700 A&P Flashcards
The digestive system is composed of two main groups of organs
the digestive canal and accessory digestive organs.
The digestive canal is a continuous tube extending from the esophagus to the anus.
The accessory digestive organs include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
Digestion includes six basic processes: ingestion, secretion, mixing and propulsion, mechanical and chemical digestion, absorption, and defecation.
Mechanical digestion consists of mastication and movements of the digestive canal that aid chemical digestion.
Chemical digestion is a series of hydrolysis reactions that break down large carbohydrates, lipids, proteins, and nucleic acids in foods into smaller molecules that are usable by body cells
Layers of the Digestive Canal
The basic arrangement of layers in most of the digestive canal, from deep to superficial, is the
- mucosa
- submucosa
- muscular layer
- serosa
The digestive canal is regulated by an intrinsic set of nerves known as the enteric nervous system (ENS) and by an extrinsic set of nerves that are part of the autonomic nervous system (ANS).
The ENS consists of neurons arranged into two plexuses: the myenteric neural plexus and the submucosal neural plexus
Although the neurons of the ENS can function independently, they are subject to regulation by the neurons of the ANS
The myenteric neural plexus is located in the muscular layer, regulates digestive canal motility.
The submucosal neural plexus, which is located in the submucosa, regulates digestive canal secretion.
Parasympathetic fibers of the vagus (X) nerves and pelvic splanchnic nerves increase digestive canal secretion and motility by increasing the activity of ENS neurons.
Sympathetic fibers from the thoracic and upper lumbar regions of the spinal cord decrease digestive canal secretion and motility by inhibiting ENS neurons.
The peritoneum is the largest serous membrane of the body; it lines the wall of the abdominal cavity and covers some abdominal organs.
Folds of the peritoneum include the mesentery, mesocolon, falciform ligament, lesser omentum, and greater omentum
The stomach connects the esophagus to the duodenum.
The principal anatomical regions of the stomach are the cardia, fundus, body, and pyloric part
Adaptations of the stomach for digestion include gastric folds; glands that produce mucus, hydrochloric acid, pepsin, gastric lipase, and intrinsic factor; and a three-layered muscular layer.
Among the substances the stomach can absorb are water, certain ions, drugs, and alcohol
The pancreas consists of a head, a body, and a tail and is connected to the duodenum via the pancreatic duct and accessory duct
Endocrine pancreatic islets secrete hormones, and exocrine pancreatic acini secrete pancreatic juice.
Pancreatic juice contains enzymes that digest
- starch (pancreatic amylase),
- proteins (trypsin, chymotrypsin, carboxypeptidase, elastase),
- triglycerides (pancreatic lipase)
- nucleic acids (ribonuclease and deoxyribonuclease)
The liver has left and right lobes; the left lobe includes a quadrate lobe and a caudate lobe. The gallbladder is a sac located in a depression on the posterior surface of the liver that stores and concentrates bile.
The lobes of the liver are made up of lobules that contain hepatocytes (liver cells), sinusoids, stellate reticuloendothelial cells, and a central vein.
Hepatocytes produce bile that is carried by a duct system to the gallbladder for concentration and temporary storage.
Bile’s contribution to digestion is the emulsification of dietary lipids.
The liver also functions in carbohydrate, lipid, and protein metabolism; processing of drugs and hormones; excretion of bilirubin; synthesis of bile salts; storage of vitamins and minerals; phagocytosis; and activation of vitamin D.
The small intestine extends from the pyloric sphincter to the ileal orifice. It is divided into duodenum, jejunum, and ileum.
Its glands secrete fluid and mucus, and the circular folds, intestinal villi, and microvilli of its wall provide a large surface area for digestion and absorption.
Microvillous border enzymes digest α-dextrins, maltose, sucrose, lactose, peptides, and nucleotides at the surface of mucosal epithelial cells
Digestive system includes six basic processes:
- Ingestion – introducing food into the alimentary canal
- Secretion – enzymes secreted along the GI tract to begin chemical breakdown
- Mixing and propulsion
- Chemical and mechanical digestion
- Absorption
- Defecation
The GI tract is regulated by an intrinsic set of nerves know as the enteric nervous system (ENS) and by an extrinsic set of nerves that are a part of the ANS.
ENS
Myenteric plexus – regulates GI tract motility
Submucosal plexus – regulates GI secretion
Principal anatomic regions of the stomach
Esophageal sphincter Cardia Fundus Body Pylorus Pyloric sphincter Oblique, 3rd layer of muscle
Stomach connects the esophagus to the duodenum
Empty about 50 mL volume but can expand to 3-4L
3-4L of gastric juice produced daily
Converts bolus of food into paste like chyme
stomach glands
Rugae – glands which produce mucus Hydrochloric acid – released by parietal cells Pepsin – released by chief cells Gastric lipase – g-cell Intrinsic factor
Pancreas
Consists of a head, body and a tail and is connected to the duodenum via the pancreatic duct and accessory duct
Endocrine pancreatic islets secrete hormones and exocrine acini secrete pancreatic juice
-Pancreatic juice contains enzymes that digest starch (pancreatic amylase), proteins (trypsin, chymotrypsin, carboxypeptidase, and elastase), triglycerides (pancreatic lipase) and nucleic acids (ribonuclease and deoxyribonuclease)
Liver Is composed of 4 lobes, 2 left and right
Lobes are made up of lobules that contain hepatocytes, sinusoids, stellate reticuloendothelial (Kupffer) cells and a central vein
- Hepatocytes produce bile that is carried by a duct system to the Gallbladder for concentration and storage
- Bile emulsifies dietary lipids by allowing lipid digesting enzymes to digest and be absorbed
-Liver also functions in carbohydrate, lipid, and protein metabolism. Processes drugs and hormones. Excretes bilirubin. Stores vitamins and minerals, phagocytosis and activation of vitamin D
Gallbladder
a sac located on the posterior surface of the liver that concentrates bile and secretes bile into the duodenum
Small Intestine
Extends from the pyloric sphincter to the ileocecal sphincter, divided into three parts
Duodenum – chemical digestion
Jejunum – most nutrient absorption
Ileum – vitamins a, b, d, k absorbed
The small intestine glands secrete fluid and mucus. The circular folds, villi and microvilli of its wall provide large surface area for digestion and absorption
- Mechanical digestion involves segmentation and migrating motility complexes
- Completes digestion of carbohydrates, proteins, and lipids, begins and completes digestion of nucleic acids
- Most of the nutrient absorption occurs in the small intestine. Absorption occurs via diffusion, facilitated diffusion, osmosis, and active transport.
Large Intestine
Extends from the ileocecal sphincter to the anus
- Divided into the cecum, colon, rectum, and anal canal
- Mucosa contains many goblet cells and the muscularis consists of teniae coli and haustra
- Mechanical movements include haustral churning, peristalsis and mass peristalsis
The last stages of chemical digestion occur in the large intestine through bacterial action
Substances are further broken down
Vitamins are synthesized
Water, ions and vitamins are absorbed
Feces consists of water, inorganic salts, epithelial cells, bacteria, and undigested foods
Defecation is a reflex aided by voluntary contractions of the diaphragm and abdominal muscles, and relaxation of the external anal sphincter
GI Summary what is released and what is absorbed
- Oral cavity – saliva amylase (enzyme) begin carbohydrate breakdown – no absorption
- Stomach – gastric juice, HCl-, pepsin (protein breakdown), intrinsic factor (helps absorption of B12) , gastrin (regulates HCl-) – can absorb alcohol, certain drugs
GI Summary what is released and what is absorbed
- Liver – secretes bile
- Gallbladder – bile dilutes acid and emulsifies fat
- Pancreas – exocrine secretes pancreatic juice
GI Summary what is released and what is absorbed
- Small intestine – secretes mucus electrolytes and water (lubricates and protects) – absorbs carbohydrates, vitamin B12 and small amounts of protein
- Large intestine – mucus secreted – water and salt absorbed, bacteria act on undigested material to be absorbed
Energy Transfer
-Nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD) are coenxymes which carry hydrogen atoms during coupled oxidation-reduction actions
- Oxidation is the removal of electrons from a substance
- Reduction is the addition of electrons to a substance
ATP can be generated three ways
Substrate level phosphorylation
Oxidative phosphorylation
Photophosphorylation
