Anatomy 142: Digestive system

Functions of saliva

Lubrication, digestion, cleaning, antibacterial, buffering

Composition of saliva

Water, electrolytes, salivary amylase, lysozymes

Propulsion

Movement from one organ to the next

Intrinsic factor significance

Necessary for absorption of B12 in small intestine

Name the layers of the digestive tract

Mucosa, submucosa, muscularis, serosa

Submucosa

Supplies blood, nerves and glands to mucosa

Mucosa

Involved in secretion and absorption

Muscularis

Responsible for peristalsis and segmentation

What is the inner lining epithelium of most of the GI tract? What is the inner lining epithelium of the esophagus?

Simple columnar for GI tract, stratified squamous epithelium in esophagus

State the functions of the villi & microvilli found in the mucosa of the small intestine

Increase surface area for absorption

Peristalsis - what is it, where does it occur?

Involuntary muscle contractions, occur in small intestine and esophagus

Mixing movements - what is it? Where does it occur?

Stomach and small intestine, its basically muscular contractions (churning) to mix food and digestive enzymes

Segmentation - what is it? Where does it occur?

Occurs in the small intestine and involves rhythmic contractions

Mass movements - what is it? Where does it occur?

Large powerful contractions that occur in the large intestine to push feces forwards

Serosa

Provides protection and support to organs, as well as reducing friction by secreting serous fluid

What are the three phases of swallowing?

Oral phase, pharyngeal phase, esophageal phase

What is the condition that would result if the lower esophageal sphincter is loose and fails to close properly?

Gastroesophageal reflux disease (GERD)

Name the three salivary glands

Parotid, sublingual, submandibular

Function of esophagus

Propels food to stomach through peristalsis

Describe the oral phase (voluntary or involuntary?)

Voluntary, Mastication and bolus formation of food

Describe the pharyngeal phase (voluntary or involuntary?)

Involuntary, bolus is shoved backwards, epiglottis and soft palate work to prevent it from entering nasal cavity and larynx

Describe the esophageal phase (voluntary or involuntary?)

Involuntary, peristaltic waves propel food to stomach

Parotid gland salivary secretion

Clear, watery secretion, rich in amylase

Sublingual gland secretion

Thick mucus secretion

Submandibular gland secretion

Mixed secretion containing water and mucus

Name the hormone that stimulates gastric juice secretion. Where is it secreted from?

Gastrin, secreted from G cells in stomach (near pyloric region)

Components of gastric juice

Pepsin, mucus, hydrochloric acid, intrinsic factor

What causes stomach ulcers?

H pylori, excess intake of coffee, alcohol

What is the condition that can result from a deficiency of intrinsic factor?

Pernicious anemia

Phases of gastric secretion

Cephalic phase, gastric phase, intestinal phase

Cephalic phase

Sight, smell, taste or thought of food triggers parasympathetic reflexes causing gastric juice to be secreted

Intestinal phase

When food enters the small intestine it stimulates intestinal cells to release intestinal gastrin which in turn promotes more gastric juice secretion from stomach wall

Gastric phase

Food being chemically and mechanically churned stimulates release of gastrin

During which phase is gastric juice secreted maximally?

Gastric phase

In which parts of the small intestine does maximum digestion and absorption take place?

Jejunum and duodenum

Factors that influence gastric juice secretion

Stimulation of parasympathetic nerves, distension of the stomach stimulates enteric nerves leading to secretion, hormone gastrin

pancreatic amylase

splits glycogen or starch (polysaccharides) into disaccharides

pancreatic lipase

breaks down lipids (triglycerides) to fatty acids & glycerol

trypsin, chymotrypsin and carboxypeptidase

digest larger proteins to smaller peptides

nucleases

digest nucleic acids (DNA & RNA)

bicarbonate ions

Make pancreatic juice alkaline to neutralize acidic chyme

Components of pancreatic juice

nuclease, bicarbonate, trypsin, lipase, amylase

Functions of gastric juice (what does each component do?)

HCL acid - Antibacterial, activates pepsinogen
Pepsin - breakdown of proteins
Mucus - Lubrication, protects stomach from acid
Intrinsic factor - B12 absorption

Why are protein-digesting enzymes of the pancreatic juice secreted in an inactive form, and how & where do the enzymes get activated?

Secreted in an inactive form to prevent the pancreas from getting digested, they are activated in the duodenum by enterokinase

Name the hormones controlling pancreatic secretion and their actions

Secretin - Stimulates secretion of bicarbonate
Cholecystokinin (CCK) - Stimulates secretion of enzymes

Where are secretin and cholecystokinin released from?

They are released from intestinal mucosa

What would stimulate the release of secretin?

Presence of acid in duodenum

What would stimulate the release of CCK?

Presence of fatty acids or amino acids in duodenum

List the components of bile

water, electrolytes, pigments, bile salts, cholestrol and phospholipids

What is the action of cholecystokinin on bile secretion?

Stimulates gallbladder contraction resulting in bile release

What is meant by the term ‘emulsification of fats’?

break down large fat globules into smaller droplets so that they can be easily digested by the enzyme pancreatic lipase

Into which part of the small intestine is bile released?

Duodenum

Chief cells release

Pepsinogen

Which cells release hydrochloric acid (HCl) into the stomach?

Parietal cells

Which cranial nerve stimulates acid secretion during the stomach's gastric

phase?

Vagus nerve

Which process, known as intestinal churning, involves a squeezing motion of the circular layer of smooth muscle in the small intestine?

Segmentation

Which enzyme catalyzes the reaction of lactose into glucose and galactose?

Lactase

Ben had most of his stomach removed in an attempt for drastic weight loss. He is at the greatest risk

for:

pernicious anemia

Name the enzymes found on the microvilli of the small intestine

Peptidase, maltase, sucrase, lactase, lipase

What are fats broken down into?

Fatty acids and glycerol

Describe the breakdown of carbohydrates in the alimentary canal

Starch → Broken down by amylase (pancreas & mouth) into maltose, isomaltose → Broken down by maltase into glucose

What are the end products of carbohydrate breakdown?

Glucose, galactose, fructose

How is glucose absorbed?

Directly into the blood from small intestine

How are proteins absorbed?

Absorbed through active transport with sodium into the blood from small intestine

Describe the breakdown of proteins

Stomach breaks proteins down into smaller chains → Continues in small intestine where it is broken down into small peptides and amino acids

How are fats absorbed?

Absorbed into blood and lymphatic system through diffusion.

Explain the digestion of fats

Digestion done through lipase from intestines and pancreas. Complete digestion requires bile salts