Basic Anatomy & Physiology II Dr. L. Bacha Chapter Outline (Marieb & Hoehn 6th or 7th ed)

two groups of organs form the digestive system (see Fig. 22.1):

1. alimentary canal what is it also called? it is a continuous muscular tube that winds through the body, from the mouth to the anus list the organs that make up alimentary canal:

why is food material in this tube technically outside the body?

2. accessory digestive organs list the accessory digestive organs:

22.1 What major processes occur during digestive system activity?List and read about the 6 essential activities of the digestive system (shown next to the colored squares in 6th edition p. 747 – 748; 7th edition p. 761 – 762; also see Figs. 22.2 and 22.3):

peristalsis is the major means of propulsion and involves what?

- what is its main effect?

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PART I

what does mechanical breakdown increase and what does it prepare food for?

what do mechanical processes include?

- describe segmentation:

what is the function of segmentation?

digestion (more specifically chemical digestion), involves what?

absorption is the passage of digested end products (plus vitamins, minerals, and water) from the lumen of the GI tract into what?

defecation eliminates indigestible substances from the body as feces

22.2 The GI tract has four layers and is usually surrounded by peritoneum

Relationship of the Digestive Organs to the Peritoneum most digestive organs reside in the abdominopelvic cavity

the abdominopelvic cavity contains the peritoneal cavity, which is lined by serous membranes called the peritoneum what does the visceral peritoneum cover?

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what does the parietal peritoneum line?

name the slitlike potential space between the parietal and visceral peritoneum:

the serous membranes lining the peritoneal cavity continuously produce a serous fluid called peritoneal fluid

- the peritoneal fluid in the peritoneal cavity lubricates the mobile digestive organs and allows them to do what?

mesenteries are sheets of peritoneum that suspend organs of the abdominopelvic cavity to the body wall and attach some organs to others

what are the functions of mesenteries?

Histology of the Alimentary Canal (see Fig. 22.5)

The walls of organs of the gastrointestinal tract from the esophagus to the anal canal have the same 4 basic layers:

1 The Mucosa ∙ the mucosa is a mucous membrane that lines the lumen of the alimentary canal from the

mouth to the anus; read about the mucosa’s major functions ∙ there are 3 layers of the mucosa:

a . epithelium - lines the lumens of the organs; the type varies with the organ (stratified squamous or simple columnar)

b. lamina propria – loose areolar connective tissuec. muscularis mucosae – thin layer of smooth muscle

2 The Submucosa ∙ the submucosa consists of connective tissue∙ it contains the submucosal plexus, a nerve plexus that controls the activity of glands of the GI tract and smooth muscle of the muscularis mucosae

3 The Muscularis Externa what is this layer responsible for?∙

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formed by either skeletal muscle (e.g. mouth, pharynx, part of the esophagus) ∙ OR smooth muscle (e.g., part of the esophagus, stomach, intestines)

∙ the muscularis externa is arranged in 2 layers (sometimes 3):1) inner circular layer2) outer longitudinal layer

∙ in several places along the gastrointestinal tract, the circular layer thickens, forming sphincters that act as what?

∙ the muscularis externa contains the myenteric plexus, a nerve plexus that controls motility of the GI tract

4 The Serosa serosa (= visceral peritoneum)

it ∙ covers many organs in the abdominopelvic cavity it is the outermost layer; what is it formed of?∙

adventitia in some cases, the outermost layer is an adventitia rather than a serosa∙ an adventitia is formed by ∙ connective tissue only; not covered by a epithelium; the

connective tissue blends with that of surrounding structures e.g., binds the esophagus to surrounding structures in the thoracic cavity∙

Here is a sketch to show the four layers (and sublayers) of the wall of a digestive organ:

Blood Supply: The Splanchnic Circulation read about the splanchnic circulation

22.3 The GI tract has its own nervous system called the enteric nervous system

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Enteric Nervous System read about the enteric nervous system, which participates in both short and long reflex arcs

(see Fig. 22.7)

⦁ Short reflexes – occur entirely within the GI wall- are mediated entirely by enteric neurons in response to what?

- the control of segmentation and peristalsis is largely due to short reflexes

⦁ Long reflexes – involve the central nervous system and extrinsic autonomic nerves

- generally speaking, what is the effect of parasympathetic inputs?

- what is the effect of the sympathetic nervous system on digestive activities?

Basic Concepts of Regulating Digestive ActivityRead about the three key concepts that govern regulation of digestive activity!

22.4 Ingestion occurs only at the mouth

The Mouth what is the mouth also called?

what forms the superior boundary (the roof) of the mouth?

posteriorly, the oral cavity is continuous with what?

read about the lips, cheeks, and the palate

The Tongue• the tongue is composed of interlacing bundles of what?

• describe the functions of the tongue:

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PART 2

• intrinsic muscles of the tongue are skeletal muscles within the tongue; they are not attached to bone; intrinsic muscles allow the tongue to do what?

• extrinsic muscles of the tongue are skeletal muscles that originate on bones of the skull or the soft palate and insert onto the tongue- they alter the position of the tongue (protrude it, retract it, move it side to side)

• define lingual frenulum and indicate its functions:

• the upper surface and sides of the tongue are covered with a variety of projections called lingual papillae (see Fig. 22.9), some of which contain microscopic taste buds

The Salivary Glands• the salivary glands secrete components of saliva• list the functions of saliva:

• there are 3 pairs of extrinsic (major) salivary glands that secrete saliva into ducts that empty into the mouth (note their location in Fig. 22.10):

1. parotid glands - describe the location of the parotid gland:

- each parotid duct opens into the oral cavity next to the second upper molar.2. submandibular glands

- the submandibular gland lies along what?

- its ducts opens into the floor of the oral cavity at the base of what?

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3. sublingual glands - the sublingual gland lies under what?

- it has numerous ducts that open into what?

Composition of Saliva mostly water; also contains electrolytes, mucin, lysozymes, IgA antibodies, and metabolic

wastes name the two digestive enzymes in saliva:

Control of Salivation the parasympathetic nervous system stimulates the secretion of watery,

enzyme rich saliva the sympathetic nervous system stimulates the release of a thick, mucin-rich saliva; strong activation of the sympathetic division almost completely inhibits release of saliva

The Teeth• the roots of teeth are located in sockets (alveoli) of what two bones?

• what is another word for chew?

Dentition and the Dental Formula 2 sets of teeth in humans (see Fig. 22.11):

primary dentition - consists of deciduous teeth permanent dentition - consists of permanent teeth

describe the features and functions of the four different types of teeth:∙ incisors -

∙ canines (cuspids) -

∙ premolars (bicuspids) and molars -

the dental formula is a shorthand way of indicating what?

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Remember “flight-or fight”…does your mouth become more moist or dry when you are scared?

- write the dental formula for the primary and permanent dentition:

Tooth Structure locate the following parts on Fig. 22.12:

∙ crown - define the crown of a tooth:

∙ gingiva – gum∙ enamel

- covers the crown of a tooth; what makes enamel the hardest substance in the body?

∙ root - define the root of a tooth:

∙ neck - define the neck of a tooth:

∙ cementum (cement) - a calcified connective tissue that covers the dentin of the root∙ periodontal ligament

- fibrous connective tissue attached to the cementum - anchors the tooth in the alveolus and acts as a shock absorber

∙ dentin - describe dentin:

- dentin also acts as a shock absorber∙ pulp cavity - a central cavity, surrounded by dentin, that contains pulp

(soft tissue with connective tissue, blood vessels and nerves) ∙ root canal - the extension of the pulp cavity through the root of the tooth∙ apical foramen - an opening at the proximal end of each root

- what does the apical foramen allow?

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Digestive Processes of the Mouth read about the 4 digestive processes that the mouth and its accessory organs are involved inMastication (Chewing) the mechanical breakdown of food begins with chewing in the mouth

22.5 The pharynx and esophagus move food from the mouth to the stomach

The Pharynx the oropharynx and laryngopharynx are both common passageways for what?

the pharynx is lined by mucous membrane; it has skeletal muscles that are involved in swallowing

The Esophagus describe the esophagus:

the esophageal hiatus is the potential opening in the diaphragm through which the esophagus passes to enter the abdomen

some features of interest: the mucosa of the esophagus has a nonkeratinized stratified squamous epithelium ∙

∙ the circular layers of muscle in the muscularis externa in the superior and inferior parts of the esophagus are normally thickened and contracted, functioning as sphincters:

upper esophageal sphincter - is between the pharynx and esophagus

gastroesophageal sphincter (lower esophageal sphincter or cardiac sphincter) - is between the esophagus and the stomach

Digestive Processes: Swallowing• the pharynx and esophagus merely serve as what?

∙ deglutition (swallowing) is a complicated process that involves the coordinated activity of what?

∙ there are two major phases of deglutition (Fig. 22.14): the buccal phase and the pharyngeal-esophageal phases

1. BUCCAL PHASE:

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the buccal phase is voluntary and occurs where?

what does the tongue do during this phase (as indicated in blue print in step 1 of Fig. 22.14 in 6th edition p. 761; 7th edition p. 775)?

2. PHARYNGEAL-ESOPHAGEAL PHASE: involuntary; subdivided into two phases:a. Pharyngeal Phase:

involuntary; begins when the bolus passes into oropharynx various cranial nerves, most importantly the vagus nerves, transmit what?

when food enters the pharynx, respiration is momentarily inhibited

during the pharyngeal phase:- the tongue blocks the mouth- the soft palate and uvula rise to close off the nasopharynx- the larynx rises so that the epiglottis covers the opening into the larynx- the upper esophageal sphincter relaxes

- this allows food to enter the esophagus as muscles of the pharynx contract

b. Esophageal Phase: the bolus is moved along the esophagus toward the stomach by wavelike peristaltic contractions (see Fig. 22. 3 (a) on p. 749) the gastroesophageal sphincter relaxes to allow the bolus to enter the stomach

22.6 The stomach temporarily stores food and begins protein digestion the chemical breakdown of proteins begins in the stomach in the stomach, food is converted to a slurry (paste-like substance) called what?

the stomach lies in the upper left quadrant of the abdominopelvic cavity Gross Anatomy of the Stomach an empty stomach has a volume of 50 ml, but fully distended, it can hold about 4 liters when empty, the mucosa and submucosa of the stomach form large, longitudinal folds called

what?

list the four main regions of the stomach and note their location in Fig. 22.15 (a):

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the pyloric sphincter (pyloric valve) is between the pyloric region of the stomach and the duodenum - it controls what?

Microscopic Anatomy of the Stomach (see Fig. 22.16)

features of the mucosa of the stomach:∙ the lining epithelium of the stomach mucosa is a simple columnar epithelium composed entirely of cells that produce alkaline mucus

∙ gastric pits - invaginations of the surface epithelium cells that line the gastric pits undergo cell division to continuously replenish the

epithelium of the stomach ∙ gastric glands

- gastric glands are continuations of the gastric pits lined by epithelial cells that secrete gastric juice

Types of Gland Cells that form the gastric glands varies with the region of the stomach:

parietal cells and chief cells are found in the gastric glands in the fundus and body regions: Parietal Cells

- what two substances do they secrete?

- indicate the various functions of the extremely acidic contents of the stomach:

- intrinsic factor is a glycoprotein required for what?

Chief Cells - what substance do chief cells produce?

- chief cells also secrete what?

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I know this is silly, but I remember that PARIETAL cells produce HCl because parietal ends in an “L”!

gastric glands in the cardiac and pyloric regions are mainly formed by cells that produce mucus

enteroendocrine cells are also present in gastric glands- these are cells that produce hormones, such as histamine, serotonin, and gastrin

The Mucosal Barrier Definitely read about how the mucosa of the stomach acts as a barrier!

Digestive Processes the Stomach (6th edition p. 764; 7th edition p. 780)

from Table 22.2 (6th edition p. 767; 7th edition p. 795) list the three major functions of the stomach:

chemical digestion in the stomach protein digestion begins by the enzyme pepsin (formed from pepsinogen, which is inactive)

- remember what cells of the gastric glands produce pepsinogen?

gastric lipases secreted by chief cells of the stomach and lingual lipase from salivary glands both have a minor role in digesting lipids in the stomach

what is the stomach’s only function that is essential to life?

what is intrinsic factor required for?

what is vitamin B12 needed for?

Regulation of Gastric SecretionThe production of acid and enzymes by the gastric mucosa is controlled by the nervous system and hormones: neural controls

- consist of both long reflexes (parasympathetic vagus nerve mediated) and short (local enteric) reflexes- in each case, what is released to stimulate output of gastric juice?

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My summary of stimulation of HCL secretion by parietal cells in the stomach:1. Parasympathetic nerve impulses stimulate the release of acetylcholine (ACh), which:

1. increases secretion of pepsinogen by chief cells2. increases secretion of HCl by parietal cells3. stimulates release of gastrin by enteroendocrine

cells (G cells)

2. Gastrin produced by G cells increases gastric secretion

3. Histamine produced by mast cells stimulates the parietal cells to secrete HCl(Note: the histamine receptors on the parietal cells are calledH2 receptors, and are different from the H1 receptors of allergic reactions.)

When only one of the three chemicals binds to parietal cell receptors, HCl secretion is scanty; when all three chemicals bind to receptors, HCl production is significant

- in contrast, activation of sympathetic nerves does what?

hormonal control of gastric secretion is mainly due to the hormone gastrin

THERE ARE THREE OVERLAPPING PHASES OF GASTRIC SECRETION THAT OCCUR DURING DIGESTION:

• CEPHALIC PHASE begins before food enters the stomach triggered by the aroma, taste, sight, or thought of food during this phase, parasympathetic nerves stimulate the salivary glands to

secrete saliva and stimulate gastric glands (via the vagus nerve) to secrete gastric juice

• GASTRIC PHASE begins when food enters the stomach distension of the stomach by food, partially digested proteins in the stomach and an increase in pH

(due to food entering the stomach) activate the parasympathetic nervous system, enteric neurons, and the release of the hormone gastrin from the stomach, which collectively:∙ increase gastric secretion by the gastric glands∙ increase motility of the stomach ∙ relax the pyloric sphincter to promote gastric emptying

• INTESTINAL PHASE begins when chyme enters the duodenum stimulation: initial distension of the duodenum stimulates cells of the intestine to release intestinal

gastrin, a hormone which stimulates gastric glands to continue secretion of gastric juice for a brief period

inhibition: continued presence of chyme in the duodenum stimulates sympathetic nerves and the production of hormones by the small intestine (secretin, cholecystokinin, and gastric inhibitory peptide), which collectively:∙ decrease production of gastric juice by the gastric glands

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∙ inhibit gastric motility and gastric emptying∙ stimulate secretion of pancreatic juice and release of bile from the gallbladder

Regulation of Gastric Motility and Emptying (6th edition p. 768; 7th edition p. 783)

the muscularis externa of the stomach has 3 layers of smooth muscle tissue stomach contractions of the muscularis externa not only accommodate its filling and cause its

emptying, but they also do what?

each wave of peristalsis causes a small amount of chyme to be forced through the pyloric sphincter into the duodenum (first part of the small intestine) to cause gastric emptying, so that gradually the stomach empties chyme into the duodenum

23.7 The liver secretes bile; the pancreas secretes digestive enzymes The LiverGross Anatomy of the Liver the liver is the second largest organ of the body it is wedge-shaped and is located just inferior to the diaphragm the liver has how many primary lobes?

blood supply of the liver: the liver receives blood from two sources:

1. hepatic artery – carries oxygenated blood2. hepatic portal vein - carries deoxygenated, nutrient-rich blood from systemic capillaries

of digestive organs (stomach, intestines, etc) to sinusoids of the liver

Microscopic Anatomy of the Liver (see Fig. 22.24) microscopic lobules of the liver are roughly hexagonal (six-sided) structures consisting of

plates of liver cells called hepatocytes, which are organized like bricks in a garden wall- the hepatocyte plates radiate outward from a what?

portal triads are located in the connective tissue where three or more lobules meet list the three basic structures that a portal triad contains:∙

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other components of a lobule:

- liver sinusoids alternate with the plates of hepatocytes and radiate from the central vein in the center of a lobule blood from branches of the hepatic artery and hepatic portal vein flows through the

sinusoids and empties into the central vein

- hepatic macrophages (Kupffer cells) occupy the sinusoids- what do these phagocytic cells remove?

functions of hepatocytes:- hepatocytes produce most plasma proteins (albumin, clotting factors, complement, etc.)- indicate the four things hepatocytes can do ( listed next to the four blue bullets (6th edition in the top right column p. 773; 7th edition in the bottom right column p. 775):

Bile: Composition and Enterohepatic Circulation features of bile:

1. what color is bile?

2. it is alkaline (pH 7.6 to 8.6)3. contains water, ions, cholesterol, etc. (NO digestive enzymes!)

4. contains bile salts (which are the only substances in bile with a digestive function)a. emulsify fat globules into fat droplets

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- bile salts disperse (emulsify) large clumps of fat molecules called fat globules into smaller clumps called fat droplets so they can more readily be chemically digested by enzymes

b.play a role in the absorption of long chain fatty acids, glycerol, cholesterol, and fat soluble vitamins by coating them, forming micelles

5. contains bile pigments, such as bilirubin, which is a normal product of RBC destruction and is excreted into bile by hepatocytes

duct system that carries bile ( see 6th edition Fig. 22.27 p. 777; 7th ed. Fig. 22.28 p. 791):

∙ bile secreted by hepatocytes enters into bile canaliculi, which are tiny intercellular canals formed by the cell membranes of adjacent hepatocytes bile canaliculi lead into bile ducts at the periphery of lobules bile ducts merge and eventually exit the liver as the common hepatic duct joins with the cystic duct from the gallbladder to form the common bile duct the common bile duct merges with the pancreatic duct and leads into the

hepatopancreatic ampulla that opens into the duodenum; the opening is controlled by the hepatopancreatic sphincter

The Gallbladder• a thin-walled muscular sac that may appear green when filled with bile• about the size of a kiwi fruit (about 10 cm (4 in) long, it snuggles in a shallow fossa on the inferior

surface of the liver from which its rounded fundus protrudes• the gallbladder stores and concentrates bile until it is needed in the small intestine;

- when the small intestine is empty, a valve around the common bile duct closes and bile backs up into the cystic duct to the gallbladder for storage

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Duct System of the Liver, Gallbladder, and Pancreas2. common hepatic duct

3. cystic duct

4. common bile duct

5. opening of accessory pancreatic duct

6. pancreatic duct

7. hepatopancreatic ampulla and sphincter

8. duodenal papilla

The Pancreas• why is the pancreas important to digestive processes?

• the pancreas extends from the right side of the body between the C-shaped duodenum, across the abdomen, to the left side near the spleen

• the endocrine tissues, called pancreatic islets, are scattered among the acini and contain cells that release two important hormones: insulin and glucagon

• the exocrine part of the pancreas is formed by clusters of epithelial cells called pancreatic acini (singular is “acinus”) that secrete pancreatic juice (see 6th ed. Fig. 22.25; 7th ed. Fig. 22.26)

- pancreatic juice is carried by the pancreatic duct and the accessory pancreatic duct from the pancreas to what specific organ (see Fig. 22.27)?

Composition of Pancreatic Juice pancreatic juice consists of:

∙ water∙ bicarbonate ions (sodium bicarbonate), which makes pancreatic juice slightly alkaline

- the slightly alkaline secretion is important because the enzymes that function in the small intestine do not function in an acid environment

∙ digestive enzymes:- the cells of the pancreatic acini produce a variety of digestive enzymes that function in the small intestine!

Bile and Pancreatic Secretion into the Small IntestineAnatomy of Duct Systems review the duct system in 6th edition Fig. 22.27; 7th edition Fig. 22.28

Regulation of Bile and Pancreatic Secretion read about how hormones and neural stimuli regulate both the secretion of bile and

pancreatic juice 22.8 The small intestine is the major site for digestion and absorption most chemical digestion and absorption of nutrients takes place in the small intestine!

Therefore, it has structural adaptations for these functions:1. great length - in the living person, the small intestine is 2 to 4 meters (7-13 ft) long2. circular folds3. villi4. microvilli

Gross Anatomy (of the Small Intestine)

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list the three subdivisions of the small intestine:

- the ileocecal valve (sphincter) is between the ileum and the cecum of the large intestine

Microscopic Anatomy Modifications of the Small Intestine for Absorption remember, most chemical digestion and absorption of nutrients takes place in the small

intestine, so there are special features of the small intestine that facilitate chemical digestion and absorption of nutrients: its great length, circular folds, villi, and microvilli

• Circular folds - permanent folds of the mucosa and submucosa; about 1 cm tall (see 6th edition Fig. 22.29 a; 7th edition Fig. 22.31 a)

- these circular folds greatly increase surface area for chemical digestion and absorption- they cause chyme to spiral slowly through the small intestine, to increase time for digestion and absorption

• Villi (singular is “villus”)- villi are finger-like projections of the mucosa (see 6th ed. Fig. 22.29; 7th ed. Fig. 22.31)- how high are the villi?

- consists of a core of lamina propria covered by simple columnar epithelium with goblet cells - the lamina propria of villi contains blood capillaries and a lacteal (a lymphatic capillary) for

absorption of nutrients

• Microvilli the simple columnar epithelium of the mucosa of the small intestine contains simple columnar absorptive epithelial cells (called enterocytes) that have microvilli - all together the microvilli form the brush border

microvilli are fingerlike projections of the cell membrane and cytoplasm of the epithelial cells∙ the cell membrane of the microvilli bears enzymes referred to a what?

∙ the microvilli increase surface area for chemical digestion and increase surface area for absorption of nutrients into the epithelial cells

Histology of the Small Intestine WallThe mucosa and submucosa are modified for the function of the small intestine. Along with having villi covered by an epithelium with microvilli, the mucosa of the small intestine has intestinal crypts (intestinal glands; crypts of Lieberkűhn):

- intestinal crypts are deep crevices between the bases of the villi- they are lined with glandular epithelial cells that secrete intestinal juice

There are five major types of cells in the epithelium of the villi and crypts:

1. Enterocytes

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Is the pH of the chyme in the stomach acidic or alkaline? You may have been noticing that various secretions produced by the small intestine or that empty into the small intestine (bile and pancreatic juice) are ALKALINE. This is important to neutralize the acidic chyme that empties from the stomach into the small intestine to create a proper pH environment for the function of enzymes that act in the small intestine.

- most numerous; they are simple columnar absorptive cells with microvilli- what are they bound by?

- in the villi, the primary responsibility of these enterocytes is what?

- in the crypts, enterocytes are primarily secretory cells that secrete what?

intestinal juice is a watery mixture that contains what? ∙

intestinal juice serves as what?∙

2. Goblet cells- what do goblet cells secrete?

3. Enteroendocrine cells - are scattered amongst the enterocytes; they secrete hormones such as secretin and cholecystokinin

4. Paneth cells – found deep in the intestinal crypts - Paneth cells fortify the small intestine’s defenses by releasing what?

- their secretions do what?

5. Stem cells- at the bases of the crypts, the stem cells continuously divide to replenish the epithelium!

Duodenal glands in the submucosa of the duodenum produce alkaline mucus: - what does the mucus help to do?

Intestinal Juice the intestinal glands normally secrete what?

is intestinal juice normally slightly alkaline?

intestinal juice is enzyme-poor because intestinal

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monosaccharides, amino acids, short-chain fatty acids, water and ions, water-soluble vitamins, etc.

long-chain fatty acids, monoglycerides, fat soluble vitamins and cholesterol, etc.

enzymes are bound to the microvilli of the brush border

Motility of the Small Intestine (6th edition p. 781; 7th edition p. 796) segmentation

- localized mixing contractions that mix chyme with the digestive juices and bring the particles of food into contact with the mucosa for chemical digestion and absorption

peristalsis - weak, wave-like contractions that propel chyme toward the large intestine see Fig. 22.3; it shows these two types of muscular contractions

Digestive Processes in the Small Intestine

chemical digestion in the small intestine is a collective effort of: 1 enzymes in pancreatic juice produced by the pancreas2 enzymes in intestinal juice 3 brush border enzymes on the microvilli produced by the epithelial cells in the small intestine

the end products of digestion listed in the box on the previous page are then absorbedAbsorption in the Small Intestine (I have summarized it here from the textbook!)

90% of absorption of nutrients takes place in the small intestine 10% takes place in the stomach and large intestine

Here is a summary of absorption:nutrients in the lumen of the small intestine

into the simple columnar absorptive epithelial cells(enterocytes)

into the underlying lamina propria

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First, a little review of chemical digestion so far:… due to the actin of enzymes in saliva produced by salivary glands and enzymes produced in the stomach, chyme entering the small intestine contains partially digested carbohydrates, proteins and lipids

A SUMMARY OF THE END PRODUCTS OF CHEMICAL DIGESTION in the GI Tract:carbohydrates monosaccharidesproteins amino acids and peptideslipids fatty acids and monoglycerides

NOTE: before lipids are chemically digested, bile salts emulsify fat globules into fat droplets

DNA and RNA sugars and nucleotides

absorption = passage of digested nutrients, water, electrolytes, etc., from the lumen of the gastrointestinal tract into the blood or lymph

LACTEALS BLOOD CAPILLARIES

22.9 The large intestine absorbs water and eliminates feces (6th edition p. 781; 7th

edition p. 797) the large intestine extends the ileocecal valve to the anus; it is ~5 ft. long, 2.5 in. in diameter what are the major digestive functions of the large intestine?

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to sinusoids of the liver via the hepatic portal vein

to blood in subclavian vein via lymphatic vessels

the long-chain fatty acids, monoglycerides, fat soluble vitamins, and cholesterol are surrounded by bile salts to form micelles to get close to the microvilli of the epithelial cells; then they are released close to the cell membrane and diffuse into the cell.

Gross Anatomy (of the Large Intestine) the colon has three bands of smooth muscle called teniae coli

- their tone puckers the wall of the large intestine into what?

Subdivisions of the Large Intestine List subdivisions of the large intestine (and locate them in 6th ed Fig. 22.31; 7th ed Fig. 22.33:

cecum – saclike; the first part of the large intestine- the ileocecal valve controls the passage of chyme from the ileum to the large intestine

appendix- what does the appendix contain and what is its role?

- additionally, the appendix serves as what?

- the twisted structure of the appendix makes it susceptible to what?

colon- list the four distinct regions of the colon (not counting the flexures) and note their locations

in 6th edition Fig. 22.31; 7th edition Fig. 22.33:

rectum- the sigmoid colon joins the rectum in the pelvic canal at the level of the third sacral vertebra

anal canal- the anal canal is the last segment of the large intestine- it lies in the perineum, entirely external to the abdominopelvic cavity- the anal canal is about how long?

- the anal canal opens to the body exterior at what opening?

- name the two sphincters of the anal canal, indicate the type of muscles that form each, and whether each is voluntary or involuntary:

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Microscopic Anatomy (of the Large Intestine) the epithelium of the large intestine forms intestinal crypts, as in the small intestine, but

there are not villi and no circular folds the mucosa of the large intestine does NOT produce digestive enzymes the simple columnar epithelium contains numerous goblet cells that produce mucus:

- what are the functions of the mucus produced by the goblet cells?

Bacterial Microbiota (Bacterial Flora) the bacterial flora of the large intestine consists of about over a thousand different types of

bacteria! the last stage of digestion occurs in the colon through the activity of bacteria in the colon

the bacteria in the large intestine:∙ ferment any remaining carbohydrates and release H+ ions, CO2 and methane gas∙ convert remaining protein to amino acid and break down amino acids∙ convert bilirubin to stercobilin, which gives feces their brown color∙ synthesize B vitamins and some vitamin K

Digestive Processes in the Large Intestine some absorption occurs in the large intestine, including absorption of some water,

electrolytes, some vitamins (B and K)

as the chyme remains in the large intestine for 12 to 24 hours, water absorption converts it to a semisolid form called feces

from Table 22.2 (6th edition p. 767; 7th edition p. 795), indicate the major functions of the large intestine?

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Motility of the Large Intestine haustral contractions:

∙ describe haustral contractions:

∙ as a haustrum fills with food residue, the distension stimulates what?

∙ these movements mix the residue, which aids in what?

mass movements (mass peristalsis)= long slow-moving, strong waves of contraction that begin in the transverse colon and force the feces in the colon into the rectum

The Defecation Reflex (6th edition Fig. 22.33; 7th edition Fig. 22.35)Mass movement drives the feces from the colon into the rectum distends the rectum initiates the urge to defecate the internal anal sphincter relaxes involuntarily; the external anal sphincter relaxes voluntarily defecation occurs

The End!

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