Chapter 6- Principles of Endocrinology Flashcards
What are the body’s 2 major communication systems?
- Nervous system
- Endocrine system
How do the nervous stem and endocrine system vary in speed?
NS- Rapid
ES- Longer delays, lasts longer
What is the endocrine system?
Ductless endocrine glands scattered throughout the body
Where do endocrine glands secrete into?
Interstitial space then into bloodstream
What do endocrine glands secrete?
Hormones
-Regulate or direct particular functions
What do hormones bind to?
Target cells with specific hormone binding receptors
What controls plasma hormone concentration?
Controlled by changes in rate of hormone secretion
What are tropic hormones?
Released by an endocrine gland and act upon another endocrine gland
How do tropic hormones regulate hormone secretion?
Influence the activity of other endocrine glands
What do tropic hormones stimulate and maintain he function of?
Endocrine target tissues
(Specific tissues affected by tropic hormone)
What kind of control maintains the plasma concentration of a hormone at a given level or set-point?
Negative-feedback
What is a negative feedback control?
Output of a system counteracts a change in input
How is a hormone’s secretion switched off?
It switches off its owns secretion
What is Diurnal rhythm?
24-hour cycles set by the CNS to carry out essential processes.
-Hormone levels vary at times of day
How do hormones influence activity of another hormone at a target cell?
- Permissiveness
2.Synergism - Antagonism
What is permissiveness?
One hormone must be present in adequate amounts for full exertion of another hormone’s effect
What is Synergism?
Occurs when actions of several hormones are complimentary
-Combined effect is greater than the sum of their separate effects
What is Antagonism?
Occurs when one hormone opposes the actions of another hormone
What most commonly causes endocrine dysfunction?
Inappropriate rates of secretion
What are types of inapropriate rates of secretion?
a. Hyposecretion (too little hormone secreted)
b.Hypersecretion (too much hormone secreted)
What are the 3 groups of hormones based on chemical nature?
- Peptides and proteins
- Steroids
- Amines
What is the chemical nature of peptide and protein hormones?
Hydrophilic
What is the chemical nature of steroid hormones?
Lipophilic
What is the chemical nature of Amine hormones?
Lipid/water solubility depends on hormone
What are peptide and protein hormones?
Most common
Are synthesised, processed and packaged before being secreted
What are steroid hormones?
Hormones derived by cholesterol from in cell stores that are modified by enzymes
What does the final product of a steroid hormone depend on?
Cell type
e.g testosterone converted to estradiol in ovaries
Can steroid hormones be stored?
No
What is an example of a steroid hormone?
Aldosterone
-Secreted by cells in the adrenal cortex
What are amine hormones?
Derived from amino acids
Examples of amines?
- Thyroid hormones
- Melatonin
3.Catecholamines
What amino acids are thyroid hormones derived from?
2 tyrosines
What amino acid is melatonin derived from?
Tryptophan
What gland secretes melatonin?
Pineal gland
What gland secretes catecholamines?
Adrenal glands
What is the chemical structure of a catecholamine?
Catechol group + amine group
Examples of catecholamines?
Norepinphrine
Epinephrine
What is the pituitary gland?
Small gland below hypothalamus.
What part of the hypothalamus does the pituitary gland connect to via a thin stalk?
Hypothalamus- infundibulum
What are the two lobes of the pituitary gland?
Posterior pituitary- nervous tissue
Anterior pituitary- glandular epithelial tissue
Does the posterior pituitary produce hormones?
NO it stores and releases hormones made by hypothalamus
What 2 peptide hormones does the posterior pituitary store/release?
1.Vasopressin
2. Oxytocin
What is the function of vasopressin?
Conserve water during urine formation
-Increases permeability of distal/collecting tubules to H2O
-Causes vasoconstriction of arterioles
What is the function of oxytocin?
-Stimulates uterine contraction during childbirth
-Stimulates milk ejection during breast-feeding
Does the anterior pituitary produce its own hormones?
YES, secretes 6 peptide hormones that it produces itself
What are the 6 peptide hormones that the anterior pituitary secretes?
- Thyroid stimulating hormone
- Adrenocorticotropic hormone
- Luteinizing hormone
- Follicle-stimulating hormone
- Growth hormone
- Prolactin
What 5/6 anterior pituitary hormones are tropic?
- Thyroid stimulating hormone
- Adrenocorticotropic hormone
- Luteinizing hormone
- Follicle-stimulating hormone
- Growth hormone
What anterior pituitary hormone is not tropic?
prolactin
What is TSH?
Thyroid stimulating hormone
-Stimulates secretion of thyroid hormone
What is ACTH?
Adrenocorticotropic hormone
-Stimulates secretion of cortisol by adrenal cortex
What is LH?
Luteinising hormone
Females- ovulation–> lutenization. Regulates ovarian secretion of female sex hormones
Males- stimulates testosterone secretion
What is FSH?
Follicle-stimulating hormone
Females- Stimulates growth and development of ovarian follicles, which stimulates secreting of oestrogen by ovaries
Males- Stimulates sperm production
What is GH?
Growth hormone
-Primary hormone responsible for regulating overall body growth; important in intermediary metabolism
What is PRL?
Prolactin
-Enhances breast development and milk production in females
What controls the release of anterior pituitary hormone release?
1 or more of the 7 Hypothalamic (hypophysiotropic) hormones
What controls Hypothalamic hypophysiotropic hormones?
Negative-feedback
What is a critical link between the brain and the endocrine system?
Hypothalamic-Hypophyseal Portal System
What is the Hypothalamic-Hypophyseal Portal System?
Vascular arrangement in which blood flows from one capillary bed through a connecting bed to another capillary bed
How do hypothalamic hormones reach the anterior pituitary?
A branch of the hypophyseal artery ramifies into a capillary bed in the lower hypothalamus, and hypothalmic hormones are secreted into that capillary blood
Blood from those capillaries drains into hypothalamic-hypophyseal portal veins. Hypothalamic-hypophyseal portal veins branch again into another series of capillaries within the anterior pituitary
Capillaries within the anterior pituitary, which carry hormones secreted by that gland, coalesce into veins that drain into the systemic venous blood
Other than GH, what does growth depend on?
- Genetics (max growth capacity)
- Adequate diet
- Free from chronic disease or bad environmental conditions
- Normal levels of growth-influencing hormones
What are the 3 growth periods?
Fetal growth
Postnatal growth spurt
Pubertal growth spurt
What is fetal growth promoted by?
Placenta hormones
no GH!!!!
When does the postnatal growth spurt occur?
During first 2 years of life
When does the Pubertal growth spurt occur?
During adolescence
What processes does growth involve?
- Cell division
- Net protein synthesis
What determines height?
Bone growth of vertebral columns and legs
How does GH promote growth?
Indirectly, by stimulating production of somatomedins from liver
What are somatomedins?
Insulin-like growth factor (IGF-1)
What does somatomedin (IGF-1) act on?
Bone and soft tissues to promote growth actions
What does somatomedin (IGF-1) stimulate?
- Protein synthesis (mostly in muscle)
- Cell division
- Lengthening and thickening of bones (chondrocytes)
-Hyperplasia and hypertrophy
How does GH promote bone thickness and length?
Stimulates osteoblast activity and proliferation of epiphyseal cartilage
When can growth of bones occur?
When plate is cartilaginous “open”
When does the cartilaginous plate ossify (“close”) ending growth?
At the end of adolescence
-Stops after puberty
What other effects does GH exert that are unrelated to growth?
Metabolic effects
What metabolic effects does GH exert?
- Increases blood fatty acid levels
- Increases blood glucose levels
How does GH increase blood fatty acid levels?
Enhances breakdown of triglyceride fat stored in adipose tissue
How does GH increase blood glucose levels?
Decreases glucose uptake by muscles
Increases glucose output by liver
When is GH secretion highest?
During adolescence
-next highest secretion is during childhood
-Lowest in adults
Why is GH secretion lowest in adults?
● Decrease in lean-body fat and bone mass
● Expansion in adipose tissue
● Thinning of skin
What are some growth hormone abnormalities?
- Hyposecretion
- Hypersecretion
What condition is a result of Hyposecretion of GH during childhood?
Dwarfism
What happens from hypo secretion of GH in adults?
Less muscle (including cardiac)
More fat
-less symptoms
What condition is a result of hyper secretion of GH during childhood?
Gigantism
What condition is a result of hyper secretion of GH as an adult?
Acromegaly
What commonly causes the hyper secretion of GH leading to Acromegaly?
A tumor of GH-producing cells of anterior pituitary
What is the Pineal gland?
Tiny, pinecone-shaped structure located in the centre of the brain
What hormone does the pineal glad secrete?
Melatonin
When is the peak level of melatonin?
During darkness
When do levels of melatonin decrease?
During light of day
What are the functions of Melatonin?
-Maintains circadian rhythms (light-dark cycle is synchronised)
-Promotes sleep
-Influences reproductive activity and onset of puberty
-Antioxidant
-Enhances immunity
What are circadian rhythms?
Daily changes in light intensity
● Major environmental cue used to adjust SCN master clock
● Photoreceptors in retina pick up light signals and transmit them directly to SCN
● SCN relays message regarding light status to pineal gland
