Homeostasis Flashcards
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)
→ Response
Why does the value of a controlled variable oscillate?
→ Time delay between sensing a change and its correction
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?
→ The core body temperature is the regulated parameter
→ changes sensed by hypothalamic or cutaneous temperature receptors
→ hypothalamus mediates effects
What happens when you have an infection to body temp?
→ Set point is changed
→ Temperature rises
→ Pyrogens change the set point to a higher level
What are the benefits of high temperature when you are sick?
→ Inhibits bacterial growth
→ Speeds up metabolic reactions
→ Increases delivery of WBC to infection sites
How is temperature increased?
→ Blood flow shifted to core to conserve heat
→ Increased muscle activity (shivering)
→ Chills stop when temperature is reached
What is blood pressure detected by?
→ Baroreceptors
Where is the control center for blood pressure and what does it do?
→ Medulla
→ Changes TPR and HR
Equation for CO?
→ HR x SV
Equation for BP?
→ CO x TPR
What happens when high BP is detected flow chart
Increased BP ↓ Baroreceptor sensing ↓ Cardiovascular control center ↓ Increased parasympathetic and decreased sympathetic inputs ↓ Decreased cardiac output
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 synthesize and release hormones
Where do other neurosecretory cells release their hormones?
→ Into the portal capillaries where they are transported directly to endocrine cells of the anterior pituitary
What does ADH do?
→ Increases vasoconstriction
What two systems are activated after a haemorrhage to restore blood pressure?
→ Baroreceptor reflex
→ ADH stimulated
Flow chart of what happens when blood pressure is decreased
Glomerulus kidney cells secrete renin
↓
Liver produces angiotensinogen
↓
converted to angiotensin I
↓
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
↓
Acts on hypothalamus - secretes ADH - thirst- collecting tubule has aquaporins
↓
Act on arteries - constrict - increased BP
What does CRH stimulate?
→ACTH
What does ACTH stimulate?
→ Cortisol level
Flow chart of how cortisol is released
Stress occurs ↓ Hypothalamus releases CRH ↓ Act on the anterior pituitary gland ↓ releases ACTH ↓ acts on adrenal cortex ↓ releases cortisol
What are examples of positive feedback mechanisms?
→ blood clotting
→ ovulation
→ childbirth
How does the blood clotting mechanism work?
→ 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
How does oxytocin work in the uterus?
→ Oxytocin stimulates contraction of uterine muscles
→ Cervix dilates and activates stretch receptors
→ Action potentials signal to hypothalamus
→ Stimulates further release of oxytocin
Draw a homeostatic feedback loop
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