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SGUL - Physiology 1 > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

What is homeostasis?

A

Maintenance of a steady internal environment about a set point.

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2
Q

What are the 5 components of a feedback system?

A
  • Regulated factor (a set point)
  • Detector/sensor (afferent path)
  • Comparator/control centre (determines set point)
  • Effector (returns variable to set point/ efferent path )
  • Response
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3
Q

Why does the value of a controlled variable oscillate?

A

→ Time delay between sensing a change and its correction

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4
Q

What are some examples of chemical concentrations that need to be maintained by homeostasis?

A
  • ions, eg. Na+ and Ca2+
  • nutrients, eg. blood glucose concentration
  • hormones
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5
Q

What are some physiological characteristics that are maintained by homeostasis?

A
  • Blood Pressure
  • Core Temperature
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6
Q

What happens to the body when you are hot?

A
  • Vasodilation
  • Sweating
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7
Q

What happens to the body when you are cold?

A
  • Shivering
  • Vasoconstriction
  • Increased metabolism
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8
Q

How is temperature sensed?

A
  • Core body temperature is the REGULATED FACTOR
  • Changes sensed by hypothalamic or cutaneous temperature receptors
  • Hypothalamus mediates effects
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9
Q

How does an infection affect the elements of the temperature homeostatic negative feedback loop?

A

Pyrogens (bacterial or viral infections) change setpoint to a higher level, causing fever.

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10
Q

When you have an infection, what are the benefits of a fever?

A
  • Inhibits bacterial growth
  • Speeds up metabolic reactions
  • Increases delivery of WBC to infection sites
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11
Q

During a fever, how is the temperature increased?

A
  • Blood flow shifted to core to conserve heat
  • Shivering
  • Chills stop when high temperature is reached
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12
Q

Describe the temperature-time course of a typical febrile attack.

A
  • Actual body temperature lags behind the rapid shift in set point
  • Regulation of body temp. maintained but less precise
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13
Q

How would the blood pressure negative feedback loop react to increased blood pressure? PART 1

A
  • Baroreceptors senses high BP through the stretching of blood vessels
  • Feedback into the cardiovascular control centre within the brain.
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14
Q

How would the blood pressure negative feedback loop react to increased blood pressure? PART 2

A
  • Decreased sympathetic activity (and increased parasympathetic activity)
  • Decreased CO and TPR, so low BP
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15
Q

Where is the control center for blood pressure and what does it do?

A
  • Medulla
  • Changes TPR and HR
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16
Q

What happens during hypertension to the set point?

A
  • Set point is reset
  • Baroreceptors are less sensitive
17
Q

What releases hormones from the posterior pituitary?

A

Neurons in the hypothalamus

18
Q

Where do other neurosecretory cells release their hormones?

A

→ Into the portal capillaries where they are transported to endocrine cells of the anterior pituitary

19
Q

What is the role of vasopressin (ADH) in control of blood pressure?

A
  • Causes vasoconstriction
  • Increases renal fluid absorption, which increases blood volume.
  • Both increase BP
20
Q

Give an example of two control systems activated after a haemorrhage to help restore blood pressure.

A
  • Baroreceptor reflex to increase CO and TPR
  • Stimulation of ADH secretion to increase blood volume
21
Q

What happens when blood pressure is decreased? PART 1

A
  • Glomerulus kidney cells secrete renin
  • Liver produces angiotensinogen
  • Converted to angiotensin I
22
Q

What happens when blood pressure is decreased? PART 2

A
  • Angiotensin II formed by ACE in the lungs
  • Acts on adrenal cortex - secretes aldosterone - kidney tubules add Na+ channels - more Na+ reabsorbed into extracellular space
23
Q

What happens when blood pressure is decreased? PART 3

A
  • Acts on hypothalamus - secretes ADH - causing insertion of aquaporins on collecting duct walls
  • Act on arteries - constrict - increased BP
24
Q

Describe the hormonal regulation of cortisol secretion. PART 1

A
  • Neurosecretory cells in the hypothalamus release CRH which travels down the portal vessels into the anterior pituitary, where it stimulates ACTH secretion.
25
Q

Describe the hormonal regulation of cortisol secretion. PART 2

A

ACTH will act on the adrenals to stimulate cortisol secretion.

26
Q

What is the difference between negative feedback control and positive feedback control? PART 1

A

With negative feedback, if there is an increase in a controlled variable, the body will put in motion processes that will eventually decrease that variable and its effects.

27
Q

What is the difference between negative feedback control and positive feedback control? PART 2

A

With positive feedback control, if there is an increase in a controlled variable, the body will instead amplify that to further increase that variable. Response of effector reinforces stimulus.

28
Q

How does the blood clotting mechanism work?

A

→ Break or tear in blood vessel wall
→ Clotting occurs as platelets adhere and release chemicals
→ Feedback cycle ends
→ Clotting proceeds until break is sealed by newly formed clot

29
Q

Describe the positive feedback control of uterine contractions in labour by oxytocin.

A
  • Oxytocin stimulates contraction of the uterine muscles.
  • Cervix dilates and activates stretch receptors.
  • Action potentials send signals to the hypothalamus.
  • Stimulates a further release of oxytocin.

SGUL - Physiology 1 (68 decks)

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