BIOLOGY

Topic Option H

Topic Outline

Hormonal Control Digestion Absorption of Digested Foods Functions of the Liver The Transport System Gas Exchange

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Option H.1 Hormonal Control

H.1.1 State that hormones are chemical messengers secreted by endocrine glands into the blood and transported by the blood to specific target cells.

Hormones are chemical messengers secreted by endocrine glands into the blood and transported by blood to specific target cells.

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H.1.2 State that hormones can be steroids, peptides and tyrosine derivatives and provide

one example of each.

Hormones can be steroids, peptides and tyrosine derivatives and provide one example of each.

H.1.3 Distinguish between the mode of action of steroid hormones and peptide hormones.

Steroids enter cells and affect genes directly. Peptides bind to receptors in the membrane which causes the

release of a secondary messenger inside the cell

H.1.4 Draw a diagram of the hypothalamus and the pituitary gland.

Drawing will be inserted at a later date.

H.1.5 Explain the control of thyroxin secretion by negative feedback.

The release of thyroxin is regulated by the pituitary gland and the hypothalamus. The hypothalamus controls the pituitary's secretion of tropic hormones, and these,

in turn, stimulate the secretion of hormones from the thyroid, adrenal cortex, and gonads (the testes or ovaries).

As the concentration of the hormones produced by these target glands rises in the blood, the hypothalamus

decreases its production of releasing hormones, the pituitary decreases its hormone production, and

production of thyroxin by the target gland also slows. By way of the hypothalamus, which receives information from many other parts of the brain, hormone production

is also regulated in response to other changes in the external and internal environments.

H.1.6 Explain the control of ADH secretion by negative feedback.

One important homeostatic function of the body is keeping

the blood volume constant. This is accomplished by regulation of the rate at which water is removed from

the bloodstream by the kidneys.

A hormone called ADH (anti-diuretic hormone) is produced by the hypothalamus and released from the pituitary gland

acts on the kidney's tubules to decrease water excretion. The production of ADH is controlled by sensory receptors in

the circulatory system, particularly in the heart, that measures blood pressure- an indirect

measure of blood volume.

When blood pressure goes up, firing of these receptors inhibits the release of ADH, and more water is excreted, reducing blood volume. As blood pressure goes down,

the stimulus from the receptors decreases, ADH production increases, water is retained by the kidney,

and blood pressure and volume increase.

Option H.2 Digestion

H.2.1 State that digestive juices are secreted into the alimentary canal by glands including salivary, stomach wall, pancreas and wall of small intestine.

Digestive juices are secreted into the alimentary canal by glands including salivary, stomach wall, pancreas and wall of small intestine.

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H.2.2 Draw the structural features of exocrine glands including secretory cells grouped into acini and ducts.

Drawing will be inserted at a later date.

H.2.2 Draw the structural features of exocrine glands including secretory cells grouped into acini and ducts.

Drawing will be inserted at a later date.

H.2.3 Explain the structural features of exocrine gland cells as seen in electron micrographs.

A group of cells surround an empty space (acini). Hormones from cells tickle into acini and then

to the duct. The hormones are then transported to the destination (duodenum, skin, etc). In short the alignment of exocrine cells around an acini increase surface area for hormone secretion.

H.2.4 State the contents of saliva, gastric juice and pancreatic juice.

Saliva is made of water and amylase. The contents of gastric juice is HCl, pepsin and mucus. Pancreatic juice

is made of trypsin, chymotrypsin, nuclease, pancreatic amylase, lipase, and sodium bicarbonate.

H.2.5 Outline the control of digestive juice secretion by nerves and hormones.

H.2.6 Outline the role of membrane-bound enzymes in the surface cells of the small intestine in

completing digestion.

Some digestive enzymes are immobilized in the surface membrane of cells on the surface of intestina

l villi. These enzymes continue working even if the cell is rubbed off the villus and mixed into

the intestinal contents.

H.2.7 Explain why cellulose remains undigested in the human alimentary canal.

Humans have no enzymes to break down the beta linkages in cellulose.

H.2.8 Explain why pepsin and trypsin

are initially synthesized as inactive precursors and how they are

subsequently activated.

They stay active first so that they don't digest your own cells. HCl activates pepsin and makes it more acidic. A basic molecule changes the pH of

trypsinogen. Thus trypsin becomes basic.

H.2.9 Outline the action of endopeptidases and exopeptidases.

H2.10 Explain the problem of lipid digestion in a hydrophilic medium and the role of bile in overcoming this problem.

Lipids tend to coalesce (lump together) and are only accessible to lipase at the lipid-water interface. Bile

breaks the lumps down and thus acts as an emulsifier. Thus the surface area for lipase to digest the lipids increases.

Option H.3 Absorption of Digested Foods

H.3.1 Draw a portion of the ileum (in transverse section) as seen under a

light microscope.

Drawing will be inserted at a later date

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H.3.2 Explain the structural features of an epithelium cell of a villus as seen in electron micrographs including

microvilli, mitochondria, pinocytotic vesicles and tight junctions.

Epithelium cells of villi contain many mitochdondria. These mitochondria produce a lot of energy, which is

necessary for absorption. Microvilli on the epithelial cells that line the villi increase surface area for absorption. Pinocytotic vesicles take fatty acds, glycerol, amino

acids and glucose from the intestines through the villi to blood vessels.

Some molecules diffuse across the villi, while others are carried. The epithelium cells are physically connected,

so nothing can squeeze between them. Moreover, tight junctions separate the proteins of the lumen side from

the blood side, so proteins cannot move and allow molevules to diffuse back to the wrong side. Thus the contents of the intestine are kept separate

from the body fluids on the opposite side.

H.3.3 Explain the mechanisms used by the ileum to absorb and transport food, including facilitated

diffusion, active transport and endocytosis.

Water and small molecules are pumped or carried across the membrane by transport proteins through facilitated diffusion or activated transport. Larger

molecules such as proteins and polysaccharides enter by endocytosis.

In endocytosis the cell takes in macromolecules by forming vesicles derived from the plasma membrane. In facilitated diffusion, little protein channels facilitated diffusion but no energy is used. In active transport, the

sodium-potassium pump pumps molecules in and out while using energy.

H.3.4 List the materials that are not absorbed and are egested.

Cellulose, lignin (protein found in wood), bile pigments, bacteria (because they have special

cell walls), and intestinal cells.

Option H.4 Functions of the Liver

H.4.1 Outline the circulation of blood through liver tissue including the hepatic artery, hepatic portal vein, sinusoids and hepatic vein.

Blood in the hepatic artery comes from the heart and full of oxygen, but it has little nutrients. On the other hand, the hepatic portal vein comes from the small intestines and is rich in nutrients (also could contain poisons, alcohol) although it lacks oxygen.

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The hepatic artery and hepatic portal vein flow together in the liver and mix their contents. The sinusoids, whichare highly permeable capillaries and which contain Kupffer's cells, absorb all the nutrients. Finally, the

sinusoids expel these nutrients through the hepatic vein into the body when necessary.

H.4.2 Explain the need for the liver to regulate levels of nutrients in the blood.

Because the body may not need all the eaten nutrients at once, the liver needs to regulate the levels of nutrients. It stores glucose in the form of glycogen, so it regulates nutrients by balancing glucose levels in the blood. The liver also breaks down fats and deaminates amino acids

where there is no glycogen left.

H.4.3 Outline the role of the liver in the storage of nutrients including carbohydrate, iron,

retinol and calciferol.

The liver stores carbohydrates as glycogen for energy reserve. It also stores iron from broken down hemoglobin

and the vitamins retinol (vitamin A - for night vision) and calciferol (vitamin D - so body can use calcium).

H.4.4 Describe the process of bile secretion.

In the liver, as Kupffer's cells break down blood cells, blood pigments that get separated from hemoglobin

are dumped into the canaliculi as bile. The canaliculi flow into the bile duct and into the gall bladder.

The gallbladder stores the bile until it is needed in the duodenum.

The contents of bile include bicarbonates, bile salts (digestion and absorption of fats) and bile pigments

(by products of red blood cell destruction). When food enters the duedenum enters the duodenum, the

sphincter oddi relaxes and allows bile to be secreted into the small intestine.

H.4.5 Describe the process of erythrocyte and hemoglobin breakdown in the liver

including phagocytosis, digestion of globin and bile pigment formation.

Erythrocytes (red blood cells), after about 4 months, are destroyed by Kupffer's cells (phagocytic) in the liver. Hemoglobin is converted to a yellow pigment (bilirubin),

the iron is stored and proteins (globin) are brokein down into amino acids. Bilirubin is transferred to

the bile duct, released into the intestines and converted by bacteria to a yellow pigment which gives the

characteristic color of feces.

H4.6 State that the liver synthesizes plasma proteins and cholesterol.

The liver synthesizes plasma proteins and cholesterol.

Option H.5 The Transport System

H.5.1 Explain the events of the cardiac cycle including atrial and ventricular systole and

diastole, and heart sounds.

The cardiac muscle does not get a nerve message from the nervous system to initiate its activity, instead it has a special type of tissue that

spontaneously generates electric activity. In the wall of the right atrium there is a group of cells that forms a special tissue called

the sino-atrial node.

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In the wall between the right atrium and the right ventricle there is another similar tissue called the atrioventricular

node (AVN). The sino atrial node (SAN), is also known as the pacemaker. It generates rhythmic electric waves that spread to the two atria causing them to contract. The electric wave spreading from the SAN reaches the

AVN and it causes it to fire an electric wave that spreads to the two ventricles.

The electric wave from the AVN travels in special muscle fibres called the bundle of His and from there through the pukinje fibers to the two ventricles. This makes

the two ventricles contract.

H.5.2 Analyse data showing pressure and volume changes in the left atrium, left ventricle and the aorta during the cardiac cycle.

The highest blood pressure pressure is owned by the aorta. This is because it receives blood from the left ventricle,

which contracts with the biggest force pushing the blood into the aorta with a big force and

resulting in high blood pressure.

Away from the aorta, pressure starts to decrease because it's further away from th left ventricle which is the pump that pushes the blood into the arteries. Thus, the pressure dampens as the blood ventricle

through the vena cava it has the lowest blood pressure.

H.5.3 Outline the mechanisms that control the heartbeat including the SA (sinoatrial) node,

AV (atrioventricular) node and conducting fibres in the ventricular walls.

SA node sends the signal across the atria for it contract. AV node sends a signal to ventricles that sweeps down through the septum of the heart to

and to sides of the ventricles. This causes the ventricle to contract from the bottom up. Conducting fibers in the ventricular walls send a signal down the septum.

H.5.4 Outline atherosclerosis and the causes of coronary thrombosis.

Artiosclerosis - if a person eats a diet high in saturated fats, plaques (deposits of lipids such as cholesterol)

develop on the inner walls of the arteries, narrowing the lumen. Thus the transport system becomes more

inefficient as less blood volume can be pumped through coronary thrombosis - the plaques can loosen and start to travel blocking smaller arteries. If such a block occurs in the heart or brain, a heart attack or a stroke occurs.

H.5.5 Discuss the factors which affect the occurance of coronary heart disease.

Risk factors include: having parents with heart attacks (genetic), old age (body wears down), being male, smoking, obesity, eating too much

saturated fat and cholesterol (clog arteries), lack of exercise (can't get rid of fatty acids).

H.5.6 Outline how tissue fluid and lymph are formed in body tissues.

Hydrostatic pressure causes fluid (H2O and small solutes such as sugar, salt, and O2) to leak out of capillaries (single celled). Blood cells and proteins

dissolved in the blood are too large to pass through and remain in the capillaries

About 85% of the fluid that leaves the blood at the arterial end of a capillary bed reenters from

the interstitial fluid at the venous end due to osmotic pressure. The rest is eventually returned

to blood vessels by the lymphatic system. The lost fluid and occasional proteins thus return

to blood via the lymph system. Fluid enters the lymph system by diffusing into lymph capillaries

intermingled among capillaries of cardiovascular system. The lymph contains the blood fluid, lipids (from small intestine) and WBC's (at lymph nodes).

H.5.7 Outline the transport functions of the lymphatic system.

Option H.6 Gas Exchange

H.6.1 Define partial pressure.

Partial pressure is the pressure exerted by each component in a mixture. The

pressure of a gas in a mixture is the same as it would exert if it occupied the same volume alone at the same temperature.

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H.6.2 Explain the oxygen dissociation curves of adult and fetal hemoglobin and myoglobin.

The oxygen dissociation curve of adult hemoglobin is to the right of the oxygen dissociation curve of

fetal hemoglobin. In other words, adult O2 saturation of hemoglobin is always lower than fetal O2 saturation

of hemoglobin at the same O2 partial pressure.

This is because fetuses don't have their own O2 source, so they must have high levels of O2 in hemoglobin for

reserve. When the O2 partial pressure is low, O2 diffuses out of hemoglobin very fast, so cells that

are low on O2 can quickly receive much O2 (since they need it the most).

The oxygen-storing protein myoglobin has a large reserve of O2 in case O2 concentrations get really low

(e.g., sprinting). When this occurs, myoglobin very quickly releases its O2 to support

the oxygen-depleted cells.

H.6.3 Describe how carbon dioxide is carried by the blood including the action of carbonic anhydrase,

the chloride shift and buffering by plasma proteins.

Carbon dioxide produced by body tissues diffuses into the interstitial fluid and into the plasma. Less than 10% remains in the plasma as dissolved CO2. The rest (70%) diffuses into red blood cells, where some (20%) is picked up and transported by hemoglobin.

Most of the CO2 reacts with H20 in the red blood cells to form carbonic acid. Red blood cells contain the enzyme

carbonic anhydrase, which catalyzes this reaction. Carbonic acid dissociates into a bicarbonate ion and hydrogen ion (H+). Hemoglobin (a plasma protein) binds most of the

H+, preventing them from acidifying the blood.

The reversibility of the carbonic acid- bicarbonate conversion also helps buffer the blood, releasing or removing H+ depending on the pH. Chlorine goes into the red blood cells when bicarbonate

comes out. This is referred to as the chloride shift.

H.6.4 Explain the role of the Bohr shift in the supply of oxygen to respiring tissues.

The Bohr shift helps the body release more O2 to respiring tissues when the pH is more acidic. During exercise, a lot of CO2 is produced, which results in larger amounts of hydrogen ions

that acidify the blood. Thus, the Bohr shift lets the body know it's exercising.

H.6.5 Explain how and why ventilation rate varies with exercise.

During inhalation, the intercostal muscles and the diaphragm contract. The volume of the lungs increases

as the diaphragm moves down and the rib cage expands. Air pressure in the lungs falls below that of the atmosphere

and air rushes into the lungs. Exhalation occurs when the rib muscles and diaphragm relax, restoring the

thoracic cavity to its smaller volume.

Thus pressure becomes greater in lungs than in the atmosphere and air rushes out. Action of the intercostal

muscles in increasing lung volume is most important during vigorous exercise. Increase in lung volume during shallow

inhalation results from the action of the diaphragm.

H.6.6 Outline the possible causes of lung cancer and asthma and their effects on the gas exchange system.

Smoking and inhaling other carcinogens (e.g., polluted areas, coal) may cause lung cancer. The effect of

lung cancer is that large cancerous cells in lungs reduce their surface area. Reaction to exercise and stress may cause asthma. The effect of asthma is that lung tissues swell, so they constrict the area of O2 absorption. Both

lung cancer and asthma result in efficient gas exchange.

H.6.7 Explain the problem of gas exchange at high altitudes and the way the body acclimatizes.

Mountain sickness may occur when a person travels quickly from a low to high altitude. Over a period of time the person becomes acclimatized: red blood cell production and ventilation rate increase. People living permanently at high altitude have greater lung surface

area and larger vital capacity than those living at sea level.

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