Digestive system

What is the digestive tract also known as?

Alimentary tract or gastrointestinal tract (GIT)

What are the main digestive organs?

Mouth, pharynx, esophagus, stomach, small intestine, large intestine.

What are the accessory organs of the digestive system?

Teeth, tongue, salivary glands, liver, gallbladder, pancreas.

What are the four layers of the histological organization of the digestive tract?

Mucosa, submucosa, muscularis externa, serosa.

What is the function of the mucosa layer in the digestive tract?

Secretion, absorption, and folding.

What role does the submucosa play in the digestive tract?

Binds mucosa to muscularis externa and contains a nerve network (ENS).

What is the muscularis externa responsible for?

Movement of substances through patterns of contraction and relaxation.

What is the function of the serosa in the digestive tract?

Allows attachment to abdominal walls.

What are the main functions of the digestive system?

Supply nutrients, electrolytes, and water to the body.

What is ingestion in the context of the digestive system?

The entry of material into the digestive tract via the mouth.

What is peristalsis?

The movement of food along the GIT through waves of muscular contraction.

What is segmentation in the digestive system?

Cycles of contraction that churn and fragment the bolus, mixing it with intestinal secretions.

What is the purpose of mechanical processing in digestion?

To increase surface area for easier breakdown of food.

What is chemical digestion?

The chemical breakdown of food into smaller absorbable molecules.

What is absorption in the digestive system?

The movement of substrates, electrolytes, vitamins, and water across the epithelium into interstitial fluid.

What is defecation?

The removal of indigestible waste products from the body.

What is the end result of the digestive process?

The body is supplied with nutrients, electrolytes, and water, while wastes are removed.

How long does it take for food to move along the small intestine?

Approximately 90-120 minutes.

What is the role of the liver in digestion?

It plays a crucial role in digestion and integration of other body systems.

What is the significance of the GI tract optimizing conditions for digestion and absorption?

It ensures ingested food is broken down into substrates available for cells.

What is the relationship between food ingested and nutrient supply?

The supply of nutrients is dependent on the food ingested, not just nutritional requirements.

What are the two main types of muscle involved in peristalsis?

Circular muscles (push food forward) and longitudinal muscles (shorten the tract).

What are the two divisions of the autonomic nervous system that control digestion?

Parasympathetic and sympathetic divisions.

How does the parasympathetic division affect digestion?

It typically stimulates digestion (rest and digest).

What is the role of the sympathetic division in digestion?

It typically inhibits digestion (fight or flight), as the gastrointestinal tract is not required in stressful situations.

What is the enteric nervous system (ENS)?

A part of the autonomic nervous system that acts on the digestive tract to control local secretion and motility.

What are the major layers of the walls of the digestive tract?

Mucosa, submucosa, muscularis, and serosa, each with specific functions in protection, secretion, and movement.

What are the six main digestive functions?

Ingestion, mechanical processing, chemical digestion, secretion, absorption, and excretion.

What are the two main types of intestinal movement?

Peristalsis and segmentation.

What is the primary function of the oral cavity in digestion?

It is the first part of the digestive tract where food is exposed, analyzed, and mechanically processed.

What is the composition of saliva?

~99.4% water, with 0.6% including IgA, lysozyme, enzymes (salivary amylase), buffers, mucins, electrolytes, and waste products.

What are the functions of saliva?

Lubrication of the mouth, cleansing of the mouth and teeth, moistening food, dissolving food for taste, and beginning chemical digestion.

What is the length of the esophagus?

About 25 cm.

What is the primary function of the esophagus?

To convey food or medications to the stomach by peristalsis.

What are the two major phases of swallowing?

Buccal phase (voluntary) and pharyngeal/oesophageal phase (involuntary).

What is the role of the stomach in digestion?

It serves as a mixing chamber where carbohydrate digestion halts, protein digestion begins, and fat digestion continues.

What are the three layers of smooth muscle in the stomach's muscularis?

Longitudinal, circular, and oblique layers.

What is chyme?

Partially digested semi-fluid material formed in the stomach.

What is the function of hydrochloric acid (HCl) in the stomach?

It denatures proteins and activates pepsinogen to pepsin.

What are the secretory cells in the stomach mucosa?

Mucous cells, parietal cells, chief cells, and G cells.

What does intrinsic factor do?

It is required for the absorption of Vitamin B12.

What hormone do G cells secrete and what is its function?

Gastrin, which stimulates parietal and chief cells to increase secretions and motility.

What are the three overlapping phases of gastric activity regulation?

Cephalic phase, gastric phase, and intestinal phase.

What occurs during the cephalic phase of gastric activity?

The CNS prepares the stomach for the arrival of food.

What happens during the gastric phase?

It builds on the cephalic phase and starts when food arrives in the stomach.

What initiates the gastric phase of digestion?

The arrival of food in the stomach.

What are the key roles of the duodenum in the intestinal phase?

It receives chyme and regulates gastric activity through hormonal signals.

What triggers the cephalic phase of gastric activity?

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

What hormones are involved in the intestinal phase and what are their functions?

Secretin reduces gastric secretion, Cholecystokinin (CCK) inhibits gastric emptying, and Gastric Inhibitory Peptide (GIP) inhibits gastric emptying and secretions.

What is the role of ghrelin in appetite regulation?

Ghrelin is an appetite stimulant that signals the body it's ready for a meal.

How does leptin function in appetite control?

Leptin is an appetite suppressant secreted by adipose tissue that inhibits neuropeptide Y (NPY), reducing hunger.

What is the relationship between insulin, CCK, and feelings of fullness?

Insulin and CCK are released during food absorption and act as satiety signals to depress hunger.

What is the primary function of the pancreas?

The pancreas has both endocrine functions (secreting insulin and glucagon) and exocrine functions (secreting digestive enzymes and buffers).

What are the three regions of the pancreas?

Head, body, and tail.

What are the components of pancreatic secretions?

Water, salts, bicarbonate, phosphate buffers, and digestive enzymes.

What is the function of pancreatic alpha-amylase?

It digests carbohydrates.

What enzymes are responsible for protein digestion in the pancreas?

Proteolytic enzymes, including trypsin and proteases.

What enzyme digests triglycerides in the pancreas?

Pancreatic lipase.

What is the liver's primary metabolic function?

It adjusts levels of circulating nutrients and performs synthetic functions.

How is blood supplied to the liver?

Through the hepatic artery (oxygenated blood) and the hepatic portal circulation (nutrient-rich blood from intestines).

What are the four lobes of the liver?

Large right lobe, smaller left lobe, caudate lobe, and quadrate lobe.

What are hepatocytes and their role in the liver?

Hepatocytes are liver cells that adjust levels of circulating nutrients.

What is the function of Kupffer cells in the liver?

They are phagocytic cells that engulf pathogens, cell debris, and damaged red blood cells.

What is the significance of bile in digestion?

Bile aids in the emulsification and digestion of fats.

What happens to bile after it is secreted by the liver?

It moves to the gallbladder for storage.

What is the daily volume of pancreatic secretions?

Approximately 1000 mL.

What is the role of the pancreatic duct?

It connects the pancreas to the duodenum, allowing pancreatic secretions to enter the small intestine.

What is the effect of obesity on leptin?

Obesity can cause leptin resistance, impairing its ability to regulate appetite.

What are the main metabolic functions of the liver?

Carbohydrate, lipid, and protein metabolism; waste removal; storage of vitamins and minerals; drug processing (metabolism/inactivation).

What are the haematological functions of the liver?

Removal of bacteria and old red and white blood cells; production of plasma proteins; removal of hormones and antibodies; removal or storage of toxins; activation of vitamin D.

What is the role of bile in the digestive system?

Aids in the digestion of lipids by emulsifying them, increasing surface area for enzymatic attack, and promoting absorption by the epithelium.

What are the main functions of the gallbladder?

Stores and concentrates bile; releases bile into the duodenum under stimulation of cholecystokinin (CCK).

What are gallstones and how do they form?

Solidified cholesterol and bile salts; form when the liver secretes bile abnormally saturated with cholesterol, leading to crystallization.

What are the epidemiological factors associated with gallstones?

The 5 Fs: Female, Fair, Forty, Fertile, Fat.

What is the approximate length of the small intestine?

About 6 meters.

What percentage of nutrient absorption occurs in the small intestine?

90%.

What structures increase the surface area of the small intestine?

Circular folds (plicae circulares), villi, and microvilli.

What are the three sections of the small intestine?

Duodenum, jejunum, and ileum.

What is the primary function of the duodenum?

Receives chyme from the stomach and mixes it with digestive enzymes from the pancreas; neutralizes acids.

What is the primary function of the jejunum?

Chemical digestion and nutrient absorption.

What is the primary function of the ileum?

Nutrient absorption, including vitamin B12 and bile salts; controls flow to the large intestine.

What are the four classes of digestive enzymes?

Carbohydrases (amylases), proteases/peptidases, lipases, and nucleases.

What do carbohydrases do?

Break bonds between simple sugars (carbohydrates).

What do proteases/peptidases do?

Break bonds between amino acids (proteins).

What do lipases do?

Separate fatty acids from glycerides (lipids).

What do nucleases do?

Break nucleotides into sugars, phosphates, and nitrogenous bases.

What are brush border enzymes?

Enzymes located on the microvilli of the intestinal lining, including disaccharidases, peptidases, and nucleases.

What is the function of bile salts in digestion?

They emulsify lipids, breaking them into smaller droplets to increase surface area for digestion.

What happens during liver failure?

There is a build-up of hormones and toxins due to impaired liver function.

What is the significance of bile production?

It is essential for the digestion and absorption of lipids and for the excretion of bilirubin.

What is the length of the large intestine?

1.5 meters long.

What are the three main divisions of the large intestine?

Caecum, Colon (Ascending, Transverse, Descending, Sigmoid), Rectum.

What is the function of the ileocecal valve?

It regulates the flow of material from the small intestine to the large intestine.

What are the two types of muscle sphincters in the anal canal?

Internal sphincter (smooth muscle) and external sphincter (skeletal muscle).

What is the primary function of the large intestine?

Reabsorption of water, compaction of feces, absorption of vitamins, and storage of fecal material.

How does the structure of the large intestine differ from the small intestine?

The large intestine has no villi or circular folds, but has haustra (expansible pouches).

What initiates the mass movement in the large intestine?

The distension of haustra as chyme enters the large intestine.

What are the two stages of digestion that occur in the large intestine?

Mechanical digestion (haustral churning and mass movement) and chemical digestion (bacterial activity).

What is the role of bacteria in the large intestine?

They aid in the final stage of digestion, producing gases, vitamins (like K and biotin), and breaking down complex polysaccharides.

What triggers the defecation reflex?

Mass movement of contents into the rectum.