Digestive system (LAB PRACTICAL) Flashcards
Mechanical digestion
Food breakdown by physical forces to prepare for further degradation by enzymes
-Mixing food in mouth by tongue
-Churning food in stomach
-Segmentation in small intestine
Chemical digestion
Enzymes breakdown food molecules into their building blocks
-Each major food group broken by different enzymes
-Carbs are broken into simple sugars by enzymes
-Protein broken to amino acids by proteases
-Fats broken to fatty acids & glycerol
Alimentary canal of digestive system
-Mouth
-Pharynx
-Esophagus
-Stomach
-Small intestine
-Large intestine
-Anus
Accessory organs
-Salivary glands
-Teeth
-Pancreas
-Liver
-Gallbladder
4 layers of alimentary canal
-Mucosa
-Submucosa
-Musclaris externa
-Serosa
Mucosa
Innermost, moist membrane composing of:
-Surface epithelium
-Small amount of CT (Lamina propia)
-Small smooth muscle layer
Submucosa
Just beneath mucosa
-Soft CT with blood vessels, nerve ending, and lymphatics
Muscularis externa
Composed of 2 layers of smooth muscle for peristalsis
-Circular layer
-Outer longitudinal layer
Serosa
And its 2 layers
Outermost layer of the wall contains fluid-producing cells, consists of:
-Visceral peritoneum: innermost layer that wraps canal organs
-Parietal peritoneum: Outer layer that lines abdominopelvic cavity
Peristalsis
Smooth muscle motion that causes waves that move a bolus
Segmentation
Smooth muscle movement that churns and fragments a bolus to promote mixing
Anatomical structure of mouth/oral cavity
-Lips to protect anterior opening
-Cheeks from lateral walls
-Uvula: Fleshy projection of soft palate for speech & food direction
-Hard palate forms anterior roof
-Soft palate forms posterior roof
Salivary glands & their 3 pairs
Glands that secrete saliva
-Parotid glands
-Submandibular glands
-Sublingual glands
Saliva
-Mixture of mucus and serous fluid
-Helps to form food bolus
-Contains salivary amylase to begin stomach digestion
-Dissolves chemicals so they can be tasted
Steps of deglutition/swallowing
- In buccal phase upper esophageal sphincter is contracted/closed and tongue presses against hard palate to move bolus to oropharynx
- Pharyngeal-esophageal phase begins as uvula and larynx rise to prevent food from entering. Tongue blocks mouth and upper esophageal sphincter relaxes to allow food into esophagus
- Constrictor muscle of pharynx contracts forcing food into esophagus inferiorly. Upper esophageal sphincter contracts after food enters
Esophagus
-10 inch long tube running from pharynx to stomach
-Conducts food via peristalsis and acts as a passageway for food only
-No chemical digestive function
Regions of the teeth
-Crown
-Neck
-Root
Crown of tooth
Exposed portion
-Enamel outer layer, hardest substance in the body
-Pulp cavity contains CT, blood vessels, and nerve fibers
-Root canal is where pulp cavity extends to root
Neck of tooth
-Region in contact with gum
-Connects crown to root
Root of tooth
-Innermost region within gums
-Cementum: Covers outer surface and attaches tooth to the periodontal membrane
Stomach
-Left side of abdominal cavity
-Food enters cardioesophageal sphincter
-Food empties into intestine via pyloric sphincter
-Rugae are internal mucosa folds
-Lesser curvature: Convcave medial surface
-Greater curvature: Convex lateral surface
Regions of stomach
-Cardiac region: near the heart
-Fundus: Expanded portion lateral to cardiac region
-Body: Midportion
-Pylorus: Funnel-shaped terminal end
Functions of stomach
-Bulk storage
-Mechanical breakdown of food
-Disruption of chemical bonds via acids and enzymes
-Production of intrinsic factor
-Temporary storage tank for food
-Chemical breakdown of protein begins
-Delivers chyme to small intestine/duodenum
-Site of food break down
Food breakdown in stomach
-Gastric juice regulated by neural and hormonal factors
-Presence of food or rising pH causing release of gastrin
-Gastrin produces protein-digesting enzymes, mucus, HCl
-Acidic pH activates pepsiongen to pepsin and provides hostile environment for microbes
-Protein-digesting enzymes such as pepsin and rennin (For milk digestion in infants)
-Alcohol and aspirin are some of the few items absorbed
Digestive & Absorptive functions of small intestine
-Majority of chemical digestion begins here
-Secretions and buffers provided by pancreas, liver, and gallbladder
-Enzymes produced by intestinal cells and pancreas
-Pancreatic ducts carry enzymes to small intestine
-Bile from liver enters via bile duct
-Site of nutrient absorption in blood
Three subdivisions of small intestine
-Duodenum: Attached to stomach, curves around head of pancreas
-Jejunum: Attached anteriorly to duodenum
-Ileum: Extends from jejunum to large intestine
Ileocecal sphincter
Transition between small and large intestine
Microvilli
Tiny projections of the plasma membrane that create a brush border appearance
Villi
Finger-like structures formed by mucosa
Circular folds
Deep folds of mucosa and submucosa
Large intestine
-Larger in diameter than small intestine but shorter in length
-Frames internal abdomen
-Cecum in sac-like first part of large intestine
Regions of colon
-Ascending: Travels up right side of abdomen
-Transverse: Travels across abdominal cavity
-Descending: Travels down left side
-Sigmoid: Enters pelvis
Appendix
-Accumulation of lymphatic tissue that sometimes becomes inflamed
-Hangs from cecum
Movements in large intesine
-Sluggish peristalsis
-Mass movements: Slow, powerful movements and occur 1-4 times per day
-Segmentation movements mix chyme with digestive juices
-Gastroenteric reflexes initiated by stretch receptors in stomach
-Gastroileal reflexes trigger relaxation of ileocecal valve
Defecation reflexx
-Caused by presence of feces in rectum
-Internal anal sphincter relaxed
-Defecation occurs with relaxation of voluntary/external anal sphincter
Pancreas
-Pancreatic duct penetrates duodenal wall
-Endocrine function: Secretion of insulin & glucagon
Exocrine secretions of pancreas
-Pancreatic juice secreted into small intestine
-Carbohydrases
-Lipases
-Nucleases
-Proteolytic enzymes
Liver
-Largest gland in the body
-Right side of body under diaphragm
-Consists of 4 lobes suspended from diaphragm and abdominal wall by falciform ligament
-Connected to gallbladder via common hepatic duct
-Performs metabolic and hematological regulation and produces bile
Histological organization of liver
-Lobules containing single-cell thick plates of hepatocytes
-Lobules unite to form common hepatic duct, duct meets cystic duct to form common bile duct
Liver function
-Fats and fatty acids picked up by liver. Some oxidized to provide energy for liver cells and the rest broken down to simpler compounds for blood.
-Manufactures bile: emulsifies dats by breaking up large globules
-Detoxifies drugs and alcohol
-Degrades hormones
-Produces cholesterol, blood proteins
-Central role in metabolism
-Can regenerate if needed
Gallbladder
-Sac found in hollow fossa of liver, hollow, pear-shaped organ
-When no digestion is occurring, bile backs up the cystic duct for storage in gall bladder
-When digestion of fatty food is occurring, bile is introduced into duodenum from gallbladder
-Stores, modifies, and concentrates bile
-Gallstones crystallized cholesterol which can cause blockages
