Human Physiology Chapter 21: Digestive System

A network of neurons in the digestive system that controls motility, secretion, and growth.

Neurons located within the enteric nervous system.

Neurons originating from the central nervous system (CNS) and connecting to the digestive system.

Reflex arcs integrated within the enteric nervous system.

Reflex arcs involving the central nervous system (CNS).

Long reflexes originating in the head.

Hormones that regulate gastrointestinal function.

A family of GI hormones which include gastrin and cholecystokinin (CCK).

Monosaccharides are absorbed in the small intestine, transported across the cell membrane, and enter the bloodstream.

Simple sugars like glucose, galactose, and fructose.

Enzymes on the surface of the small intestine that break down disaccharides into monosaccharides.

A process where monosaccharides are absorbed along with sodium ions across a cell membrane.

The site where most carbohydrate digestion and absorption occurs, allowing nutrients to be transported across cell membranes.

Di- and tri-peptides are absorbed through endocytosis.

Exopeptidases break terminal peptide bonds for amino acid release. Aminopeptidase and carboxypeptidase also break peptide bonds, using an H2O molecule and ATP.

Amino acids are transported into capillaries from villi.

Amino acids eventually travel to the liver.

A cellular process which the cell engulfs substances, forming a vesicle.

Enzymes that hydrolyze terminal peptide bonds from the ends of polypeptides.

An enzyme that cleaves amino acids from the N-terminus of peptide chains.

An enzyme that hydrolyzes peptide bonds at the carboxyl-terminal end of peptide chains.

A sphincter muscle located at the junction between the small intestine (ileum) and the large intestine (colon). It controls the movement of chyme from the ileum into the colon.

Strong peristaltic contractions that propel the chyme in large segments along the colon, typically occurring 3-4 times a day.

Localized contractions of circular muscle in the colon that mix the chyme and help to absorb water and electrolytes.

The horizontal section of the colon, located between the ascending and descending colon.

The vertical portion of the colon located after the transverse colon, which carries waste downwards towards the rectum.

The gastrocolic reflex stimulates mass movements in the colon, which propels the chyme towards the rectum.

Haustra are the pouches found in the large intestine that give it a segmented appearance.

The ileocecal valve is a sphincter muscle that controls the passage of chyme from the small intestine to the large intestine.

The defecation reflex is triggered by distension of the rectum, leading to relaxation of the internal anal sphincter and contraction of the external anal sphincter.

The sigmoid colon is a flexible S-shaped portion of the colon that allows for storage of feces before elimination.

The large intestine primarily concentrates waste by absorbing water and electrolytes, while bacteria break down undigested material.

Bacteria in the colon break down undigested food, producing substances like fatty acids that colonocytes use for energy.

Lipid-soluble substances produced by bacterial breakdown in the colon can be absorbed into the bloodstream.

Colonocytes, the cells lining the colon, obtain energy from fatty acids produced by bacterial breakdown.

Intestinal glands secrete fluid to help with digestion and absorption of nutrients.

Diarrhea can be caused by excessive fluid loss, often due to a lack of absorption in the intestines.

The ileum, the last part of the small intestine, connects to the large intestine through the ileocecal valve.

Sac-like pouches called haustra are formed by the circular muscle layer in the colon.

The GI tract wall has four layers: mucosa, submucosa, muscularis externa, and serosa. Each layer contributes to the function of the digestive system.

The innermost layer of the GI tract wall, containing epithelial cells that line the lumen, connective tissue, and a thin layer of smooth muscle.

The layer beneath the mucosa, containing blood vessels, lymphatics, nerves, and glands.

The muscle layer responsible for GI tract motility, consisting of two layers: circular and longitudinal muscle.

The outermost layer of the GI tract wall, a thin membrane that protects and lubricates the organs.

Our bodies produce more fluid for digestion than we ingest. About 2 liters come from food and drinks, and 7 liters come from secretions.

Inactive forms of digestive enzymes that are secreted into the gut and activated when needed.

The coordinated movement of food through the digestive tract. Peristalsis moves food forward, while segmentation mixes it.

Spontaneous depolarizations in GI smooth muscle cells that drive rhythmic contractions.

Tonic contractions last for minutes or hours, maintaining a constant pressure. Phasic contractions are brief, lasting only seconds, and are responsible for rhythmic movements.

Digestion, absorption, secretion, and motility are the four fundamental processes that the digestive system uses to break down food, absorb nutrients, and eliminate waste.

Autodigestion is the process of the digestive system's own enzymes breaking down its own tissues. This is a dangerous process that can damage the digestive organs.

Mass balance is the process of maintaining a constant volume of fluid in the body. The digestive system plays a crucial role in regulating fluid intake and excretion to ensure mass balance.

The digestive system plays a vital role in defending against pathogens and foreign substances that enter the body through food and drink.

The submucosa is a layer of connective tissue that supports the mucosa and contains blood vessels, lymphatics, nerves, and glands.

Pepsin breaks down proteins in the stomach, starting the digestion process.

Transcytosis is a process where small peptides are carried intact across cells, without being broken down.