Lecture 4: Mechanism of Hormonal Regulation

Question 1

Hormonal Alterations

Answer 1

Abnormalities in endocrine function may be caused by elevated or depressed hormone levels

Question 2

Causes of Hormonal Alterations

Answer 2

(a) faulty feedback systems (b) dysfunction of the gland (c) altered metabolism of hormones (d) dysfunction of carrier proteins, or (e) production of hormones from non-endocrine tissues.

Question 3

Failure of Target Cells to Respond to Normal Stimulation is Due to:

Answer 3

(a) cell surface receptor–associated disorders (b) intracellular disorders (c) circulating hormone inhibitors.

Question 4

Functions of the Endocrine System

Answer 4

→ Differentiation of reproductive system and CNS in fetus → Stimulation of growth and development – growth hormone → Coordination of the male and female reproductive systems – sex hormone →Maintenance of internal environment – homeostatic - Ex. Insulin – regulating blood sugars → Adaptation to emergency demands of body - Regulating ones flight or flight response

Question 5

General Characteristics of Hormones

Answer 5

→ Specific rates and rhythms of secretion - Diurnal, pulsatile, and cyclic and patterns that depend on circulating substances → Operate within feedback systems - Positive or negative feedback loops (majority controlled by negative feedback loop) → Affect only target cells with appropriate receptors → Excreted by kidneys (or other organs) or deactivated by liver or cellular mechanisms ***Hormones have different levels throughout the day In negative feedback loop - Hormone secretion that increases the level of hormone and trying to complete a physiological effect - Positive feedback loop > Milk production in newborns (prolactin) > Oxytocin (labour + delivery – promotes birth stretch) *****

Question 6

Release of Hormones

Answer 6

→ In response to an alteration in the cellular environment → To maintain a regulated level of certain substances or other hormones

→ Tropic hormones – precursor hormones that lead to the release of different hormones

Question 7

Regulation of Hormones

Answer 7

→ regulated by chemical, hormonal, or neural factors - Subject to neg feedback system

Question 8

Feedback Loops

Answer 8

• Hypothalamus (regulatory control centre) dictates the release of hormones + factors that are replaced to inhibit – effects the anterior pituitary glands – which is responsible for the release of trophic hormones – tropic hormone effect the target hormone – hormone is released – physiological effect produced
• Longer feedback loop is when it goes back all the way through the hypothalamus – shorter feedback look goes back to the target organ

Question 9

Hormone Transport and Action

Answer 9

• ˜Hormones are released into the circulatory system by endocrine glands
  
  • Target cell
  • Upregulation
  • Downregulation
  • Hormone effects:
    
    • Direct effects – lead to obvious changes in the cell function
    • Permissive effects – less obvious and help to facilitate cell function

Question 10

Mechanism of Hormone Action: Water-soluble Hormones

Answer 10

• ˜Water-soluble hormones circulate in free, unbound forms
  
  • Short-acting response
  • Bind to surface receptors b/c water soluble

Question 11

Mechanism of Hormone Action: Lipid-soluble Hormones

Answer 11

• Rapid and long-lasting response
• Diffuse freely across the plasma and nuclear membranes and bind

Question 12

Mechanism of Hormone Action: Upregulation

Answer 12

• Up regulation is used by cells to increase their sensitivity to a specific hormone
• Hormone bind to a receptor or to create a specifc reaction – the target cells produce more receptors that are specific to that hormone
• inhibitor prevents this

Question 13

Mechanism of Hormone Action: Down Regulation

Answer 13

• Occur either due to down regulation of target cells of its normal process (degrade, destroy or get rid of) on the target cell membrane – the accumulation of receoports
• Activate the present recepors on the target side
• Increase the spcificity to the target horomone for the hormones to bind
• inhibitor prevents this

Question 14

Hormone Receptors

Answer 14

• Located in the plasma membrane or in the intracellular compartment of the target cell
  
  • All hormones rely on some sort of receptors
  • A water soluble hormone cannot perfuse across a cell membrane

Question 15

Water-soluble Hormones

Answer 15

• High molecular weight
• Cannot diffuse across the plasma membrane
• first messenger
  
  • •Hormone
  • Signal transduction
• Second messenger molecules
  
  • Calcium
  • Cyclic adenosine monophosphate (cAMP)
  • Cyclic guanosine monophosphate (cGMP)
  • Tyrosine kinase system

Inositol triphosphate (IP3)

Question 16

Lipid-soluble Hormones

Answer 16

• Easily diffuse across the plasma membrane and bind to cytosolic or nuclear receptors

Question 17

Water-soluble Hormones: Non-Steroid

Answer 17

• Water-soluble hormones act as first messengers, binding to receptors in the cell’s plasma membrane.
• The signals initiated by hormone-receptor binding are then transmitted into the cell by the action of second messengers (i.e., cyclic adenosine monophosphate, cyclic guanosine monophosphate, or tyrosine kinase) and mediate the action of the hormone on the target cell (i.e., protein synthesis or cellular growth).

Question 18

Lipid-soluble Hormones: Steroid

Answer 18

• Lipid-soluble hormones (including steroid and thyroid hormones) cross the plasma membrane by diffusion. These hormones diffuse directly into the cell nucleus and bind to nuclear receptors. Rapid responses of steroid hormones may be mediated by plasma membrane receptors.
• b/c steroid hormones are lipid soluble they are able to cross the plasma membrane of the target organ cell
• Once in the cell, they pass through the cytoplasm + enter the nucleus where they bind with a receptor to form a hormone receptor complex
• The complex acts on DNA which causes the formation of a new protein in the cytoplasm that produces specific effects in the target cell
• The hormone receptor complex induces DNA to make RNA which leaves the nucleus and carries info to the ribosome – making a protein in the cytoplasm

Question 19

Steroid Hormone Mechanism

Answer 19

• SH can go directly into the target cell + nucleus to bind to the receptor cell to help with the development of the protein

Question 20

Pituitary Gland

Answer 20

• Responsible for the anterior and posterior pituitary
• Connected to the CNS through the hypothalamus (regulatory control center in the brain to dive homeostasis processes)
• The hypo secretes/releasing or inhibits
• Hormone of the pituitary are regulated in 3 ways
  
  • the secretion of peptide hormones or releasing hormones from the hypo
  • regulated by the feedback effects of the hormones that have been
• secreted by the target hormones
  
  • direct effects of the neurotransmitters – connection to the hypothalamus

Question 21

Anterior Pituitary: ˜Adrenocorticotropic hormone (ACTH)

Answer 21

• A precursor hormone
• Corticotropic releasing hormone that facilitates its release

Question 22

Anterior Pituitary: Somatotropic Hormone

Answer 22

• Growth hormone
• Prolactin – hormone that’s under the positive feedback loop
  
  • Stimulates the release of prolactin, prolactin inhibiting factor (dopamine) inhibits the releasing factors

Question 23

Anterior Pituitary: Glycoprotein Hormones

Answer 23

• Follicle-stimulating hormone
• Luteinizing hormone
• Thyroid-stimulating hormone
  
  • Releases the thyroid hormone

Question 24

Anterior Pituitary: Hypophyrial Portal System

Answer 24

• Release of hormones into the portal circulation

Question 25

Posterior Pituitary Hormones

Answer 25

• ˜Synthesized with their binding proteins in the supraoptic and paraventricular nuclei of the hypothalamus

Question 26

Hormones Secreted by the Posterior Pituitary

Answer 26

• Antidiuretic hormone (ADH)
  
  • Controls plasma osmolality
  • High levels of ADH will help with high levels of fluid retention
  • Decrease in urine volume or urine output
• Oxytocin
  
  • Uterine contractions and milk ejection in lactating women
  • Positive feedback loop – the stretch receptors in the birth canal help to secrete more oxytocin to help promote the birth of the baby
  • Has a similar effect to ADH – antidiuretic type of effect

Question 27

Thyroid Gland

Answer 27

• Two lobes lie on either side of the trachea
• Isthmus – portion of the thyroid gland
• Follicles (follicle cells surrounding colloid)
• Parafollicular cells (C cells)
  
  • Secrete calcitonin – helps with the upregulation of osteoblast + regulates bone formation
• Regulation of thyroid hormone secretion
  
  • Thyrotropin-releasing hormone and thyroid-stimulating hormone

Question 28

Thyroid Hormone

Answer 28

• Secreted in response to TSH
• 90% T4 (thyroxine) and 10% T3 (triiodothyronine)
  
  • Most T4 then converted to T3
• Bound to thyroxine-binding globulin, thyroxine-binding prealbumin, albumin, or lipoproteins
• Affects growth and maturation of tissues, cell metabolism, heat production, and oxygen consumption

Question 29

Parathyroid Gland

Answer 29

• Small glands located behind the upper and lower poles of the thyroid gland
• Produce parathyroid hormone (PTH)
  
  • Increases serum calcium and decreases serum phosphate
  • Antagonist of calcitonin (thus increases bone resorptionand serum calcium)
  • Vitamin D (cofactor) needed for PTH function

Question 30

Thyroid Follicle Cells

Answer 30