2ab revision notes

7/27/2019 2ab Revision Notes

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Human Biology 2A/B 2012 Study Notes

Organization of the body

o Organism: Body systems that are all integrated into one living thing.o System: A group of organs that work together for a common purpose. For

example the respiratory system.o Organs: Two or more tissues make up an organ. The lung is an example of an

organ.o Tissues: Specialised cells that carry out a common function. e.g. a group of

muscle cells make up muscle tissue.o Cells: Basic unit of the body. Carry out different functions. Red blood cells,

white blood cells, etc.The basic structural and functional unit of a living organism.

o Organelles: Structures that carry out specific functions inside a cell.

Cytoplasm is a jelly-like substance that makes up the cell. This substance suspends

organelles in the cell.

Organelle Functionso Endoplasmic reticulum: Membranes of E.R provide a surface for chemical

reactions to oc cur on.


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o Stores and transports material. Network of channels formed by parallel

membranes. Rough: proteins Smooth: other material (molecules). Produces lipids (fats) which make up cell

membrane. Golgi body (complex): Series of flattened, membranous bags stacked upon

each other. G.A positioned near nucleus. Package, modify, sec rete proteins(materials). Vesicles contain material being removed/ transported in or out.

Ribosomes: Protein synthesis oc curs. Contains RNA (which enables protein

production). Nucleus controls ribosomes. Free ribosomes : Production for cell Attached ribosomes: Production for transport out of cell to other cells Lysosome:Contains digestive enzymes to break down materials (lipids,

proteins, etc.). Also digests worn out organelles. Nuclear membrane:Separates nucleus from cytoplasm. Controls movement of

material (in/out of cell).

7. Nucleolus:Contains RNA; helps in protein production.8. Nucleus:Controls cell functions and cell division.9. Chromatin:Long thin strands, involved in reproduction of cell.

10.Centrioles:Involved in reproduction of cell; spindle fibres.

11.Mitochondria:Cellular respiration (energy production)

12.Cytoskeleton (microtubules): Give shape to the cell and assists with cellmovement.

Endocytosis:The process by which the vesicle is formed. A cell surrounding someextra-cellular material with a fold of cell membrane, the enfolding membrane then

breaks away. The material is enclosed within the cell in the form of a small bubbleliquid sac which is called a vesicle.

Two forms of endocytosis include: Phagoc ytosis (cell-eating) : This is when the material engulfed includessolid

particles. Pinocytosis (cell-drinking) : Material taken in is liquid.

Exocytosis:Process in which the contents of a vesicle are pushed out through thecell membrane. The membrane around the vesicle fuses with the cell membrane

and the vesicle contents are pushed out to the exterior.

Transport Mechanisms

Passive Transport: Cells energy does not have to be used to transport materialswhich come in/out of the cell.

Active Transport:Requires cell's energy for transfer of materials to occur.

Cell membranes are d ifferentially permeable which means they allow certain ions

and molecules to pass through, but restrictmovement of others.

Three basic processes that result in transport of materials into, or out of the cell: Diffusion:

Carrier mediated transport3. Vesicular transport


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1. Diffusion:Spreading of particles in random motion from a high region of high

concentration to a region of low c oncentration. This is also known as net

diffusion. The greater the conc entration difference the 'steeper' the diffusion

gradient and the faster diffusion will occur.

Alcohol, steroids and fat-soluble substances can easily enter the cells because

they can diffuse through the lipid portions of the membrane. Oxygen diffusesinto the cell as it is constantly used for cellular respiration. Concentration inside

the cell is higher than conc entration if oxygen outside the cell.

Osmosis:Diffusion of water across a differentially permeable membrane from aregion of high water molecules concentration (e.g ditilled water) to a region

of low water concentration (e.g. salt water).

Small molecules (e.g. water) are able to pass through pores in the cell

membrane however larger molecules such as sugar, starch, proteins are not

able to pass through at all.

As shown above, beaker is divided by a semi-permeable membrane. On one side is

a sugar solution on t he other is pure water. The concentration of water molecules is

less in the sugar solution than the pure water solution. As water molecules pass

through the membrane they distribute themselves easily over the whole beaker, butthe sugar molecules remain on the same side of the membrane. due to the

difference in concentration of water molecules, more water molecules will move

from the water to the sugar solution than in the opposite direction. The sugarsolution will gain water.

The higher level on one side is known as osmotic pressure. The higher the

conc entration of solute, the higher the osmotic pressure.

2. Carrier mediated transport is the transfer of special proteins bind that bind to

an ion or molecule in t he cell membrane and help it to move across the cell

membrane. However they only work with one particular ion or molecule.

Many substances that a cell needs are too large to pas through the cell membraneby simple diffusion and move through the cell membrane through a process called


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facilitated diffusion. This is a passive process that moves substances from a highconcentration on one side of the membrane to a lower concentration on the

opposite side. This is a type of carrier mediated transportin which the transportedmolecule

binds to a carrier protein which then changes shape to move the molecule to

the opposite side of the membranewhere it is released. Once all the carrier molecules are in use the process cannot go any faster

which make sit slower than simple diffusion. All cells transport glucose molecules through their membranes by facilitated

diffusion.

Active Transport is the movement of substances across the cell membrane againstthe concentration gradient using c ellular energy. Substances that are more

concentrated inside the cell can still be absorbed. In the same way, some less

concentrated materials can be exported from the cell.

Energy for the cell's active processes come from the mitochondria. At themitochondria cellular respiration breaks down glucose to release energy that the

cell can use.

Vesicular TransportAn active proc ess in which materials move in/out of the cell through vesicles. Two

basic types of vesicular transport includes endocytosis and exoc ytosis.

MetabolismAll the chemical reactions that occur in the body. Made up of two different types of

chemical reactions: catabolism or anabolism.


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Catabolic reactions release energy whereas anabolic reaction use energy.

Metabolism concerns the maintenance of a balance of energy released and used.

Enzymes are proteins that allow chemical reactions to take place at normal body

temperature. Without enzymes chemical reactions would be too slow (organic

catalysts). Breaking molecules apart and putting molecules back together is whatenzymes do. There are specific enzymes for each chemical reaction needed tomake the cell function.

Maltese enzyme is a protein shaped to accept a maltose molecule and break

the bond. The bond is broken and the molecules are released.

3. A single maltose enzyme can break 1000 maltose bonds per second and only

accepts maltose molecules.

Factors which affect enzyme activity rate include temperature and pH. Enzymeactivity decreases at pH levels higher or lower than the required level. Enzymes also

have an optimum working temperature. In humans that is a temperature of 37*C.

Cellular respiration is a metabolic process which occurs in any cell. It is a processby which organic molecules, taken in as food, are broken down in cells to releaseenergy for the cell's activities. Cellular respiration is a chemical processand is not tobe confused with respiration (breathing).

The main material involved with cellular respiration isglucose(C6H12O6)

Respiration can be summarised as an equation:C6H12O6+ 6O2 6CO2 + 6H2O + energy

The breakdown of glucose to carbon dioxide and water involves over 20 reactions

which occur sequentially one after the other. At each step a compound is formed

and catalysed by a different enzyme. Small amounts of energy are released as the

reactions proceed. The release of energy is controlled and does not occur at once.

There are three main processes in cellular respiration:

1. Glycolysis

This is the first step in which one glucose molecule is broken down, in a series of ten

steps, into two pyruvate molecules. Glycolysis oc curs in the cell's cytoplasm and isan anaerobic process in that it requires no energy. Pyruvic acid is then converted


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to lac tic ac id. Production of lactic acid is called anaerobic respiration.Glycolysis ofone glucose molecule releases enough energy to convert ADP to ATP. Anaerobic

respiration a llows cells to produce energy in the absence of no energy.

2. Krebs cycle (citric acid cycle)

This is a process of aerobic respiration and occurs in the cell's mitochondrion. Thepyruvic acid (glycolysis) is broken down into carbon dioxide and water. In the

mitochondrion there are enzymes available to use the pyruvic acid to form 2 more

ATP molecules.

3. Electron Transport System

Generates more than 34 ATP molecules of ATP from the products of glycolysis.

Energy from cellular respiration is important as the body uses this energy as heat energy to keep

the body at a constant temperature. The remaining energy is used to form ATP (adenosine

triphosphate)

Adenosine triphosphateis formed when an inorganic phosphate group is joined to a

molecule of adenosine diphosphate. The phosphate groups in ATP are joined by high chemical

bonds. Some of the energy from cellular respiration is stored in the bond between the ADP

molecule and the third phosphate group.

The cell's nucleus contains DNAwhich carry genetic informationthat determines the structure of

the cell. DNA (deoxyribonucleic acid) molecules are in the form of long strands and have a twisted

spiral shape in called a double helix.

The DNA is made up of bases known as nucleotides that are attached to sugar and phosphatemolecules. Nucleotides are the units that make up the DNA structure:


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Adenine pairs with Thymine

Cytosine pairs with Guanine

Each strand of DNA is bound to special proteins called histones. DNA strands are coiled around the

histones so that these long molecules can fit into a small space. In a cell that is not dividing the

coiled DNA forms a tangled network called chromatin.

When a cell divides, exact copies of each DNA molecule in the tangled mass of chromatin is

distributed to the daughter cells.

Mitosis

The division of the cell in which the nucleus is divided and ensures that each body cell recieves

exactly the same DNA as that possessed by the parent cell.

Interphase: DNA molecules duplicate. Molecules form exact copies of themselves. The

quantity of DNA in the nucleus doubles between one cell division and the next.


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There are four main stages of mitosis:

Prophase

First stage of mitosis after interphase. Pairs of centrioles become visible and move to

opposite ends of the cell. Chromatin coils to become chromosomes. Nucleolus and nucleus break down. Spindle fibres grow from centrioles. Centrioles move to opposite poles of the cell.

Metaphase

Chromosomes lie along the middle of the cell. Some spindle fibres attach to centromeres. Anaphase

Centromeres divide in two.

Spindle fibres pull new chromosomes to opposite poles of the cell. Each pole (future daughter cell) possess an identical set of genes.


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Telophase

Chromosomes gather at each pole of cell. Chromatin uncoils. New nuclear membrane appears at each pole. New nucleolus appears in each nucleus. Mitotic spindle disappears. Cytokinesis also takes place while telophase is occurring. The division of the cytoplasm is

known as cytokinesis. A furrow develops in the cytoplasm between the nuclei. The furrow gradually deepens until it

cuts the cytoplasm into two parts each with it's own nucleus.

Mitosis and cytoplasmic division result in the formation of two daughter cells. Each daughter cell

contains the same number of chromosomes as the parent cell. An altercation in the passing of

hereditary material is known as a mutation.

Protein synthesis

During interphase, the DNA molecules undergo the process of replication; form exact copies of

themselves. The two linked chains of DNA molecule separate and each seperated section containshalf of the original information, which serves as a template for the nucleotides that will form in the

new half.


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DNA carries genetic code which provides instructions for protein synthesis(combining of amino

acids to form large protein molecules). Protein that is made is essential for chemical reactions that

occur in the cell which are controlled by enzymes which are also proteins. Proteins are also

important as they make up most of the structural materials of cell.

The specific types of proteins that can be made are determined by genes. The order in which thefour bases (adenosine ,thymine, cytosine and guanine) occur in a DNA molecule is the genetic code.

Each of sequence of the three base is the code for a particular amino-acid.

Amino acids are assembled at the ribosomes in the cytoplasm of the cell. Instructions/information

contained in the DNA located in the nucleus must be accurately transferred to the ribosomes.

The information is gotten form the DNA to the ribosomes via the RNA (carries the message).

RNA differs from in DNA in that it is only a single strand of sugars and phosphates and thus

the bases occurs singly. RNA also contains the base uracil (U) instead of thymine.During protein synthesis the DNA unzips, separating its bases with the help of an enzyme.Messenger RNA move in and take a copy of one side of the DNA strand. Then it moves out of the

nucleus heading for the ribosome. Ribosomes are organelles found attached to the endoplasmic

reticulum or surrounding the cytoplasm. They help build protein molecules from amino acids.

The messenger RNA attaches itself on to the ribosomes while the transfer RNA brings the correct

amino acid to ribosome. The three bases of messenger RNA found on the ribosome must match up

with the three bases on the transfer RNA before the right amino acid is found. The three bases on

the ribosomes are called a codon/triplet. The body has 22 different kinds of amino acids. They

combine to form a protein molecule.


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Cell differentiation

It is the process in which unspecialised cells develop characteristics and functions of particular

types of cells.

Cell expansionMultiplication or reproduction by cell division of a population of identical cells descended from a

single progenitor.

Transcription:Formation of complementary RNA.

Translation:synthesis of RNA using a DNA molecule as the blueprint. There is a corresponding RNA

nucleotide for each DNA molecule.

Messenger: copies info to ribosomes Transfer: brings amino acids from the cytoplasm to the ribosomes.

Cells need nutrients to supply energy and matter for synthesis. These nutrients may be

organic or inorganic.

There are six groups of nutrients:

1. Water: fluid in which other substances dissolve in. water molecules take part in some

reactions.

2. Carbohydrates: main source of energy for cells. Complex carbohydrates are broken

down into simple sugars through the process of cellular respiration and in turn release

energy.

3. Lipids (fats): broken down to fatty acids and glycerol which enter the glycolysis

pathway and is broken down to release energy.4. Proteins: Broken down into amino acids. Most important proteins made are enzymes.

Enzymes control metabolism by controlling the rate of chemical reactions that occur in

the body. Proteins can also be used as a source of energy, only if there is an

inadequate amount of carbohydrates or lipids.

5. Minerals: Part of enzymes. May function as co-factors of enzymes or may be part of

substances like ATP that are involved in metabolism.

6. Vitamins: Act as co-enzymes for many chemical reactions of metabolism.

Organic Substances

Contain large amounts of carbons. Large molecules. Most carbon contain carbon, hydrogen and oxygen ONLY!

e.g. Glucose

Sucrose

*Twice as many hydrogen as oxygen ALWAYS.

Monosaccharides are simple sugars. These are sugars such as glucose, fructose and

galactose.

Disaccharides are two simple sugars joined together. (i.e. sucrose, maltose and lactose)

Polysaccharides are large numbers of simple sugars joined together ( e.g. starch, glycogen

and cellulose)

Protein


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*Contains carbon, hydrogen, oxygen and nitrogen (may have sulfur or phosphorus)

*Amino acids are the building blocks of protein. They are needed to be absorbed by cells.

*Amino acid + Amino acid = Dipeptide bond

*10 or more bonds are known as polypeptide bonds.

*Proteins consist of 100 or more peptide bonds.

Lipids

Same 3 elements as carbohydrates Larger molecules - a smaller amount of oxygen compared to carbon and hydrogen. Lipids - fatty acids + glycerol Saturated or Unsaturated

Nucleic acids Contain carbon, hydrogen, oxygen, nitrogen and phosphates. Made up of smaller units called nucleotides(sugar phosphate and nitrogen base)

Vitamins

*Organic compounds

*Don't supply energy but are needed for energy release from carbohydrates,proteins and lipids.

(vitamin D and Vitamin E)


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Non-organic substances

Minerals e.g. calcium, iron, phosphate, potassium and sodium Water (H2O) Essential for body functions

A balanced dietInvolves getting the correct amount of all the nutrients required for the body to function at its

optimum level.

*Malnutrition: Occurs when you do no not get the correct amount of all nutrients required. They

may be deficient in certain areas (e.g. proteins, vitamins, minerals, etc)

Factors affecting a balanced diet include:

Basal Metabolic Rate Amount of energy needed when body is at rest during metabolism. Level of activity Age

Gender

DigestionBody cells require simple sugars, amino acids, fatty acids, vitamins and minerals and water in order

to function properly. Vitamins, minerals and water are in the form of small molecules and are able to

pass through the differentially permeable membrane surrounding each cell. Carbohydrates,

proteins and fats are larger molecules which need to be broken down into smaller particles which

can be absorbed by the cell.

Digestion is the process where large carbohydrate, protein and fat molecules are broken down into

smaller particles by physical and chemical means in order to be absorbed by the blood and into the

cells.The organs of the digestive system are structured to carry out six basic activities:

1. Ingestion of food and water

2. Mechanical digestion of food

3. Chemical digestion of food

4. Movement of food along the alimentary canal

5. Absorption of digested food and water into the blood and lymph

6. Elimination of material that is not absorbed.


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Mechanical digestion

Breakdown into smaller particles.

e.g.:

Teeth: Physical process; breaking & grinding food. Stomach: Churning and mixing Muscle:Peristalsis(a series of wave-like muscle contractions that moves food (bolus)

down the oesophagus and through the intestines.) Bile: Increases surface area; emulsifies fats

Chemical digestion

Breakdown of food molecules into smaller, simple molecules by the action of enzymes.

Mouth (saliva)^Salivary amylase- breaks down starch molecules into smaller units.

Stomach (gastric protease = protein broken down into polypeptides (amino acids) Small intestine: Intestinal amylase, protease, lipase

The Mouth

Saliva

The intake of food is known as ingestion. It occurs at the mouth.


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The action of the jaw and teeth begins mechanical digestion where the food is broken

up into small pieces.

As the food is chewed it is mixed with saliva. A fluid which is secreted by three pairs of

salivary glands. It contains mucus and a digestive enzyme, salivary amylase which

begins chemical digestion of starch.

*Mucus: - lubricates food

Holds food in lumps Dissolves food-taste receptors are stimulated.

Teeth

4 incisors: Chisel shaped teeth for cutting and biting. 2 canines: On each side of the incisors. Conical teeth used for tearing. 4 pre-molars: On each side of the jaw, for grinding and crushing. 6 molars: Grinding and crushing, three on each side of the jaw.

After chewing, the food is formed by the tongue into a lump (bolus).

It is then swallowed as the tongue moves backwards and upwards,

pushing the food into the back of the mouth, the pharynx. The

pharynx leads into the oesophagus (23-25 cm long) that connects the

pharynx to the stomach.


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The Alimentary canal

Has 4 layers:1.Mucose: Mucus membrane lining the entire alimentary canal.2.Submucose: Consists of glands and connective tissues, through

which blood vessels, lymph vessels and nerves run.

3.Muscular: Circular muscle; muscle fibres arranged in circles

around the canal. Longitude muscle. Fibres arranged along the

length of the canal.

4.Serose: Outer layer of connective tissue.


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The stomach

From the oesophagus the food enters the stomach which has a j-

shape. When empty the stomach lies in longitudinal folds known as a

rugae.

The stomach lining is made up of mucosa which is specialised for thesecretion of gastric juice. Gastric juice is secreted by gastric glands

located in gastric pits in the mucosa.


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Gastric juice contains HCl, mucus and digestive enzymes which are secreted by different cells

in gastric pits. The stomach has an oblique muscle layer allowing it to contract in a variety of

ways to churn food and mix it with gastric juice.

The food is then converted to a thick 'soupy' liquid called chyme.

Most of the chemical digestion in the stomach deals with the start of protein digestion. The enzyme pepsin (gastric protease) breaks the bonds between certain amino acids, formingsmaller polypeptides.

Pepsin is secreted in an inactive form (pepsinogen) before it is activated when it comes into

contacted with HCl (low pH) Protein stays in the stomach longer which leads to more efficient protein digestion. The low pH kills bacteria entering the stomach with food.

In infants, rennin is also secreted which coagulates ( changes to solid) protein in the milk. Nutrients are not absorbed into the blood through the stomach as the internal surface is

covered by a thick layer of mucus. However, some alcohol and a few drugs may be absorbed

by the stomach.

At the lower end of the stomach is a thickening of circular muscle which results in constrictionknown as the pyloric sphincter. This sphincter prevents the stomach contents moving through,

or intestinal content from flowing back.

After 2-8 hour the stomach contents are gradually pushed into the next part of the alimentary

canal, the small intestine.

Small intestine: Digestion

The small intestine is approximately 6 metres long, the longest part of the alimentary canal (6m

long!)

It receives the cyme pushed through by the pyloric sphincter form the stomach.


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The first part of the small intestine is theduodenum; which is 25cm long and extends from the

bottom end of the stomach in a curve around the pancreas.

Digestion continues in the small intestine by the influence of: -

1. intestinal juicewhich is secreted by the lining,2. pancreatic juicewhich is secreted by the pancreas.

3. bilewhich is secreted by the liver but is stored in the gall bladder.

The mucosa and sub mucosa are modified to suit the functions of the small intestine. Both layers

have permanent folds that extend into the interior of the small intestine.

Mucosa has finger-like projections extending form folded surface known as the villi. Microscopic

projections, called microvilli project the external surface area of the villi.

These three modifications: folding, villi& microvilliserve to greatly increase the internal surface

area.

The main mixing movement in the small intestine is segmentation. Circular muscle fibres contract

forming segments. Contents of the small intestine are 'sloshed' back and forth mixing with digestive

enzymes.

Pancreatic juice, which has a pH of 8, enters the duodenum and helps to neutralise the acid that has

come with the material from the stomach.

Many enzymes are involved in digestion of food are contained in pancreatic juice. These include:

Pancreatic amylase:Breaks down starch into disaccharides

Trypsin ( pancreatic protease): splits proteins into smaller units Ribonuclease & deoxyribonuclease:Digest RNA and DNA Pancreatic lipases:Enzymes that breakdown fats into fatty acids and glycerol


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Intestinal juice contains enzymes such as:

Maltese/sucrose/lactase: breakdown

disaccharides(maltose/sucrose/lactose) into monosaccharaides Intestinal peptidase: breakdown of peptides into individual amino acids. Intestinal lipase: Breakdown monoglycerides into glycerol and free fatty

acids.Bile does not contain digestive enzymes but do contain bile salts which are

very important in the digestion of fatty acids. These salts act as an emulsifier

and break fats into tiny droplets.

The small intestine completes the chemical breakdown of large food

molecules.

Small Intestine: Absorption

Most of the absorption occurs in the small intestine. After food is mechanically

and chemically digested in the mouth, stomach and intestine, it is in the form

that can move through cells lining the villi and into the blood and lymph. This

movement is known as absorption.

Nutrients are absorbed through the internal surface of the small intestine; this

is because absorption requires a large surface area. The structure of the villus

is ideally suited for its function of nutrient absorption.

Inside each villus there is alymph capillary called lacteal surrounded by a

network of blood capillaries.

Monosaccharides such as glucose, fructose and galactose are actively

absorbed. They pass through cells on outside of the villi and into the blood

capillaries. Amino Acids are actively absorbed as well. Fatty acids and glycerol are absorbed by simple diffusion. In the cells of

villi, glycerol and fatty acids recombine to form triglycerides, which arecoated in protein. They enter lacteals as tiny droplets of chylomicrons.

Fat-soluble vitamins are absorbed in association with the fatty acids and

glycerol. Water-soluble vitamins are absorbed by simple diffusion into the blood

capillaries. Water is absorbed by osmosis.


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Substances that are absorbed into the are carried to the liver via hepatic portal vein.

In the liver, they may be removed for processing or carried to other blood cells. Fats absorbed into the lacteals are transported in the lymph system, which empties the blood.

Liver


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Besides processing digested foods the liver plays vital roles:

1. Blood glucose regulation

The liver regulates the blood glucose level by taking glucose from blood into cells or release

glucose (storedglycogen) from cells into the blood. This is controlled by pancreatic hormones insulin an glucagon. Insulin reduces blood glucose concentration. Glucagon increases blood glucose concentration. Glycogenolysis: glycogen breaks down into glucose. Glycogenesis: glucose is converted to glycogen.2. Deamination

Any excess amino acids that cannot be stored are converted in the liver into carbohydrates.

This process involves the removal of the amino group NH2 from the amino acid molecule, a

process known as deamination.

The amino group is converted into ammonia NH3, then into urea, which is filtered by the

kidneys and excreted in urine.3. Bile formation Bile salts emulsify fats for easier chemical digestion by enzymes.4. Plasma protein production

5. Blood-clotting factors production

Many chemical substances required for clotting is produced by the liver (e.g. prothrombin,

fibrinogen)6. Storage

In addition to storing glycogen, the liver also stores iron and the fat soluble vitamins A & D.

7. Toxin and hormone breakdown

Toxins and drugs are broken down into harmless substances. Hormones that circulate in the

blood are also inactivated in the liver.8. Heat production

Heat is released as a by-product of many chemical reactions. It is important for maintaining

constant body temperature.

9. Lipid metabolism

When glycogen stores in the liver are full, excess glucose is converted to fat. This fat is

transported to fatty tissues for storage.

Between meals, fat storage tissues release fatty acids in the blood. Liver converts fatty acids into

substances that are used by tissues as energy source.

The Large intestine

The large intestine (colon)n is about 1.5 m long and is named 'large' as it has a wider diameter than

the small intestine. It is arranged in an inverted 'U' shape.

There are no villi in the large intestine and no digestive juices are secreted however the lining

secretes large amounts of mucus.

Structure: At the part where ileum joins large intestine, there is a blind pouch called caecum. The

caecum is about 6cm long and ends in a tube- the appendix.

The final part of the large intestine (colon) is the rectum which opens to the exterior at the anus.

Around the anal opening is a circular muscle, the anal sphincter.


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Movement of materials through the large intestine is very slow (18-24 hrs.). During this time most of

the remaining water is absorbed, so that the contents become more solid.

Colonic bacteria(micro flora) break down much of the remaining organic compounds. Some bacteria

produce vitamins, which arethen absorbed through the walls into the blood. Mineral nutrients are

also absorbed.In addition, short chains of fatty acids are produced in digesting fibre. They are also

vital for proper function of the colon.

The semi-solid material left after water absorption and bacterial action makes up faeces.

The Rectum

The semi-solid material in the colon is pushed by peristalsis into the rectum. As the rectum

stretches, it triggers a response to defecation - the emptying of the contents of the rectum.

Expelled faeces contain:

Water Undigested food material, particularly cellulose Bile pigments, which gives the faeces colour Remains of cells that have broken away from the internal lining of the alimentary canal

Excretion is different from defection in that it involves the removal of metabolic waste, waste that

has been produced by chemical activity of the body cells. Except for bile pigments, the contents of

faeces are not metabolic waste so defecation is better referred to as elimination rather than

excretion.

Amylase Protease Lipase

Enzyme Salivary Amylase Pepsin Pancreatic Lipase

Source Salivary Glands Chief cells instomach lining

Pancreas

Substrate Starch Proteins Triglycerides suchas fats and oils

Products Maltose Smallpolypeptides

Fatty Acids andGlycerol

Optimum pH pH 7 pH 1.5 - 2 pH 7


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Circulatory System

The circulatory system acts as the body's internal transport system which circulates blood flow

throughout the body. It is the link between cells inside the body, which have certain requirements

and the environment outside the body to supply those requirements.

The HeartThe heart is an organ which acts as a pump to push blood around the body. It is located in the

middle of the chest cavity between the two lungs. The right atrium is bigger than the left.

Around the heart is a membrane called the pericardium which acts to hold the heart in place but

allows the heart to move as it beats. This muscle prevents the heart from overstretching.

The wall of the heart is made up of a special type of muscle, called the cardiac muscle.

Arteries: carries blood away from heart Veins: Carry blood back to heart

Capillaries: tiny vessels that carry blood between the cells

Circulation of Blood

Double circulation: This is the process in which blood passes through the heart twice. As explained in

the diagram below blood from the body enters the right atrium and into the right ventricle with the

aid of the tricuspid valves. The blood then enters the pulmonary artery and into the lungs. The blood

then returns to the heart via the left atrium and into the left ventricle. The blood then moves into

the aorta which transfers the blood back into the heart.


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Circulation of blood through the lungs:

As deoxygenated blood flows through the capillaries of the lungs, oxygen diffuses from the air intothe blood and carbon dioxide diffuses from the blood into the air. The blood becomes oxygenated.


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Circulation of blood through the body:

As oxygenated blood flows through the capillaries of the body, oxygen and nutrients diffuse from the

blood into the body cells, and carbon dioxide and other wastes diffuse from the cells into the blood.

The blood then becomes deoxygenated.

The transport medium (blood)

Blood is made up of a liquid part known as plasma and a liquid part consisting of cells and cell

fragments called formed elements. The formed elements that are suspended in the blood

plasma include red blood cells, erythrocytes and white blood cells, leucocytes.

Haemoglobin is able to combine with oxygen to form oxyhaemoglobin. Oxyhaemoglobin can be

easily broken down to release oxygen.

Oxygenated blood is blood with a proportion of oxygen. Oxyhaemoglobin is bright red in colour, sothe blood in the arteries is red. Haemoglobin is dark red or purplish in colour.

The deoxygenated blood in the veins (except veins from lungs) is therefore dark red.

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