APHY 101 1.4

Core Learning Objectives

• List and describe the key concepts in anatomy and physiology.

• List and describe the underlying mechanisms in anatomy and physiology.

• Recognize that core themes recur throughout the study of body systems, highlighted by feature sections such as "Reconnect" and "A Glimpse Ahead".

Key Concepts in Anatomy and Physiology

• The Cell:

  • All living organisms on Earth consist of cells, ranging from single-celled bacteria and protozoans to complex multicelled organisms like humans.

  • Understanding anatomy and physiology is, in a central way, understanding what conditions keep cells alive and well.

• The Internal Environment:

  • The internal environment is the environment within the body in which cells live.

  • Each cell is bounded by a cell membrane:

    • Intracellular fluid: Fluid contained inside the cell.

    • Extracellular fluid: Fluid outside the cell, forming the immediate environment of the cell.

  • Even though extracellular fluid is outside each cell's membrane, it is designated as the internal environment because it is inside the body.

  • While the environment outside the body may vary, human cells can survive only if the internal environment is maintained relatively constant.

• Homeostasis:

  • Pronunciation: (hoh-mee-oh-STAY-sis)

  • Definition: The maintenance of a relatively constant internal environment.

  • The human body is essentially a community of cells in which different cells perform different functions, almost all of which are geared toward maintaining homeostasis.

  • Reproductive Exception: Cells involved in reproduction do not have a direct role in maintaining homeostasis, but they perform the special role of continuing the species.

• Interdependency of Cells:

  • Because different cells contribute to homeostasis in distinct ways, cells depend on one another.

  • If some cells are unable to function, other cells and even the entire organism may suffer.

  • Heart Attack Example: Loss of cells from the heart as a result of a heart attack places an additional workload on remaining heart cells. If the loss of functional cells is substantial, the organism may die.

• Structure and Function:

  • Structure and function are interrelated.

  • An understanding of structure illuminates function, and vice versa.

Underlying Mechanisms and Processes

• Structural Hierarchy and Homeostasis:

  • Cells form more-complex body structures such as tissues, organs, and organ systems, all of which contribute to homeostasis through specific recurring mechanisms.

• Gradients and Permeability:

  • Substances move between cells and throughout the body in multiple ways, frequently moving from high to low, which is referred to as moving down a gradient.

  • Pressure Gradient: Movement from high pressure to low pressure (e.g., blood flow through blood vessels, or air moving in and out of the lungs).

  • Concentration Gradient: Movement of substances from areas of high concentration to areas of low concentration by a process called diffusion.

  • Membrane Permeability:

    • Because a cell membrane bounds each cell, membrane permeability (what it allows in or out) is critical.

    • Permeant: If a substance can pass through a cell membrane, that substance is said to be permeant.

    • Permeable: The cell membrane is said to be permeable to that substance.

    • When considering whether a given substance can enter or leave a cell by diffusion, one must account for both the concentration gradient and whether the cell membrane is permeable to that particular substance.

• Cellular Differentiation (Gene Leads to Protein Leads to Function):

  • Pronunciation: (DIF-er-en-shee-AY-shun)

  • Despite the wide range of cellular structures and functions throughout the body, all of a person's cells originate from a single fertilized egg.

  • Cells become specialized through the process of cellular differentiation.

  • Different cell types, such as muscle cells and nerve cells, access the information encoded in different genes to make specific proteins.

  • The proteins that any cell makes determine that cell's function.

• Cell Membrane Mechanisms:

  • The cell membrane determines which substances can enter a cell and which cannot.

  • It allows cells to respond to certain signals while ignoring other signals.

• Cell-to-Cell Communication:

  • Cooperation among cells requires cell-to-cell communication via a variety of mechanisms.

  • Many of these mechanisms involve the cell membrane and specialized molecules on the membrane called membrane receptors.

• Feedback Loops:

  • For systems to maintain homeostasis, cells must signal other cells when the internal environment has been compromised so that adjustments can be made.

  • When the instability has been corrected, cells must signal that adjustments are no longer necessary.

  • These homeostatic mechanisms work through a form of cell-to-cell communication called a feedback loop.

  • Feedback loops can be either negative or positive, depending on what they control.

• Balance:

  • To maintain a relatively constant internal environment, the body must replace substances that are lost and eliminate substances that are in excess.

  • Replacement Example: As proteins are made and used to build stronger muscle cells, the chemicals that proteins are made of (amino acids) must be replaced in the diet or produced in the body.

  • Elimination Example: Carbon dioxide produced by cellular activity must be removed from the internal environment via the lungs.

  • General Rule: Input must be balanced by output. Conditions or substances in excess (such as extra heat production) must be matched by increased elimination (such as increased heat loss). Shortages must be matched by increased intake or production.

• Energy Processes:

  • All processes in the body involve some form of energy.

  • Heat Energy: Keeps cells chemically active.

  • Chemical Energy: Released from chemical reactions in a form that cells can use to power cellular functions.

Questions & Discussion

• Question: How are cells interdependent on each other?

  • Answer: Cells are specialized to make unique contributions to maintaining homeostasis. They work together as tissues, which form organs, which in turn form organ systems. Some cells detect changes in the internal environment and communicate with other cells, which then initiate responses to correct the changes. Cells that defend an organism against infection or disease contribute to the health of other cells in the organism, and of the entire organism.

• Question: How is balance related to the internal environment?

  • Answer: For the internal environment to be maintained constant, input must be balanced by output. Substances or conditions that are in excess (such as extra heat production) must be matched by increased elimination (such as increased heat loss). Shortages must be matched by increased intake or production.