ISSA Chapter 4: Supporting Systems 5

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Chapter Goals:

  • Be able to name and discuss the body’s supporting organ systems outside of the movement systems in chapter 3.
  • Be able to differentiate between the types of respiration the body can perform.
  • List the endocrine hormone functions.
  • Find the organs of the digestive system and their individual differences.

There are 11 organ systems in the human body, 3 of which are responsible for movement with the nervous, muscular, and skeletal systems.

The remaining primary systems in the text will be the digestive, integumentary, lymphatic, endocrine, circulatory, and respiratory systems.

The Circulatory System

This system comprises the heart, arteries, veins, capillaries, and blood, and it is fully responsible for blood circulation throughout the body.

The main function is the facilitation of oxygen and carbon dioxide, thus transporting oxygen from the lungs to the body tissues and then moving carbon dioxide from the tissues to the lungs to be expelled.

This is a closed system, which is a physical system that does not allow for the movement of matter into or out of the system.

The arteries are blood vessels that carry oxygenated blood away from the heart and to the tissues.

Veins are the blood vessels responsible for carrying the blood to the heart and removing waste so that the blood can pick up more oxygen.

Capillaries are where the actual exchange of nutrients will happen. These capillaries are blood vessels that stem from the bigger ones and work to form a network between arterioles and venules.

The Cardiovascular System

The primary structures of the cardiovascular system are the blood vessels and the heart.

Blood Vessels

There are five types of blood vessels in our bodies. The blood vessels that carry oxygenated blood away from the heart and to the body’s tissues are the arteries.

The arteries narrow, and blood moves further from the heart through the arterioles.

The arterioles further distribute the blood and its nutrients via the capillaries.

From there, the venules collect the nutrients that need to be expelled from the body and transport them via blood to the veins.

The veins reach the heart and then go through the process all over again.

The Heart

The heart has four chambers of cardiac muscle and is known as the myocardium.

The left and right atriums are the two upper chambers of the heart, and the left and right ventricles are the two lower chambers of the heart.

The right atrium will receive the deoxygenated blood from the body.

From there, it will move to the right ventricle, where it is pumped through the pulmonary arteries to the lungs and receives oxygen.

The oxygenated blood will return from the lungs through the pulmonary veins to the left atrium, which is then moved to the left ventricle through the aorta and to the rest of the body.

The aorta is the primary artery in the body that supplies oxygenated blood to the circulatory system.

Circulation in the heart is called pulmonary circulation. Blood flow between the heart and the rest of the body is called systemic circulation.

Our hearts beat somewhere around 100,000 times per day.

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The oxygenated blood returning from the lungs will move to the pulmonary vein into the heart’s left atrium.

This left atrium contracts, pushing the blood down into the left ventricle where it will contract and the blood moves through the aorta and out into the body’s circulation.

Blood returns to the heart without oxygen via the superior vena cava and the inferior ven cava. This returns to the right atrium and is pumped when it is filled.

There are valves in the heart to keep the blood from flowing on its own.

There is a rhythm to the movement of blood through the body and lungs: the heartbeat.

A cardiac cycle is an alternating cycle of contraction and relaxation during one heartbeat.

Systole is the contraction phase, and diastole is the relaxation phase.

In the heart, nodes control the electrical signals and contractions.

The sinoatrial node is the pacemaker of the heart and it generates the first electrical signal of a heartbeat and stimulates the atria to contract.

The atrioventricular node is the nerve node between the right atrium and right ventricle that propagates the electrical signal from the SA node to more distant heart nerves that cause ventricular contraction.

The stroke volume is the amount of blood that the left ventricle pushes out in one contraction.

Heart rate is the number of beats per minute.

The medulla oblongata handles changes in heart rate.

In unconditioned people, stroke volumes are likely lower, and the heart rate at rest and during activity will likely be higher.

Pulse is defined as the rhythmic throbbing of the arteries as blood is propelled through them.

Blood pressure is the force of the blood pushing against the walls of the arteries in the two cardiac cycle phases.

Blood pressure is written as the systolic over the diastolic, or the pressure when the heart beats over the pressure when the heart relaxes.

Normal blood pressure is 120 / 80 mm Hg.

Hypertension is defined as high blood pressure levels starting at 140 / 90.

Cardiac output measures how much blood the heart is pumping per minute.

Blood volume is the total volume of blood within the circulatory system.

Peripheral resistance of arteries is the elasticity of artery walls.

Blood viscosity is the thickness of the blood moving through circulation.


Blood is a specialized type of connective tissue within all body areas besides epithelial tissue. It comprises 55 – 60 percent plasma, 40 percent red blood cells, and 2 percent white blood cells and platelets.

Red blood cells are called erythrocytes and they are the most numerous form of cells in the body.

The function of erythrocytes is to carry oxygen around the body. Platelets help form blood clots to stop bleeding and promote wound healing.

White blood cells are integral to the body’s immune response. There are basophils, neutrophils, eosinophils, monocytes, and lymphocytes.

The Lymphatic System

The lymphatic system is considered to be a part of the circulatory system.

In exercise, the lymphatic system regulates fluid volume and tissue pressure.

The system’s major parts are the lymph nodes, tonsils, spleen, and thymus.

The system has lymph, which is a colorless fluid that carries white blood cells.

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The main overall functions of the lymph system are to balance interstitial fluids, absorb fats and fat-soluble vitamins, and defend against illness and disease.

The Respiratory System

The respiratory system is made up of the: nose, nasal cavities, pharynx, larynx, trachea, bronchi, and lungs.

The main function of this system is to bring in fresh air while moving bad gases like carbon dioxide that are produced.

Some other functions include providing oxygen for metabolic processes, removing waste products from metabolism, and regulating the blood pH.

Respiration is defined as breathing and the process through which the respiratory system completes these tasks.

Pulmonary ventilation is also breathing, but more specifically, this is the air exchange between the lungs and ambient air.

Pulmonary Ventilation

Air moves to the lungs during inspiration and out of the lungs when going through expiration.

This air movement is controlled by changes in atmospheric pressure caused by the contraction and relaxation of the diaphragm.

Gases will move from high-pressure areas to lower pressure areas in what is known as diffusion.

As the volume increases in the thoracic cavity, pressure in the alveoli decreases so air is pulled into the lungs.

The opposite occurs during expiration.

External Respiration

The exchange of gases between the lungs and blood is known as external respiration, which happens at the alveoli.

Alveoli facilitate the exchange of gases between the lungs and blood.

Internal Respiration

Internal respiration happens at the cellular level. Once external respiration has occurred, oxygen binds to the hemoglobin, and the blood carries this to the cells through the circulatory system.

Carbon dioxide binds to hemoglobin on the way back to the lungs, where it is carried out for expiration.

The Endocrine System

This system regulates growth, development, homeostasis, reproduction, and metabolic activities through chemical messengers, which we call hormones.

The body’s endocrine glands will release, store, and create these hormones.

Exocrine glands also produce and release substances through ducts or openings on the body’s surface.


These substances are made of amino acids, lipids, or peptides.

Estrogen and testosterone, the sex hormones, are secreted by the adrenal cortex and they are lipid hormones known as steroids.

Let’s look at the hormone function of the main hormones in the text:

  • Growth hormone stimulates tissue growth, mobilize fatty acids for energy, and inhibits carb metabolism.
  • Thyrotropin stimulates the production and release of cortisol, aldosterone, and other adrenal hormones.
  • Corticotropin stimulates the release and production of cortisol, aldosterone, and some other adrenal hormones.
  • Gonadotropin stimulates the production of estrogens and progesterone by the ovaries and testosterone in the male testes.
  • Prolactin works to inhibit testosterone and mobilize fatty acids.
  • Endorphins block pain, promote euphoria, and affect feeding and the female menstrual cycle.
  • Vasopressin controls the excretion of water by the kidneys.
  • Oxytocin stimulates the muscles in the breasts and uterus. It is most important in birth and lactation.
  • Cortisol promotes the use of fatty acids and catabolism of protein, conservation of blood sugar, insulin antagonist, and has some effects which cause anti-inflammation.
  • Aldosterone promotes sodium retention, potassium, and water in the kidneys.
  • Epinephrine and norepinephrine work to facilitate sympathetic activity, increase cardiac output, regulate blood vessels, increase catabolism for glycogen, and release fatty acids.
  • Thyroxine and triiodothyronine are used for the stimulation of metabolic rate along with the regulation of cell growth and activity.
  • Insulin promotes CHO transportation into the cells, increases catabolism, and decreases blood glucose levels. It also promotes fatty acid and amino acid cell transportation.
  • Glucagon promotes the release of glucose from the liver to the blood and increases fat metabolism.
  • Parathormone works to raise blood calcium levels and lowers blood phosphate.
  • Estrogen and progesterone control the menstrual cycle, increase fat deposits, and promote female sex characteristics.
  • Testosterone controls the size of the muscles, increases the number of red blood cells, decreases body fat levels, and promotes male sex characteristics.
  • Renin stimulates aldosterone secretion.

Endocrine Glands

Endocrine glands will secrete hormones right into the blood so that they may reach their targeted cells.

The major glands will be:

  • Hypothalamus: this main role is to keep homeostasis.
  • Pineal gland: the only hormone gland that is known to secrete melatonin.
  • Pituitary gland: these hormones work to control other portions of the endocrine system like the testes, ovaries, thyroid gland, and adrenal glands.
  • Thyroid: this has the main function of regulating our metabolism.
  • Parathyroid: there are four of these, and they help to regulate the calcium levels in the body.
  • Thymus: This is only active in puberty, and it stimulates the development of T lymphocytes, which have a role in the lymphatic system’s defense against illness and infection.
  • Adrenal: the adrenal glands are attached to the kidneys and comprise the adrenal cortex and adrenal medulla.
  • Pancreas: the role is to keep a balance in blood glucose.
  • Ovaries: The ovaries are important for secreting the essential female reproductive hormones.
  • Testes: these are responsible for keeping the male reproductive system healthy.


This hormone is primarily made in the testes and males and ovaries of females, though adrenal glands also secrete a small amount.

It is the primary anabolic hormone involved in tissue growth and repair, besides growth hormone and insulin-like growth factors.

Training can affect testosterone levels.

Growth Hormone (GH)

This is secreted from the pituitary gland and made from 190 or more amino acids.

Growth hormones can increase protein synthesis, increase fat breakdown, increase collagen synthesis, and decrease glucose utilization.

Growth hormone peaks in adolescence and can later be kept high by getting good nutrition, sleep, and training.

Insulin-Like Growth Factors

Insulin-like growth factors from the liver mediate many effects of growth hormones. These travel via the blood by way of attaching to proteins.


Released via the pancreas, insulin increases the cellular uptake of glucose-synthesizing muscle glycogen, which will decrease blood glucose levels.

In prolonged workouts, blood glucose reduction and decreased insulin can increase fatty tissue mobilization for energy production.


The adrenal gland is a catabolic hormone that causes muscle protein breakdown.

Moderate to low exercise may reduce blood cortisol instead of increasing it.


These are the fight or flight hormones of epinephrine, norepinephrine, and dopamine, and they come from the adrenal glands to respond to stress.

Exocrine Glands

These glands release secretions that are carried to an epithelial or skin surface, and they are secreted by ducts.

The body can expel things such as mucus, proteins, water, enzymes, and ions. These substances are non-hormonal in nature, but their production is controlled via hormones.

The Digestive System

This system will break down food into smaller molecules for energy production at the cell level.

There are six primary functions of the digestive system so that it can break down foods to use for energy.

  1. Ingestion: this is done by taking in food through the mouth
  2. Mechanical digestion: this is the process of chewing your food and the mixing/churning within our stomachs, which further helps break down food
  3. Chemical digestion: enzymes are released to break food down more in the digestive tract
  4. Movements: food moves through the digestive system by way of rhythmic contractions of the smooth muscles in the digestive tract
  5. Absorption: the broken down molecules are absorbed by cell membranes in the lining of the small intestine and they go through the blood and lymph capillaries to spread through the body
  6. Elimination: this is the removal of waste products and particles that can’t be digested

The primary locations for the digestive system will be the mouth, esophagus, stomach, small intestine, large intestine, rectum, liver, gallbladder, and pancreas.


Food enters our body through the mouth, which has four different digestive processes to go through.

The mouth will physically break food down by chewing, mixing saliva with food to create a bolus, using digestive enzymes to start the chemical breakdown process, and regulating the temperature of food by cooling or heating it.


The esophagus serves as the transport conduit for food and liquid traveling to the stomach. It goes from the mouth to the stomach.

It makes use of involuntary muscle actions to move the food along.


This muscular sac has about two quarts of volume and it is responsible for the storage and slow release of food to the small intestine, digestion by way of chemical secretions, physical activity of churning foods, and transport of ingested food down the gut.

A mucus layer lubricates the stomach wall and buffers against acidic secretions.

The stomach may absorb some nutrients like water, glucose, alcohol, aspirin, and other drugs and vitamins..

Small Intestine

This organ is around 12 feet long and comprises three parts: the duodenum, jejunum, and ileum.

The small intestine is where the majority of digestion and absorption takes place. Tons of villi line the small intestine and create surface area.

As simple nutrients pass by these villi, they are transported to the blood vessels and then the liver.

Large Intestine and Rectum

This intestine is around 3 feet long and has the final location for absorbing water, minerals, and vitamins.

The decomposition of fecal matter by bacteria will produce gas here. The amount of gas depends on the nutrient substrate that makes it to the colon.

This is essentially the site of getting ready for waste products of digestion and then expelling these things.


The liver has the functions:

  • Secreting plasma proteins, carrier proteins, hormones, prohormones, and apolipoproteins.
  • Production and secretion of bile salts
  • Storing fat-soluble vitamins
  • Detoxifying and filtrating
  • Carb, protein, and lipid metabolism


This is attached to the liver but still somewhat separate.

The main function is to store the bile used for digestion. This bile comprises water, bile salts, bile pigments, and cholesterol.


This is found behind the stomach and it will have a role in endocrine and exocrine functions in the body while also releasing the digestive enzymes of amylase, trypsin, peptidase, and lipase.

The Integumentary System

This is the largest human organ system. It covers the whole human body and consists of the skin, hair, and nails.

The main functions will be to protect internal organ systems from disease and damage, prevent water and fluid loss, and regulate the body’s temperature.

The skin has three total layers:

  • The epidermis is the outermost layer, making the skin taut and creating a waterproof barrier.
  • The dermis is beneath the first layer and it holds the blood cells, sweat glands, hair roots, and connective tissue.
  • The hypodermis is the deepest layer of skin and it holds subcutaneous fat and connective tissues.
ISSA Chapter 4: Supporting Systems 6
ISSA Chapter 4: Supporting Systems 7
ISSA Chapter 4: Supporting Systems 8
Tyler Read - Certified Personal Trainer with PTPioneer

Tyler Read

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