NPB101: Homeostasis Lectures 2-3

A. Gomes Spring 2025

Microvilli

Increases surface area for absorption

Centrioles

aids in cell division/replication in animal cells only

Rough endoplasmic reticulum

modification and packaging of newly synthesized proteins

Smooth ER function

synthesis of lipids

Golgi apparatus

• System of membranes that modifies and packages proteins for export by the cell

• Adds carbohydrate units needed for signaling

Ribosomes

site of protein synthesis

Vacuoles

• Store nutrients and water on which a cell can rely for its survival.

• Store the waste from the cell and prevents the cell from contamination

Nucleus

DNA

Nucleolus

RNA

Plasma membrane

selectively permeable barrier that separates the cell’s interior from the external environment, regulating the passage of molecules and maintaining cell integrity

Lysosome

degrade proteins, organelles, mitochondria

Cytoplasm

jelly-like substance within a cell that contains organelles, enzymes, and various molecules, and is involved in cellular processes (ex. glycolysis)

Four Primary Types of Tissues

• Muscle (contraction)

• Nervous (signals)

• Epithelial (exchange)

• Connective (structural support)

Muscle (contraction)

• skeletal

• cardiac

• smooth

Nervous (signals)

• central

• peripheral

Epithelial (exchange)

Tissue that covers outside of the body and lines organs and cavities

• epithelial sheets (form boundaries)

• glands (secretion)

Connective (structural support)

Body tissue that provides support for the body and connects all of its parts

• tendons

• bones

• blood

Circulatory system examples

Circulates blood around the body, delivering oxygen and nutrients to organs and cells, carrying waste products away

• heart, blood vessels, blood

Digestive system

Mechanical and chemical processes that provide nutrients via the mouth, esophagus, stomach and intestines. Eliminates waste from the body

• mouth, esophagus, stomach, intestines, related organs

respiratory system

lungs and major airways

Urinary system

kidneys and associated structures

skeletal system

bones and joints

immune system

WBCs and lymphoid organs

muscular system

skeletal muscles

integumentary system

skin and related structures

nervous system

brain, spinal cord, nerves, and sense organs

endocrine system

all hormone- secreting glands

reproductive system

male and female gonads and related organs

Homeostasis

the maintenance of a dynamic steady state in the internal, environment (Independent of our minds)

Homeostasis Examples

• concentration of nutrients

• partial pressure of O2 and CO2

• Concentration of metabolic waste products

• blood pH

• Blood osmolarity

• concentration of Na+, K+ and other electrolytes

• blood volume and pressure

• body temperature

Dynamic constancy and example

Homeostasis refers to the dynamic mechanisms that detect and respond to deviations in physiological variables from their “set point” (set range) values by initiating effector responses that restore the variables to the optimal physiological range.

Example: Deviations in glucose concentration in blood (vary short term, fairly constant in the long term).

Homeostatic Control System

interconnected network of body components that work together to maintain a given factor relatively constant (never truly constant)

How would the control system maintain homeostasis?

• Sensor detected deviation from Set Point

• Control Center

• Response involving Effectors

Sensor detected deviation from Set Point (Control System)

detect deviations from normal (alpha and beta cells)

Control Center (Control System)

Integrate this information with other information (ex. pancreas)

Response involving Effectors (Control System)

Make adjustments to restore the factor to normal (insulin and glucagon)

Negative feedback

A primary mechanism of homeostasis, whereby a change in a physiological variable that is being monitored triggers a response that counteracts the initial fluctuation.

What do the intrinsic and extrinsic systems generally operate on?

Negative feedback

Afferent Signal

Sends the information from the sensor to the control center/integrator (sometimes it is not needed if the sensor and control center are the same cell)

Efferent Signal

Used to send information from the control center to the effectors (cells/organs) that need to perform an action to help restore homeostasis

When glucose concentration is high…?

Beta cells of the pancreas release insulin to lower glucose levels

When glucose concentration is low …?

Alpha cells of the pancreas release glucagon to increase glucose levels

Intrinsic (local) control systems

“built in” to an organ or tissue

• e.g., increased CO2 production by exercising skeletal muscle leads to relaxation of smooth muscle and dilation of blood vessels, increased blood flow brings more O2

Extrinsic control systems

contained outside of an organ system, permitting coordinated regulation of several organs

• e.g., low blood pressure is detected by the nervous system, which causes an increase in heart rate and constriction of blood vessels

• e.g., high blood glucose is detected by the endocrine system which exerts hormonal control [insulin]

Pathophysiology

abnormal functioning of the body associated with disease (Disruption in Homeostasis)

What happens when homeostatic disruption becomes very severe?

Death

How do cells of the body talk to each other to maintain homeostasis? (3 main, 2 subs each)

• Direct Intercellular Communication

  • Gap Junctions

  • Transient direct linkup of cells surface markers

• Indirect Intercellular Communication via Extracellular Chemical Messengers

  • Paracrine secretion

  • Neurotransmitter secretion

• Endocrine Signaling

  • Hormones

  • Neurohormones

Hormone

extracellular signaling molecule that is released into the blood and acts at its receptors in distal tissues to elicit a physicological response

Nervous system vs Endocrine System

• Nervous System

  • “wired” system

  • short distance (diffuses across synaptic cleft)

  • dependent on close anatomic relationship btwn neurons and target cells

  • fast and brief

• Endocrine System

  • “wireless” system

  • long distance (carried by blood)

  • dependent on specificity of target cell binding and responsiveness to particular hormone

  • slow and long

Does positive feedback contribute to homeostasis?

no

Positive feedback

Amplifies the initial change, moves the system away from the set point, important in processes such as childbirth

Feedforward mechanisms

operate without detectors and activate homeostatic mechanisms and anticipate when a change is likely to occur

• Can be done in response to an anticipated once in a lifetime event

• Can be done through body rhythms

Alterations in Homeostasis where set points can change

• In sickness

• As we age

• Throughout the day

What 3 fluids are exchanged in homeostasis?

Cells exchange materials from the intracellular fluid, with the interstitial fluid (extracellular space) and blood (specifically plasma)