lecture 22 Flashcards
Identify and describe the gross anatomy of the large intestine, rectum and anal canal, including their location relative to other body structures.
o Large Intestine: It is the final part of the gastrointestinal (GI) tract, approximately 1.5 meters in length, and it surrounds the small intestine in a horseshoe shape. It is composed of the cecum, colon (ascending, transverse, descending, and sigmoid), rectum, and anal canal. It is primarily responsible for absorbing water and electrolytes from indigestible food matter and forming feces.
o Rectum: It is the last 12-15 cm of the large intestine, leading to the anal canal. It stores feces temporarily until defecation.
o Anal Canal: The anal canal is approximately 2-4 cm long, and it is the terminal portion of the GI tract, through which feces are expelled from the body. It contains the internal anal sphincter (smooth muscle) and external anal sphincter (skeletal muscle).
Identify the specific segments and related flexures of the large intestine.
o Cecum: The pouch-like beginning of the large intestine, located in the lower right abdomen, where the small intestine empties into.
o Ascending Colon: Travels upward on the right side of the abdomen.
o Right Colic (Hepatic) Flexure: The bend between the ascending colon and the transverse colon, near the liver.
o Transverse Colon: Travels horizontally across the abdomen from the right to the left side.
o Left Colic (Splenic) Flexure: The bend between the transverse colon and the descending colon, near the spleen.
o Descending Colon: Travels down the left side of the abdomen.
o Sigmoid Colon: The S-shaped portion that leads into the rectum.
Describe the general functions of the large intestine.
o Water and Electrolyte Absorption: The large intestine reabsorbs water and electrolytes, converting the liquid chyme into more solid feces.
o Fermentation of Undigested Carbohydrates: The microbiome in the colon ferments some undigested carbohydrates, producing gases and short-chain fatty acids.
o Storage of Feces: The rectum stores fecal matter until defecation.
o Formation of Feces: Indigestible food remnants are compacted into feces for eventual expulsion.
Describe the specializations of the large intestine tunics (e.g., composition of the muscularis [muscularis externa]) compared to the tunics of the rest of the GI tract.
o Muscularis Externa: The muscularis externa in the large intestine is specialized in that it contains taeniae coli (three longitudinal muscle bands) and haustra (pouch-like segments). This differs from the smooth, continuous muscle layer in the rest of the GI tract.
o Mucosa: The mucosal lining of the large intestine is smooth (without villi) and contains many goblet cells that secrete mucus, which lubricates the colon and helps fecal movement.
Relate the specializations of the large intestine tunics (e.g., composition of the muscularis [muscularis externa]) to the organ’s functions.
o The taeniae coli contract to produce haustral churning, aiding in the movement and mixing of contents. This facilitates water absorption and helps form feces.
o The specialized muscular structure allows for mass movement of contents, pushing fecal matter towards the rectum for eventual expulsion.
Compare and contrast the location, composition, and innervation (i.e., somatic versus autonomic) of the internal and external anal sphincters.
o Internal Anal Sphincter: Composed of smooth muscle and controlled by the autonomic nervous system (involuntary control). It maintains closure of the anal canal.
o External Anal Sphincter: Composed of skeletal muscle and controlled by the somatic nervous system (voluntary control), allowing for the conscious control of defecation.
Compare and contrast the following: peristalsis, mixing waves, segmentation, and mass movement.
o Peristalsis: A series of wave-like muscle contractions that move food along the digestive tract.
o Mixing Waves: Movements that mix food in the stomach and small intestine, enhancing digestion.
o Segmentation: Alternating contraction and relaxation of segments of the intestine to mix contents and aid digestion, particularly in the small intestine.
o Mass Movement: Large, forceful contractions in the colon that push contents toward the rectum for elimination.
Describe the defecation reflex and how it is affected by somatic and autonomic innervation.
The defecation reflex is initiated when stretch receptors in the rectum are activated by the presence of feces, signaling the urge to defecate.
Autonomic Nervous System: The internal anal sphincter relaxes due to parasympathetic input.
Somatic Nervous System: Voluntary control of the external anal sphincter allows conscious control over defecation.
List the enzymes, their sources, their substrates, and their products of chemical digestion (enzymatic hydrolysis). - carbs
Carbohydrates:
Enzyme: Amylase (salivary and pancreatic)
Substrate: Starch
Product: Maltose
List the enzymes, their sources, their substrates, and their products of chemical digestion (enzymatic hydrolysis). - proteins
Proteins:
Enzyme: Pepsin (stomach), trypsin, chymotrypsin (pancreatic)
Substrate: Proteins
Product: Amino acids, peptides
List the enzymes, their sources, their substrates, and their products of chemical digestion (enzymatic hydrolysis). - lipids
Lipids:
Enzyme: Lipase (pancreatic)
Substrate: Triglycerides
Product: Fatty acids, monoglycerides
Identify the locations of chemical digestion of macromolecules (e.g., carbohydrates, proteins, lipids).
o Carbohydrates: Begins in the mouth (salivary amylase), continues in the small intestine (pancreatic amylase).
o Proteins: Begins in the stomach (pepsin), continues in the small intestine (trypsin, chymotrypsin).
o Lipids: Begins in the small intestine, where bile salts emulsify fats, and pancreatic lipase completes digestion.
Describe the functions, production, and regulation of secretion of hydrochloric acid (HCl).
o Hydrochloric Acid (HCl) is secreted by parietal cells in the stomach.
Function: Denatures proteins, activates pepsinogen to pepsin, and provides an acidic environment for digestion.
Regulation: Stimulated by the presence of food, particularly proteins. Gastrin is a key hormone that stimulates HCl production.
Define emulsification, and explain how and where bile salts facilitate fat digestion.
o Emulsification: The process by which bile salts break large fat globules into smaller droplets, increasing the surface area for lipase action. This occurs in the small intestine.
o Bile salts aid in fat digestion by facilitating the breakdown of fats into fatty acids and monoglycerides.
Describe the role of bacteria (microbiome) in digestion.
o Bacteria in the large intestine ferment undigested carbohydrates, producing gases and short-chain fatty acids that can be absorbed for energy.
o They also synthesize certain vitamins (e.g., vitamin K, B vitamins) and play a role in the immune system.
List the organs and specific structures that facilitate the absorption of nutrients (e.g., monosaccharides, amino acids, fatty acids, monoglycerides).
o Small Intestine: Villi and microvilli increase surface area for nutrient absorption (monosaccharides, amino acids, fatty acids).
o Large Intestine: Absorbs water, electrolytes, and some vitamins.
Explain the transport processes involved in the absorption of various nutrients.
o Monosaccharides and amino acids are absorbed via active transport (requires energy).
o Fatty acids and monoglycerides are absorbed via simple diffusion, then reassembled into triglycerides and transported as chylomicrons.
Explain how the digestive system relates to other body systems to maintain homeostasis.
The digestive system works in conjunction with other systems (e.g., circulatory, nervous) to maintain nutrient balance, regulate energy storage, and remove waste products, contributing to overall homeostasis.
System connections
Digestive and muscular: the digestive system provides nutrients and energy for the muscular system to be able to work on growth and repair in the body. The muscular system helps the digestive to function through things like the muscles in the GI tract allowing peristalsis.
Digestive and nervous: the CNS is crucial in regulating the digestive system and can do many things including: stimulate reflexes int eh digestive tract, release hormones related to hunger and other things to influence digestion to occur, and send many kinds of nerve signals for things like motility
