Class 9 Digestive System

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Digestive System Functions: Digestion Breaking down food into usable nutrients Absorption Transferring nutrients into bloodstream Excretion Expelling out non-digestible and non-useable materials.

The Alimentary Canal Continuous hollow tube extending from mouth to anus. Mouth, pharynx, esophagus, stomach, small intestine, large intestine, anal canal 4

Accessory Organs Organs that contribute to the digestive process, but are not part of the alimentary canal and the food does not travel through. Salivary Glands, liver, gall bladder, pancreas 5

Four Layers 6

Four Layers

Movements of the Alimentary Canal Peristalsis Propels contents forward Alternates between circular and longitudinal muscles. Mixing Movements Uses circular and longitudinal muscles simultaneously to cause a “mixing” or “churning” type of movement. Mixing can be done all along the canal, but is most noticeable in the stomach.

The Mouth 9

Mouth Functions Small amount of digestion (starch/CHO) Receive food Taste Receive food Moisten food and prepare for further processing

Salivary Glands Exocrine glands composed of mucous and serous cells Parotid Largest of the main glands, secretes mostly serous fluid Submandibular secretes equal amounts of serous and mucous fluids Sublingual secretes mostly mucous fluid Saliva components: 98% water 2% - antibacterial components, mucus, electrolytes (Na, Ca, K, Mg), amylase (salivary) Salivary Amylase breaks down CHO, therefore…….. CHO DIGESTION BEGINS IN THE MOUTH 11

The Pharynx 12

Swallowing known as deglutination allows food to pass from the mouth to the pharynx to the esophagus can start as a “voluntary” action, but quickly becomes involuntary “Bolus” passes along hard palate then to soft palate with tongue pushing towards oropharynx. bolus is prevented from gaining entry into the larynx by the epiglottis

The Esophagus Pierces the diaphragm through the esophageal hiatus Circular muscles that close off before entering the stomach: cardiac sphincter ( aka gastroesophageal sphincter, lower esophageal sphincter) Function – propel food into stomach THERE IS NO DIGESTIVE FUNCTION 14

The Stomach 15

PROTEIN DIGESTION BEGINS IN THE STOMACH Gastric glands Function Mucous cells secretes mucous Parietal cells secretes HCl (acid), intrinsic factor (protein released to allow intestine to absorb vit B12) Chief cells secretes pepsinogen (an inactive form of pepsin). Once this mixes with HCl, it becomes pepsin and is able to breakdown protein into amino acids. temporary storage tank for food site for mechanical and chemical breakdown of proteins…. PROTEIN DIGESTION BEGINS IN THE STOMACH **cells in the lining of the mucosa continuously secrete bicarbonate to protect the stomach lining from self digestion. So this, along with mucous, protects the lining.

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The Pancreas 18

Functions of the Pancreas: Releases enzymes that digest fats, proteins, carbohydrates, and nucleic acids Produces alkaline (basic) fluid to neutralize acidic chyme in small intestine Produces insulin and glucagon to regulate sugar metabolism Pancreatic juice pancreatic amylase breaks down CHO pancreatic lipase breaks down fats proteinase (Trypsin) breaks down proteins nuclease breaks down nucleic acid into nucleotides (from DNA and RNA) * Pancreatic juice is very alkaline, which helps neutralizes the fluid and allows the intestine to absorb properly.

Liver 20

Hepatic Portal System 21

Liver Lobes: 2 lobes, left and right Hepatic Lobules: cylindrical structures which are the functional units of the liver. Contain: hepatocytes, bile canals and ducts, artery (hepatic), vein (hepatic portal on perimeter and central vein draining sinusoids into hepatic veins), sinusoids (blood filled spaces between hepatocytes), Kupffer cells (specialized macrophages).

Liver Functions Makes and secretes bile Stores some vitamins and iron Detoxification Stores glucose Modifies fats so the body can use them more efficiently Forms plasma proteins Helps excrete by-products of RBC (bilirubin) into bile Synthesizes urea (by-product of protein metabolism), released into blood and sent out in urine

Bile Emulsify fats Stored in the gall bladder & becomes 5x more concentrated Produced by Hepatocytes Pasty yellow/green substance Contents: bilirubin, cholesterol, salts, water, sodium and potassium and sometimes small amounts of copper and other metals About 1 liter per day is made by the liver About 95% of all salts found in bile are reabsorbed in the body in the lower small intestine

The Gallbladder 26

The Small Intestine 27

Structures of the Intestinal Wall 28

The Large Intestine 29

Defecation Reflex 30

Thank goodness!!!