Digestive System- Accessory Organs Flashcards
(41 cards)
1
Q
Digestive System Accessory Organs
A
- Pancreas
- Liver
- Gall bladder
2
Q
The Pancreas
A
- The pancreas is an elongated organ, light tan or pinkish in color, that lies in close proximity to the duodenum
- Pancreatic duct connects with the duodenum
- It is covered with a very thin connective tissue capsule which extends inward dividing the gland into lobules
3
Q
Histology of the Pancreas
A
- Partitions of connective tissue divide the interior of the pancreas into distinct lobes
- Blood vessels of the pancreatic ducts are located within these connective tissue septum
- In each lobule:
– Ducts branch repeatedly->
ending in pockets called pancreatic acini - Each acinus is lined with simple cuboidal epithelium
- Pancreatic islets (endocrine tissues) are scattered among the acini
4
Q
The Pancreas- Exocrine
A
- Secrete into ducts
- Secretes “pancreatic juice”
- Acinar cells; enzymatic secretions
- Duct cells; aqueous NaHCO3 (sodium bicarbonate)
5
Q
The Pancreas- Endocrine
A
- Release secretory products (hormones)-> blood
- Glycaemic homeostasis
- Islets of Langerhan
- Insulin/glucagon
6
Q
Exocrine Cells
A
Acinar cells
Duct cells
7
Q
Acinar cells
A
- Produce small volume of primary
secretion - Water, electrolytes, and digestive
enzymes
8
Q
Duct cells
A
- Produce bicarbonate-rich fluid
- Large volume
9
Q
Endocrine- Pancreatic islets
A
Alpha cells
Beta cells
Delta cells
F cells
10
Q
Alpha cells
A
glucagon; glucagon raises blood glucose levels
11
Q
Beta cells
A
insulin; lowers blood glucose levels
12
Q
Delta cells
A
somatostatin; suppresses release of glucagon and insulin; slows rate of food absorption and enzyme secretion along digestive tract
13
Q
F cells
A
pancreatic polypeptide; inhibits gallbladder contractions and regulates production of pancreatic enzymes
14
Q
Pancreatic Juice
A
composed of 2 secretory products critical to proper digestion:
– Digestive enzymes (secreted from Acinar cells)
– Bicarbonate (a base) (secreted from epithelial cells lining the ducts)
15
Q
Types of Digestive Enzymes
A
Proteases
Pancreatic Lipase
Amylase
16
Q
Proteases
A
Digestion of proteins is initiated by pepsin in the stomach, but the bulk of protein digestion is due to the pancreatic proteases.
2 major pancreatic proteases: Trypsin and Chymotrypsin
17
Q
Pancreatic Lipase
A
- Major form of dietary fat is triglyceride, or neutral lipid.
– A triglyceride molecule cannot be directly absorbed across the intestinal mucosa.
– It must first be digested into a 2-monoglyceride and two free fatty acids. - The enzyme that performs this is Pancreatic lipase, which is delivered into the lumen of the gut in pancreatic juice.
- Bile salts are also needed –from liver
18
Q
Amylase
A
- The major dietary carbohydrate is starch.
- the enzyme that hydrolyses starch to maltose.
- also present in saliva.
19
Q
Bicarbonate and Water
A
- Epithelial cells in pancreatic ducts are the source of the bicarbonate and water secreted by the pancreas.
- In pancreatic duct cells, the bicarbonate is secreted into the lumen of the duct and hence into pancreatic juice– buffering the duodenum and preventing damage from stomach acid
20
Q
The Liver
A
- lies in the abdominal cavity, in contact with diaphragm
- Its mass is divided into several lobes, the number and size of which vary among species – four lobes in humans
- In most mammals, a greenish sac - the gallbladder - is seen attached to the liver
- The common bile duct delivers bile from the liver and gallbladder into the duodenum
21
Q
Gross anatomy of the liver
A
- Tough fibrous capsule
- Covered by layer of visceral peritoneum
- Right & left lobes
- Further subdividing lobes
- Anteriorly:
– falciform ligament divides left/right lobes becoming round ligament/ligamentum teres - Posteriorly:
– depression for inferior vena cava - Caudate & quadrate lobes also visible
22
Q
Liver Hepatocytes
A
- Cuboidal epithelia
- Two hepatocytes forming plates/cords
- Bile canaliculus between hepatocytes
- Sinusoids lined with fenestrated capillaries between plates
- Basal surface has microvilli that project into sinusoids
- Apical surface forms canaliculi
23
Q
Liver Hepatic lobules
A
- Each lobe is divided into lobules
- 100,000 liver lobules = functional units of liver
- Adjacent lobules separated by interlobular septum (connective tissue)
- Hepatocytes form irregular plates arranged in a hexagon shape
– Plates are one cell thick - Within a lobule, sinusoids between adjacent plates empty into central vein.
– Sinusoids contain Kupffer cells- phagocytic cells
– Blood enters liver sinusoids from small branches of the hepatic portal vein (Venous blood) and hepatic artery (arterial blood)
24
Q
Histological Organisation of the Liver
A
- Hepatic lobes consist of +100,000 lobules
- Lobules are separated by connective tissue at the interlobular septum
- Central vein
- Hepatocytes radiate outwards (cords/plates)
- Sinusoids spaces between plates lined with fenstrated capillaries
- Bile canaliculi channels arising between hepatocytes
25
Liver Portal area of the lobule
* There are 6 portal areas in each lobule
* Portal area contains:
- branch of hepatic portal vein
- branch of hepatic artery
- small branch of bile duct
26
Liver- Metabolic Regulation
– Metabolism – Carbohydrate, Fat & Protein
– Detoxification – toxins, ammonia, etc.
– Storage – Vitamins (B12), carbohydrates etc. e.g. glycogen
27
Liver- Haematological Regulation
– Secretory – bile – Bile acids, salts & pigments
– Excretory – Bilirubin
– Synthesis – Albumin, coagulation factors
28
Liver- Bile Functions
– Emulsification of lipids in duodenum
– Excretion of lipid soluble waste
29
Liver- Non-digestive functions (hepatobiliary system)
* Synthesis of plasma proteins
* Synthesis of clotting factors
* Synthesis of the inactive angiotensinogen (blood pressure)
* Phagocytosis of damaged red blood cells
* Breakdown of circulating hormones (insulin and epinephrine) and immunoglobulins (IgA etc)
* Inactivation of lipid-soluble drugs
30
Liver- Digestive & metabolic functions (hepatobiliary system)
* Synthesis and secretion of bile
* Storage of glycogen and lipid reserves
* Maintaining normal blood glucose, amino acid and fatty acid concentrations within blood
* Synthesis and release of cholesterol bound to transport proteins
* Inactivation of toxins
* Storage of iron
* Storage of fat-soluble vitamins
31
Liver- Vitamin & Mineral Storage
* Fat soluble vitamins (A,D, E and K) absorbed from the blood and stored in the liver (Vit B 12 also stored but not fat soluble)
* These reserves are called on when the diet contains inadequate amounts of those vitamins
* Liver converts iron reserves to ferritin (essential for haemoglobin) and stores this protein-iron complex
32
Liver- Removal of Waste products
* Removal of ammonia from the body by synthesis of urea.
– Ammonia is very toxic and if not rapidly and efficiently removed from the circulation, will result in central nervous system disease.
* Other waste products, circulating toxins and drugs are also removed from the blood for inactivation, storage or excretion.
33
Liver- Drug Inactivation
* Liver removes and breaks down circulating drugs, limiting drug duration.
* Rate at which liver removes drug is important.
* If absorbed quickly, drug must be administered every few hours to keep plasma concentrations at therapeutic levels.
34
Liver Hepatic Vascular system
* The circulatory system of the liver is unlike that seen in any other organ:
– The majority (75%) of the liver's blood supply is venous blood
* Roughly 75% of the blood entering the liver is from the portal vein.
– All of the venous (waste) blood returning from the small and large intestine, stomach, pancreas and spleen enters this vein
* The remaining 25% of the blood supply to the liver is arterial blood from the hepatic artery.
– This provides the liver tissue with oxygen and nutrients
* Converging at the hilus (porta hepatis)
* Venous return via hepatic veins-inferior vena cava
* The hepatic portal vein and hepatic artery empty together and mix as they enter sinusoids in the liver.
* Sinusoids are vascular channels (leaky capillaries) lined with highly fenestrated or "holey" endothelial cells and surrounded by hepatocytes.
* As blood flows through the sinusoids:
– plasma is filtered into the space between endothelium and hepatocytes, providing a major fraction of the body's lymph
– Plasma proteins are secreted
– Solutes are absorbed from the plasma
35
Hepatic veins
carry blood AWAY from liver
36
Hepatic Portal vein
carry blood TO liver
37
The Biliary System
* a series of channels and ducts that conveys bile - a secretory and excretory product of hepatocytes - from the liver into the lumen of the small intestine
* Biliary canal is the space between the apical surfaces of the hepatocytes that form cords
* Hepatocytes secrete bile into the canals, and those secretions flow parallel to the sinusoids,– but in the opposite direction that blood flows – towards the portal area.
*Small bile ducts, join into larger and larger ducts, eventually forming the common bile duct, which dumps bile into the duodenum.
*The gall bladder is another important structure in the biliary system.
*This is a sac-like structure adhering to the liver.
*During periods of time when bile is not flowing into the intestine, it is diverted into the gall bladder, where it is dehydrated and stored until needed.
38
The Gallbladder
* Hollow, pear-shaped organ
* Stores, modifies, and concentrates bile
* There are two important functions of bile:
- Bile acids are critical for digestion and absorption of fats and fat soluble vitamins in the small intestine.
- Many waste products are eliminated from the body by secretion into bile and subsequent elimination in faeces
39
Liver disease
* Any condition that severely damages the liver represents a serious threat to life
* The liver can regenerate itself after injury, but liver function will not recover fully unless normal vascular patterns return
* Conditions such as Cirrhosis and Hepatitis interfere with liver function
– they cause structural changes to occur
40
Alcoholic Fatty Liver
yellow appearance
Can be Reversible
41
Cirrhosis
End stage liver disease
Irreversible
