Muscles, the pressures of blood, and the wonder of breathing… (Day 49)

Histological Smooth Muscle

Wow its start of week 7, I am already halfway through my first semester and whats worse is this is only a 2 day week as Thursday is a bank holiday here in Slovakia and Wednesday and Friday are Rectors Days which means no classes.

Today it snowed, so I decided to do a video diary to show you instead of tell you here (todays topics continue below the video!):

This morning was Histology, still one of my favourite classes and was on muscles which was pretty interesting. To be fair I wish I understood how a single initial stem cell can be programmed to take on so many different shapes, forms and functions… Hopefully one day ay? 🙂 Now there are three different types of muscle which are formed from cells called myocytes which are; smooth muscle, skeletal muscle, and cardian muscle. Each of these muscle types has a different cellular structure and arrangment.

Smooth muscle has spindle shaped fibres with a oval shaped central nucleus with no banding. The nucleus is the dark oval shape on the pink colour strands.

Histological Smooth MuscleSkeletal muscle looks similar, however the muscle fibres have banding (lighter and darker lines) in addition to the nucleus being located to the side of the cell. The section  below has the longitudinal fibres (on the left) in addition to a cross sectional view on the right showing the bundles of the fibres.

Histological Skeletal Muscle SectionThe final section is cardiac muscle which are under involuntary control, these look different as they have long branching fibres forming a mesh like structure. with the nucleus centrally located.

Histological Cardiac MuscleThen it was time for physiology, today’s lecture was on blood pressures and the science of respiration (aka how to breathe). Obviously blood would be pretty useless to the cells that make up the body if it stayed in the tubes of the body so there are different mechanisms for it to leave the capillaries. There are two different circulation systems within mammals, the pulmonary circulation and the systemic circulation. The pulmonary circulation forms a loop from the right side of the heart to the lungs where blood is oxygenated before then returning to the heart to be pumped back out via the left ventricle to the rest of the body. Anyways back to blood pressure, obviously the pressure is highest at the time of ventricular contraction when the heart pushes the blood out of the left ventricle into the aorta. Its then logical for the pressure in the aorta to be highest followed by arteries, then arterioles, and finally capillaries. This is repeated in reverse on the veinous side with the vena cava having a low pressure as the blood reenters the heart.

So anyways onto respiration, common knowledge is that air contains Oxygen that we breathe in which then gets into our blood which goes around our body and gives cells energy to move (massive oversimplification but meh!)…The respiratory system is also responsible for the regulation of blood pH (or acidity), Olfaction (the sense of smell), and for the protection of the lungs via coughing and sneezing.

So the essential thing with oxygen getting from the lungs into the blood is Dalton’s Law of pressures in addition to the Young-Laplace equation which deals with surface or wall tension. Back to the beginning though; there are 4 different volumes which are considered when looking at respiration:

  • Tidal Volume (TV) is the air that moves in and out of the lungs with each breathe ~500ml
  • Inspiratory Reserve Volume (IRV) is the air that can be forcefully inhaled after the Tidal Volume ~2100 – 3200ml
  • Expiratory Reserve Volume (ERV) is the air that can be forcefully exhaled after the Tidal Volume ~1000 – 1200ml
  • Residual Volume (RV) is air left in the lung after strenous expiration ~1200ml

Now in addition to this there is also dead space which contains air that is not used composed of the respiratory passage (trachea) between the mouth and lungs. The respiratory system is then devided into two parts, the Upper Respiratory Tract (URT) with the mouth, nose, nasal cavity, pharynx (and associated structures), and the larynx. The Lower Respiratory Tract (LRT) comprises of the trachea, lungs and alveoli. The surface area of the LRT is somewhere around 100000 square meters (now thats a staggering number!). Now most of this comprises of tissue just 1 cell think to allow easy transport of oxygen between the lungs and the blood in the capilaries.

Now Oxygen within the blood is carried by haemoglobin molecules which have the ability to each bind 4 oxygen molecules (I hate chemistry!) which is know as oxyhemoglobin. When all four hemes are bound it is refered to as Saturated Haemoglobin, and when just 1-3 of the hemes are bound it is known as Unsaturated Haemoglobin. The rate of binding is affected by the pressure of the air in lungs, the temperature, age and health of the animal.

I’m way over todays word count so I am going to leave it here! Hope you enjoyed todays diary and the video!