Digestive and Urinary

What is digestion?

Digestion is the process by which food substances are altered (broken down) into forms that can be absorbed through cell membranes.

The process by which food substances are altered (broken down) into forms that can be absorbed through cell membranes.

digestion

What are the six processes of digestion in order?

Ingestion → Propulsion → Mechanical digestion → Chemical digestion → Absorption → Defecation

What is ingestion?

Taking food into the mouth.

Taking food into the mouth

ingestion

What is propulsion, and what two processes does it include?

Propulsion is the movement of food through the alimentary canal and includes swallowing and peristalsis.

The movement of food through the alimentary canal and includes swallowing and peristalsis.

propulsion

What is mechanical digestion?

The physical breakdown of food into smaller particles.

The physical breakdown of food into smaller particles.

mechanical digestion

What is chemical digestion, and what primarily carries it out?

The chemical breakdown of foodstuffs by chemicals, especially enzymes.

Breakdown of foodstuffs by chemicals, especially enzymes.

chemical digestion

What is absorption?

The absorption of digestive products through cell membranes.

What is defecation?

The elimination of indigestible materials.

The elimination of indigestible materials.

defecation

What are the two major structural divisions of the digestive system?

The alimentary canal and the accessory organs (structures).

How do the alimentary canal and accessory organs differ?

• The alimentary canal is the tube through which food passes from the mouth to the anus

• Accessory organs release secretions into the alimentary canal.

What is the approximate length of the alimentary canal?

Where does it extend from and to?

Which organ accounts for most of its length?

How is it specialized?

It is approximately 9 meters long

Extends from the mouth to the anus

Most of its length is due to the small intestine

It is specialized in certain regions

What are the four layers of the alimentary canal wall from innermost to outermost?

Mucosa → Submucosa → Muscularis → Serosa

What structures compose the mucosa?

Epithelium, underlying connective tissue, and muscle.

What are the primary functions of the mucosa?

Secretion and absorption.

What features of the mucosa increase digestive efficiency, and how does each help?

• Folds increase the surface area for absorption.

• Tubular invagination glands secrete digestive substances into the digestive tract.

What structures are found in the submucosa?

The submucosa contains:

• dense irregular connective tissue

• glands

• blood vessels

• lymphatic vessels

• nerves

What are the functions of the submucosa?

It nourishes the surrounding tissues and carries away absorbed materials.

How is the muscularis organized, and what are its two layers?

The muscularis is composed of two innervated coats of smooth muscle:

• Inner circular coat

• Outer longitudinal coat

What is the orientation of the inner circular coat of the muscularis, and what happens when it contracts?

It encircles the tube (the hollow interior of the alimentary canal), and when it contracts, the diameter of the lumen decreases.

What is the orientation of the outer longitudinal coat of the muscularis, and what happens when it contracts?

It runs lengthwise along the tube, and when it contracts, the tube shortens.

What is the lumen?

The lumen is the hollow interior of the alimentary canal through which food passes.

Which organ of the alimentary canal contains three muscle layers, and what are they?

The stomach contains three muscle layers:

• Oblique

• Circular

• Longitudinal

What is the serosa, what does it produce, and what is its function?

The serosa is the outer serous membrane.

It produces lubricating serous fluid, which allows digestive organs to slide freely against one another.

What is the serosa called in the abdominal cavity, and what is it called in the esophagus?

In the abdominal cavity it is the visceral peritoneum; in the esophagus it is called the adventitia.

What is mixing (segmentation), and what are its functions?

Mixing (segmentation) is the contraction of small segments of smooth muscle that:

• Mixes food with digestive juices.

• Aids in the physical breakdown of food.

How does peristalsis propel food through the alimentary canal?

During peristalsis, a ring of muscle contracts behind the food while the smooth muscle ahead relaxes, forcing the food into the relaxed area and propelling it forward.

Which organs are considered the accessory organs of the digestive system?

• Salivary glands

• liver

• gallbladder

• pancreas.

What are the primary functions of the mouth in digestion?

It receives food, begins mechanical digestion, and mixes food with saliva.

What are the functions of the lips and cheeks during digestion?

The lips sense food temperature. The cheeks hold food in place and contain muscles used for chewing.

What are the two primary functions of the tongue during digestion?

It mixes food with saliva and moves food toward the oropharynx.

What are tongue papillae, and what are their functions?

Tongue papillae contain taste buds and provide friction to help handle food.

What is the palate, and what happens to the soft palate and uvula during swallowing?

The palate forms the roof of the oral cavity.

During swallowing, the soft palate and uvula move upward to block the nasopharynx.

What is the function of the teeth in digestion?

They mechanically break food into smaller particles.

What are the two sets of teeth?

Primary (deciduous) teeth

secondary (permanent) teeth.

What do the salivary glands secrete?

Saliva and mucus.

What do serous cells secrete, and what is the function of each secretion?

Serous cells secrete a watery fluid containing:

• Salivary amylase, which breaks starch into simple sugars.

• Lysozyme, which has antibacterial activity.

Where does carbohydrate digestion first begin, and which enzyme begins it?

Carbohydrate digestion first begins in the mouth because of salivary amylase.

What do mucous cells secrete, and what are the functions of their secretion?

Mucous cells secrete mucus, which binds food together and acts as a lubricant.

Which salivary gland is composed mainly of serous cells?

The parotid gland

Which salivary gland contains both serous and mucous cells?

The submandibular gland.

Which salivary gland is composed mainly of mucous cells?

The sublingual gland.

How does seeing, smelling, tasting, or thinking about good food affect parasympathetic activity and salivation?

It increases parasympathetic activity, stimulating the salivary glands and increasing salivation.

How does seeing, smelling, tasting, or thinking about bad food affect parasympathetic activity and salivation?

It decreases parasympathetic activity, resulting in decreased salivation.

Which neurotransmitter is primarily associated with parasympathetic stimulation of digestion?

Which is primarily associated with sympathetic inhibition of digestion?

Parasympathetic: acetylcholine (ACh)

Sympathetic: norepinephrine (NE)

Which regions of the pharynx serve as passageways for both food and air?

The oropharynx and laryngopharynx

Which type of epithelium lines the oropharynx and laryngopharynx?

Stratified squamous epithelium

Which tonsils are located in the oropharynx?

The palatine and lingual tonsils.

What occurs during the voluntary (buccal) phase of swallowing?

Food is chewed and mixed with saliva, the tongue forms a bolus, and the tongue pushes the bolus into the oropharynx.

What initiates the involuntary pharyngeal-esophageal phase of swallowing?

Receptors detect food at the pharyngeal opening, initiating the swallow reflex.

During the involuntary phase of swallowing, what happens to the soft palate and uvula, and why?

They rise to block the nasopharynx, preventing food from entering the nasal cavity.

During the involuntary phase of swallowing, what happens to the hyoid bone, larynx, and epiglottis, and why?

The hyoid bone and larynx rise while the epiglottis tips downward, blocking the larynx and trachea to prevent food from entering the respiratory tract.

How is the bolus transported from the oropharynx to the esophagus during swallowing?

A peristaltic wave carries the bolus from the oropharynx through the laryngopharynx into the esophagus.

How is the bolus transported from the esophagus to the stomach?

A peristaltic wave carries the bolus through the esophagus into the stomach.

Where is the esophagus located?

Between the laryngopharynx and the stomach.

What are the structural characteristics of the esophagus, including its lining, length, and special features?

The esophagus is a collapsible, muscular tube about 25 cm long, lined with stratified squamous epithelium, and contains numerous mucous glands.

What is the function of the mucous glands of the esophagus?

They secrete mucus for lubrication.

What is the esophageal hiatus?

An opening in the diaphragm through which the esophagus passes.

What is the gastroesophageal (cardiac) sphincter, where is it located, and what is its function?

It is a circular smooth muscle valve located between the esophagus and stomach that prevents backflow of stomach contents into the esophagus (acid reflux).

What is the shape and location of the stomach?

• The stomach is a J-shaped, pouch-like organ

• Located in the upper left portion of the abdominal cavity.

What are the four functions of the stomach?

• It receives food, mixes it with gastric juice

• Initiates protein digestion

• Performs some absorption

• Sends food to the duodenum

What are the four regions of the stomach?

• Cardia (cardiac region)

• Fundus (fundic region)

• Body

• Pylorus (pyloric region).

What is the pyloric sphincter?

Where is it located?

What is its function?

• It is a circular muscle valve

• Located between the stomach and duodenum

• Prevents backflow of material from the duodenum into the stomach.

What are rugae, which layers form them, and what are their functions?

Rugae are folds of the mucosa and submucosa that increase surface area and allow the stomach to expand.

What are the four secretory cell types found in the gastric glands?

• Mucous (goblet) cells

• parietal cells

• Chief cells

• Enteroendocrine cells.

Where are mucous (goblet) cells located within the gastric glands, and what do they secrete?

They are located in the neck of the gland and secrete thin acidic mucus.

What substances do parietal cells secrete, and what is the function of each?

Parietal cells secrete:

• Hydrochloric acid (HCl; approximately pH 2), which activates pepsinogen to pepsin.

• Intrinsic factor, which is required for vitamin B₁₂ absorption.

What do chief cells secrete?

How is it activated?

What is the function of its active form?

• Chief cells secrete pepsinogen

• It’s activated by HCl to form pepsin

• Pepsin chemically digests proteins.

Where does protein digestion first begin, and which enzyme begins it?

Protein digestion first begins in the stomach because of pepsin.

Which hormone is secreted by enteroendocrine cells, and what is its function?

Gastrin is secreted by enteroendocrine cells and stimulates increased gastric juice production.

Besides the mucus secreted by mucous (goblet) cells, what do the surface mucosal cells secrete?

Why is it important?

They secrete a thick alkaline mucus that protects the stomach from HCl and pepsin.

What are the events of swallowing (deglutition) in order, from the voluntary phase until the bolus reaches the stomach?

1. The tongue voluntarily pushes the bolus into the oropharynx.

2. The soft palate and uvula rise to block the nasopharynx.

3. The hyoid bone and larynx rise while the epiglottis tips downward to block the larynx and trachea.

4. A peristaltic wave carries the bolus from the oropharynx → laryngopharynx → esophagus.

5. A peristaltic wave carries the bolus through the esophagus to the stomach

Is gastric juice produced only when food enters the stomach, and what determines its rate of production?

No. Gastric juice is produced continuously, but its rate of production varies and is controlled by neural and hormonal mechanisms.

What sensory or digestive stimuli initiate neural stimulation of gastric secretion?

Seeing, tasting, or smelling pleasant food and the entry of food into the stomach.

During neural regulation of gastric secretion, which autonomic division sends impulses to the stomach, and which neurotransmitter is released?

The parasympathetic division sends impulses to the stomach, causing the release of acetylcholine (ACh).

How does acetylcholine affect the gastric glands, and what is the resulting gastric juice rich in?

ACh stimulates the gastric glands to secrete large amounts of gastric juice rich in hydrochloric acid and pepsin.

In addition to directly stimulating the gastric glands, how do parasympathetic impulses increase gastric juice production hormonally?

They stimulate stomach cells to release gastrin.

How does gastrin affect the gastric glands?

Gastrin increases their secretory activity, resulting in even more gastric juice production.

What are the three phases of gastric secretion, in order, and are they voluntary or involuntary?

• The cephalic, gastric, and intestinal phases

• All three are involuntary

When does the cephalic phase occur, and why is it described as a conditioned reflex?

It occurs before food enters the stomach and is a learned response triggered by sensory cues or thoughts associated with food.

What stimuli can trigger the cephalic phase of gastric secretion?

The smell, sight, taste, or thought of food.

During the cephalic phase, what pathway carries signals from the brain to the stomach?

The brain sends parasympathetic impulses through the vagus nerves to the stomach.

What is the final effect of vagal parasympathetic stimulation during the cephalic phase?

It stimulates the gastric glands and increases gastric secretions.

What initiates the gastric phase of gastric secretion?

Food fills and distends the stomach, activating stretch receptors.

How does stomach distension increase gastric juice production during the gastric phase?

Activated stretch receptors initiate a reflex that causes ACh release, leading to increased gastric juice production.

What initiates the intestinal phase of gastric secretion according to the study guide?

Food filling the small intestine.

Which hormone is released during the stimulatory intestinal phase?

Where is it produced?

What does it do?

• Intestinal gastrin is produced by the small intestine.

• Travels to the stomach

• Stimulates additional gastric juice production.

How do ordinary gastrin and intestinal gastrin differ in their source?

• Ordinary gastrin is released by stomach cells, whereas intestinal gastrin is released by the small intestine

• Both stimulate gastric juice production.

What is cholecystokinin?

What is it released by?

What stimulates its release?

• CCK is a hormone

• Released by the small intestine

• When chyme rich in lipids and proteins enters the duodenum.

What effect does CCK have on the stomach?

It decreases gastric motility.

What effect does CCK have on the pancreas?

It stimulates the production and release of more pancreatic juice.

What effect does CCK have on the gallbladder?

It stimulates contraction of the gallbladder’s muscular wall.

What effect does CCK have on the hepatopancreatic sphincter?

What is the other name for the sphincter?

• It relaxes the hepatopancreatic sphincter.

• Also called the sphincter of Oddi.

What four coordinated effects does CCK produce after lipid- and protein-rich chyme enters the duodenum?

It decreases gastric motility, increases pancreatic juice production and release, contracts the gallbladder, and relaxes the hepatopancreatic sphincter.

What stimulates the enterogastric reflex, and what is its effect on food entry into the duodenum?

Duodenal stretch stimulates the reflex, which inhibits and slows the entry of food into the duodenum.