Class 1: Introduction to Human Physiology

Question 1

Describe the interrelationships between molecules, cells, tissues, organs, and organ systems in the human body.

Answer 1

Molecular: all molecules (group of atoms bound together)

Cellular: molecules make up cells (basic units of life)

Tissue: groups of similar cells (muscle, neural, epithelial, connective)

Organ System: group of two or more tissues form organs

Organismal: organs work together to carry out bodily functions

Question 2

Diagram the body plan, showing the various organ systems and their interrelationships with one another and with the external environment.

Answer 2

Order: atom, molecule, cell, tissue, organ, organ system, organism

ICF: fluid found within cells

ECF: composed of interstitial fluid (space between cells) and blood plasma (fluid portion of blood)

Nutrients and wastes move between the external and internal environment by crossing a cell layer.

Question 3

Describe the main components of a feedback system.

Answer 3

Stimulus, sensor (receptor), input signal, control (integrating center), output signal, target (effectors), and response

Question 4

Compare and contrast negative and positive feedback and feedforward systems. Give an example of each in the human body.

Answer 4

Negative: opposes the initial stimulus
Stimulus - plasma glucose levels increase
Sensor - sensor detects the increase
Input Signal - sensor sends an input signal to the control center
Control - pancreatic beta cells
Output Signal - insulin
Target - skeletal muscle, fat, liver
Response - plasma glucose levels decrease

Positive: reinforces the initial stimulus
Stimulus - cervix stretches during labor
Sensor - stretch detectors detect the degree of stretch
Input Signal - sensors send an input signal to the control center
Control - brain
Output Signal - oxytocin
Target - muscles within the uterine wall
Response - further contraction of the uterus

Feedforward: occur when the body is anticipating a change
Example - The mouth salivates and signals are sent to increase stomach acid in preparation for eating.

Question 5

Explain homeostasis. Provide an example.

Answer 5

The maintenance of a relatively stable environment by regulating changes in a controlled variable (temperature, blood pressure, glucose, oxygen, pH)

Example: When the blood pressure increases, blood vessels dilate and heart rate decreases. When blood pressure decreases, blood vessels will constrict and heart rate increases.

Question 6

Explain integration. Provide an example.

Answer 6

When any different cells, tissues, or organs come together to form a specific function. It is necessary to maintain homeostasis.

Example: The central nervous system and musculoskeletal systems work together to regulate movement.

Question 7

Explain mechanism of action. Provide an example.

Answer 7

It refers to how a physiological process occurs.

Example: The presynaptic neuron releases neurotransmitters at the synapse. They bind to ligand gated ion channels, which open and allow ions to move down their electrochemical gradient to generate a postsynaptic potential.

Question 8

Explain communication. Provide an example.

Answer 8

Cells communicate with each other to complete specific functions. It can occur over short or long distances.

Example: Hormones are produced by specific cell types and move from the cell to the blood where they circulate until they reach their target tissue and bind to their receptor.

Question 9

Explain structure-function relationships. Provide an example.

Answer 9

Structure is the arrangement of components making up a cell, tissue, organ, etc. Function describes the physiological purpose of the structure.

Example: Type 1 alveolar cells are long, thin, and flat. They facilitate diffusion of gases from alveoli into the long. Their structure minimizes the distance gases must diffuse.

Question 10

Define what a set point is and how this relates to homeostasis.

Answer 10

The set point is a range of a controlled variable that is considered stable/optimally healthy to maintain homeostasis.

Question 11

Identify whether the molecule described is part of the cell’s external or internal environment.

1. Glucose found within the plasma
2. Glucose found within the urine in the urinary bladder.

Answer 11

1. Internal - Plasma is one of the two components of the internal environment.
2. External - Fluid in the lungs, gut, and urinary system are part of the external environment.

Question 12

Below is an example of the reflex arc known as the swallowing reflex.

1. After swallowing a bite of food, the food stretches the soft pallet which is in the back of the
   mouth.
2. These physical changes caused by food hitting the soft pallet trigger mechanoreceptors
   (receptors sensitive to changes in length).
3. Afferent sensory neurons send signals to the central brain.
4. The brain sends a message to skeletal muscle present in the esophagus through efferent nerves
   which causes the soft pallet to elevate, the glottis to close, and the opening of the upper
   esophageal sphincter.
5. Food can move deeper in the esophagus/into the stomach and the back of the mouth is cleared.
   The soft pallet, glottis, and upper esophageal sphincter return to their original positions

Identify the following: stimulus, receptor, afferent pathway, integrating center, efferent pathway, effector(s), and response(s).

What kind of feedback is this?

Answer 12

Stimulus: food stretching the soft pallet
Receptor: mechanoreceptors
Afferent Pathway: afferent sensory neurons
Integrating Center: the brain
Efferent Pathway: efferent motor neurons
Effector(s): soft pallet, glottis, upper esophageal sphincter
Response(s): food is moved further down the esophagus and into the stomach until the mouth is cleared, decreasing the degree of stretch of the soft pallet

Negative feedback; the response opposes the stimulus

Question 13

Consider the following scenarios. Identify the type of mechanism.

1. You are heading to the gym for your regular workout. Before even beginning to exercise, you notice that your heart rate increases.
2. You are waiting for the bus on a cold, winter day. You notice you begin to shiver and feel yourself getting a little bit warmer.
3. A newborn begins nursing; milk production continues until the newborn stops nursing.

Answer 13

1. Feedforward; The body is undergoing a change in anticipation of exercise.
2. Negative feedback; The response (shivering/increased body temp) opposes the stimulus (decreased body temp)
3. Positive feedback; The initial stimulus reinforces the response. An outside factor is required to stop the loop.