Anatomy and Physiology II Ch. 22 Digestive

Divisions of the Small Intestine:

The small intestine consists of three divisions—the (1) duodenum, (2) jejunum, and (3) ileum

microvilli

The smallest folds, the microvilli, are found in the plasma membrane of the enterocytes. Each enterocyte has as many as 3000 microvilli, which gives the cell the appearance of a bristle brush, or brush border. Digestive enzymes produced and secreted by enterocytes catalyze reactions that break down disaccharides, and peptidases, which catalyze reactions that break down peptides.

stomach tissue layers

The stomach has the same four tissue layers as the rest of the alimentary canal, with a mucosa, submucosa, muscularis externa, and serosa. The muscularis externa and mucosa are modified to better suit the stomachs functions

Functions of the Stomach

The stomach performs three primary functions: secretion, propulsion, and digestion

Motility of the Stomach.

The stomach's motility enables it to perform three actions: (1) receive food from the esophagus, (2) churn the incoming bolus into chyme, and (3) control the rate at which chyme empties into the small intestine.

Absorption of Vitamins

Vitamins are chemicals generally provided by the diet that are involved in a host of metabolic reactions (Table 22.2). There are two types of vitamins: water-soluble vitamins, which are polar molecules; and fat-soluble vitamins, A, D, E, and K, which are lipid-based and mostly nonpolar.

how much of what shit does alimentary canal absorb?

a lot of water, electrolytes, and vitamins

The Esophagus. what kinds of shit does it have? primary functions?

a muscular tube about 25 cm (10 in.) long found posterior to the trachea, which transports a bolus from the pharynx to the stomach (Figure 22.8) 1. The esophageal mucosa, lined with stratified squamous nonkeratinized epithelium, contains esophageal glands which secrete mucus to lubricate the bolus as it passes through the esophagus. At the esophagus' inferior end, the gastroesophageal sphincter regulates the passage of the bolus into the stomach. This sphincter prevents the contents of the stomach from re-entering the esophagus. 2. The primary functions of the esophagus are propulsion and a small amount of secretion of mostly mucus.

defecation reflex

a. Stretch receptors transmit the sensation of rectal distention to the spinal cord. b. Parasympathetic neurons cause smooth muscle in the sigmoid colon and rectum to contract, and the internal anal sphincter to relax. c. Impulses from the cerebral cortex trigger relaxation of the external anal sphincter and contraction of the levator ani muscle.

The large intestine is active in

absorbing water and electrolytes, which is critical for maintaining fluid, electrolyte, and acid-base homeostasis.

small intestine. nickname? main functions? cells?

also known as small bowel. 6-meter-long (almost 20 feet). longest portion of the alimentary canal. Four main processes occur in the small intestine: (1) secretion, (2) digestion, (3) absorption, and (4) propulsion. Cells of the small intestine, known as enterocytes, produce multiple digestive enzymes, hormones, and mucus.

what affects the amount of water present in feces?

anything that increases or decreases the motility of the large intestine

purpose of DS

breaks down food items into nutrients that can delivered by the bloodstream to the cells in the body by a set of organs

Submucosa

composed of dense irregular connective tissue with blood and lymphatic vessels and submucosal glands. Nerve clusters of the enteric nervous system referred to as the submucosal plexus, or Meissner's plexus, regulates secreton and blood flow to it area.

the pancreas is a

gland with both endocrine and exocrine functions

Stomach Muscularis Externa

in the stomach, there is an additional inner layer of smooth muscle in the stomach's body with its fibers oriented obliquely. This oblique layer of smooth muscle allows the stomach to perform churning, a motion that pummels the food into a liquid called chyme.

duodenum

initial segment of the small intestine that begins at the pylorus and is the shortest of the three divisions, measuring only about 25 cm (10 in.) long. The duodenum houses the major duodenal papilla, which is where secretions from the gallbladder and pancreas enter the small intestine. The duodenal submucosa contains specialized glands called duodenal (Brunner's) glands, which produce alkaline mucus to protect the duodenum from the acidic chyme.

Pancreatic Juice. What is the composition of this juice?

is the collective secretions of the pancreatic acinar and duct cells. Pancreatic juice consists of water and multiple digestive enzymes and other proteins. In addition, duct cells also secrete bicarbonate ions, a base, which make pancreatic juice alkaline. Alkaline juice helps neutralize the acidic chyme that enters the duodenum from the stomach and protects the duodenum from damage by the acid.

The proximal large intestine

is the primary site of water and electrolyte absorption and bacterial activity, and exhibits two main types of motility: a type of segmentation or churning and a mass movement or mass peristalsis.

The Peritoneal Membrane

largest serous membrane in the body, which consists of an outer parietal peritoneum and an inner visceral peritoneum. Between these two peritoneal layers we find the peritoneal cavity, which contains serous fluid. The visceral peritoneum folds over on itself around certain organs, particularly the small intestine, to form structures called mesenteries, which support and bind these organs together and keep the small intestine in a particular shape that fits within the abdominopelvic cavity. Two mesenteries—the greater omentum and lesser omentum—are especially prominent.

The large intestine receives

material from the small intestine that was not digested or absorbed, and is a passageway for feces to exit the body.

Histology of the Alimentary Canal innermost to outermost

mucosa, submucosa, muscularis externa, serosa

Pancreatic secretionrates

occurs at a basal rate between meals. During eating, pancreatic secretion rises due to parasympathetic and hormonal stimulation

where is the large intestine

or large bowel, runs along the border of the abdominal cavity, surrounding the small intestine and other abdominal organs like a frame

Serosa

outer layer covering the organs within the peritoneal cavity or the adventitia in organs outside the cavity. The serosa, or visceral peritoneum, is composed of simple squamous epithelium and loose connective tissue.

The distal large intestine

performs a small amount of absorption, primarily of water, but its main role is to store fecal material until it is ready to be expelled during defecation. When mass movements force fecal material into the normally empty rectum, it initiates the parasympathetic-mediated defecation reflex

The large intestine has two functional segments. what do they consist of?

proximal and distal. The proximal large intestine consists of the ascending and transverse colon, and the distal large intestine consists of the descending and sigmoid colon, rectum, and anal canal

regulation of motility by the endocrine system

regulates digestive processes by secreting hormones.

The tasks of the large intestine also include

secretion (primarily in the form of mucus), propulsion, and defecation.

Swallowing or deglutition

specialized type of propulsion that pushes a bolus of food from the oral cavity through the pharynx and esophagus to the stomach (Figure 22.9). Swallowing consists of the following three phases: voluntary, pharyngeal, and esophageal. Control of swallowing is almost entirely neural. The voluntary phase is under control of the cerebral cortex, and the remaining two phases are regulated by the medulla and the enteric nervous system. Summarize each phase: 1. Voluntary phase: The tongue pushes the bolus posteriorly toward the oropharynx. 2. Pharyngeal phase: The bolus enters the oropharynx; the soft palate and epiglottis seal off the nasopharynx and larynx, respectively. 3. Esophageal phase: Peristaltic waves move the bolus down the esophagus to the stomach.

Blood Supply to the Abdominal Digestive Organs

the blood vessels that supply and drain the abdominal digestive organs are called the splanchnic Tcirculation.

Gross Anatomy of the Large Intestine

the different regions of the large intestines are: cecum with vermiform appendix, colon (ascending, transvterse, descending, and sigmoid), rectum, and anal canal.

abdominopelvic digestive organs: common shit

the peritoneal membrane, blood supply from the splanchnic circulation, nerve supply from (1) celiac plexus, (2) superior mesenteric plexus, and (3) inferior mesenteric plexus.

Digestion

the process of digestion breaks food down into smaller and smaller pieces until only individual nutrient molecules remain: 1. Two types of digestion are mechanical digestion, in which food is physically broken into smaller parts, and chemical digestion, in which the chemical bonds between food molecules are broken. 2. Most digestive enzymes catalyze hydrolysis reactions that use a water molecule to break a bond between two molecules. Digestive enzymes speed up these reactions by a process known as enzymatic hydrolysis. 3. Once nutrients are digested into component molecules, they must enter the body.

ileum

the small intestine's final segment, is also intraperitoneal, measures about 3.6 meters (10.8 feet) in length, it terminates at the portion of the large intestine called the cecum. The ileocecal valve is a sphincter that controls the movement of materials from the ileum into the cecum and prevents materials in the large intestine from flowing backward into the ileum.

Chemical digestion of proteins does not begin until they reach

the stomach, where they encounter the enzyme pepsin

what's neat about the abdominopelvic digestive organs?

they share a common set of serous membranes, blood vessels, and nerves

Muscularis externa

thick smooth muscle layer found in most of the alimentary canal, is composed of two layers of smooth muscle that are arranged in an inner circular and outer longitudinal layers. The motility of the muscularis externa is regulated by groups of nerves of the enteric nervous system called the myenteric plexus, or Auerbach's plexus.

The Pharynx. divisions? function?

throat. sits posterior to the nasal and oral cavities and consists of three divisions: the nasopharynx, oropharynx, and laryngopharynx 1. Of these three divisions, only the oropharynx and laryngopharynx are part of the alimentary canal. Both divisions are lined with stratified squamous epithelium to protect them from abrasion by food. 2. The primary function of the pharynx is propulsion in the form of swallowing, during which the bolus passes through the pharynx and into the esophagus.

main pancreatic duct

travels down the middle of the pancreas where it which receives secretions from acinar cells.

what is bile made of and what are the functions

which is a liquid that contains multiple components, including water, electrolytes, and organic compounds. Bile serves two critical functions: (1) It is required for the digestion and absorption of lipids. Emulsification is mechanical digestion necessary for the chemical digestion and absorption of lipids. (2) It is the mechanism by which the liver excretes wastes and other substances that the kidneys cannot excrete. The liver performs a host of other functions, including nutrient metabolism, detoxification, and excretion.

Digestion and Absorption of Proteins

1. Chief cells of the gastric glands produce the inactive precursor pepsinogen. Pepsinogen requires a pH of about 2 to become pepsin, and pepsin is inactivated completely at a pH of 7. Activated pepsin catalyzes reactions that digest proteins into smaller polypeptides, oligopeptides, and some free amino acids. 2. The majority of protein digestion takes place in the small intestine with the help of pancreatic enzymes and brush border enzymes.There are five pancreatic enzymes that digest proteins, all of which are released as inactive precursors (Figure 22.29): a. The first pancreatic enzyme to become activated is the precursor trypsinogen, which becomes the active enzyme trypsin, when it encounters enzymes on the intestinal brush border. b. Trypsin catalyzes the reactions that convert the other pancreatic enzymes to their active forms, and activates additional trypsinogen as it is secreted by the pancreas. These enzymes catalyze reactions that digest proteins and polypeptides into oligopeptides and some free amino acids. 3. The final enzymes to act on proteins are associated with the enterocytes. There are multiple brush border enzymes that catalyze the digestion of oligopeptides into free amino acids. 4. To be absorbed in the small intestine, proteins consumed for nutrition must generally be broken down into small oligopeptides and free amino acids. 5. Oligopeptides and free amino acids cross the enterocyte apical membrane primarily by secondary active transport membrane proteins that use a sodium ion gradient established by the Na+/K+ pump. Within the enterocyte, oligopeptides are broken down into free amino acids. The free amino acids then exit the basal enterocyte membrane by facilitated diffusion, after which they enter the capillaries in the villus. Like carbohydrates, the amino acids are then delivered to the liver for processing via the hepatic portal vein.

Motility of the Small Intestine

1. During fasting, the small intestine exhibits slow, rhythmic contractions along its length in a pattern called the migrating motor complex. What is the function of this complex? These contractions clear any remaining material from the small intestine, including leftover food and secretions, requiring about 2 hours to push digesting food from the duodenum to the ileocecal valve. 2. The small intestine undergoes two types of movement during eating: peristalsis and segmentation. The vagus nerve appears to regulate both peristalsis and segmentation

Acid Secretion from the Stomach

1. Gastric glands of the stomach secrete multiple exocrine products, including hydrochloric acid (HCl) released by parietal cells. 2. During eating, gastric acid secretion changes from the basal rate under the influence of the parasympathetic nervous system and multiple hormones. Secretion can be divided into three phases based on the primary source of regulation: the cephalic phase, gastric phase, and intestinal phase.

regulation of motility by the nervous system

1. In the oral cavity, the pharynx, the superior portion of the esophagus, and the last portion of the large intestine, motility is due to skeletal muscle. Motility takes several forms, including swallowing, churning, peristalsis, and defecation. 2. Each type of motility is regulated by the nervous system and/or the endocrine system. Nervous system regulation of motility consists of the nerves of the autonomic nervous system, or ANS. The sympathetic nervous system and the parasympathetic nervous system generally have opposite effects on gastrointestinal motility—sympathetic activity inhibits digestive processes, and parasympathetic activity stimulates them. 3. Motility is regulated by a group of nerves known collectively as the enteric nervous system, or ENS.

Basic Digestive Functions and Processes

1. The Peritoneal Membrane 2. Blood Supply from splanchnic circulation. 3. nerve supply from 3 clusters: (1) celiac plexus, (2) superior mesenteric plexus, and (3) inferior mesenteric plexus.

types of organs in the DS

1. The organs of the alimentary canal, also known as the gastrointestinal (GI) tract or digestive tract includes the oral cavity (mouth), pharynx, esophagus, stomach, small intestine, and large intestine. 2. The accessory organs are not part of the alimentary canal but assist in digestion in some way. They are located around the alimentary canal and include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

How many salivary glands in oral cavity?

3. parotid, submandibular, sublingual.they all secrete saliva thru ducts into the oral cavity

secretin

Another stimulatory hormone that is released by duodenal cells in response to acid and lipids in the duodenum. Secretin primarily triggers duct cells to secrete bicarbonate ions.

Digestion and Absorption of Carbohydrates:

Digestion begins in the mouth with the help of salivary amylase from the salivary glands, which catalyzes the reactions that break long polysaccharides into shorter oligosaccharides. Chemical digestion of carbohydrates resumes in the small intestine, where polysaccharides and oligosaccharides encounter pancreatic amylase

Lipid Absorption

Due to their nonpolar nature, lipids face several water-based barriers that deter them from passing into the cytosol of the enterocytes, including the mucus lining of the small intestine and the polar phosphate heads of the enterocytes' plasma membranes. Describe the process of lipid absorption. a. Micelles escort lipids to the enterocyte plasma membrane. b. Lipids pass through the phospholipid bilayer and enter the cytosol. c. Lipids are reassembled into triglycerides and packaged into chylomicrons. d. Chylomicrons are released into the interstitial fluid and then enter a lacteal. 4. Lipids are not delivered directly to the liver via the hepatic portal vein after absorption. The hepatic portal vein delivers the leftover bile salts to the liver, where they are used to make new bile

Absorption of Electrolytes.

Electrolytes are both taken in from the diet and present in secretions from digestive organs.

cell types in gastric glands

Enteroendocrine cells, near the bottom of the gastric pit, secrete hormones that influence digestion. G cells, a type of enteroendocrine cell, secrete the hormone gastrin, which stimulates secretions from other cells known as parietal cells. Chief cells secrete the inactive precursor enzyme pepsinogen. When pepsinogen encounters an acidic pH, it becomes the active enzyme pepsin, which begins protein digestion in the stomach. Parietal cells secrete the hydrochloric acid (HCl), responsible for the acidic pH of gastric juice. Acid is an important component of gastric juice because (1) it activates pepsinogen, (2) destroys many disease-causing organisms, and (3) stimulates parietal cell production of the chemical intrinsic factor, which is required for intestinal absorption of vitamin B12. Mucous neck cells, near the top, or "neck," of the gland, secrete acidic mucus that prevents the neutralization of the acid produced by the parietal cells.

Digestion and Absorption of Nucleic Acids:

Nucleic acids in the food we eat begin chemical digestion in the small intestine with the help of pancreatic enzymes called nucleases. The hepatic portal system then takes them via the blood to the liver to be metabolized.

Chemical digestion of carbohydrates

Oligosaccharide digestion is completed by reactions catalyzed by enzymes that are products of enterocytes on the brush border of the small intestine, including the enzymes lactase, maltase, and sucrase 2. After carbohydrates have been digested into monosaccharides, such as glucose, galactose, and fructose, they are ready to be absorbed. Once in the blood, they are delivered to the liver via the hepatic portal vein for processing. a. Both glucose and galactose are transported across the enterocyte's apical membrane by a secondary active transport mechanism known as the Na+/glucose cotransporter. b. Fructose crosses the apical enterocyte membrane by binding a channel that mediates its facilitated diffusion across the membrane.

Absorption of Water

On average, over 9 liters of water enter the small intestine each day. About 8 liters are absorbed into the enterocytes of the small intestine. Most of the remaining water is absorbed into the enterocytes of the large intestine, leaving only about 0.1 liter of water to be excreted in feces. Water absorption occurs exclusively by osmosis, which requires a concentration gradient

cholecystokinin (CCK)

One hormonal mediator of pancreatic secretion is produced by duodenal enteroendocrine cells in response to the presence of lipids and partially digested proteins in the duodenum. CCK acts on acinar cells to trigger the secretion of digestive enzymes and other proteins.

What are the components of saliva?

Saliva is a fluid containing water, enzymes, mucus, and other solutes.

What is the function of saliva?

Saliva moistens, lubricates, and cleanses the oral mucosa.

What is salivation?

Salivation refers to the process of secretion from the three pairs of salivary glands and is primarily controlled by the parasympathetic nervous system in a reflex arc.

Bile Secretion

Secretion occurs in response to gallbladder contraction and sphincter relaxation at the hepatopancreatic ampulla. This activity is mostly accomplished by CCK and to a small extent by the vagus nerve. The most potent stimulus for bile production and release is bile itself, specifically bile salts.

Histology of the Liver

The "liver lobule," the basic unit of the liver, has the following histological features. Liver lobules are separated from one another by septa that branch in from the connective tissue capsule of the liver. Lobules are composed of flattened plates of cells, called hepatocytes, that are arranged in the shape of a hexagon and stacked on top of one another with a small central vein. a. Portal triad, found at each of the six corners of the lobule, are composed of the following three structures: a hepatic arteriole, a portal venule, and a small bile duct that carries bile. b. Hepatic arterioles and portal venules both drain into large, leaky capillaries, called hepatic sinusoids that pass between rows of hepatocytes. Blood flows slowly through the sinusoids as materials are exchanged between the blood and hepatocytes, eventually draining into the central vein. Central veins merge and drain into the hepatic veins, which in turn feed into the inferior vena cava. c. Bile flows through the liver lobule in the opposite direction, from the hepatocytes into tiny ducts called bile canaliculi, which eventually drain into a bile duct.

Gross Anatomy of the Stomach

The esophagus pierces the diaphragm and passes through the esophageal hiatus to empty into the J-shaped organ known as the stomach (Figure 22.10). The stomach sits primarily in the left upper quadrant just inferior to the diaphragm. 1. The stomach has five anatomical regions: (1) cardia, (2) fundus, (3) body, (4) pyloric antrum, and (5) pylorus. 2. The pylorus contains a sphincter, the pyloric sphincter, which controls the flow of ingested food between the stomach and the small intestine. 3. The interior of the stomach contains folds called rugae that allow the stomach to expand considerably.

The Gallbladder and Its Relationship to the Liver

The gallbladder is a small sac that sits on the posterior liver that receives most of the bile from the common hepatic duct. Bile release is stimulated by CCK, which triggers contraction of the smooth muscle in the wall of the gallbladder, causing the gallbladder to release bile into cystic duct which joins the common hepatic duct to form the common bile duct. The common bile duct joins the main pancreatic duct near the duodenum to form the hepatopancreatic ampulla. The ampulla is surrounded by a ring of smooth muscle called the hepatopancreatic sphincter, which controls the emptying of bile and pancreatic fluids into the duodenum. The contents of the hepatopancreatic ampulla then empty into the duodenum at the major duodenal papilla.

Mucosa

The innermost, which faces the lumen, consists of these components: lamina propria, muscularis mucosae, and regenerative epithelial cells

Structure and Functions of the Small Intestine

The internal surface of the small intestine contains three progressively smaller types of folds. Most of the absorption that occurs within the alimentary canal takes place in this region, and these folds increase the surface area available for absorption about 400 to 600 times

Bacteria in the Large Intestine

The large intestine hosts a staggering number of bacteria; bacteria make up as much as 60% of the dry mass of feces.

circular folds

The largest type of folds, visible with the naked eye as ridges in the wall, are called circular folds or plicae circulars (Figure 22.15a). Circular folds involve both the mucosa and submucosa of the small intestine, which increase surface area. These folds also slow down the transit of chyme through the small intestine, which gives the nutrients more time to be digested, and the small intestine cells, called enterocytes, more time to absorb nutrients.

Functions of the Liver

The liver has one of the most diverse sets of functions of any organ in the body. It releases both endocrine and exocrine secretions, and it converts harmful chemicals into nontoxic substances that the body can eliminate. The liver's main digestive function is to produce bile

anatomy and location of the liver

The liver, covered by a thin connective tissue capsule and visceral peritoneum, is composed of four lobes: right, left, caudate, and quadrate. The pyramid-shaped liver is located in the right upper quadrant just inferior to the diaphragm surface.

Digestion of lipids how are lipid globulues broken up? process of lipid digestion?

The majority (90%) of lipids taken in by the diet are triglycerides, which consist of three fatty acid molecules bound to a glycerol core molecule: 1. Lipid Digestion: Nonpolar lipids tend to stick together, forming large globules rather than distributing evenly in a water-based solution. Lipid globules can be broken up into smaller particles in two ways. Describe these two methods. a. The first is by mechanical digestion—mastication in the mouth, churning in the stomach, and segmentation in the small intestine. b. The second way involves bile salts in the small intestine. Bile salts are amphiphilic molecules with polar and nonpolar parts. When bile salts mix with lipids, their nonpolar parts interact with the lipids, while their polar parts interact with the surrounding watery fluid. This breaks up the lipid globules into smaller pieces by the process of emulsification. The end result is multiple tiny lipid droplets each coated with bile salts, a mixture called an emulsion, which gives digestive enzymes enough surface area on which to work to digest the lipids. 2. The process of lipid digestion proceeds as follows (Figure 22.30): a. Lipids are broken apart by stomach churning and broken down by gastric lipase. b. Lipids enter the small intestine and are emulsified by bile salts. c. Pancreatic lipase catalyzes reactions that digest the lipids into free fatty acids and monoglycerides. d. Bile salts remain associated with the digested lipids to form micelles.

jejunum

The middle portion of small intestine begins at the duodenojejunal flexure and sits within the peritoneal cavity. where it measures about 2.5 meters (7.5 feet) in length and is the most active site for chemical digestion and absorption.

villi

The mucosa folds into projections called villi, in which each villus consists of a layer of enterocytes surrounding a central core of blood capillaries and a lymphatic vessel called a lacteal. Between villi the mucosa indents to form intestinal crypts, which house glands with both enteroendocrine cells and mucus-secreting goblet cells.

Histology of the Large Intestine

The mucosa of the large intestine lacks lacks villi and its cells lack microvilli. The muscularis externa of the large intestine is unique in that its longitudinal layer is not continuous throughout most of its length. This layer is gathered into three bands or ribbons of muscle called taeniae coli (Figure 22.17a). Their constant tension bunches the colon into pockets referred to as haustra. The serosa, or visceral peritoneum, contains fat-filled pouches known as epiploic appendages

Stomach Mucosa

The mucosa of the stomach is heavily indented to form deep structures called gastric pits (Figure 22.11). Gastric glands, found at the base of the gastric pits, are multiple branched glands that contain both endocrine cells that secrete hormones into the bloodstream and exocrine cells that secrete an acidic, enzyme-containing fluid called gastric juice into the lumen of the stomach. There are four main types of cells in gastric glands, each of which secretes a different product. From deep to superficial, these cell types are as follows

Nerve Supply to the Digestive Organ

The organs of the digestive system are extensively supplied with nerves, most of which are branches from the autonomic nervous system. The nerves of the sympathetic and parasympathetic divisions that serve the digestive organs are located in three main clusters: (1) celiac plexus, (2) superior mesenteric plexus, and (3) inferior mesenteric plexus.

anatomy and histology of the pancreas

The pancreas, found primarily in the left upper quadrant of the abdomen is composed of three regions: head, body, and tail.

which are accessory organs and exocrine glands?

The pancreas, liver, and gallbladder are accessory organs and exocrine glands that secrete a product through a duct to the outside of the body.These accessory organs secrete their products into the alimentary canal, which appears to be within the body, but the alimentary canal is open to the external environment on each end.