luca.ansaloni@unibg · Mouth Fauces = opening between the oral cavity and throat (oropharynx) (like...

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Mouth, Pharynx, and Esophagus

anatomy and functions of 3 main organs of upper alimentary canal Mouth Pharynx Esophagus

3 associated accessory organs tongue salivary glands teeth

Mouth = cheeks + tongue + palate, also called oral cavity (or buccal cavity) lips, or labia (singular = labium) = at entrance, outer covering is skin, transitioning to a mucous membrane in mouth proper, very vascular with a thin layer of keratin ( "red“), with huge representation on cerebral cortex ( kissing!), covering orbicularis oris muscle (=regulating what comes in and goes out) labial frenulum = midline fold of mucous membrane attaching inner surface of each lip to gum cheeks = oral cavity’s sidewalls, outer covering skin, their inner covering mucous membrane (=non-keratinized, stratified squamous epithelium), between them connective tissue and buccinator muscles.

oral vestibule = pocket-like part framed on the inside by gums and teeth, and on outside by cheeks and lips

Mouth Fauces = opening between the oral cavity and throat (oropharynx) (like the kitchen "faucet"). oral cavity proper = runs from gums and teeth to fauces . Palate = arched shape of the roof of your mouth allows you to handle both digestion and respiration at the same time; anterior region = serving as a wall (or septum) between oral and nasal cavities, being rigid shelf against which tongue can push food, created by maxillary and palatine bones (=hard palate); post region= soft palate, composed mainly of skeletal muscle (manipulating, subconsciously, soft palate = to yawn, swallow, or sing) uvula = fleshy bead of tissue dropping down from center of posterior edge of soft palate (vestigial organ? serving to keep foods and liquid from entering nasal cavity and also contributing to snoring)

Mouth palatoglossal and palatopharyngeal arch = 2 muscular folds extending downward from soft palate, on either side of uvula, lying respectively next to base of tongue and behind it, forming superior and lateral margins of fauces palatine tonsil = clusters of lymphoid tissue, between these 2 arches, protecting pharynx lingual tonsil = located at the base of tongue

Mouth: lip

Tongue = facilitating ingestion, mechanical digestion, chemical digestion (lingual lipase), sensation (of taste, texture, and temperature of food), swallowing, and vocalization, attached to mandible, styloid processes of temporal bones, and hyoid bone and positioned over floor of oral cavity, a medial septum extends the entire length of tongue, dividing it into symmetrical halves; beneath its mucous membrane covering,

Tongue each half of tongue is composed of same number and type of intrinsic [=those within tongue, longitudinalis inferior, longitudinalis superior, transversus linguae, and verticalis linguae muscles, allowing to change size and shape of tongue, facilitating both swallowing and speech] and extrinsic [= originating outside tongue and inserting into connective tissues within tongue, mylohyoid (raising tongue), hyoglossus (pulling it down and back), styloglossus (pulling it up and back) and genioglossus (pulling it forward), performing 3 important digestive functions: (1) position food for optimal chewing, (2) gather food into a bolus (rounded mass), and (3) position food so it can be swallowed] skeletal muscles

Tongue Papillae = extensions of lamina propria of mucosa, which are covered in stratified squamous epithelium, located at top and sides of tongue and divided in fungiform papillae [mushroom shaped, covering large area of tongue, tend to be larger toward rear of tongue and smaller on tip and sides] and filiform papillae [long and thin, containing taste buds and touch receptors] helping tongue move food around in mouth and creating an abrasive surface Lingual glands = in lamina propria of tongue secrete mucus and watery serous fluid, containing enzyme lingual lipase (minor role in breaking down triglycerides but not working until it is activated in stomach) lingual frenulum = fold of mucous membrane on underside of tongue, tethering it to floor of mouth (congenital anomaly ankyloglossia = lingual frenulum too short or otherwise malformed, impairing speech: must be corrected with surgery)

Tongue

Salivary Glands

Major Salivary Glands = outside oral mucosa 3 pairs of glands, secreting majority of saliva into ducts opening into mouth: • submandibular glands = in floor of mouth, secreting through submandibular ducts. • sublingual glands = below tongue, using lesser sublingual ducts to secrete into oral cavity. • parotid glands = between skin and masseter muscle (near ears), secreting through parotid duct (located near second upper molar tooth).

=many small salivary glands housed within mucous membranes of mouth and tongue, constantly secreting saliva, either directly into oral cavity or indirectly through ducts (an average of 1 to 1.5 liters of saliva/each day): usually just enough saliva is present to moisten mouth and teeth, but increases when eating, because it is essential to moisten food and initiate chemical digestion of carbohydrates.

Salivary Glands

Salivary Glands Saliva = essentially (95.5 %) water + 4.5 % [=complex mixture of ions, glycoproteins, enzymes, growth factors, and waste products] salivary amylase = perhaps most important ingredient in saliva initiating breakdown of carbohydrates (not enough time in mouth to allow all carbohydrates break down, but salivary amylase continues acting until inactivated by stomach acids) Bicarbonate + phosphate ions = chemical buffers, maintaining saliva at a pH 6.35-6.85. Salivary mucus = lubricate food, facilitating movement in mouth, bolus formation, and swallowing. immunoglobulin A + lysozyme = antimicrobial epidermal growth factor Regulation of Salivation • autonomic nervous system regulates salivation (secretion of saliva):

parasympathetic stimulate - sympathetic reduce salivation • chemicals stimulating taste receptors on tongue impulses to superior and

inferior salivatory nuclei in brain stem parasympathetic impulses through fibers in glossopharyngeal and facial nerves, stimulating salivation

Teeth = organs similar to bones used to tear, grind, and otherwise mechanically break down food

Types of Teeth 2 sets of teeth (= dentition): 20 deciduous teeth, or baby teeth, first appearing at about 6 mos of age; between approximately age 6 and 12, replaced by 32 permanent teeth, moving from center of mouth toward side: • 8 incisors, 4 top + 4 bottom • 4 canines • 8 premolars (or bicuspids) • 12 molars

Teeth: Anatomy of a Tooth

2 main parts of a tooth: 1. crown (= portion projecting above gum line, 2. root (embedded within maxilla+mandible), both containing inner pulp cavity with loose connective tissue inside through which run nerves and blood vessels [root canal = pulp cavity that runs through root of tooth]; surrounding pulp cavity is dentin (=bone-like tissue) covered in root by an even harder bone-like layer called cementum and in crown by an outer layer of enamel (hardest substance in body)

= secured in alveolar processes (sockets) of maxilla and mandible by connective tissue called periodontal ligament gingivae (gums) = soft tissues that line alveolar processes and surround necks of teeth.

3 subdivisions: superior, nasopharynx, involved only in breathing and speech, other 2 subdivisions, oropharynx and laryngopharynx, used for both breathing and digestion: oropharynx begins inferior to nasopharynx and continue below with laryngopharynx, connecting to esophagus, whereas anterior portion connects to larynx, allowing air to flow into bronchial tree;

Pharynx = (involved in both digestion and respiration, when food enters pharynx, involuntary muscle contractions close off air passageways) short tube of skeletal muscle lined with mucous membrane, running from posterior oral and nasal cavities to opening of esophagus and larynx;

histologically, wall of oropharynx is similar to that of oral cavity, with mucosa of stratified squamous epithelium endowing with mucus-producing glands.

Pharynx During swallowing, elevator skeletal muscles of pharynx contract, raising and expanding pharynx to receive bolus of food, then relax and constrictor muscles of pharynx contract, forcing bolus into esophagus and initiating peristalsis, meanwhile soft palate and uvula rise reflexively to close off entrance to nasopharynx and larynx is pulled superiorly with cartilaginous epiglottis folding inferiorly to cover glottis

Esophagus

= muscular tube connecting pharynx to stomach (running a mainly straight route through mediastinum of thorax, but to enter abdomen penetrates diaphragm through an opening (esophageal hiatus) approximately 25.4 cm (10 in) in length, located post to trachea, and remaining collapsed when not engaged in swallowing

Esophagus Passage of Food through Esophagus upper esophageal sphincter (continuous

with inferior pharyngeal constrictor) = controls movement of food from pharynx into esophagus.

upper two-thirds of esophagus = both smooth and skeletal muscle fibers, with the latter fading out in the bottom third of esophagus

rhythmic waves of peristalsis, which begin in upper esophagus, propel bolus of food toward stomach, meanwhile, secretions from esophageal mucosa lubricate esophagus and food, that passes from esophagus into stomach at lower esophageal sphincter (also called gastroesophageal or cardiac sphincter), relaxing to let food pass into stomach, and then contracting to prevent stomach acids from backing up into esophagus.

Esophagus Histology of the Esophagus mucosa with non-keratinized, stratified squamous epithelium, with a layer of basal and parabasal cells, protecting against erosion from food particles + lamina propria containing mucus-secreting glands + muscularis layer changing according to location: in upper third muscularis is skeletal muscle, in middle third, both skeletal and smooth muscle and in lower third, it is smooth muscle + adventitia, most superficial layer of esophagus not covered by a fold of visceral peritoneum.

Esophagus

Esophagus Digestive functions

Stomach FUNCTION

temporary holding chamber = meal can be ingested far more quickly than it can be digested and absorbed by small intestine: stomach holds food and parses only small amounts into small intestine at a time; foods not processed in order are eaten, but mixed together with digestive juices in stomach (= chyme), released into small intestine.

plays several important roles in chemical digestion, including continued digestion of carbohydrates and initial digestion of proteins and triglycerides

little if any nutrient absorption occurs in stomach, with exception of negligible amount of nutrients in alcohol

Stomach: structure 4 main regions in stomach: 1. cardia (or cardiac region) = point where

esophagus connects to stomach and through which food passes into stomach

2. Fundus = dome-shaped and located inferior to diaphragm, above and left of cardia

3. Body = below fundus, main part of stomach

4. Pylorus = funnel-shaped, connecting stomach (pyloric antrum) to duodenum (=narrower end, called pyloric canal, with smooth muscle pyloric sphincter located at latter point of connection and controls stomach emptying)

In absence of food, stomach deflates inward, and mucosa and submucosa fall into a large fold (=ruga).

greater curvature = convex lateral surface lesser curvature = concave medial border held in place by lesser omentum (extending from liver to lesser curvature) and

greater omentum (running from greater curvature to posterior abdominal wall)

Stomach:structure

Stomach: histology

wall made of same 4 layers as rest of alimentary canal, but with adaptations for unique functions of this organ to: a) Muscularis = in addition to typical circular and longitudinal smooth muscle layers, muscularis has an inner oblique (= in addition to moving food through canal, stomach can vigorously churn food, mechanically breaking it down into smaller particles)

Stomach: histology

b) mucosa

Stomach: histology

b) Mucosa = epithelial lining consists only of surface mucus cells, secreting a protective coat of alkaline mucus + vast number of gastric pits dot surface of epithelium, marking entry to each gastric gland, secreting complex digestive fluid referred to as gastric juice;

Stomach: histology walls of gastric pits made up primarily of mucus cells, but gastric glands made up of different types of cells: glands of cardia and pylorus = primarily mucus-secreting cells pyloric antrum = mucus and a number of hormones, including majority of

stimulatory hormone, gastrin fundus and body = (much larger glands) site of most chemical digestion,

producing most of gastric secretions, due to a variety of secretory cells:

Stomach: histology

Stomach: histology 1. Parietal cells—located primarily in middle region of

gastric glands (among the most highly differentiated of the body’s epithelial cells) producing both hydrochloric acid (HCl, responsible for high acidity [pH 1.5 to 3.5] needed to activate protein-digesting enzyme, pepsin, and also killing much of bacteria ingested with food and helping to denature proteins, making them more available for enzymatic digestion) and intrinsic factor (glycoprotein necessary for absorption of vitamin B12 in small intestine).

2. Chief cells—located primarily in basal regions of gastric glands, secreting pepsinogen (inactive proenzyme form of pepsin, with HCl necessary for its conversion from pepsinogen)

3. Mucous neck cells— (gastric glands in upper part of stomach) secreting thin, acidic mucus that is much different from the mucus secreted by the goblet cells of the surface epithelium (role not currently known)

4. Enteroendocrine cells— secreting various hormones into interstitial fluid of lamina propria (including gastrin released mainly by enteroendocrine G cells)

Stomach: histology

Small Intestine: generality

Chyme released from the stomach enters small intestine, which is primary digestive organ in body.

Not only where most digestion occurs, also where practically all absorption occurs.

longest part of alimentary canal: about 3.05 meters (10 feet) long in a living person (twice as long in a cadaver due to loss of muscle tone).

smaller diameter of only about 2.54 cm (1 in), compared with 7.62 cm (3 in) for the large intestine.

in addition to its length, folds and projections of lining of small intestine work to give it an enormous surface area, which is approximately 200 m2 , more than 100 times surface area of your skin: necessary for complex processes of digestion and absorption

Small Intestine: structure

coiled tube of small intestine is subdivided into 3 regions: duodenum, jejunum, and ileum


hepatopancreatic ampulla (ampulla of Vater) = located in duodenal wall, marks transition from ant portion of alimentary canal to mid-region, where bile duct (through which bile passes from the liver) and main pancreatic duct (through which pancreatic juice passes from pancreas) join, opening into duodenum at a tiny volcano-shaped structure called major duodenal papilla (where hepatopancreatic sphincter, sphincter of Oddi, regulates flow of both bile and pancreatic juice from ampulla into duodenum).

Duodenum = shortest region ( 25.4-cm, 10-in), beginning at pyloric sphincter, bends post behind peritoneum, becoming retroperitoneal, and then makes a C-shaped curve around head of pancreas before ascending anteriorly again to return to peritoneal cavity and join jejunum, therefore being subdivided into 4 segments: superior, descending, horizontal, and ascending duodenum.

Small Intestine: structure jejunum = about 0.9 meters (3 feet) long (in life),

[means “empty” in Latin], without clear demarcation between it and ileum.

ileum = longest part of small intestine, measuring about 1.8 meters (6 feet) : thicker, more vascular, more developed mucosal folds than jejunum, joins cecum, at ileocecal sphincter (or valve); both tethered to posterior abdominal wall by the mesentery;

large intestine frames these 3 parts of small

intestine. Parasympathetic nerve fibers from vagus nerve

and sympathetic nerve fibers from thoracic splanchnic nerve = extrinsic innervation to small intestine

superior mesenteric artery = main arterial supply veins running parallel to arteries, drain into

superior mesenteric vein = nutrient-rich blood from small intestine is then carried to liver via hepatic portal vein.

Small Intestine: Histology wall composed of same 4 layers typically present in alimentary system, but 3 features of mucosa and submucosa are unique, increasing absorptive surface area more than 600-fold, include circular folds, villi, and microvilli (these adaptations most abundant in proximal 2/3 of small intestine, where majority of absorption occurs)

(a) The absorptive surface of

the small intestine is vastly

enlarged by the presence of

circular folds, villi, and

microvilli. (b) Micrograph of

the circular folds. (c)

Micrograph of the villi. (d)

Electron micrograph of the

microvilli.

Small Intestine: Histology Circular folds = (also called plica circulare), deep ridge in mucosa and submucosa, beginning near proximal part of duodenum and ending near middle of ileum, facilitating absorption, because their shape causes chyme to spiral, rather than move in a straight line, through small intestine, slowing movement of chyme and providing time needed for nutrients to be fully absorbed. Villi = within circular folds, small (0.5–1 mm long) hairlike vascularized projections called villi (singular = villus), giving mucosa a furry texture, being about 20 to 40 villi mm2, increasing surface area tremendously; mucosal epithelium, primarily composed of absorptive cells, covering villi, that (in addition to muscle and connective tissue to support its structure) contains a capillary bed composed of 1 arteriole and 1 venule, as well as a lymphatic capillary called lacteal: breakdown products of carbohydrates and proteins (sugars and amino acids) enter bloodstream directly, but lipid breakdown products absorbed by lacteals and transported to bloodstream via lymphatic system. Microvilli = much smaller (1 µm) than villi, being cylindrical apical surface extensions of plasma membrane of mucosa’s epithelial cells, supported by microfilaments, combined microscopic appearance suggests a mass of bristles (brush border), containing at surface enzymes that finish digesting carbohydrates and proteins, estimating 200 million microvilli per mm2, greatly expanding surface area of the plasma membrane and thus greatly enhancing absorption.

Small Intestine: Histology Intestinal Glands = mucosa between villi is dotted with deep crevices that each lead into a tubular intestinal gland (crypt of Lieberkühn), formed by cells lining crevices , producing intestinal juice, a slightly alkaline (pH 7.4 to 7.8) mixture of water and mucus (daily about 0.95 to 1.9 lts secreted in response to distention of small intestine or irritating effects of chyme on intestinal mucosa). duodenal glands (Brunner’s glands) = submucosa of duodenum, only site of complex mucus-secreting, producing a bicarbonate-rich alkaline mucus buffering acidic chyme as it enters from stomach. roles of cells in small intestinal mucosa:

Small Intestine: Histology

Intestinal MALT = lamina propria of small intestine mucosa is studded with quite a bit of MALT: in addition to solitary lymphatic nodules, aggregations of intestinal MALT (= typically referred to as Peyer’s patches, concentrated in distal ileum, most prominent in young people and becoming less distinct in elders, coinciding with general activity of our immune system) serving to keep bacteria from entering bloodstream.

Small Intestine (and Large Intestine…): Histology

Small Intestine: Histology

Large Intestine

= terminal part of alimentary canal, with function: finish absorption of nutrients

and water, synthesize certain vitamins, form feces, eliminate feces running from appendix to anus, and framing small intestine on 3 sides small intestine (large = more than twice of small intestine, about 3 inches) Subdivisions = 4 main regions: cecum, colon, rectum, anus (ileocecal valve = located at opening between ileum and large intestine, controling flow of chyme)

Cecum = sac-like structure, suspended inferior to ileocecal valve, about 6 cm long, receiving contents of ileum, and continuing absorption of water and salts (appendix or vermiform appendix = winding tube attached to cecum, 7.6-cm long containing lymphoid tissue, suggesting an immunologic function, generally considered vestigial, but postulated a survival advantage in diarrheal illness, where may serve as bacterial reservoir to repopulate enteric bacteria for those surviving the initial phases of illness; mesoappendix = mesentery of appendix, tethering to mesentery of ileum) Colon = follows cecum: ascending colon, right colic flexure (hepatic flexure), transverse colon (with last third of this begins region defined as hindgut), left colic flexure (splenic flexure), descending colon, sigmoid colon (=entering the pelvis inferiorly, s-shaped, extending medially to midline ); ascending and descending colon, and rectum located retroperitoneally, meanwhile transverse and sigmoid colon tethered to post abd wall by mesocolon

Large Intestine

Large Intestine

Foregut, midgut, hindgut…

Large Intestine

Rectum = in pelvis, near third sacral vertebra, final 20.3 cm (8 in) of alimentary canal, extending anterior to sacrum and coccyx, with 3 lateral bends creating a trio of internal transverse folds called the rectal valves (helping separate feces from gas to prevent simultaneous passage of feces and gas). Anal Canal = located in perineum, completely outside of abdominopelvic cavity, 3.8–5 cm (1.5–2 in) long, opening to exterior at anus (2 sphincters: internal anal sphincter made of smooth muscle, with involuntary contractions and external anal sphincter made of skeletal muscle, under voluntary control)

Large Intestine

3 features unique to large intestine: 1. Teniae coli = three bands of smooth

muscle that make up longitudinal muscle layer of muscularis of large intestine, except at its terminal end (tonic contractions bunch up colon into a succession of pouches =

2. Haustra (singular = hostrum) = responsible for wrinkled appearance of colon

3. epiploic appendages = small, fat-filled sacs of visceral peritoneum, attached to teniae coli, purpose unknown.

Although rectum and anal canal have neither teniae coli nor haustra, they do have well-developed layers of muscularis that create the strong contractions needed for defecation.

Large Intestine: Histology several notable differences between walls of large and small intestines: few enzyme-secreting cells found

in the wall of large intestine, and no circular folds or villi.

other than in anal canal, mucosa of colon is simple columnar epithelium made mostly of enterocytes (absorptive cells) and goblet cells.

wall of large intestine far more intestinal glands, containing a vast population of enterocytes (absorbing water and salts as well as vitamins produced by your intestinal bacteria) and goblet cells (secreting mucus that eases movement of feces and protects intestine from effects of acids and gases produced by enteric bacteria).

Large Intestine: Histology

Accessory Organs in Digestion

Chemical digestion in small intestine relies on activities of 3 accessory digestive organs: 1. liver = to produce bile and

export it to duodenum. 2. gallbladder = primarily

stores, concentrates, and releases bile.

3. pancreas = produces pancreatic juice, which contains digestive enzymes and bicarbonate ions, and delivers it to duodenum.

Liver = largest gland in body, weighing about 1,5 kg in an adult, also one of most important, being an accessory digestive organ and playing number of roles in metabolism and regulation. lies inferior to diaphragm in right upper quadrant of abd cavity, receiving protection from

surrounding ribs. divided in 2 primary lobes (large right and a much smaller left lobe), in right lobe, some

anatomists also identify an inferior quadrate and a posterior caudate lobe, defined by internal features

connected to abd wall and diaphragm by 5 peritoneal folds referred to as ligaments: 1. falciform ligament, 2. ligamentum teres hepatis (both actually remnants of umbilical vein, separating right and left lobes anteriorly), 3-4. lateral ligaments, and 5 coronary ligament. + lesser omentum tethers liver to lesser curvature of stomach.

The human liver is divided by the falciform ligament into an anatomical right lobe and left lobe. However, the liver also has a functional right and left side, divided by Cantlie's line: a hypothetical line from the gallbladder fossa to the middle hepatic vein. Each functional hemi-liver is composed of two sections: on the right, an anterior section (segments 5 and 8) and a posterior section (segments 6 and 7) separated by the right hepatic vein; and on the left, a lateral section (segments 2 and 3) and a medial section (segment 4) separated by the left hepatic vein and the falciform ligament (not shown). Each segment can be individually resected. Black dashed lines show the demarcations between sections.

Liver

Liver

Diaphragmatic surface 1 - coronary ligament of liver; 2 - aperture; 3 - triangular ligament of the liver; 4 - sickle ligament of the liver; 5 - the right lobe of the liver; 6 - Left lobe of the liver; 7 - Round ligament of liver; 8 - a sharp lower edge; 9 - gall bladder

Liver Lower surface 1 - Left lobe of the liver; 2 - the triangular ligament of the liver; 3 - Rear (tailed) fraction of the liver; 4 - adrenal indentation; 5 - kidney indentation; 6 - proper hepatic artery; 7 - Vienna gate; 8 - the common bile duct; 9 - common hepatic duct; 10 - cystic duct; 11 - the right lobe of the liver; 12 - duodenal-intestinal indentation; 13 - Round ligament of liver; 14 - colon-intestinal indentation; 15 - Front (square) share; 16 - gall bladder

Liver • porta hepatis = (“gate to the liver”)

where hepatic artery and hepatic portal vein enter liver (running along with common hepatic duct behind lateral border of lesser omentum on way to their destinations)

• hepatic artery delivers oxygenated blood from heart to liver, hepatic portal vein delivers partially deoxygenated blood containing nutrients (+ drugs and toxins) absorbed from the small intestine and actually supplies more oxygen to liver than do much smaller hepatic arteries; after processing bloodborne nutrients and toxins, liver releases nutrients needed by other cells back into the blood, which drains into central vein and then through hepatic vein to inferior vena cava.

• hepatic portal circulation = all blood from alimentary canal passes through liver (explaining liver most common site for alimentary canal cancers metastasis

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luca.ansaloni@unibg · Mouth Fauces = opening between the oral cavity and throat (oropharynx) (like...

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