Lecture 8 : Liver and Kidneys Flashcards
(33 cards)
Liver Anatomy
The liver located in the upper right-hand
portion of the abdominal cavity, beneath the
diaphragm, and on top of the stomach, right
kidney, and intestines
Shaped like a cone, the liver is a dark reddish-
brown organ that weighs about 1.8 kg in men
and 1.3 kg in women (~3 pounds)
Liver Functions
Production of bile, which helps carry away waste and
break down fats in the small intestine during digestion
Production of certain proteins for blood plasma
Production of cholesterol and special proteins to help
carry fats through the body
Conversion of excess glucose into glycogen for storage
(glycogen can later be converted back to glucose for
energy) and to balance and make glucose as needed
Regulation of blood levels of amino acids, which form the
building blocks of proteins
Liver functions…2
Processing of haemoglobin for use of its iron content (the
liver stores iron)
Conversion of poisonous ammonia to urea (urea is an end
product of protein metabolism and is excreted in the urine)
Clearing the blood of drugs and other poisonous substances
Regulating blood clotting
Resisting infections by making immune factors and
Removing bacteria from the bloodstream
Clearance of bilirubin, also from red blood cells
If there is an accumulation of bilirubin, the skin and eyes turn yellow
Functional units of the Liver
Organizational units of the liver includes:
1) Classic (hepatic) Lobule
2) Portal Lobule
3) Hepatic Acinus
Hepatic Lobule
Hepatic lobules are microscopic units that make up the liver and are the functional unit
of the liver and are organized into a hexagonal shape (a six-sided prism about 2 mm long
and 1 mm in diameter)
It is delimited by interlobular connective tissue
(only little, if any, visible in humans; plentiful
in e.g. pigs)
In its corners we find the portal triads
In cross sections, the lobule is filled by cords
of hepatic parenchymal cells, hepatocytes,
which radiate from the central vein and are
separated by vascular sinusoids
Hepatic Lobule Contents
Hepatocytes: Liver cells that line up in radiating
rows within the lobules
Sinusoids: Small blood vessels that diffuse oxygen
and nutrients into the liver cells
Portal triad: A cluster of branches of the hepatic
artery, hepatic portal vein, and bile duct at the
corners of the lobule
Central vein: A vein in the middle of the lobule that
receives blood from the sinusoids
Liver Histology
Hepatocytes are separated by sinusoids, which are lined by fenestrated endothelial cells
The space of Disse lies between the endothelial cells and hepatocytes
Kupffer and satellite cells
Kupffer Cells: main function is phagocytosis and defence of the liver against bacteria,
endotoxemia and viral infections, and are the largest pool of tissue macrophages in the
body
- They will phagocytose and partially degrade bacterial antigens before handing them on to
the hepatocytes for excretion into the bile
Hepatic stellate cells (HSCs):
play a key role in liver development,
regeneration, and Fibrosis
- They are also involved in
inflammation and cancer
Bile & Gallbladder
When the liver has broken down harmful
substances, its by-products are excreted into
the bile or blood
Bile by-products enter the intestine and leave
the body in the form of faeces
Bile aids in the breakdown and digestion of fats
in the small intestine
Bile is a watery secretion generated by hepatic
cells, transported to the gallbladder for concentration and storage, and delivered into the
duodenum
Bile acts as a detergent, emulsifying fats and enabling better action of pancreatic enzymes
on food particles
Bile contains:
Mostly cholesterol
Bile acids (also called bile salts- such as potassium and sodium)
Bilirubin (a breakdown product or red blood cells)
Also: Water and Copper and other metals (attached to proteins)
Liver physiological functions (Glycogenesis)
Glycogen (animal starch), is a branched polysaccharide that serves as
a reserve of carbohydrates in the body; it is stored in the liver and
muscle and readily available as an immediate energy source
Glycogenesis: The formation of glycogen from glucose is known as
glycogenesis
Glycogenolysis (Glycogen metabolism): is the breakdown of glycogen to form glucose
The primary hormones that regulate the cycle of glycogenesis and gluconeogenesis are
insulin, glucagon, and cortisol
Impaired glycogen metabolism, characterized by abnormal glycogen accumulation, is
associated with inherited metabolic disorders and is collectively known as glycogen storage
diseases
Liver physiological functions (Gluconeogenesis)
Gluconeogenesis
The brain, eye, and kidney are some of the organs that
have glucose as the sole metabolic fuel source
Prolonged fasting or vigorous exercise depletes glycogen
stores, making the body switch to de-novo glucose
synthesis to maintain blood levels of this monosaccharide
Gluconeogenesis is the process that allows the body to form glucose from non-hexose
precursors, particularly glycerol, lactate, pyruvate, propionate, and glucogenic amino
acids.
Lipid Metabolism
Lipid metabolism in the liver refers
to the complex process where the
liver actively regulates the uptake,
storage, and release of lipids (fats)
in the body, primarily by:
- Synthesizing lipoproteins
- Breaking down fatty acids through
beta-oxidation
- Producing bile acids to aid in fat
digestion
Liver essentially acts as the central hub for maintaining systemic lipid homeostasis
Liver physiological functions – Storage
Glycogen
Some fats
Vitamins:
- A: Vision, Growth, epithelial maintenance, reproduction
- B12: production of RBCs; deficiency: megaloblastic anaemia
- D: initial hydroxylation of D3 to 25- OH D3- ; final hydroxylation in kidney to 1-
25 –OH D3: Ca2+ absorption in GIT
- E: antioxidant- prevents lipid peroxidation and formation of free radicals
- K: blood clotting
Minerals, such as iron and copper
Liver Physiological functions – Synthesis
Synthesis of Bile salts (Used in small
intestine for emulsification of fats)
Converts Vitamin D3 to partially active form
of vitamin 1-25-hydroxyvitamin D3 (regulates
body Ca2+ levels, mineralisation of bone)
Plasma Proteins e.g. Globulins, albumin,
fibrinogen (coagulation)
Liver function- Iron Homeostasis
The iron hormone hepcidin and its
receptor and cellular iron exporter
ferroportin (Fpn) control the major
fluxes of iron into blood plasma:
intestinal iron absorption, the delivery
of recycled iron from macrophages,
and the release of stored iron from
hepatocytes.
Iron is an essential trace element for nearly every living organism, because it readily
accepts or donates electrons, free iron is highly reactive and toxic
Iron Metabolism
The average adult human contains ∼3–4 g iron,
most of which is in erythrocyte haemoglobin (∼2–3 g
iron)
Other iron-rich tissues include the liver and the
spleen, the major reserve organs for iron where iron
is stored in macrophages and hepatocytes in a
specialized cytoplasmic iron storage protein, ferritin
Muscle contains iron predominantly in myoglobin,
an oxygen storage protein
All cells contain smaller concentrations in iron-
containing proteins essential for energy production,
synthetic metabolism, and other important
functions
Iron is distributed to tissues through blood plasma which contains only 2–4 mg iron,
bound to the iron-transport protein transferrin
Plasma iron turns over every few hours as
∼20–25 mg iron a day move through this
compartment
Of all cells, erythrocytes have the highest
concentration of iron, ∼1 mg/ml packed
volume
Alcoholic Steatohepatitis
Hepatic steatosis, more commonly
known as fatty liver disease, occurs
when excess fat accumulates in the liver
Fatty liver disease is one of the most
common causes of chronic liver disease
in the developed world, affecting up to
one in every four individuals
Fatty liver disease starts with simple
steatosis, also known as fatty change,
which can progress to more advanced
stages, such as steatohepatitis, fibrosis,
and, ultimately, cirrhosis
The Gallbladder
The gallbladder is a small, pear-shaped, muscular storage sac that holds bile and is
interconnected to the liver by ducts known as the biliary tract
Bile is a greenish yellow, thick, sticky fluid and consists of bile salts, electrolytes (dissolved
charged particles, such as sodium and bicarbonate), bile pigments, cholesterol, and other
fats (lipids)
Bile salts aid in digestion by making cholesterol, fats, and
fat-soluble vitamins easier to absorb from the intestine
Bilirubin is the main pigment in bile (a waste product that
is formed from haemoglobin
Functions of the Gallbladder
Bile has two main functions:
Aiding in digestion
Eliminating certain waste products (mainly haemoglobin and excess cholesterol)
from the body
Control of Bile secretion
Cholecystokinin (CCK):
Released by the upper small
intestine in response to fat and
amino acids in the duodenum and
stimulates the gallbladder to
contract and release bile into the
small intestine
It also stimulates the pancreas to
release digestive enzymes
Secretin: Released by the small
intestine in response to acid in
the duodenum and stimulates the
pancreas to release bicarbonate
Gallbladder Pathology: Gallstones
The major pathological conditions of gallbladder include:
Cholelithiasis: Gallstones (cholelithiasis) are hardened pieces of
bile that form in gallbladder or bile ducts and are common, especially
in females. Gallstones don’t always cause problems, unless they get
stuck in biliary tract and block the bile flow
Biliary Colic: Biliary colic is a steady or intermittent ache in the
upper abdomen, usually under the right side of the rib cage. It
happens when something blocks the normal flow of bile from the
gallbladder
Cholecystitis: inflammation of the gallbladder, usually caused by a
gallstone blocking the gallbladder’s opening. Symptoms include pain
in the upper right abdomen, nausea, vomiting, and fever
Cholangitis: Cholangitis is swelling (inflammation) of the bile duct
system that results from infection. The bile duct system carries bile
from your liver and gallbladder into the first part of your small intestine
(the duodenum)
kidney functions
Urinary system include: the kidneys, renal pelvis, ureters, bladder and urethra &
remove wastes and extra fluid from the body
They also remove acid that is produced by the cells and maintain a healthy balance
of water, salts, and minerals (sodium, calcium, phosphorus, and potassium)
Kidneys also make hormones:
- Erythropoietin (EPO): A hormone that stimulates the production of red blood cells
in the bone marrow. EPO is released in response to bleeding or moving to high
altitudes.
- Renin: An enzyme that starts the renin-angiotensin-aldosterone system (RAAS) that
controls blood pressure and extracellular volume
- 1,25-dihydroxy vitamin D3: The active form of vitamin D that helps maintain
calcium homeostasis. It’s produced by the proximal tubule cells
- Kallikreins: A group of enzymes that produce bradykinin, a vasorelaxing peptide
Kidney
Bean-shaped organs, with medial concavity and
lateral convexity, weighing about 150 to 200 g in males -
120 to 135 g in females
Length of 10 to 12 cm, width of 5 to 7 cm, and
thickness of 3 to 5 cm
Located retroperitoneally on the posterior abdominal
wall and are found between the T12 and L3
The right kidney is usually slightly more inferior in
position than the left kidney, likely because of the liver
Kidney: Cortex & Medulla
The kidney is composed of two regions: the cortex & medulla
The cortex
Includes renal corpuscles, convoluted tubules, straight tubules, collecting tubules,
collecting ducts, and vasculature
The Medulla
Medullary rays, comprised of straight tubules and
collecting ducts, extend into the cortex from the medulla
