Homostasis - Circulatory System Part 3 - 28 and 2

Structural Similarities of Arteries and Veins

The walls of both arteries and veins have three similar layers. On the outside, a layer of connective tissue with elastic fiber allows the vessel to stretch and recoil. A middle layer has smooth muscle and more elastic fibers. Lining the lumen of all blood vessels is an endothelium, a single layer of flattened cells that minimizes resistance to blood flow. 

Adaptations of Structure to Functions - Arteries

• Carry blood away from the heart to the tissues
• Carry oxygenated blood EXCEPT pulmonary artery
• Thick muscular walls provide strength to accommodate blood pumped rapidly and at high pressure by the heart and their elasticity (elastic recoil) helps maintain blood pressure even when the heart relaxes.

Adaptations of Structure to Functions - Veins 

• Carries blood TOWARDS the heart from the tissues 
• Carry deoxygenated blood EXCEPT pulmonary vein
• The thinner-walled veins convey blood back to the heart at low velocity and pressure. Blood flows through the veins mainly because skeletal muscle contractions squeeze blood in veins.
• Have valves to prevent backflow of blood hence blood flow only towards the heart.

 Adaptation of Structure to Functions - Blood Capillaries  

• Very thin-walled 
• Very small in diameter
• The exchange of substances (mainly diffusion) between the blood and interstitial fluid that bathes the cells takes place across the thin endothelial walls of the capillaries.  

Functional Comparison Between Arteries and Veins

 Arteries

• Transport blood away from the heart
• Transports blood under higher pressure (than veins)
• Carry Oxygenated Blood (except in the case of the Pulmonary Artery) 

Veins

• Transport blood towards the heart
• Transports blood under lower pressure (than arteries)
• Carry De-oxygenated Blood (except in the case of the Pulmonary Vein)

Structural Comparision Between Arteries and Veins

Arteries 

• Have relatively more muscle/elastic tissue 
• Have relatively narrow lumens
• Do not have valves (except for the semi-lunar valves of the pulmonary artery and the aorta)

Veins

• Have relatively less muscle/elastic tissue
• Have relatively wide lumens
• Have valves throughout the main veins of the body. These are to prevent blood flowing in the wrong direction, as this could (in theory) return waste materials to the tissues. 

Homostasis - Circulatory System Part 2 - 28 and 29 August 2012

The heart

Has involuntary muscle, 4 chambers (right atria, left atria, right ventricle and left ventricle). 

The ventricles  

The ventricle pumps blood at high pressure out to the arteries (to the lungs or other parts of the body).

The pressure generated by the left ventricle is greater than that generated by the right ventricle as the systemic circuit is more extensive than the pulmonary circuit. 

The atrium 

The atrium receives blood at lower pressure from the veins (coming from the lungs or other parts of the body).

The pressure generated by the atria is lower than that generated by the ventricles since the distance from atria to ventricles is less than that from ventricles to circulatory system.

The valves 

1) Ensure that the blood flows in the correct direction. 

2) Very important; without them, the flow of blood would be chaotic. 

3) Found in the heart and veins.

Tricuspid valve

• Separates the right atrium from the right ventricle. 
• It opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle. 
• It closes as the right ventricle contracts, preventing the blood from returning to the right atrium; thereby forcing it to exit through the pulmonary valve into the pulmonary artery. 

Bicuspid valve / Mitral valve

• Separates the left atrium from the left ventricle. 
• It opens to allow the oxygenated blood collected in the left atrium to flow into the left ventricle. 
• It closes as the left ventricle contracts, thereby forcing it to exit through the aortic valve into the aorta.  

Pulmonary valve 

• Separates the right ventricle from the pulmonary artery. 
• As the ventricles contracts, it opens to allow the de-oxygenated blood collected in the right ventricle to flow into the lungs. 
• It closes as the ventricles relax, preventing blood from returning to the heart.

Aortic valve 

• Separates the left ventricle from the aorta.
• As the ventricle contracts, it opens to allow the oxgenated blood collected in the left ventricle to flow throughout the body.
• It closes as the ventricles relax, preventing blood from returning to the heart. 

Superior and Inferior Vena Cava

Superior Vena Cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the head and upper body feed into the Superior Vena Cava, which empties into the righ atrium.

Inferior Vena Cava is the other main vein that brings de-oxygenated blood from the body to the heart. Veins from the legs and the lower torso feed into the Inferior Vena Cava, which empties into the right atrium.

Aorta

Carries oxygenated blood from the left ventricle to the systematic circulation. The aorta is an elastic artery and as such is quite distensible. When the left ventricle contracts to force into the aorta, the aorta expands. This stretching gives the potential energy that will help to maintain blood pressure during diastole, as during this time the aorta contracts passively. 

Pulmonary Artery    

The pulmonary arteries carry blood from the heart to the lungs. They are the only arteries other than the umbilical arteries in the fetus that carry de-oxygenated blood. 

In the human heart, the pulmonary trunk (pulmonary artery or main pulmonary artery) begins at the base of the right ventricle. It is short and wide - about 5cm in length and 3cm in diameter. It then branches into 2 pulmonary arteries (left and right), which deliver de-oxygenated blood to the corresponding lung. 

Pulmonary vein

The 4 pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart. They are the only veins in the post-fetal human body that carry oxygenated blood. 

Chordae Tendineae

The chordae tendineae, or heart strings, are cord-like tendons that connect the papillary muscles to the tricuspid valve and bicuspid valve. When the right ventricle of the heart contracts, the blood pressure pushes the tricuspid valve which closes and prevents backflow of the blood into the right atrium. The chordae tendineae prevents the flaps from being averted into the right atrium. Similarly, these cord-like tendons hold in position other flaps like the bicuspid valve.

Papillary muscle

In anatomy, the papillary muscles of the heart serve to limit the movement of the mitral and tricuspid valves. These muscles contract to tighten the chodae tendineae, which in turn prevent inversion.

This occurs in respond to pressure gradients. Instead, they brace the valves against the high pressure, preventing regurgitation of ventricular blood back into the atrial cavities. 

Coronary arteries 

The heart is composed primarily of cardiac muscle that continuously contract and relaxes, it must have a constant supply of oxygen and nutrients. 

The coronary arteries are a network of blood vessels that carry oxygen and nutrient rich blood to the cardiac muscle tissues. The larger vessels travel along the surface of the heart. The smaller branches, the cappilaries, penetrate the heart muscle. They are so small that the Red Blood Cells must travel in a single file.  

Homostasis - Circulatory System Part 1 - 28 and 29 August 2012

Mechanism of Nutrition of Amoeba - Ingestion

The food is ingested at the point where it comes in touch with the cell surface with the help of pseudopodia. Pseudopodia engulf the food into the cytoplasm. The process of ingestion takes about 2 minutes.

Mechanism of Nutrition of Amoeba - Digestion and absorptionDigestion - Pseudopodia secretes a sticky and toxic fluid which adheres and kills the prey. It is then taken in by invagination to form a food vacuole whereby chemical digestion takes place.

Absorption - The food is converted into diffusible form and it is readily absorbed by the cytoplasm. The vacuole and becomes progressively smaller as the food is absorbed by diffusion.

 Mechanism of Nutrition of Amoeba - Assimilation and Egestion

Assimilation - These nutrients are used to build new protoplasm and to provide energy for the amoeba.

Egestion - The egestion takes place by exocytosis. There is no particular point from which the egestion takes place. As the amoeba moves forward, the undigested matter is shifted to the back and eliminated as food pellets through a temporary opening formed at any nearest point on the cell membrane. 

Transport in Humans 

Main transport system is called the Circulatory System. 

The Circulatory system works with 
1) the Respiratory system (Exchanges Carbon dioxide and Oxygen)
2) the Digestive system (Carries nutrients and wastes to/from the cells)
3) Works with the Excretory system (Carries waste to kidney for removal)

Human Circulatory System 

Consist of 
1) Cardiovascular System (Made up of Heart, Blood Vessels, Blood)
2) Lymphatic System (Made up of Lymph, Lymph nodes, Lymph vessels)

Cardiovascular System

Consists of 4 components 

1. Blood - The main 'transportation service' that handles the distribution of nutrients, oxugen and hormones to the various regions of the body.

2. Arteries and Veins - A system of tubes that form the transport route where blood flows.

3. Heart - The motor of this transport service.

4. Capillaries - are sites of exchange.

Divided into 

1. Pulmonary System and heart (Pulmonary = lungs)

2. Coronary System (Coronary = heart)

3. Systemic Circulation (Systemic = rest of body)

Double Circulation in Mammals 

Blood passes through the heart twice for each complete circuit of the body. 

Deoxygenated blood flows from the main circulation of the body to the heart, then to the lungs and oxygenated blood returned back to the heart (pulmonary circulation) before it is pumped into the main circulation and circulated to all parts of the body except the lungs (systematic circulation).

 

Homostasis - Nutrition part 2 (The digestive system) - 23 August 2012

The Digestive System 

The alimentary canal

It is a series of connected tubes which functions to carry out digestion

It consists of the mouth, esophagus (previously known as gullet in primary school), stomach, small intestine, large intestine, rectum and anus. 

The accessory organs 

It consists of salivary glands, gall bladder, liver and pancreas.

Digestion 

There are two types of digestion - mechanical digestion and chemical digestion.

Mechanical digestion

In simple terms, it means moving parts breaking down food substances.

Example: Mouth and stomach from the alimentary canal.

Chemical digestion 

Chemical digestion refers to the breaking down of food substances chemically. Note that chemical digestion requires enzymes. 

Example: Mouth, stomach and small intestine from the alimentary canal.

Enzymes = chemical substances that break things down. Therefore, they are involved in chemical digestion. 

The different digestion and where it takes place in our human body

We learn 3 different digestion in sec 1, namely Carbohydrate digestion, Protein digestion and Fat digestion.

Mouth: Only carbohydrate digestion takes place here, where polysaccharides are broken down into smaller polysaccharides and/or maltose)

Stomach: No carbohydrate digestion and fat digestion take place in the stomach; only protein digestion takes place. It is also where protein digestion starts. Proteins are broken down into small polypeptides here.

Lumen of small intestine: Carbohydrate digestion takes place. Polysaccharides are broken down into maltose and other disaccharides by an enzyme from the pancreas. Protein digestion also takes place; polypeptides are broken down into amino acids. Fat digestion takes place here too. Fat droplets are broken down into glycerol and fatty acids by an enzyme from pancreas.

Epithelium of small intestine: Carbohydrate digestion takes place. Disaccharides are broken down into monosaccharides by an enzyme which comes from the small intestine. Protein digestion takes place; polypeptides are broken down into amino acids. Fat digestion also takes place, fat droplets are broken down into glycerol and fatty acids by an enzyme from pancreas.

Note that the enzymes from the pancreas take part in carbohydrate digestion and lipid digestion (fat digestion). Bile is produced in the gall bladder and salivary amylase is produced in the salivary glands. 

The small intestine 

The small intestine is approximately 6 meters long. 

Duodenum: Where the fat globules are broken up into fat droplets by bile salts.

Ileum: More digestion, less absorption as most of the food substances are not simple substances.

Jojenum: Less digestion, more absorption as most of the food substances have been digested already.

Villi 

Villus is a single protrusion.

 

Epithelial cells in the small intestine

- Has microvilli

 

(taken from cellfunctioning.wikispaces.com, edited by me)

Homostasis - Nutrition Part 1 - 22 August 2012

There are 5 main food groups, Carbohydrates, Proteins, Lipids, Inorganic substances and Dietary fibre.

Carbohydrates

Carbohydrates consist of monosaccharides, disaccharides and polysaccharides.

Monosaccharides

There are 3 types of monosaccharides that we have learnt - Glucose, Fructose and Galactose.

Formulas:

Glucose + Glucose = Maltose
Fructose + Glucose = Sucrose
Galactose + Glucose = Lactose

Disaccharides

Disaccharides are when 2 monosaccharides. 

Polysaccharides

Polysaccharides are when multiple monosaccharides are combined.

Proteins

Proteins are broken down into polypeptides and polypeptides can then be further broken down into amino acids. The reverse can also occur (ie Amino acids combine to form polypeptides and polypeptides can then combine to form proteins.)

Deficiency: Kwashiokor (characterised as a bloated stomach)

Lipids/Fats       

Lipids, also known as fats, is broken down into glycerol and fatty acids. Glycerol can combine with fatty acids to form lipids.

Inorganic substances comprises vitamins and and minerals.

Vitamins 

We have learnt 5 types of vitamins, namely Vitamin A, C, D, E and K.

Vitamin A

Deficiency results in night blindness.
Source: Carrot, dark-green leafy vegetables, eggs

Vitamin C

Deficiency results in scurvy.
Source: Fresh citrus foods, green vegetables

Vitamin D

Deficiency results in rickets.
Source: Sunlight, fortified milk and margarine, eggs and butter, cod liver oil.

Vitamin E

Deficiency results in anemla.
Source: Vegetable oils like soyabean oil and corn oil.

Vitamin K

Deficiency results in excessive bleeding.
Source: Sunlight, fortified milk and margarine, eggs and butter, produced by the micro-flauna found in the large intestine.

Minerals consists of calcium and iron.

Calcium 

Deficiency results in rickets.
Source: Cereals, green vegetables, eggs and fruits.

Iron

Deficiency results in anemla.
Source: Liver, meat, eggs and green vegetables.

Dietary fibre

Deficiency results in constipation. 

Osmosis - 14 and 21 August 2012

Osmosis - What is Osmosis?

Osmosis is the net movement of water molecules down the concentration gradient through a partially permeable membrane.

Water moves freely through pores in the partially permeable membrane. Some solutes are too large to move across the membrane.

Diffusion and Osmosis... what is the relationship?

Diffusion

• Movement of particles in general 
• Can occur both in the presence and absence of a membrane. 

Osmosis 

• Movement of water molecules only. 
• Water molecules move across a partially permeable membrane.  

 Water Potential ( )

Water potential is a measure of the tendency of water molecules to move from one area to another. 

Water molecules move from a region of high water potential to a region of low water potential.

Relating Water Potential to Osmosis...

Since water potential is a measure of the tendency of water molecules to move from one area to another, we can also define osmosis as:

The net movement of water through a selectively permeable membrane from a region of high water potential to a region of low water potential. 

Osmosis in animal cells

Animal cells

• Structure is simple
• Cytoplasm is surrounded by a partially permeable cell membrane. 

If placed in a hypertonic solution (solution has higher concentration of solutes than the cytoplasm)...

Water will leave the cell by osmosis as the cell has a higher water potential than its surroundings. The cell will lose volume and shrink (crenate). Water loss only ceases if the concentration of the cytoplasm rises to that of the surrounding solution.

Note that 'cenate' can only be used for animal cells!

If placed in a hypotonic solution (solution that has a lower concentration of solutes than the cytoplasm)

Water enters the cell by osmosis as the surrounding solution has a higher water potential than the cell. Hence, the cell gains volume and expands. Since the cell membrane cannot resist expansion, the cell eventually bursts (cytolysis)

Note that the term 'cytolysis' is only to be used for animal cells! Find out why later! 

The plant cell 

• Plant cells are structurally more complex.
• They are surrounded by a cellulose cell wall which is freely permeable to water, not elastic and is able to resist cell expansion.
• Each plant cell contains a large central vacuole which contains a solution of salt, sugars and ions and is  bound by a partially permeable membrane. 

Osmosis in plant cell 

If placed in a hypotonic solution (solution has a lower concentration of solutes than the cytoplasm)...

Water enters the vacuole by osmosis. The vacuole swells, pushing the cytoplasm against the cell wall. The inelastic cell wall resists expansion and the cell becomes rigid, also known as turgid. It can be described as in a state of turgor.

Young plants, which have little woody tissue, rely on turgor for support against wind and gravity.

If placed in a hypertonic solution (solution has a higher concentration of solutes than the cytoplasm)...

Water leaves the cytoplasm and vacuole by osmosis. The cytoplasm and vacuole shrinks. pulling the cell membrane away from the cell wall. The cell is now plasmolysed or is in a state of plasmolysis. The tissue becomes flaccid.

A non-woody plant which loses lots of water has many plasmolysed cells, and as a result, the plant wilts. No longer fully filled with water, the tissue loses support and becomes floppy or flaccid.

Plasmolysis vs Crenation       

Plasmolysis is the shrinking of a plant cell cytoplasm (due to loss of water), and the cell membrane moves away from cell wall.

However, crenation is the shrinking of animal cell.

Isotonic solution

An isotonic solution has the same concentration of solutes as the cytoplasm. It also has the same water potential as the cytoplasm.


In both animal and plant cells, there is no net movement of water molecules into or out of the cell.


Therefore, the cells neither shrinks nor expands when placed in an isotonic solution.

Diffusion part 2 - 2 August 2012

Applications of diffusion in Biology

Example 1

To stay alive, the amoeba which is a unicellular organism needs to obtain nutrients and remove waste efficiently by the process called diffusion.

Example 2

Chemical substances must be able to move from one place to another in order to keep the living organisms alive and growing. For example, food substances need to move from one cell to another, move in & out of the cell and move from one part of the cell to another.



One way through these processes can occur is by diffusion across membranes.

Example 3

There are 2 types of membranes - The partially permeable membrane and the permeable membrane



Partially permeable membrane

A partially permeable membrane allows some substances to pass through.

Permeable membrane


A permeable membrane allows all substances to pass through.

Diffusion across a permeable membrane

An example of a partially permeable membrane is the visking tubing.

Other examples

• Movement of carbon dioxide during photosynthesis.

• Movement of oxygen and carbon dioxide in animals.

Conclusion

• Diffusion is an important process where substances are moved without use of energy.
•  It is the net movement of particles (or molecules; or ions) from a region of higher concentration to a region of lower concentration.
•  Thus the movement is down a concentration gradient.
• It is important to bear in mind that:
  – The movement is random.
  – The greater the concentration gradient, the faster the
  rate of diffusion.