Homeostasis Flashcards

1
Q

Physiology

A

-how living organisms function, from molecules to human beings

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2
Q

Homeostasis

A
  • defining feature of physiology
  • involves the maintenance of nearly constant conditions in the internal environment
  • control of numerous Vital parameters- arterial pressure, blood volume, body temperature, nutrients
  • dynamic constancy
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3
Q

Steady state

A
  • maintenance of nearly constant conditions over time
  • not the same as equilibrium
  • need to put in energy
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4
Q

Equilibrium

A
  • a system when its solute concentrations and other parameters are constant in time without requiring the input of energy from metabolism or other sources
  • no energy
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5
Q

Cell environment response to changes

A
  • single cells maintain their internal environment in response to changes in the external environment
  • semi-permeable cell membrane facilitated the process that provided nutrients to the cell using diffusion, endocytosis etc
  • damage to plasma membrane= impair metabolic function, lead to cell death if cell can’t restore homeostasis
  • human body contains 100 trillion
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6
Q

Multicellular organisms adapt to changes

A
  • in multicellular organisms the basic homeostatic mechanisms of single celled organisms are mirrored by integration of specialized organ systems that create a stable environment for cells
  • allows for specialization of cellular functions and a layer of protection for the systems
    ex: lungs exchange gases, digestive tract- uptake of nutrients and water
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7
Q

Organs vs organ systems

A

-Organs- 2 or more kinds of tissues
-Organ systems- collection of organs that perform a general function
- 11:
Circulatory, Digestive, Endocrine, Immune, Integumentary, Lymphatic, Musculoskeletal, Nervous, Reproductive, Respiratory, Urinary
-the functions of organ systems are essential to survival of the body

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8
Q

Concept of mass balance

A
  • for a system at steady state for metabolism means that any substance taken in by the body is nearly equal to the amount leaving the body plus that removed by metabolism
  • the central compartment (POOL) is usually extracellular fluid (which includes blood plasma)
  • it receives substances from intake, synthesis, and release from cells
  • it loses by excretion, metabolism, and upstake into cells
  • in steady state it is in balance
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9
Q

Basal metabolic rate (BMR)

A
  • energy expenditure at rest (kcal/hr/sq meter body surface area)
  • largest in daily energy useage (60%), thermic effect of food 8%, nonexercise activity (7%), purposeful physical activity (25%)
  • all the chemical processes involved in energy production, energy release and growth- anabolic (formation) or catabolic (breakdown)
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10
Q

Resting metabolic rate

A
  • 70 kg man requires 2100 kcal/day
  • BMR is less than RMR
  • RMR increased in males because of increased muscle
  • RMR declines with age (reduced muscle)
  • Increased by thyroid hormone, growth hormone, testosterone, epi/norepi
  • RMR is higher in people living in arctic vs tropical regions (10-20%)
  • malnutrition decreases metabolic rate
  • components of energy expenditure
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11
Q

Homeostasis and maintaining body fluid balance and electrolytes

A
  • net fluid balance- fluid input needs to match fluid output
  • if intake (from food and beverages) exceeds output (urine, fluid in feces, insensible losses), the organism is in positive balance, and urine volume will increase to eliminate excess fluid
  • negative fluid balance occurs when intake is less than output, in this case integrated responses will increase thirst and decrease additional fluid losses, until homeostasis is restored
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12
Q

Elements in Extracellular fluid are tightly controlled

A
  • need to maintain control over numerous vital parameters to survive and grow
  • some elements are controlled within extremely narrow ranges (pH) whereas others fluctuate over broader ranges (plasma glucose)
  • loss of control over one or more of these manifests as illness and requires medical attention.
  • oxygen, carbon dioxide, sodium ion, potassium ion, calcium, chloride, bicarbonate ion, glucose, body temp, acid-base
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13
Q

Homeostasis is a dynamic process

A
  • external environmental conditions that can be far from constant, common physiological variables in healthy humans are maintained within a predictable range
  • some variables undergo fairly dramatic swings over the course of a day, yet are still considered to be in balance
  • after a typical meal blood glucose levels rise considerably
  • hemostatic compensatory mechanisms (endocrine) quickly respond to restore blood glucose to pre-meal levels without overshooting to a significant degree in the opposite direction
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14
Q

Negative feedback

A
  • major process used to maintain a stable internal environment (homeostasis)
  • it is the initation of responses that counter deviations of a controlled variable from a normal range
  • negative feedback loops often operate as part of a larger network of control
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15
Q

Feedforward control

A
  • also regulates body systems, particularly when a change with time is desirable (heart rate and breathing increase in anticipation of exercise_
  • feedforward and negative feedback also act in combination
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16
Q

Positive feedback

A

-accelerates a process and thus can be unstable; it is less common in nature than negative feedback, but important in many cases

17
Q

Negative Feedback at Molecular Level

A
  • Homeostatic control is redundant, exerted at many levels
  • enzyme: product formed from a substrate by an enzyme negatively feeds back to inhibit further activation of the enzyme- end product inhibition, can be done by chemical modification of the enzyme by reaction product
  • ex: energy stores depleted, glucose is metabolized to make ATP. Atp levels restore, inhibit specific enzymes that breakdown glucose
18
Q

Negative Feedback at Systems Level

A
  • major control of the synthesis and secretion of thyroid hormones from the thyroid gland is via the hypothalamic-pituitary axis
  • thyrotropin-releasing hormone (TRH) from the hypothalamus acts on the anterior pituitary gland to increase secretion of the thyroid stimulating hormone (TSH)
  • TSH acts on the thyroid gland to increase synthesis and secretion of TH
  • TH acts on target tissues through body to increase BMR and heat generation
  • TH neg feeds on anterior pituitary to prevent too much or too little TSH release
  • common to endocrine system- adrenal gland, gonads
19
Q

Gain

A
  • capacity of the system to restore a controlled variable to its set point after a perturbation
  • the degree of effectiveness with which a control system maintains constant conditions is determined by the gain of negative feedback
  • the higher the gain, the better it is to restore a controlled variable to its set point in response to a perturbation
  • gain= correction/remaining error, it is 4 for baroreceptor system. In response to hemorrhage the person would get thirsty
  • feedback for temp has gain of 25-30
20
Q

Problems with positive feedback

A
  • recovery of heart pumping by negative feedback after 1 L blood lost
  • death is caused by positive feedback when 2 L removed
  • the initiating stimulus causes more of the same- decreased blood pressure, decreased blood flow to the heart- the heart is weakened further- diminishing blood flow and death
21
Q

Useful positive feedback

A
  • blood clotting after vessel rupture
  • uterine contractions during childbirth
  • estrogen effects on the pituitary-hypothalamus before ovulation
  • generation of an all or none action potential via Na+ channel activation
  • calcium-induced calcium release in heart
22
Q

Generalization about Homeostasis

A
  • stability of internal environment based on balancing inputs and outputs
  • in neg feedback a change in variable being regulated brings about the responses that tend to move the variable in the direction opposite the original change- that is, back toward the initial value (set point)
  • cannot maintain complete constant- there is a narrow range of normal valves
  • set points can be reset higher or lower
  • all homeostatic control systems can’t all be regulated in the normal ranges in every environmental challenges- need hierarchy of importance