Digestive System ctd.

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Zool1011 A. Williams

The Pharynx

structure of the digestive system that has a deep layer of longitudinally oriented skeletal muscles and a superficial layer of circular skeletal muscles divided into superior, middle and inferior pharyngeal constrictors.

superior, middle, and inferior pharyngeal constrictors

they force food downward during swallowing as they are continuous with the esophagus

The Esophagus

a straight muscular tube extending from a level of the larynx as a continuation of the inferior pharyngeal constrictor. It runs parallel and posterior to the trachea to a level of the primary bronchi, at which point, it moves anterior and to the left to penetrate the diaphragm through the esophageal hiatus. It opens into the stomach by way of the gastroesophageal (cardiac) sphincter

The Stomach

a muscular sac in the upper left abdominal cavity immediately inferior to the diaphragm. It functions primarily as a food storage organ. When empty, is has a volume of 50 ml. When very full, it may hold up to 4 l. It mechanically breaks up food particles, liquefies the food (bolus), and begins the chemical digestion of proteins and a small amount of fat, producing a mixture of semi-digested food called chyme.

Chyme

semi-digested food.

Lesser curvature/ greater curvature

The stomach is J-shaped, with a ____ on its medial margin, and a ______ along its lateral margin.

The stomach is divided into four regions

the cardiac region, fundic region, body, and pyloric region.

Pyloric Sphincter

The pyloric region terminates at the ________, a muscular ring leading to the duodenum.

Muscularis propria/ longitudinal layer/ circular layer/ oblique layer:

_____, the three layers of smooth muscle responsible for the churning action of the stomach; outer _____, middle _____, and inner _____

Mucosa & submucosa/ rugae [wrinkles]

_____ and _____form folds called _____ within the interior of the stomach for gastric expansion

The Liver

a reddish-brown gland located inferior to the diaphragm in the right hypochondriac and epigastric regions. It is the largest gland of the body and performs a tremendous variety of functions, including the secretion of bile for digestive purposes.

The liver has four lobes

right lobe, left lobe, and two inferior subdivisions of the right lobe... quadrate and caudate lobes

falciform ligament

separates the right & left lobes of the liver.

round ligament

exists in the liver as an inferior extension of the falciform; it is a remnant of the umbilical vein

caudate lobe

lobe of the liver that occurs between the inferior vena cava and the falciform ligament.

quadrate lobe

lobe of the liver that occurs between the gallbladder and falciform ligament

gallbladder

adheres to a depression on the inferior surface of the liver between the right and quadrate lobes

porta hepatis [gateway to liver]

on the inferior surface, is the site of vessel and duct entry to and from the liver

Hepatocytes/ hepatic lobules/ central vein

The liver parenchyma consists of _____ mostly arranged in cylinders called ______; about 1 mm in diameter and 2 mm long; the center is identified by a _____ passing through its core

bile canaliculi/ bile ductules

The liver secretes bile into narrow channels, ______, between sheets of hepatocytes. Bile passes from canaliculi into the small ________.

Hepatic ducts/ common hepatic duct

From the ductules, bile exits the liver by the right and left _____ _____. These two ducts converge to form the _____ _____ _____

common bile duct

formed from the union of the common hepatic duct and the duct from the gallbladder, the cystic duct.

Hepatopancreatic ampulla

The common bile duct joins the pancreatic duct, forming the _____ _____ with distal sphincter. The sphincter regulates the passage of bile and pancreatic secretion into the duodenum.

The Pancreas

a soft, spongy gland posterior to the greater curvature of the stomach and outside the peritoneal cavity (retroperitoneal). It has both endocrine and exocrine functions.

pancreatic islets

The endocrine part of the pancreas is the_____, which secrete insulin and glucagon.

Exocrine tissue

Most of the pancreas is _____ that secretes 1,200-1,500 ml of pancreatic juice per day. This secretion ends up in the main pancreatic duct running lengthwise through the gland. It empties into the small intestine through the hepatopancreatic ampulla or by way of a smaller accessory pancreatic duct in some people.

Pancreatic juice

an alkaline mixture of water, enzymes, sodium bicarbonate, and other electrolytes.

Acinar/ gland ducts

The _____ cells secrete the enzymes, whereas the _____ secrete the sodium bicarbonate.

Bicarbonate

buffers the hydrochloric acid from the stomach.

The Small Intestine

Nearly all chemical digestion and nutrient absorption occurs here. Circular folds (plicae circulares), villi, and microvilli all serve to increase the surface area inside. Divided into three parts... duodenum, jejunum, and Ileum.

1. Duodenum [twelve fingers]

constitutes the first 25cm (10"); it receives the stomach contents, pancreatic juice, and bile; stomach acid is neutralized here via pancreatic juices and secretions from duodenal (Brunner's) glands

2. Jejunum [empty]

middle portion of the small intestine; extends approximately 2.5m (8'); duodenal glands are typically absent since chyme has been neutralized by this point

3. Ileum [twisted]

distal portion of the small intestine; forms the last 3.6m (12'); ends at the ileocecal junction; histologically, it has an increased number of goblet cells in the mucosa and lymphoid tissue (Peyer's patches) in the submucosa

ileocecal junction

where the small intestine joins the large intestine

Villi (sin. Villus)

the fingerlike projections of the intestinal mucosa which maximize its absorptive surface area; the largest of these are in the duodenum; These become progressively smaller distally. They are covered with two kinds of epithelial cells— columnar absorptive cells and mucus-secreting goblet cells

The core of the villus is filled with areolar tissue containing a capillary network

an arteriole, a venule, and a lymphatic capillary called a lacteal for the adsorption of emulsified fats

Chyle

The milky fluid produced from digested fats. It is conveyed from lacteals into larger lymphatic vessels; from the lymphatics, it is eventually transferred to the venous circulation

Caecum

a blind pouch of the large intestine inferior to the ileocecal valve. Attached to its lower end is the vermiform appendix.

Ascending colon

begins at the ileocecal valve and passes up the right side of the abdominal cavity near the right lobe of the liver.

Transverse colon

extension of the ascending colon that passes horizontally across the upper abdominal cavity,

Descending colon:

the transverse colon turns 90o downward, and becomes the _____ _____.

Sigmoid colon/ Rectum

At the pelvic inlet, the colon turns medially and downward, forming a roughly S-shaped portion called the_____. Within the pelvic cavity, the colon straightens and becomes the _____.

Rectal valves

The rectum has three internal folds called _____ which enable it to retain feces while passing gas (flatus).

Anal Canal

The final 3 cm of large intestine is the _____ which passes through the levator ani muscle and terminates at the anus. Here the mucosa forms longitudinal ridges (anal columns) with depressions between them (anal sinuses).

Internal anal sphincter/ external anal sphincter

The anus is regulated by two sphincters—an _____ composed of smooth muscle, and an ______ composed of skeletal muscle.

The Anus

the external orifice of the anal canal

Anal verge

The surrounding external epithelium forms the ______ (analogous to vermillion border of oral labia) which is the point where the non-keratinized stratified squamous epithelium of the anal canal becomes true keratinized skin marked by the presence of hair follicles and integumentary glands.

Mucosa of the Large Intestine

has a simple columnar epithelium in all regions except the anal canal, where it is non-keratinized stratified squamous epithelium. The surface is rather flat in appearance; there are no circular folds or villi

Intestinal crypts (crypts of Lieberkühn)/ goblet cells:

_____ are abundant and deep compared to those of small intestine; _____ are most abundant in the intestinal crypts of the colon

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