What is physiology?
It is the study of normal functioning of a living organism and its component parts, including all of its chemical and physical processes.
Cell is the smallest unit of structure which is capable of carrying out all life processes. Cells that carry out similar functions aggregate together to form tissues. Different tissues, carrying out different functions, may aggregate to form organs, and various organs come together to form organ systems.
Cells → Tissues → Organs → Organ system
There are 10 common physiological organ systems that we are going to be reviewing:
- Integumentary system
- Musculoskeletal system
- Respiratory system
- Digestive system
- Urinary system
- Reproductive system
- Circulatory system
- Endocrine system
- Nervous system
- Immune system
Our body continuously monitors various physiological parameters (such as blood pressure, body temperature, glucose concentration in blood, etc.) and tries to keep them within a range to keep our body healthy. This ability of our body to maintain relatively stable environment is called homeostasis.
Whenever physiological parameters go beyond their normal functioning range, our body takes necessary steps to correct the state and brings it back to the normal range. This is the result of physiological control systems, which consist of input signal, a controller and output signal. Whenever physiological control systems fail to maintain homeostasis for a period of time, a disease state or pathological condition may result. Studying of body functions in a disease state is called pathophysiology.
Also read: Importance of biology
As you know, our external environment changes from time to time. How does our body protects its cells from environment change?
Answer: cells are surrounded by extracellular fluid (ECF) which acts as buffer.
As we study various physiological organ systems, there are four major themes that are often encountered. These themes are as follows:
1) Homeostasis and control systems – explain how the internal stable state is maintained and which actions are taken to correct any changes.
2) Energy use – how the cells obtain energy for work
3) Structure-Function relationship – the structure of most organs is related to the functions they carry
4) Communication – different ways by which cells of the body communicate with each other.
Basic Chemistry for Physiology
Structure of Atoms
In order to understand what molecules do in our body, we need to understand what they are made up of and the type of properties they possess. Atoms are the building blocks of all matter and they are very tiny (diameter of 1-5 angstroms, Å) and composed of protons, neutrons and electrons.
Protons are positively charged (+).
Neutrons are neutral.
Electrons are negatively charged (-).
Protons and neutrons cluster together in the center of the atom, forming a dense body called nucleus. Rest of the atom includes rapidly moving electrons in their specific orbits (because the size of electrons is very small, most of an atom’s volume is empty space).
If you look at the periodic table, there are more than 100 known elements. How do we classify atoms? How do we know which atom is of which element.
The answers to those questions come from the number of protons each atom has. The number of protons that an atom has in the nucleus is called the atomic number. On the period table, you can see the elements listed by their atomic number. If an atom contains one proton, it is a hydrogen atom. If it contains two protons, it is helium atom.
When you add the total mass of the protons and neutron present in the nucleus, you get the atomic mass. Atomic mass is expressed in two types of units, amu (atomic mass unit) and Da (Dalton).
1 amu = 1.6605 x 1o-27 = 1 Da
For atoms of specific element, number of protons remain constant, but number of neutrons might change. Those atoms, which have different number of neutrons, are called isotopes. All isotopes of an element have same chemical properties.
Some isotopes, called radioisotopes, emit radiation energy (alpha, beta and gamma) and they are used in medicine for diagnosis and treatment. X-rays are one example.
Importance of Electrons in Physiology
Electrons play four very important roles in physiology. They are involved in the formation of covalent bonds, ions, free radicals and in the capture and transfer of energy.
Covalent bonds → Electrons on two different atoms are shared to form strong covalent bonds, which give rise to molecules. A molecule that contains atoms of more than one element is called a compound.
Ions → Electrically charged atom as a result of gain/loss of electrons.
Radicals → Atoms containing at least one unpaired electron, commonly as a result of radiation from un/natural sources.
High-energy electrons → Electrons on some atoms can capture energy and transfer it to other atoms. This energy can be used for synthesis, movement and variety of other life processes.
Why are Free Radicals so Damaging?
Radical have at least one unpaired electron which is continuously looking to gain another one for stability. Molecule which donated the second electron to the radical then becomes a radical, leading to a chain reaction of free radicals. These radical can disrupt the normal functions of the cells. Free radicals contribute to aging and a number of other diseases. That’s one reason why health care providers recommend consuming lots of vegetables and fruits. Fruits, vegetables and vitamins supplements contain antioxidants which prevent radical damage by providing an electron without becoming a radical themselves.
Bonds Between Atoms
Covalent bonds are formed when two atoms share electrons between them to maintain octet. Electrons are not always shared evenly because some atoms have stronger tendency to pull electron toward them than the others. In that case, molecules develop regions of positive and negative charge, and are callerpolar molecules. Regions of molecule of positive charge are termed “delta positive” (δ+) and regions of negative charge are called “delta negative” (δ–). How strongly an atom pulls electrons towards itself is represented by its electronegativity.
Now, when electrons between atoms are shared evenly, there are no positive or negative regions. In that case, the resulting molecule is nonpolar.
Ionic bonds form when atoms gain or loose electrons completely. Ionic bonds are disrupted in water. (Example: NaCl)
Hydrogen bonding is not really a “bond” but a weak attractive force between a hydrogen atom and an oxygen, fluorine, or nitrogen atom of the same or different molecule. Hydrogen bonds are weak but they can be really strong when present in large numbers.
Van der Waals are weak, non-specific attractions between the nucleus of one atom and electrons of another atom. They are always present!