Chapter 23 objectives: the digestive system

Saliva

97% water (hypo-osmotic), slightly acidic, pH can vary, solutes include: electrolytes (Na, K, Cl, PO4, HCO3), salivary amylase (breakdown of starch and glycogen), glycoprotein mucin, lysozyme, IgA, and metabolic wastes, salivation is increased by PSNS (serous enzyme rich saliva), the SNS stimulation leads to mucin-rich saliva release, extremely strong sympathetic stimulation leads to dry mouth.

Parietal cells

HCl (pH 1.5-3.5, activates pepsin), intrinsic factors are glycoprotein which is required for Vitamin B12 absorption

LLLLLOOOOKKKK AAAATTTT FFFIIIGGGUUURRREEESSS!!!!!

NNNNNOOOOOWWWWWW!!!!!!!

LLLLOOOOKKKK AAATTT PPPRRREEEVVVIIIOOOOOUUUUUSSSS CCCHHHAAAPPPTTTEEERRRR!!!!

NNNNNOOOOOWWWWWWW!!!!

LOOK AT FIGURES!!!!!

THERE ARE MANY!!!

Mucous neck cells

acidic mucus

Sinusoid

blood percolates through these, the nutrients are removed and processed, wastes are removed, blood ends up in the central vein of each lobule, and eventually to the inferior vena cava.

Chemical digestion

break down food molecules into chemical building blocks that can be absorbed (monomers), ends in small intestine.

Metaplasia

can be Barrett's esophagitis, where the tissue around the sphincter switches from pseudostratified columnar to simple squamous epithelium.

GERD

can be detected by the first symptom of gastroesophageal reflux disease, which is heartburn, acidic gastric juice refluxes into the esophagus.

Regulation of pancreatic juice secretion

chime entering duodenum causes duodenal enteroendocrine cells to release CCK and secretin, CCK and secretin enter the bloodstream, then CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3-rich pancreatic juice.

Bile salts

cholesterol derivatives, distribute fats throughout watery intestinal contents (emulsify), provide large surface area for fat-digesting enzymes to work on, facilitate fat and cholesterol absorption, recycled through enterohepatic circulation that is returned to liver through the hepatic portal blood, resecreted in newly formed bile.

3 modifications for absorption

circular folds (plicae circulares), villi which has epithelia that is absorptive columnar enterocytes, and microvilli that create a brush border and has brush border enzymes.

Pancreatic juice

clear about 1.5 L/day, made of water, enzymes, bicarbonate ions (by epithelial cells lining the ducts) pH 8, in addition to proteases: pancreatic amylase, lipases and nucleases.

Digestive processes of small intestine

digestion and absorption of fats, carbs, and proteins, relies on bile, digestive enzymes, and bicarbonate ions released from liver and pancreas, segmentation takes place and is initiated by interstitial cells of Cajal, those in the duodenum depolarize more frequently than those in ileum, the contents get moved toward the ileocecal valve, intensity of segmentation is altered by long and short reflexes and hormones, PSNS enhances and SNS decreases activity, true peristalsis occurs after absorption.

Alimentary canal (GI tract)

digests and absorbs, includes: mouth, pharynx, esophagus, stomach, small intestine, and large intestine

Mesentery

double layer of peritoneum that provides routes for blood vessels, lymphatics, and nerves, it holds organs in place and also stores fat.

Chyme

fluid and food inside of the stomache.

Gallbladder

green muscular sac the size of a kiwi, found on ventral surface of liver, stores bile that is not immediately needed for digestion, concentrates bile by absorbing water and ions, bile is expelled through its cystic duct then flows into bile duct, too much cholesterol or too few bile salts cause crystallization of cholesterol to form gallstones.

Long neural reflexes

have external and internal stimuli, the external stimuli includes sight, smell, taste, and thought of food, the internal stimuli activate all the receptors, and the impulses go to the central nervous system, which sends out extrinsic visceral (autonomic) efferents to the local (intrinsic) nerve plexus (the "gut brain") and the effectors are smooth muscles or glands and the response is a change in the contractile or secretory activity.

Accessory digestive organs

include the teeth, tongue, and gallbladder

Mucosa

includes the epithelium, lamina propria, and muscularis mucosae. Enter lion please much meat.

Muscularis externa

includes the longitudinal muscle and circular muscle.

Accessory glands

includes the salivary glands, liver, and pancreas.

Serosa

includes: epithelium (mesothelium), and connective tissue.

Digestive processes

ingestion, propulsion, mechanical digestion, chemical digestion, absorption, and defecation. The digestive tract is a "disassembly line" I promise my dog can do absolute duty.

Alimentary canal includes

intrinsic nerve plexuses, mucosa, submucosa, muscularis externa, serosa, lumen, and mesentery. From esophagus to anal canal, have walls with these four tunics. just look at figure

Lobule

is hexagonal, it has a portal triad that has a hepatic artery branch, a hepatic portal vein branch (that carries venous blood with nutrients from digestive vescera), and a bile duct.

Submandibular

is serous and mucous (which produces mucous) glands

Liver

largest gland of the body, accessory organ associated with small intestine, has many metabolic and regulatory functions, and the digestive functions are to produce bile for export to duodenum, the bile emulsifies fat, it is locates primarily in the upper right quadrant under the diaphragm protected by the ribs, has 4 lobes, and the falciform ligament separates the right and left lobes anteriorly, it also suspends the liver from the diaphragm and anterior abdominal wall.

Large intestine

major function is to absorb H20 from indigestible food residues and eliminate them from body as feces, mucosa is simple columnar epithelium with no circular folds, villi, nor digestive enzyme-secreting cells, mucosa is thicker than in small intestine with deep crypts that have mucus-producing goblet cells that ease feces movement and protects the wall from acids and gases produced by bacteria in colon, anal columns are lined by stratified squamous epithelium.

Chief cells

make pepsinogen

Absorption

most nutrients are absorbed through small intestinal villi by active transport (ATP) to capillary in villus and on to hepatic portal vein to liver, exception is lipids that have passive diffusion to lacteals in villus.

Sublingual

mostly mucous glands

4 types of secretory cells

mucous neck cells, parietal cells, chief cells, enteroendocrine cells.

Parotid

only serous glands, which secrete water, enzymes, ions, and mucin

Extrinsic salivary glands

parotid, submandibular, and sublingual

Retroperitoneal organs

parts of small and large intestine, this also includes the pancreas.

Gastric contractile activity

peristaltic waves act primarily in pyloric region to mix and move chime through pyloric valve ( about 3 ml at a time), interstitial cells of cajal are in the longitudinal muscle layer and are pacemaker cells that set BER (basic electrical rhythm) with a cyclic slow waves of stomach about 3 waves/ min, factors that increase secretory activity also increase the strength of stomach contraction.

Propulsion

peristaltic waves move from the fundus toward the pylorus.

Gastroesophageal sphincter

physiological sphincter, kept closed by diaphragm when food is not being swallowed

Esophagus

pierces the diaphragm at esophageal hiatus, enters stomach at cardiac orifice contains the gastroesophageal sphincter and is made of stratified squamous epithelium.

Enteroendocrine cells

release hormones directly in lamina propria, these hormones are gastrin, histamine, endorphins, serotonin, cholecystokinin, and somatostatin CHEGSS

Tongue

repositions the food between teeth during chewing, helps form food bolus, helps form consonant sounds, fungiform and circumvallate papillae house taste buds.

Anatomy of stomach wall

simple columnar lining epithelium is composed of mucous cells that secrete protective alkaline mucus, gastric glands that produce gastric juices

Oral cavity

site for chewing, mixing, and moistening food, stratified squamous epithelium, and mucosal cells produce defensins on injury.

Gastric emptying

stomach and duodenum work in tandem, the stomach normally empties within 4 hours after a meal.

Deglutition

swallowing it is the coordination of tongue, soft palate, pharynx, and is over 22 separate muscle groups, is a voluntary buccal phase, involuntary pharyngeal-esophageal phase which is controlled by swallowing center in medulla and lower pons.

Pancreas

tadpole shaped and extends from tail to head, accessory exocrine digestive organ, produces many enzymes that breakdown all categories of foods, this releases pancreatic juice through the main pancreatic duct (fuses with bile duct), acini within the pancreas is full of RER also has an endocrine function where the islets of Langerhans release insulin and glucagon.

Regulation of bile release into small intestine

the chime entering the duodenum causes duodenal enteroendocrine cells to release CCK and secretin, CCK and secretin enter the bloodstream, then bile salts and secretin transported via bloodstream stimulate liver to produce bile more rapidly, CCK causes gallbladder to contract and hepatopancreatic sphincter to relax, then bile enters the duodenum, during cephalic and gastric phases, vagal nerve stimulates gallbladder to contract weakly.

Peritonitis

the inflammation of peritoneum, the causes can be a burst appendix or a piercing abdominal wound.

Short neural reflex

the internal (GI tract) stimuli cause chemoreceptors, osmoreceptors, or mechanoreceptors to stimulate the local (intrinsic) nerve plexus ("the gut brain"), and the effectors include the smooth muscle or glands, the response is the change in contractile or secretory activity.

Grinding

the most vigorous peristalsis and mixing action occur close to the pylorus.

Retropulsion

the pyloric end of the stomach acts as a pump that delivers small amounts of chime into the duodenum, simultaneously forcing most of its contained material backward into the stomach.

Segmentation

they alternately contract and relax, contracting right in the middle of the food so it can break up and mix better, the food mixing and slow food propulsion occur.

Food passes into oro then laryngopharynx

they have stratified squamous epithelium, the outer layer of skeletal muscle helps propel food into the esophagus.

Peristalsis

they move the food along the tract by contracting right behind the food and relaxing in front of it to allow it to flow down the digestive tract.

Small intestine

virtually all absorption happens here, 1st part is the duodenum, 2nd part is the jejunum, 3rd part is the ileum.

Emesis

vomiting, sensory impulses to medullary emetic center.

Bile

yellow-green alkaline solution is composed of bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes.