BBS2041 FLASHCARDS

What are the two main divisions of the digestive system?

Accessory digestive organs and the alimentary canal. Accessory organs assist digestion while the alimentary canal is the continuous tube food travels through.

What organs belong to the alimentary canal?

Pharynx esophagus stomach small intestine and large intestine. These form the continuous digestive tract.

What are accessory digestive organs?

Teeth tongue salivary glands liver gallbladder and pancreas. They support digestion but food does not pass through them.

What are the four layers of the GI tract wall?

Mucosa submucosa muscularis externa and serosa. These layers are consistent throughout the digestive tract.

What are the three components of the mucosa?

Epithelium lamina propria and muscularis mucosae. Together they allow secretion absorption and local movement.

What is the function of the mucosa?

Secretion absorption and protection. It produces enzymes and absorbs nutrients.

Why is the mucosa renewed rapidly?

To maintain protection against damage and infection. High turnover ensures integrity.

What is the function of the submucosa?

Provides elasticity and contains blood vessels lymphatics and nerves. Supports the mucosa.

What is the submucosal plexus?

A network of nerves in the submucosa. It regulates secretion and blood flow.

What is the function of the muscularis externa?

Peristalsis and segmentation. It moves and mixes food.

What are the two layers of muscularis externa?

Inner circular and outer longitudinal layers. They work together to propel food.

What is the myenteric plexus?

A nerve network controlling gastrointestinal motility. It is located between muscle layers.

What is the function of the serosa?

Reduces friction and provides structural support. It is the outer protective layer.

What is the main function of the stomach?

Mechanical mixing and protein digestion. It converts bolus into chyme.

What are the three parts of the stomach?

Fundus body and pylorus. Each region has a specific role.

What is the function of the fundus?

Storage and relaxation. It accommodates incoming food.

What is the function of the stomach body?

Mixing and chemical digestion. It is the main digestive region.

What is the pylorus?

The lower stomach region controlling emptying. It acts as a gate to the duodenum.

What is chyme?

A semi liquid mixture of food and gastric juices. It is produced by stomach mixing.

What is the pH of the stomach?

Approximately 1 to 2. This highly acidic environment supports digestion.

What do parietal cells secrete?

Hydrochloric acid and intrinsic factor. These are essential for digestion and vitamin B12 absorption.

What are the functions of hydrochloric acid?

It denatures proteins activates enzymes and kills bacteria. It is essential for digestion.

What do chief cells secrete?

Pepsinogen. This is the inactive precursor of pepsin.

What activates pepsinogen?

Hydrochloric acid. It converts pepsinogen into active pepsin.

What does pepsin do?

It breaks down proteins. It is an endopeptidase.

What do G cells secrete?

Gastrin. It stimulates acid secretion.

What does histamine do in the stomach?

It stimulates hydrochloric acid secretion. It acts via H2 receptors.

What is intrinsic factor?

A protein needed for vitamin B12 absorption. It is secreted by parietal cells.

Why does the stomach not digest itself?

A protective mucus layer and tight junctions prevent autodigestion.

What is receptive relaxation?

The stomach relaxes when food enters. This prevents pressure increase.

What is gastric accommodation?

The stomach stretches without increasing tension. This allows storage.

What is peristalsis in the stomach?

Wave like contractions that mix food into chyme.

What is retropulsion?

Back and forth movement of chyme. This enhances mixing.

What controls stomach emptying?

Signals from the duodenum and the enterogastric reflex. This prevents overload.

What are the three parts of the small intestine?

Duodenum jejunum and ileum. Each has specialized roles.

What is the function of the duodenum?

It receives bile and pancreatic enzymes. It is the main digestion site.

What is the function of the jejunum?

Major nutrient absorption occurs here due to large surface area.

What is the function of the ileum?

Absorption and immune function. It is the final section.

What are circular folds?

Mucosal folds that slow chyme movement. They improve absorption.

What are villi?

Finger like projections that increase surface area. They contain blood and lymph vessels.

What are microvilli?

Tiny projections forming the brush border. They maximize absorption.

What is the brush border?

An enzyme rich microvilli layer where final digestion occurs.

What is the main function of the large intestine?

Water absorption and feces formation. It is not a major digestion site.

What are the parts of the large intestine?

Cecum colon rectum and anus. These form the final digestive sections.

Why are there no villi in the large intestine?

There is no major nutrient absorption. The focus is on water absorption.

What is the function of gut bacteria?

Vitamin production and fermentation. They produce vitamin K and some B vitamins.

What are taenia coli?

Longitudinal muscle bands in the colon. They aid movement of feces.

What is defecation?

The elimination of waste. It is the final step of digestion.

Why does carbohydrate digestion stop in the stomach?

Hydrochloric acid denatures salivary amylase. The acidic environment inactivates the enzyme.

Which enzyme continues carbohydrate digestion in the small intestine?

Pancreatic amylase. It breaks polysaccharides into oligosaccharides.

What are the final products of carbohydrate digestion?

Glucose galactose and fructose. Only monosaccharides can be absorbed.

Which enzymes complete carbohydrate digestion at the brush border?

Lactase maltase and sucrase. They convert disaccharides into monosaccharides.

What does lactase do?

It breaks lactose into glucose and galactose. Deficiency leads to lactose intolerance.

What does maltase do?

It breaks maltose into two glucose molecules. This is a final digestion step.

What does sucrase do?

It breaks sucrose into glucose and fructose. This enables absorption.

How are glucose and galactose absorbed into the enterocytes?

Via the SGLT1 transporter. This is sodium dependent secondary active transport.

Why is sodium important for glucose absorption?

It drives the SGLT1 transporter. The sodium gradient powers glucose uptake.

How does glucose leave enterocytes?

Via the GLUT2 transporter. This is facilitated diffusion into the blood.

How is fructose absorbed?

Via the GLUT5 transporter. This is sodium independent facilitated diffusion.

Where do absorbed monosaccharides go?

To the liver via the portal circulation. The liver processes and distributes them.

Why is glucose the main circulating sugar?

It can be used directly by most tissues. It is the primary energy source.

What happens to excess glucose?

It is stored as glycogen or converted into fat. This prevents high blood glucose.

Where does protein digestion begin?

In the stomach. Pepsin starts breaking down proteins.

What activates pepsinogen?

Hydrochloric acid. It converts it into active pepsin.

What type of enzyme is pepsin?

An endopeptidase. It cuts internal peptide bonds.

What happens to proteins in the small intestine?

They are further digested by pancreatic enzymes. This produces smaller peptides.

Which pancreatic enzymes digest proteins?

Trypsin chymotrypsin elastase and carboxypeptidase. They work together to break proteins.

What activates trypsinogen?

Enteropeptidase. It converts trypsinogen into trypsin.

Why is trypsin important?

It activates other digestive enzymes. This creates a cascade effect.

What are exopeptidases?

Enzymes that remove terminal amino acids. They produce single amino acids.

Where does final protein digestion occur?

At the brush border. Aminopeptidases and dipeptidases act here.

How are amino acids absorbed?

Via sodium dependent transporters. This is secondary active transport.

How are dipeptides and tripeptides absorbed?

Via hydrogen dependent cotransport. A different transporter system is used.

What happens to dipeptides inside enterocytes?

They are broken down into amino acids. Cytoplasmic enzymes perform this.

Why are multiple transport systems needed for protein absorption?

Different peptides have different properties. This increases efficiency.

Where does fat digestion begin?

In the mouth via lingual lipase. It starts lipid breakdown.

What happens to fats in the stomach?

Gastric lipase continues digestion. Diglycerides are formed.

Where does most fat digestion occur?

In the small intestine. Pancreatic lipase is the main enzyme.

What is emulsification?

The breakdown of fat into small droplets. This increases surface area for enzymes.

What do bile salts do?

They emulsify fats. Their amphipathic nature allows interaction with fat and water.

Why are bile salts amphipathic?

They have both hydrophilic and hydrophobic regions. This allows fat digestion in water.

What are micelles?

Complexes of bile salts and lipids. They transport lipids to the intestinal cells.

Why are micelles necessary?

Lipids are hydrophobic and cannot travel freely in water. Micelles make transport possible.

What enzyme digests triglycerides?

Pancreatic lipase. It produces fatty acids and monoglycerides.

How do lipids enter enterocytes?

By diffusion or via transport proteins. They are lipid soluble.

What happens to lipids inside enterocytes?

They are reassembled into triglycerides. This occurs in the smooth endoplasmic reticulum.

What are chylomicrons?

Lipoprotein particles that transport lipids. They are formed in the Golgi apparatus.

Why can chylomicrons not enter blood capillaries?

They are too large. They enter the lymphatic system instead.

Where do chylomicrons go first?

Into lacteals in the lymphatic system. They later enter the bloodstream.

What is the thoracic duct?

A lymph vessel that empties into the bloodstream. It delivers chylomicrons.

What happens to fatty acids in circulation?

They are transported bound to albumin. They are used for energy or storage.

Which tissues mainly use fatty acids?

Muscle heart and adipose tissue. These are major energy users.

Why can the brain not use fatty acids?

They do not cross the blood brain barrier. The brain relies on glucose or ketones.

What is the main purpose of glycolysis?

To convert glucose into pyruvate and generate ATP. It is the first step of energy metabolism.

Where does glycolysis occur?

In the cytosol. It does not require mitochondria.

Is glycolysis aerobic or anaerobic?

Anaerobic. It does not require oxygen.

What is the overall result of glycolysis?

One glucose molecule is converted into two pyruvate molecules. Each pyruvate has three carbons.

What is the energy investment phase of glycolysis?

The initial phase where ATP is consumed. Two ATP are used to activate glucose.

Why is ATP invested in glycolysis?

To make glucose more reactive. This allows further breakdown.

What is the energy payoff phase of glycolysis?

The phase where ATP and NADH are produced. Energy is extracted from intermediates.