Anatomy and Physiology of the Liver, Animation — Transcript

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1. 0:03The liver is one of the most important organs.
2. 0:06In addition to being an essential blood filter and the largest exocrine and endocrine gland,
3. 0:11it has hundreds of other functions concerning almost every body system.
4. 0:14The liver has 4 lobes: right, left, quadrate and caudate.
5. 0:20A unique feature of the liver is that it has a dual blood supply, namely:
6. 0:25- the proper hepatic artery carrying oxygenated blood from the aorta, and
7. 0:30- the hepatic portal vein carrying venous drainage from most of the gastrointestinal
8. 0:34(GI) tract, plus the spleen and pancreas.
9. 0:38This is how substances absorbed through the GI tract, including nutrients, toxins and
10. 0:43pathogens, are first screened and processed in the liver before they can reach the general
11. 0:48circulation.
12. 0:50These 2 vessels enter the liver via an opening in its inferior surface, which also serves
13. 0:55as the exit point for the common hepatic duct carrying bile.
14. 0:59Blood leaves the liver in hepatic veins, at its superior surface, and immediately drains
15. 1:04into the inferior vena cava.
16. 1:07A liver contains nearly a million of functional units called hepatic lobules.
17. 1:12A lobule is typically shaped like a 6-sided prism, appearing as a hexagon in cross-section.
18. 1:19At the corners of the hexagon are hepatic triads which are branches of the hepatic portal
19. 1:24vein, hepatic artery and bile duct.
20. 1:27In the center is a central vein - a branch of hepatic vein.
21. 1:31About 80% of the liver mass is made of specialized epithelial cells called hepatocytes, which
22. 1:38carry out most of liver functions.
23. 1:41In a lobule, hepatocytes are arranged in plates, or cords, mostly 1-cell thick, separated by
24. 1:48blood-filled channels called sinusoids.
25. 1:51Sinusoids are basically capillaries with fenestrated endothelium and no basement membrane.
26. 1:57This unusual tissue arrangement allows each hepatocyte to be fully submerged in blood
27. 2:03plasma, enabling free exchange of substances.
28. 2:07Blood from the portal vein and hepatic artery mixes together in sinusoids; after substance
29. 2:12exchange with hepatocytes, it pools into central veins, and exits the liver via hepatic veins.
30. 2:20Other cells of the hepatic tissue include liver-specific macrophages (Kupffer cells),
31. 2:25natural killer cells, and stellate cells with a variety of functions.
32. 2:31As an exocrine gland, the liver produces bile to aid with digestion of fats.
33. 2:37Bile is secreted into tiny canaliculi sandwiched between hepatocytes, then pooled into bile
34. 2:43ductules of the triads, and ultimately into left and right hepatic ducts, which converge
35. 2:49and exit the liver as the common hepatic duct.
36. 2:52Bile flows into the small intestine during digestion.
37. 2:56Outside mealtimes, it is diverted to the gallbladder for concentration and storage.
38. 3:01Metabolic wastes, such as bilirubin - a byproduct of red blood cell breakdown, can be secreted
39. 3:07in bile and excreted from the body.
40. 3:10As an endocrine gland, the liver directly synthesizes several hormones, and is involved
41. 3:16in the metabolism of many others.
42. 3:19The liver acts as a gatekeeper controlling substances that can enter the circulation,
43. 3:23both quantitatively and qualitatively.
44. 3:26It processes the nutrients and regulates the amount of nutrients that can pass into the
45. 3:31blood.
46. 3:32For example, after a meal, when glucose spikes from digestion of carbs, the liver converts
47. 3:38excess glucose into glycogen for storage.
48. 3:41When the body is fasting, glycogen is converted back to glucose to be released to the blood.
49. 3:47Likewise, the liver also serves as a storage for several vitamins and minerals.
50. 3:52The liver has a central role in lipid metabolism.
51. 3:55It synthesizes endogenous cholesterol and fats, and pack them, together with dietary
52. 4:01lipids, into particles of very-low-density lipoprotein to deliver them to other organs,
53. 4:06via the bloodstream.
54. 4:08Excess cholesterol is transported back to the liver, where it is secreted in bile and
55. 4:13excreted in feces.
56. 4:15The free amino acids resulting from protein digestion are also processed in the liver,
57. 4:21where they are synthesized into new proteins and pro-enzymes.
58. 4:25In fact, the liver is responsible for production of many plasma protein including albumin and
59. 4:31clotting factors.
60. 4:33Excess free amino acids, which can be harmful, are converted to other forms of energy storage,
61. 4:38or broken down to urea to be removed in waste.
62. 4:43The liver is a detoxification organ.
63. 4:45It screens the blood for potentially toxic substances and pathogens, and removes them
64. 4:51before they can reach the rest of the body.
65. 4:53Similarly, it also metabolizes, and may inactivate, orally administered medicines.
66. 4:59This is known as the first-pass effect.
67. 5:02For this reason, some medicines must be taken via other routes to bypass liver metabolism.
68. 5:08On the other hand, some drugs are specifically designed as pro-drugs, which only become active
69. 5:14after being metabolized by the liver.