session 14 - digestive system part 2 - Pancreas, Liver, Small Intestine Flashcards
What are the 2 major ducts of the pancreas that facilitate secretions into small intestine?
- Pancreatic duct (duct of Wirsung)
- Accessory duct (duct of Santorini)
Name the exocrine portion of the pancreas and its function?
oAcini -dark clusters
- 99% of gland
- Exocrine portion
- Secrete pancreatic juice
Name the endocrine portion of the pancreas and its function ?
o Islets of Langerhans-pale staining cells
- 1% of gland
- Endocrine portion
- Secrete hormones glucagon, insulin, somatostatin, and pancreatic polypeptide
Composition and Functions of Pancreatic Juice
oa clear, colourless liquid
oProduced 1.2-1.5 liters/day
opH of 7.1 to 8.2
oContains water, some salts, sodium bicarbonate, and several enzymes
oSodium bicarbonate: converts the acid stomach contents to a slightly alkaline pH (7.1-8.2), halting stomach pepsin activity and promoting activity of pancreatic enzymes
Name the digestive enzymes of pancreatic juice
- Pancreatic amylase: digest Starch
- Pancreatic lipase: digest triglycerides
- Proteases: digest proteins
- Trypsinogen -activated by enterokinase (a brush border enzyme)
- Chymotrypsinogen-activated by trypsin
- Procarboxypeptidase-activated by trypsin
- Proelastase-activated by trypsin
- Trypsin inhibitor -combines with any trypsin produced inside pancreas
Regulation of pancreatic secretions
What hormones are secreted by small intestine to regulate pancreatic secretions?
oSecretin
•Stimulates secretion of pancreatic juice that are rich in bicarbonate ions, promotes normal growth and maintenance of pancreas, enhances effects of CCK.
oGlucose-dependent insulinotropic peptide (GIP)
•Stimulates pancreatic beta cells to release insulin.
oCholecystokinin (CCK)
•Stimulates secretion of pancreatic juice rich in digestive enzymes, promotes normal growth and maintenance of pancreas, enhances effects of secretin. Also Responsible for making gallbladder contract to release its secretion into the small intestine.
Hepatocytes:
Major functional cells of the liver
- Metabolic, secretory, and endocrine functions
- Secrete bile:a yellow, brownish, or olive-green liquid serves as both an excretory product and a digestive secretion.
Explain the function of the Hepatic sinusoids and Central Vein in the liver
Liver sinusoid is a blood vessel that serves as a location for mixing the oxygen rich blood from the hepatic artery and the Nutrient rich blood coming from the gut (portal vein)
The nutrient rich blood is circulating through and the hepatocytes can do all their metabolic functions on the blood. Once that’s all done that fluid/blood goes into the central vein where its destined to then go back into the inferior vena cava
Function of the gallbladder
- To concentrate the bile produced by the liver (ten times more concentrated) by absorbing water and ions.
- To store bile until it is needed in the small intestine.
(Really high concentrated bile stored - when we’ve just had a really high fat meal and we need the bile coming into the small intestine - the contraction of the gallbladder releases empties a really potent form of bile right into the spot we need it to emulsifier those fats)
Define the Blood supply to the liver
and explain why it’s different to other organ blood supply
oDouble blood supply: from
- Hepatic artery: oxygenated blood from branch of the aorta
- Hepatic portal vein: Nutrient rich blood from stomach, spleen and intestines (this normall doesnt happen, veins usually carry the blood away!)
oHepatic vein: All blood eventually leave the liver via hepatic vein
Function of Bile
Play a role in emulsification, the breakdown of large lipid globules into a suspension of small lipid globules.
–Aid in the absorption of lipids following their digestion.
Emulsification - breaks down the large droplets of fat into smaller droplets and increases the surface area.
By increasing surface area the enzymes that we have in our small intestine can eat away readily.
Improves fat digestion
Functions of the liver
oCarbohydrate metabolism
maintains normal blood glucose level by
- Glycogenolysis:Break down glycogen to glucose and release the glucose into the bloodstream
- Gluconeogenesis:Convert certain amino acids, triglyceridesand lactic acid to glucose.
- Glycogenesis: Converts glucose to glycogen and triglycerides for storage.
Functions of Liver
oLipid metabolism
- Storage: Hepatocytes store some triglycerides;
- Lipolysis: Break down fatty acids to generate ATP;
- Lipogenesis: Synthesize lipoproteins, which transport fatty acids, triglycerides, and cholesterol to and from body cells;
- Cholesterol synthesize
- Synthesize bile salts from cholesterol
Functions of Liver
oProtein Metabolism:
- Deamination: Removes NH2 (amine group) from amino acids so can use what is left as energy source
- Urea cycle: Converts resulting toxic ammonia from the removal of NH2 (Deamination) into urea for excretion by the kidney
- Protein synthesis: Synthesizes plasma proteins alpha and beta globulins, albumin, prothrombin, and fibrinogen.
- Converts one amino acid into another amino acids
Some functions of the Liver
oProcessing of drugs and hormones:
- Detoxify substances such as alcohol and excrete drugs such as penicillin, erythromycin, and sulfonamides into bile.
- Chemically alter or excrete thyroid hormones and steroid hormones such as estrogens and aldosterone.
oSynthesis of bile and bile salts
oExcretion of waste products:
•Bilirubin from RBC recycling
Functions of the small intestine
extends from the pyloric sphincter to the ileocecal sphincter
- Mix chyme with digestive juices and bring food into contact with mucosa for absorption
- Completes digestion of carbohydrates, proteins, and lipids; begins and completes digestion of nucleic acids. ( last step of digestion and absorption)
- Absorbs about 90% of nutrients and water that pass through digestive system.
Subdivisions of the small intestine
- Duodenum - 1st part of small intestine, small
- Jejunum - 2nd part, a little longer
- Ileum - 3rd part, the longest
Mucosa layer of the small intestine is composed of
oThe epithelial layer: Simple columnar epithelium
•contains Absorptive cells and Goblet cells
oIntestinal glands: formed by glandular epithelial cells.
•Deep crevices
oLamina propria: areolar connective tissue with mucosa-associated lymphoid tissue (MALT)
(Immune function - Lymph nodules full of lymphatic tissue (b cells and T cells )very important in the gut immune access in the small intestine)
- Solitary lymphatic nodules: most numerous in the distal part of the ileum
- Peyer’s patches: in the ileum
oMuscularis mucosae: smooth muscle
What are the Cells of Intestinal glands:
- Absorptive cell
- Goblet cell
- Paneth cells
- Enteroendocrine cells:
- S cells
- –CCK cells
- –K cells
o Intestinal Juice: the secretion of absorptive , goblet and paneth cells
Submucosa of the small intestine contains
•Duodenal (Brunner’s) glands: In duodenum, secrete an alkaline mucus that helps neutralize gastric acid in the chyme.
Muscularis of the small intestine contains
2 layers of smooth muscles
outer, thinner longitudinal and the inner, thicker circular fibers layer.
oSerosa layer of the small intestine consists of
Visceral peritoneum
•completely surrounds the small intestine except for a major portion of the duodenum.
Name the Special structural features of the small intestine and their function
- Circular folds (Plicae circularis)
- Villi
- Microvilli
oFunction:
•Massive increase in surface area of the small intestine to facilitate the process of digestion and absorption
(If unfolded the Surface area would cover half a tennis court)
Function of the circular folds structure of the small intestine
•Enhance absorption by increasing surface area and causing the chyme to spiral, rather than move in a straight line, as it passes through the small intestine
Function of the villi projections on the small intestine
Finger-like projections of the mucosa
oFunctions:
- Increase the surface area of the epithelium available for absorption and digestion
- Gives the intestinal mucosa a velvety appearance
- Nutrients absorbed by the epithelial cells covering the villus pass through the wall of a capillary or a lacteal to enter blood or lymph, respectively
Functions of the microvilli of the small intestine ?
oFunctions:
- Form brush border, extending into the lumen of the small intestine
- Increase the surface area of the plasma membrane and allows larger amounts of digested nutrients can diffuse into absorptive cells in a given period.
- Contains several brush-border enzymes that have digestive functions
What does intestinal juice contain and its Function
•Contains water and mucus, brush-border enzymes andlysozyme
Function:
•Absorption of substances from the chyme as they come in contact with the villi.
What are the brush border enzymes and their function?
- Carbohydrate digesting enzymes: ɑ-dextrinase, maltase, sucrase, and lactase
- Protein-digesting enzymes:peptidases (aminopeptidase and dipeptidase)
- Nucleotide-digesting enzymes: nucleosidases and phosphatases
Function
- Digestion at brush border
- Digestion in the lumen of the small intestine
What are the two types of mechanical digestion in the small intestine?
oSegmentation:Localized, mixing contractions that occur in portions of intestine distended by a large volume of chyme.
oMigrating motility complex (MMC): peristalsis that occurs in the small intestine that Moves the contents of the small intestine from one end to the other
Regulation of secretion and motility in the small intestine
Explain the role of enteric reflexes and sympathetic impulses?
oEnteric reflexes that respond to the presence of chyme
- increase intestinal motility
- VIP (vasoactive intestinal polypeptide) - ( a hormone ) stimulates the production of intestinal juice
- segmentation depends on distention which sends impulses to the enteric plexus and CNS
–distention ( swelling) produces more vigorous peristalsis (moving the contents of the small intestine from one end to the other)
oSympathetic impulses decrease motility
Describe chemical digestion in the small intestine
oDigestion by pancreatic juice, bile, and intestinal juice.
oBreakdown of nutrients into absorbable forms
- carbohydrates
- proteins
- lipids
