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Home , Anal canal, Fauces (throat), Palatopharyngeal arch

Ingegneria delle tecnologie per la salute

Fondamenti di anatomia e istologia

aa. 2016-17

Digestive System DIGESTIVE SYSTEM

Overview of the Digestive System function of DS is to break down the foods, release their nutrients, and absorb those nutrients ( is workhorse of DS) DIGESTIVE SYSTEM

digestive system does not work in isolation! DIGESTIVE SYSTEM

Digestive System Organs

1. Alimentary 2. Accessory Canal Organs Structures DIGESTIVE SYSTEM 1. Alimentary Canal Organs DIGESTIVE SYSTEM 1. Alimentary Canal Organs = gastrointestinal (GI) tract or gut = a one-way tube about 7-8 mts in length during life (10-11 mts after death, once smooth muscle tone is lost), beginning at and terminating at (between those: , , , and small and large intestines) to fit functional needs of the body main function of alimentary canal organs = nourish the body both mouth and anus are open to external environment: thus, food and wastes within alimentary canal are technically considered to be outside the body. only through the process of absorption nutrients in food enter into and nourish the body’s ―inner space.‖ DIGESTIVE SYSTEM 2. Accessory Structures DIGESTIVE SYSTEM 2. Accessory Structures = aids in breakdown of food: within mouth, teeth and begin mechanical , whereas salivary glands begin chemical digestion  once food products enter small intestine, gallbladder, liver, and pancreas release secretions (bile + enzymes) essential for digestion called accessory organs because they sprout from lining cells of developing gut (mucosa) and augment its function (= vital contributions), maintaining a connection to gut by way of ducts, even after complete development 1. Alimentary canal length 1. Alimentary canal functions Histology of Alimentary Canal

Layers: 1. mucosa, 2. , 3. muscularis, 4. serosa , continuing with mesentery

Throughout its length, the alimentary tract is composed of the same 4 tissue layers, varying details of their structural arrangements to fit their specific functions. Histology of Alimentary Canal

 mucosa = , because of mucus production of gut , consisting: a. epithelium b. c. muscularis mucosa Histology of Alimentary Canal

 mucosa b. lamina propria = layer of loose a. epithelium = (in mouth, pharynx, esophagus, anal canal = non- connective tissue containing numerous keratinized, stratified squamous epithelium, in stomach, blood and lymphatic vessels, intestines = simple columnar epithelium); in direct contact transporting nutrients absorbed and also with : interspersed among epithelial cells = goblet cells, serving immune function by housing secreting mucus and fluid, + enteroendocrine cells, secreting clusters of lymphocytes = mucosa- hormones into interstitial spaces between cells; epithelial cells associated lymphoid tissue (MALT), = very brief lifespan, averaging from only a couple of days particularly substantial in distal (= (mouth) to about a week (gut). Peyer’s patches)  immune system evolved as means of defending against pathogens encountered within because alimentary canal is exposed to foodborne bacteria and foreign matter c. muscularis mucosa (not to be confused with the muscularis layer) = thin layer of smooth muscle in constant state of tension, pulling mucosa of stomach and small intestine into undulating folds, dramatically increasing surface area available for digestion and absorption Histology of Alimentary Canal

 Submucosa = lying immediately beneath mucosa, broad layer of dense connective tissue connecting mucosa to underlying muscularis and including blood and lymphatic vessels (transporting absorbed nutrients), with submucosal glands releasing digestive secretions and additional submucosal plexus (=dense branching network of )  muscalaris = (also called muscularis externa), in small intestine [= double layer of smooth muscle: inner circular layer + outer longitudinal layer  their contractions promote mechanical digestion, expose more of food to digestive chemicals, and move food along canal], in mouth, pharynx, anterior part of esophagus, and external anal [= made up of skeletal muscle,  voluntary control over and ], in stomach [= addition of a third layer, oblique muscle], in colon [= 2 layers as small intestine, but longitudinal layer segregated into 3 narrow parallel bands, tenia coli, making it to look like series of pouches rather than a simple tube]  serosa = portion of alimentary canal superficial to muscularis, present only in regions of alimentary canal within abdominal cavity, consisting of a layer of visceral peritoneum overlying a layer of loose connective tissue [instead of serosa, mouth, pharynx, and esophagus = dense sheath of collagen fibers called , serving to hold alimentary canal in place near ventral surface of vertebral column]. Histology of Alimentary Canal Histology of Alimentary Canal Histology of Alimentary Canal Histology of Alimentary Canal DIGESTIVE SYSTEM: Supply

• Intrinsic innervation = provided by enteric nervous system, running from esophagus to anus, containing approximately 100 million motor, sensory, and interneurons (unique to this system compared to all other parts of peripheral nervous system), grouped into 2 plexuses: myenteric plexus (plexus of Auerbach, lying in muscularis layer, responsible for motility, especially rhythm and force of contractions of muscularis), submucosal plexus (plexus of Meissner, in submucosal layer, responsible for regulating digestive secretions and reacting to presence of food) • Extrinsic innervations = provided by , including both sympathetic (fight-or-flight response, restricts activity of enteric neurons, thereby decreasing GI secretion and motility) and parasympathetic nerves (rest-and-digest response increases GI secretion and motility by stimulating neurons of enteric nervous system) DIGESTIVE SYSTEM: Blood Supply

 blood vessels serving DS have 2 functions: 1.transport protein and carbohydrate absorbed by mucosal cells after digestion (lipids absorbed via lacteals of lymphatic system), 2.supply organs with nutrients + O2 needed to drive cellular processes.  a) more anterior parts of alimentary canal = supplied with blood by branching off aortic arch and thoracic aorta; b) below this point = supplied with blood by arteries branching from the abdominal aorta [celiac trunk = liver, stomach, , sup and inf mesenteric arteries = remaining small and large intestines].  collecting nutrient-rich blood from small intestine (where most absorption occurs)   liver (nutrients are either processed or stored for later use)  bak to heart (during ―resting and digesting,‖ about 1/4 of blood pumped enters arteries serving the intestines). The Peritoneum

= a broad serous membranous sac made up of squamous epithelial tissue, surrounded by connective tissue, holding in place digestive organs within abd cavity, composed of 2 different regions: parietal peritoneum, lining abd wall, and visceral peritoneum, enveloping abd organs  peritoneal cavity = space bounded by visceral and parietal peritoneal surfaces, with few milliliters of watery fluid acting as lubricant to minimize friction between serosal surfaces of peritoneum. The Peritoneum

 visceral peritoneum includes multiple large folds, enveloping various abd organs, holding them to dorsal surface of body wall and containing blood vessels, lymphatic vessels, and nerves  5 major peritoneal folds  first portion of small intestine (called duodenum), pancreas, and portions of (ascending and , and ) remain completely or partially posterior to peritoneum [retroperitoneal organs] Digestive System Processes and Regulation

DS uses mechanical and chemical activities to break food down into absorbable substances Digestive System Processes and Regulation

Digestive Processes: 6 activities 1. Ingestion = entry of food into the alimentary canal through the mouth, where is chewed (increasing surface area of food and allowing an appropriately sized bolus to be produced) and mixed with saliva, containing enzymes that begin breaking down carbohydrates + some lipid digestion via lingual lipase. 2. Propulsion = movement of food through digestive tract including both voluntary process of swallowing and involuntary process of peristalsis (consisting of sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, to propel food along and also playing a role in mixing food with digestive juices). Digestive System Processes and Regulation

3. Mechanical digestion = purely physical process not changing chemical nature of food., but making it smaller to increase both surface area and mobility: includes mastication, or chewing, tongue movements , mechanical churning in stomach (creating an acidic “soup” called chyme), segmentation in small intestine (consisting of localized contractions of circular muscle of the muscularis layer, isolating small sections of intestine, moving their contents back and forth while continuously subdividing, breaking up, and mixing the contents, in order to mix food with digestive juices and facilitate absorption) 4. Chemical digestion =starting in the mouth, digestive secretions break down complex food molecules into their chemical building blocks , varying in composition, but typically contain water, various enzymes, acids, and salts and is completed in small intestine 5. Absorption = entering of nutrients in bloodstream, which takes place primarily within small intestine, through epithelial cells (lipids absorbed into lacteals and transported via lymphatic vessels to bloodstream , ie subclavian veins near heart) 6. Defecation = final step of undigested materials removed from the body as feces Digestive System Processes and Regulation

In some cases, a single organ is in charge of a digestive process (for example, ingestion occurs only in mouth and defecation only in anus). However, most digestive processes involve interaction of several organs and occur gradually as food moves through alimentary canal. Some chemical digestion occurs in mouth. Some absorption can occur in mouth and stomach, for example, alcohol and aspirin. Regulatory Mechanisms regulatory mechanisms working to maintain optimal conditions in lumen needed for digestion and absorption, stimulating digestive activity through mechanical and chemical activity, are controlled both extrinsically and intrinsically and can be divided in: 1.Neural Controls 2.Hormonal Controls

Regulatory Mechanisms

1. Neural Controls walls of alimentary canal contain a variety of sensors helping regulate digestive functions, including mechanoreceptors, chemoreceptors, and osmoreceptors, capable of detecting mechanical, chemical, and osmotic stimuli, respectively  appropriate reflex furthering process of digestion, sending a message that activates glands that secrete digestive juices into lumen, or stimulate muscles within alimentary canal, thereby activating peristalsis and segmentation walls of entire alimentary canal embedded with nerve plexuses interacting with CNS and other nerve plexuses—either within the same digestive organ or in different ones: interactions prompt several types of reflexes: extrinsic nerve plexuses orchestrate long reflexes, which involve central and autonomic nervous systems and work in response to stimuli from outside digestive system. Short reflexes orchestrated by 2 intrinsic nerve plexuses (enteric nervous system) within alimentary canal wall, regulating activities in one area of digestive tract and coordinating local peristaltic movements and stimulating digestive secretions. Regulatory Mechanisms

2. Hormonal Controls variety of hormones involved in digestive process, secreted by specialized epithelial cells, called endocrinocytes, entering bloodstream, through which they can reach their target organs (gut and its accessory organs).

Gastrin = main digestive hormone of stomach, secreted in response to presence of food, stimulating secretion of gastric acid

[produced by duodenum:] Secretin = stimulates a watery secretion of bicarbonate by the pancreas Cholecystokinin (CCK) = stimulates secretion of pancreatic enzymes and bile from liver and release of bile from gallbladder Gastric inhibitory peptide (GIP) = inhibits gastric secretion and slows gastric emptying and motility. Mouth, Pharynx, and Esophagus and functions of

3 main organs of upper alimentary canal  Mouth  Pharynx  Esophagus

3 associated accessory organs  tongue  salivary glands  teeth Mouth = + tongue + , also called oral cavity (or buccal cavity) • , 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 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 and teeth, and on outside by cheeks and lips Mouth • = opening between the oral cavity and (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 (=); posterior region= , composed mainly of skeletal muscle (manipulating, subconsciously, soft palate = to yawn, swallow, or sing) Mouth

• 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. • palatoglossal and = 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 • = 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; Tongue

• beneath its mucous membrane covering, 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!

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 helping tongue move food around in mouth and creating an abrasive surface

Tongue (singular papilla) are small, nipple-like structures on the upper surface of the tongue that give the tongue its characteristic rough texture. 4 types of papillae with different structures, named accordingly: circumvallate papillae (vallate papillae), fungiform papillae, filiform papillae and foliate papillae (all except filiform papillae associated with taste buds) Tongue Tongue Taste buds contain taste receptor cells, which are also known as gustatory cells, involved in detecting the 5 elements oftaste perception: salty, sour, bitter, sweet and umami; through the combination of these elements we detect "flavors." Via small openings in the tongue epithelium, called taste pores, parts of the food dissolved in saliva come into contact with the taste receptors. These are located on top of the taste receptor cells that constitute the taste buds. The taste receptor cells send information detected by clusters of various receptors and ion channels to the gustatory areas of the brain via the seventh, ninth and tenth cranial nerves. On average, the human tongue has 2,000–8,000 taste buds. Tongue Tongue 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 = lingual frenulum too short or otherwise malformed, impairing speech: must be corrected with surgery) Tongue Tongue Tongue Tongue Tongue

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