Physiology of the Circulatory System

Physiology is a branch of biology that describes how organisms function and adapt to different environments. One of the most important organ systems that define an organism's physiology is the circulatory system, which transports blood, nutrients, oxygen, and hormones throughout the body. In humans, a measure of the circulatory system's function can be obtained by taking the blood pressure. The term blood pressure describes the lateral pressure produced by blood upon vessel walls.

One of the most important applications of blood pressure measurement is checking for increased blood pressure, a condition termed hypertension. One in every three adults in the United States suffers from hypertension, and it is one of the leading causes of cardiovascular disease. The equipment needed for a traditional indirect measurement of blood pressure includes a stethoscope and a sphygmomanometer. The sphygmomanometer consists of a blood pressure cuff containing a distensible bladder, and a rubber bulb with an adjustable valve which, when closed, helps in cuff inflation, and when open releases the built-up pressure. It also consists of tubing connecting the cuff to the bulb and to the manometer which displays the cuff's pressure in millimeters of mercury. In order to record the blood pressure reading the examiner wraps the cuff around the brachial artery, places a stethoscope over this artery, inflates the cuff above the expected systolic pressure, and then deflate it while auscultating and observing the manometer simultaneously. Initially, when the cuff is fully inflated, the artery is squeezed, and the blood flow is halted. Thus, there is no sound upon auscultation. Upon deflation, the first appearance of the Korotkoff sounds signifies the systolic pressure, which is audible due to the turbulent flow in the partially squeezed artery. Further deflation causes a continual decreasing cuff pressure, and the Korotkoff sounds remain audible throughout, up until the point where the cuff pressure is below the minimal arterial pressure. This reading denotes the diastolic pressure. The fraction of systolic over diastolic is recorded as the final blood pressure reading.

Another important indicator of human physiology is the respiration rate, the number of breaths per minute. The air we breathe in travels through our trachea, into our lungs through the bronchi. Inside the lungs it passes through the bronchioles to ultimately enter the specialized air sacs called alveoli. The alveoli are surrounded by blood capillaries which allow diffusion of inhaled oxygen into our bloodstream, and facilitate excretion of carbon dioxide, thus maintaining our system's homeostasis. For mammals like humans maintaining homeostasis includes preserving a relatively constant body temperature independent of the surrounding environmental temperature. This property makes us endotherms. Therefore, our metabolic rate and respiration rate stay relatively constant. On the contrary, nearly all fish, including goldfish, have an internal body temperature that almost matches the temperature of the environment surrounding them. Such organisms are called ectotherms. Since they don't actively maintain a constant internal temperature their metabolic and respiration rate changes to compensate for variation in surrounding environmental temperature. The respiration rate in fishes can be measured by counting the gill beats, the rise and fall of the operculum, or gill cover, per minute. There is one more factor that affects the respiration rate of aquatic organisms. Note, that a fish breathes in the dissolved oxygen present in its environment. And the amount of available dissolved oxygen in the water is dependent on the water's temperature. It decreases with increased temperature which also, in turn, affects the respiration rate.

In this lab you will examine the human circulatory system by measuring blood pressure under different conditions, and then study the effects of temperature on respiration using fish.