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Digestion & excretion physiology > Lecture 6: liver, bile & jaundice > Flashcards

Lecture 6: liver, bile & jaundice Flashcards

1
Q

What is the liver?

A

an organ in the body that is situated in the upper right quadrant of the abdominal cavity

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2
Q

Describe are the functions of the liver?

A
  • synthesis and secretion of** bile **
  • carbohydrate metabolism - liver contains glycogen, it can form glucose through gluconeogenesis
  • fat metabolism - facilitated by bile salts
  • detoxification- inactivation of hormones, removal and detox of drugs through first pass metabolism etc
    *** iron storage **
  • synthesises and secretes IGF-1 & IGF-2 in response to secretion of growth hormone
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3
Q

what is the liver’s accessory organ & and what is it’s function?

A
  • gall bladder
  • stores bile synthesised by liver
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4
Q

what are the **structural units **of the liver called?

A
  • hepatic lobules
  • roughly hexagonal in shape
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5
Q

Describe the components of hepatic lobules

A
  • they contain a central vein that lies at the centre of each lobule
  • portal triads - branch of the hepatic artery, branch of the portal vein & a** bile duct**
  • the hepatocytes radiate from the central vein - arranged like a spongle like structure
  • sinusoids - branching blood vessels around hepatocytes
  • bile cannaliculus - space between hepatocytes that communicates with bile duct
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6
Q

What are the hepatic acinus?

A
  • this is the functional unit of the liver
  • it is situated around the afferent vascular system of liver
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7
Q

What are the different types of cells in the liver?

A
  • hepatocytes - most abundant
  • Kupffer cells - macrophages of the liver
  • endothelial cells (fenestrated)
  • hepatic stellate cells
  • cholangiocytes- bile secretion & motility
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8
Q

what is the** space between the hepatocytes & the sinusoidal wall** called?

A
  • space of Disse
  • contains a system of supoporting collagen fibres & drained by terminal lymphatic vessels
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9
Q

Describe the hepatic circulation

A
  • the liver receives 25% of the cardiac output at rest
  • hepatic artery carries oxygenated blood from the aorta to liver
  • portal vein delivers nutrient rich but deoxygenated blood from the stomach, intestines and spleen
  • **small portal venules **lying in the septa between the lobules receive blood from portal veins
  • small hepatic arterioles in septa receive blood from hepatic artery
  • from the venules and arterioles , blood flows into the** sinusoids **
  • blood returns from liver to systemic ciruclation via hepatic vein
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10
Q

what does the blood in the portal vein contain?

A
  • it conatins breakdown products of haemoglobin from the spleen & digested nutrients from the GIT
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11
Q

what do the sinusoids form?

A
  • they essentially form a** leaky capillary network** from which blood flows from the portal vein and hepatic artery to the central vein of the lobules
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12
Q

where does the deoxygenated blood that has flowed into the central veins go to?

A

empties into the hepatic veins, which join the inferior vena cava

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13
Q

what are the** 2 types of cells** that line sinusoids?

A
  • endothelial cells
  • phagocytic kupffer cells (macrophages) - they remove debris and pathogens from the ciruclation by phagocytosis
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14
Q

Describe hepatocytes

A
  • large polyhedral cells that have rough and smooth ER, mitochondria and lysosomes
  • microvilli are present on their plasma membrane which provides a large surface area for exchanges of substances with the blood
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15
Q

What are the 3 zones of the hepatic acinus?

A
  1. zone 1- most oxygenated zone - carries out gluconeogenesis & oxidation of fatty acids
  2. zone 2 - intermediate zone
  3. zone 3 -least well oxygenated - glycolosis (anaerobic process - glucose to pyruvic acid), lipogenesis
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16
Q

Where does the liver gets its oxygen from?

A
  • hepatic artery - 15ml of oxygen per min
    * portal vein - 36ml of oxygen per min (still delivering a substantial amount of oxygen to liver, but o2 delivery can decrease due to increase in GIT activity and oxyegn demand)
17
Q

what fluid do the hepatocytes secrete?

A
  • they secrete a fluid called hepatic bile into the bile canaliculi
18
Q

what does hepatic bile contain?

A
  • hepatic bile contains bile salts, bile pigments, cholesterol, mucus & lecithin
19
Q

what happens to the hepatic bile after it passes through the bile ducts?

A
  • the ductal epithelial cells (line bile duct)** modify **this primary secretion by secreting a watery, bicarbonate rich fluid that increases the volume of bile
  • ductal epithelial cells add the aqueous component
20
Q

What** hormone** stimulates the ductal epithelial cells that line the bile duct?

A

secretin

21
Q

What are the functions of bile?

A
  • emulsification of lipids
  • hormonal action
  • elimination of waste products eg bilirubin
22
Q

what are the precursors for bile salts?

A

the bile acids
2 types - primary and secondary bile acids

23
Q

what are the primary bile acids?

A
  • cholic acid and chenodeoxycholic acid are synthesised from cholesterol in the hepatocytes
24
Q

what are** secondary bile acids**?

A
  • deoxycholic acid & lithocholic acid
  • they are formed in the intestine by the dehydroxylating action of bacteria on the primary acids
25
Q

what happens to the primary bile acids before their secretion as bile salts into the bile?

A
  • they are conjugated (reversibly combined) with amino acids such as glycine & taurine to form water soluable bile salts
26
Q

how does** bile emulsify lipids**?

note emulsify means - mixing 2 liquids that are normally not mixable

A
  • bile salts have both hydrophobic and hydrophillic regions (they are amphipathic)
  • they aggregate to form micelles when they reach a certain conc in the bile
  • the hydrophillic group face the aqueous medium while the hydrophobic groups face eachother to form a core
27
Q

How does bile act as hormones?

ie signalling molecules, where is the receptor expressed etc

A
  • bile acids can also function as signalling molecules
  • GPBA (G protein coupled receptor for bile acids) is expressed on several cells
    1. These include enterochromaffin cells (neuroendocrine cells in GIT) & enteric neurons ** to control perastalisis
    2. also on     brown fat and skeletal muscle** for energy homeostasis
    3. also expressed on **monocytes and macrophages ** - anti - infalmmatory effect
28
Q

how are bile salts recycled?

A
  • bile salts that enter the intestine via the bile duct are reabsorbed into the portal circulation via the portal vein in the terminal ileum via specific transporters
29
Q

what** transporter** allows bile acids to return to the liver?

A
  • they return to the hepatocytes via Na+ dependent organic anion transporter
30
Q

What is bile acid solubility altered by?

A
  • hydroxylation
  • conjugation - this increases the water solubility of bile salts, which makes them relatively impermeable in the duodenum - which causes accumulation in the lumen
31
Q

what is the role of the gall bladder?

A
  • it stores the bile that isnt required immediately for digestion
  • it also concentrates the bile by absorbing Na+, Cl-, bicarbonate and water
32
Q

Explain the phases of gall bladder contraction

A
    • cephalic phase - thought and taste of food - GB emptying
  2. **gastric phase **- vagus stimulated by gastric distension- GB emptying
  3. intestinal phase
    * presence of acid in duodenum causes a release of hormone secretin which causes the ductal epithelail cells to produce bicarb rich secretion
    * presence of fat in duodenum causes CCK secretion which stimulates contraction of GB
33
Q

how does bile remove waste products eg bilirubin?

A
  • bilirubin is a component of bile
  • bilirubin is formed when old red blood cells are broken down in the spleen
  • in hepatocytes, the bilirubin becomes conjugated
34
Q

what occurs if there is an accumulation of bilirubin in the blood?

A
  • jaundice occurs if bilirubin is not being removed in bilary secretions
  • yellow colour of the skin, the sclera of the eyes
35
Q

what are gallstones?

A
  • any excess cholesterol that cannot be dispersed into micelles may form crystals in the bile and contribute to the formation of gall stones

Digestion & excretion physiology (24 decks)

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