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Define alimentary canal and accessory organs and list organs that belong to each
alimentary canal- continuous tube through which food passes directly
consists of oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine
accessory organs- not part of the alimentary canal but assist in digestion in some way; located around alimentary canal and include teeth, tongue, salivary glands, liver, gallbladder, and pancreas
Describe the major functions of the digestive system
Main Functions of the Digestive System 1. Food Breakdown & Nutrient Absorption
Takes in food and breaks it down into nutrients for body cells.
2. Fluid & Electrolyte Balance
Regulates water and electrolyte intake.
Maintains acid-base homeostasis by delivering nutrients to the blood.
3. Nutrient Intake & Hormone Production
Absorbs essential vitamins and minerals.
Produces hormones that support digestion and metabolism.
4. Waste Excretion
Eliminates metabolic wastes from the body.
Describe the six basic processes of the digestive system
Ingestion: This is the process of taking food and water into the digestive system, which occurs via the mouth under normal conditions. It is the first step in the digestive process.
Secretion: Digestive organs contain both endocrine and exocrine glands that secrete a variety of substances, such as mucus, enzymes, acid, and hormones, to aid other digestive processes. These secretions are crucial for breaking down food into its component nutrients.
Propulsion: Ingested food and liquids pass from one digestive organ to the next by the process of propulsion. This is largely accomplished by rhythmic contractions of smooth muscle in the alimentary canal, known as peristalsis, and is aided by mucus secreted by multiple organs.
Digestion: This process involves breaking down food into smaller components. It includes:
Mechanical digestion: Physically breaking down food into smaller parts, such as through mastication (chewing) in the mouth, churning in the stomach, and segmentation in the small intestine.
Chemical digestion: Breaking chemical bonds between food molecules, which varies for each nutrient because digestive enzymes are specific for a single type of bond in a single type of nutrient.
Absorption: Once food particles are digested, they move through the wall of the alimentary canal into blood or lymphatic vessels. This process allows nutrients, water, electrolytes, and vitamins to be absorbed into the bloodstream.
Excretion: Certain ingested materials are not digestible or usable by the body. These materials are excreted as waste
Think of your digestive system as a factory that processes food. Here’s how it works in simple steps:
Ingestion: This is when you put food and water into your mouth. It’s like loading raw materials into the factory.
Secretion: Various parts of your digestive system release special fluids (like mucus, enzymes, acids, and hormones). These fluids help break down the food into smaller pieces, much like a factory uses tools and chemicals to process raw materials.
Propulsion: Your muscles push the food along the digestive tract. This movement, called peristalsis, is like a conveyor belt moving items through different stages in the factory.
Digestion:
Mechanical Digestion: This is the physical breakdown of food. Chewing, stomach churning, and intestinal segmentation are like cutting and grinding the raw materials.
Chemical Digestion: Special enzymes and acids break down the food’s chemicals into tiny molecules, similar to how a factory uses chemicals to transform raw materials into useful products.
Absorption: Once the food is broken down, the useful nutrients, water, and vitamins pass through the walls of the digestive tract into the blood. This is like the factory packaging up the finished products and sending them out for use in the body.
Excretion: Finally, any parts of the food that aren’t needed are packaged up as waste and removed from the body, just like discarded scraps from the factory.
Briefly explain regulation of motility by the endocrine and nervous systems.
Nervous System Regulation:
The autonomic nervous system (ANS) plays a significant role in regulating digestive motility. It includes the enteric nervous system (ENS), which is a self-contained branch of the ANS that extends from the esophagus to the anus. The ENS operates independently of the central nervous system (CNS) and is responsible for local control of digestive functions.
The ENS coordinates the rhythmic contractions of smooth muscle in the alimentary canal, known as peristalsis, which propels food through the digestive tract.
Endocrine System Regulation:
The endocrine system regulates digestive motility through hormones. Various digestive organs secrete hormones that influence motility and other digestive processes.
These hormones can either stimulate or inhibit muscle contractions in the digestive tract, thereby affecting the rate and strength of peristalsis and other movements
The movement of food through your digestive system (motility) is controlled by two main systems:
Nervous System:
The enteric nervous system (ENS), a part of the autonomic nervous system, sends signals to the smooth muscles in your gut. These signals create rhythmic contractions (peristalsis) that push food along the digestive tract.
Endocrine System:
Hormones released by digestive organs adjust the speed and strength of these muscle contractions. Some hormones can speed up the movement, while others slow it down, ensuring that food is digested properly.
Describe the peritoneal membranes and the peritoneal cavity. Define intraperitoneal, retroperitoneal and mesenteries.
Peritoneal Membranes
Peritoneal Membranes: These are the largest serous membranes in the body, consisting of two layers:
Parietal Peritoneum: Lines the inner surface of the body wall.
Visceral Peritoneum (Serosa): Folds in on itself to cover the abdominal organs, forming the outer tissue layer of these organs.
Peritoneal Cavity
Peritoneal Cavity: The space between the parietal and visceral peritoneum, filled with serous fluid to reduce friction between moving organs.
Definitions
Intraperitoneal: Organs that are completely surrounded by the visceral peritoneum and are located within the peritoneal cavity.
Retroperitoneal: Organs that are located behind the peritoneum and are only partially covered by the peritoneum.
Mesenteries: Folds of the peritoneum that support and stabilize the intraperitoneal organs, providing pathways for blood vessels, nerves, and lymphatics
Discuss the basic functions of the oral cavity, the teeth, and the tongue. Include definitions of bolus, deglutition and mastication.
Oral Cavity:
Functions: Ingestion, secretion, chemical and mechanical digestion, and propulsion.
Houses two accessory organs: the teeth and the tongue.
Teeth:
Function: Masticate (chew) ingested food, grinding it into smaller pieces.
Mastication increases the surface area of food for digestive enzymes.
Tongue:
Function: Involved during the ingestion phase of digestion.
Movement of the tongue during chewing helps turn food into a bolus. The tongue also pushes the bolus posteriorly during swallowing.
Definitions:
Bolus: A moist, chewed mass of food.
Mastication: The process of chewing food.
Deglutition: The process of swallowing.
List the two types of cells in a salivary gland and explain what product each produces and when. List the three pairs of salivary glands
Serous Cells:
Produce watery secretions with enzymes (like salivary amylase), electrolytes, and a little mucin to start breaking down starches during eating.
Mucous Cells:
Secrete mucus that lubricates food for swallowing, keeps the mouth moist, and protects mucous membranes.
Salivary Glands:
Parotid Glands: Near the ears; produce mainly enzyme-rich serous saliva.
Submandibular Glands: Under the jaw; produce both serous and mucous secretions.
Sublingual Glands: Under the tongue; produce mostly mucous saliva.
Together, these glands create saliva, which aids digestion, cleanses the mouth, and helps prevent harmful bacteria growth.
Describe the composition and functions of saliva
Composition and Functions of Saliva
Composition: Water, electrolytes, mucus, enzymes (amylase, lysozyme), IgA, and bicarbonate.
Functions: Moistens food, begins digestion, neutralizes acid, kills bacteria, and aids in taste perception.
Describe the role of the pharynx in regards to digestion.
The pharynx's role in digestion is primarily propulsion, specifically swallowing. During deglutition, the bolus passes through the pharynx and into the esophagus. Also, the pharynx houses tonsils, which perform defensive functions.
Propulsion: Swallowing, or deglutition, is the primary digestive function of the pharynx.
Defense: The pharynx also houses the palatine and lingual tonsils which protect the alimentary canal from pathogens.
Describe the structure and functions of the esophagus including the roles of the upper esophageal sphincter and the gastroesophageal sphincter.
The esophagus is a muscular tube about 25 cm (10 inches) long that connects the pharynx to the stomach. It is located behind the trachea and its primary function is to transport food (bolus) from the mouth to the stomach. The esophagus is lined with a type of tissue called stratified squamous nonkeratinized epithelium, which helps protect it from abrasion as food passes through. It also contains glands that secrete mucus to lubricate the bolus.
There are two important sphincters associated with the esophagus:
Upper Esophageal Sphincter (UES): This sphincter is located at the junction of the pharynx and esophagus. It controls the passage of the bolus into the esophagus during swallowing.
Gastroesophageal Sphincter (also known as the Lower Esophageal Sphincter or LES): This sphincter is located at the lower end of the esophagus, where it meets the stomach. It regulates the passage of the bolus into the stomach and prevents the contents of the stomach from re-entering the esophagus, which helps protect the esophagus from stomach acids.
The esophagus primarily functions in propulsion, moving food from the mouth to the stomach, and secretes a small amount of mucus to aid in this process.
The esophagus is like a flexible, muscular tunnel about 25 cm (10 inches) long that carries food from your throat to your stomach. It’s lined with a tough, protective layer and produces a bit of mucus to help food slide down easily.
There are two "doors" or sphincters along this tunnel:
Upper Esophageal Sphincter (UES): Located at the top where the throat meets the esophagus, this door opens to let food in when you swallow.
Lower Esophageal Sphincter (LES): Found at the bottom where the esophagus meets the stomach, this door opens to let food enter the stomach and closes to keep stomach acid from coming back up.
Explain the process of deglutition, including the three phases.
Deglutition, or swallowing, moves food from your mouth to your stomach in three steps:
Voluntary Phase: You actively push the chewed food (bolus) from your mouth to the back of your throat.
Pharyngeal Phase: Automatically, your soft palate lifts to block the nasal passages and your epiglottis covers the windpipe, directing the bolus into the esophagus.
Esophageal Phase: Rhythmic muscle contractions (peristalsis) in the esophagus move the bolus down into your stomach.
Describe the histology of the stomach and the cells of the gastric glands. Include the functions of the types of cells the gastric glands contain. Define chyme
The stomach's histology includes four tissue layers plus an additional oblique muscle layer for churning.
The mucosa has gastric pits containing columnar and goblet cells.
Gastric glands contain enteroendocrine cells (hormones), chief cells (pepsinogen), parietal cells (hydrochloric acid), and mucous neck cells (acidic mucus).
Chyme is a liquid formed by churning food in the stomach.
Describe the acid secretion function of the stomach including the three regulatory phases. Define enterogastric reflex.
Acid Secretion: Parietal cells secrete HCl.
Phases:
Cephalic: Sight/smell/taste of food stimulates acid.
Gastric: Food in stomach and partially digested proteins stimulate acid.
Intestinal: Chyme in duodenum triggers the enterogastric reflex.
The enterogastric reflex is triggered by chyme in the duodenum. It decreases vagal activity and acid secretion.
Explain the motility of the stomach in terms of its receptive function, churning function and emptying function
Motility enables stomach to receive food from esophagus, churn incoming bolus into chyme, and control rate at which chyme empties into small intestine
1. Receptive function: when food or liquid is swallowed, gastroesophageal sphincter and smooth muscle of fundus and body of stomach relax to allow stomach to fill (controlled by gastric pacemaker cells)
2. Churning function: after a meal, smooth muscle layers of stomach begin to produce waves of peristalsis
-Peristalsis propels bolus to pylorus, where small amounts of chyme are propelled through pyloric sphincter into duodenum
3. Emptying function: control movement of chyme into duodenum; different materials pass through pyloric sphincter at different rates
-Liquids move rapidly from stomach to duodenum
-Solids must be converted to a nearly liquid state before they are able to enter small intestine
-Control of gastric emptying is critical because duodenum must mix incoming chyme thoroughly before it moves to rest of small intestine; two reasons...
1. Chyme is acidic, and duodenum must mix it with bicarbonate ions to avoid damaging intestinal mucosa
2. Chyme is generally very concentrated and must be diluted with water from pancreatic juice to prevent chyme from drawing water into intestinal lumen by osmosis
Describe the functions of the small intestine and discuss the histology and functions of the small intestine’s circular folds, villi, and microvilli.
Main processes occur in small intestine: secretion, digestion, absorption, and propulsion
1. Enterocytes produce multiple digestive enzymes, hormones, and mucus (enzymes responsible for chemical digestion)
2. After nutrients are digested chemically, they are absorbed across enterocytes into either blood or lymph, along with water, vitamins, and other substances
3. Also mixes and propels its contents along its length and into large intestine
Three smaller folds increase SA for absorption by 400-600x...
Circular Folds(largest):
1. folds to slow down transit of chyme, giving more time for digestion and absorption (enterocytes are absorbing cells)
Villi: mucosa folds into projections called villi
1. Between villi mucosa indents to form intestinal crypts which house glands with enteroendocrine cells and mucus-secreting goblet cells
2. central core with capillaries and a lacteal
Microvilli(smallest): found in plasma membrane of enterocytes
1. Each enterocyte has as many as 3000 microvilli; gives cell appearance of a bristle brush
2. Digestive enzymes produced and secreted by enterocytes catalyze reactions that break down disaccharides and peptides
Describe motility in the small intestine during fasting and eating.
Motility in the Small Intestine
During Fasting:
Migrating Motor Complex (MMC):
Slow, rhythmic contractions occur.
Clears remaining material, including leftover food and secretions.
Takes about 2 hours to push digesting food from the duodenum to the ileocecal valve.
During Eating:
Peristalsis:
Alternating contractions of longitudinal and circular smooth muscle propel chyme toward the ileum.
Segmentation (Churning):
Contractions of circular smooth muscle create a squeezing motion.
Aids in mechanical digestion and mixing chyme with digestive enzymes and bile.
Describe the functions of the large intestine and discuss the histology of the large intestines.
Functions:
1. Absorption - absorb water/electrolytes
2. Secretion - propulsion and defecation
3. Houses numerous bacteria that synthesize vitamins
Histology:
1. No villi or microvilli (reflects absorption is not primary function)
2. Mucosa rich with goblet cells for protection/lubrication
3. 10x more bacteria than cells in body (60% of dry mass of feces)
4. Bacteria, normal flora (gut flora) consist of about 500 different bacterial species that coexist with humans in a symbiotic (mutually beneficial) relationship
Describe the functions of the bacteria within the large intestines.
Functions:
1. Produce vitamins - such as vitamin K (necessary for blood clotting)
2. Metabolize undigested material
3. Deter growth of harmful bacteria
4. Stimulate immune system - during infancy, normal flora induce immune tolerance to their own antigens; stimulate development of MALT
Describe roles of the proximal and distal portions of the large intestines and explain the motility of the large intestine.
Proximal large intestine: ascending and transverse colon
1. primary site of water and electrolyte absorption and bacterial activity
Motility:
1. Type of segmentation (churning)
a. Circular muscle of each haustrum contracts repeatedly
b. Controlled by local neurons of ENS
2. Propulsive motion known as a mass movement
a. Mass movements occur three to four times per day, and appear to be triggered by food consumption
b. multiple haustra undergo peristalsis; propels their contents toward distal large intestine
Distal large intestine: descending and sigmoid colon, rectum, and anal canal
1. mainly storage and minimal absorption of water
Describe the pancreas and its digestive functions.
Main pancreatic duct - both pancreatic juice and enzymes
Alimentary canal - only enzymes
Functions:
1. secretes enzymes that are released into ducts of pancreas that empty into alimentary canal; makes pancreatic juice
2. Duct cells also secrete bicarbonate ions, a base, which make pancreatic juice alkaline (helps neutralize acidic chyme)
3. digestive enzymes, secreted by acinar cells, are crucial in chemical digestion
. Describe liver functions that pertain to digestion. Explain the role of bile. Define emulsification.
Main digestive function of liver is to produce bile
Two critical functions of Bile:
a. Required for digestion and absorption of lipids
b. Mechanism by which liver excretes wastes and other substances that kidneys cannot excrete
1. main organic compound of bile is bile salts which are amphiphilic (both polor and nonpolar parts). can interact with both lipids and watery envirement
2. Emulsification - bile coats lipids to physically break them down into smaller pieces
Describe the other functions of the liver.
The liver has diverse functions including: nutrient metabolism (processing nutrients)
detoxification (converting harmful substances into non-toxic forms)
excretion (bilirubin, modifying substances for kidney excretion). It also excretes bilirubin, a waste product of hemoglobin breakdown.
Describe the function of the gallbladder and trace the pathway of bile to the small intestine.
Function of the Gallbladder:
Storage and Concentration: The gallbladder stores bile received from the liver via the common hepatic duct. It concentrates bile by removing water, making it more effective for digestion.
Release of Bile: When food, especially fatty food, enters the small intestine, a hormone called cholecystokinin (CCK) is released. CCK triggers the contraction of the gallbladder, causing it to release bile.
Pathway of Bile to the Small Intestine:
Bile Production: Bile is produced by the liver and travels through the hepatic ducts.
Storage in Gallbladder: Bile is stored in the gallbladder via the cystic duct.
Release into Cystic Duct: Upon stimulation by CCK, the gallbladder contracts, releasing bile back into the cystic duct.
Flow through Common Bile Duct: Bile then flows from the cystic duct into the common bile duct.
Entry into Small Intestine: The common bile duct joins with the main pancreatic duct to form the hepatopancreatic ampulla, which is surrounded by the hepatopancreatic sphincter. This sphincter controls the release of bile into the duodenum, the first segment of the small intestine.
Explain the two types of digestion. Explain the process of enzymatic hydrolysis reactions of nutrient molecules
Two Types of Digestion: Mechanical (physical breakdown) and chemical (breaking chemical bonds).
Enzymatic Hydrolysis: Digestive enzymes catalyze hydrolysis reactions, using water to break bonds in nutrient molecules. This breaks down food into smaller molecules.
Imagine you have a big chain made of many links. Enzymatic hydrolysis is like using water along with tiny scissors (the digestive enzymes) to cut that chain into individual links. These smaller pieces are easier for your body to absorb and use for energy and building new tissues.
Describe the digestion and absorption of carbohydrates, proteins, lipids and nuclei acids. Include the names of all enzymes involved. Define micelle
Carbohydrates:
Digestion:
Begins in the mouth with salivary amylase, which breaks down polysaccharides into oligosaccharides.
In the small intestine, pancreatic amylase continues the process, converting oligosaccharides into disaccharides.
Brush border enzymes (e.g., lactase, maltase, sucrase) further break down disaccharides into monosaccharides (glucose, galactose, fructose).
Absorption:
Monosaccharides are absorbed in the small intestine via active transport (glucose and galactose) and facilitated diffusion (fructose).
Proteins:
Digestion:
Begins in the stomach with pepsin, which is activated from its precursor pepsinogen in an acidic environment.
In the small intestine, pancreatic enzymes such as trypsin, chymotrypsin, and carboxypeptidase further digest proteins into smaller peptides and amino acids.
Absorption:
Amino acids and small peptides are absorbed through the intestinal wall via active transport mechanisms.
Lipids:
Digestion:
Begins in the stomach with lingual lipase and continues in the small intestine where pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides.
Bile salts from the liver emulsify fats, increasing the surface area for lipase action.
Absorption:
Fatty acids and monoglycerides are absorbed into intestinal cells, where they are reassembled into triglycerides and packaged into chylomicrons for transport via lymphatic vessels.
Nucleic Acids:
Digestion:
Begins in the small intestine with pancreatic nucleases, which break down nucleic acids into nucleotides.
Brush border enzymes further digest nucleotides into nitrogenous bases, sugars, and phosphate groups.
Absorption:
These components are absorbed into the bloodstream through active transport mechanisms.
Definition of Micelle
Micelles are tiny droplets formed by bile salts that help transport fats through the watery environment of the intestines, making fat digestion and absorption easier
Describe the absorption of water, electrolytes and both types of vitamins
Absorption of Water, Electrolytes, and Vitamins1. Water and Electrolytes Absorption
The alimentary canal absorbs large amounts of water, electrolytes, and vitamins.
Primary site: Small intestine (absorbs about 8 liters of the 9 liters that enter daily).
Secondary site: Large intestine, which absorbs remaining water and electrolytes.
2. Vitamin Absorption
Water-Soluble Vitamins (B Complex, C):
Absorbed in the small intestine through diffusion across enterocyte membranes.
Fat-Soluble Vitamins (A, D, E, K):
Packaged into micelles with fats and absorbed along with lipids.
monomer and polymers
Here’s a simple breakdown:
Monomers are the small building blocks.
Polymers are long chains made by linking many monomers together.
Carbohydrates:
Monomers: Simple sugars (monosaccharides like glucose).
Polymers: Many sugars linked together (disaccharides like sucrose and polysaccharides like starch and glycogen).
Proteins:
Monomers: Amino acids.
Polymers: Chains of amino acids (polypeptides, which make up proteins).
Nucleic Acids:
Monomers: Nucleotides.
Polymers: Long chains (DNA and RNA).
Lipids:
Lipids aren’t classic polymers, but they’re built from smaller units like fatty acids and glycerol (for example, in triglycerides).
