Chapter 24: The Digestive System Flashcards
What are the functions of the digestive system?
- ingestion
- mechanical processing
- digestion
- secretion
- absorption
- excretion
Digestive System Function: Ingestion
- materials enter the digestive tract via the mouth (oral cavity
- the process of swallowing is called delutition
Digestive System Function: Mechanical Processing
- crushing and shearing the ingested material to make it easier to propel along the digestive tract
- processes of chewing is called mastication
- increases the surface area allowing for enzymatic attack and subsequent breakdown of the material
Digestive System Function: Digestion
- refers to the chemical breakdown of food into small organic fragments allowing for absorption by the digestive epithelium
- proteins, carbohydrates, lipids, nucleic acids must all be broken down to their monomers (building blocks) before it can be absorbed (done by digestive enzymes)
Digestive System Function: Secretion
- release of water, acids, enzymes, buffers, salts by the epithelium of the digestive tract and by glandular organs
Digestive System Function: Absorption
- movement of organic monomers, electrolytes, vitamins and water across the epithelium and into the interstitial fluid of the digestive tract
Digestive System Function: Excretion
- removal of waste products from body fluids
- ejection of material as feces from the digestive tract is called defection or egestion
The Digestive System is divided into 2 main groups:
- Digestive Tract Organs
2. Accessory Digestive Organs
Digestive Tract Organs
- make up the Alimentary Canal (Gastrointestinal (GI) Tract)
- digestion and absorption
Accessory Digestive Organs
assist in the process of digestion and absorption
List the Digest Tract Organs
- Mouth (Oral Cavity)
- Pharynx
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Rectum
- Anus
List the Accessory Digestive Organs
- Salivary Glands
- Liver
- Gallbladder
- Pancreas
Salivary Glands
secrete salivary amylase that begins carbohydrate digestion/breakdown
Liver
a large metabolic organ that lies under the diaphragm and is made of 100,000 lobules
Gallbladder
stores bile from liver and sends it to small intestine
Functions of the Pancreas
- Exocrine produces pancreatic juice:
- Endocrine gland produces hormones that are released into the bloodstream after eating:
- insulin and glucagon
Mouth (oral cavity)
- has 3 pairs of salivary glands
- stratified squamous epithelial tissue
- has tonsils at the back of the mouth and other lymphatic tissues important in fighting disease
- has teeth that begin mechanical breakdown of food (mastication)
- has tongue that tastes and pushes food for chewing and swallowing
Pharynx
common passageway for solid foods, liquid and air
-material that is swallowed and enters the pharynx is now referred to as a bolus (mass of masticated material)
Esophagus
- hollow muscular tube where peristalsis pushes food to stomach
- length is approximately 1 foot
- first third is skeletal muscle
Stomach: Function
- stores food, starts digestion of proteins
- produces gastric juice that contains pepsin (an enzyme that breaks down protein)
- mechanical breakdown of the bolus liquefying it into a semi-liquid/solid paste called Chyme
Small Intestine: Main functions
- mixes chyme with digestive enzymes for final breakdown
- absorbs nutrient molecules into body
- secretes digestive hormones into blood
Large Intestine
also known as the large bowl ~5 feet
larger in diameter but shorter than the small intestines
Rectum
Stores and regulates elimination of feces
Pathway of Food
Mouth -> Pharynx -> Esophagus -> Stomach -> Small Intestines -> Large Intestines -> Rectum -> Anus
4 Major Layers that Makeup the Wall of the Alimentary (GI) Tract
- Mucosa (innermost layer)
- Submucosa (second layer)
- Muscularis Externa (third layer)
- Serosa (outermost layer)
Mucosa layer
- produces mucus (line with mucous membranes) that protect lining
- simple columnar epithelial tissue
- involved in absorption (in certain regions of GI tract)
- also produces digestive enzymes and hormones (in certain regions of GI tract)
Submucosa layer
layer of loose areolar connective tissue that contain blood vessels, lymphatic vessels and nerves
Muscularis Externa layer
made of 2 layers of smooth muscle that move food along the GI tract (in the stomach, there are 3 layers)
Serosa layer
part of the peritoneum
Enteric Nervous System
- “brains of the gut”
- accounts for intrinsic control of digestion which consists of 2 major intrinsic nerve plexuses.
.. (add more later)
What are the two major intrinsic nerve plexuses?
- Submucosal Nerve Plexus
2. Myenteric Nerve Plexus (lies between circular and longitudinal muscles of the muscularis externa)
Tongue
covered in taste buds called Gustatory cells and assist in the mechanical breakdown and swallowing of food (deglutition) and moves it toward the pharynx
What are the three pairs of salivary glands?
- parotid (cheek area)
- sublingual (under the tongue)
- submandibular (jaw area)
Saliva contains
- water, mucins (lubricant
- mucous
- lysozyme
- salivary amylase
- lingual lipase
- electrolytes
- IgA
2 Types of Teeth
- Primary Dentition (aka deciduous teeth or baby teeth) - 20 deciduous teeth
- Secondary Dentition (aka permanent teeth or adult teeth) - 32 permanent teeth
The Process of Swallowing
- Voluntary Phase
2. Involuntary Phase
Voluntary Phase of Swallowing
the beginning of food being swallowed from the mouth into the pharynx
Involuntary Phase of Swallowing
- once the food is in the pharynx swallowing becomes a reflex.
- the epiglottis covers the glottis to make sure food is routed into the esophagus
- food moves down the esophagus through peristalsis
Peristalsis
rhythmic contractions
Stomach: Structure
- thick-walled J-shaped organ that lies on the left side of the body beneath the diaphragm
- mucosa layer has deep folds called rugae and gastric pits that lead into gastric glands that secrete gastric juice
What are the three smooth muscle layers in the muscularis layer of the stomach?
- Oblique (inner)
- Circular (middle)
- Longitudinal (outer)
What are the 4 types of secreting cells?
- Chief Cells
- Parietal Cells
- Enteroendocrine Cells (G cells)
- Mucus Neck Cells
Chief Cells
produce Pepsinogen (inactive enzyme that breaks down protein)
Parietal Cells
- produces intrinsic factor (helps the absorption of Vitamin B12 in the small intestines)
- produces Hydrochloric Acid (HCl) which makes the stomach extremely acidic (pH of 2)
- This acidic condition activates Pepsinogen -> Pepsin (an active enzyme)
Enteroendocrine Cells (G Cells)
- produces Gastrin
- other secretions: Histamine, Serotonin & Somatostatin
Mucus Neck Cells
produce mucus (thin, soluble)
Small Intestines: Structure
- main site of absorption for the entire GI tract (90%) of absorption
- consists of cells called Brush Border cells (Absorptive Cells)
- smaller in diameter than the large intestines, but longer than the large intestines (~18-20 feet long)
Brush Border cells (Absorptive cells)
absorb the organic building blocks and also has attached enzymes called brush border enzymes
lactose
galactose + glucose
Sucrose
glucose + fructose
Maltose
glucose + glucose
Pancreas
an elongated, spongy organ found tucked behind the stomach (~6 inches)
Products of Pancreatic Juice
- Digestive Enzymes: Carbohydrase, lipase, nucleases, and proteases.
- Bicarbonate ion
Glucagon
hormone released when blood sugar falls
Insulin
hormone released when blood sugar rises
Carbohydrases
breaks down carbohydrates
Lipase
breaks down lipids, fats
Nucleases
breaks down DNA and RNA
Proteases
breaks down proteins
Bicarbonate ion
helps neutralize stomach acids
Metabolic Pathway
metabolic reactions (catabolic and anabolic) reactions involved in a series of steps
What are the 6 functions of the liver?
- filters blood from GI tract to remove poisons and detoxify the blood
- breaks down hemoglobin
- removes iron, vitamins A, D, E, D and B12 from blood and stores them
- removes glucose as glycogen and breaks it down to help retain blood glucose levels
- makes plasma proteins and helps regulate cholesterol levels by making bile salts
- Produces Bile, while the Gallbladder stores bile
During the digestion process, the gallbladder
- will contract releasing the bile into the duodenum.
- bile emulsifies the lipids and fats allowing further breakdown by lipases
Hepatic Portal System
-substances (amino acids, monosaccharides, components of nucleotides but NOT including glycerol or fatty acids) that are absorbed in the small intestine are filtered through the liver via the hepatic portal system
Absorption of lipids are absorb via the
lymphatic system. NOT the Hepatic Portal System.
Hepatic Portal system Pathway
Hepatic Portal Venule -> Hepatic Portal Vein -> LIVER -> Hepatic Vein -> HEART -> Hepatic Artery
5 Functions of the Large Intestines
- re-absorption of water to prevent dehydration
- absorption of vitamins (B complex and K) produced by the normal flora
- compaction of the intestinal contents into feces and elimination through the anus
- storage of feces
- cecum has projection called the appendix that may play a role in fighting infections
4 Divisions of the Large Intestines
- Cecum (pouch-like)
- Colon: ascending, transverse, descending, sigmoid
- Rectum
- Anal Canal
deglution
process of swallowing.
bolus
soft mass of chewed food
chyme
the semifluid mass of partly digested food expelled by the stomach into the duodenum
rugae
one of the folds of mucous membrane on the internal surface of the stomach
cardia
the upper opening of the stomach, where the esophagus enters
fundus
- Located at the uppermost section of the stomach.
- Its function is to store accumulated gas, which is produced as a by product of digestion, and to store extra food as needed.
pyloric sphincter
- band of smooth muscle at the junction between the pylorus of the stomach and the duodenum of the small intestine.
- acts as a valve to controls the flow of partially digested food from the stomach to the small intestine
gastroesophageal sphincter
ring of smooth muscle fibers that allows food into the stomach from the esophagus, but prevents gastric juices and partially digested food (chyme) to regurgitate back into the esophagus
pylorus
- the opening from the stomach into the duodenum (small intestine)
- prevent intestinal contents from reentering the stomach when the small intestine contracts and to limit the passage of large food particles or undigested material into the intestine
gastric juice
the digestive fluid, containing pepsin and other enzymes, secreted by the glands of the stomach
gastric pit
any of the numerous depressions in the mucous membrane lining the stomach into which the gastric glands discharge their secretions
enamel
- covers the pulp area filled with nerves and blood vessels
- made of calcium salts and protects the tooth from wear and tear
dentin
calcified connective tissue that makes up a majority of the tooth
root canal
an extension of the pulp cavity that contains the nerves and blood vessels
pulp cavity
contains pulp (connective tissue containing nerves and blood vessels)
cementum
bone like substance that attaches the root to the periodontal ligament
What are the three divisions of the stomach?
- fundus (superior portion)
- body (main portion)
- antrum/pylorus (inferior portion)
plicae circularis
- deep, permanent folds of the mucosa and submucosa of the duodenum
- slows chime, increasing the amount of surface area available for the absorption of nutrients.
villus/villi
- fingerlike projections of the mucosa of the small intestine
- increase surface area for absorption of nutrients
microvilli
- make up the brush border of the small intestine
- increase surface area for absorption of nutrients
brush border enzymes
- (located in the microvilli) within the GIT (gastrointestinal tract)
- are involved in the terminal process of the digestion of carbohydrates and proteins.
pancreatic juice
contains digestive enzymes and releases it into the duodenum of the small intestines
Enzyme Formula
Enzyme (E) + Substrate (S) -> ES Complex -> E + Product (P)
Optimum enzymatic action or function at
specific temperature and/or pH
active site
egion of an enzyme where substrate molecules bind and undergo a chemical reaction
catabolism
the breakdown of complex molecules in living organisms to form simpler ones, together with the release of energy
anabolism
the synthesis of complex molecules in living organisms from simpler ones together with the storage of energy
hydrolysis
the chemical breakdown of a compound due to reaction with water
dehydration
chemical reaction that involves the loss of a water molecule from the reacting molecule
List the major enzymes that are used in carbohydrate digestion
- salivary amylase
- pancreatic amylase
- maltase
- lactase
List the major enzymes that are used in protein digestion
- pepsin
- trypsin
- peptidases
List the major enzymes that are used in nucleic acid digestion
- nuclease
2. nucleosidases
List the major enzymes that are used in fat digestion
- lipase
Salivary Amylase: Produced by? Site of Action? What does it digest?
Produced by salivary glands.
Site of Action: mouth
Digests: starch + H2O -> maltose
Pancreatic Amylase: Produced by? Site of Action? What does it digest?
Produced by: pancreas
Site of Action: small intestine
Digests: starch + water -> maltose
Maltase: Produced by? Site of Action? What does it digest?
Produced by: small intestine
Site of Action: small intestine
Digests: maltose + H2O -> glucose + glucose
Lactase: Produced by? Site of Action? What does it digest?
Produced by: small intestine
Site of Action: small intestine
Digests: lactose + H2O -> glucose + galactose
Pepsin: Produced by? Site of Action? What does it digest?
Produced by: gastric glands
Site of Action: stomach
Digests: Protein + H2O –> peptides
Trypsin: Produced by? Site of Action? What does it digest?
Produced by: pancreas
Site of Action: small intestine
Digests: protein + H2O -> peptides
Peptidases: Produced by? Site of Action? What does it digest?
Produced by: small intestine
Site of Action: small intestine
Digests: peptide + H2O –> amino acids
Nuclease: Produced by? Site of Action? What does it digest?
Produced by: pancreas
Site of Action: small intestine
Digests: RNA and DNA + H2O –> nucleotides
Nucleosidases: Produced by? Site of Action? What does it digest?
Produced by: small intestine
Site of Action: small intestine
Digests: nucleotides + H2O -> base + sugar + phosphate
Lipase: Produced by? Site of Action? What does it digest?
Produced by: pancreas
Site of Action: small intestine
Digests: fat droplet + H2O -> monoglycerides + fatty acids
emulsification
- The breakdown of fat globules in the duodenum into tiny droplets, which provides a larger surface area on which the enzyme pancreatic lipase can act to digest the fats into fatty acids and glycerol.
- assisted by bile
chylomicron
- a droplet of fat present in the blood or lymph after absorption from the small intestine
- transport dietary fats and cholesterol from intestines to tissues
List the steps in carbohydrate digestion
- pancreatic amylase breaks down starch and glycogen into oligosaccharides and disaccharides
- brush border enzymes break oligosaccharides and disaccharides into monosaccharides
How are monosaccharides and amino acids absorbed?
- monosaccharide/amino acids are con-transported across the apical membrane of the absorptive epithelial cell. (uses Na+ concentration gradient established by Na+ and -K+ ATPase pump in the basolateral membrane)
- monosaccharide/amino acids exit across the basolateral membrane by facilitated division and enter the capillary via intercellular clefts
List the steps in protein digestion
- pancreatic proteases break down proteins and protein fragments into smaller pieces and some individual amino acids
- brush border enzymes break down protein fragments into amino acids
List the steps in fat digestion
- emusfication - bile salts in the duodenum break large fat globule into smaller fat droptlets
- digestion - pancreatic lipases hydrolyze triglycerides, yielding monoglycerides and free fatty acids
- micelle formation - micelles (consisting of fatty acids, monoglycerides and bile salts) ferry their contents to epithelial cells
How are fatty acids and monoglycerides absorbed?
- diffusion- fatty acids and monoglycerides diffuse from micelles into epithelial cells
- chylomicron formation - fatty acids and monoglycerides are recombine and packed with other fatty substances and proteins to form chylomicrons
- chlyomicrons are extruded from the epithelial cells by exocytosis, enter lacteals and are carried away from the intestine in lymph
HDL (high-density lipoprotein)
well-behaved “good cholesterol.” This friendly scavenger cruises the bloodstream. As it does, it removes harmful bad cholesterol from where it doesn’t belong.
LDL (low-density lipoprotein)
- the “bad” cholesterol that carries mostly fat and only a small amount of protein from the liver to other parts of the body
- It collects in the walls of your blood vessels, where it can cause blockages.
VLDL (very low-density lipoprotein)
- contains very little protein
- main purpose of VLDL is to distribute the triglyceride produced by your liver.
- high VLDL cholesterol level can cause the buildup of cholesterol in your arteries and increases your risk of heart disease and stroke.
Gastrin
a stomach hormone that stimulates Chief cells and Parietal cells and contraction of the muscularis
Histamine
stimulates parietal cells
Serotonin & Somatostatin
both stimulate contraction
