Week 12: Chp 55: Assessment of Gastrointestinal Function Flashcards
What is the gastrointestinal system responsible for?
intake, digestion, and elimination of foods and fluids, and proper functioning is key to adequate nutrition
- known as the alimentary tract, begins with the esophagus and ends with the anus
- responsible for the digestion and absorption of nutrients and expelling of metabolic wastes
What are the two divisions of the GI system?
- Alimentary Tract
- Accessory Organs
If normal intake can not be through the mouth, how else is nutrition delivered?
nutrition may be delivered directly to the stomach or small intestine
Where does digestion begin?
begins in the mouth and continues in the stomach and small intestine
-the large intestine is responsible for reabsorption of fluids and electrolytes and elimination of waste products
What is the large intestine responsible for?
the reabsorption of fluids and electrolytes and elimination of waste products
What are the accessory organs?
teeth, tongue, salivary glands, liver, gallbladder, and pancreas
The GI tract consists of what?
the mouth, pharynx, esophagus, stomach, small intestine, and large intestine
The Mouth
where digestion begins, where the mechanical (mastication) and chemical breakdown of food occurs
The mechanical breakdown of ingested food occurs through the process of what?
mastication (chewing)
Mastication
- chewing
- the mechanical breakdown of ingested food
- saliva, which contains amylase, lipase, and lysozyme, is excreted from a group of glands: parotid, sublingual, and submandibular glands
- amylase is responsible for the chemical breakdown of carbohydrates, whereas lipase chemically digests fat; digestion of proteins actually occurs in the stomach
- lysozyme has antimicrobial properties that destroy the cell wall of bacteria in the mouth
Chemical breakdown
Saliva, which contains amylase, lipase, and lysozyme, is excreted from a group of glands: parotid, sublingual, and submandibular glands
- amylase is responsible for the chemical breakdown of carbohydrates, where a lipase chemically digests fat
- lysozyme has antimicrobial properties that destroy the cell wall of bacteria in the mouth
Deglutition
“swallowing”
consists of two phases and involves the pharynx, esophageal muscles, and the following cranial nerves CN V (trigeminal), CN VII (facial), CN IX (glossopharyngeal), and CN XII (hypoglossal)
-the buccal (mouth) phase involves the tongue and the pharyngeal muscles, and the esophageal phase involves the palate and esophageal muscles
-peristaltic movement of the esophagus moves the bolus of food into the stomach
2 phases of deglutition
“Swallowing”
- Buccal (mouth) phase: involves the tongue and the pharyngeal muscles
- Esophageal phase: involves the palate and esophageal muscles
The Esophagus: What is it and the location
is a hollow muscular tube that extends from approximately the vertebral levels of C6 to T7
-it is positioned inferior (below) to the pharynx and posterior (behind) to the trachea and passes through the diaphragm via a space known as the esophageal hiatus and then connects to the stomach
The Esophagus and what it does
the peristaltic movements push the food bolus downward as the esophagus constricts above the bolus and dilates below the bolus
-in normal digestion, the lower esophageal sphincter protects the esophageal mucosa from regurgitation of partially digested food and the acid produced in the stomach
What happens in the stomach?
digestion of protein -specialized cells secrete chemicals essential to the digestive functions of the stomach >Mucous Cells >Parietal Cells >Chief Cells >Enteroendocrine Cells
Stomach Cells: Mucous cells
secrete mucus that protects the stomach lining
Stomach Cells: Parietal Cells
secrete hydrochloric acid that aids in the conversion of food to chyme (partly digestive semiliquid food), as well as convert gastric lipase and pepsinogen to active forms
-also secrete intrinsic factor, a chemical needed for the absorption of vitamin B12, an important component of hemoglobin synthesis
Stomach Cells: Chief Cells
secrete the enzymes gastric lipase, which digests approximately 15% of dietary fat, and pepsinogen, which is responsible for protein digestion
Stomach Cells: Enteroendocrine cells
secrete hormones needed for digestion:
>Gastrin: stimulates secretion of hydrochloric acid and enzymes, and intestinal motility
>Serotonin: stimulates gastric motility
>Histamine: stimulates secretion of hydrochloric acid
>Somatostatin: inhibitory hormone that delays emptying of the stomach, reduces absorption in the small intestine, and inhibits secretions from the gallbladder and pancreas
Gastric Motility is influenced by?
smooth muscle regulated by the sympathetic and parasympathetic nervous systems
Before meals the stomach has a volume of what?
has a volume of 50 mL, but can hold up to 4 L at its fullest
-swallowing stimulates the swallowing center in the medulla oblongata to signal the stomach to stretch to receive food
What does the peristaltic contraction controlled by the pacemaker cells of the smooth muscle do in the stomach?
churn the food and mix it with gastric secretions
The stomach has 4 landmark areas
- the cardiac area (small segment below the gastroesophageal sphincter)
- fundic area (uppermost segment)
- corpus (body, and largest segment)
- pyloric area (lowermost segment and consists of the antrum, a narrow funnel that leads to the pyloric canal)
The small area right beyond the pyloric canal of the stomach is called the what?
the pylorus, and it connects to the duodenum
The passage of chyme into the duodenum is controlled by what?
the pyloric sphincter, which is a ring of smooth muscle surrounding the pylorus
Rugae
the lining the of stomach has folds known as rugae that allow for stretching of the lining in order to facilitate absorption
Through hormonal and neurological feedback systems, gastric secretion activity occurs in three phases:
- Cephalic phase
- Gastric Phase
- Intestinal Phase
Gastric Secretion Activity: Cephalic Phase
First phase
-mental and sensory stimuli activate the vagus nerve (CN X) to stimulate gastric secretion
Gastric Secretion Activity: Gastric Phase
Second Phase
-the presence of carbohydrates, fat, and partially digested protein stimulates the release of acetylcholine, histamine, and the hormone gastrin
>these chemicals stimulate the parietal cells to secrete hydrochloric acid and intrinsic factor, whereas the stimulation of the chief cells results in the secretion of pepsinogen
>Hydrochloric acid converts pepsinogen to pepsin, the enzyme responsible for the digestion of proteins
Gastric Secretion Activity: Intestinal Phase
the presence of chyme stretches the duodenum
-initially, the duodenal stretch leads to the release of intestinal gastrin and the stimulation of the vagus nerve, which stimulates the stomach; however, the presence of acid and semi digested food in the duodenum also begins the inhibitory phase; signals from the medulla stimulate the sympathetic and parasympathetic nervous systems, which inhibit gastric activity; the secretion of secretin and cholecystokinin also inhibits gastric motility and enzyme secretions
The Liver
second largest organ of the body (skin is first)
- attached beneath the diaphragm, and positioned largely across the right upper quadrant and extends into the left upper quadrant
- segmented into 4 lobes separated by ligaments that suspend the liver under the rib cage and diaphragm in the abdominal cavity
- the inferior view has two grooved areas where the inferior vena cava, hepatic vein and artery, common hepatic duct, and gallbladder are positioned
- 25% of the cardiac output flows through the dual blood supply system, an oxygen-rich supply from the hepatic artery and a nutrient-rich supply from the portal vein
- 20% of the bodys total oxygen consumption is utilized by the liver
- the blood supply from the portal vein receives nutrients from the stomach, intestines, spleen, and pancreas
Major functions of the liver
-absorption and metabolism of nutrients
-degradation of toxins, hormones, and medications
-synthesis of proteins (clotting factors, albumin, several clotting factors, fibrinogen, and prothrombin)
>Kupffer cells are responsible for detoxifying the blood of bacteria
-liver aids in digestion of fat by producing bile acids and lecithin
List of Functions of the liver
- Digestion
- Vitamin and mineral metabolism
- Protein metabolism
- Carbohydrate Metabolism
- Lipid Metabolism
- Plasma protein synthesis
- Detoxification
- Phagocytosis
Liver Functions: Digestion
- emulsification of fat
- absorption of dietary fat
Liver Functions: Vitamin and mineral metabolism
- storage of vitamins A, B12, D, Ferritin
- Excretes excess calcium
Liver Functions: Protein Metabolism
- deamination and transamination of amino acids
- converts ammonia to urea
Liver Functions: Carbohydrate Metabolism
- conversion of dietary fructose and galactose to glucose
- conversion of lactic acid to pyruvic acid or glucose-6-phosphate
- storage and release of glycogen
- synthesizes glucose from fat and amino acids when glycogen stores are low
Liver Functions: Lipid metabolism
- synthesis of fat, cholesterol, and phospholipids
- produces ketone bodies, VLDL, and HDL
Liver Functions: Plasma Protein Synthesis
synthesizes blood plasma proteins: albumin, fibrinogen, prothrombin
Liver Functions: Detoxification
detoxifies alcohol and medications that are metabolized in the liver; deactivates thyroxine and metabolizes bilirubin and excretes it as bile pigment
Liver Function: Phagocytosis
aids in the elimination of bacteria in the blood
-Kupffer cells detoxify the blood of bacteria
Kupffer Cells
cells in the liver that are responsible for detoxifying the blood of bacteria
What constitute the majority of hepatic cells and are responsible for many of the functions of the liver?
hepatocytes
The Gallbladder
located in the right upper quadrant, the gallbladder, a pear-shaped sac, is attached to the inferior portion of the liver and is responsible for bile storage and concentration
-bile is needed for the emulsification of fat
Bile
need for the emulsification of fat
- contains phospholipids (lecithin), bile pigments (bilirubin), and bile salts
- about 500 to 1000 mL of bile is excreted from the liver and stored in the gallbladder; Bile leaves the liver and passes through a ductal system: Hepatic ducts–>common hepatic ducts–>cystic duct and into gallbladder
What happens to bile after ingestion of a meal?
after ingestion of a meal, bile exits the gallbladder via the cystic duct that communicates with the bile duct
- the terminal end of the bile duct connects with the terminal end of the pancreatic duct to form the hepatopancreatic ampulla in the pancreas; this ampulla connects with the duodenal papilla, which contains the hepatopancreatic sphincter (sphincter of Oddi) that opens during digestion and releases bile to the small intestine to emulsify the dietary fat
- bile is released from the gallbladder to the duodenum of the small intestine
The pancreas position and location
a gland that is positioned inferior (below) to the stomach in the right upper quadrant
- it has 3 landmarks: the head, which is surrounded by the duodenum; the body, and the tail
- the pancreatic duct is in the middle of the pancreas and extends from the tail to the head, where it joins the bile duct
Endocrine Functions of the pancreas
-produces insulin and glucagon
Exocrine Functions of the Pancreas
as an exocrine gland, it secretes 1200 to 1500 mL daily of liquid known as pancreatic juice that contains water, sodium bicarbonate, proenzymes needed for protein digestion, and the pancreatic enzymes needed for carbohydrate (amylase), fat (lipase, phospholipase A, and cholesterol esterase), and DNA and RNA (deoxyribonucleases, ribonucleases) digestion
- the digestion of these nutrients is essential for cellular metabolism
- the release of these enzymes is secreted through the acinar cells of the pancreas and is regulated by neural and hormonal feedback systems
What does pancreatic juice contain?
-water
-sodium bicarbonate
-proenzymes needed for protein digestion
-pancreatic enzymes needed for carbohydrate, fat, and DNA and RNA digestion
>carbohydrate (amylase)
>fat (lipase, phospholipase A, cholesterol esterase)
>DNA and RNA (deoxyribonucleases, ribonucleases)
What stimulates the release of pancreatic enzymes during the cephalic phase?
Acetylcholine
How Pancreatic enzymes are released
pancreatic enzymes are stored in the duodenum and released as chyme arrives
- cholecystokinin is released from the jejunum and duodenum when gastric acid, long fatty chains, and certain amino acids are present
- the release of cholecystokinin stimulates the release of pancreatic enzymes that contract the gallbladder and relax the hepatopancreatic sphincter for the release of bile into the duodenum
- secretin is released from the small intestine in response to the presence of the acidic chyme in the small intestine; the release of secretin stimulates the liver and pancreas to release sodium bicarbonate, which neutralizes the acidic chyme and protects the intestinal lining
Role of Cholecystokinin
is released from the jejunum and duodenum when gastric acid, long fatty chains, and certain amino acids are present
-the release of Cholecystokinin stimulates the release of pancreatic enzymes that contract the gallbladder and relax the hepatopancreatic sphincter for the release of bile into the duodenum
The role of Secretin
is released from the small intestine in response to the presence of the acidic chyme in the small intestine
-release of secretin stimulates the liver and pancreas to release sodium bicarbonate, which neutralizes the acidic chyme and protects the intestinal lining