Mechanics of Breathing and the Pathway of Air upon Inhalation and Exhalation

Food to Feces and In Between Pathway for FoodOverview of the Gastrointestinal SystemLuke MacLeod, Wara Lounsbury, Tejinder Kaur, and James OBrien

Overview

Large IntestineOral CavityGeneral Structure and Functions of the Digestive SystemGeneral Arrangement of the Abdominal GI OrgansSmall IntestinePharynxEsophogus (The Swallowing Process)StomachRectum/AnusQuestions

Functions of the Digestive System

IngestionDigestionSecretionPropulsionEliminationAbsorption

Explain briefly each process and tie in how each organ contributes to the process throughout the presentationThe digestive system comprises of organs that:Ingest foodTransport the ingested foodDigest the food into smaller componentsAbsorb the necessary nutrients into the blood stream and;Expel the waste products from the body

So What Makes up the Gastrointestinal Tract (GI)?

Oral CavityPharynxEsophagusStomachSmall IntestineLarge IntestineAnus

Upper Lower

Two Categories: Digestive and Accessory DigestiveThe digestive organs make up the gastrointestinal (GI) tract The accessory digestive organs include the salivary glands, tongue, pancreas, liver, and gall bladder

General Arrangement of Abdominal GI OrgansTunics of the GI Tract:From esophagus to large intestine: 4 layersMucosaSubmucosaMuscularisAdventitia/serosa

McKinley, M. P., O'Loughlin, V. D., Pennefather-O'Brien, E., & Harris, R. T. (2015).Human anatomy. Page

Mucosa-3 components: superficial epithelium lining; lamina propria, muscularis mucosae (thin layer of smooth muscle)Submucosa-dense irregular connective tissue, blood and lymph vessels, nerves Muscularis-2 layers of smooth muscle. Inner circular layer (inner layer of smooth muscle) and outer longitudinal layer (outside layer of smooth muscle) Adventitia-outer most layer made of areolar connective tissue with elastic fibres and collagen-retroperitoneal organs contain adventitia because they are somewhat covered by visceral peritoneum serosa-same make up as adventitia but is covered by a layer of visceral peritoneum-intraperitoneal organs contain serosa

Oral CavityEntrance to the GI tractTwo distinct regions: Vestibule Oral Cavity Proper Is comprised of these main components:

CheeksTonguePalateSalivary GlandsTeeth

Teeth: collectively known as thedentition. Teeth are responsible for mastication, the first part of the mechanical digestion process.

Cheeks: The buccinator muscles compress the cheeks against the teeth to hold solid materials in place during chewing.

Tongue: manipulates and mixes ingested materials during chewing and helps compress the materials against the palate to turn them into a bolus. The tongue also performs important functions in swallowing.

Palate:Thepalateforms the roof of the oral cavity and acts as a barrier to separate it from the nasal cavity.There is a hard plate helps the tongue manipulate materials before swallowing and the soft plate prevents ingested materials from entering the nasal region

Salivary glands: collectively produce and secretesaliva, a fluid that assists in the initial activities of digestion.

Muscles of MasticationThere are four muscles that are involved in mastication:MasseterTemporalisLateral PterygoidMedial Pterygoid

The masseter: elevates and retracts the jaw, the most powerful muscle in the body in terms of ability to exert pressure Temporalis: elevates and brings the jaw forwardLateral: bring the jaw forward as wellMedial: elevates the mandible, and assists in closing the mouth

All four of the muscles are skeletal muscles that are innervated by the mandibular nerve, which is a branch of the trigeminal nerve

http://visitcore.com/featured-muscles-the-muscles-of-mastication/

PharynxComprised of three skeletal muscle pairs:Constrictors aid in propulsion3 Sections of Pharynx:NasopharynxOropharynxLaryngopharynxWorks with epiglottis to prevent bolus from entering airway

Superior (beginning)MiddleInferior (end)Pharyngeal Constrictors

The sequential contraction of the constrictors moves the bolus down the pharynx to the esophagus by narrowing the diameter of the pharynx behind the bolus

While the constrictors are pushing the bolus, the epiglottis shuts over the larynx and trachea (opening to airways)

Esophagus25 cm longPathway for bolus from pharynx to stomach Connects to the stomach by passing esophageal hiatus Contains 2 sphincters:Upper esophageal sphincterLower esophageal sphincter HISTOLOGY:Different mucosa: instead of columnar epithelial cells, has stratified squamous cells

peristalsis= rhythmic smooth muscle contractions

Why different epithelial cells? No absorption , which is what the simple columnar is useful for, so stratified aquamous for more protection from still mostly intact bolus

Pic: http://blogberlinmd.com/photorii/histology-of-esophagus

The Swallowing ProcessAlso called deglutitionProcess of moving ingested materials from the oral cavity to the stomachThree phasesOccurs as a result of coordinated muscular activities that force the bolus (chewed substance) (1) Into the pharynx from the oral cavity (2) through the pharynx, and(3) into the esophagus on the way to the stomach

VoluntaryPharyngealEsophageal

Thevoluntary phaseoccurs after ingestion. Food and saliva mix in the oral cavity. Chewing forms a bolus that is mixed and manipulated by the tongue and then pushed superiorly against the hard palate.

The appearance of the bolus at the entryway to the oropharynx initiates the pharyngeal phase. During this phase, (1) the soft palate and uvula elevate to block the passageway between the nasopharynx and oropharynx; (2) the bolus enters the oropharynx; and (3) the larynx and laryngeal opening elevate toward the epiglottis, ultimately covering and sealing the glottis to prevent swallowed materials from entering the trachea.

Theesophageal phaseis involuntary. It is the time (about 5 to 8 seconds) during which the bolus passes through the esophagus and into the stomach.

Stomach

Muscular J shaped sac occupying the left upper quadrant of the abdomenContinues digestion of bolus into chyme Consists of the: Cardia , fundus, body, and pylorus (pyloric antrum and pyloric canal)Thick muscularis layer is made up of three smooth muscle layersOblique layer, middle circular layer, and an outer longitudinal layer

Figure 26.12McKinley, M. P., O'Loughlin, V. D., Pennefather-O'Brien, E., & Harris, R. T. (2015).Human anatomy. Page

The stomach follows the esophagus in the GI tract. It is a J-shaped sack which resides in the upper left quadrant of the abdomen. Rugae are gastric folds within the stomach that allow it to expand as food enters, and contract as food leaves. Its purpose is to complete the digestion of the bolus from the oral cavity into chyme. The stomach itself is made up of four main components: the cardia, the fundus, the body, and finally the pylorus. The cardia is the narrow region anterior to the stomach lumen which connects to the esophagus posteriorly, at the cardiac orifice. The fundus is then the region that lies both lateral and superior to the esophagus. The body of the stomach is the largest region of the stomach, and follows posteriorly to both the cardia and fundus regions. The pylorus is the terminal region of the stomach. It begins to narrow and is divided into two regions: the pyloric antrum and pyloric canal. The pyloric antrum is the wider region of the pylorus, while the pyloric canal is more tapered and connects to the duodenum. This region is known as the pyloric orifice, and to mediate the entry of chyme into the duodenum, there is a pyloric sphincter consisting of circular smooth muscles surrounding the orifice.

Cells of the Stomach

There are five cells which are used in the stomach for secretion. The first are surface mucous cells. They line the stomach lumen and continuously secrete mucin in order to protect the stomach lining from the acidic environment. The mucous neck cells are interspersed amongst parietal cells and secrete acidic mucin in order to maintain acidic conditions in the stomach. The parietal cells are the ones that secrete hydrochloric acid into the stomach lumen in order to assist in protein deanimation. Parietal cells can also secrete an intrinsic factor that binds to vitamin B12, assisting in its absorption later on in the small intestine. Chief cells then secrete pepsinogen, which turns into the active enzyme pepsin by the acidic environment of the stomach. This ensures that the enzymes do not start digesting stomach lining immediately after secretion. Finally, the enteroendocrine cells secrete the hormone gastrin which regulates the chief and parietal cells.

Overview of the Small IntestineHas 3 segments:

Common features: Circular folds: increase surface area so more nutrients can be absorbed Villi: projections of mucosa used for digestion, made of columnar epithelial cells, with microvilli, and goblet cellsIntestinal glands: invaginations of the mucosa, made of various cells

Circular folds: are part of the mucosa and submucosa layer, and slow down the flow of chyme to maximize absorption

Villi: they increase the SA for absorption, and are formed out of columar epithelial cells and goblet cells. On the columnar epithelial cells there are microvilli on the apical surface to further increase the SA. The goblet cells release mucous to lubricate the passage of chyme. The villi each have their own capillary network, so nutrients can swiftly enter the bloodstream after absorption, and in the center is a lacteal, which is used for absorbing lipids

Intestinal glands: found in between some of the villi, lined with: columnar epithelial cells, goblet cells, and enteroendocrine cells (releases hormones like secretin, and CCK, that help with digestion and signalling)

Pic: http://www.webmd.com/digestive-disorders/small-intestinehttps://craniumcommander.wikispaces.com/Digestive+System+-+Physiology

Entering the Small Intestine: DuodenumChyme enters the duodenum (25 inches long), where digestion primarily occursBrunners glands, release alkaline mucus to neutralize acidic chyme, and to activate digestive enzymesAt middle of the duodenum (Ampulla of Vater) pancreatic juice and bile enter the duodenum via the major duodenal papilla Pancreatic juice and bile break down lipids, proteins and carbohydrates of the chymeJoins the jejunum at the duodenojejunal flexure

Its the shortest segment of the small intestine- only 10-12 inches long, and the superior end attaches to the pyloric sphincter, the inferior end attaches to the jejenumJourneying through the small intestine, the chyme, which is already partially digested is digested further, breaking down proteins, lipids and carbohydrates, to allow for absorption later in the small intestine. Firstly, Brunners glands secrete alkaline mucus to neutralize the acidic chyme, and to create an environment thats favourable for the activation of the digestive enzymes. Digestion occurs via the secretion of pancreatic juice (contains digestive enzymes) by pancreatic acinar cells and bile, by the gall bladder. Secretion occurs due to neural and endocrine signals. Neural signalling involves the vagus nerve (parasympathetic nervous system, rest and digest), whereas endocrine involves hormones secreted by the enteroendocrine cells- CCK, gastrin, and secretin. These are secreted and mixed with the chyme at the middle of the duodenum- the Ampulla of Vater.

Entering the Jejunum: Site of Absorption Chyme enters the jejunum, where absorption primarily occurs along with digestion, from the duodenum Villi are long and finger-likeUnlike the duodenum, there arent any specific glands in the submucosaSmooth muscles contract in localized manner called segmentations to mix chyme up and increase contact with walls

The smooth muscles contract in a localized manner called segmentations to mix up the chyme and increase contact with the walls of the jejenumCELLS: composed of villi and microvilli, in order to maximize the surface area for absorption- most of nutrients are absorbed here Absorption of carbohydrates, lipids and proteins occurs in the microvilliThe villi contains a lacteal, which allows for absorption of digested lipids

End of the Small Intestine: Ileum

Chyme enters the ileum from the jejunumThe longest segment: 2 4 m longNutrients are absorbed here, as is much of the waterTerminal end has lymphatic tissue, known as Peyers patches in the mucosa: they examine the chyme for pathogensContains Paneth cells: release antimicrobial substances Joins the cecum at the ileocecal sphincter

ILEUM: chyme enters from the jejenum (2- 4 m long)Last of the nutrients and water are absorbed here: water flows passively through the cells, and nutrients absorption occurs via the microvilli and villi Joins the cecum (part of the large intestine) via the ileocecal sphincter, which controls the flow of chyme into the large intestineTerminal end has lymphatic tissue, known as Peyers patches examine the chyme for any pathogens, and Paneth cells release antimicrobial substances

Large IntestineAbsorbs most the water and ions in the chyme, so it becomes feces occurs via aldosterone mediated sodium uptake Chyme enters the large intestine at the cecum Inferior to the cecum is the verniform appendix4 segments, along with bends: ascending colon right colic flexure transverse colon left colic flexure descending colon sigmoid flexure sigmoid colonFecal matter moves through large intestine by haustra muscle contractions

Appendix: is lined by lymphocyte filled lymphatic nodules

Histology and Muscles of Large IntestineHISTOLOGY:Lined with simple columnar epithelial cells and goblet cells, but lacking villiMany lymphatic cells are in the lamina propria layerMUSCLES:Teniae coli: longitudinal smooth muscles forming bundles, cause appearance of sacs (haustra)

Rectum/AnusRECTUM:ANATOMY: Stretch receptors, and renal ampulla FUNCTION: Stores fecal matter until excreted ANAL CANAL:Internal (involuntary) and external (voluntary) sphincters Divided by the pectinate line:

The external sphincter is under voluntary control, while the internal is SM, so its involuntary- both must be relaxed in order for fecal matter to be released

Questions?What is the benefit of the oral cavity breaking down food into smaller portions during the initial stages of digestion? Why are there more circular folds in the duodenum than in the ileum?

answer: smaller food particles allow for an increase in the surface area exposed to the saliva secreted by the salivary glands. This means that more food is exposed to the digestive enzymes at once, increasing the digestive efficiency during mastication and salivation. More specifically, more amylases are able to cleave the sugar compounds through hydrolysis. Because more absorption occurs in the duodenum than in the ileum, so the circular folds increase the SA for absorption where it most occurs

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Sources cont.Tariq, M. I. (2014). Bowel Obstruction. Retrieved October 19, 2016, from http://www.steadyhealth.com/articles/bowel-obstructionseveral-disorders-are-known-to-cause-this-disorderThe Muscles of Mastication. (n.d.). Retrieved October 19, 2016, from http://visitcore.com/featured-muscles-the-muscles-of-mastication/