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Chapter 13: the digestive system

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1 Chapter 13: the digestive system
Ms. Luaces – honors anatomy & physiology

2 Read & answer question at the end
Csi case #13 – pg. 488 Read & answer question at the end

3 Overview The digestive system allows the body to break down complex molecules into simple ones needed for body energy, tissue and cell development Made up of 2 components: The digestive tract (alimentary canal): Mouth, esophagus, stomach, small intestine, large intestine and rectum Accessory digestive organs (produce secretions to help with digestion and food absorption): salivary glands, pancreas, liver, and gallbladder

4 overview The digestive system is one of the first organs to develop from the endoderm during week 4 of development – gastrulation Accessory organs don’t begin to develop until week 5 (liver and pancreas) up until week 40 (liver). The liver only produces blood cells for the fetus at this time At birth, the digestive system is fully formed and releases meconium (waste product – green/black, sticky substances made of bile, mucus, and epithelial cells)

5 Mouth & pharynx The mouth is involved in both chemical (saliva) and mechanical (breakdown) digestion The anterior portion is made up of the lips (labia) which hold sensory receptors that detect temperature and texture of food Inside you find the oval (buccal) cavity, housing the teeth and where food is moistened

6 Mouth & pharynx The palate forms the roof of the buccal cavity
Hard palate (roof – maxillary and palatine bones) Soft palate (posterior back portion – contains uvula) At the base of the buccal cavity, we have the Oropharynx Contains the epiglottis – separates the respiratory system from the pharynx Tongue (lingual membrane) – contains taste buds, 4 intrinsic muscles, and 3 extrinsic muscles Intrinsic muscles allow the tongue to take a variety of shapes, assist with speech and swallowing while extrinsic muscles form most of the muscle mass and allows the tongue to retract, raise, and depress the tongue

7 Mouth & pharynx Lingual tonsils are found at the base of the tongue and are lymphatic tissues to fight throat infections Salivary glands release saliva and moisten food to start chemical digestion 3 major salivary glands Parotid: in cheeks; largest; watery section Sublingual: underneath the tongue; mucous section Submandibular: under the mandible; mixture of water and mucous

8 Mouth & pharynx Mechanical breakdown of food involves the 2 jaw bones, hard palate, and the teeth Permanent teeth consist of 16 teeth in each jaw – 32 total 4 central teeth in each jaw bone – incisors (cut up food) 4 canine (cuspid) teeth – hold and tear food 8 bicuspids (premolars) – break down food into fine particles 6 molars – grind food Extra 2 molars (wisdom teeth) – farthest back ; may/may not develop between years old depending on space left

9 Esophagus & Stomach The esophagus: Located behind the epiglottis
Muscular tube that carries food & liquids to the stomach Has an upper sphincter (closes the larynx during swallowing) and a lower sphincter – cardiac sphincter (closes entrance to stomach) Has 4 distinct tissue layers: mucosa, submucosa, muscularis layer, and serosa/adventitia

10 Esophagus & Stomach Mucosa: layer of epithelium that secretes mucus
Innermost layer Connected to lamina propria and has a boundary before submucosa made of smooth muscle and connective tissue called muscularis mucosae layer – thicker in the esophages to assist with passage of food Submucosa: layer of connective tissue that supports the shape of the esophagus Muscularis Layer: layer of smooth muscles to contract and move food / liquid through the digestive tract Serosa / Adventitia: thick covering of connective tissue filled with nerves to send signals to the muscles

11 Esophagus & Stomach Sphincters prevent backflow of material into previous organs Cardiac sphincter (at base of esophagus) prevents acid reflux (heartburn) Pyloric sphincter closes off the bottom of the stomach

12 Esophagus & Stomach The stomach:
Large, sac-like organ with 4 layers that can store 3 pints of food for digestion Stomach’s mucosa secretes acid and protein digestion enzymes and is designed to protect the stomach from digesting itself Divided into upper (cardiac), middle (fundic) and lower (pyloric) regions

13 Esophagus & Stomach Cardiac region: Fundic region: Pyloric region:
Secretes mucus Fundic region: Contains parietal cells (produce hydrochloric acid), chief cells (produce digestive enzymes), mucous neck cells (produces mucus when stimulated) and gastric stem cells (replaces gland cells) Pyloric region: Also secretes mucus

14 Esophagus & Stomach The stomach is composed of 3 thick layers of smooth muscle: Oblique: directly underneath the submucosa Stomach squeezing Circular: thick bands of muscle that mix food Longitudinal: mix and move digested food out of the stomach

15 Small Intestine Long narrow tube that tightly loops back and forth
Composed of the: Duodenum: receives partially digested food; where most digestion takes place Jejunum: where nutrients are absorbed Ileum: remaining nutrients are absorbed All areas contain fingerlike projections called villi and microvilli (increase surface area for absorption) and lacteals (collections of lymphatic vessels)

16 Small Intestine Most common cells found in the small intestine are the enterocytes (absorptive cells) – found mostly in the jejunum Enteroendocrine cells produce hormones that regulate digestion Paneth cells found in mucosa areas called crypts produce antibacterial enzymes that kill harmful bacteria but promote beneficial microorganism growth Peyer’s patches (collections of lymphatic tissue) in the duodenum help fight infection and are involved in immune response to food allergies

17 Small Intestine Composed of an inner circular layer (mixing food) and outer longitudinal layer (transport of food) of muscle Contains many extensive networks of nerves to send signals Attached to mesenteries to hold it in place and are also places for blood vessels to innervate Separated from the large intestine by the ileoceccal valve

18 Large intestine Also known as the colon – much larger in diameter and shorter than small intestine Contains: Cecum: small, swollen region that contains the appendix (common site of infection - appendicitis) Ascending colon: travels vertically up on right side to hepatic flexure (below liver) Transverse colon: runs parallel and connects at the splenic flexure (below spleen) Descending colon: travels vertically down on left side Sigmoid colon: s-shape end that spills into the anal canal

19 Large intestine Main functions: absorb electrolytes, vitamins and water ; remove undigested materials Contains no villi but many absorptive cells that use active transport to move electrolytes into its many capillaries Contains many bacteria and a type of yeast to help break down waste – essential!

20 Large intestine Ends in the rectum, a muscular storage area for undigested wastes Anal canal is the transitional region to the anus, which is rich in apocrine and eccrine sweat glands The anal sphincter has internal and external bands of muscle

21 Csi – case break Knowing the major parts of the alimentary canal (digestive tract) now, think about what area of this is malfunctioning in our patient. Turn to Pg. 503 and read the CSI Case Break, and respond in your notes

22 Glandular structures: pancreas
Lies posterior to the stomach and divided into glandular lobules surrounded by connective tissue that is each connected to blood vessels, nerves and ducts Has both endocrine and exocrine functions Endocrine: islets of Langerhans, which secrete glucagon – raises blood glucose (alpha cells) and insulin – lowers blood glucose (beta cells) Exocrine: saclike cluster of serous glands called acini – have granules with active and inactive digestive enzymes

23 Glandular structures: pancreas
Exocrine (cont): Inactive enzymes: zymogens, converted into active enzymes once they enter the digestive tract Ductal system of the pancreas originates in the acini that feeds into large duct called pancreatic duct  common bile duct  duodenum The yellow-green bile contains acids, cholesterol, glyceride fats, and salts to help in fat digestion Cholesterol is secreted from the liver through bile (also contains bilirubin, pigments, and broken down RBC’s)

24 Glandular structures: liver
Carries out the most complex functions using 4 lobes: left and right (make up most of the mass) and quadrate and caudate lobe. Left & right lobe separated by the falicform ligament

25 Glandular structures: liver
Two blood vessels enter the liver at the hilum Hepatic artery: provides blood for the liver cells Hepatic vein: carries wastes from the liver lobes to the inferior vena cava Haptic portal vein transfer food from the small intestine to the liver

26 Glandular structures: liver
Composed of hepatocytes: unusual cells with 2 or more nuclei that live about 5 months and are slow at carrying out mitosis Capable of regeneration (small pieces of liver have regrown lobes) Arteries going to the hepatocytes empty into sinusoids (exchange atmospheric gases, nutrients and wastes) and contain Kupffer cells that remove microorganisms Please refer to Pg. 507 for some of the many jobs the liver does

27 Glandular structures: gallbladder
Located underneath the right lobe of the liver Receives bile through the bile ductwork and releases it through the cystic duct, where it joins the common hepatic duct to form the common bile duct into the small intestine Main job: store and concentrate bile If bile has too much bilirubin, cholesterol, or bile salts, bile flow is blocked by the formation of gallstones (very painful!)


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