question

Who founded the Lunaria island?

answer

Alonzo Mirallas, a selenologist, hence the name of the island

question

Where does the pancreas lie and extend do?

answer

Pancreas lies posterior to the stomach and extends laterally from the duodenum toward the spleen

question

How long is the pancreas and what shape does it make?

answer

It is 15cm and forms a C-shape alongside the duodenum

question

What does retroperitoneal mean? Link this to the pancreas x

answer

situated or occurring behind the peritoneum(serous membrane that forms the lining of the abdominal cavity). The pancreas is retroperitoneal and is firmly bound to the posterior wall of the abdominal cavity

question

What texture does the surface of the pancreas have?

answer

a lumpy, lobular texture, with a thin, transparent capsule of connective tissue that wraps the entire organ

question

Describe the blood supply of the pancreas

answer

branches of both the coeliac a and superior mesenteric. splenic artery runs along the top margin of the pancreas, and supplies the neck, body and tail of the pancreas through its pancreatic branches, the largest called the greater pancreatic artery

question

Describe the nervous supply of the pancreas

answer

Parasympathetic fibres from the vagus nerve. Sympathetic fibres travel across from branches of the splanchnic nerves

question

What divides the interior of the pancreas into distinct lobules?

answer

Partitions of connective tissue divide the interior of the pancreas into distinct lobules. The blood vessels and tributaries of the pancreatic ducts are situated within these connective tissue septa

question

What sort of gland is the pancreas an example of and what is this?

answer

The pancreas is an example of a compound tubuloalveolar gland, a gland that has secretory units of short tubules

question

What do the ducts end in in each lobule?

answer

In each lobule, the ducts branch repeatedly before ending in blind pockets called pancreatic acini.

question

What is each pancreatic acinus lined with? What do the acinar cells produce?

answer

Each pancreatic acinus is lined with simple cuboidal epithelium. The acinar cells produce the pancreatic enzymes which are released into the duodenum via the ducts

question

What do the ductal cells in the pancreas release?

answer

The ductal cells release bicarbonate ions, which helps to neutralise the stomach acidity of the chyme

question

What do pancreatic islets do, where do they lie, and what percentage of the pancreas' cell population do they make up?

answer

Pancreatic islets, the endocrine tissues of the pancreas, are scattered among the acini. The islets account for only 1% of the cell population of the pancreas.

question

What segments is the small intestine composed of?

answer

3 segments - duodenum, jejenum, and the ileum

question

What is the small intestine the primary site of?

answer

absorption and digestion of nutrients, as a result the structure is specifically adapted for these functions

question

What does the small intestine's length provide?

answer

It's length provides a large surface area for digestion and absorption. This surface area is further increased by the presence of circular folds (plicae circulares), villi, and microvilli

question

What is the entire inner wall of the small intestine marked by?

answer

marked by circular folds of a mucous membrane called the plicae circulares, permanent ridges that do not lose their elasticity when the intestine is distended

question

What is each microvilli covered by and why?

answer

a fuzzy coat known as the brush border which contains many digestive enzymes

question

Where does the small intestine begin at and where does it end at?

answer

Begins at the pyloric sphincter and ends at the opening of the large intestine

question

What's the ileocecal valve and what does it do?

answer

The ileocecal valve, a sphincter between the small and large intestine, is normally closed so that the contents of the large intestine cannot reflux into the small intestine

question

List four types of cells found in the small intestine

answer

absorptive cells, goblet cells, granular cells, enteroendocrine cells

question

What does each of the four types of cell in the small intestine do?

answer

absorptive cells: digestive enzymes, absorption, goblet cells: produces mucus, granular cells (cells of Paneth): produces enzymes (lysosome, capable of phagocytosis), enteroendocrine cells: hormone production

question

what hormones do enteroendocrine cells produce?

answer

secretin, CCK, GIP

question

What is found at the base of the intestinal villi?

answer

entrances to intestinal glands (crypts of Lieberkuhn). These glandular pockets extend deep into the underlying lamina propria

question

What glands does the duodenum have?

answer

numerous mucosal glands, both in the epithelium and deep to it. It' submucosa has duodenal glands (Brunners glands)

question

What do duodenal/Brunners glands in the submucosa produce?

answer

Mucus that protects the epithelium from the acidity of chime leaving the stomach

question

What does the duodenum contain that helps raise the pH of chime?

answer

Contains bicarbonate ions which help to raise the pH of chime. The pH increases from 1-2 to 7-8

question

Describe the intestinal blood supply

answer

The superior mesenteric artery provides blood to the entire small intestine and extends branches up until the middle third of the transverse colon. The inferior mesenteric artery provides blood to the left third of the transverse colon and the sigmoid col

question

What digestive/absorptive processes take place in the duodenum?

answer

Mixing secretions from the pancreas, liver, and its own food, neutralisation of acid, further digestion and absorption

question

What digestive/absorptive processes take place in the jejunum?

answer

Completing breakdown of food, and beginning nutrient absorption

question

What digestive/absorptive processes take place in the ileum?

answer

Nutrient absorption, absorption of bile in the terminal ileum

question

What is the folded surface of the small intestine covered with?

answer

Finger-like projections called villi

question

What is the surface of villi formed mainly by?

answer

formed mainly by columnar absorptive epithelial cells (enterocytes) bound by tight junctions at their apical surfaces

question

What does the mucosal surface of the enterocytes that form villi consist of?

answer

Consists of many tiny processes called microvilli which constitute the brush border. Because the microvilli greatly increase the surface area of the plasma membrane, larger amounts of digested nutrients can diffuse into absorptive cells in a given period

question

How many litres of intestinal juice is secreted each day?

answer

About 1-2L of intestinal juice, a clear yellow fluid, is secreted each day. The intestinal fluid is slightly alkaline (pH 7.6)

question

What do pancreatic and intestinal juice do together?

answer

provide a liquid medium that aids the absorption of substances from chime in the small intestine

question

What do the absorptive cells of the small intestine do?

answer

synthesise several digestive enzymes known as brush border enzymes, and insert them in the plasma membrane of the microvilli. Thus, enzymatic digestion occurs at the surface of the absorptive cells that line the villi

question

Give three classes of brush border enzymes, with examples of each

answer

Carbohydrate-digesting enzymes - alpha dextrinase, maltase, sucrase, lactase, protein-digesting enzymes - amino-peptidase and dipeptidase, nucleotide-digesting enzymes - nucleosidases, phosphatases

question

Where does carbohydrate digestion begin and how?

answer

in mouth. salivary alpha amylase, secreted from the parotid and submandibular glands hydrolyse starch into maltose and other small polymers

question

How are carbs digested in the stomach?

answer

Digestion continues in the stomach until the amylase is inactivated by gastric acid

question

What happens to carbs in the pancreas?

answer

Pancreatic secretions contain pancreatic alpha amylase, which is almost identical to the amylase in saliva. Eventually the breakdown results in disaccharides, trisaccharides and dextrin, which are not broken down any further until the small intestine

question

What does the small intestine do to the products of carb breakdown?

answer

The action of brush border enzymes breaks down di/tri-saccharides into monosaccharides, prior to absorption

question

what happens to lactose, sucrose, and maltose in the small intestine?

answer

lactose broken down into galactose and glucose via lactase, sucrose is broken down into fructose and glucose via sucrase, and maltose is broken down into glucose via maltase

question

How do enterocytes absorb monosaccharides?

answer

by facilitated diffusion and cotransport mechanisms. The contransport system that takes up glucose also brings sodium ions into the cell

question

How is fructose absorbed?

answer

By sodium independent facilitated diffusion

question

Cotransport of glucose and sodium?

answer

The cotransport that takes up glucose brings sodium ions into the cell, A sodium ion and a glucose molecule must bind to the carrier protein before they can move into the cell. The sodium is later then actively pumped back into the lumen via Na+/K+ pumps

question

Where does protein digestion begin?

answer

The stomach

question

Describe protein digestion in the stomach.

answer

The enzyme pepsin breaks down collagen to allow other enzymes to penetrate meats and digest cellular proteins. Most protein digestion occurs through the actions of pancreatic proteolytic enzymes

question

What happens when chyme enters the duodenum?

answer

Enteropeptidase from the small intestine triggers the conversion of trypsinogen to trypsin. Buffers increase the pH to 7-8. Pancreatic proteases begin working.

question

What do trypsin and chymotrypsin do?

answer

break down protein molecules into small polypeptides

question

What does carboxypolypeptidase do?

answer

cleaves amino acids from the carboxyl ends of the polypeptides

question

What does proelastase give rise to and what does that do?

answer

Proelastase gives rise to elastase, which then digests the elastin fibres that hold meat together

question

Where is the last stage of the digestion of proteins?

answer

Carried out in the intestinal lumen by enterocytes, which contain multiple peptidases that break down remaining tripeptides and dipeptides into amino acids

question

How are amino acids from the breakdown of proteins transported?

answer

Amino acids are actively transported with Na+ and dipeptides/tripeptides are actively transported with H+. They then diffuse across the basolateral surface into the bloodstream

question

What does fat digestion begin with?

answer

Lingual lipase from glands of the tongue

question

What happens once fat reaches the duodenum?

answer

CCK causes the release of bile salts and pancreatic lipase

question

What do the lingual and pancreatic lipases do?

answer

break down triglycerides into free fatty acids (FFAs) and monoglycerides

question

How do bile salts improve chemical digestion?

answer

By emulsifying the lipid drops into tiny emulsion droplets, thereby providing better access for pancreatic lipase

question

Describe micelle formation

answer

The monoglycerides and fatty acids interact with bile salts in the surrounding chyme to form small lipid-bile salt complexes called micelles. The micelle then fuses with the intestinal epithelium, releasing the fatty contents into the cytoplasm

question

How can short chain fatty acids enter cells?

answer

By simple diffusion without the need of a micelle

question

Once the monosaccharides and fatty acids have entered a cell what then happens to them?

answer

They are then resynthesized into triglycerides and coated with proteins resulting in a complex known as a chylomicron

question

What happens to chylomicrons once they leave the cell?

answer

These chylomicrons leave the absorptive ells via exocytosis and enter then lacteal (the lymphatic vessels of the small intestine which absorb digested fats) and then transported by way of lymphatic vessels

question

What happens once chylomicrons reach the thoracic duct?

answer

They enter the blood at the left subclavian vein with molecules of bile salt projecting outward covering the surface of the micelle

question

which vitamins are fat soluble?

answer

A, D, E and K

question

What can fat-soluble vitamins do?

answer

easily dissolve in lipids. They enter the duodenum in fat droplets, mixed with triglycerides. The vitamins remain in association with these lipids as they form emulsion droplets and, after further digestion, micelles

question

Where is vitamin K produced and what is it absorbed with?

answer

Vitamin K produced in the colon is absorbed with other lipids releases through bacteria

question

Normally water soluble vitamins are easily absorbed by diffusion across the digestive epithelium. What's different about B12?

answer

Can't be absorbed by the intestinal mucosa in normal amounts, must be bound to intrinsic factor secreted from parietal cells of the stomach. This complex is then absorbed in the ileum.

question

How is calcium absorbed and where?

answer

Absorbed in the duodenum and jejunum via a cell-mediated active transport pathway. This is under the influence of 1,25DHCC

question

How is phosphorous absorbed and where?

answer

Absorbed in the upper small intestine as inorganic phosphate by sodium co-transport

question

How is iron absorbed and where?

answer

Absorbed at proximal duodenum. Taken into enterocyte by divalent metal transporter (DMT1), which is an electrogenic pump. Iron is exported from the enterocyte to the circulating plasma through ferroportin

question

How is zinc transported and where?

answer

Zinc transporters have been identified in the villi.

question

Other minerals absorbed by the small intestine?

answer

Copper and magnesium

question

What is the electrical activity during a fasting state of the gut?

answer

During an interprandial (fasting) state, the electrical activity that controls contractile behaviour is known as the migrating motility complex (MMC). This is a cyclic contraction sequence that occurs every 90 minutes

question

what is the migrating motility complex regulated by?

answer

The hormone Motilin, and aims to cleanse the stomach and small intestine.

question

What is motilin and what is it produced by?

answer

a polypeptide hormone produced by M cells of the small intestine; it is seen as the 'housekeeper' of the gut. It helps cleanse the GI tract in time for the next meal. It also stimulates contraction of the gastric fundus and enhances gastric emptying

question

Name a motilin agonist

answer

Erythromycin

question

Describe the four stages of gut motility in the fasting state

answer

Prolonged period of quiescence, Increased frequency of contractility, a few minutes of peak electrical and mechanical activity, declining activity merging to next phase

question

During the fed state what is disrupted

answer

migrating motility complex

question

Name four things that happen during the fed state

answer

segmentation contractions, peristaltic waves, pendular contractions, villus movements

question

describe segmentation contractions

answer

non-synchronised contractions of the circular smooth muscle to mix chyme

question

describe peristaltic waves

answer

arise from duodenal bulb which generates its own BER of about 12/min. It propagates through the circular smooth muscle layer towards the end of the ileum. Major form of propulsion

question

describe pendular contractions

answer

rhythmic contractions of the longitudinal smooth muscle to mix the chyme

question

describe villus movements

answer

contraction of the muscularis mucosae, micro mixing at the surface of the mucosa

question

why is the pancreas described as a dual function gland?

answer

has both exocrine and endocrine glands

question

describe the exocrine gland (acini and duct system)

answer

makes up 99% of the pancreas and assists the digestive system by producing and releasing digestive enzymes and bicarbonate ions, also known as pancreatic juice

question

describe the endocrine glands (islets of Langerhans)

answer

made up of cell clusters known as islets of Langerhans. Its role is to produce and secrete important hormones which secrete in the bloodstream, alpha cells secrete glucagon, beta cells produce insulin, delta cells produce somatostatin

question

Describe the composition of pancreatic juice

answer

a clear, colourless liquid consisting mostly of water, some salts, sodium bicarbonate, and several enzymes. The sodium bicarbonate gives the pancreatic juice a slightly alkaline pH (7.1-8.2) that buffers the acidic gastric juice in the chyme

question

what does the sodium bicarbonate in the pancreatic juice do to pepsin?

answer

stops the action of pepsin from the stomach and creates the proper pH for the action of digestive enzymes in the small intestine. It also protects the mucosa.

question

List four types of enzymes found in pancreatic juice

answer

Pancreatic amylase, protein digesting enzymes, pancreatic lipase, nucleic acid digesting enzymes

question

Describe hormonal effects on the pancreas.

answer

When chyme arrives at the duodenum, secretin is released, triggering the release of pancreatic juice. CCK also stimulates the production and release of pancreatic enzymes

question

what does vagal stimulation do to secretion of pancreatic enzymes?

answer

increases the secretion of pancreatic enzymes. This stimulation occurs during the cephalic phase (before the food even reaches the stomach), this head start is important because enzyme synthesis takes quite a while

question

What does enteropeptidase do inside the duodenum?

answer

Enteropeptidase in the brush border and lumen triggers the conversion of trypsinogen to trypsin, an active protease.

question

What does trypsin do?

answer

Activates the other proenzymes, producing chymotrypsin, carboxypeptidase, and elastase. Each enzyme attacks peptide bonds linking specific amino acids and ignores others.

question

Why is trypsin important?

answer

Trypsin is a major trigger for the activation of many other proenzymes, which are converted into their active forms

question

which enzymes are released in their active forms?

answer

amylase, lipase, ribonuclease, deoxyribonuclease

question

what's chronic pancreatitis?

answer

Chronic inflammation of the pancreas, leading to destruction of exocrine and endocrine. Characterised by the presence of chronic inflammatory lesions on the pancreas, which results in pancreatic dysfunction of weeks and months

question

List some causes of chronic pancreatitis

answer

alcohol (60-80%), genetic (trypsinogen activation is promoted by cationic tryspinogen mutations), autoimmune (raised Ig4 levels in the serum, which causes inflammation of the pancreas), recurrent acute pancreatitis

question

What is the basic pathophysiology of chronic pancreatitis?

answer

Increase in activated trypsin as a result of increased trypsinogen activation, or by impaired inactivation/clearance of the activated trypsin from the pancreas

question

What does the increased in activated trypsin activity lead to?

answer

The increased enzyme activity within the pancreas leads to the precipitation of proteins in the duct lumen in the form of plugs. These then form a nidus for calcification but are also the cause of ductal obstruction, leading to ductal hypertension

question

what happens in alcohol related chronic pancreatitis?

answer

the alcohol impairs calcium regulation, leading to increased levels. These in turn promote trypsinogen activation as well as diminishing the inactivation pathway

question

how do patients with chronic pancreatitis present?

answer

pain usually in the epigastric region and often radiates through into the back. The pattern of pain may be episodic, with short period of severe pain, or chronic unremitting (never settles)

question

What is common during periods of abdominal pain in patients with chronic pancreatitis?

answer

during periods of abdominal pain, anorexia is common and weight loss may be severe

question

what percentage of acinar cells are destroyed in chronic pancreatitis and now?

answer

90% of the acinar cells are destroyed as pancreatic juice is not being made and lack of digestion and absorption if parts of the small bowel have been removed

question

what's secondary to any obstruction in the common bile duct?

answer

Jaundice

question

what's steatorrhoea ?

answer

incomplete breakdown and absorption of fats in the diet therefore abnormal quantities of fat are released with the faeces

question

what might happen to blood glucose and why in pancreatic insufficiency?

answer

may be elevated due to endocrine insufficiency

question

what might you see on a CT scan of someone with chronic pancreatitis?

answer

(contrast enhanced) - pancreatic calcifications, enlargement of the pancreas, ductal dilation and vascular problems

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