Endocrine System & Homeostasis

Question 1

Homeostasis

Steady state

Homeorhesis

Goal of these systems

Answer 1

• Homeostasis: Maintenance of a constant internal environment
• Steady state: balance between demands placed on body and the physiological response to those demands
• Homeorhesis: steady state trajectory as animals develops or environment changes
• Goal is to regulate some physiological variable at or near a constant value (where it works at optimum)

Question 2

Homeostatic systems

Answer 2

• Body temperatures
• Blood pressure
• Body weight
• Immune system
• Electrolyte balance
• water balance

Question 3

Homeostasis - definition

Answer 3

• The internal environment of the body is in a dynamic state of equilibrium (internal conditions vary, but within relatively narrow limits)
  
  • wide variety of chemical, thermal and neural factors act and interact in complex ways to maintain homeostasis

Question 4

Internal components of homeostasis

Answer 4

• Conc. of O and CO2
• pH of internal environment
• Conc. of nutrients and waste products
• conc. of salt and other electrolytes
• Volume and pressure of extracellular fluid
• body temperature

Question 5

Biological control system components

• 3 parts
  
  • what the components do together

Answer 5

-Series of interconnected components that serve to maintain a physical or chemical parameter at or near constant
includes;
-Receptor: capable of detecting changes
-Integrating centre: assesses input and initiates response
-Effector: Corrects changes to internal environment

Question 6

Cycle of Biological control system (4 steps)

Answer 6

1. Stimulus excites receptor
2. Receptor signals the integrating center of a disturbance
3. Signals effector to correct disturbance
4. Effector corrects disturbance and removes stimulus

Question 7

2 types of control system in homeostasis

Answer 7

1. Autoregulation (local control, intrinsic): when cells, tissues, organs or systems automatically change in response to signals within themselves (e.g. blood supply to activate muscles)
2. Extrinsic control (by nervous and endocrine system): changes stimulated by signals from outside of the cell, organ or system

Question 8

2 ways extrinsic control is excerted

Answer 8

• Nervous Control: brain and spinal cord signals cause change; response is rapid but short term
• Endocrine control: glands produce hormones that cause changes; response is slower, but lasts longer
• both work together

Question 9

Nervous system

• what is it
• what it forms in homeostasis

Answer 9

• Is a network of billions of nerve cells linked together in a highly organised fashion to form the rapid control centre of the body
• It forms the integrating centre for homeostasis, movement and almost all other body functions

Question 10

Organisation of the nervous system (2 big divisions)

Answer 10

2 big divisions;

1. Central Nervous system; includes brain and spinal cord; is the centre of integration and control
2. Peripheral nervous system: The nervous system outside of the brain and spinal cord; consists of 31 spinal nerves and 12 Cranial nerves

Question 11

Autonomic Nervous system

• what is it apart of
• what it does
• how it can further be divided

Answer 11

-Is part of the motor efferent division of the peripheral nervous system
*is INVOLUNTARY
-conducts impulses from CNS to smooth muscle, cardiac muscle and glands
Can be divided into Sympathetic nervous system (Fight or flight) and Parasympathetic nervous system (Rest and digest)

Question 12

Chemical communication (2 ways)

Answer 12

• only a few mechanisms used within a human for chemical communication
• Direct communication occurs via gap junctions
• Second type of communication = chemical messengers (some of which form the basis of the endocrine system

Question 13

Gap Junctions

-what they link & what they allow to occur

Answer 13

• Link adjacent cells

- Connexons form channels that link cytosol of adjacent cells -> allows ions and small molecules to move between cells

Question 14

Chemical Messengers

• what secreted by
• what they do and how they work (briefly)

Answer 14

• Secretory cells release chemical messengers into the extracellular fluid
• Messenger binds to specific receptors on target cell to cause cell response
• binding of messenger to receptor triggers a response in the target cell
  
  • doesn’t have to go into cell

Question 15

List 6 types of chemical messengers

Answer 15

1. Classic endocrines
2. Paracrines
3. Autocrines
4. Cytokines
5. Neurotransmitters
6. Neurohormones

Question 16

Chemical Messengers

• classic endocrines
• paracrines
• plus examples

Answer 16

• Classic Endocrines: secreted by one cell and diffuse to a distant target cell to cause an effect
  
  • largest group
  • control long term homeostatic processes such as growth, reproduction, aging, apetite
• Paracrines: scecreted by one cell and diffuse to a nearby target cell
  - e.g. histamine (released in damaged tissue - involved in inflammatory response); growth factors

Question 17

Chemical messengers

• Autocrine
• Cytokine

Answer 17

• Autocrine: similar to paracrines, but bind to receptors on the same cell that secreted them
  
  • often an autocrine also functions as a paracrine or other messenger (e.g. growth factors)
• Cytokines: Secreted by a cell and then either act locally and/or diffuse to neighbouring target cell and/or transported to distant cells
  
  • part of immune response system
    
    • e.g. interleukins & interferons; groups of small proteins released from WBC as part of immune response

Question 18

Chemical Messengers

• Neurotransmitters
• Neurohormones

Answer 18

• Neurotransmitters: released into Interstitial fluid secreted from neurons at axon terminal, then bind to target cell
  
  • AKA synaptic signalling
  • e.g. acetylcholine, involved in triggering contraction of skeletal muscle
• Neurohormones: hormones secreted by neurons but which diffuse into the blood for transport to target cells
  
  • e.g. vasopression from posterior pituitary gland

Question 19

Negative Feedback

• what it is
• e.g.

Answer 19

• Response reverses the initial disturbance in homeostasis
  e. g. blood pressure at rest;
• Heart action causes increasing blood pressure
• Baroreceptors in carotid artery relay info to brain that blood pressure has increased
• Brain signals to heart to contract more slowly
• Blood pressure decreases

Question 20

Integration of nervous and endocrine systems during stress

Answer 20

• both work together
• After nervous stimulation Adrenal meulla secretes epinephrine and norepinephrine (i.e. adrenaline) -> gets organs ready for fight or flight
• Endocrine system releases hormones into blood, which eventually makes its way to appropriate organs for a response to be carried out

*Endocrine pathway is slower than nervous

Question 21

Positive Feedback

• what is it
• e.g.

Answer 21

• The output enhances the original stimulus
  e. g. regulation of blood clotting
• break or tear in blood vessel wall
• clotting occurs as platelets adhere to site and release chemicals
• released chemicals attract more platelets
• clotting proceeds until break is sealed by newly formed clot

Question 22

Loss of homeostatic control -> Diabetes

• what is it
• what it can lead to

Answer 22

• it is a serious disorder of carbohydrate metabolism
• Most common endocrine disorder
  
  • can lead to blindness and complications can = death
• most diabetics = type 2 (non-insulin dependent)
  - have cells that don’t respond to insulin -> most common in adults who are overweight

Question 23

Diabetes

-what it results in

Answer 23

• Results in hyperglycemia (glucose lvls too high)
  
  • glucose not taken up into cells -> excreted into urine
• fat and protein stores mobilised as alternative energy source -> they are depleted
• Increased fat metabolism results in formation of keton bodies (are acidic) and can build up and cause ketoacidosis (blood and body fluids become acidic)
  
  • ketones also carry Na and K with them -> lead to water loss
    
    • electrolyte balance also accompanies water loss