Homeostasis and Feedback Systems Quiz

Applied Homeostasis

• Homeostasis is the body's internal equilibrium maintained through constant interactions of regulatory processes.
• Homeostasis is a dynamic state—not static, but a constant adjustment.
• Body's internal equilibrium can shift within a narrow range. (e.g. blood glucose level normally stays between 70-110 mg/dL).
• All body structures contribute to maintaining the internal environment within normal limits.

Desired Learning Outcomes

• Explain homeostasis at a cellular level.
• Differentiate between homeostasis and allostasis.
• Explain adaptation, acclimatization, biological clock & apoptosis.
• Describe the effects of increased demand/stress on a cell.

Intro: The Cell

• Cell theory (Schleiden & Schwann, 1839): Cells are the functional & structural unit of living organisms.
• All life is composed of one or more cells formed from pre-existing cells.
• Cells are the smallest form of life as it is the structural basis for living organisms.
• A cell is the basic living unit in the body.

The Cell

• The human body contains approximately 100 trillion cells.
• Each cell is uniquely adapted to perform specific functions.
• Cells all have basic functional characteristics such as metabolism.
• Cells deliver end products to the surrounding medium.
• Cells can reproduce additional cells of their own kind.
• Cells, tissues, organs and systems.

Internal Environment

• The proper functioning of body cells depends on the precise regulation of the composition of the interstitial fluid surrounding them .
• This interstitial fluid is often called the body’s internal environment.
• Blood plasma and interstitial fluid exchange substances.
• Substances move across the tiny blood capillaries' thin walls.
• Capillaries give cells the needed materials (e.g., glucose, oxygen, ions).
• They also remove wastes (e.g., carbon dioxide) from the interstitial fluid.
• Unicellular organisms (e.g., amoeba) are dependent on the external environment.
• Multicellular organisms are largely independent from their external surroundings, with an internal environment.

Internal Environment (Extracellular Fluid)

• Internal environment is a watery medium bathing all the cells of the body – Extracellular Fluid (ECF).
• ECF comprises blood plasma.
• Also includes Interstitial fluid surrounding the cells.
• Intracellular fluid (ICF) is the fluid within cells.

Cell-Cell Communication

• Cells communicate with each other for conveying physiological information.
• Four basic cell-to-cell communication methods:
  • Gap junctions: Allow direct cytoplasmic transfer of electrical and chemical signals between adjacent cells.
  • Contact-dependent signals: Require interaction between surface molecules on one cell membrane and another.
  • Local communication: Uses paracrine and autocrine signals that diffuse through extracellular fluid to reach target cells.
  • Long-distance communication: Uses a combination of electrical signals (nerve cells) and chemical signals (blood). (e.g., hormones)

Important characteristics of cell-cell communication types

• Gap junctions: Are not all alike, differing across tissues. 20 different connexin isoforms. Only way to allow direct transfer of electric signals between cells.
• Contact-dependent signals: Mediated by Cell adhesion molecules (CAMs) which occur in immune system development and growth. CAMs act as receptors and link to cytoskeleton and intracellular enzymes allowing signal transfer in both directions across cell membranes.

Local communication (Paracrine and Autocrine Signals)

• In some cases, one molecule can act as both an autocrine and paracrine signal. - Cells release paracrine signals.
• Signal molecules reach their target cells by diffusing through interstitial fluid.
• The signaling range is limited to adjacent cells due to diffusion distance.
• Histamine (a paracrine molecule), is an example released from damaged cells in response to skin injury.

Long-distance communication (Electrical or Chemical)

• Communication is by nervous and endocrine systems.
• Endocrine system utilizes hormones.
• Hormones are secreted into the blood for circulation throughout the body.
• Hormones only act on target cells that have receptors for the hormone.
• Nervous system uses a combination of chemical and electrical signals.
• In neurons, an electrical signal travels along a nerve cell (neuron) until it reaches the end.
• This signal becomes a chemical signal (neurocrine).
• If a molecule quickly diffuses from the neuron to a target cell, it's called a neurotransmitter.
• If the molecule takes longer for action and is through the blood, it's called a neurohormone.

Cellular Signaling (Primarily Chemical)

• Cells can detect both chemical and physical signals.
• Physical signals are generally converted to chemical signals at the receptor level.
• Receptors sense diverse stimuli but initiate limited cellular signals.
• Receptors have ligand-binding and effector domains.
• Same ligand might have different effects depending on effector domain.
• Ligand binding triggers receptor conformation change.
• Signal sorting and integration happen in signaling pathways (often multistep, with secondary messengers).
• Second messengers enable readily diffusible information transfer throughout the cell.

Overview of Cell Signaling

• Signal molecules bind to receptors on the cell membrane.
• Plasma membrane is where signals are received.
• Transduction: Relay molecules in a signal transduction pathway.
• Response: Activation of cellular response inside the cell.

Intro-Homeostasis

• Homeostasis: Maintenance of internal equilibrium through regulatory processes.
• In response to changing conditions, the body's equilibrium shifts within compatible limits.
• Blood glucose levels (e.g, 70 to 110 mg/dL).

Feedback control Systems of Homeostasis

• Feedback systems, also called loops, constantly monitor and adjust internal conditions.
• Each monitored variable (like temperature, BP, or blood glucose) is called a Controlled Condition
• A disruption of a controlled condition is called a stimulus.

Components of Feedback Systems

• Receptor: Body structure sensing changes in a controlled condition; sends input to control centre.
• Control center: Determines set point and analyses the input, generating an appropriate response/output.
• Effector: Receives output from control center, causing changes in controlled condition.

Feedback System Diagram

• Shows how one part of the system feeds the information back to the others to continuously create homeostasis.

Feedback System Types

• Negative feedback: Response negates or reverses the stimulus. (e.g., maintaining body temperature).
• Positive feedback: Response reinforces the stimulus. (e.g., childbirth).

Negative feedback example

• Example is blood glucose regulation.
• Sensors detect high blood glucose.
• Control center (pancreas) releases insulin
• Effectors (cells) take up glucose from blood.
• Blood glucose falls to normal level.

Components of a Feedback System

• Receptors detect and send signals
• Control center receives, processes, and decides on feedback
• Effectors perform the feedback (action)

Homeostatic Mechanisms

• Congenital metabolic disorders (inherited causes).
• Aging (with Homeostenosis): Homeostenosis refers to a decrease in homeostatic functions and ability associated with aging.
• Chromosomal abnormalities (genetic causes).
• Environmental factors (e.g., UV radiation, pollutants.)

Homeostatic Imbalance

• Disturbances of homeostasis, normal body equilibrium
• Negative feedback mechanisms may overwhelm
• Positive feedback mechanisms can be destructive.

Examples of Homeostatic Imbalance in body systems

• Integumentary system (e.g., burns, skin cancer)
• Skeletal system (e.g., scoliosis, osteoporosis)
• Muscular system (e.g., muscular dystrophy)
• Nervous system (e.g., multiple sclerosis, Alzheimer’s)
• Endocrine system (e.g., goiter, diabetes, pituitary dwarfism)
• Cardiovascular system (e.g., atherosclerosis)
• Lymphatic system (e.g., immunodeficiencies like AIDS, autoimmune disorders)
• Respiratory system (e.g., bronchitis, emphysema)
• Digestive system (e.g., heartburn, ulcers)
• Urinary system (e.g., kidney stones, polycystic kidney disease)
• Reproductive system (e.g., pelvic inflammatory disease, cancer)

Homeostasis Model vs. Allostasis Model

• Homeostasis maintains constant internal conditions.
• Allostasis adjusts internal conditions in response to changing anticipated needs (i.e., anticipating future changes).

Features of homeostasis

• Stability of internal conditions
• Maintaining of life
• pH, concentration of ions, osmolality, blood glucose, blood oxygen

Features of allostasis

• Adapting to changing internal/external environments
• Blood pressure, heart-rate, body core temperature, hormones, sleep-wake cycles, and metabolic energy

Acclimatization

• Physiological or behavioral changes within an organism
• In response natural climate or environment.
• Usually completely reversible
• E.g., elevated altitude, physiological responses in red blood cell count increase to compensate for lower oxygen concentration.

Apoptosis

• Programmed cell death is tightly regulated in humans.
• Removing damaged cells and assisting in development.
• Cell removal mechanism.
• Abnormalities can be linked to neurodegenerative diseases.

Necrosis

• Uncontrolled cell death.
• Features are cell swelling, inflammation, and membrane integrity loss.
• Different from Apoptosis as it is not a regulated process.

Biological Clock

• Inherent biological mechanism influencing cyclical behaviors and physiological processes.
• Daily, monthly, and seasonal changes within the body are common examples.
• Control of circadian rhythms (e.g., sleep-wake cycles, temperature, hormone levels).

Suprachiasmatic Nucleus (SCN)

• Master biological clock controlling daily (circadian) rhythms

Applied Physiology of Homeostasis with Examples

• Blood glucose regulation: Hormones (insulin & glucagon) regulate blood glucose levels.
• Blood pressure control: A balance of hormonal control and nerves maintain blood pressure.
• Examples from patient cases (dehydrated patient example).

Test your knowledge on homeostasis and the feedback systems in the human body. This quiz covers key concepts such as receptors, control centers, and the effects of imbalances. Understand how the internal environment is regulated and the roles of various body fluids.