The Endocrine System Flashcards
What are exocrine glands
Glands that secrete their products into ducts
What are endocrine glands
Ductless and release hormones into the blood
What are hormones
Hormones are chemical messengers carried by the blood to target cells
What does the endocrine system consist of
Glands and organs that secrete hormones
What are the functions of hormones
Regulation
Control growth and development
Regulate operation of the reproductive system
Help establish circadian rhythm
What are the 3 major structural classes of hormones
Amines
Peptides and proteins
Steroids
Examples of amines
Thyroid hormones
Dopamine
Catecholamines (epinephrine and norepinephrine)
Examples of peptides and proteins
The majority of hormones are peptides eg, insulin
Examples of steroids
Aldosterone
Cortisol
Androgens (testosterone)
Estrogens
How are peptide and catecholamine hormones transported
They are water soluble so therefore circulate dissolved in the plasma
Some peptide hormones bind to plasma
How are steroid and thyroid hormones transported
They circulate mainly bound to plasma proteins
Which organs remove hormones from the plasma
The liver and kidneys
By metabolising or excreting them
Where are receptors for steroid and thyroid hormones
Inside target cells
Where are receptors for peptide hormones and catecolamines
On the plasma membrane
What does the responsiveness of a target cell depend on
1) the hormone’s concentration in the blood
2) the abundance of the target cells hormone receptors
3) influences exerted by other hormones
What effects can hormonal interactions have
- permissive
- synergistic
- antagonistic
What inputs control hormonal secretion
1) plasma concentration of anion or nutrient that the hormone regulates
2) neural input to the endocrine glands
3) other hormones
What is a hormone that stimulates the secretion of another hormone referred to
A tropic hormone
What is the posterior pituitary gland
Hormones are synthesised in the hypothalamus, axons pass it down the infundibulum, terminate in the posterior pituitary and release hormones eg, oxytocin
What does the anterior pituitary gland secrete
GH, TSH, ACTH, prolactin, FSH and LH
What type of hormones are follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Gonadotropic hormones
What controls secretion of the anterior pituitary gland hormones
Hypophysiotropic hormones via the portal vessels connecting the hypothalamus and anterior pituitary gland
Where is the thyroid gland located
Within the neck in front of the trachea
What does the thyroid gland produce
Thyroxine (T4) and triiodothyronine (T3)
What are the actions of thyroid hormones
Increased oxidative substrate metabolism
Increased mitochondrial enzyme activity
Increased carbohydrate and lipid metabolism
Role of T3
Required for normal production of growth hormones from the anterior pituitary gland
Important developmental hormone for the nervous system
What mediates the secretion of cortisol during stress
The hypothalamus - anterior pituitary gland system
What are the physiological functions of cortisol during non-stressful situations
- Cortisol affects the responsiveness of smooth muscle cells to epinephrine and norepinephrine, thus helping to maintain BP
- Cortisol required to maintain the certain enzymes conc. involved in metabolic homeostasis so glucose conc. doesn’t drop too far below normal
- Has anti-inflammatory and anti-immune functions
Physiological functions of cortisol in stressful situations
- Enhanced vascular reactivity, improving cardiovascular performance
- Unidentified protective elements against the damaging influences of stress
- Inhibition of inflammation and specific immune responses
- inhibition of nonessential functions (eg, reproduction and growth)
Physiological functions of cortisol in stressful situations - effect on metabolism
- Stimulation of protein catabolism in bone, lymph, muscle and elsewhere
- Stimulation of liver uptake of amino acids and their conversion to glucose
- Maintenance of plasma glucose concentration
- Stimulation of triglyceride catabolism in adipose tissue, with release of glycerol and fatty acids into the blood
When is cortisol highest
In the morning
When is cortisol lowest
At night
Which hormones are most important to growth
Growth hormone
T3
Testosterone and estradiol
Insulin like growth factors 1 and 2
Insulin (mainly during fetal life)
What stimulates growth hormone
Growth hormone-releasing hormone (GHRH)
What inhibits growth hormone
Somatostatin (STT)
What does growth hormone stimulate the release of
IGF-1
What does IGF-1 do
Acts locally to stimulate cell division
When is growth hormone highest
During adolescence
Where is testosterone produced
By the testes
Also produced in smaller quantities in the ovaries and the adrenal cortex (females)
What does testosterone promote
Muscle growth and development of male sex characteristics
Where is oestrogen and progesterone produced
Ovaries
What does oestrogen and progesterone promote
Development of female sex characteristics, regulates menstrual cycle and adipose tissue growth
Oestrogen also promotes endothelia function
Where is dehydroepiandrosterone (DHEA) produced
In the adrenal cortex
What are DHEAs
Precursors for sex hormones such as testosterone and estradiol
When does DHEA and DHEA-S production peak
Age 20-30 and then declines progressively with ags
What happens to DHEA/S following exercise
It increases following low and moderate intensity exercise in young but not older adults
