Homeostasis: Maintaining Internal Balance in Biological Systems, Slides of Physiology

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Topic 4

Homeostas

is

Part 1: Homeostasis

Overview

Starting Physiology

Physiology Section-Learning Outcomes

• 1. Demonstrate basic knowledge of facts, terms and concepts in Physiology. Develop a solid comprehension of the physiological processes that underlie animal body function
• (^) 2. Recognize interrelationships and interdependenc e among the 11 organ systems. Understand the physiological integration of the organ systems to maintain homeostasis
• (^) 3. Understand the basis for the evolution of adaptations in the design of organ systems among differing organisms (and when comparing less complex to more complex organisms).
• 4. Realize the interplay (and significance) of form and function. Note that the structure of physiological systems is optimized for purpose.
• (^) 5. Acquire a solid comprehension of normal physiology to serve as a foundation for the understanding of pathophysiology.

Internal Responses

• (^) They are the physiological processes of

your body

• (^) Carried to maintain the physical and

chemical parameters

• (^) Allows proper and efficient functioning of the body’s component (cells, tissues, organs, and organ systems)
• (^) Example: Reduce urinary output when you are dehydrated (Anti- diuretic hormone: ADH)
• (^) ADH will act on kidneys to help reabsorb more water.

How does your body maintain homeostasis (in general)?

**1. Nervous (major control system)

2. Endocrine (major control system)**
3. Muscular
4. Skeletal
5. Integumentary
6. Circulatory
7. Lymphatic/Immune
8. Respiratory
9. Digestive
10. Excretory
11. Reproductive

Osmotic Balance Example

• (^) Interstitial fluid contains ions (osmotic balance) and complex molecules (energy source) - (^) Involved in removal of wastes - (^) Waste removal = circulatory system and excretory system.
• Note: Interstitial fluid (or tissue fluid) is a solution - (^) Bathes and surrounds the cells of multicellular animals. - (^) Comprises main component of the extracellular fluid (ECF) including plasma - (^) Plasma = the liquid component of the blood

Homeostasis During Exercise (Cardio…Eww)

• Exercise: muscles use more oxygen, (produce more CO 2 ) - Chemoreceptors sense the change from normal levels - (^) Intrinsic controls cause dilation of the blood vessels - (^) Allows more blood into those active muscles - (^) bring in more O 2 , take away CO 2 - (^) Active hyperemia : increased blood flow through a tissue associated with increased metabolic activity

Intrinsic Control: Vasodilation Continued

• Note: Acetylcholine is released by autonomic nerves in the walls of the blood vessel

Controlling Homeostasis

• (^) Body is sensing and reacting to changes in homeostasis - (^) (eg., decrease in oxygen, increase in CO2) in muscle tissue during rigorous exercise)
• Body uses intrinsic controls to initiate a response and thus re- establish homeostasis
• But can we simply stop after detecting a problem and responding to it?

Negative Feedback

• Sensor(or sensory receptor): Specialized cells or neuronal endings that detect a change - (^) Factors such as pressure, temperature, pH, concentrations of molecules, etc
• In response to this change (or stimulus), a signal is initiated. Sensory Transduction is crucial:
• (^) Stimulus (or change) is converted into an action potential (AP)
• (^) Action potential is transmitted along axons towards the central nervous system (CNS) where it is integrated
• (^) Example: Sensory cells (rods and cones) in the retina convert the physical energy of light signals into electrical impulses (APs) that travel to the brain

Baroreceptors

• Baroreceptors are neurons (or neuronal endings) in the walls of the atria of the heart, the aortic arch, and the carotid sinuses. - (^) are mechanical stretch receptors - (^) generate electrical impulses (action potentials) when stretched. Detect the amount of stretch in vessel walls
• (^) Sensitive to changes in blood pressure
  • Blood pressure: pressure exerted by the blood upon the walls of the blood vessels
• (^) Relay signals (APs) to the brainstem to elicit the appropriate response to restore homeostasis

Baroreceptors and Homeostasis

Continued

• (^) Send signals (Action Potentials=APs) to the brainstem.
• Brainstem sends signals via autonomic nervous system (involuntary: heart rate, digestion, respiration rate, etc) to elicit changes
• (^) Example of signals: Baroreceptors decrease their rate of firing (APs) when blood pressure drops - Example: When a person stands up, - (^) blood temporarily pools in the legs (particularly in the elderly due to varicose veins- enlarged/dilated ) - (^) causing a drop in venous return to the heart: causes blood pressure to fall (postural hypotension).
• (^) As blood pressure falls (on standing up):
  • (^) The baroreceptors are stretched less
  • (^) Rate firing action potentials to cardiac inhibitory centers decreases
  • (^) This increases cardiac output, which increases blood pressure
  • Homeostasis is restored

Chemorecep tors

• Found in the aorta and carotid arteries (and other locations)
• Can detect O2 content in the blood
• (^) If O2 content falls below normal (set point), chemoreceptors send signals (APs) to brainstem
• Brainstem integrates this information with the information from the baroreceptors
• Sends the signal to increase the rate and force of the heartbeat (and respiration)

Quick Question: Is Osmolarity the same as tonicity?

pH Homeostasis

Body has a buffering systems, such as:

CO2+H2O  H2CO3HCO

-

+ H

+ (carbonic acid) (bicarbonate)

to tightly regulate blood pH (range=7.35-7.45)

The above is called the bicarbonate buffering

reaction

 Quick Question: What might cause the plasma to be too acidic?