Week 1 Body Systems

Introduction to Organization, Systems Overview, and Homeostasis

There are levels of organization in the human body, which are arranged in order of complexity. This hierarchy will take us from the most basic, an atom, to the most complex, an organism. An organism's organ systems must maintain a balanced, normal state to survive. As a result, we will also cover organ systems and homeostasis in this concept.

Which of the following represent the smallest unit that is capable of sustaining life?; Cell

What is the most common mechanism our body uses to maintain homeostasis?; Negative Feedback Loop

Hematopoiesis is a function of which organ system?; Skeletal System

Levels of Organization in the Human Body

A structure and function hierarchy that demonstrates the interdependence of each component of the human body. Each level's organization will eventually impact the structure and function of subsequent levels.

Chemical Level of Organization

The body is organized in the following manner, beginning with the smallest component and progressing to the largest.

• Atoms​

  • Atoms are tiny spheres of matter so small that they are invisible.​

  • Atoms cannot be generated, destroyed, or subdivided.​

• Molecules​

  • Combinations of atoms form larger chemical groupings, called molecules.​

  • Molecules consist of groups of atoms held together by a chemical bond.​

  • Examples:​

    • Water molecule​

    • Glucose (monosaccharide)​

    • A monomer is a small, molecular building block.​

      • Amino acids (monomer)​

      • Nucleotides (monomer)

Levels of Organization: Organelle, Cell, and Tissue

• An organelle is a structure composed of molecules that is organized in such a way that it can perform a specific function.​

• An organelle resembles an organ.​

• Organelles allow a cell to live.​

• Organelles cannot exist outside of the cell.​

• However, without organelles, the cell cannot survive.​

  • Examples: Nucleus, endoplasmic reticulum, golgi apparatus, lysosomes, and mitochondria.

• Composed of atoms, molecules, and organelles (microscopic structures within cells) that work together to perform a given function.​

• The cell is the smallest structural and functional unit of all life forms that can carry out life processes.​

• The cell is the smallest unit of living organisms. 

• A collection of cells of similar structure organized to carry out one or more particular functions.​

• Although it is frequently said that the cell is the basic functional unit of the body, it is really the tissues, through the collaborative efforts of their individual cells, that are responsible for maintaining body functions.​

  • Example: cardiac tissue

Levels of Organization: Macromolecules

In turn, molecules combine with other atoms to form larger and more complex chemicals known as macromolecules (macro = large). ​

• Polypeptides (proteins) are formed when amino acids combine with other amino acids.​

• Polysaccharides are formed when glucose (a monomer) combines with other monosaccharides.​

• Polynucleotides (nucleic acids) are formed when nucleotides combine with other nucleotides.

Levels of Organization: Organ, Organ System, and Organism

An organ is defined as a structure made up of several different kinds of tissues arranged so that, together, they can perform a special function. In other words, an organ is a structural part of a system of the body that is composed of tissues and cells that enable it to perform a particular function. ​

• Example: liver, spleen

An organ system is a higher level of organization that consists of related organs with a common function. At the system level, an organ system is also called the organ-system level.​

• The human body is composed of 11 organ systems. ​

• An example is the digestive system, which breaks down & absorbs food. Its organs include the mouth, salivary glands, pharynx (throat), esophagus (food tube), stomach, small intestine, large intestine, liver, gallbladder, and pancreas. 

An organism consists of all the systems within the human body functioning all together as part of the overall maintenance of the health and well-being of the human organism.​

• An organism is the highest and most complex level of organization.​

• Example: Humans

Overview of the Eleven Body Systems

As we just learned, the human body is composed of eleven organ systems. Each system is composed of two or more organs that work together for a given function.  ​

In order for the organism (in this case, the human body) to sustain life, all organ systems must have an interrelationship, whereby each organ system carries out a specific function but all work to carry out basic life processes of the human body.​

The 11 organ systems, their components, and functions will be discussed.

Transition to the 11 Organ Systems

Organs are typically classified based on their primary function. However, some organs belong to more than one system, and thereby may serve more than one purpose.  ​

Example, the male urethra:​

• Functions as a passageway for fluid in both the urinary and reproductive systems.​

• Is the passageway for urine in the urinary system.​

• Is the passageway for semen in the reproductive system.

Organ Systems Providing Movement, Protection, and Support

Integumentary System

Functions:​

• Protects internal organs by acting as a barrier​

• Acts as the body’s first line of defense​

• Regulates body temperature​

• Synthesizes vitamin D​

• Excretes various waste through perspiration​

Major components:​

• Skin​

• Accessory structures​

  • Hair ​

  • Nails ​

  • Glands 

Skeletal Sysytem

Function ​

• Provides structural support​

• Protects internal organs​

• Provides movement​

• Plays a major role in blood cell formation (hematopoiesis)​

• Stores calcium​

Components ​

• Bones ​

• Joints ​

• Ligaments 

Muscular System

Functions​

• Provides movement​

• Maintains posture​

• Heat production​

Components​

• Typically refers to skeletal muscle (but also includes smooth and cardiac muscles)​

• Tendons 

Organ Systems Providing Regulation, Communication, and Control

Nervous System

Functions​

• Provides direct and rapid communication between body systems​

• Controls all other body systems and their functions​

• Processes sensory information​

Components​

• Brain ​

• Spinal cord

Endocrine System

Functions​

• Regulates metabolism, growth, reproduction​

• Utilizes hormones that are secreted by glands into the blood stream​

Components​

• Hypothalamus​

• Pituitary gland​

• Pineal gland​

• Thyroid gland​

• Parathyroid glands​

• Thymus ​

• Adrenal glands​

• Pancreas​

• Testis and ovaries

Organ Systems That Transport Fluids

Cardiovascular System

Functions​

• Transports gases, nutrients, hormones, and waste​

• Plays a role in the distribution of body heat​

Components​

• Blood​

• Heart​

• Blood vessels​

• Arteries​

• Veins​

• Capillaries 

Blood flow in the human circulatory system. The superior vena cava, pulmonary arteries, inferior vena cava, heart, aorta, pulmonary veins, and the blood flow to the digestive system and lower limbs are labeled.

Lymphatic System

Functions​

• Transports lymph throughout the body​

• Plays a vital role in immunity (detect, fight pathogens, and disease)​

• Plays a role in fluid balance​

• Transportation and absorption of fats​

Components​

• Thymus​

• Spleen​

• Lymph nodes​

• Lymphatic nodules​

• Lymphatic vessels

What is the organ system that communicates and regulates other organs using hormones?; Endocrine System

Which organ systems provide regulation, communication, and control (RCC) of most other systems?; Endocrine and Nervous System

Blood is a component of which of the following organ system?; Cardiovascular System

Respiratory System

The respiratory system is an organ system that participates in breathing.

Functions​

• Gas exchange (taking in oxygen and expelling carbon dioxide)​

• Olfaction​

• Sound production​

Components​

• Nasal cavity​

• Pharynx​

• Trachea​

• Bronchi​

• Lungs​

• Bronchioles ​

• Alveoli

Digestive System

The disgestive stystem is an organ system that play a role in what the body takes in and what the body puts out.

Functions​

• Breaks down food into absorbable nutrients to provide the body with energy​

• Rids the body of waste ​

Components​

• Gastrointestinal tract (alimentary canal)​

• Oral cavity​

• Esophagus​

• Stomach​

• Small intestines​

• Large intestines​

• Rectum​

• Anus ​

• Digestive accessory organs​

• Salivary glands​

• Liver​

• Gallbladder​

• Pancreas 

Urinary System

The urinary system is the organ system that regulates the body's water intake and output.

Functions​

• Eliminates waste from the body​

• Regulation of blood volume, blood pressure, blood composition, and blood pH​

Components​

• Kidneys​

• Ureters​

• Urinary bladder​

• Urethra 

Female and Male Reproduction Systems

Female Reproductive System

Functions​

• Production of sex hormones​

• Production of sex cells​

• Maintenance of female sex characteristics​

• Nurture developing fetus​

Components​

• Ovaries​

• Oviducts (uterine tubes, fallopian tubes)​

• Uterus​

• Vagina ​

• Breasts (mammary glands)

Male Reproductive System

Functions​

• Production of sex hormones​

• Production of sex cells​

• Maintenance of male sex characteristics​

Components​

• Testis​

• Epididymis​

• Vas deferens​

• Scrotum​

• Penis ​

• Urethra​

• Male reproductive accessory glands​

• Seminal vesicles ​

• Prostate gland​

• Bulbourethral glands

Transition to Homeostasis

As we just learned, the human body is composed of 11 organ systems. In order for the organism (in this case, the human body) to sustain life, all organ systems must have an interdependent relationship, whereby each organ system carries out a specific function, but all work to carry out basic life processes of the human body.​

All body systems and their components are surrounded by the same environment. Ideally, this “internal environment” should remain at a constant and steady state for the body structures to work properly, and for the organism to sustain life. Therefore, all organ systems have evolved to keep all variables of this internal environment constant and stable. This is a process that we call homeostasis. Homeostasis is a unifying theme and the foundation of human physiology.

Homeostasis

Homeostasis is defined as the ability to maintain a relatively constant internal environment. Multiple physical and chemical variables within the body are subject to fluctuation; these include temperature, pH, blood pressure, and all of the dissolved components of plasma, such as glucose, sodium, potassium, calcium, and bicarbonate.​

To maintain homeostasis, the homeostatic control system must be able to:​

• Detect deviations from normal in the internal environment that must be held within normal.​

• Integrate this information with any other relevant information.​

• Make appropriate adjustments in the activity of the body parts responsible for restoring this factor to its desired value. 

Definition of stimulus: Any disruption or change in a controlled condition or environment that causes deviations from normalcy or equilibrium and elicits a bodily response.​

A homeostatic system must have a sensor that monitors and detects changes provoked by a stimulus. Upon detecting those changes, the changes are then relayed to the command center (located in the central nervous system or endocrine system).​

The command center, in turn, processes this information and determines the best course of action to correct the deviation and restore homeostasis. The control center modifies the system via the effectors to restore levels to the homeostatic range. An effector is a cell, tissue or an organ that executes the information it receives from the command center to produce an effect that restores stability and normalcy in physiologic functions. 

Receptor: detects and provides information about the stimuli.​

​Command Center: decision-maker that maintains the set point​.

​Effector: muscle or gland that responds to the control center & causes the necessary change in the internal environment.

Homeostatic mechanisms work by incorporating feedback mechanisms.

There are 2 types of feedback mechanisms:​

• Positive feedback ​

• ​Negative feedback

Homeostasis Example 

Homeostatic control systems operate locally via intrinsic, or local controls that are already built into an organ.​

For example, as an exercising skeletal muscle rapidly uses up oxygen to generate energy to support its contractile activity, the oxygen concentration within the skeletal muscle falls. This local chemical change acts directly on the smooth muscle in the walls of the blood vessels supplying the exercising muscle, causing the smooth muscle to relax so that the vessels dilate, or open widely. As a result, increased blood flows through the dilated vessels into the exercising muscles, bringing in more oxygen. This local mechanism helps maintain an optimal level of oxygen immediately around the exercising muscle’s cells.

Positive Feedback Mechanism

Amplification or augmentation of functional bodily response induced by a stimulus. Amplification or augmentation stimulus & response operate in the same direction.​

​Example:

• Labor & Delivery: The onset of regular uterine contractions that cause cervical change induces release of oxytocin release. Oxytocin release intensifies uterine contractions which in turn spur release of more oxytocin hormone. The process continues until full cervical dilation (10 cm) is achieved.

Positive Feedback Example: Clotting Cascade (Blood Clotting)

The body's effort to repair damage caused by any injury leading to excessive blood loss. The loop is initiated when injured tissue releases signal chemicals that activate blood platelets. Platelets that have been activated release chemicals that activate additional platelets, resulting in a rapid cascade and blood clot formation.

Negative Feedback 

Negative Feedback: Negative feedback is the most common form of homeostatic control in biological systems. Negative feedback loops reverse the stimulus. A critical consequence of negative feedback control is that it allows the system to resist deviation of a given parameter from a preset range (set point). In negative feedback, the stimulus and response are operating in opposite directions to each other.​

A response that causes the level of a variable to change in a direction opposite to that of the initial change. Because the response returns the variable back to its baseline level, it has a stabilizing effect on the body. ​

Takeaway Summary:​

• A change in some steady state triggers a response that is the opposite (negative) to the change.​

• A bodily response is generated to counteract the effects of the stimulus​.

• Stimulus & response operate in opposite directions​.

• Most common form of feedback mechanism.

• Examples are regulation of blood sugar and regulation of body temperature.

Review the tabs to learn about negative feedback examples.

Negative Feedback Example

An example of negative feedback is the regulation of blood sugar (glucose). 

If blood glucose gets too high:​

• The body responds by secreting the hormone insulin from beta islet cells within the pancreas to bring it back down.​

​Likewise, if blood glucose gets too low:​

• The body responds by secreting the hormone glucagon from alpha islet cells within the pancreas to bring it back up.

Physiological Response

Stimulus: Hyperglycemia from eating a candy bar.​

↓​

Sensor: Symptoms of hyperglycemia (polyuria; polydipsia; visual changes) = glucose levels > 100​

↓​

Command Center: Pancreas releases glucose-lowering hormone insulin into the circulation.​

↓​

Effector: Liver & Skeletal Muscle​

• Insulin promotes the transfer and uptake of glucose from blood into the liver and skeletal muscle. This action coupled with the conversion of glucose into the storage form glycogen causes lowering of hyperglycemia and restoration of glucose levels within the normal range.

Negative feedback example: A patient suffering from dehydration will have a low blood volume. Antidiuretic hormone (ADH) is secreted by the body in response to dehydration. The function of the hormone ADH is to decrease the amount of urine produced by the kidneys and thereby restore homeostatic levels of blood volume. What is the stimulus in this situation?; 

This is an example of negative feedback mechanism regulating volume status. ​

Stimulus: Dehydration​

Control Center: posterior pituitary gland (site of ADH secretion)​

Effector: Response that the target tissue of ADH, which is the kidney, will do in response to ADH acting on it. 

When examining a client’s/patient’s blood, hypercalcemia (elevated blood calcium) is detected. The thyroid gland secretes the calcitonin hormone into the blood. Calcitonin prevents calcium reabsorption in the kidneys, causing calcium to be excreted in the urine. This eventually returns the patient's calcium level to homeostasis. The stimulus and response operated in; Negative Response

Thermoregulation

Temperature regulation (also known as thermoregulation) is an essential component of homeostasis in humans. A negative feedback loop is the means of achieving this. The normal body temperature is 37 degrees Celsius (98.6 degrees Fahrenheit). The ideal temperature range for optimal body function is 97 to 99.9 degrees Fahrenheit (36.1 to 37.2 Celsius), and the temperature will oscillate within this range as the negative feedback loop completes its cycle.​

The skin (which measures external ambient temperature) and the hypothalamus (which detects core body temperature) contain temperature sensors. The hypothalamus measures blood temperature directly and receives impulses from thermoreceptors in skin and mucous membranes.​

Responses​

If the body is too hot, the following things will occur in an attempt to cool it:​

• Increased acetylcholine release, resulting in vasodilation.​

• Sweating (evaporation) is due to the activation of sweat glands all over the body.​

If the body is too cold, the following things will occur in an attempt to warm it:​

• The increased adrenaline release results in increased vasoconstriction.​

• Shivering is a type of repeated muscle contraction, and increased muscle contraction means increased demand for ATP (requires more ATP) and, therefore, more respiration, of which heat is released as a by-product.  

Most variables require constant regulation because they are in a constant state of change, and therefore require negative feedback regulatory mechanisms. Positive feedback only occurs in instances where the variable changes infrequently, and therefore does not require constant regulation.

Most variables of the body require constant regulation because they fluctuate frequently, and therefore require negative feedback mechanisms.

A few variables such as response to blood loss and labor are infrequent events that do not require constant regulation, and therefore will require positive feedback mechanisms.

If the response of the stimulus further exaggerates the stimulus, then this is an example of a positive feedback mechanisms, as the response may be causing the system to move farther away from homeostasis.

Hypoglycemia triggering the release of the hormone glucagon, which would cause blood glucose levels to rise, is an example of what type of feedback?; Negative

Integumentary, skeletal, and muscular systems all provide protection, support, and movement. 

The pancreas belongs to the digestive and endocrine systems. The ovaries and testes are both endocrine and reproductive organs. The male urethra belongs to both the urinary and reproductive systems.

The trachea is a component of the respiratory system.

The spleen is one of the major organs of the lymphatic system.

Arteries, veins, and capillaries are the major components of the circulatory system.

Sweat glands and oil glands are accessory structures of the integumentary system.

Ligaments connect bone to bone and are a component of the skeletal system.