Anatomy 2: Digestive System Test

How does the histology of the large intestine aid in absorption?

(reread)Absorbing diff things. Mucosa of large intestine absorbs water and vitamins. Nutrients absorbed in small intestine. The thin wall aids in absorption. Abundance of mucous cells. The glands are deeper in the small intestine. The mucosa of the large intestine does not produce enzymes. Muscularis externa the muscular bands have been reduced to teniae coli in large intestine. Mucosa in large intestine doesn't have villi. plexus

Put the layers of the digestive tract wall in order from the lumen to the deepest layer

- The lumen - mucosa -Digestive epithelium -Lamina propria -Muscularis mucosae - Submucosa - Muscularis externa - Serosa

Which salivary gland produces a serous secretion containing large amounts of salivary amylase?

parotid

The esophagus

- A hollow muscular tube -about 25 cm(10 in) long and 2cm (.8 in) wide - begins posterior to cricoid cartilage - enters abdominopelvic cavity through the esophageal hiatus -resting muscle tone: in the circular muscle layer the superior 3 cm (1.2 in) of esophagus prevents air from entering - It enters the abdominopelvic cavity through the esophageal hiatus, an opening in the diaphragm. The esophagus empties into the stomach anterior to vertebra T7. - The esophagus is innervated by parasympathetic and sympathetic fibers from the esophageal plexus - A comparable zone at the inferior end of the esophagus normally remains in a state of active contraction - This state prevents the backflow (reflux) of materials from the stomach into the esophagus - The wall of the esophagus contains mucosal, submucosal, and muscularis layers - The mucosa of the esophagus contains a nonkeratinized, stratified squamous epithelium - The mucosa and submucosa are packed into larger folds that extend the length of the esophagus

Teeth

- The bulk of each tooth consists of a mineralized matrix called dentin, it lacks cells - The pulp cavity receives blood vessels and nerves through the root canal, a narrow tunnel located at the root, or base of the tooth - Blood vessels and nerves enter the root canal through an opening called the apical foramen to supply the pulp cavity - Collagen fibers of the periodontal ligament extend from the dentin of the root to the alveolar bone, creating a strong articulation known as a gomphosis - A layer of cementum covers the dentin of the root. Cementum protects and firmly anchors the periodontal ligament - A shallow groove called the gingival sulcus surrounds the neck of each tooth - A layer of enamel covers the dentin of the crown. It contains calcium phosphate, hardest biologically manufactured material - Adequate amounts of calcium, phosphates, and vitamin D3 during childhood are essential if the enamel coating is to be complete and resistant to decay - The alveolar processes of the maxillae and the mandible form the maxillary(upper) and mandibular(lower) arcades - These arcades contain four different types of teeth - Incisors: blade shaped, front of mouth, single root - The cuspids: conical with sharp ridgeline and a pointed tip. Single root - Bicuspids: premolars, flattened crown with prominent ridges, have one or two roots - Molars: very large, flattened crowns. Molars in upper jaw have three roots, molars in lower jaw have two roots - Deciduous teeth are temporary teeth of primary dentition. 20 teeth - These teeth are later replaced by secondary dentition, or permanent dentition of the larger adult jaws - Three additional molars appear on each side of the upper and lower jaws as the person ages. 32 teeth total. - The third molars or wisdom teeth may not erupt before age 21. - Any teeth that develop in locations that do not allow them to erupt are called impacted teeth. They can be surgically removed to prevent the formation of abscesses

How does the histology of the various regions of the small intestine (duodenum, jejunum, ileum) change and how does this change help their function?

- The duodenum has few circular folds and their villi are small. The primary function of the duodenum is to receive chyme. - Over the proximal half of the jejunum circular folds and villi are very prominent. Thereafter, the circular folds and villi are very prominent. This reduction parallels a reduction in absorptive activity. - The distal portions of the ileum lack circular folds. The lamina propria there contains 20-30 masses of lymphoid tissue called aggregated lymphoid nodules, or Peyer's patches. The lymphocytes in the aggregated lymphoid nodules protect the small intestine from bacteria that normally inhabit the large intestine

The Pharynx( Throat)

- a common passageway for solid food, liquids, and air regions of pharynx: -nasopharynx - oropharynx - larngopharynx food passes through the oropharynx and larngopharynx to the esophagus - The pharyngeal constrictor muscles push the bolus toward and into the esophagus - The palatopharyngeus and stylopharyngeus muscles elevate the larynx - The palatal muscles elevate the soft palate and adjacent portions of the pharyngeal wall - These muscles work with muscles of the oral cavity and esophagus to start swallowing which pushes the bolus along the esophagus and into the stomach

Parts of the large intestine

- cecum: pouchlike first portion - colon: largest portion - rectum: the last 15 cm of digestive tract - Material arriving from the ileum first enters an expanded pouch called the cecum - The cecum collects and stores materials from the ileum and begins the process of compaction - Lymphoid nodules dominate the mucosa and submucosa of the appendix. The primary junction of the appendix is an organ of the lymphatic system - The colon has a large diameter and a thinner wall than the small intestine - The walls of the colon forms a series of pouches, or haustra - Haustra permit the colon to expand and elongate - Three separate longitudinal bands of smooth muscle-called teniae coli run along the outer surfaces of the colon - The serosa of the colon contains numerous teardrop shaped sacs of fat called omental appendices - We can subdivide the colon into four regions: the ascending colon, transverse colon, descending colon, and sigmoid colon

The Gallbladder

- hollow pear-shaped muscular sac - stores and concentrates bile prior to excretion into small intestine -located in the fossa on the posterior surface of the liver's right lobe - The gallbladder is a hollow, pear-shaped organ that stores and concentrates bile prior to its excretion into the small intestine - It is located in a fossa in the posterior surface of the livers right lobe - The gallbladder is divided into three regions 1) the fundus 2) the body 3) the neck - The cystic duct extends from the gallbladder to the point where it unites with the common hepatic duct to form the common bile duct - A major function of the gallbladder is bile storage, but it is released into the duodenum only under the stimulation of the intestinal hormone CCK - Whenever chyme enters the duodenum, CCK is released, relaxing the hepatopancreatic sphincter and stimulating contractions of the gallbladder that push bile into the small intestine. The amount of CCK secreted increased markedly when the chyme contains large amounts of lipids - The composition of bile gradually changes as it remains in the gall bladder. - If bile becomes too concentrated, crystals of insoluble minerals and salts begins to form. These deposits are called gallstones - In cholecytitis gallstones are so large that they can damage the wall of the gallbladder or block the cystic duct or common bile duct

The small intestine

-Plays a key role in digestion and absorption of nutrients -90% of nutrient absorption occurs in the small intestine -chemical digestion is completed here an the products of digestion are absorbed - The mucosa of the small intestine produces only a few of the enzymes involved. The pancreas provides digestive enzymes, as well as buffers that help neutralize chyme - The liver secretes bile, a solution stored in the gallbladder for discharge into the small intestine - Bile contains buffers and bile salts, compounds that facilitate the digestion and absorption of lipids - Ninety percent of nutrient absorption takes place in the small intestine. Most of the rest occurs in the large intestine - The small intestine has three segments: the duodenum, the jejunum, and the ileum - The duodenum is the portion of the small intestine is a "mixing bowl". It receives chyme from the stomach and digestive secretions from the pancreas and liver - The duodenum is in a retroperitoneal position between vertebrae L1 and L4 - The jejunum is the site of bulk chemical digestion and nutrient absorption - The ilium is the final segment of the small intestine and the longest. It ends at the ileocecal valve. This sphincter controls the flow of material from the ileum into the cecum of the large intestine - The small intestine fills much of the peritoneal cavity. Its position is stabilized by the mesentery proper - The stomach, large intestine, abdominal wall, and pelvic girdle restrict movement of the small intestine during digestion - The primary blood vessels involved are branches of the superior mesenteric artery and the superior mesenteric vein

Process of absorption of nutrients

-breaks down physical structure of food - disassembles component molecules - molecules released into bloodstream are: absorbed by cells broken down to provide energy for ATP synthesis or used to synthesize carbohydrates, proteins, and lipids - Food contains large organic molecules many of them insoluble. - Digestive enzymes break the bonds between simple sugars, proteases split the linkages between amino acids, and lipases separate fatty acids from glycerides - Digestive enzymes secreted by the salivary glands, tongue, stomach, and pancreas are mixed into the ingested material as it passes along the digestive tract - The final enzymatic steps involve brush border enzymes which are attached to the exposed surfaces of intestinal microvilli

Pancreas

-lies posterior to stomach. From duodenum toward spleen - bound to the posterior wall of the abdominal cavity. Wrapped in thin, connective tissue capsule - The pancreas lies posterior to the stomach - It is retroperitoneal and is firmly bound to the posterior wall of the abdominal cavity. The surface of the pancreas has a lumpy, lobular texture. - Arterial blood reaches the pancreas by way of branches of the splenic, superior mesenteric, and common hepatic arteries. The pancreatic arteries and pancreaticoduodenal arteries are the major branches from these vessels. The splenic vein and its branches drain the pancreas - The pancreas is primarily an exocrine organ. It produces digestive enzymes and buffers. The large pancreatic duct delivers these secretions to the duodenum. The pancreatic duct extends within the attached mesentery to reach the duodenum, where it meets the common bile duct from the liver and gallbladder. The two ducts then empty into the duodenal ampulla. When present(3-10% of people), the accessory pancreatic duct usually empties into the duodenum independently, outside the duodenal ampulla

Tongue

-manipulates materials inside the mouth Functions 1) mechanical processing by compression, abrasion, and distortion 2) manipulation to assist in chewing, and to prepare material for swallowing 3) Sensory analysis by touch, temperature, and taste receptors 4) Secretion of mucins and the enzyme lingual lipase: works over a broad range (3-6) enabling it to start lipid digestion immediately

In order to understand the disease in Mr. Volpe's alimentary canal, one must know the layers that make up its walls. Identify the four basic layers of the stomach, the tissues that make up each layer, and the general function of each layer.

1. Longitudinal muscle layer · Made of muscle tissue · Responsible for peristalsis which allows food to mix 2. Circular muscle layer · Made of muscle tissue · Controls the movement of the chyme into the duodenum by controlling the pyloric sphincter 3. Oblique muscle layer · Made of muscle tissue overlying mucosa · Responsible for mixing and churning which is essential for formation of chyme 4. Rugae · Made up of the mucosal epithelium · Allow the gastric lumen to expand allowing the stomach to stretch

Dr. Lorraine suspects a peptic ulcer. This is an inflammatory lesion in the stomach or duodenal mucosa, which may extend through all layers of the alimentary canal wall. Describe the basic histological (tissue) structure of the stomach and in the duodenum, and explain how this uniqueness determines the function of the stomach and the duodenum.

1. Mucosa which is made up of: · Digestive Epithelium-Made up of simple columnar epithelium containing mucus cells. Enteroendocrine cells are scattered among the columnar cells. These cells secrete hormones that coordinate the activities of the digestive system · Lamina propria-Layer of areolar tissue that contains blood vessels, sensory nerve endings, lymphatic vessels, smooth muscle cells, and scattered lymphoid tissues. In the stomach and duodenum, it also contains the secretory cells of mucus glands. It also has a narrow sheet of smooth muscle and elastic fibers called the muscularis mucosae. The smooth muscle cells here are arranged into two concentric layers, the inner circular layer and the outer longitudinal layer. 2. Submucosa · It is a layer of dense irregular connective tissue that binds the mucosa to the muscularis externa. In some regions it also contains exocrine glands that secrete buffers and enzymes into the lumen of the digestive track. It also contains the submucosal plexus, which is a network of intrinsic nerve fibers and scattered neurons. 3. Muscularis Externa · Smooth muscle cells dominate this region, arranged in an inner circular layer and an outer longitudinal layer. These layers play an essential role in mechanical processing and moving materials along the digestive track. This layer also contains the myenteric plexus, which is a network that contains parasympathetic ganglia, sensory neurons, interneurons, and sympathetic postganglionic nerve fibers, which help control digestion. 4. Serosa · This layer is a serous membrane that covers the muscularis externa along most portions of the digestive track. Serosa lubricates and bind the connecting tissues.

Four regions of the colon

1. ascending colon 2. transverse colon 3. descending colon 4. sigmoid colon - The ascending colon begins at the superior border of the cecum and ascends. The colon bends sharply to - the left at the right colic flexure. This bend marks the end of the ascending colon and the beginning of the transverse colon - The transverse colon curves anteriorly from the right colic flexure and crosses the abdomen from right to left - It is separated from the anterior abdominal wall by the layers of the greater omentum - Near the spleen, the colon makes a 90 turn at the left colic flexure and becomes the descending colon - The descending colon proceeds inferiorly along the left side until reaching the iliac fossa formed by the inner surface of the left ileum - At the iliac fossa, the descending colon curves at the sigmoid flexure and becomes the sigmoid colon - The sigmoid flexure is the start of the sigmoid colon - The sigmoid colon lies posterior to the urinary bladder. The sigmoid colon empties into the rectum. - Aside from skin cancers, colorectal cancer is the third most common cancer in the US, affecting both men and women. Standard screening involves checking the feces for blood. - The 5-year survival rate for people whose cancer is found at an early stage and treated immediately is greater than 90 percent. - The large intestine receives blood from branches of the superior mesenteric and inferior mesenteric arteries. The superior mesenteric and inferior mesenteric veins collect venous blood from the large intestine - The rectum forms the last 15 cm of the digestive tract - It is an expandable organ for the temporary storage of feces - The movement of fecal material into the rectum triggers the urge defecate - The last portion of the rectum, the anal canal, contains small longitudinal folds called anal columns - The anus is the exit of the anal canal

transport of solids and liquids from the pharynx to the stomach

1.Buccal phase: begins with the compression of the bolus against the hard palate. Subsequent retraction of the tongue then forces the bolus into the oropharynx. Once the bolus is in the oropharynx, reflex responses begin and the bolus is moved toward the stomach. 2.Pharyngeal phase: Elevation of the larynx and folding of the epiglottis direct the bolus past the closed glottis. At the same time, the uvula and soft palate block the passage back to the nasopharynx 3.Esophageal phase: begins as the contraction of pharyngeal muscles forces the bolus through the entrance to the esophagus 4. The approach of the bolus triggers the opening of the lower esophageal sphincter. The bolus then continues into the stomach

Physiology of the pancreas

1000 mL pancreatic juice per day controlled by hormones from duodenum contain pancreatic enzymes pancreatic enzymes include: pancreatic alpha-amylase:an enzyme that breaks down certain starches. similar to salivary amylase pancreatic lipase: breaks down certain complex lipids releasing products (such as fatty acids) that can be easily absorbed nucleases: break down RNA or DNA proteolytic enzymes: break apart proteins. These enzymes include proteases, which break apart large protein complexes and peptidases which break small peptide chains into individual amino acids(70% of pancreatic enzymes).

How are intestinal villi critical in the aiding of absorption in the small intestine

Each circular fold supports a forest of villi, and epithelial cells bearing microvilli cover each villus. This arrangement increases the total surface area for absorption by a factor of more than 600.

Why is Mr. Volpe's dyspepsia relieved by food, and aggravated 2-4 hours after a meal?

His dyspepsia is relieved temporarily by eating because the acid in the stomach is digesting the food. The salivary amylase and the lingual lipase, which digest carbohydrates and liquids, are generally active for 1-2 hours after a meal. Mr. Volpe's stomach feels aggravated 2-4 hours after a meal because the acid in the stomach is no longer attacking the food; it is attacking the stomach itself.

How does the chemical composition of saliva help to initiate the digestive process?

It has salivary amylase which breaks down complex carbs

What are the functions of saliva?

Lubricating the mouth, moistening and lubricating food in the mouth, dissolving chemicals that can stimulate taste buds and provide sensory information about the food. Flushes surfaces, buffers in the saliva keep the pH of mouth near 7, help control populations of oral bacteria

What is pancreatic juice and how would it cause damage in the pancreas? What cells are affected? How?

Pancreatic juice is an alkaline mixture of digestive enzymes, water, and ion. Pancreatic juice is secreted by excretory cells, during pancreatitis there is a blockage of excretory ducts due to inflammation of the pancreas so the juice can't be secreted. Then lysosomes in the damaged cells activate the proenzymes and autolysis begins.

What are intestinal glands and what do they do?

Renew epithelial surface. The disintegration of the shed cells adds enzymes to the lumen, most importantly brush border enzymes

Stomach acid production is done in such a way as to protect the lining of the stomach. Write out the detailed steps of the production and secretion of hydrochloric acid by the stomach. What is the alkaline tide? How does this affect the pH of blood?

Steps in HCL production: 1. Hydrogen ions are generated inside of parietal cells as the enzyme carbonic anhydrase which converts CO2 and H20 to carbonic acid. This then dissociates. 2. A countertransport mechanism ejects the bicarbonate ions into the interstitial fluid and imports chloride ions in the cell 3. Chloride ions diffuse across the cell and exit through open chloride channels into the lumen of the gastric gland 4. Hydrogen ions are actively transported into the lumen of the gastric gland The alkaline tide occurs during the production of HCl by the parietal cells in the stomach when the parietal cells secret bicarbonate ions into the blood. This usually occurs after eating and causes a temporary increase in pH.

How is saliva secreted into the oral cavity?

The ducts. The autonomic nervous system normally controls salivary secretions. Each salivary gland has parasympathetic and sympathetic innervation

As Dr. Lorraine is listening to Mr. Volpe's complaints she automatically visualizes the organs in the epigastric region that are the potential source of his problems. Where is the epigastric region and what organs associated with digestion are located in that area?

The epigastric region, one of the 9 abdominopelvic regions, is the uppermost middle region. It contains the stomach, liver, pancreas, and the small intestine.

Cirrhosis affects the regular function of the liver due to inflammation and the replacement of the liver lobules by fibrous tissue. How many lobes is the liver composed of? What is the basic functional unit of the liver?

The liver has four lobes, which are the right lobe, left lobe, quadrate lobe, and caudate lobe. The basic functional unit of the liver is liver lobules.

Mrs. Fender's jaundice is caused by the accumulation of bilirubin in her blood and tissues. What is the normal fate of bilirubin, and what role does the liver play? Explain how Mrs. Fender's cirrhosis is related to her jaundice.

The normal fate of bilirubin is that it is released from macrophages and bound to albumin and is transported to the liver for excretion in bile. Bilirubin then moves to the large intestine and is converted to urobilin and stercobilin by bacteria and then excreted in the feces. Cirrhosis is the replacement of healthy liver lobules to fibrous tissue, which can lead to jaundice. This is because the hardening of the liver lobules can cause the bile ducts to become blocked, therefore the liver may not be able to absorb or excrete bilirubin. Circulating bilirubin levels increase and begin to diffuse in peripheral tissues giving them a yellow color, which is known as jaundice.

The liver has a portal vein as well as a hepatic vein. It also has unique exchange blood vessels similar to capillaries, called "sinusoids." How do these unique structures determine the function of the organ?

The portal vein drains blood from the spleen, stomach, pancreas and intestines to the liver, where its nutrients and toxins are extracted. The hepatic vein transports the livers deoxygenated and filtered blood from the liver lobules to the inferior vena cava through the systemic circuit. The sinusoids in the liver lack a basement membrane, so large openings between the endothelial cells allows solutes to pass into and out of the bloodstream and into the spaces surrounding the hepatocytes, which allows hepatocytes to absorb solutes from the plasma and secrete materials such as plasma proteins. The lining of the sinusoids contains endothelial cells and kupffer cells which are part of the monocyte-macrophage system.

Mr. Volpe asks, "What do the bacteria have to do with the ulcer?" Dr. Lorraine tells him that the H. pylori increases stomach acid secretion and, at the same time, breaks down the lining of your stomach and duodenum. What is the source and normal function of acid in the stomach and what regulates its production?

The source of acid in the stomach is from the parietal cells in the gastric glands for HCl. The normal function of acid in the stomach is to kill most of the microorganisms digested with food; denature proteins and inactivates most enzymes in food; helps break down plant cell walls and connective tissues in meat; and it is essential in the activation and function of pepsin which is a protein digesting enzyme secreted by chief cells. Chief cells secrete pepsinogen. Keep at pH of 1.5-2. · Acid production is regulated by the CNS, short reflexes of the enteric nervous systems which are coordinated in the wall of the stomach, and hormones of the digestive tract. Gastrin is what regulates the production of the stomach acid

One year after Mr. Volpe's therapy, Dr. Lorraine performs a follow-up endoscopy and is delighted to see a healed and healthy duodenum. Describe what she sees through the lens of her endoscope as she looks at the lining of the duodenum.

There would be no ulcer, you could see the plicae circulares, and it would appear shiny because there is a healthy amount of mucous being produced.

Alcoholic cirrhosis results in hard scar tissue replacing the soft healthy tissue of the liver. How would this exchange/replacement affect Mrs. Fender's livers' metabolic regulation? How would it affect her hematologic regulation?

This replacement would affect her livers' metabolic regulation in the inferior region. The scar tissue formed as a result of cirrhosis would not be able to extract nutrients and toxins through the blood. Mrs. Fender had hyperglycemia because the hepatocytes were not able to remove the glucose from the bloodstream. She was also emaciated, due to failure of the liver to properly metabolize lipids and amino acids. Furthermore, her hematologic regulation would also be affected. Her bruising and prolonged prothrombin time is due to the reduced ability of hepatocytes to synthesize and release plasma proteins, including clotting proteins, transport proteins, and complement proteins. Lastly the elevated liver enzyme levels is due to the enzymes still being produced in the liver by the healthy cells, but the exchange not being able to take place in the affected portion.

What are circular folds?

Tranverse folds in the intestinal lining, also known as plicae circulares. They're permanent features and increase surface area available for absorption

In what layer(s) can you find sensory nerve cells, parasympathetic ganglia, and sympathetic postganglionic fibers?

submucosal plexus: network of intrinsic nerve fibers and scattered neurons. This network also contains sensory neurons, parasympathetic ganglionic neurons, and sympathetic postganglionic fibers that innervate the mucosa and submucosa

Now that you are an expert in the digestive system, use Spotlight Figure 24-27 and the rest of section 24.8 to diagram what happens to each of the components of a delicious slice of pepperoni pizza as it travels through the digestive system What happens to the crust? The pepperoni? The cheese?

the crust:- The digestion of complex carbs proceeds in two steps. One step involves carbohydrases produced by the salivary glands and pancreas. The other step uses brush border enzymes - The digestion of complex carbohydrates involves two enzymes-salivary amylase and pancreatic alpha-amylase - Salivary amylase breaks down starches (complex carbohydrates) into a mixture composed mostly of disaccharides (two simple sugars). Salivary amylase continues to digest the starches and glycogen in the food for one to two hours before stomach acid renders the enzyme inactive - In the duodenum, pancreatic alpha-amylase breaks down the remaining complex carbohydrates. Any disaccharides or trisaccharides produced and any present I the food are not broken down further until they contact the intestinal mucosa - Brush border enzymes of the intestinal microvilli break disaccharides and trisaccharides into monosaccharides. The enzyme maltase splits bonds between the two glucose molecules of the disaccharide maltose. Sucrase breaks the disaccharide sucrose into glucose and fructose, another six carbon sugar. Lactase hydrolyzes the disaccharide lactose into an molecule of glucose and one of galactose - The intestinal epithelium then absorbs the monosaccharides by facilitated diffusion and cotransport mechanisms - 1) Facilitated diffusion moves only one molecule or ion through the plasma membrane, whereas cotransport moves more than one molecule or ion through the membrane at the same time 2) facilitated diffusion does not require ATP. Cotransport by itself does not consume ATP, but the cell must often expend ATP to preserve homeostasis 3) Facilitated diffusion does not take place if there is an opposing concentration gradient for the particular molecule or ion. By contrast, cotransport can take place despite an opposing concentration gradient for one of the transported substances - The cotransport system that takes up glucose also brings sodium ions into the cell. Both a sodium ion and a glucose molecule must bind to the carrier protein before they can move into the cell. These mechanisms deliver valuable nutrients to the cytoplasm, but they also bring in sodium ions that must be ejected by th sodium-potassium exchange pump - These monosaccharides diffuse into the capillaries of the villus for eventual transport to the liver in the hepatic portal vein cheese:- Lipid digestion involves lingual lipase from glands of the tongue and pancreatic lipase from the pancreas - The most important and abundant dietary lipids are triglycerides. They consist of three fatty acids attached to a single molecule of glycerol - Lipases are water soluble enzymes and lipids tend to form large drops that exclude water molecules. As a result, lipases can attack only the exposed surfaces of the lipid drops - Bile salts improve chemical digestion by emulsifying the lipid drops into tiny emulsion droplets, thereby providing better access for pancreatic lipase - As these molecules are released, they interact with bile salts in the surrounding chyme to form small lipid-bile salt complexes called micelles - When a micelle contacts the intestinal epithelium, the lipids diffuse across the plasma membrane and enter the cytoplasm. The intestinal cells synthesize new triglycerides from the monoglycerides and fatty acids.These triglycerides in company with absorbed steroids, phospholipids, and fat-soluble vitamins, are then coated with proteins. The resulting complexes are known as chylomicrons - The intestinal cells then secrete the chylomicrons into interstitial fluid by exocytosis - Most of the chylomicrons diffuse into the intestinal lacteals - From the lacteals, the chylomicrons proceed along the lymphatic vessels and through the thoracic duct. They finally enter the bloodstream at the left subclavian vein pepperoni:- Proteins have very complex structures so protein digestion is both complex and time consuming. Proteolytic enzymes must access individual proteins. - This step involves mechanical processing in the oral cavity through mastication and chemical processing in the stomach. - Acid disrupts tertiary and secondary protein structure, exposing peptide bonds to enzymatic attack - Pepsin works effectively at pH of 1.5-2.0. It breaks the peptide bonds within a polypeptide chain - Trypsin, chymotrypsin, and elastase are like pepsin in that they break specific peptide bonds within a polypeptide - The epithelial surfaces of the small intestine contain several peptidases, notably dipeptidases. These enzymes break short peptide chains into individual amino acids. - Once in the interstitial fluid the amino acids diffuse into the intestinal capillaries for transport to the liver by means of the hepatic portal vein - Acid also disrupts tertiary and secondary protein structure by exposing peptide bonds to enzymatic attack - Pepsin works effectively at a pH of 1.5-2.0. It breaks the peptide bonds within a polypeptide chain - Trypsin, chymotrypsin, and elastase are like pepsin in that they break specific peptide bonds within a polypeptide - The epithelial surfaces of the small intestine contain several peptidases, notably dipeptidases. The enzymes break short peptide chains into individual amino acids - Once in the interstitial fluid, the amino acids diffuse into the interstitial capillaries for transport to the liver by means of the hepatic portal vein

Salivary glands

three pairs secrete into oral cavity 1. parotid gland: produce a serous secretion containing large amounts of salivary amylase. Breaks down starches. secretion drained by a parotid gland 2. Sublingual salivary glands: produce a mucous secretion that acts as a buffer and lubricant. numerous sublingual glands open along either side of the lingual frenulum 3. Submandibular salivary glands: secrete a mixture of buffers, glycoproteins called mucins and salivary amylase. The submandibular ducts open on either side of the lingual frenulum immediately posterior to the teeth each pair has distinctive cellular organization and produces saliva with different properties