Homeostasis and Cell Physiology

Flashcards testing core concepts of human homeostasis, body temperature regulation, fever pathogenesis, cell membrane structure, membrane proteins, cellular communication, body fluid compartments, and tonicity.

What is the definition of homeostasis?

Homeostasis is defined as the maintenance of a relatively stable internal environment essential for normal cell function and the survival of the organism.

What are the two major regulatory control systems responsible for homeostasis in the body?

1. The Nervous System, which utilizes neural communication accomplished by nerve cells. 2. The Endocrine System, which utilizes hormonal communication accomplished by hormones.

What is normal human body temperature, and why is its regulation critical?

Normal body temperature is $37^\text{C} \text{ } 0.5^\text{C}$ ($98.6 \text{ } 0.05^\text{F}$). Regulation is critical because optimal enzyme activity occurs at this temperature, whereas elevated temperatures denature proteins and depress neurons.

How do core temperature and shell temperature differ in location and variability?

Core temperature involves structures within the skull, thoracic, and abdominal cavities and remains relatively constant. Shell temperature involves the skin and fluctuates substantially between $20^\text{C}$ and $40^\text{C}$.

What serves as the major agent of heat transfer between the body core and shell?

Blood serves as the major agent of heat transfer between the core and shell.

How does heat production shift from rest to vigorous exercise?

At rest, vital organs account for most heat production. During vigorous exercise, heat production from skeletal muscles can increase 30 to 40 times.

What are the four main sources of heat gain in the body?

1. Thermic effect of food (Specific dynamic action of food). 2. Muscular exercise. 3. Hormones like epinephrine and thyroid hormones. 4. Brown fat in infants and other biological activities.

What are the primary mechanisms of heat loss from the body?

1. Conduction, radiation, and convection (when environmental temperature is lower than body temperature). 2. Vaporization of water in respiratory passages and skin, as well as a small amount lost in urine and feces.

What are the five main components of the reflex thermoregulatory mechanism?

1. Receptors (cold and warm receptors in skin, spinal cord, and hypothalamus). 2. Sensory neurons. 3. Control center (the hypothalamus, which adjusts the set point of core temperature). 4. Motor neurons. 5. Effectors (sweat glands, skeletal muscles, and skin blood vessels).

What physiological responses occur in response to cold weather?

Vasoconstriction, shivering (involuntary muscle contraction), contraction of arrector pili muscles in skin (raising skin hairs to trap an insulating layer of air), hormonal responses (increased adrenaline and thyroxine), and behavioral changes.

According to this diagram, what is the step-by-step mechanism and pathogenesis of fever?

Infections or LPS cause monocyte activation, releasing pyrogenic cytokines (IL-1, TNF\alpha, IL-6). These travel via circulation to the endothelium of the hypothalamus to generate PGE2. PGE2 acts on EP3 receptors to release neurotransmitters and cAMP in the hypothalamic thermoregulatory center, elevating the set-point and initiating peripheral heat conservation and production to manifest as fever.

What is the etymological origin and definition of Physiology?

Physiology comes from the Greek physis (meaning nature) and logos (meaning study). It is defined as the study of the vital functions of the living organism.

What is the thickness and percentage composition of the cell membrane?

The cell membrane is $7.5\text{ to }10\text{ nanometers}$ thick. Its composition by mass is 55% proteins, 42% lipids, and 3% carbohydrates.

How is a phospholipid molecule structured, and why is it termed amphipathic?

A phospholipid has a polar, hydrophilic head made of one glycerol molecule and a phosphate group (soluble in water), and non-polar, hydrophobic tails made of two fatty acids (insoluble in water). It is termed amphipathic because it possesses both hydrophilic and hydrophobic parts.

How do carrier proteins, channels, and pumps differ in their mechanism of transport relative to concentration gradients?

Carrier proteins (by binding substances and changing conformation) and channel proteins transport substances along their concentration gradient, whereas pumps transport substances against their concentration gradient.

What are the three types of gated membrane channels and their activation triggers?

1. Voltage-gated channels: open by alterations in membrane potential (e.g., $\text{Na}^+$ channel). 2. Ligand-gated channels: open and close by binding a ligand (e.g., acetylcholine receptor). 3. Mechanosensitive channels: open by mechanical stretch.

What are the four types of extracellular chemical messengers used in indirect intercellular communication?

1. Autocrine (acts on the same cell). 2. Paracrine (acts on neighboring cells). 3. Endocrine (acts via the bloodstream). 4. Neurocrine (excreted by neurons).

How is Total Body Water (TBW) distributed across body fluid compartments?

Total body water accounts for 60% of body weight, divided into 2/3 intracellular fluid (ICF) and 1/3 extracellular fluid (ECF, $14\text{ L}$). ECF is further divided into 3/4 interstitial fluid ($10.5\text{ L}$), 1/4 intravascular/plasma ($3.5\text{ L}$), and transcellular fluid.

How do Extracellular Fluid (ECF) and Intracellular Fluid (ICF) differ in electrolyte composition?

ECF contains large quantities of $\text{Na}^+$, $\text{Cl}^-$, and $\text{OH}^-$ ions, with small quantities of $\text{K}^+$ and $\text{Ca}^{2+}$. ICF contains large quantities of $\text{K}^+$ and $\text{Mg}^{2+}$, with small quantities of $\text{Na}^+$, $\text{Cl}^-$, and almost no $\text{Ca}^{2+}$.

What is the normal osmolarity of body fluids, and how are solutions classified by tonicity relative to plasma?

The normal osmolarity of body fluids is $300\text{ mOsm/L}$. Solutions are classified as Isotonic ($= 300\text{ mOsm/L}$), Hypotonic ($< 300\text{ mOsm/L}$), or Hypertonic ($> 300\text{ mOsm/L}$).

Based on this figure, how does exposure to isotonic, hypotonic, and hypertonic solutions affect red blood cell (RBC) morphology?

In an Isotonic solution, RBCs do not gain or lose $\text{H}_2\text{O}$. In a Hypotonic solution, water enters and RBCs enlarge (swell). In a Hypertonic solution, water leaves and RBCs shrink.