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Option H Assessment statements
Abi S.
Eleah W.
Richard M.
John R.
Hormonal Control
• A hormone is a form of chemical communication.
Hormones are secreted by endocrine cells placed
throughout the body and transported in the blood to target
cells. Hormones can be steroids, which pass through the
cell membrane and affect the genetic expression of a cell,
or proteins, which bind to receptors on the surface of cell
membranes to release secondary messengers inside cells.
The most prominent center for hormonal control is in the
brain, with the pituitary gland and the hypothalamus. The
hypothalamus is linked to the pituitary through the portal
vein (to the anterior lobe), which carries hormones that
trigger the release of other hormones, and also through
neurosecretory cells (the posterior lobe) receive impulses
that trigger hormone release.
• The secretion of ADH is an example of hormone control of a
process in the body. Osmoreceptor cells in the
hypothalamus monitor the osmolarity of the blood, and
when an increase is detected, the hypothalamus sends
signals to the posterior pituitary to release ADH into the
bloodstream, where it travels to the kidney and allows
more water to be collected. As the osmolarity of the blood
returns to homeostasis, negative feedback reduces the
amount of ADH released.
Digestion
• Digestive juices are secreted into the alimentary canal by
glands, including salivary glands, gastric glands in the
stomach wall, the pancreas, and the wall of the small
intestine.
• The initial release of gastric juice occurs under nerve
stimulation after sight or smell of food, and is sustained
under the influence of gastrin secreted when food is in the
stomach.
• Exocrine glands are responsible for the release of digestive
fluids and secrete their products into ducts. They have a
duct portion and a glandular portion. At the end of each
branch is an acinus formed by serous cells (secrete
proteins), and mucous cells (secrete mucus).
• Saliva consists of water, electrolytes, salivary amylase,
mucus, and lysozyme.
• Gastric juice consists of water, mucus, enzymes such as
pepsin and rennin, and HCl.
• Pancreatic juice consists of water, bicarbonate, enzymes
(amylase, lipase, carboxypeptidase, trypsinogen)
• Some of the enzymes (maltase, lactase and sucrase) are immobilized on
the membranes of the intestinal epithelium cells in the intestinal villi. The
active sites of theses enzymes are oriented toward the lumen of the
intestine and remain functional after the cells have been sloughed off into
the lumen.
• Human lack the enzyme cellulase, and thus the capacity to digest
cellulose. In some animals the symbiotic relationship developed with
cellulose-digesting bacteria.
• Pepsinogen and trypsinogen are initially inactive to prevent self-digestion
of the cells that produce the enzymes. Pepsinogen is converted into
pepsin by the acidity of the hydrochloric acid in the stomach. Trypsinogen
is converted into trypsin by the action of enteropeptidase (the enzyme
that is bound to the membranes of the small intestine) in the pancreas.
• A stomach ulcer is an open sore in the stomach wall,
where digestive juices - mostly acid and the enzyme
pepsin - have begun to eat away the stomach lining.
About 80 per cent of ulcers are caused by the
bacterium Helicobacter pylori, a corkscrew-shaped
bacterium that survives in the stomach by producing
the enzyme urease, which neutralizes stomach acid
and allows the bacterium to colonize the stomach's
mucous lining, opening up the stomach wall to erosion
bt digestive fluids, to the point of creating an ulcer or
vulnerability to stomach cancer.
• Lipids tend to coalesce, in an aqeuous environment, due to
their water insolubility, and are only accessable to lipase at
a lipid-water interfaces. When the lipids clump it decreases
the surface area-volume ratio, meaning the lipase have less
surface to attach to.
• Bile molecules have a hydrophobic end and a hydrophilic
end which emulsifies the lipids, exposing the maximum
lipid surface area to lipases. Lipase is water-soluble, but has
a hydrophobic active site.
Absorption
• Ileum- last section of the small intestines.
• Absorption of nutrients.
• Facilitated diffusion is need for substances when absorption
occurs.
• Epithelial cells:
– Villi- huge surface area
– Microvilli- face lumen of gut
– Mitochondria- ATP
– Pinocytotic vesicles- fluids up-taken or released in tiny
vesicles.
– Tight Junctions-binds epithelial cells so only way in
tissue is through the epithelium.
Liver Function
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The liver is served by the hepatic artery, which delivers oxygenated blood, and it is
drained by the hepatic vein. In addition, there is a portal vein, the hepatic portal
vein that brings blood to the liver directly from the small intestine.
The blood brought by the hepatic portal vein is deoxygenated, because it has
already flowed through the wall of the stomach of the intestines. The level of
nutrients in this blood varies considerably, depending on the amount of digested
food that is being absorbed.
Inside the liver the hepatic portal vein divides up into vessels called sinusoids.
These vessels are wider than normal capillaries and have more porous walls,
consisting of a single layer of very thin cells, with many pores or gaps between the
cells and no basement membrane. Blood flowing along the sinusoids is therefore
in close contact with the surrounding hepatocytes. The sinusoids drain into wider
vessels that are branches of the hepatic vein. Blood from the liver is carried by the
hepatic vein to the right side of the heart via the inferior vena cava.
The hepatic artery supplies the liver with oxygenated blood from the left side of
the heart via the aorta. Branches of the hepatic artery join the sinusoids at various
points along their length, providing the hepatocytes with the oxygen that they
need for aerobic cell respiration.
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The normal level of blood glucose in humans is about 90mg per 100cm3(90mg 100cm-3). On arrival
in the liver sinusoids, excess glucose is withdrawn from the plasma solution and used in
metabolism or stored as glycogen. Glycogen reserves are also stored elsewhere in the body,
particularly in the skeletal muscles. Respiring tissues of the body receive glucose supplies from the
blood circulation. For most tissues, it is a principal substrate for respiration. As the level of blood
glucose falls due to respiration in tissues, glycogen reserves in the liver are converted back to
glucose to maintain the normal plasma concentration.
The liver cells also adjust the level of amino acids as the blood passes along the liver sinusoids. A
pool of amino acids is maintained in the plasma, in the liver and in other tissues undergoing rapid
protein synthesis. Amino acids are constantly being built up into proteins, which then function as
enzymes, components of membranes, and structural components (e.g. collagen fibres, keratin). The
demand for new proteins on a daily basis is very high. Most proteins are short-lived, but the body
cannot store amino acids. Instead, excess amino acids are deaminated in the liver. The organic acid
part of each amino acid is removed and respired, or converted to fat or carbohydrate.
By this deamination process, the liver ensures that soluble ammonia is not formed and released in
the tissues. Urea is removed from the blood in the kidneys. The fatty acids (and glycerol) that reach
the liver are combined to form triglycerides. These are combined with proteins in the liver, and may
be stored there. Alternatively they are transported in the blood plasma, mostly as low-density
lipoproteins (LDLs), to the tissues. Here lipids may be stored as food reserves (fat), or immediately
broken down and respired as a source of energy.
• When certain nutrients are in excess in the blood,
hepatocytes absorb and store them, releasing them when
they are at too low a level. For example, when the blood
glucose level is too high, insulin stimulates hepatocytes to
absorb glucose and convert it to glycogen for storage.
When the blood glucose is too low, glucagon stimulates
hepatocytes to break down glycogen and release glucose
into the blood. Iron, retinol (vitamin A) and calciferol
(vitamin D) are also stored in the liver.
• The liver is the site of synthesis of all the blood proteins,
including globulins, albumin, prothrombin and fibrinogen.
Also, most of the cholesterol required by the body on a
daily basis is manufactured in the liver (but the remainder
is taken in as part of the diet).
• The liver detoxifies harmful substances such as alcohol (see
below), or renders drugs and toxins that have entered the
blood stream into harmless forms for excretion from the
blood circulation in the kidneys. Drugs such as the
antibiotics penicillin and erythromycin are handled in this
way, as are sulphonamides. Hormones such as thyroid
hormone, and steroid hormones such as oestrogen,
testosterone, and aldosterone are similarly inactivated,
ready for removal from the blood.
• Erythrocytes, also called red blood cells, have a fairly short lifespan
of about 120 days. The plasma membrane becomes fragile and
eventually ruptures, releasing the hemoglobin into the blood
plasma. The hemoglobin is absorbed by phagocytosis, chiefly in the
liver. Some of the cells in the walls of the sinusoids are phagocytic.
They are called Kupffer cells. Inside the Kupffer cells hemoglobin
splits into heme groups and globins. The globins are hydrolysed to
amino acids, which are released into the blood. Iron is removed
from the heme groups, to leave a yellow-coloured substance called
bile pigment or bilirubin. The iron and the bile pigment are released
into the blood. Much of the iron is carried to bone marrow, where it
is used in the production of hemoglobin in new red blood cells. The
bile pigment is absorbed by hepatocytes and forms part of the bile.
• Hemoglobin → globins – amino acids
and → heme groups - iron – bile pigment
• Cirrhosis of the liver – a chronic inflammation of the liver in
which liver cells are destroyed and replaced by fibrous or
adipose (lipid-containing) connective tissue
The Transport System
• The flow of blood through the heart is influenced by the
valves and nodes that regulate heartbeat. First, the
sinoatrial node, which receives signals from the brain about
how quickly to contract, signals the atria to contract. Blood
moves from the high pressure in the atria to low pressure in
the ventricles, and the atrioventricular valves close to
prevent blood from flowing back into the atria. Then, the
atrioventricular node, which receives a signal from the SA
node, signals the ventricles to contract, pushing blood out
of the heart and causing the semilunar valves to close.
• If the body is not taken care of, heart disease can occur. The
most common issues are atherosclerosis, or buildup of
plaque in blood vessels, and coronary heart disease. Plaque
can build up when there is so much cholesterol and lipids in
the diet that they stick to the walls of blood vessels, and if
red blood cells catch on the plaque and release clotting
factors, a clot can form that blocks off the vessel. Coronary
heart disease can occur based on genetic predisposition,
age, smoking, obesity, low exercise, and eating a diet high
in fat and cholesterol.
Gas Exchange
Partial pressure- exerted on an object by an individual gas;
measure of oxygen.
• Hemoglobin in adult and fetal
– (HBF)- fetal higher oxygen curve to left
– (HB)- Adult low oxygen curve to right.
• Myoglobin- muscle mass
– Delivers extra oxygen to actively respiring muscles
– On curve- to left of hemoglobin and rises steeply and
levels off
• Co2 produced by body tissue diffuses into interstitial fluid and
into plasma.
• Less than 10 % remains in plasma
• 70% diffuses into red blood cells
• 20% picked up and transported by hemoglobin.
• CO2 reacts with H2Oin red blood cells to form carbonic acid.
• Hemoglobin binds with most h+ preventing from acidifying
the blood.