DIGESTIVE SYSTEM

Anatomy of the digestive system.

Click here for a diagram that summarizes the functions of the digestive system.

Another name for the digestive system is the alimentary canal. Here are some few important points to note:

1. Carbohydrate digestion begins in the mouth where the enzyme amylase is present. Amylase breaks down complex carbohydrates into simple sugars.

2. The tongue rolls the food into the ball-form called bolus.

3. Food travels down the esophagus by the peristalsis. This involves the rhythmic relaxation and contractions of the smooth muscles with forward propulsion.

4. The stomach secretes hydrochloric acid (HCl), mucus, and pepsinogen (an enzyme). Pepsinogen is activated to pepsin, which digest protein. Note: Protein digestion starts in the stomach.

5. The small intestine consist of the duodenum, jejenum, and ileum.

6. The Gall Bladder stores bile. Bile is the yellow-greenish substance produced by the liver.

7. Bile helps to emulsify fat.

8. The pancreas is both an exocrine and endocrine gland. As an exocrine gland, it produces digestive juices and enzymes.

9. Fat digestion starts in the duodenum.

10. Absorption of digested food occurs in the ileum (third part of the small intestine).

11. Villi are present in the small intestine. They increase the surface area for absorption.

12. The large intestine stores the feces and also absorbs water.

QUESTIONS FOR THE DAY

Label the numbered parts and state their functions:



Answers to the numbered parts.

ENDOCRINE SYSTEM

An endocrine gland is a gland without ducts. The secretions are released directly into the blood. The endocrine glands secrete hormones that regulate various metabolic activities in the body.
Here is a good diagram of the endocrine system. Click here. You can be given a diagram like this and you could be asked to identify the various glands.

Hypothalamus: The hypothalamus produces eight (8) hormones. Some of the hormones stimulate the pituitary gland to produce other hormones.

1. Thyrotropin-releasing hormone - This acts on the pituitary to release thyroid stimulating hormone (TSH)
2. Growth hormone-releasing hormone-This acts on the pituitary to release growth hormone (GH)
3. Gonadotropin-releasing hormone -This acts on the pituitary to release gonadotropins, namely, Follicle stimulating hormone (FSH) and Luteinizing hormone (LH).
4. Corticotropin-releasing hormone -This acts on the pituitary to release adrenocorticotropic hormone.
5. Oxytocin -This causes uterine contractions and also helps with secretion of the breast milk during lactation.
6. Dopamine - It is a neuroendocrine transmitter. Acts as a neuro-transmitter and also stimulates the release of othe hormones.
7. Vasopressin (Antidiuretic hormone -ADH) - Acts on the kidneys to prevent the lost of water via the urine.
8. Somatostatin - It inhibits the release of growth hormone.

Pituitary gland: Has an anterior (hormone-producing glandular) portion and a posterior (neural) portion which is an extension of the hypothalamus.  Two hormones ( Oxytocin and ADH) produced by the hypothalamus are stored in the posterior pituitary later release.

Four of the six pituitary hormones are tropic hormones. They regulate the function of other endocrine glands.Here are the hormones produced by the anterior portion:

1.  Growth hormone (GH): It stimulates growth of all body tissues but especially skeletal muscle and bone. GH mobilizes fats, stimulates protein synthesis, and inhibits glucose uptake and metabolism. Over production can lead to gigantism while underproduction can lead to dwarfism.

2. Thyroid-stimulating hormone (TSH): This promotes normal development and activity of the thyroid gland. 

3. Adrenocorticotropic hormone (ACTH): This stimulates the adrenal cortex to release  corticosteroids. 

4. The gonadotropins (follicle-stimulating hormone (FSH) and luteinizing hormone (LH)): These regulate the functions of the gonads in both sexes. 

     (a) FSH stimulates sex cell production.  

     (b) LH stimulates gonadal hormone production. 

5. Prolactin (PRL): This promotes milk production in humans females. 

The posterior portion stores and releases two hypothalamic hormones:

1. Oxytocin: This stimulates powerful uterine contractions during labor and delivery of babies. It also causes milk ejection in nursing women. 

2. Antidiuretic hormone (ADH): This stimulates the kidney tubules to reabsorb and conserve water. This results in the production of small volumes of highly concentrated urine and decreased plasma osmolality. Underproduction leads to a condition called diabetes insipidus, where the affected person passes a lot of diluted urine.

Thyroid gland

It produces the thyroid hormone (TH), which includes thyroxine (T4) and triiodothyronine (T3). It increases the rate of cellular metabolism. 

Calcitonin, is produced by the parafollicular cells of the thyroid gland. It decreases the blood calcium levels.

Parathyroid glands

It secretes parathyroid hormone (PTH), which causes an increase in blood calcium levels.

Pancreas

The pancreas is both an exocrine and an endocrine gland. Exocrine means that it has ducts. The endocrine portion (islets of langerhans) releases insulin and glucagon. It also releases smaller amounts of other hormones to the blood.

Glucagon, released by alpha (α) cells - It increases the glucose level in the blood.

Insulin is released by beta (β) cells - It reduces the glucose level in the blood. It increases the rate of glucose uptake and metabolism by most body cells. 

Gonads

The ovaries of the female release two main hormones - estrogens and progesterone. Estrogens stimulate maturation of the female reproductive system and development of the secondary sexual characteristics. Progesterone works with estrogens in establishing the menstrual cycle.

The testes of the male produce testosterone. It promotes maturation of the male reproductive organs, development of secondary sex characteristics, and production of sperm by the testes.

Pineal gland

The pineal gland produces the hormone  melatonin, which influences daily rhythms such as sleep and wake patterns.

Thymus 
It is an important organ of the immune system during the developmental stages of life. It vanished by the time of birth. The T-cells mature here.

METABOLIC REACTIONS

Metabolism is the building up (synthesis) or the breakdown of substances in the living organism. It consists of anabolism and catabolism.

Anabolism is the formation or synthesis of complex substances from simple ones. That is, A + B -----> C.
An example of anabolic reaction is photosynthesis.

Catabolism is the breakdown of complex substances into simple ones. That is, C -----> A + B.
An example of catabolic reaction is respiration.

What is photosynthesis?
This is the process whereby  plants produce their food (glucose) using carbon dioxide, water, and energy from the sun,  in the presence of chlorophyll (the green pigment in the leaves). Chlorophyll is contained in the chloroplast and it traps the energy from the sunlight. Glucose is the main product formed and oxygen is given off as waste.

This the equation that summarizes photosynthesis: 6CO₂ + 6H₂O à C₆H₁₂O₆ + 6O₂
This is carbon dioxide: CO₂ 
This is water: H₂O
This is glucose: C₆H₁₂O₆
This is oxygen: O₂

Note: You should know this equation off-hand. 

Water goes up from the roots through the plant vessel called xylem.
The glucose formed in the leaves are transported to storage sites via the plant vessel called phloem.

The glucose is stored as starch in the plants.

Respiration
Respiration involves the breakdown of glucose in the presence of oxygen to release energy in the form of ATP (ATP stands for adenosine  triphosphate, the energy currency). ATP is generated in the mitochondrium. Respiration is a combustion reaction since oxygen is needed.

There are three (3) stages in the process of respiration.
1. Glycolysis: Glucose is activated and broken down to pyruvate.
2. Kreb's cycle (also known as the Tricarboxylic Acid Cycle - TCA cycle): Some ATP, NADH, FADH_{2 are produce here.}

3. Electron Transport Chain (ETC): Most ATP's are produced here.

This equation summarizes the reaction of respiration:
 C₆H₁₂O₆ + 6O₂  à6CO₂ + 6H₂O 

Know this very well. It is simply the reverse of photosynthesis reaction.

In the absence of oxygen, pyruvate is converted into lactic acid, which  causes muscle cramps. When oxygen is available, the lactic acid is changed back to pyruvate which is then used up in the Kreb's cycle.

Fermentation
This is the process whereby glucose is changed to alcohol in the absence of oxygen.

ELECTROMAGNETISM AND MAGNETS

Magnetism

There is a magnetic field around a magnet. This is a mathematical representation of the interaction between the magnetic material and electrical current. It is represented by magnetic field lines which moves out of the north pole into the south pole.

Diagram of magnetic field lines.

It is very important to note the direction of the arrows on the field lines.

Interaction between two magnets
1. North and South poles attract (opposite pole attract). Diagram of attractive forces.
2. North and north poles will repel; south and south poles will repel (Like poles repel).

Diagram of repulsive forces for north to north poles.

Diagram of repulsive forces for south to south poles.

Electromagnetism is the study that involves the use of electricity to create magnet and vice versa (that is, using a magnet to generate electricity).

What is a solenoid?

The solenoid is a long coil containing a large number of close turns of insulated copper wire. A magnetic field  is produced by the current carrying solenoid. The strength of magnetic field produced by a current carrying solenoid is directly proportional to the number of turns and the strength in the solenoid. It is also dependent on the nature of "core material" used in making the solenoid. When soft iron rods are used as cores, they produce the strongest magnetism. Solenoids are used for making electromagnets. 

What is an electromagnet? Diagram

When an electric current flows through a soft iron rod placed inside a solenoid, a temporary magnet is created. It acts as a magnet only so long as the current is flowing in the solenoid. This combination of a solenoid and a soft iron core is called an electromagnet. An electromagnet, therefore, consists of a long coil of insulated copper wire wound on a soft iron core.

Here are some uses of electromagnets:

1. Used in cranes to lift heavy metal.

2.  Used in electric bells

3. Used in radio speakers

4. Used in microphones

5.  Used in dynamos

TYPES OF ELECTRICAL CIRCUITS

There are two types of electrical circuit arrangements.
1. Parallel circuits: There is an alternate path to the flow of the current if other paths are blocked.

Note on diagram below: The symbol "R" represents any form of resistance such as bulb resistors, etc. The symbol "E" represents a cell such as battery, a current generator.

2. Series circuit: There is only one path for the current to flow. When this path is blocked, there will be no flow of current.
   
 Animation in a series circuit.

UNITS OF ELECTRICAL QUANTITIES

Variable	Symbol	Unit	Symbol
Voltage	V	Volts	V
Current	I	Ampere	A
Resistance Power	R P	Ohm Watt	Ω W

Formulas you should know:

1. Voltage = Current x Resistance

2. Power = Voltage x Current

You should be able to use these formulas in calculations.

THE BLOOD

Once again you do not need too much detail to pass any entrance test so we will keep it very short and simple. Just the basics is what you need!

The blood is made up of the plasma (liquid part) and the formed cells (blood cells). It distributes nutrients to the cells, carries oxygen from the lungs to the cells, carbon dioxide from cells to the lungs, transports waste to various organs to be excreted or degraded, transports hormones and various chemicals, and it helps to maintain the body's temperature.

Picture showing the components of blood.

Plasma is made up of serum and fibrinogen. Serum is the part of plasma that does not clot. Fibrinogen is inactive but when activated to fibrin, then clotting occurs.

The formed cells arise from the bone marrow. They are:
1. Erythrocytes (Red Blood Cells a.k.a RBC's): These transport oxygen. Oxygen is carried by hemoglobin in the RBC. Iron is needed for RBC production in addition to other nutrients such as Vitamin B.  "Haem" represents iron and "globin" represents protein. So hemoglobin is iron plus attached to four protein units. Lack of iron can lead to reduced RBC production referred to as anemia. RBC's have a life span of 120 days.

2. Thrombocytes (Platelets): These are not actual cells but fragments of cells. They are invlove with the formation of blood clots.

3. Leucocytes (White Blood Cells a.k.a WBC's): These cells defend the body against infections. These are the types of WBC's: Neutrophils, Eosinophils, Basophils, Lymphocytes, and monocytes. Basically, the neutrophils are more involved in fighting bacteria infections. Eosinophils and basophils play roles in allergic reactions and parasitic infections. Lymphocytes are vital to fighting viral infections and monocytes are like scavengers that get rid of cancer cells and dead cells including bacteria.

ANSWERS TO QUESTIONS FOR THE DAY

1. What is the pulmonary circulation?
This starts from the right ventricle to pulmonary artery, to the pulmonary vein, and ends at the left atrium.

2. What is the systemic circulation?
This starts from the left ventricle to aorta, to the tissues/organs, to the  inferior vena cava/superior vena cava, and then back to the right atrium.

3. What will happen when the tricuspid valves fail to function well?
Some blood will be pumped backwards from the right ventricles into the right atrium.

4. What will happen when the bicuspid valves fail to function properly?
Some blood will be pumped backwards from the left ventricles into the left atrium.

5. What will happen when the left ventricle fails to pump blood into the aorta?
There will be pooling of blood (collection of blood backwards) into the left atruim and then into the pulmonary circulation. This will lead to fluid collection in the lungs. This is what occurs when there is left heart failure.

QUESTIONS FOR THE DAY

1. What is the pulmonary circulation?

2. What is the systemic circulation?

3. What will happen when the tricuspid valves fail to function well?

4. What will happen when the bicuspid valves fail to function properly?

5. What will happen when the left ventricle fails to pump blood into the aorta?

OVERVIEW OF THE CARDIOVASCULAR (CIRCULATORY) SYSTEM

We will look at the basic concept and structure of the cardiovascular system today. You only need to know the basic structure of the general circulation to pass the test. We will begin by looking at the structure of the heart.

Diagram of the cardiovascular system.

The heart consists of four chambers:
1. Left ventricle
2. Left atrium
3. Right ventricle
4. Right atrium

The right side of the heart carries deoxygenated blood while the left side carries oxygenated blood.

Deoxygenated blood return to the right atrium from lower parts of the body via the inferior vena cava and from the upper part via the superior vena cava.

The right ventricle pumps deoxygenated blood to the lung via the pulmonary artery. Note that all arteries carry deoxygenated blood except the pulmonary artery.

Oxygenated blood return to the left atrium from the lung via the pulmonary vein. Note that all vein carry deoxygenated blood except the pulmonary vein.

The left ventricle pumps the oxygenated blood to the other parts of the body via the aorta (the largest artery in the body)

There are valves between the atria and ventricles. The one on the left is called the mitral valve (bicuspid valve) and the right one is called the tricuspid valve. These valves prevent the back flow of blood.

CHEMICAL BONDS

Basic concept on chemical bonds

1. Ionic bond: The bond formed when one atom looses electrons and the other accepts  

      them. It is formed when a metal bonds to a non-metal, example: NaCl

Original electronic configuration : Na  2:8:1                      Cl    2:8:7

Sodium loses one electron from its outermost shell (valence shell)  to become   Na+ 2:8                   and  chlorine gains this electron to become Cl^-   2:8:8   

 Hence  Na⁺Cl^{-    ----------->} NaCl

2. Covalent bond: This is the bond formed through the sharing of electrons. It is formed

    when non-metal bond to each other. Examples: H₂, Cl₂, HCl

Illustration of covalent bonding

Water is neither purely ionic nor purely covalent because the electrons are not shared equally. The more electronegative element, oxygen, tends to pull the shared electrons from the less electronegative (electropositive), hydrogen atom. One end, or pole, of the molecule has a partial positive charge (+), and the other end has a partial negative charge (-).Water is best described as a polar compound.

As a rule, when the difference between the electronegativities of two elements is less than 1.2, we assume that the bond between atoms of these elements is covalent. When the difference is larger than 1.8, the bond is assumed to be ionic. Compounds for which the electronegativity difference is between about 1.2 and 1.8 are best described as polar, or polar covalent.

Hydrogen bonding: When hydrogen atoms are joined in a polar covalent bond with a small atom of high electronegativity such as O, F or N, the partial positive charge on the hydrogen is highly concentrated because of its small size. If the hydrogen is close to another oxygen, fluorine or nitrogen in another molecule, then there is a force of attraction termed a dipole-dipole interaction. This attraction is known as hydrogen bonding.

Hydrogen bonding has a very important effect on the properties of water and ice. Hydrogen bonding is also very important in proteins and nucleic acids and therefore in life processes. 

THE REFLEX ARC

When a person steps on a sharp object, the response is immediate. It does not initially involve the brain. This involves the reflex arc which occurs in the spinal cord. The reflex arc consists of the sensory neuron (also called the afferent neuron), which transmits the stimuli of pain to the spinal cord. Within the spinal cord, it relays with the interneuron which decodes the message and sends the response to the muscles of the limbs via the motor neuron (also called efferent neuron) to bring about an action.

Diagram showing the reflex arc.

BE INSPIRATION

Today, we will take a little break from the academics and to enjoy this inspirational message. Believe in your ability and capabilities to brace the storms of life to soar high up in the skies beyond reasonable comprehension.  It is fact that God has equipped you with the necessary tools so that you can do all things if you apply yourself diligently it. We all have the potential to succeed if we look beyond our short-falls, weaknesses, disabilities, challenges, and whatever our socioeconomic backgrounds may be. 

As in the poem by Longfellow:

 The heights by great men, reached and kept;
 Were not attained by sudden flights;
 But they, while their companions slept,
 Were toiling upward in the night.

It takes hard work to make it into a  nursing school and to sail through it to the end. Working hard will not break your bones! Apply yourself to your set goals and in the end, you will succeed.

Keep learning and the best of luck in all your endeavors!

STRUCTURE OF THE HUMAN BRAIN

The brain is very complex but we will discuss the basic concepts needed for the exam.

1. Cerebrum: This forms the bulk of the brain and it is responsible for the intellectual functions such as thinking, learning, motor skills, sensory functions, personality, etc.
2. Cerebellum: This is the center that helps with balancing of the body during various movements.
3. Medulla oblongata: This is the cardio-respiratory center. It controls the rate of the heart and also the rate of respiration. It is closely related to first cervical bone which has the protrusion called the dens. When the dens fractures during a whiplash injury, it can compress on the medulla and then the heart and respiratory system will fail to function.
4. Thalamus: This relays motor and sensory signals to the cerebral cortex. It regulates consciousness, sleep, and alertness. 
5. Hypothalamus: The hypothalamus is responsible for certain metabolic processes such as the synthesis and secretion of certain neurohormones (often called releasing hormones or hypothalamic hormones). It also plays a role in autonomic nervous system by controling body temperature, hunger, important aspects of parenting and attachment behaviors, thirst, fatigue, sleep, and circadian rhythms.
6. Pons: This acts as a relay station between the cerebrum and the cerebellum. It is also plays a role in sleep and dreaming.

THE EAR STRUCTURE

Click here to look at the Diagram of the human ear

There are three parts of the human ear. We will not deal with the fine details here. Just know the basic things.
1. Outer ear: This extends from the pinna (ear lobe) to the tympanic membrane/tympanum (ear drum). It has the auditory canal or meatus. This conducts sound to the middle ear.
2. Middle ear: The middle ear house the three bony structure called incus (anvil), malleus (hammer), and stapes (stirrup). They vibrate to transmit the sound waves to the inner ear.
3. Inner ear: The houses the cochlear, semi-circular canals, and the vestibule. There are three semi-circular canals arranged at right angles to each other (superior, lateral, and posterior semi-circular canals)

Important to note: The cochlear is the organ for hearing. The semi-circular canals are the organ for balancing.

Think about what will happen when the cochlear or semi-circular canal is damage.