BME350 - L21

What are the six main organs that form the gastrointestinal (GI) tract?

The oral cavity, pharynx, esophagus, stomach, small intestine, and colon (large intestine).

What are the six accessory organs of the digestive system mentioned in the text?

The teeth, tongue, salivary glands, gall bladder, liver, and pancreas.

What is the primary function of the small intestine in contrast to the large intestine?

The small intestine's primary function is to retrieve nutrients, while the large intestine's is to expel waste.

What are the five major digestive processes listed in order?

Intake of food, digestion, absorption of nutrients, secretion of digestive enzymes & fluids, and motility.

What is the definition of digestion as a major digestive process?

It is the breakdown of food into nutrients.

What is the definition of motility as a major digestive process?

It is the exclusion of non-digestible material from the body.

Which layer of the GI wall is composed of various epithelial cells and lines the tract?

The Mucosa.

The _____ contributes to the distensibility and elasticity of the GI tract.

Submucosa.

Which layer of the GI wall contains an elaborate network of sensory, motor, and interneurons that regulate local stimuli?

The Submucosa.

In the Muscularis Externa, which muscle type generates spontaneous depolarizations known as slow-wave potentials?

The circular muscle.

In the Muscularis Externa, which muscle type is multi-unit and depends on neural input for contraction?

The longitudinal muscle.

What is the outermost layer of the GI tract wall, which secretes a lubricating fluid?

The Serosa.

What is the term for reflexes where the sight, smell, sound, or thought of food prepares the digestive system for an anticipated meal?

Feedforward reflexes.

The _____ integrates sensory information and responses that control secretion by GI epithelial cells and influence motility via myenteric neurons.

Enteric Nervous System (ENS).

How does the Human Enteric Nervous System (ENS) function in relation to the Central Nervous System (CNS)?

The ENS functions autonomously, independent of efferent signals from the CNS.

What stimulus causes a reflex wave of peristaltic contraction in the human enteric nervous system?

Increased intraluminal pressure.

What two initial digestive processes occur in the oral cavity?

Mastication (chewing) and chemical breakdown by salivary amylase.

What types of muscle are found in the wall of the esophagus?

The esophagus contains both skeletal and smooth muscle.

What is the muscle type of the upper esophageal sphincter versus the lower esophageal sphincter?

The upper sphincter is skeletal muscle, while the lower sphincter is smooth muscle.

What are the two primary functions of the stomach?

The stomach stores food and its gastric glands secrete gastric juice.

What four main components does saliva contain?

Bicarbonate, mucous, salivary amylase, and lysozyme.

What is the function of bicarbonate in saliva?

It helps in the neutralization of acids.

What is the function of salivary amylase?

It begins the chemical breakdown of food (specifically carbohydrates).

What is the function of lysozyme in saliva?

It kills bacteria.

Which part of the stomach has a thin, easily expandable wall to accommodate food?

The fundus.

What are the longitudinal folds in the mucosa of the stomach body that flatten as the stomach expands?

Rugae.

Which part of the stomach has the thickest muscle layer to propel chyme into the small intestine?

The antrum.

What is the process of propelling chyme from the stomach to the small intestine called?

Gastric emptying.

In which parts of the stomach are gastric pits found?

They are found in the walls of the fundus and the body of the stomach.

What types of cells do gastric pits contain?

They contain a variety of secretory cells, both exocrine and endocrine.

What is unique about the stomach lumen's environment compared to the rest of the GI tract?

It is the only place in the GI tract that is acidic.

Goblet cells, found throughout the GI tract, secrete what type of substance?

They secrete mucin, a type of alkaline mucous.

Neck cells, found only in gastric glands, secrete what type of substance to protect the stomach?

They secrete a thin, acidic mucous.

What is the primary function of the highly acidic environment (pH as low as 2) in the stomach?

It is necessary for activating pepsinogen into the proteolytic enzyme pepsin.

Besides activating pepsinogen, what are two other functions of the stomach's acidic environment?

It denatures proteins in food and kills many food-borne bacteria.

What is the protective layer of mucous and bicarbonate secreted from neck and goblet cells in the stomach called?

The gastric mucosal barrier.

What medical condition can result from acid penetrating the gastric mucosal barrier?

An ulcer formation.

What structure regulates the passage of chyme between the stomach and the small intestine?

The pyloric sphincter.

What is the primary site of both digestion and absorption of nutrients, ions, water, and minerals?

The small intestine.

Within what portion of the small intestine is the majority of absorption completed?

The majority of absorption is completed within the first 20% of the small intestine.

Which region of the small intestine receives pancreatic juice and bile?

The duodenum.

The exocrine portion of the pancreas produces _____ _____, which is rich in bicarbonate.

pancreatic juice

What are the four types of enzymes found in pancreatic juice?

Pancreatic amylase, lipases, proteinases, and nucleases.

What finger-like projections increase the surface area of the small intestine's epithelium by about tenfold?

Villi.

What two structures for nutrient absorption are contained within the villi of the small intestine?

Blood vessels and a lacteal (part of the lymphatic system).

What is the function of the Crypts of Lieberkühn in the proximal small intestine?

Epithelial cells in these crypts secrete a bicarbonate-rich fluid.

What is the specific vein that carries nutrient-rich blood from the intestinal capillaries to the liver?

The hepatic portal vein.

Why must oral medications often be given in higher doses than intravenous medications?

The liver metabolizes and clears the drugs from the bloodstream before they reach systemic circulation.

What is the function of the gall bladder?

It stores and concentrates bile secreted by the liver, releasing it during meals.

What are the four major anatomical regions of the colon?

The ascending, transverse, descending, and sigmoid regions.

What is the primary function of the ascending, transverse, and descending segments of the colon?

They are specialized for ion and water absorption from chyme.

What is the primary function of the sigmoid colon?

It acts as a storage depot for feces after absorption is complete.

What is the wormlike appendage with no known function that can become blocked and inflamed?

The appendix.

Which anal sphincter is composed of smooth muscle and is under involuntary control?

The internal anal sphincter.

Which anal sphincter is composed of skeletal muscle and is under voluntary control?

The external anal sphincter.

What are the two main purposes of GI motility?

Movement of food from mouth to anus, and mechanical mixing of food.

What is the benefit of mechanically mixing food in the GI tract?

It increases the surface area of food particles, maximizing their exposure to digestive enzymes.

Term: Tonic smooth muscle contractions.

Sustained contractions lasting for minutes or hours, such as in sphincters.

Term: Phasic smooth muscle contractions.

Contraction-relaxation cycles lasting only a few seconds, such as in the posterior stomach and small intestine.

How are groups of smooth muscle cells in the GI tract electrically connected?

They are connected by gap junctions, creating contracting segments.

Spontaneous depolarization in GI smooth muscle is caused by the slow diffusion of which two ions into the cell?

Sodium ($Na^+$) and Calcium ($Ca^{2+}$).

Unlike skeletal muscle, GI smooth muscle does not follow the _____ law.

all-or-none

What is the typical rate of slow waves per minute in GI smooth muscle?

3-12 waves per minute.

Do slow waves in GI smooth muscle always trigger a muscle contraction?

No, unlike in cardiac muscle, slow waves do not always trigger a contraction.

How is the strength of a GI smooth muscle contraction determined?

It varies directly with the frequency of action potentials.

The duration of a GI smooth muscle contraction varies directly with the duration of the _____.

slow wave