Module 10: Digestive System Flashcards
What comprises the digestive system?
(1) Alimentary canal (straight or linear path)
(2) Accessory Organs
What comprises the Alimentary Canal?
mouth, pharynx, esophagus, stomach, small intestine, large intestine
What comprises the Accessory Organs?
teeth, tongue, gallbladder, salivary glands, liver, pancreas
This major process involves the taking food into the digestive tract. It is one of the major roles of the mouth.
Ingestion
This major process involves moving food through the canal,
includes swallowing and peristalsis. It mainly involves the mouth, pharynx, and the esophagus due to peristalsis.
Propulsion
This major process involves preparing for digestion by enzymes, included chewing, mixing with saliva, churning in the stomach, segmentation.
Mechanical Breakdown
This major process involves enzymatic degradation of food
molecules. This is the major role of the small intestine and stomach.
Digestion
This major process involves the passage of end-products from lumen to blood or lymph.
Absorption
This major process involves the elimination of indigestible substances. It involves your sigmoidal colon and the anus.
Defecation
This is the most extensive membrane in the abdominopelvic cavity that is composed of layer of smooth epithelial tissue. It extends over your body’s surface area.
Peritoneum (derived from the Greek word peritonion, which means to stretch round)
This peritoneum covers the external surface of digestive organs.
Visceral Peritoneum
This peritoneum lines the body wall.
Parietal Peritoneum
This potential space containing fluid secreted by serous membranes which allows digestive organs to glide easily across one another.
Peritoneal Cavity
This is a double layer of peritoneum that 1) provide routes for blood vessels, lymph and nerves, 2) holds organ in place, 3) store fat
Mesentery
This is the connective tissue of organs in the abdominal cavity
Mesentery
This is a form of mesentery connecting lesser curvature of stomach to liver and diaphragm
Lesser Omentum
This is a form of mesentery connecting greater curvature of the stomach to transverse colon and posterior body wall
Greater Omentum
What are the three salivary glands that aids in the formation of the saliva?
(1) Parotid
(2) Sublingual
(3) Submandibular
This part of the saliva aids your immune system.
Immunoglobulin
How much fluid does peritoneal cavity contain?
100 mL (serous fluid)
This condition pertains to the inflammation of the peritoneum due to the friction between the visceral and parietal peritoneum, thus leading to a board like abdomen.
Peritonitis
Are there any organs in the peritoneum?
No, but all the organs in the system is contained in the abdominopelvic cavity.
How does the peritoneum play an important part for patients with kidney problems?
The peritoneum is used to clear out the blood of patients that have none functioning kidneys.
This pertains to the posterior region of the peritoneum, where the pancreas, the kidneys, and the duodenum, as well as the rectum and the urinary bladder are located.
Retroperitoneum
What are the four (4) tunics of the alimentary canal?
(1) Mucosa
(2) Sub-mucosa (under the mucosa)
(3) Muscularis externa
(4) Serosa (exterior tunic)
The mucosa is constituted of what?
(1) Epithelium
(2) Lamina propria
(3) Muscularis mucosae
The muscularis externis is composed of what?
(1) circular layer
(2) longitudinal layer
(3) oblique layer (which allows churning)
The serosa is composed of what?
(1) connective tissue
(2) Epithelium (mesothelium)
This layer is where mucus is produced which aids in propelling the food down to the alimentary canal.
Mucosa layer (muscularis mucosae)
In this layer, this is where the blood vessels, the lymph, and the nerves run.
Submucosa
What is the relationship between the glands of the submucosa and the mucosa?
The glands in the submucosa is connected to the mucosa which allows the secretion of enzymes and hormones to the alimentary canal.
This layer is composed of a circular and longitudinal layer that allows the process of propulsion, segmentation and peristalsis down to the alimentary canal with the use of muscles.
Muscularis Externis
If the serosa is not connected to any peritoneum, then it is called “____________”
Adventitia
This pertains to the hollowed openings.
Lumen
This is the condition wherein the hiatus slides to a hollowed opening.
Hiatal Hernia
This is the condition when the canal weakens which leads to outpouching of the hiatus.
Herniation
This helps in taking in and excreting the blood or fluid during blood flow.
abdominal aorta
This anatomical structure helps in the perfusion.
Superior mesenteric artery
What are the branches of the mesenteric artery which allows for blood flow for the upper area of the abdominopelvic cavity.
(1) Middle Colic artery
(2) Intestinal artery
(3) Right Colic Artery
(4) Ileocolic Artery
What are the branches of the mesenteric artery which allows for blood flow for the lower area of the abdominopelvic cavity.
(1) Left colic artery
(2) Sigmoidal artery
(3) Superior rectal artery
This innervates and supplies blood in the abdominopelvic cavity in terms of arterial blood flow.
Mesenteric artery
This condition pertains to the presence of edema in the patient’s abdominopelvic cavity.
Asities
This condition pertains to the problem in the portal hepatic vein, which connects the blood supply of the abdomen and the liver as well as the major veins.
Portal Hypertension
This vein connects the blood supply of the abdomen and the liver as well as the major veins
Portal Vein
This pertains to the collection of venous rich blood from the viscera to the liver.
Hepatic Portal Circulation
How much cardiac output does the stomach receive after ingestion?
1/4
This reflex occurs because the abdominal region receives 1/4 of your cardiac output, which results to the decrease in blood flow in your brain or decrease in perfusion.
Splanchnic Reflex
What are the two connections in the enteric nervous system from the CNS to the PNS?
(1) Submucosal Nerve Plexus
(2) Myenteric Nerve Plexus
This is the in-house nerve supply of the alimentary canal that regulates digestive system activity and innervates to the abdominal cavity.
Enteric Nervous System
Explain the flow in the enteric nervous system.
(1) Internal Stimuli (changes in the GI tract stretch, lumen pH, or solute concentration.
(2) The chemoreceptors (chemical), osmoreceptors (pressure), or mechanoreceptors (stretch) will convey the internal stimuli the CNS
(3) You can also receive external stimuli from the sight, smell, taste, and thought of the food.
(4) The stimulus will travel to the local (intrinsic nerve plexus or the gut brain to the effectors like smooth muscle or glands
(5) Therefore, resulting to a response like changes in contractile and secretory activity
This occur entirely within the gastrointestinal wall and is in charge of stimuli.
Short Reflexes
This is called the oral cavity, bounded by lips in the anterior, cheeks laterally, palate superiorly and tongue inferiorly
Mouth
The mouth continues with the ______________.
Oropharynx
The mouth is line with what?
Lined with stratified squamous epithelium (withstands friction) and slightly keratinized to prevent abrasion while eating
This is the pouch-like structure that allows storage.
Oral Vestibule
These are salivary glands that allows the secretion of saliva, which then prompts the initial stage of digestion.
Submandibular and sublingual ducts
This is a small flesh that is responsible for the gag reflex.
Uvula
This is a common passage for food, water and air, wherein the epiglottis closes to block the larynx so the patient does not aspirate food and water.
Laryngopharynx
What are the three (3) salivary glands?
(1) Parotid
(2) Sublingual
(3) Submandibular
This salivary gland is located in the anterior portion of your ear. It has ducts that allow secretions to be delivered into the oral cavity.
Parotid Salivary gland
This salivary gland is located below the jaw.
Submandibular salivary gland
This salivary gland is located inferior to the tongue.
Sublingual salivary gland
What are the functions of the salivary glands?
(1) Cleanses the mouth
(2) Dissolves the food chemicals for
tasting
(3) Moisten foods and helps compact it a bolus
(4) Contains amylase to digest starchy foods
This is an enzyme responsible for breaking down or digestion of starch.
amylase (salivary amylase)
What are the three (3) kinds of pharynx?
(1) Nasopharynx (connected to the nose)
(2) Oropharynx (connected to the oral cavity)
(3) Laryngopharynx
This is the pharynx or common passage of food, fluid, and air.
Laryngopharynx
This is a muscular tube about 25cm and collapsed when not propelling food
Esophagus
What happens to the epiglottis when food moves through the laryngopharynx?
Once food moves through the laryngopharynx, epiglottis will close the larynx and food will posteriorly move to the esophagus and not to the trachea
This is surrounded by circular smooth muscle that keeps it closed when food is not being swallowed.
Gastroesophageal sphincter (Cardiac Sphincter)
These help protect the tube from reflux of stomach acid.
Mucous cells at the sides
This sphincter posterior to the pharynx prevents the backflow of blood and food going back to your oral cavity, which is a closing area.
Upper esophageal sphincter
This sphincter is also known gastroesophageal sphincter that is a connection between your stomach and esophagus.
Lower esophageal sphincter
What happens when you eat too much and you have a weak esophageal sphincter?
The patient will get heart burn due to the reflux. Hence it is important to not lie down after ingesting many food.
What are three (3) phases in the pharynx in terms of food propulsion?
(1) Buccal phase
(2) Pharyngeal-esophageal phase
(3) Pharyngeal-esophageal phase continues
Explain the buccal phase.
The upper esophageal sphincter is contracted (closed). The tongue presses against the hard palate, forcing the food bolus into the oropharynx.
Explain the pharyngeal-esophageal phase.
(1) The tongue blocks the mouth. The soft palate and its uvula rise, closing off the nasopharynx.
(2) The larynx rises so that the epiglottis blocks the trachea. The upper esophageal sphincter relaxes, food enters the esophagus.
Explain the continuation of the pharyngeal-esophageal phase.
(1)The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly
(2) The upper esophageal sphincter contracts after food enters.
(3) Peristalsis moves food through the esophagus to the stomach (circular and longitudinal muscles contract to allow food to move down)
(4) The gastroesophageal sphincter surrounding the cardial orifice opens. After the food enters the sphincter closes to prevent regurgitation
This is a wave of contraction moves food through digestive tract.
Peristalsis
How does peristalsis work?
(1) A wave of smooth muscle relaxation moves ahead of the bolus, allowing the digestive tract to expand.
(2) A wave of contraction behind the bolus propels it (squeezes it to move) through the digestive tract.
This lies in the left upper quadrant hidden by the liver and the diaphragm. It contains four layers.
Stomach
How much can the stomach contain?
50mL is empty but can hold around 4L of food
What are the four (4) layers of the stomach?
(1) Serosa (outermost layer)
(2) Muscularis Externa
(3) Submucosa
(4) Mucosa
This layer of the stomach is modified because it needs churning or intense mechanical breakdown of the food.
Muscularis Externa
This is the top part of the stomach.
Fundus
What are the smaller portions constituting the stomach?
(1) Pyloric sphincter
(2) Pyloric canal
(3) Pyloric antrum (near the pylorus of the stomach)
This sphincter connects the stomach and the small intestine.
Pyloric sphincter
What are the modified layers of the stomach?
(1) Mucosa
(2) Muscularis Externa
This layer allows food to be pummeled, churned, mixed to physically break it down into smaller fragments
Muscularis Externa
This is composed of mucous cells that produce a cloudy, protective layer consisting of insoluble mucus that traps bicarbonate-rich fluid beneath it
Mucosa
This is important to trap bicarbonate rich fluid and neutralize hydrochloric acid so that they won’t erode.
Mucous
This will allow hydrochloric acid to enter the stomach from the gastric pits
Parietal cells
This hormone in the stomach increases HCl secretion, stimulates gastric emptying, stimulates the contraction of the intestinal muscle, relaxes the ileocecal valve and stimulate mass movements.
Gastrin
What is the site and stimulus of production of gastrin>
stomach mucosa (G cells); food (partially digested proteins, acetylcholine released by nerve fibers
What are the target organs of the gastrin?
(1) Stomach (Parietal cells)
(2) small intestine
(3) Ileocecal Valve
(4) Large intestine
This hormone that acts in digestion activates the parietal cells to release HCl.
Histamine (H2)
What is the site and stimulus of production of histamine?
Stomach mucosa; food in the stomach
What is the target tissue of histamine?
Stomach
This hormone aiding in digestion inhibits the stomach’s secretory activity, potentiates secretion actions on the organs, increases the output of enzyme rich pancreatic juice, stimulates organs to contract and expel stored bile, and relaxes sphincter to allow entry of bile and pancreatic juice into the duodenum.
Cholecystokinin (CCK)
What is the site and stimulus of production of the Cholecystokinin (CCK)?
Duodenal mucosa; fatty chyme (partially digested protein)
What are the target organs of the Cholecystokinin (CCK)?
(1) Stomach
(2) Liver/pancreas
(3) Gallbladder
(4) hepatopancreatic sphincter
This hormone in digestion inhibits HCl production and stimulates insulin release.
Glucose-dependent insulinotropic peptide or gastric inhibitory peptide
What is the site and the stimulus for production of Glucose-dependent insulinotropic peptide or gastric inhibitory peptide?
Duodenal mucosa; fatty chyme
This hormone for digestion stimulates gastric glands and motility.
Intestinal gastrin
This hormone for digestion stimulates migrating motor complex
Motilin
What is the site and stimulus for production of intestinal gastrin?
duodenal mucosa; acidic and partially digested foods in the duodenum
What is the site and stimulus for production of motilin?
Duodenal mucosa; fasting periodic release every 1 1/2 - 2 hours by neural stimuli
What is the target organ of motilin?
Proximal duodenum
What is the site and stimulus for production of secretin?
duodenal mucosa; acidic chyme (also partially digested proteins and fats)
What is the target organs of the secretin?
(1) Stomach
(2) Pancreas
(3) Liver
This hormone in digestion causes contraction of stomach muscle.
Serotonin
What is the site and stimulus for production of serotonin?
stomach mucosa; food in the stomach
This hormone in digestion inhibits gastric secretion of all products, inhibits GI blood flow; thus inhibiting intestinal absorption and inhibits the contraction and bile release.
Somatostatin
What is the site and stimulus of production for somatostatin?
Stomach mucosa and duodenal mucosa; food in the stomach and stimulation by sympathetic nerve fibers
What are the target organs of somatostatin?
(1) Stomach
(2) Pancreas
(3) Small intestine
(4) Gallbladder and Liver
This hormone in digestion stimulates buffer secretion, increases blood flow through intestinal capillaries, relaxes intestinal smooth muscle, increases secretion and inhibits acid secretion
Vasoactive Intestinal Peptide (VIP)
What is the site and stimulus for production of Vasoactive Intestinal Peptide (VIP)?
Enteric neurons; chyme containing partially digested foods
What are the digestive processes in the stomach?
(1) Propulsion by longitudinal and the circular muscles from the muscularis externa
(2) Mechanical breakdown by the churning of the oblique, longitudinal and circular muscles
(3) Digestion
(4) Absorption
What are the target organs of Vasoactive Intestinal Peptide (VIP)?
(1) small intestine
(2) Pancreas
(3) Stomach
How does protein digestion begin in the stomach?
Protein digestion begins by HCL produced by the stomach
This is the most important protein-digesting enzyme
Pepsin
These pass easily from mucosa to blood.
Alcohol and aspirin
This is secreted by the stomach, required to absorb Vitamin B12 to produce mature RBCs (Pernicious anemia)
Intrinsic Factor
What are the phases (stimulatory and inhibitory events) that happen in the stomach?
(1) Cephalic Phase
(2) Gastric Phase
(3) Intestinal Phase
Explain the stimulatory event of the cephalic phase?
(1) Sight and thought food will stimulate the taste and smell receptors
(2) They travel to the cerebral cortex, where hypothalamus and medulla oblongata will be stimulated
(3) Thus allowing the vagus nerve to secrete gastric juices
Explain the stimulatory event of the gastric phase?
(1) Stomach distension activates stretch receptors or food chemicals likes peptides and caffeine and rising ph activate chemoreceptors
(2) They stimulate long reflexes (via medulla oblongata and vagus nerve) or short reflexes as well as g cells
(3) This allows the gastrin to be released to the blood; thus stimulating the stomach’s secretory activity
Explain the intestinal phase.
(1) presence of partially digested foods in the duodenum or distension of the duodenum when the stomach begins to empty
(2) Stimulates the intestinal (enteric) gastrin to release to blood
(3) This allows the gastrin to be released to the blood; thus stimulating the stomach’s secretory activity
Explain the inhibitory event of the cephalic phase.
(1) loss of appetite or depression
(2) the stimulus travels to the cerebral cortex
(3) This decreases the parasympathetic activity (rest and digest), therefore inhibiting secretory activity
Explain the inhibitory event of the gastric phase.
(1) Excessive acidity in the stomach and emotional stress
(2) Stimulus travels to g cells and activates the sympathetic nervous system which overrides parasympathetic controls
(3) which decreases gastrin release to the blood
Explain the inhibitory event of the intestinal phase.
(1) Distension of duodenum due to the presence of fatty, acidic, and hypertonic chyme
(2) Stimulates enterogastric reflex (involving both short and long reflexes) and the release of enterogastrones like secretin and cholecystokinin
(3) Therefore decreasing gastric release
Explain the mechanism of HCl secretion
(1) Blood capillaries contain bicarbonate
(2) Carbon dioxide will mix with water to form carbonic anhydrase which will become carbonic acid
(3) Carbonic acid will divide into bicarbonate and hydrogen ions
(4) Bicarbonate will go back to the blood vessels and hydrochloric acid will be released
(potassium ions will go in and out of the parietal cells)
These cells allow the secretion of hydrochloric acid.
Parietal Cells
Explain gastric motility
(1) Propulsion: Peristaltic waves move from the fundus (top) to the pylorus (bottom part) via longitudinal muscles
(2) Grinding: In this the pyloric valve is slightly opened. This is the most vigorous peristalsis and mixing action occur close to the pylorus. The pyloric end of the stomach acts as a pump that delivers small amount of chyme to the duodenum,
(3) Retropulsion: The pyloric valve is closed. The peristaltic wave closes the pyloric valve, forcing most of the contents of the pylorus backward into the stomach.
This produces bile for export into the duodenum. This is the largest gland in the body.
Liver
The liver is the largest gland in the body that occupies what?
right hypochondriac and epigastric region
What are the four(4) lobes of the liver?
(1) Left lobe (anterior)
(2) Right lobe (anterior)
(3) Caudate (posterior - middle)
(4) Quadrate lobe (posterior)
This contains the hepatic artery proper (left) and hepatic portal vein (right)
Porta Hepatis
These are sesame seed-sized functional units in the liver.
Liver lobules
The smallest part of the liver lobules. They are in charge of processing bloodborne nutrients, temporarily storing fat soluble vitamins and detoxification
Hepatocytes
This contain the hepatic artery, hepatic portal vein and
bile duct
Portal Triad
This is where the bile enter
Portal duct
How much bile can hepatocytes secrete?
Secrete some 900mL of bile/day
What are the functions of the liver?
- Digestive and excretory functions (fat digestion)
- Store and process nutrients
- Detoxifies harmful chemicals
- Synthesizes new molecules
How much bile can a liver secrete each day?
700mL
This dilutes and neutralizes stomach acid and break down fats
Bile
This condition pertains to a yellowish discoloration in the skin which may indicate a liver problem.
Jaundice
Explain the process of bile secretion and release.
(1) Vagus nerve stimulation (red arrow) causes the gallbladder to contract,
thereby releasing bile into the duodenum.
(2) Secretin, produced by the duodenum (purple arrows) and carried through the blood to the liver, stimulates bile secretion by the liver (green arrows inside the liver).
(3) Cholecystokinin, produced by the duodenum (pink arrows) and carried through the blood to the gallbladder, stimulates the gallbladder to contract and the sphincters to relax, thereby releasing bile into the duodenum (green arrow outside the liver).
(4) Bile salts also stimulate bile secretion. Over 90% of bile salts are reabsorbed in the ileum and returned to the liver (green arrows), where they stimulate additional secretion of bile salts.
Explain enterohepatic circulation?
(1) Bile salts are secreted into the portal vein to the duodenum
(2) As bile salts travel through the small intestine, they allow lipid digestion and absorption to occur
(3) 95% of bile salts are reabsorbed by the ileum (last part of the small intestine)
(4) Reabsorbed bile salts travel to the hepatic portal vein back to the liver where they are recycled . Only 5% of bile salts are newly synthesized each time
This produces enzymes that break down all foodstuffs. It has both endocrine and exocrine roles.
Pancreas
The exocrine role of the pancreas include production of pancreatic juice from the following parts _________.
(1) Acini
(2) Ducts
What are the 4 pancreatic enzymes?
(1) Protease
(2) Amylase
(3) Lipase
(4) Nucleases
Why are pancreatic enzymes inactivated?
These enzymes are produced in inactive forms then activated in the duodenum because if they are activated, a person may digest their pancreas
What are the major proteases?
(1) Trypsin
(2) Chymotrypsin
(3) Carboxypeptidase
(aids in protein digestion)
This is where the pancreatic juices are excreted.
Pancreatic Ducts
This is the opening for the common bile duct and pancreatic juices.
Papillae
These are in charge of the production of insulin.
Islet of Langerhans (immediately distributed to the bloodstream)
These cells secrete pancreatic enzymes.
Acini Cells
This is a thin- walled muscular sac that appears green when filled with bile. It also stores bile that is not immediately needed for digestion and concentrates it by absorbing some of its water and ions.
Gallbladder
What happens when there is too much cholesterol or too few bile salts in the gallbladder?
Too much cholesterol or too few bile salts allow cholesterol to crystallize and forms gallstones (RUQ pain).
Explain control of pancreatic secretions.
(1) Parasympathetic stimulation from the vagus nerve causes the pancreas to release a secretion rich in digestive enzymes
(2) Secretin, released from the duodenum, stimulates the pancreas to release a watery secretion, rich in bicarbonate ions
(3) Cholecystokinin, released from the duodenum. causes the pancreas to release a secretion rich in digestive enzymes.
Explain the mechanisms promoting secretion and release of bile and pancreatic juice.
(1) CCK and secretin are secreted by duodenal enteroendocrine cells.
* Cholecystokinin (CCK) release is stimulated by proteins and fats in chyme.
* Secretin release is stimulated by acidic chyme.
* CCK and secretin enter the circulation and cause the following four events
(2) Pancreatic secretion: CCK induces secretion by acinar cells of enzyme- rich pancreatic juice.
* Secretin causes secretion by duct cells of HCO, rich pancreatic juice.
* Vagus nerve weakly stimulates during cephalic and gastric phases
(3) Bile secretion by liver:
* Bile salts returning from enterohepatic circulation are the most powerful stimulus for bile secretion.
* Secretin is a minor stimulus.
(4) Gallbladder contraction:
*CCK causes gallbladder contraction.
* Vagus nerve stimulates weak gallbladder contraction during cephalic and gastric phases.
(5) Hepatopancreatic sphincter relaxation:
* CCK causes hepatopancreatic sphincter to relax. Bile and pancreatic juice enter duodenum.
This is where digestion is completed. This is also known as the major absorptive organ. It starts from the pyloric sphincter to the ileocecal valve
Small Intestine
How many hours does chyme take to pass through?
3 to 5 hours
This contains microvilli, absorptive, goblet, granular and endocrine cells, connected to the pancreatic ducts and contains bile
Duodenum
This is for the absorption of nutrients, has more goblet cells than duodenum, with Brunner’s glands, more vascular than ileum
Jejunum
This has the has the most goblet cells, contains Peyerʼs patches
Ileum
These cells allow the generation of the mucous.
Goblet cells
This sphincter connects the stomach and the small intestine.
Pyloric Sphincter
This is a band of tissue in your belly. It helps keep the small intestine in place and allows its contents to move along. (Used to differentiate the upper and lower GI tract; located in the duodenum and jejunum)
Ligament of Treitz
These are deep, permanent folds of the mucosa and submucosa and will slow down the chyme allowing more time for nutrients to be absorbed
Circular Folds
These are fingerlike projections that increase absorptive surface
Villi
These are cytoplasmic extensions that bear enzymes
which digests carbohydrates and proteins
Microvilli
These are simple columnar cells endowed with microvilli that secrete intestinal juice (mucus and carrier fluid) - absorptive cells.
Enterocytes
These are the source of secretin and cholecystokinin which inhibit gastric secretion
Enteroendocrine cells
These releases defensins and lysozymes
Paneth cells
These divides to form daughter cells that become other cell types
Stem cells
These includes Peyerʼs patches that contains Ig-A secreting plasma cells for intestinal pathogens
Mucosa-associated lymphoid tissue
This organ frames the small intestines on three
sides. Functions to absorb most of the remaining water from the indigestible food residues, store it temporarily and then eliminate as semisolid feces or stool, absorbs metabolites produced by resident bacteria
Large Intestines
Where does the large intestine span from?
From the ileocecal valve to the anus
This prevents the movement of food back to the small intestine
Ileocecal Valve
This is the anatomical structure in the large intestine that is connected to the appendix. This is the first proximal part of the large intestine.
Cecum
This is the most distal part of the colon.
Sigmoidal colon
This anatomical structure allows voluntary control of feces excretion.
Rectal Sphincter
This is important in the large intestine because it can help digest foods that aren’t digestible by the human body. It also functions by fermentation (fatty acids can be absorbed from indigestible carbohydrates) and vitamin synthesis especially B and K are synthesized by bacteria
Resident Bacteria or Bacterial Flora
What makes the large intestines different from the small intestine?
No circular folds or villi. The mucosa is thicker with more number of goblet cells to ease passage of feces and protect the wall from irritation by acids and gases released by bacteria
What does fermentation produce?
It produces gases (smelly dimethyl sulfide or fart) around 500mL each day.
Explain the motility of the large intestines.
(1) Feces move into and distend the rectum stimulating stretch receptors. The receptors transmit signals along afferent fibers to the spinal cord neurons. (impulses from cerebral cortex - conscious control).
(2) A spinal reflex is initiated in which parasympathetic motor fibers stimulate contraction of the rectum and sigmoidal colon and relaxation of the anal sphincter.
(Involuntary - internal anal sphincter & voluntary - external anal sphincter).
(3) if it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so that feces may pass.
These are generated from the break down of carbohydrates.
Monosaccharides
These are generated from the break down of lipids.
(1) fatty Acids
(2) mono-glycerides
These are generated from the break down of proteins.
Amino acids
How are carbohydrates digested?
(1) Starch are broken down by salivary amylase and pancreatic amylase into oligosaccharides and disaccharides.
(2) Lactose will form galactose and glucose. Maltose will form glucose and sucrose will form glucose and fructose.
(3) Glucose and galactose are absorbed via cotransport with Na+
(4) Fructose passes via facilitated diffusion
(5) All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi and are transported to the liver via the hepatic portal vein.
What are the brush border enzymes in the small intestine?
(1) Dextranase
(2) Glucoamylase
(3) Lactase
(4) Maltase
(5) Sucrase
How are proteins digested?
(1) Proteins are broken down by pepsin in the stomach glands with the presence of HCl into large polypeptides
(2) Large polypeptides are broken down by pancreatic enzymes like trypsin, chymotrypsin, and carboxypeptidase to form small polypeptides and peptides
(3) Small polypeptides and peptides are disintegrated by brush border enzymes to form amino acids.
What are the brush border enzymes used to break down small peptides into amino acids?
(1) Aminopeptidase
(2) Carboxypeptidase
(3) Dipeptidase
How are amino acids absorbed?
(1) Amino acids are absorbed via cotransport with Na+
(2) Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed into amino acids within the cells
(3) Infrequently, transcytosis of small peptides occur
How are fats digested?
(1) Unemulsified triglycerides undergo are broken down by lingual and gastric lipase (minor importance)
(2) They are emulsified by the detergent action of the salted ducted in from the liver
(3) And they are further broken down by pancreatic lipase to form monoglycerides and fatty acids
(4) Fatty acids and monoglycerides enter the intestinal cells via diffusion
(5) Fattya acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells. The resulting chylomicrons are extruded by exocytosis.
(6) The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic ducts
How are nucleic acid digested?
(1) Nucleic acids are broken down by pancreatic ribonuclease and deoxyribonuclease along brush border enzymes to form pentose sugars, n-containing bases, and phosphate ions.
(2) Units enter the intestinal cells by active transport via membrane carriers
(3) Units are absorbed and transporter to the liver via the hepatic portal vein
How does water move in the stomach?
Water can move across the intestinal wall in either direction (may be to the blood or back to the intestine. The movement depends on osmotic pressures
How many percentage of water entering the intestine is absorbed?
99%
