Lecture 22: Homeostasis & The Endocrine System

Question 1

Define homeostasis

Answer 1

Maintaining a relatively constant internal environment that differs to the external environment and remains constant even when there are environmental changes

Question 2

What is the negative feedback system and what are the components?

Answer 2

A mechanism by which animals that regulate internal environments achieve homeostasis
It is a loop that detects a change that triggers a response to REDUCE the stimulus

1. set point
2. stimulus
3. sensor
4. control center
5. effector
6. response

Question 3

Describe the set point of a negative feedback system

Answer 3

a variable maintained near a particular value

ex. body temperature at 37 degrees celsius

Question 4

Describe the stimulus of a negative feedback system

Answer 4

anything that fluctuates the variable above or below the set point

ex. a change in salinity

Question 5

Describe the sensor/receptor of a negative feedback system

Answer 5

Recognizes the stimulus and sends information to the control centre

Question 6

Describe the control centre of a negative feedback system

Answer 6

Triggers a response

ex. the hypothalamus

Question 7

Describe the effector of a negative feedback system

Answer 7

Carries out a response

ex. muscles or capillaries

Question 8

Describe the response of a negative feedback system

Answer 8

Whatever activity brings the variable back to the set point –> reduces the stimulus

ex. sweating to cool body temperature down

Question 9

Define thermoregulation

Answer 9

The process by which animals maintain an internal temperature within an optimum range that can differ from the external environment

Question 10

Define endotherms and ectotherms - give examples of animals

Answer 10

endotherms: use internal metabolism to produce heat to maintain body temperature
- ex. birds and mammals

ectotherms: have body temperatures that are determined by external conditions
- ex. amphibians, reptiles (not birds), most fish, invertebrates

Question 11

Describe the steps of the negative feedback loop of thermoregulation for body temperature increase

Answer 11

1. set point/homeostasis: internal body temperature around 37 degrees C
2. stimulus: body temperature increases above set point
3. sensor/receptor: warm temperature receipts detect stimulus and signal the thermostat in the hypothalamus
4. control centre: hypothalamus triggers a response in the effectors
5. effectors:
   - blood vessels/capillaries in skin dilate to fill with blood and bring to skin surface so heat can radiate out of body
   - sweat glands secrete sweat to evaporate out of body –> cools body
6. response: sweating and heat loss reduce body temperature (stimulus) back to the set point and stops the loop

Question 12

Describe the steps of the negative feedback loop of thermoregulation for a body temperature decrease

Answer 12

1. set point/homeostasis: body temperature around 37 degrees C
2. stimulus: body temperature decreases below set point
3. receptors: temperature receptors detect stimulus and signal thermostat in hypothalamus
4. control centre: hypothalamus activates warming mechanisms in the effectors
5. effectors:
   - skeletal muscles contract rapidly to cause shivering and generate heat
   - blood vessels in skin contract to reduce heat loss through surface
6. responses: muscle contractions and capillary contractions reduces stimulus by increasing body temperature to set point and stopping the loop

Question 13

Describe the endocrine system

Answer 13

A system that regulates the body by short- and long-distance CHEMICAL signalling between cells and organs

Question 14

define hormone

Answer 14

Molecules that function as chemical signals that are secreted by the endocrine system (usually an endocrine gland) that circulate throughout the body in the blood in order to trigger a response

Question 15

define target cells

Answer 15

cells that have the specific receptor molecules to which a hormone binds and can respond to the signal

some target cells can have receptors for multiple hormones

Question 16

define endocrine gland and distinguish it to an exocrine gland

Answer 16

Endocrine glands are DUCTLESS glands that secrete hormones directly into interstitial fluid surrounding cells.
- ex. adrenal glands, pituitary glands

Whereas,

Exocrine glands have ducts and secrete substances OUT of the body (through digestive tract or surface).
- ex. sweat glands, salivary glands, mammary glands, the pancreas

Question 17

How does the hypothalamus interact with the anterior and poster pituitary glands

Answer 17

The hypothalamus receives information from nerves throughout the body and responds by initiating appropriate endocrine signals that travel to the pituitary gland

Question 18

What is the posterior pituitary glands role?

Answer 18

the PPG is an extension of the hypothalamus that stores hormones produced by the hypothalamus

It receives hormones from neurosecretory cells of the hypothalamus that trigger the PPG to secrete the stored hormones in response to a nerve (electrical) impulse sent from the hypothalamus

Question 19

Which 2 hormones are released from the posterior pituitary gland?

Answer 19

Antidiuretic Hormone: sent to the kidneys

Oxytocin: sent to the mammary glands and uterine muscles

Question 20

What is the anterior pituitary glands role?

Answer 20

synthesizes and secretes its own hormones in response to a hormonal signal from the hypothalamus.

Many of the hormones synthesized by the APG regulate the function of other endocrine glands or cells

Question 21

Describe the function of the pancreas, what are the main hormones produced by it?

Answer 21

The pancreas is an endocrine gland that functions in GLUCOSE HOMEOSTASIS by responding to blood glucose levels by releasing a hormone into the blood

• insulin
• glucagon

Question 22

Describe the function of the thyroid glands

Answer 22

releases hormones regulating - blood pressure

• heart rate
• muscle tone
• digestive functions
• reproductive functions

Question 23

describe the function of the adrenal glands, what are the main hormones produced by it?

Answer 23

releases stress hormones (epinephrine and norepinephrine)

to trigger fight or flight responses (related to the sympathetic nervous system)

Question 24

Describe the role of ADH

Answer 24

released by the Posterior pituitary gland in response to high salt concentration in the bloodstream via an electrical signal from the hypothalamus. This occurs when there is too much water loss and a high salt concentration in the blood. It is sent to the collecting duct of the kidney to increase the permeability of the collecting duct to reabsorb more water and reduce further water loss.

Question 25

Describe the role of oxytocin

Answer 25

A hormone secreted by the posterior pituitary gland when the hypothalamus releases an electrical impulse to send it to the mammary glands to produce milk when a baby suckles the nipple
- also sent to the uterine muscles to contract during child birth

• works on a positive feedback system –> more suckling = more milk

Question 26

Describe how the negative feedback system works for an increase of blood glucose levels

Answer 26

stimulus: blood-glucose levels increases above the set point (high blood glucose levels)

receptor/control centre: the pancreas receives the information and releases the hormone signal

hormone signal: insulin is released by the pancreas into the bloodstream to bind to a target cell

effectors:
large cells in the liver trigger a response

response: the liver takes up glucose and converts it into glycogen to be stored in the liver

the blood glucose levels will drop back to set point and reduce the stimulus and stop the feedback loop.

Question 27

Describe how the negative feedback system works for an decrease of blood glucose levels

Answer 27

stimulus: blood glucose levels decrease below set point (low blood glucose levels)

receptor/control centre: the pancreas receives the information of stimulus and releases the hormone signal

hormone signal: glucagon released by the pancreas into the bloodstream

glucagon binds to target cells in the liver (effector) to trigger a response

response: the liver breaks down the stored glycogen into glucose and releases it into the blood stream to increase blood glucose levels –> decreasing the stimulus and stopping the feedback loop.

Question 28

What happens to human blood if the blood-glucose levels are too high?

Answer 28

Glucose can coat the red blood cells, creating a thick viscous liquid, and damage the blood vessels

Question 29

What happens to humans if blood-glucose levels are too low?

Answer 29

Cells do not receive enough sugar to do cellular respiration and produce ATP so they cannot function properly to produce energy for work

Question 30

Describe glucose and glycogen

Answer 30

Glucose is the sugar molecule that circulates in the bloodstream

Glycogen is a collection of sugar molecules bonded together by the liver and stored in the liver when there is sufficient glucose in the bloodstream

Question 31

What is the liver’s function in blood glucose level regulation

Answer 31

The liver interconverts glucose and glycogen when triggered by the pancreas to do so

Glucose too high:
glucose –> glycogen –> stored in liver

Glucose too low:
glycogen –> glucose –> circulates in blood

Question 32

Describe glucagon and insulin

Answer 32

Insulin is a hormone released by the pancreas to trigger the liver to take up glucose and convert it into glycogen

glucagon is a hormone released by the pancreas to trigger the liver to break down glycogen into glucose