3/24/08 Digestive System Chapter 22 – Day 1

3/24/08 Digestive system  Respiratory System ♦Brings O 2 to the body  Cardiovascular System ♦Brings O 2 to the cells  In tissues O 2 is used for cellular respiration, BUT…  O 2 is only one of the ingredients – you also need ♦Glucose  Digestive System ♦Brings glucose to the body ♦Other sources of nutrients ♦And other building blocks to make cells

3/24/08 Digestive system  Food is broken down & processed  Nutrients are absorbed  Waste products are eliminated  All of this happens in the digestive tract  A.K.A. alimentary canal or GI tract  The digestive tracts is a long, continuous muscular tube starting at the esophagus

3/24/08 Digestive system Fig

3/24/08 Digestive system - Processes  In order for nutrients to reach cells the digestive system carries out several processes ♦Ingestion = food in the mouth ♦Mechanical processing = physically breaking food into bits ♦Digestion = enzymes and hormones ♦Absorption = organic molecules enter interstitial fluid ♦Excretion = elimination of unwanted materials

3/24/08 Fig Digestive system – Cell/Tissue layers  The digestive system has a distinct system of tissue layers  There is an “open” surface inside the GI tract – epithelial tissue covering on outside  4 layers – from inside to outside ♦These are there ALL ALONG the GI tract ♦Mucosa innermost layer ♦Submucosa ♦Muscularis externa ♦Serosa outermost layer

3/24/08 Cell/Tissue layers - MUCOSA  Digestive epithelium  Connective tissue – lamina propria  (smooth) muscle tissue – muscularis mucosa  Type of epithelium varies along the GI tract ♦Pharynx & esophagus handle large masses of food = stratified epithelium ♦In the stomach – food becomes liquid & passes to intestines ♦A great deal of absorption happens in the intestines Simple columnar epithelium Secrete mucous Highly folded epithelial surface (small intestine)  Lamina propria – areolar connective tissue right below basement membrane of epithelium  Contains blood vessels, nerves, mucous glands (in the intestines this is where you find the Peyer’s patches)  Muscularis mucosa = smooth muscle – helps movement in the GI tract

3/24/08 Cell/Tissue layers - SUBMUCOSA  Dense connective tissue  Nerve network ♦Submucosal plexus  Communication with the nervous system – helps muscle movement

3/24/08 Cell/Tissue layers – MUSCULARIS EXTERNA  Smooth Muscle Tissue  Nerve network ♦Mysenteric plexus  More forceful contractions for movement  2 layers of muscle ♦Longitudinal ♦Circular  Allows 2 types of movement ♦Rocking motion ♦Forward movement

3/24/08 Cell/Tissue layers – SEROSA  Fibrous tissue on outside  Protective covering which helps in attachment to abdominal wall Fig. 22.3

3/24/08 Other important general features  Membranes ♦Perotineal cavity 2 membrane layers ♦Encloses abdominal portion of digestive tract ♦Serosa = visceral peritoneum (inner layer) ♦Parietal peritoneum = lines abdominal wall (outer layer) ♦Additional serous membrane connects serosa/visceral to parietal peritoneum ♦The space between the 2 layers if filled with fluid Peritoneal fluid Secreted by cells of the peritoneum

3/24/08 Other important general features  Mesenteries ♦Sheets of serous membrane allow blood vessels, nerves, and lymph vessels to pass through & network ♦Stabilize the position of the GI tract Prevents “flopping around” ♦OMENTUS – associated with the stomach (Fig ) Lesser omentum & greater omentum Contains adipose tissue (fat around the belly) ♦Mesentery proper Within small intestine, between loops ♦Mesocolon Stabilizes large intestine ♦Areas without mesentaries = pancreas & duodenum – which are attached to the abdominal wall for stability

3/24/08 Secretions  Within the digestive tract – secretions are evident throughout ♦Mucus To lubricate food & “walls” ♦Digestive enzymes Break chemical bonds ♦Electrolytes Buffers pH Cofactor for enzymes  Parts of digestive system & direction of food…  Explore important structures, secretions, absorption, digestion process, movement of food

3/24/08 Alvioli – Capillary Interface Fig

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3/24/08 Mechanics of Respiration  Ventilation ♦= mechanical process ♦involves the diaphragm and skeletal muscles (intercostal muscles)  Breathing consists of 2 phases: ♦Inspiration air is taken into the lungs ♦Expiration Air passes out of the lungs

3/24/08 Alvioli – Capillary Interface Fig