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Endocrinology > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

What is homeostasis?

A

maintenance of a steady state/internal environment

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2
Q

What can alter homeostasis?

A

Either a physiological or pathological challenge causes a change in body homeostasis

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3
Q

What responds to maintain homeostasis?

A

Body’s physiological systems

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4
Q

What are the components of a feedback system?

A

Regulated factor
- set point (via hypothalamus), operating [range], “error
signal

Detector/sensor
- afferent path

Comparator/control centre
- determines set point of variable, compares and maintains
variable at set point
- Intrinsic: local – cell or tissue autoregulates
- Extrinsic: endocrine system, nervous system

Effector
- returns variable to set point (efferent path)

Response

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5
Q

Explain how a negative feedback loop works

A

If [factor] gets too high, it is detected by sensors and a signal is sent to the control centre to limit the release of that factor

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6
Q

How does the negative feedback loop affect a [low] factor?

A

If [factor] is low there is no negative feedback, positive response continues until levels get too high

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7
Q

What are the controlled chemical substances in the body?

A

Circulating concentrations of chemical substances

  • Ions e.g. Na+, Ca2+
  • Nutrients e.g. blood glucose concentration
  • Hormones
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8
Q

What are the controlled physical entities of the body?

A

Physical entity

  • Blood pressure
  • Core temperature
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9
Q

How does the body respond to being too cold?

A

shivering, vasoconstriction, increased metabolism (↑)

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10
Q

How does the body respond to a rise in temperature?

A

vasodilatation, sweating (↓)

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11
Q

Describe the physiological control of core body temperature

A

36.5 degrees is set point
The hypothalamus receives signals from cutaneous and hypothalamic temp. receptors detecting either heat loss or heat gain
Effect caused by sending signals to effector organs
once set point achieved, negative feedback loop activated to limit response as back to normal

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12
Q

What is the pathological effect on core body temperature?

A

Pathological → With infection the set point is changed and body temperature rises

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13
Q

How do pyrogens (bacteria/virus) affect body temperature?

A

Pyrogens (bacterial or viral infections) change the set point to a higher level resulting in fever

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14
Q

What are the benefits of a higher temperature during infection?

A

inhibits bacterial growth
speeds up metabolic reactions
Increases delivery of white blood cells to infection sites

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15
Q

Describe how body temperature is increased due to pathology?

A

Blood flow shifted to core to conserve heat
Increased muscle activity (shivering)
Chills stop when high temp reached

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16
Q

Explain how body temperature changes and is maintained during a fever

A

The actual body temperature lags behind the rapid shift in set point and even though regulation is maintained during the fever it is less precise

17
Q

What is the consequence of long term elevated BP?

A

Chronic elevated BP can lead to hypertension → stroke /CVS diseases

18
Q

Describe the series of events that follow an increase in BP

A
  1. Increased BP
  2. Detected by baroreceptors (stretch)
  3. Signal sent to CVS control centre - medulla
  4. ↑p/s input - decreased CO
  5. ↓ sympathetic activity - decreased CO + TPR
19
Q

What is hypertension?

A

The resetting the sensitivity of the baroreceptors

20
Q

What is the role of the neurones in the hypothalamus?

A

Neurones in the hypothalamus synthesise and release hormones from the posterior pituitary

21
Q

What do neurosecretory cells in the hypothalamus do?

A

Release their hormones into portal capillaries in which they are transported directly to endocrine cells of the anterior pituitary gland

22
Q

Name some hormones released by neurosecretory cells of the hypothalamus

A

Vasopressin (ADH)
CRH (corticotropin-releasing hormone) stimulates ACTH secretion
ACTH (adrenocorticotropic hormone) stimulates cortisol secretion

23
Q

What is the effect of a haemorrhage on BP?

A

After a haemorrhage blood volume and hence blood pressure are reduced

24
Q

What homeostatic control systems are activated to help restore BP after a haemorrhage?

A
  • Baroreceptor reflex - increases CO + TPR

- Vasopressin (ADH) secretion to increase blood volume

25
Q

What stimuli activate pituitary to release ADH?

A

Angiotensin II
Hyperosmolarity
Decreased atrial receptor firing
Sympathetic stimulation

26
Q

What are the effects of Vasopressin (ADH)?

A

Renal fluid absorption - increases BV
Vasoconstriction

These increase the arterial pressure

27
Q

Which system integrates feedback loops in the control of Na balance, BP and fluid volume?

A

Renin-Aldosterone-Angiotensin II system

RAAS

28
Q

How is circulating [cortisol] controlled?

A
  1. Hypothalamus secretes CRH
  2. Activates anterior pituitary to secrete ACTH
  3. ACTH acts on adrenal cortex to secrete cortisol
  4. If adrenal cortex over-secretes, negative feedback loop
    to hypothalamus to inhibit CRH release
29
Q

What factors increase [cortisol]?

A

Cortisol concentrations increased by stress and circadian rhythms (body clock)

30
Q

Describe the effect of a negative feedback loop

A

Increase in a controlled variable causes a decrease in a controlled variable

31
Q

Define a positive feedback loop

A

An increase in a controlled variable stimulates further increase in a controlled variable

32
Q

Name systems operating via a positive feedback mechanism

A

blood clotting, ovulation, childbirth

33
Q

Explain how the positive feedback mechanism of oxytocin controls uterine contractions in labour

A
  1. Labour oxytocin stimulates contraction of uterine
    muscles
  2. Cervix dilates and activate stretch receptors
  3. Action potentials signal to hypothalamus
  4. Stimulates further release of oxytocin

Endocrinology (12 decks)

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