Homeostasis

Question 1

What are the 5 components of a feedback system?

Answer 1

→ Regulated factor ( a set point)
→ Detector/sensor (afferent path)
→ Comparator / control centre (determines set point)
→ Effector (returns variable to set point)
→ Response

Question 2

Why does the value of a controlled variable oscillate?

Answer 2

→ Time delay between sensing a change and its correction

Question 3

What happens to the body when you are hot?

Answer 3

→ Vasodilation

→ Sweating

Question 4

What happens to the body when you are cold?

Answer 4

→ Shivering
→ Vasoconstriction
→ Increased metabolism

Question 5

How is temperature sensed?

Answer 5

→ The core body temperature is the regulated parameter
→ changes sensed by hypothalamic or cutaneous temperature receptors
→ hypothalamus mediates effects

Question 6

What happens when you have an infection to body temp?

Answer 6

→ Set point is changed
→ Temperature rises
→ Pyrogens change the set point to a higher level

Question 7

What are the benefits of high temperature when you are sick?

Answer 7

→ Inhibits bacterial growth
→ Speeds up metabolic reactions
→ Increases delivery of WBC to infection sites

Question 8

How is temperature increased?

Answer 8

→ Blood flow shifted to core to conserve heat
→ Increased muscle activity (shivering)
→ Chills stop when temperature is reached

Question 9

What is blood pressure detected by?

Answer 9

→ Baroreceptors

Question 10

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

Answer 10

→ Medulla

→ Changes TPR and HR

Question 11

Equation for CO?

Answer 11

→ HR x SV

Question 12

Equation for BP?

Answer 12

→ CO x TPR

Question 13

What happens when high BP is detected flow chart

Answer 13

Increased BP 
↓
Baroreceptor sensing 
↓ 
Cardiovascular control center
↓
Increased parasympathetic and decreased sympathetic inputs 
↓
 Decreased cardiac output

Question 14

What happens during hypertension to the set point?

Answer 14

→ Set point is reset

→ Baroreceptors are less sensitive

Question 15

What releases hormones from the posterior pituitary?

Answer 15

→ Neurons in the hypothalamus synthesize and release hormones

Question 16

Where do other neurosecretory cells release their hormones?

Answer 16

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

Question 17

What does ADH do?

Answer 17

→ Increases vasoconstriction

Question 18

What two systems are activated after a haemorrhage to restore blood pressure?

Answer 18

→ Baroreceptor reflex

→ ADH stimulated

Question 19

Flow chart of what happens when blood pressure is decreased

Answer 19

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

Question 20

What does CRH stimulate?

Answer 20

→ACTH

Question 21

What does ACTH stimulate?

Answer 21

→ Cortisol level

Question 22

Flow chart of how cortisol is released

Answer 22

Stress occurs
↓
Hypothalamus releases CRH 
↓
Act on the anterior pituitary gland 
↓ 
releases ACTH 
↓
acts on adrenal cortex
↓
releases cortisol

Question 23

What are examples of positive feedback mechanisms?

Answer 23

→ blood clotting
→ ovulation
→ childbirth

Question 24

How does the blood clotting mechanism work?

Answer 24

→ 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

Question 25

How does oxytocin work in the uterus?

Answer 25

→ Oxytocin stimulates contraction of uterine muscles
→ Cervix dilates and activates stretch receptors
→ Action potentials signal to hypothalamus
→ Stimulates further release of oxytocin

Question 26

Draw a homeostatic feedback loop

Answer 26

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