Homeostasis

Question 1

What is the key integrator of homeostatic systems?

Answer 1

Hypothalamus

Question 2

What are homeostatic systems not limited to?

Answer 2

Autonomic nervous system

Question 3

What is the largest threat to thermoregulation and why?

Answer 3

Overheating

-We have no mechanism for cooling out body but we do have mechanisms to heat it up

Question 4

How do we resist hypothermia?

Answer 4

Heat conservation & increased heat production (shivering)

Question 5

What is the body’s set point?

Answer 5

37C (if it drops below or above we feel cold and hot)

Question 6

How do we vasodilate (to avoid too high of temperature)?

Answer 6

1. Local temperature sensors cause release of NO
2. NO stimulates Guanylyl Cyclase (enzyme) which converts GTP to cGMP
3. Then cGMP causes MLCK to relax =vasodilate
   {cGMP–> activates protein kinase G which phosphorylates proteins and decreases intracellular calcium –> relaxing muscles}

Question 7

What do core temperature sensors do when you’re hot?

Answer 7

Send signals to the CNS to activate sympathetic nerve outflow (both adrenergic & cholinergic). This increases skin blood flow and increases sweating.

Question 8

What are two mechanisms the body uses to avoid too low of temperature?

Answer 8

1. Cold stimulates skin receptors to release NE which constricts blood vessels.
2. Core temp sensors stimulate CNS to increase sympathetic nervous system outflow –> causes decreased skin blood flow.

Question 9

IMPORTANT: What causes a fever???

Answer 9

1. Pyrogen (IL-1, IL-6, TNF-alpha) stimulates hypothalamus

2. Hypothalamus produces PGE2 in medial pre-optic area causing shivering and increased metabolic rate

Question 10

What is important to remember about fevers?

Answer 10

1. PGE2 change the set point

2. Hypothalamic temperature does NOT change, it receives input from sensors elsewhere

Question 11

What causes hot flashes in nearly 80% of post-menopausal women?

Answer 11

An extremely narrow (unmeasurable) thermoregulatory zone

Question 12

What is blood pressure determined by?

Answer 12

BP = (Cardiac output/Flow) X (Peripheral resistance)
BP = (Heart rate) X (Stroke volume) X (Total peripheral resistance)

Question 13

What do sympathetic nerves do in regulation of blood pressure?

Answer 13

1. Interact with beta1 receptors to stimulate heart rate
2. Interact with beta1 receptors to increase stoke volume
3. Interact with alpha1 receptors to increase resistance

Question 14

What type of system is the vagus nerve associated with in bp regulation? What does vagus nerve do to bp?

Answer 14

1. Parasympathetic nerve

2. Releases ACh to interact with muscarinic receptors in the heart to slow heart rate

Question 15

How to baroreceptors regulate blood pressure? (simple version)

Answer 15

1. If bp is low, sensory fibers are less stimulated
2. Sensory fibers stimulate inhibitiroy interneurons less
3. Inhibitory interneurons do NOT inhibit rest of pathway
4. Rest of pathway is stimulated which causes constriction of the muscle (stimulation of sympathetic nerve ending)
5. Constriction of the muscle causes an increase in bp (vasoconstriction)

Question 16

Where are stretch receptors located?

Answer 16

Carotid arteries & Aortic arch

Question 17

Pathway from stretch receptors to Nucleus Tractus Solitarius (NTS)?

Answer 17

1. Stretch receptors sense stretch (blood pressure) [High bp]
2. As blood pressure increases, firing rate increases
3. Impulses are carried by glossopharyngeal and vagus nerve to medulla
4. Nerves terminate in NTS of medulla.

Question 18

What is the pathway from the NTS to the change in bp?

Answer 18

1. Neurons in the NTS suppress neurons in rostal ventrolateral medulla (sympathoexcitatory area)
2. These neurons excite sympathetic preganglionic neurons in the interomediolateral column of the thoracic cord.
3. Sympathetics usually increase heart rate (beta1), stroke volume (beta1) and resistance (alpha1) to raise bp.
4. Since input from baroreceptors inhibits activation of sympathetic nerves (and release of NE to elevate heart rate, stroke volume, resistance) the net effect is lessened intensity of the increase in bp (decrease in bp)

Question 19

What might causes orthostatic hypotension in people my age?

Answer 19

Dehydration (less blood volume = lower bp

Question 20

What happens if the bp in the carotid and aorta drops?

Answer 20

1. Less activation of glossopharyngeal & vagus nerve
2. Less stimulation of NTS
3. Less inhibition of rostral ventrolateral medulla
4. Greater stimulation of preganglionic sympathetics in thoracic cord
5. Increases heart rate, stroke volume and resistance
6. Lessens drop in blood pressure

Question 21

What is the pump that generates pressure differentials when we breathe?

Answer 21

Diaphragm and External Intercostals

Question 22

What is our breathing pacemaker that initiates breathing?

Answer 22

Pre-Boetzinger area of ventrolateral medulla

Question 23

How does the pacemaker (Pre-Boetzinger area) work?

Answer 23

Stimulates C3-C5 via the phrenic nerve to innervate the diaphragm

Question 24

What type of nerve is the phrenic nerve that innervates the diaphragm?

Answer 24

Somatic, releases ACh onto nicotinic receptors on the diaphragm. (all somatic nerves coming off spinal cord release ACh onto nicotinic)

Question 25

How do you get Hydrogen ion from Carbon dioxide?

Answer 25

Carbonic anhydrase (CA)

Question 26

What is the main input into the Pre-Boetzinger area?

Answer 26

Parafacial respiratory center

Question 27

What does the parafacial respiratory center sense?

Answer 27

• CO2 (actually H+) and excites Pre-Boetzinger area

- It also directly excites muscles involved in active expiration (abdominals)

Question 28

What happens if you have a lack of carbon dioxide sensors?

Answer 28

(CO2 sensors are in parafacial respiratory center)

• Hyperventilation while sleeping (Fatal if untreated)
• People with this condition need to connect a device while they’re sleeping

Question 29

What nerve does the pacemaker control? What happens when you activate this nerve?

Answer 29

• Phrenic nerve

- Cause diaphragm to contract

Question 30

What is the voluntary mechanism that controls urination?

Answer 30

External sphincter consists of skeletal muscle & is VOLUNTARY
-ACh stimulating nicotinic receptors (like all skeletal muscles)

Question 31

What is the involuntary mechanism that controls urination?

Answer 31

Internal sphincter and detrusor (wall) are innervated by the parasympathetic nervous system (involuntary)
-ACh stimulating muscarinic receptors

Question 32

How do you think bladder filling is sensed?

Answer 32

Stretch receptor - barorecptor!

Question 33

What happens when the bladder fills?

Answer 33

It sends afferent signals to the medial prefrontal cortex, which normally suppresses voiding.

Question 34

How will you treat incontinence (drugs)?

Answer 34

Anti-muscarinic drugs/muscarinic receptor antagonists

Question 35

What is the role of the pontine micturition center?

Answer 35

-Activates sacral cord to stimulate preganglionic parasympathetic nerves (involuntary control)
[-Also activates inhibitory interneurons influencing motoneurons innervating the external urethral sphincter]
-NET: relaxation of external (voluntary) sphincter and contraction of the urinary bladder via parasympathetic nerves

Question 36

What neurotransmitter does the parasympathetic nervous system use primarily?

Answer 36

Acetylcholine!

Question 37

What is dis-inhibited during urination?

Answer 37

Micturition center

Question 38

How is urination controlled?

Answer 38

Activation of pudendal nerve to relax external sphincter.

[Involuntarily - mediated by activation of parasympathetic nerves]