located in the stomach.

o   Name the three phases of gastric activity. What is the source of control for each phase?

cephalic phase:

• CNS control

• stomach responds to sensations or thoughts of food

• stomach responds to emotional state

  Gastric phase:

• intrinsic control

• stomach, digestion, nutrient levels, and gastric pH

  intestinal phase:

• intestinal control

• stretching of duodenum

• presence of nutrients in duodenum

o   Which mesentery suspends the liver to the ventral body wall?

the falciform ligament (strip of mesentery) attaches the liver to the ventral body wall

o   Compare hepatitis with cirrhosis? Features? Causes?

Hepatitis:

• inflammation of the livers

• caused by a viral infection, drug toxicity, and wild mushroom poisoning

  cirrhosis:

• chronic liver inflammation

• liver becomes fatty and fibrous

• caused by chronic hepatitis and alcoholism

o   What digestive substance does the liver produce?

The liver produces bile (fat emulsifier)

o   What type of molecule is broken down by bile?

Bile primarily helps in the breakdown of fats, specifically triglycerides, into smaller molecules that can be easily absorbed by the intestine.

o   Name the structures responsible for secretion of pancreatic juice.

The structures responsible for the secretion of pancreatic juice are the acinar cells of the pancreas.

o   Name the digestive enzymes found in pancreatic juice. What is digested by each enzyme?

• Amylase: Digests carbohydrates (starches) into simpler sugars.

• Lipase: Breaks down fats (lipids) into fatty acids and glycerol.

• Proteases (such as trypsin and chymotrypsin): Break proteins down into smaller peptides and amino acids.

o   Why is the pH of pancreatic juice basic?

The pH of pancreatic juice is basic because it neutralizes the acidic chyme coming from the stomach, creating an optimal environment for enzymes to function efficiently.

o   Where is bile stored and concentrated?

Bile is stored and concentrated in the gallbladder before being released into the small intestine to aid in the digestion and absorption of fats.

o   What are gallstones? Why do they form?

gallstones are crystalized cholesterol. Forms from too much cholesterol and too few bile salts

o   Does the gallbladder produce bile?

No, the gallbladder does not produce bile; it merely stores and concentrates bile produced by the liver.

o   Bile leaves the liver through which ducts?

Bile leaves the liver through the hepatic ducts, which then merge to form the common bile duct before entering the duodenum.

o   Bile leaves the gallbladder through which ducts?

Bile leaves the gallbladder through the cystic duct, which connects to the common bile duct, allowing bile to flow into the duodenum as needed.

o   To which segment of the intestines do hepatic and pancreatic ducts connect?

They connect to the duodenum, specifically at the ampulla of Vater, where bile and pancreatic juice are released to aid in digestion.

o   Proteases are produced by the pancreas in inactive forms. How does this help to protect the pancreas? Where are these proteases activated?

This prevents the enzymes from digesting pancreatic tissue itself, and they are activated in the small intestine upon entering an alkaline environment.

o   What are the three segments of the small intestine?

• duodenum

• jejunum

• ileum

o   Of the 3 segments of the small intestine, which does the most absorption?

The ileum is responsible for the majority of nutrient absorption, particularly vitamin B12 and bile salts.

o   What are villi and what is their function?

Villi are tiny, finger-like projections that line the surface of the ileum, increasing the surface area for absorption and facilitating the uptake of nutrients into the bloodstream.

o   What are microvilli and what is their function?

Microvilli are even smaller hair-like structures that extend from the surface of each villus, further enhancing the absorptive surface area and enabling more efficient nutrient absorption by creating a brush border effect.

o   Where do you find intestinal crypts?

Intestinal crypts are found within the mucosal layer of the small intestine, specifically located between the villi.

o   What are lacteals and which nutrient gets absorbed through them? How are all other nutrients absorbed?  Where are lacteals found?

Lacteals are specialized lymphatic capillaries found within each intestinal villus. They primarily absorb dietary fats, specifically triglycerides, which are broken down into fatty acids and glycerol before entering the lymphatic system.

o   In which layer of the duodenum wall are duodenal glands found?

Duodenal glands are located within the submucosal layer of the duodenum. They secrete alkaline mucus.

o   What is the function of duodenal glands?

The function of duodenal glands is to produce a secretion that neutralizes gastric acid, providing an optimal pH for the activity of digestive enzymes in the small intestine.

o   Where are enteroendocrine cells found? What substances do they secrete?

Enteroendocrine cells are found within the epithelium of the gastrointestinal tract, particularly in the stomach and small intestine, and they secrete various hormones such as gastrin, secretin, and cholecystokinin.

o   What is the function of absorptive cells? Where are they found?

Absorptive cells are specialized epithelial cells primarily located in the villi of the small intestine, and their main function is to absorb nutrients such as carbohydrates, proteins, and fats from the intestinal lumen into the bloodstream.

o   What is the function of Goblet cells? Where are they found?

Goblet cells are found throughout the lining of the gastrointestinal tract, particularly abundant in the intestinal and respiratory tracts, and their primary function is to secrete mucus.

o   What are the functions of CCK and secretin? How do they affect stomach activity? How do they affect liver and pancreas activity?

• CCK is released from the small intestine in response to fatty acids and amino acids; it stimulates gallbladder contraction to release bile, facilitates the secretion of digestive enzymes from the pancreas, and slows gastric emptying to promote nutrient absorption.

• Secretin, released in response to acidic chyme in the small intestine, prompts the pancreas to produce bicarbonate to neutralize stomach acid and helps regulate water homeostasis. Together, these hormones enhance digestive efficiency by coordinating the functions of the stomach, liver, and pancreas.

o   What is the function of the ileocecal valve?

The ileocecal valve regulates the flow of material from the small intestine into the large intestine, preventing backflow and helping to control the rate of digestion and absorption.

o   Which digestive activities happen in the large intestine?

The large intestine is responsible for the absorption of water and electrolytes, the fermentation of indigestible food residues by gut bacteria, and the formation and storage of feces prior to excretion.

o   What do the bacteria in our colon digest? What do they make?

The bacteria in our colon primarily digest indigestible carbohydrates, such as fiber, producing short-chain fatty acids and gases as byproducts.

o   Describe the steps of the defecation reflex.

parasympathetic signals:

• started by dimension in the rectum

• stimulate contraction of sigmoid colon and rectum

• relax the internal anal sphincter

  conscious control:

• relaxation of external anal sphincter

o   Which step of defecation is under conscious control?

under conscious control: the relaxation of the external anal sphincter

o   Which steps of defecation are under parasympathetic control?

parasympathetic control: the contraction of the sigmoid colon and rectum and the relaxation of the internal anal sphincter

o   Which nutrients are digested by each of these enzymes? From where and to where is each enzyme secreted?

• Amylase: secreted from the salivary glands into the mouth, digests carbohydrates.

• Pepsin: secreted from the stomach lining into the stomach, digests proteins.

• Lipase: secreted from the pancreas into the small intestine, digests fats.