Cellular Resp

Essay text:

Divided into two parts: · Alimentary tract o Or Gastrointestinal tract o Hollow tube from mouth to anus o Food material inside the tract is considered to be outside the body b/c the canal is open to the external environment at both ends o It digests food and absorbs the digested fragments o Organs include § Mouth § Pharynx § Esophagus § Stomach § Small intestine § Large intestine · Accessory digestive organs o Organs include § Teeth § Tongue § Gall bladder § Salivary glands § Liver § Pancreas o The teeth and tongue are in the oral cavity while digestive glands and gallbladder lie outside the GI tract and connect to it by ducts o Most of the accessory digestive organs are in the abdomino-pelvic cavity § Covered by a serous membrane called the visceral peritoneum § Parietal peritoneum covering the abdominal walls of the abdomino-pelvic cavity § B/w these two layers is a thin layer of fluid produced by the serous membranes · Lubricates b/c these organs are moving § Organs are held in place, and anchored to the abdominal wall (b/c they are moving) by mesentery · A double layer of peritoneum o Sheet of two serous membranes fused back to back that extends to the digestive organs from the body wall · Also a fat storage area · Provide routes for blood vessels, lymphatics and nerves to reach the digestive viscera GI tract · Hollow tube w/ 4 distinct layers o Central is the hollow portion called the lumen o Mucosa § Layer closest to the lumen § Wet epithelial membrane (simple columnar epithelium) § Often w/ a lot of goblet cells to secret mucous · Mucous lubricates food to help it pass through the canal · Mucous lining protects the wall of the GI tract from digestive enzymes (in the stomach and small intestine) and HCl from the stomach?PROTECTIVE § Epithelial layer rests on a thin layer of loose connective tissue called lamina propria · Has a lot of blood vessels to get broken down nutrients into the blood so they can be distributed to tissues · Blood vessels also nourish the epithelium § Beyond the lamina propria is a thin layer of smooth muscle called the muscularis mucosae · Contraction of this layer moves the epithelium around so food trapped in the mucosa is dislodged and proceeds through the tract · In the small intestine this layer throws the mucosa into a series of small folds that increases the surface area greatly o Submucosa § Layer of dense connective tissue just external to the mucosa § Contains lots of blood vessels, lymphatic vessels, lymphoid follicles and nerve fibers § Has a rich supply of elastic fibers that enables the stomach to regain its normal shape after temporarily storing a large meal § The vascular network supplies the surrounding tissues of the GI tract wall o Muscularis externa § Muscular layer § Responsible for segmentation and peristalsis § In most of the GI tract it is 2 layers of smooth muscle · Inner circular layer · Outer longitudinal layer · In several places along the tract, the circular layer thickens, forming sphincters that act as valves to prevent the backflow and control food passage from one organ to the next o Visceral peritoneum or Serosa § Protective outermost layer § Formed by areolar connective tissue covered w/ mesothelium (a single layer of squamous epithelial cells) ** FUNCTIONAL ANATOMY OF THE GI TRACT** · Oral cavity (mouth) o Extends form the lips anteriorly to the oropharynx o Lined w/ stratified squamous epithelium § Protective § On gums, hard palate and dorsum of the tongue the epithelium is keratinized to give extra protection against abrasion when eating o Lips and cheeks § Lips extend from the bottom of the nose to indentation on the chin § What we call lips (where lipstick is applied) is called the red margin · This area is red b/c it is poorly keratinized · No sweat glands, no sebaceous glands o Causes dryness and cracking due to the elements § Lips and cheeks help to keep food b/w the teeth when we chew and play a small role in speech · Lips formed by the obicularis oris muscle · Cheeks are formed largely by the buccinators o The palate § Hard anteriorly · Is the rigid surface that the tongue forces food against when chewing § Soft posteriorly · Mobile fold formed mostly of skeletal muscle · Uvula projects downward from it o Uvula and soft palate rise to close off the nasopharynx when we swallow o The tongue § Occupies the floor of the mouth and fills most of the oral cavity when the mouth is closed § Skeletal muscle covered w/ epithelium § During chewing, it grips food and constantly repositions it b/w the teeth § Also mixes the food w/ saliva forming a compact mass called the bolus and pushes it back into the oropharynx · Before the oropharynx, usage of the tongue is voluntary · After the oropharynx, movement is involuntary and controlled by the medulla and pons § Has both intrinsic and extrinsic skeletal muscle fibers · Intrinsic o Confined in the tongue and not attached to bone o Muscle fibers running in several planes allow the tongue to change shape (but not position) as necessary for speech and swallowing · Extrinsic o Extend the tongue from their points of origin on the bones of the skull or the soft palate o Protrude, retract and move the tongue from side to side § Lingual frenulum is a fold of mucosa that secures the tongue to the floor of the mouth so that it cannot be swallowed § Papillae are rough peg-like projections of the tongue · Filiform o Conical in shape o Give the tongue surface its rough texture that aids in licking and provides friction for manipulating food · Fungiform o Mushroom-shaped o Scattered widely on the tongue surface o Each has a vascular core, giving them a reddish tint o Some are on the esophagus · Circumvallate o 10-12 arranged in a V, located at the back of the tongue o Resemble fungiform but have a surrounding groove · Tastebuds are located on the fungiform and circumvallate papillae o Pick up tastes that are sweet, salty, sour and bitter o Japanese suggest another tastebud, the umami, which means delicious § Makes you crave protein in red meat § Beyond the cirumvallate is the sulcus terminalis, a groove that distinguishes the anterior two thirds of the tongue in the oral cavity from the posterior 1/3 in the oropharynx o Salivary glands § Extrinsic salivary glands produce most of the saliva · Parotid glands o 2 masses, 1 in front of each ear o Secretion is mostly a watery fluid from serous cells o Become inflamed w/ mumps · Submanibular glands o Secretes a watery fluid (serous cells) plus mucous (mucous cells) called seromucous o Size of a walnut located along the medial aspect of the mandibular body · Sublingual glands o Anterior to the submandibular gland under the tongue o These are mucous glands § Intrinsic salivary glands also called buccal glands are scattered through the oral cavity mucosa § Saliva · 97-99...