Anatomy of the Digestive System
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The Digestive System Anatomy of the Digestive System We need food for cellular utilization: organs of digestive system form essentially a long !nutrients as building blocks for synthesis continuous tube open at both ends !sugars, etc to break down for energy ! alimentary canal (gastrointestinal tract) most food that we eat cannot be directly used by the mouth!pharynx!esophagus!stomach! body small intestine!large intestine !too large and complex to be absorbed attached to this tube are assorted accessory organs and structures that aid in the digestive processes !chemical composition must be modified to be useable by cells salivary glands teeth digestive system functions to altered the chemical and liver physical composition of food so that it can be gall bladder absorbed and used by the body; ie pancreas mesenteries Functions of Digestive System: The GI tract (digestive system) is located mainly in 1. physical and chemical digestion abdominopelvic cavity 2. absorption surrounded by serous membrane = visceral peritoneum 3. collect & eliminate nonuseable components of food this serous membrane is continuous with parietal peritoneum and extends between digestive organs as mesenteries ! hold organs in place, prevent tangling Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 1 Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 2 is suspended from rear of soft palate The wall of the alimentary canal consists of 4 layers: blocks nasal passages when swallowing outer serosa: tongue visceral peritoneum, lines ventral border of mouth cavity mainly fibrous and areolar CT with some pockets of adipose CT is skeletal muscle covered with mucous membrane muscularis contains taste buds several layers of smooth muscle frenulum is thin fold of mucous membrane on submucosa blood vessels, lymphatic vessels, nerves, ventral surface of tongue that anchors the connective tissue tongue to the floor of the mouth inner mucosa: short frenulum ! “tongue tied” small band of muscle tissue, muscularis mucosa Teeth mucus membrane lining two sets contains goblet cells that secrete mucous for protection deciduous (=baby teeth) (20) these layers are modified within various organs begin at 6 months; shed 6-13 yrs ! some have muscle layers well developed permanent teeth (32) ! some with mucous lining modified for secretion each tooth has a of digestive juices ! some with mucous lining modified for absorption crown (above gum) neck is where crown, gum and root meet 1. Mouth (Buccal Cavity, Oral Cavity) root (below gum) bordered above by hard and soft palate imbedded in socket forms partition between mouth and nasal passages gingivitis = inflammation of gum surrounding teeth; can lead to uvula Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 3 Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 4 periodontal disease Salivary Glands kinds of teeth modified for specific functions 3 Pairs of salivary glands: incisors – 4+4; cut, knip sublingual canines – 2+2; holding onto prey submandibular premolars – 4+4; cutting, crushing parotid molars – 6+6; chewing, grinding, crushing largest, below ears each tooth is composed of several layers: mumps = acute infection of parotid gland secrete saliva (enzymes and mucous for enamel digestion) very hard outer surface 2. Pharynx (throat) on upper exposed crown only resists bacterial attack cannot regenerate if damaged already discussed dentin 3. Esophagus below enamel less hard, similar to bone matrix collapsible tube ~ 10” long decays quickly of enamel is penetrated extends from pharynx to stomach pulp !gets food through thorax to abdominal cavity living portion of tooth consists of blood vessels, nerves posterior to trachea and heart cementum pierces diaphragm on root of tooth only outer surface uses peristalsis to move food to stomach holds root into socket in jaws ! can swallow upsidedown Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 5 Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 6 drains into stomach through the cardiac orifice Muscle layers are very well developed in stomach surrounded by the lower esophageal sphincter circular longitudinal 4. Stomach oblique muscular sac just below diaphragm and liver Help to break up food by churning action alimentary canal expands to form stomach results in milky white liquid = chyme 50 mL when empty; up to 1.5 L after meal sphincter muscles close both stomach openings: Major functions of stomach: cardioesphageal sphincter (=lower esophageal sphincter) 1. physical digestion – churning action heartburn !doesn’t close properly 2. chemical digestion – esp proteins pyloric sphincter 3. limited absorption (some water, alcohol, certain drugs) cholic in babies ! doesn’t open properly given smooth muscle relaxers divided into 4 regions: cardiac mucosal lining of stomach is folded into rugae to fundus allow for expansion with a meal body pyloris within the mucous lining of stomach are glandular tubes called gastric pits cardioesophageal sphincter lesser curvature cardiac fundus !within gastric pits are numerous microscopic gastric glands: pyloric sphincter body ! secrete mucous for protection greater curvature ! secretes various digestive enzymes pyloris ! secretes HCl Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 7 Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 8 central portion mostly in umbilical region 5. Small Intestine especially rich blood supply most digestion and absorption occurs here absorbs most nutrients, water & salts longest part of alimentary canal: ileum ! 1” diameter x 10’ long (living) or 20’ long (cadaver) ~5’ mainly in hypogastric region Major functions of small intestine: joins to caecum of large intestine absorbs and reclaims bile salts and some additional nutrients 1. most chemical digestion of food (duodenum) mucosal lining of the small intestine is folded into plicae 2. secretes hormones which direct secretion of digestive juices by stomach, gall bladder, the intestinal mucosa also contains small finger-like pancreas projections = villi 3. most absorption of digested foodstuffs ~1mm tall (jejunum & ileum) each villus contains absorptive epithelial cells small intestine fills most of abdominal cavity and goblet cells held in place by mesenteries (=serous membranes) core of villus is filled with areolar tissue of lamina propria subdivided into 3 functional regions: within this is an arteriole, capillary bed, venule duodenum and ~10” long lymphatic capillary = lacteal uppermost drains pyloric stomach 6. Large Intestine receives ducts from gall bladder and pancreas jejunum 2.5” diameter x 6’ long ~4’ Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 9 Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 10 valve-like sphincter separates small from large intestine = ileocecal valve on the outer surface of the large intestine are 3 longitudinal bands of muscle tissue Major functions of large intestine: = taenia coli 1. absorb additional water as needed by body ! muscle tone within these bands produces pouches = haustrae 2. absorb small amount of additional nutrients that allow distention some Vit K and B’s made by bacteria in lg intestine rectum 3. collects, concentrates and rids body of last 7-8” undigested wastes ends at anus subdivided into 3 regions: held shut by two anal sphincters: cecum internal anal sphincter of smooth muscle external anal sphincter of skeletal muscle blind ended sac that extends from point of attachment to small intestine Intestinal Flora contains appendix ! ~3.5” (9cm) long our bacterial symbionts exist as a complex interacting significant source of lymphocytes community with specific characteristics colon we’re finding that each person has a unique set of microorganisms on their skin and in their guts subdivided into: the abundance of certain bacteria in your feces correlates with your age, gender, body mass index, and ascending colon nationality transverse colon descending colon our gut bacteria provide many benefits: sigmoid colon Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 11 Human Anatomy & Physiology: Digestive System; Ziser Lecture Notes, 2014.4 12 !help break down hard to digest fibers and starches use of antibiotics can cause dramatic and long term changes in our gut flora and increase risk of some !make essential vitamins and additional nutrients chronic diseases !protect us from pathogens, toxins and some carcinogens in the future: !activate our immune systems to better resist infections eg. might be able to test for changes in kinds and numbers of gut bacteria change and adapt as your foods change species as an early indication of certain diseases eg. doctors may prescribe bacterial supplements to improve ! those better able to metabolize dominant food tend to physical health increase eg. fecal transplants: restores bowel flora to a healthy state gut bacteria affect our mood and behavior: 7. Serous Membranes correlations have been found between gut flora and some psychiatric disorders such as depression, autism and schizophrenia body wall and organs of abdomen are lined with peritoneum obesity, diabetes, Crohn’s disease, colitis, celiac disease, irritable bowel syndrome all may be the !parietal peritoneum result of an imbalanced microbial ecosystem in our !visceral peritoneum guts most, but not all, of the visceral organs are completely some forms of severe