Homeostasis Flashcards
What is homeostasis?
Maintenance of a steady internal environment about a set point.
What are the 5 components of a feedback system?
- Regulated factor (a set point)
- Detector/sensor (afferent path)
- Comparator/control centre (determines set point)
- Effector (returns variable to set point/ efferent path )
- Response
Why does the value of a controlled variable oscillate?
→ Time delay between sensing a change and its correction
What are some examples of chemical concentrations that need to be maintained by homeostasis?
- ions, eg. Na+ and Ca2+
- nutrients, eg. blood glucose concentration
- hormones
What are some physiological characteristics that are maintained by homeostasis?
- Blood Pressure
- Core Temperature
What happens to the body when you are hot?
- Vasodilation
- Sweating
What happens to the body when you are cold?
- Shivering
- Vasoconstriction
- Increased metabolism
How is temperature sensed?
- Core body temperature is the REGULATED FACTOR
- Changes sensed by hypothalamic or cutaneous temperature receptors
- Hypothalamus mediates effects
How does an infection affect the elements of the temperature homeostatic negative feedback loop?
Pyrogens (bacterial or viral infections) change setpoint to a higher level, causing fever.
When you have an infection, what are the benefits of a fever?
- Inhibits bacterial growth
- Speeds up metabolic reactions
- Increases delivery of WBC to infection sites
During a fever, how is the temperature increased?
- Blood flow shifted to core to conserve heat
- Shivering
- Chills stop when high temperature is reached
Describe the temperature-time course of a typical febrile attack.
- Actual body temperature lags behind the rapid shift in set point
- Regulation of body temp. maintained but less precise
How would the blood pressure negative feedback loop react to increased blood pressure? PART 1
- Baroreceptors senses high BP through the stretching of blood vessels
- Feedback into the cardiovascular control centre within the brain.
How would the blood pressure negative feedback loop react to increased blood pressure? PART 2
- Decreased sympathetic activity (and increased parasympathetic activity)
- Decreased CO and TPR, so low BP
Where is the control center for blood pressure and what does it do?
- Medulla
- Changes TPR and HR
What happens during hypertension to the set point?
- Set point is reset
- Baroreceptors are less sensitive
What releases hormones from the posterior pituitary?
Neurons in the hypothalamus
Where do other neurosecretory cells release their hormones?
→ Into the portal capillaries where they are transported to endocrine cells of the anterior pituitary
What is the role of vasopressin (ADH) in control of blood pressure?
- Causes vasoconstriction
- Increases renal fluid absorption, which increases blood volume.
- Both increase BP
Give an example of two control systems activated after a haemorrhage to help restore blood pressure.
- Baroreceptor reflex to increase CO and TPR
- Stimulation of ADH secretion to increase blood volume
What happens when blood pressure is decreased? PART 1
- Glomerulus kidney cells secrete renin
- Liver produces angiotensinogen
- Converted to angiotensin I
What happens when blood pressure is decreased? PART 2
- 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
What happens when blood pressure is decreased? PART 3
- Acts on hypothalamus - secretes ADH - causing insertion of aquaporins on collecting duct walls
- Act on arteries - constrict - increased BP
Describe the hormonal regulation of cortisol secretion. PART 1
- Neurosecretory cells in the hypothalamus release CRH which travels down the portal vessels into the anterior pituitary, where it stimulates ACTH secretion.
