Lec 22: Endocrine System

Question 1

Difference between endocrine and exorcine galnds

Answer 1

Question 2

Difference between endocrine system and autonomic nervous system

Answer 2

Question 3

Hormones don’t have to use the bloodstream to reach their targets

Answer 3

Question 4

Hormone

Answer 4

Chemical substance released into the
ECF that regulates the metabolic
function of other cells in the body

hormones must bind to specific
receptors

Question 5

hormones are specific; level of target cell activation depends on:

Answer 5

(i) hormone concentration
(ii) target cell receptor content
(iii) affinity of hormone for receptor

Question 6

Mechanism of Hormone Action:

Answer 6

hormones alter levels of cell activity:
» membrane permeability/potential (channels)
» synthesis of enzymes within cells
» enzyme activation/deactivation
» induction of secretory activity
» stimulation of mitosis

Question 7

3 structural groups of hormones

Answer 7

(i) amino acids, peptides, proteins
(ii) steroid hormones (derivatives of cholesterol)
(iii) eicosanoids (derivatives of arachidonic acid) – e.g. prostaglandins

Question 8

2 main mechanisms of action

Peptide/protein hormones:

Answer 8

water soluble, so cannot cross plasma membrane;

bind to a cell surface receptor » activation of membrane- bound G protein » production of 2nd messenger

Question 9

Steroid hormones:

Answer 9

lipid soluble; they can enter the nucleus and activate gene transcription

Question 10

hormones are potent

Answer 10

don’t need much to get a significant effect because the effects are amplified

Question 11

Blood Level depends on:

Answer 11

• rate of synthesis
• rate of degradation/clearance from blood

Question 12

Half-Life

Answer 12

persistence of a hormone in the blood; usually < 1 min to a week

Question 13

time to onset

Answer 13

• if enzyme activation - rapid (minutes)
• if enzyme synthesis - hours to days

Question 14

Control of Hormone Release

Answer 14

usually negative feedback (setpoint); sometimes positive feedback (goal)

Question 15

3 types of stimuli:

Answer 15

humoral, neural & hormonal

Question 16

Humoral stimuli

Answer 16

hormone secretion in direct response to change in blood level of a nutrient, ion [eg: parathyroid hormone (PTH) & blood
calcium; insulin & blood glucose]

Question 17

Neural stimuli:

Answer 17

not as common, eg: sympathetic ns & epinephrine release by adrenal medulla, hypothalamic neurons & oxytocin release

Question 18

Hormonal stimuli:

Answer 18

3-tiered system involving hypothalamus, pituitary & target endocrine gland - concept of hypothalamic-pituitary axis

Question 19

Hormonal Stimulus (an example of the 3-tiered system)

Answer 19

Thyroid-releasing hormone (TRH)
(hypothalamus)
↓
Thyroid-stimulating hormone (TSH)
(anterior pituitary)
↓
Thyroid hormones (T3 & T4)
(thyroid gland)

Question 20

Hypothalamus

Answer 20

is neural; produces a number of releasing factors (hormones) which travel to anterior pituitary via the hypophyseal portal system

Question 21

Hypophyseal Portal System

Answer 21

a system of blood vessels in the microcirculation at the base of the brain, connecting the hypothalamus with the anterior pituitary

Question 22

Hypophyseal Portal System (function)

Answer 22

is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland

Question 23

Pituitary Gland

Answer 23

• size & shape of a pea
• infundibulum connects pituitary to
  hypothalamus

Question 24

Posterior Lobe

Answer 24

• consists of axon terminals
• can think of it as a hormone storage area
• antidiuretic hormone (SON)
  oxytocin (PVN)

Question 25

antidiuretic hormon

Answer 25

chemical produced in the brain that causes the kidneys to release less water, decreasing the amount of urine produced

high ADH level causes the body to produce less urine. A low level results in greater urine production

Question 26

oxytocin

Answer 26

natural hormone that stimulates uterine contractions in childbirth and lactation after childbirth. It also affects aspects of human behavior and the male and female reproductive systems

Question 27

Table

Answer 27

Question 28

The Complete Hypothalamic-Pituitary-Target Organ System

Answer 28

Question 29

Summary

Autonomic Nervous System

Answer 29

• sympathetic versus parasympathetic motor output
• fast response
• pathways to reach target organs

Question 30

Summary

Endocrine System

Answer 30

• hormones released into extracellular fluid and often travel to
  target organs via bloodstream
• slower response time but response can be long-lived
• different chemical classes of hormones with associated
  mechanisms of action